Dermal fibroblasts are a dynamic and diverse population of cells whose functions in skin in many respects remain unknown. Normal adult human skin contains at least three distinct subpopulations of fibroblasts, which occupy unique niches in the dermis. Fibroblasts from each of these niches exhibit distinctive differences when cultured separately. Specific differences in fibroblast physiology are evident in papillary dermal fibroblasts, which reside in the superficial dermis, and reticular fibroblasts, which reside in the deep dermis. Both of these subpopulations of fibroblasts differ from the fibroblasts that are associated with hair follicles. Fibroblasts engage in fibroblast-epidermal interactions during hair development and in interfollicular regions of skin. They also play an important role in cutaneous wound repair and an ever-increasing role in bioengineering of skin. Bioengineered skin currently performs important roles in providing (1) a basic understanding of skin biology, (2) a vehicle for testing topically applied products and (3) a resource for skin replacement.

Introduction

Dermal fibroblasts are an essential component of skin; they not only produce and organize the extracellular matrix of the dermis but they also communicate with each other and other cell types, playing a crucial role in regulating skin physiology. Other resident cells include epidermal, vascular and neural cells (Ansel et al., 1996; Detmar, 1996; Werner and Smola, 2001). In addition, skin contains various cells of hematopoietic origin. These include a constitutive population of dendritic cells and a more ephemeral population of leukocytes that includes monocytes/macrophages, neutrophils and lymphocytes (Nestle and Nickoloff, 1995; Gonzalez-Ramos et al., 1996; Lugovic et al., 2001). Dermal fibroblasts represent a heterogeneous population of cells defined according to their location within the dermis (Fig. 1). Two subpopulations of fibroblasts reside in distinct dermal layers: the papillary and reticular dermis (Cormack, 1987). Fibroblasts cultured from each of these layers have different characteristics (Harper and Grove, 1979; Azzerone and Macieira-Coelho, 1982; Schafer et al., 1985; Sorrell et al., 1996; Sorrell et al., 2004). A third group is associated with hair follicles. These lie in the dermal papilla region of the follicle and along its shaft (Reynolds and Jahoda, 1991; Jahoda and Reynolds, 1996). Other subpopulations of dermal fibroblasts might also exist; however, the focus of this Commentary is the fibroblast subpopulations that exhibit stable and well-characterized differences in culture.

Fig. 1.

Adult human skin is a layered organ consisting of an epidermis that is attached to a dermis by an elaborate connective tissue structure, the basement membrane (BM). The basal surface of the epidermis is indented by dermal and vascular components called dermal papillae (*). The dermis is divided into two functional layers, the papillary dermis and reticular dermis. These two layers are separated by a vascular plexus, the rete subpapillare. This plexus is fed by another vascular plexus, the rete cutaneum, located at the base of the reticular dermis. Skin also contains hair follicles (HF) and glands (not shown). Two distinct populations of dermal fibroblasts have been cultured from the interfollicular dermis, the region between hair follicles. Papillary fibroblasts (PF) are cultured from skin dermatomed at a depth of 0.3 mm and reticular fibroblasts (RF) are cultured from skin located at a depth below 0.7 mm. Hair follicle fibroblasts are obtained by carefully plucking or dissecting hairs from the skin and then placing these hairs or segments of these hair follicles onto surfaces of plastic culture dishes. Hair follicles contain two subsets of cells: the follicular sheath cells and dermal papilla cells.

Fig. 1.

Adult human skin is a layered organ consisting of an epidermis that is attached to a dermis by an elaborate connective tissue structure, the basement membrane (BM). The basal surface of the epidermis is indented by dermal and vascular components called dermal papillae (*). The dermis is divided into two functional layers, the papillary dermis and reticular dermis. These two layers are separated by a vascular plexus, the rete subpapillare. This plexus is fed by another vascular plexus, the rete cutaneum, located at the base of the reticular dermis. Skin also contains hair follicles (HF) and glands (not shown). Two distinct populations of dermal fibroblasts have been cultured from the interfollicular dermis, the region between hair follicles. Papillary fibroblasts (PF) are cultured from skin dermatomed at a depth of 0.3 mm and reticular fibroblasts (RF) are cultured from skin located at a depth below 0.7 mm. Hair follicle fibroblasts are obtained by carefully plucking or dissecting hairs from the skin and then placing these hairs or segments of these hair follicles onto surfaces of plastic culture dishes. Hair follicles contain two subsets of cells: the follicular sheath cells and dermal papilla cells.

Papillary and reticular dermal fibroblasts

The papillary dermis is approximately 300-400 μm deep. This depth is variable and depends upon such factors as age and anatomical location. Typically, the superficial portion of the papillary dermis is arranged into ridge-like structures, the dermal papillae, which contain microvascular and neural components that sustain the epidermis (Cormack, 1987). Dermal papillae greatly extend the surface area for epithelial-mesenchymal interactions and delivery of soluble molecules to the epidermis. A vascular plexus, the rete subpapillare, demarcates the lower limit of the papillary dermis (Figs 1, 2). The reticular layer of the dermis extends from this superficial vascular plexus to a deeper vascular plexus, the rete cutaneum, which serves as the boundary between the dermis and hypodermis. Hair follicles and their associated dermal cells extend into and often through the reticular dermis to terminate in the hypodermis, a tissue rich in adipocytes.

Fig. 2.

The papillary and reticular dermis is separated by a vascular plexus, the rete subpapillare. The papillary dermis contains a higher density of cells than does the reticular dermis. Dermal papillae extend the surface area of the epithelial-mesenchymal boundary. Bar, 45 μm.

Fig. 2.

The papillary and reticular dermis is separated by a vascular plexus, the rete subpapillare. The papillary dermis contains a higher density of cells than does the reticular dermis. Dermal papillae extend the surface area of the epithelial-mesenchymal boundary. Bar, 45 μm.

Mechanical separation of skin (dermatoming) into defined papillary and reticular layers allows establishment of explant cultures of cells from each layer. Papillary fibroblasts divide at faster rates than do site-matched reticular fibroblasts (Harper and Grove, 1979; Azzerone and Macieira-Coelho, 1982; Schafer et al., 1985; Sorrell et al., 1996; Sorrell et al., 2004). Reticular dermal fibroblasts seeded into type I collagen lattices contract them faster than do papillary dermal fibroblasts (Schafer et al., 1985; Sorrell et al., 1996). When grown to confluence in monolayer culture, the papillary cells attain a higher cell density partly because they are not fully contact inhibited (Schafer et al., 1985; Sorrell et al., 2004).

Extracellular matrix differences

The papillary dermis and reticular dermis differ in both the composition and organization of their respective extracellular matrices (Table 1). The papillary dermis is characterized by thin, poorly organized collagen fiber bundles, consisting primarily of type I and type III collagens, which contrast with the thick, well-organized fiber bundles in the reticular dermis (Cormack, 1987). Collagen fiber bundles in the papillary dermis contain more type III collagen than do those in the reticular dermis (Meigel et al., 1977). Other matrix molecules are also differentially apportioned between the papillary and reticular dermis. Immunohistochemical studies of normal adult skin highlight structural and compositional differences in proteoglycan deposition (Fig. 3). The proteoglycan decorin is intensely expressed in the papillary dermis, but is otherwise dispersed between collagen fiber bundles in the reticular dermis. By contrast, versican associates with microfibrils in the papillary dermis, but is more extensively expressed in elastic fibers of the reticular dermis (Zimmermann et al., 1994; Sorrell et al., 1999a). The non-fibrillar collagen types XII and XVI, along with tenascin-C, are characteristically found in the papillary dermis; whereas, collagen type IV and tenascin-X are primarily restricted to the reticular dermis (Lightner et al., 1993; Wälchli et al., 1994; Lethias et al., 1996; Berthod et al., 1997; Akagi et al., 1999; Grässel et al., 1999).

Table 1.

Distribution of selected extracellular matrix molecules in dermal compartments

Matrix component Papillary dermis Reticular dermis Hair follicle
Collagens I and III   High ratio of type III to I   Low ratio of type III to I   Present  
Collagen IV   Present in basement membrane   Absent   Present in dermal papillae  
Collagen VI   Present at dermal-epidermal junction (DEJ)   Weakly present   Present in dermal sheaths  
Collagen XII   Present   Low to absent   High expression around follicular sheath  
Collagen XIV   Low to absent   Present   Low expression  
Collagen XVI   Present in DEJ-region   Absent   Unknown  
Tenascin-C   Present in DEJ-region   Absent   Present in sheaths and dermal papillae  
Tenascin-X   Weak in DEJ-region   Present   Not associated  
Versican   Diffuse in DEJ-region, present in matrix fibrils   Present in association with elastic fibers   Present in dermal papillae  
Decorin   Present   Present   Unknown  
Matrix component Papillary dermis Reticular dermis Hair follicle
Collagens I and III   High ratio of type III to I   Low ratio of type III to I   Present  
Collagen IV   Present in basement membrane   Absent   Present in dermal papillae  
Collagen VI   Present at dermal-epidermal junction (DEJ)   Weakly present   Present in dermal sheaths  
Collagen XII   Present   Low to absent   High expression around follicular sheath  
Collagen XIV   Low to absent   Present   Low expression  
Collagen XVI   Present in DEJ-region   Absent   Unknown  
Tenascin-C   Present in DEJ-region   Absent   Present in sheaths and dermal papillae  
Tenascin-X   Weak in DEJ-region   Present   Not associated  
Versican   Diffuse in DEJ-region, present in matrix fibrils   Present in association with elastic fibers   Present in dermal papillae  
Decorin   Present   Present   Unknown  
Fig. 3.

Immunohistochemical studies indicate that the papillary dermis (Pap) contains high levels of the proteoglycan decorin (A). The reticular dermis (Retic) contains elastic fibers oriented parallel to the epidermis that contain the proteoglycan versican. Microfibrils containing versican are also present in the papillary dermis as is diffuse versican at the DEJ (panel B). The epidermis (E) does not contain detectable levels of these two proteoglycans. The dashed line indicates the approximate demarcation between the papillary and reticular layers (adapted from Sorrell et al., 1999a, with kind permission from Kluwer Academic Publishers). Bar, 87 μm.

Fig. 3.

Immunohistochemical studies indicate that the papillary dermis (Pap) contains high levels of the proteoglycan decorin (A). The reticular dermis (Retic) contains elastic fibers oriented parallel to the epidermis that contain the proteoglycan versican. Microfibrils containing versican are also present in the papillary dermis as is diffuse versican at the DEJ (panel B). The epidermis (E) does not contain detectable levels of these two proteoglycans. The dashed line indicates the approximate demarcation between the papillary and reticular layers (adapted from Sorrell et al., 1999a, with kind permission from Kluwer Academic Publishers). Bar, 87 μm.

Experimental studies have explored the issue of whether cultured papillary and reticular fibroblasts produce different amounts and types of extracellular matrix molecule that might account for the observed differences in skin (Table 2). In monolayer cultures, Schönherr et al. found that papillary dermal fibroblasts secrete significantly more decorin than did corresponding reticular cells, and papillary fibroblasts contain more decorin mRNA (Schönherr et al., 1993). By contrast, the two cellular populations produce identical amounts of biglycan. Another study found that site-matched papillary and reticular fibroblasts differ in the relative levels of the proteoglycans decorin and versican that they produce (Sorrell et al., 1999b).

Table 2.

Expression of extracellular matrix molecules by monolayer cultures of dermal fibroblasts

Matrix component Papillary fibroblasts Reticular fibroblasts
Collagens I and III   Produced - ratio same as for reticular cells   Produced - ratio same as for papillary cells  
Collagens V and VI   Produced   Produced  
Collagen XII   Produced   Produced  
Collagen XIV   Not produced in monolayer culture   Not produced in monolayer culture  
Collagen XVI   Produced at high levels   Produced at low levels  
Tenascin-C   Produced   Produced  
Tenascin-X   Not studied   Not studied  
Versican   Produced at low levels   Produced at high levels  
Decorin   Produced at high levels   Produced at low levels  
Matrix component Papillary fibroblasts Reticular fibroblasts
Collagens I and III   Produced - ratio same as for reticular cells   Produced - ratio same as for papillary cells  
Collagens V and VI   Produced   Produced  
Collagen XII   Produced   Produced  
Collagen XIV   Not produced in monolayer culture   Not produced in monolayer culture  
Collagen XVI   Produced at high levels   Produced at low levels  
Tenascin-C   Produced   Produced  
Tenascin-X   Not studied   Not studied  
Versican   Produced at low levels   Produced at high levels  
Decorin   Produced at high levels   Produced at low levels  

Akagi et al. found that fibroblasts derived from the upper, middle and lower thirds of the dermis produced significantly different amounts of mRNA for the α1(XVI) of type XVI collagen (Akagi et al., 1999). By contrast, Tajima and Pinnell quantified the amounts of type I and type III collagens produced by monolayer cultures to see whether synthetic differences might account for the observed in vivo differences (Tajima and Pinnell, 1981). They found no differences in the production of type I and type III collagens by these two populations of cultured cells, although they noted an elevated amount of type I procollagen in the medium of papillary fibroblast cultures. Thus, cultured papillary and reticular fibroblasts exhibit stable differences in the production of some, but not all, extracellular matrix molecules.

Fibroblasts and basement membrane formation

The epidermis of the skin is firmly attached to the underlying dermis by a complex multi-molecular structure, the basement membrane (Burgeson and Christiano, 1997; Aumailley and Rousselle, 1999). The organization of basement membrane to form a morphologically identifiable structure results from a cooperative effort of both keratinocytes and fibroblasts (Fleischmajer et al., 1993; Marinkovich et al., 1993; Smola et al., 1998; Moulin et al., 2000). Marinkovich et al. studied the cellular origin of various basement membrane molecules by probing skin equivalents (Fig. 4) that contain bovine keratinocytes and human dermal fibroblasts with species-specific antibodies (Marinkovich et al., 1993). Type IV and VII collagen and laminin-1 produced by fibroblasts appeared in a linear array at the dermal-epidermal junction (DEJ). Keratinocytes also produced and organized type IV and VII collagen, laminin-5, other laminins and perlecan. Other studies have shown that fibroblasts are the principal source of entactin/nidogen (Contard et al., 1993; Fleischmajer et al., 1995). Marinkovich et al. then postulated that a differentiated population of fibroblasts exists at the DEJ of skin that both produces basement membrane components and helps keratinocytes organize them (Marinkovich et al., 1993).

Fig. 4.

A skin equivalent consists minimally of a dermal equivalent and differentiated epidermis cultured first submerged then at the air-liquid interface in a three-dimensional context. Fibroblasts (arrows) encased in a type I collagen lattice provide dermal support for the epidermis. The epidermis is stratified and contains differentiated layers typically found in normal skin, including the (1) basal, (2) spinous, (3) granular and (4) cornified layers. Bar, 44 μm.

Fig. 4.

A skin equivalent consists minimally of a dermal equivalent and differentiated epidermis cultured first submerged then at the air-liquid interface in a three-dimensional context. Fibroblasts (arrows) encased in a type I collagen lattice provide dermal support for the epidermis. The epidermis is stratified and contains differentiated layers typically found in normal skin, including the (1) basal, (2) spinous, (3) granular and (4) cornified layers. Bar, 44 μm.

Coculture of fibroblasts and keratinocytes modifies the activities of both cell types. Keratinocytes induce the expression of transforming growth factor (TGF)-β2 by dermal fibroblasts (Smola et al., 1994). Fibroblasts regulate the production of laminins and type VII collagen by keratinocytes, possibly through TGF-β signaling (König and Bruckner-Tuderman, 1991; König and Bruckner-Tuderman, 1994; Monical and Kefalides, 1994). The kinetics of basement membrane formation has also been studied in organotypic coculture models in which fibroblasts were either present or omitted (Smola et al., 1998). Specific basement membrane components gradually appeared at the DEJ; however, the kinetics varied, depending on whether fibroblasts were present. The production of type IV collagen, laminin-1 and type VII collagen by keratinocytes cultured alone was significantly delayed or absent, suggesting that fibroblasts influenced the production of these matrix molecules. On the dermal side, the steady-state mRNA levels of type IV collagen α1 message in fibroblasts were significantly enhanced when keratinocytes were present. Together, these studies indicate that elements of basement membrane production are co-regulated by fibroblasts and keratinocytes.

Not all dermal fibroblasts interact equally well with keratinocytes in the formation of a basement membrane. Moulin et al. showed that myofibroblasts obtained from wound sites do not support keratinocyte differentiation and basement membrane formation to the same extent as do normal dermal fibroblasts (Moulin et al., 2000). Consequently, the ability was compared of site-matched papillary and reticular dermal fibroblasts to support basement membrane formation (Sorrell et al., 2004). Papillary dermal fibroblasts appeared to induce basement membrane formation faster when reticular fibroblasts were present. Therefore, fibroblasts adjacent to the epidermis might either produce more extracellular matrix components of the basement membrane and/or produce soluble factors that influence keratinocytes to re-establish a basement membrane.

Intercellular communication and interfollicular dermal fibroblasts

Fibroblasts engage in paracrine and autocrine interactions in skin (Gilchrest et al., 1983; Boxman et al., 1993; Smola et al., 1993; Kupper and Groves, 1995; Moulin, 1995; Schröder, 1995; Slavin, 1996; Smith et al., 1997; Kondo, 2000; Werner and Smola, 2001). Rheinwald and Green developed a culture system in which irradiated mesenchymal cells support the growth of adult human keratinocytes (Rheinwald and Green, 1975). This led to the identification of mesenchyme-derived factors that regulate keratinocyte proliferation, including keratinocyte growth factor (KGF)-1. This is a member of the fibroblast growth factor (FGF) family that is exclusively produced by mesenchymal cells (Rubin et al., 1995; Werner, 1998). However, only epithelial cells express the KGF receptor and, hence, respond to KGF-1. Fibroblasts also produce other factors that regulate the proliferation of cultured keratinocytes and play roles in wound repair. These include granulocyte-macrophage colony-stimulating factor (GM-CSF), FGF-10 (also known as KGF-2), parathyroid-hormone-related protein, hepatocyte growth factor/scatter factor (HGF/SF), epidermal growth factor (EGF) and interleukin 6 (IL-6) (Waelti et al., 1992; Boxman et al., 1993; Rubin et al., 1993; Smola et al., 1993; Sato et al., 1995; Igarashi et al., 1996; Blomme et al., 1999; Breuhahn et al., 2000; Mann et al., 2001; Marchese et al., 2001; Werner and Smola, 2001).

Fibroblasts release growth factors/cytokines that play a significant role in wound repair by modulating the activity of keratinocytes. Smola et al. found that coculture of fibroblasts and keratinocytes results in increased levels of KGF-1, IL-6 and GM-CSF mRNAs (Smola et al., 1993). The level of KGF-1 mRNA and the amount of protein released into culture medium by cultured dermal fibroblasts were upregulated by treatment of these cells with IL-1 (Brauchle et al., 1994; Chedid et al., 1994; Maas-Szabowski and Fusenig, 1996). KGF-1 in turn enhanced the release of IL-1α by keratinocytes. Thus, a paracrine loop is established in situations where dermal fibroblasts and keratinocytes coexist (Maas-Szabowski et al., 1999).

Soluble factors released by fibroblasts do not possess inductive characteristics with respect to interfollicular keratinocytes. Nonetheless, these factors can modulate specific aspects of epidermal formation. Overexpression of KGF-1 results in a hyperproliferative epidermis. This might result from enhanced proliferation of basal keratinocytes and suppression of terminal differentiation (Guo et al., 1993; Hines and Allen-Hoffmann, 1996; Szabowski et al., 2000; Andreadis et al., 2001). Excessive KGF-1 might also induce flattening of the basal surface of the epidermis (Andreadis et al., 2001). By contrast, overexpression of GM-CSF results in increased apoptosis of cultured keratinocytes, and overexpression of KGF-2 could accelerate keratinocyte differentiation (Breuhahn et al., 2000; Suzuki et al., 2000; Marchese et al., 2001). These observations have led to the proposal that the epidermal response to fibroblast-derived signaling molecules depends upon the ratio of these factors. Fusenig and coworkers have proposed that the ratio of KGF-1 to GM-CSF presented to epidermal cells determines the status of this tissue (Maas-Szabowski et al., 2001). Site-matched papillary and reticular dermal fibroblasts differ significantly in the release of KGF-1 and GM-CSF into culture medium. Typically, the ratio of GM-CSF to KGF-1 is higher in papillary fibroblasts than in corresponding reticular cells (Sorrell et al., 2004). Thus, these two populations of cells exert subtle differences on epidermal proliferation and differentiation.

Communication between fibroblasts and keratinocytes appears to involve AP-1 target genes in dermal fibroblasts. Szabowski et al. examined fibroblasts from Jun-knockout and JunB-knockout mouse embryos and found that the Jun-/- cells produce very low levels of KGF-1 and GM-CSF, whereas JunB-/- cells produce elevated levels of these factors (Szabowski et al., 2000). Incorporation of these fibroblasts into bi-layered skin equivalents with normal adult human keratinocytes for the epidermal layer led to strikingly different results. Epidermal layers on skin equivalents containing Jun-/- fibroblasts were atrophic, basal cell proliferation was reduced, and terminal differentiation was delayed. JunB-/- fibroblasts caused epidermal hyperplasia. IL-1 and other inflammatory factors, such as tumor necrosis factor (TNF)-α, activate AP-1-mediated transcription and enhance the activity of NF-κB (Angel and Szabowski, 2002). Differences in the phenotypes of fibroblasts in skin might be related to how these cells respond to external signals and modulate the diverse group of genes regulated by AP-1 transcription factors.

Dermal fibroblastic cells are associated with hair follicles

Hair follicles are skin appendages formed predominantly by cells of epidermal origin. Mesenchymal cells of the dermis play a vital role in their formation in fetal skin and an equally significant role in regulating their cyclic growth, rest and regression phases in adults (Kulessa et al., 2000; Botchkarev, 2003). In fetal skin, mutual inductive events between localized dermal and epidermal cells proceed in a stringent spatiotemporal manner. First, an as-yet-undefined signal emanating from the dermis induces the formation of thickened epidermal placodes (Holbrook and Minami, 1991; Hardy, 1992; Millar, 2002; Botchkarev et al., 1999; Botchkarev et al., 2002). Differentiated epidermal cells provide a second signal that induces localized mesenchymal cells to condense and form a defined pellet of cells immediately beneath the epidermal placodes (Holbrook and Minami, 1991; Hardy, 1992). These cells stimulate the proliferation of epidermal cells in the placode, which drives the production of hair follicles deep into the dermal matrix (Hardy, 1992; Millar, 2002; Botchkarev, 2003). Simultaneously, condensed mesenchymal cells produce proteases that clear a path for this ingrowth (Karelina et al., 1993; Karelina et al., 1994; Karelina et al., 2000). Once elongation is complete, keratinocytes in the matrix region at the base of the follicle envelop the dermal papilla cells and leave a narrow opening through which the vasculature and nerves penetrate (Hardy, 1992; Millar, 2002; Botchkarev, 2003). Condensed mesenchymal cells also give rise to a second population of dermal cells during the period in which follicles actively invade the dermal matrix. These dermal cells form a thin connective tissue sheath along the shaft of the follicle (Jahoda and Reynolds, 2000).

The fibroblast in cutaneous wound repair

Fibroblasts play a crucial role in cutaneous wound repair (Martin, 1997). These cells are attracted to wound sites by the localized release of growth factors/cytokines such as platelet-derived growth factor (Pierce et al., 1991). The first wave of fibroblasts enters the wound site along with sprouting vasculature. These cells differentiate into a specialized, but ephemeral, cell type called the myofibroblast (Sappino et al., 1990; Grinnell, 1994).

Myofibroblasts, in response to monocyte/macrophage-derived factors, produce a provisional wound matrix that is enriched in fetal-like fibronectin and hyaluronan (Clark, 1990; Gailit and Clark, 1994; Juhlin, 1997; Singer and Clark, 1999). These cells also provide the motive force to contract the wound (Sappino et al., 1990). Myofibroblasts disappear from the wound site, apparently by apoptosis, and are replaced by a second wave of fibroblasts that initiate the formation of a collagenous matrix (Grinnell et al., 1999). However, their ability to organize it is impaired, which results in the formation of scar tissue (Gailit and Clark, 1994; Shah et al., 1994; Shah et al., 1995; Singer and Clark, 1999). Fetal skin is repaired without scar formation (Adzick and Lorenz, 1994; Armstrong and Ferguson, 1995; Liechty et al., 2000). This is mainly owing to differences in fetal and adult fibroblast phenotypes (Schor et al., 1985; Olsen and Uitto, 1989; Cullen et al., 1997; Gosiewska et al., 2001). The low level of growth factors/cytokine production by fetal cells, especially TGF-β1, appears to be a major factor in the absence of scar formation (Shah et al., 1994; Shah et al., 1995; Eckes et al., 2000). The aberrant fibroblast phenotype also appears to contribute to fibrotic disorders, such as keloid formation and scleroderma (Garner et al., 1993; Ghahary et al., 1994; Ghahary et al., 1996; Sollberg et al., 1994; Kirk et al., 1995; Nakaoka et al., 1995; Herrick et al., 1996; Hasan et al., 1997; Agren et al., 1999). Signals such as TGF-β and connective tissue growth factor play a significant role in the latter process (Grotendorst, 1997).

The dermal fibroblast in bioengineering

Much of our current knowledge regarding fibroblast physiology is derived from studies of these cells grown on a plastic substrate as monolayer cultures. Fibroblasts cultured in this manner retain many of their phenotypic characteristics (see above). Nonetheless, monolayer-cultured fibroblasts exhibit significant metabolic differences from in vivo fibroblasts. For example, fibroblasts in monolayer culture actively proliferate and produce many different types of extracellular matrix molecule. Both of these characteristics are either suppressed or greatly diminished in three-dimensional organotypic cultures much in the same manner as in vivo (Mauch et al., 1988; Kono et al., 1990; Geesin et al., 1993; Grinnell, 1994; Mio et al., 1996; Ivarsson et al., 1998; Rosenfeldt and Grinnell, 2000).

Dermal and skin equivalents as biological models

The application of three-dimensional organotypic cultures to tissue-specific modeling studies has undergone significant development (Schmeichel and Bissell, 2003). Dermal and skin equivalents were among the first examples of such organotypic cultures (Bell et al., 1979; Bell et al., 1981; Bell et al., 1983; Asselineau et al., 1986). These culture systems provide a resource for basic studies in skin biology, testing for topically applied products, and as a replacement for human skin. For example, environmental aging of skin due to chronic exposure to UV irradiation poses cosmetic challenges and increased risk of skin cancers (Gilchrest, 1996). Bernerd and Asselineau studied the effects of UV irradiation in a skin equivalent model (Bernerd and Asselineau, 1997). They found that `sunburn' cells were generated in the epidermis by an acute UVB exposure in much the same manner as occurs in skin. Furthermore, downregulation of keratinocyte differentiation markers occurred at early time points following UVB exposure. These situations were repaired in skin equivalents that were maintained in culture for extended periods of time. In another study, they found that UVA exposure induces responses specific to the dermal compartment of skin equivalents (Bernerd and Asselineau, 1998). Fibroblasts in the upper regions of the `dermal' component of the skin equivalents underwent apoptosis and disappeared from the constructs. Over time, fibroblasts at the bottom of the skin equivalent were induced to proliferate and migrated into the upper region of the construct. This was accompanied by an increase in metalloproteinase (MMP)-1 synthesis by resident fibroblasts, which presumably enabled the cells to migrate within the collagen gel.

Michel et al. have investigated skin equivalents as potential tools for percutaneous absorption (Michel et al., 1993). They prepared human skin equivalents such that a constant surface area was present and found that absorption of chemical agents depends on the thickness of the epidermis and its stratum corneum. This process was not entirely equivalent to that observed in mice, but was sufficient to suggest that it might be used as an effective model for pharmacological and cosmetic testing. Development of skin equivalents that contain other types of cell, such as immunocompetent cells and vascular endothelial cells (Regnier et al., 1997; Guironnet et al., 2001; Ponec, 2002; Supp et al., 2002), might also provide insight into biological and pharmacological responses.

Dermal and skin equivalents for skin replacement

Several groups have employed skin equivalents for wound management for acute and chronic wounds (Boyce, 1996; Singer and Clark, 1999; Coulomb and Dubertret, 2002). Boyce and colleagues (Boyce, 1996; Boyce and Warden, 2002; Boyce et al., 2002) used skin equivalents prepared from autologous human keratinocytes and fibroblasts for grafting onto wound sites and found that these grafts are equivalent to autologous split-thickness skin grafts. Furthermore, the requirement for harvesting donor skin was less than that for conventional skin autografts. Inclusion of a `dermal' component provides an environment that promotes vascularization of the graft, and fibroblasts play an active role in the replacement of the dermal matrix (Demarchez et al., 1992; Supp et al., 2002).

Concluding remarks

Fibroblasts represent a diverse population of cells (Fries et al., 1994). Phenotypic differences are manifested in a variety of ways: extracellular matrix production and organization, production of growth factors/cytokines, and participations in inflammatory responses (Fries et al., 1994; Smith et al., 1997; Doane and Birk, 1991; Limeback et al., 1982; Derdak et al., 1992; Stephens et al., 2001). In the skin, two forms of fibroblast heterogeneity have been noted. Intrasite heterogeneity relates to the position of fibroblasts in the context of epidermal structures. Thus, papillary, reticular and hair-follicle-associated fibroblasts differ from each other. A second type of heterogeneity is based upon the anatomical location within the body. Thus, interfollicular fibroblasts from scalp, face, trunk, leg, and so on exhibit subtle differences from each other. Less is currently known about these intersite differences in fibroblasts. Chang et al. have shown that human dermal fibroblasts obtained from various anatomical sites express different homeobox transcription factors (Chang et al., 2002). The AP-1 family of transcription factors is important in regulating the production of factors that regulate epithelial-mesenchymal interactions, cellular proliferation and extracellular matrix production (Angel and Szabowski, 2002; Shaulian and Karin, 2002). Papillary and reticular dermal fibroblasts differ in these characteristics. Therefore, additional studies related to this family of factors might help us to understand the differences between subpopulations of dermal fibroblasts.

Fibroblast diversity in the skin raises questions that will require experiments to provide answers. Inductive influences from the epidermis result in the differentiation of fibroblasts associated with hair follicles. However, the factor(s) or event(s) that drives the differentiation of papillary and reticular cells are unknown. Furthermore, our knowledge of the physiological characteristics that differentiate papillary from reticular fibroblasts remains limited. Additional information in this regard will expand our conceptualization of the function of fibroblasts in skin. There is currently limited information that suggests that AP-1 and homeobox genes and their regulators play roles in determining fibroblast diversity. Additional studies are required to define the roles of these and possibly other regulatory genes in establishing and maintaining fibroblast diversity. With the increased reliance on the development and application of three-dimensional skin equivalents for biological and clinical purposes, it will be necessary to be more selective about the choice of fibroblast to be employed.

Finally, the term `dermal fibroblast' is an oversimplification. In reality, dermal fibroblasts are a dynamic, diverse population of cells. This means that we should take greater care defining the population of dermal fibroblast that is used in experimental studies. We are only beginning to understand the function of these cells in defining the structure and organization of skin and their complex intercellular interactions. Our current knowledge of fibroblast physiology is largely based upon monolayer culture studies. These studies more closely reflect the status of these cells in an early wound repair situation. The use of three-dimensional dermal and skin equivalents in future studies should provide more relevant information regarding possible physiological differences between fibroblast subpopulations in vivo. Much work will be required in the future if we are to understand and appreciate fully this diverse population of cells.

Acknowledgements

We gratefully acknowledge Irwin Schafer (Case Western Reserve University) and Daniel Asselineau and Hervé Pageon (L'Oréal Life Sciences, Clichy, France) for providing the adult site-matched dermal fibroblasts used in experimental studies in this laboratory, and David Carrino and Marilyn Baber for expert advice and creative collaboration. Financial support for studies in this laboratory was provided by L'Oréal Life Sciences and the National Institutes of Health.

References

References
Adzick, N. S. and Lorenz, H. P. (
1994
). Cells, matrix, growth factors, and the surgeon. The biology of scarless fetal wound repair.
Ann. Surg.
220
,
10
-18.
Agren, M. S., Steenfos, H. H., Dabelsteen, S., Hansen, J. B. and Dabelsteen, E. (
1999
). Proliferation and mitogenic response to PDGF-BB of fibroblasts isolated from chronic venous leg ulcers is ulcer-age dependent.
J. Invest. Dermatol.
112
,
463
-469.
Akagi, A., Tajima, S., Ishibashi, A., Yamaguchi, N. and Nagai, Y. (
1999
). Expression of type XVI collagen in human skin fibroblasts: enhanced expression in fibrotic skin diseases.
J. Invest. Dermatol.
113
,
246
-250.
Andreadis, S. T., Hamoen, K. E., Yarmush, M. L. and Morgan, J. R. (
2001
). Keratinocyte growth factor induces hyperproliferation and delays differentiation in a skin equivalent model system.
FASEB J.
15
,
898
-906.
Angel, P. and Szabowski, A. (
2002
). Function of AP-1 target genes in mesenchymal-epithelial cross-talk in skin.
Biochem. Pharmacol.
64
,
949
-956.
Ansel, J. C., Kaynard, A. H., Armstrong, C. A., Olerud, J., Bunnett, N. and Payan, D. (
1996
). Skin-nervous system interactions.
J. Invest. Dermatol.
106
,
198
-204.
Armstrong, J. R. and Ferguson, M. W. J. (
1995
). Ontogeny of the skin and the transition from scar-free to scarring phenotype during wound healing in the pouch young of a marsupial, Monodelphis domestica.
Dev. Biol.
169
,
242
-260.
Asselineau, D., Bernard, B. A., Bailly, C., Darmon, M. and Prunieras, M. (
1986
). Human epidermis reconstructed by culture: is it `normal'?
J. Invest. Dermatol.
86
,
181
-186.
Aumailley, M. and Rousselle, P. (
1999
). Laminins of the dermo-epidermal junction.
Matrix Biol.
18
,
19
-28.
Azzarone, B. and Macieira-Coelho, A. (
1982
). Heterogeneity of the kinetics of proliferation within human skin fibroblastic cell populations.
J. Cell Sci.
57
,
177
-187.
Bell, E., Ivarsson, B. and Merrill, C. (
1979
). Production of a tissue-like structure by contraction of collagen lattices by human fibroblasts of different proliferative potential in vitro.
Proc. Natl. Acad. Sci. USA
76
,
1274
-1278.
Bell, E., Ehrlich, H. P., Buttle, D. J. and Nakatsuji, T. (
1981
). Living tissue formed in vitro and accepted as skin equivalent tissue of full thickness.
Science
211
,
1052
-1054.
Bell, E., Sher, S., Hull, B., Merrill, C., Rosen, S., Chamson, A., Asselineau, D., Dubertret, L., Coulomb, B., Lapiere, C. et al. (
1983
). The reconstitution of living skin.
J. Invest. Dermatol.
81
,
2s
-10s.
Bernerd, F. and Asselineau, D. (
1997
). Successive alteration and recovery of epidermal differentiation and morphogenesis after specific UVB-damages in skin reconstructed in vitro.
Dev. Biol.
183
,
123
-138.
Bernerd, F. and Asselineau, D. (
1998
). UVA exposure of human skin reconstructued in vitro induces apoptosis of dermal fibroblasts: subsequent connective tissue repair and implications in photoaging.
Cell Death Differ.
5
,
792
-802.
Berthod, F., Germain, L., Guignard, R., Lethias, C., Garrone, R., Damour, O., van der Rest, M. and Auger, F. A. (
1997
). Differential expression of collagens XII and XIV in human skin and in reconstructed skin.
J. Invest. Dermatol.
108
,
737
-742.
Blomme, E. A. G., Sugimoto, Y., Lin, Y. C., Capen, C. C. and Rosol, T. J. (
1999
). Parathyroid hormone-related protein is a positive regulator of keratinocyte growth factor expression by normal dermal fibroblasts.
Mol. Cell. Endocrinol.
152
,
189
-197.
Botchkarev, V. A. (
2003
). Bone morphogenetic proteins and their antagonists in skin and hair follicle biology.
J. Invest. Dermatol.
120
,
35
-47.
Botchkarev, V. A., Botchkareva, N. V., Roth, W., Nakamura, M., Chen, L. H., Herzog, W., Lindner, G., McMahorn, J. A., Peters, C., Lauster, R. et al. (
1999
). Noggin is a mesenchymally derived stimulator of hair-follicle induction.
Nat. Cell Biol.
1
,
158
-164.
Botchkarev, V. A., Botchkareva, N. V., Sharov, A. A., Funa, K., Huber, O. and Gilchrest, B. A. (
2002
). Modulation of BMP signaling by noggin is required for induction of the secondary (Nontylotrich) hair follicles.
J. Invest. Dermatol.
118
,
3
-10.
Boxman, I., Lowik, C., Aarden, L. and Ponc, M. (
1993
). Modulation of IL-6 production and IL-1 activity by keratinocyte-fibroblast interaction.
J. Invest. Dermatol.
101
,
316
-324.
Boyce, S. T. (
1996
). Cultured skin substitutes: a review.
Tissue Eng.
2
,
255
-266.
Boyce, S. T. and Warden, G. D. (
2002
). Principles and practices for treatment of cutaneous wounds with cultured skin substitutes.
Am. J. Surg.
183
,
445
-456.
Boyce, S. T., Kagan, R. J., Yakuboff, K. P., Meyer, N. A., Rieman, M. T., Greenhalgh, D. G. and Warden, G. D. (
2002
). Cultured skin substitutes reduce donor skin harvesting for closure of excised, full-thickness burns.
Ann. Surg.
235
,
269
-279.
Brauchle, M., Angermeyer, K., Hubner, G. and Werner, S. (
1994
). Large induction of keratinocyte growth factor expression by serum growth factors and pro-inflammatory cytokines in cultured fibroblasts.
Oncogene
9
,
3199
-3204.
Breuhahn, K., Mann, A. Müller, G., Wilhelmi, A., Schirmacher, P., Enk, A. and Blessing, M. (
2000
). Epidermal overexpression of granulocyte-macrophage colony-stimulating factor induces both keratinocyte proliferation and apoptosis.
Cell Growth Differ.
11
,
111
-121.
Burgeson, R. E. and Christiano, A. M. (
1997
). The dermal-epidermal junction.
Curr. Opin. Cell Biol.
9
,
651
-658.
Chang, H. Y., Chi, J.-S., Dudoit, S., Bondre, C., van de Rijn, M. and Botstein, D. (
2002
). Diversity, topographic differentiation, and positional memory in human fibroblasts.
Proc. Natl. Acad. Sci. USA
99
,
12877
-12882.
Chedid, M., Rubin, J. S., Csaky, K. G. and Aaronson, S. A. (
1994
). Regulation of keratinocyte growth factor gene expression by interleukin 1.
J. Biol. Chem.
269
,
10753
-10757.
Clark, R. A. F. (
1990
). Fibronectin matrix deposition and fibronectin receptor expression in healing and normal skin.
J. Invest. Dermatol.
94
,
128s
-134s.
Contard, P., Bartel, R. L., Jacobs, L., II, Perlish, J. S., Macdonald, E. D., II, Handler, L., Cone, D. and Fleischmajer, R. (
1993
). Culturing keratinocytes and fibroblasts in a three-dimensional mesh results in epidermal differentiation and formation of a basal lamina-anchoring zone.
J. Invest. Dermatol.
100
,
35
-39.
Cormack, D. H. (
1987
). The integumentary system. In
Ham's Histology
, 9th edn., pp.
450
-474. Philadelphia: J.B. Lippincott Company.
Coulomb, B. and Dubertret, L. (
2002
). Skin cell culture and wound healing.
Wound Repair Regen.
10
,
109
-111.
Cullen, B., Silcock, D., Brown, L. J., Gosiewska, A. and Geesin, J. C. (
1997
). The differential regulation and secretion of proteinases from fetal and neonatal fibroblasts by growth factors.
Int. J. Biochem. Cell Biol.
29
,
241
-250.
Demarchez, M., Hartmann, D. J., Regnier, M. and Asselineau, D. (
1992
). The role of fibroblasts in dermal vascularization and remodeling of reconstructued human skin after transplantation onto the nude mouse.
Transplantation
54
,
317
-326.
Derdak, S., Penney, D. P., Keng, P., Felch, M. E., Brown, D. and Phipps, R. P. (
1992
). Differential collagen and fibronectin production by Thy 1+ and Thy 1- lung fibroblast subpopulations.
Am. J. Physiol.
263
,
L282
-L290.
Detmar, M. (
1996
). Molecular regulation of angiogenesis in the skin.
J. Invest. Dermatol.
106
,
207
-208.
Doane, K. J. and Birk, D. E. (
1991
). Fibroblasts retain their tissue phenotype when grown in three-dimensional collagen gels.
Exp. Cell Res.
195
,
432
-442.
Eckes, B., Zigrino, P., Kessler, D., Holtkotter, O., Shephard, P., Mauch, C. and Krieg, T. (
2000
). Fibroblast-matrix interactions in wound healing and fibrosis.
Matrix Biol.
19
,
325
-332.
Fleischmajer, R., MacDonald, E. D., II, Contard, P. and Perlish, J. S. (
1993
). Immunochemistry of a keratinocyte-fibroblast co-culture model for reconstruction of human skin.
J. Histochem. Cytochem.
41
,
1359
-1366.
Fleischmajer, R., Schechter, A., Bruns, M., Perlish, J. S., MacDonald, E. D., Pan, T.-C., Timpl, R. and Chu, M.-L. (
1995
). Skin fibroblasts are the only source of nidogen during early basal lamina formation in vitro.
J. Invest. Dermatol.
105
,
597
-601.
Fries, K. M., Blieden, T., Looney, R. J., Sempowski, G. D., Silvera, M. R., Willis, R. A. and Phipps, R. P. (
1994
). Evidence of fibroblast heterogeneity and the role of fibroblast subpopulations in fibrosis.
Clin. Immunol. Immunopathol.
72
,
283
-292.
Gailit, J. and Clark, R. A. F. (
1994
). Wound repair in the context of extracellular matrix.
Curr. Opin. Cell Biol.
6
,
717
-725.
Garner, W. L., Karmiol, S., Rodriguez, J. L., Smith, D. J. and Phan, S. H. (
1993
). Phenotypic differences in cytokine responsiveness of hypertrophic scar versus normal dermal fibroblasts.
J. Invest. Dermatol.
101
,
875
-879.
Geesin, J. C., Brown, L. J., Gordon, J. S. and Berg, R. A. (
1993
). Regulation of collagen synthesis in human dermal fibroblasts in contracted collagen gels by ascorbic acid, growth factors, and inhibitors of lipid peroxidation.
Exp. Cell Res.
206
,
283
-290.
Ghahary, A., Shen, Y. J., Scott, P. G. and Tredget, E. E. (
1994
). Expression of mRNA for transforming growth factor-β1 is reduced in hypertrophic scar and normal dermal fibroblasts following serial passage in vitro.
J. Invest. Dermatol.
103
,
684
-686.
Ghahary, A., Shen, Y. J., Nedelec, B., Wang, R., Scott, P. G. and Tredget, E. E. (
1996
). Collagenase production is lower in post-burn hypertrophic scar fibroblasts than in normal fibroblasts and is reduced by insulin-like growth factor-1.
J. Invest. Dermatol.
106
,
476
-481.
Gilchrest, B. A. (
1996
). A review of skin ageing and its medical therapy.
Br. J. Dermatol.
135
,
867
-873.
Gilchrest, B. A., Karassik, R. L., Wilkins, L. M., Vrabel, M. A. and Maciag, T. (
1983
). Autocrine and paracrine growth stimulation of cells derived from human skin.
J. Cell. Physiol.
117
,
235
-240.
Gonzalez-Ramos, A., Cooper, K. D. and Hammerberg, C. (
1996
). Identification of a human dermal macrophage population responsible for constitutive restraint of primary dermal fibroblast proliferation.
J. Invest. Dermatol.
106
,
305
-311.
Gosiewska, A., Yi, C.-F., Brown, L. J., Cullen, B., Silcock, D. and Geesin, J. C. (
2001
). Differential expression and regulation of extracellular matrix-associated genes in fetal and neonatal fibroblasts.
Wound Repair Regen.
9
,
213
-222.
Grässel, S., Unsöld, C., Schäcke, H., Bruckner-Tuderman, L. and Bruckner, P. (
1999
). Collagen XVI is expressed by human dermal fibroblasts and keratinocytes and is associated with the microfibrillar apparatus in the upper papillary dermis.
Matrix Biol.
18
,
309
-317.
Grinnell, F. (
1994
). Fibroblasts, myofibroblasts, and wound contraction.
J. Cell Biol.
124
,
401
-404.
Grinnell, F., Zhu, M., Carlson, M. A. and Abrams, J. M. (
1999
). Release of mechanical tension triggers apoptosis of human fibroblasts in a model of regressing granulation tissue.
Exp. Cell Res.
248
,
608
-619.
Grotendorst, G. R. (
1997
). Connective tissue growth factor: a mediatior of TGF-β action on fibroblasts.
Cytokine Growth Factor Rev.
8
,
171
-179.
Guironnet, G., Dezutter-Dambuyant, C., Gaudillere, A., Marechal, S., Schmitt, D. and Peguet-Navarro, J. (
2001
). Phenotypic and functional outcome of human monocytes or monocyte-derived dendritic cells in a dermal equivalent.
J. Invest. Dermatol.
116
,
933
-939.
Guo, L., Yu, Q.-C. and Fuchs, E. (
1993
). Targeting expression of keratinocyte growth factor to keratinocytes elicits striking changes in epithelial differentiation in transgenic mice.
EMBO J.
12
,
973
-986.
Hardy, M. H. (
1992
). The secret life of the hair follicle.
Trends Genet.
8
,
55
-61.
Harper, R. A. and Grove, G. (
1979
). Human skin fibroblasts derived from papillary and reticular dermis: differences in growth potential in vitro.
Science
204
,
526
-527.
Hasan, A., Murata, H., Falabella, A., Ochoa, S., Zhou, L., Badiavas, E. and Falanga, V. (
1997
). Dermal fibroblasts from venous ulcers are unresponsive to the action of transforming growth factor-β.
J. Dermatol. Sci.
16
,
59
-66.
Herrick, S. E., Ireland, G. W., Simon, D., McCollum, C. N. and Ferguson, M. W. J. (
1996
). Venous ulcer fibroblasts compared with normal fibroblasts show differences in collagen but not fibronectin production under both normal and hypoxic conditions.
J. Invest. Dermatol.
106
,
187
-193.
Hines, M. D. and Allen-Hoffmann, B. L. (
1996
). Keratinocyte growth factor inhibits cross-linked envelope formation and nucleosomal fragmentation in cultured human keratinocytes.
J. Biol. Chem.
271
,
6245
-6251.
Holbrook, K. A. and Minami, S. I. (
1991
). Hair follicle embryogenesis in the human. Characterization of events in vivo and in vitro.
Ann. N. Y. Acad. Sci.
642
,
167
-196.
Igarashi, M., Finch, P. W. and Aaronson, S. A. (
1996
). Characterization of recombinant human fibroblast growth factor (FGF)-10 reveals functional similarities with keratinocyte growth factor (FGF-7).
J. Biol. Chem.
273
,
13230
-13235.
Ivarsson, M., Mcwhirter, A., Borg, T. K. and Rubin, K. (
1998
). Type I collagen synthesis in cultured human fibroblasts: regulation by cell spreading, platelet-derived growth factor and interactions with collagen fibers.
Matrix Biol.
16
,
409
-425.
Jahoda, C. A. B. and Reynolds, A. J. (
1996
). Dermal-epidermal interactions. Adult follicle-derived cell populations and hair growth.
Dermatol. Clin.
14
,
573
-583.
Jahoda, C. A. B. and Reynolds, A. J. (
2000
). Hair follicle dermal sheath cells: unsung participants in wound healing.
Lancet
358
,
1445
-1448.
Juhlin, L. (
1997
). Hyaluronan in skin.
J. Intern. Med.
242
,
61
-66.
Karelina, T. V., Hruza, G. J., Goldberg, G. I. and Eisen, A. Z. (
1993
). Localization of 92-kDa type IV collagenase in human skin tumors: comparison with normal human fetal and adult skin.
J. Invest. Dermatol.
100
,
159
-165.
Karelina, T. V., Goldberg, G. I. and Eisen, A. Z. (
1994
). Matrilysin (PUMP) correlates with dermal invasion during appendageal development and cutaneous neoplasia.
J. Invest. Dermatol.
103
,
482
-487.
Karelina, T. V., Bannikov, G. A. and Eisen, A. Z. (
2000
). Basement membrane zone remodeling during appendageal development in human fetal skin. The absence of type VII collagen is associated with gelatinase-A (MMP2) activity.
J. Invest. Dermatol.
114
,
371
-375.
Kirk, T. Z., Mark, M. E., Chua, C. C., Chua, B. H. and Mayes, M. D. (
1995
). Myofibroblasts from scleroderma skin synthesize elevated levels of collagen and tissue inhibitor of metalloproteinase (TIMP-1) with two forms of TIMP-1.
J. Biol. Chem.
270
,
3423
-3428.
Kondo, S. (
2000
). The roles of cytokines in photoaging.
J. Dermatol. Sci.
23
,
S30
-S36.
Kono, T., Tanii, T., Furukawa, M., Mizuno, N., Kitajima, J., Ishii, M., Hamada, T. and Yoshizato, K. (
1990
). Cell cycle analysis of human dermal fibroblast cultured on or in hydrated type I collagen lattices.
Arch. Dermatol. Res.
282
,
258
-262.
König, A. and Bruckner-Tuderman, L. (
1991
). Epithelial-mesenchymal interactions enhance expression of collagen VII in vitro.
J. Invest. Dermatol.
96
,
803
-808.
König, A. and Bruckner-Tuderman, L. (
1994
). Transforming growth factor-β promotes deposition of collagen VII in a modified organotypic skin model.
Lab. Invest.
70
,
203
-209.
Kulessa, H., Turk, G. and Hogan, B. L. M. (
2000
). Inhibition of Bmp signaling affects growth and differentiation in the anagen hair follicle.
EMBO J.
19
,
6664
-6674.
Kupper, T. S. and Groves, R. W. (
1995
). The interleukin-1 axis and cutaneous inflammation.
J. Invest. Dermatol.
105
,
62s
-66s.
Lethias, C., Descollonges, Y., Boutillon, M.-M. and Garrone, R. (
1996
). Flexilin: a new extracellular matrix glycoprotein localized on collagen fibers.
Matrix Biol.
15
,
11
-19.
Liechty, K. W., Adzick, N. S. and Crombleholme, T. M. (
2000
). Diminished interleukin 6 (IL-6) production during scarless human fetal wound repair.
Cytokine
12
,
671
-676.
Lightner, V. A., Gumkowski, F., Bigner, D. D. and Erickson, H. P. (
1993
). Tenascin/hexabrachion in human skin: biochemical identification and localization by light and electron microscopy.
J. Cell Biol.
108
,
2483
-2493.
Limeback, H., Sodek, J. and Aubin, J. E. (
1982
). Variation in collagen expression by cloned periodontal ligament cells.
J. Periodontol. Res.
18
,
242
-248.
Lugovic, L., Lipozenocic, J. and Jakic-Razumovic, J. (
2001
). Atopic dermatitis: immunophenotyping of inflammatory cells in skin lesions.
Int. J. Dermatol.
40
,
489
-494.
Maas-Szabowski, N. and Fusenig, N. E. (
1996
). Interleukin-1-induced growth factor expression in postmitotic and resting fibroblasts.
J. Invest. Dermatol.
107
,
849
-855.
Maas-Szabowski, N., Shimotoyodome, A. and Fusenig, N. E. (
1999
). Keratinocyte growth regulation in fibroblast cocultures via a double paracrine mechanism.
J. Cell Sci.
112
,
1843
-1853.
Maas-Szabowski, N., Szabowski, A., Stark, H.-J., Andrecht, S., Kolbus, A., Schorpp-Kistner, M., Angel, P. and Fusenig, N. E. (
2001
). Organotypic cocultures with genetically modified mouse fibroblasts as a tool to dissect molecular mechanisms regulating keratinocyte growth and differentiation.
J. Invest. Dermatol.
116
,
816
-820.
Mann, A., Breuhahn, K., Schirmacher, P. and Blessing, M. (
2001
). Keratinocyte-derived granulocyte-macrophage colony stimulating factor accelerates wound healing: stimulation of keratinocyte proliferation, granulation tissue formation, and vascularization.
J. Invest. Dermatol.
117
,
1382
-1390.
Marchese, C., Felici, A., Visco, V., Lucania, G., Igarashi, M., Picardo, M., Frati, L. and Torrisi, M. R. (
2001
). Fibroblast growth factor 10 induces proliferation and differentiation of human primary cultured keratinocytes.
J. Invest. Dermatol.
116
,
623
-628.
Marinkovich, M. P., Keene, D. R., Rimberg, C. S. and Burgeson, R. E. (
1993
). Cellular origin of the dermal-epidermal basement membrane.
Dev. Dyn.
197
,
255
-267.
Martin, P. (
1997
). Wound healing - aiming for perfect skin regeneration.
Science
276
,
75
-81.
Mauch, C., Hatamochi, A., Scharffetter, K. and Krieg, T. (
1988
). Regulation of collagen synthesis in fibroblasts within a three-dimensional collagen gel.
Exp. Cell Res.
178
,
493
-503.
Meigel, W. N., Gay, S. and Weber, L. (
1977
). Dermal architecture and collagen type distribution.
Arch. Dermatol. Res.
259
,
1
-8.
Michel, M., Germain, L. and Auger, F. A. (
1993
). Anchored skin equivalent cultured in vitro: a new tool for percutaneous absorption studies.
In Vitro Cell. Dev. Biol. Anim.
29
,
834
-837.
Millar, S. E. (
2002
). Molecular mechanisms regulating hair follicle development.
J. Invest. Dermatol.
118
,
216
-225.
Mio, T., Adachi, Y., Romberger, D. J., Ertel, R. F. and Rennard, S. L. (
1996
). Regulation of fibroblast proliferation in three-dimensional collagen gel matrix.
In Vitro Cell. Dev. Biol. Anim.
32
,
427
-433.
Monical, P. L. and Kefalides, N. A. (
1994
). Coculture modulates laminin synthesis and mRNA levels in epidermal keratinocytes and dermal fibroblasts.
Exp. Cell. Res.
210
,
154
-159.
Moulin, V. (
1995
). Growth factors in skin wound healing.
Eur. J. Cell Biol.
68
,
1
-7.
Moulin, V., Auger, F. A., Garrel, D. and Germain, L. (
2000
). Role of wound healing myofibroblasts on re-epithelialization of human skin.
Burns
26
,
3
-12.
Nakaoka, H., Miyauchi, S. and Miki, Y. (
1995
). Proliferating activity of dermal fibroblasts in keloids and hypertrophic scars.
Acta Derm. Verereol.
75
,
102
-104.
Nestle, F. O. and Nickoloff, B. J. (
1995
). A fresh morphological and functional look at dermal dendritic cells.
J. Cutan. Pathol.
22
,
385
-392.
Olsen, D. R. and Uitto, J. (
1989
). Differential expression of type IV procollagen and laminin genes by fetal vs adult skin fibroblasts in culture: determination of subunit mRNA steady-state levels.
J. Invest. Dermatol.
93
,
127
-131.
Pierce, G. F., Mustoe, T. A., Altrock, B. W., Deuel, T. F. and Thomason, A. (
1991
). Role of platelet-derived growth factor in wound healing.
J. Cell. Biochem.
45
,
319
-326.
Ponec, M. (
2002
). Skin constructs for replacement of skin tissues for in vitro testing.
Adv. Drug Deliv. Rev.
54
,
S19
-S30.
Regnier, M., Staquet, M.-J., Schmitt, D. and Schmidt, R. (
1997
). Integration of Langerhans cells into a pigmented reconstructed human epidermis.
J. Invest. Dermatol.
109
,
510
-512.
Reynolds, A. J. and Jahoda, C. A. B. (
1991
). Inductive properties of hair follicle cells.
Ann. N. Y. Acad. Sci.
642
,
226
-241.
Rheinwald, J. G. and Green, H. (
1975
). Formation of a keratinizing epithelium in culture by a cloned cell line derived form a teratoma.
Cell
6
,
317
-330.
Rosenfeldt, H. and Grinnell, F. (
2000
). Fibroblast quiescence and the disruption of ERK signaling in mechanically unloaded collagen matrices.
J. Biol. Chem.
275
,
3088
-3092.
Rubin, J. S., Bottaro, D. P. and Aaronson, S. A. (
1993
). Hepatocyte growth factor/scatter factor and its receptor, the c-met proto-oncogene product.
Biochim. Biophys. Acta
1155
,
357
-371.
Rubin, J. S., Bottaro, D. P., Chedid, M., Miki, T., Ron, D., Cheon, G., Taylor, W. G., Fortney, E., Sakata, H., Finch, P. W. et al. (
1995
). Keratinocyte growth factor.
Cell Biol. Int.
19
,
399
-411.
Sappino, A. P., Schurch, W. and Gabbiani, G. (
1990
). Differentiation repertoire of fibroblastic cells: expression of cytoskeletal proteins as marker of phenotypic modulations.
Lab. Invest.
63
,
144
-161.
Sato, C., Tsuboi, R., Shi, C.-M., Rubin, J. S. and Ogawa, H. (
1995
). Comparative study of hepatocyte growth factor/scatter factor and keratinocyte growth factor effects on human keratinocytes.
J. Invest. Dermatol.
104
,
958
-963.
Schafer, I. A., Pandy, M., Ferguson, R. and Davis, B. R. (
1985
). Comparative observation of fibroblasts derived from the papillary and reticular dermis of infants and adults: growth kinetics, packing density ant confluence and surface morphology.
Mech. Ageing Dev.
31
,
275
-293.
Schmeichel, K. L. and Bissell, M. J. (
2003
). Modeling tissue-specific signaling and organ function in three dimensions.
J. Cell Sci.
116
,
2377
-2388.
Schönherr, E., Beavan, L. A., Hausser, H., Kresse, H. and Culp, L. A. (
1993
). Differences in decorin expression by papillary and reticular fibroblasts in vivo and in vitro.
Biochem. J.
290
,
893
-899.
Schor, S. L., Schor, A. M., Rushton, G. and Smith, L. (
1985
). Adult, foetal and transformed fibroblasts display different migratory phenotypes on collagen gels: evidence for an isoformic transition during foetal development.
J. Cell Sci.
73
,
221
-234.
Schröder, J.-M. (
1995
). Cytokine networks in skin.
J. Invest. Dermatol.
105
,
20S
-24S.
Shah, M., Foreman, D. M. and Ferguson, M. W. J. (
1994
). Neutralising antibody to TGF-β1,2 reduces cutaneous scarring in adult rodents.
J. Cell Sci.
107
,
1137
-1157.
Shah, M., Foreman, D. M. and Ferguson, M. W. J. (
1995
). Neutralization of TGF-β1 and TGF-β2 or exogenous addition of TGF-β3 to cutaneous rat wounds reduces scarring.
J. Cell Sci.
108
,
985
-1002.
Shaulian, E. and Karin, M. (
2002
). AP-1 as a regulator of cell life and death.
Nat. Cell Biol.
4
,
E131
-E136.
Singer, A. J. and Clark, R. A. F. (
1999
). Cutaneous wound healing.
N. Engl. J. Med.
341
,
738
-746.
Slavin, J. (
1996
). The role of cytokines in wound healing.
J. Pathol.
178
,
5
-10.
Smith, R. S., Smith, T. J., Blieden, T. M. and Phipps, R. P. (
1997
). Fibroblasts as sentinel cells. Synthesis of chemiokines and regulation of inflammation.
Am. J. Pathol.
151
,
317
-322.
Smola, H., Thiekötter, G. and Fusenig, N. E. (
1993
). Mutual induction of growth factor gene expression by epidermal-dermal cell interaction.
J. Cell Biol.
122
,
417
-429.
Smola, H., Thiekötter, G., Baur, M., Stark, H.-J., Breitkreutz, D. and Fusenig, N. E. (
1994
). Organotypic and epidermal-dermal cocultures of normal human keratinocytes and dermal cells: regulation of transforming growth factor α, β1, and β2 mRNA levels.
Toxicol. In Vitro
8
,
641
-650.
Smola, H., Stark, H.-J., Thiekötter, G., Mirancea, N., Krieg, T. and Fusenig, N. E. (
1998
). Dynamics of basement membrane formation by keratinocyte-fibroblast interactions in organotypic skin culture.
Exp. Cell Res.
239
,
399
-410.
Sollberg, S., Mauch, C., Eckes, B. and Krieg, T. (
1994
). The fibroblast in systemic sclerosis.
Clin. Dermatol.
12
,
379
-385.
Sorrell, J. M., Baber, M. A. and Caplan, A. I. (
1996
). Construction of a Bilayered dermal equivalent containing human papillary and reticular dermal fibroblasts: use of fluorescent vital dyes.
Tissue Eng.
2
,
39
-49.
Sorrell, J. M., Carrino, D. A., Baber, M. A., Asselineau, D. and Caplan, A. I. (
1999a
). A monoclonal antibody which recognizes a glycosaminoglycan epitope in both dermatan sulphate and chondroitin sulphate proteoglycans of human skin.
Histochemical J.
31
,
549
-558.
Sorrell, J. M., Carrino, D. A., Baber, M. A. and Caplan, A. I. (
1999b
). Versican in human fetal skin development.
Anat. Embryol. (Berl.)
199
,
45
-56.
Sorrell, J. M., Baber, M. A. and Caplan, A. I. (
2004
). Site-matched papillary and reticular human dermal fibroblasts differ in their release of specific growth factors/cytokines and in their interaction with keratinocytes.
J. Cell. Physiol.
E-pub ahead of print 16 Dec. 2003.
Stephens, P. S., Davies, K. J., Occleston, N., Pleass, R. D., Kon, C., Daniels, J., Khaw, P. T. and Thomas, D. W. (
2001
). Skin and oral fibroblasts exhibit phenotypic differences in extracellular matrix reorganization and matrix metalloproteinase activity.
Br. J. Dermatol.
144
,
229
-237.
Supp, D. M., Wilson-Landy, W. and Boyce, S. T. (
2002
). Human dermal microvascular endothelial cells form vascular analogs in cultured skin substitutes after grafting to athymic mice.
FASEB J.
16
,
797
-804.
Suzuki, K., Yamanishi, K., Mori, O., Kamikawa, M., Andersen, B., Kato, S., Toyoda, T. and Yamada, G. (
2000
). Defective terminal differentiation and hypoplasia of the epidermis in mice lacking the Fgf10 gene.
FEBS Lett.
481
,
53
-56.
Szabowski, A., Maas-Szabowski, N., Andrecht, S., Kolbus, A., Schorpp-Kristner, M., Fusenig, N. E. and Angel, P. (
2000
). c-Jun and JunB antagonistically control cytokine-regulated mesenchymal-epidermal interaction in skin.
Cell
103
,
745
-755.
Tajima, S. and Pinnell, S. R. (
1981
). Collagen synthesis by human skin fibroblasts in culture: studies of fibroblasts explanted from papillary and reticular dermis.
J. Invest. Dermatol.
77
,
410
-412.
Waelti, E. R., Inaebnit, S. P., Rast, H. P., Hunziker, T., Limat, A., Braathen, L. R. and Wiesmann, U. (
1992
). Co-culture of human keratinocytes on post-mitotic human dermal fibroblast feeder cells: production of large amounts of interleukin 6.
J. Invest. Dermatol.
98
,
805
-808.
Wälchli, C., Koch, M., Chiquet, M., Odermatt, B. F. and Trueb, B. (
1994
). Tissue-specific expression of the fibril-associated collagens XII and XIV.
J. Cell Sci.
107
,
669
-681.
Werner, S. (
1998
). Keratinocyte growth factor: a unique player in epithelial repair processes.
Cytokine Growth Factor Rev.
9
,
153
-165.
Werner, S. and Smola, H. (
2001
). Paracrine regulation of keratinocyte proliferation and differentiation.
Trends Cell Biol.
11
,
143
-146.
Zimmermann, D. R., Dours-Zimmermann, M. T., Schubert, M. and Bruckner-Tuderman, L. (
1994
). Versican is expressed in the proliferating zone in the epidermis and in association with the elastic network of the dermis.
J. Cell Biol.
124
,
817
-825.