Previous studies have shown that static equilibrium compression of cartilage tissue in vivo and in vitro decreases chondrocyte synthesis of aggrecan molecules. In order to identify mechanisms of cellular response to loading, we have investigated alterations in cell and nucleus structure and the accompanying changes in the synthesis of aggrecan in statically compressed cartilage explants. Using glutaraldehyde fixation and quantitative autoradiography of compressed and radiolabeled cartilage disks we spatially localized newly synthesized aggrecan. Using stereological tools to analyze these same specimens we estimated the cell and nucleus volume, surface area and directional radii. We found that aggrecan synthesis was reduced overall in compressed tissue disks. However, the compression induced a spatial (radial) inhomogeneity in aggrecan synthesis which was not present in uncompressed disks. This spatial inhomogeneity appeared to be directly related to mechanical boundary conditions and the manner in which the load was applied and, therefore, may represent a spatially specific functional adaptation to mechanical loading. Coincident with reduced aggrecan synthesis, we observed reductions in cell and nucleus volume and radii in the direction of compression which were in approximate proportion to the reduction in tissue thickness. Cell and nucleus dimensions perpendicular to the direction of compression did not change significantly. Therefore the observed deformation of the cell and nucleus in statically compressed cartilage approximately followed the dimensional changes imposed on external specimen surfaces. The strong correlation observed between local changes in aggrecan synthesis and alterations in cell and nucleus structure also lend support to certain hypotheses regarding the intracellular signal transduction pathways that may be important in the biosynthetic response of chondrocytes to mechanical loading.

Akeson
W. H.
,
Woo
S. L.
,
Amiel
D.
,
Coutts
R. D.
,
Daniel
D.
(
1973
).
The connective tissue response to immobility: biochemical changes in periarticular connective tissue of the immobilized rabbit knee.
Clin. Orthop
93
,
356
362
Ausio
J.
(
1992
).
Structure and dynamics of transcriptionally active chromatin.
J. Cell Sci
102
,
1
5
Baddeley
A. J.
,
Gundersen
H. J. G.
,
Cruz Orive
L. M.
(
1986
).
Estimation of surface area from vertical sections.
J. Microsc
142
,
259
276
Boustany
N. N.
,
Gray
M. L.
,
Black
A. C.
,
Hunziker
E. B.
(
1995
).
Correlation between the synthetic activity and glycosaminoglycan concentration in epiphysial cartilage raises questions about the regulatory role of interstitial pH.
J. Orthop. Res
13
,
733
739
Burridge
K.
,
Turner
C. E.
,
Romer
L. H.
(
1992
).
Tyrosine phosphorylation of paxillin and pp125FAKaccompanies cell adhesion to extracellular matrix: A role in cytoskeletal assembly.
J. Cell Biol
119
,
893
903
Buschmann
M. D.
,
Gluzband
Y. A.
,
Grodzinsky
A. J.
,
Kimura
J. H.
,
Hunziker
E. B.
(
1992
).
Chondrocytes in agarose culture synthesize a mechanically functional extracellular matrix.
J. Orthop. Res
10
,
745
758
Buschmann
M. D.
,
Gluzband
Y. A.
,
Grodzinsky
A. J.
,
Hunziker
E. B.
(
1995
).
Mechanical compression modulates matrix biosynthesis in chondrocyte/agarose culture.
J. Cell Sci
108
,
1497
1508
Buschmann
M. D.
,
Grodzinsky
A. J.
(
1995
).
A molecular model of proteoglycan-associated electrostatic forces in cartilage mechanics.
J. Biomech. Eng
117
,
179
192
Caterson
B.
,
Lowther
D. A.
(
1978
).
Changes in the metabolism of the proteoglycans from sheep articular cartilage in response to mechanical stress.
Biochim. Biophys. Acta
540
,
412
422
Cook
P. R.
(
1989
).
The nucleoskeleton and the topology of transcription.
Eur. J. Biochem
185
,
487
501
Copray
J. C.
,
Jansen
H. W.
,
Duterloo
H. S.
(
1985
).
Effects of compressive forces on proliferation and matrix synthesis in mandibular condylar cartilage of the rat in vitro.
Arch. Oral Biol
30
,
299
304
Cruz Orive
L. M.
,
Hunziker
E. B.
(
1986
).
Stereology for anisotropic cells: Application to growth cartilage.
J. Microsc
143
,
47
80
Dillon
N.
,
Grosveld
F.
(
1993
).
Transcriptional regulation of multigene loci: Multilevel control.
Trends Genet
9
,
134
137
Durr
J.
,
Goodman
S.
,
Potocnik
A.
,
Vondermark
H.
,
Vondermark
K.
(
1993
).
Localization of-1-integrins in human cartilage and their role in chondrocyte adhesion to collagen and fibronectin.
Exp. Cell Res
207
,
235
244
Enomoto
M.
,
Leboy
P. S.
,
Menko
A. S.
,
Boettiger
D.
(
1993
).
-1 Integrins mediate chondrocyte interaction with type-I collagen, type-II collagen, and fibronectin.
Exp. Cell Res
205
,
276
285
Frank
E. H.
,
Grodzinsky
A. J.
(
1987
).
Cartilage electromechanics I. Electrokinetic transduction and the effects of electrolyte pH and ionic strength.
J. Biomech
20
,
615
627
Freeman
P. M.
,
Natarajan
R. N.
,
Kimura
J. H.
,
Andriacchi
T. P.
(
1994
).
Chondrocyte cells respond mechanically to compressive loads.
J. Orthop. Res
12
,
311
20
Georgatos
S. D.
,
Blobel
G.
(
1987
).
Two distinct attachment sites for vimentin along the plasma membrane and the nuclear envelope in avian erythrocytes: A basis for a vectorial assembly of intermediate filaments.
J. Cell Biol
105
,
105
115
Goldman
R.
,
Goldman
A.
,
Green
K.
,
Jones
J.
,
Lieska
N.
,
Yang
H. Y.
(
1985
).
Intermediate filaments: Possible functions as cytoskeletal connecting links between the nucleus and the cell surface.
Ann. NY Acad. Sci
455
,
1
17
Gray
M. L.
,
Pizzanelli
A. M.
,
Grodzinsky
A. J.
,
Lee
R. C.
(
1988
).
Mechanical and physiochemical determinants of the chondrocyte biosynthetic response.
J. Orthop. Res
6
,
777
792
Guilak
F.
,
Ratcliffe
A.
,
Mow
V. C.
(
1995
).
Chondrocyte deformation and local tissue strain in articular cartilage: A confocal microscopy study.
J. Orthop. Res
13
,
410
421
Gundersen
H. J.
(
1988
).
The nucleator.
J. Microsc
151
,
3
21
Gundersen
H. J.
,
Bagger
P.
,
Bendtsen
T. F.
,
Evans
S. M.
,
Korbo
L.
,
Marcussen
N.
,
Moller
A.
,
Nielsen
K.
,
Nyengaard
J. R.
,
Pakkenberg
B.
, et al. 
(
1988
).
The new stereological tools: disector, fractionator, nucleator and point sampled intercepts and their use in pathological research and diagnosis.
APMIS
96
,
857
881
Heinegard
D.
,
Oldberg
A.
(
1989
).
Structure and biology of cartilage and bone matrix noncollagenous macromolecules.
FASEB J
3
,
2042
2051
Hershey
J. W.
(
1991
).
Translational control in mammalian cells.
Annu. Rev. Biochem
60
,
717
755
Hesketh
J. E.
,
Pryme
I. F.
(
1991
).
Interaction between mRNA, ribosomes and the cytoskeleton.
Biochem. J
277
,
1
10
Hunziker
E. B.
,
Schenk
R. K.
(
1989
).
Physiological mechanisms adopted by chondrocytes in regulating longitudinal bone growth in rats.
J. Physiol
414
,
55
71
Ingber
D. E.
,
Madri
J. A.
,
Folkman
J.
(
1987
).
Endothelial growth factors and extracellular matrix regulate DNA synthesis through modulation of cell and nuclear expansion.
In Vitro Cell Dev. Biol
23
,
387
394
Jiang
L. W.
,
Schindler
M.
(
1988
).
Nuclear transport in 3T3 fibroblasts: Effects of growth factors, transformation and cell shape.
J. Cell Biol
106
,
13
19
Jones
I. L.
,
Klamfeldt
A.
,
Sandstrom
T.
(
1982
).
The effect of continuous mechanical pressure upon the turnover of articular cartilage proteoglycans in vitro.
Clin. Orthop
165
,
283
289
Jurvelin
J.
,
Kiviranta
I.
,
Saamanen
A. M.
,
Tammi
M.
,
Helminen
H. J.
(
1990
).
Indentation stiffness of young canine knee articular cartilage--influence of strenuous joint loading.
J. Biomech
23
,
1239
1246
Kim
Y. J.
,
Sah
R. L. Y.
,
Grodzinsky
A. J.
,
Plaas
A. H. K.
,
Sandy
J. D.
(
1994
).
Mechanical regulation of cartilage biosynthetic behavior: physical stimuli.
Arch. Biochem. Biophys
311
,
1
12
Kim
Y. J.
,
Bonasser
L. J.
,
Grodzinsky
A. J.
(
1995
).
The role of cartilage streaming potential, fluid flow and pressure in the stimulation of chondrocyte biosynthesis during dynamic compression.
J. Biomech
28
,
1055
1066
Kiviranta
I.
,
Jurvelin
J.
,
Tammi
M.
,
Saamanen
A. M.
,
Helminen
H. J.
(
1987
).
Weight bearing controls glycosaminoglycan concentration and articular cartilage thickness in the knee joints of young beagle dogs.
Arthritis Rheum
30
,
801
809
Kiviranta
I.
,
Tammi
M.
,
Jurvelin
J.
,
Saamanen
A. M.
,
Helminen
H. J.
(
1988
).
Moderate running exercise augments glycosaminoglycans and thickness of articular cartilage in the knee joint of young beagle dogs.
J. Orthop. Res
6
,
188
195
Knudson
C. B.
,
Knudson
W.
(
1993
).
Hyaluronan-binding proteins in development, tissue homeostasis and disease.
FASEB J
7
,
1233
1241
Korver
T. H.
,
van de Stadt
R. J.
,
Kiljan
E.
,
van Kampen
G. P.
,
van der Korst
J. K.
(
1992
).
Effects of loading on the synthesis of proteoglycans in different layers of anatomically intact articular cartilage in vitro.
J. Rheumatol
19
,
905
912
Larsson
T.
,
Aspden
R. M.
,
Heinegard
D.
(
1991
).
Effects of mechanical load on cartilage matrix biosynthesis in vitro.
Matrix
11
,
388
394
Moller
A.
,
Strange
P.
,
Gundersen
H. J.
(
1990
).
Efficient estimation of cell volume and number using the nucleator and the disector.
J. Microsc
159
,
61
71
Mow
V. C.
,
Kuei
S. C.
,
Lai
W. M.
,
Armstrong
C. G.
(
1980
).
Biphasic creep and stress relaxation of articular cartilage in compression: Theory and experiments.
J. Biomech. Eng
102
,
73
84
Mow
V. C.
,
Holmes
M. H.
,
Lai
W. M.
(
1984
).
Fluid transport and mechanical properties of articular cartilage: A review.
J. Biomech
17
,
377
394
Ohshima
H.
,
Urban
J. P.
(
1992
).
The effect of lactate and pH on proteoglycan and protein synthesis rates in the intervertebral disc.
Spine
17
,
1079
1082
Olah
E. H.
,
Kostenszky
K. S.
(
1972
).
Effect of altered functional demand on the glycosaminoglycan content of the articular cartilage of dogs.
Acta Biol. Acad. Sci. Hung
23
,
195
200
Palmoski
M.
,
Perricone
E.
,
Brandt
K. D.
(
1979
).
Development and reversal of a proteoglycan aggregation defect in normal canine knee cartilage after immobilization.
Arthritis Rheum
22
,
508
517
Palmoski
M. J.
,
Brandt
K. D.
(
1984
).
Effects of static and cyclic compressive loading on articular cartilage plugs in vitro.
Arthritis Rheum
27
,
675
681
Pante
N.
,
Aebi
U.
(
1993
).
The nuclear pore complex.
J. Cell Biol
122
,
977
984
Parkkinen
J. J.
,
Lammi
M. J.
,
Helminen
H. J.
,
Tammi
M.
(
1992
).
Local stimulation of proteoglycan synthesis in articular cartilage explants by dynamic compression in vitro.
J. Orthop. Res
10
,
610
620
Sah
R. L.
,
Kim
Y. J.
,
Doong
J. Y.
,
Grodzinsky
A. J.
,
Plaas
A. H.
,
Sandy
J. D.
(
1989
).
Biosynthetic response of cartilage explants to dynamic compression.
J. Orthop. Res
7
,
619
636
Salter
R. B.
,
Simmonds
D. F.
,
Malcolm
B. W.
,
Rumble
E. J.
,
MacMichael
D.
,
Clements
N. D.
(
1980
).
The biological effect of continuous passive motion on the healing of full-thickness defects in articular cartilage.
J. Bone Joint Surg
62
,
1232
1251
Schneiderman
R.
,
Keret
D.
,
Maroudas
A.
(
1986
).
Effects of mechanical and osmotic pressure on the rate of glycosaminoglycan synthesis in the human adult femoral head cartilage: An in vitro study.
J. Orthop. Res
4
,
393
408
Sims
J. R.
,
Karp
S.
,
Ingber
D. E.
(
1992
).
Altering the cellular mechanical force balance results in integrated changes in cell, cytoskeletal and nuclear shape.
J. Cell Sci
103
,
1215
1222
Singer
R. H.
(
1992
).
The cytoskeleton and mRNA localization.
Curr. Opin. Cell Biol
4
,
15
19
Slowman
S. D.
,
Brandt
K. D.
(
1986
).
Composition and glycosaminoglycan metabolism of articular cartilage from habitually loaded and habitually unloaded sites.
Arthritis Rheum
29
,
88
94
Spector
D. L.
(
1993
).
Macromolecular domains within the cell nucleus.
Annu. Rev. Cell Biol
9
,
265
315
Stairmand
J. W.
,
Holm
S.
,
Urban
J. P.
(
1991
).
Factors influencing oxygen concentration gradients in the intervertebral disc. A theoretical analysis.
Spine
16
,
444
449
Urban
J. P.
,
Hall
A. C.
,
Gehl
K. A.
(
1993
).
Regulation of matrix synthesis rates by the ionic and osmotic environment of articular chondrocytes.
J. Cell. Physiol
154
,
262
270
Vale
R. D.
(
1987
).
Intracellular transport using microtubule-based motors.
Annu. Rev. Cell Biol
3
,
347
378
Yen
A.
,
Pardee
A. B.
(
1979
).
Role of nuclear size in cell growth initiation.
Science
204
,
1315
1317
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