The people behind the papers – Alfahdah Alsudayri and Lihua Ye

Lihua Ye (left) and Alfahdah Alsudayri (right)

Lihua, can you give us your scientific biography and what are the questions your lab is trying to answer?

LY: I did my PhD in Dr Ryan Anderson's laboratory to study pancreatic β-cell regeneration using the zebrafish model. The beauty and power of in vivo imaging and genetic manipulation of the zebrafish model captured me. At the end of my PhD, my mother was diagnosed with irritable bowel syndrome, which made me interested in microbiota-gut-brain communication. Following my PhD, I was fortunate to receive mentorship from Drs John Rawls and Rodger Liddle at Duke University. Their expertise helped me to develop zebrafish as a new model system for studying microbiota-gut-brain communication in a cellular and microbial-specific manner. I am interested in the EECs, which are the frontline sensory cells in the intestine epithelium that integrate both nutrient and microbial information. My lab is interested in understanding how EECs sense diverse information in the intestinal lumen and how EECs transmit such information to the nervous system to regulate gastrointestinal function and brain activity. Finally, we hope to understand whether and how we can manipulate EEC-associated signalling for disease treatment.

Alfahdah, how did you come to work in Lihua's lab?

AA: Lihua was starting her lab at Ohio State University and the research she was conducting was at the intersection of many cutting-edge fields; I couldn't miss the chance to be a part of it. Lihua was immensely passionate about the zebrafish as a model, and her enthusiasm was contagious. When working with zebrafish, you can appreciate how well they serve as a visualisation tool and how they facilitate understanding with such dynamic imaging.

Before your work, what was known about how environmental factors regulate the maturation and function of EECs?

LY: EECs exhibit plasticity. Environmental factors such as diet and gut microbiota may affect EEC number, transcriptomics and hormone expression profile. For example, using the gnotobiotic approach, a previous study demonstrated that gut microbiota regulate serotonin biosynthesis in a subtype of EECs called enterochromaffin cells (Yano et al., 2015). Another study demonstrates that EECs in germ-free and conventionally raised adult animals display different transcriptomic signatures (Arora et al., 2018). We have also shown that the nutrient-sensing ability of EECs may be silenced in response to high-fat feeding (Ye et al., 2019). However, most of the previous studies have been focused on adult animals. Little is known about the EECs during the embryonic or postnatal development stage. Immediately after birth, the intestines are colonised by commensal microbiota. The early postnatal commensal microbiota colonisation is considered a major event that promotes the host developmental process. We think our research provides new evidence to suggest that gut microbiota colonisation is crucial in supporting the development and function of postnatal EECs, and gut microbiota may support the maturation of EECs by promoting their mitochondrial function.

Can you give us the key results of the paper in a paragraph?

LY: By directly imaging and tracking the cellular and mitochondrial calcium activity of EECs in live zebrafish larvae, our results reveal that the morphology, and cellular and mitochondrial activity of EECs are dynamically regulated during the EEC maturation process. Most importantly, our results reveal that gut microbiota play crucial roles in promoting EEC maturation and mitochondrial function.

Did you expect to find from your transcriptional analysis that gut microbiota promote the expression of genes associated with mitochondrial function?

LY: Not at all, we were surprised to find mitochondrial genes were highly expressed in the transcriptional analysis. This is part of what our paper both highlights and elucidates, but we are just becoming knowledgeable in.

Alfahdah, when doing the research, did you have any particular result or eureka moment that has stuck with you?

AA: What surprised me the most was seeing, in real time, the maturation of the EEC mitochondria in the germ-free and conventionalised zebrafish – a phenomenon we called ‘EEC awakening’. Instead of having one eureka moment, I was consistently amazed by how significantly gut microbiota impacted the morphology, function and development of the EECs.

And what about the flipside: any moments of frustration or despair?

AA: Moments of frustration were rare; we collaborated as a team to emphasise and complement our individual strengths, while mitigating potential weaknesses.

Can you postulate the molecular mechanisms of how signals from the gut microbiota regulate EEC mitochondrial function?

LY: EECs express different receptors that may sense microbial information. For example, a microbially derived short chain fatty acid regulates EECs via free fatty acid receptor 2 (FFAR2). Tryptophan metabolites generated by gut bacteria may also affect EECs through aryl hydrocarbon receptor (AhR), pregnane X receptor (PxR) or transient receptor potential ankyrin 1 (Trpa1). In addition, EECs are also known to interact with microbially modified bile acids through G-protein-coupled bile acid receptor 1 (GPBAR1). We are currently using genetic and pharmaceutical approaches to manipulate different EEC receptor signalling to examine whether and how EEC encoded microbial sensing receptors are required to promote EEC mitochondrial function. We are also using gnotobiotic approaches to screen different commensal bacterial strains to examine the microbial specificity in promoting EEC mitochondria function.

Why did you choose to submit this paper to Development?

LY: Development is a highly respected journal and was our first choice because of the nature of our data. As our data were consistently pointing us in a developmental direction, we concluded it would add the most value to the developmental biology literature and help shed light on an area that we only have scratched the surface of.

Alfahdah, what is next for you after this paper?

AA: I am excited for what our lab has to come! We are working on publishing new data and establishing our lab here at Ohio State University. Eventually, I plan on conducting translational research to apply our findings in clinical settings.

Lihua, where will this story take your lab next?

LY: We are interested in continuing to understand the microbial and molecular mechanisms by which gut microbiota regulate the development and mitochondrial function of EECs. It is well known that mitochondria are the key organelle that provides energy, and mitochondrial metabolism affects the cellular differentiation process. However, little is known about the function and regulation mechanisms of mitochondria in EECs. We are currently collaborating with Dr Lufang Zhou and Dr Katie Drerup to develop new optogenetic tools to manipulate EEC mitochondrial function in zebrafish. We hope to use these new tools to understand how EEC mitochondrial function affects gut-brain nutrient-sensing capacity, feeding behaviour and metabolism.

Finally, let's move outside the lab – what do you like to do in your spare time?

AA: Outside the lab, I enjoy connecting with my family and friends, despite being in different time zones! I also like traveling, painting and volunteering as much as I can.

LY: Outside the lab, I enjoy time with my family and friends, and attending church worship. I love nature and animals. Hiking, going to the zoo and reading books are my favourite activities.