At the mention of serotonin, people commonly think of its role as regulating anxiety, mood, and happiness in the brain. However, 95% of the body’s serotonin is produced by enterochromaffin (EC) cells present in the tissue lining of the gut (1) before being taken up by platelets that circulate it throughout the body (2). The EC cell releases serotonin in response to mechanical and chemical stimulation, and this release differs depending on whether the body has been fed or is fasted (3). Gut-derived serotonin is important for regulating:
- Stretch and contraction of the gut
- Gut sensation
- The ability for platelets to clot blood
- Bone development
- Blood pressure
- Metabolism (1)
There are still many questions regarding how the EC cell releases serotonin. Recent studies from Dr. Beyder’s laboratory of Mayo Clinic discovered that a mechanosensitive ion channel called Piezo2 is present in human and mouse EC cells, and that Piezo2 is important for serotonin release in EC cell models after a mechanical force like pressure is applied (4, 5). In the broad scheme of things, understanding the role of Piezo2 in EC cell serotonin release and in regulation of blood serotonin levels could lead to future drug developments for gastrointestinal diseases.
Dr. Beyder’s laboratory created a mouse model with the Piezo2 gene knocked out of the gastrointestinal tissue lining the gut. These knockout mice can be compared to the control mice that do not have the Piezo2 gene removed to see how Piezo2 affects the physiology of the gut. My aims for my ten week research fellowship were:
- To determine the role of Piezo2 in mechanosensitive EC cell serotonin release from primary EC cells from fed and fasted epithelial Piezo2 knockout and control mice
- To determine the role of Piezo2 in systemic serotonin levels in fed and fasted epithelial Piezo2 knockout and control mice
As is the case with most research, everything did not turn out as planned!
In the first few weeks of my research project, I had already faced unexpected complications. I was planning to collect cells from mouse colon and place them on a special plate with the proper nutrients and environment to help them grow into what is called a primary culture. However, we were not able to take pictures to show that the primary cultures were present since we did not have a microscope lens that could fit the wells in the plate. With the limited time I had for the project, my team decided to focus on measuring whole gut serotonin instead. This highlights how quickly a research project can change and the many approaches a scientist can take to solve a problem. There were also times I would try a new technique to yield better results, but would ultimately go back to the original technique. Overall, the general research process was to look back to see how an experiment was done in the past, and then complete a series of trial and error cycles from there to optimize the protocol for my specific project.
Amid the journal clubs and experiments, this summer I learned about the collaborative efforts required to be successful as a scientist. I shared equipment and bench space with other researchers in the lab, so we had to coordinate a schedule so that everyone could complete their experiments. I enjoyed getting to know the other members of the lab, many with diverse backgrounds and specialties. Every week the department had a lab meeting where someone from each lab would take turns presenting research updates. It was a great opportunity to learn about other projects that related to the enteric nervous system and new adjustments made to fix problems. That being said, life as a researcher has its challenges. There were days I would spend hours preparing an experiment, only to made a mistake that could have been prevented if I would have asked the right person. If I had to give any advice from my summer experience, I would say don’t be afraid to ask for help – especially if you are feeling discouraged! Everyone in a lab develops his or her own expertise in something, which makes it impossible to know everything. But one of the beauties of science is that there is still a lot for us to learn, and sometimes the most frustrating failures can bring unexpected discoveries.
- Mawe GM, Hoffman JM. Serotonin signalling in the gut–functions, dysfunctions and therapeutic targets. Nature Reviews: Gastroenterology and Hepatology 10: 473-86, 2013; 10.1038/nrgastro.2013.105.
- Berger M, Gray JA, Roth BL. The expanded biology of serotonin. Annu Rev Med. 60: 355-66, 2009; 10.1146/annurev.med.60.042307.110802.
- Sumara G, Sumara O, Kim JK, Karsenty G. Gut-derived serotonin is a multifunctional determinant to fasting adaptation. Cell Metab. 16: 588-600, 2012; 10.1016/j.cmet.2012.09.014.
- Wang F, Knutson K, Alcaino C, Linden DR, Gibbons SJ, Kashyap PK, Grover M, Oeckler R, Gottlieb PA, Li HJ, Leiter AB, Farrugia G, Beyder A. Mechanosensitive ion channel Piezo2 is important for enterochromaffin cell response to mechanical forces. J Physiol. 595: 79-91, 2016; 10.1113/JP272718 PMCID: PMC27392819.
- Alcaino C, Knutson K, Gottlieb PA, Farrugia G, Beyder A. Mechanosensitive ion channel Piezo2 is inhibited by D-GsMTx4. Channels. 11: 245-253, 2017; 10.1080/19336950.2017.1279370.