lab | APS Undergraduate Researcher

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.

A visual representation of serotonin release from EC cells and platelet uptake. Reference: Modified from Mawe & Hoffman. Nature Rev Gastro & Hep. 2013. (1)

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.

After collecting and preparing samples, I ran a test called an enzyme-linked immunosorbent assay (ELISA) that quantifies the amount of serotonin in a sample.

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.

References

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.

Alecia Alto attends the University of Minnesota Rochester in Rochester, MN. She is a 2017 Undergraduate Summer Research Fellow (UGSRF) doing research in Dr. Arthur Beyder’s lab at Mayo Clinic in Rochester, MN. After graduating with a bachelor or science in health sciences, she is considering a career as a physician scientist.

Credit: Paul M. Choate, University of Florida.

This past summer, I was awarded an American Physiological Society Integrative Organismal Systems Physiology (APS IOSP) fellowship, which enabled me to perform 10 weeks of intense research at my home institution, Penn State University. During those 10 weeks, I got to delve deeper into what it means to be a true research scientist. I also learned the importance of networking, and being truthful in my own work.

During my summer fellowship, I worked in an entomology lab under my research mentor Dr. Ruud Schilder studying Gryllus firmus, a sand field cricket usually found throughout the southeastern U.S. In nature, this species usually exists as either a long winged or short winged morph¹. My research project entailed the use of a respirometer setup (shown below), a device that can be used for studying metabolic rate in small animals to examine whether metabolic rates differ significantly during development of these two morphs. In other words, are long-winged morphs more energetically costly to produce than short-winged morphs? Our research is still ongoing, and I am extremely excited awaiting to see the results when completed. Understanding metabolic rate in the cricket community is particularly important because it can tell us a lot about their reproductive power as well as specific differences in their energetic pursuits.

Respirometer setup. Credit: Avril C, Schilder Research Lab

When we look at smaller animals in comparison to larger animals, it appears that the smaller animals’ tissues are more active than that of their larger counter parts¹. What we are trying to figure out is if this general rule applies to size difference during cricket development as well (ontogeny). In other words, my research will hopefully lead to an answer of the following the questions: Are the tissues of smaller more immature crickets more active than fully matured crickets? Does metabolic rate vary across the two different morphs significantly, across age, or both?

I cannot thank the American Physiological Society enough for allowing me this opportunity. I hope other STEM students will take the initiative to do a program like this sometime throughout their undergraduate career. In our endless evolving world, we need more research scientists to unlock the key and take leadership. In closing, I want to leave readers with two questions:

How important is scientific research in today’s society?
In 10 years, do you see the research scientist profession growing significantly? Why or Why not?

References:

Zera, Anthony J., Jeffry Sall, and Kimberly Grudzinski. “Flight Muscle Polymorphism in the Cricket Gryllus Firmus: Muscle Characteristics and Their Influence on the Evolution of Flightlessness.” Physiol Biochem Zool Physiological and Biochemical Zoology 70.5 (1997): 519-29. Web.

Avril Cooper is a senior majoring in Biology at Penn State University. After graduation, she plans on pursuing a master’s degree in medical science and eventually going on to medical school.