PhD Graduates

HAOCHENG LU Eugene Chen Lab

“The Role of Transcription Factor EB in the Vascular Wall Biology”

JEANINE RUGGERI Howard Crawford Lab

“Determining the Role of Discoidin Domain Receptors in the Pathogenesis of Pancreatic Ductal Adenocarcinoma”

ANDREW SCHWARTZ Yatrik Shah Lab

“Hepcidin/Ferroportin/HIF-2 Regulation of Iron Metabolism at the Systemic and Cellular Level “

SUROJIT SURAL Allen Hsu/Scott Pletcher Labs

“Roles of HSB-1 in Regulation of Heat Shock Factor Activity, Histone Levels, Mitochondrial Function and Longevity”

KEVIN SWIFT Gina Poe Lab

“Locus Coeruleus Optogenetic timulation and the Estrous Cycle Manipulate Sleep Character stics and Memory Consolidation”

by James Dau (Reprinted from Discover Rackham: https://rackham.umich.edu/discover-rackham/frostyreception)

There’s no mistaking when it’s cold outside, but how our bodies know that has been an open question. Molecular & Integrative Physiology Ph.D. student Elizabeth Ronan is working to understand where that chilly feeling comes from.

The ability to sense temperature is essential for the survival of humans and most other organisms. Being able to feel when, and in which direction, the temperature is changing tells us when to seek shelter, bundle up, or pay more attention to how much water we’re drinking. Understanding how our bodies convey this critical information about our surroundings has been the subject of considerable research over the years, with important implications for medical therapies and pain management.

These efforts have yielded significant progress in understanding how the body senses heat. Scientists have been able to produce experiments that pinpointed the body’s heat receptors, as well as how they function. Administering cold with similar precision has proven much more challenging, however, and as a result there has been much less progress on the opposite end of the thermometer. While past research has identified one cold receptor—called TRPM8—it only activates at around 26 degrees Celsius (about 79 degrees Fahrenheit), and anyone who’s endured a mid-December polar vortex knows the body is capable of feeling much colder temperatures. Thanks to a new approach and the creative adaptation of existing lab technologies, however, Department of Molecular & Integrative Physiology Ph.D. student Elizabeth Ronan and her colleagues in the lab of Shawn Xu, the Bernard W. Agranoff Collegiate Professor in the Life Sciences, have finally begun chipping away at this long-frozen question.

“Cold sensitivity has been a long-term project in our lab,” Ronan says. “Past research has shown receptors for cool temperatures, but this research is the first time a sensor for noxious, painful cold has been found to exist in nature.”

An Elegans Solution As is often the case, the key to deciphering the riddle of cold sensation came from one of the most unassuming places, in this case a diminutive roundworm named Caenorhabditis elegans, commonly known as C. elegans. Widely used as a model organism in research, C. elegans possesses an easily manipulated genetic code, with at least 70 percent of its genes highly conserved in higher-order species, including humans. In addition, and with particular importance for Ronan and her fellow researchers, the worm is the only organism for which scientists have a complete connectome—a comprehensive map of every connection between neurons in its body, akin to a wiring diagram for a living organism.

“C. elegans is ideal for exploring basic, evolutionarily conserved mechanisms,” Ronan explains. “Because its genome is relatively simple, it’s a lot easier to identify new genes that would be much harder to find in more complex species. Combined with knowing how every one of its neurons are connected, it’s an ideal model for sensory biology.”

That still left the question of having the right technology, the same issue that had plagued cold sensation researchers for years. Fortunately, C. elegans provided an answer for that, too.

Previous work in the Xu lab identified that the intestine of C. elegans is cold-sensitive, playing an important role in extending its lifespan under cold temperatures. The researchers discovered that in cold environments, the genes mediating longevity are activated, extending its lifespan at low temperatures. This discovery presented an ideal way to perform an unbiased genetic screen for the elusive cold sensor.

Many labs that host biological, genetic, or biomedical research employ devices called quantitative polymerase chain reaction (qPCR) thermocyclers. Conventionally used to amplify and quantify DNA, qPCR thermocyclers are capable of rapidly heating and cooling dozens of test tubes at once while measuring fluorescence intensity to quantify gene expression level. And it didn’t escape the team’s notice that C. elegans were just about the right size to fit in a test tube.

To identify new cold sensing genes, the team placed C. elegans specimens expressing GCaMP—a genetically encoded calcium indicator that increases in fluorescence when activated—in the intestine directly into the qPCR test tube wells, and observed that upon cooling in the thermocycler they could detect an increase in intestine fluorescent intensity. Taking

advantage of its easily manipulated genome, they then generated 30,000 unique mutant strains of C. elegans. With one strain in each of the thermocycler’s 96 test tube wells, they dropped the temperature and observed which worms responded to the newly frigid conditions and which did not. The researchers identified that those lacking cold responses possessed mutations in the gene encoding a glutamate receptor called GLR-3.

In response to sudden drops in temperature, worms with normal GLR-3 functionality increased what Ronan calls avoidance behavior—the worms began to move backward and turn, looking for an escape to more favorable conditions—while mutant strains that did not showed no change. Further experiments conducted by Ronan confirmed that GLR-3 was required for the cold avoidance response.

“We found that GLR-3 activated at 18 degrees Celsius, well below the threshold of the cool sensor TRPM8,” Ronan says. “These experiments showed its importance for noxious cold sensing, now we had to see if it was filling the same role in other species and, ultimately, how it was doing so.”

Mice, fish, and humans all possess a homolog—a gene related to another gene by common ancestry—to GLR-3, called GluK2. In order to test whether GluK2 provides the same service as its ancestral counterpart, Ronan and her colleagues conducted heterologous experiments—in which scientists express genes in cell lines—on all three homologs and confirmed that their expression does, in fact, confer cold sensitivity just like GLR-3 in C. elegans. The team also confirmed that DRG neurons—peripheral sensory neurons in mammals that detect a variety of external stimuli—in mice also depend on GluK2 for their response to cold.

Ronan says additional research to determine how exactly GLR-3 and GluK2 sense cold is already under way. That research could eventually lead to better medical therapies, but it’s already yielded a more complete understanding of how the body functions.

“We’re laying the foundation for understanding the mechanisms that drive cold response that future research and future scientists can use to directly benefit human health,” Ronan says. “We’ve provided a big missing piece in temperature sensation, one that can help us understand how our own bodies survive and function.”

Christin Carter-Su Lab Anabel Flores et al. Crucial Role of the SH2B1 PH Domain for the Control of Energy Balance. Diabetes 2019; 68: 2049-2062

Malcolm Low Lab Daniela Orquera et al. The homeodomain transcription factor NKX2.1 is essential for the early specification of melanocortin neuron identity and activates Pomc expression in the developing hypothalamus. Journal of Neuroscience 2019; 39: 4023-4035

Ormond MacDougald Lab Ziru Li et al. G-CSF partially mediates effects of sleeve gastrectomy on the bone marrow niche. Journal of Clinical Investigation 2019;129:2404–2416

Suzanne Moenter Lab Caroline Adams et al. Changes in both neuron intrinsic properties and neurotransmission are needed to drive the increase in GnRH neuron firing rate during estradiol positive feedback. Journal of Neuroscience 2019, 39: 2091-2101

Ling Qi Lab Yewei Ji et al. Toll-like receptors TLR2 and TLR4 block the replication of pancreatic β cells in diet-induced obesity. Nature Immunology 2019; 20: 677–686

We hope our successes this past year makes you proud of the University of Michigan Department of Molecular & Integrative Physiology. Our philanthropy funds play a key role in strengthening our department, faculty, and trainees. We hope you will play part and join many others in supporting Molecular & Integrative Physiology by making a gift to the funds below.

Bishr Omary Physiology Postdoctoral Awards & Symposium Fund Your gift will be used to support Molecular & Integrative Physiology postdoctoral career development in a variety of ways that include postdoc recognitions, the annual symposium, a named lectureship in conjunction with the annual symposium, postdoc travel and small grants, and other postdoctoral career development activities. Donate online at https://www.giving.umich.edu/give/335629

Graduate Education Fund in Physiology Your gift will propel the development of future biomedical researchers currently enrolled in the Molecular & Integrative Physiology PhD Program. These individuals are studying the mechanistic basis of human diseases such as cancer, diabetes, and obesity. Donate online at http://victors.us/mipgraduate

John and Margaret Faulkner Lectureship You will be supporting an annual lectureship by a prominent invited speaker selected by the students and faculty in honor of John and Margaret Faulkner. Donate online at http://victors.us/faulknerfund

Master’s Education Fund in Physiology The MS in Physiology is designed for students who plan to pursue employment in a research laboratory, or to continue their education as PhD, medical, dental or other health professional schools. Your gift will provide financial assistant to master students. Donate online at http://victors.us/mipmaster

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Physiology Summer Research Fellows Fund Your gift will support undergraduate students that are interested in research in physiology and/or biomedical sciences. This fund provides financial support to summer research fellows, their research and the summer program activities. Donate online at http://victors.us/mipsummer

SEEK Fund The Science Engagement and Education for Kids (SEEK) is an outreach effort driven by the physiology students and department members to promote science in the community. This fund supports the development of outreach educational program and outreach activities. Donate online at http://victors.us/mipseek

If you would like to discuss making a major donation to any of the above funds, leaving a gift for us in your will, or offering a pledge or gift of appreciated stock, please contact Chrissy Barua, our development officer, at 734-763-4938, or cebarua@umich.edu.