Tag Archives: muscle physiology

PoWeRful mice and the effect of satellite cell depletion
Alec Dupont
Junior, biomedical science major
Auburn University

My Research Project

My project involved examining the adaptation of skeletal muscle to resistance exercise in mice that had been depleted of muscle stem cells (satellite cells). Generally, muscle growth is accompanied by an increase in protein synthesis and the differentiation of satellite cells into muscle nuclei. During this project, we examined if growth happens without the addition of satellite cells into muscle. As certain clinical populations have reduced satellite cell content and muscle mass, our project aimed to provide insights into how muscles respond to a growth stimulus with the loss of this cell population.

We used Progressive Weighted Wheel running (PoWeR) as a model for resistance exercise. PoWeR involves voluntary running activity of the mice in weighted running wheels. The weight placed on the running wheel is gradually increased over the course of four to eight weeks, overloading the musculature and causing a growth response called muscle hypertrophy. Using a genetic mouse model that allowed for the selective depletion of satellite cells, we compared sedentary- and resistance-exercised mice in groups of satellite cell-replete (vehicle treated) and -depleted (tamoxifen treated) mice. We compared muscle hypertrophy and other physiological adaptations between groups to determine the effects of satellite cell depletion. At the completion of this project, we hoped to gain a further understanding of the role satellite cells play in muscle growth.

Realities of Research

My main focus for the summer was using muscle tissue from the PoWeR mice, and making it possible to obtain data and useful information. I accomplished this through immunohistochemistry, a laboratory technique where we cut cross sections of the muscle and stain them for proteins of interest. This staining allowed us to visualize the sections under the microscope, image them and quantify the images using different forms of software. This technique presented certain challenges because the tissue must be carefully prepared and stored to prevent degradation. Poor quality tissue introduced variability outside of what is normal to the mice models. For example, having to overcome challenges and work to optimize a stain meant visualizing newly formed RNA in muscle nuclei. The stain can appear too dull and the quality would not be high enough to draw conclusions unless the procedure was optimized. Overcoming these challenges provided stunning images and reliable data. We found that although satellite cells were not absolutely required for muscle growth in response to weighted wheel running, there was a decrease in growth in the satellite cell depleted mice.

Life as a Scientist

The day-to-day life of a research scientist presented me with a constantly changing experience that was more engaging than the traditional classroom setting. There was always a new aspect of the project to investigate. It was incredibly satisfying to see your work come together in data that tell a cohesive story. The process of getting there was occasionally tedious though. For example, we’d normalize our data to the number of fibers in the muscle cross section and when the software couldn’t count for us, we were forced to count by hand. When the sections were between 600 and 800 fibers in a study with 48 mice, that part of research tended to drag. But that was only a minor inconvenience to a necessary bump in the road towards a satisfying research project.

Alec Dupont is a junior at Auburn University in Auburn, Alabama, studying biomedical science. He is a 2019 Undergraduate Summer Research Fellow (UGSRF) working under Dr. Charlotte Peterson at the Center for Muscle Biology at the University of Kentucky in Lexington. Alec’s work is funded by the American Physiological Society’s UGSRF program and a grant from the National Institute of Health to Dr. Charlotte Peterson and Dr. John McCarthy (AR060701).

Understanding Muscle Force During Cyclic Movements: Does Titin Play a Role?

During cyclic every day movements, such as running, jumping, and walking, our muscles go through cycles of shortening and stretching. While there has been extensive research on muscle function for the last 50 years, there is no current muscle model that can accurately predict natural movements. For example, when active muscle is stretched, it produces more force than expected based on current theories of muscle contraction. Likewise, when active muscle shortens, it produces less force than predicted by current theories. For years, scientists have been measuring properties of muscles under highly controlled conditions. The classic force-velocity relationship shows that force generated by a muscle is inversely related to the velocity of the shortening. However, this relationship changes during natural, more life-like movements. Recent work suggests that for a given velocity, muscle force is higher during cyclic contractions than the traditional force-velocity relationship. My research investigates the role of the elastic protein titin in the force-velocity relationship measured under different conditions. Using a mouse model with a mutation in titin, I conducted in vitro muscle experiments to compare the force-velocity relationship in cyclic and controlled (isotonic) conditions. Hopefully, my results will shed light on titin’s role as a spring in active muscle. If titin truly does store energy like a spring, this could account for the extra force and lack of force in the stretch-shortening cycles. This research will allow us to better understand movement on a whole organism scale, which can prove quite useful in prosthetic design and bioengineering, for example.

Much like the active muscle, doing research in a lab goes through cycles, except instead of stretch-shortening cycles, it is periods of challenge and reward. Some days, you go into lab, collect great data, and leave feeling utterly fulfilled. However, other days, you go into lab and it seems as though you spent your entire day trouble-shooting. Mainly though, our experiments worked and we were able to collect useable data. We have yet to fully analyze our results, but preliminary results seem to support our expectations.

In general, I have found my lab group experience to be very similar to my experience with playing college soccer. Both activities involve a group of people working toward a common goal. While in soccer, your team is working together to win, in the lab, there are many scientists working together to uncover a truth. Collecting and analyzing data is a collaborative effort and, to me, that was the best part of summer research. Working as part of a lab team allows you the opportunity to constantly learn and build off of others. It teaches you to adapt, be open to new ideas, and to use your time efficiently. The worst part of day-to-day life in the lab, is that sometimes data collection does not go as planned and you need to figure out what went wrong.  However, this aspect doesn’t seem so bad when you have your lab team to help brainstorm.

Overall, my time in the lab has been an incredible experience. It has helped me grow as both an individual and as a scientist and has stimulated my interest in future research opportunities. It is an experience I would highly recommend to other undergraduate students!

Lindsay Piwinski attends Pitzer College in Claremont, CA. She is a 2017 Undergraduate Summer Research Fellow (UGSRF) doing research with Drs. Jenna Monroy (Pitzer College) and Kiisa Nishikawa (Northern Arizona University, Flagstaff, AZ). She hopes to attend graduate school in the future and continue pursuing research.