Coray Preece and Robert Hyldahl, Exercise Sciences
Fibroblasts play a key role in repairing injured tissue by secreting collagen and growth factors into the tissue. In states of disease and overuse, fibroblast activity (i.e. greater fibroblast content and collagen secreting activity) can lead to skeletal muscle fibrosis, in which myofibers are replaced by collagen, decreasing strength and muscle elasticity. It has been shown in previous studies that TGF-beta signaling directly increases fibroblast proliferation and collagen secretion. It has also been shown that inhibition of TGF-beta signaling reduces known symptoms of muscular dystrophies including decreased fibrosis and increased muscular strength. SGI-1252 is a novel small molecule that our lab has developed over the past 2 years. SGI-1252 inhibits a pathway important for muscle growth called myostatin (TGF-beta member). The purpose of my original project was to determine how treatment of cultured fibroblasts with the novel small molecule SGI-1252 affects proliferation and collagen expression. Shortly after submission a concurrent project in our lab showed that treatment of mice with SGI-1252 showed no significant growth in muscle, contrary to our hypothesis based on our knowledge of the myostatin pathway. Based on the results in muscle growth that we saw in the mice treated with SGI-1252, we decided to consider the alternative pathways that could be affecting the muscle growth. This lead us to the JAK/STAT pathway. Recent studies have highlighted a role for the JAK/STAT signaling pathway in the regulation of muscle satellite cell behavior and differentiation. Stimulation of the JAK/STAT pathway could cause a decrease in the differentiation of muscle fibers and explain the results found during our myostatin experiment. Based on this knowledge, my mentor, Dr. Hyldahl, and I decided to change the aims of my research to test the effects of SGI-1252 on the JAK/STAT pathway. To test these effects, the compound, SGI-1252, was administered orally (400mg/kg) in a 10% dextrose solution to wild type mice (n=6) 3 times per week for 8 weeks. A control group (n=6) received only the dextrose solution. After the 8 weeks, mice that were treated with SGI-1252 showed a significant increase in the number of Pax7+ satellite cells relative to controls (1852 ± 387 vs 2780 ± 657 SC/mm-3, p=0.02)(Figure 1B and C). This lead us to infer that SGI- 1252 effectively shut down the differentiation of these satellite cells. To further test our hypothesis, we looked at the effect of SGI-1252 on the expression of MyoD and Myogenin(Figure 2). The loss and replacement of Pax7 with MyoD and Myogenin instructs the dividing satellite cells to differentiate, whereas inhibition of STAT3 activity (JAK/STAT pathway) attenuates myogenic differentiation. We found a significant decrease in the expression of MyoD and Myogenin in SGI-1252 treated myoblasts, further supporting the idea that SGI-1252 causes an attenuation in satellite cell differentiation.
This project has been submitted to the Journal of Clinical and Experimental Pharmacology and Physiology. The project was also presented at the Myology Institute at the University of Florida.
The best part of my mentoring experience has been watching how one project grows and changes into another based on what we learn from the original aims. I am learning that there are endless paths that science can take and it is exciting to watch all the different things that Dr. Hyldahl’s lab has accomplished and the goals they have for the future. Being a part of the ongoing progress they make has allowed me to understand the process of research and gain an appreciation for what has to happen to further the current knowledge we have about any given subject. I don’t have any suggestions for improvement.
The trust that my mentor Dr. Hyldahl put in me to complete the research with accuracy and in a timely manner helped me to grow to fill my given roles and accept responsibility for any assignments that he had for me. This aim for quality work has spilled over into my schooling and personal life and has made me a better student and husband.
I would like to express my gratitude for the donor who funded my project. Due to their contribution to the Office of Research and Creative Activities, I was able to pursue a research objective that I wouldn’t have been able to otherwise. This has allowed me to learn and grow and obtain valuable experience that you can’t get in a classroom. This will be a huge catalyst to my success as I pursue medical school in the future and will a building block in my growth.