Occurrence of obesity has steadily increased in the human population and, along with it, associated health complications such as systemic insulin resistance, which can lead to the development of type 2 diabetes mellitus. Obesity is a complex metabolic disorder that often leads to chronic inflammation and an overall decline in human and animal health. In mouse skeletal muscle, obesity has been shown to impair muscle regeneration after injury, however, the mechanism underlying these changes in satellite cell (SC) biology have yet to be explored. To test the negative impacts of obesity on SC behaviors, we fed C57BL/6 mice normal chow (NC, control) or high-fat diet (HFD) for 10 wks and performed SC proliferation and differentiation assays in vitro. SCs from HFD mice formed colonies with smaller numbers (P < 0.001) compared to those isolated from NC mice, and this observation was confirmed (P < 0.05) by BrdU incorporation. Moreover, in vitro differentiation assays consisting of equally seeded SCs derived from NC and HFD muscles showed that HFD SCs exhibited compromised (P < 0.001) differentiation capacity compared to NC SCs. Immunocytochemical staining of cultured SCs demonstrated that the percentage of Pax7+/MyoD- (self-renewed) SC subpopulation decreased (P < 0.001) with HFD treatment group compared to the control. In single fiber explants, a higher ratio of SCs experienced apoptotic events as revealed by the expression of cleaved caspase 3 (P < 0.001). To investigate further the impact of obesity on SC quiescence and cycling properties in vivo, we used an inducible H2B-GFP mouse model to trace the turnover rate of GFP and thus cell division under normal and obese conditions. Flow cytometric analysis revealed that SCs from HFD treatment cycled faster (P < 0.001) than their NC counterparts, as reflected by the quicker loss of the GFP intensity. To test for SC muscle regenerative capacity in vivo, we used cardiotoxin (CTX) to induce wide-spread muscle damage in the tibialis anterior muscle. After analysis we found that HFD leads to a compromised, though mild, impairment in muscle regeneration. Taken together, these findings suggest that obesity negatively affects SC quiescence, proliferation, differentiation, and self-renewal in vitro, ex vivo and in vivo. / MS / The prevalence of obesity in the human population has steadily increased over the past decades and, along with it, associated health complications such as systemic insulin resistance, which can lead to the development of type 2 diabetes mellitus. Obesity is a complex metabolic disorder that often leads to chronic inflammation and an overall decline in human and animal health. Along with the multitude of health disorders associated with obesity, in mouse skeletal muscle, obesity has been shown to impair muscle regeneration after injury. The mechanisms underlying the impairment in muscle regeneration as seen in obesity are unknown. To better understand how obesity affects skeletal muscle, we looked at satellite cells (SC). Satellite cells, or muscle stem cells, are skeletal muscle resident cells that play a vital role in muscle repair after damage. To test the negative impacts of obesity on SC behaviors, we fed mice normal chow (NC, control) or high-fat diet (HFD) for 10 wks to obtain an obesogenic mouse model. Our first experiments involved culturing the SCs derived from the HFD and NC mouse muscles and growing them in an artificial environment. These experiments showed SCs derived from HFD mice had a decreased ability to replicate and divide compared to those isolated from NC mice. Moreover, the SCs from the HFD mice exhibited compromised capacity to form myotubes in culture, an essential part in muscle regeneration after damage. Our next set of experiments conducted looked at individual muscle fibers isolated from mouse muscle. In these experiments the SCs on the HFD muscle fibers had a higher ratio of SCs experiencing cell death in comparison to the control. To test the SC cycling properties in the living mouse we used a mouse model to trace the activity and cell division of SCs under normal and obese conditions. Using this model revealed that SCs from HFD treatment cycled faster than their control counterparts, even in the absence of notable muscle damage. To test for SC muscle regenerative capacity after muscle damage, we used cardiotoxin (CTX) to induce wide-spread muscle damage in the tibialis anterior muscle (leg muscle) of the living mouse. After analysis we found that HFD leads to a compromised, though mild, impairment in muscle regeneration. Taken together, these findings suggest that obesity negatively affects SC behaviors and function.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/87757 |
| Date | 22 February 2019 |
| Creators | Geiger, Ashley Elizabeth |
| Contributors | Animal and Poultry Sciences, Gerrard, David E., Shi, Hao, Rhoads, Robert P., Johnson, Sally E. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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