Dietary Cholesterol and Resistance Training as Countermeasures to Accelerated Muscle Loss
Lee, Teak Veng
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Cholesterol plays an important role in physiology, serving as a membrane constituent and steroid hormone precursor. Recently, cholesterol has also been associated with skeletal muscle homeostasis, leading to the purpose of this research, which was to examine the role of cholesterol metabolism during perturbations of skeletal muscle homeostasis. We evaluated skeletal muscle responses and proteins involved in cholesterol metabolism [sterol regulatory element-binding protein-2 (SREBP-2) and low-density lipoprotein-receptor (LDL-R)] under conditions of unloading, exercise and dietary cholesterol (D-CL) administration. We hypothesized that skeletal muscle mass, fractional synthesis rates (FSR), SREBP-2, and LDL-R would be lower in unloaded muscle while exercise and D-CL would have a positive effect. The first study examined the effect of hindlimb unloading (HU) on muscle mass, SREBP-2, and LDL-R. HU animals showed lower muscle mass and a trend towards lower gastrocnemius SREBP-2 than cage controls (CC). The second study examined the effect of D-CL and resistance training (RT) on lean mass, FSR, SREBP-2, and LDL-R in ambulatory rats. Unexpectedly, rats performing exercise without added resistance [(RT-Control (RTC)] had greater lean mass responses than the RT groups. However, RT groups had higher plantaris to body mass ratio and FSR than RTC (plantaris FSR only) and CC (both variables) animals. RT plus high D-CL administration resulted in greater plantaris FSR than the RT group consuming normal D-CL. Quadriceps SREBP-2 trended towards an increase in response to RT. The third study investigated the effect of D-CL and RT on muscle mass, FSR, SREBP-2, and LDL-R in the context of HU. HU and HU rats performing RT had lower muscle mass than CC. HU rats showed higher liver mature LDL-R than CC but showed a trend towards lower gastrocnemius SREBP-2 than CC. There was no difference in FSR among activity or D-CL groups. These studies show evidence of shifts in content of proteins related to cholesterol metabolism and muscle FSR when muscle activity is manipulated from RT to complete unloading. However, effects such as elevated FSR with RT and high D-CL were not consistent throughout the studies, leaving doubt of the effect of activity on cholesterol metabolism.