Estrogen Deficiency-Induced Phosphoproteomic Alterations In Skeletal Muscle Of Female Mice

Abstract

Dynapenia, the age-related loss of muscle strength without the loss of muscle mass, significantly impacts the physical function and overall quality of life in older adults, thereby decreasing their health span. Skeletal muscle strength loss has been shown to occur earlier and is greater in aging females than males. Furthermore, clinical and preclinical studies have measured associations between skeletal muscle strength loss and the age at which circulating estrogen begins to decline in females. Despite copious years of skeletal muscle research, the molecular mechanisms underlying muscle strength loss in aging females remain poorly understood. Age-related protein phosphorylation changes have been reported in skeletal muscle of males, and protein phosphorylation alterations have been shown in cardiac muscle across age and sex. However, the extent and magnitude of these changes in the skeletal muscle phosphoproteome of females in response to estrogen deficiency have yet to be determined. This dissertation aims to further our molecular understanding of how estrogen deficiency impacts skeletal muscle function (i.e., the force-generating capacity of muscle) in females by investigating the skeletal muscle phosphoproteome using high-throughput mass spectrometry coupled with bioinformatic analyses and computational modeling. First, using an ovariectomy model, we determined the physiological remodeling of the skeletal muscle phosphoproteome associated with estrogen deficiency. Next, due to the controversies related to using an ovariectomy model to implicate estrogen-related changes in aging females and because the primary function of skeletal muscle is contraction (i.e., molecular force generation), we sought to discern estrogen deficiency-associated protein phosphorylation alterations in contracted skeletal muscle via evoked electrical stimulations in ovariectomized and natural aging ovarian-senescent female mice compared to their respective controls. Examining the phosphoproteomic alterations in resting, non-contracted, and contracted skeletal muscle of estrogen-deficient females, we identified novel phosphosites, candidate kinases and phosphatases, as well as illuminated key pathways that are sensitive to estrogen levels that may contribute to the loss of skeletal muscle strength. This dissertation provides new avenues for further research and novel targets for the development of therapeutics and interventions to mitigate the loss of skeletal muscle strength in females.