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SKELETAL MUSCLE ATROPHY ASSOCIATED POTASSIUM CHANNEL HERG1A AFFECTS GLOBAL CALCIUM HOMEOSTASIS IN C2C12 MYOTUBESGuha, Shalini 01 December 2024 (has links) (PDF)
Skeletal muscle is the most abundant muscle in the body and performs important bodily functions such as movement, body temperature regulation, joint stabilization, etc. It requires calcium ions (Ca2+) for proper function, growth, development, and repair. Regulated Ca2+ signaling is crucial for muscle health and perturbation of Ca2+ signaling can, therefore, lead to a multitude of muscle pathophysiologies, one of which is atrophy. Skeletal muscle atrophy results from loss of proteins leading to loss of muscle mass and, unfortunately, there are no effective pharmacological therapies presently available for it. The only truly effective treatment includes exercise and proper diet. Physical activity is not a feasible option for ailing and aging populations who have the most occurrence of skeletal muscle atrophy. Thus, it is imperative to explore various molecular mechanisms which can initiate and contribute to skeletal muscle atrophy in order to elucidate possible pharmacological interventions. That is where this dissertation comes into place. The potassium (K+) channel, ERG1A, induces atrophy in the skeletal muscle of mice when ectopically expressed. Indeed, the human homolog of this atrophy-inducing K+ channel increases basal cytosolic Ca2+ concentration in cultured mouse skeletal muscle cells, C2C12. Here, we sought to discover the sources of the increased cytosolic Ca2+. To that end, we explored the effect of HERG1A overexpression on multiple important calcium signaling pathways. We discovered that HERG1A affects various Ca2+ signaling mechanisms in skeletal muscle cells. We show that HERG1A enhances the very abundant extracellular Ca2+ entry mechanism of SOCE (store operated calcium entry) to increase cytosolic Ca2+ levels. We also show that HERG1A also increases RyR1 (ryanodine receptor 1) signaling along with ECCE (excitation coupled calcium entry) in skeletal muscle cells. Most interestingly, we connected all these HERG1A-modulated pathways by showing that HERG1A modulates the global Ca2+ homeostasis regulator, Calsequestrin1 (CSQ1) both at the level of transcription and translation. This suggests that HERG1A is a global Ca2+ homeostasis regulator itself. We speculate that HERG1A is affecting the various Ca2+ signaling mechanisms in cells via its regulation of the levels of CSQ1 and thereby modulating the availability of cytosolic Ca2+ in the cells. This dissertation thus summarizes the vastness of HERG1A regulation of Ca2+ homeostasis in skeletal muscle cells. Furthermore, this dissertation also shows how HERG1A affects various mechanisms in skeletal muscle cells which could also have roles in apoptosis and cancer. Most importantly, HERG1A in skeletal muscle cells has been shown to have a real and significant impact on the functioning of multiple cellular signaling pathways and not the levels of the members of such pathways which reveals for the first time a mechanistic control of the intracellular pathways in skeletal muscle cells by this voltage gated K+ channel.
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