TITLE

Failure to communicate: Dysregulated muscle paracrine signaling due to mitochondrial dysfunctio

ABSTRACT

Muscle matters. Skeletal muscle accounts for nearly half of our body mass, and serves as a central endocrine and metabolic hub. Deficits in muscle health lead to declines in quality of life, reduced mobility, and poor disease outcomes. In short, muscle health is human health. Despite its importance, skeletal muscle health receives relatively little attention in the field of environmental health. Chronic exposure to unsafe levels of arsenic via contaminated drinking water affects nearly 200 million people worldwide. And while much attention has been paid to arsenic-associated cancers, less focus is given to cardiometabolic disease, and even less to skeletal muscle deficits. While arsenic-induced muscle deficits are recognized, mechanisms for these effects remain uncertain. Mitochondrial dysfunction is a consistent observation in studies of arsenic exposure. While paracrine signaling via extracellular vesicles (EVs) is increasingly being recognized as an important factor in muscle health. The aim of this dissertation research was to investigate a link between these factors, testing the global hypothesis that arsenic exposure disrupts muscle progenitor cell (MPC)-driven regeneration through mitochondrial dysregulation of EV-mediated paracrine signaling.

We first used gene delivery of the anti-geronic protein Klotho to show how mitochondrial function and muscle regeneration respond to treatment at different ages. We found that Klotho improved mitochondrial integrity in old animals, leading to healthier regeneration, but at extreme age the effect was lost. Having demonstrated the importance of mitochondrial health for muscle regeneration we then considered the effects that arsenic has on EV signaling. Using a novel 3D skeletal muscle construct model to isolate MPC-specific effects of arsenic exposure, we found that arsenic causes MPCs to release EVs that confer deleterious effects on muscle regeneration in recipient cells. Finally, we investigated the contribution of mitochondrial function to this effect. Using the mitochondrial protectant SS-31 we showed that aberrant EV signaling is a product of arsenic-induced mitochondrial dysfunction. We also characterized the bioenergetic consequences of this dysfunction in MPCs, showing how they are communicated in EVs. Overall, these studies identified a crucial signaling hub responsible for the perpetuation of arsenic-induced muscle dysfunction, potentially contributing to future efforts to reverse these consequences.