The Rho guanine dissociation inhibitor α inhibits skeletal muscle Rac1 activity and insulin action

The molecular events governing skeletal muscle glucose uptake have pharmacological potential for managing insulin resistance in conditions such as obesity, diabetes, and cancer. With no current pharmacological treatments to target skeletal muscle insulin sensitivity, there is an unmet need to identify the molecular mechanisms that control insulin sensitivity in skeletal muscle. Here, the Rho guanine dissociation inhibitor & alpha; (RhoGDI & alpha;) is identified as a point of control in the regulation of insulin sensitivity. In skeletal muscle cells, RhoGDI & alpha; interacted with, and thereby inhibited, the Rho GTPase Rac1. In response to insulin, RhoGDI & alpha; was phosphorylated at S101 and Rac1 dissociated from RhoGDI & alpha; to facilitate skeletal muscle GLUT4 translocation. Accordingly, siRNA-mediated RhoGDI & alpha; depletion increased Rac1 activity and elevated GLUT4 translocation. Consistent with RhoGDI & alpha;'s inhibitory effect, rAAV-mediated RhoGDI & alpha; overexpression in mouse muscle decreased insulin-stimulated glucose uptake and was detrimental to whole -body glucose tolerance. Aligning with RhoGDI & alpha;'s negative role in insulin sensitivity, RhoGDI & alpha; protein content was elevated in skeletal muscle from insulin-resistant patients with type 2 diabetes. These data identify RhoGDI & alpha; as a clinically relevant controller of skeletal muscle insulin sensitivity and whole -body glucose homeostasis, mechanistically by modulating Rac1 activity. SignificanceCurrently, no pharmacological therapies treat skeletal muscle insulin resistance in pathological conditions such as type 2 diabetes, age-associated diseases, and cancer. Therefore, there is an unmet need to identify the molecular mechanisms controlling skeletal muscle insulin sensitivity. Using a multitude of model systems, including myoblasts, myotubes, mouse skeletal muscle, and human muscle, we identify the Rho guanine dissociation inhibitor & alpha; (RhoGDI & alpha;) as a point of control in regulating skeletal muscle insulin sensitivity. RhoGDI & alpha;'s functions have never before been described in skeletal muscle. We show that RhoGDI & alpha; inhibits muscle insulin action mechanistically by modulating Rac1 activity, thereby, highlighting RhoGDI & alpha; as a new clinically relevant controller of skeletal muscle insulin sensitivity and whole -body glucose homeostasis.