Targeting PAK1 to improve functional beta-cell mass and insulin sensitivity

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DESCRIPTION (provided by applicant): As blood sugars rise during development of pre-diabetes, cardiovascular consequences such as stroke, myocardial infarction and mortality are already increasing by 2-4 fold, yet there remains a fundamental gap in understanding how and why pre-diabetes develops. The inability to predict, within a population with similar risk factors for diabetes, which are more susceptible than others represents an important problem because, until it is resolved, strategies to prevent/treat pre-diabetes/dysglycemia will remain largely untenable. Strategies to halt dysglycemia require a multi-pronged approach, since the pathophysiology involves both peripheral insulin resistance and pancreatic �ell dysfunction. Factors that are linked to failures in both processes are in-demand for therapeutic focus; we have identified the p21-activated kinase, PAK1, as such a factor. Further, losses of PAK1 abundance are associated with diabetes and obesity in human islets and human skeletal muscle, tissues that are key to regulating insulin release and insulin sensitivity, respectively. Thus, the long-term goal is to understand how the PAK1 pathways in these tissues can be manipulated to treat/prevent pre-diabetes, ultimately halting progression to frank diabetes. The objective of this particular application is to discriminate how PAK1 functions (PAK1 plays roles in signaling as well as scaffolding in other cell types) in �ell insulin secretion and skeletal muscle insulin action in vivo and at the molecular level. PAK1 pathways are known in other cell types to evoke dynamic actin cytoskeleton changes, and preliminary data suggest such changes to be part of insulin release and glucose clearance mechanisms. Preliminary data show that classic whole-body PAK1 knockout mice fed a 42% fat diet for just 10 weeks develop fasting hyperglycemia, insulin insufficiency and severe glucose intolerance. Additionally, restoration of PAK1 abundance or signaling in islet �ells restores insulin secretion and reduces �ell apoptosis. These findings give rise to the central hypotheses, that a) PAK1 is a central regulator of glucose homeostasis via functions in actin remodeling-regulated exocytosis events in both �ells and skeletal muscle cells, and b) that PAK1 deficiency culminates in heightened susceptibility to glycemic dysregulation and pre-diabetes. The rationale for the proposed research is that once it is known how PAK1 is needed in �ells versus skeletal muscle cells, that the PAK1 pathways can be manipulated to avert pre-diabetic dysglycemia. This hypothesis will be tested in two Specific Aims: 1) Delineate the mechanism(s) for PAK1 actions in �ell function and survival, 2) Elucidate the mechanism(s) by which PAK1 promotes skeletal muscle insulin sensitivity. Aims will be accomplished using innovative inducible �ell and skeletal muscle PAK1 knockout mice and live-cell imaging biosensors with biochemical assays, and relevant human islet and muscle tissues. Results of these interrogations are expected to positively impact efforts to ameliorate pre-diabetes, because the identified effectors and mechanisms are highly likely to provide new therapeutic targets.