The objective of this application is to examine how augmented muscle mass, a by-product of the exercise intervention commonly prescribed for treatment of obesity and sarcopenia, can prevent and rescue metabolic and vascular dysfunction in sarcopenic obesity. The core hypothesis of this application is that targeting skeletal muscle function in aging can ameliorate metabolic dysfunction and oxidant-induced hypertension in obesity and lay the groundwork for establishment of an independent research program directed toward determining if obesity-derived cardiometabolic dysfunction can be rescued through augmented mass with aging and specific fiber types. The goals of this application will be accomplished by examining the effect of augmented muscle mass, through myostatin deletion, on cardiometabolic function in a mouse model of obesity (the db/db mouse). Experimental methods include in vivo blood pressure using telemetry in conscious mice, vascular function assessments using pressure myography of isolated vessels, and metabolic function using metabolic chambers, glucose tolerance tests, whole body quantification of lean mass and adiposity via DXA Piximus, and blood lipid profiles. Our data indicate that increasing muscle mass in obese mice protects against the loss of muscle mass and strength, glycemic control and vascular dysfunction, which accompany obesity in the db/db mouse. Importantly, our preliminary data indicate that these improvements to metabolic and cardiovascular function prevent hypertension in the db/db mouse. Further, this application will determine the relative contribution to organ specific oxidant stress, namely vascular NOX1 and renal NOX4 in a model of sarcopenic obesity. The model currently used (constitutive myostatin deletion) involves lifelong augmented muscle. A key question remains unanswered; can augmented muscle rescue/reverse obesity-derived cardiovascular dysfunction or is lifelong fitness essential? The applicant intends to focus his transition to independence on answering these key questions. I will use a novel inducible knockout of myostatin in a db/db mouse to determine if augmented muscle mass can rescue metabolic and vascular dysfunction after development of a fully obese phenotype. This will serve to mimic the patient population and allow for results to translate to the clinic. Additionally, literature suggests that skeletal muscle fiber type plays a crucial role in outcomes. The myostatin model used results in predominantly glycolytic skeletal muscle expansion and it would be advantageous to determine if a mouse model of obesity with predominantly oxidative skeletal muscle expansion (PGC1?) would have similar cardiometabolic improvements.
The tandem threat of aging and obesity is rising in the U.S., resulting in a disease termed ?sarcopenic obesity?, in which the aged experience synergistic muscle loss with both pathologies in combination with increases in body mass and adiposity. Combating the obesity epidemic and encouraging healthy aging is a top priority for the NIH/NIA and they recommend that doctors work closely with obese patients to encourage lifestyle changes, specifically exercise (more muscle mass), while simultaneously treating obese-induced pathologies (glycemic control and high blood pressure). This application seeks to understand the role of muscle mass and its influence on blood pressure regulation and will identify specific pathways and mechanisms induced by increased muscle mass to therapeutically treat obesity-induced hypertension and it?s many other complications.
