Fellowship for Jason Groshong: Studies on Insulin Resistance in Human Skeletal Muscle

The American Diabetes Association reports that mortality in persons with type 2 diabetes mellitus is due primarily to heart disease and stroke. Dysfunctional insulin response is a major determinant of type 2 diabetes that leads to two major symptoms, high serum fatty acids and high blood glucose. Skeletal muscle is the major depot of glucose utilization, yet muscle as a therapeutic target for diabetic intervention has not been fully exploited. Our lab reported total macrophage infiltration is elevated in human muscle with obesity and insulin resistance. Preliminary data suggest that M2 macrophages also predominate in muscle with obesity, but their contribution to peripheral insulin resistance is unknown. The current view suggests that M1 macrophages are classically pro-inflammatory and inhibitory to insulin signaling. This investigation will utilize a human cell culture model to dissect the role of M1 pro-inflammatory and M2 anti-inflammatory macrophages on insulin signaling in muscle cells derived from insulin sensitive and insulin resistant subjects. Overall we hypothesize that the insulin response in cultured human muscle cells will be modified distinctly as a result of activation of signaling pathways following exposure to the secretory products from different macrophage subtypes. These studies may uncover novel targets and lead to a model to test innovative drugs to prevent or treat insulin resistance. In our first aim we will determine the effects of different macrophage subtypes on insulin response in muscle cells. We will utilize muscle cells differentiated in culture to myotubes to quantify insulin response by the sequentially linked and measurable events: IRS1 phosphorylation, Akt phosphorylation, glucose transporter insertion into the plasma membrane, and ultimately glucose uptake. These insulin dependent events will be measured after pretreatment with conditioned media derived from M1 and M2 subtype macrophages. Our second aim will investigate how different macrophage treatments alter inflammatory mediators of insulin response in muscle cells distinctly. We will quantify signaling pathways in myotubes, particularly NFkB, JNK and STAT in response to conditioned media from M1 and M2 subtype macrophages, relative to the insulin response. The study will attempt to establish associations between the different polarized macrophages and activation of signaling pathways in muscle cells altering the insulin response.