Abstract 20140: Minibrain Relate Kinase / Dyrk1B Links Skeletal Muscle Glycolytic Metabolism with Insulin Resistance and Causes Metabolic Syndrome

We have identified a novel nonconservative mutation in Minibrain related serine/threonine kinase (Mirk/ Dyrk1B) in outlier kindreds with metabolic syndrome. The mutation substitutes cysteine for arginine (R102C) and segregates with most traits of metabolic syndrome, including central obesity, diabetes and hypertension. Oral glucose tolerance test (OGTT) in young nondiabetic mutation carriers revealed insulin resistance compared to noncarrier family members. Since skeletal muscle (SM) is the largest organ for glucose uptake and metabolism, we obtained Vastus Lateralis biopsies of mutation carriers and their unaffected relatives and examined them for gene/protein expression by deep RNA sequencing (RNA-Seq) and Western blot analysis and for fiber composition by immunostaining. The fiber composition data demonstrated fewer slow-twitch fibers (35% vs. 75%) and more fast -twitch fibers (65% vs. 25%) in SM of mutation carriers vs. controls. Interestingly, there were increased protein expression levels of fast-twitch fiber type proteins (MYH11, MYLPF), pyruvate dehydrogenase kinase, pyruvate kinase, and neuronal nitric oxide synthase in SM of mutation carriers vs. noncarriers. Consistent with these findings, the protein expression levels of the master regulator of cellular energy metabolism mitochondrial biogenesis, PPAR-gamma coactivator (PGC-1a), were reduced and the nuclear expression levels of FOXO1 and NFAT were increased. Similar findings were observed when wildtype and mutant (R102C) Dyrk1B were overexpressed in C2C12 cells. The overexpression of the kinase deficient Dyrk1B (Y271/273F) similarly resulted in reduced expression of PGC-1a and increased expression of nuclear FOXO1, suggesting kinase independent effects. Taken together, these findings suggest that enhanced kinase-independent activities of Dyrk1B, either through increased expression or by its gain of function mutation R102C induce insulin resistance by promoting glycolytic metabolism and reducing oxidative phosphorylation. In conclusion, Dyrk1B is a potential target for development of novel drugs that aim to enhance skeletal muscle insulin sensitivity.