1367-P: A Submembrane Cytoskeleton-Dependent Mechanism Modulates Mitochondrial Homeostasis and Skeletal Muscle Bioenergetics

Human variants in the ubiquitously expressed cytoskeletal scaffolding protein Ankyrin B (AnkB) , which is enriched in skeletal muscle (SKM) , have been identified as risk factors for diabetes and obesity. Mice harboring pathogenic variants exhibit reductions in levels of the predominant 220-kDa AnkB isoform in several tissues, including SKM and impaired systemic glucose regulation. To understand the specific metabolic role of AnkB in SKM, we developed a conditional knock-out mouse in which 220-kDa AnkB is knocked out only in SKM (SKM-AnkB-KO) . SKM-AnkB-KO mice display glucose mishandling that persists with age, as well as decreases in activity and exercise capacity, measured by indirect calorimetry and voluntary running wheel analysis. Histological evaluations of aged SKM-AnkB-KO mice showed general disorganization of muscle fibers and the presence of centralized nuclei. This is accompanied by increases in lean muscle mass and in the cross-sectional area of mitochondria-rich soleus muscle, suggesting the development of muscle hypertrophy over time. Electron microscopy analysis revealed the presence of hyperfused mitochondria in SKM-AnkB-KO mice. This morphological change was concomitant with up-regulation of transcripts in pathways associated with energetic stress, including AMPK signaling, redox signaling and mTOR signaling, assessed by RNA-seq, and with alterations in mitochondrial respiration in isolated muscle fibers. Interestingly, SKM-AnkB-KO mice mi SKM-AnkB-KO mice also exhibit increases in protein levels of electron transport chain proteins. Through proteomics and biochemical analysis, we uncovered that AnkB directly associates with several mitochondrial proteins and co-fractionates with mitochondrial in SKM. Together, these data suggest a direct role of AnkB in SKM mitochondrial metabolism that is distinct from its previously characterized role in insulin signaling in other tissues and cytoskeletal organization in SKM.