Search

Elevated circulating branched‐chain amino acids (BCAA) have been linked with the severity of insulin resistance across numerous populations, implicating heightened BCAA metabolism as a potential therapy for insulin resistance. Recently, the angiotensin II type 1 receptor (AT1R) inhibitor Valsartan (VAL) was identified as a potent inhibitor of branched‐chain alpha‐keto acid dehydrogenase kinase (BCKDK), a negative regulator of BCAA metabolism. This work investigated the effect of VAL on myotube metabolism and insulin sensitivity under both insulin sensitive and insulin resistant conditions. C2C12 myotubes were treated with or without VAL at 8 µM for 24 h, both with and without hyperinsulinemic‐induced insulin resistance. Oxygen consumption and extracellular acidification were used to measure mitochondrial and glycolytic metabolism, respectively. Gene expression was assessed via qRT‐PCR, and insulin sensitivity was assessed via Western blot. Insulin resistance significantly reduced both basal and peak mitochondrial function which were rescued to control levels by concurrent VAL. Changes in mitochondrial function occurred without substantial changes in mitochondrial content or related gene expression. Insulin sensitivity and glycolytic metabolism were unaffected by VAL, as was lipogenic signaling and lipid content. Additionally, both VAL and insulin resistance depressed Bckdha expression. Interestingly, an interaction effect was observed for extracellular isoleucine, valine, and total BCAA (but not leucine), suggesting VAL may alter BCAA utilization in an insulin sensitivity‐dependent manner. Insulin resistance appears to suppress mitochondrial function in a myotube model which can be rescued by VAL. Further research will be required to explore the implications of these findings in more complex models. Significance Statement: The angiotensin II type 1 receptor (AT1R) inhibitor Valsartan rescued reduced mitochondrial function during insulin resistance in a myotube model of skeletal muscle. These findings provide proof‐of‐concept data suggesting Valsartan may provide metabolic benefits beyond blood pressure lowering effects. [ABSTRACT FROM AUTHOR]

Type 2 diabetes is characterized by elevated blood glucose and reduced insulin sensitivity in target tissues. Moreover, reduced mitochondrial metabolism and expressional profile of genes governing mitochondrial metabolism (such as peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha [PGC‐1α]) are also reduced during insulin resistance. Epigenetic regulation via DNA methylation of genes including PGC‐1α may contribute to diminished mitochondrial capacity, while hypomethylation of PGC‐1α (such as that invoked by exercise) has been associated with increased PGC‐1α expression and favorable metabolic outcomes. The purpose of the present report is to characterize the effects of DNA hypomethylation on myotube metabolism and expression of several related metabolic targets. C2C12 myotubes were treated with 5‐Aza‐2′‐deoxycytidine (5‐Aza) for either 24 or 72 h both with and without hyperinsulinemic‐induced insulin resistance. Mitochondrial and glycolytic metabolism were measured via oxygen consumption and extracellular acidification rate, respectively. Metabolic gene and protein expression were assessed via quantitative real time polymerase chain reaction and western blot analysis, respectively. Though expression of PGC‐1α and other related targets remained unaltered, insulin resistance and 5‐Aza treatment significantly reduced mitochondrial metabolism. Similarly, peak glycolytic metabolism was diminished by 5‐Aza‐treated cells, while basal glycolytic metabolism was unaltered. 5‐Aza also reduced the expression of branched‐chain amino acid (BCAA) catabolic components, however BCAA utilization was enhanced during insulin resistance with 5‐Aza treatment. Together the present work provides proof‐of‐concept evidence of the potential role of DNA methylation in the regulation of mitochondrial metabolism and the potential interactions with insulin resistance in a model of skeletal muscle. Significance statement: Epigenetics are important in the regulation of muscle metabolism. DNA methylation status of vital metabolic targets are often altered in the muscle of those with insulin resistance. We demonstrate nonspecific DNA hypomethylation via 5‐Aza reduces myotube metabolism as well as expression of branched‐chain amino acid catabolic enzymes in both insulin sensitive and insulin resistant myotubes. [ABSTRACT FROM AUTHOR]

Brush border membrane vesicles (BBMV) from rabbit kidney proximal tubule cells, prepared with different internal solute concentrations (cellobiose buffer 13, 18 or 85 mosM) developed an hydrostatic pressure difference across the membrane of 18.7 mosM, that causes a membrane tension close to 5 x 10(-5) N cm-1. When subjected to several hypertonic osmotic shocks an initial delay of osmotic shrinkage (a lag time), corresponding to a very small change in initial volume was apparent. This initial osmotic response, which is significantly retarded, was correlated with the initial period of elevated membrane tension, suggesting that the water permeability coefficient is inhibited by membrane stress. We speculate that this inhibition may serve to regulate cell volume in the proximal tubule.