Brophy, Colleen M.

OBJECTIVE The contribution of mitochondrial dysfunction to skeletal muscle insulin resistance remains elusive. Comparative proteomics are being applied to generate new hypotheses in human biology and were applied here to isolated mitochondria to identify novel changes in mitochondrial protein abundance present in insulin-resistant muscle. RESEARCH DESIGN AND METHODS Mitochondria were isolated from vastus lateralis muscle from lean and insulin-sensitive individuals and from obese and insulin-resistant individuals who were otherwise healthy. Respiration and reactive oxygen species (ROS) production rates were measured in vitro. Relative abundances of proteins detected by mass spectrometry were determined using a normalized spectral abundance factor method. RESULTS NADH- and FADH2-linked maximal respiration rates were similar between lean and obese individuals. Rates of pyruvate and palmitoyl-dl-carnitine (both including malate) ROS production were significantly higher in obesity. Mitochondria from obese individuals maintained higher (more negative) extramitochondrial ATP free energy at low metabolic flux, suggesting that stronger mitochondrial thermodynamic driving forces may underlie the higher ROS production. Tandem mass spectrometry identified protein abundance differences per mitochondrial mass in insulin resistance, including lower abundance of complex I subunits and enzymes involved in the oxidation of branched-chain amino acids (BCAA) and fatty acids (e.g., carnitine palmitoyltransferase 1B). CONCLUSIONS We provide data suggesting normal oxidative capacity of mitochondria in insulin-resistant skeletal muscle in parallel with high rates of ROS production. Furthermore, we show specific abundance differences in proteins involved in fat and BCAA oxidation that might contribute to the accumulation of lipid and BCAA frequently associated with the pathogenesis of insulin resistance.

ABSTRACT Activation of cyclic nucleotide‐dependent signaling pathways leads to phosphorylation of the small heat shock‐related protein, HSP20, on serine 16, and relaxation of vascular smooth muscle. In this study, we used an enhanced protein transduction domain (PTD) sequence to deliver HSP20 phosphopeptide analogs into porcine coronary artery. The transduction of phosphoHSP20 analogs led to dose‐dependent relaxation of coronary artery smooth muscle. Peptides containing the protein transduction domain coupled to a random orientation of the same amino acids did not. Direct fluorescence microscopy of arterial rings incubated with fluorescein isothiocyanate (FITC)‐PTD or FITC‐PTD‐HSP20 peptides showed a diffuse peptide uptake. Mass spectrometric immunoassays (MSIAs) of smooth muscle homogenates were used to determine whether the phosphopeptide analogs affected the phosphorylation of endogenous HSP20. Treatment with the phosphodiesterase inhibitor papaverine led to a mass shift of 80 Da. However, there was no mass shift of HSP20 in muscles treated with phosphoHSP20 analogs. This suggests that the PTD‐phosphoHSP20 peptide alone is sufficient to inhibit force maintenance and likely has a direct effect on the target of phosphorylated HSP20. These results suggest that transduction of phosphopeptide analogs of HSP20 directly alters physiological responses of intact muscles. The data also support a direct role for phosphorylated HSP20 in mediating vasorelaxation.