Megan E. Rosa

Mitochondrial quality control, promoted by PGC‐1α, is dysregulated by Western diet‐induced obesity and partially restored by moderate physical activity in mice

Skeletal muscle mitochondrial degeneration is a hallmark of insulin resistance/obesity marked by lost function, enhanced ROS emission, and altered morphology which may be ameliorated by physical activity (PA). However, no prior report has examined mitochondrial quality control regulation throughout biogenesis, fusion/fission dynamics, autophagy, and mitochondrial permeability transition pore (MPTP) in obesity. Therefore, we determined how each process is impacted by Western diet (WD)‐induced obesity and whether voluntary PA may alleviate derangements in mitochondrial quality control mechanisms. Despite greater mitochondrial content following WD (COX‐IV and Cytochrome C), induction of biogenesis controllers appears impaired (failed induction of PGC‐1α). Mitochondrial fusion seems diminished (reduced MFN2, Opa1 proteins), with no significant changes in fission, suggesting a shift in balance of dynamics regulation favoring fission. Autophagy flux was promoted in WD (reduced p62, increased LC3II:I ratio); however, mitophagy marker BNIP3 is reduced in WD which may indicate reduced mitophagy despite enhanced total autophagy flux. MPTP regulator Ant mRNA is reduced by WD. Few processes were impacted by physical activity. Finally, mitochondrial quality control processes are partially promoted by PGC‐1α, as PGC‐1α transgenic mice display elevated mitochondrial biogenesis and autophagy flux. Additionally, these mice exhibit elevated Mfn1 and Opa1 mRNA, with no change in protein content suggesting these factors are transcriptionally promoted by PGC‐1α overexpression. These data demonstrate dysfunctions across mitochondrial quality control in obesity and that PGC‐1α is sufficient to promote multiple, but not necessarily all, aspects of mitochondrial quality control. Mitochondrial quality control may therefore be an opportune target to therapeutically treat metabolic disease.

microRNA‐16 Is Downregulated During Insulin Resistance and Controls Skeletal Muscle Protein Accretion

Insulin resistant diabetes, currently at epidemic levels in developed countries, begins in the skeletal muscle and is linked to altered protein turnover. microRNAs downregulate targeted mRNA translation decreasing the amount of translated protein, thereby regulating many cellular processes. Regulation of miRNAs and their function in skeletal muscle insulin resistance is largely unexplored. The purpose of this study was to identify the effects of insulin resistance on contents of skeletal muscle miRNAs with potential functions in protein turnover. We examined miRs ‐1, ‐16, ‐23, ‐27, ‐133a, ‐133b, and ‐206 in muscles of Zucker rats. miR‐1 was 5‐ to 10‐fold greater in obesity, whereas miRs‐16 and ‐133b were repressed ∼50% in obese compared to lean rats, with no other alterations in miRNA contents. miR‐16 correlated to protein synthesis in lean, but not obese rats. miR‐16 reduction by lipid overload was verified in‐vivo by diet‐induced obesity and in‐vitro using a diacylglycerol analog. A role for miR‐16 in protein turnover of skeletal myocytes was established using transient overexpression and anti‐miR inhibition. miR‐16 overexpression resulted in lower protein synthesis (puromycin incorporation, ∼25–50%), mTOR (∼25%), and p70S6K1 (∼40%) in starved and insulin stimulated myoblasts. Conversely, anti‐miR‐16 increased basal protein synthesis (puromycin incorporation, ∼75%), mTOR (∼100%), and p70S6K1 (∼100%). Autophagy was enhanced by miR‐16 overexpression (∼50% less BCL‐2, ∼100% greater LC3II/I, ∼50% less p62) and impaired with miR‐16 inhibition (∼45% greater BCL‐2, ∼25% less total LC3, ∼50% greater p62). This study demonstrates reduced miR‐16 during insulin resistance and establishes miR‐16 control of protein accretion in skeletal muscle. J. Cell. Biochem. 117: 1775–1787, 2016.

Translational machinery of mitochondrial mRNA is promoted by physical activity in Western diet-induced obese mice.

Mitochondria‐encoded proteins are necessary for oxidative phosphorylation; however, no report has examined how physical activity (PA) and obesity affect mitochondrial mRNA translation machinery. Our purpose was to determine whether Western diet (WD)‐induced obesity and voluntary wheel running (VWR) impact mitochondrial mRNA translation machinery and whether expression of this machinery is dictated by oxidative phenotype.