Determining the Role of Skeletal Muscle microRNA-133a in Early-Onset Insulin Resistance

Fetal exposure to diabetes during pregnancy increases the risk for early‐onset insulin resistance in the offspring; however, the key molecular regulators responsible for fetal metabolic programming have not been characterized in muscle tissue. We demonstrate that prenatal exposure to gestational diabetes decreased the soleus muscle expression of microRNA‐133a in offspring. Using tandem mass spectrometry techniques we identify a conserved phosphorylation motif within the MEF2 and SRF transcription factors that is targeted by PKCδ and regulates microRNA‐133a expression and mitochondrial function in response to a lipotoxic signal. Reconstitution of MEF2 function in cultured myotubes by expression of a neutralizing mutation in this identified phosphorylation motif restores microRNA‐133a expression and mitochondrial membrane potential during lipotoxicity. Furthermore, overnight exposure to palmitate reduced mitochondrial oxygen consumption and insulin‐stimulated glucose uptake, which were reversed when cells were transfected with microRNA‐133a mimicking oligonucleotides. Mechanistically, we demonstrate that microRNA‐133a regulates mitochondrial function through translational inhibition of a mitophagy and cell death modulating protein, called Nix. In addition, Nix‐and palmitate‐induced mitochondrial depolarization were attenuated by the beta2‐adrenergic agonist clenbuterol. Finally, we show that rodents exposed to gestational diabetes during fetal development display muscle diacylglycerol accumulation, concurrent with insulin‐resistance, PKCδ activation, and elevated Nix expression as young adult rats. Our data identifies a novel pathway whereby fetal exposure to diabetes reduces microRNA‐133a, alters skeletal muscle metabolism, and may predispose the offspring to early‐onset insulin resistance.Support or Funding InformationSupported by Children's Hospital Foundation of Manitoba, and NSERC Canada to Joseph Gordon and CIHR to Vernon Dolinsky.