Oral or Poster Presentation
Concurrent Session 2C - DOHaD
Introduction: The development of gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy and puts offspring at greater risk for insulin resistance, type 2 diabetes, and low cardiorespiratory fitness; however, the cellular mechanisms responsible remain unknown. Previously, we observed elevated protein levels of the mitophagy receptor Nix in muscle of rodent offspring exposed to GDM and/or a high-fat/sucrose diet concurrent with peripheral insulin resistance. Therefore, we sought to test the hypothesis that Nix plays an adaptive role in cellular metabolism by mediating both mitophagy and altering cellular signaling.
Methods: We used a model of contracting cultured myotubes to examine role of Nix in mitophagy by using fluorescent biosensors and western blotting to assess levels of calcium, mitophagy, and cellular signaling. Additionally, we generated a skeletal-muscle Nix knockout mouse to determine the effect of Nix on metabolism by evaluating blood glucose and peripheral insulin-signaling in response to insulin.
Results: Post-contraction, we observed increases in Nix (1.9-fold) and mitochondrial biogenesis proteins (PGC1α 2.5-fold, NRF2 1.4-fold) concurrent with elevated levels of mitophagy (1.4-fold). To determine if Nix was responsible for this increase, we knocked-down Nix and found that contraction no longer increased levels of mitophagy. Next, we assessed levels of the calcium-regulated transcription factor NFAT because of its role in muscle adaptation to energy stress. First, we found that contraction increased levels of nuclear calcium (2-fold) which did not occur when Nix was knocked-down. Furthermore, levels of the active form of NFAT protein were elevated by contraction. Early experiments with the skeletal-muscle Nix knockout mouse confirmed muscle-specific knockout and suggest enhanced sensitivity to insulin in knockout mice.
Conclusion: These data, along with our previous studies, support the notion that Nix plays both physiological and pathological roles in regulating mitophagy in muscle during contraction and following exposure to lipotoxicity/GDM, respectively.