Increased Insulin Sensitivity by High-Altitude Hypoxia in Mice with High-Fat Diet-Induced Obesity Is Associated with Activated AMPK Signaling and Subsequently Enhanced Mitochondrial Biogenesis in Skeletal Muscles

Abstract

<b><i>Background:</i></b> This study aimed to investigate whether and how high altitude-associated ambient hypoxia affects insulin sensitivity in mice fed a high-fat diet (HFD). <b><i>Methods:</i></b> Mice were randomly divided into a control group (with normal diet feeding and low-altitude housing), LA/HFD group (with HFD feeding and low-altitude housing), and HA/HFD group (with HFD feeding and high-altitude housing). <b><i>Results:</i></b> After 8 weeks, mice in the HA/HFD group showed improved insulin sensitivity-related indices compared with the LA/HFD group. In mice residing in a low-altitude region, HFD significantly impaired mitochondrial respiratory function and mitochondrial DNA content in skeletal muscles, which was partially reversed in mice in the HA/HFD group. In addition, the fatty acid oxidation-related enzyme gene <i>CPT1</i> (carnitine palmitoyltransferase 1) and genes related to mitochondrial biogenesis such as peroxisome proliferator-activated receptor-γ coactivator-1α (<i>PGC-1α</i>), nuclear respiratory factor 1 (<i>NRF1</i>), and mitochondrial transcription factor A (<i>Tfam</i>) were upregulated in the skeletal muscles of mice housed at high altitude, in comparison to in the LA/HFD group. Furthermore, AMPK (adenosine monophosphate-activated protein kinase) signaling was activated in the skeletal muscles, as evidenced by a higher expression of phosphorylated AMPK (p-AMPK) and protein kinase B (p-AKT) in the HA/HFD group than in the LA/HFD group. <b><i>Conclusion:</i></b> Our study suggests that high-altitude hypoxia improves insulin sensitivity in mice fed an HFD, which is associated with AMPK activation in the skeletal muscle and consequently enhanced mitochondrial biogenesis and fatty acid oxidation. This work provides a molecular explanation for why high altitude is associated with a reduced incidence of insulin resistance in the obese population.