The HIF-1 response to simulated ischemia in mouse skeletal muscle cells neither enhances glycolysis nor prevents myotube cell death

Abstract

Hypoxia-inducible factor (HIF) plays an important role in regulating gene expression in response to ischemia. Although activation of HIF-1 in muscle tissue was found during ischemia in vivo, the meaning and mechanisms in isolated cells are still incompletely understood. We studied activation of HIF-1 in skeletal muscle cells cultured in either their undifferentiated myoblast state or differentiated into myotubes. HIF-1 was activated in myoblasts and myotubes by hypoxia and simulated ischemia. Induction of adrenomedullin mRNA and, to a lesser extent, VEGF mRNA correlated well with the induction of HIF-1alpha protein in both cell types. Enzymes of glycolysis-like lactate dehydrogenase and pyruvate kinase showed upregulation of their mRNA only under hypoxic conditions but not during simulated ischemia. Phosphofructokinase mRNA showed no significant upregulation at all. Although HIF-1 was activated in myotubes during simulated ischemia, myotubes died preceded by a loss of ATP. Myoblasts survived simulated ischemia with no decrease in ATP or ATP turnover. Furthermore, pharmacological inhibition of HIF-1 hydroxylases by dimethyloxalylglycine (DMOG) increased HIF-1alpha accumulation and significantly upregulated the expression of adrenomedullin, VEGF, lactate dehydrogenase, and pyruvate kinase in myoblasts and myotubes. However, DMOG provided no protection from cell death. Our data indicate that HIF-1, although activated in myotubes during simulated ischemia, cannot protect against the loss of ATP and cell viability. In contrast, myoblasts survive ischemia and thus may play an important role during regeneration and HIF-1-induced revascularization.

The response of human skeletal muscle tissue to hypoxia

“…However, the exact pathway by which HIF-1 acts on muscle tissue in response to exercise-induced hypoxia and ultimately on exercise tolerance remains a : ? [26] : [53] Lactate dehydrogenase A Yes Glucose metabolism : [50] ? [54] ?…”

Differential contribution of key metabolic substrates and cellular oxygen in HIF signalling

“…The importance of glucose and glutamine for HIF-α signalling in hypoxia has been shown in a number of publications, including studies on different cancer cell lines, myocytes and stem cells [31][32][33][34][35][36][37]. The negative effect of glucose and glutamine deprivation on HIF-1α levels was demonstrated in human fibrosarcoma and pancreatic cancer cells and related to a decrease in protein translation [31,33].…”

Phosphatidylinositol-3-kinase (PI3K) activity decreases in C2C12 myotubes during acute simulated ischemia at a cost to their survival

“…Acute ischemia of muscle tissue can result from prolonged arterial clamping during surgery, acute atherosclerotic thrombosis, and arterial embolism or may be due to traumatic injury and vessel destruction (Dehne et al, 2007).…”