Conclusions
Repeated exposure of differentiating adipocytes to transient hypoxia is able to reprogram the cells for increased TG accumulation and enhanced insulin sensitivity. The metabolic alterations were observed in postdifferentiated cells under normoxia. The reprogramming involves AMPK activation and gene expression in the metabolic pathways in cytosol and mitochondria.
Methods
The impact of transient hypoxia on metabolic reprogramming was investigated in 3T3-L1 cells before and after differentiation. Glucose uptake, fatty acid oxidation, lipolysis and mitochondria were examined to determine the hypoxia effects. Preadipocytes were exposed to transient hypoxia (4 h day(-1)) in the course of differentiation. Insulin sensitivity and triglyceride (TG) accumulation was examined in the cells at the end of differentiation to determine the reprogramming effects. AMP-activated protein kinase (AMPK) activity and gene expression were determined by quantitative reverse transcriptase-PCR and western blotting in search for mechanism of the reprogramming.
Results
In acute response to hypoxia, adipocytes exhibited an increase in insulin-dependent and -independent glucose uptake. Fatty acid β-oxidation and pyruvate dehydrogenase activity were decreased. Multiple exposures of differentiating adipocytes to transient hypoxia enhanced insulin signaling, TG accumulation and expression of antioxidant genes in differentiated adipocytes in the absence of hypoxia. The metabolic memory was associated with elevated AMPK activity and gene expression (GLUT1, PGC-1α, PPARγ, SREBP, NRF-1, ESRRα, LPL). The enhanced insulin sensitivity was blocked by an AMPK inhibitor. Conclusions: Repeated exposure of differentiating adipocytes to transient hypoxia is able to reprogram the cells for increased TG accumulation and enhanced insulin sensitivity. The metabolic alterations were observed in postdifferentiated cells under normoxia. The reprogramming involves AMPK activation and gene expression in the metabolic pathways in cytosol and mitochondria.