Chronic hypoxia impairs the differentiation of 3T3‐L1 fibroblast in culture: Role of sustained protein kinase C activation

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Abstract
The effect of hypoxia on 3T3‐L1 cell differentiation was examined in confluent cultures incubated with differentiation medium (DM) followed by incubation in growth medium (GM). Control cultures remained in GM throughout the incubation period. Eight days after the incubation, cells were assessed either for changes in morphology by staining with Oil Red O/hematoxylin or harvested to measure protein kinase C activity. Morphological examination of stained cells showed almost complete differentiation of normoxic cells to adipocytes when exposed to DM. By contrast hypoxia caused a dramatic inhibition of differentiation under similar media conditions with only 34 ± 4% of cells accumulating fat deposits. Cultures sustained in GM under normoxic or hypoxic conditions were devoid of any fat deposits, reflecting an undifferentiated phenotype. Normoxic cells exposed to DM exhibited a significantly lower membrane to cytosolic ratio of protein kinase C in comparison with cells maintained in GM, which is consistent with differentiated and undifferentiated phenotypes, respectively. In comparison with normoxic cells incubated in DM, cells exposed to hypoxia under similar media conditions exhibited a significantly higher membrane to cytosolic ratio of protein kinase C, indicating sustained activation of the enzyme. In addition, cells in differentiation medium exposed to hypoxia in the presence of the protein kinase C inhibitors staurosporine or H7 exhibited a significant increase in the number of fat accumulating cells when compared with hypoxic controls. These studies indicate that chronic hypoxia impairs the differentiation of 3T3‐L1 cells to adipocytes in association with the sustained activation of protein kinase C, which appears to play a role in mediating this process.