The research suggests that
adiponectin plays an important role in sensitizing
insulin action. It is interesting to find that the lower levels of
adiponectin exist in the plasma of obese and
Type 2 diabetes subjects and in the adipose tissue of obese, db/db mice, and
insulin-resistant individuals. However, the underlying mechanism by which
adiponectin expression is inhibited remains largely unknown. In this study, we reported that adipogenesis was inhibited by the stable over-expression of
protein kinase C θ (PKCθ) in 3T3-L1 pre - adipocytes. The prolonged treatment of mature 3T3-L1 adipocytes with
palmitate, a kind of saturated
free fatty acid, reduced
adiponectin expression at both
mRNA level and
protein level, accompanied with the enhanced phosphorylation of PKCθ and
extracellular signal-regulated kinase (ERK), and the impaired expression of
peroxisome proliferator-activated receptor γ2 (PPARγ2)
mRNA. Either
PD98059, an ERK inhibitor or PKCθ pseudosubstrate, a specific PKCθ inhibitor, restored palmiate-inhibited PPARγ2
mRNA expression and subsequent
adiponectin expression. In addition, the over-expression or activation of PKCθ resulted in the enhanced phosphorylation of ERK in the mature 3T3-L1 adipocytes. PKCθ pseudosubstrate significantly reduced the
phorbol 3-myristate 12-acetate (PMA)-induced phosphorylation of ERK. The data suggested that PKCθ-dependent activity of ERK resulted in the impaired expression of PPARγ2
mRNA leading to the reduction of
adiponectin expression in the mature 3T3-L1 adipocytes.