Background: To elucidate the regulation of peroxisome proliferator-activated receptor gamma (PPARgamma) and its roles in mesangial cells, we examined the expression of PPARgamma1 and effects of its ligands on cell phenotypes and angiotensin II-induced contractile response in cultured rat mesangial cells under a high (20 mmol/L) glucose condition.
Methods: The effects of tumor necrosis factor alpha (TNFalpha), protein kinase C (PKC) activation, antisense DNA for PPARgamma1, PPARgamma ligands and PD98059 were examined in mesangial cells cultured in either 5 mmol/L or 20 mmol/L glucose. The expressions of PPARgamma1 protein and alpha-smooth muscle actin (alphaSMA) as a marker of phenotype of cells were determined by Western blot. The expression of PPARgamma1 mRNA was determined by a reverse transcription-polymerase chain reaction method. The reduction of cell surface area in response to angiotensin II was measured by microscope to determine cellular contraction.
Results: PKC activation, TNFalpha, and 20 mmol/L glucose decreased PPARgamma1 at both protein and mRNA levels, which was inhibited by PD98059, a specific inhibitor of mitogen-activated protein kinase (MAPK). Decreases of PPARgamma1 protein and contractile response and an increase of alphaSMA occurred simultaneously in the cells treated with 20 mmol/L glucose after 5 days, which were attenuated to the normal levels by PPARgamma ligands. The antisense DNA also induced the decrease of PPARgamma1 protein, contractile dysfunction, and increase of alphaSMA.
Conclusion: MAPK suppresses PPARgamma1 at the transcriptional level, and the reduction of PPARgamma1 in cultured rat mesangial cells under the high glucose condition induces phenotypic change and loss of contractile function. PPARgamma ligands recover both reductions of PPARgamma 1 protein and contractile response.