High glucose stimulates expression of p27(Kip1) in cultured mouse mesangial cells: relationship to hypertrophy

Hypertrophy of mesangial cells is an early hallmark of diabetic nephropathy. We have previously shown that murine mesangial cells (MMC), cultured in high-glucose medium, are arrested in the G(1) phase of the cell cycle and undergo hypertrophy. This study was undertaken to test whether high glucose-containing medium influences the expression of p27(Kip1), an inhibitor of G(1) phase active cyclin-dependent kinases (CDK). Incubation of MMC, in the absence of other factors for 48-96 h, in medium containing high D-glucose (450 mg/dl), stimulated p27(Kip1) protein expression but failed to influence mRNA abundance. These effects were independent of the osmolarity of the medium. High glucose-stimulated expression of p27(Kip1) involved activation of protein kinase C and was partly dependent on induction of transforming growth factor-beta (TGF-beta). Immunoprecipitation experiments revealed that only small amounts of p27(Kip1) protein from MMC grown in high-glucose medium preferentially associates with CDK2 but not with CDK4. The p27(Kip1) antisense, but not missense, oligonucleotides inhibited high glucose-stimulated total protein synthesis and facilitated G(1) phase exit. Our data showed for the first time that expression of p27(Kip1) protein is pivotal in mesangial cell hypertrophy induced by high ambient glucose. These findings may be important in the deciphering of molecular processes causing diabetic glomerular hypertrophy.