The effect of FoxO1 on the proliferation of rat mesangial cells under high glucose conditions.

BACKGROUND: Hyperproliferation of glomerular mesangial cells (MCs) is a major pathological characteristic in the early stage of diabetic nephropathy (DN). We have previously confirmed that forkhead transcription factor O1 (FoxO1) was significantly downregulated in both the renal cortex of DN rats and MCs cultured under high-glucose (HG) conditions, but the effects and mechanisms of FoxO1 involved in the hyperproliferation of MCs are still unclear. This study aims to investigate whether FoxO1 regulates the hyperproliferation of MCs induced under high-glucose conditions, through modulating the cyclin-dependent kinase inhibitor (CKI), p27.

METHODS: Lentiviral vectors of LV-constitutively active FoxO1 (CA-FoxO1) and LV-small interfering RNA (siRNA)-FoxO1 were constructed to up- and downregulate FoxO1. Similarly, LV-NC-FoxO1 was used as negative control (NC). Rat MCs were cultured in normal glucose (5.6 mM) medium, HG (30 mM) medium, HG with LV-NC-FoxO1, HG with LV-CA-FoxO1 and HG with LV-siRNA-FoxO1 for 72 h. Cell proliferation, cell cycle progression, messenger RNA and protein expression of FoxO1, p27, cyclin D1 and CDK4 were detected by methyl thiazolyl tetrazolium assay, flow cytometry, quantitative real-time polymerase chain reaction and western blotting, respectively.

RESULTS: MCs exposed to HG medium triggered hyperproliferation of MCs. Nevertheless, overexpression of FoxO1 caused by LV-CA-FoxO1 promoted cell cycle arrest at the G0/G1 phase and attenuated proliferation, which was associated with upregulation of p27 and downregulation of cyclin D1 and CDK4. Moreover, specific degradation of FoxO1 by LV-siRNA-FoxO1 caused a decrease of p27, increase of cyclin D1 and CDK4, overrode the limited cell cycle and stimulated proliferation of MCs.

CONCLUSIONS: Overexpression of FoxO1 caused upregulation of p27, which promoted cell cycle arrest and inhibited hyperproliferation of MCs induced by HG. Degradation of FoxO1 caused an increase in p27 and stimulated MC proliferation. These findings unveil part of the molecular mechanism of FoxO1 regulation of MC hyperproliferation induced by HG.