All-trans retinoic acid protects renal tubular epithelial cells against hypoxia induced injury in vitro.

BACKGROUND: It has been reported that the all-trans retinoic acid (atRA)-mediated protective effects in various cells are related to the inhibition of nuclear factor (NF)-κB activities. There exists some evidence that an increase in vascular endothelial growth factor (VEGF), which is expressed by proximal tubular epithelial cells and regulated by NFκB, may play a critical role in maintaining peritubular capillary endothelium in renal disease. By stimulating the production of VEGF, hypoxia is involved in tubulointerstitial fibrosis processes in various renal diseases.

METHODS: NRK52E cells survival rate was proportional to absorbance in dimethyl-thiazol-diphenyltetrazoliumbromide tests. Quantitative real-time polymerase chain reaction and Western blot were performed to assay the expression of VEGF, p65, and Scpep1. The activation of NFκB was determined by electrophoretic mobility shift assay. Co-immunoprecipitation analysis demonstrates that whether the Scpep1 and NFκB protein interacted.

RESULTS: We demonstrated that the hypoxia-mimicking agent CoCl2 triggered hypoxia injury of rat proximal tubular epithelial cells and significantly reduced cell viability. Addition of atRA increased the cell survival rate. Under CoCl(2)-mimicking hypoxic conditions, the expression of VEGF and p65 increased. The addition of atRA significantly attenuated the expression of VEGF and p65. There was a similar variation of NFκB/DNA binding activities. atRA not only activated distinct pathways to stimulate the expression of Scpep1, a retinoid-inducible gene, under normoxic conditions, but also acted as a CoCl(2)-mimicking hypoxia.

CONCLUSION: The protective effects of atRA against hypoxia-induced injury might be involved in suppression of VEGF expression via stimulating Scpep1 distinct pathways and inhibiting the NFκB pathway.