Enhanced ecto-apyrase activity of stimulated endothelial or mesangial cells is downregulated by glucocorticoids in vitro.

Endothelial as well as mesangial cells show enhanced activity of ecto-apyrase following pro-inflammatory stimulation in vitro. Since this ecto-enzyme appears to be able to regulate plasma hemopexin, which latter molecule plays a role in the pathogenesis of corticosteroid responsive nephrotic syndrome, the question was raised whether glucocorticoids are potentially able to downregulate ecto-apyrase activity of these cells. Therefore, cell cultures of endothelial or mesangial were stimulated with or without lipopolysaccharide (10 ng/ml). Parallel cultures were supplemented with prednisolone with or without the glucocorticoid receptor antagonist mifepristone in various concentrations. After 24 h, cytospins were prepared and cytochemically stained for ecto-apyrase activity. mRNA for apyrase of these cells was detected using reverse transcription–polymerase chain reaction (RT-PCR). Apyrase activity of either cells or soluble apyrase (0.16 U/ml buffer) with or without supplementation of prednisolone were biochemically assayed for their phosphatase activity. The results show significantly decreased ecto-apyrase activity of lipopolysaccharide-stimulated cells after treatment with prednisolone as compared to non-prednisolone-treated cells. Preincubation with mifepristone did not inhibit the effect of prednisolone. Identical mRNA signals for apyrase were found in prednisolone and non-prednisolone-treated cells. Interestingly, soluble apyrase also showed a significant decrease of activity following preincubation with prednisolone. It is concluded that prednisolone is able to downregulate ecto-apyrase of stimulated endothelial or mesangial cells, which may potentially inhibit the conversion of hemopexin to its pro-inflammatory isoform. As blocking of the cytosolic glucocorticoid receptor showed no effect upon the prednisolone action, whereas prednisolone is able to affect soluble apyrase per se, it is felt that this particular action of prednisolone may (at least partly) be mediated through a non-genomic pathway.