Glucocorticoids protect renal mesangial cells from apoptosis by increasing cellular sphingosine-1-phosphate

Abstract

Neutral ceramidase (NCDase) and sphingosine kinases (SphKs) are key enzymes regulating cellular sphingosine-1-phosphate (S1P) levels. In this study we found that stress factor-induced apoptosis of rat renal mesangial cells was significantly reduced by dexamethasone treatment. Concomitantly, dexamethasone increased cellular S1P levels, suggesting an activation of sphingolipid-metabolizing enzymes. The cell-protective effect of glucocorticoids was reversed by a SphK inhibitor, was completely absent in SphK1-deficient cells, and was associated with upregulated mRNA and protein expression of NCDase and SphK1. Additionally, in vivo experiments in mice showed that dexamethasone also upregulated SphK1 mRNA and activity, and NCDase protein expression in the kidney. Fragments (2285, 1724, and 1126 bp) of the rat NCDase promoter linked to a luciferase reporter were transfected into rat kidney fibroblasts and mesangial cells. There was enhanced NCDase promoter activity upon glucocorticoids treatment that was abolished by the glucocorticoid receptor antagonist RU-486. Single and double mutations of the two putative glucocorticoid response element sites within the promoter reduced the dexamethasone effect, suggesting that both glucocorticoid response elements are functionally active and required for induction. Our study shows that glucocorticoids exert a protective effect on stress-induced mesangial cell apoptosis in vitro and in vivo by upregulating NCDase and SphK1 expression and activity, resulting in enhanced levels of the protective lipid second messenger S1P.

Downregulation of sphingosine 1-phosphate (S1P) receptor 1 by dexamethasone inhibits S1P-induced mesangial cell migration

“…Our results provide strong evidence that part of the renal protective actions of glucocorticoids can be explained by targeting SK-1, S1P 1 and S1P receptor metabolism in resident glomerular cells. Förster et al (2010) demonstrated that dexamethasone alters sphingolipid metabolism by upregulation of neutral ceramidase and SK-1 expression and activity and by this protects mesangial cells from stress-induced apoptosis via enhanced formation of intracellular S1P. In addition, we demonstrate here for the first time that dexamethasone markedly reduced the expression of S1P 1 in isolated mesangial cells and mouse glomeruli, which lead to lower S1P-induced mesangial cell migration.…”

“…Whether this could explain the reduced S1P 1 expression upon dexamethasone stimulation in renal mesangial cells is not yet proven. However, we previously reported that both, glitazones (rosiglitazone and troglitazone) and dexamethasone indeed enhance the expression and activity of SK-1 (Förster et al, 2010;Koch et al, 2012), but still have opposite effects on S1P 1…”

“…Typically, glucocorticoids act via activation of GR, which is expressed in renal mesangial cells (Förster et al, 2010) and subsequent binding and activation of specific response elements, so-called GREs, in the promoter of target genes. Förster et al (2010) demonstrated that upregulation of neutral ceramidase by dexamethasone is directly regulated via functional GREs.…”

“…Typically, glucocorticoids act via activation of GR, which is expressed in renal mesangial cells (Förster et al, 2010) and subsequent binding and activation of specific response elements, so-called GREs, in the promoter of target genes. Förster et al (2010) demonstrated that upregulation of neutral ceramidase by dexamethasone is directly regulated via functional GREs. However, downregulation of gene expression by dexamethasone treatment, as we demonstrated here for S1P 1 , could be the result of either direct binding to putative negative GREs or by transrepression involving the interaction between GR and a range of transcription factors like activator protein-1 or nuclear factor-κB (for review, see De Bosscher et al, 2003).…”

“…In general, modulating sphingolipid pathways could be an attractive target for new treatment strategies and, moreover, might explain the known beneficial effects of classical renal protective drugs. In this context, we recently showed that glucocorticoids, e.g., dexamethasone, which are commonly used for the treatment of chronic inflammatory kidney diseases, have a protective effect on stress-induced apoptosis of glomerular mesangial cells (Förster et al, 2010). The authors demonstrated that this action involves activation of the sphingomyelin signaling module accompanied by a coordinated expression and stimulation of neutral ceramidase and SK-1 activities, which in turn result in increased cellular S1P levels and protection from staurosporine-induced apoptosis.…”