Nitric oxide induces MIP‐2 transcription in rat renal mesangial cells and in a rat model of glomerulonephritis

Abstract

Nitric oxide is a crucial mediator of several forms of glomerulonephritis. We examined the effects of NO on the mRNA expression pattern in glomerular mesangial cells by using a low-stringency reverse transcriptase-polymerase chain reaction method and detected a cDNA fragment that was induced by interleukin 1b (IL-1b) and further up-regulated by the NO donor diethylenetriamine-nitric oxide (DETA-NO). Each respective cDNA fragment was found to match with the cDNAs of rat macrophage inflammatory protein 2 (MIP-2) and GRO/cytokine-induced neutrophil chemoattractant 2b (CINC-2b). Further characterization of MIP-2 regulation by Northern blot analysis confirmed an NO- and IL-1b-dependent increase in MIP-2 mRNA levels. Moreover, inhibition of IL-1b-induced endogenous NO formation by the NO-synthase (NOS) inhibitor L-NMMA markedly attenuated MIP-2 protein expression. We cloned 770 bp of the 5'-flanking region of rat MIP-2 and fused this fragment to a luciferase reporter gene. Transfection of the construct into mesangial cells resulted in a 3.5-fold increase in luciferase activity in cells treated with DETA-NO when compared to controls, suggesting a transcriptional mechanism for NO-induced MIP-2 expression. Deletion and mutational analysis identified critical nuclear factor (NF)-kB and NF-IL-6 binding sites required for NO regulation of MIP-2. In vivo, inhibition of NO synthesis in the Thy-1.1 model of mesangioproliferative glomerulonephritis by the specific inducible-NOS inhibitor L-NIL resulted in a marked reduction of MIP-2 mRNA expression. Furthermore, infiltration of neutrophils into the glomerulus was dramatically attenuated in L-NIL-treated rats.