Nitric Oxide Inhibition of Transforming Growth Factor-β and Collagen Synthesis in Mesangial Cells

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Abstract
Culture of mesangial cells (MCs) in 5.6 vs. 30.0 mmol/1 glucose for 3 weeks induced a sustained increase in protein kinase C (PKC) activity, transforming growth factor (TGF)-β1 mRNA, bioactive TGF-β, and collagen synthesis. Nitric oxide (NO), generated exogenously by the NO donor S-nitroso-N-acetyl, D,L-penicillamine (SNAP) or endogenously after the exposure of MC to interleukin-1β (IL-1β), suppressed bioactive TGF-β in MCs cultured in 5.6 or 30.0 mmol/1 glucose and suppressed or abolished increases in TGF-β1 mRNA and collagen synthesis induced by high concentrations of glucose or phorbol 12,13-dibutyrate without altering values obtained with normal glucose concentrations. SNAP had a transient suppressive effect on PKC activity, which may explain at least in part some of the actions of SNAP. The selective inhibitor of PKC, bisindolylmaleimide (GFX), mimicked NO action. The ability of SNAP and IL-lβ to suppress TGF-β and collagen synthesis was not mediated by cGMP, since the cGMP analog, 8-Br-PET-cGMP, did not mimic NO action and an antagonist of cGMP-dependent protein kinase, Rp-8-pCPT-cGMPs, did not prevent the inhibitory actions of SNAP. N-ω-L-arginine methyl ester (NMMA) increased TGF-β in glomerular capillary endothelial cells (GCECs) and stimulated collagen synthesis by MC in a co-culture with GCECs. Captopril inhibited TGF-β and collagen synthesis and increased cGMP in co-cultures of GCECs and MCs. These effects of captopril were abolished by NMMA, implying mediation by NO. Thus, endogenous NO produced by GCECs may modulate TGF-β production by both GCECs and MCs and act to suppress matrix protein synthesis by MCs.

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