Signaling Mechanism Involving PPARα‐ligand‐Mediated Increase in NO Production

Abstract

Clofibrate (CF), a peroxisome proliferator activated receptor α (PPARα) ligand increases nitric oxide (NO) production via PPARαf{dependent and ‐independent pathways. As PKA/PKC are involved in NO production, we investigated whether PKA/PKC signaling pathways are involved in CF‐mediated increase in NO. NO production (over 30 min) was determined in proximal tubular (PT) suspensions isolated from PPARα knock‐out (KO) and wild type (WT) mice challenged with CF (2μM) using NO specific dye DAF‐FM2. WT and KO mice were also treated with CF (250 mg/kg; i.p, 7 days) and renal homogenate was used for protein expression. NO signal in the PT was significantly lower in PPARα KO mice (21¡Ó2%). CF enhanced NO production (WT: 88¡Ó12%; KO: 86¡Ó6%) that was abolished by LNAME (3 μM). PKA 14–22 (20 μM), a PKA inhibitor, reduced CF‐mediated NO production (WT: 56¡Ó5%; KO: 46¡Ó2%). Similarly, chelerythrine (3 μM), a PKC inhibitor, reduced NO production (WT: 47¡Ó4%; KO: 45¡Ó2%). CF also increased eNOS and iNOS mRNA and iNOS protein expression in the KO but not in WT mice and did not affect PKC or PKA protein. These data suggest that CF increased NO production by inducing iNOS gene via a PPARα‐independent mechanism. We conclude that although CF did not influence PKA/PKC protein expression, but PKC/PKA signaling pathways are required for CF‐mediated enhanced acute NO production.