Pioglitazone increases renal tubular cell albumin uptake but limits proinflammatory and fibrotic responses

Abstract

Background: Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, which are known to be critical factors in lipid metabolism, have also been reported to reduce proteinuria. The mechanism and its relevance to progressive nephropathy have not been determined. The aims of this study were to assess the direct effects of a PPARgamma agonist on tubular cell albumin uptake, proinflammatory and profibrotic markers of renal pathology, using an opossum kidney model of proximal tubular cells.

Methods: Cells were exposed to pioglitazone (10 micromol/L) in the presence and absence of low-density lipoprotein (LDL) 100 microg/mL +/- exposure to albumin 1 mg/mL. Results were expressed relative to control (5 mmol/L glucose) conditions.

Results: Pioglitazone caused a dose-dependent increase in tubular cell albumin uptake (P < 0.0001). Despite the increase in albumin reabsorption, no concurrent increase in inflammatory or profibrotic markers were observed. Exposure to LDL increased monocyte chemoattractant protein-1 (MCP-1) (P < 0.05) and transforming growth factor-beta1 (TGF-beta1) (P < 0.05) production, which were reversed in the presence of pioglitazone. LDL induced increases in MCP-1 and TGF-beta1 were independent of nuclear factor-kappaB (NF-kappaB) transcriptional activity. In contrast, tubular exposure to albumin increased tubular protein uptake, in parallel with an increase in MCP-1 (P= 0.05), TGF-beta1 (P < 0.02) and NF-kappaB transcriptional activity (P < 0.05), which were unaffected by concurrent exposure to pioglitazone.

Conclusion: These findings suggest that dyslipidemia potentiates renal pathology through mechanisms that may be modified by PPARgamma activation independent of NF-kappaB transcriptional activity. In contrast, tubular exposure to protein induces renal damage through NF-kappaB-dependent mechanisms that are unaffected by PPARgamma activation.