The effect of high glucose and PPAR-γ agonists on PPAR-γ expression and function in HK-2 cells

Abstract

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) are ligand-activated transcription factors that regulate cell growth, inflammation, lipid metabolism, and insulin sensitivity. PPAR-gamma in the human kidney has been described. However, the role of PPAR-gamma in proximal tubular cells with respect to cell growth and inflammation in diabetic nephropathy is largely unknown. We evaluated the effect of high (30 mM) D-glucose, thiazolidinedione pioglitazone (10 microM), and the selective PPAR-gamma agonist L-805645 (8 microM) on PPAR-gamma expression, growth, and inflammatory parameters in the proximal tubular model of HK-2 cells. PPAR-gamma was present in HK-2 cells and upregulated with 30 mM D-glucose to 177 +/- 31.2% of control (P < 0.05). PPAR-gamma activation was induced by pioglitazone to a similar level to that observed by exposure to high glucose but maximally induced by the selective agonist L-805645. However, L-805645 reduced cell viability in both 5 and 30 mM d-glucose to 73.8 +/- 3.1 and 77.6 +/- 1.4% of control (both P < 0.0001). In parallel, thymidine incorporation was reduced with L-805645 in both 5 and 30 mM D-glucose to 33.3 +/- 3.4 and 37.9 +/- 2.2%, respectively (both P < 0.0001). Flow cytometry demonstrated increased apoptosis and G(1) phase arrest in association with an increase in p21(cip1/waf1) in cells exposed to L-805645. Exposure to 30 mM D-glucose did not significantly change AP-1 promoter activity (89.0 +/- 5.5% of control); however, the addition of L-805645 significantly reduced it to 62.2 +/- 2.7% of control (P < 0.0001). Thirty nanomolar D-glucose induced transforming growth factor-beta(1) to 137.7 +/- 16.9% of control (P < 0.05), and L-805645 was able to suppress this to 68.7 +/- 5.7% of control (P < 0.01 vs. d-glucose). Exposure to 30 mM D-glucose reduced monocyte chemoattractant protein 1 levels to 78.6 +/- 7.1% (P < 0.05) of control, with the reduction more marked in the presence of either pioglitazone (P < 0.01) or L-805645 (P < 0.01). In summary, high glucose upregulates PPAR-gamma and when significantly induced demonstrates anti-proliferative and anti-inflammatory effects.

Pioglitazone Inhibits Cell Growth and Reduces Matrix Production in Human Kidney Fibroblasts

“…However, subsequently, PPAR-␥ has been confirmed in human kidney (20,21), and several groups have since identified the presence of PPAR-␥ message and protein in major components of the glomerulus, in mesangial cells, and in endothelial cells in animal models (9,22,23). Studies in our laboratory have also confirmed that in several in vitro proximal tubular cell models, these cells also express PPAR-␥ (7,15). This study additionally confirms that PPAR-␥ is functionally expressed in the human CF.…”

“…For determining the extent to which apoptosis contributed to a reduction in cell number, the pre-G1 peak was determined by flow cytometric analysis, as described previously (15).…”

Erythromycin ameliorates renal injury via anti-inflammatory effects in experimental diabetic rats

“…Mezzano et al [30] reported that the activation of NF-κB and chemokines such as CCL2 and RANTES (regulated upon activation, normal T expressed and secreted) was strongly upregulated in renal tissues of human diabetic nephropathy. Moreover, high glucose upregulates peroxisome proliferator-activated receptor-γ (PPAR-γ), and PPAR-γ agonists exert antifibrotic, anti-proliferative and anti-inflammatory effects in renal proximal tubular cells under high glucose conditions by attenuating the increase in activator protein-1, TGFB1 and the downstream production of the extracellular matrix protein [31,32]. These data also suggest that inflammatory mechanisms are involved in the progression of diabetic nephropathy.…”

High Glucose-Induced Thioredoxin-Interacting Protein in Renal Proximal Tubule Cells Is Independent of Transforming Growth Factor-β1

“…1,2 Hence the proximal tubule cells are an ideal model in which to unravel the cellular mechanisms underpinning the tubulointerstitial changes in diabetic nephropathy that ultimately predict a progressive decline in renal function. Furthermore, we and others 3,4 have determined that exposure of these cells to elevated glucose concentrations has an important priming effect on the cells that may facilitate the generation of a profibrotic response.…”