Telmisartan, an angiotensin II receptor type 1 blocker (ARB), was recently reported to promote lipolysis in mice by acting as a peroxisome proliferator-activated receptor (PPAR)-δ activator, although in clinical studies, it has also been recognized to activate PPAR-γ as a major cause of its pleiotropic actions. The aim of this study was to investigate whether telmisartan activates endogenous PPAR-δ and thereby exerts anti-fibrotic effects in human mesangial cells (HMC). Immunohistochemical analysis of human renal biopsy specimens revealed that PPAR-δ protein was detected in the HMC of glomeruli with moderately proliferative changes. In the HMC, both GW0742, an authentic PPAR-δ agonist, and telmisartan enhanced PPAR response element (PPRE)-luciferase activity dose dependently, and these increases were blunted by GSK0660, a specific PPAR-δ antagonist, but not by GW9662, a PPAR-γ antagonist. Telmisartan also upregulated the expression of PPAR-δ target genes related to fatty acid oxidation; that is, heart type-fatty acid-binding protein and uncoupling protein-2. These effects were inhibited by both PPAR-δ antagonism and PPAR-δ gene silencing. Transforming growth factor-β1 (TGF-β1) increased the expression of plasminogen activator inhibitor-1 (PAI-1), TGF-β1 and collagen IV. The PAI-1 expression was mediated, at least in part by the phosphorylation of extracellular signal-regulated kinases (ERKs). Telmisartan suppressed TGF-β1-stimulated PAI-1 and collagen IV expression and ERK phosphorylation, and these effects were weakened by PPAR-δ antagonism, whereas eprosartan, a non-PPAR activating ARB, did not affect TGF-β1-stimulated PAI-1 expression. These results indicate that in HMC telmisartan activates endogenous PPAR-δ and may prevent TGF-β1-induced fibrotic changes by reducing ERK phosphorylation in a PPAR-δ-dependent manner, and thus, might be useful for treating hypertensive patients with renal and metabolic disorders.

Background: Chronic hypoxia may play a pivotal role in the development of diabetic nephropathy (DN). However, the precise mechanisms underlying progressive hypoxia-induced glomerular injury remain unclear. Methods: We housed db/db mice in a hypoxia chamber (12% O2) for up to 16 weeks beginning at 8 weeks of age. Various urine, serum and kidney abnormalities and glomerular messenger RNA (mRNA) expression were compared with those in age-matched db/db mice housed under normoxia. Results: Levels of urinary albumin and podocalyxin (PCX) were significantly higher in hypoxic mice early during hypoxia. Ultracentrifugation of urine samples revealed that podocytes in the hypoxic mice shed PCX-positive microparticles into the urine. After 16 weeks of hypoxia, the mice also had higher hematocrits with lower serum glucose and various degrees of mesangiolytic glomerulosclerosis with microaneurysms and the infrequent occurrence of nodular lesions. Immunohistologically, hypoxic mice showed significantly decreased endothelial cell densities early during hypoxia and decreased podocyte densities later. In both hypoxic and normoxic mice, glomerular macrophage and transforming growth factor-β1 (TGF-β1) staining significantly increased with aging, without changes in vascular endothelial growth factor or endothelial nitric oxide synthase (eNOS). Glomerular mRNA expression of monocyte chemoattractant protein-1, eNOS and TGF-β1 was significantly enhanced in the hypoxic mice. Conclusions: These results indicate that chronic hypoxia induces advanced glomerulosclerosis with accelerated albuminuria triggered by mesangiolysis and podocyte injury in a murine model of DN.

Background. Long-term treatment with glucocorticoids (GCs) reportedly exaggerates renal fibrosis in chronic progressive inflammatory kidney disease. GCs induce the gene expression of plasminogen activator inhibitor-1 (PAI-1), a fibrosis enhancer in non-renal cells. Tumour necrosis factor-alpha (TNF-α) reduces the gene expression of 11β-hydroxysteroid dehydrogenase (HSD) 2, an inactivator of GCs, and may enhance GC activity. However, the individual and collective effects of adrenal steroids, TNF-α and HSD2 status on PAI-1 production are unknown in human proximal renal tubular epithelial cells (HPTECs). Methods. Confluent HPTECs were treated with adrenal steroids (10 nM to 10 μM) or TNF-α (10 ng/ml) for up to 48 h. The mRNA amounts of the target genes were determined by TaqMan quantitative PCR, and the PAI-1 protein amounts were measured by an immunoassay. Results. Dexamethasone (DXA) maximally increased the amounts of PAI-1 mRNA and protein at 100 nM. Aldosterone (Ald) increased PAI-1 expression dose dependently, but the effect was over 100-fold weaker than that of DXA. The PAI-1-increasing effects of DXA and Ald were abolished completely by U-486, a specific inhibitor of the glucocorticoid receptor (GR) but not by spironolactone, a specific inhibitor of the mineralocorticoid receptor. The effect of DXA was also blocked partially by AG1478 and herbimycin A, tyrosine kinase inhibitors. DXA further increased TNF-α-stimulated PAI-1 expression via the GR. Although TNF-α treatment caused an 80% reduction in the gene expression of HSD2, an inactivator of GCs, HSD2 inhibition did not enhance DXA-induced PAI-1 production. Conclusions. DXA induces basal and TNF-α-stimulated PAI-1 expression via the GR pathway, regardless of HSD2 status in HPTECs. Excess GCs may serve as a pro-fibrotic factor in chronic inflammatory kidney diseases.

Background. Hypoxia and inflammation, an unavoidable milieu for renal tubular cells during the development of renal fibrosis, reportedly up-regulate production of plasminogen activator inhibitor-1 (PAI-1), a promoter of tissue fibrosis. Peroxisome proliferator-activated receptor (PPAR)-γ agonists may modulate renal fibrosis progression via their anti-inflammatory effects in a PPAR-γ-dependent or -independent manner. However, no information is known about the effects of PPAR-γ agonists on PAI-1 expression in human proximal renal tubular cells (HPTECs) under hypoxia and/or inflammation. Methods. Confluent HPTECs were exposed to normoxia (18% O ₂ ), hypoxia (1% O ₂ ) and/or TNF-α at 10 ng/mL for up to 48 h. The cells were incubated with two PPAR-γ ago- nists, 15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) and pioglitazone. Precise amounts of PAI-1 mRNA and protein were measured by TaqMan quantitative PCR and immunoassay, respectively. PPAR response element (PPRE) activity induced by 15d-PGJ2 was measured by transfection with PPRE-luciferase construct. Results. Basal PAI-1 was significantly increased, in a dose-dependent manner, by 15d-PGJ2. It also enhanced hypoxia-, TNF-α- and hypoxia plus TNF-α-stimulated PAI-1 expression at the mRNA and protein levels. Pioglitazone had no influence on PAI-1 protein production. Although 15d-PGJ2 enhanced PPRE activity significantly in the HPTECs expressing PPAR-γ, a specific inhibitor for PPAR-γ, GW9662, did not diminish 15d-PGJ2-induced PAI-1 expression. In contrast, a non-selective tyrosine kinase (TK) inhibitor, genisteine or a MEK1 (MAPK kinase) inhibitor, PD98059, inhibited 15d-PGJ2-induced PAI-1 production completely. Conclusions. The endogenous PPAR-γ agonist, 15d-PGJ2, increased PAI-1 expression independently of PPAR-γ via the activation of TK or MAP kinase in HPTECs and may act as an enhancer of PAI-1 production in the kidney under hypoxic and inflammatory conditions.