Bezafibrate suppresses rat antiglomerular basement membrane crescentic glomerulonephritis

The Role of Peroxisome Proliferator-Activated Receptors in Kidney Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Accumulating evidence suggests that PPARs may play an important role in the pathogenesis of kidney disease. All three members of the PPAR subfamily, PPARα, PPARβ/δ, and PPARγ, have been implicated in many renal pathophysiological conditions, including acute kidney injury, diabetic nephropathy, and chronic kidney disease, among others. Emerging data suggest that PPARs may be potential therapeutic targets for renal disease. This article reviews the physiological roles of PPARs in the kidney and discusses the therapeutic utility of PPAR agonists in the treatment of kidney disease.

Group 1 innate lymphoid cells are involved in the progression of experimental anti-glomerular basement membrane glomerulonephritis and are regulated by peroxisome proliferator-activated receptor α

Innate lymphoid cells play an important role in the early effector cytokine-mediated response. In Wistar Kyoto rats, CD8⁺ non-T lymphocytes (CD8⁺Lym) infiltrate into glomeruli during the development of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Here, we examined the profiles and roles of CD8⁺Lym in anti-GBM glomerulonephritis. The regulation of CD8⁺Lym by peroxisome proliferator-activated receptor (PPAR)-α in anti-GBM glomerulonephritis was also evaluated. Glomerular infiltrating CD8⁺Lym were lineage-negative cells that showed markedly high expression of IFN-γ and T-bet mRNAs but not Eomes, indicating these cells are group 1 innate lymphoid cells. In anti-GBM glomerulonephritis, the glomerular mRNAs of innate lymphoid cell-related cytokines (IFN-γ and TNF-α) and chemokines (CXCL9, CXCL10, and CXCL11) are significantly increased. Treatment with a PPARα agonist ameliorated renal injury, with reduced expression of these mRNAs. In vitro, enhanced IFN-γ production from innate lymphoid cells upon IL-12 and IL-18 stimulation was reduced by the PPARα agonist. Moreover, CXCL9 mRNA in glomerular endothelial cells and CXCL9, CXCL10, and CXCL11 mRNAs in podocytes and macrophages were upregulated by IFN-γ, whereas the PPARα agonist downregulated their expression. We also detected the infiltration of innate lymphoid cells into glomeruli in human anti-GBM glomerulonephritis. Thus, innate lymphoid cells are involved in the progression of anti-GBM glomerulonephritis and regulated directly or indirectly by PPARα. Our findings suggest that innate lymphoid cells could serve as novel therapeutic targets for anti-GBM glomerulonephritis.

Peroxisome proliferator-activated receptor agonists in a battle against the aging kidney

As aging is a complex phenomenon characterized by intraindividual and interindividual diversities in the maintenance of the homeostatic condition of cells and tissues, changes in renal function are not uniform and depend on associated diseases and environmental factors. Multiple studies have investigated the possible underlying mechanisms of age-related decline in kidney function. Evolutionary, molecular, cellular and systemic theories have been postulated to explain the primary disease independent age-related changes and adaptive responses. As peroxisome proliferator-activated receptors (PPARs) are involved in a broad spectrum of biological processes, PPAR activation might have an effect on the prevention of cell senescence. In this review, we will focus on the experimental and clinical evidence of PPAR agonists in a battle against the aging kidney.

PPARα Activation Protects against Anti-Thy1 Nephritis by Suppressing Glomerular NF-κB Signaling

The vast increase of chronic kidney disease (CKD) has attracted considerable attention worldwide, and the development of a novel therapeutic option against a representative kidney disease that leads to CKD, mesangial proliferative glomerulonephritis (MsPGN) would be significant. Peroxisome proliferator-activated receptor α (PPARα), a member of the steroid/nuclear receptor superfamily, is known to perform various physiological functions. Recently, we reported that PPARα in activated mesangial cells exerted anti-inflammatory effects and that the deficiency of PPARα resulted in high susceptibility to glomerulonephritis. To investigate whether PPARα activation improves the disease activity of MsPGN, we examined the protective effects of a PPARα agonist, clofibrate, in a well-established model of human MsPGN, anti-Thy1 nephritis, for the first time. This study demonstrated that pretreatment with clofibrate (via a 0.02% or 0.1% clofibrate-containing diet) continuously activated the glomerular PPARα, which outweighed the PPARα deterioration associated with the nephritic process. The PPARα activation appeared to suppress the NF-κB signaling pathway in glomeruli by the induction of IκBα, resulting in the reduction of proteinuria and the amelioration of the active inflammatory pathologic glomerular changes. These findings suggest the antinephritic potential of PPARα-related medicines against MsPGN. PPARα-related medicines might be useful as a treatment option for CKD.

Quantitative histological analysis of SM22α (transgelin) in an adriamycin-induced focal segmental glomerulosclerosis model

BACKGROUND/AIMS

SM22α, transgelin, has been revealed to be specifically expressed in glomerular epithelial cells and interstitial cells, according to the nature of the renal injury. In this study, quantitative analyses of SM22α positivity were performed to investigate the pathological significance of its expression.

METHODS

Kidney samples of adriamycin nephropathy underwent immunohistochemistry with a newly established anti-SM22α monoclonal antibody. The SM22α positivity was quantified by an image analyzer. The correlation of the histological values with biochemical data was investigated statistically. Microstructural localization of SM22α was studied by immunoelectron microscopy.

RESULTS

SM22α was expressed along the dense basal microfilaments of degenerating podocytes, and diffusely in interstitial cells. Both the extent and intensity of SM22α expression in glomerular and tubulointerstitial area were correlated with the deterioration of renal function and the severity of proteinuria. Stepwise multiple linear regression analysis revealed that the extent of its positivity in glomerular or tubulointerstitial area was the determinant of the amount of proteinuria or the deterioration of creatinine clearance (Ccr), respectively. Inversely, the deterioration of Ccr was the most important predictor of SM22α expression.

CONCLUSION

SM22α expression in podocytes and interstitial cells represented the severity of proteinuria and the deterioration of renal function. SM22α expression in renal tissues might be a hallmark of kidney diseases.

PPAR{alpha} attenuates the proinflammatory response in activated mesangial cells

The activated mesangial cell is an important therapeutic target for the control of glomerulonephritis. The peroxisome proliferator-activated receptor alpha (PPARalpha) has attracted considerable attention for its anti-inflammatory effects; however, its roles in the mesangial cells remain unknown. To determine the anti-inflammatory function of PPARalpha in mesangial cells, wild-type and Ppara-null cultured mesangial cells were exposed to lipopolysaccharide (LPS). LPS treatment caused enhanced proinflammatory responses in the Ppara-null cells compared with wild-type cells, as revealed by the induction of interleukin-6, enhanced cell proliferation, and the activation of the nuclear factor (NF)-kappaB signaling pathway. In wild-type cells resistant to inflammation, constitutive expression of PPARalpha was undetectable. However, LPS treatment induced the significant appearance and substantial activation of PPARalpha, which would attenuate the proinflammatory responses through its antagonizing effects on the NF-kappaB signaling pathway. The induction of PPARalpha was coincident with the appearance of alpha-smooth muscle actin, which might be associated with the phenotypic changes of mesangial cells. Moreover, another examination using LPS-injected wild-type mice demonstrated the appearance of PPARalpha-positive cells in glomeruli, suggesting in vivo correlation with PPARalpha induction. These results suggest that PPARalpha plays crucial roles in the attenuation of inflammatory response in activated mesangial cells. PPARalpha might be a novel therapeutic target against glomerular diseases.

Lipid droplet-associated proteins protect renal tubular cells from fatty acid-induced apoptosis

Proteinuria is a major cause of tubulointerstitial kidney damage, and free fatty acids bound to albumin are thought to play an important role in its pathogenesis. However, the mechanism whereby proteinuria causes tubulointerstitial damage to the kidney is unclear. Using primary human renal proximal tubular cells, we observed that albumin replete with fatty acids (rBSA) and defatted albumin (dBSA) complexed with linoleic acid (LA) induced significantly more apoptosis than did defatted albumin alone. Oxidative stress was partially involved in apoptotic induction by LA/dBSA but not by rBSA. Administration of fatty acid-bound BSA increased the number of lipid droplets (LDs) and the LD-associated proteins, adipocyte differentiation-related protein and TIP47. LDs are organelles that store esterified fatty acids, and the LD-associated proteins are presumed to facilitate LD formation. Knockdown of adipocyte differentiation-related protein or TIP47 by RNA interference enhanced induction of apoptosis by both rBSA and LA/dBSA. Apoptotic induction was observed similarly when either rBSA or LA/dBSA was applied to only the apical surfaces of polarized LLC-PK1 cells. The present results suggest that LDs and LD-associated proteins have protective effects against apoptosis induced by fatty acid-bound albumin by sequestering free fatty acids. Therapeutic manipulation of these LD-associated proteins could aid in the amelioration of nephritic diseases.

WY14,643, a PPARalpha ligand, attenuates expression of anti-glomerular basement membrane disease

Peroxisome proliferator-activated receptor alpha (PPARalpha) ligands are medications used to treat hyperlipidaemia and atherosclerosis. Increasing evidence suggests that these agents are immunosuppressive. In the following studies we demonstrate that WY14,643, a PPARalpha ligand, attenuates expression of anti-glomerular basement membrane disease (AGBMD). C57BL/6 mice were fed 0.05% WY14,643 or control food and immunized with the non-collagenous domain of the alpha3 chain of Type IV collagen [alpha3(IV) NC1] in complete Freund's adjuvant (CFA). WY14,643 reduced proteinuria and greatly improved glomerular and tubulo-interstitial lesions. However, the PPARalpha ligand did not alter the extent of IgG-binding to the GBM. Immunohistochemical studies revealed that the prominent tubulo-interstitial infiltrates in the control-fed mice consisted predominately of F4/80(+) macrophages and WY14,643-feeding decreased significantly the number of renal macrophages. The synthetic PPARalpha ligand also reduced significantly expression of the chemokine, monocyte chemoattractant protein (MCP)-1/CCL2. Sera from mice immunized with AGBMD were also evaluated for antigen-specific IgGs. There was a significant increase in the IgG1 : IgG2c ratio and a decline in the intrarenal and splenocyte interferon (IFN)-gamma mRNA expression in the WY14,643-fed mice, suggesting that the PPARalpha ligand could skew the immune response to a less inflammatory T helper 2-type of response. These studies suggest that PPARalpha ligands may be a novel treatment for inflammatory renal disease.

PPAR-α and -γ agonists attenuate diabetic kidney disease in the apolipoprotein E knockout mouse

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)-alpha and PPAR-gamma agonists are widely used in diabetes. In addition to their effects on lipid and glucose homeostasis, these agents have been postulated to have independent renoprotective actions. In the current study, we assess the efficacy of the PPAR-alpha agonist, gemfibrozil, the PPAR-gamma agonist rosiglitazone and the non-thiazolidinedione PPAR-alpha/gamma coagonist, compound 3q, on kidney structure and function in streptozotocin-treated apolipoprotein E knockout mice.

METHODS

Control and streptozotocin-diabetic mice were randomized to receive rosiglitazone (20 mg/kg/day), gemfibrozil (100 mg/kg/day), or compound 3q (3 mg/kg/day) by gavage, or no treatment for a period of 20 weeks. Renal fibrosis was assessed by standard histology and collagen IV immunohistochemistry. Kidney function was assessed by urinary albumin excretion and creatinine clearance.

RESULTS

Diabetes in this model was associated with an increase in glomerulosclerosis, tubulointerstitial fibrosis and increased collagen IV deposition in the glomeruli and tubules. All three agents significantly attenuated glomerulosclerosis, tubulointerstitial expansion and collagen IV deposition. The increase in albuminuria and the decline in kidney function associated with diabetes in this model were also attenuated by each of these agents, with no superiority observed among various treatment groups. These renoprotective effects were observed in the absence of changes in glucose, insulin or lipid levels or a reduction in blood pressure.

CONCLUSIONS

Combined with their independent anti-atherosclerotic actions, and their important effects on dyslipidaemia and insulin resistance, PPAR agonists may be useful for the prevention of diabetic complications, including kidney disease, even in type 1 diabetes.