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

The therapeutic effect of Shenhua tablet against mesangial cell proliferation and renal inflammation in mesangial proliferative glomerulonephritis

Shenhua tablet (SH), a formulation of traditional Chinese medicine, exerts renoprotective effect on chronic kidney diseases, and it has been found to restrain inflammation, but the mechanism is still unclear. Here, we explored the potential renoprotection of SH in mesangial proliferative glomerulonephritis (MsPGN) rat model induced by anti-Thy1 antibody. Administration of SH reduced urinary albumin/creatinine ratio (UACR) and significantly attenuated mesangial cell proliferation and renal inflammation. Notably, SH protected rats against renal inflammation, which was associated with decreasing macrophage infiltration and promoting macrophage anti-inflammatory activity. Network analysis combined with arrays identified the Janus kinase signal transducer and activator of transcription (JAK-STAT) signaling pathway as the main pathways of SH could target inflammation. Furthermore, it was confirmed that mesangial cell proliferation, which response to inflammation, were alleviated by ASS1 expression enhanced after SH administration both in vivo and in vitro. Collectively, SH has the beneficial on relieving the progression of MsPGN to alleviate inflammation and mesangial proliferation by inhibiting STAT3 phosphorylation and maintains the expression level of ASS1, might be an effective strategy for treating MsPGN.

Pemafibrate Protects against Fatty Acid-Induced Nephropathy by Maintaining Renal Fatty Acid Metabolism

As classical agonists for peroxisomal proliferator-activated receptor alpha (PPARα), fibrates activate renal fatty acid metabolism (FAM) and provide renoprotection. However, fibrate prescription is limited in patients with kidney disease, since impaired urinary excretion of the drug causes serious adverse effects. Pemafibrate (PEM), a novel selective PPARα modulator, is mainly excreted in bile, and, thus, may be safe and effective in kidney disease patients. It remains unclear, however, whether PEM actually exhibits renoprotective properties. We investigated this issue using mice with fatty acid overload nephropathy (FAON). PEM (0.5 mg/kg body weight/day) or a vehicle was administered for 20 days to 13-week-old wild-type male mice, which were simultaneously injected with free fatty acid (FFA)-binding bovine serum albumin from day 7 to day 20 to induce FAON. All mice were sacrificed on day 20 for assessment of the renoprotective effect of PEM against FAON. PEM significantly attenuated the histological findings of tubular injury caused by FAON, increased the renal expressions of mRNA and proteins related to FAM, and decreased renal FFA content and oxidative stress. Taken together, PEM exhibits renoprotective effects through the activation and maintenance of renal FAM and represents a promising drug for kidney disease.

Loquat leaf polysaccharides improve glomerular injury in rats with anti-Thy 1 nephritis via peroxisome proliferator-activated receptor alpha pathway

Chronic glomerulonephritis frequently develops into renal failure that cannot be completely cured. Based on the success of anti-inflammatory Chinese herbs in treating chronic nephritis, our goal was to investigate the therapeutic effects and mechanism of action of loquat leaf polysaccharides (LLPS) on chronic anti-Thy-1 nephritis. A rat model of glomerulonephritis was used to study the effects of 8 weeks of enalapril or LLPS treatment. Twenty-four-hour rat urinary protein excretions were measured every week for 8 weeks. Then, all animals were sacrificed, renal-related biochemical parameters were analyzed, and histology and electron microscopy examinations of renal tissue samples were conducted. Renal cortex tissue was used to detect markers of renal fibrosis. RNA sequencing (RNA-seq) and in vitro experiments explored the signaling pathway involved in LLPS treatment effects. Compared with the disease control group, LLPS treatment significantly decreased the levels of serum creatinine and blood urea nitrogen, reduced urinary protein excretion, glomerular mesangial cell proliferation, and extracellular matrix hyperplasia, and attenuated the expression of proteins associated with podocyte injury and renal fibrosis. RNA-seq results showed that peroxisome proliferator-activated receptor (PPAR) is a potential signaling pathway involved in LLPS treatment of chronic glomerulonephritis. Increases in PPARα and plasminogen activator inhibitor-1 (PAI-1) caused by glomerulonephritis were inhibited by LLPS in vitro. Furthermore, when an agonist of PPARα (BMS-687453) was used to stimulate PPARα activity, LLPS treatment suppressed the expression of fibrosis factor PAI-1 partially via PPARα inhibition. These findings demonstrate that LLPS improved glomerular injury in rats with anti-Thy 1 nephritis via the PPARα pathway.

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 α attenuates high-cholesterol diet-induced toxicity and pro-thrombotic effects in mice

Peroxisome proliferator-activated receptor α (PPARα) is involved in the regulation of fatty acid and cholesterol metabolism. A high-cholesterol (HC) diet increases the risk of developing cardiovascular diseases (CVD); however, it is unclear whether the toxic effects of cholesterol involve changes in thrombotic factor expression, and whether PPARα is necessary for such effects. To investigate this possibility, we fed a HC diet to wild-type (WT) and Ppara-null mice and measured cholesterol and triglyceride contents, liver histology, serum/plasma levels of coagulation factors, hepatic expression of the coagulation factors, liver/serum sulfatide levels, hepatic sulfatide metabolism, hepatic expression of lipid transporters, and hepatic oxidative stress and its relating enzymes. In Ppara-null mice, the HC diet caused triglyceride accumulation and exacerbated inflammation and oxidative stress in liver, increased levels of coagulation factors, including tissue factor, plasminogen activator inhibitor-1 and carboxypeptidase B2 in blood and liver, and decreased levels of anti-thrombotic sulfatides in serum and liver. These changes were much less marked in WT mice. These findings imply that cholesterol overload exerts its toxic effects at least in part by enhancing thrombosis, secondary to abnormal hepatic lipid metabolism, inflammation, and oxidative stress. Moreover, we reveal for the first time that PPARα can attenuate these toxic effects by transcriptional regulation of coagulation factors and sulfatides, in addition to its known effects of controlling lipid homeostasis and suppressing inflammation and oxidative stress. Therapies aimed at activating PPARα might prevent HC diet-induced CVD through modulating various pro- and anti-thrombotic factors.

Peroxisome proliferator-activated receptor α-dependent renoprotection of murine kidney by irbesartan

Activation of renal peroxisome proliferator-activated receptor α (PPARα) is renoprotective, but there is no safe PPARα activator for patients with chronic kidney disease (CKD). Studies have reported that irbesartan (Irbe), an angiotensin II receptor blocker (ARB) widely prescribed for CKD, activates hepatic PPARα. However, Irbe's renal PPARα-activating effects and the role of PPARα signalling in the renoprotective effects of Irbe are unknown. Herein, these aspects were investigated in healthy kidneys of wild-type (WT) and Ppara-null (KO) mice and in the murine protein-overload nephropathy (PON) model respectively. The results were compared with those of losartan (Los), another ARB that does not activate PPARα. PPARα and its target gene expression were significantly increased only in the kidneys of Irbe-treated WT mice and not in KO or Los-treated mice, suggesting that the renal PPARα-activating effect was Irbe-specific. Irbe-treated-PON-WT mice exhibited decreased urine protein excretion, tubular injury, oxidative stress (OS), and pro-inflammatory and apoptosis-stimulating responses, and they exhibited maintenance of fatty acid metabolism. Furthermore, the expression of PPARα and that of its target mRNAs encoding proteins involved in OS, pro-inflammatory responses, apoptosis and fatty acid metabolism was maintained upon Irbe treatment. These renoprotective effects of Irbe were reversed by the PPARα antagonist MK886 and were not detected in Irbe-treated-PON-KO mice. These results suggest that Irbe activates renal PPARα and that the resultant increased PPARα signalling mediates its renoprotective effects.

Peroxisome proliferator activated receptor alpha inhibits hepatocarcinogenesis through mediating NF-κB signaling pathway

Peroxisome proliferator-activated receptor alpha (PPARα) ligands have been reported to suppress cancer growth. However, the role of PPARα in hepatocarcinogenesis remains unclear. We investigated the functional significance of PPARα in hepatocellular carcinoma (HCC). PPARα-knockout (PPARα^-/-) mice were more susceptible to diethylnitrosamine (DEN)-induced HCC at 6 months compared with wild-type (WT) littermates (80% versus 43%, P < 0.05). In resected HCCs, TUNEL-positive apoptotic cells were significantly less in PPARα^-/- mice than in WT mice (P < 0.01), commensurate with a reduction in cleaved caspase-3 and caspase-7 protein expression. Ki-67 staining showed increased cell proliferation in PPARα^-/- mice (P < 0.01), with concomitant up-regulation of cyclin-D1 and down-regulation of p15. Moreover, ectopic expression of PPARα in HCC cells significantly suppressed cell proliferation and induced apoptosis. The anti-tumorigenic function of PPARα was mediated via NF-κB as evidenced by inhibition of NF-κB promoter activity, diminution of phosphor-p65, phosphor-p50 and BCL2 levels, and enhancing IkBα protein. Chromatin immunoprecipitation analysis confirmed PPARα directly binds to the IkBα promoter. In conclusion, PPARα deficiency enhances susceptibility to DEN-initiated HCC. PPARα suppresses tumor cell growth by inhibiting cell proliferation and inducing cell apoptosis via direct targeting IκBα and NF-κB signaling pathway.

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.

Peroxisome proliferator-activated receptor α mediates enhancement of gene expression of cerebroside sulfotransferase in several murine organs

Sulfatides, 3-O-sulfogalactosylceramides, are known to have multifunctional properties. These molecules are distributed in various tissues of mammals, where they are synthesized from galactosylceramides by sulfation at C3 of the galactosyl residue. Although this reaction is specifically catalyzed by cerebroside sulfotransferase (CST), the mechanisms underlying the transcriptional regulation of this enzyme are not understood. With respect to this issue, we previously found potential sequences of peroxisome proliferator-activated receptor (PPAR) response element on upstream regions of the mouse CST gene and presumed the possible regulation by the nuclear receptor PPARα. To confirm this hypothesis, we treated wild-type and Ppara-null mice with the specific PPARα agonist fenofibrate and examined the amounts of sulfatides and CST gene expression in various tissues. Fenofibrate treatment increased sulfatides and CST mRNA levels in the kidney, heart, liver, and small intestine in a PPARα-dependent manner. However, these effects of fenofibrate were absent in the brain or colon. Fenofibrate treatment did not affect the mRNA level of arylsulfatase A, which is the key enzyme for catalyzing desulfation of sulfatides, in any of these six tissues. Analyses of the DNA-binding activity and conventional gene expression targets of PPARα has demonstrated that fenofibrate treatment activated PPARα in the kidney, heart, liver, and small intestine but did not affect the brain or colon. These findings suggest that PPARα activation induces CST gene expression and enhances sulfatide synthesis in mice, which suggests that PPARα is a possible transcriptional regulator for the mouse CST gene.