PPARα Activation Research Articles

Fibrates Affect Levels of Phosphorylated p38 in Intestinal Cells in a Differentiation-Dependent Manner.

Fibrates are widely used hypolipidaemic agents that act as ligands of the peroxisome proliferator-activated receptor α (PPARα). p38 is a protein kinase that is mainly activated by environmental and genotoxic stress. We investigated the effect of the PPARα activators fenofibrate and WY-14643 and the PPARα inhibitor GW6471 on the levels of activated p38 (p-p38) in the colorectal cancer cell lines HT-29 and Caco2 in relation to their differentiation status. Fibrates increased p-p38 in undifferentiated HT-29 cells, whereas in other cases p-p38 expression was decreased. HT-29 cells showed p-p38 predominantly in the cytoplasm, whereas Caco2 cells showed higher nuclear positivity. The effect of fibrates may depend on the differentiation status of the cell, as differentiated HT-29 and undifferentiated Caco2 cells share similar characteristics in terms of villin, CYP2J2, and soluble epoxide hydrolase (sEH) expression. In human colorectal carcinoma, higher levels of p-p38 were detected in the cytoplasm, whereas in normal colonic surface epithelium, p-p38 showed nuclear positivity. The decrease in p-p38 positivity was associated with a decrease in sEH, consistent with in vitro results. In conclusion, fibrates affect the level of p-p38, but its exact role in the process of carcinogenesis remains unclear and further research is needed in this area.

Oleoylethanolamide Protects against Acute Ischemic Stroke by Promoting PPARα-Mediated Microglia/Macrophage M2 Polarization.

Oleoylethanolamide (OEA) has been demonstrated to be a feasible protectant in ischemic stroke. However, the mechanism for OEA-afforded neuroprotection remains elusive. The present study aimed to investigate the neuroprotective effects of OEA on peroxisome proliferator-activated receptor α (PPARα)-mediated microglia M2 polarization after cerebral ischemia. Transient middle cerebral artery occlusion (tMCAO) was induced for 1 h in wild-type (WT) or PPARα-knock-out (KO) mice. Mouse small glioma cells (BV2) microglia and primary microglia cultures were used to evaluate the direct effect of OEA on microglia. A coculture system was used to further elucidate the effect of OEA on microglial polarization and ischemic neurons' fate. OEA promoted the microglia switch from an inflammatory M1 phenotype to the protective M2 phenotype and enhanced the binding of PPARα with the arginase1 (Arg1) and Ym1 promoter in WT mice but not in KO mice after MCAO. Notably, the increased M2 microglia caused by OEA treatment were strongly linked to neuron survival after ischemic stroke. In vitro studies confirmed that OEA shifted BV2 microglia from (lipopolysaccharide) LPS-induced M1-like to M2-like phenotype through PPARα. Additionally, the activation of PPARα in primary microglia by OEA led to an M2 protective phenotype that enhanced neuronal survival against oxygen-glucose deprivation (OGD) in the coculture systems. Our findings demonstrate the novel effects of OEA in enhancing microglia M2 polarization to protect neighboring neurons by activating the PPARα signal, which is a new mechanism of OEA against cerebral ischemic injury. Therefore, OEA might be a promising therapeutic drug for stroke and targeting PPARα-mediated M2 microglia may represent a new strategy to treat ischemic stroke.

Osteocytes contribute via nuclear receptor PPAR-alpha to maintenance of bone and systemic energy metabolism.

The view that bone and energy metabolism are integrated by common regulatory mechanisms is broadly accepted and supported by multiple strands of evidence. This includes the well-characterized role of the PPARγ nuclear receptor, which is a common denominator in energy metabolism and bone metabolism. Little is known, however, about the role of PPARα nuclear receptor, a major regulator of lipid metabolism in other organs, in bone. A side-by-side comparative study of 5-15 mo old mice with global PPARα deficiency (αKO) and mice with osteocyte-specific PPARα deficiency (αOTKO) in order to parse out the various activities of PPARα in the skeleton that are of local and systemic significance. This study included transcriptome analysis of PPARα-deficient osteocytes, and analyses of bone mass and bone microarchitecture, systemic energy metabolism with indirect calorimetry, and differentiation potential of hematopoietic and mesenchymal bone cell progenitors. These analyses were paired with in vitro studies of either intact or silenced for PPARα MLO-A5 cells to determine PPARα role in osteocyte bioenergetics. In osteocytes, PPARα controls large number of transcripts coding for signaling and secreted proteins which may regulate bone microenvironment and peripheral fat metabolism. In addition, PPARα in osteocytes controls their bioenergetics and mitochondrial response to stress, which constitutes up to 40% of total PPARα contribution to the global energy metabolism. Similarly to αKO mice, the metabolic phenotype of αOTKO mice (both males and females) is age-dependent. In younger mice, osteocyte metabolism contributes positively to global energetics, however, with aging the high-energy phenotype reverts to a low-energy phenotype and obesity develops, suggesting a longitudinal negative effect of impaired lipid metabolism and mitochondrial dysfunction in osteocytes deficient in PPARα. However, bone phenotype was not affected in αOTKO mice except in the form of an increased volume of marrow adipose tissue in males. In contrast, global PPARα deficiency in αKO mice led to enlarged bone diameter with a proportional increase in number of trabeculae and enlarged marrow cavities; it also altered differentiation of hematopoietic and mesenchymal marrow cells toward osteoclast, osteoblast and adipocyte lineages, respectively. PPARα role in bone is multileveled and complex. In osteocytes, PPARα controls the bioenergetics of these cells, which significantly contributes to systemic energy metabolism and their endocrine/paracrine function in controlling marrow adiposity and peripheral fat metabolism.

Adipolin protects against renal injury via PPARα-dependent reduction of inflammasome activation

Although chronic kidney disease (CKD) is a major health problem worldwide, its underlining mechanism is incompletely understood. We previously identified adipolin as an adipokine which provides benefits for cardiometabolic diseases. Here, we investigated the role of adipolin in the development of CKD. Adipolin-deficiency exacerbated urinary albumin excretion, tubulointerstitial fibrosis and oxidative stress of remnant kidneys in mice after subtotal nephrectomy through inflammasome activation. Adipolin positively regulated the production of ketone body, β-hydroxybutyrate (BHB) and expression of a catalytic enzyme producing BHB, HMGCS2 in the remnant kidney. Treatment of proximal tubular cells with adipolin attenuated inflammasome activation through the PPARα/HMGCS2-dependent pathway. Furthermore, systemic administration of adipolin to wild-type mice with subtotal nephrectomy ameliorated renal injury, and these protective effects of adipolin were diminished in PPARα-deficient mice. Thus, adipolin protects against renal injury by reducing renal inflammasome activation through its ability to induce HMGCS2-dependent ketone body production via PPARα activation.

Therapeutic roles of PPARα activation in ocular ischemic diseases.

Ocular ischemia is one of the leading causes of blindness. It is related to various ocular diseases and disorders, including age-related macular degeneration, diabetic retinopathy, glaucoma, and corneal injury. Ocular ischemia occurs due to an abnormal supply of oxygen and nutrients to the eye, resulting in ocular metabolic dysfunction. These changes can be linked with pathologic conditions in the eye, such as inflammation, neovascularization, and cell death, ultimately leading to vision loss. The current treatment care for ocular ischemia is limited. Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor protein functioning in regulating lipid metabolism, fatty acid oxidation, and glucose homeostasis. Recently, PPARα activation has been suggested as a useful therapeutic target in treating ocular ischemia. However, its applications have not been well summarized. In this review, we cover an overview of the therapeutic roles of PPARα activation in various ocular ischemic conditions with recent experimental evidence and further provide clinical implications of its therapeutic applications. Our review will enable more approaches to comprehensively understand the therapeutic roles of PPARα activation for preventing ocular ischemic diseases.

1,3-dichloro-2-propanol caused lipid droplets accumulation by suppressing neutral lipases via BMAL1 in hepatocytes.

Circadian rhythm regulates body physiology and metabolism to adapt to the external environment. 1,3-dichloro-2-propanol (1,3-DCP) is a food pollutant formed during food processing. Our study explored whether toxicity of 1,3-DCP was related to circadian rhythm. We discovered that 1,3-DCP caused lipid droplets (LDs) accumulation via suppression of neutral lipases ATGL and HSL in mice liver and HepG2 cells. Meanwhile, 1,3-DCP caused rhythmic disruption of key circadian rhythm molecules BMAL1/CLOCK at protein and mRNA levels in HepG2 cells. Studies have shown that BMAL1 regulates PPARα by binding to the promoter E-box. 1,3-DCP inhibited PPARα expression. A PPARα activator WY-14643 up-regulated ATGL and HSL expression. BMAL1 overexpression up-regulated PPARα, ATGL and HSL expression. WY-14643 or BMAL1 overexpression attenuated 1,3-DCP-caused LDs accumulation in HepG2 cells. The results revealed that 1,3-DCP caused LDs accumulation by neutral lipases suppression via inhibiting key circadian rhythm protein BMAL1, indicating that circadian rhythm can be related to the regulation of LDs accumulation caused by 1,3-DCP.

Ginsenoside Rb1 promotes the activation of PPARα pathway via inhibiting FADD to ameliorate heart failure

PurposeGinsenoside Rb1 (GRb1), a dammarane-type triterpene saponin compound mainly distributed in ginseng (Panax ginseng), has been demonstrated to ameliorate cardiovascular diseases. However, it remains unclear whether GRb1 alleviates heart failure (HF) by maintaining cardiac energy metabolism balance. Therefore, this work aimed to investigate the cardiac benefits of GRb1 against cardiac energy deficit and explore its mechanism of action. Methods and resultsIsoproterenol (ISO) induced HF Sprague–Dawley rats were administrated with GRb1 or fenofibrate for 6 weeks. ISO-induced primary neonatal rat cardiomyocytes (NRCMs) were used as the in vitro model. In vivo, GRb1 significantly improved the structural and metabolic disorder, as demonstrated by the restoration of cardiac function, inhibition of cardiac hypertrophy and fibrosis, and increased adenosine triphosphate (ATP) generation. In vitro, GRb1 effectively protected mitochondrial function and scavenged excessive reactive oxygen species. Moreover, in ISO-induced NRCMs, GRb1 significantly inhibited the abnormal upregulation of Fas-associated death domain (FADD), promoted transcriptional activation of peroxisome proliferator-activated receptor-alpha (PPARα), improved the aberrant expression of cardiac energy metabolism-related enzymes and cardiac fatty acid oxidation, and subsequently increased the synthesis of ATP. Noticeably, GRb1 could inhibit the increased binding between FADD and PPARα, which contributed to the activation of PPARα. Furthermore, GRb1 strengthened the thermal stabilization of FADD and might bind to FADD directly. ConclusionsCollectively, it’s part of the in-depth mechanism of GRb1’s cardio-protection that GRb1 could directly bind to FADD and counteract its negative role in the transcription of PPARα thus ameliorating cardiac energy derangement and HF.

Unraveling the Role of Peroxisome Proliferator-Activated Receptor β/Δ (PPAR β/Δ) in Angiogenesis Associated with Multiple Myeloma.

Growing evidence suggests a role for peroxisome proliferator-activated receptor β/δ (PPAR β/δ) in the angiogenesis, growth, and metastasis of solid tumors, but little is known about its role in multiple myeloma (MM). Angiogenesis in the bone marrow (BM) is characteristic of disease transition from monoclonal gammopathy of undetermined significance (MGUS) to MM. We examined the expression and function of PPAR β/δ in endothelial cells (EC) from the BM of MGUS (MGEC) and MM (MMEC) patients and showed that PPAR β/δ was expressed at higher levels in MMEC than in MGEC and that the overexpression depended on myeloma plasma cells. The interaction between myeloma plasma cells and MMEC promoted the release of the PPAR β/δ ligand prostaglandin I2 (PGI2) by MMEC, leading to the activation of PPAR β/δ. We also demonstrated that PPAR β/δ was a strong stimulator of angiogenesis in vitro and that PPAR β/δ inhibition by a specific antagonist greatly impaired the angiogenic functions of MMEC. These findings define PGI2-PPAR β/δ signaling in EC as a potential target of anti-angiogenic therapy. They also sustain the use of PPAR β/δ inhibitors in association with conventional drugs as a new therapeutic approach in MM.

Calponin 2 harnesses metabolic reprogramming to determine kidney fibrosis

ObjectiveIn the fibrotic kidneys, the extent of a formed deleterious microenvironment is determined by cellular mechanical forces. This process requires metabolism for energy. However, how cellular mechanics and metabolism are connected remains unclear. MethodsA multi-disciplinary approach was employed: the fibrotic kidney disease models were induced by renal ischemia-reperfusion injury and unilateral ureteral obstruction in Calponin 2 (CNN2) knockdown mice. Proteomics, bioinformatics, and in vivo and in vitro molecular experimental pathology studies were performed. ResultOur proteomics revealed that actin filament binding and cell metabolism are the two most dysregulated events in the fibrotic kidneys. As a prominent actin stabilizer, CNN2 was predominantly expressed in fibroblasts and pericytes. In CKD patients, CNN2 levels was markedly induced in blood. In mice, CNN2 knockdown preserves kidney function and alleviates fibrosis. Global proteomics profiled that CNN2 knockdown enhanced the activities of the key rate-limiting enzymes and regulators of fatty acid oxidation (FAO) in the diseased kidneys. Inhibiting carnitine palmitoyltransferase 1α in the FAO pathway resulted in lipid accumulation and extracellular matrix deposition in the fibrotic kidneys, which were restored after CNN2 knockdown. Bioinformatics and chromatin immunoprecipitation showed that CNN2 interactor, estrogen receptor 2 (ESR2), binds peroxisome proliferator-activated receptor-α (PPARα) to transcriptionally regulate FAO downstream target genes expression amid kidney fibrosis. In vitro, ESR2 knockdown repressed the mRNA levels of PPARα and the key genes in the FAO pathway. Conversely, activation of PPARα reduced CNN2-induced matrix inductions. ConclusionsOur results suggest that balancing cell mechanics and metabolism is crucial to develop therapeutic strategies to halt kidney fibrosis.

Oleic acid stimulates cell proliferation and BRD4–L-MYC-dependent glucose transporter transcription through PPARα activation in ovarian cancer cells

Fatty acids (FAs) play important roles in cell membrane structure maintenance, energy production via β-oxidation, and as extracellular signaling molecules. Prior studies have demonstrated that exposure of cancer cells to FAs affects cell survival, cell proliferation, and cell motility. Oleic acid (OA) has somewhat controversial effects in cancer cells, with both pro- and anti-cancer effects, depending on cell type. Our prior findings suggested that OA enhances cell survival in serum starved HNOA ovarian cancer cells by activating glycolysis, but not β-oxidation. Here, we pharmacologically examined the cellular mechanisms by which OA stimulates glycolysis in HNOA cells. OA induced cell cycle progression, leading to increase in cell number through peroxisome proliferator activated receptor (PPAR) α activation. OA-induced glycolysis was mediated by increased GLUT expression, and increases in GLUT expression were mediated by increased L-MYC expression. Furthermore, L-MYC expression was due to BRD4 activation. These findings suggested involvement of the BRD4–L-MYC–GLUT axis in OA-stimulated glycolysis. These results suggested that OA could activate PPARα to stimulate two pathways: glycolysis and cell cycle progression, and provided insight into the role of OA in ovarian cancer cell growth.

PPARα Inhibits Astrocyte Inflammation Activation by Restoring Autophagic Flux after Transient Brain Ischemia

Astrocyte inflammation activation is an important cause that hinders the recovery of motor function after cerebral ischemia. However, its molecular mechanism has not yet been clearly clarified. The peroxisome proliferator-activated receptor α (PPARα) is a ligand-activated nuclear transcriptional factor. This study aims to further clarify the role of PPARα in astrocyte inflammation activation after cerebral ischemia and to explore the underlying mechanism. Astrocyte activation was induced in an in vivo model by transient middle cerebral artery occlusion (tMCAO) in mice. The in vitro model was induced by an oxygen-glucose deprivation/reoxygenation (OGD/R) in a primary culture of mouse astrocyte. PPARα-deficient mice were used to observe the effects of PPARα on astrocyte activation and autophagic flux. Our results showed that PPARα was mainly expressed in activated astrocytes during the chronic phase of brain ischemia and PPARα dysfunction promoted astrocyte inflammatory activation. After cerebral ischemia, the expressions of LC3-II/I and p62 both increased. Autophagic vesicle accumulation was observed by electron microscopy in astrocytes, and the block of autophagic flux was indicated by an mRFP-GFP-LC3 adenovirus infection assay. A PPARα deficit aggravated the autophagic flux block, while PPARα activation preserved the lysosome function and restored autophagic flux in astrocytes after OGD/R. The autophagic flux blocker bafilomycin A1 and chloroquine antagonized the effect of the PPARα agonist on astrocyte activation inhibition. This study identifies a potentially novel function of PPARα in astrocyte autophagic flux and suggests a therapeutic target for the prevention and treatment of chronic brain ischemic injury.

Effect of Bezafibrate, a PPARα Activator, on Acute and Subacute Inflammation in Male Wistar Rats

Aim To investigate the anti-inflammatory effect of bezafibrate on acute and subacute inflammation in adult male Wistar rats. Methods The study was carried out in adult male Wistar rats and they were allocated into three groups, that is, control, aspirin and bezafibrate, after obtaining clearance from Institutional Animal Ethics Committee. Acute inflammation was studied using carrageenan-induced rat paw oedema, and the volume displacement due to paw oedema using the plethysmograph. Subacute inflammation was studied using foreign body induced granuloma models. Analysis was performed using one-way ANOVA followed by post hoc tests of Dunnett’s. The value p < 0.05 was considered statistically significant. Results Bezafibrate showed a significant anti-inflammatory effect in acute as well as subacute models of inflammation when compared to control in the present study. Conclusions In patients receiving bezafibrate for hyperlipidemia, its anti-inflammatory potential may have an additional benefit in preventing complication of atherosclerosis.

Estimation of Per- and Polyfluorinated Alkyl Substance Induction Equivalency Factors for Humpback Dolphins by Transactivation Potencies of Peroxisome Proliferator-Activated Receptors.

The potential risks of per- and polyfluoroalkyl substance (PFAS) accumulation in nearshore dolphins are not well understood. Here, transcriptional activities of 12 PFAS on peroxisome proliferator-activated receptors (PPAR-α, -β/δ, and -γ) in Indo-Pacific humpback dolphins (Sousa chinensis) were evaluated. All PFAS activated scPPAR-α in a dose-dependent manner. PFHpA exhibited the highest induction equivalency factors (IEFs). The order of IEFs for other PFAS was as follows: PFOA > PFNA > PFHxA > PFPeA > PFHxS > PFBA > PFOS > PFBuS ≈ PFDA ≫ PFUnDA and PFDoDA (not activated). The total induction equivalents (∑IEQs, 5537 ng/g wet weight) indicated that more attention should be paid to investigating contamination levels in dolphins, especially in PFOS (82.8% contribution to the ∑IEQs). The scPPAR-β/δ and -γ were not affected by any PFAS, except for PFOS, PFNA, and PFDA. Furthermore, PFNA and PFDA could induce higher PPAR-β/δ and PPAR-γ-mediated transcriptional activities than PFOA. Compared to human beings, PFAS might be more potent PPAR-α activators in humpback dolphins, suggesting that the dolphins may be more susceptible to the adverse effects of PFAS. Our results may be instructive for understanding the impacts of PFAS on marine mammal health due to the identical PPAR ligand-binding domain.

Sirtuin 6-A Key Regulator of Hepatic Lipid Metabolism and Liver Health.

Sirtuin 6 (SIRT6) is an NAD-dependent deacetylase/deacylase/mono-ADP ribosyltransferase, a member of the sirtuin protein family. SIRT6 has been implicated in hepatic lipid homeostasis and liver health. Hepatic lipogenesis is driven by several master regulators including liver X receptor (LXR), carbohydrate response element binding protein (ChREBP), and sterol regulatory element binding protein 1 (SREBP1). Interestingly, these three transcription factors can be negatively regulated by SIRT6 through direct deacetylation. Fatty acid oxidation is regulated by peroxisome proliferator activated receptor alpha (PPARα) in the liver. SIRT6 can promote fatty acid oxidation by the activation of PPARα or the suppression of miR-122. SIRT6 can also directly modulate acyl-CoA synthetase long chain family member 5 (ACSL5) activity for fatty acid oxidation. SIRT6 also plays a critical role in the regulation of total cholesterol and low-density lipoprotein (LDL)-cholesterol through the regulation of SREBP2 and proprotein convertase subtilisin/kexin type 9 (PCSK9), respectively. Hepatic deficiency of Sirt6 in mice has been shown to cause hepatic steatosis, inflammation, and fibrosis, hallmarks of alcoholic and nonalcoholic steatohepatitis. SIRT6 can dampen hepatic inflammation through the modulation of macrophage polarization from M1 to M2 type. Hepatic stellate cells are a key cell type in hepatic fibrogenesis. SIRT6 plays a strong anti-fibrosis role by the suppression of multiple fibrogenic pathways including the transforming growth factor beta (TGFβ)-SMAD family proteins and Hippo pathways. The role of SIRT6 in liver cancer is quite complicated, as both tumor-suppressive and tumor-promoting activities have been documented in the literature. Overall, SIRT6 has multiple salutary effects on metabolic homeostasis and liver health, and it may serve as a therapeutic target for hepatic metabolic diseases. To date, numerous activators and inhibitors of SIRT6 have been developed for translational research.

PPARα Induces the Expression of CAR That Works as a Negative Regulator of PPARα Functions in Mouse Livers.

The nuclear receptor peroxisome proliferator-activated receptor α (PPARα) is a transcription factor that controls the transcription of genes responsible for fatty acid metabolism. We have recently reported a possible drug-drug interaction mechanism via the interaction of PPARα with the xenobiotic nuclear receptor constitutive androstane receptor (CAR). Drug-activated CAR competes with the transcriptional coactivator against PPARα and prevents PPARα-mediated lipid metabolism. In this study, to elucidate the crosstalk between CAR and PPARα, we focused on the influence of PPARα activation on CAR's gene expression and activation. Male C57BL/6N mice (8-12 weeks old, n = 4) were treated with PPARα and CAR activators (fenofibrate and phenobarbital, respectively), and hepatic mRNA levels were determined using quantitative reverse transcription PCR. Reporter assays using the mouse Car promoter were performed in HepG2 cells to determine the PPARα-dependent induction of CAR. CAR KO mice were treated with fenofibrate, and the hepatic mRNA levels of PPARα target genes were determined. Treatment of mice with a PPARα activator increased Car mRNA levels as well as genes related to fatty acid metabolism. In reporter assays, PPARα induced the promoter activity of the Car gene. Mutation of the putative PPARα-binding motif prevented PPARα-dependent induction of reporter activity. In electrophoresis mobility shift assay, PPARα bound to the DR1 motif of the Car promoter. Since CAR has been reported to attenuate PPARα-dependent transcription, CAR was considered a negative feedback protein for PPARα activation. Treatment with fenofibrate induced the mRNA levels of PPARα target genes in Car-null mice more than those in wild-type mice, suggesting that CAR functions as a negative feedback factor for PPARα.

PRDX6 Promotes Fatty Acid Oxidation via PLA2-Dependent PPARα Activation in Rats Fed High-Fat Diet.

Aims: Nonalcoholic fatty liver disease (NAFLD) is becoming the most common chronic liver disease globally, which is defined as an excess accumulation of fat caused by the imbalance of lipogenesis and lipid catabolism. Recently, increasing evidence suggests that peroxiredoxin 6 (PRDX6) is involved in the pathogenesis and progression of NAFLD. However, little is known regarding its role in liver lipid catabolism. Results: We found that PRDX6 level was significantly increased in liver tissues after high-fat diet (HFD) treatment. PRDX6 knockout (KO) exacerbated HFD-induced hepatic steatosis. PRDX6 KO did not affect messenger RNA (mRNA) and protein levels of peroxisome proliferator-activated receptor alpha (PPARα). However, PRDX6 KO decreased the mRNA and protein levels of carnitine palmitoyltransferase-1alpha (CPT-1α) and acyl-CoA oxidase 1 (ACOX1), the target genes of PPARα. PRDX6 KO also did not activate AMP-activated protein kinase (AMPK)α/proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), the upstream signal of PPARα. However, PRDX6 KO reduces the levels of PPARα activators, the oxidized fatty acids (9- and 13-hydroxyoctadecadienoic acid) in HFD rats. More interestingly, PRDX6 promoted the production of oxidized fatty acids by hydrolyzing oxidized low-density lipoprotein (Ox-LDL), which depends on its phospholipase A2 (PLA2) activity. PRDX6 mutation on its PLA2 and its competitive phospholipase inhibitor inhibited the production of the oxidized fatty acids as well as the activation of PPARα. Furthermore, PRDX6 overexpression enhanced the transcriptional activation of PPARα. Innovation and Conclusion: This study elucidates for the first time the role of PLA2 enzyme activity of PRDX6 in fatty acid oxidation and reveals a novel mechanism of PRDX6 involved in liver steatosis. Antioxid. Redox Signal. 38, 1184-1200.

Lysine 222 in PPAR γ1 functions as the key site of MuRF2-mediated ubiquitination modification

Peroxisome proliferator-activated receptor gamma (PPAR γ) plays key roles in the development, physiology, reproduction, and homeostasis of organisms. Its expression and activity are regulated by various posttranslational modifications. We previously reported that E3 ubiquitin ligase muscle ring finger protein 2 (MuRF2) inhibits cardiac PPAR γ1 protein level and activity, eventually protects heart from diabetic cardiomyopathy; furthermore, by GST-pulldown assay, we found that MuRF2 modifies PPAR γ1 via poly-ubiquitination and accelerates PPAR γ1 proteasomal degradation. However, the key ubiquitination site on PPAR γ that MuRF2 targets for remains unclear. In the present study, we demonstrate that lysine site 222 is the receptor of MuRF2-mediated PPAR γ1 ubiquitination modification, using prediction of computational models, immunoprecipitation, ubiquitination assays, cycloheximide chasing assay and RT-qPCR. Our findings elucidated the underlying details of MuRF2 prevents heart from diabetic cardiomyopathy through the PPAR γ1 regulatory pathway.

WY14643 Increases Herpesvirus Replication and Inhibits IFNβ Production Independently of PPARα Expression.

Peroxisome proliferator activated receptor (PPAR) agonists are commonly used to treat metabolic disorders in humans because they regulate fatty acid oxidation and cholesterol metabolism. In addition to their roles in controlling metabolism, PPAR agonists also regulate inflammation and are immunosuppressive in models of autoimmunity. We aimed to test whether activation of PPARα with clinically relevant ligands could impact gammaherpesvirus infection using murine gammaherpesvirus-68 (MHV68, MuHV-4). We found that PPAR agonists WY14643 and fenofibrate increased herpesvirus replication in vitro. In vivo, WY14643 increased viral replication and caused lethality in mice. Unexpectedly, these effects proved independent of PPARα. We found that WY14643 suppressed production of type I interferon after MHV68 infection in vitro and in vivo. Taken together, our data indicate that caution should be employed when using PPARα agonists in immuno-metabolic studies, as they can have off-target effects on viral replication through the inhibition of type I interferon production. IMPORTANCE PPAR agonists are used clinically to treat both metabolic and inflammatory disorders. Because viruses are known to rewire host metabolism to their own benefit, the intersection of immunity, metabolism, and virology is an important research area. Our article is an important contribution to this field for two reasons. First, it shows a role for PPARα agonists in altering virus replication. Second, it shows that PPARα agonists can affect virus replication in a manner independent of their predicted target. This knowledge is valuable for anyone seeking to use PPARα agonists as a research tool.

Fatty acids negatively regulate platelet function through formation of noncanonical 15-lipoxygenase-derived eicosanoids.

The antiplatelet effect of polyunsaturated fatty acids is primarily attributed to its metabolism to bioactive metabolites by oxygenases, such as lipoxygenases (LOX). Platelets have demonstrated the ability to generate 15-LOX-derived metabolites (15-oxylipins); however, whether 15-LOX is in the platelet or is required for the formation of 15-oxylipins remains unclear. This study seeks to elucidate whether 15-LOX is required for the formation of 15-oxylipins in the platelet and determine their mechanistic effects on platelet reactivity. In this study, 15-HETrE, 15-HETE, and 15-HEPE attenuated collagen-induced platelet aggregation, and 15-HETrE inhibited platelet aggregation induced by different agonists. The observed anti-aggregatory effect was due to the inhibition of intracellular signaling including αIIbβ3 and protein kinase C activities, calcium mobilization, and granule secretion. While 15-HETrE inhibited platelets partially through activation of peroxisome proliferator-activated receptor β (PPARβ), 15-HETE also inhibited platelets partially through activation of PPARα. 15-HETrE, 15-HETE, or 15-HEPE inhibited 12-LOX in vitro, with arachidonic acid as the substrate. Additionally, a 15-oxylipin-dependent attenuation of 12-HETE level was observed in platelets following ex vivo treatment with 15-HETrE, 15-HETE, or 15-HEPE. Platelets treated with DGLA formed 15-HETrE and collagen-induced platelet aggregation was attenuated only in the presence of ML355 or aspirin, but not in the presence of 15-LOX-1 or 15-LOX-2 inhibitors. Expression of 15-LOX-1, but not 15-LOX-2, was decreased in leukocyte-depleted platelets compared to non-depleted platelets. Taken together, these findings suggest that 15-oxylipins regulate platelet reactivity; however, platelet expression of 15-LOX-1 is low, suggesting that 15-oxylipins may be formed in the platelet through a 15-LOX-independent pathway.

Activation of PPARα Exhibits Therapeutic Efficacy in a Mouse Model of Juvenile Neuronal Ceroid Lipofuscinosis.

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a fatal inherited neurodegenerative disease of children that occurs because of defective function of the lysosomal membrane glycoprotein CLN3. JNCL features glial activation and accumulation of autofluorescent storage material containing subunit c of mitochondrial ATP synthase (SCMAS), ultimately resulting into neuronal loss. Until now, no effective therapy is available for JNCL. This study underlines the possible therapeutic importance of gemfibrozil, an activator of peroxisome proliferator-activated receptor α (PPARα) and a lipid-lowering drug approved by the Food and Drug Administration in an animal model of JNCL. Oral gemfibrozil treatment reduced microglial and astroglial activation, attenuated neuroinflammation, restored the level of transcription factor EB (TFEB; the master regulator of lysosomal biogenesis), and decreased the accumulation of storage material SCMAS in somatosensory barrel field (SBF) cortex of Cln3Δex7/8 (Cln3ΔJNCL) mice of both sexes. Accordingly, gemfibrozil treatment also improved locomotor activities of Cln3ΔJNCL mice. While investigating the mechanism, we found marked loss of PPARα in the SBF cortex of Cln3ΔJNCL mice, which increased after gemfibrozil treatment. Oral gemfibrozil also stimulated the recruitment of PPARα to the Tfeb gene promoter in vivo in the SBF cortex of Cln3ΔJNCL mice, indicating increased transcription of Tfeb in the CNS by gemfibrozil treatment via PPARα. Moreover, disease pathologies aggravated in Cln3ΔJNCL mice lacking PPARα (Cln3ΔJNCLΔPPARα) and gemfibrozil remained unable to decrease SCMAS accumulation, reduce glial activation, and improve locomotor performance of Cln3ΔJNCLΔPPARα mice. These results suggest that activation of PPARα may be beneficial for JNCL and that gemfibrozil may be repurposed for the treatment of this incurable disease.SIGNIFICANCE STATEMENT Despite intense investigations, no effective therapy is available for JNCL, an incurable inherited lysosomal storage disorder. Here, we delineate that oral administration of gemfibrozil, a lipid-lowering drug, decreases glial inflammation, normalizes and/or upregulates TFEB, and reduces accumulation of autofluorescent storage material in SBF cortex to improve locomotor activities in Cln3Δex7/8 (Cln3ΔJNCL) mice. Aggravation of disease pathology in Cln3ΔJNCL mice lacking PPARα (Cln3ΔJNCLΔPPARα) and inability of gemfibrozil to decrease SCMAS accumulation, reduce glial activation, and improve locomotor performance of Cln3ΔJNCLΔPPARα mice delineates an important role of PPARα in this process. These studies highlight a new property of gemfibrozil and indicate its possible therapeutic use in JNCL patients.