PPARα Agonist Research Articles

PPAR-α Agonist Fenofibrate Ameliorates Sjögren Syndrome-Like Dacryoadenitis by Modulating Th1/Th17 and Treg Cell Responses in NOD Mice.

PurposeTo investigate the effects and mechanisms of fenofibrate, a synthetic ligand of peroxisome proliferator-activated receptor α (PPAR-α), on autoimmune dacryoadenitis in a mouse model of Sjögren syndrome (SS) dry eye.MethodsMale nonobese diabetic (NOD) mice were fed chow with or without 0.03% fenofibrate for 8 weeks, and clinical scores were determined by assessing tear secretion, fluorescein, and hematoxylin and eosin staining. Intracellular IFN-γ, IL-17, and Foxp3 in CD4+ T cells were measured by flow cytometry. The expressions of Th1, Th17, and Treg cell-related transcription factors and cytokines were detected by real-time PCR. The levels of PPAR-α and liver X receptor β (LXR-β) were detected with real-time PCR and Western blotting.ResultsFenofibrate efficiently diminished the lymphocytic inflammation in lacrimal glands (LGs), increased tear secretion, and decreased corneal fluorescein staining in NOD mice. Meanwhile, treatment of fenofibrate evidently reduced the proportion of Th1 and Th17 cells and increased the proportion of Treg cells in vivo and vitro, together with decreased expression of T-bet, IFN-γ, RORγt, and IL-17, as well as increased expression of Foxp3 and TGF-β1 in LGs. Furthermore, fenofibrate significantly upregulated the expressions of PPAR-α and LXR-β at the protein and mRNA levels.ConclusionsFenofibrate potently attenuated LG inflammation in a model of autoimmune dry eye, and this effect might partially result from regulating Th1/Th17/Treg cell responses by activating PPAR-α/LXR-β signaling. These data suggest that fenofibrate may be a novel class of therapeutic agent for SS-associated dacryoadenitis.

Angiopoietin-Like Protein 4 Is Involved in Manganese Superoxide Dismutase-Mediated Suppression of Breast Cancer Cell Growth.

This study aims to understand the molecular basis of manganese superoxide dismutase (MnSOD) impacts on breast cancer cell growth. Modulation of the level of MnSOD by genetic engineering led significant changes in the expression of angiopoietin-like protein 4 (ANGPTL4) and activity of peroxisome proliferator-activated receptor α (PPARα) in MCF7 cells. PPARα agonist increased ANGPTL4 expression inhibited by MnSOD. Proliferation of MCF7 cells was inhibited by MnSOD, however, ANGPTL4 transduction into MCF7 cells with MnSOD overexpression significantly stimulated cell proliferation. MnSOD induced G0/G1 cell cycle arrest, nevertheless, ANGPTL4 transduction significantly reduced the percentage of cells in G0/G1 phase overexpressing MnSOD. In conclusion, MnSOD suppressed the expression of ANGPTL4 in breast cancer cells via the PPARα signaling pathway, and ANGPTL4 was involved in MnSOD-mediated proliferation inhibition and cell cycle arrest.

Saikosaponin D attenuates metabolic associated fatty liver disease by coordinately tuning PPARα and INSIG/SREBP1c pathway

BackgroundMetabolic associated fatty liver disease (MAFLD) is a progressive chronic liver disease, yet there is still a lack of effective pharmacological therapies at present. Saikosaponin D (SSd) has been reported to exhibit hepatoprotective and anti-steatosis activities in our previous research. PurposeThe current study aims to further investigate the underlying mechanisms of SSd on MAFLD from the perspectives of the crosstalk between fatty acid (FA) biosynthesis and catabolism to provide strong support for further clinical management of MAFLD. MethodsA MAFLD mouse model induced by a high-fat diet and glucose-fructose water (HFSW) was used for in vivo study. HepG2 cells, primary mouse hepatocytes and adipocytes were further employed for in vitro studies. ResultsSSd improved intracellular lipid accumulation both in the liver and adipose tissues in HFSW-fed mice. Mechanistically, SSd may serve as a potent PPARα agonist, and the activation of PPARα by SSd in both hepatocytes and adipocytes not only promoted FA oxidation but also concurrently induced INSIG1/2 expression, which subsequently inhibited SREBP1c maturation and ultimately FA synthesis. Moreover, the regulative effect of SSd on lipid metabolism was abolished by the PPARα inhibitor, GW6471. ConclusionThis study demonstrated that SSd improved lipid homeostasis by coordinately regulating PPARα activation-mediated both inhibition of SREBP1c-dependent FA biosynthesis and induction of FA degradation, and thus shed novel light on the discovery of SSd-based therapeutic strategies for MAFLD.

Co-Ultramicronized Palmitoylethanolamide/Luteolin Restores Oligodendrocyte Homeostasis via Peroxisome Proliferator-Activated Receptor-α in an In Vitro Model of Alzheimer's Disease.

Oligodendrocytes are cells fundamental for brain functions as they form the myelin sheath and feed axons. They perform these critical functions thanks to the cooperation with other glial cells, mainly astrocytes. The astrocyte/oligodendrocyte crosstalk needs numerous mediators and receptors, such as peroxisome proliferator-activated receptors (PPARs). PPAR agonists promote oligodendrocyte precursor cells (OPCs) maturation in myelinating oligodendrocytes. In the Alzheimer’s disease brain, deposition of beta-amyloid (Aβ) has been linked to several alterations, including astrogliosis and changes in OPCs maturation. However, very little is known about the molecular mechanisms. Here, we investigated for the first time the maturation of OPCs co-cultured with astrocytes in an in vitro model of Aβ1–42 toxicity. We also tested the potential beneficial effect of the anti-inflammatory and neuroprotective composite palmitoylethanolamide and luteolin (co-ultra PEALut), which is known to engage the isoform alfa of the PPARs. Our results show that Aβ1–42 triggers astrocyte reactivity and inflammation and reduces the levels of growth factors important for OPCs maturation. Oligodendrocytes indeed show low cell surface area and few arborizations. Co-ultra PEALut counteracts the Aβ1–42-induced inflammation and astrocyte reactivity preserving the morphology of co-cultured oligodendrocytes through a mechanism that in some cases involves PPAR-α. This is the first evidence of the negative effects exerted by Aβ1–42 on astrocyte/oligodendrocyte crosstalk and discloses a never-explored co-ultra PEALut ability in restoring oligodendrocyte homeostasis.

Impact of concomitant fibrates on immunotherapy outcomes for advanced non-small cell lung cancer.

Peroxisome proliferator-activated receptor agonists such as fibrates restore oxidative metabolism in cytotoxic T-lymphocytes, thereby enhancing response to immune checkpoint inhibitors (ICI) in preclinical models. However, there is no evidence in humans on the clinical impact of fibrates as an adjunct to ICI. In this cohort study of Veterans with non-small cell lung cancer (NSCLC) receiving ICI, fibrate exposure was defined as a prescription filled within 90 days of an ICI infusion. Overall survival (OS), measured from the start of ICI, was compared between exposed and unexposed Veterans. Cox multivariable analysis (MVA) was used to identify factors associated with OS. A sensitivity analysis of Veterans with stage IV NSCLC who received docetaxel without ICI was similarly performed. The ICI cohort included 3593 Veterans, of whom 301 (8.5%) coincidentally received a fibrate. Veterans receiving fibrates were more likely to be older, white, male, and married, and to have greater comorbidity burden, but less likely to receive chemotherapy. Coincidental fibrates were associated with improved OS both on MVA (HR 0.86, 95%CI 0.75-0.99) and in a matched subset (HR 0.75, 95%CI 0.63-0.90). In contrast, among the cohort of 968 Veterans treated with chemotherapy, fibrates did not have a significant impact on OS by MVA (HR 0.99, 95%CI 0.79-1.25) or in a matched subset (HR 1.02, 95%CI CI 0.75-1.39). Concomitant fibrates are associated with improved OS among NSCLC patients receiving ICI but not among those receiving chemotherapy. This hypothesis-generating observation supports a potential role for fibrates as an adjunct to immunotherapy.

PPARα Signaling: A Candidate Target in Psychiatric Disorder Management.

Peroxisome proliferator-activator receptors (PPARs) regulate lipid and glucose metabolism, control inflammatory processes, and modulate several brain functions. Three PPAR isoforms have been identified, PPARα, PPARβ/δ, and PPARγ, which are expressed in different tissues and cell types. Hereinafter, we focus on PPARα involvement in the pathophysiology of neuropsychiatric and neurodegenerative disorders, which is underscored by PPARα localization in neuronal circuits involved in emotion modulation and stress response, and its role in neurodevelopment and neuroinflammation. A multiplicity of downstream pathways modulated by PPARα activation, including glutamatergic neurotransmission, upregulation of brain-derived neurotrophic factor, and neurosteroidogenic effects, encompass mechanisms underlying behavioral regulation. Modulation of dopamine neuronal firing in the ventral tegmental area likely contributes to PPARα effects in depression, anhedonia, and autism spectrum disorder (ASD). Based on robust preclinical evidence and the initial results of clinical studies, future clinical trials should assess the efficacy of PPARα agonists in the treatment of mood and neurodevelopmental disorders, such as depression, schizophrenia, and ASD.

Synthesis, in vitro, in silico and in vivo hypoglycemic and lipid-lowering effects of 4-benzyloxy-5-benzylidene-1,3-thiazolidine-2,4-diones mediated by dual PPAR α/γ modulation

In current work, we prepared a series of nine 4-benzyloxy-5-benzylidene-1,3-thiazolidine-2,4-diones using a two-step pathway. Compounds 1–9 were tested in vitro using a set of three proteins recognized as important targets in diabetes and related diseases: PPARα, PPARγ, and GLUT-4. Compounds 1–3, 5, and 7 showed significant increases in the mRNA expression of PPARγ and GLUT-4, whereas compounds 1–3 did it over PPARα. Compounds 1–3 were identified as a dual PPAR α/γ modulators and were selected for evaluating the in vivo antidiabetic action at 100 mg/kg dose, being orally actives and decreasing blood glucose concentration in a hyperglycemic mice model, as well as reducing the triacylglycerides levels in normolipidemic rats. Docking and molecular dynamics studies were conducted to clarify the dual effect and binding mode of compounds 1–3 on both PPARs. Compounds 2 and 3 exhibited robust in vitro and in vivo efficacy and could be considered dual PPAR modulators with antidiabetic and antidyslipidemic effects.

Palmitoylethanolamide (PEA) Inhibits SARS-CoV-2 Entry by Interacting with S Protein and ACE-2 Receptor.

Lipids play a crucial role in the entry and egress of viruses, regardless of whether they are naked or enveloped. Recent evidence shows that lipid involvement in viral infection goes much further. During replication, many viruses rearrange internal lipid membranes to create niches where they replicate and assemble. Because of the close connection between lipids and inflammation, the derangement of lipid metabolism also results in the production of inflammatory stimuli. Due to its pivotal function in the viral life cycle, lipid metabolism has become an area of intense research to understand how viruses seize lipids and to design antiviral drugs targeting lipid pathways. Palmitoylethanolamide (PEA) is a lipid-derived peroxisome proliferator-activated receptor-α (PPAR-α) agonist that also counteracts SARS-CoV-2 entry and its replication. Our work highlights for the first time the antiviral potency of PEA against SARS-CoV-2, exerting its activity by two different mechanisms. First, its binding to the SARS-CoV-2 S protein causes a drop in viral infection of ~70%. We show that this activity is specific for SARS-CoV-2, as it does not prevent infection by VSV or HSV-2, other enveloped viruses that use different glycoproteins and entry receptors to mediate their entry. Second, we show that in infected Huh-7 cells, treatment with PEA dismantles lipid droplets, preventing the usage of these vesicular bodies by SARS-CoV-2 as a source of energy and protection against innate cellular defenses. This is not surprising since PEA activates PPAR-α, a transcription factor that, once activated, generates a cascade of events that leads to the disruption of fatty acid droplets, thereby bringing about lipid droplet degradation through β-oxidation. In conclusion, the present work demonstrates a novel mechanism of action for PEA as a direct and indirect antiviral agent against SARS-CoV-2. This evidence reinforces the notion that treatment with this compound might significantly impact the course of COVID-19. Indeed, considering that the protective effects of PEA in COVID-19 are the current objectives of two clinical trials (NCT04619706 and NCT04568876) and given the relative lack of toxicity of PEA in humans, further preclinical and clinical tests will be needed to fully consider PEA as a promising adjuvant therapy in the current COVID-19 pandemic or against emerging RNA viruses that share the same route of replication as coronaviruses.

Adipose triglyceride lipase-mediated lipid catabolism is essential for bronchiolar regeneration.

The lung airways are constantly exposed to inhaled toxic substances, resulting in cellular damage that is repaired by local expansion of resident bronchiolar epithelial club cells. Disturbed bronchiolar epithelial damage repair lies at the core of many prevalent lung diseases, including chronic obstructive pulmonary disease, asthma, pulmonary fibrosis, and lung cancer. However, it is still not known how bronchiolar club cell energy metabolism contributes to this process. Here, we show that adipose triglyceride lipase (ATGL), the rate-limiting enzyme for intracellular lipolysis, is critical for normal club cell function in mice. Deletion of the gene encoding ATGL, Pnpla2 (also known as Atgl), induced substantial triglyceride accumulation, decreased mitochondrial numbers, and decreased mitochondrial respiration in club cells. This defect manifested as bronchiolar epithelial thickening and increased airway resistance under baseline conditions. After naphthalene‑induced epithelial denudation, a regenerative defect was apparent. Mechanistically, dysfunctional PPARα lipid-signaling underlies this phenotype because (a) ATGL was needed for PPARα lipid-signaling in regenerating bronchioles and (b) administration of the specific PPARα agonist WY14643 restored normal bronchiolar club cell ultrastructure and regenerative potential. Our data emphasize the importance of the cellular energy metabolism for lung epithelial regeneration and highlight the significance of ATGL-mediated lipid catabolism for lung health.

An integrated network pharmacology and cell metabolomics approach to reveal the role of rhein, a novel PPARα agonist, against renal fibrosis by activating the PPARα–CPT1A axis

BackgroundRhein, an anthraquinone compound, displays extensive antifibrotic effects; however, its potential mechanisms are not fully understood. In this study, we explored the underlying molecular mechanism of action of rhein. MethodAn integrated network pharmacology and cell metabolomics approach was developed based on network pharmacology and bioinformatics method, and then successfully applied to speculate the potential targets of rhein and construct a rhein–target–metabolic enzyme–metabolite network. Thereafter, the antifibrotic mechanism of rhein was validated in TGF-β- and oleic acid- induced HK-2 and NRK-52E cells in vitro as well as a unilateral ischemia–reperfusion injury Sprague-Dawley rat model. ResultsBased on the construction of the rhein–target–metabolic enzyme–metabolite network, we found that rhein played an antifibrotic role through the PPAR–α–CPT1A–l-palmitoyl–carnitine axis. In vitro experiments demonstrated that rhein effectively activated the expression of PPARα and its downstream proteins (CPT1A and ACOX1) to alleviate lipid accumulation and fibrosis development. In vivo experiments indicated that rhein attenuated renal fibrosis mainly by activating the fatty acid oxidation pathway and improving lipid metabolism. ConclusionTaken together, our findings reveal that rhein is a novel agonist of PPARα, which contributes to its renoprotection through the regulation of the PPARα–CPT1A axis. Moreover, our study provides a novel insight into an integrated network pharmacology–metabolomics strategy for uncovering the pharmacological mechanisms of drugs from the system perspective.

Excessive selenium affects neural development and locomotor behavior of zebrafish embryos

Selenium is an essential micronutrient derived from daily diet to maintain the normal growth and development of vertebrates. Excessive selenium intake will induce cardiovascular toxicity, reproductive toxicity and neurotoxicity. However, there have been few studies of the toxic effects of selenium on neural development and locomotor behavior. In this study, newly fertilized zebrafish embryos were treated with selenium. As a result, selenium treatment at the concentration of 0.5 µM decreased the moving speed and distance and blunted the touch response of zebrafish embryos. TUNEL assay and immunofluorescence analysis revealed that selenium induced nervous system impairment including promoted cell apoptosis, proliferation and neuroinflammation, and decreased neurons in zebrafish embryos. RNA-seq and RT-PCR results indicated that selenium treatment significantly decreased the expression of the dopaminergic neuron, motor neuron, GABAergic neuron and neurotransmitter transport marker genes in zebrafish embryos. The expression of PPAR signaling pathway marker genes was significantly down-regulated in selenium-treated embryos. Two PPAR agonists (rosiglitazone and bezafibrate) and an anti-cancer drug (cisplatin) were tested for their effects to alleviate selenium-induced locomotor defects. Rosiglitazone and bezafibrate could restore the expression of some neural marker genes but could not fully rescue the selenium-induced locomotor behavior defects. The supplementation of cisplatin could restore the dysfunctional locomotor behavior and the abnormal expression of the PPAR and neural marker genes to almost the normal levels. In conclusion, the results of this study reveal that selenium-induced neural development and locomotor behavior defects are caused by multiple complex factors including PPAR signaling, and all the factors might be recovered by cisplatin through unknown mechanisms.

Advances in PPARs Molecular Dynamics and Glitazones as a Repurposing Therapeutic Strategy through Mitochondrial Redox Dynamics against Neurodegeneration.

Peroxisome proliferator-activated receptors (PPARs) activity has significant implications for the development of novel therapeutic modalities against neurodegenerative diseases. Although PPAR-α, PPAR-β/δ, and PPAR-γ nuclear receptor expressions are significantly reported in the brain, their implications in brain physiology and other neurodegenerative diseases still require extensive studies. PPAR signaling can modulate various cell signaling mechanisms involved in the cells contributing to on- and off-target actions selectively to promote therapeutic effects as well as the adverse effects of PPAR ligands. Both natural and synthetic ligands for the PPARα, PPARγ, and PPARβ/δ have been reported. PPARα (WY 14.643) and PPARγ agonists can confer neuroprotection by modulating mitochondrial dynamics through the redox system. The pharmacological effect of these agonists may deliver effective clinical responses by protecting vulnerable neurons from Aβ toxicity in Alzheimer's disease (AD) patients. Therefore, the current review delineated the ligands' interaction with 3D-PPARs to modulate neuroprotection, and also deciphered the efficacy of numerous drugs, viz. Aβ aggregation inhibitors, vaccines, and γ-secretase inhibitors against AD; this review elucidated the role of PPAR and their receptor isoforms in neural systems, and neurodegeneration in human beings. Further, we have substantially discussed the efficacy of PPREs as potent transcription factors in the brain, and the role of PPAR agonists in neurotransmission, PPAR gamma coactivator-1α (PGC-1α) and mitochondrial dynamics in neuroprotection during AD conditions. This review concludes with the statement that the development of novel PPARs agonists may benefit patients with neurodegeneration, mainly AD patients, which may help mitigate the pathophysiology of dementia, subsequently improving overall the patient's quality of life.

Proximal Tubule‐Specific Transgenic Overexpression of Peroxisome Proliferator‐Activated Receptor Alpha Prevents the Development of Hypertension in Dahl Salt‐Sensitive Rats

The Dahl salt‐sensitive rat (Dahl SS) is a well investigated model of hypertension that mimics human salt sensitive hypertension. These rats develop a significant increase in blood pressure and renal disease when challenged with a high salt diet compared to salt‐resistant strains. Prolonged high salt feeding results in extensive renal pathology, including glomerular and proximal tubular pathology, tubular casting, and interstitial fibrosis. It has been shown that clofibrate, a lipid lowering peroxisome proliferator‐activated receptor alpha (PPARα) agonist, can prevent the hypertensive phenotype in Dahl SS rats. PPARα is a ligand activated transcription factor that regulates β‐oxidation of fatty acids (FAO). The proximal tubule is a very metabolically active tubular segment that relies primarily on FAO to meet its high energy requirements. Reduced FAO can lead to proximal tubular damage and renal dysfunction. To investigate the impact of PPARα‐mediated FAO during a high‐salt challenge, we developed a novel transgenic Dahl SS strain with a proximal tubule‐specific promoter from the sodium/glucose cotransporter 2 gene (Sglt2). This resulted in the overexpression of Ppara only in the proximal tubule (SSTgPTPpara). At 9 weeks of age, male wild‐type rats and heterozygous transgenic SSTgPTPpara rats were placed on a 4.0% NaCl, high salt diet (n=6/group). Following a 14‐day high salt challenge, rats were anesthetized for carotid blood pressure recording. Proximal tubule‐specific transgenic overexpression of PPARα in heterozygous SSTgPTPpararats had lower systolic blood pressure when compared to wild‐type littermates (161.2.6 ± 12.0 mmHg vs.122.8 ± 4.2 mmHg; mean ± SEM; p <0.05, t‐test), as well as mean arterial pressure and diastolic blood pressure. Immunohistochemical analysis confirmed an increase in PPARA protein within proximal tubules of the renal cortex, relative to other nephron segments. In conclusion, proximal tubule specific‐transgenic overexpression of PPARα reduced salt‐sensitive hypertension, suggesting that proximal tubules may be one of the primary sites of anti‐hypertensive actions of clofibrate in Dahl SS rats. This also indicates that the SSTgPTPpara rat model could be useful for studying the contribution of dysregulated proximal tubule metabolism to salt‐sensitive hypertension and renal pathology in the Dahl SS rat.

Alcoholic fatty liver is blunted by rFGF21 administration in mice lacking adipose FGFR1: the role of FGF21 in PPARα‐mediated regulation of adipose tissue mass

Fibroblast growth factor 21 (FGF21) regulates lipid metabolism via fibroblast growth factor receptor 1 (FGFR1). FGF21 protects against alcoholic fatty liver, which is still observed in mice lacking liver FGFR1, suggesting the involvement of extra‐hepatic FGFR1 in mediating alcoholic fatty liver. We have previously shown that, in a chronic Lieber‐DeCarli model, the peroxisome proliferator‐activated receptor‐α (PPARα) agonist WY‐14,643 induced FGF21 and adipose atrophy but failed to protect against alcoholic fatty liver in mice lacking adipose FGFR1. In this study we tested the role of the FGF21 in regulation of adipose tissue mass and ethanol induced‐hepatic fat (triglyceride, TG) accumulation in mice lacking adipose FGFR1. In binge alcohol model, male adipose FGFR1 knockout mice (fgfr1adipoQ‐cre) and corresponding normal control (fgfr1fl/fl) mice were fed liquid control diet with or without 20 mg/L WY‐14,643 for 2 weeks followed by a binge ethanol gavage at 5 g/kg, adipose tissue mass and serum free fatty acid were decreased by WY‐14,643 in the fgfr1adipoQ‐cremice but not in the fgfr1fl/flmice. However, in contrast to the chronic model, the binge ethanol‐induced liver TG accumulation was blunted by WY‐14,643 to a greater extent in the fgfr1adipoQ‐cremice than in the fgfr1fl/flmice. Consistently, on top of WY‐14,643 feeding, circulating FGF21 was elevated by binge ethanol to a greater extent in the fgfr1adipoQ‐cre mice than in the fgfr1fl/fl mice. To test the involvement of the FGF21 in adipose atrophy and the less extent of hepatic fat accumulation in the fgfr1adipoQ‐cremice, recombinant mouse FGF21 (rFGF21) was injected intraperitoneally at 0.4 mg/kg to the 3‐week ethanol fed fgfr1adipoQ‐cre mice and fgfr1fl/fl mice during the last 10 days of the ethanol feeding. Consistent with FGFR1‐dependent effects of WY‐14,643 on adipose atrophy and liver fat accumulation, on the top of chronic ethanol diet, rFGF21 administration induced adipose atrophy, blunted liver TG accumulation and serum TG elevation to a greater extent in the fgfr1adipoQ‐cre mice than in the fgfr1fl/fl mice. These results indicated the consistency of adipose FGFR1 dependent effect of WY‐14,643 and FGF21 in PPARα‐mediated regulation of adipose tissue mass and fat mobilization from adipose tissues to the liver.

PPARα agonist WY-14,643 induces the PLA2/COX-2/ACOX1 pathway to enhance peroxisomal lipid metabolism and ameliorate alcoholic fatty liver in mice

Peroxisome proliferator-activated receptor α (PPARα) regulates fatty acid oxidation (FAO). Usually, very-long chain fatty acids are first activated by acyl-CoA synthetase (ACS) to generate acyl-CoA for oxidation by acyl-CoA oxidase (ACOX) in peroxisomes, and the resultant shorter chain fatty acids will be further oxidized in mitochondria. ACS long-chain family member 4 (ACSL4) preferentially uses arachidonic acid (AA) as substrates to synthesize arachidonoyl-CoA. Arachidonoyl-CoA is usually esterified into phospholipids. When AA is released by phospholipase A2 (PLA2) from phospholipids, it will be used for prostaglandin synthesis by cyclooxygenases (COX). In this study, when PPARα agonist WY-14,643 was mixed in liquid Lieber-DeCarli ethanol or control diets and fed to mice, liver PLA2, COX-2, and ACOX1 were induced but ACSL4 was inhibited, suggesting that AA released by PLA2 from phospholipid will be metabolized to prostaglandin via COX-2 instead of being synthesized into acyl-CoA by ACSL4. However, liver prostaglandin E2 (PGE2), a major component of prostaglandin, was not increased with the induced COX-2 but decreased by WY-14,643. ACOX1 specific inhibitor mixed in the liquid diets restored both the WY-14,643-suppressed liver TG and PGE2, but COX-2 specific inhibitor celecoxib mixed in the liquid diets reversed the WY-14,643-suppressed liver TG but not liver PGE2 contents. These results suggest that induction of PLA2, COX-2 and ACOX1 orchestrates to increase oxidation of AA/PGE2, which constitutes one new mechanism by which PPARα induces peroxisomal FAO and inhibits ethanol-induced liver fat accumulation.

Interactions between nuclear receptors glucocorticoid receptor α and peroxisome proliferator–activated receptor α form a negative feedback loop

Both nuclear receptors glucocorticoid receptor α (GRα) and peroxisome proliferator-activated receptor α (PPARα) are involved in energy and lipid metabolism, and possess anti-inflammation effects. Previous studies indicate that a regulatory loop may exist between them. In vivo and in vitro studies showed that glucocorticoids stimulate hepatic PPARα expression via GRα at the transcriptional level. This stimulation of PPARα by GRα has physiological relevance and PPARα is involved in many glucocorticoid-induced pathophysiological processes, including gluconeogenesis and ketogenesis during fasting, insulin resistance, hypertension and anti-inflammatory effects. PPARα also synergizes with GRα to promote erythroid progenitor self-renewal. As the feedback, PPARα inhibits glucocorticoid actions at pre-receptor and receptor levels. PPARα decreases glucocorticoid production through inhibiting the expression and activity of type-1 11β-hydroxysteroid dehydrogenase, which converts inactive glucocorticoids to active glucocorticoids at local tissues, and also down-regulates hepatic GRα expression, thus forming a complete and negative feedback loop. This negative feedback loop sheds light on prospective multi-drug therapeutic treatments in inflammatory diseases through a combination of glucocorticoids and PPARα agonists. This combination may potentially enhance the anti-inflammatory effects while alleviating side effects on glucose and lipid metabolism due to GRα activation. More investigations are needed to clarify the underlying mechanism and the relevant physiological or pathological significance of this regulatory loop.

The Role of Interferon Regulatory Factors in Non-Alcoholic Fatty Liver Disease and Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is becoming the most common chronic liver disease with many metabolic comorbidities, such as obesity, diabetes, and cardiovascular diseases. Non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, accompanies the progression of hepatic steatosis, inflammation, cell death, and varying degree of liver fibrosis. Interferons (IFNs) have been shown to play important roles in the pathogenesis of NAFLD and NASH. Their regulating transcriptional factors such as interferon regulatory factors (IRFs) can regulate IFN expression, as well as genes involved in macrophage polarization, which are implicated in the pathogenesis of NAFLD and advanced liver disease. In this review, the roles of IRF-involved signaling pathways in hepatic inflammation, insulin resistance, and immune cell activation are reviewed. IRFs such as IRF1 and IRF4 are also involved in the polarization of macrophages that contribute to critical roles in NAFLD or NASH pathogenesis. In addition, IRFs have been shown to be regulated by treatments including microRNAs, PPAR modulators, anti-inflammatory agents, and TLR agonists or antagonists. Modulating IRF-mediated factors through these treatments in chronic liver disease can ameliorate the progression of NAFLD to NASH. Furthermore, adenoviruses and CRISPR activation plasmids can also be applied to regulate IRF-mediated effects in chronic liver disease. Pre-clinical and clinical trials for evaluating IRF regulators in NAFLD treatment are essential in the future direction.

Functional and Structural Insights into Human PPARα/δ/γ Subtype Selectivity of Bezafibrate, Fenofibric Acid, and Pemafibrate.

Among the agonists against three peroxisome proliferator-activated receptor (PPAR) subtypes, those against PPARα (fibrates) and PPARγ (glitazones) are currently used to treat dyslipidemia and type 2 diabetes, respectively, whereas PPARδ agonists are expected to be the next-generation metabolic disease drug. In addition, some dual/pan PPAR agonists are currently being investigated via clinical trials as one of the first curative drugs against nonalcoholic fatty liver disease (NAFLD). Because PPARα/δ/γ share considerable amino acid identity and three-dimensional structures, especially in ligand-binding domains (LBDs), clinically approved fibrates, such as bezafibrate, fenofibric acid, and pemafibrate, could also act on PPARδ/γ when used as anti-NAFLD drugs. Therefore, this study examined their PPARα/δ/γ selectivity using three independent assays—a dual luciferase-based GAL4 transactivation assay for COS-7 cells, time-resolved fluorescence resonance energy transfer-based coactivator recruitment assay, and circular dichroism spectroscopy-based thermostability assay. Although the efficacy and efficiency highly varied between agonists, assay types, and PPAR subtypes, the three fibrates, except fenofibric acid that did not affect PPARδ-mediated transactivation and coactivator recruitment, activated all PPAR subtypes in those assays. Furthermore, we aimed to obtain cocrystal structures of PPARδ/γ-LBD and the three fibrates via X-ray diffraction and versatile crystallization methods, which we recently used to obtain 34 structures of PPARα-LBD cocrystallized with 17 ligands, including the fibrates. We herein reveal five novel high-resolution structures of PPARδ/γ–bezafibrate, PPARγ–fenofibric acid, and PPARδ/γ–pemafibrate, thereby providing the molecular basis for their application beyond dyslipidemia treatment.

Restoring cellular NAD(P)H levels by PPARα and LXRα stimulation to improve mitochondrial complex I deficiency

Mitochondrial complex I (CI), the first multiprotein enzyme complex of the oxidative phosphorylation system, plays a crucial role in cellular energy production. CI deficiency is associated with a variety of clinical phenotypes, including Leigh syndrome. At the cellular level, an increased NAD(P)H concentration is one of the hallmarks in CI-deficiency. AimsHere, we aimed to attenuate increased NAD(P)H levels by stimulation of ATP-dependent cassette (ABC)A1 and ABCG1-mediated cellular cholesterol efflux with various PPARα and LXRα agonists. Main methodsMitochondrial CI-deficient fibroblasts and chemically-induced CI-deficient HeLa cells were used to study the dose-dependent effects of various PPARα and LXRα agonists on cellular NAD(P)H levels and cholesterol efflux. Key findingsIn patient-derived mitochondrial CI-deficient fibroblasts, GW590735, astaxanthin, oleoylethanolamide, and GW3965 significantly reduced the enhanced NAD(P)H levels in CI-deficient fibroblasts. Similar effects were observed in chemically-induced CI-impaired HeLa cells, in which BMS-687453, Wy14643, GW7647, T0901317, DMHCA also demonstrated a beneficial effect. Surprisingly, no effect on ABCA1- and ABCG1-mediated cholesterol efflux in HeLa cells and fibroblasts was found after treatment with these compounds. The reduction in NAD(P)H levels by GW590735 could be partially reversed by inhibition of fatty acid synthase and β-oxidation, which suggests that its beneficial effects are possibly mediated via stimulation of fatty acid metabolism rather than cholesterol efflux. SignificanceCollectively, PPARα and LXRα stimulation resulted in attenuated cellular NAD(P)H levels in CI-impaired HeLa cells and patient-derived fibroblasts and could eventually have a therapeutic potential in CI deficiency.

Pemafibrate attenuates pulmonary fibrosis by inhibiting myofibroblast differentiation

Background and ObjectiveIdiopathic pulmonary fibrosis is a chronic progressive disease associated with substantial morbidity and mortality despite advances in medical therapy. Increasing evidence suggests that peroxisome proliferator-activated receptors (PPARs) play important roles in the fibrosis-related diseases and their agonists may become effective therapeutic targets. Pemafibrate is a selective PPARα agonist, but the efficacy against pulmonary fibrosis and mechanisms involved have not been systematically evaluated. Thus, the aims of this study were to explore the role of PPARα in the pulmonary fibrosis and to assess the effect of pemafibrate in vivo and in vitro. MethodsThe effects of pemafibrate were evaluated in bleomycin-challenged murine pulmonary fibrosis model and transforming growth factor-beta 1 (TGF-β1) stimulated lung fibroblasts. ResultsBleomycin instillation induced body weight loss, declined lung function, pulmonary fibrosis, and extensive collagen deposition in the mice, accompanied with decreased pulmonary expression of PPARα, all of which were partially improved by pemafibrate at a dose of 2 mg/kg. Besides, pemafibrate effectively inhibits TGF-β1-induced myofibroblast differentiation and extracellular matrix (ECM) production in vivo and in vitro. Furthermore, we showed that pemafibrate not only inhibited pulmonary expression of NLRP3 and cleaved caspase-1 in bleomycin-inhaled mice, but also repressed activation of NLRP3/caspase-1 axis in TGF-β1 stimulated lung fibroblasts. ConclusionOur data suggest that pemafibrate exerts a marked protection against from the development of pulmonary fibrosis, which could constitute a novel candidate for the treatment for pulmonary fibrosis.