PPARδ Activation Research Articles

Elafibranor alleviates alcohol-related liver fibrosis by restoring intestinal barrier function

We discuss the article by Koizumi et al published in the World Journal of Gastroenterology . Our focus is on the therapeutic targets for fibrosis associated with alcohol-related liver disease (ALD) and the mechanism of action of elafibranor (EFN), a dual agonist of peroxisome proliferator-activated receptor α (PPARα) and peroxisome PPAR δ (PPARδ). EFN is currently in phase III clinical trials for the treatment of metabolic dysfunction-associated fatty liver disease and primary biliary cholangitis. ALD progresses from alcoholic fatty liver to alcoholic steatohepatitis (ASH), with chronic ASH eventually leading to fibrosis, cirrhosis, and, in some cases, hepatocellular carcinoma. The pathogenesis of ALD is driven by hepatic steatosis, oxidative stress, and acetaldehyde toxicity. Alcohol consumption disrupts lipid metabolism by inactivating PPARα, exacerbating the progression of ALD. EFN primarily activates PPARα, promoting lipolysis and β-oxidation in ethanol-stimulated HepG2 cells, which significantly reduces hepatic steatosis, apoptosis, and fibrosis in an ALD mouse model. Additionally, alcohol disrupts the gut-liver axis at several interconnected levels, contributing to a proinflammatory environment in the liver. EFN helps alleviate intestinal hyperpermeability by restoring tight junction protein expression and autophagy, inhibiting apoptosis and inflammatory responses, and enhancing intestinal barrier function through PPARδ activation.

Abstract 4136030: Fatty acids disturb cardiomyocyte proliferation by increasing PDK4 and HMGCS2 via PPARδ activation

Background: Almost all cardiac diseases are difficult to cure entirely because cardiomyocytes rarely proliferate to recover cardiac damage. In fact, most mammals have a capacity to regenerate cardiomyocytes immediately after birth. Newborn infant drastically changes cardiac metabolism from glycolysis to oxidative phosphorylation using fatty acids. Previous research revealed that lipid metabolism had a negative influence on cardiomyocyte cell cycle but the mechanism has not been clarified completely. Objective: This study was performed to elucidate the way fatty acid metabolism affects cardiomyocyte proliferation. Methods and results: Isolated and cultured neonatal rat cardiomyocytes (NRCM) were treated with the mixture of palmitic acid, oleic acid, and L-carnitine (FA mix) for 24 hours. Realtime RT-PCR revealed that FA mix increased the mRNA expressions of pyruvate dehydrogenase kinase 4 (PDK4), a fatty acid metabolism regulator, and HMG-CoA synthase 2 (HMGCS2), a ketogenic factor, as well as β-oxidation-related enzymes in dose dependent manner. Simultaneously, the results of immunofluorescent staining showed that FA mix decreased cardiomyocytes expressing Ki67, a cell cycle marker. GW501516, a peroxisome proliferator-activated receptor δ (PPARδ) agonist, also increased fatty acid metabolism factors with the reduction of Ki67 positive cardiomyocytes, whereas fenofibrate, a PPARα agonist, or pioglitazone, a PPARγ agonist, caused little or no change in these phenotypes. Moreover, NRCM pretreated with GSK3787, a PPARδ antagonist, before FA mix stimulation suppressed the upregulations of fatty acid metabolism factors and the reduction of Ki67 expressing cardiomyocytes. Finally, the lentiviral vectors which expressed PDK4 or HMGCS2 were produced to investigate these proteins suppressed NRCM cell cycle directly. Either overexpressing PDK4 or HMGCS2 decreased Ki67 positive NRCM without the upregulation of each other or β-oxidation-related enzymes. Conclusion: Fatty acids disturbed NRCM proliferation by upregulating PDK4 and HMGCS2 through the activation of PPARδ independently from β-oxidation.

The Loss of PPARγ Expression and Signaling Is a Key Feature of Cutaneous Actinic Disease and Squamous Cell Carcinoma: Association with Tumor Stromal Inflammation.

Given the importance of peroxisome proliferator-activated receptor (PPAR)-gamma in epidermal inflammation and carcinogenesis, we analyzed the transcriptomic changes observed in epidermal PPARγ-deficient mice (Pparg-/-epi). A gene set enrichment analysis revealed a close association with epithelial malignancy, inflammatory cell chemotaxis, and cell survival. Single-cell sequencing of Pparg-/-epi mice verified changes to the stromal compartment, including increased inflammatory cell infiltrates, particularly neutrophils, and an increase in fibroblasts expressing myofibroblast marker genes. A comparison of transcriptomic data from Pparg-/-epi and publicly available human and/or mouse actinic keratoses (AKs) and cutaneous squamous cell carcinomas (SCCs) revealed a strong correlation between the datasets. Importantly, PPAR signaling was the top common inhibited canonical pathway in AKs and SCCs. Both AKs and SCCs also had significantly reduced PPARG expression and PPARγ activity z-scores. Smaller reductions in PPARA expression and PPARα activity and increased PPARD expression but reduced PPARδ activation were also observed. Reduced PPAR activity was also associated with reduced PPARα/RXRα activity, while LPS/IL1-mediated inhibition of RXR activity was significantly activated in the tumor datasets. Notably, these changes were not observed in normal sun-exposed skin relative to non-exposed skin. Finally, Ppara and Pparg were heavily expressed in sebocytes, while Ppard was highly expressed in myofibroblasts, suggesting that PPARδ has a role in myofibroblast differentiation. In conclusion, these data provide strong evidence that PPARγ and possibly PPARα represent key tumor suppressors by acting as master inhibitors of the inflammatory changes found in AKs and SCCs.

The cytokine Meteorin-like inhibits anti-tumor CD8+ T cell responses by disrupting mitochondrial function

Tumor-infiltrating lymphocyte (TIL) hypofunction contributes to the progression of advanced cancers and is a frequent target of immunotherapy. Emerging evidence indicates that metabolic insufficiency drives Tcell hypofunction during tonic stimulation, but the signals that initiate metabolic reprogramming in this context are largely unknown. Here, we found that Meteorin-like (METRNL), a metabolically active cytokine secreted by immune cells in the tumor microenvironment (TME), induced bioenergetic failure of CD8+ Tcells. METRNL was secreted by CD8+ Tcells during repeated stimulation and acted via both autocrine and paracrine signaling. Mechanistically, METRNL increased E2F-peroxisome proliferator-activated receptor delta (PPARδ) activity, causing mitochondrial depolarization and decreased oxidative phosphorylation, which triggered a compensatory bioenergetic shift to glycolysis. Metrnl ablation or downregulation improved the metabolic fitness of CD8+ Tcells and enhanced tumor control in several tumor models, demonstrating the translational potential of targeting the METRNL-E2F-PPARδ pathway to support bioenergetic fitness of CD8+ TILs.

Effects of elafibranor on liver fibrosis and gut barrier function in a mouse model of alcohol-associated liver disease.

Alcohol-associated liver disease (ALD) is a leading cause of liver-related morbidity and mortality, but there are no therapeutic targets and modalities to prevent ALD-related liver fibrosis. Peroxisome proliferator activated receptor (PPAR) α and δ play a key role in lipid metabolism and intestinal barrier homeostasis, which are major contributors to the pathological progression of ALD. Meanwhile, elafibranor (EFN), which is a dual PPARα and PPARδ agonist, has reached a phase III clinical trial for the treatment of metabolic dysfunction-associated steatotic liver disease and primary biliary cholangitis. However, the benefits of EFN for ALD treatment is unknown. To evaluate the inhibitory effects of EFN on liver fibrosis and gut-intestinal barrier dysfunction in an ALD mouse model. ALD-related liver fibrosis was induced in female C57BL/6J mice by feeding a 2.5% ethanol (EtOH)-containing Lieber-DeCarli liquid diet and intraperitoneally injecting carbon tetrachloride thrice weekly (1 mL/kg) for 8 weeks. EFN (3 and 10 mg/kg/day) was orally administered during the experimental period. Histological and molecular analyses were performed to assess the effect of EFN on steatohepatitis, fibrosis, and intestinal barrier integrity. The EFN effects on HepG2 lipotoxicity and Caco-2 barrier function were evaluated by cell-based assays. The hepatic steatosis, apoptosis, and fibrosis in the ALD mice model were significantly attenuated by EFN treatment. EFN promoted lipolysis and β-oxidation and enhanced autophagic and antioxidant capacities in EtOH-stimulated HepG2 cells, primarily through PPARα activation. Moreover, EFN inhibited the Kupffer cell-mediated inflammatory response, with blunted hepatic exposure to lipopolysaccharide (LPS) and toll like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling. EFN improved intestinal hyperpermeability by restoring tight junction proteins and autophagy and by inhibiting apoptosis and proinflammatory responses. The protective effect on intestinal barrier function in the EtOH-stimulated Caco-2 cells was predominantly mediated by PPARδ activation. EFN reduced ALD-related fibrosis by inhibiting lipid accumulation and apoptosis, enhancing hepatocyte autophagic and antioxidant capacities, and suppressing LPS/TLR4/NF-κB-mediated inflammatory responses by restoring intestinal barrier function.

Activation of PPARδ in bone marrow endothelial progenitor cells improves their hematopoiesis-supporting ability after myelosuppressive injury

Dysfunctional bone marrow (BM) endothelial progenitor cells (EPCs) with high levels of reactive oxygen species (ROS) are responsible for defective hematopoiesis in poor graft function (PGF) patients with acute leukemia or myelodysplastic neoplasms post-allotransplant. However, the underlying mechanism by which BM EPCs regulate their intracellular ROS levels and the capacity to support hematopoiesis have not been well clarified. Herein, we demonstrated decreased levels of peroxisome proliferator-activated receptor delta (PPARδ), a lipid-activated nuclear receptor, in BM EPCs of PGF patients compared with those with good graft function (GGF). In vitro assays further identified that PPARδ knockdown contributed to reduced and dysfunctional BM EPCs, characterized by the impaired ability to support hematopoiesis, which were restored by PPARδ overexpression. Moreover, GW501516, an agonist of PPARδ, repaired the damaged BM EPCs triggered by 5-fluorouracil (5FU) in vitro and in vivo. Clinically, activation of PPARδ by GW501516 benefited the damaged BM EPCs from PGF patients or acute leukemia patients in complete remission (CR) post-chemotherapy. Mechanistically, we found that increased expression of NADPH oxidases (NOXs), the main ROS-generating enzymes, may lead to elevated ROS level in BM EPCs, and insufficient PPARδ may trigger BM EPC damage via ROS/p53 pathway. Collectively, we found that defective PPARδ contributes to BM EPC dysfunction, whereas activation of PPARδ in BM EPCs improves their hematopoiesis-supporting ability after myelosuppressive therapy, which may provide a potential therapeutic target not only for patients with leukemia but also for those with other cancers.

PPARδ agonist protects against osteoarthritis by activating AKT/mTOR signaling pathway-mediated autophagy.

Osteoarthritis (OA) is the most prevalent degenerative joint disease, and PPARs are involved in its pathogenesis; however, the specific mechanisms by which changes in PPARδ impact the OA pathogenesis yet to be discovered. The purpose of this study was to ascertain how PPARδ affects the onset and development of OA. In vitro, we found that PPARδ activation ameliorated apoptosis and extracellular matrix (ECM) degradation in OA chondrocytes stimulated by IL-1β. In addition, PPARδ activation may modulate AKT/mTOR signaling to partially regulate chondrocyte autophagy and apoptosis. In vivo, injection of PPARδ agonist into the articular cavity improved ECM degradation, apoptosis and autophagy in rats OA models generated by destabilization medial meniscus (DMM), eventually delayed degeneration of articular cartilage. Thus, targeting PPARδ for OA treatment may be a possibility.

High-Fat Diet Induced PPARδ Promotes Self-renewal of Preleukemic Progenitors in Development of Acute Promyelocytic Leukemia.

From risk association between acute promyelocytic leukemia (APL) and obese-overweight individuals, Mazzarella and colleagues hypothesized that a high-fat diet (HFD) promotes development of APL. Using mouse APL model (PML-RARα knock-in), the authors demonstrated that linoleic acid drives activation of PPARδ in hematopoietic progenitors, and that activation of PPARδ increases proliferation of progenitor cells with PML-RARA expression toward APL. Involvements of PPARδ on regulation of stem cell renewal and proliferation were shown in colorectal cancers earlier, but this study newly demonstrates in hematopoietic progenitors, while suggesting use of diet rich in linoleic acid with caution. See related article by Mazzarella et al., p. 59.

Highly potent and selective PPARδ agonist reverses memory deficits in mouse models of Alzheimer's disease.

Rationale: Alzheimer's disease (AD) is a progressive neurodegenerative disease accompanied by neurotoxicity, excessive inflammation, and cognitive impairment. The peroxisome proliferator-activated receptor (PPAR) δ is a potential target for AD. However, its regulatory mechanisms and therapeutic potential in AD remain unclear. We aimed to investigate if the activation of PPARδ using a highly selective and potent agonist could provide an effective therapeutic strategy against AD. Methods: We synthesized a novel PPARδ agonist, 5a, containing a selenazole group and determined the X-ray crystal structure of its complex with PPARδ. The drug-like properties of 5a were assessed by analyzing cytochrome P450 (CYP) inhibition, microsomal stability, pharmacokinetics, and mutagenicity. We investigated the anti-inflammatory effects of 5a using lipopolysaccharide (LPS)-stimulated BV-2 microglia and neuroinflammatory mouse model. The therapeutic efficacy of 5a was evaluated in AD mice with scopolamine-induced memory impairment and APP/PS1 by analyzing cognitive function, glial reactivity, and amyloid pathology. Results: Compound 5a, the most potent and selective PPARδ agonist, was confirmed to bind hPPARδ in a complex by X-ray crystallographic analysis. PPARδ activation using 5a showed potent anti-inflammatory effects in activated glial cells and mouse model of neuroinflammation. Administration of 5a inhibited amyloid plaque deposition by suppressing the expression of neuronal beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), and reduced abnormal glial hyperactivation and inflammatory responses, resulting in improved learning and memory in the APP/PS1 mouse model of AD. Conclusion: We identified that specific activation of PPARδ provides therapeutic effects on multiple pathogenic phenotypes of AD, including neuroinflammation and amyloid deposition. Our findings suggest the potential of PPARδ as a promising drug target for treating AD.

Exercise alleviates diabetic kidney disease through PPARδ-CPT1α pathway-dependent fatty acid β-oxidation

<p>Diabetic kidney disease (DKD), a severe diabetic complication affecting approximately one-third of diabetic patients, is the leading cause of end-stage chronic kidney disease. The benefits of regular exercise for patients with DKD have been well documented, particularly in overweight patients with DKD. However, the underlying mechanisms are incompletely understood. The present study demonstrates that exercise improves kidney function in diabetic <i>db/db</i> mice through activating PPARδ-mediated fatty acid β-oxidation (FAO). Twelve-week treadmill running exercise improved kidney function in <i>db/db</i> mice. Metabolomics and transcriptomics profiling analysis collectively revealed that dysregulation of FAO in <i>db/db</i> mice was largely corrected by running exercise. KEGG pathway enrichment revealed that PPAR pathway, a critical signalling cascade in FAO and exercise, is involved in DKD, suggesting PPARδ activation protects renal function through promoting FAO. Which was confirmed by improved renal function and enhanced FAO in <i>db/db</i> mice treated with PPARδ agonist GW501516. Oppositely, PPARδ-specific inhibitor GSK0660 abolished exercise-mediated improvement in renal function and FAO. In combining with gene expression profiling data we identified CPT1α, the rate-limiting enzyme in fatty acid oxidation, was suppressed in the kidney of diabetic mice and reversed by exercise and the PPARδ agonist GW501516. The findings hint at a potential role for the PPARδ-CPT1α pathway in exercise-induced improvements in diabetic renal function and may warrant further exploration of the PPARδ-CPT1α pathway as a therapeutic target in DKD.</p>

GW501516 (Cardarine): Pharmacological and Clinical Effects

GW501516/Cardarine is a nuclear hormone that activates the PPARδ genes involved in cell differentiation and exerts a primary regulation in maintaining health conditions and preventing diseases. PPARδ activation stimulates the mitochondrial function in various tissues improving lipid metabolism and energy homeostasis. PPARδ receptors are expressed mainly in active metabolic tissues such as skeletal muscles, the heart, the liver, and neurons. PPARδ activation increases fatty acid oxidation, saving glycogen stores, so they find indications for the treatment of metabolic diseases, especially dyslipidemia and type-2 diabetes mellitus (T2DM), and hypertriglyceridemia. The pancreatic β-cell function is improved. In the heart, PPARδ improves cardiomyocytes function and reduces fibrosis. In the liver, it reduces the fat deposit, suppressing inflammation. Cardarine seems to be effective in preventing β-amyloid deposition and Alzheimer’s disease. In the skeletal muscles, cardarine induces a strong activation of mitochondrial biogenesis, increasing oxidative muscle capacity and endurance exercise capacity, and for this reason, it was included in the list of doping agents by WADA. However, some controversies on cancer risk stimulation exist. This review aims to evaluate the clinical benefits and side effects of GW501516/ cardarine.

A tau fragment links depressive-like behaviors and cognitive declines in Alzheimer's disease mouse models through attenuating mitochondrial function.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease characterized by extracellular senile plaques including amyloid-β peptides and intracellular neurofibrillary tangles consisting of abnormal Tau. Depression is one of the most common neuropsychiatric symptoms in AD, and clinical evidence demonstrates that depressive symptoms accelerate the cognitive deficit of AD patients. However, the underlying molecular mechanisms of depressive symptoms present in the process of AD remain unclear. Depressive-like behaviors and cognitive decline in hTau mice were induced by chronic restraint stress (CRS). Computational prediction and molecular experiments supported that an asparagine endopeptidase (AEP)-derived Tau fragment, Tau N368 interacts with peroxisome proliferator-activated receptor delta (PPAR-δ). Further behavioral studies investigated the role of Tau N368-PPAR-δ interaction in depressive-like behaviors and cognitive declines of AD models exposed to CRS. We found that mitochondrial dysfunction was positively associated with depressive-like behaviors and cognitive deficits in hTau mice. Chronic stress increased Tau N368 and promoted the interaction of Tau N368 with PPAR-δ, repressing PPAR-δ-mediated transactivation in the hippocampus of mice. Then we predicted and identified the binding sites of PPAR-δ. Finally, inhibition of AEP, clearance of Tau N368 and pharmacological activation of PPAR-δ effectively alleviated CRS-induced depressive-like behaviors and cognitive decline in mice. These results demonstrate that Tau N368 in the hippocampus impairs mitochondrial function by suppressing PPAR-δ, facilitating the occurrence of depressive-like behaviors and cognitive decline. Therefore, our findings may provide new mechanistic insight in the pathophysiology of depression-like phenotype in mouse models of Alzheimer's disease.

Fisetin, a dietary flavonoid, promotes transintestinal cholesterol excretion through the activation of PPARδ

Fisetin, a dietary polyphenol abundantly found in strawberries, exhibits a broad spectrum of health-promoting activities, including antihyperlipidemic effects. This study aimed to investigate the regulatory effect of fisetin on cholesterol elimination through novel transintestinal cholesterol excretion (TICE) pathway. A hypercholesterolemic mouse model and human colon epithelial cancer cell line Caco-2 were utilized to conduct the study. In hypercholesterolemic mice, fisetin (25 mg/kg) treatment reduced serum total cholesterol by 46.48% and significantly decreased lipid accumulation in the liver. Furthermore, fisetin administration led to a substantial increase in the fecal neutral sterol contents, including coprostanol, coprostanone, dihydrocholesterol, and cholesterol. Specifically, these sterol contents increased by approximately 224.20%, 151.40%, 70.40% and 50.72% respectively. The fluorescence intensity of 22-NBD-cholesterol in intestinal perfusion increased by 95.94% in fisetin group (25 mg/kg), indicating that fisetin stimulated TICE. In high cholesterol-induced Caco-2 cells, fisetin at a concentration of 30 μM reduced total cholesterol and free cholesterol by 37.21% and 45.30% respectively, stimulated cholesterol excretion, and inhibited cholesterol accumulation. Additionally, fisetin upregulated the gene and protein expression of cholesterol efflux transporters ABCG5/G8 and ABCB1, while downregulating the cholesterol uptake regulator NPC1L1. Furthermore, fisetin increased LDLR protein expression and decreased PCSK9 expression. Notably, fisetin significantly activated nuclear receptor PPARδ in Caco-2 cells. PPARδ antagonist pretreatment counteracted the regulatory effects of fisetin on TICE regulators, suggesting fisetin lowered cholesterol through enhancing TICE by activation of intestinal PPARδ. Fisetin could be used as functional dietarysupplement for eliminating cholesterol and reducing the incidence of cardiovascular diseases.

PPARδ activation improves cardiac mitochondrial homeostasis in desmin deficient mice but does not alleviate systolic dysfunction

Peroxisome proliferator-activated receptor (PPAR) δ is a major transcriptional regulator of cardiac energy metabolism with pleiotropic properties, including anti-inflammatory, anti-oxidative and cardioprotective action. In this study, we sought to investigate whether pharmacological activation of PPARδ via intraperitoneal administration of the selective ligand GW0742 could ameliorate heart failure and mitochondrial dysfunction that have been previously reported in a characterized genetic model of heart failure, the desmin null mice (Des−/−). Our studies demonstrate that treatment of Des−/− mice with the PPARδ agonist attenuated cardiac inflammation, fibrosis and cardiac remodeling. In addition, PPARδ activation alleviated oxidative stress in the failing myocardium as evidenced by decreased ROS levels. Importantly, PPARδ activation stimulated mitochondrial biogenesis, prevented mitochondrial and sarcoplasmic reticulum vacuolar degeneration and improved the mitochondrial intracellular distribution. Finally, PPARδ activation alleviated the mitochondrial respiratory dysfunction, prevented energy depletion and alleviated excessive autophagy and mitophagy in Des−/− hearts. Nevertheless, improvement of all these parameters did not suffice to overcome the significant structural deficiencies that desmin deletion incurs in cardiomyocytes and cardiac function did not improve significantly. In conclusion, pharmacological PPARδ activation in Des−/− hearts exerts protective effects during myocardial degeneration and heart failure by preserving the function and quality of the mitochondrial network. These findings implicate PPARδ agonists as a supplemental constituent of heart failure medications.

Berberine activates PPARδ and promotes gut microbiota-derived butyric acid to suppress hepatocellular carcinoma

BackgroundPeroxisome proliferator-activated receptors (PPARs) are a family of ligand-inducible transcription factors that govern various essential metabolic activities in the liver and other organs. Recently, berberine (BBR) has been characterized as a modulator of PPARs; however, the matter of whether PPARs are involved in the inhibitory effect of BBR on hepatocellular carcinoma (HCC) is not well understood. PurposeThis study aimed to investigate the role of PPARs in the suppressive effect of BBR on HCC and to elucidate the relative mechanism. MethodsWe studied the role of PPARs in the anti-HCC effects of BBR both in vitro and in vivo. The mechanism whereby BBR regulated PPARs was studied using real-time PCR, immunoblotting, immunostaining, luciferase, and a chromatin immunoprecipitation coupled PCR assay. Additionally, we used adeno-associated virus (AAV)-mediated gene knockdown to address the effect of BBR more effectively. ResultsWe demonstrated that PPARδ played an active role in the anti-HCC effect of BBR, rather than PPARα or PPARγ. Following a PPARδ-dependent manner, BBR increased BAX, cleaved Caspase 3, and decreased BCL2 expression to trigger apoptotic death, thereby suppressing HCC development both in vitro and in vivo. It was noted that the interactions between PPARδ and the apoptotic pathway resulted from the BBR-induced upregulation of the PPARδ transcriptional function; that is, the BBR-induced activation of PPARδ could mediate the binding with the promoters of apoptotic genes such as Caspase 3, BAX, and BCL2. Moreover, gut microbiota also contributed to the suppressive effect of BBR on HCC. We found that BBR treatment restored the dysregulated gut microbiota induced by the liver tumor burden, and a functional gut microbial metabolite, butyric acid (BA), acted as a messenger in the gut microbiota-liver axis. Unlike BBR, the effects of BA suppressing HCC and activating PPARδ were not potent. However, BA was able to enhance the efficacy of BBR by reducing PPARδ degradation through a mechanism to inhibit the proteasome ubiquitin system. Additionally, we found that the anti-HCC effect of BBR or a combination of BBR and BA was much weaker in mice with AAV-mediated PPARδ knockdown than those in the control mice, suggesting the critical role of PPARδ. ConclusionIn summary, this study is the first to report that a liver-gut microbiota-PPARδ trilogy contributes to the anti-HCC effect of BBR. BBR not only directly activated PPARδ to trigger apoptotic death but also promoted gut microbiota-derived BA production, which could reduce PPARδ degradation to enhance the efficacy of BBR.

Peroxisome proliferator-activated receptor δ improves the features of atherosclerotic plaque vulnerability by regulating smooth muscle cell phenotypic switching.

Vascular smooth muscle cells (SMCs) undergo phenotypic switching during sustained inflammation, contributing to an unfavourable atherosclerotic plaque phenotype. PPARδ plays an important role in regulating SMC functions; however, its role in atherosclerotic plaque vulnerability remains unclear. Here, we explored the pathological roles of PPARδ in atherosclerotic plaque vulnerability in severe atherosclerosis and elucidated the underlying mechanisms. Plasma levels of PPARδ were measured in patients with acute coronary syndrome (ACS) and stable angina (SA). SMC contractile and synthetic phenotypic markers, endoplasmic reticulum (ER) stress, and features of atherosclerotic plaque vulnerability were analysed for the brachiocephalic artery of apolipoprotein E-knockout (ApoE-/- ) mice, fed a high-cholesterol diet (HCD) and treated with or without the PPARδ agonist GW501516. In vitro, the role of PPARδ was elucidated using human aortic SMCs (HASMCs). Patients with ACS had significantly lower plasma PPARδ levels than those with SA. GW501516 reduced atherosclerotic plaque vulnerability, a synthetic SMC phenotype, ER stress markers, and NLRP3 inflammasome expression in HCD-fed ApoE-/- mice. ER stress suppressed PPARδ expression in HASMCs. PPARδ activation inhibited ER stress-induced synthetic phenotype development, ER stress-NLRP3 inflammasome axis activation and matrix metalloproteinase 2 (MMP2) expression in HASMCs. PPARδ inhibited NFκB signalling and alleviated ER stress-induced SMC phenotypic switching. Low plasma PPARδ levels may be associated with atherosclerotic plaque vulnerability. Our findings provide new insights into the mechanisms underlying the protective effect of PPARδ on SMC phenotypic switching and improvement the features of atherosclerotic plaque vulnerability.

THE ROLE OF PPARδ-DRIVEN β-OXIDATION IN BONE HEALTH DURING AGING

Abstract Musculoskeletal disorders are a significant complication of aging, leading to increased morbidity and mortality. However, current understanding of the mechanisms by which aging affects skeletal health is limited. Osteocytes are the most numerous and long-lived bone cells and play key roles in maintaining bone mass by responding to anabolic signals such as mechanical loading. Energy metabolism is dysregulated in many cells with aging, however regulation of energy metabolism in osteocytes and how this is affected during aging and by mechanical loading remains undefined. To investigate this, we first used IDG-SW3 osteocyte cells to determine the effects of mechanical loading on osteocytes in vitro by applying fluid flow shear stress (FFSS). FFSS increased Pparδ and Cpt1 expression, key promoters of fatty acid β-oxidation (FAO). Pharmacological antagonism of PPARδ or CPT1 resulted in dysregulated expression of key bone remodeling genes and impaired ATP release in response to FFSS. In vivo, mechanical loading significantly increased FAO in tibia cortical bone. However, FAO was impaired in the bones from aged mice. To further elucidate the role of osteocyte FAO, we deleted PPARδ specifically in osteocytes (PPARδ cKO), which resulted in decreased FAO and bone volume in female PPARδ cKO mice. Lastly, treatment of aging mice with the PPARδ activator GW0742 resulted in significantly increased bone mineral content, density and trabecular bone volume. These findings suggest important functions of osteocyte energy metabolism during aging and with mechanical loading on bone and identify PPARδ-driven FAO as a novel therapeutic target for improving skeletal health with aging.

Rapid acceleration of KRAS-mutant pancreatic carcinogenesis via remodeling of tumor immune microenvironment by PPARδ

Pancreatic intraepithelial neoplasia (PanIN) is a precursor of pancreatic ductal adenocarcinoma (PDAC), which commonly occurs in the general populations with aging. Although most PanIN lesions (PanINs) harbor oncogenic KRAS mutations that initiate pancreatic tumorigenesis; PanINs rarely progress to PDAC. Critical factors that promote this progression, especially targetable ones, remain poorly defined. We show that peroxisome proliferator-activated receptor-delta (PPARδ), a lipid nuclear receptor, is upregulated in PanINs in humans and mice. Furthermore, PPARδ ligand activation by a high-fat diet or GW501516 (a highly selective, synthetic PPARδ ligand) in mutant KRASG12D (KRASmu) pancreatic epithelial cells strongly accelerates PanIN progression to PDAC. This PPARδ activation induces KRASmu pancreatic epithelial cells to secrete CCL2, which recruits immunosuppressive macrophages and myeloid-derived suppressor cells into pancreas via the CCL2/CCR2 axis to orchestrate an immunosuppressive tumor microenvironment and subsequently drive PanIN progression to PDAC. Our data identify PPARδ signaling as a potential molecular target to prevent PDAC development in subjects harboring PanINs.

PPARδ Activation Mitigates 6-OHDA-Induced Neuronal Damage by Regulating Intracellular Iron Levels.

Intracellular iron accumulation in dopaminergic neurons contributes to neuronal cell death in progressive neurodegenerative disorders such as Parkinson’s disease. However, the mechanisms of iron homeostasis in this context remain incompletely understood. In the present study, we assessed the role of the nuclear receptor peroxisome proliferator-activated receptor δ (PPARδ) in cellular iron homeostasis. We identified that PPARδ inhibited 6-hydroxydopamine (6-OHDA)-triggered neurotoxicity in SH-SY5Y neuroblastoma cells. PPARδ activation with GW501516, a specific PPARδ agonist, mitigated 6-OHDA-induced neuronal damage. Further, PPARδ activation also suppressed iron accumulation, which contributes to 6-OHDA-induced neuronal damage. PPARδ activation attenuated 6-OHDA-induced neuronal damage in a similar manner to that of the iron chelator deferoxamine. We further elucidated that PPARδ modulated cellular iron homeostasis by regulating expression of divalent metal transporter 1, ferroportin 1, and ferritin, but not transferrin receptor 1, through iron regulatory protein 1 in 6-OHDA-treated cells. Interestingly, PPARδ activation suppressed 6-OHDA-triggered generation of reactive oxygen species and lipid peroxides. The effects of GW501516 were abrogated by shRNA knockdown of PPARδ, indicating that the effects of GW501516 were PPARδ-dependent. Taken together, these findings suggest that PPARδ attenuates 6-OHDA-induced neurotoxicity by preventing intracellular iron accumulation, thereby suppressing iron overload-associated generation of reactive oxygen species and lipid peroxides, key mediators of ferroptotic cell death.

Endothelial PPARδ facilitates the post-ischemic vascular repair through interaction with HIF1α.

Rationale: Restoration of vascular perfusion in peripheral arterial disease involves a combination of neovessel formation and the functional restoration of vascular endothelium. Previous studies indicated that ligand-dependent PPARδ activation enhances angiogenesis. However, how PPARδ is triggered by hypoxia and its downstream effects during post-ischemic vascular repair was not well understood.Methods: We induced experimental hindlimb ischemia in endothelial cell selective Ppard knockout induced by Cdh5-Cre mediated deletion of floxed Ppard allele in mice and their wild type control and observed blood perfusion, capillary density, vascular relaxation, and vascular leakage.Results: Deletion of endothelial Ppard delayed perfusion recovery and tissue repair, accompanied by delayed post-ischemic angiogenesis, impaired restoration of vascular integrity, more vascular leakage and enhanced inflammatory responses. At the molecular level, hypoxia upregulated and activated PPARδ in endothelial cells, whereas PPARδ reciprocally stabilized HIF1α protein to prevent its ubiquitin-mediated degradation. PPARδ directly bound to the oxygen-dependent degradation domain of HIF1α at the ligand-dependent domain of PPARδ. Importantly, this HIF1α-PPARδ interaction was independent of PPARδ ligand. Adeno-associated virus mediated endothelium-targeted overexpression of stable HIF1α in vivo improved perfusion recovery, suppressed vascular inflammation, and enhanced vascular repair, to counteract with the effect of Ppard knockout after hindlimb ischemia in mice.Conclusions: In summary, hypoxia-induced, ligand-independent activation of PPARδ in ECs stabilizes HIF1α and serves as a critical regulator for HIF1α activation to facilitate the post-ischemic restoration of vascular homeostasis.