Mitochondrial-derived microprotein MOTS-c attenuates immobilization-induced skeletal muscle atrophy by suppressing lipid infiltration.

Mitochondrial open reading frame of the 12S ribosomal RNA type-c (MOTS-c), a mitochondrial microprotein, has been described as a novel regulator of glucose and lipid metabolism. In addition to its role as a metabolic regulator, MOTS-c prevents skeletal muscle atrophy in high fat-fed mice. Here, we examined the preventive effect of MOTS-c on skeletal muscle mass, using an immobilization-induced muscle atrophy model, and explored its underlying mechanisms. Male C57BL/6J mice (10 wk old) were randomly assigned to one of the three experimental groups: nonimmobilization control group (sterilized water injection), immobilization control group (sterilized water injection), and immobilization and MOTS-c-treated group (15 mg/kg/day MOTS-c injection). We used casting tape for the immobilization experiment. After 8 days of the experimental period, skeletal muscle samples were collected and used for Western blotting, RNA sequencing, and lipid and collagen assays. Immobilization reduced ∼15% of muscle mass, whereas MOTS-c treatment attenuated muscle loss, with only a 5% reduction. MOTS-c treatment also normalized phospho-AKT, phospho-FOXO1, and phospho-FOXO3a expression levels and reduced circulating inflammatory cytokines, such as interleukin-1b (IL-1ß), interleukin-6 (IL-6), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1), in immobilized mice. Unbiased RNA sequencing and its downstream analyses demonstrated that MOTS-c modified adipogenesis-modulating gene expression within the peroxisome proliferator-activated receptor (PPAR) pathway. Supporting this observation, muscle fatty acid levels were lower in the MOTS-c-treated group than in the casted control mice. These results suggest that MOTS-c treatment inhibits skeletal muscle lipid infiltration by regulating adipogenesis-related genes and prevents immobilization-induced muscle atrophy.NEW & NOTEWORTHY MOTS-c, a mitochondrial microprotein, attenuates immobilization-induced skeletal muscle atrophy. MOTS-c treatment improves systemic inflammation and skeletal muscle AKT/FOXOs signaling pathways. Furthermore, unbiased RNA sequencing and subsequent assays revealed that MOTS-c prevents lipid infiltration in skeletal muscle. Since lipid accumulation is one of the common pathologies among other skeletal muscle atrophies induced by aging, obesity, cancer cachexia, and denervation, MOTS-c treatment could be effective in other muscle atrophy models as well.

Fat and proteolysis due to methionine, tryptophan, and niacin deficiency leads to alterations in gut microbiota and immune modulation in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is one of the intractable diseases. Nutritional components associated with IBD have been identified, and it is known that excessive methionine intake exacerbates inflammation, and that tryptophan metabolism is involved in inflammation. Analysis of the gut microbiota has also progressed, where Lactobacillus regulate immune cells in the intestine and suppress inflammation. However, whether the methionine and tryptophan metabolic pathways affect the growth of intestinal Lactobacillus is unknown. Here we show how transient methionine, tryptophan, and niacin deficiency affects the host and gut microbiota in mouse models of colitis (induced by dextran sodium sulfate) fed a methionine-deficient diet (1K), tryptophan and niacin-deficient diet (2K), or methionine, tryptophan, and niacin-deficient diet (3K). These diets induced body weight decrease and 16S rRNA analysis of mouse feces revealed the alterations in the gut microbiota, leading to a dramatic increase in the proportion of Lactobacillus in mice. Intestinal RNA sequencing data confirmed that the expression of several serine proteases and fat-metabolizing enzymes were elevated in mice fed with methionine, tryptophan, and niacin (MTN) deficient diet. In addition, one-carbon metabolism and peroxisome proliferator-activated receptor (PPAR) pathway activation were also induced with MTN deficiency. Furthermore, changes in the expression of various immune-related cytokines were observed. These results indicate that methionine, tryptophan, and niacin metabolisms are important for the composition of intestinal bacteria and host immunity. Taken together, MTN deficiencies may serve as a Great Reset of gut microbiota and host gene expression to return to good health.

Impact of pemafibrate on lipid profile and insulin resistance in hypertriglyceridemic patients with coronary artery disease and metabolic syndrome.

This study examined the effects of pemafibrate, a selective peroxisome proliferator-activated receptor α agonist, on the serum biochemical parameters of male patients with coronary artery disease and metabolic syndrome (MetS). This was a post hoc analysis of a randomized, crossover study that treated hypertriglyceridemia with pemafibrate or bezafibrate for 24 weeks, followed by a crossover of another 24 weeks. Of the 60 patients enrolled in the study, 55 were male. Forty-one of 55 male patients were found to have MetS. In this sub-analysis, male patients with MetS (MetS group, n = 41) and those without MetS (non-MetS group, n = 14) were compared. The primary endpoint was a change in fasting serum triglyceride (TG) levels during pemafibrate therapy, and the secondary endpoints were changes in insulin resistance-related markers and liver function parameters. Serum TG levels significantly decreased (MetS group, from 266.6 to 148.0 mg/dL, p < 0.001; non-MetS group, from 203.9 to 97.6 mg/dL, p < 0.001); however, a percent change (%Change) was not significantly different between the groups (- 44.1% vs. - 51.6%, p = 0.084). Serum insulin levels and homeostasis model assessment of insulin resistance significantly decreased in the MetS group but not in the non-MetS group. %Change in liver enzyme levels was markedly decreased in the MetS group compared with that in the non-MetS group (alanine aminotransferase, - 25.1% vs. - 11.3%, p = 0.027; gamma-glutamyl transferase, - 45.8% vs. - 36.2%, p = 0.020). In conclusion, pemafibrate can effectively decrease TG levels in patients with MetS, and it may be a more efficient drug for improving insulin resistance and liver function in such patients.

Misalignment of Circadian Rhythms in Diet-Induced Obesity.

The biological clocks of the circadian timing system coordinate cellular and physiological processes and synchronize them with daily cycles. While the central clock in the suprachiasmatic nucleus (SCN) is mainly synchronized by the light/dark cycles, the peripheral clocks react to other stimuli, including the feeding/fasting state, nutrients, sleep-wake cycles, and physical activity. During the disruption of circadian rhythms due to genetic mutations or social and occupational obligations, incorrect arrangement between the internal clock system and environmental rhythms leads to the development of obesity. Desynchronization between the central and peripheral clocks by altered timing of food intake and diet composition leads to uncoupling of the peripheral clocks from the central pacemaker and to the development of metabolic disorders. The strong coupling of the SCN to the light-dark cycle creates a situation of misalignment when food is ingested during the "wrong" time of day. Food-anticipatory activity is mediated by a self-sustained circadian timing, and its principal component is a food-entrainable oscillator. Modifying the time of feeding alone greatly affects body weight, whereas ketogenic diet (KD) influences circadian biology, through the modulation of clock gene expression. Night-eating behavior is one of the causes of circadian disruption, and night eaters have compulsive and uncontrolled eating with severe obesity. By contrast, time-restricted eating (TRE) restores circadian rhythms through maintaining an appropriate daily rhythm of the eating-fasting cycle. The hypothalamus has a crucial role in the regulation of energy balance rather than food intake. While circadian locomotor output cycles kaput (CLOCK) expression levels increase with high-fat diet-induced obesity, peroxisome proliferator-activated receptor-alpha (PPARα) increases the transcriptional level of brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like 1 (BMAL1) in obese subjects. In this context, effective timing of chronotherapies aiming to correct SCN-driven rhythms depends on an accurate assessment of the SCN phase. In fact, in a multi-oscillator system, local rhythmicity and its disruption reflects the disruption of either local clocks or central clocks, thus imposing rhythmicity on those local tissues, whereas misalignment of peripheral oscillators is due to exosome-based intercellular communication.Consequently, disruption of clock genes results in dyslipidemia, insulin resistance, and obesity, while light exposure during the daytime, food intake during the daytime, and sleeping during the biological night promote circadian alignment between the central and peripheral clocks. Thus, shift work is associated with an increased risk of obesity, diabetes, and cardiovascular diseases because of unusual eating times as well as unusual light exposure and disruption of the circadian rhythm.

RAR Inhibitors Display Photo-Protective and Anti-Inflammatory Effects in A2E Stimulated RPE Cells In Vitro through Non-Specific Modulation of PPAR or RXR Transactivation.

N-retinylidene-N-retinylethanolamine (A2E) has been associated with age-related macular degeneration (AMD) physiopathology by inducing cell death, angiogenesis and inflammation in retinal pigmented epithelial (RPE) cells. It was previously thought that the A2E effects were solely mediated via the retinoic acid receptor (RAR)-α activation. However, this conclusion was based on experiments using the RAR "specific" antagonist RO-41-5253, which was found to also be a ligand and partial agonist of the peroxisome proliferator-activated receptor (PPAR)-γ. Moreover, we previously reported that inhibiting PPAR and retinoid X receptor (RXR) transactivation with norbixin also modulated inflammation and angiogenesis in RPE cells challenged in the presence of A2E. Here, using several RAR inhibitors, we deciphered the respective roles of RAR, PPAR and RXR transactivations in an in vitro model of AMD. We showed that BMS 195614 (a selective RAR-α antagonist) displayed photoprotective properties against toxic blue light exposure in the presence of A2E. BMS 195614 also significantly reduced the AP-1 transactivation and mRNA expression of the inflammatory interleukin (IL)-6 and vascular endothelial growth factor (VEGF) induced by A2E in RPE cells in vitro, suggesting a major role of RAR in these processes. Surprisingly, however, we showed that (1) Norbixin increased the RAR transactivation and (2) AGN 193109 (a high affinity pan-RAR antagonist) and BMS 493 (a pan-RAR inverse agonist), which are photoprotective against toxic blue light exposure in the presence of A2E, also inhibited PPARs transactivation and RXR transactivation, respectively. Therefore, in our in vitro model of AMD, several commercialized RAR inhibitors appear to be non-specific, and we propose that the phototoxicity and expression of IL-6 and VEGF induced by A2E in RPE cells operates through the activation of PPAR or RXR rather than by RAR transactivation.

Roles of peroxisome proliferator-activated receptors in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC), the main pathological type of liver cancer, is linked to risk factors such as viral hepatitis, alcohol intake and non-alcoholic fatty liver disease (NAFLD). Recent advances have greatly improved our understanding that NAFLD is playing a major risk factor for HCC. Peroxisome proliferator-activated receptors (PPARs) are a class of transcription factors divided into three subtypes: PPARα (PPARA), PPARδ/ß (PPARD) and PPARγ (PPARG). As important nuclear receptors, PPARs are involved in many physiological processes, and PPARs can improve NAFLD by regulating lipid metabolism, accelerating fatty acid oxidation and inhibiting inflammation. In recent years, some studies have shown that PPARs can participate in the occurrence and development of HCC by regulating metabolic pathways. In addition, PPAR modulators have been reported to inhibit the proliferation and metastasis of HCC cells and can enhance the curative effect of conventional treatments. This article reviews the role of PPARs in the occurrence and development of HCC, as well as its value in the diagnosis, treatment and prognosis of HCC, in order to provide directions for future research.

UK-Wide Multicenter Evaluation of Second-line Therapies in Primary Biliary Cholangitis.

BACKGROUND & AIMS: Thirty-to-forty percent of patients with primary biliary cholangitis inadequately respond to ursodeoxycholic acid. Our aim was to assemble national, real-world data on the effectiveness of obeticholic acid (OCA) as a second-line treatment, alongside non-licensed therapy with fibric acid derivatives (bezafibrate or fenofibrate). METHODS: This was a nationwide observational cohort study conducted from August 2017 until June 2021. RESULTS: We accrued data from 457 patients; 349 treated with OCA and 108 with fibric acid derivatives. At baseline/pre-treatment, individuals in the OCA group manifest higher risk features compared with those taking fibric acid derivatives, evidenced by more elevated alkaline phosphatase values, and a larger proportion of individuals with cirrhosis, abnormal bilirubin, prior non-response to ursodeoxycholic acid, and elastography readings >9.6kPa (P < .05 for all). Overall, 259 patients (OCA) and 80 patients (fibric acid derivatives) completed 12 months of second-line therapy, yielding a dropout rate of 25.7% and 25.9%, respectively. At 12 months, the magnitude of alkaline phosphatase reduction was 29.5% and 56.7% in OCA and fibric acid groups (P < .001). Conversely, 55.9% and 36.4% of patients normalized serum alanine transaminase and bilirubin in the OCA group (P < .001). The proportion with normal alanine transaminase or bilirubin values in the fibric acid group was no different at 12 months compared with baseline. Twelve-month biochemical response rates were 70.6% with OCA and 80% under fibric acid treatment (P = .121). Response rates between treatment groups were no different on propensity-score matching or on sub-analysis of high-risk groups defined at baseline. CONCLUSION: Across the population of patients with primary biliary cholangitis in the United Kingdom, rates of biochemical response and drug discontinuation appear similar under fibric acid and OCA treatment.

Current Therapeutical Approaches Targeting Lipid Metabolism in NAFLD.

Nonalcoholic fatty liver disease (NAFLD, including nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH)) is a high-prevalence disorder, affecting about 1 billion people, which can evolve to more severe conditions like cirrhosis or hepatocellular carcinoma. NAFLD is often concomitant with conditions of the metabolic syndrome, such as central obesity and insulin-resistance, but a specific drug able to revert NAFL and prevent its evolution towards NASH is still lacking. With the liver being a key organ in metabolic processes, the potential therapeutic strategies are many, and range from directly targeting the lipid metabolism to the prevention of tissue inflammation. However, side effects have been reported for the drugs tested up to now. In this review, different approaches to the treatment of NAFLD are presented, including newer therapies and ongoing clinical trials. Particular focus is placed on the reverse cholesterol transport system and on the agonists for nuclear factors like PPAR and FXR, but also drugs initially developed for other conditions such as incretins and thyromimetics along with validated natural compounds that have anti-inflammatory potential. This work provides an overview of the different therapeutic strategies currently being tested for NAFLD, other than, or along with, the recommendation of weight loss.

Anti-Inflammatory Activity of Black Soldier Fly Oil Associated with Modulation of TLR Signaling: A Metabolomic Approach.

Dietary intervention in the treatment of ulcerative colitis involves, among other things, modifications in fatty acid content and/or profile. For example, replacing saturated long chain fatty acids with medium chain fatty acids (MCFAs) has been reported to ameliorate inflammation. The Black Soldier Fly Larvae's (BSFL) oil is considered a sustainable dietary ingredient rich in the MCFA C12:0; however, its effect on inflammatory-related conditions has not been studied until now. Thus, the present study aimed to investigate the anti-inflammatory activity of BSFL oil in comparison to C12:0 using TLR4- or TLR2-activated THP-1 and J774A.1 cell lines and to assess its putative protective effect against dextran sulfate sodium (DSS)-induced acute colitis in mice. BSFL oil and C12:0 suppressed proinflammatory cytokines release in LPS-stimulated macrophages; however, only BSFL oil exerted anti-inflammatory activity in Pam3CSK4-stimulated macrophages. Transcriptome analysis provided insight into the possible role of BSFL oil in immunometabolism switch, involving mTOR signaling and an increase in PPAR target genes promoting fatty acid oxidation, exhibiting a discrepant mode of action compared to C12:0 treatment, which mainly affected cholesterol biosynthesis pathways. Additionally, we identified anti-inflammatory eicosanoids, oxylipins, and isoprenoids in the BSFL oil that may contribute to an orchestrated anti-inflammatory response. In vivo, a BSFL oil-enriched diet (20%) ameliorated the clinical signs of colitis, as indicated by improved body weight recovery, reduced colon shortening, reduced splenomegaly, and an earlier phase of secretory IgA response. These results indicate the novel beneficial use of BSFL oil as a modulator of inflammation.

Breast cancer-associated skeletal muscle mitochondrial dysfunction and lipid accumulation is reversed by PPARG.

The peroxisome proliferator-activated receptors (PPARs) have been previously implicated in the pathophysiology of skeletal muscle dysfunction in women with breast cancer (BC) and animal models of BC. This study investigated alterations induced in skeletal muscle by BC-derived factors in an in vitro conditioned media (CM) system and tested the hypothesis that BC cells secrete a factor that represses PPAR-γ (PPARG) expression and its transcriptional activity, leading to downregulation of PPARG target genes involved in mitochondrial function and other metabolic pathways. We found that BC-derived factors repress PPAR-mediated transcriptional activity without altering protein expression of PPARG. Furthermore, we show that BC-derived factors induce significant alterations in skeletal muscle mitochondrial function and lipid accumulation, which are rescued with exogenous expression of PPARG. The PPARG agonist drug rosiglitazone was able to rescue BC-induced lipid accumulation but did not rescue effects of BC-derived factors on PPAR-mediated transcription or mitochondrial function. These data suggest that BC-derived factors alter lipid accumulation and mitochondrial function via different mechanisms that are both related to PPARG signaling, with mitochondrial dysfunction likely being altered via repression of PPAR-mediated transcription, and lipid accumulation being altered via transcription-independent functions of PPARG.

Liver-targeting drugs and their effect on blood glucose and hepatic lipids.

The global epidemic of non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) and the high prevalence among individuals with type 2 diabetes has attracted the attention of clinicians specialising in liver disorders. Many drugs are in the pipeline for the treatment of NAFLD/NASH, and several glucose-lowering drugs are now being tested specifically for the treatment of liver disease. Among these are nuclear hormone receptor agonists (e.g. peroxisome proliferator-activated receptor agonists, farnesoid X receptor agonists and liver X receptor agonists), fibroblast growth factor-19 and -21, single, dual or triple incretins, sodium-glucose cotransporter inhibitors, drugs that modulate lipid or other metabolic pathways (e.g. inhibitors of fatty acid synthase, diacylglycerol acyltransferase-1, acetyl-CoA carboxylase and 11ß-hydroxysteroid dehydrogenase type-1) or drugs that target the mitochondrial pyruvate carrier. We have reviewed the metabolic effects of these drugs in relation to improvement of diabetic hyperglycaemia and fatty liver disease, as well as peripheral metabolism and insulin resistance.

Cadmium-mediated lung injury is exacerbated by the persistence of classically activated macrophages.

Heavy metals released into the environment have a significant effect on respiratory health. Lung macrophages are important in mounting an inflammatory response to injury, but they are also involved in repair of injury. Macrophages develop mixed phenotypes in complex pathological conditions and polarize to a predominant phenotype depending on the duration and stage of injury and/or repair. Little is known about the reprogramming required for lung macrophages to switch between these divergent functions; therefore, understanding the mechanism(s) by which macrophages promote metabolic reprogramming to regulate lung injury is essential. Here, we show that lung macrophages polarize to a pro-inflammatory, classically activated phenotype after cadmium-mediated lung injury. Because metabolic adaptation provides energy for the diverse macrophage functions, these classically activated macrophages show metabolic reprogramming to glycolysis. RNA-Seq revealed up-regulation of glycolytic enzymes and transcription factors regulating glycolytic flux in lung macrophages from cadmium-exposed mice. Moreover, cadmium exposure promoted increased macrophage glycolytic function with enhanced extracellular acidification rate, glycolytic metabolites, and lactate excretion. These observations suggest that cadmium mediates the persistence of classically activated lung macrophages to exacerbate lung injury.

Bilirubin remodels murine white adipose tissue by reshaping mitochondrial activity and the coregulator profile of peroxisome proliferator-activated receptor α.

Activation of lipid-burning pathways in the fat-storing white adipose tissue (WAT) is a promising strategy to improve metabolic health and reduce obesity, insulin resistance, and type II diabetes. For unknown reasons, bilirubin levels are negatively associated with obesity and diabetes. Here, using mice and an array of approaches, including MRI to assess body composition, biochemical assays to measure bilirubin and fatty acids, MitoTracker-based mitochondrial analysis, immunofluorescence, and high-throughput coregulator analysis, we show that bilirubin functions as a molecular switch for the nuclear receptor transcription factor peroxisome proliferator-activated receptor α (PPARα). Bilirubin exerted its effects by recruiting and dissociating specific coregulators in WAT, driving the expression of PPARα target genes such as uncoupling protein 1 (Ucp1) and adrenoreceptor ß 3 (Adrb3). We also found that bilirubin is a selective ligand for PPARα and does not affect the activities of the related proteins PPARγ and PPARδ. We further found that diet-induced obese mice with mild hyperbilirubinemia have reduced WAT size and an increased number of mitochondria, associated with a restructuring of PPARα-binding coregulators. We conclude that bilirubin strongly affects organismal body weight by reshaping the PPARα coregulator profile, remodeling WAT to improve metabolic function, and reducing fat accumulation.

CDKN2A/p16INK4a suppresses hepatic fatty acid oxidation through the AMPKα2-SIRT1-PPARα signaling pathway.

In addition to their well-known role in the control of cellular proliferation and cancer, cell cycle regulators are increasingly identified as important metabolic modulators. Several GWAS have identified SNPs near CDKN2A, the locus encoding for p16INK4a (p16), associated with elevated risk for cardiovascular diseases and type-2 diabetes development, two pathologies associated with impaired hepatic lipid metabolism. Although p16 was recently shown to control hepatic glucose homeostasis, it is unknown whether p16 also controls hepatic lipid metabolism. Using a combination of in vivo and in vitro approaches, we found that p16 modulates fasting-induced hepatic fatty acid oxidation (FAO) and lipid droplet accumulation. In primary hepatocytes, p16-deficiency was associated with elevated expression of genes involved in fatty acid catabolism. These transcriptional changes led to increased FAO and were associated with enhanced activation of PPARα through a mechanism requiring the catalytic AMPKα2 subunit and SIRT1, two known activators of PPARα. By contrast, p16 overexpression was associated with triglyceride accumulation and increased lipid droplet numbers in vitro, and decreased ketogenesis and hepatic mitochondrial activity in vivo Finally, gene expression analysis of liver samples from obese patients revealed a negative correlation between CDKN2A expression and PPARA and its target genes. Our findings demonstrate that p16 represses hepatic lipid catabolism during fasting and may thus participate in the preservation of metabolic flexibility.

Peroxisomal oxidation of erucic acid suppresses mitochondrial fatty acid oxidation by stimulating malonyl-CoA formation in the rat liver.

Feeding of rapeseed (canola) oil with a high erucic acid concentration is known to cause hepatic steatosis in animals. Mitochondrial fatty acid oxidation plays a central role in liver lipid homeostasis, so it is possible that hepatic metabolism of erucic acid might decrease mitochondrial fatty acid oxidation. However, the precise mechanistic relationship between erucic acid levels and mitochondrial fatty acid oxidation is unclear. Using male Sprague-Dawley rats, along with biochemical and molecular biology approaches, we report here that peroxisomal ß-oxidation of erucic acid stimulates malonyl-CoA formation in the liver and thereby suppresses mitochondrial fatty acid oxidation. Excessive hepatic uptake and peroxisomal ß-oxidation of erucic acid resulted in appreciable peroxisomal release of free acetate, which was then used in the synthesis of cytosolic acetyl-CoA. Peroxisomal metabolism of erucic acid also remarkably increased the cytosolic NADH/NAD+ ratio, suppressed sirtuin 1 (SIRT1) activity, and thereby activated acetyl-CoA carboxylase, which stimulated malonyl-CoA biosynthesis from acetyl-CoA. Chronic feeding of a diet including high-erucic-acid rapeseed oil diminished mitochondrial fatty acid oxidation and caused hepatic steatosis and insulin resistance in the rats. Of note, administration of a specific peroxisomal ß-oxidation inhibitor attenuated these effects. Our findings establish a cross-talk between peroxisomal and mitochondrial fatty acid oxidation. They suggest that peroxisomal oxidation of long-chain fatty acids suppresses mitochondrial fatty acid oxidation by stimulating malonyl-CoA formation, which might play a role in fatty acid-induced hepatic steatosis and related metabolic disorders.

Garcinoic acid prevents ß-amyloid (Aß) deposition in the mouse brain.

Garcinoic acid (GA or δ-T3-13'COOH), is a natural vitamin E metabolite that has preliminarily been identified as a modulator of nuclear receptors involved in ß-amyloid (Aß) metabolism and progression of Alzheimer's disease (AD). In this study, we investigated GA's effects on Aß oligomer formation and deposition. Specifically, we compared them with those of other vitamin E analogs and the soy isoflavone genistein, a natural agonist of peroxisome proliferator-activated receptor γ (PPARγ) that has therapeutic potential for managing AD. GA significantly reduced Aß aggregation and accumulation in mouse cortical astrocytes. Similarly to genistein, GA up-regulated PPARγ expression and apolipoprotein E (ApoE) efflux in these cells with an efficacy that was comparable with that of its metabolic precursor δ-tocotrienol and higher than those of α-tocopherol metabolites. Unlike for genistein and the other vitamin E compounds, the GA-induced restoration of ApoE efflux was not affected by pharmacological inhibition of PPARγ activity, and specific activation of pregnane X receptor (PXR) was observed together with ApoE and multidrug resistance protein 1 (MDR1) membrane transporter up-regulation in both the mouse astrocytes and brain tissue. These effects of GA were associated with reduced Aß deposition in the brain of TgCRND8 mice, a transgenic AD model. In conclusion, GA holds potential for preventing Aß oligomerization and deposition in the brain. The mechanistic aspects of GA's properties appear to be distinct from those of other vitamin E metabolites and of genistein.

Agonist binding directs dynamic competition among nuclear receptors for heterodimerization with retinoid X receptor.

Retinoid X receptor (RXR) plays a pivotal role as a transcriptional regulator and serves as an obligatory heterodimerization partner for at least 20 other nuclear receptors (NRs). Given a potentially limiting/sequestered pool of RXR and simultaneous expression of several RXR partners, we hypothesized that NRs compete for binding to RXR and that this competition is directed by specific agonist treatment. Here, we tested this hypothesis on three NRs: peroxisome proliferator-activated receptor gamma (PPARγ), vitamin D receptor (VDR), and retinoic acid receptor alpha (RARα). The evaluation of competition relied on a nuclear translocation assay applied in a three-color imaging model system by detecting changes in heterodimerization between RXRα and one of its partners (NR1) in the presence of another competing partner (NR2). Our results indicated dynamic competition between the NRs governed by two mechanisms. First, in the absence of agonist treatment, there is a hierarchy of affinities between RXRα and its partners in the following order: RARα > PPARγ > VDR. Second, upon agonist treatment, RXRα favors the liganded partner. We conclude that recruiting RXRα by the liganded NR not only facilitates a stimulus-specific cellular response but also might impede other NR pathways involving RXRα.

Palmitoylethanolamide counteracts hepatic metabolic inflexibility modulating mitochondrial function and efficiency in diet-induced obese mice.

Peroxisome proliferator-activated receptor (PPAR)-α activation controls hepatic lipid homeostasis, stimulating fatty acid oxidation, and adapting the metabolic response to lipid overload and storage. Here, we investigate the effect of palmitoylethanolamide (PEA), an endogenous PPAR-α ligand, in counteracting hepatic metabolic inflexibility and mitochondrial dysfunction induced by high-fat diet (HFD) in mice. Long-term PEA administration (30 mg/kg/die per os) in HFD mice limited hepatic lipid accumulation, increased energy expenditure, and markedly reduced insulin resistance. In isolated liver mitochondria, we have demonstrated PEA capability to modulate mitochondrial oxidative capacity and energy efficiency, leading to the reduction of intracellular lipid accumulation and oxidative stress. Moreover, we have evaluated the effect of PEA on mitochondrial bioenergetics of palmitate-challenged HepG2 cells, using Seahorse analyzer. In vitro data showed that PEA recovered mitochondrial dysfunction and reduced lipid accumulation in insulin-resistant HepG2 cells, increasing fatty acid oxidation. Mechanistic studies showed that PEA effect on lipid metabolism was limited by AMP-activated protein kinase (AMPK) inhibition, providing evidence for a pivotal role of AMPK in PEA-induced adaptive metabolic setting. All these findings identify PEA as a modulator of hepatic lipid and glucose homeostasis, limiting metabolic inflexibility induced by nutrient overload.

DNA methylation of FTO promotes renal inflammation by enhancing m6A of PPAR-α in alcohol-induced kidney injury.

Alcohol consumption is one of the risk factors for kidney injury. The underlying mechanism of alcohol-induced kidney injury remains largely unknown. We previously found that the kidney in a mouse model of alcoholic kidney injury had severe inflammation. In this study, we found that the administration of alcohol was associated with the activation of NLRP3 inflammasomes and NF-κB signaling, and the production of pro-inflammatory cytokines. Whole-genome methylation sequencing (WGBS) showed that the DNA encoding fat mass and obesity-associated protein (FTO) was significantly methylated in the alcoholic kidney. This finding was confirmed with the bisulfite sequencing (BSP), which showed that alcohol increased DNA methylation of FTO in the kidney. Furthermore, inhibition of DNA methyltransferases (DNMTs) by 5-azacytidine (5-aza) reversed alcohol-induced kidney injury and decreased the mRNA and protein levels of FTO. Importantly, we found that FTO, the m6A demethylase, epigenetically modified peroxisome proliferator activated receptor-α (PPAR-α) in a YTH domain family 2 (YTHDF2)-dependent manner, which resulted in inflammation in alcoholic kidney injury models. In conclusion, our findings indicate that alcohol increases the methylation of PPAR-α m6A by FTO-mediated YTHDF2 epigenetic modification, which ultimately leads to the activation of NLRP3 inflammasomes and NF-κB-driven renal inflammation in the kidney. These findings may provide novel strategies for preventing and treating alcoholic kidney diseases.

Human hepatic in vitro models reveal distinct anti-NASH potencies of PPAR agonists.

Non-alcoholic steatohepatitis (NASH) is a highly prevalent, chronic liver disease characterized by hepatic lipid accumulation, inflammation, and concomitant fibrosis. Up to date, no anti-NASH drugs have been approved. In this study, we reproduced key NASH characteristics in vitro by exposing primary human hepatocytes (PHH), human skin stem cell-derived hepatic cells (hSKP-HPC), HepaRG and HepG2 cell lines, as well as LX-2 cells to multiple factors that play a role in the onset of NASH. The obtained in vitro disease models showed intracellular lipid accumulation, secretion of inflammatory chemokines, induced ATP content, apoptosis, and increased pro-fibrotic gene expression. These cell systems were then used to evaluate the anti-NASH properties of eight peroxisome proliferator-activated receptor (PPAR) agonists (bezafibrate, elafibranor, fenofibrate, lanifibranor, pemafibrate, pioglitazone, rosiglitazone, and saroglitazar). PPAR agonists differently attenuated lipid accumulation, inflammatory chemokine secretion, and pro-fibrotic gene expression.Based on the obtained readouts, a scoring system was developed to grade the anti-NASH potencies. The in vitro scoring system, based on a battery of the most performant models, namely PHH, hSKP-HPC, and LX-2 cultures, showed that elafibranor, followed by saroglitazar and pioglitazone, induced the strongest anti-NASH effects. These data corroborate available clinical data and show the relevance of these in vitro models for the preclinical investigation of anti-NASH compounds.