Peroxisome Proliferator-Activated Receptor Alpha Mediates the Beneficial Effects of Atorvastatin in Experimental Colitis

Extracellular vesicles: a new frontier in diagnosing and treating graft-versus-host disease after allogeneic hematopoietic cell transplantation

Graft-versus-host disease (GvHD) is a prevalent complication following allogeneic hematopoietic stem cell transplantation (HSCT) and is characterized by relatively high morbidity and mortality rates. GvHD can result in extensive systemic damage in patients following allogeneic HSCT (allo-HSCT), with the skin, gastrointestinal tract, and liver frequently being the primary target organs affected. The severe manifestations of acute intestinal GvHD often indicate a poor prognosis for patients after allo-HSCT. Endoscopy and histopathological evaluation remain employed to diagnose GvHD, and auxiliary examinations exclude differential diagnoses. Currently, reliable serum biomarkers for the diagnosis and differential diagnosis of GvHD are scarce. As an essential part of standard transplant protocols, early application of immunosuppressive drugs effectively prevents GvHD. Among them, steroids represent first-line therapeutic agents, and the JAK2 inhibitor ruxolitinib represents the second-line therapeutic agent. Currently, no efficacious treatment modality exists for steroid-resistant aGvHD. Therefore, the diagnosis and treatment of GvHD still face significant medical demands. Extracellular vesicles (EVs) are nanometer to micrometer-scale biomembrane vesicles containing various bioactive components, such as proteins, nucleotides, and metabolites. Distinctive changes in serum-derived EV components occur in patients after allo-HSCT; Hence, EVs are expected to be potential biomarkers for diagnosing and treating GvHD. Furthermore, cell-free therapeutics characterized by EVs derived from mesenchymal stem cells (MSCs) have manifested remarkable therapeutic efficacy in preclinical models and preclinical trials of GvHD. Customized engineered EVs with fewer toxic and side effects for the combined treatment of GvHD hold broad prospects for clinical translation. This review article examines the potential value of translating EVs into clinical applications for the diagnosis and treatment of GvHD. It summarizes the latest advancements and prospects of engineered EVs applying GvHD.

Elafibranor: A promising treatment for alcoholic liver disease, metabolic-associated fatty liver disease, and cholestatic liver disease

Liver diseases pose a significant threat to human health. Although effective therapeutic agents exist for some liver diseases, there remains a critical need for advancements in research to address the gaps in treatment options and improve patient outcomes. This article reviews the assessment of Elafibranor's effects on liver fibrosis and intestinal barrier function in a mouse model of alcoholic liver disease (ALD), as reported by Koizumi et al in the World Journal of Gastroenterology. We summarize the impact and mechanisms of Elafibranor on ALD, metabolic-associated fatty liver disease, and cholestatic liver disease based on current research. We also explore its potential as a dual agonist of PPARα/δ, which is undergoing Phase III clinical trials for metabolic-associated steatohepatitis. Our goal is to stimulate further investigation into Elafibranor's use for preventing and treating these liver diseases and to provide insights for its clinical application.

ADORA3 activation promotes goblet cell differentiation via enhancing HMGCS2-mediated ketogenesis in ulcerative colitis

ADORA3 is mainly expressed in intestinal tract, and has the potential to promote the expression of mucin 2 (MUC2), the function-related factor of goblet cells, under asthma conditions. This study aims to confirm the induction and mechanisms of ADORA3 activation on goblet cells in ulcerative colitis (UC). A significant decrease in ADORA3 expression was found in mucosal biopsies from UC patients and in the colons of colitis mice. This reduction correlated negatively with disease severity and positively with goblet cell number. ADORA3 activation mitigated dextran sulfate sodium (DSS)-induced colitis and facilitated ATOH1-mediated goblet cell differentiation in both in vivo and in vitro. Metabolomics analysis unveiled that ADORA3 activation bolstered ketogenesis, leading to elevated levels of the metabolite BHB. Subsequently, BHB heightened the activity of HDAC1/2, augmenting histone acetylation at the H3K9ac site within the promoter region of the ATOH1 gene. Furthermore, the reason for ADORA3 activation to enhance ketogenesis was attributed to controlling the competitive binding among β-arrestin2, SHP1 and PPARγ. This results in the non-ligand-dependent activation of PPARγ, thereby promoting the transcription of HMGCS2. The exact mechanisms by which ADORA3 promoted goblet cell differentiation and alleviated UC were elucidated using MRS1191 and shHMGCS2 plasmid. Collectively, ADORA3 activation promoted goblet cell differentiation and alleviated UC by enhancing ketogenesis via the "BHB-HDAC1/2-H3K9ac" pathway.

The Versatile Role of Peroxisome Proliferator-Activated Receptors in Immune-Mediated Intestinal Diseases

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that sense lipophilic molecules and act as transcription factors to regulate target genes. PPARs have been implicated in the regulation of innate immunity, glucose and lipid metabolism, cell proliferation, wound healing, and fibrotic processes. Some synthetic PPAR ligands are promising molecules for the treatment of inflammatory and fibrotic processes in immune-mediated intestinal diseases. Some of these are currently undergoing or have previously undergone clinical trials. Dietary PPAR ligands and changes in microbiota composition could modulate PPARs' activation to reduce inflammatory responses in these immune-mediated diseases, based on animal models and clinical trials. This narrative review aims to summarize the role of PPARs in immune-mediated bowel diseases and their potential therapeutic use.

Atorvastatin improved ulcerative colitis in association with gut microbiota-derived tryptophan metabolism

AIMS

Atorvastatin is a commonly used cholesterol-lowering drug that possesses non-canonical anti-inflammatory properties. However, the precise mechanism underlying its anti-inflammatory effects remains unclear.

MATERIALS AND METHODS

The acute phase of ulcerative colitis (UC) was induced using a 5 % dextran sulfate sodium (DSS) solution for 7 consecutive days and administrated with atorvastatin (10 mg/kg) from day 3 to day 7. mRNA-seq, histological pathology, and inflammatory response were determined. Intestinal microbiota alteration, tryptophan, and its metabolites were analyzed through 16S rRNA sequencing and untargeted metabolomics.

KEY FINDINGS

Atorvastatin relieved the DSS-induced UC in mice, as evidenced by colon length, body weight, disease activity index score and pathological staining. Atorvastatin treatment reduced the level of pro-inflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α). Atorvastatin also relieved the intestinal microbiota disorder caused by UC and decreased the proliferation of pernicious microbiota such as Akkermansia and Bacteroides. Atorvastatin dramatically altered tryptophan metabolism and increased the fecal contents of tryptophan, indolelactic acid (ILA), and indole-3-acetic acid (IAA). Furthermore, atorvastatin enhanced the expression level of aryl hydrocarbon receptor (AhR) and interleukin-22 (IL-22) and further promoted the expression level of intestinal tight junction proteins, such as ZO-1 and occludin, in colitis mice.

SIGNIFICANCE

These findings indicated that atorvastatin could alleviate UC by regulating intestinal flora disorders, promoting microbial tryptophan metabolism, and repairing the intestinal barrier.

Intestinal retinol saturase is implicated in the development of obesity and epithelial homeostasis upon injury

Retinol saturase (RetSat) is an oxidoreductase involved in lipid metabolism and the cellular sensitivity to peroxides. RetSat is highly expressed in metabolic organs like the liver and adipose tissue and its global loss in mice increases body weight and adiposity. The regulation of RetSat expression and its function in the intestine are unexplored. Here, we show that RetSat is present in different segments of the digestive system, localizes to intestinal epithelial cells, and is upregulated by feeding mice high-fat diet (HFD). Intestine-specific RetSat deletion in adult mice did not affect nutrient absorption and energy homeostasis basally, but lowered body weight gain and fat mass of HFD-fed mice, potentially via increasing locomotor activity. Moreover, jejunal expression of genes related to β-oxidation and cholesterol efflux was decreased, and colonic cholesterol content was reduced upon RetSat deletion. In colitis, which we show to downregulate intestinal RetSat expression in humans and mice, RetSat ablation improved epithelial architecture of the murine colon. Thus, intestinal RetSat expression is regulated by dietary interventions and inflammation, and its loss reduces weight gain upon HFD feeding and alleviates epithelial damage upon injury.NEW & NOTEWORTHY Retinol saturase (RetSat) is an oxidoreductase with unknown function in the intestine. We found that RetSat localizes in intestinal epithelial cells and that its deletion reduced weight gain and fat mass in obese mice. In colitis, which decreased intestinal RetSat expression in humans and mice, RetSat ablation improved the epithelial architecture of the murine colon, presumably by decreasing ROS production, thus rendering RetSat a novel target for metabolic and inflammatory bowel disease.

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

BACKGROUND

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.

AIM

To evaluate the inhibitory effects of EFN on liver fibrosis and gut-intestinal barrier dysfunction in an ALD mouse model.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

Gemfibrozil Improves Microcirculatory Oxygenation of Colon and Liver without Affecting Mitochondrial Function in a Model of Abdominal Sepsis in Rats

Recent studies observed, despite an anti-hyperlipidaemic effect, a positive impact of fibrates on septic conditions. This study evaluates the effects of gemfibrozil on microcirculatory variables, mitochondrial function, and lipid peroxidation levels with regard to its potential role as an indicator for oxidative stress in the colon and liver under control and septic conditions and dependencies on PPARα-mediated mechanisms of action. With the approval of the local ethics committee, 120 Wistar rats were randomly divided into 12 groups. Sham and septic animals were treated with a vehicle, gemfibrozil (30 and 100 mg/kg BW), GW 6471 (1 mg/kg BW, PPARα inhibitor), or a combination of both drugs. Sepsis was induced via the colon ascendens stent peritonitis (CASP) model. Then, 24 h post sham or CASP surgery, a re-laparotomy was performed. Measures of vital parameters (heart rate (HR), mean arterial pressure (MAP), and microcirculation (µHbO2)) were recorded for 90 min. Mitochondrial respirometry and assessment of lipid peroxidation via a malondialdehyde (MDA) assay were performed on colon and liver tissues. In the untreated sham animals, microcirculation remained stable, while pre-treatment with gemfibrozil showed significant decreases in the microcirculatory oxygenation of the colon. In the CASP animals, µHbO2 levels in the colon and the liver were significantly decreased 90 min after laparotomy. Pre-treatment with gemfibrozil prevented the microcirculatory aberrations in both organs. Gemfibrozil did not affect mitochondrial function and lipid peroxidation levels in the sham or CASP animals. Gemfibrozil treatment influences microcirculation depending on the underlying condition. Gemfibrozil prevents sepsis-induced microcirculatory aberrances in the colon and liver PPARα-independently. In non-septic animals, gemfibrozil impairs the microcirculatory variables in the colon without affecting those in the liver.

The Microbiota-Dependent Worsening Effects of Melatonin on Gut Inflammation

Dysbiosis and disturbances in gut homeostasis may result in dysregulated responses, which are common in inflammatory bowel diseases (IBD). These conditions may be refractory to the usual treatments and novel therapies are still necessary to reach a more successful regulation of intestinal immunity. The hormone melatonin (MLT) has been raised as a therapeutic alternative because of its known interactions with immune responses and gut microbiota. Hence, we evaluated the effects of MLT in experimental colitis that evolves with intestinal dysbiosis, inflammation and bacterial translocation. C57BL/6 mice were exposed to dextran sulfate sodium and treated with MLT. In acute colitis, the hormone led to increased clinical, systemic and intestinal inflammatory parameters. During remission, continued MLT administration delayed recovery, increased TNF, memory effector lymphocytes and diminished spleen regulatory cells. MLT treatment reduced Bacteroidetes and augmented Actinobacteria and Verrucomicrobia phyla in mice feces. Microbiota depletion resulted in a remarkable reversion of the colitis phenotype after MLT administration, including a counter-regulatory immune response, reduction in TNF and colon macrophages. There was a decrease in Actinobacteria, Firmicutes and, most strikingly, Verrucomicrobia phylum in recovering mice. Finally, these results pointed to a gut-microbiota-dependent effect of MLT in the potentiation of intestinal inflammation.

The PPARα Regulation of the Gut Physiology in Regard to Interaction with Microbiota, Intestinal Immunity, Metabolism, and Permeability

Peroxisome proliferator-activated receptor alpha (PPARα) is expressed throughout the mammalian gut: in epithelial cells, in the villi of enterocytes and in Paneth cells of intestinal crypts, as well as in some immune cells (e.g., lamina propria macrophages, dendritic cells) of the mucosa. This review examines the reciprocal interaction between PPARα activation and intestinal microbiota. We refer to the published data confirming that microbiota products can influence PPARα signaling and, on the other hand, PPARα activation is able to affect microbiota profile, viability, and diversity. PPARα impact on the broad spectrum of events connected to metabolism, signaling (e.g., NO production), immunological tolerance to dietary antigens, immunity and permeability of the gut are also discussed. We believe that the phenomena described here play a prominent role in gut homeostasis. Therefore, in conclusion we propose future directions for research, including the application of synthetic activators and natural endogenous ligands of PPARα (i.e., endocannabinoids) as therapeutics for intestinal pathologies and systemic diseases assumed to be related to gut dysbiosis.

Blockade of PGK1 and ALDOA enhances bilirubin control of Th17 cells in Crohn's disease

Unconjugated bilirubin (UCB) confers Th17-cells immunosuppressive features by activating aryl-hydrocarbon-receptor, a modulator of toxin and adaptive immune responses. In Crohn's disease, Th17-cells fail to acquire regulatory properties in response to UCB, remaining at an inflammatory/pathogenic state. Here we show that UCB modulates Th17-cell metabolism by limiting glycolysis and through downregulation of glycolysis-related genes, namely phosphoglycerate-kinase-1 (PGK1) and aldolase-A (ALDOA). Th17-cells of Crohn's disease patients display heightened PGK1 and ALDOA and defective response to UCB. Silencing of PGK1 or ALDOA restores Th17-cell response to UCB, as reflected by increase in immunoregulatory markers like FOXP3, IL-10 and CD39. In vivo, PGK1 and ALDOA silencing enhances UCB salutary effects in trinitro-benzene-sulfonic-acid-induced colitis in NOD/scid/gamma humanized mice where control over disease activity and enhanced immunoregulatory phenotypes are achieved. PGK1 and/or ALDOA blockade might have therapeutic effects in Crohn's disease by favoring acquisition of regulatory properties by Th17-cells along with control over their pathogenic potential.

hUC-EVs-ATO reduce the severity of acute GVHD by resetting inflammatory macrophages toward the M2 phenotype

Background

Both extracellular vesicles from mesenchymal stromal cell-derived human umbilical cords (hUC-EVs) and arsenic trioxides (ATOs) have been demonstrated to treat acute graft-versus-host disease (aGVHD) via immunomodulation. Apart from immunomodulation, hUC-EVs have a unique function of drug delivery, which has been proposed to enhance their efficacy. In this study, we first prepared ATO-loaded hUC-EVs (hUC-EVs-ATO) to investigate the therapeutic effect and potential mechanisms of hUC-EVs-ATO in a mouse model of aGVHD after allogeneic hematopoietic stem cell transplantation (HSCT).

Methods

An aGVHD model was established to observe the therapeutic effects of hUC-EVs-ATO on aGVHD. Target organs were harvested for histopathological analysis on day 14 after transplantation. The effects of hUC-EVs-ATO on alloreactive CD4⁺ were evaluated by flow cytometry in vivo and in vitro. Flow cytometry, RT-PCR, immunofluorescence colocalization analysis and Western blot (Wb) analysis were performed to examine macrophage polarization after hUC-EV-ATO treatment. The cytokines in serum were measured by a cytometric bead array (CBA). TEM, confocal microscopy and Wb were performed to observe the level of autophagy in macrophages. A graft-versus-lymphoma (GVL) mouse model was established to observe the role of hUC-EVs-ATO in the GVL effect.

Results

The clinical manifestations and histological scores of aGVHD in the hUC-EVs-ATO group were significantly reduced compared with those in the ATO and hUC-EVs groups. The mice receiving hUC-EVs-ATO lived longer than the control mice. Notably, hUC-EVs-ATO interfering with alloreactive CD4⁺ T cells differentiation were observed in aGVHD mice but not in an in vitro culture system. Additional studies showed that depletion of macrophages blocked the therapeutic effects of hUC-EVs-ATO on aGVHD. Mechanistically, hUC-EVs-ATO induced autophagic flux by inhibiting mammalian target of rapamycin (mTOR) activity to repolarize M1 to M2 macrophages. Additionally, using a murine model of GVL effects, hUC-EVs-ATO were found not only to reduce the severity of aGVHD but also to preserve the GVL effects. Taken together, hUC-EVs-ATO may be promising candidates for aGVHD treatment.

Conclusions

hUC-EVs-ATO enhanced the alleviation of aGVHD severity in mice compared with ATO and hUC-EVs without weakening GVL activity. hUC-EVs-ATO promoted M1 to M2 polarization via the mTOR-autophagy pathway. hUC-EVs-ATO could be a potential therapeutic approach in aGVHD after allo-HSCT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13045-022-01315-2.

Downregulation of CPT1A exerts a protective effect in dextran sulfate sodium-induced ulcerative colitis partially by inhibiting PPARα signaling pathway

Ulcerative colitis (UC) is a chronic inflammatory bowel disease that may progress to colorectal cancer in severe cases. Carnitine palmitoyltransferase-1A (CPT1A) has been reported to be upregulated in colorectal cancer. This paper aims to explore the role of CPT1A in UC and its pathogenesis. An in vivo mice model of UC was constructed by administrating 3% dextran sulfate sodium (DSS). The expression level of CPT1A was examined by quantitative real-time polymerase chain reaction and Western blot. The intestinal damage, inflammatory response and oxidative stress were assessed by hematoxylin and eosin staining, colon length, and commercial kits. Thereafter, an in vitro cell model of UC was established by stimulating HT-29 cells with 2% DSS. The peroxisome proliferator-activated receptor α (PPARα) signaling agonist GW7647 was used for treatment. Cell viability and apoptosis was assayed by cell counting kit-8 assay and terminal dUTP nick-end labeling assay, respectively. The inflammatory cytokines and oxidative stress-related factors was evaluated using corresponding commercial detection kits. In DSS-induced mice model of UC, CPT1A expression was upregulated. Interference of CPT1A attenuated histological damage, the disease activity index and colon length in colitis. We also found downregulation of CPT1A inhibited inflammatory response and oxidative stress, and inhibited PPARα signaling pathway in UC mice. Additionally, in DSS-induced HT-29 cells, downregulation of CPT1A promoted cell viability, reduced cell apoptosis, inflammatory response, and oxidative stress, which was partly abolished by additional treatment with GW7647. In summary, downregulation of CPT1A exerts a protective effect in DSS-induced UC partially through suppressing PPARα signaling, suggesting that CPT1A might be a potential target for the treatment of UC.