The Impact of PPARγ Genetic Variants on IBD Susceptibility and IBD Disease Course

PPARγ: A turning point for irritable bowel syndrome treatment

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal (GI) disorder with negative impacts on quality of life of patients. Although the etiology of the disease is still unclear, there are a set of mechanisms and factors involved in IBS pathogenesis. Visceral hypersensitivity, impaired gut barrier, along with minor inflammation and oxidative stress are the most important triggers for IBS induction. Activation of peroxisome proliferator activated receptor-γ (PPAR-γ) has been shown to improve gut barrier, downregulate pro-inflammatory cytokines, reduce free radical production through antioxidative mechanisms, and exert anti-nociceptive effects against somatic pain. An electronic search in PubMed, Google Scholar, Scopus, and Cochrane library was performed and relevant clinical, in vivo and in vitro articles published between 2004 and June 2020 were collected. Search terms included "Irritable Bowel Syndrome" OR "IBS" OR "visceral hypersensitivity" OR "motility dysfunction" AND "peroxisome proliferator activated receptors" OR "PPAR". Herein, the efficacy of PPARγ signaling as a potential target for IBS treatment is reviewed.

Nuclear Receptors in the Pathogenesis and Management of Inflammatory Bowel Disease

Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the transcription of target genes. Previous epidemiological and genetic studies have documented the association of NRs with the risk of inflammatory bowel disease (IBD). Although the mechanisms of action of NRs in IBD have not been fully established, accumulating evidence has demonstrated that NRs play complicated roles in regulating intestinal immunity, mucosal barriers, and intestinal flora. As one of the first-line medications for the treatment of IBD, 5-aminosalicylic acid (5-ASA) activates peroxisome proliferator-activated receptor gamma (PPARγ) to attenuate colitis. The protective roles of rifaximin and rifampicin partly depend on promoting pregnane X receptor (PXR) expression. The aims of this review are to discuss the roles of several important NRs, such as PPARγ, PXR, vitamin D receptor (VDR), farnesoid X receptor (FXR), and RAR-related orphan receptor gammat (RORγt), in the pathogenesis of IBD and management strategies based on targeting these receptors.

Clinical relevance of peroxisome proliferator-activated receptor-γ gene polymorphisms with sepsis

BACKGROUND

Peroxisome proliferator-activated receptor-γ (PPARγ) is a regulator of inflammation. This study aimed to explore associations between PPARγ gene single-nucleotide polymorphisms (SNPs) and susceptibility to and clinical outcome of sepsis in the North China Han population.

METHODS

This study included 303 patients with sepsis and 303 controls. We conducted genetic typing for 13 common PPARγ gene SNPs (improved multiplex ligation detection reaction), linkage disequilibrium mapping, and haplotype inference. Associations between SNP genotypes/haplotypes and sepsis susceptibility and outcome (septic shock, organ dysfunction, or death) were assessed using unconditional logistic regression analysis.

RESULTS

For rs2972164, patients with genotypes CT/CT+TT had higher risk of sepsis than genotype CC (odds ratio [95% CI]: 1.74 [1.05-2.86], P = .03 and 1.72 [1.06-2.80], P = .026, respectively); the T allele was associated with increased sepsis risk compared with the C allele (1.64 [1.04-2.58], P = .033). For rs1801282, genotypes CG/CG+GG had lower risk of sepsis than genotype CC (0.55 [0.33-0.92], P = .024 and 0.57 [0.35-0.95], P = .03, respectively); the G allele was associated with decreased sepsis risk compared with the C allele (0.62 [0.39-1.01], P = .055). For rs4135275, genotypes AG/AG+GG had higher risk of severe organ dysfunction (multiple organ dysfunction syndrome score >8) than genotype AA (2.66 [1.16-6.09], P = .038 and 2.21 [1.00-4.85], P = .042, respectively). Haplotype TAT (rs2972164, rs4684846, and rs17036188) was associated with increased sepsis risk (1.66 [1.03-2.67], P = .038).

CONCLUSIONS

No mutation was correlated with septic shock or death. PPARγ gene polymorphisms may play a role in the occurrence and progression of sepsis in the North China Han population.

Ciglitazone, a peroxisome proliferator-activated receptor gamma ligand, inhibits proliferation and differentiation of th17 cells

Peroxisome proliferator-activated receptor gamma (PPARγ) was identified as a cell-intrinsic regulator of Th17 cell differentiation. Th17 cells have been associated with several autoimmune diseases, including experimental autoimmune encephalomyelitis (EAE), inflammatory bowel disease (IBD), and collagen-induced arthritis. In this study, we confirmed PPARγ-mediated inhibition of Th17 cell differentiation and cytokine production at an early stage. Treatment with ciglitazone, a PPARγ ligand, reduced both IL-1β-mediated enhancement of Th17 differentiation and activation of Th17 cells after polarization. For Th17 cell differentiation, we found that ciglitazone-treated cells had a relatively low proliferative activity and produced a lower amount of cytokines, regardless of the presence of IL-1β. The inhibitory activity of ciglitazone might be due to decrease of CCNB1 expression, which regulates the cell cycle in T cells. Hence, we postulate that a pharmaceutical PPARγ activator might be a potent candidate for treatment of Th17-mediated autoimmune disease patients.

Nuclear control of the inflammatory response in mammals by peroxisome proliferator-activated receptors

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that play pivotal roles in the regulation of a very large number of biological processes including inflammation. Using specific examples, this paper focuses on the interplay between PPARs and innate immunity/inflammation and, when possible, compares it among species. We focus on recent discoveries establishing how inflammation and PPARs interact in the context of obesity-induced inflammation and type 2 diabetes, mostly in mouse and humans. We illustrate that PPAR γ ability to alleviate obesity-associated inflammation raises an interesting pharmacologic potential. In the light of recent findings, the protective role of PPAR α and PPAR β / δ against the hepatic inflammatory response is also addressed. While PPARs agonists are well-established agents that can treat numerous inflammatory issues in rodents and humans, surprisingly very little has been described in other species. We therefore also review the implication of PPARs in inflammatory bowel disease; acute-phase response; and central, cardiac, and endothelial inflammation and compare it along different species (mainly mouse, rat, human, and pig). In the light of the data available in the literature, there is no doubt that more studies concerning the impact of PPAR ligands in livestock should be undertaken because it may finally raise unconsidered health and sanitary benefits.

PPARγ in Inflammatory Bowel Disease

Peroxisome proliferator-activated receptor gamma (PPARγ) is member of a family of nuclear receptors that interacts with nuclear proteins acting as coactivators and corepressors. The colon is a major tissue which expresses PPARγ in epithelial cells and, to a lesser degree, in macrophages and lymphocytes and plays a role in the regulation of intestinal inflammation. Indeed, both natural and synthetic PPARγ ligands have beneficial effects in different models of experimental colitis, with possible implication in the therapy of inflammatory bowel disease (IBD). This paper will specifically focus on potential role of PPARγ in the predisposition and physiopathology of IBD and will analyze its possible role in medical therapy.