Fibrosis is a pathophysiological process of wound repair that leads to the deposit of connective tissue in the extracellular matrix. This complication is mainly associated with different pathologies affecting several organs such as lung, liver, heart, kidney, and intestine. In this fibrotic process, macrophages play an important role since they can modulate fibrosis due to their high plasticity, being able to adopt different phenotypes depending on the microenvironment in which they are found. In this review, we will try to discuss whether the macrophage phenotype exerts a pivotal role in the fibrosis development in the most important fibrotic scenarios.

Intestinal epithelial cells (IECs) constitute a defensive physical barrier in mucosal tissues and their disruption is involved in the etiopathogenesis of several inflammatory pathologies, such as Ulcerative Colitis (UC). Recently, the succinate receptor SUCNR1 was associated with the activation of inflammatory pathways in several cell types, but little is known about its role in IECs. We aimed to analyze the role of SUCNR1 in the inflammasome priming and its relevance in UC. Inflammatory and inflammasome markers and SUCNR1 were analyzed in HT29 cells treated with succinate and/or an inflammatory cocktail and transfected with SUCNR1 siRNA in a murine DSS model, and in intestinal resections from 15 UC and non-IBD patients. Results showed that this receptor mediated the inflammasome, priming both in vitro in HT29 cells and in vivo in a murine chronic DSS-colitis model. Moreover, SUNCR1 was also found to be involved in the activation of the inflammatory pathways NFкB and ERK pathways, even in basal conditions, since the transient knock-down of this receptor significantly reduced the constitutive levels of pERK-1/2 and pNFкB and impaired LPS-induced inflammation. Finally, UC patients showed a significant increase in the expression of SUCNR1 and several inflammasome components which correlated positively and significantly. Therefore, our results demonstrated a role for SUCNR1 in basal and stimulated inflammatory pathways in intestinal epithelial cells and suggested a pivotal role for this receptor in inflammasome activation in UC.

Background Fibrosis is a complication commonly present in Crohn’s disease (CD) patients with a structuring (B2) or penetrating (B3) behaviour, with no available treatment. This process is characterized by an excessive extracellular matrix deposition, mainly associated with a dysregulated function of myofibroblasts. We analyse here, the expression of markers of senescence in human intestinal fibroblasts. Methods Human small intestinal fibroblasts (HSIF; P10760, Innoprot, Spain) were treated during 48h with 2µg/mL of DLL4, 20ng/ml of TNFα, 2ng/ml of IL-1β, 5ng/ml of TGFβ1, and 100ng/ml of. In some cases, fibroblasts were treated with 20nM of siRNA to ETS1 gene (siETS21) or negative control (NC). Gene expression profiles were analysed by RT-qPCR. Results Treatment of fibroblasts with IL-1β significantly increased the mRNA expression of a) different senescence-associated secretory phenotype (SASP) factors (IL-1α, IL-1β, IL-8, and Serpine1); b) a metalloprotease ADAM12 and the chitinase CHI3L1 and c) the transcription factor related to senescence ETS proto-oncogene 1 (ETS1), all compared with vehicle treatment. Treatment with PDGF significantly increased the mRNA expression of ADAM12, ETS1, PTEN and the transcription factor, E2F5, while it induced a non-significant increase in the expression of senescence markers such as P16, P21, P53 and MCL1. Treatment with TGFβ1 did not significantly alter the expression of markers reported above and it only significantly increased the expression of IGFBP3 gene, another SASP factor. Both DLL4 and TNFα failed to significantly modify the expression of any of the above markers. Finally, a cellular model of depletion of ETS1 showed that siETS1 fibroblasts in basal conditions exhibited decreased levels of IL-8 and BCL2. Conclusion In human primary intestinal fibroblasts, treatment with IL1b increased the expression of senescence associated secretory phenotype while treatment with PDGF increased the expression of markers involved in cell cycle arrest. The induction of ETS1 by both treatments and the involvement of this transcription factor regulating gene expression in basal conditions, suggest a relevant role for ETS1 in the activation of intestinal fibroblasts

Background Ulcerative colitis (UC) is characterized by a diffuse, continuous, and chronic inflammation of mucosa and submucosa layers in the colon1. Inflammasome complex is involved in the intestinal homeostasis regulation, but its role in UC has not been established yet. We have recently reported that SUCNR1 mediates intestinal inflammation and fibrosis2. We aim to analyze the role of SUCNR1 in inflammasome activation and UC. Methods Intestinal resections from UC and non-IBD patients were obtained. HT29 cells were treated with succinate 1mM and an inflammasome activator cocktail (TNF-α 25ng/ml, IFN-γ 20 ng/ml and LPS 1µg/ml) for 24 hours and transfected with SUCNR1 siRNA. Chronic DSS-colitis was induced in wild-type (WT) and SUNCR1-/- (KO) mice with 4 cycles of DSS. Gene expression and protein levels of SUCNR1 and inflammasome markers were analyzed by qPCR, WesternBlot and ELISA. Histology of murine tissue was analyzed by Hematoxylin-Eosin staining. Results were expressed as fold induction (mean±SEM, n≥5). Statistical analysis was performed with one-way ANOVA followed by Newman-Keuls test. Correlations were analyzed with the Spearman coefficient. Results In UC patients, gene expression of SUCNR1 (4.47±1.70), Nlrp3 (1.97±0.38), Caspase-1 (2.08±0.33) and IL-1β (6.90±2.02) were significantly increased vs non-IBD. SUCNR1 positively correlates with the expression of Caspase-1 (r=0.46) and ASC (r=0.45). Protein levels of SUCNR1 (151.00±8.29), Nlrp3 (215.20±53.35) and Caspase-1 (518.30±231.50) were increased in UC vs non-IBD. HT29 cells treated with succinate and inflammasome cocktail showed an increased gene expression of SUCNR1 (4.45±1.17), Nlrp3 (3.13±0.29), Caspase-1 (70.40±16.14), ASC (2.38±0.37), IL-18 (2.52±0.31) and IL-1β (2.32±0.18). Of interest, siSUCNR1 cells treated with the cocktail and succinate showed a significant reduction in the expression of Nlrp3 (1.00±0.15), IL-1β (0.98±0.21), and ASC (1.19±0.14). In parallel, protein levels of Caspase-1 in siSUCNR1 cells treated with cocktail and succinate were significantly reduced (609.00±116.20) vs non-transfected cells (1095.00±148.30). IL-1β levels were also significantly reduced in siSUCNR1 cells (148.60±16.13) vs non-transfected cells (744.70±94.06). Finally, WT-DSS mice exhibited a worse colon histology and an increased protein expression of Caspase-1 (170.60±32.20), compared with KO-DSS (61.39±4.59). Conclusion SUCNR1 is increased and positively correlates with the expression of inflammasome components in UC patients. Moreover, SUCNR1 mediates inflammasome activation and its absence ameliorates chronic DSS-colitis. Hence, SUCNR1 might be a potential pharmacological target for UC treatment. Reference