Advances in stem cell therapy for peritoneal fibrosis: from mechanisms to therapeutics

Inhibition of Caspase-1 Suppresses GSDMD-mediated Peritoneal Mesothelial Cell Pyroptosis and Inflammation in Peritoneal Fibrosis

Pyroptosis, belonging to programmed cell death, is shown to be mediated by gasdermin D (GSDMD) and gains more and more attention in innate immunity and multiple diseases. However, the role of GSDMD-mediated pyroptosis in peritoneal fibrosis (PF) remains unclear. This study observed NLRP3 inflammasome activation and pyroptosis in the peritoneum of long-term peritoneal dialysis (PD) patients with PF. Moreover, it is found that high glucose (HG) can induce the activation of NLRP3 inflammasome by regulating TLR4/NF-κB and JNK/p38 MAPK signaling in human peritoneal mesothelial cells (HPMCs), leading to subsequent Caspase-1 activation. The cleaved Caspase-1 promoted pyroptosis-related transmembrane pore formation through activating GSDMD-N, and stimulated the HPMCs to secrete inflammatory factors including IL-1β and IL-18. GSDMD global deletion or pharmacologic pretreatment with Caspase-1 specific inhibitor VX-765 effectively inhibited the pyroptosis and inflammation, thereby ameliorating PF. Additionally, treatment with VX-765 and transfected with Caspase-1 siRNA or GSDMD siRNA also inhibited the transmembrane pore formation and inflammatory factors secretion in HG-induced HPMCs. Consistent with these results, delayed treatment with VX-765 also alleviated PF, indicating the therapeutic effect of VX-765. Taken together, the results demonstrate that pyroptosis may be a novel therapeutic target for peritoneal fibrosis.

Unravelling the role of Sildenafil and SB204741 in suppressing fibrotic potential of peritoneal fibroblasts obtained from PD patients

Introduction: Peritoneal fibrosis (PF) results in technique failure in peritoneal dialysis (PD) patients. Peritoneal fibroblasts are characterized by increase in the ACTA2 gene, responsible for alpha smooth muscle actin (α-SΜΑ), extracellular matrix (ECM) production, and inflammatory cytokines production, which are the are key mediators in the pathogenesis of PF. 5-hydroxytryptamine (5-HT; serotonin) induces ECM synthesis in fibroblasts in a transforming growth factor-beta 1 (TGF-β1) dependent manner. The purpose of our study was to identify the potential mechanism and role of sildenafil and 5HT2B receptor inhibitor (SB204741) combination in attenuating PD-associated peritoneal fibrosis. Methods: Studies were performed to determine the effect of TGF-β1, sildenafil, and SB204741 on human peritoneal fibroblasts (HPFBs) isolated from the parietal peritoneum of patients in long-term PD patients (n = 6) and controls (n = 6). HPFBs were incubated with TGF-β1 (10 ng/mL) for 1 h and later with TGF-β1 (10 ng/mL)/[sildenafil (10 µM) or SB204741 (1 µM)] and their combination for 24 h (post-treatment strategy). In the pre-treatment strategy, HPFBs were pre-treated with sildenafil (10 µM) or SB204741 (1 µM) and a combination of the two for 1 h and later with only TGF-β1 (10 ng/mL) for 24 h. Results: The anti-fibrotic effects of the combination of sildenafil and SB204741 were greater than that of each drug alone. In TGF-β1-stimulated HPFBs, pro-fibrotic genes (COL1A1, COL1A2, ACTA2, CTGF, FN1, and TGFB1) exhibited higher expression than in controls, which are crucial targets of sildenafil and SB204741 against peritoneal fibrosis. The synergistic approach played an anti-fibrotic role by regulating the pro- and anti-fibrotic gene responses as well as inflammatory cytokine responses. The combination treatment significantly attenuated peritoneal fibrosis, as evident by the almost complete amelioration of ACTA2 expression, restoration of anti-fibrotic genes (MMP2/TIMP1), and, at least, by reducing the expression of pro-inflammatory cytokines (IFN-γ, IL-4, IL-17, IL-1β, IL-6, TNF-α, and TGF-β1) along with an increase in IL-10 levels. Discussion: Taken together, the above research evidences that the combination of sildenafil and SB204741 may have therapeutic potential in suppressing peritoneal fibrosis due to peritoneal dialysis.