Macrophage Sphingosine 1-Phosphate Receptor 2 Blockade Attenuates Liver Inflammation and Fibrogenesis Triggered by NLRP3 Inflammasome

Abstract

NLR family pyrin domain containing 3 (NLRP3) inflammasome accompanies chronic liver injury and is a critical mediator of inflammation-driven liver fibrosis. Sphingosine 1-phosphate (S1P)/S1P Receptor (S1PR) signaling participates in liver fibrogenesis by affecting bone marrow (BM)-derived monocytes/macrophage (BMM) activation. However, the relationship between S1P/S1PR signaling and NLRP3 inflammasome in BMMs remains unclear. Here, we found significantly elevated gene expression of NLRP3 inflammasome components (NLRP3, pro-interleukin-1β, and pro-interleukin-18) and the activation of NLRP3 inflammasome significantly elevated during murine chronic liver injury induced by a bile duct ligation operation, a methionine-choline-deficient and high-fat diet, or carbon tetrachloride intraperitoneal injection. Moreover, the increased expression of sphingosine kinase 1 (SphK1), the rate-limiting synthetic enzyme of S1P, was positively correlated with NLRP3 inflammasome components in both patients and mouse model livers. Flow cytometry analysis and immunofluorescence staining showed BMMs contributed to the significant proportion of NLRP3 + cells in murine inflammatory livers, but not Kupffer cells, dendritic cells, endothelial cells, T cells, and hepatocytes. Focusing on macrophages, S1P promoted NLRP3 inflammasome priming and activation in a dose-dependent manner. Blockade of S1PR 2 by JTE-013 (antagonist of S1PR 2) or S1PR 2-siRNA inhibited S1P-induced NLRP3 inflammasome priming and inflammatory cytokine (interleukin-1β and interleukin-18) secretion, whereas blockade of S1PR 1 or S1PR 3 had no such effect. in vivo, a β1,3-d-glucan-encapsulated siRNA particle (GeRP) delivery system is capable of silencing genes in macrophages specifically. Treatment with S1PR 2 siRNA-GeRPs markedly reduced NLRP3 inflammasome priming and activation and attenuated liver inflammation and fibrosis. Together, the conclusions indicated that targeting macrophage S1PR 2 retarded liver inflammation and fibrogenesis via downregulating NLRP3 inflammasome, which may represent an effective therapeutic strategy for chronic liver injury.

An update on the regulatory mechanisms of NLRP3 inflammasome activation

“…11,[29][30][31] Sphingosine 1-phosphate (S1P)/S1P receptor (S1PR) signaling is involved in the upregulation of NLRP3 priming through elevation of the gene expression of NLRP3 inflammasome components. 32 Recently, the inhibition of bromodomain-containing protein 4 (BRD4), in the bromodomain and extraterminal domain (BET) family member of epigenetic readers, was reported to activate NF-κB signaling and enhance NLRP3 expression at the transcriptional level. 33 Upon TLR/IL-1R signaling, TRAF6 is involved in the priming step of NLRP3 inflammasome activation through both transcriptional and nontranscriptional regulation of NLRP3.…”

Targeting S1PRs as a Therapeutic Strategy for Inflammatory Bone Loss Diseases—Beyond Regulating S1P Signaling

“…It is likely that S1PR2 interacts with various signaling molecules in the lipid rafts, subsequently modulating bone homeostasis. S1pr2 −/− mice reduced IL-13, IL-4, CCL17, and CCL24 in the bronchoalveolar lavage fluid and inhibited lung fibrosis induced by bleomycin STAT6 [47] Vitamin D and its analog reduced S1PR2 mRNA levels in monocytes and alleviated ovariectomy-induced osteoporosis Unclear [58] An IL-6 receptor antibody decreased S1PR2 mRNA levels in monocytes and alleviated collagen-induced bone loss Unclear [59] Treatment with S1PR2 siRNA or JTE013 in mice alleviated liver inflammation and fibrosis induced by bile duct ligation NLRP3 inflammasome [44,49] Inhibition of S1PR2 by JTE013 reduced osteoporosis induced by RANKL Cell migration from blood to bone tissues [39] Inhibition of S1PR2 by JTE013 attenuated periodontal inflammation and alveolar bone loss induced by tooth ligature placement PI3K, NF-κB, MAPKs…”

“…In a ligature-induced periodontitis animal study, oral topical administration of JTE013 significantly decreased IL-1β, IL-6, and TNF mRNA levels in gingival mucosa tissues when compared with a vehicle treatment group [ 40 ]. Additionally, in a bile duct ligation-induced cholestatic liver injury study in mice, treatment with a glucan-encapsulated S1PR2 siRNA significantly attenuated IL-1β and IL-18 in the liver, as well as serum IL-1β and IL-18 levels, compared with controls [ 44 ]. Zhao et al [ 45 ] revealed that S1PR2 is a receptor for bile acid.…”

“…Therefore, it is important to evaluate the role of S1PR2 in cell chemotaxis stimulated by inflammatory cytokines. A previous study showed that treatment with a S1PR2 siRNA reduced IL-1β and IL-18 mRNA levels in liver induced by bile duct ligation [ 44 ], and treatment with JTE013 reduced IL-1β induced by deoxycholic acid [ 45 ]. Therefore, it is possible that JTE013 reduced inflammatory cytokines in the liver induced by bile duct ligation and subsequently decreased macrophage chemotaxis.…”

A novel S1PR4 functional antagonist prevents nonalcoholic steatohepatitis by deactivating the NLRP3 inflammasome without causing lymphopenia

“…Receptor-mediated S1P signaling has become attractive therapeutic targets in several diseases such as chronic in ammatory disease, autoimmunity, cancer, and metabolic disease [6][7][8][9][10] . In the liver, S1PR2 participates in cholestasisinduced liver injury 11,12 and other causes of hepatic brosis 13 . S1PR1 and S1PR3 are involved in hepatic stellate cell motility and activation 14 and play a crucial role in the angiogenic process required for brosis development 15 .…”