Myeloid‐Cell–Specific IL‐6 Signaling Promotes MicroRNA‐223‐Enriched Exosome Production to Attenuate NAFLD‐Associated Fibrosis

Abstract

BaCKgRoUND aNDS aIMS: NAFLD is associated with elevation of many cytokines, particularly IL-6; however, the role of IL-6 in NAFLD remains obscure. The aim of this study was to examine how myeloid-specific IL-6 signaling affects NAFLD by the regulation of antifibrotic microRNA-223 (miR-223) in myeloid cells.appRoaCH aND ReSUltS: Patients with NAFLD or NASH and healthy controls were recruited, and serum IL-6 and soluble IL-6 receptor α (sIL-6Rα) were measured. Compared to controls, serum IL-6 and sIL-6Rα levels were elevated in NAFLD/NASH patients. IL-6 levels correlated positively with the number of circulating leukocytes and monocytes. The role of IL-6 in NAFLD was investigated in Il6 knockout (KO) and Il6 receptor A (Il6ra) conditional KO mice after high-fat diet (HFD) feeding. HFD-fed Il6 KO mice had worse liver injury and fibrosis, but less inflammation, compared to wild-type mice. Hepatocyte-specific Il6ra KO mice had more steatosis and liver injury, whereas myeloid-specific Il6ra KO mice had a lower number of hepatic infiltrating macrophages (IMs) and neutrophils with increased cell death of these cells, but greater liver fibrosis (LF), than WT mice. Mechanistically, the increased LF in HFD-fed, myeloid-specific Il6ra KO mice was attributable to the reduction of antifibrotic miR-223 and subsequent upregulation of the miR-223 target gene, transcriptional activator with PDZ-binding motif (TAZ), a well-known factor to promote NASH fibrosis. In vitro, IL-6 treatment up-regulated exosome biogenesis-related genes and subsequently promoted macrophages to release miR-223-enriched exosomes that were able to reduce profibrotic TAZ expression in hepatocytes by exosomal transfer. Finally, serum IL-6 and miR-223 levels were elevated and correlated with each other in NAFLD patients.CoNClUSIoNS: Myeloid-specific IL-6 signaling inhibits LF through exosomal transfer of antifibrotic miR-223 into hepatocytes, providing therapeutic targets for NAFLD therapy.

MicroRNA-223 restricts liver fibrosis by inhibiting the TAZ-IHH-GLI2 and PDGF signaling pathways via the crosstalk of multiple liver cell types

“…Mice were injected with CCl 4 for 4 weeks followed by Gfp-or miR-223 expressing adenovirus injection for 2 weeks. As we previously reported, overexpression of miR-223 led to decreased fibrogenic gene expression and attenuated CCl 4 -induced liver fibrosis [23]. In the current study, we demonstrated that TAZ and IHH protein levels in hepatocytes were markedly decreased in mice injected with miR-223-expressing adenovirus (Ad-miR-223) (Fig.…”

“…Restoration of hepatic miR-223 ameliorates steatosis and fibrosis in HFD-fed Ldlr KO mice 15 . In addition, the therapeutic effect of adenovirus-mediated overexpression of miR-223 was also recently demonstrated in liver fibrosis induced by chronic CCl 4 treatment 23 . In the current study, we demonstrated that overexpression of miR-223 in hepatocytes can also ameliorate CCl 4- induced liver fibrosis by secreting TAZ-targeting IHH and by releasing miR-223-enriched EVs.…”

MicroRNAs in the Pathogenesis of Nonalcoholic Fatty Liver Disease

“…For example, IL-6 reportedly stimulates myeloid cells to release exosomes containing miR-223 that are absorbed by hepatocytes. Subsequently, miR-223 alleviates liver fibrosis by suppressing the expression of its profibrotic target genes, including Nlrp3, Igf1r, Cxcl10, and TAZ [88]. Additionally, hepatocytes can absorb neutrophil-derived miR-223-enriched EVs in a LDLR-and apolipoprotein E (APOE)-dependent manner [99].…”

“…It is increasingly recognized that EVs are involved in the occurrence and development of hepatic inflammation in NASH. The function of miR-223-enriched EVs in inflammation has been excellently illustrated by Wang et al [88] and He et al [99].…”

“…Inflammatory cells also release EVs to interact with hepatocytes. For example, IL-6 induces macrophages to release miR-223-enriched EVs, which are internalized by hepatocytes and lead to a reduction in the expression of profibrotic TAZ [88]. Neutrophils can also release miR-223-enriched EVs and ameliorate hepatic inflammation and fibrosis [99].…”