Myofibroblasts produce the fibrous scar in hepatic fibrosis. In the carbon tetrachloride (CCl 4 ) model of liver fibrosis, quiescent hepatic stellate cells (HSC) are activated to become myofibroblasts. When the underlying etiological agent is removed, clinical and experimental fibrosis undergoes a remarkable regression with complete disappearance of these myofibroblasts. Although some myofibroblasts apoptose, it is unknown whether other myofibroblasts may revert to an inactive phenotype during regression of fibrosis. We elucidated the fate of HSCs/myofibroblasts during recovery from CCl 4 - and alcohol-induced liver fibrosis using Cre-LoxP–based genetic labeling of myofibroblasts. Here we demonstrate that half of the myofibroblasts escape apoptosis during regression of liver fibrosis, down-regulate fibrogenic genes, and acquire a phenotype similar to, but distinct from, quiescent HSCs in their ability to more rapidly reactivate into myofibroblasts in response to fibrogenic stimuli and strongly contribute to liver fibrosis. Inactivation of HSCs was associated with up-regulation of the anti-apoptotic genes Hspa1a/b, which participate in the survival of HSCs in culture and in vivo.

Background IL-17 signaling has been implicated in lung and skin fibrosis. Here we examined the role of IL-17 signaling in the pathogenesis of liver fibrosis. Methods Using cholestatic and hepatotoxic models of liver injury, the development of liver fibrosis in wild type mice was compared to IL-17RA−/− mice, and to bone marrow chimeric mice devoid of IL-17 signaling in immune cells and Kupffer cells (IL-17RA−/−→wt and IL-17A−/− →wt mice), or in liver resident cells (Wt→ IL-17RA−/− mice). Results We determined that IL-17A and its receptor is highly induced in liver injury and has a strong pro-fibrogenic effect on both inflammatory and liver resident cells. IL-17 signaling facilitates production of IL-6, IL-1β, and TNF-α by inflammatory cells, and increases the expression of TGF-β1, the major pro-fibrogenic cytokine. IL-17 directly induces collagen Type I production in hepatic stellate cells (HSCs) via activation of the Stat3 signaling pathway. Mice devoid of Stat3 signaling in HSCs (GFAPStat3−/− mice) are less susceptible to fibrosis. Furthermore, deletion of IL-23 in immune cells results in attenuation of liver fibrosis, while deletion of IL-22 exacerbates fibrosis. Administration of IL-22 and IL-17E (IL-25, a negative regulator of IL-23) protects mice from BDL-induced liver fibrosis. Conclusions IL-17 induces liver fibrosis through multiple mechanisms and may serve as an attractive target for anti-fibrotic therapy.

Significance Liver resident activated hepatic stellate cells (aHSCs), and activated portal fibroblasts (aPFs) are the major source of the fibrous scar in the liver. aPFs have been implicated in liver fibrosis caused by cholestatic liver injury, whereas fibrosis in hepatotoxic liver injury is attributed to aHSCs. However, the contribution of aPFs to cholestatic fibrosis is not well characterized because of difficulties in cell purification and the lack of identified aPF-specific markers. We have developed a novel flow cytometry-based method of aPFs purification from the nonparenchymal cell fraction of collagen-α1(I)-GFP mice and have identified potential aPF-specific markers. The goal of this study is to determine whether aPFs contribute to cholestatic liver fibrosis and identify the mechanism(s) of their activation.

Highlights d Tumor-secreted CTSC promotes breast-to-lung metastasis by regulating neutrophils d CTSC activates membrane-bound PR3 of neutrophils to upregulate IL-1b secretion d CTSC enhances neutrophil recruitment into metastatic niches and induces NETosis d Targeting CTSC with AZD7986 effectively inhibits lung metastasis in mice