Fibroblast-specific protein 1 identifies an inflammatory subpopulation of macrophages in the liver.

Cirrhosis is the end result of chronic liver disease. Hepatic stellate cells (HSC) are believed to be the major source of collagen-producing myofibroblasts in cirrhotic livers. Portal fibroblasts, bone marrow-derived cells, and epithelial to mesenchymal transition (EMT) might also contribute to the myofibroblast population in damaged livers. Fibroblast-specific protein 1 (FSP1, also called S100A4) is considered a marker of fibroblasts in different organs undergoing tissue remodeling and is used to identify fibroblasts derived from EMT in several organs including the liver. The aim of this study was to characterize FSP1-positive cells in human and experimental liver disease. FSP1-positive cells were increased in human and mouse experimental liver injury including liver cancer. However, FSP1 was not expressed by HSC or type I collagen-producing fibroblasts. Likewise, FSP1-positive cells did not express classical myofibroblast markers, including αSMA and desmin, and were not myofibroblast precursors in injured livers as evaluated by genetic lineage tracing experiments. Surprisingly, FSP1-positive cells expressed F4/80 and other markers of the myeloid-monocytic lineage as evaluated by double immunofluorescence staining, cell fate tracking, flow cytometry, and transcriptional profiling. Similar results were obtained for bone marrow-derived and peritoneal macrophages. FSP1-positive cells were characterized by increased expression of COX2, osteopontin, inflammatory cytokines, and chemokines but reduced expression of MMP3 and TIMP3 compared with Kupffer cells/macrophages. These findings suggest that FSP1 is a marker of a specific subset of inflammatory macrophages in liver injury, fibrosis, and cancer.

Hepatocytes do not undergo epithelial-mesenchymal transition in liver fibrosis in mice.

UNLABELLED: The origin of fibrogenic cells in liver fibrosis remains controversial. We assessed the emerging concept that hepatocytes contribute to production of extracellular matrix (ECM) in liver fibrosis through epithelial-mesenchymal transition (EMT). We bred triple transgenic mice expressing ROSA26 stop beta-galactosidase (beta-gal), albumin Cre, and collagen alpha1(I) green fluorescent protein (GFP), in which hepatocyte-derived cells are permanently labeled by beta-gal and type I collagen-expressing cells are labeled by GFP. We induced liver fibrosis by repetitive carbon tetrachloride (CCl(4)) injections. Liver sections and isolated cells were evaluated for GFP and beta-gal as well as expression of alpha-smooth muscle actin (alpha-SMA) and fibroblast-specific protein 1 (FSP-1). Upon stimulation with transforming growth factor beta-1, cultured hepatocytes isolated from untreated liver expressed both GFP and beta-gal with a fibroblast-like morphological change but lacked expression of other mesenchymal markers. Cells from CCl(4)-treated livers never showed double-positivity for GFP and beta-gal. All beta-gal-positive cells exhibited abundant cytoplasm, a typical morphology of hepatocytes, and expressed none of the mesenchymal markers including alpha-SMA, FSP-1, desmin, and vimentin. In liver sections of CCl(4)-treated mice, GFP-positive areas were coincident with fibrotic septa and never overlapped X-gal-positive areas. CONCLUSION: Type I collagen-producing cells do not originate from hepatocytes. Hepatocytes in vivo neither acquire mesenchymal marker expression nor exhibit a morphological change clearly distinguishable from normal hepatocytes. Our results strongly challenge the concept that hepatocytes in vivo acquire a mesenchymal phenotype through EMT to produce the ECM in liver fibrosis.

Angiotensin-converting-enzyme 2 inhibits liver fibrosis in mice.

UNLABELLED: The renin-angiotensin system (RAS) plays a major role in liver fibrosis. Recently, a homolog of angiotensin-converting-enzyme 1 (ACE1), termed ACE2, has been identified that appears to be a negative regulator of the RAS by degrading Ang II to Ang(1-7). The aim of this study was to characterize the long-term effects of gene deletion of ACE2 in the liver, to define the role of ACE2 in acute and chronic liver disease, and to characterize the role of Ang(1-7) in hepatic stellate cell (HSC) activation. Ace2 knockout (KO) mice and wild-type (wt) littermates underwent different models of acute and chronic liver injury. Liver pathology was analyzed by histology, immunohistochemistry, alpha smooth muscle actin (alpha-SMA) immunoblotting, and quantitative polymerase chain reaction (qPCR). Murine HSCs were isolated by collagenase-pronase-perfusion, and density gradient centrifugation. One-year-old ace2 KO mice spontaneously developed an inflammatory cell infiltration and mild hepatic fibrosis that was prevented by treatment with irbesartan. Ace2 KO mice showed increased liver fibrosis following bile duct ligation for 21 days or chronic carbon tetrachloride (CCl(4)) treatment. In contrast, ace2 KO mice subjected to acute liver injury models did not differ from wt littermates. Treatment with recombinant ACE2 attenuated experimental fibrosis in the course of cholestatic and toxic liver injury. HSCs express the Ang(1-7) receptor Mas and Ang(1-7) inhibited Ang II-induced phosphorylation of extracellular signal-regulated kinase (ERK)-1/2 in cultured HSCs. CONCLUSION: ACE2 is a key negative regulator of the RAS and functions to limit fibrosis through the degradation of Ang II and the formation of Ang(1-7). Whereas loss of ACE2 activity worsens liver fibrosis in chronic liver injury models, administration of recombinant ACE2 shows therapeutic potential.

Overexpression of interleukin-1beta in the murine pancreas results in chronic pancreatitis.

BACKGROUND & AIMS: Chronic pancreatitis is a significant cause of morbidity and a known risk factor for pancreatic adenocarcinoma. Interleukin-1beta is a proinflammatory cytokine involved in pancreatic inflammation. We sought to determine whether targeted overexpression of interleukin-1beta in the pancreas could elicit localized inflammatory responses and chronic pancreatitis. METHODS: We created a transgenic mouse model (elastase sshIL-1beta) in which the rat elastase promoter drives the expression of human interleukin-1beta. Mice were followed up for up to 2 years. Pancreata of elastase sshIL-1beta mice were analyzed for chronic pancreatitis-associated histologic and molecular changes. To study the potential effect of p53 mutation in chronic pancreatitis, elastase sshIL-1beta mice were crossed with p53(R172H) mice. RESULTS: Three transgenic lines were generated, and in each line the pancreas was atrophic and occasionally showed dilation of pancreatic and biliary ducts secondary to proximal fibrotic stenosis. Pancreatic histology showed typical features of chronic pancreatitis. There was evidence for increased acinar proliferation and apoptosis, along with prominent expression of tumor necrosis factor-alpha; chemokine (C-X-C motif) ligand 1; stromal cell-derived factor 1; transforming growth factor-beta1; matrix metallopeptidase 2, 7, and 9; inhibitor of metalloproteinase 1; and cyclooxygenase 2. The severity of the lesions correlated well with the level of human interleukin-1beta expression. Older mice displayed acinar-ductal metaplasia but did not develop mouse pancreatic intraepithelial neoplasia or tumors. Elastase sshIL-1beta*p53(R172H/+) mice had increased frequency of tubular complexes, some of which were acinar-ductal metaplasia. CONCLUSIONS: Overexpression of interleukin-1beta in the murine pancreas induces chronic pancreatitis. Elastase sshIL-1beta mice consistently develop severe chronic pancreatitis and constitute a promising model for studying chronic pancreatitis and its relationship with pancreatic adenocarcinoma.

Fibrosis in autoimmune and cholestatic liver disease.

Autoimmune and cholestatic liver disease account for a significant part of end-stage liver disease and are leading indications for liver transplantation. Especially cholestatic liver diseases (primary biliary cirrhosis and primary sclerosing cholangitis) appear to be different from other chronic liver diseases with regards to pathogenesis. Portal fibroblasts located in the connective tissue surrounding bile ducts appear to be different from hepatic stellate cells with regards to expression of marker proteins and response the profibrogenic and mitogenic stimuli. In addition there is increasing evidence for a cross talk between activated cholangiocytes and portal myofibroblasts. Several animal models have improved our understanding of the mechanisms underlying these chronic liver diseases. In the present review, we discuss the current concepts and ideas with regards to myofibroblastic cell populations, mechanisms of fibrosis, summarize characteristic histological findings and currently employed animal models of autoimmune and cholestatic liver disease.