Bone marrow-derived fibrocytes participate in pathogenesis of liver fibrosis

Fibrocytes in the fibrotic lung: altered phenotype detected by flow cytometry

Fibrocytes are bone marrow hematopoietic-derived cells that also express a mesenchymal cell marker (commonly collagen I) and participate in fibrotic diseases of multiple organs. Given their origin, they or their precursors must be circulating cells before recruitment into target tissues. While most previous studies focused on circulating fibrocytes, here we focus on the fibrocyte phenotype in fibrotic tissue. The study's relevance to human disease is heightened by use of a model in which bleomycin is delivered systemically, recapitulating several features of human scleroderma including multi-organ fibrosis not observed when bleomycin is delivered directly into the lungs. Using flow cytometry, we find in the fibrotic lung a large population of CD45(high) fibrocytes (called Region I) rarely found in vehicle-treated control mice. A second population of CD45+ fibrocytes (called Region II) is observed in both control and fibrotic lung. The level of CD45 in circulating fibrocytes is far lower than in either Region I or II lung fibrocytes. The chemokine receptors CXCR4 and CCR5 are expressed at higher levels in Region I than in Region II and are present at very low levels in all other lung cells including CD45+/collagen I- leucocytes. The collagen chaperone HSP47 is present at similar high levels in both Regions I and II, but at a higher level in fibrotic lung than in control lung. There is also a major population of HSP47(high)/CD45- cells in fibrotic lung not present in control lung. CD44 is present at higher levels in Region I than in Region II and at much lower levels in all other cells including CD45+/collagen I- leucocytes. When lung fibrosis is inhibited by restoring caveolin-1 activity using a caveolin-1 scaffolding domain peptide (CSD), a strong correlation is observed between fibrocyte number and fibrosis score. In summary, the distinctive phenotype of fibrotic lung fibrocytes suggests that fibrocyte differentiation occurs primarily within the target organ.

Role of NADPH oxidases in liver fibrosis

SIGNIFICANCE

Hepatic fibrosis is the common pathophysiologic process resulting from chronic liver injury, characterized by the accumulation of an excessive extracellular matrix. Multiple lines of evidence indicate that oxidative stress plays a pivotal role in the pathogenesis of liver fibrosis. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) is a multicomponent enzyme complex that generates reactive oxygen species (ROS) in response to a wide range of stimuli. In addition to phagocytic NOX2, there are six nonphagocytic NOX proteins.

RECENT ADVANCES

In the liver, NOX is functionally expressed both in the phagocytic form and in the nonphagocytic form. NOX-derived ROS contributes to various kinds of liver disease caused by alcohol, hepatitis C virus, and toxic bile acids. Recent evidence indicates that both phagocytic NOX2 and nonphagocytic NOX isoforms, including NOX1 and NOX4, mediate distinct profibrogenic actions in hepatic stellate cells, the main fibrogenic cell type in the liver. The critical role of NOX in hepatic fibrogenesis provides a rationale to assess pharmacological NOX inhibitors that treat hepatic fibrosis in patients with chronic liver disease.

CRITICAL ISSUES

Although there is compelling evidence indicating a crucial role for NOX-mediated ROS generation in hepatic fibrogenesis, little is known about the expression, subcellular localization, regulation, and redox signaling of NOX isoforms in specific cell types in the liver. Moreover, the exact mechanism of NOX-mediated fibrogenic signaling is still largely unknown.

FUTURE DIRECTIONS

A better understanding through further research about NOX-mediated fibrogenic signaling may enable the development of novel anti-fibrotic therapy using NOX inhibition strategy. Antio

The antifibrinolytic drug tranexamic acid reduces liver injury and fibrosis in a mouse model of chronic bile duct injury

Hepatic fibrin deposition has been shown to inhibit hepatocellular injury in mice exposed to the bile duct toxicant α-naphthylisothiocyanate (ANIT). Degradation of fibrin clots by fibrinolysis controls the duration and extent of tissue fibrin deposition. Thus, we sought to determine the effect of treatment with the antifibrinolytic drug tranexamic acid (TA) and plasminogen activator inhibitor-1 (PAI-1) deficiency on ANIT-induced liver injury and fibrosis in mice. Plasmin-dependent lysis of fibrin clots was impaired in plasma from mice treated with TA (1200 mg/kg i.p., administered twice daily). Prophylactic TA administration reduced hepatic inflammation and hepatocellular necrosis in mice fed a diet containing 0.025% ANIT for 2 weeks. Hepatic type 1 collagen mRNA expression and deposition increased markedly in livers of mice fed ANIT diet for 4 weeks. To determine whether TA treatment could inhibit this progression of liver fibrosis, mice were fed ANIT diet for 4 weeks and treated with TA for the last 2 weeks. Interestingly, TA treatment largely prevented increased deposition of type 1 collagen in livers of mice fed ANIT diet for 4 weeks. In contrast, biliary hyperplasia/inflammation and liver fibrosis were significantly increased in PAI-1(-/-) mice fed ANIT diet for 4 weeks. Overall, the results indicate that fibrinolytic activity contributes to ANIT diet-induced liver injury and fibrosis in mice. In addition, these proof-of-principle studies suggest the possibility that therapeutic intervention with an antifibrinolytic drug could form a novel strategy to prevent or reduce liver injury and fibrosis in patients with liver disease.

Fibroblasts in fibrosis: novel roles and mediators

Fibroblasts are the most common cell type of the connective tissues found throughout the body and the principal source of the extensive extracellular matrix (ECM) characteristic of these tissues. They are also the central mediators of the pathological fibrotic accumulation of ECM and the cellular proliferation and differentiation that occurs in response to prolonged tissue injury and chronic inflammation. The transformation of the fibroblast cell lineage involves classical developmental signaling programs and includes a surprisingly diverse range of precursor cell types—most notably, myofibroblasts that are the apex of the fibrotic phenotype. Myofibroblasts display exaggerated ECM production; constitutively secrete and are hypersensitive to chemical signals such as cytokines, chemokines, and growth factors; and are endowed with a contractile apparatus allowing them to manipulate the ECM fibers physically to close open wounds. In addition to ECM production, fibroblasts have multiple concomitant biological roles, such as in wound healing, inflammation, and angiogenesis, which are each interwoven with the process of fibrosis. We now recognize many common fibroblast-related features across various physiological and pathological protracted processes. Indeed, a new appreciation has emerged for the role of non-cancerous fibroblast interactions with tumors in cancer progression. Although the predominant current clinical treatments of fibrosis involve non-specific immunosuppressive and anti-proliferative drugs, a variety of potential therapies under investigation specifically target fibroblast biology.

Evolving concepts in the pathogenesis of NASH: beyond steatosis and inflammation

Non-alcoholic steatohepatitis (NASH) is characterised by hepatic steatosis and inflammation and, in some patients, progressive fibrosis leading to cirrhosis. An understanding of the pathogenesis of NASH is still evolving but current evidence suggests multiple metabolic factors critically disrupt homeostasis and induce an inflammatory cascade and ensuing fibrosis. The mechanisms underlying these changes and the complex inter-cellular interactions that mediate fibrogenesis are yet to be fully elucidated. Lipotoxicity, in the setting of excess free fatty acids, obesity, and insulin resistance, appears to be the central driver of cellular injury via oxidative stress. Hepatocyte apoptosis and/or senescence contribute to activation of the inflammasome via a variety of intra- and inter-cellular signalling mechanisms leading to fibrosis. Current evidence suggests that periportal components, including the ductular reaction and expansion of the hepatic progenitor cell compartment, may be involved and that the Th17 response may mediate disease progression. This review aims to provide an overview of the pathogenesis of NASH and summarises the evidence pertaining to key mechanisms implicated in the transition from steatosis and inflammation to fibrosis. Currently there are limited treatments for NASH although an increasing understanding of its pathogenesis will likely improve the development and use of interventions in the future.

Tracking the elusive fibrocyte: identification and characterization of collagen-producing hematopoietic lineage cells during murine wound healing

Fibrocytes are a unique population of circulating cells reported to exhibit characteristics of both hematopoietic and mesenchymal cells, and play an important role in wound healing. However, putative fibrocytes have been found to lose expression of hematopoietic surface markers such as CD45 during differentiation, making it difficult to track these cells in vivo with conventional methodologies. In this study, to distinguish hematopoietic and nonhematopoietic cells without surface markers, we took advantage of the gene vav 1, which is expressed solely on hematopoietic cells but not on other cell types, and established a novel transgenic mouse, in which hematopoietic cells are irreversibly labeled with green fluorescent protein and nonhematopoietic cells with red fluorescent protein. Use of single-cell transcriptional analysis in this mouse model revealed two discrete types of collagen I (Col I) expressing cells of hematopoietic lineage recruited into excisional skin wounds. We confirmed this finding on a protein level, with one subset of these Col I synthesizing cells being CD45+ and CD11b+, consistent with the traditional definition of a fibrocyte, while another was CD45- and Cd11b-, representing a previously unidentified population. Both cell types were found to initially peak, then reduce posthealing, consistent with a disappearance from the wound site and not a loss of identifying surface marker expression. Taken together, we have unambiguously identified two cells of hematopoietic origin that are recruited to the wound site and deposit collagen, definitively confirming the existence and natural time course of fibrocytes in cutaneous healing.

Mechanisms of fibrogenesis in liver cirrhosis: The molecular aspects of epithelial-mesenchymal transition

Liver injuries are repaired by fibrosis and regeneration. The cause of fibrosis and diminished regeneration, especially in liver cirrhosis, is still unknown. Epithelial-mesenchymal transition (EMT) has been found to be associated with liver fibrosis. The possibility that EMT could contribute to hepatic fibrogenesis reinforced the concept that activated hepatic stellate cells are not the only key players in the hepatic fibrogenic process and that other cell types, either hepatic or bone marrow-derived cells could contribute to this process. Following an initial enthusiasm for the discovery of this novel pathway in fibrogenesis, more recent research has started to cast serious doubts upon the real relevance of this phenomenon in human fibrogenetic disorders. The debate on the authenticity of EMT or on its contribution to the fibrogenic process has become very animated. The overall result is a general confusion on the meaning and on the definition of several key aspects. The aim of this article is to describe how EMT participates to hepatic fibrosis and discuss the evidence of supporting this possibility in order to reach reasonable and useful conclusions.

Inhibition of murine fibrocyte differentiation by cross-linked IgG is dependent on FcγRI

Monocyte-derived, fibroblast-like cells, called fibrocytes, participate in wound-healing and the formation of fibrotic lesions. Aggregated or cross-linked IgG are key effectors in infections, autoimmune diseases, anaphylaxis, and immunotherapy. Cells, including monocytes and fibrocytes, bind IgG using FcγRs, and aggregated or cross-linked IgG inhibits fibrocyte differentiation. Mice have four different FcγRs, and which of these, if any, mediate the cross-linked IgG effect on fibrocyte differentiation is unknown. We find that in mice, deletion of FcγRI or the common signaling protein FcRγ significantly reduces the ability of cross-linked IgG or IgG2a to inhibit fibrocyte differentiation. Cells from FcγRIIb/III/IV KO mice are still sensitive to cross-linked IgG, whereas cells from FcγRI/IIb/III/IV KO mice are insensitive to cross-linked IgG. These observations suggest that IgG-mediated inhibition of fibrocyte differentiation is mediated by FcγRs, with FcγRI mediating most of the signaling.

The chemokine receptor CXCR6 contributes to recruitment of bone marrow-derived fibroblast precursors in renal fibrosis

Bone marrow-derived fibroblasts in circulation are of hematopoietic origin, proliferate, differentiate into myofibroblasts, and express the chemokine receptor CXCR6. Since chemokines mediate the trafficking of circulating cells to sites of injury, we studied the role of CXCR6 in mouse models of renal injury. Significantly fewer bone marrow-derived fibroblasts accumulated in the kidney of CXCR6 knockout mice in response to injury, expressed less profibrotic chemokines and cytokines, displayed fewer myofibroblasts, and expressed less α-smooth muscle actin in the obstructed kidneys compared with wild-type mice. CXCR6 deficiency inhibited total collagen deposition and suppressed expression of collagen I and fibronectin in the obstructed kidneys. Furthermore, wild type mice engrafted with CXCR6^−/− bone marrow cells displayed fewer bone marrow-derived fibroblasts in the kidneys with obstructive injury and showed less severe renal fibrosis compared with wild-type mice engrafted with CXCR6^+/+ bone marrow cells. Transplant of wild type bone marrow into CXCR6^−/− recipients restored recruitment of myeloid fibroblasts and susceptibility to fibrosis. Hematopoietic fibroblasts migrate into injured kidney and proliferate and differentiate into myofibroblasts. Thus, CXCR6, together with other chemokines and their receptors, may play important roles in the recruitment of bone marrow-derived fibroblast precursors into the kidney and contribute to the pathogenesis of renal fibrosis.

Cellular and molecular mechanisms in liver fibrogenesis

Liver fibrogenesis is a dynamic and highly integrated molecular, tissue and cellular process, potentially reversible, that drives the progression of chronic liver diseases (CLD) towards liver cirrhosis and hepatic failure. Hepatic myofibroblasts (MFs), the pro-fibrogenic effector cells, originate mainly from activation of hepatic stellate cells and portal fibroblasts being characterized by a proliferative and survival attitude. MFs also contract in response to vasoactive agents, sustain angiogenesis and recruit and modulate activity of cells of innate or adaptive immunity. Chronic activation of wound healing and oxidative stress as well as derangement of epithelial-mesenchymal interactions are "major" pro-fibrogenic mechanisms, whatever the etiology. However, literature has outlined a complex network of pro-fibrogenic factors and mediators proposed to modulate CLD progression, with some of them being at present highly debated in the field, including the role of epithelial to mesenchymal transition and Hedgehog signaling pathways. Hypoxia and angiogenesis as well as inflammasomes are recently emerged as ubiquitous pro-inflammatory and pro-fibrogenic determinants whereas adipokines are mostly involved in CLD related to metabolic disturbances (metabolic syndrome and/or obesity and type 2 diabetes). Finally, autophagy as well as natural killer and natural killer-T cells have been recently proposed to significantly affect fibrogenic CLD progression.

Monitoring fibrogenic progression in the liver

The clinical course of chronic liver diseases is significantly dependent on the progression rate of fibrosis which is the unstructured replacement of injured parenchyma by extracellular matrix. Despite intensive studies, the clinical opportunities for patients with fibrosing liver diseases have not improved. This will be changed by increasing knowledge of new pathogenetic mechanisms, which complement the "canonical principle" of fibrogenesis. The latter is based on the activation of hepatic stellate cells and their transdifferentiation to myofibroblasts induced by hepatocellular injury and consecutive inflammatory mediators such as TGF-β. Stellate cells express a broad spectrum of matrix components. New mechanisms indicate that the heterogeneous pool of (myo-)fibroblasts can be supplemented by epithelial-mesenchymal transition (EMT) from cholangiocytes and potentially also from hepatocytes to fibroblasts, by influx of bone marrow-derived fibrocytes in the damaged liver tissue and by differentiation of a subgroup of monocytes to fibroblasts after homing in the damaged tissue. These processes are regulated by the cytokines TGF-β and BMP-7, chemokines, colony-stimulating factors, metalloproteinases and numerous trapping proteins. They offer innovative diagnostic and therapeutic options. As an example, modulation of TGF-β/BMP-7 ratio changes the rate of EMT, and so the simultaneous determination of these parameters and of the connective tissue growth factor (CTGF) in serum might provide information on fibrogenic activity. Also, proteomic and glycomic approaches of serum are under investigation to set up specific protein profiles in patients with liver fibrosis. The aim of this article is to present the current pathogenetic concepts of liver fibrosis and to discuss established and novel diagnostic approaches to reflect the process of hepatic fibrogenesis in the medical laboratory.

Hepatic stellate cells that coexpress LRAT and CRBP-1 partially contribute to portal fibrogenesis in patients with human viral hepatitis

BACKGROUND & AIMS

Precisely what type of cells mainly contributes to portal fibrosis, especially in chronic viral hepatitis, such as hepatic stellate cells (HSCs) in the parenchyma or myofibroblasts in the portal area, still remains unclear. It is necessary to clarify the characteristics of cells that contribute to portal fibrosis in order to determine the mechanism of portal fibrogenesis and to develop a therapeutic target for portal fibrosis. This study was undertaken to examine whether LRAT+/CRBP-1+ HSCs contribute to portal fibrosis on viral hepatitis.

METHODS

Antibodies to lecithin:retinol acyltransferase (LRAT), cellular retinol-binding protein-1 (CRBP-1) and widely ascertained antibodies to HSCs (alpha-smooth muscle actin, neurotrophin-3) and endothelial cells (CD31) were used for immunohistochemical studies to assess the distribution of cells that contribute to the development of portal fibrosis with the aid of fluorescence microscopy. A quantitative analysis of LRAT+/CRBP-1+ HSCs was performed.

RESULTS

The number of LRAT+/CRBP-1+ HSCs was increased in fibrotic liver in comparison with normal liver in the portal area and fibrous septa. The number of double positive cells was less than 20% of all cells/field in maximum.

CONCLUSION

This study provides evidence that functional HSCs coexpressing both LRAT and CRBP-1 that continue to maintain the ability to store vitamin A contribute in part to the development of portal fibrogenesis in addition to parenchymal fibrogenesis in patients with viral hepatitis.

Proteinase activated receptor 1 mediated fibrosis in a mouse model of liver injury: a role for bone marrow derived macrophages

Liver fibrosis results from the co-ordinated actions of myofibroblasts and macrophages, a proportion of which are of bone marrow origin. The functional effect of such bone marrow-derived cells on liver fibrosis is unclear. We examine whether changing bone marrow genotype can down-regulate the liver's fibrotic response to injury and investigate mechanisms involved. Proteinase activated receptor 1 (PAR1) is up-regulated in fibrotic liver disease in humans, and deficiency of PAR1 is associated with reduced liver fibrosis in rodent models. In this study, recipient mice received bone marrow transplantation from PAR1-deficient or wild-type donors prior to carbon tetrachloride-induced liver fibrosis. Bone marrow transplantation alone from PAR1-deficient mice was able to confer significant reductions in hepatic collagen content and activated myofibroblast expansion on wild-type recipients. This effect was associated with a decrease in hepatic scar-associated macrophages and a reduction in macrophage recruitment from the bone marrow. In vitro, PAR1 signalling on bone marrow-derived macrophages directly induced their chemotaxis but did not stimulate proliferation. These data suggest that the bone marrow can modulate the fibrotic response of the liver to recurrent injury. PAR1 signalling can contribute to this response by mechanisms that include the regulation of macrophage recruitment.

Paracrine functions of fibrocytes to promote lung fibrosis

Fibrocytes are derived from the bone marrow and are found in the circulation. They can be recruited to sites of injury and contribute to repair/remodeling. In vitro evidence suggests that fibrocytes may differentiate into fibroblasts to promote lung fibrosis. However, in vivo evidence for this is sparse. This review summarizes recent literature which may suggest that fibrocytes function to promote fibrosis via paracrine actions. In this way, secretion of growth factors, proteases and matricellular proteins may strongly influence the actions of resident epithelial and mesenchymal cells to promote repair and resolution or to tip the scale toward pathologic remodeling.

Understanding the origin, activation and regulation of matrix-producing myofibroblasts for treatment of fibrotic disease

Fibrosis and scar formation results from chronic progressive injury in virtually every tissue and affects a growing number of people around the world. Myofibroblasts drive fibrosis, and recent work has demonstrated that mesenchymal cells, including pericytes and perivascular fibroblasts, are their main progenitors. Understanding the cellular mechanisms of pericyte/fibroblast-to-myofibroblast transition, myofibroblast proliferation and the key signalling pathways that regulate these processes is essential to develop novel targeted therapeutics for the growing patient population suffering from solid organ fibrosis. In this review, we summarize the current knowledge about different progenitor cells of myofibroblasts, discuss major pathways that regulate their transdifferentiation and discuss the current status of novel targeted anti-fibrotic therapeutics in development.

Smoothelin, a new marker to determine the origin of liver fibrogenic cells

AIM: To explore this hypothesis that smooth muscle cells may be capable of acquiring a myofibroblastic phenotype, we have studied the expression of smoothelin in fibrotic conditions.

METHODS: Normal liver tissue (n = 3) was obtained from macroscopically normal parts of hepatectomy, taken at a distance from hemangiomas. Pathological specimens included post-burn cutaneous hypertrophic scars (n = 3), fibrotic liver tissue (n = 5), cirrhotic tissue (viral and alcoholic hepatitis) (n = 5), and hepatocellular carcinomas (n = 5). Tissue samples were fixed in 10% formalin and embedded in paraffin for immunohistochemistry or were immediately frozen in liquid nitrogen-cooled isopentane for confocal microscopy analysis. Sections were stained with antibodies against smoothelin, which is expressed exclusively by smooth muscle cells, and α-smooth muscle actin, which is expressed by both smooth muscle cells and myofibroblasts.

RESULTS: In hypertrophic scars, α-smooth muscle actin was detected in vascular smooth muscle cells and in numerous myofibroblasts present in and around nodules, whereas smoothelin was exclusively expressed in vascular smooth muscle cells. In the normal liver, vascular smooth muscle cells were the only cells that express α-smooth muscle actin and smoothelin. In fibrotic areas of the liver, myofibroblasts expressing α-smooth muscle actin were detected. Myofibroblasts co-expressing α-smooth muscle actin and smoothelin were observed, and their number was slightly increased in parallel with the degree of fibrosis (absent in liver with mild or moderate fibrosis; 5% to 10% positive in liver showing severe fibrosis). In cirrhotic septa, numerous myofibroblasts co-expressed α-smooth muscle actin and smoothelin (more than 50%). In hepatocellular carcinomas, the same pattern of expression for α-smooth muscle actin and smoothelin was observed in the stroma reaction surrounding the tumor and around tumoral cell plates. In all pathological liver samples, α-smooth muscle actin and smoothelin were co-expressed in vascular smooth muscle cells.

CONCLUSION: During development of advanced liver fibrosis, a subpopulation of myofibroblasts expressing smoothelin may be derived from vascular smooth muscle cells, illustrating the different cellular origins of myofibroblasts.

Signaling pathways involved in isoprostane-mediated fibrogenic effects in rat hepatic stellate cells

Despite evidence supporting a potential role for F2-isoprostanes (F2-IsoP's) in liver fibrosis, their signaling mechanisms are poorly understood. We have previously provided evidence that F2-IsoP's stimulate hepatic stellate cell (HSC) proliferation and collagen hyperproduction by activation of a modified form of isoprostane receptor homologous to the classic thromboxane receptor (TP). In this paper, we examined which signal transduction pathways are set into motion by F2-IsoP's to exert their fibrogenic effects. HSCs were isolated from rat liver, cultured to their activated myofibroblast-like phenotype, and then treated with the isoprostane 15-F2t-isoprostane (15-F2t-IsoP). Inositol trisphosphate (IP3) and adenosine 3',5'-cyclic monophosphate (cAMP) levels were determined using commercial kits. Mitogen-activated protein kinase (MAPK) and cyclin D1 expression was assessed by Western blotting. Cell proliferation and collagen synthesis were determined by measuring [(3)H]thymidine and [(3)H]proline incorporation, respectively. 15-F2t-IsoP elicited an activation of extracellular-signal-regulated kinase (ERK), p38 MAPK, and c-Jun NH2-terminal kinase (JNK), which are known to be also regulated by G-protein-coupled receptors. Preincubation with specific ERK (PD98059), p38 (SB203580), or JNK (SP600125) inhibitors prevented 15-F2t-IsoP-induced cell proliferation and collagen synthesis. 15-F2t-IsoP decreased cAMP levels within 30 min, suggesting binding to the TPβ isoform and activation of Giα protein. Also, 15-F2t-IsoP increased IP3 levels within a few minutes, suggesting that the Gq protein pathway is also involved. In conclusion, the fibrogenic effects of F2-IsoP's in HSCs are mediated by downstream activation of MAPKs, through TP binding that couples via both Gqα and Giα proteins. Targeting TP receptor, or its downstream pathways, may contribute to preventing oxidative damage in liver fibrosis.

Randomized placebo-controlled trial of mesenchymal stem cell transplantation in decompensated cirrhosis

BACKGROUND & AIMS

There has been great interest in recent years to take advantage of bone marrow stem cells to treat cirrhosis. Our uncontrolled trial showed promising results for bone marrow mesenchymal stem cell (MSC) transplantation in cirrhosis. Therefore, we conducted a randomized, placebo-controlled trial to evaluate the efficacy of autologous MSC transplantation in cirrhosis.

METHODS

The enrolled patients with decompensated cirrhosis were randomly assigned to receive MSC or placebo infusions. A median of 195 million (range: 120-295 million) cultured MSCs were infused through a peripheral vein. The primary outcome was absolute changes in MELD score. Secondary outcomes were absolute changes in Child score, liver function tests and liver volumes between the MSC and placebo group 12 months after infusion.

RESULTS

A total of 27 patients were enrolled. Of these, 15 patients received MSC and 12 patients received placebo. One patient in the MSC group and one patient in the placebo group were lost to follow-up. Three patients in the MSC group died of liver failure 3 months (one patient), or 5 months (two patients) after cellular infusion. The baseline MELD scores of the deceased patients were significantly higher than those who remained alive in either group (20.0 vs. 15.1; P = 0.02). The absolute changes in Child scores, MELD scores, serum albumin, INR, serum transaminases and liver volumes did not differ significantly between the MSC and placebo groups at 12 months of follow-up.

CONCLUSION

Based on this randomized controlled trial, autologous bone marrow MSC transplantation through peripheral vein probably has no beneficial effect in cirrhotic patients. Further studies with higher number of patients are warranted to better clarify the impact of MSC infusion through peripheral vein or portal vein in cirrhosis.

Associations between fibrocytes and postcontrast myocardial T1 times in hypertrophic cardiomyopathy

Background

Fibrocytes are bone marrow‐derived mesenchymal progenitors that have been linked to various fibrotic disorders. This study was undertaken to investigate whether fibrocytes are increased in diffuse myocardial fibrosis in humans.

Methods and Results

Thirty‐seven patients with hypertrophic cardiomyopathy (HCM) and 20 healthy controls were recruited. Cardiac magnetic resonance imaging with postcontrast T₁ mapping was performed to non‐invasively quantify diffuse myocardial fibrosis and these patients were classified into 2 groups (T₁<470 ms or T₁≥470 ms, as likely or unlikely to have diffuse fibrosis, respectively). Circulating fibrocytes (CD45+/CD34+/collagen I+) were measured by flow cytometry. Peripheral blood mononuclear cells (PBMCs) were cultured for 13 days and fibrocytes were quantitated by flow cytometry (CD45+/collagen I+) and real‐time PCR (gene expression of matrix proteins). Plasma cytokines/chemokines mediating fibrocyte trafficking and differentiation were measured by multiplex assays. Circulating fibrocytes were decreased in HCM patients compared to controls. The proportion of fibrocytes derived from PBMCs was increased in patients with diffuse fibrosis compared with those without or controls (31.1±4.1% versus 18.9±3.9% and 10.9±2.0%, P<0.05 and P<0.001, respectively), and the proportion of fibrocytes was inversely correlated with T₁ time (r=−0.37, P=0.03). Plasma levels of stromal cell‐derived factor‐1 were elevated in patients with diffuse fibrosis compared with those without or controls (5131±271 pg/mL versus 3893±356 pg/mL and 4172±185 pg/mL, respectively, both P<0.05).

Conclusions

HCM patients with diffuse fibrosis as assessed by postcontrast T₁ mapping have elevated plasma SDF and an enhanced ability of PBMCs to differentiate into fibrocytes, suggesting that fibrocytes may contribute to the pathogenesis of myocardial fibrosis.

CCR2 regulates the uptake of bone marrow-derived fibroblasts in renal fibrosis

Recent studies have shown that bone marrow-derived fibroblasts contribute significantly to the pathogenesis of renal fibrosis. However, the molecular mechanisms underlying the recruitment of bone marrow-derived fibroblasts into the kidney are incompletely understood. Bone marrow-derived fibroblasts express the chemokine receptor--CCR2. In this study, we tested the hypothesis that CCR2 participates in the recruitment of fibroblasts into the kidney during the development of renal fibrosis. Bone marrow-derived collagen-expressing GFP⁺ fibroblasts were detected in the obstructed kidneys of chimeric mice transplanted with donor bone marrow from collagen α1(I)-GFP reporter mice. These bone marrow-derived fibroblasts expressed PDGFR-β and CCR2. CCR2 knockout mice accumulated significantly fewer bone marrow-derived fibroblast precursors expressing the hematopoietic marker-CD45 and the mesenchymal markers-PDGFR-β or procollagen I in the obstructed kidneys compared with wild-type mice. Furthermore, CCR2 knockout mice displayed fewer bone marrow-derived myofibroblasts and expressed less α-SMA or FSP-1 in the obstructed kidneys compared with wild-type mice. Consistent with these findings, genetic deletion of CCR2 inhibited total collagen deposition and suppressed expression of collagen I and fibronectin. Moreover, genetic deletion of CCR2 inhibits MCP-1 and CXCL16 gene expression associated with a reduction of inflammatory cytokine expression and macrophage infiltration, suggesting a linear interaction between two chemokines/ligand receptors in tubular epithelial cells. Taken together, our results demonstrate that CCR2 signaling plays an important role in the pathogenesis of renal fibrosis through regulation of bone marrow-derived fibroblasts. These data suggest that inhibition of CCR2 signaling could constitute a novel therapeutic approach for fibrotic kidney disease.

Circulating fibrocytes and Crohn's disease

Background

Despite advances in medical therapy, there remains no effective preventive or non-surgical therapeutic option for fibrostenotic Crohn's disease (CD). Symptomatic recurrences are common, necessitating reintervention. Intestinal fibroblasts mediate stricture formation, but their exact source is unclear. Recent evidence indicates that circulating fibrocytes drive fibrosis through differentiation into fibroblasts and the production of extracellular matrix proteins. The aim of this review is to describe current understanding of the pathophysiology underlying fibrosis in CD, the cellular and molecular biology of fibrocytes and their role in CD.

Methods

The electronic literature (January 1972 to December 2012) on ‘circulating fibrocytes’ and ‘Crohn's fibrosis’ was reviewed.

Results

Circulating fibrocytes appear universally involved in organ fibrosis. A complex array of cytokines, chemokines and growth factors regulate fibrocyte biology, and these are associated with fibrogenesis in CD. The cytokines transforming growth factor β1, connective tissue growth factor and interleukin 13, overexpressed in the strictured Crohn's intestine, promote fibrocyte generation and/or differentiation.

Conclusion

Levels of circulating fibrocytes are raised in conditions marked by exaggerated fibrosis. These and other observations prompt a characterization of fibrocyte activity in CD with a view to investigating a pathogenic role.

Transplantation of mesenchymal stem cells for the treatment of liver diseases, is there enough evidence?

Mesenchymal stem cells or multipotent mesenchymal stromal cells (MSCs) have been extensively investigated in small animal models to treat both acute and chronic liver injuries. Mechanisms of action are not clearly elucidated but may include their ability to differentiate into hepatocyte-like cells, to reduce inflammation, and to enhance tissue repair at the site of injury. This approach is controversial and evidence in large animals is missing. Side effects of MSC infusion such as the contribution to a fibrotic process have been reported in experimental settings. Nevertheless, MSCs moved quickly from bench to bedside and over 280 clinical trials are registered, of which 28 focus on the treatment of liver diseases. If no severe side-effects were observed so far, long-term benefits remain uncertain. More preclinical data regarding mechanisms of action, long term safety and efficacy are warranted before initiating large scale clinical application. The proposal of this review is to visit the current state of knowledge regarding mechanisms behind the therapeutic effects of MSCs in the treatment of experimental liver diseases, to address questions about efficacy and risk, and to discuss recent clinical advances involving MSC-based therapies.

Interaction of hepatic stellate cells with diverse types of immune cells: foe or friend?

Activated hepatic stellate cells (HSCs) have been considered as a major type of cells in liver fibrosis by producing a huge amount of extracellular matrix, especially collagen fibers, and profibrotic mediators such as transforming growth factor-beta, interleukin-6 and monocyte chemoattractant protein-1. Recently, accumulated evidence suggests that the liver is an immunologic organ because of enrichment of diverse types of immune cells and that their interactions with HSCs are closely related with the progression of liver fibrosis. However, the underlying mechanisms of interaction between HSCs and immune cells remain largely unknown. Recently, several studies have demonstrated that natural killer cells, M2 macrophages, regulatory T cells, and bone marrow derived CD11b(+) Gr1(+) immature cells ameliorate liver fibrosis, whereas neutrophils, M1 macrophages, CD8 T cells, natural killer T cells and interleukin-17-producing cells accelerate liver fibrosis. However, there are still controversial issues about their functions during liver fibrogenesis. In this review, we summarize the diversity roles of immune cells (e.g. profibrotic/antifibrotic or both) in regulating the activation of HSCs during hepatic fibrogenesis, in which several producible mediators by HSCs play important roles in the interaction with them. Moreover, the current cell-based therapies using immune cells against liver fibrosis are discussed.

Cellular mechanisms of tissue fibrosis. 5. Novel insights into liver fibrosis

Liver fibrosis is the common scarring reaction associated with chronic liver injury that results from prolonged parenchymal cell injury and/or inflammation. The fibrogenic response is characterized by progressive accumulation of extracellular matrix components enriched in fibrillar collagens and a failure of matrix turnover. This process is driven by a heterogeneous population of hepatic myofibroblasts, which mainly derive from hepatic stellate cells and portal fibroblasts. Regression of fibrosis can be achieved by the successful control of chronic liver injury, owing to termination of the fibrogenic reaction following clearance of hepatic myofibroblasts and restoration of fibrolytic pathways. Understanding of the complex network underlying liver fibrogenesis has allowed the identification of a large number of antifibrotic targets, but no antifibrotic drug has as yet been approved. This review will highlight recent advances regarding the mechanisms that regulate liver fibrogenesis and fibrosis regression, with special focus on novel signaling pathways and the role of inflammatory cells. Translation of these findings to therapies will require continued efforts to develop multitarget therapeutic approaches that will improve the grim prognosis of liver cirrhosis.

Contribution of Myofibroblasts of Different Origins to Liver Fibrosis

The most common cause of liver failure is cirrhosis, due to progressive liver fibrosis and other architectural changes in the liver. Fibrosis occurs after liver injury or stress and results directly from an imbalance between the processes of extracellular matrix synthesis (fibrogenesis) and degradation (fibrolysis). Although research studies have identified several promising targets at the molecular level, current therapies to prevent and treat hepatic fibrosis in patients have only shown limited success. It is well established that liver myofibroblasts are the primary effector cells responsible for the extensive extracellular matrix accumulation and scar formation observed during hepatic fibrosis, in both clinical and experimental settings. Thus, as the major fibrogenic cells implicated in wound healing and tissue repair response, liver myofibroblasts could represent excellent targets for antifibrotic therapies. Still, the exact natures and identities of liver myofibroblasts precursors have yet to be resolved, and their relative contribution to hepatic fibrosis to be determined. The goal of this review is to examine the relative importance of liver myofibroblast precursors in the pathogenesis of liver fibrosis.

Mechanism of autoimmune hepatic fibrogenesis induced by an adenovirus encoding the human liver autoantigen cytochrome P450 2D6

Autoimmune hepatitis type 2 (AIH-2) is a severe autoimmune liver disease with unknown etiology. We recently developed the CYP2D6 mouse model for AIH-2, in which mice are challenged with an adenovirus (Ad-2D6) expressing human cytochrome P450 2D6 (hCYP2D6), the major autoantigen in AIH-2. Such mice develop chronic hepatitis with cellular infiltrations and generation of hCYP2D6-specific antibodies and T cells. Importantly, the CYP2D6 model represents the only model displaying chronic fibrosis allowing for a detailed investigation of the mechanisms of chronic autoimmune-mediated liver fibrogenesis. We found that hCYP2D6-dependent chronic activation of hepatic stellate cells (HSC) resulted in an increased extracellular matrix deposition and elevated expression of α-smooth muscle actin predominantly in and underneath the liver capsule. The route of Ad-2D6 infection dramatically influenced the activation and trafficking of inflammatory monocytes, NK cells and hCYP2D6-specific T cells. Intraperitoneal Ad-2D6 infection caused subcapsular fibrosis and persistent clustering of inflammatory monocytes. In contrast, intravenous infection caused an accumulation of hCYP2D6-specific CD4 T cells throughout the liver parenchyma and induced a strong NK cell response preventing chronic HSC activation and fibrosis. In summary, we found that the location of the initial site of inflammation and autoantigen expression caused a differential cellular trafficking and activation and thereby determined the outcome of AIH-2-like hepatic damage and fibrosis.

Myofibroblasts

PURPOSE OF REVIEW

Interest in the myofibroblast as a key player in propagation of chronic progressive fibrosis continues to elicit many publications, with focus on its cellular origins and the mechanisms underpinning their differentiation and/or transition. The objective of the review is to highlight this recent progress.

RECENT FINDINGS

The epithelial origin of the myofibroblast in fibrosis has been challenged by recent studies, with the pericyte suggested as a possible precursor instead. Additional signaling pathways, including Notch, Wnt, and hedgehog, are implicated in myofibroblast differentiation. The importance of NADPH oxidase 4 was highlighted recently to suggest a potential link between cellular/oxidative stress and the genesis of the myofibroblast. Recent observations on the importance of lysophosphatidic acid in fibrosis suggest that this may be due, in part, to its ability to regulate myofibroblast differentiation. Finally, there is increasing evidence for the role of epigenetic mechanisms in regulating myofibroblast differentiation, including DNA methylation and miRNA regulation of gene expression.

SUMMARY

These recent discoveries open up a whole new array of potential targets for novel antifibrotic therapies. This is of special importance given the current bleak outlook for chronic progressive fibrotic diseases, such as scleroderma, due to lack of effective therapies.

Translating an understanding of the pathogenesis of hepatic fibrosis to novel therapies

The response to injury is one of wound healing and fibrogenesis, which ultimately leads to fibrosis. The fibrogenic response to injury is a generalized one across virtually all organ systems. In the liver, the injury response, typically occurring over a prolonged period of time, leads to cirrhosis (although it should be pointed out that not all patients with liver injury develop cirrhosis). The fact that many different diseases result in cirrhosis suggests a common pathogenesis. The study of hepatic fibrogenesis over the past 2 decades has been remarkably active, leading to a considerable understanding of this process. It clearly has been shown that the hepatic stellate cell is a central component in the fibrogenic process. It also has been recognized that other effector cells are important in the fibrogenic process, including resident fibroblasts, bone marrow-derived cells, fibrocytes, and even perhaps cells derived from epithelial cells (ie, through epithelial to mesenchymal transition). A key aspect of the biology of fibrogenesis is that the fibrogenic process is dynamic; thus, even advanced fibrosis (or cirrhosis) is reversible. Together, an understanding of the cellular basis for liver fibrogenesis, along with multiple aspects of the basic pathogenesis of fibrosis, have highlighted many exciting potential therapeutic opportunities. Thus, although the most effective antifibrotic therapy is simply treatment of the underlying disease, in situations in which this is not possible, specific antifibrotic therapy is likely not only to become feasible, but will soon become a reality. This review highlights the mechanisms underlying fibrogenesis that may be translated into future antifibrotic therapies and to review the current state of clinical development.

Bone marrow contributions to fibrosis

Bone marrow transplant experiments in mice using labelled donor bone marrow have indicated that following injury bone marrow derived cells can circulate and home to the injured organs. In particular fibrocytes and myofibroblasts are capable of contributing to the wound healing response, including collagen deposition. In chronic injury this can lead to a pathological degree of fibrosis. Experiments have shown that this can be a relatively insignificant contribution to the scar forming population in certain organs and that the majority of the scar forming cells are intrinsic to the organ. Conversely, in certain circumstances, the circulating cells become major players in the organs fibrotic response. Whilst cell tracking experiments are relatively simple to perform, to actually determine a functional contribution to a fibrotic response more sophisticated approaches are required. This can include the use of bone marrow transplantation from recipients with collagen reporter systems which gives a read out of bone marrow derived cells that are transcriptional active for collagen production in a damaged organ. Another technique is to use bone marrow transplants from donors that have a mutation in the collagen to demonstrate a functional difference in fibrosis when bone marrow transplants performed. Recent reports have identified factors mediating recruitment of circulating fibrocytes to injured organs, such as CXCL12 and CXCL16 and shown that blocking these factors reduced fibrocyte recruitment and subsequent fibrosis. The identification of such factors may enable the development of novel therapies to block further fibrocyte engraftment and fibrosis in situations of pathological scarring. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Cellular mechanisms of tissue fibrosis. 1. Common and organ-specific mechanisms associated with tissue fibrosis

Fibrosis is a pathological scarring process that leads to destruction of organ architecture and impairment of organ function. Chronic loss of organ function in most organs, including bone marrow, heart, intestine, kidney, liver, lung, and skin, is associated with fibrosis, contributing to an estimated one third of natural deaths worldwide. Effective therapies to prevent or to even reverse existing fibrotic lesions are not yet available in any organ. There is hope that an understanding of common fibrosis pathways will lead to development of antifibrotic therapies that are effective in all of these tissues in the future. Here we review common and organ-specific pathways of tissue fibrosis.

Implication for bone marrow derived stem cells in hepatocyte regeneration after orthotopic liver transplantation

The liver has the outstanding ability to regenerate itself and restore parenchymal tissue after injury. The most common cell source in liver growth/regeneration is replication of preexisting hepatocytes although liver progenitor cells have been postulated to participate in liver regeneration in cases of massive injury. Bone marrow derived hematopoietic stem cells (BM-HSC) have the formal capacity to act as a source for hepatic regeneration under special circumstances; however, the impact of this process in liver tissue maintenance and regeneration remains controversial. Whether BM-HSC are involved in liver regeneration or not would be of particular interest as the cells have been suggested to be an alternative donor source for the treatment of liver failure. Data from murine models of liver disease show that BM-HSC can repopulate liver tissue and restore liver function; however, data obtained from human liver transplantation show only little evidence for liver regeneration by this mechanism. The cell source for liver regeneration seems to depend on the nature of regeneration process and the extent of injury; however, the precise mechanisms still need to be resolved. Current data suggest, that in human orthotopic liver transplantation, liver regeneration by BM-HSC is a rather rare event and therefore not of clinical relevance.

Regulation and role of connective tissue growth factor in AngII-induced myocardial fibrosis

Exposure of rodents to angiotensin II (AngII) is a common model of fibrosis. We have previously shown that cellular infiltration of bone marrow-derived progenitor cells (fibrocytes) occurs before deposition of extracellular matrix and is associated with the production of connective tissue growth factor (CTGF). In the present study, we characterized the role of CTGF in promoting fibrocyte accumulation and regulation after AngII exposure. In animals exposed to AngII using osmotic minipumps (2.0 μg/kg per min), myocardial CTGF mRNA peaked at 6 hours (21-fold; P < 0.01), whereas transforming growth factor-β (TGF-β) peaked at 3 days (fivefold; P < 0.05) compared with saline control. Early CTGF expression occurred before fibrocyte migration (1 day) into the myocardium or ECM deposition (3 days). CTGF protein expression was evident by day 3 of AngII exposure and seemed to be localized to resident cells. Isolated cardiomyocytes and microvascular endothelial cells responded to AngII with increased CTGF production (2.1-fold and 2.8-fold, respectively; P < 0.05), which was abolished with the addition of anti-TGF-β neutralizing antibody. The effect of CTGF on isolated fibrocytes suggested a role in fibrocyte proliferation (twofold; P < 0.05) and collagen production (2.3-fold; P < 0.05). In summary, we provide strong evidence that AngII exposure first resulted in Smad2-dependent production of CTGF by resident cells (6 hours), well before the accumulation of fibrocytes or TGF-β mRNA up-regulation. In addition, CTGF contributes to fibrocyte proliferation in the myocardium and enhances fibrocyte differentiation into a myofibroblast phenotype responsible for ECM deposition.

Mechanical aspects of lung fibrosis: a spotlight on the myofibroblast

Contractile myofibroblasts are responsible for the irreversible alterations of the lung parenchyma that hallmark pulmonary fibrosis. In response to lung injury, a variety of different precursor cells can become activated to develop myofibroblast features, most notably formation of stress fibers and expression of α-smooth muscle actin. Starting as an acute and beneficial repair process, myofibroblast secretion of collagen and contraction frequently becomes excessive and persists. The result is accumulation of stiff scar tissue that obstructs and ultimately destroys lung function. In addition to being a consequence of myofibroblast activities, the stiffened tissue is also a major promoter of the myofibroblast. The mechanical properties of scarred lung and fibrotic foci promote myofibroblast contraction and differentiation. One essential element in this detrimental feed-forward loop is the mechanical activation of the profibrotic growth factor transforming growth factor-β1 from stores in the extracellular matrix. Interfering with myofibroblast contraction and integrin-mediated force transmission to latent transforming growth factor-β1 and matrix proteins are here presented as possible therapeutic strategies to halt fibrosis.

Low molecular weight heparin inhibits circulating fibrocytes differentiation by modulating neuronal nitric oxide synthase and TGF-β1/Smad pathway

BACKGROUND/AIMS

Circulating fibrocytes (CFs) have been placed at the center of a number of fibrosing conditions. Recently, attention has been drawn to the non-anticoagulant activities of low molecular weight heparin (LH), especially its anti-fibrotic effects. The purpose of this study was to investigate the effects of LH on CFs differentiation and possible underlying mechanisms.

METHODS/RESULTS

CFs were cultured from human peripheral blood mononuclear cells and identified by dual-immunofluorescence staining. Incubation with LH inhibited CFs trans-differentiation by upregulating CD34 and downregulating pro-Collagen I and a-SMA in a concentration- and time-dependent manner, all of which were detected by flow cytometry. Similar effects were observed after incubation with L-NAME, an inhibitor of NOS. NO production was measured by Griess methods and markedly decreased in CFs treated with LH. Three NOS isoforms were assessed by western blot and nNOS was the predominant isoform involved in this process. Additionally, LH and L-NAME had similar down-regulating effects on the expression of TGF-β1 and pSmad2/3, which indicated that TGF-β/Smad pathway might be a downstream signaling of nNOS/NO during LH treatment.

CONCLUSION

These results suggested that LH could exhibit anti-fibrotic effects by inhibiting CFs transdifferentiation, in which the involvement of nNOS/NO and TGF-β/Smad pathway were identified.

Tissues use resident dendritic cells and macrophages to maintain homeostasis and to regain homeostasis upon tissue injury: the immunoregulatory role of changing tissue environments

Most tissues harbor resident mononuclear phagocytes, that is, dendritic cells and macrophages. A classification that sufficiently covers their phenotypic heterogeneity and plasticity during homeostasis and disease does not yet exist because cell culture-based phenotypes often do not match those found in vivo. The plasticity of mononuclear phagocytes becomes obvious during dynamic or complex disease processes. Different data interpretation also originates from different conceptual perspectives. An immune-centric view assumes that a particular priming of phagocytes then causes a particular type of pathology in target tissues, conceptually similar to antigen-specific T-cell priming. A tissue-centric view assumes that changing tissue microenvironments shape the phenotypes of their resident and infiltrating mononuclear phagocytes to fulfill the tissue's need to maintain or regain homeostasis. Here we discuss the latter concept, for example, why different organs host different types of mononuclear phagocytes during homeostasis. We further discuss how injuries alter tissue environments and how this primes mononuclear phagocytes to enforce this particular environment, for example, to support host defense and pathogen clearance, to support the resolution of inflammation, to support epithelial and mesenchymal healing, and to support the resolution of fibrosis to the smallest possible scar. Thus, organ- and disease phase-specific microenvironments determine macrophage and dendritic cell heterogeneity in a temporal and spatial manner, which assures their support to maintain and regain homeostasis in whatever condition. Mononuclear phagocytes contributions to tissue pathologies relate to their central roles in orchestrating all stages of host defense and wound healing, which often become maladaptive processes, especially in sterile and/or diffuse tissue injuries.

HAb18G/CD147 promotes activation of hepatic stellate cells and is a target for antibody therapy of liver fibrosis

BACKGROUND & AIMS

Activated hepatic stellate cells (HSCs) located in the Disse's space play a crucial role in liver fibrosis. HAb18G/CD147, a tumor-related glycoprotein, is highly expressed in hepatocellular carcinoma cells and fibroblasts. Whether HAb18G/CD147 plays an important role in the hepatic fibrogenesis is unknown.

METHODS

Immunohistochemistry for HAb18G/CD147 and α-smooth muscle actin expression in diseased liver tissues was used for correlation analysis. The function of HAb18G/CD147 in fibrogenesis was evaluated with the human HSCs LX-2 cell line and carbon tetrachloride-induced mouse liver fibrosis model. The specific antibody HAb18 targeting HAb18G/CD147 was injected intravenously into the mouse to investigate whether HAb18G/CD147 could be a potential target for liver fibrosis treatment.

RESULTS

HAb18G/CD147 is highly expressed on activated HSCs in the sinusoid. The positive rates of HAb18G/CD147 expression in human HBV-related liver cirrhosis, liver biopsy with HBV and liver adjacent to hemangioma were 95.6% (65/68), 14.8% (8/54) and 6.4% (8/125), respectively. HAb18G/CD147 expression was significantly correlated with the Child-Pugh grade (r=0.2848, p=0.0186) and with the expression of α-smooth muscle actin in HSCs (r=0.4434, p=0.0002) in liver cirrhosis. Transforming growth factor-β1 upregulated HAb18G/CD147 expression in LX-2 cells. Transfection of HAb18G/CD147 promoted the profibrogenic genes expression. In mouse liver fibrosis model, HAb18G/CD147 expression increased with the development of fibrogenesis and decreased during the liver fibrosis spontaneous recovery. The HAb18 targeting HAb18G/CD147 could attenuate liver fibrosis.

CONCLUSIONS

These data suggest that HAb18G/CD147 plays a role in HSC activation and is a potential therapeutic target in fibrosis/cirrhosis.

The mandibular ridge oral mucosa model of stromal influences on the endothelial tip cells: an immunohistochemical and TEM study

This study aimed to evaluate by immunohistochemistry and transmission electron microscopy (TEM) the morphological features of the oral mucosa endothelial tip cells (ETCs) and to determine the immune and ultrastructural patterns of the stromal nonimmune cells which could influence healing processes. Immune labeling was performed on bioptic samples obtained from six edentulous patients undergoing surgery for dental implants placement; three normal samples were collected from patients prior to the extraction of the third mandibular molar. The antibodies were tested for CD34, CD117(c-kit), platelet derived growth factor receptor-alpha (PDGFR-α), Mast Cell Tryptase, CD44, vimentin, CD45, CD105, alpha-smooth muscle actin, FGF2, Ki67. In light microscopy, while stromal cells (StrCs) of the reparatory and normal oral mucosa, with a fibroblastic appearance, were found positive for a CD34/CD44/CD45/CD105/PDGFR-α/vimentin immune phenotype, the CD117/c-kit labeling led to a positive stromal reaction only in the reparatory mucosa. In TEM, non-immune StrCs presenting particular ultrastructural features were identified as circulating fibrocytes (CFCs). Within the lamina propria CFCs were in close contact with ETCs. Long processes of the ETCs were moniliform, and hook-like collaterals were arising from the dilated segments, suggestive for a different stage migration. Maintenance and healing of oral mucosa are so supported by extensive processes of angiogenesis, guided by ETCs that, in turn, are influenced by the CFCs that populate the stromal compartment both in normal and reparatory states. Therefore, CFCs could be targeted by specific therapies, with pro- or anti-angiogenic purposes.

Fibrocytes are associated with the fibrosis of coronary heart disease

Fibrocytes contribute significantly to fibrosis in many cardiac diseases. However, it is not clear whether fibrocytes are associated with the fibrosis in coronary heart disease (CHD). The aim of this study was to determine whether fibrocytes are involved in cardiac fibrosis in CHD. We identified the presence of fibrocytes in CHD heart by immunofluorescence and confocal microscopy, examined the collagen volume fraction by Masson's Trichrome staining, and evaluated the correlation between fibrocytes and cardiac fibrosis. In conjunction, we examined the location of CXCL12, a homing factor and specific ligand for CXCR4, by immunohistochemistry. Fibrocytes were identified in 26 out of 27 CHD hearts and in 10 out of 11 normal hearts. Combinations, including CD34/αSMA, CD34/procollagen-I, CD45/αSMA, CXCR4/procollagen-I and CXCR4/αSMA, stained significantly more fibrocytes in CHD hearts as compared with those in normal hearts (p<0.05). There were positive correlations between the collagen volume fraction and the amount of fibrocytes (r=0.558; p=0.003<0.01) and between the number of CXCR4(+) fibrocytes and the CXCL12(+) cells (r=0.741; p=0.000<0.01) in CHD hearts. Based upon these findings, we conclude that fibrocytes, likely recruited through the CXCR4/CXCL12 axis, may contribute to the increase in the fibroblast population in CHD heart.

Extracellular matrix degradation in liver fibrosis: Biochemistry and regulation

Fibrosis is a highly conserved wound healing response and represents the final common pathway of virtually all chronic inflammatory injuries. Over the past 3 decades detailed analysis of hepatic extracellular matrix synthesis and degradation using approaches incorporating human disease, experimental animal models and cell culture have highlighted the extraordinarily dynamic nature of tissue repair and remodelling in this solid organ. Furthermore emerging studies of fibrosis in other organs demonstrate that basic common mechanisms exist, suggesting that bidirectionality of the fibrotic process may not solely be the preserve of the liver. In this review we will examine the cellular and molecular mechanisms that govern extracellular matrix degradation and fibrosis resolution, and highlight how manipulation of these processes may result in the development of effective anti-fibrotic therapies. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Bone marrow progenitor cells do not contribute to liver fibrogenic cells

AIM

To investigate the contribution of bone marrow (BM) cells to hepatic fibrosis.

METHODS

To establish a model of chimerism, C57Bl/6 female mice were subjected to full-body irradiation (7 Gy) resulting in BM myeloablation. BM mononuclear cells obtained from male transgenic mice expressing enhanced green fluorescent protein (GFP) were used for reconstitution. Engraftment was confirmed by flow cytometry. To induce liver injury, chimeric animals received carbon tetrachloride (CCl(4)) 0.5 mL/kg intraperitoneally twice a week for 30 d (CCl(4) 30 d) and age-matched controls received saline (Saline 30 d). At the end of this period, animals were sacrificed for post mortem analysis. Liver samples were stained with hematoxylin and eosin to observe liver architectural changes and with Sirius red for collagen quantification by morphometric analysis. α-smooth muscle actin (α-SMA) was analyzed by confocal microscopy to identify GFP+ cells with myofibroblast (MF) characteristics. Liver tissue, BM and peripheral blood were collected and prepared for flow cytometric analysis using specific markers for detection of hepatic stellate cells (HSCs) and precursors from the BM.

RESULTS

Injury to the liver induced changes in the hepatic parenchymal architecture, as reflected by the presence of inflammatory infiltrate and an increase in collagen deposition (Saline 30 d = 11.10% ± 1.12% vs CCl(4) 30 d = 12.60% ± 0.73%, P = 0.0329). Confocal microscopy revealed increased reactivity against α-SMA in CCl(4) 30 d compared to Saline 30 d, but there was no co-localization with GFP+ cells, suggesting that cells from BM do not differentiate to MFs. Liver flow cytometric analysis showed a significant increase of CD45+/GFP+ cells in liver tissue (Saline 30 d = 3.2% ± 2.2% vs CCl(4) 30 d = 5.8% ± 1.3%, P = 0.0458), suggesting that this increase was due to inflammatory cell infiltration (neutrophils and monocytes). There was also a significant increase of common myeloid progenitor cells (CD117+/CD45+) in the livers of CCl(4)-treated animals (Saline 30 d = 2.16% ± 1.80% vs CCl(4) 30 d = 5.60% ± 1.30%, P = 0.0142). In addition the GFP-/CD38+/CD45- subpopulation was significantly increased in the CCl(4) 30 d group compared to the Saline 30 d group (17.5% ± 3.9% vs 9.3% ± 2.4%, P = 0.004), indicating that the increase in the activated HSC subpopulation was not of BM origin.

CONCLUSION

BM progenitor cells do not contribute to fibrosis, but there is a high recruitment of inflammatory cells that stimulates HSCs and MFs of liver origin.

NaCl potentiates human fibrocyte differentiation

Excessive NaCl intake is associated with a variety of fibrosing diseases such as renal and cardiac fibrosis. This association has been attributed to increased blood pressure as the result of high NaCl intake. However, studies in patients with high NaCl intake and fibrosis reveal a connection between NaCl intake and fibrosis that is independent of blood pressure. We find that increasing the extracellular concentration of NaCl to levels that may occur in human blood after high-salt intake can potentiate, in serum-free culture conditions, the differentiation of freshly-isolated human monocytes into fibroblast-like cells called fibrocytes. NaCl affects the monocytes directly during their adhesion. Potassium chloride and sodium nitrate also potentiate fibrocyte differentiation. The plasma protein Serum Amyloid P (SAP) inhibits fibrocyte differentiation. High levels of extracellular NaCl change the SAP Hill coefficient from 1.7 to 0.8, and cause a four-fold increase in the concentration of SAP needed to inhibit fibrocyte differentiation by 95%. Together, our data suggest that NaCl potentiates fibrocyte differentiation. NaCl-increased fibrocyte differentiation may thus contribute to NaCl-increased renal and cardiac fibrosis.

Angiotensin II induces skin fibrosis: a novel mouse model of dermal fibrosis

Introduction

Systemic sclerosis (SSc) is an autoimmune inflammatory disorder of unknown etiology characterized by fibrosis of the skin and internal organs. Ang II (angiotensin II), a vasoconstrictive peptide, is a well-known inducer of kidney, heart, and liver fibrosis. The goal of this study was to investigate the profibrotic potential of Ang II in the mouse skin.

Methods

Ang II was administered by subcutaneous osmotic mini pumps to C57BL/6 male mice. Collagen-content measurements were performed with Gomori Trichrome staining and hydroxyproline assay. The mRNA expression level of collagens, TGF-β1, TGF-β2, TGF-β3, CTGF, αSMA, CD3, Emr1, CD45/B220, MCP1, and FSP1 were quantified with real-time polymerase chain reaction (PCR). Immunostaining was performed for markers of inflammation and fibrosis, including, phospho-Smad2, αSMA, CD3, Mac3, CD45/B220, and CD163B. Fibrocytes were identified by double staining with CD45/FSP1 and CD45/PH4. Endothelial cells undergoing endothelial-to-mesenchymal transition (EndoMT) were identified by double staining with VE-cadherin/FSP1.

Results

Ang II-infused mice develop prominent dermal fibrosis in the area proximal to the pump, as shown by increased collagen and CTGF mRNA levels, increased hydroxyproline content, and more tightly packed collagen fibers. In addition, elevated mRNA levels of TGF-β2 and TGF-β3 along with increased expression of pSmad2 were observed in the skin of Ang II-treated mice. Dermal fibrosis was accompanied by an increased number of infiltrating fibrocytes, and an increased number of αSMA-positive cells, as well as CD163B⁺ macrophages in the upper dermis. This correlated with significantly increased mRNA levels of αSMA, Emr1, and MCP1. Infiltration of CD3-, CD45/B220-, and Mac3-positive cells was observed mainly in the hypodermis. Furthermore, an increased number of double-positive VE-cadherin/FSP1 cells were detected in the hypodermis only.

Conclusions

This work demonstrates that Ang II induces both inflammation and fibrosis in the skin via MCP1 upregulation and accumulation of activated fibroblasts. Additionally, our data suggest that populations of these fibroblasts originate from circulating blood cells. Ang II infusion via osmotic minipumps could serve as a useful mouse model of skin fibrosis to gain new insights into pathogenic mechanisms and to test new antifibrotic therapies.

Mucosal healing and fibrosis after acute or chronic inflammation in wild type FVB-N mice and C57BL6 procollagen α1(I)-promoter-GFP reporter mice

Background

Injury and intestinal inflammation trigger wound healing responses that can restore mucosal architecture but if chronic, can promote intestinal fibrosis. Intestinal fibrosis is a major complication of Crohn’s disease. The cellular and molecular basis of mucosal healing and intestinal fibrosis are not well defined and better understanding requires well characterized mouse models.

Methods

FVB-N wild type mice and C57BL6 procollagen α1(I)-GFP reporter mice were given one (DSS1) or two (DSS2) cycles of 3% DSS (5 days/cycle) followed by 7 days recovery. Histological scoring of inflammation and fibrosis were performed at DSS1, DSS1+3, DSS1+7, DSS2, DSS2+3, and DSS2+7. Procollagen α1(I)-GFP activation was assessed in DSS and also TNBS models by whole colon GFP imaging and fluorescence microscopy. Colocalization of GFP with α-smooth muscle actin (α-SMA) or vimentin was examined. GFP mRNA levels were tested for correlation with endogenous collagen α1(I) mRNA.

Results

Males were more susceptible to DSS-induced disease and mortality than females. In FVB-N mice one DSS cycle induced transient mucosal inflammation and fibrosis that resolved by 7 days of recovery. Two DSS cycles induced transmural inflammation and fibrosis in a subset of FVB-N mice but overall, did not yield more consistent, severe or sustained fibrosis. In C57BL6 mice, procollagen α1(I)-GFP reporter was activated at the end of DSS1 and through DSS+7 with more dramatic and transmural activation at DSS2 through DSS2+7, and in TNBS treated mice. In DSS and TNBS models GFP reporter expression localized to vimentin⁺ cells and much fewer α-SMA⁺ cells. GFP mRNA strongly correlated with collagen α1(I) mRNA.

Conclusions

One DSS cycle in FVB-N mice provides a model to study mucosal injury and subsequent mucosal healing. The procollagen α1(I)-GFP transgenic provides a useful model to study activation of a gene encoding a major extracellular matrix protein during acute or chronic experimental intestinal inflammation and fibrosis.

Gremlin in the pathogenesis of hepatocellular carcinoma complicating chronic hepatitis C: an immunohistochemical and PCR study of human liver biopsies

Background

The possible role of secretory products of fibrous tissue in the development of hepatocellular carcinoma (HCC) complicating chronic hepatitis C was investigated. Our hypothesis was that gremlin, secreted by fibroblasts, inhibited bone morphogenic protein (BMP), which mediates stem cell maturation into adult functioning hepatocytes, and thus, arrest stem cell maturation and promoted their proliferation in an immature state possibly culminating into development of HCCs.

Results

Protein expression of cytokeratin 19 (CK19) and fibroblast growth factor 2 (FGF-2), and mRNA expression of gremlin and BMP-7 were studied in 35 cases of chronic hepatitis, cirrhosis and HCC complicating chronic hepatitis C. CK19 expression was higher in cases of cirrhosis (0.004), which correlated with the grade (r = 0.64, p = 0.009) and stage (r = 0.71, p = 0.001). All HCCs were negative for CK19. Stem cell niche activation (as indicated as a ductular reaction) was highest in cases of cirrhosis (p = 0.001) and correlated with CK19 expression (r = 0.42, p = 0.012), the grade(r = 0.56, p = 0.024) and stage (0.66, p = 0.006). FGF-2 expression was highest in HCCs and correlated with the grade (r = 0.6, p = 0.013), stage (0.72, p = 0.002), CK19 expression (r = 0.71, p = 002) and ductular reaction (0.68, p = 0.004) in hepatitis cases. Higher numbers of cirrhosis cases and HCCs (p = 0.009) showed gremlin expression, which correlated with the stage (r = 0.7, p = 0.002). Gremlin expression correlated with that of CK19 (r = 0.699, p = 0.003) and FGF2 (r = 0.75, p = 0.001) in hepatitis cases.

Conclusions

Fibrosis promotes carcinogenesis by fibroblast-secreted gremlin that blocks BMP function and promotes stem cell activation and proliferation as well as possibly HCC development.

Role of sphingosine 1-phosphate and lysophosphatidic acid in fibrosis

This review highlights an emerging role for sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) in many different types of fibrosis. Indeed, both LPA and S1P are involved in the multi-process pathogenesis of fibrosis, being implicated in promoting the well-established process of differentiation of fibroblasts to myofibroblasts and the more controversial epithelial-mesenchymal transition and homing of fibrocytes to fibrotic lesions. Therefore, targeting the production of these bioactive lysolipids or blocking their sites/mechanisms of action has therapeutic potential. Indeed, LPA receptor 1 (LPA(1)) selective antagonists are currently being developed for the treatment of fibrosis of the lung as well as a neutralising anti-S1P antibody that is currently in Phase 1 clinical trials for treatment of age related macular degeneration. Thus, LPA- and S1P-directed therapeutics may not be too far from the clinic. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.