Secondary lymphoid tissue chemokine (SLC/CCL21)/CCR7 signaling regulates fibrocytes in renal fibrosis

Inhibition of CTGF ameliorates peritoneal fibrosis through suppression of fibroblast and myofibroblast accumulation and angiogenesis

Peritoneal fibrosis (PF) is a serious complication in various clinical settings, but the mechanisms driving it remain to be fully determined. Connective tissue growth factor (CTGF) is known to regulate fibroblast activities. We therefore examined if CTGF inhibition has anti-fibrotic effects in PF. PF was induced by repetitive intraperitoneal injections of chlorhexidine gluconate (CG) in mice with type I pro-collagen promoter-driven green fluorescent protein (GFP) expression to identify fibroblasts. FG-3019, an anti-CTGF monoclonal antibody, was used to inhibit CTGF. CG-induced PF was significantly attenuated in FG-3019-treated mice. CG challenges induced marked accumulations of proliferating fibroblasts and of myofibroblasts, which were both reduced by FG-3019. Levels of peritoneal CTGF expression were increased by CG challenges, and suppressed in FG-3019-treated mice. FG-3019 treatment also reduced the number of CD31⁺ vessels and VEGF-A-positive cells in fibrotic peritoneum. In vitro studies using NIH 3T3 fibroblasts and peritoneal mesothelial cells (PMCs) showed that CTGF blockade suppressed TGF-β₁-induced fibroblast proliferation and myofibroblast differentiation, PMC mesothelial-to-mesenchymal transition, and VEGF-A production. These findings suggest that the inhibition of CTGF by FG-3019 might be a novel treatment for PF through the regulation of fibroblast and myofibroblast accumulation and angiogenesis.

High sodium diet converts renal proteoglycans into pro-inflammatory mediators in rats

BACKGROUND

High dietary sodium aggravates renal disease by affecting blood pressure and by its recently shown pro-inflammatory and pro-fibrotic effects. Moreover, pro-inflammatory modification of renal heparan sulfate (HS) can induce tissue remodeling. We aim to investigate if high sodium intake in normotensive rats converts renal HS into a pro-inflammatory phenotype, able to bind more sodium and orchestrate inflammation, fibrosis and lymphangiogenesis.

METHODS

Wistar rats received a normal diet for 4 weeks, or 8% NaCl diet for 2 or 4 weeks. Blood pressure was monitored, and plasma, urine and tissue collected. Tissue sodium was measured by flame spectroscopy. Renal HS and tubulo-interstitial remodeling were studied by biochemical, immunohistochemical and qRT-PCR approaches.

RESULTS

High sodium rats showed a transient increase in blood pressure (week 1; p<0.01) and increased sodium excretion (p<0.05) at 2 and 4 weeks compared to controls. Tubulo-interstitial T-cells, myofibroblasts and mRNA levels of VCAM1, TGF-β1 and collagen type III significantly increased after 4 weeks (all p<0.05). There was a trend for increased macrophage infiltration and lymphangiogenesis (both p = 0.07). Despite increased dermal sodium over time (p<0.05), renal concentrations remained stable. Renal HS of high sodium rats showed increased sulfation (p = 0.05), increased L-selectin binding to HS (p<0,05), and a reduction of sulfation-sensitive anti-HS mAbs JM403 (p<0.001) and 10E4 (p<0.01). Hyaluronan expression increased under high salt conditions (p<0.01) without significant changes in the chondroitin sulfate proteoglycan versican. Statistical analyses showed that sodium-induced tissue remodeling responses partly correlated with observed HS changes.

CONCLUSION

We show that high salt intake by healthy normotensive rats convert renal HS into high sulfated pro-inflammatory glycans involved in tissue remodeling events, but not in increased sodium storage.

The non-canonical NF-κB pathway in immunity and inflammation

The nuclear factor-κB (NF-κB) family of transcription factors is activated by canonical and non-canonical signalling pathways, which differ in both signalling components and biological functions. Recent studies have revealed important roles for the non-canonical NF-κB pathway in regulating different aspects of immune functions. Defects in non-canonical NF-κB signalling are associated with severe immune deficiencies, whereas dysregulated activation of this pathway contributes to the pathogenesis of various autoimmune and inflammatory diseases. Here we review the signalling mechanisms and the biological function of the non-canonical NF-κB pathway. We also discuss recent progress in elucidating the molecular mechanisms regulating non-canonical NF-κB pathway activation, which may provide new opportunities for therapeutic strategies.

Recent Advances in Magnetic Resonance Imaging Assessment of Renal Fibrosis

CKD is a global public health problem. Renal fibrosis is a final common pathway leading to progressive loss of function in CKD. The degree of renal fibrosis predicts the prognosis of CKD. Recent studies have shown that bone marrow-derived fibroblasts contribute significantly to the development of renal fibrosis, which may yield novel therapeutic strategy for fibrotic kidney disease. Therefore, it is imperative to accurately assess the degree of renal fibrosis noninvasively to identify those patients who can benefit from antifibrotic therapy. In this review, we summarize recent advances in the assessment of renal fibrosis by magnetic resonance imaging.

Lymphangiogenesis: fuel, smoke, or extinguisher of inflammation's fire?

Lymphangiogenesis is a recognized hallmark of inflammatory processes in tissues and organs as diverse as the skin, heart, bowel, and airways. In clinical and animal models wherein the signaling processes of lymphangiogenesis are manipulated, most studies demonstrate that an expanded lymphatic vasculature is necessary for the resolution of inflammation. The fundamental roles that lymphatics play in fluid clearance and immune cell trafficking from the periphery make these results seemingly obvious as a mechanism of alleviating locally inflamed environments: the lymphatics are simply providing a drain. Depending on the tissue site, lymphangiogenic mechanism, or induction timeframe, however, evidence shows that inflammation-associated lymphangiogenesis (IAL) may worsen the pathology. Recent studies have identified lymphatic endothelial cells themselves to be local regulators of immune cell activity and its consequential phenotypes - a more active role in inflammation regulation than previously thought. Indeed, results focusing on the immunocentric roles of peripheral lymphatic function have revealed that the basic drainage task of lymphatic vessels is a complex balance of locally processed and transported antigens as well as interstitial cytokine and immune cell signaling: an interplay that likely defines the function of IAL. This review will summarize the latest findings on how IAL impacts a series of disease states in various tissues in both preclinical models and clinical studies. This discussion will serve to highlight some emerging areas of lymphatic research in an attempt to answer the question relevant to an array of scientists and clinicians of whether IAL helps to fuel or extinguish inflammation. Impact statement Inflammatory progression is present in acute and chronic tissue pathologies throughout the body. Lymphatic vessels play physiological roles relevant to all medical fields as important regulators of fluid balance, immune cell trafficking, and immune identity. Lymphangiogenesis is often concurrent with inflammation and can potentially aide or worsen disease progression. How new lymphatic vessels impact inflammation and by which mechanism is an important consideration in current and future clinical therapies targeting inflammation and/or vasculogenesis. This review identifies, across a range of tissue-specific pathologies, the current understanding of inflammation-associated lymphangiogenesis in the progression or resolution of inflammation.

Circulating fibrocyte mobilization in negative pressure wound therapy

Non‐healing diabetic wounds are difficult to treat. They also create heavy financial burdens for both patients and society. Negative pressure wound therapy (NPWT) has been adopted to treat intractable wounds and has proved to be effective. However, the mechanisms that underlie the effects of this treatment are not entirely understood. Circulating fibrocytes are unique haematopoietic‐derived stem cells that have been reported to play a pivotal role in wound healing. Here, we have investigated the effect of NPWT on fibrocyte mobilization and the role of fibrocyte mobilization in the healing of diabetic wounds during NPWT. We show that the NPWT group exhibited 2.6‐fold to 12.1‐fold greater numbers of tail vein‐injected PKH‐26‐labelled fibrocytes in the diabetic wound sites compared with the control group. We also demonstrate that the full‐thickness skin wounds treated with NPWT exhibit significantly reduced mRNA and protein expression, blood vessel density and proliferating cells when exogenous fibrocyte mobilization is inhibited. We speculate that systemic mobilization of fibrocytes during NPWT may be a mechanism for healing intractable wounds in a diabetic rat model experiment and that enhancement of cell mobilization may represent a potential treatment idea for intractable wound healing across all fields of surgery.

Identification and Function of Fibrocytes in Skeletal Muscle Injury Repair and Muscular Dystrophy

We identified and characterized the function of CD45⁺/collagen I⁺ fibrocytes in acutely injured skeletal muscle of wild-type (WT) and Ccr2^-/- mice, and in quadriceps and diaphragm muscles of mdx^5cv mice, a mouse model for Duchenne muscular dystrophy. Fibrocytes were not detected in peripheral blood of WT mice after acute muscle injury or mdx^5cv mice. Fibrocytes were detected in acutely injured muscles and in mdx^5cv quadriceps and diaphragm muscles. These cells expressed F4/80 and CCR2, and they were mostly Ly6C^lo They expressed a low level of collagens but a high level of profibrotic growth factors as compared with i.m. fibroblasts. Fibrocyte expression of collagens and profibrotic growth factors was not increased in Ccr2^-/- mice as compared with WT controls. Fibrocyte expression of both proinflammatory and profibrotic cytokines was significantly higher in mdx^5cv diaphragm than in mdx^5cv quadriceps. In cocultures, fibrocytes from the mdx^5cv diaphragm stimulated a higher level of fibroblast expression of extracellular matrix genes than did those from the mdx^5cv quadriceps. Our findings suggest that i.m. fibrocytes most likely originate from infiltrating monocytes/macrophages and differentiate within injured muscles. They likely contribute to the normal muscle injury repair by producing growth factors. They do not appear to contribute to the persistent muscle fibrosis associated with poor injury repair in Ccr2^-/- mice. However, they likely contribute to the persistent inflammation and progressive fibrosis in the mdx^5cv diaphragm.

Basic Fibroblast Growth Factor Induces Angiogenic Properties of Fibrocytes to Stimulate Vascular Formation during Wound Healing

The role of fibrocytes in wound angiogenesis remains unclear. We therefore demonstrated the specific changes in fibrocyte accumulation for angiogesis in basic fibroblast growth factor (bFGF)-treated wounds. bFGF-treated wounds exhibited marked formation of arterioles and inhibition of podoplanin⁺ lymph vessels that were lacking in vascular endothelial growth factor-A-treated wounds. Real-time PCR in bFGF-treated wounds manifested enhanced expression of CD34, CD31, and bFGF mRNA and reduced expression of podoplanin and collagen type I, III, and IV mRNA. Double immunofluorescence staining focusing on fibrocyte detection in bFGF-treated wounds showed increased formation of capillary-like structures composed of CD34⁺/procollagen I⁺ fibrocytes, with a lack of capillary-like structures formed by CD45⁺/procollagen I⁺ or CD11b⁺/procollagen I⁺ fibrocytes. However, vascular endothelial growth factor-A-treated wounds lacked capillary-like structures composed of CD34⁺/procollagen I⁺ fibrocytes, with increased numbers of CD34⁺/fetal liver kinase-1⁺ endothelial progenitor cells. Furthermore, fibroblast growth factor receptor 1 siRNA injection into wounds, followed by bFGF, inhibited the formation of capillary-like structures composed of CD34⁺/procollagen I⁺ fibrocytes, together with inhibited mRNA expression of CD34 and CD31 and enhanced mRNA expression of collagen type I, indicating the requirements of bFGF/fibroblast growth factor receptor 1 system for capillary structure formation. This study highlights the angiogenic properties of CD34⁺/procollagen I⁺ fibrocytes specifically induced by bFGF, providing new insight into the active contribution of fibrocytes for vascular formation during wound healing.

Intersection of Chemokine and TSH Receptor Pathways in Human Fibrocytes: Emergence of CXCL-12/CXCR4 Cross Talk Potentially Relevant to Thyroid-Associated Ophthalmopathy

Fibrocytes are monocyte progenitor cells that have been implicated in normal and pathological tissue remodeling. Among the prominent chemokine receptors expressed by these cells is CXC motif receptor 4 (CXCR4), which, with its cognate ligand CXCL motif ligand 12 (CXCL-12), directs fibrocytes to sites of fibrosis. Fibrocytes have been implicated in the pathogenesis of thyroid-associated ophthalmopathy, the ocular manifestation of Graves' disease (GD), by virtue of their unique accumulation as CD34⁺ orbital fibroblasts (OFs). Fibrocytes also express high levels of functional TSH receptor (TSHR). Here, we determined CXCL-12 and CXCR4 expression in fibrocytes and GD-OF and whether that pathway interacts with TSHR. CXCL-12 is highly expressed in GD-OF, whereas CXCR4 levels are dramatically higher in fibrocytes. Levels of these proteins are differentially regulated by TSH in a cell type-specific manner. Further, CXCL-12 enhances the induction by TSH of IL-6 in fibrocytes but attenuates this induction in GD-OF. In contrast, in pure CD34⁺ OF, the interplay between TSH and CXCL-12 reverts to that observed in fibrocytes. Our results indicate that CXCL-12 enhances TSH actions in fibrocytes but inhibits them in GD-OF, a dichotomy imposed by factors emanating from CD34^- OF. They also suggest a potentially important modulatory role for CD34^- OF in determining the factors that influence pathological TSHR signaling in the TAO orbit.

Blocking the 4-1BB Pathway Ameliorates Crystalline Silica-induced Lung Inflammation and Fibrosis in Mice

Long term pulmonary exposure to crystalline silica leads to silicosis that manifests progressive interstitial fibrosis, eventually leading to respiratory failure and death. Despite efforts to eliminate silicosis, clinical cases continue to occur in both developing and developed countries. The exact mechanisms of crystalline silica-induced pulmonary fibrosis remain elusive. Herein, we find that 4-1BB is induced in response to crystalline silica injury in lungs and that it is highly expressed during development of experimental silicosis. Therefore, we explore the role of 4-1BB pathway during crystalline silica-induced lung injury and find that a specific inhibitor blocking the pathway could effectively alleviate crystalline silica-induced lung inflammation and subsequent pulmonary fibrosis in vivo. Compared to controls, the treated mice exhibited reduced Th1 and Th17 responses. The concentrations of pro-inflammatory cytokines in bronchoalveolar lavage fluid (BALF), including tumor necrosis factor (TNF)-α, interferon (IFN)-γ and interleukin (IL)-17A following crystalline silica challenge were also reduced in inhibitor-treated mice. Although there was no significant alteration in Th2 cytokines of IL-4 and IL-13, another type of pro-fibrogenic cell, regulatory T cell (Treg) was significantly affected. In addition, one of the major participants in fibrogenesis, fibrocyte recruited less due to the blockade. Furthermore, we demonstrated the decreased fibrocyte recruitment was associated with chemokine reductions in lung. Our study discovers the 4-1BB pathway signaling enhances inflammatory response and promotes pulmonary fibrosis induced by crystalline silica. The findings here provide novel insights into the molecular events that control crystalline silica-induced lung inflammation and fibrosis through regulating Th responses and the recruitment of fibrocytes in crystalline silica-exposed lung.

CXCL16 regulates renal injury and fibrosis in experimental renal artery stenosis

Recent studies have shown that inflammation plays a critical role in the initiation and progression of hypertensive kidney disease, including renal artery stenosis. However, the signaling mechanisms underlying the induction of inflammation are poorly understood. We found that CXCL16 was induced in the kidney in a murine model of renal artery stenosis. To determine whether CXCL16 is involved in renal injury and fibrosis, wild-type and CXCL16 knockout mice were subjected to renal artery stenosis induced by placing a cuff on the left renal artery. Wild-type and CXCL16 knockout mice had comparable blood pressure at baseline. Renal artery stenosis caused an increase in blood pressure that was similar between wild-type and CXCL16 knockout mice. CXCL16 knockout mice were protected from RAS-induced renal injury and fibrosis. CXCL16 deficiency suppressed bone marrow-derived fibroblast accumulation and myofibroblast formation in the stenotic kidneys, which was associated with less expression of extracellular matrix proteins. Furthermore, CXCL16 deficiency inhibited infiltration of F4/80(+) macrophages and CD3(+) T cells in the stenotic kidneys compared with those of wild-type mice. Taken together, our results indicate that CXCL16 plays a pivotal role in the pathogenesis of renal artery stenosis-induced renal injury and fibrosis through regulation of bone marrow-derived fibroblast accumulation and macrophage and T-cell infiltration.

Non-canonical NFκB activation promotes chemokine expression in podocytes

TNF-like weak inducer of apoptosis (TWEAK) receptor Fn14 is expressed by podocytes and Fn14 deficiency protects from experimental proteinuric kidney disease. However, the downstream effectors of TWEAK/Fn14 in podocytes are poorly characterized. We have explored TWEAK activation of non-canonical NFκB signaling in cultured podocytes. In cultured podocytes, TWEAK increased the expression of the chemokines CCL21, CCL19 and RANTES in a time-dependent manner. The inhibitor of canonical NFκB activation parthenolide inhibited the CCL19 and the early RANTES responses, but not the CCL21 or late RANTES responses. In this regard, TWEAK induced non-canonical NFκB activation in podocytes, characterized by NFκB2/p100 processing to NFκB2/p52 and nuclear migration of RelB/p52. Silencing by a specific siRNA of NIK, the upstream kinase of the non-canonical NFκB pathway, prevented CCL21 upregulation but did not modulate CCL19 or RANTES expression in response to TWEAK, thus establishing CCL21 as a non-canonical NFκB target in podocytes. Increased kidney Fn14 and CCL21 expression was also observed in rat proteinuric kidney disease induced by puromycin, and was localized to podocytes. In conclusion, TWEAK activates the non-canonical NFκB pathway in podocytes, leading to upregulation of CCL21 expression. The non-canonical NFκB pathway should be explored as a potential therapeutic target in proteinuric kidney disease.

CXCL16 Deficiency Attenuates Renal Injury and Fibrosis in Salt-Sensitive Hypertension

Inflammation plays an important role in the pathogenesis of hypertensive kidney disease. However, the molecular mechanisms underlying the induction of inflammation are not completely understood. We have found that CXCL16 is induced in the kidney in deoxycorticosterone acetate (DOCA)-salt hypertension. Here we examined whether CXCL16 is involved in DOCA-salt-induced renal inflammation and fibrosis. Wild-type and CXCL16 knockout mice were subjected to uninephrectomy and DOCA-salt treatment for 3 weeks. There was no difference in blood pressure at baseline between wild-type and CXCL16 knockout mice. DOCA-salt treatment resulted in significant elevation in blood pressure that was comparable between wild-type and CXCL16 knockout mice. CXCL16 knockout mice exhibited less severe renal dysfunction, proteinuria, and fibrosis after DOCA-salt treatment compared with wild-type mice. CXCL16 deficiency attenuated extracellular matrix protein production and suppressed bone marrow–derived fibroblast accumulation and myofibroblast formation in the kidneys following DOCA-salt treatment. Furthermore, CXCL16 deficiency reduced macrophage and T cell infiltration into the kidneys in response to DOCA-salt hypertension. Taken together, our results indicate that CXCL16 plays a key role in the pathogenesis of renal injury and fibrosis in salt-sensitive hypertension through regulation of bone marrow–derived fibroblast accumulation and macrophage and T cell infiltration.

Fibroblasts, an inconspicuous but essential player in colon cancer development and progression

Tumor microenvironments have a crucial role in cancer initiation and progression, and share many molecular and pathological features with wound healing process. Unless treated, tumors, however, do not heal in contrast to wounds that heal within a limited time framework. Wounds heal in coordination of a myriad of types of cells, particularly endothelial cells, leukocytes, and fibroblasts. Similar sets of cells also contribute to cancer initiation and progression, and as a consequence, anti-cancer treatment strategies have been proposed and tested by targeting endothelial cells and/or leukocytes. Compared with endothelial cells and leukocytes, less attention has been paid to the roles of cancer-associated fibroblasts (CAFs), fibroblasts present in tumor tissues, because their heterogeneity hinders the elucidation on them at cellular and molecular levels. Here, we will discuss the origin of CAFs and their crucial roles in cancer initiation and progression, and the possibility to develop a novel type of anti-cancer treatment by manipulating the migration and functions of CAFs.

Senescence in chronic allograft nephropathy

Despite increasing numbers of patients on dialysis, the numbers of renal transplants performed yearly have remained relatively static. During the last 50 years, there have been many advances in the pharmacology of prevention of organ rejection. However, most patients will suffer from a slow but steady decline in renal function leading to graft loss. The most common cause of long-term graft loss is chronic allograft nephropathy (CAN). Therefore, elucidating and understanding the mechanisms involved in CAN is crucial for achieving better posttransplant outcomes. It is thought that the development of epithelial to mesenchymal transition (EMT) in proximal tubules is one of the first steps towards CAN, and has been shown to be a result of cellular senescence. Cells undergoing senescence acquire a senescence associated secretory phenotype (SASP) leading to the production of interleukin-1 alpha (IL-1α), which has been implicated in several degenerative and inflammatory processes including renal disease. A central mediator in SASP activation is the production of reactive oxygen species (ROS), which are produced in response to numerous physiological and pathological stimuli. This review explores the connection between SASP and the development of EMT/CAN in an effort to suggest future directions for research leading to improved long-term graft outcomes.

Links between coagulation, inflammation, regeneration, and fibrosis in kidney pathology

Acute kidney injury (AKI) involves nephron injury leading to irreversible nephron loss, ie, chronic kidney disease (CKD). Both AKI and CKD are associated with distinct histological patterns of tissue injury, but kidney atrophy in CKD involves tissue remodeling with interstitial inflammation and scarring. No doubt, nephron atrophy, inflammation, fibrosis, and renal dysfunction are associated with each other, but their hierarchical relationships remain speculative. To better understand the pathophysiology, we provide an overview of the fundamental danger response programs that assure host survival upon traumatic injury from as early as the first multicellular organisms, ie, bleeding control by coagulation, infection control by inflammation, epithelial barrier restoration by re-epithelialization, and tissue stabilization by mesenchymal repair. Although these processes assure survival in the majority of the populations, their dysregulation causes kidney disease in a minority. We discuss how, in genetically heterogeneous population, genetic variants shift balances and modulate danger responses toward kidney disease. We further discuss how classic kidney disease entities develop from an insufficient or overshooting activation of these danger response programs. Finally, we discuss molecular pathways linking, for example, inflammation and regeneration or inflammation and fibrosis. Understanding the causative and hierarchical relationships and the molecular links between the danger response programs should help to identify molecular targets to modulate kidney injury and to improve outcomes for kidney disease patients.

Role of Bone Marrow-Derived Fibroblasts in Renal Fibrosis

Renal fibrosis represents a common pathway leading to progression of chronic kidney disease. Renal interstitial fibrosis is characterized by extensive fibroblast activation and excessive production and deposition of extracellular matrix (ECM), which leads to progressive loss of kidney function. There is no effective therapy available clinically to halt or even reverse renal fibrosis. Although activated fibroblasts/myofibroblasts are responsible for the excessive production and deposition of ECM, their origin remains controversial. Recent evidence suggests that bone marrow-derived fibroblast precursors contribute significantly to the pathogenesis of renal fibrosis. Understanding the molecular signaling mechanisms underlying the recruitment and activation of the bone marrow-derived fibroblast precursors will lead to novel therapy for the treatment of chronic kidney disease. In this review, we summarize recent advances in our understanding of the recruitment and activation of bone marrow-derived fibroblast precursors in the kidney and the development of renal fibrosis and highlights new insights that may lead to novel therapies to prevent or reverse the development of renal fibrosis.

Depletion of CD8+ T Cells Exacerbates CD4+ T Cell-Induced Monocyte-to-Fibroblast Transition in Renal Fibrosis

Bone marrow-derived monocyte-to-fibroblast transition is a key step in renal fibrosis pathogenesis, which is regulated by the inflammatory microenvironment. However, the mechanism by which the inflammatory microenvironment regulates this transition is not fully understood. In this study, we examined how the CD8(+) T cell/IFN-γ microenvironment regulates the monocyte-to-fibroblast transition in renal fibrosis. Genetic ablation of CD8 promoted a monocyte-to-fibroblast transition and increased renal interstitial fibrosis, whereas reconstitution of CD8 knockout (KO) mice with CD8(+) T cells decreased fibrosis. However, depletion of CD4(+) T cells in CD8 KO mice also reduced fibrosis. To elucidate the role of CD4(+) T cells in mediating CD8-regulated monocyte-to-fibroblast transition, CD4(+) T cells were isolated from obstructed kidneys of CD8 KO or wild-type mice. CD4(+) T cells isolated from CD8 KO obstructed kidney expressed more IL-4 and GATA3 and less IFN-γ and T-bet and showed increased monocyte-to-fibroblast transition in vitro compared with those isolated from wild-type obstructed kidney. To examine the role of IFN-γ-expressing CD8(+) T cells, we reconstituted CD8 KO mice with CD8(+) T cells isolated from IFN-γ KO mice. The IFN-γ KO CD8(+) cells had no effect on IL-4, GATA3, IFN-γ, and T-bet mRNA expression in obstructed kidneys or renal fibrosis. Taken together, our findings identify the axis of CD8(+) T cells and IFN-γ-CD4(+) T cells as an important microenvironment for the monocyte-to-fibroblast transition, which negatively regulates renal fibrosis.

Controversies over the Epithelial-to-Mesenchymal Transition in Liver Fibrosis

Liver fibrosis is a universal consequence of chronic liver diseases. It is accompanied by activation of collagen-producing myofibroblasts, resulting in excessive deposition of extracellular matrix. The origin of myofibroblasts in the fibrotic liver has not been completely resolved and remains a matter of debate. Recently, the epithelial-to-mesenchymal transition (EMT) was proposed as one of the mechanisms that give rise to collagen-producing myofibroblasts in liver fibrosis. However, subsequent studies contradicted this hypothesis, and the EMT theory has become one of the most controversial and debatable issues in the field of liver fibrosis research. This review will summarize the existing literature on EMT in liver fibrosis and will analyze the causes for the contradictory results to draw a reasonable conclusion based on current knowledge in the field.

Tanshinone IIA Attenuates Renal Fibrosis after Acute Kidney Injury in a Mouse Model through Inhibition of Fibrocytes Recruitment

Acute kidney injury (AKI) is associated with an increased risk of developing advanced chronic kidney disease (CKD). Yet, effective interventions to prevent this conversion are unavailable for clinical practice. In this study, we examined the beneficial effects of Tanshinone IIA on renal fibrosis in a mouse model of folic acid induced AKI. We found that Tanshinone IIA treatment significantly attenuated the folic acid elicited kidney dysfunction on days 3, 14, and 28. This effect was concomitant with a much lessened accumulation of fibronectin and collagen in tubulointerstitium 28 days after folic acid injury, denoting an ameliorated renal fibrosis. The kidney protective and antifibrotic effect of Tanshinone IIA was likely attributable to an early inhibition of renal recruitment of fibrocytes positive for both CD45 and collagen I. Mechanistically, Tanshinone IIA treatment not only markedly diminished renal expression of chemoattractants for fibrocytes such as TGFβ1 and MCP-1, but also significantly reduced circulating fibrocytes at the acute phase of kidney injury. These data suggested that Tanshinone IIA might be a novel therapy for preventing progression of CKD after AKI.

Origin of Matrix-Producing Cells That Contribute to Aortic Fibrosis in Hypertension

Various hypertensive stimuli lead to exuberant adventitial collagen deposition in large arteries, exacerbating blood pressure elevation and end-organ damage. Collagen production is generally attributed to resident fibroblasts; however, other cells, including resident and bone marrow-derived stem cell antigen positive (Sca-1(+)) cells and endothelial and vascular smooth muscle cells, can produce collagen and contribute to vascular stiffening. Using flow cytometry and immunofluorescence, we found that adventitial Sca-1(+) progenitor cells begin to produce collagen and acquire a fibroblast-like phenotype in hypertension. We also found that bone marrow-derived cells represent more than half of the matrix-producing cells in hypertension, and that one-third of these are Sca-1(+). Cell sorting and lineage-tracing studies showed that cells of endothelial origin contribute to no more than one fourth of adventitial collagen I(+) cells, whereas those of vascular smooth muscle lineage do not contribute. Our findings indicate that Sca-1(+) progenitor cells and bone marrow-derived infiltrating fibrocytes are major sources of arterial fibrosis in hypertension. Endothelial to mesenchymal transition likely also contributes, albeit to a lesser extent and pre-existing resident fibroblasts represent a minority of aortic collagen-producing cells in hypertension. This study shows that vascular stiffening represents a complex process involving recruitment and transformation of multiple cells types that ultimately elaborate adventitial extracellular matrix.

TSLP Is a Potential Initiator of Collagen Synthesis and an Activator of CXCR4/SDF-1 Axis in Keloid Pathogenesis

Recently, thymic stromal lymphopoietin (TSLP), which is well studied in allergic diseases, has been reported in fibrotic diseases, including idiopathic pulmonary fibrosis and atopic dermatitis fibrosis. However, the role of TSLP in keloid is obscure. In this study, we assessed the expression of TSLP in keloid tissue and investigated the possible role of TSLP in keloid pathogenesis. We observed that TSLP expression was increased in keloid tissue compared to normal tissue. Furthermore, TSLP treatment induced increased collagen I and collagen III expression in fibroblasts via transforming growth factor-?; however, there was higher expression in keloid fibroblasts compared to normal fibroblasts. Stromal cell-derived factor-1?, which was recently reported to enhance wound healing through recruiting bone marrow-derived mesenchymal stem cells to the wound area, increased after TSLP treatment in fibroblasts and was primarily expressed in ?-smooth muscle action-positive myofibroblasts in keloid tissue. Furthermore, fibrocytes expressing CXCR4, a stromal cell-derived factor-1? receptor, were significantly increased in keloid tissue compared to normal tissue. Finally, intradermal TSLP injection on BALB/c mice increased stromal cell-derived factor-1? expression and CXCR4(+) fibrocytes infiltration. Our data suggest that TSLP is a potent inducer of collagen and transforming growth factor-? production in keloid fibroblasts. In addition, it might activate the CXCR4/stromal cell-derived factor-1 axis to increase fibrocyte infiltration into the keloid tissue.

Fibrocytes Differ from Macrophages but Can Be Infected with HIV-1

Fibrocytes (fibroblastic leukocytes) are recently identified as unique hematopoietic cells with features of both macrophages and fibroblasts. Fibrocytes are known to contribute to the remodeling or fibrosis of various injured tissues. However, their role in viral infection is not fully understood. In this study, we show that differentiated fibrocytes are phenotypically distinguishable from macrophages but can be infected with HIV-1. Importantly, fibrocytes exhibited persistently infected cell-like phenotypes, the degree of which was more apparent than macrophages. The infected fibrocytes produced replication-competent HIV-1, but expressed HIV-1 mRNA at low levels and strongly resisted HIV-1-induced cell death, which enabled them to support an extremely long-term HIV-1 production at low but steady levels. More importantly, our results suggested that fibrocytes were susceptible to HIV-1 regardless of their differentiation state, in contrast to the fact that monocytes become susceptible to HIV-1 after the differentiation into macrophages. Our findings indicate that fibrocytes are the previously unreported HIV-1 host cells, and they suggest the importance of considering fibrocytes as one of the long-lived persistently infected cells for curing HIV-1.

Trypsin, Tryptase, and Thrombin Polarize Macrophages towards a Pro-Fibrotic M2a Phenotype

For both wound healing and the formation of a fibrotic lesion, circulating monocytes enter the tissue and differentiate into fibroblast-like cells called fibrocytes and pro-fibrotic M2a macrophages, which together with fibroblasts form scar tissue. Monocytes can also differentiate into classically activated M1 macrophages and alternatively activated M2 macrophages. The proteases thrombin, which is activated during blood clotting, and tryptase, which is released by activated mast cells, potentiate fibroblast proliferation and fibrocyte differentiation, but their effect on macrophages is unknown. Here we report that thrombin, tryptase, and the protease trypsin bias human macrophage differentiation towards a pro-fibrotic M2a phenotype expressing high levels of galectin-3 from unpolarized monocytes, or from M1 and M2 macrophages, and that these effects appear to operate through protease-activated receptors. These results suggest that proteases can initiate scar tissue formation by affecting fibroblasts, fibrocytes, and macrophages.

TSH-Mediated TNFα Production in Human Fibrocytes Is Inhibited by Teprotumumab, an IGF-1R Antagonist

Purpose

Fibrocytes (FC) are bone marrow-derived progenitor cells that are more abundant and infiltrate the thyroid and orbit in Graves orbitopathy (GO). FCs express high levels of thyrotropin receptor (TSHR) and insulin-like growth factor-1 receptor (IGF-1R). These receptors are physically and functionally associated, but their role in GO pathogenesis is not fully delineated. Treatment of FCs with thyroid stimulating hormone (TSH) or M22 (activating antibody to TSHR) induces the production of numerous cytokines, including tumor necrosis factor α (TNFα). Teprotumumab (TMB) is a human monoclonal IGF-1R blocking antibody currently in clinical trial for GO and inhibits TSHR-mediated actions in FCs.

Aim

To characterize the molecular mechanisms underlying TSH-induced TNFα production by FCs, and the role of IGF-1R blockade by TMB.

Design

FCs from healthy and GD patients were treated with combinations of TSH, M22, MG132 and AKTi (inhibitors of NF-κB and Akt, respectively), and TMB. TNFα protein production was measured by Luminex and flow cytometry. Messenger RNA expression was quantified by real time PCR.

Results

Treatment with TSH/M22 induced TNFα protein and mRNA production by FCs, both of which were reduced when FCs were pretreated with MG132 and AKTi (p<0.0001). TMB decreased TSH-induced TNFα protein production in circulating FCs from mean fluorescent index (MFI) value of 2.92 to 1.91, and mRNA expression in cultured FCs from 141- to 52-fold expression (p<0.0001). TMB also decreased M22-induced TNFα protein production from MFI of 1.67 to 1.12, and mRNA expression from 6- to 3-fold expression (p<0.0001).

Conclusion

TSH/M22 stimulates FC production of TNFα mRNA and protein. This process involves the transcription factor NF-κB and its regulator Akt. Blocking IGF-1R attenuates TSH/M22-induced TNFα production. This further delineates the interaction of TSHR and IGF1-R signaling pathways. By modulating the proinflammatory properties of FCs such as TNFα production, TMB may be a promising therapeutic agent for GO.

Mefunidone attenuates tubulointerstitial fibrosis in a rat model of unilateral ureteral obstruction

BACKGROUND

Inflammation has a crucial role in renal interstitial fibrosis, which is the common pathway of chronic kidney diseases. Mefunidone (MFD) is a new compound which could effectively inhibit the proliferation of renal fibroblasts in vitro. However, the overall effect of Mefunidone in renal fibrosis remains unknown.

METHODS

Sprague-Dawley rats were randomly divided intro 6 groups: sham operation, unilateral ureteral obstruction (UUO), UUO/Mefunidone (25, 50, 100mg/kg/day) and UUO/PFD (500mg/kg/day). The rats were sacrificed respectively on days 3, 7, and 14 after the operation. Tubulointerstitial injury index, interstitial collagen deposition, expression of fibronectin (FN), α-smooth muscle actin (α-SMA), type I and III collagen and the number of CD3+ and CD68+ cells were determined. The expressions of proinflammatory cytokines, p-ERK, p-IκB, and p-STAT3 were measured in human renal proximal tubular epithelial cells of HK-2 or macrophages.

RESULTS

Mefunidone treatment significantly attenuated tubulointerstitial injury, interstitial collagen deposition, expression of FN, α-SMA, type I and III collagen in the obstructive kidneys, which correlated with significantly reduced the number of T cells and macrophages in the obstructive kidneys. Mechanistically, Mefunidone significantly inhibited tumor necrosis factor-α (TNF-α-) or lipopolysaccharide (LPS)-induced production of proinflammatory cytokines. This effect is possibly due to the inhibition of phosphorylation of ERK, IκB, and STAT3.

CONCLUSION

Mefunidone treatment attenuated tubulointerstitial fibrosis in a rat model of UUO, at least in part, through inhibition of inflammation.

JAK3/STAT6 Stimulates Bone Marrow-Derived Fibroblast Activation in Renal Fibrosis

Renal fibrosis is a final common manifestation of CKD resulting in progressive loss of kidney function. Bone marrow-derived fibroblast precursors contribute significantly to the pathogenesis of renal fibrosis. However, the signaling mechanisms underlying the activation of bone marrow-derived fibroblast precursors in the kidney are not fully understood. In this study, we investigated the role of the Janus kinase 3 (JAK3)/signal transducer and activator of transcription (STAT6) signaling pathway in the activation of bone marrow-derived fibroblasts. In cultured mouse monocytes, IL-4 or IL-13 activated STAT6 and induced expression of α-smooth muscle actin and extracellular matrix proteins (fibronectin and collagen I), which was abolished by a JAK3 inhibitor (CP690,550) in a dose-dependent manner or blocked in the absence of STAT6. In vivo, STAT6 was activated in interstitial cells of the obstructed kidney, an effect that was abolished by CP690,550. Mice treated with CP690,550 accumulated fewer bone marrow-derived fibroblasts in the obstructed kidneys compared with vehicle-treated mice. Treatment with CP690,550 also significantly reduced myofibroblast transformation, matrix protein expression, fibrosis development, and apoptosis in obstructed kidneys. Furthermore, STAT6-deficient mice accumulated fewer bone marrow-derived fibroblasts in the obstructed kidneys, produced less extracellular matrix protein, and developed much less fibrosis. Finally, wild-type mice engrafted with STAT6(-/-) bone marrow cells displayed fewer bone marrow-derived fibroblasts in the obstructed kidneys and showed less severe renal fibrosis compared with wild-type mice engrafted with STAT6(+/+) bone marrow cells. Our results demonstrate that JAK3/STAT6 has an important role in bone marrow-derived fibroblast activation, extracellular matrix production, and interstitial fibrosis development.

Targeting tubulointerstitial remodeling in proteinuric nephropathy in rats

Proteinuria is an important cause of tubulointerstitial damage. Anti-proteinuric interventions are not always successful, and residual proteinuria often leads to renal failure. This indicates the need for additional treatment modalities by targeting the harmful downstream consequences of proteinuria. We previously showed that proteinuria triggers renal lymphangiogenesis before the onset of interstitial inflammation and fibrosis. However, the interrelationship of these interstitial events in proteinuria is not yet clear. To this end, we specifically blocked lymphangiogenesis (anti-VEGFR3 antibody), monocyte/macrophage influx (clodronate liposomes) or lymphocyte and myofibroblast influx (S1P agonist FTY720) separately in a rat model to investigate the role and the possible interaction of each of these phenomena in tubulointerstitial remodeling in proteinuric nephropathy. Proteinuria was induced in 3-month old male Wistar rats by adriamycin injection. After 6 weeks, when proteinuria has developed, rats were treated for another 6 weeks by anti-VEGFR3 antibody, clodronate liposomes or FTY720 up to week 12. In proteinuric rats, lymphangiogenesis, influx of macrophages, T cells and myofibroblasts, and collagen III deposition and interstitial fibrosis significantly increased at week 12 vs week 6. Anti-VEGFR3 antibody prevented lymphangiogenesis in proteinuric rats, however, without significant effects on inflammatory and fibrotic markers or proteinuria. Clodronate liposomes inhibited macrophage influx and partly reduced myofibroblast expression; however, neither significantly prevented the development of lymphangiogenesis, nor fibrotic markers and proteinuria. FTY720 prevented myofibroblast accumulation, T-cell influx and interstitial fibrosis, and partially reduced macrophage number and proteinuria; however, it did not significantly influence lymphangiogenesis and collagen III deposition. This study showed that proteinuria-induced interstitial fibrosis cannot be halted by blocking lymphangiogenesis or the influx of macrophages. On the other hand, FTY720 treatment did prevent T-cell influx, myofibroblast accumulation and interstitial fibrosis, but not renal lymphangiogenesis and proteinuria. We conclude that tubulointerstitial fibrosis and inflammation are separate from lymphangiogenesis, at least under proteinuric conditions.

Summary: Targeting lymphangiogenesis, inflammation or fibrosis separately in a rat model of proteinuric nephropathy showed that treating any of these changes alone is not effective in treating the disease.

Bone marrow-derived fibrocytes contribute to liver fibrosis

Chronic liver injury often leads to hepatic fibrosis, a condition associated with increased levels of circulating TGF-β1 and lipopolysaccharide, activation of myofibroblasts, and extensive deposition of extracellular matrix, mostly collagen Type I. Hepatic stellate cells are considered to be the major(1) but not the only source of myofibroblasts in the injured liver.(2) Hepatic myofibroblasts may also originate from portal fibroblasts, mesenchymal cells, and fibrocytes.(3) Since the discovery of fibrocytes in 1994 by Dr. Bucala and colleagues, this bone marrow (BM)-derived collagen Type I-producing CD45(+) cells remain the most fascinating cells of the hematopoietic system. Due to the ability to differentiate into collagen Type I producing cells/myofibroblasts, fibrocytes were implicated in the pathogenesis of liver, skin, lung, and kidney fibrosis. However, studies of different organs often contain controversial results on the number of fibrocytes recruited to the site of injury and their biological function. Furthermore, fibrocytes were implicated in the pathogenesis of sepsis and were shown to possess antimicrobial activity. Finally, in response to specific stimuli, fibrocytes can give rise to fully differentiated macrophages, suggesting that in concurrence with the high plasticity of hematopoietic cells, fibrocytes exhibit progenitor properties. Here, we summarize our current understanding of the role of CD45(+)Collagen Type I(+) BM-derived cells in response to fibrogenic liver injury and septicemia and discuss the most recent evidence supporting the critical role of fibrocytes in the mediation of pro-fibrogenic and/or pro-inflammatory responses.

Renal allograft fibrosis: biology and therapeutic targets

Renal tubulointerstitial fibrosis is the final common pathway of progressive renal diseases. In allografts, it is assessed with tubular atrophy as interstitial fibrosis/tubular atrophy (IF/TA). IF/TA occurs in about 40% of kidney allografts at 3-6 months after transplantation, increasing to 65% at 2 years. The origin of renal fibrosis in the allograft is complex and includes donor-related factors, in particular in case of expanded criteria donors, ischemia-reperfusion injury, immune-mediated damage, recurrence of underlying diseases, hypertensive damage, nephrotoxicity of immunosuppressants, recurrent graft infections, postrenal obstruction, etc. Based largely on studies in the non-transplant setting, there is a large body of literature on the role of different cell types, be it intrinsic to the kidney or bone marrow derived, in mediating renal fibrosis, and the number of mediator systems contributing to fibrotic changes is growing steadily. Here we review the most important cellular processes and mediators involved in the progress of renal fibrosis, with a focus on the allograft situation, and discuss some of the challenges in translating experimental insights into clinical trials, in particular fibrosis biomarkers or imaging modalities.

The long pentraxin PTX3 promotes fibrocyte differentiation

Monocyte-derived, fibroblast-like cells called fibrocytes are associated with fibrotic lesions. The plasma protein serum amyloid P component (SAP; also known as pentraxin-2, PTX2) inhibits fibrocyte differentiation in vitro, and injections of SAP inhibit fibrosis in vivo. SAP is a member of the pentraxin family of proteins that includes C-reactive protein (CRP; PTX1) and pentraxin-3 (PTX3). All three pentraxins are associated with fibrosis, but only SAP and CRP have been studied for their effects on fibrocyte differentiation. We find that compared to SAP and CRP, PTX3 promotes human and murine fibrocyte differentiation. The effect of PTX3 is dependent on FcγRI. In competition studies, the fibrocyte-inhibitory activity of SAP is dominant over PTX3. Binding competition studies indicate that SAP and PTX3 bind human FcγRI at different sites. In murine models of lung fibrosis, PTX3 is present in fibrotic areas, and the PTX3 distribution is associated with collagen deposition. In lung tissue from pulmonary fibrosis patients, PTX3 has a widespread distribution, both in unaffected tissue and in fibrotic lesions, whereas SAP is restricted to areas adjacent to vessels, and absent from fibrotic areas. These data suggest that the relative levels of SAP and PTX3 present at sites of fibrosis may have a significant effect on the ability of monocytes to differentiate into fibrocytes.

Contribution of bone marrow-derived fibrocytes to liver fibrosis

Since the discovery of fibrocytes in 1994 by Dr. Bucala and colleagues, these bone marrow (BM)-derived collagen Type I producing CD45(+) cells remain the most fascinating cells of the hematopoietic system. Despite recent reports on the emerging contribution of fibrocytes to fibrosis of parenchymal and non-parenchymal organs and tissues, fibrocytes remain the most understudied pro-fibrogenic cellular population. In the past years fibrocytes were implicated in the pathogenesis of liver, skin, lung, and kidney fibrosis by giving rise to collagen type I producing cells/myofibroblasts. Hence, the role of fibrocytes in fibrosis is not well defined since different studies often contain controversial results on the number of fibrocytes recruited to the site of injury versus the number of fibrocyte-derived myofibroblasts in the same fibrotic organ. Furthermore, many studies were based on the in vitro characterization of fibrocytes formed after outgrowth of BM and/or peripheral blood cultures. Therefore, the fibrocyte function(s) still remain(s) lack of understanding, mostly due to (I) the lack of mouse models that can provide complimentary in vivo real-time and cell fate mapping studies of the dynamic differentiation of fibrocytes and their progeny into collagen type I producing cells (and/or possibly, other cell types of the hematopoietic system); (II) the complexity of hematopoietic cell differentiation pathways in response to various stimuli; (III) the high plasticity of hematopoietic cells. Here we summarize the current understanding of the role of CD45(+) collagen type I(+) BM-derived cells in the pathogenesis of liver injury. Based on data obtained from various organs undergoing fibrogenesis or other type of chronic injury, here we also discuss the most recent evidence supporting the critical role of fibrocytes in the mediation of pro-fibrogenic and/or pro-inflammatory responses.

Circulating fibrocytes as biomarker of prognosis in Hermansky-Pudlak syndrome

RATIONALE

The rate of progression of most interstitial lung diseases (ILD) is unpredictable. Fibrocytes are circulating bone marrow-derived cells that have been implicated in the pathogenesis of lung fibrosis. Hermansky-Pudlak syndrome (HPS), a genetic cause of ILD in early adulthood, allows for study of biomarkers of ILD in a homogeneous population at near-certain risk of developing fibrotic lung disease.

OBJECTIVES

To test the hypothesis that, in subjects with HPS, the number or phenotype of circulating fibrocytes predicts progression and outcome of ILD.

METHODS

We measured circulating fibrocyte counts and chemokine levels in a cohort of subjects with HPS and healthy control subjects and correlated the results to disease outcome.

MEASUREMENTS AND MAIN RESULTS

In a cross-sectional analysis, peripheral blood fibrocyte concentrations were markedly elevated in a subset of subjects with HPS who had ILD but not subjects without lung disease or normal control subjects. The blood concentration of fibrocytes expressing the chemokine receptor CXCR4 correlated significantly with the plasma concentration of the CXCR4 ligand, CXCL12. In a longitudinal study, we found marked episodic elevations in circulating fibrocyte counts over a median follow-up period of 614 days. Elevations in both maximal values and final values of peripheral blood CXCR4(+) fibrocyte concentration were strongly associated with death from ILD.

CONCLUSIONS

CXCR4(+) fibrocyte concentration may be useful as a biomarker for outcome of ILD in subjects with HPS.

Role of platelet-derived growth factor/platelet-derived growth factor receptor axis in the trafficking of circulating fibrocytes in pulmonary fibrosis

Circulating fibrocytes have been reported to migrate into the injured lungs, and contribute to fibrogenesis via CXCL12-CXCR4 axis. In contrast, we report that imatinib mesylate prevented bleomycin (BLM)-induced pulmonary fibrosis in mice by inhibiting platelet-derived growth factor receptor (PDGFR), even when it was administered only in the early phase. The goal of this study was to test the hypothesis that platelet-derived growth factor (PDGF) might directly contribute to the migration of fibrocytes to the injured lungs. PDGFR expression in fibrocytes was examined by flow cytometry and RT-PCR. The migration of fibrocytes was evaluated by using a chemotaxis assay for human fibrocytes isolated from peripheral blood. The numbers of fibrocytes triple-stained for CD45, collagen-1, and CXCR4 were also examined in lung digests of BLM-treated mice. PDGFR mRNA levels in fibrocytes isolated from patients with idiopathic pulmonary fibrosis were investigated by real-time PCR. Fibrocytes expressed both PDGFR-α and -β, and migrated in response to PDGFs. PDGFR inhibitors (imatinib, PDGFR-blocking antibodies) suppressed fibrocyte migration in vitro, and reduced the number of fibrocytes in the lungs of BLM-treated mice. PDGF-BB was a stronger chemoattractant than the other PDGFs in vitro, and anti-PDGFR-β-blocking antibody decreased the numbers of fibrocytes in the lungs compared with anti-PDGFR-α antibody in vivo. Marked expression of PDGFR-β was observed in fibrocytes from patients with idiopathic pulmonary fibrosis compared with healthy subjects. These results suggest that PDGF directly functions as a strong chemoattractant for fibrocytes. In particular, the PDGF-BB-PDGFR-β biological axis might play a critical role in fibrocyte migration into the fibrotic lungs.

Flow Cytometric Identification of Fibrocytes in the Human Circulation

Because the incidence of organ fibrosis increases with age, various fibrosing disorders are projected to account for significant increases in morbidity, mortality, and healthcare costs in the years to come. Treatments for these diseases are scarce and better understanding of the immunopathogenesis of fibrosis and its relationship to aging are sorely needed. One area of interest in this field is the role that fibrocytes might play in the development of tissue remodeling and fibrosis. Fibrocytes are mesenchymal progenitor cells presumed to be of monocyte origin that possess the tissue remodeling properties of tissue resident fibroblasts such as extracellular matrix production and α-SMA-related contractile properties, as well as the immunologic functions typically attributed to macrophages including production of cytokines and chemokines, antigen presentation, regulation of leukocyte trafficking, and modulation of angiogenesis. Fibrocytes could participate in the development of age-related fibrosing disorders through any or all of these functions. This chapter presents methods that have been developed for the study of circulating human fibrocytes. Protocols for the quantification of fibrocytes in the human circulation will be presented along with discussion of the technical challenges that are frequently encountered in this field. It is hoped that this information will facilitate further investigation of the relationship between fibrocytes, aging, and fibrosis, and perhaps uncover new areas of study in these difficult-to-treat and deadly diseases.

A brief exposure to tryptase or thrombin potentiates fibrocyte differentiation in the presence of serum or serum amyloid p

A key question in both wound healing and fibrosis is the trigger for the initial formation of scar tissue. To help form scar tissue, circulating monocytes enter the tissue and differentiate into fibroblast-like cells called fibrocytes, but fibrocyte differentiation is strongly inhibited by the plasma protein serum amyloid P (SAP), and healthy tissues contain very few fibrocytes. In wounds and fibrotic lesions, mast cells degranulate to release tryptase, and thrombin mediates blood clotting in early wounds. Tryptase and thrombin are upregulated in wound healing and fibrotic lesions, and inhibition of these proteases attenuates fibrosis. We report that tryptase and thrombin potentiate human fibrocyte differentiation at biologically relevant concentrations and exposure times, even in the presence of concentrations of serum and SAP that normally completely inhibit fibrocyte differentiation. Fibrocyte potentiation by thrombin and tryptase is mediated by protease-activated receptors 1 and 2, respectively. Together, these results suggest that tryptase and thrombin may be an initial trigger to override SAP inhibition of fibrocyte differentiation to initiate scar tissue formation.

Fibrocyte trafficking in patients with chronic obstructive asthma and during an acute asthma exacerbation

BACKGROUND

Fibrocytes express several chemokine receptors (CCR7 and CXCR4) that regulate their recruitment and trafficking into tissue-damage sites in response to specific chemokine gradients (CCL19 and CXCL12).

OBJECTIVE

We investigated whether these chemoattractants and S100A9, through the receptor for advanced glycation end-products (RAGE; ie, its receptor), are involved in fibrocyte trafficking in patients with chronic obstructive asthma (COA) and during an acute exacerbation (AE) in patients without airflow obstruction (Asthma AE group).

METHODS

We collected peripheral blood from 14 asthmatic patients with normal pulmonary function, 14 patients with COA, 11 patients in the Asthma AE group, and 14 healthy subjects. Isolated circulating fibrocytes were used for migration assay. Expression of CCR7, CXCR4, S100A9, and RAGE in fibrocytes was measured by using flow cytometry. CCL19 and CXCL12 expression in bronchial tissues was determined by using immunohistochemistry and RT-PCR.

RESULTS

There were higher numbers of circulating fibrocytes in patients in the Asthma AE group and patients with COA. The expression of CXCL12 in bronchial tissues and CXCR4 in circulating fibrocytes was higher in the Asthma AE group and, to a lesser extent, in patients with COA. The expression of CCL19 in bronchial tissues and CCR7 in fibrocytes was higher in patients with COA. CXCL12/CXCR4 and CCL19/CCR7 enhanced fibrocyte transmigration in the Asthma AE group and in patients with COA, respectively. The upregulated expression of S100A9 and RAGE in fibrocytes of patients in the Asthma AE group and those with COA contributes to the enhanced basal migratory motility of fibrocytes.

CONCLUSION

The CXCR4/CXCL12 axis contributes to chemotaxis of fibrocytes in patients in the Asthma AE group, whereas the CCR7/CCL19 axis plays an important role in patients with COA. S100A9 enhances the basal migratory motility of fibrocytes from patients in the Asthma AE group and patients with COA.

Recent advances in renal interstitial fibrosis and tubular atrophy after kidney transplantation

Although kidney transplantation has been an important means for the treatment of patients with end stage of renal disease, the long-term survival rate of the renal allograft remains a challenge. The cause of late renal allograft loss, once known as chronic allograft nephropathy, has been renamed “interstitial fibrosis and tubular atrophy” (IF/TA) to reflect the histologic pattern seen on biopsy. The mechanisms leading to IF/TA in the transplanted kidney include inflammation, activation of renal fibroblasts, and deposition of extracellular matrix proteins. Identifying the mediators and factors that trigger IF/TA may be useful in early diagnosis and development of novel therapeutic strategies for improving long-term renal allograft survival and patient outcomes. In this review, we highlight the recent advances in our understanding of IF/TA from three aspects: pathogenesis, diagnosis, and treatment.

Lymphangiogenesis in renal diseases: passive bystander or active participant?

Lymphatic vessels (LVs) are involved in a number of physiological and pathophysiological processes such as fluid homoeostasis, immune surveillance, and resolution of inflammation and wound healing. Lymphangiogenesis, the outgrowth of existing LVs and the formation of new ones, has received increasing attention over the past decade on account of its prominence in organ physiology and pathology, which has been enabled by the development of specific tools to study lymph vessel functions. Several studies have been devoted to renal lymphatic vasculature and lymphangiogenesis in kidney diseases, such as chronic renal transplant dysfunction, primary renal fibrotic disorders, proteinuria, diabetic nephropathy and renal inflammation. This review describes the most recent findings on lymphangiogenesis, with a specific focus on renal lymphangiogenesis and its impact on renal diseases. We suggest renal lymphatics as a possible target for therapeutic interventions in renal medicine to dampen tubulointerstitial tissue remodelling and improve renal functioning.

Origin of myofibroblasts and cellular events triggering fibrosis

Renal fibrosis is a major hallmark of chronic kidney disease that is considered to be a common end point of various types of renal disease. To date, the biological meaning of fibrosis during the progression of chronic kidney diseases is unknown and possibly depends on the cell type contributing to extracellular matrix production. During the past decade, the origin of myofibroblasts in the kidney has been intensively investigated. Determining the origins of renal myofibroblasts is important because these might account for the heterogeneous characteristics and behaviors of myofibroblasts. Current data strongly suggest that collagen-producing myofibroblasts in the kidney can be derived from various cellular sources. Resident renal fibroblasts and cells of hematopoietic origin migrating into the kidney seem to be the most important ancestors of myofibroblasts. It is likely that both cell types communicate with each other and also with other cell types in the kidney. In this review, we will discuss the current knowledge on the origin of scar-producing myofibroblasts and cellular events triggering fibrosis.

Interferon-γ and other inflammatory mediators in cardiomyocyte signaling during Chagas disease cardiomyopathy

Chagas disease cardiomyopathy (CCC), the main consequence of Trypanosoma cruzi (T.cruzi) infection, is an inflammatory cardiomyopathy that develops in up to 30% of infected individuals. The heart inflammation in CCC patients is characterized by a Th1 T cell-rich myocarditis with increased production of interferon (IFN)-γ, produced by the CCC myocardial infiltrate and detected at high levels in the periphery. IFN-γ has a central role in the cardiomyocyte signaling during both acute and chronic phases of T.cruzi infection. In this review, we have chosen to focus in its pleiotropic mode of action during CCC, which may ultimately be the strongest driver towards pathological remodeling and heart failure. We describe here the antiparasitic protective and pathogenic dual role of IFN-γ in Chagas disease.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and kidney disease

PURPOSE OF REVIEW

The tumor necrosis factor-like weak inducer of apoptosis (TWEAK) cytokine has been linked to kidney injury by functional studies in experimental animals, and has biomarker potential in kidney disease.

RECENT FINDINGS

TWEAK was known to promote tubular cell injury and kidney inflammation. Recent studies have expanded these observations, identifying additional targets of TWEAK relevant to kidney injury. Thus, TWEAK upregulates the chemokine and cholesterol scavenger receptor CXCL16 and downregulates the antiaging and antifibrotic molecule Klotho in tubular cells. Furthermore, fibrogenic TWEAK actions on renal fibroblasts were described. TWEAK or factor-inducible molecule 14 targeting decreased the kidney fibrosis resulting from immune and nonimmune kidney injury induced by transient tubular or glomerular insults or by persistent urinary tract obstruction. TWEAK might also contribute to the link between chronic kidney disease and kidney cancer, as suggested by its role in other genitourinary cancers. Progress has also been made in TWEAK targeting. A phase I clinical trial showed that TWEAK targeting is well tolerated in humans, and an ongoing trial is exploring efficacy in lupus nephritis. Nanomolecules and inhibitors of epidermal growth factor receptor pathway may also protect from the adverse effects of TWEAK in the kidney.

SUMMARY

These findings suggest that TWEAK targeting has clinical potential in kidney injury of immune and nonimmune origin.

The types of hepatic myofibroblasts contributing to liver fibrosis of different etiologies

Liver fibrosis results from dysregulation of normal wound healing, inflammation, activation of myofibroblasts, and deposition of extracellular matrix (ECM). Chronic liver injury causes death of hepatocytes and formation of apoptotic bodies, which in turn, release factors that recruit inflammatory cells (neutrophils, monocytes, macrophages, and lymphocytes) to the injured liver. Hepatic macrophages (Kupffer cells) produce TGFβ1 and other inflammatory cytokines that activate Collagen Type I producing myofibroblasts, which are not present in the normal liver. Secretion of TGFβ1 and activation of myofibroblasts play a critical role in the pathogenesis of liver fibrosis of different etiologies. Although the composition of fibrogenic myofibroblasts varies dependent on etiology of liver injury, liver resident hepatic stellate cells and portal fibroblasts are the major source of myofibroblasts in fibrotic liver in both experimental models of liver fibrosis and in patients with liver disease. Several studies have demonstrated that hepatic fibrosis can reverse upon cessation of liver injury. Regression of liver fibrosis is accompanied by the disappearance of fibrogenic myofibroblasts followed by resorption of the fibrous scar. Myofibroblasts either apoptose or inactivate into a quiescent-like state (e.g., stop collagen production and partially restore expression of lipogenic genes). Resolution of liver fibrosis is associated with recruitment of macrophages that secrete matrix-degrading enzymes (matrix metalloproteinase, collagenases) and are responsible for fibrosis resolution. However, prolonged/repeated liver injury may cause irreversible crosslinking of ECM and formation of uncleavable collagen fibers. Advanced fibrosis progresses to cirrhosis and hepatocellular carcinoma. The current review will summarize the role and contribution of different cell types to populations of fibrogenic myofibroblasts in fibrotic liver.

The contribution of epithelial-mesenchymal transition to renal fibrosis differs among kidney disease models

The impact of the epithelial-mesenchymal transition (EMT) to the formation of renal fibrosis has been debated in several lineage-tracing studies, with conflicting findings. Such disparities may have arisen from varying experimental conditions such as different disease models, the mouse strain, and type of genetic alteration used. In order to determine the contribution of these factors to EMT, we generated four kidney disease models in several mouse strains genetically modified to express enhanced green fluorescence protein (EGFP) in cortical tubular epithelial cells under the control of the γ-glutamyl transpeptidase promoter. Using this approach, the EMT was visible and quantifiable based on a count of EGFP-positive interstitial cells in the fibrotic kidney sections of the four renal disease models found to be either EMT-prone or -resistant. The EMT-prone models consisted of unilateral ureteral obstruction and ischemic nephropathy in SJL mice. The EMT-resistant models consisted of ureteral obstruction in C57B/6 and F1(C57B/6 × SJL) mice, adriamycin nephrosis in 129 mice, and nephrotoxic serum nephritis in SJL mice. Analyses of these renal disease models suggest the emergence of EMT-derived fibroblasts arises in a disease-specific and strain-dependent manner. Thus, when considering molecular mechanisms and involvement of the EMT in renal fibrosis, it is important to take into account the experimental conditions, particularly the mouse strain and type of disease model.

Transforming growth factor β3 attenuates the development of radiation-induced pulmonary fibrosis in mice by decreasing fibrocyte recruitment and regulating IFN-γ/IL-4 balance

Radiation-induced pulmonary fibrosis is a frequently occurred complication from radiotherapy of thoracic tumors. The transforming growth factor-β (TGF-β) superfamily plays a key regulatory role in pulmonary fibrosis. As TGF-β3 showed the potential anti-fibrotic properties especially in scar-less wound healing as opposed to the fibrotic function of TGF-β1, we sought to explore the role of TGF-β3 in radiation-induced pulmonary fibrosis. A single thoracic irradiation of 20 Gy was applied in mice to establish the model of radiation-induced pulmonary fibrosis and the mice were treated by intraperitoneal injections of recombinant TGF-β3 weekly after irradiation. We found that TGF-β3 decelerated the progress of radiation-induced pulmonary fibrosis and hindered the recruitment of fibrocytes to lung. In addition, Th1 response was suppressed as shown by diminished IFN-γ in bronchoalveolar lavage fluid (BALF) after irradiation, and enhancement of Th2 response was marked by increased IL-4 in BALF. TGF-β3 administration significantly attenuated these effects and increased the percentage of Tregs in lung during the progression of pulmonary fibrosis. Taken together, these data suggest that TGF-β3 might be involved in the regulatory mechanism for attenuation of radiation-induced pulmonary fibrosis.