Evasion of apoptosis by myofibroblasts: a hallmark of fibrotic diseases.

Background:Systemic Sclerosis (SSc) is a rare autoimmune disease characterized by an abnormal remodelling of tissue matrix, leading to fibrosis of skin and internal organs. Although progresses have been made in...

In fibrotic conditions increases in TG2 activity has been linked to an increase in the deposition of extracellular matrix proteins. Using TG2 transfected Swiss 3T3 fibroblasts expressing TG2 under the control of the tetracycline-regulated inducible promoter, we demonstrate that induction of TG2 not only stimulates an increase in collagen and fibronectin deposition but also an increase in the expression of these proteins. Increased TG2 expression in these fibroblasts led to NF-kappaB activation, resulting in the increased expression of transforming growth factor (TGF) beta(1). In addition, cells overexpressing TG2 demonstrated an increase in biologically active TGFbeta(1) in the extracellular environment. A specific site-directed inhibitor of TG abolished the NF-kappaB and TGFbeta1 activation and the subsequent elevation in the synthesis and deposition of extracellular matrix proteins, confirming that this process depends on the induction of transglutaminase activity. Treatment of TG2-induced fibroblasts with nontoxic doses of nitric oxide donor S-nitroso-N-acetylpenicillamine resulted in decreased TG2 activity and apprehension of the inactive enzyme on the cell surface. This was paralleled by a reduction in activation of NF-kappaB and TGFbeta(1) production with a subsequent decrease in collagen expression and deposition. These findings support a role for NO in the regulation of TG2 function in the extracellular environment.

Increased synthesis and deposition of extracellular matrix (ECM) proteins in the trabecular meshwork (TM) is associated with TM dysfunction and intraocular pressure (IOP) elevation in glaucoma. However, it is not understood how ECM accumulation leads to TM dysfunction and IOP elevation. Using a mouse model of glucocorticoid (GC)-induced glaucoma, primary human TM cells and human post-mortem TM tissues, we show that increased ECM accumulation leads to endoplasmic reticulum (ER) stress in the TM. The potent GC, dexamethasone (Dex) increased the secretory protein load of ECM proteins in the ER of TM cells, inducing ER stress. Reduction of fibronectin, a major regulator of ECM structure, prevented ER stress in Dex-treated TM cells. Overexpression of fibronectin via treatment with cellular fibronectin also induced chronic ER stress in primary human TM cells. Primary human TM cells grown on ECM derived from Dex-treated TM cells induced ER stress markers. TM cells were more prone to ER stress from ECM accumulation compared to other ocular cell types. Moreover, increased co-localization of ECM proteins with ER stress markers was observed in human post-mortem glaucomatous TM tissues. These data indicate that ER stress is associated with increased ECM accumulation in mouse and human glaucomatous TM tissues.

Increased synthesis and deposition of extracellular matrix proteins in the blood vessel wall are implicated in vascular disorders such as atherosclerosis, restenosis and hypertension. (Liau and Chan 1989). The increase in extracellular matrix proteins can be mostly attributed to smooth muscle cells (SMC’s) within vascular lesions (Mecham et al 1987). It is presumed that modulation of SMC’s from their normally quiescent, contractile phenotype to a proliferative synthetic phenotype results in increased synthesis of extracellular matrix proteins. Studies have also demonstrated that signals elicited from the extracellular matrix (ECM) may play a role in the regulation of this SMC phenotypic modulation (Yamamoto et al 1993; Hedin et al 1988). The mechanism by which ECM can alter the phenotypic state of SMC’s is not well understood but clearly involves the induction of intracellular signals as a consequence of ECM ligand - cell surface integrin binding. These signals must subsequently exert downstream molecular events altering gene expression and ultimately cell phenotype. The research project presented in this thesis examined the influence various extracellular matrix substrates have on vascular SMC behaviour in vitro. Initial observations demonstrated that SMC’s cultured on different matrix substrates exhibit distinct morphological growth patterns. Functional differences in SMC proliferation and migration rates were also observed in response to seeding on different ECM surfaces. Analysis of the expression levels of known SMC phenotypic protein markers between SMC’s cultured on different matrix substrates did not reveal any significant differences in protein expression. Slight upregulation of Myosin Light Chain Kinase (MLCK)-210 kd isoform was observed in SMC’s cultured on cellular fibronectin, Collagen III and Vitronectin substrates. The Meta-vinculin protein was upregulated in SMC’s cultured on fibronectin coated substrates. In order to identify altered gene expression patterns induced by ECM adhesion, SMC populations cultured on fibronectin coated plastic and SMC’s grown on uncoated plastic were selected for analysis by the differential display technique. Differential display is a recently developed PCR based technique that allows the identification of differentially expressed genes between related cell populations (Liang and Pardee 1992). Much effort was spent optimising the differential display procedure to overcome such limitations as primer redundancy and high false positive selection rates. However, as a result of the persistence of false positives only one gene, meta-vinculin was confirmed as being differentially expressed between SMC populations cultured on fibronectin coated and uncoated tissue culture plastic surfaces. It was concluded that the failure to identify a significant number of fibronectin modulated genes was probably a result of limitations in the differential display procedure as carried out in this study, and may also possibly be due to the existence of only very minor differences in phenotype between SMC’s grown on plastic with or without fibronectin precoating.

Influence of endothelin-1 receptors antagonists on extracellular matrix protein synthesis in culture of human scleroderma skin fibroblasts

POS0330 NINTEDANIB (TYROSINE KINASE INHIBITOR) DOWNREGULATES THE TRANSITION OF CULTURED SYSTEMIC SCLEROSIS FIBROCYTES INTO MYOFIBROBLASTS AND THEIR PRO-FIBROTIC ACTIVITY

Scleroderma (systemic sclerosis; SSc) is an autoimmune disease characterized by vasculopathy and widespread organ fibrosis. Altered fibroblast function, both in vivo and in vitro, is well documented and illustrated by augmented synthesis and deposition of extracellular matrix proteins. We undertook this study to investigate the possibility that epigenetic mechanisms mediate the emergence and persistence of the altered SSc fibroblast phenotype. The effects of DNA methyltransferase and histone deacetylase inhibitors on collagen expression and the level of epigenetic mediators in fibroblasts were examined. The effects of transient transfection of SSc fibroblasts with FLI1 gene and normal cells with FLI1 antisense construct on collagen expression were determined. The methylation status of the FLI1 promoter was tested in cultured cells and in SSc and normal skin biopsy specimens. Increased levels of epigenetic mediators in SSc fibroblasts were noted. The addition of epigenetic inhibitors to cell cultures normalized collagen expression in SSc fibroblasts. The augmented collagen synthesis by SSc fibroblasts was linked to epigenetic repression of the collagen suppressor gene FLI1. Heavy methylation of the CpG islands in the FLI1 promoter region was demonstrated in SSc fibroblasts and skin biopsy specimens. The results of this study indicate that epigenetic mechanisms may mediate the fibrotic manifestations of SSc. The signal transduction leading to the SSc fibrotic phenotype appears to converge on DNA methylation and histone deacetylation at the FLI1 gene.

Renal fibrosis is scarring and tissue hardening caused by the excess deposition of extracellular matrix proteins in response to chronic inflammation. Renal fibrosis is the primary cause of a progressive loss of renal function, and is an important therapeutic target because it ultimately leads to end-stage renal failure, which can be treated only by either dialysis or kidney transplantation. There is no effective treatment that specifically targets renal fibrosis. Myofibroblasts are known to evade apoptosis by activating molecular mechanisms in response to pro-survival biomechanical and growth factor signals from the fibrotic microenvironment. In this study, we screened and selected compounds that selectively cause cell death in myofibroblasts in vitro and studied their possible potency against renal fibrosis in a mouse model. Several proteasome inhibitors induced selective cell death in myofibroblasts differentiated from the human fibroblast cell line (MRC5). The in vivo antifibrotic effect of Delanzomib (Dz), one of the proteasome inhibitors most sensitive to myofibroblasts in vitro, was investigated in a Unilateral Ureteric Obstruction (UUO) mouse model. Treatment with Dz decreased the expression levels of the actin-alpha-2 (ACTA2) and collagen-type-1-alpha-1 (COL1A1) genes in the kidney, which are common fibrosis markers. These results suggest that Dz might be a compound that suppresses renal fibrosis by inducing selective cell death of myofibroblasts, although further investigation is required.

The causes of cancer include the cellular accumulation reactive oxygen species (ROS), which overrides the cellular antioxidants such as superoxide dismutase, from intrinsic aging, genetics, and exposure to environmental pollutants and ultraviolet (UV) radiation. The ROS damage biomolecules such as DNA (including p53 gene), RNA, and lipids, and activate inflammatory, angiogenic, and extracellular matrix (ECM) remodeling proteins; which collectively facilitate carcinogenesis. The 1α,25-dihydroxyvitamin D3 (Vitamin D) has anti-carcinogenic potential from its antioxidant, anti-inflammatory, and endocrine properties. We examined the anti-carcinogenic mechanism of vitamin D through the beneficial regulation of oxidative stress effects (oxidative DNA/RNA damage, superoxide dismutase expression, membrane damage, and p53 promoter activity), and expression (at the protein, mRNA and/or promoter levels) of inflammatory mediators (interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α)), angiogenic mediators (transforming growth factor-β (TGF-β), and vascular endothelial growth factor (VEGF)), and the ECM remodeling proteins (matrix metalloproteinases (MMP)-1 and MMP-2) by vitamin D in melanoma cells. Vitamin D inhibited oxidative DNA/RNA damage and membrane damage; and stimulated superoxide dismutase expression and p53 promoter activity in melanoma cells. It inhibited the expression of IL-1, TNF-α, TGF-β, VEGF, MMP-1 and MMP-2 by transcriptional or post-transcriptional mechanisms. We conclude that vitamin D is beneficial to melanoma cells through the inhibition of oxidative DNA/RNA damage, membrane damage, and the expression of inflammatory, angiogenic and ECM remodeling proteins; and the stimulation of superoxide dismutase expression and p53 promoter activity.

AB0168 NINTEDANIB (TYROSINE-KINASE INHIBITOR) INHIBITS THE TRANSITION OF CIRCULATING FIBROCYTES ISOLATED FROM SYSTEMIC SCLEROSIS PATIENTS INTO MYOFIBROBLASTS: AN IN VITROSTUDY

Chronic tubulointerstitial nephritis (TIN), characterized by tubular atrophy, interstitial fibrosis and inflammation, is a major prognostic determinant of chronic kidney disease, regardless of the original cause of the kidney disease. Understanding the pathogenesis of TIN has been hampered by the lack of an adequate experimental model. However, the demonstration that the renal lesions of obstructive uropathy induced by experimental urinary obstruction (UO) has provided an excellent model to study the pathogenesis of TIN in general and especially congenital obstructive nephropathy, the most common cause of pediatric end-stage renal disease. Since relief of experimental UO is technically possible, this model is particularly useful for studying the potential reversibility of TIN. Experimental UO is usually created by the unilateral ligation of a ureter. This induces progressive tubular epithelial cell injury, including apoptosis, proliferation, loss of differentiation and atrophy; interstitial inflammatory cell infiltrates composed predominantly of macrophages and T cells; and interstitial fibrosis characterized by an increase and activation of interstitial fibroblasts, deposition of extracellular matrix proteins and loss of peritubular capillaries. These changes collectively lead to progressive scarring and the loss of renal parenchyma and kidney function. The glomeruli and large blood vessels remain either normal or show mild changes later in the course of the disease. In addition to TIN, congenital obstructive nephropathy causes marked derangement of renal and glomerular development. Relief of UO does not seem to reverse TIN. In fact, the renal lesions of obstructive uropathy not only persist, but also progress long after UO is relieved in both adult and neonatal rats. The pathogenesis of UO-induced TIN has been well studied, at least in part because of the ready application of this model to mice, in which genetic manipulation including gene deletion or transfection of putative pathogenic molecules is technically feasible. Experimental UO immediately induces mechanical stretching of tubular epithelial cells and activates the renin-angiotensin system, leading to profound changes of the cells, including neo-expression of a large number of molecules which control cell cycle (e.g. caspases, intrinsic and extrinsic death pathway molecules, inhibitors of cyclin-dependent kinases p27 and p21, reactive oxygen species, and catalase), hypoxic response (HIF- α), epithelial-mesenchymal transformation (e.g. hepatocyte growth factor, bone morphogenic protein 7 and nestin), and the upregulation of cytokines and growth factors (e.g. TGFβ-1, EGF, PDGF, VEGF and TNF-α) as well as chemokines (MCP-1, osteopontin, IL-1, ICAM-1, VCAM-1 and selectins). Inflammatory cells are recruited immediately after UO, probably under the effect of the renin-angiotensin system and later by tubular cell-derived chemokines. Several chemokines and their receptors are also expressed by the infiltrating inflammatory cells, thereby augmenting the recruitment of additional inflammatory cells through an autocrine loop. These molecules are probably also responsible for an increased number interstitial fibroblasts, which are derived not only from the proliferation of resident interstitial fibroblasts, but also from the renal homing of bone marrow-derived fibrocytes and the transformation of tubular epithelial cells, endothelial cells and pericytes into interstitial fibroblasts. Activated interstitial fibroblasts are responsible for the increased synthesis of extracellular matrix protein. This together with an impairment of various fibrolytic pathways leads to the increased deposition of extracellular matrix protein. In summary, typical features of TIN are regularly induced in the experimental model of obstructive uropathy. This versatile model has contributed much to elucidate the mechanism of TIN. The translation of this body of knowledge into TIN in general and its effective treatment of obstructive uropathy remains to be explored.

In response to tissue injury, fibroblasts differentiate into professional repair cells called myofibroblasts, which orchestrate many aspects of the normal tissue repair programme including synthesis, deposition and contraction of extracellular matrix proteins, leading to wound closure. Successful tissue repair responses involve termination of myofibroblast activities in order to prevent pathologic fibrotic scarring. Here, we discuss the cellular and molecular mechanisms limiting myofibroblast activities during physiological tissue repair, including myofibroblast deactivation, apoptosis, reprogramming and immune clearance of senescent myofibroblasts. In addition, we summarize pathological mechanisms leading to myofibroblast persistence and survival, a hallmark of fibrotic diseases. Finally, we discuss emerging anti-fibrotic therapies aimed at targeting myofibroblast fate such as senolytics, gene therapy, cellular immunotherapy and CAR-T cells.

Dermal fibroblasts—A heterogeneous population with regulatory function in wound healing

Cell type-specific transforming growth factor-β (TGF-β) signaling in the regulation of salivary gland fibrosis and regeneration

Activation of the immune system and increased synthesis of extracellular matrix proteins by fibroblasts are hallmarks in the pathogenesis of systemic sclerosis (SSc). The mechanisms that initiate the accumulation of inflammatory cells are still unknown. Chemokines are a family of small molecules that are divided into subfamilies according to the position of NH2-terminal cysteine motif. A new nomenclature for chemokines recently has been introduced in an attempt to overcome the confusion resulting from a number of different names for the same chemokines. Recent data indicate that chemokines, and in particular MCP-1 (CCL2), might be involved in the pathogenesis of SSc at different levels. MCP-1 is highly upregulated in skin specimens from SSc patients compared with those from healthy controls. Dermal fibroblasts release MCP-1, which is able to induce and perpetuate the migration of inflammatory cells into the skin. Interestingly, data from animal models, as well as from in vitro studies, indicate that MCP-1 might also be involved in the increased synthesis of extracellular matrix proteins, by either direct or indirect mechanisms. In conclusion, chemokines represent interesting candidates for target-directed therapies for SSc. This concept has to be confirmed by further studies using animal models for SSc and other fibrotic diseases.