DDR2 receptor promotes MMP-2-mediated proliferation and invasion by hepatic stellate cells

Focusing on discoidin domain receptors in premalignant and malignant liver diseases

Discoidin domain receptors (DDRs) are receptor tyrosine kinases on the membrane surface that bind to extracellular collagens, but they are rarely expressed in normal liver tissues. Recent studies have demonstrated that DDRs participate in and influence the processes underlying premalignant and malignant liver diseases. A brief overview of the potential roles of DDR1 and DDR2 in premalignant and malignant liver diseases is presented. DDR1 has proinflammatory and profibrotic benefits and promotes the invasion, migration and liver metastasis of tumour cells. However, DDR2 may play a pathogenic role in early-stage liver injury (prefibrotic stage) and a different role in chronic liver fibrosis and in metastatic liver cancer. These views are critically significant and first described in detail in this review. The main purpose of this review was to describe how DDRs act in premalignant and malignant liver diseases and their potential mechanisms through an in-depth summary of preclinical in vitro and in vivo studies. Our work aims to provide new ideas for cancer treatment and accelerate translation from bench to bedside.

Inflammation and Fibrogenesis in MAFLD: Role of the Hepatic Immune System

Metabolic (dysfunction)-associated fatty liver disease (MAFLD) is the definition recently proposed to better circumscribe the spectrum of conditions long known as non-alcoholic fatty liver disease (NAFLD) that range from simple steatosis without inflammation to more advanced liver diseases. The progression of MAFLD, as well as other chronic liver diseases, toward cirrhosis, is driven by hepatic inflammation and fibrogenesis. The latter, result of a “chronic wound healing reaction,” is a dynamic process, and the understanding of its underlying pathophysiological events has increased in recent years. Fibrosis progresses in a microenvironment where it takes part an interplay between fibrogenic cells and many other elements, including some cells of the immune system with an underexplored or still unclear role in liver diseases. Some therapeutic approaches, also acting on the immune system, have been probed over time to evaluate their ability to improve inflammation and fibrosis in NAFLD, but to date no drug has been approved to treat this condition. In this review, we will focus on the contribution of the liver immune system in the progression of NAFLD, and on therapies under study that aim to counter the immune substrate of the disease.

The biological effect of recombinant humanized collagen on damaged skin induced by UV-photoaging: An in vivo study

The application of medical devices to repair skin damage is clinically accepted and natural polymer enjoys an important role in this field, such as collagen or hyaluronic acid, etc. However, the biosafety and efficacy of these implants are still challenged. In this study, a skin damage animal model was prepared by UV-photoaging and recombinant humanized type III collagen (rhCol III) was applied as a bioactive material to implant in vivo to study its biological effect, comparing with saline and uncrosslinked hyaluronic acid (HA). Animal skin conditions were non-invasively and dynamically monitored during the 8 weeks experiment. Histological observation, specific gene expression and other molecular biological methods were applied by the end of the animal experiment. The results indicated that rhCol III could alleviate the skin photoaging caused by UV radiation, including reduce the thickening of epidermis and dermis, increase the secretion of Collagen I (Col I) and Collagen III (Col III) and remodel of extracellular matrix (ECM). Although the cell-material interaction and mechanism need more investigation, the effect of rhCol III on damaged skin was discussed from influence on cells, reconstruction of ECM, and stimulus of small biological molecules based on current results. In conclusion, our findings provided rigorous biosafety information of rhCol III and approved its potential in skin repair and regeneration. Although enormous efforts still need to be made to achieve successful translation from bench to clinic, the recombinant humanized collagen showed superiorities from both safety and efficacy aspects.

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Investigated the biological effect of recombinant humanized collagen type III (rhCol III) in vivo.

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Provided the safety and efficacy evidence for rhCol III in skin damage repair.

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Preliminary mechanism discussion on the biological effect of rhCol III.

A human multi-lineage hepatic organoid model for liver fibrosis

To investigate the pathogenesis of a congenital form of hepatic fibrosis, human hepatic organoids were engineered to express the most common causative mutation for Autosomal Recessive Polycystic Kidney Disease (ARPKD). Here we show that these hepatic organoids develop the key features of ARPKD liver pathology (abnormal bile ducts and fibrosis) in only 21 days. The ARPKD mutation increases collagen abundance and thick collagen fiber production in hepatic organoids, which mirrors ARPKD liver tissue pathology. Transcriptomic and other analyses indicate that the ARPKD mutation generates cholangiocytes with increased TGFβ pathway activation, which are actively involved stimulating myofibroblasts to form collagen fibers. There is also an expansion of collagen-producing myofibroblasts with markedly increased PDGFRB protein expression and an activated STAT3 signaling pathway. Moreover, the transcriptome of ARPKD organoid myofibroblasts resemble those present in commonly occurring forms of liver fibrosis. PDGFRB pathway involvement was confirmed by the anti-fibrotic effect observed when ARPKD organoids were treated with PDGFRB inhibitors. Besides providing insight into the pathogenesis of congenital (and possibly acquired) forms of liver fibrosis, ARPKD organoids could also be used to test the anti-fibrotic efficacy of potential anti-fibrotic therapies.

Alpha-single chains of collagen type VI inhibit the fibrogenic effects of triple helical collagen VI in hepatic stellate cells

The interaction of extracellular matrix (ECM) components with hepatic stellate cells (HSCs) is thought to perpetuate fibrosis by stimulating signaling pathways that drive HSC activation, survival and proliferation. Consequently, disrupting the interaction between ECM and HSCs is considered a therapeutical avenue although respective targets and underlying mechanisms remain to be established. Here we have interrogated the interaction between type VI collagen (CVI) and HSCs based on the observation that CVI is 10-fold upregulated during fibrosis, closely associates with HSCs in vivo and promotes cell proliferation and cell survival in cancer cell lines. We exposed primary rat HSCs and a rat hepatic stellate cell line (CFSC) to soluble CVI and determined the rate of proliferation, apoptosis and fibrogenesis in the absence of any additional growth factors. We find that CVI in nanomolar concentrations prevents serum starvation-induced apoptosis. This potent anti-apoptotic effect is accompanied by induction of proliferation and acquisition of a pronounced pro-fibrogenic phenotype characterized by increased α-smooth muscle actin, TGF-β, collagen type I and TIMP-1 expression and diminished proteolytic MMP-13 expression. The CVI-HSC interaction can be disrupted with the monomeric α2(VI) and α3(VI) chains and abrogates the activating CVI effects. Further, functional relevant α3(VI)—derived 30 amino acid peptides lead to near-complete inhibition of the CVI effect. In conclusion, CVI serves as a potent mitogen and activating factor for HSCs. The antagonistic effects of the CVI monomeric chains and peptides point to linear peptide sequences that prevent activation of CVI receptors which may allow a targeted antifibrotic therapy.

The Journey of DDR1 and DDR2 Kinase Inhibitors as Rising Stars in the Fight Against Cancer

Discoidin domain receptor (DDR) is a collagen-activated receptor tyrosine kinase that plays critical roles in regulating essential cellular processes such as morphogenesis, differentiation, proliferation, adhesion, migration, invasion, and matrix remodeling. As a result, DDR dysregulation has been attributed to a variety of human cancer disorders, for instance, non-small-cell lung carcinoma (NSCLC), ovarian cancer, glioblastoma, and breast cancer, in addition to some inflammatory and neurodegenerative disorders. Since the target identification in the early 1990s to date, a lot of efforts have been devoted to the development of DDR inhibitors. From a medicinal chemistry perspective, we attempted to reveal the progress in the development of the most promising DDR1 and DDR2 small molecule inhibitors covering their design approaches, structure-activity relationship (SAR), biological activity, and selectivity.

Astragali Radix Contributes to the Inhibition of Liver Fibrosis via High-Mobility Group Box 1-Mediated Inflammatory Signaling Pathway

Astragali Radix (AR), the dried root of Astragali Radix membranaceus (Fisch.) Bge. or Astragali Radix membranaceus (Fisch.) Bge. var. mongholicus (Bge) Hsiao, is a commonly used traditional Chinese medicine for the treatment of liver diseases. This study aimed to comprehensively evaluate the pharmacological action and explore the potential mechanism of AR on liver fibrosis. Rats were administered with carbon tetrachloride for eight weeks, followed by oral treatment with AR for six weeks. The efficacy was confirmed by measuring liver function and liver fibrosis levels. The underlying mechanisms were explored by detecting the expression of related proteins. AR significantly decreased the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), collagen IV (COL-IV), hyaluronic acid (HA), laminin (LN), and precollagen type III (PCIII). In addition, AR inhibited the deposition of collagen and the activation of hepatic stellate cells. Those data strongly demonstrated that AR alleviated liver fibrosis by CCl₄. In order to illustrate the potential inflammatory, the mRNA levels of IL-6, TNF-α, and IL-1β were detected. Subsequently, immunohistochemistry analysis was performed to further verify the expression of type I collagen. Finally, the expression of key proteins in the inflammatory signaling pathway was detected. AR significantly reduced the expression of high-mobility group box 1 (HMGB1), TLR4, Myd88, RAGE, and NF-κ B p65 genes and proteins. In addition, western blotting showed AR decreased the protein expression of RAGE, p-MEK1/2, p-ERK1/2, and p-c-Jun. Taken together, our data reveal that AR significantly inhibits liver fibrosis by intervening in the HMGB1-mediated inflammatory signaling pathway and secretion signaling pathway. This study will provide valuable references for the in-depth research and development of Astragali Radix against liver fibrosis.

Complex roles of discoidin domain receptor tyrosine kinases in cancer

Discoidin domain receptors, DDR1 and DDR2 are members of the receptor tyrosine kinase (RTK) family that serves as a non-integrin collagen receptor and were initially identified as critical regulators of embryonic development and cellular homeostasis. In recent years, numerous studies have focused on the role of these receptors in disease development, in particular, cancer where they have been reported to augment ECM remodeling, invasion, drug resistance to facilitate tumor progression and metastasis. Interestingly, accumulating evidence also suggests that DDRs promote apoptosis and suppress tumor progression in various human cancers due to which their functions in cancer remain ill-defined and presents a case of an interesting therapeutic target. The present review has discussed the role of DDRs in tumorigenesis and the metastasis.

Dynamically remodeled hepatic extracellular matrix predicts prognosis of early-stage cirrhosis

Liver cirrhosis remains major health problem. Despite the progress in diagnosis of asymptomatic early-stage cirrhosis, prognostic biomarkers are needed to identify cirrhotic patients at high risk developing advanced stage disease. Liver cirrhosis is the result of deregulated wound healing and is featured by aberrant extracellular matrix (ECM) remodeling. However, it is not comprehensively understood how ECM is dynamically remodeled in the progressive development of liver cirrhosis. It is yet unknown whether ECM signature is of predictive value in determining prognosis of early-stage liver cirrhosis. In this study, we systematically analyzed proteomics of decellularized hepatic matrix and identified four unique clusters of ECM proteins at tissue damage/inflammation, transitional ECM remodeling or fibrogenesis stage in carbon tetrachloride-induced liver fibrosis. In particular, basement membrane (BM) was heavily deposited at the fibrogenesis stage. BM component minor type IV collagen α5 chain expression was increased in activated hepatic stellate cells. Knockout of minor type IV collagen α5 chain ameliorated liver fibrosis by hampering hepatic stellate cell activation and promoting hepatocyte proliferation. ECM signatures were differentially enriched in the biopsies of good and poor prognosis early-stage liver cirrhosis patients. Clusters of ECM proteins responsible for homeostatic remodeling and tissue fibrogenesis, as well as basement membrane signature were significantly associated with disease progression and patient survival. In particular, a 14-gene signature consisting of basement membrane proteins is potent in predicting disease progression and patient survival. Thus, the ECM signatures are potential prognostic biomarkers to identify cirrhotic patients at high risk developing advanced stage disease.

Therapeutic efficiency of bone marrow-derived mesenchymal stem cells for liver fibrosis: A systematic review of in vivo studies

Although multiple drugs are accessible for recovering liver function in patients, none are considered efficient. Liver transplantation is the mainstay therapy for end-stage liver fibrosis. However, the worldwide shortage of healthy liver donors, organ rejection, complex surgery, and high costs are prompting researchers to develop novel approaches to deal with the overwhelming liver fibrosis cases. Mesenchymal stem cell (MSC) therapy is an emerging alternative method for treating patients with liver fibrosis. However, many aspects of this therapy remain unclear, such as the efficiency compared to conventional treatment, the ideal MSC sources, and the most effective way to use it. Because bone marrow (BM) is the largest source for MSCs, this paper used a systematic review approach to study the therapeutic efficiency of MSCs against liver fibrosis and related factors. We systematically searched multiple published articles to identify studies involving liver fibrosis and BM-MSC-based therapy. Analyzing the selected studies showed that compared with conventional treatment BM-MSC therapy may be more efficient for liver fibrosis in some cases. In contrast, the cotreatment presented a more efficient way. Nevertheless, BM-MSCs are lacking as a therapy for liver fibrosis; thus, this paper also reviews factors that affect BM-MSC efficiency, such as the implementation routes and strategies employed to enhance the potential in alleviating liver fibrosis. Ultimately, our review summarizes the recent advances in the BM-MSC therapy for liver fibrosis. It is grounded in recent developments underlying the efficiency of BM-MSCs as therapy, focusing on the preclinical in vivo experiments, and comparing to other treatments or sources and the strategies used to enhance its potential while mentioning the research gaps.

Silencing of sinusoidal DDR1 reduces murine liver metastasis by colon carcinoma

Liver metastasis depends on the collagenous microenvironment generated by hepatic sinusoidal cells (SCs). DDR1 is an atypical collagen receptor linked to tumor progression, but whether SCs express DDR1 and its implication in liver metastasis remain unknown. Freshly isolated hepatic stellate cells (HSCs), Kupffer cells (KCs), and liver sinusoidal endothelial cells (LSECs), that conform the SCs, expressed functional DDR1. HSCs expressed the largest amounts. C26 colon carcinoma secretomes increased DDR1 phosphorylation in HSCs and KCs by collagen I. Inhibition of kinase activity by DDR1-IN-1 or mRNA silencing of DDR1 reduced HSCs secretion of MMP2/9 and chemoattractant and proliferative factors for LSECs and C26 cells. DDR1-IN-1 did not modify MMP2/9 in KCs or LSECs secretomes, but decreased the enhancement of C26 migration and proliferation induced by their secretomes. Gene array showed that DDR1 silencing downregulated HSCs genes for collagens, MMPs, interleukins and chemokines. Silencing of DDR1 before tumor inoculation reduced hepatic C26 metastasis in mice. Silenced livers bore less tumor foci than controls. Metastatic foci in DDR1 silenced mice were smaller and contained an altered stroma with fewer SCs, proliferating cells, collagen and MMPs than foci in control mice. In conclusion, hepatic DDR1 promotes C26 liver metastasis and favors the pro-metastatic response of SCs to the tumor.

Intestinal stenosis in Crohn's disease shows a generalized upregulation of genes involved in collagen metabolism and recognition that could serve as novel anti-fibrotic drug targets

BACKGROUND AND AIMS

Crohn's disease (CD) can be complicated by intestinal fibrosis. Pharmacological therapies against intestinal fibrosis are not available. The aim of this study was to determine whether pathways involved in collagen metabolism are upregulated in intestinal fibrosis, and to discuss which drugs might be suitable to inhibit excessive extracellular matrix formation targeting these pathways.

METHODS

Human fibrotic and non-fibrotic terminal ileum was obtained from patients with CD undergoing ileocecal resection due to stenosis. Genes involved in collagen metabolism were analyzed using a microfluidic low-density TaqMan array. A literature search was performed to find potential anti-fibrotic drugs that target proteins/enzymes involved in collagen synthesis, its degradation and its recognition.

RESULTS

mRNA expression of collagen type I (COL1A1, 0.76 ± 0.28 versus 37.82 ± 49.85, p = 0.02) and III (COL3A1, 2.01 ± 2.61 versus 68.65 ± 84.07, p = 0.02) was increased in fibrotic CD compared with non-fibrotic CD. mRNA expression of proteins involved in both intra- and extracellular post-translational modification of collagens (prolyl- and lysyl hydroxylases, lysyl oxidases, chaperones), collagen-degrading enzymes (MMPs and cathepsin-K), and collagen receptors were upregulated in the fibrosis-affected part. A literature search on the upregulated genes revealed several potential anti-fibrotic drugs.

CONCLUSION

Expression of genes involved in collagen metabolism in intestinal fibrosis affected terminal ileum of patients with CD reveals a plethora of drug targets. Inhibition of post-translational modification and altering collagen metabolism might attenuate fibrosis formation in the intestine in CD. Which compound has the highest potential depends on a combination anti-fibrotic efficacy and safety, especially since some of the enzymes play key roles in the physiology of collagen.

Hepatic Stellate Cell-Macrophage Crosstalk in Liver Fibrosis and Carcinogenesis

Chronic liver injury due to viral hepatitis, alcohol abuse, and metabolic disorders is a worldwide health concern. Insufficient treatment of chronic liver injury leads to fibrosis, causing liver dysfunction and carcinogenesis. Most cases of hepatocellular carcinoma (HCC) develop in the fibrotic liver. Pathological features of liver fibrosis include extracellular matrix (ECM) accumulation, mesenchymal cell activation, immune deregulation, and angiogenesis, all of which contribute to the precancerous environment, supporting tumor development. Among liver cells, hepatic stellate cells (HSCs) and macrophages play critical roles in fibrosis and HCC. These two cell types interplay and remodel the ECM and immune microenvironment in the fibrotic liver. Once HCC develops, HCC-derived factors influence HSCs and macrophages to switch to protumorigenic cell populations, cancer-associated fibroblasts and tumor-associated macrophages, respectively. This review aims to summarize currently available data on the roles of HSCs and macrophages in liver fibrosis and HCC, with a focus on their interaction.

The liver fibrosis niche: Novel insights into the interplay between fibrosis-composing mesenchymal cells, immune cells, endothelial cells, and extracellular matrix

Liver fibrosis is a hepatic wound-healing response caused by chronic liver diseases that include viral hepatitis, alcoholic liver disease, non-alcoholic steatohepatitis, and cholestatic liver disease. Liver fibrosis eventually progresses to cirrhosis that is histologically characterized by an abnormal liver architecture that includes distortion of liver parenchyma, formation of regenerative nodules, and a massive accumulation of extracellular matrix (ECM). Despite intensive investigations into the underlying mechanisms of liver fibrosis, developments of anti-fibrotic therapies for liver fibrosis are still unsatisfactory. Recent novel experimental approaches, such as single-cell RNA sequencing and proteomics, have revealed the heterogeneity of ECM-producing cells (mesenchymal cells) and ECM-regulating cells (immune cells and endothelial cells). These approaches have accelerated the identification of fibrosis-specific subpopulations among these cell types. The ECM also consists of heterogenous components. Their production, degradation, deposition, and remodeling are dynamically regulated in liver fibrosis, further affecting the functions of cells responsible for fibrosis. These cellular and ECM elements cooperatively form a unique microenvironment: a fibrotic niche. Understanding the complex interplay between these elements could lead to a better understanding of underlying fibrosis mechanisms and to the development of effective therapies.

Sevoflurane Inhibits Proliferation and Invasion of Human Ovarian Cancer Cells by Regulating JNK and p38 MAPK Signaling Pathway

Aim

Sevoflurane is a halogen inhaled anesthetic, and we aimed to probe the effect of sevoflurane on proliferation and invasion of human ovarian cancer (OC) and its mechanism.

Methods

OC cell lines were divided into 4 groups including control, sevoflurane low concentration (1.7%), medium concentration (3.4%) and high concentration (5.1%) groups. Flow cytometry and MTT assay were, respectively, employed to detect the cell apoptosis and proliferation. Transwell assay was applied to measure the cell migration and invasion viability. The gene and protein expressions were assessed using qRT-PCR and Western blot. The expressions of MAPK signaling pathway-related proteins were evaluated by Western blot. The p38 and JNK inhibitors were, respectively, added into the high concentration group to analyze the relationship between sevoflurane and modulatingmitogen-activated protein kinase (MAPK) pathway in OC. Nude mice models were constructed to explore the effect of sevoflurane on OC tumor growth in vivo.

Results

Sevoflurane inhibited OC proliferation in vitro and in vivo. It could also promote OC cell apoptosis in a dose-dependent manner. Sevoflurane suppressed the OC cell migration and invasion, and these effects were positively correlated with the dose of sevoflurane. Moreover, sevoflurane treatment inhibited the expressions of PCNA, Twist, cleaved-caspase-3/caspase-3, MMP-2 and MMP-9. In addition, sevoflurane repressed the phosphorylation of JNK and p38 MAPK. When the MAPK pathway was interdicted, the cell proliferation, apoptosis, migration and invasion activity were recovered after sevoflurane treatment.

Conclusion

Sevoflurane affected cell biological activities in OC by regulating JNK and p38 MAPK signaling pathway.

Discoidin domain Receptor 2: A determinant of metabolic syndrome-associated arterial fibrosis in non-human primates

Collagen accumulation and remodeling in the vascular wall is a cardinal feature of vascular fibrosis that exacerbates the complications of hypertension, aging, diabetes and atherosclerosis. With no specific therapy available to date, identification of mechanisms underlying vascular fibrogenesis is an important clinical goal. Here, we tested the hypothesis that Discoidin Domain Receptor 2 (DDR2), a collagen-specific receptor tyrosine kinase, is a determinant of arterial fibrosis. We report a significant increase in collagen type 1 levels along with collagen and ECM remodeling, degradation of elastic laminae, enhanced fat deposition and calcification in the abdominal aorta in a non-human primate model of high-fat, high-sucrose diet (HFS)-induced metabolic syndrome. These changes were associated with a marked increase in DDR2. Resveratrol attenuated collagen type I deposition and remodeling induced by the HFS diet, with a concomintant reduction in DDR2. Further, in isolated rat vascular adventitial fibroblasts and VSMCs, hyperglycemia increased DDR2 and collagen type I expression via TGF-β1/SMAD2/3, which was attenuated by resveratrol. Notably, gene knockdown and overexpression approaches demonstrated an obligate role for DDR2 in hyperglycemia-induced increase in collagen type I expression in these cells. Together, our observations point to DDR2 as a hitherto unrecognized molecular link between metabolic syndrome and arterial fibrosis, and hence a therapeutic target.

TGF-β in Hepatic Stellate Cell Activation and Liver Fibrogenesis-Updated 2019

Liver fibrosis is an advanced liver disease condition, which could progress to cirrhosis and hepatocellular carcinoma. To date, there is no direct approved antifibrotic therapy, and current treatment is mainly the removal of the causative factor. Transforming growth factor (TGF)-β is a master profibrogenic cytokine and a promising target to treat fibrosis. However, TGF-β has broad biological functions and its inhibition induces non-desirable side effects, which override therapeutic benefits. Therefore, understanding the pleiotropic effects of TGF-β and its upstream and downstream regulatory mechanisms will help to design better TGF-β based therapeutics. Here, we summarize recent discoveries and milestones on the TGF-β signaling pathway related to liver fibrosis and hepatic stellate cell (HSC) activation, emphasizing research of the last five years. This comprises impact of TGF-β on liver fibrogenesis related biological processes, such as senescence, metabolism, reactive oxygen species generation, epigenetics, circadian rhythm, epithelial mesenchymal transition, and endothelial-mesenchymal transition. We also describe the influence of the microenvironment on the response of HSC to TGF-β. Finally, we discuss new approaches to target the TGF-β pathway, name current clinical trials, and explain promises and drawbacks that deserve to be adequately addressed.

"Let my liver rather heat with wine" - a review of hepatic fibrosis pathophysiology and emerging therapeutics

Cirrhosis is characterized by extensive hepatic fibrosis, and it is the 14th leading cause of death worldwide. Numerous contributing conditions have been implicated in its development, including infectious etiologies, medication overdose or adverse effects, ingestible toxins, autoimmunity, hemochromatosis, Wilson’s disease and primary biliary cholangitis to list a few. It is associated with portal hypertension and its stigmata (varices, ascites, hepatic encephalopathy, combined coagulopathy and thrombophilia), and it is a major risk factor for hepatocellular carcinoma. Currently, orthotopic liver transplantation has been the only curative modality to treat cirrhosis, and the scarcity of donors results in many people waiting years for a transplant. Identification of novel targets for pharmacologic therapy through elucidation of key mechanistic components to induce fibrosis reversal is the subject of intense research. Development of robust models of hepatic fibrosis to faithfully characterize the interplay between activated hepatic stellate cells (the principal fibrogenic contributor to fibrosis initiation and perpetuation), hepatocytes and extracellular matrix components has the potential to identify critical components and mechanisms that can be exploited for targeted treatment. In this review, we will highlight key cellular pathways involved in the pathophysiology of fibrosis from extracellular ligands, effectors and receptors, to nuclear receptors, epigenetic mechanisms, energy homeostasis and cytokines. Further, molecular pathways of hepatic stellate cell deactivation are discussed, including apoptosis, senescence and reversal or transdifferentiation to an inactivated state resembling quiescence. Lastly, clinical evidence of fibrosis reversal induced by biologics and small molecules is summarized, current compounds under clinical trials are described and efforts for treatment of hepatic fibrosis with mesenchymal stem cells are highlighted. An enhanced understanding of the rich tapestry of cellular processes identified in the initiation, perpetuation and resolution of hepatic fibrosis, driven principally through phenotypic switching of hepatic stellate cells, should lead to a breakthrough in potential therapeutic modalities.

Discoidin domain receptors: Micro insights into macro assemblies

Assembly of cell-surface receptors into specific oligomeric states and/or clusters before and after ligand binding is an important feature governing their biological function. Receptor oligomerization can be mediated by specific domains of the receptor, ligand binding, configurational changes or other interacting molecules. In this review we summarize our understanding of the oligomeric state of discoidin domain receptors (DDR1 and DDR2), which belong to the receptor tyrosine kinase family (RTK). DDRs form an interesting system from an oligomerization perspective as their ligand collagen(s) can also undergo supramolecular assembly to form fibrils. Even though DDR1 and DDR2 differ in the domains responsible to form ligand-free dimers they share similarities in binding to soluble, monomeric collagen. However, only DDR1b forms globular clusters in response to monomeric collagen and not DDR2. Interestingly, both DDR1 and DDR2 are assembled into linear clusters by the collagen fibril. Formation of these clusters is important for receptor phosphorylation and is mediated in part by other membrane components. We summarize how the oligomeric status of DDRs shares similarities with other members of the RTK family and with collagen receptors. Unraveling the multiple macro-molecular configurations adopted by this receptor-ligand pair can provide novel insights into the intricacies of cell-matrix interactions.

Hyaluronan synthase 2-mediated hyaluronan production mediates Notch1 activation and liver fibrosis

Hyaluronan (HA), a major extracellular matrix glycosaminoglycan, is a biomarker for cirrhosis. However, little is known about the regulatory and downstream mechanisms of HA overproduction in liver fibrosis. Hepatic HA and HA synthase 2 (HAS2) expression was elevated in both human and murine liver fibrosis. HA production and liver fibrosis were reduced in mice lacking HAS2 in hepatic stellate cells (HSCs), whereas mice overexpressing HAS2 had exacerbated liver fibrosis. HAS2 was transcriptionally up-regulated by transforming growth factor-β through Wilms tumor 1 to promote fibrogenic, proliferative, and invasive properties of HSCs via CD44, Toll-like receptor 4 (TLR4), and newly identified downstream effector Notch1. Inhibition of HA synthesis by 4-methylumbelliferone reduced HSC activation and liver fibrosis in mice. Our study provides evidence that HAS2 actively synthesizes HA in HSCs and that it promotes HSC activation and liver fibrosis through Notch1. Targeted HA inhibition may have potential to be an effective therapy for liver fibrosis.

Recent advances in the understanding of Dupuytren's disease

Dupuytren's disease (DD) is a common fibrotic disorder of the hand and can significantly impair hand function. Although the exact pathogenesis of this disorder remains to be elucidated, immunological, genetic and cellular factors likely interact. In this review, we summarise recent advances in the understanding of DD pathogenesis and look to the future for potential novel therapeutic targets. In addition, we discuss the therapeutic options in DD with a focus on the need for more rigorous evidence to allow a meaningful comparison of different treatment modalities.

Overexpression of Tumor Necrosis Factor-Like Ligand 1 A in Myeloid Cells Aggravates Liver Fibrosis in Mice

Macrophages are the master regulator of the dynamic fibrogenesis-fibrosis resolution paradigm. TNF-like ligand 1 aberrance (TL1A) was found to be able to induce intestinal inflammation and fibrosis. Furthermore, significantly increased TL1A had been detected in liver tissues and mononuclear cells of patients with primary biliary cirrhosis (PBC). This study was to investigate the effect of myeloid cells with constitutive TL1A expression on liver fibrogenesis. We found that TL1A expressions in liver tissues and macrophages were significantly increased in mice with liver fibrosis induced by injection of carbon tetrachloride (CCl₄). TL1A overexpression in myeloid cells induced liver function injury, accelerated the necrosis and apoptosis of hepatocytes, recruited macrophages, and promoted activation of hepatic stellate cells (HSCs) and fibrosis. In vitro results of our study showed that TL1A overexpression in macrophages promoted secretion of platelet-derived growth factor-BB (PDGF-BB), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β). Culturing macrophages with TL1A overexpression could accelerate the activation and proliferation of primary HSCs. These results indicated that constitutive TL1A expression in myeloid cells exacerbated liver fibrosis, probably through macrophage recruitment and secretion of proinflammatory and profibrotic cytokines.

Design, Synthesis, and Biological Evaluation of 3-(Imidazo[1,2- a]pyrazin-3-ylethynyl)-4-isopropyl- N-(3-((4-methylpiperazin-1-yl)methyl)-5-(trifluoromethyl)phenyl)benzamide as a Dual Inhibitor of Discoidin Domain Receptors 1 and 2

Discoidin-domain receptors 1 and 2 (DDR1 and DDR2) are new potential targets for anti-inflammatory-drug discovery. A series of heterocycloalkynylbenzimides were designed and optimized to coinhibit DDR1 and DDR2. One of the most promising compounds, 5n, tightly bound to DDR1 and DDR2 proteins with K_d values of 7.9 and 8.0 nM; potently inhibited the kinases with IC₅₀ values of 9.4 and 20.4 nM, respectively; and was significantly less potent for a panel of 403 wild-type kinases at 1.0 μM. DDR1- and DDR2-kinase inhibition by 5n was validated by Western-blotting analysis in primary human lung fibroblasts. The compound also dose-dependently inhibited lipopolysaccharide (LPS)-induced interleukin 6 (IL-6) release in vitro and exhibited promising in vivo anti-inflammatory effects in an LPS-induced-acute-lung-injury (ALI) mouse model. Compound 5n may serve as a lead compound for new anti-inflammatory drug discovery.

Mechanical signaling through the discoidin domain receptor 1 plays a central role in tissue fibrosis

The preservation of tissue and organ architecture and function depends on tightly regulated interactions of cells with the extracellular matrix (ECM). These interactions are maintained in a dynamic equilibrium that balances intracellular, myosin-generated tension with extracellular resistance conferred by the mechanical properties of the extracellular matrix. Disturbances of this equilibrium can lead to the development of fibrotic lesions that are associated with a wide repertoire of high prevalence diseases including obstructive cardiovascular diseases, muscular dystrophy and cancer. Mechanotransduction is the process by which mechanical cues are converted into biochemical signals. At the core of mechanotransduction are sensory systems, which are frequently located at sites of cell-ECM and cell-cell contacts. As integrins (cell-ECM junctions) and cadherins (cell-cell contacts) have been extensively studied, we focus here on the properties of the discoidin domain receptor 1 (DDR1), a tyrosine kinase that mediates cell adhesion to collagen. DDR1 expression is positively associated with fibrotic lesions of heart, kidney, liver, lung and perivascular tissues. As the most common end-point of all fibrotic disorders is dysregulated collagen remodeling, we consider here the mechanical signaling functions of DDR1 in processing of fibrillar collagen that lead to tissue fibrosis.

TWIST1 induces expression of discoidin domain receptor 2 to promote ovarian cancer metastasis

The mesenchymal gene program has been shown to promote the metastatic progression of ovarian cancer; however, specific proteins induced by this program that lead to these metastatic behaviors have not been identified. Using patient derived tumor cells and established human ovarian tumor cell lines, we find that the Epithelial-to –Mesenchymal Transition inducing factor TWIST1 drives expression of Discoidin Domain Receptor 2 (DDR2), a receptor tyrosine kinase (RTK) that recognizes fibrillar collagen as ligand. The expression and action of DDR2 was critical for mesothelial cell clearance, invasion and migration in ovarian tumor cells. It does so, in part, by upregulating expression and activity of matrix remodeling enzymes that lead to increased cleavage of fibronectin and spreading of tumor cells. Additionally, DDR2 stabilizes SNAIL1, allowing for sustained mesenchymal phenotype. In patient derived ovarian cancer specimens, DDR2 expression correlated with enhanced invasiveness. DDR2 expression was associated with advanced stage ovarian tumors and metastases. In vivo studies demonstrated that the presence of DDR2 is critical for ovarian cancer metastasis. These findings indicate that the collagen receptor DDR2 is critical for multiple steps of ovarian cancer progression to metastasis, and thus, identifies DDR2 as a potential new target for the treatment of metastatic ovarian cancer.

Mechanotransduction-modulated fibrotic microniches reveal the contribution of angiogenesis in liver fibrosis

The role of pathological angiogenesis on liver fibrogenesis is still unknown. Here, we developed fibrotic microniches (FμNs) that recapitulate the interaction of liver sinusoid endothelial cells (LSECs) and hepatic stellate cells (HSCs). We investigated how the mechanical properties of their substrates affect the formation of capillary-like structures and how they relate to the progression of angiogenesis during liver fibrosis. Differences in cell response in the FμNs were synonymous of the early and late stages of liver fibrosis. The stiffness of the early-stage FμNs was significantly elevated due to condensation of collagen fibrils induced by angiogenesis, and led to activation of HSCs by LSECs. We utilized these FμNs to understand the response to anti-angiogenic drugs, and it was evident that these drugs were effective only for early-stage liver fibrosis in vitro and in an in vivo mouse model of liver fibrosis. Late-stage liver fibrosis was not reversed following treatment with anti-angiogenic drugs but rather with inhibitors of collagen condensation. Our work reveals stage-specific angiogenesis-induced liver fibrogenesis via a previously unrevealed mechanotransduction mechanism which may offer precise intervention strategies targeting stage-specific disease progression.

DDR2 facilitates papillary thyroid carcinoma epithelial mesenchymal transition by activating ERK2/Snail1 pathway

The upregulation of discoidin domain receptor tyrosine kinase 2 (DDR2) has been reported to be associated with poor prognosis and metastasis in numerous tumor types by inducing epithelial-mesenchymal transition (EMT); however, the expression profile of DDR2 in papillary thyroid carcinoma (PTC) with local metastasis and the effect of DDR2 on PTC cells remain unknown. The aim of the present study was to investigate the expression levels of DDR2 in tumor tissues of patients with PTC with local metastasis and cell lines and to determine the effect of DDR2 on EMT in PTC cells. In the present study, it was demonstrated that DDR2 was significantly increased in tumor tissues of patients with PTC with local metastasis and human PTC cell lines. The overexpression of DDR2 by lentiviral transfection decreased E-cadherin protein, increased Vimentin protein, and promoted cell migration and invasion. The inhibition of DDR2 reversed transforming growth factor-β- and collagen I-induced EMT. EMT induced by DDR2 overexpression was suggested to be dependent on increased Snail1 protein level following extracellular signal-regulated kinase (ERK)2 activation. The inhibition of Snail1 or ERK2 was sufficient to abrogate DDR2-induced PTC cell EMT. In conclusion, these results indicate that DDR2 is upregulated in PTC tissues with local metastasis. Overexpression of DDR2 induced EMT in PTC cells by activating ERK2 and stabilizing Snail1, making it a promising therapeutic target for reducing PTC local or distant metastasis.

A Genome-wide Association Study of Dupuytren Disease Reveals 17 Additional Variants Implicated in Fibrosis

Individuals with Dupuytren disease (DD) are commonly seen by physicians and surgeons across multiple specialties. It is an increasingly common and disabling fibroproliferative disorder of the palmar fascia, which leads to flexion contractures of the digits, and is associated with other tissue-specific fibroses. DD affects between 5% and 25% of people of European descent and is the most common inherited disease of connective tissue. We undertook the largest GWAS to date in individuals with a surgically validated diagnosis of DD from the UK, with replication in British, Dutch, and German individuals. We validated association at all nine previously described signals and discovered 17 additional variants with p ≤ 5 × 10⁻⁸. As a proof of principle, we demonstrated correlation of the high-risk genotype at the statistically most strongly associated variant with decreased secretion of the soluble WNT-antagonist SFRP4, in surgical specimen-derived DD myofibroblasts. These results highlight important pathways involved in the pathogenesis of fibrosis, including WNT signaling, extracellular matrix modulation, and inflammation. In addition, many associated loci contain genes that were hitherto unrecognized as playing a role in fibrosis, opening up new avenues of research that may lead to novel treatments for DD and fibrosis more generally. DD represents an ideal human model disease for fibrosis research.

Mechanisms of hepatic stellate cell activation

Hepatic fibrosis is a dynamic process characterized by the net accumulation of extracellular matrix resulting from chronic liver injury of any aetiology, including viral infection, alcoholic liver disease and NASH. Activation of hepatic stellate cells (HSCs) - transdifferentiation of quiescent, vitamin-A-storing cells into proliferative, fibrogenic myofibroblasts - is now well established as a central driver of fibrosis in experimental and human liver injury. Yet, the continued discovery of novel pathways and mediators, including autophagy, endoplasmic reticulum stress, oxidative stress, retinol and cholesterol metabolism, epigenetics and receptor-mediated signals, reveals the complexity of HSC activation. Extracellular signals from resident and inflammatory cells including macrophages, hepatocytes, liver sinusoidal endothelial cells, natural killer cells, natural killer T cells, platelets and B cells further modulate HSC activation. Finally, pathways of HSC clearance have been greatly clarified, and include apoptosis, senescence and reversion to an inactivated state. Collectively, these findings reinforce the remarkable complexity and plasticity of HSC activation, and underscore the value of clarifying its regulation in hopes of advancing the development of novel diagnostics and therapies for liver disease.

Naringenin prevents experimental liver fibrosis by blocking TGFβ-Smad3 and JNK-Smad3 pathways

AIM

To study the molecular mechanisms involved in the hepatoprotective effects of naringenin (NAR) on carbon tetrachloride (CCl₄)-induced liver fibrosis.

METHODS

Thirty-two male Wistar rats (120-150 g) were randomly divided into four groups: (1) a control group (n = 8) that received 0.7% carboxy methyl-cellulose (NAR vehicle) 1 mL/daily p.o.; (2) a CCl₄ group (n = 8) that received 400 mg of CCl₄/kg body weight i.p. 3 times a week for 8 wk; (3) a CCl₄ + NAR (n = 8) group that received 400 mg of CCl₄/kg body weight i.p. 3 times a week for 8 wk and 100 mg of NAR/kg body weight daily for 8 wk p.o.; and (4) an NAR group (n = 8) that received 100 mg of NAR/kg body weight daily for 8 wk p.o. After the experimental period, animals were sacrificed under ketamine and xylazine anesthesia. Liver damage markers such as alanine aminotransferase (ALT), alkaline phosphatase (AP), γ-glutamyl transpeptidase (γ-GTP), reduced glutathione (GSH), glycogen content, lipid peroxidation (LPO) and collagen content were measured. The enzymatic activity of glutathione peroxidase (GPx) was assessed. Liver histopathology was performed utilizing Masson’s trichrome and hematoxylin-eosin stains. Zymography assays for MMP-9 and MMP-2 were carried out. Hepatic TGF-β, α-SMA, CTGF, Col-I, MMP-13, NF-κB, IL-1, IL-10, Smad7, Smad3, pSmad3 and pJNK proteins were detected via western blot.

RESULTS

NAR administration prevented increases in ALT, AP, γ-GTP, and GPx enzymatic activity; depletion of GSH and glycogen; and increases in LPO and collagen produced by chronic CCl₄ intoxication (P < 0.05). Liver histopathology showed a decrease in collagen deposition when rats received NAR in addition to CCl₄. Although zymography assays showed that CCl₄ produced an increase in MMP-9 and MMP-2 gelatinase activity; interestingly, NAR administration was associated with normal MMP-9 and MMP-2 activity (P < 0.05). The anti-inflammatory, antinecrotic and antifibrotic effects of NAR may be attributed to its ability to prevent NF-κB activation and the subsequent production of IL-1 and IL-10 (P < 0.05). NAR completely prevented the increase in TGF-β, α-SMA, CTGF, Col-1, and MMP-13 proteins compared with the CCl₄-treated group (P < 0.05). NAR prevented Smad3 phosphorylation in the linker region by JNK since this flavonoid blocked this kinase (P < 0.05).

CONCLUSION

NAR prevents CCl₄ induced liver inflammation, necrosis and fibrosis, due to its antioxidant capacity as a free radical inhibitor and by inhibiting the NF-κB, TGF-β-Smad3 and JNK-Smad3 pathways.

A liver microphysiological system of tumor cell dormancy and inflammatory responsiveness is affected by scaffold properties

Distant metastasis is the major cause of breast cancer-related mortality, commonly emerging clinically after 5 or more years of seeming 'cure' of the primary tumor, indicating a quiescent dormancy. The lack of relevant accessible model systems for metastasis that recreate this latent stage has hindered our understanding of the molecular basis and the development of therapies against these lethal outgrowths. We previously reported on the development of an all-human 3D ex vivo hepatic microphysiological system that reproduces several features of liver physiology and enables spontaneous dormancy in a subpopulation of breast cancer cells. However, we observed that the dormant cells were localized primarily within the 3D tissue, while the proliferative cells were in contact with the polystyrene scaffold. As matrix stiffness is known to drive inflammatory and malignant behaviors, we explored the occurrence of spontaneous tumor dormancy and inflammatory phenotype. The microphysiological system was retrofitted with PEGDa-SynKRGD hydrogel scaffolding, which is softer and differs in the interface with the tissue. The microphysiological system incorporated donor-matched primary human hepatocytes and non-parenchymal cells (NPCs), with MDA-MB-231 breast cancer cells. Hepatic tissue in hydrogel scaffolds secreted lower levels of pro-inflammatory analytes, and was more responsive to inflammatory stimuli. The proportion of tumor cells entering dormancy was markedly increased in the hydrogel-supported tissue compared to polystyrene. Interestingly, an unexpected differential response of dormant cells to varying chemotherapeutic doses was identified, which if reflective of patient pathophysiology, has important implications for patient dosing regimens. These findings highlight the metastatic microphysiological system fitted with hydrogel scaffolds as a critical tool in the assessment and development of therapeutic strategies to target dormant metastatic breast cancer.

The C. elegans Discoidin Domain Receptor DDR-2 Modulates the Met-like RTK-JNK Signaling Pathway in Axon Regeneration

The ability of specific neurons to regenerate their axons after injury is governed by cell-intrinsic regeneration pathways. However, the signaling pathways that orchestrate axon regeneration are not well understood. In Caenorhabditis elegans, initiation of axon regeneration is positively regulated by SVH-2 Met-like growth factor receptor tyrosine kinase (RTK) signaling through the JNK MAPK pathway. Here we show that SVH-4/DDR-2, an RTK containing a discoidin domain that is activated by collagen, and EMB-9 collagen type IV regulate the regeneration of neurons following axon injury. The scaffold protein SHC-1 interacts with both DDR-2 and SVH-2. Furthermore, we demonstrate that overexpression of svh-2 and shc-1 suppresses the delay in axon regeneration observed in ddr-2 mutants, suggesting that DDR-2 functions upstream of SVH-2 and SHC-1. These results suggest that DDR-2 modulates the SVH-2–JNK pathway via SHC-1. We thus identify two different RTK signaling networks that play coordinated roles in the regulation of axonal regeneration.

An axon’s ability to regenerate after injury is governed by cell-intrinsic regeneration pathways. The C. elegans JNK MAP kinase pathway is required for the regrowth of neurons after injury. Previously, we identified several svh genes involved in JNK-mediated signaling. Among them, the svh-1 and svh-2 genes encode a growth factor and its receptor tyrosine kinase (RTK), respectively. This SVH-1–SVH-2 signaling cascade positively regulates axon regeneration through the JNK pathway. In the present study, we investigate the role of the svh-4/ddr-2 gene, which encodes an RTK containing a discoidin domain that is activated by collagen. Indeed, DDR-2 functions downstream of EMB-9 collagen type IV. Here, we show that the ddr-2 and emb-9 mutations delay initiation of regeneration after axon injury. Furthermore, we demonstrate that DDR-2 modulates the SVH-1–SVH-2–JNK pathway through the scaffold protein SHC-1. Thus, two different RTK signaling networks play coordinated roles in the regulation of axonal regeneration.

The Role of Cancer-Associated Fibroblasts and Fibrosis in Liver Cancer

Liver cancer is the second leading cause of cancer mortality worldwide, causing more than 700,000 deaths annually. Because of the wide landscape of genomic alterations and limited therapeutic success of targeting tumor cells, a recent focus has been on better understanding and possibly targeting the microenvironment in which liver tumors develop. A unique feature of liver cancer is its close association with liver fibrosis. More than 80% of hepatocellular carcinomas (HCCs) develop in fibrotic or cirrhotic livers, suggesting an important role of liver fibrosis in the premalignant environment (PME) of the liver. Cholangiocarcinoma (CCA), in contrast, is characterized by a strong desmoplasia that typically occurs in response to the tumor, suggesting a key role of cancer-associated fibroblasts (CAFs) and fibrosis in its tumor microenvironment (TME). Here, we discuss the functional contributions of myofibroblasts, CAFs, and fibrosis to the development of HCC and CCA in the hepatic PME and TME, focusing on myofibroblast- and extracellular matrix-associated growth factors, fibrosis-associated immunosuppressive pathways, as well as mechanosensitive signaling cascades that are activated by increased tissue stiffness. Better understanding of the role of myofibroblasts in HCC and CCA development and progression may provide the basis to target these cells for tumor prevention or therapy.

Versican: a novel modulator of hepatic fibrosis

Little is known about the deposition and turnover of proteoglycans in liver fibrosis, despite their abundance in the extracellular matrix. Versican plays diverse roles in modulating cell behavior in other fibroproliferative diseases, but remains poorly described in the liver. Hepatic fibrosis was induced by carbon tetrachloride treatment of C57BL/6 mice over 4 weeks followed by recovery over a 28-day period. Primary mouse hepatic stellate cells (HSCs) were activated in culture and versican was transiently knocked down in human (LX2) and mouse HSCs. Expression of versican, A Disintegrin-like and Metalloproteinase with Thrombospondin-1 motifs (ADAMTS)-1, -4, -5, -8, -9, -15, and -20, and markers of fibrogenesis were studied using immunohistochemistry, real-time quantitative PCR, and western blotting. Immunohistochemistry showed increased expression of versican in cirrhotic human livers and the mouse model of fibrosis. Carbon tetrachloride treatment led to significant increases in versican expression and the proteoglycanases ADAMTS-5, -9, -15, and -20, alongside TNF-α, α-smooth muscle actin (α-SMA), collagen-1, and TGF-β expression. During recovery, expression of many of these genes returned to control levels. However, expression of ADAMTS-5, -8, -9, and -15 showed delayed increases in expression at 28 days of recovery, which corresponded with decreases in versican V0 and V1 cleavage products (G1-DPEAAE(1401) and G1-DPEAAE(441)). Activation of primary HSCs in vitro significantly increased versican, α-SMA, and collagen-1 expression. Transient knockdown of versican in HSCs led to decreases in markers of fibrogenesis and reduced cell proliferation, without inducing apoptosis. Versican expression increases during HSC activation and liver fibrosis, and proteolytic processing occurs during the resolution of fibrosis. Knockdown studies in vitro suggest a possible role of versican in modulating hepatic fibrogenesis.

Signaling of extracellular matrices for tissue regeneration and therapeutics

Cells receive important regulatory signals from their extracellular matrix (ECM) and the physical property of the ECM regulates important cellular behaviors like cell proliferation, migration and differentiation. A large part of tissue formation and regeneration depends on cellular interaction with its ECM. A comprehensive understanding of the mechanistic biochemical pathway of the ECM components is necessary for the design of a biomaterial scaffold for tissue engineering. Depending on the type of tissue, the ECM requirement might be different and this would influence its downstream intracellular cell signaling. Here, we reviewed the ECM and its signaling pathway by discussing: 1) classification of the ECM into hard, elastic and soft tissue based on its physical properties, 2) proliferation and differentiation control of the ECM, 3) roles of membrane receptor and its intracellular regulation factor, 4) ECM remodeling via inside-out signaling. By providing a comprehensive overview of the ECM's role in mechanotransduction and the self-regulatory effect of cells back on the ECM, we hope to provide a better insight of the physical and biochemical cues from the ECM. A sound understanding on the in vivo ECM has implication on the choice of materials and surface coating of biomimetic scaffolds used for tissue regeneration and therapeutics in a cell-free scaffold.

Orphan nuclear receptor NR4A2 inhibits hepatic stellate cell proliferation through MAPK pathway in liver fibrosis

Hepatic stellate cells (HSCs) play a crucial role in liver fibrosis, which is a pathological process characterized by extracellular matrix accumulation. NR4A2 is a nuclear receptor belonging to the NR4A subfamily and vital in regulating cell growth, metabolism, inflammation and other biological functions. However, its role in HSCs is unclear. We analyzed NR4A2 expression in fibrotic liver and stimulated HSCs compared with control group and studied the influence on cell proliferation, cell cycle, cell apoptosis and MAPK pathway after NR4A2 knockdown. NR4A2 expression was examined by real-time polymerase chain reaction, Western blotting, immunohistochemistry and immunofluorescence analyses. NR4A2 expression was significantly lower in fibrotic liver tissues and PDGF BB or TGF-β stimulated HSCs compared with control group. After NR4A2 knockdown α-smooth muscle actin and Col1 expression increased. In addition, NR4A2 silencing led to the promotion of cell proliferation, increase of cell percentage in S phase and reduced phosphorylation of ERK1/2, P38 and JNK in HSCs. These results indicate that NR4A2 can inhibit HSC proliferation through MAPK pathway and decrease extracellular matrix in liver fibrogenesis. NR4A2 may be a promising therapeutic target for liver fibrosis.

Myeloperoxidase-Hepatocyte-Stellate Cell Cross Talk Promotes Hepatocyte Injury and Fibrosis in Experimental Nonalcoholic Steatohepatitis

AIMS

Myeloperoxidase (MPO), a highly oxidative enzyme secreted by leukocytes has been implicated in human and experimental nonalcoholic steatohepatitis (NASH), but the underlying mechanisms remain unknown. In this study, we investigated how MPO contributes to progression from steatosis to NASH.

RESULTS

In C57Bl/6J mice fed a diet deficient in methionine and choline to induce NASH, neutrophils and to a lesser extent inflammatory monocytes are markedly increased compared with sham mice and secrete abundant amounts of MPO. Through generation of HOCl, MPO directly causes hepatocyte death in vivo. In vitro experiments demonstrate mitochondrial permeability transition pore induction via activation of SAPK/JNK and PARP. MPO also contributes to activation of hepatic stellate cells (HSCs), the most important source of collagen in the liver. In vitro MPO-activated HSCs have an activation signature (MAPK and PI3K-AKT phosphorylation) and upregulate COL1A1, α-SMA, and CXCL1. MPO-derived oxidative stress also activates transforming growth factor β (TGF-β) in vitro, and TGF-β signaling inhibition with SB-431542 decreased steatosis and fibrosis in vivo. Conversely, congenital absence of MPO results in reduced hepatocyte injury, decreased levels of TGF-β, fewer activated HSCs, and less severe fibrosis in vivo.

INNOVATION AND CONCLUSION

Cumulatively, these findings demonstrate important cross talk between inflammatory myeloid cells, hepatocytes, and HSCs via MPO and establish MPO as part of a proapoptotic and profibrotic pathway of progression in NASH, as well as a potential therapeutic target to ameliorate this disease.

DDR2 facilitates hepatocellular carcinoma invasion and metastasis via activating ERK signaling and stabilizing SNAIL1

BACKGROUND

Several studies have found that DDR2 is up-regulated in many tumor types and facilitates tumor progression. However, the role of DDR2 in hepatocellular carcinoma (HCC) progression and its downstream signaling pathways remain unclear.

METHODS

DDR2 expression was assessed in several cell lines and 112 pairs of HCC and matched adjacent noncancerous liver tissues. Clinical significance of DDR2 in HCC was analyzed. Phosphorylated DDR2 (p-DDR2) expression was detected by immunoblotting to evaluate its correlation with DDR2. The effect of DDR2 on HCC cell migration and invasion were examined. Cycloheximide chase experiments were performed to detect the half-life of SNAIL1. Moreover, DDR2 expression was detected by immunohistochemistry to evaluate its correlation with SNAIL1. The regulatory effect of DDR2 on ERK signaling, SNAIL1, EMT, MT1-MMP and MMP2 was confirmed by immunoblotting. The effect of type I collagen on DDR2/ERK2/SNAIL1 signaling was assessed.

RESULTS

DDR2 was more highly expressed in HCC than in non-HCC tissues. DDR2 overexpression was correlated with clinicopathological features of poor prognosis. Clinical analysis revealed that DDR2 is an independent prognostic marker for predicting overall survival and disease free survival of HCC patients. Overexpression of DDR2 is associated with p-DDR2 amplification. In vitro studies showed that DDR2 facilitates HCC cell invasion, migration and EMT via activating ERK2 and stabilizing SNAIL1. DDR2 can up-regulate MT1-MMP and MMP2 expression through ERK2/SNAIL1 signaling in HCC. Additionally, collagen I can induce DDR2/ERK2/SNAIL1 signaling activation in HCC cells.

CONCLUSIONS

Our findings suggest that DDR2 plays an important role in promoting HCC cell invasion and migration, and may serve as a novel therapeutic target in HCC.

Abnormal Accumulation of Collagen Type I Due to the Loss of Discoidin Domain Receptor 2 (Ddr2) Promotes Testicular Interstitial Dysfunction

Background

Loss of functional allele for discoidin domain receptor 2 (Ddr2) results in impaired Leydig cell response to luteinizing hormone (LH), low testosterone production and arrested spermatogenesis in older male Ddr2^slie/slie mice. However, the underlying mechanism responsible for this phenotype remains unknown. Herein, we reported for the first time that the deregulated expression of Ddr2 cognate ligand, namely collagen type I (COL1), may account for the disruption of the testicular steroidogenesis in Ddr2^slie/slie mutant testes.

Methodology/Principal Findings

Expression of Ddr2 increased gradually along postnatal development, whereas COL1 expression became negligible from adulthood onwards. In Ddr2^slie/slie mutant testis, however, in contrast to the undetectable staining of Ddr2, COL1 expression was constantly detected, with the highest values detected during adulthood. In the experimental vasectomy model, Ddr2^slie/slie mutant mice exhibited an early androgen deficiency than wild-type mice, along with the accumulation of fibrotic tissue in the interstitium. Functionally, ablation of endogenous Ddr2 resulted in a significant decrease of testosterone (T) level in TM3 cells in the presence of higher concentration of COL1 treatment. Conversely, overexpression of Ddr2 could help TM3 cells to maintain a normal testicular steroidogenesis even in the presence of high concentration of COL1. Additionally, attenuated expression of Ddr2 correlates to the deregulated level of serum T levels in human pathological testes.

Conclusions

Abnormal accumulation of interstitial COL1 may be responsible for the steroidogenic dysfunction in Ddr2^slie/slie mutant testes.

Minor Type IV Collagen α5 Chain Promotes Cancer Progression through Discoidin Domain Receptor-1

Type IV collagens (Col IV), components of basement membrane, are essential in the maintenance of tissue integrity and proper function. Alteration of Col IV is related to developmental defects and diseases, including cancer. Col IV α chains form α1α1α2, α3α4α5 and α5α5α6 protomers that further form collagen networks. Despite knowledge on the functions of major Col IV (α1α1α2), little is known whether minor Col IV (α3α4α5 and α5α5α6) plays a role in cancer. It also remains to be elucidated whether major and minor Col IV are functionally redundant. We show that minor Col IV α5 chain is indispensable in cancer development by using α5(IV)-deficient mouse model. Ablation of α5(IV) significantly impeded the development of Kras^G12D-driven lung cancer without affecting major Col IV expression. Epithelial α5(IV) supports cancer cell proliferation, while endothelial α5(IV) is essential for efficient tumor angiogenesis. α5(IV), but not α1(IV), ablation impaired expression of non-integrin collagen receptor discoidin domain receptor-1 (DDR1) and downstream ERK activation in lung cancer cells and endothelial cells. Knockdown of DDR1 in lung cancer cells and endothelial cells phenocopied the cells deficient of α5(IV). Constitutively active DDR1 or MEK1 rescued the defects of α5(IV)-ablated cells. Thus, minor Col IV α5(IV) chain supports lung cancer progression via DDR1-mediated cancer cell autonomous and non-autonomous mechanisms. Minor Col IV can not be functionally compensated by abundant major Col IV.

Collagens, the major extracellular matrix components in most vertebrate tissues, provide cells with structural and functional support. Collagens are trimers of collagen α chains. Multiple trimers are formed by highly homologous α chains for certain types of collagens (e.g. α1α1α2, α3α4α5 and α5α5α6 heterotrimers for type IV collagen). Type IV collagens are named as major type (α1α1α2) or minor type (α3α4α5 and α5α5α6), mainly reflecting the abundance and tissue distribution, but not the importance of their biological functions. High similarity in sequence and domain structure of the α chains does not necessarily imply that major and minor type IV collagens share the same cell surface receptors and intracellular signaling pathways. In this study, we generated an α5(IV) chain deficient mouse model lacking minor type IV collagens. We found that the mutant mice have delayed development of Kras^G12D-driven lung cancer without affecting major type IV collagen expression. α5(IV), but not α1(IV), ablation impaired non-integrin collagen receptor discoidin domain receptor-1 (DDR1)-ERK signaling, suggesting that major and minor type IV collagens are functionally distinct from each other.

Role of methionine adenosyltransferase α2 and β phosphorylation and stabilization in human hepatic stellate cell trans-differentiation

Myofibroblastic trans-differentiation of hepatic stellate cells (HSCs) is an essential event in the development of liver fibrogenesis. These changes involve modulation of key regulators of the genome and the proteome. Methionine adenosyltransferases (MAT) catalyze the biosynthesis of the methyl donor, S-adenosylmethionine (SAMe) from methionine. We have previously shown that two MAT genes, MAT2A and MAT2B (encoding MATα2 and MATβ proteins respectively), are required for HSC activation and loss of MAT2A transcriptional control favors its up-regulation during trans-differentiation. Hence MAT genes are intrinsically linked to the HSC machinery during activation. In the current study, we have identified for the first time, post-translational modifications in the MATα2 and MATβ proteins that stabilize them and favor human HSC trans-differentiation. Culture-activation of human HSCs induced the MATα2 and MATβ proteins. Using mass spectrometry, we identified phosphorylation sites in MATα2 and MATβ predicted to be phosphorylated by mitogen-activated protein kinase (MAPK) family members (ERK1/2, V-Raf Murine Sarcoma Viral Oncogene Homolog B1 [B-Raf], MEK). Phosphorylation of both proteins was enhanced during HSC activation. Blocking MEK activation lowered the phosphorylation and stability of MAT proteins without influencing their mRNA levels. Silencing ERK1/2 or B-Raf lowered the phosphorylation and stability of MATβ but not MATα2. Reversal of the activated human HSC cell line, LX2 to quiescence lowered phosphorylation and destabilized MAT proteins. Mutagenesis of MATα2 and MATβ phospho-sites destabilized them and prevented HSC trans-differentiation. The data reveal that phosphorylation of MAT proteins during HSC activation stabilizes them thereby positively regulating trans-differentiation.

Evaluation of discoidin domain receptor-2 (DDR2) expression level in normal, benign, and malignant human prostate tissues

Discoidin domain receptor (DDR) is a new member of the receptor tyrosine kinase family. There are two isoforms of discoidin domain receptor (DDR), DDR1 and DDR2. These receptors play a major role in the adhesion, motility and cell proliferation. Due to the important role of DDR2 in the development of tumor extension, this receptor is pivotal in the field of carcinogenesis. The aim of this study was to investigate the mRNA and protein expression of DDR2, in the malignant, benign prostatic hyperplasia (BPH) and normal tissues of patients with prostate cancer. In this study the gene and protein expression of DDR2 in adjacent normal (n=40), BPH (n=40), and malignant (n=40) prostate tissue were measured using real-time PCR and Western blotting. Then, the correlation of DDR2 gene and protein expression with prognostic factors such as age, tumor grade, tumor stage, lymph node involvement, and serum prostate-specific antigen (PSA) concentration were evaluated. The relative mRNA and protein expression level of DDR2 in malignant and benign prostate tissue was significantly higher than those of adjacent normal tissues (P<0.01). This expression was found to increase approximately 3.5 and 2.1 fold for mRNA and protein levels, respectively. Spearman test indicated a significant correlation between DDR2 mRNA and protein expression with prognostic factors such as tumor grade, stage, lymph node involvement, and serum PSA concentration. However, significant correlation with age was not observed. These findings suggest that DDR2 is a cancer-related gene associated with the aggressive progression of prostate cancer patients.

Discoidin domain receptor functions in physiological and pathological conditions

The discoidin domain receptors, DDR1 and DDR2, are nonintegrin collagen receptors that are members of the receptor tyrosine kinase family. Both DDRs bind a number of different collagen types and play important roles in embryo development. Dysregulated DDR function is associated with progression of various human diseases, including fibrosis, arthritis, and cancer. By interacting with key components of the extracellular matrix and displaying distinct activation kinetics, the DDRs form a unique subfamily of receptor tyrosine kinases. DDR-facilitated cellular functions include cell migration, cell survival, proliferation, and differentiation, as well as remodeling of extracellular matrices. This review summarizes the current knowledge of DDR-ligand interactions, DDR-initiated signal pathways and the molecular mechanisms that regulate receptor function. Also discussed are the roles of DDRs in development and disease progression.

Discoidin domain receptor 2 germline gene deletion leads to altered heart structure and function in the mouse

Discoidin domain receptor 2 (DDR2) is a fibrillar collagen receptor that is expressed in mesenchymal cells throughout the body. In the heart, DDR2 is selectively expressed on cardiac fibroblasts. We generated a germline DDR2 knockout mouse and used this mouse to examine the role of DDR2 deletion on heart structure and function. Echocardiographic measurements from null mice were consistent with those from a smaller heart, with reduced left ventricular chamber dimensions and little change in wall thickness. Fractional shortening appeared normal. Left ventricular pressure measurements revealed mild inotropic and lusitropic abnormalities that were accentuated by dobutamine infusion. Both body and heart weights from 10-wk-old male mice were ~20% smaller in null mice. The reduced heart size was not simply due to reduced body weight, since cardiomyocyte lengths were atypically shorter in null mice. Although normalized cardiac collagen mass (assayed by hydroxyproline content) was not different in null mice, the collagen area fraction was statistically higher, suggesting a reduced collagen density from altered collagen deposition and cross-linking. Cultured cardiac fibroblasts from null mice deposited collagen at a slower rate than wild-type littermates, possibly due to the expression of lower prolyl 4-hydroxylase α-isoform 1 enzyme levels. We conclude that genetic deletion of the DDR2 collagen receptor alters cardiac fibroblast function. The resulting perturbations in collagen deposition can influence the structure and function of mature cardiomyocytes.

Identification of novel driver mutations of the discoidin domain receptor 2 (DDR2) gene in squamous cell lung cancer of Chinese patients

BACKGROUND

Although many of the recently approved genomically targeted therapies have improved outcomes for patients in non-small-cell lung cancer (NSCLC) with lung adenocarcinoma, little is known about the genomic alterations that drive lung squamous cell cancer (SCC) and development of effective targeted therapies in lung SCC is a promising area to be further investigated. Discoidin domain receptor 2 (DDR2), is a novel receptor tyrosine kinases that respond to several collagens and involved in tissue repair, primary and metastatic cancer progression.

METHODS

Expression of DDR2 mRNA was analyzed in 54 lung SCC tissues by qRT-PCR. Over-expression approaches were used to investigate the biological functions of DDR2 and its' mutations in lung SCC cells. Conventional Sanger sequencing was used to investigate the mutations of DDR2 gene in 86 samples. The effect of DDR2 and its' mutations on proliferation was evaluated by MTT and colony formation assays; cell migration and invasion was evaluated by trasnwell assays. Lung SCC cells stably transfected with pEGFP-DDR2 WT, pEGFP-DDR2-S131C or empty vector were injection into nude mice to study the effect of DDR2 and its' mutation on tumorigenesis in vivo. Protein and mRNA expression levels of E-cadherin and MMP2 were determined by qRT-PCR and western blot analysis. Differences between groups were tested for significance using Student's t-test (two-tailed).

RESULTS

In this study, we found that DDR2 mRNA levels were significantly decreased in 54 lung SCC tissues compared with normal lung tissues. Moreover, there were 3 novel DDR2 mutations (G531V, S131C, T681I) in 4 patients and provide the mutation rate of 4.6% in the 86 patients with lung SCC. The mutation of S131C in DDR2 could promote lung SCC cells proliferation, migration and invasion via inducing MMP-2, but reducing E-cadherin expression.

CONCLUSIONS

These data indicated that the novel DDR2 mutation may contribute to the development and progression of lung SCC and this effect may be associated with increased proliferation and invasiveness, at least in part, via regulating E-cadherin expression.

Overexpression of DDR2 contributes to cell invasion and migration in head and neck squamous cell carcinoma

Background Discoidin domain receptor 2 (DDR2) is a unique receptor tyrosine kinase (RTK) that is activated by fibrillar collagens. Although DDR2 contributes to the metastasis of some tumors, its role in head and neck squamous cell carcinoma (HNSCC) remains unknown. The aim of this study was to investigate the expression level, clinical and pathological significance, and biologic function of DDR2 in HNSCC. Methods Real-time quantitative PCR, western blot, and immunohistochemical staining were employed to assess the expression levels of DDR2 in HNSCC specimens. Adenovirus-mediated overexpression of DDR2 was used to evaluate its consequences on cell proliferation, invasion, migration, and the process of hypoxia-induced epithelial-mesenchymal transition (EMT). Then nude mouse xenograft and tail vein metastasis models were utilized to validate the in vitro results. Results DDR2 was highly expressed in high grade HNSCC tissues and lowly expressed in low grade HNSCC tissues, but absent or rarely expressed in cancer-associated normal tissues. Both the frequency and expression intensity of DDR2 were significantly associated with tumor pathologic stage and lymph node metastasis. In vitro, DDR2 overexpression in HNSCC cells failed to alter cell proliferation but markedly accelerates cell invasion and migration as well as hypoxia-induced EMT. In vivo, elevated expression of DDR2 speeds up the metastasis of HNSCC cells to the lung. Conclusion DDR2 plays an important role in HNSCC metastasis, and might be a promising target for future therapies in this type of cancer.

Whole genome analyses of a well-differentiated liposarcoma reveals novel SYT1 and DDR2 rearrangements

Liposarcoma is the most common soft tissue sarcoma, but little is known about the genomic basis of this disease. Given the low cell content of this tumor type, we utilized flow cytometry to isolate the diploid normal and aneuploid tumor populations from a well-differentiated liposarcoma prior to array comparative genomic hybridization and whole genome sequencing. This work revealed massive highly focal amplifications throughout the aneuploid tumor genome including MDM2, a gene that has previously been found to be amplified in well-differentiated liposarcoma. Structural analysis revealed massive rearrangement of chromosome 12 and 11 gene fusions, some of which may be part of double minute chromosomes commonly present in well-differentiated liposarcoma. We identified a hotspot of genomic instability localized to a region of chromosome 12 that includes a highly conserved, putative L1 retrotransposon element, LOC100507498 which resides within a gene cluster (NAV3, SYT1, PAWR) where 6 of the 11 fusion events occurred. Interestingly, a potential gene fusion was also identified in amplified DDR2, which is a potential therapeutic target of kinase inhibitors such as dastinib, that are not routinely used in the treatment of patients with liposarcoma. Furthermore, 7 somatic, damaging single nucleotide variants have also been identified, including D125N in the PTPRQ protein. In conclusion, this work is the first to report the entire genome of a well-differentiated liposarcoma with novel chromosomal rearrangements associated with amplification of therapeutically targetable genes such as MDM2 and DDR2.

Discoidin domain receptors in disease

Discoidin domain receptors, DDR1 and DDR2, lie at the intersection of two large receptor families, namely the extracellular matrix and tyrosine kinase receptors. As such, DDRs are uniquely positioned to function as sensors for extracellular matrix and to regulate a wide range of cell functions from migration and proliferation to cytokine secretion and extracellular matrix homeostasis/remodeling. While activation of DDRs by extracellular matrix collagens is required for normal development and tissue homeostasis, aberrant activation of these receptors following injury or in disease is detrimental. The availability of mice lacking DDRs has enabled us to identify key roles played by these receptors in disease initiation and progression. DDR1 promotes inflammation in atherosclerosis, lung fibrosis and kidney injury, while DDR2 contributes to osteoarthritis. Furthermore, both DDRs have been implicated in cancer progression. Yet the mechanisms whereby DDRs contribute to disease progression are poorly understood. In this review we highlight the mechanisms whereby DDRs regulate two important processes, namely inflammation and tissue fibrosis. In addition, we discuss the challenges of targeting DDRs in disease. Selective targeting of these receptors requires understanding of how they interact with and are activated by extracellular matrix, and whether their cellular function is dependent on or independent of receptor kinase activity.

Phosphoproteomics of collagen receptor networks reveals SHP-2 phosphorylation downstream of wild-type DDR2 and its lung cancer mutants

Collagen is an important extracellular matrix component that directs many fundamental cellular processes including differentiation, proliferation and motility. The signalling networks driving these processes are propagated by collagen receptors such as the β1 integrins and the DDRs (discoidin domain receptors). To gain an insight into the molecular mechanisms of collagen receptor signalling, we have performed a quantitative analysis of the phosphorylation networks downstream of collagen activation of integrins and DDR2. Temporal analysis over seven time points identified 424 phosphorylated proteins. Distinct DDR2 tyrosine phosphorylation sites displayed unique temporal activation profiles in agreement with in vitro kinase data. Multiple clustering analysis of the phosphoproteomic data revealed several DDR2 candidate downstream signalling nodes, including SHP-2 (Src homology 2 domain-containing protein tyrosine phosphatase 2), NCK1 (non-catalytic region of tyrosine kinase adaptor protein 1), LYN, SHIP-2 [SH2 (Src homology 2)-domain-containing inositol phosphatase 2], PIK3C2A (phosphatidylinositol-4-phosphate 3-kinase, catalytic subunit type 2α) and PLCL2 (phospholipase C-like 2). Biochemical validation showed that SHP-2 tyrosine phosphorylation is dependent on DDR2 kinase activity. Targeted proteomic profiling of a panel of lung SCC (squamous cell carcinoma) DDR2 mutants demonstrated that SHP-2 is tyrosine-phosphorylated by the L63V and G505S mutants. In contrast, the I638F kinase domain mutant exhibited diminished DDR2 and SHP-2 tyrosine phosphorylation levels which have an inverse relationship with clonogenic potential. Taken together, the results of the present study indicate that SHP-2 is a key signalling node downstream of the DDR2 receptor which may have therapeutic implications in a subset of DDR2 mutations recently uncovered in genome-wide lung SCC sequencing screens.

Discoidin domain receptor 2 (DDR2) regulates body size and fat metabolism in mice

Discoidin domain receptor 2 (DDR2) is a receptor tyrosine kinase that is activated by fibrillar collagens, which act as its endogenous ligand. DDR2 regulates cell proliferation, cell adhesion, migration, extracellular matrix remodeling and reproductive functions. Both DDR2 null allele mice and mice with a recessive, loss-of-function allele for Ddr2 exhibit dwarfing and a reduction in body weight. However, the detailed mechanisms by which DDR2 exerts its positive systemic regulation of whole body size, local skeletal size and fat tissue volume remain to be clarified. To investigate the systemic role of DDR2 in body size regulation, we produced transgenic mice in which the DDR2 protein is overexpressed, then screened the transgenic mice for abnormalities using systematic mouse abnormality screening. The modified-SHIPRA screen revealed that only the parameter of body size was significantly different among the genotypes. We also discovered that the body length was significantly increased, while the body weight was significantly decreased in transgenic mice compared to their littermate controls. We also found that the epididymal fat pads were significantly decreased in transgenic mice compared to normal littermate mice, which may have been the cause of the leptin decrement in the transgenic mice. The new insight that DDR2 might promote metabolism in adipocyte cells is very interesting, but more experiments will be needed to elucidate the direct relation between DDR2 and adipose-derived hormones. Taken together, our data demonstrated that DDR2 might play a systemic role in the regulation of body size thorough skeletal formation and fat metabolism.