Hic-5 is required for myofibroblast differentiation by regulating mechanically dependent MRTF-A nuclear accumulation

Targeting Fibroblast-Endothelial Interactions in LAM Pathogenesis: 3D Spheroid and Spatial Transcriptomic Insights for Therapeutic Innovation

Lymphangioleiomyomatosis (LAM) is a progressive lung disease with limited treatments, largely due to an incomplete understanding of its pathogenesis. Lymphatic endothelial cells (LECs) invade LAM cell clusters, which include HMB-45-positive epithelioid cells and smooth muscle α-actin-expressing LAM-associated fibroblasts (LAMFs). Recent evidence shows that LAMFs resemble cancer-associated fibroblasts, with LAMF-LEC interactions contributing to disease progression. To explore these mechanisms, we used spatial transcriptomics on LAM lung tissues and identified a gene cluster enriched in kinase signaling pathways linked to myofibroblasts and co-expressed with LEC markers. Kinase arrays revealed elevated PDGFR and FGFR in LAMFs. Using a 3D co-culture spheroid model of primary LAMFs and LECs, we observed increased invasion in LAMF-LEC spheroids compared to non-LAM fibroblasts. Treatment with sorafenib, a multikinase inhibitor, significantly reduced invasion, outperforming Rapamycin. We also confirmed TSC2-null AML cells as key VEGF-A secretors, which was suppressed by sorafenib in both AML cells and LAMFs. These findings highlight VEGF-A and bFGF as potential therapeutic targets and suggest multikinase inhibition as a promising strategy for LAM.

One Sentence Summary

Using 3D spheroids and spatial transcriptomics, we identified LAMFs and LECs as key contributors to LAM, with bFGF and VEGF-A as potential therapeutic targets.

HBI-8000 improves heart failure with preserved ejection fraction via the TGF-β1/MAPK signalling pathway

Heart failure with preserved ejection fraction (HFpEF) accounts for approximately 50% of total heart failure patients and is characterized by peripheral circulation, cardiac remodelling and comorbidities (such as advanced age, obesity, hypertension and diabetes) with limited treatment options. Chidamide (HBI-8000) is a domestically produced benzamide-based histone deacetylase isoform-selective inhibitor used for the treatment of relapsed refractory peripheral T-cell lymphomas. Based on our in vivo studies, we propose that HBI-8000 exerts its therapeutic effects by inhibiting myocardial fibrosis and myocardial hypertrophy in HFpEF patients. At the cellular level, we found that HBI-8000 inhibits AngII-induced proliferation and activation of CFs and downregulates the expression of fibrosis-related factors. In addition, we observed that the HFpEF group and AngII stimulation significantly increased the expression of TGF-β1 as well as phosphorylated p38MAPK, JNK and ERK, whereas the expression of the above factors was significantly reduced after HBI-8000 treatment. Activation of the TGF-β1/MAPK pathway promotes the development of fibrotic remodelling, and pretreatment with SB203580 (p38MAPK inhibitor) reverses this pathological change. In conclusion, our data suggest that HBI-8000 inhibits fibrosis by modulating the TGF-β1/MAPK pathway thereby improving HFpEF. Therefore, HBI-8000 may become a new hope for the treatment of HFpEF patients.

Knockdown of mechanosensitive adaptor Hic-5 ameliorates post-traumatic osteoarthritis in rats through repression of MMP-13

Osteoarthritis (OA) is the most common joint disease associated with articular cartilage destruction. Matrix metalloproteinase-13 (MMP-13) has an essential role in OA pathogenesis by degradation of collagen II, a major component of articular cartilage. Hydrogen peroxide-inducible clone-5 (Hic-5; TGFB1I1), a transforming growth factor-β-inducible mechanosensor, has previously been reported to promote OA pathogenesis by upregulating MMP-13 expression in mouse osteoarthritic lesions. In our current study, immunohistochemical analysis showed that Hic-5 protein expression was increased in human OA cartilage compared with normal cartilage. Functional experiments demonstrated that Hic-5 and MMP-13 expression was increased by mechanical stress, and mechanical stress-induced MMP-13 expression was suppressed by Hic-5 siRNA in human chondrocytes. Moreover, intracellular localization of Hic-5 shifted to the nucleus from focal adhesions in human chondrocytes subjected to mechanical stress, and nuclear Hic-5 increased MMP-13 gene expression. In vivo, intra-articular injection of Hic-5 siRNA decreased the Osteoarthritis Research Society International score and MMP-13 protein expression in articular cartilage of OA rats. Our findings suggest that Hic-5 regulates transcription of MMP-13 in human chondrocytes, and Hic-5 may be a novel therapeutic target for OA because OA progression was suppressed by intra-articular injection of Hic-5 siRNA in rats.

The Role of Myofibroblasts in Physiological and Pathological Tissue Repair

Myofibroblasts are the construction workers of wound healing and repair damaged tissues by producing and organizing collagen/extracellular matrix (ECM) into scar tissue. Scar tissue effectively and quickly restores the mechanical integrity of lost tissue architecture but comes at the price of lost tissue functionality. Fibrotic diseases caused by excessive or persistent myofibroblast activity can lead to organ failure. This review defines myofibroblast terminology, phenotypic characteristics, and functions. We will focus on the central role of the cell, ECM, and tissue mechanics in regulating tissue repair by controlling myofibroblast action. Additionally, we will discuss how therapies based on mechanical intervention potentially ameliorate wound healing outcomes. Although myofibroblast physiology and pathology affect all organs, we will emphasize cutaneous wound healing and hypertrophic scarring as paradigms for normal tissue repair versus fibrosis. A central message of this review is that myofibroblasts can be activated from multiple cell sources, varying with local environment and type of injury, to either restore tissue integrity and organ function or create an inappropriate mechanical environment.

Contribution of Endothelial Laminin-Binding Integrins to Cellular Processes Associated with Angiogenesis

Endothelial cells engage extracellular matrix and basement membrane components through integrin-mediated adhesion to promote angiogenesis. Angiogenesis involves the sprouting of endothelial cells from pre-existing vessels, their migration into surrounding tissue, the upregulation of angiogenesis-associated genes, and the formation of new endothelial tubes. To determine whether the endothelial laminin-binding integrins, α6β4, and α3β1 contribute to these processes, we employed RNAi technology in organotypic angiogenesis assays, as well in migration assays, in vitro. The endothelial depletion of either α6β4 or α3β1 inhibited endothelial sprouting, indicating that these integrins have non-redundant roles in this process. Interestingly, these phenotypes were accompanied by overlapping and distinct changes in the expression of angiogenesis-associated genes. Lastly, depletion of α6β4, but not α3β1, inhibited migration. Taken together, these results suggest that laminin-binding integrins regulate processes associated with angiogenesis by distinct and overlapping mechanisms.

Click-functionalized hydrogel design for mechanobiology investigations

The advancement of click-functionalized hydrogels in recent years has coincided with rapid growth in the fields of mechanobiology, tissue engineering, and regenerative medicine. Click chemistries represent a group of reactions that possess high reactivity and specificity, are cytocompatible, and generally proceed under physiologic conditions. Most notably, the high level of tunability afforded by these reactions enables the design of user-controlled and tissue-mimicking hydrogels in which the influence of important physical and biochemical cues on normal and aberrant cellular behaviors can be independently assessed. Several critical tissue properties, including stiffness, viscoelasticity, and biomolecule presentation, are known to regulate cell mechanobiology in the context of development, wound repair, and disease. However, many questions still remain about how the individual and combined effects of these instructive properties regulate the cellular and molecular mechanisms governing physiologic and pathologic processes. In this review, we discuss several click chemistries that have been adopted to design dynamic and instructive hydrogels for mechanobiology investigations. We also chart a path forward for how click hydrogels can help reveal important insights about complex tissue microenvironments.

Myofibroblasts: Function, Formation, and Scope of Molecular Therapies for Skin Fibrosis

Myofibroblasts are contractile, α-smooth muscle actin-positive cells with multiple roles in pathophysiological processes. Myofibroblasts mediate wound contractions, but their persistent presence in tissues is central to driving fibrosis, making them attractive cell targets for the development of therapeutic treatments. However, due to shared cellular markers with several other phenotypes, the specific targeting of myofibroblasts has long presented a scientific and clinical challenge. In recent years, myofibroblasts have drawn much attention among scientific research communities from multiple disciplines and specialisations. As further research uncovers the characterisations of myofibroblast formation, function, and regulation, the realisation of novel interventional routes for myofibroblasts within pathologies has emerged. The research community is approaching the means to finally target these cells, to prevent fibrosis, accelerate scarless wound healing, and attenuate associated disease-processes in clinical settings. This comprehensive review article describes the myofibroblast cell phenotype, their origins, and their diverse physiological and pathological functionality. Special attention has been given to mechanisms and molecular pathways governing myofibroblast differentiation, and updates in molecular interventions.

Hypertrophic Scarring: Current Knowledge of Predisposing Factors, Cellular and Molecular Mechanisms

Hypertrophic scarring (HSc) is an age-old problem that still affects millions of people physically, psychologically, and economically. Despite advances in surgical techniques and wound care, prevention and treatment of HSc remains a challenge. Elucidation of factors involved in the development of this common fibroproliferative disorder is crucial for further progress in preventive and/or therapeutic measures. Our knowledge about pathophysiology of HSc at the cellular and molecular level has grown considerably in recent decades. In this article, current knowledge of predisposing factors and the cellular and molecular mechanisms of HSc has been reviewed.

Integrin α4β1 is required for IL-1α- and Nrf2-dependent, Cox-2 induction in fibroblasts, supporting a mechanism that suppresses α-SMA expression

Growth and repair processes, both normal and pathological, require reciprocal interactions between cells and their microenvironment. Integrins are bidirectional, cell surface receptors that transduce mechanical and chemical signals to and from the extracellular matrix. We recently reported that keratinocyte α3β1 is required for interleukin (IL)-1α secretion. Importantly, IL-1α regulates fibroblast Cox-2 expression and prostaglandin E2 (PGE₂ ) secretion, thereby linking keratinocyte integrin function to a paracrine signal that suppresses the myofibroblast phenotype. We now report that fibroblast integrin α4β1 is required for this IL-1α-induced, Cox-2 expression. Moreover, Cox-2 induction by IL-1α requires Nuclear factor erythroid 2-related factor 2 (Nrf2), the master regulator of redox homeostasis; and integrin α4β1 is necessary to maintain IL-1α-dependent, Nrf2 levels. Treating fibroblasts with a Nrf-2 activating compound inhibits TGF-β-dependent, alpha smooth muscle actin (α-SMA) expression and stress fibre formation. Our data suggest that fibroblast integrin α4β1 regulates-depending on microenvironmental cues-the differentiated state of fibroblasts through a signalling network in which IL-1α, Cox-2 and Nrf2 participate.

The inflammatory speech of fibroblasts

Activation of fibroblasts is a key event during normal tissue repair after injury and the dysregulated repair processes that result in organ fibrosis. To most researchers, fibroblasts are rather unremarkable spindle-shaped cells embedded in the fibrous collagen matrix of connective tissues and/or deemed useful to perform mechanistic studies with adherent cells in culture. For more than a century, fibroblasts escaped thorough classification due to the lack of specific markers and were treated as the leftovers after all other cells have been identified from a tissue sample. With novel cell lineage tracing and single cell transcriptomics tools, bona fide fibroblasts emerge as only one heterogeneous sub-population of a much larger group of partly overlapping cell types, including mesenchymal stromal cells, fibro-adipogenic progenitor cells, pericytes, and/or perivascular cells. All these cells are activated to contribute to tissue repair after injury and/or chronic inflammation. "Activation" can entail various functions, such as enhanced proliferation, migration, instruction of inflammatory cells, secretion of extracellular matrix proteins and organizing enzymes, and acquisition of a contractile myofibroblast phenotype. We provide our view on the fibroblastic cell types and activation states playing a role during physiological and pathological repair and their crosstalk with inflammatory macrophages. Inflammation and fibrosis of the articular synovium during rheumatoid arthritis and osteoarthritis are used as specific examples to discuss inflammatory fibroblast phenotypes. Ultimately, delineating the precursors and functional roles of activated fibroblastic cells will contribute to better and more specific intervention strategies to treat fibroproliferative and fibrocontractive disorders.

Discovery and validation of novel protein markers in mucosa of portal hypertensive gastropathy

Background

Portal hypertension induced esophageal and gastric variceal bleeding is the main cause of death among patients of decompensated liver cirrhosis. Therefore, a standardized, biomarker-based test, to make an early-stage non-invasive risk assessment of portal hypertension, is highly desirable. However, no fit-for-purpose biomarkers have yet been identified.

Methods

We conducted a pilot study consisting of 5 portal hypertensive gastropathy (PHG) patients and 5 normal controls, sampling the gastric mucosa of normal controls and PHG patients before and after endoscopic cyanoacrylate injection, using label-free quantitative (LFQ) mass spectrometry, to identify potential biomarker candidates in gastric mucosa from PHG patients and normal controls. Then we further used parallel reaction monitoring (PRM) to verify the abundance of the targeted protein.

Results

LFQ analyses identified 423 significantly differentially expressed proteins. 17 proteins that significantly elevated in the gastric mucosa of PHG patients were further validated using PRM.

Conclusions

This is the first application of an LFQ-PRM workflow to identify and validate PHG–specific biomarkers in patient gastric mucosa samples. Our findings lay the foundation for comprehending the molecular mechanisms of PHG pathogenesis, and provide potential applications for useful biomarkers in early diagnosis and treatment.

Trial registration and ethics approval: Trial registration was completed (ChiCTR2000029840) on February 25, 2020. Ethics Approvals were completed on July 17, 2017 (NYSZYYEC20180003) and February 15, 2020 (NYSZYYEC20200005).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-021-01787-5.

Suppression of MKL1 promotes adipocytic differentiation and reduces the proliferation of myxoid liposarcoma cells

Myxoid liposarcoma (MLS) is thought to occur due to defective adipocytic differentiation in mesenchymal stem cells. A promising strategy for MLS treatment is the prevention of sarcomagenesis by promoting the terminal differentiation of MLS cells into adipocytes. Previous studies have reported that the suppression of megakaryoblastic leukemia 1 (MKL1) expression induces adipocytic differentiation in preadipocyte cell lines. The present study aimed to investigate the effects of MKL1 suppression on MLS cells. In the present study, MKL1 knockdown was demonstrated to promote the adipocytic differentiation of an MLS-derived cell line, designated 1955/91, under adipogenic conditions. This suggests that therapeutic targeting of the MKL1-associated molecular pathway has potential as a promising method of MLS treatment. However, the induction of adipogenesis by MKL knockdown was incomplete, and Oil Red O staining indicated that intracellular lipid droplets were only sporadically generated. Conversely, MKL1 knockdown reduced the growth of the MLS cells. As adipocytic differentiation in vitro requires cellular confluence, the decreased growth rate of the MLS cells following MKL1 knockdown could be attributed to the incomplete induction of adipogenesis. Translocated in liposarcoma-CCAAT/enhancer-binding protein homologous protein (TLS-CHOP) is an MLS-specific oncoprotein that is thought to play key roles in sarcomagenesis and the suppression of adipocytic differentiation. However, the results of western blotting analyses suggest that TLS-CHOP has limited effects on MKL1 expression in MLS cells and that MKL1 knockdown hardly affects TLS-CHOP expression. Thus, it is postulated that the inhibitory effect of TLS-CHOP on adipogenesis is not associated with MKL1 expression. However, MKL1 and the molecular pathway involving MKL1 appear to be attractive targets for the differentiation therapy of MLS.

Exploring microRNAs in diabetic chronic cutaneous ulcers: Regulatory mechanisms and therapeutic potential

Diabetic chronic cutaneous ulcers (DCU) are one of the serious complications of diabetes mellitus, occurring mainly in diabetic patients with peripheral neuropathy. Recent studies have indicated that microRNAs (miRNAs/miRs) and their target genes are essential regulators of cell physiology and pathology including biological processes that are involved in the regulation of diabetes and diabetes-related microvascular complications. in vivo and in vitro models have revealed that the expression of some miRNAs can be regulated in the inflammatory response, cell proliferation, and wound remodelling of DCU. Nevertheless, the potential application of miRNAs to clinical use is still limited. Here, we provide a contemporary overview of the miRNAs as well as their associated target genes and pathways (including Wnt/β-catenin, NF-κB, TGF-β/Smad, and PI3K/AKT/mTOR) related to DCU healing. We also summarize the current development of drugs for DCU treatment and discuss the therapeutic challenges of DCU treatment and its future research directions.

Paxillin family of focal adhesion adaptor proteins and regulation of cancer cell invasion

The paxillin family of proteins, including paxillin, Hic-5, and leupaxin, are focal adhesion adaptor/scaffolding proteins which localize to cell-matrix adhesions and are important in cell adhesion and migration of both normal and cancer cells. Historically, the role of these proteins in regulating the actin cytoskeleton through focal adhesion-mediated signaling has been well documented. However, studies in recent years have revealed additional functions in modulating the microtubule and intermediate filament cytoskeletons to affect diverse processes including cell polarization, vesicle trafficking and mechanosignaling. Expression of paxillin family proteins in stromal cells is also important in regulating tumor cell migration and invasion through non-cell autonomous effects on the extracellular matrix. Both paxillin and Hic-5 can also influence gene expression through a variety of mechanisms, while their own expression is frequently dysregulated in various cancers. Accordingly, these proteins may serve as valuable targets for novel diagnostic and treatment approaches in cancer.

The myofibroblast at a glance

In 1971, Gabbiani and co-workers discovered and characterized the “modification of fibroblasts into cells which are capable of an active spasm” (contraction) in rat wound granulation tissue and, accordingly, named these cells ‘myofibroblasts’. Now, myofibroblasts are not only recognized for their physiological role in tissue repair but also as cells that are key in promoting the development of fibrosis in all organs. In this Cell Science at a Glance and the accompanying poster, we provide an overview of the current understanding of central aspects of myofibroblast biology, such as their definition, activation from different precursors, the involved signaling pathways and most widely used models to study their function. Myofibroblasts will be placed into context with their extracellular matrix and with other cell types communicating in the fibrotic environment. Furthermore, the challenges and strategies to target myofibroblasts in anti-fibrotic therapies are summarized to emphasize their crucial role in disease progression.

Laminin-511 and α6 integrins regulate the expression of CXCR4 to promote endothelial morphogenesis

During angiogenesis, endothelial cells engage components of the extracellular matrix through integrin-mediated adhesion. Endothelial expression of laminin-411 and laminin-511 is known to promote vessel stability. However, little is known about the contribution of these laminins to endothelial morphogenesis. We used two organotypic cell culture angiogenesis assays, in conjunction with RNAi approaches, to demonstrate that depletion of either the α4 chain of laminin-411 (LAMA4) or the α5 chain of laminin-511 (LAMA5) from endothelial cells inhibits sprouting and tube formation. Depletion of α6 (ITGA6) integrins resulted in similar phenotypes. Gene expression analysis indicated that loss of either laminin-511 or α6 integrins inhibited the expression of CXCR4, a gene previously associated with angiogenic endothelial cells. Pharmacological or RNAi-dependent inhibition of CXCR4 suppressed endothelial sprouting and morphogenesis. Importantly, expression of recombinant CXCR4 rescued endothelial morphogenesis when α6 integrin expression was inhibited. Additionally, the depletion of α6 integrins from established tubes resulted in the loss of tube integrity and laminin-511. Taken together, our results indicate that α6 integrins and laminin-511 can promote endothelial morphogenesis by regulating the expression of CXCR4 and suggest that the α6-dependent deposition of laminin-511 protects the integrity of established endothelial tubes.

Increased expression of the transforming growth factor β–inducible gene HIC-5 in systemic sclerosis skin and fibroblasts: a novel antifibrotic therapeutic target

Objective

SSc is a systemic fibrotic disease affecting skin, numerous internal organs and the microvasculature. The molecular pathogenesis of SSc tissue fibrosis has not been fully elucidated, although TGF-β1 plays a crucial role. The Hic-5 protein encoded by the TGF-β1-inducible HIC-5 gene participates in numerous TGF-β-mediated pathways, however, the role of Hic-5 in SSc fibrosis has not been investigated. The aim of this study was to examine HIC-5 involvement in SSc tissue fibrosis.

Methods

Affected skin from three patients with diffuse SSc and dermal fibroblasts cultured from affected and non-affected SSc skin were examined for HIC-5 and COL1A1 gene expression. Real-time PCR, IF microscopy, western blotting and small interfering RNA–mediated HIC-5 were performed.

Results

HIC-5 and COL1A1 transcripts and Hic-5, type 1 collagen (COL1) and α-smooth muscle actin (α-SMA) protein levels were increased in clinically affected SSc skin compared with normal skin and in cultured dermal fibroblasts from affected SSc skin compared with non-affected skin fibroblasts from the same patients. HIC-5 knockdown caused a marked reduction of COL1 production in SSc dermal fibroblasts.

Conclusion

HIC-5 expression is increased in affected SSc skin compared with skin from normal individuals. Affected SSc skin fibroblasts display increased HIC-5 and COL1A1 expression compared with non-affected skin fibroblasts from the same patients. Hic-5 protein was significantly increased in cultured SSc dermal fibroblasts. HIC-5 mRNA knockdown in SSc fibroblasts caused >50% reduction of COL1 production. Although these are preliminary results owing to the small number of skin samples studied, they indicate that Hic-5 plays a role in the profibrotic activation of SSc dermal fibroblasts and may represent a novel molecular target for antifibrotic therapy in SSc.

Hic-5 deficiency attenuates hepatic ischemia reperfusion injury through TLR4/NF-κB signaling pathways

AIM

To explore the role and mechanism of Hydrogen peroxide-inducible clone-5 (Hic-5) in hepatic ischemia reperfusion injury.

METHODS

Hic-5 KO and WT mice were used to establish the liver ischemia reperfusion model (HI/R). Primary hepatocytes were isolated to establish hypoxic reoxygenation model (H/R). AST and ALT were measured by automatic biochemical analyzer. Liver tissue sections were stained with HE and Tunnel. RNA and proteins were extracted from liver tissues, and expressions of Il-6, Il-10, CCL-2, CXCL-10, P65, Caspase-3, TLR4 and FADD were detected at gene and protein levels. Liver cell apoptosis was detected by flow cytometry and immunofluorescence. Primary hepatocytes were stimulated by LPS to establish a model of hepatocyte apoptosis, and cell inflammation and apoptosis-related proteins were detected.

RESULTS

After HI/R, ALT and AST in serum were up-regulated, some hepatocyte apoptosis were observed in pathological sections. Hic-5 expression was increased in WT mice after HI/R, and liver damage were severer than KO mice. The expression of IL-6, CCL-2 and CXCL-10 in the liver of KO mice was low, and the expression of IL-10 was high. Further studies showed that KO mice showed lower expression of P65, Caspase3 and TLR4. In H/R model, hepatocytes also showed the same trend. Finally, after LPS stimulation, the results showed that the inflammation and apoptosis induced by LPS were significantly reduced in Hic-5 knocked hepatocytes.

CONCLUSION

Hic-5 was found to promote inflammation through NF-kb signaling pathway and apoptosis through TLR4-FADD signaling pathway in mice with HI/R, thus aggravating liver injury in mice.

Evasion of apoptosis by myofibroblasts: a hallmark of fibrotic diseases

Organ fibrosis is a lethal outcome of autoimmune rheumatic diseases such as systemic sclerosis. Myofibroblasts are scar-forming cells that are ultimately responsible for the excessive synthesis, deposition and remodelling of extracellular matrix proteins in fibrosis. Advances have been made in our understanding of the mechanisms that keep myofibroblasts in an activated state and control myofibroblast functions. However, the mechanisms that help myofibroblasts to persist in fibrotic tissues remain poorly understood. Myofibroblasts evade apoptosis by activating molecular mechanisms in response to pro-survival biomechanical and growth factor signals from the fibrotic microenvironment, which can ultimately lead to the acquisition of a senescent phenotype. Growing evidence suggests that myofibroblasts and senescent myofibroblasts, rather than being resistant to apoptosis, are actually primed for apoptosis owing to concomitant activation of cell death signalling pathways; these cells are poised to apoptose when survival pathways are inhibited. This knowledge of apoptotic priming has paved the way for new therapies that trigger apoptosis in myofibroblasts by blocking pro-survival mechanisms, target senescent myofibroblast for apoptosis or promote the reprogramming of myofibroblasts into scar-resolving cells. These novel strategies are not only poised to prevent progressive tissue scarring, but also have the potential to reverse established fibrosis and to regenerate chronically injured tissues.

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.

Alleviation of murine osteoarthritis by deletion of the focal adhesion mechanosensitive adapter, Hic-5

Excessive mechanical stress is a major cause of knee osteoarthritis. However, the mechanism by which the mechanical stress begets osteoarthritis development remains elusive. Hydrogen peroxide-inducible clone-5 (Hic-5; TGFβ1i1), a TGF-β inducible focal adhesion adaptor, has previously been reported as a mediator of mechanotransduction. In this study, we analyzed the in vivo function of Hic-5 in development of osteoarthritis, and found that mice lacking Hic-5 showed a significant reduction in development of osteoarthritis in the knee. Furthermore, we found reduced expression of catabolic genes, such as metalloproteinase-13 and a disintegrin and metalloproteinase with thrombospondin type 1 motif 5 in osteoarthritic lesions in mice lacking Hic-5. During osteoarthritis development, Hic-5 is detected in chondrocytes of articular cartilage. To investigate the role of Hic-5 in chondrocytes, we isolated chondrocytes from articular cartilage of wild type and Hic-5-deficient mice. In these primary cultured chondrocytes, Hic-5 deficiency resulted in suppression of catabolic gene expression induced by osteoarthritis-related cytokines such as tumor necrosis factor α and interleukin 1β. Furthermore, Hic-5 deficiency in chondrocytes suppressed catabolic gene expression induced by mechanical stress. Revealing the regulation of chondrocyte catabolism by Hic-5 contributes to understanding the pathophysiology of osteoarthritis induced by mechanical stress.

MicroRNA-145-5p regulates fibrotic features of recessive dystrophic epidermolysis bullosa skin fibroblasts

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is a skin fragility disorder caused by mutations in the COL7A1 gene encoding type VII collagen, a cutaneous basement membrane component essential for epidermal-dermal adhesion. Hallmarks of the disease are unremitting blistering and chronic wounds with severe inflammation and fibrosis. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression also implicated in fibrotic processes. However, the role of miRNAs in RDEB fibrosis is almost unexplored.

OBJECTIVES

Our study aimed to identify miRNAs deregulated in primary RDEB skin fibroblasts (RDEBFs) and to characterize their function in RDEB fibrosis.

METHODS

Real-time quantitative polymerase chain reaction (qRT-PCR) was used to screen RDEBFs for expression levels of a group of miRNAs deregulated in hypertrophic scars and keloids, pathological conditions with abnormal wound healing and fibrosis. Contractility, proliferation and migration rate were evaluated by different in vitro assays in RDEBFs transfected with a miR-145-5p inhibitor. Expression levels of fibrotic markers and miR-145-5p targets were measured using qRT-PCR and western blot.

RESULTS

The miR-143/145 cluster was upregulated in RDEBFs compared with fibroblasts from healthy subjects. RDEBFs transfected with a miR-145-5p inhibitor showed attenuated fibrotic traits of contraction, proliferation and migration, accompanied by reduced expression of the contractile proteins α-smooth muscle actin and transgelin. These effects were associated with upregulation of Krüppel-like factor 4 transcriptional repressor and downregulation of Jagged1, a known inducer of fibrosis.

CONCLUSIONS

Our results highlight the profibrotic role of miR-145-5p and its regulatory networks in RDEB, shedding light on novel disease pathomechanisms and targets for future therapeutic approaches. What's already known about this topic? Recessive dystrophic epidermolysis bullosa (RDEB) is a highly disabling genetic skin disease caused by mutations in the collagen VII gene and characterized by unremitting blistering and defective wound healing, leading to inflammation and fibrosis. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression in health and disease, and their deregulation has been implicated in fibrotic skin conditions. To date, only miR-29 has been associated with injury-driven fibrosis in RDEB. What does this study add? In patients with RDEB, miR-145-5p is overexpressed in RDEB skin fibroblasts (RDEBFs), where it plays a profibrotic role, as its inhibition reduces RDEBF fibrotic traits (contraction, proliferation and migration). miR-145-5p inhibition in RDEBFs determines the reduction of contractile markers α-smooth muscle actin and transgelin through upregulation of Krüppel-like factor 4, a transcriptional repressor of contractile proteins, and downregulation of Jagged1 (JAG1), an inducer of fibrosis. What is the translational message? Our findings expand the knowledge on miRNA-driven pathomechanisms implicated in RDEB fibrosis. miR-145-5p and its targets (e.g. JAG1) could represent relevant molecules for the development of novel therapeutic strategies to counteract fibrosis progression in patients with RDEB.

The Leptin induced Hic-5 expression and actin puncta formation by the FAK/Src-dependent pathway in MCF10A mammary epithelial cells

Introduction: Leptin is a hormone secreted by adipocytes that has been associated with the epithelial-mesenchymal transition (EMT). Additionally, leptin promotes the migration and invasion of mammary epithelial cells through the activation of FAK and Src kinases, which are part of a regulatory complex of signaling pathways that promotes the expression of proteins related to the formation of proteolytic structures involved in the invasion and progression of cancer. Recently, overexpression and activation of Hic-5 during the EMT have been shown to induce the formation of actin puncta; these structures are indicative of the formation and functionality of invadopodia, which promote the local degradation of extracellular matrix components and cancer metastasis. Objective: To evaluate the role of FAK and Src kinases in the expression of Hic-5 during the epithelial-mesenchymal transition induced by leptin in MCF10A cells. Materials and methods: We used specific inhibitors of FAK (PF-573228) and Src (PP2) to evaluate Hic-5 expression and subcellular localization by Western blot and immunofluorescence assays and to investigate the formation of actin puncta by epifluorescence in MCF10A cells stimulated with leptin. Results: Leptin induced an increase in Hic-5 expression and the formation of actin puncta. Pretreatment with inhibitors of FAK (PF-573228) and Src (PP2) promoted a decrease in Hic-5 expression and actin puncta formation in the non-tumorigenic mammary epithelial cell line MCF10A. Conclusion: In MCF10A cells, leptin-induced Hic-5 expression and perinuclear localization, as well as the formation of actin puncta through a mechanism dependent on the kinase activity of FAK and Src.

Light-emitting diode irradiation using 660 nm promotes human fibroblast HSP90 expression and changes cellular activity and morphology

We evaluated changes in cell viability and morphology in response to low-level light irradiation and underlying variations in the levels of heat shock proteins (HSPs). Human fibroblasts were irradiated with a light-emitting diode (LED) array at 660 nm (50 mW for 15, 30, and 60 minutes). Cell viability and morphological changes were evaluated via epifluorescence analysis; we also assessed cell viability and length changes. The expression levels of adenosine triphosphate (ATP) and various HSPs (HSP27, 60, 70, and 90) were analyzed by immunohistochemical staining, Western blotting and microarray analysis. After LED irradiation, cellular viability and morphology changed. Of the several HSPs analyzed, the HSP90 level increased significantly, suggesting that this protein played roles in the morphological and cellular changes. Thus, low-level irradiation triggered cellular changes mediated by increased HSP90 expression; this may explain why skin irradiation enhances wound-healing.

Ablation of SUN2-containing LINC complexes drives cardiac hypertrophy without interstitial fibrosis

The cardiomyocyte cytoskeleton, including the sarcomeric contractile apparatus, forms a cohesive network with cellular adhesions at the plasma membrane and nuclear--cytoskeletal linkages (LINC complexes) at the nuclear envelope. Human cardiomyopathies are genetically linked to the LINC complex and A-type lamins, but a full understanding of disease etiology in these patients is lacking. Here we show that SUN2-null mice display cardiac hypertrophy coincident with enhanced AKT/MAPK signaling, as has been described previously for mice lacking A-type lamins. Surprisingly, in contrast to lamin A/C-null mice, SUN2-null mice fail to show coincident fibrosis or upregulation of pathological hypertrophy markers. Thus, cardiac hypertrophy is uncoupled from profibrotic signaling in this mouse model, which we tie to a requirement for the LINC complex in productive TGFβ signaling. In the absence of SUN2, we detect elevated levels of the integral inner nuclear membrane protein MAN1, an established negative regulator of TGFβ signaling, at the nuclear envelope. We suggest that A-type lamins and SUN2 play antagonistic roles in the modulation of profibrotic signaling through opposite effects on MAN1 levels at the nuclear lamina, suggesting a new perspective on disease etiology.

Mechanical regulation of myofibroblast phenoconversion and collagen contraction

Activated fibroblasts promote physiological wound repair following tissue injury. However, dysregulation of fibroblast activation contributes to the development of fibrosis by enhanced production and contraction of collagen-rich extracellular matrix. At the peak of their activities, fibroblasts undergo phenotypic conversion into highly contractile myofibroblasts by developing muscle-like features, including formation of contractile actin-myosin bundles. The phenotype and function of fibroblasts and myofibroblasts are mechanically regulated by matrix stiffness using a feedback control system that is integrated with the progress of tissue remodelling. The actomyosin contraction machinery and cell-matrix adhesion receptors are critical elements that are needed for mechanosensing by fibroblasts and the translation of mechanical signals into biological responses. Here, we focus on mechanical and chemical regulation of collagen contraction by fibroblasts and the involvement of these factors in their phenotypic conversion to myofibroblasts.

Keratinocyte Integrin α3β1 Promotes Secretion of IL-1α to Effect Paracrine Regulation of Fibroblast Gene Expression and Differentiation

After cutaneous injury, keratinocytes secrete paracrine factors that regulate wound cell functions; dysregulation of this signaling can lead to wound pathologies. Previously, we established that keratinocyte integrin α3β1 promotes wound angiogenesis through paracrine stimulation of endothelial cells. We hypothesize here that α3β1-dependent paracrine signaling from keratinocytes regulates the differentiation state of myofibroblasts. We report that epidermal α3-knockout mice exhibit more wound myofibroblasts and fewer cyclooxygenase 2 (Cox-2)-positive dermal cells than controls. We also found that conditioned medium from α3-expressing mouse keratinocytes (MKα3⁺), but not from α3-null MK cells (MKα3^-), induces expression of Cox-2 in fibroblasts in a time- and dose-dependent manner and that this induction is mediated by IL-1α. Compared with MKα3^- cells, MKα3⁺ cells secrete more IL-1α and less IL-1RA, a natural IL-1 receptor antagonist. Treatment with an IL-1α neutralizing antibody, recombinant IL-1RA, or IL-1 receptor-targeting small interfering RNA suppresses MKα3⁺ conditioned medium-dependent induction of Cox-2 expression in fibroblasts. Finally, active recombinant IL-1α is sufficient to induce Cox-2 in fibroblasts and to inhibit transforming growth factor-β-induced α-SMA expression. Our findings support a role for keratinocyte integrin α3β1 in controlling the secretion of IL-1α, a paracrine factor that regulates the wound myofibroblast phenotype.

MicroRNAs as biological regulators in skin disorders

microRNAs are being investigated as promising therapeutic targets and biomarkers for different disease conditions. miRNAs serve as essential regulators of cell differentiation, proliferation and survival. The involvement of miRNAs in the functioning and regulation of the skin cells and skin diseases is a rapidly advancing area in dermatological research. miRNAs have been identified to play a key role in the pathogenesis, diagnosis, and treatment of the skin diseases. Skin is one of the largest organs of the body, primarily functioning as the first line of defence against external insults including bacteria, virus and other pathogens. Various miRNAs have been identified to demonstrate significant effects in various skin inflammatory conditions such as wounds, cancer, psoriasis, scleroderma, dermatomyositis. The current review explores the possible roles of the miRNAs in skin disorders and reports relating to the clinical trials involving skin diseases and miRNAs. The review has also compiled the information of the databases available, which correlates the miRNAs with different diseases and give details about targeting interactions of miRNA.

Signaling Mechanisms of Myofibroblastic Activation: Outside-in and Inside-Out

Myofibroblasts are central mediators of fibrosis. Typically derived from resident fibroblasts, myofibroblasts represent a heterogeneous population of cells that are principally defined by acquired contractile function and high synthetic ability to produce extracellular matrix (ECM). Current literature sheds new light on the critical role of ECM signaling coupled with mechanotransduction in driving myofibroblastic activation. In particular, transforming growth factor β1 (TGF-β1) and extra domain A containing fibronectin (EDA-FN) are thought to be the primary ECM signaling mediators that form and also induce positive feedback loops. The outside-in and inside-out signaling circuits are transmitted and integrated by TGF-β receptors and integrins at the cell membrane, ultimately perpetuating the abundance and activities of TGF-β1 and EDA-FN in the ECM. In this review, we highlight these conceptual advances in understanding myofibroblastic activation, in hope of revealing its therapeutic anti-fibrotic implications.

Abrogation of transforming growth factor-β-induced tissue fibrosis in TBRIcaCol1a2Cre transgenic mice by the second generation tyrosine kinase inhibitor SKI-606 (Bosutinib)

Transforming growth factor-β (TGF-β) plays a crucial role in the pathogenesis of Systemic Sclerosis (SSc) and other fibrotic disorders. TGF-β-mediated c-Abl and Src kinase activation induces strong profibrotic cascade signaling. The purpose of this study was to test in vivo the antifibrotic activity of Bosutinib (SKI-606), a second generation c-Abl and Src kinase inhibitor, on TGF-β induced cutaneous and pulmonary fibrosis. For this purpose, we employed the TBRIcaCol1a2Cre transgenic mice expressing an inducible constitutively active TGF-β receptor 1 constitutively activated by Col1a promoter-mediated Cre recombinase. The mice were treated parenterally with 2.5, 5.0 or 10.0 mg/kg/day of Bosutinib for 42 days. Skin and lungs from control and Bosutinib-treated mice (n = 6 per group) were assessed by histopathology, measurement of tissue hydroxyproline content, PCR analysis of tissue fibrosis associated gene expression, and evidence of myofibroblast activation. Mice with constitutive TGF-β-1 signaling displayed severe cutaneous and pulmonary fibrosis. Bosutinib administration decreased collagen deposition and hydroxyproline content in the dermis and lungs in a dose-dependent manner. Bosutinib also reversed the marked increase in profibrotic and myofibroblast activation-associated gene expression. These results demonstrate that constitutive TGF-β-1-signaling-induced cutaneous and pulmonary fibrosis were abrogated in a dose-related manner following parenteral administration of the c-Abl and Src tyrosine kinase inhibitor, Bosutinib. These results indicate that Bosutinib may be a potential therapeutic agent for tissue fibrosis in SSc and other fibroproliferative disorders.

Paxillin actions in the nucleus

Paxillin is a group III LIM domain protein that is best characterized as a cytoplasmic scaffold/adaptor protein that functions primarily as a mediator of focal adhesion. However, emerging studies indicate that paxillin's functions are far broader. Not only does paxillin appear to regulate cytoplasmic kinase signaling, but it also cycles between the cytoplasm and nucleus, and may serve as an important regulator of mRNA trafficking and subsequent translation. Herein, we provide some insights suggesting that paxillin, like its relative Hic-5, has nuclear binding partners and mediates critical processes within the nucleus, at least in part functioning as coregulator of nuclear receptors and nuclear kinases to mediate genomic signaling.

IL-17-driven intestinal fibrosis is inhibited by Itch-mediated ubiquitination of HIC-5

Intestinal fibrosis is a major complication in inflammatory bowel diseases, but the regulatory mechanism that inhibits fibrosis remains unclear. Here we demonstrate that Itch^-/-myofibroblasts express increased amounts of profibrotic collagen type I and α-SMA in response to IL-17. Mechanistically, we demonstrate that Itch directly binds to HIC-5 and targets it for K63-linked ubiquitination to inhibit IL-17-driven intestinal fibrosis. Reconstitution of Itch^-/- myofibroblasts with wild-type Itch but not the Itch-C830A mutant normalized the expression of profibrotic genes. Similarly, shRNA-mediated inhibition of HIC-5 normalized the expression of profibrotic gene expression. Thus, we have uncovered a novel mechanism by which Itch negatively regulates intestinal fibrosis.

Role of MicroRNA in Proliferation Phase of Wound Healing

Wound healing is a complex biological process that is generally composed of four phases: hemostasis, inflammation, proliferation, and remodeling. The proliferation phase is crucial for effective healing compared to other phases. Many critical events occur during this phase, i.e., migration of fibroblasts, re-epithelialization, angiogenesis and wound contraction. Chronic wounds are common and are considered a major public health problem. Therefore, there is the increasing need to discover new therapeutic strategies. MicroRNA (miRNA) research in the field of wound healing is in its early phase, but the knowledge of the recent discoveries is essential for developing effective therapies for the treatment of chronic wounds. In this review, we focused on recently discovered miRNAs which are involved in the proliferation phase of wound healing in the past few years and their role in wound healing.

What can target kidney fibrosis?

Fibrosis, a characteristic of all chronic kidney diseases, is now recognized to be an independent predictor of disease progression. Deposition of pathological matrix in the walls of glomerular capillaries, the interstitial space and around arterioles both predicts and contributes to functional demise of the nephron and its surrounding vasculature. Recent identification of the major cell populations of fibroblast precursors in the kidney interstitium as pericytes and tissue-resident mesenchymal stem cells, and in the glomerulus as podocytes, parietal epithelial and mesangial cells, has enabled the study of the fibrogenic process in much greater depth directly in the fibroblast precursors. These cells are not only matrix-producing cells, but are also important innate immune surveillance cells that regulate the inflammatory process, exacerbate tissue damage by release of radicals and cytokines, and contribute to parenchymal and microvascular dysfunction by aberrant wound-healing responses. Innate immune signaling in fibroblasts and their precursors is intimately intertwined with the process of fibrogenesis. In addition, genomic and genetic studies also point to defective responses in loci close to genes involved in solute transport, metabolism, autophagy, protein handling and vascular homeostasis, principally in the epithelium and endothelium, as upstream drivers of the fibrotic process, indicating that cellular crosstalk is vital for development of fibrosis. As we move beyond TGFβ inhibition as a central target for fibrosis, targeting innate immune signaling and metabolic dysfunction appear increasingly tenable alternative targets for novel therapies.

MRTFs- master regulators of EMT

Recent evidence implicates the myocardin-related transcription factors (MRTFs) as key mediators of the phenotypic plasticity leading to the conversion of various cell types into myofibroblasts. This review highlights the function of MRTFs during development, fibrosis and cancer, and the role of MRTFs during epithelial-mesenchymal transitions (EMTs) underlying these processes. EMT is a sequentially orchestrated process where cells undergo a rearrangement of their cell contacts and activate a fibrogenic and myogenic expression program. MRTFs interact with and regulate the major signaling pathways and the expression of key markers and transcription factors involved in EMT. These functions indicate a central role for MRTFs in controlling the process of EMT. Developmental Dynamics 247:396-404, 2018. © 2017 Wiley Periodicals, Inc.

Focal adhesion kinase family is involved in matrix contraction by transdifferentiated Müller cells

Transdifferentiated Müller cells that adopt a fibroblastic/myofibroblastic phenotype have been identified in epiretinal membranes (ERMs) in several ocular disorders, and have been implicated to play a role in the formation and/or the contraction of ERMs. We have previously demonstrated that dasatinib, a dual inhibitor of Src-family kinases and Abl kinase, can prevent matrix contraction by transdifferentiated Müller cells. In this study, we examined molecules involved in matrix contraction downstream of primary dasatinib targets. Tyrosine phosphorylation of focal adhesion kinase (FAK) family members FAK and PYK2 was significantly reduced by dasatinib, and select inhibitors for these kinases PF431396, which inhibits both FAK and PYK2, and PF573228, which only inhibits FAK and not PYK2, significantly reduced matrix contraction by transdifferentiated Müller cells. Dasatinib and PF431396 significantly reduced phosphorylation of Hic-5, a protein implicated to play a role in focal adhesions and cell signaling. Our data shows that FAK family members are involved in matrix contraction by transdifferentiated Müller cells, and also implicates that Hic-5 is situated downstream of the FAK family within the signaling pathway.

Substrate stiffness-dependent regulation of the SRF-Mkl1 co-activator complex requires the inner nuclear membrane protein Emerin

The complex comprising serum response factor (SRF) and megakaryoblastic leukemia 1 protein (Mkl1) promotes myofibroblast differentiation during wound healing. SRF-Mkl1 is sensitive to the mechanical properties of the extracellular environment; but how cells sense and transduce mechanical cues to modulate SRF-Mkl1-dependent gene expression is not well understood. Here, we demonstrate that the nuclear lamina-associated inner nuclear membrane protein Emerin stimulates SRF-Mkl1-dependent gene activity in a substrate stiffness-dependent manner. Specifically, Emerin was required for Mkl1 nuclear accumulation and maximal SRF-Mkl1-dependent gene expression in response to serum stimulation of cells grown on stiff substrates but was dispensable on more compliant substrates. Focal adhesion area was also reduced in cells lacking Emerin, consistent with a role for Emerin in sensing substrate stiffness. Expression of a constitutively active form of Mkl1 bypassed the requirement for Emerin in SRF-Mkl1-dependent gene expression and reversed the focal adhesion defects evident in Emd^KO fibroblasts. Together, these data indicate that Emerin, a conserved nuclear lamina protein, couples extracellular matrix mechanics and SRF-Mkl1-dependent transcription.

Neonatal expression of RNA-binding protein IGF2BP3 regulates the human fetal-adult megakaryocyte transition

Hematopoietic transitions that accompany fetal development, such as erythroid globin chain switching, play important roles in normal physiology and disease development. In the megakaryocyte lineage, human fetal progenitors do not execute the adult morphogenesis program of enlargement, polyploidization, and proplatelet formation. Although these defects decline with gestational stage, they remain sufficiently severe at birth to predispose newborns to thrombocytopenia. These defects may also contribute to inferior platelet recovery after cord blood stem cell transplantation and may underlie inefficient platelet production by megakaryocytes derived from pluripotent stem cells. In this study, comparison of neonatal versus adult human progenitors has identified a blockade in the specialized positive transcription elongation factor b (P-TEFb) activation mechanism that is known to drive adult megakaryocyte morphogenesis. This blockade resulted from neonatal-specific expression of an oncofetal RNA-binding protein, IGF2BP3, which prevented the destabilization of the nuclear RNA 7SK, a process normally associated with adult megakaryocytic P-TEFb activation. Knockdown of IGF2BP3 sufficed to confer both phenotypic and molecular features of adult-type cells on neonatal megakaryocytes. Pharmacologic inhibition of IGF2BP3 expression via bromodomain and extraterminal domain (BET) inhibition also elicited adult features in neonatal megakaryocytes. These results identify IGF2BP3 as a human ontogenic master switch that restricts megakaryocyte development by modulating a lineage-specific P-TEFb activation mechanism, revealing potential strategies toward enhancing platelet production.

Hic-5 remodeling of the stromal matrix promotes breast tumor progression

The remodeling of the stromal extracellular matrix (ECM) plays a crucial, but incompletely understood role during tumor progression and metastasis. Hic-5, a focal adhesion scaffold protein, has previously been implicated in tumor cell invasion, proliferation and metastasis. To investigate the role of Hic-5 in breast tumor progression in vivo, Hic-5^−/− mice were generated and crossed with the Mouse Mammary Tumor Virus-Polyoma Middle T Antigen (MMTV-PyMT) mouse. Tumors from the Hic-5^−/−;PyMT mice exhibited increased latency and reduced growth, with fewer lung metastases, as compared to Hic-5^+/−;PyMT mice. Immunohistochemical analysis showed that Hic-5 is primarily expressed in the cancer associated fibroblasts (CAFs). Further analysis revealed that the Hic-5^−/−;PyMT tumor stroma contains fewer CAFs and exhibits reduced ECM deposition. The remodeling of the stromal matrix by CAFs has been shown to increase tumor rigidity to indirectly regulate FAK Y397 phosphorylation in tumor cells to promote their growth and invasion. Accordingly, the Hic-5^−/−;PyMT tumor cells exhibited a reduction in FAK Y397 phosphorylation. Isolated Hic-5^−/−;PyMT CAFs were defective in stress fiber organization and exhibited reduced contractility. These cells also failed to efficiently deposit and organize the ECM in two and three dimensions. This, in turn, impacted three dimensional MDA-MB-231 tumor cell migration behavior. Thus, using a new knockout mouse model, we have identified Hic-5 expression in CAFs as a key requirement for deposition and remodeling of the stromal ECM to promote non-cell autonomous breast tumor progression.

The role of α-smooth muscle actin in fibroblast-mediated matrix contraction and remodeling

Cardiac myofibroblasts play an important role in myocardial remodeling. Although α-smooth muscle actin (α-SMA) expression is the hallmark of mature myofibroblasts, its role in regulating fibroblast function remains poorly understood. We explore the effects of the matrix environment in modulating cardiac fibroblast phenotype, and we investigate the role of α-SMA in fibroblast function using loss- and gain-of-function approaches. In murine myocardial infarction, infiltration of the infarct border zone with abundant α-SMA-positive myofibroblasts was associated with scar contraction. Isolated cardiac fibroblasts cultured in plates showed high α-SMA expression localized in stress fibers, exhibited activation of focal adhesion kinase (FAK), and synthesized large amounts of extracellular matrix proteins. In contrast, when these cells were cultured in collagen lattices, they exhibited marked reduction of α-SMA expression, negligible FAK activation, attenuated collagen synthesis, and increased transcription of genes associated with matrix metabolism. Transforming Growth Factor-β1-mediated contraction of fibroblast-populated collagen pads was associated with accentuated α-SMA synthesis. In contrast, serum- and basic Fibroblast Growth Factor-induced collagen pad contraction was associated with reduced α-SMA expression. α-SMA siRNA knockdown attenuated contraction of collagen pads populated with serum-stimulated cells. Surprisingly, α-SMA overexpression also reduced collagen pad contraction, suggesting that α-SMA is not sufficient to promote contraction of the matrix. Reduced contraction by α-SMA-overexpressing cells was associated with attenuated proliferative activity, in the absence of any effects on apoptosis. α-SMA may be implicated in contraction and remodeling of the extracellular matrix, but is not sufficient to induce contraction. α-SMA expression may modulate cellular functions, beyond its effects on contractility.

The myofibroblast in wound healing and fibrosis: answered and unanswered questions

The discovery of the myofibroblast has allowed definition of the cell responsible for wound contraction and for the development of fibrotic changes. This review summarizes the main features of the myofibroblast and the mechanisms of myofibroblast generation. Myofibroblasts originate from a variety of cells according to the organ and the type of lesion. The mechanisms of myofibroblast contraction, which appear clearly different to those of smooth muscle cell contraction, are described. Finally, we summarize the possible strategies in order to reduce myofibroblast activities and thus influence several pathologies, such as hypertrophic scars and organ fibrosis.