The big five in fibrosis: Macrophages, myofibroblasts, matrix, mechanics, and miscommunication

Engineered exosomes: a promising strategy for tendon-bone healing

BACKGROUND

Due to the spatiotemporal complexity of the composition, structure, and cell population of the tendon-bone interface (TBI), it is difficult to achieve true healing. Recent research is increasingly focusing on engineered exosomes, which are a promising strategy for TBI regeneration.

AIM OF REVIEW

This review discusses the physiological and pathological characteristics of TBI and the application and limitations of natural exosomes in the field of tendon-bone healing. The definition, loading strategies, and spatiotemporal properties of engineered exosomes were elaborated. We also summarize the application and future research directions of engineered exosomes in the field of tendon-bone healing.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Engineered exosomes can spatially deliver cargo to targeted sites and temporally realize the sustained release of therapeutic molecules in TBI. This review expounds on the multidifferentiation of engineered exosomes for tendon-bone healing, which effectively improves the biological and biomechanical properties of TBI. Engineered exosomes could be a promising strategy for tendon-bone healing.

Pharmacological antagonism of Ccr2+ cell recruitment to facilitate regenerative tendon healing

Successful tendon healing requires sufficient deposition and remodeling of new extracellular matrix at the site of injury, with this process mediating in part through fibroblast activation via communication with macrophages. Moreover, resolution of healing requires clearance or reversion of activated cells, with chronic interactions with persistent macrophages impairing resolution and facilitating the conversion to fibrotic healing. As such, modulation of the macrophage environment represents an important translational target to improve the tendon healing process. Circulating monocytes are recruited to sites of tissue injury, including the tendon, via upregulation of cytokines including Ccl2, which facilitates recruitment of Ccr2+ macrophages to the healing tendon. Our prior work has demonstrated that Ccr2-/- can modulate fibroblast activation and myofibroblast differentiation. However, this approach lacked temporal control and resulted in healing impairments. Thus, in the current study we have leveraged a Ccr2 antagonist to blunt macrophage recruitment to the healing tendon in a time-dependent manner. We first tested the effects of Ccr2 antagonism during the acute inflammatory phase and found that this had no effect on the healing process. In contrast, Ccr2 antagonism during the early proliferative/granulation tissue period resulted in significant improvements in mechanical properties of the healing tendon. Collectively, these data demonstrate the temporally distinct impacts of modulating Ccr2+ cell recruitment and Ccr2 antagonism during tendon healing and highlight the translational potential of transient Ccr2 antagonism to improve the tendon healing process.

Cytokine priming enhances the antifibrotic effects of human adipose derived mesenchymal stromal cells conditioned medium

BACKGROUND

Fibrosis is a pathological scarring process characterized by persistent myofibroblast activation with excessive accumulation of extracellular matrix (ECM). Fibrotic disorders represent an increasing burden of disease-associated morbidity and mortality worldwide for which there are limited therapeutic options. Reversing fibrosis requires the elimination of myofibroblasts, remodeling of the ECM, and regeneration of functional tissue. Multipotent mesenchymal stromal cells (MSC) have antifibrotic properties mediated by secreted factors present in their conditioned medium (MSC-CM). However, there are no standardized in vitro assays to predict the antifibrotic effects of human MSC. As a result, we lack evidence on the effect of cytokine priming on MSC's antifibrotic effects. We hypothesize that the MSC-CM promotes fibrosis resolution in vitro and that this effect is enhanced following MSC cytokine priming.

METHODS

We compared the antifibrotic effects of resting versus interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) primed MSC-CM in four in vitro assays: prevention of fibroblast activation, myofibroblasts deactivation, ECM degradation and fibrosis resolution in lung explant cultures. Furthermore, we performed transcriptomic analysis of myofibroblasts treated or not with resting or primed MSC-CM and proteomic characterization of resting and primed MSC-CM.

RESULTS

We isolated MSC from adipose tissue of 8 donors, generated MSC-CM and tested each MSC-CM independently. We report that MSC-CM treatment prevented TGF-β induced fibroblast activation to a similar extent as nintedanib but, in contrast to nintedanib, MSC-CM reduced fibrogenic myofibroblasts (i.e. transcriptomic upregulation of apoptosis, senescence, and inflammatory pathways). These effects were larger when primed rather than resting MSC-CM were used. Priming increased the ability of MSC-CM to remodel the ECM, reducing its content of collagen I and fibronectin, and reduced the fibrotic load in TGF-β treated lung explant cultures. Priming increased the following antifibrotic proteins in MSC-CM: DKK1, MMP-1, MMP-3, follistatin and cathepsin S. Inhibition of DKK1 reduced the antifibrotic effects of MSC-CM.

CONCLUSIONS

In vitro, MSC-CM promote fibrosis resolution, an effect enhanced following MSC cytokine priming. Specifically, MSC-CM reduces fibrogenic myofibroblasts through apoptosis, senescence, and by enhancing ECM degradation. Future studies will establish the in vivo relevance of MSC priming to fibrosis resolution.

The intervention of macrophages in progressive fibrosis characterizing systemic sclerosis: A systematic review

BACKGROUND AND AIM

Systemic sclerosis (SSc) is an immune mediated connective tissue disease characterized by microvascular dysfunction, aberrant immune response, and progressive fibrosis. Although the immuno-pathophysiological mechanisms underlying SSc are not fully clarified, they are often associated with a dysfunctional macrophage activation toward an alternative (M2) phenotype induced by cytokines [i.e., IL-4, IL-10, IL-13, and transforming growth factor (TGF-β)] involved in the fibrotic and anti-inflammatory process. A spectrum of macrophage activation state has been identified ranging from M1 to M2 phenotype, gene expression of phenotype markers, and functional aspects. This systematic review aims to analyze the importance of M2 macrophage polatization during the immune mediated process and the identification of specific pathways, cytokines, and chemokines involved in SSc pathogenesis. Moreover, this review provides an overview on the in vitro and in vivo studies aiming to test therapeutic strategies targeting M2 macrophages.

METHODS

A systematic literature review was performed according to the preferred Reported Items for Systematic Reviews and Meta-Analyses (PRISMA). The search encompassed the online medical databases PubMed and Embase up to the 30th of June 2024. Original research manuscripts (in vitro study, in vivo study), animal model and human cohort, were considered for the review. Exclusion criteria encompassed reviews, case reports, correspondences, and conference abstracts/posters. The eligible manuscripts main findings were critically analyzed, discussed, and summarized in the correspondent tables.

RESULTS

Out of the 77 screened abstracts, 49 papers were deemed eligible. Following a critical analysis, they were categorized according to the primary (29 original articles) and secondary (20 original articles) research objectives of this systematic review. The data from the present systematic review suggest the pivotal role of M2 macrophages differentiation and activation together with the dysregulation of the immune system in the SSc pathogenesis. Strong correlations have been found between M2 macrophage presence and clinical manifestations in both murine and human tissue samples. Interestingly, the presence of M2 cell surface markers on peripheral blood monocytes has been highlighted, suggesting a potential biomarker role for this finding. Therapeutic effects reducing M2 macrophage activities have been observed and/or tested for existing and for new drugs, demonstrating potential efficacy in modulating the pro-fibrotic immune response for treatment of SSc.

CONCLUSIONS

The increased M2 macrophage activation in course of SSc seems to offer new insights on the self-amplifying inflammatory and fibrotic response by the immune system on such disease. Therefore, the revaluation of immunomodulatory and ongoing antifibrotic therapies, as well as novel therapeutical approaches in SSc that contribute to limit the M2 macrophage activation are matter of intense investigations.

The Myofibroblast Fate of Therapeutic Mesenchymal Stromal Cells: Regeneration, Repair, or Despair?

Mesenchymal stromal cells (MSCs) can be isolated from various tissues of healthy or patient donors to be retransplanted in cell therapies. Because the number of MSCs obtained from biopsies is typically too low for direct clinical application, MSC expansion in cell culture is required. However, ex vivo amplification often reduces the desired MSC regenerative potential and enhances undesired traits, such as activation into fibrogenic myofibroblasts. Transiently activated myofibroblasts restore tissue integrity after organ injury by producing and contracting extracellular matrix into scar tissue. In contrast, persistent myofibroblasts cause excessive scarring-called fibrosis-that destroys organ function. In this review, we focus on the relevance and molecular mechanisms of myofibroblast activation upon contact with stiff cell culture plastic or recipient scar tissue, such as hypertrophic scars of large skin burns. We discuss cell mechanoperception mechanisms such as integrins and stretch-activated channels, mechanotransduction through the contractile actin cytoskeleton, and conversion of mechanical signals into transcriptional programs via mechanosensitive co-transcription factors, such as YAP, TAZ, and MRTF. We further elaborate how prolonged mechanical stress can create persistent myofibroblast memory by direct mechanotransduction to the nucleus that can evoke lasting epigenetic modifications at the DNA level, such as histone methylation and acetylation. We conclude by projecting how cell culture mechanics can be modulated to generate MSCs, which epigenetically protected against myofibroblast activation and transport desired regeneration potential to the recipient tissue environment in clinical therapies.

Form-deprivation myopia promotes sclera M2-type macrophages polarization in mice

PURPOSE

To explore the phenotype of sclera macrophages in form-deprivation (FD) myopia mice and the effects of M2 macrophage in FD myopia development.

METHODS

C57BL/6 mice were under 2 weeks of unilateral FD treatment. and they were separated into two groups, including an intraperitoneally injected(IP) vehicle group and Panobinostat (LBH589) (10 mg/kg per body weight) treatment group. All biometric parameters were measured before and after treatments, and the type and density of sclera macrophages were identified by immunofluorescence and RT-qPCR. In vitro, we analyzed the M2 macrophage and primary human sclera fibroblast (HSF) co-culture system by using the transcriptome sequencing method. Gene ontology (GO) and KEGG enrichment analyses were used to pinpoint the biological functions and pathways associated with the identified Differentially Expressed Genes (DEGs). The hub genes were investigated using the STRING database and Cytoscape software and were confirmed using RT-qPCR.

RESULTS

We found that the M2-type sclera macrophage density and expression increased in FD-treated eyes. The results showed that LBH589 inhibited the M2 macrophage polarization, and reduced FDM development. GO and KEGG analyses revealed that the DEGs were predominantly involved in the synthesis and breakdown of the extracellular matrix (ECM), as well as in pathways related to ECM-receptor interaction and the PI3K-Akt signaling pathway. Five hub genes (FN-1, MMP-2, COL1A1, CD44, and IL6) were identified, and RT-qPCR validated the variation in expression levels among these genes.

CONCLUSION

M2 macrophage polarization occurred in the sclera in FDM mice. Panobinostat-mediated inhibition of M2 macrophage polarization may decrease FDM progression, as M2 macrophages are crucial in controlling ECM remodeling by HSFs.

Biliary fibrosis is an important but neglected pathological feature in hepatobiliary disorders: from molecular mechanisms to clinical implications

Fibrosis resulting from pathological repair secondary to recurrent or persistent tissue damage often leads to organ failure and mortality. Biliary fibrosis is a crucial but easily neglected pathological feature in hepatobiliary disorders, which may promote the development and progression of benign and malignant biliary diseases through pathological healing mechanisms secondary to biliary tract injuries. Elucidating the etiology and pathogenesis of biliary fibrosis is beneficial to the prevention and treatment of biliary diseases. In this review, we emphasized the importance of biliary fibrosis in cholangiopathies and summarized the clinical manifestations, epidemiology, and aberrant cellular composition involving the biliary ductules, cholangiocytes, immune system, fibroblasts, and the microbiome. We also focused on pivotal signaling pathways and offered insights into ongoing clinical trials and proposing a strategic approach for managing biliary fibrosis-related cholangiopathies. This review will offer a comprehensive perspective on biliary fibrosis and provide an important reference for future mechanism research and innovative therapy to prevent or reverse fibrosis.

Fibrosis-on-Chip: A Guide to Recapitulate the Essential Features of Fibrotic Disease

Fibrosis, which is primarily marked by excessive extracellular matrix (ECM) deposition, is a pathophysiological process associated with many disorders, which ultimately leads to organ dysfunction and poor patient outcomes. Despite the high prevalence of fibrosis, currently there exist few therapeutic options, and importantly, there is a paucity of in vitro models to accurately study fibrosis. This review discusses the multifaceted nature of fibrosis from the viewpoint of developing organ-on-chip (OoC) disease models, focusing on five key features: the ECM component, inflammation, mechanical cues, hypoxia, and vascularization. The potential of OoC technology is explored for better modeling these features in the context of studying fibrotic diseases and the interplay between various key features is emphasized. This paper reviews how organ-specific fibrotic diseases are modeled in OoC platforms, which elements are included in these existing models, and the avenues for novel research directions are highlighted. Finally, this review concludes with a perspective on how to address the current gap with respect to the inclusion of multiple features to yield more sophisticated and relevant models of fibrotic diseases in an OoC format.

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

The term 'fibroblast' often serves as a catch-all for a diverse array of mesenchymal cells, including perivascular cells, stromal progenitor cells and bona fide fibroblasts. Although phenotypically similar, these subpopulations are functionally distinct, maintaining tissue integrity and serving as local progenitor reservoirs. In response to tissue injury, these cells undergo a dynamic fibroblast-myofibroblast transition, marked by extracellular matrix secretion and contraction of actomyosin-based stress fibres. Importantly, whereas transient activation into myofibroblasts aids in tissue repair, persistent activation triggers pathological fibrosis. In this Review, we discuss the roles of mechanical cues, such as tissue stiffness and strain, alongside cell signalling pathways and extracellular matrix ligands in modulating myofibroblast activation and survival. We also highlight the role of epigenetic modifications and myofibroblast memory in physiological and pathological processes. Finally, we discuss potential strategies for therapeutically interfering with these factors and the associated signal transduction pathways to improve the outcome of dysregulated healing.

Pharmacological Antagonism of Ccr2+ Cell Recruitment to Facilitate Regenerative Tendon Healing

Successful tendon healing requires sufficient deposition and remodeling of new extracellular matrix at the site of injury, with this process mediating in part through fibroblast activation via communication with macrophages. Moreover, resolution of healing requires clearance or reversion of activated cells, with chronic interactions with persistent macrophages impairing resolution and facilitating the conversion the conversion to fibrotic healing. As such, modulation of the macrophage environment represents an important translational target to improve the tendon healing process. Circulating monocytes are recruited to sites of tissue injury, including the tendon, via upregulation of cytokines including Ccl2, which facilitates recruitment of Ccr2+ macrophages to the healing tendon. Our prior work has demonstrated that Ccr2-/- can modulate fibroblast activation and myofibroblast differentiation. However, this approach lacked temporal control and resulted in healing impairments. Thus, in the current study we have leveraged a Ccr2 antagonist to blunt macrophage recruitment to the healing tendon in a time-dependent manner. We first tested the effects of Ccr2 antagonism during the acute inflammatory phase and found that this had no effect on the healing process. In contrast, Ccr2 antagonism during the late inflammatory/ early proliferative period resulted in significant improvements in mechanical properties of the healing tendon. Collectively, these data demonstrate the temporally distinct impacts of modulating Ccr2+ cell recruitment and Ccr2 antagonism during tendon healing and highlight the translational potential of transient Ccr2 antagonism to improve the tendon healing process.

Integrative analysis identifies molecular features of fibroblast and the significance of fibrosis on neoadjuvant chemotherapy response in breast cancer

BACKGROUND

The molecular features of fibroblasts and the role of fibrosis in neoadjuvant chemotherapy (NAC) response and breast cancer (BRCA) prognosis remain unclear. Therefore, this study aimed to investigate the impact of interstitial fibrosis on the response and prognosis of patients with BRCA undergoing NAC treatment.

MATERIALS AND METHODS

The molecular characteristics of pathologic complete response (pCR) and non-pCR (npCR) in patients with BRCA were analyzed using multiomics analysis. A clinical cohort was collected to investigate the predictive value of fibrosis in patients with BRCA.

RESULTS

Fibrosis-related signaling pathways were significantly upregulated in patients with npCR. npCR may be associated with distinct and highly active fibroblast subtypes. Patients with high fibrosis had lower pCR rates. The fibrosis-dependent nomogram for pCR showed efficient predictive ability [training set: area under the curve [AUC]=0.871, validation set: AUC=0.792]. Patients with low fibrosis had a significantly better prognosis than those with high fibrosis, and those with a high fibrotic focus index had significantly shorter overall and recurrence-free survival. Therefore, fibrosis can be used to predict pCR. Our findings provide a basis for decision-making in the treatment of BRCA.

CONCLUSIONS

npCR is associated with a distinct and highly active fibroblast subtype. Furthermore, patients with high fibrosis have lower pCR rates and shorter long-term survival. Therefore, fibrosis can predict pCR. A nomogram that includes fibrosis can provide a basis for decision-making in the treatment of BRCA.

The Diagnosis of Intestinal Fibrosis in Crohn's Disease-Present and Future

Crohn's disease (CD) progresses with periods of remission and exacerbations. During exacerbations, chronic inflammation leads to tissue destruction. As a result, intestinal fibrosis may develop in response to the ongoing inflammatory process. Fibrosis in CD should be considered the result of the response of the intestinal wall (over) to the presence of inflammation in the deep structures of the intestinal wall. In the absence of ideal noninvasive methods, endoscopic evaluation in combination with biopsy, histopathological analysis, stool analysis, and blood analysis remains the gold standard for assessing both inflammation and fibrosis in CD. On the contrary, the ability to identify markers of intestinal fibrosis would help to develop new diagnostic and therapeutic methods to detect early stages of fibrosis. It is speculated that miRNAs may, in the future, become biomarkers for early noninvasive diagnosis in the treatment of intestinal fibrosis. The purpose of this review is to summarise existing diagnostic methods for Crohn's disease and present recent scientific reports on molecular testing.

Subpopulations of fibroblasts derived from human iPS cells

Organ fibrosis causes collagen fiber overgrowth and impairs organ function. Cardiac fibrosis after myocardial infarction impairs cardiac function significantly, pulmonary fibrosis reduces gas exchange efficiency, and liver fibrosis disturbs the natural function of the liver. Its development is associated with the differentiation of fibroblasts into myofibroblasts and increased collagen synthesis. Fibrosis has organ specificity, defined by the heterogeneity of fibroblasts. Although this heterogeneity is established during embryonic development, it has not been defined yet. Fibroblastic differentiation of induced pluripotent stem cells (iPSCs) recapitulates the process by which fibroblasts acquire diversity. Here, we differentiated iPSCs into cardiac, hepatic, and dermal fibroblasts and analyzed their properties using single-cell RNA sequencing. We observed characteristic subpopulations with different ratios in each organ-type fibroblast group, which contained both resting and distinct ACTA2+ myofibroblasts. These findings provide crucial information on the ontogeny-based heterogeneity of fibroblasts, leading to the development of therapeutic strategies to control fibrosis.

DIREN mitigates DSS-induced colitis in mice and attenuates collagen deposition via inhibiting the Wnt/β-catenin and focal adhesion pathways

BACKGROUND

DIREN is a SHE ethnic medicine with stasis-resolving, hemostasis, clearing heat, and removing toxin effects. It is clinically used in the treatment of gastrointestinal bleeding, such as ulcerative colitis (UC).

AIM OF THE STUDY

Fibrosis is one of the pathological changes in the progression of UC, which can make it challenging to respond to a treatment. We aimed to illuminate the role of DIREN in DSS-induced UC and tried to unveil its related mechanisms from two perspectives: intestinal inflammation and collagen deposition.

MATERIALS AND METHODS

A 2.5 % dextran sulfate sodium (DSS) water solution was used to induce colitis in mice. The therapeutic effect of DIREN was assessed using the disease activity index, histopathological score, and colon length. Masson and Sirius Red staining was used to observe the fibrosis in the colon. Apoptosis of colonic epithelial cells was observed by TUNEL immunofluorescence staining. RNA-seq observed differential genes and enrichment pathways. Immunohistochemistry and RT-qPCR were used to detect the expression of molecules related to fibrosis and focal adhesion signaling in colon tissue.

RESULTS

The administration of DIREN resulted in a reduction of disease activity index (DAI) in mice with UC while simultaneously promoting an increase in colon length. DIREN mitigated the loss of goblet cells in the colon of UC mice and maintained the integrity of the intestinal mucosa barrier. Masson staining revealed a reduction in colonic fibrosis with DIREN treatment, while Sirius red staining demonstrated a decrease in collagen Ⅰ deposition. DIREN reduced apoptosis of colonic epithelial cells and the expression of genes, such as CDH2, ITGA1, and TGF-β2. Additionally, the results of GSEA analysis of colon tissue transcriptome showed that the differentially expressed genes were enriched in the focal adhesion pathway. DIREN was found to downregulate the protein expression of BAX, N-cadherin, β-catenin, Integrin A1, and Vinculin while upregulating the protein expression of BCL2. Additionally, it led to the co-expression of N-cadherin and α-SMA.

CONCLUSION

DIREN exerts a protective effect against DSS-induced UC by ameliorating colonic fibrosis via regulation of focal adhesion and the WNT/β-catenin signaling pathway, thereby inhibiting fibroblast migration and reducing collagen secretion.

TGF-β1 induces formation of TSG-6-enriched extracellular vesicles in fibroblasts which can prevent myofibroblast transformation by modulating Erk1/2 phosphorylation

Extracellular vesicles have emerged as important mediators of cell-to-cell communication in the pathophysiology of fibrotic diseases. One such disease is Peyronie's disease (PD), a fibrotic disorder of the penis caused by uncontrolled transformation of resident fibroblasts to alpha-smooth muscle actin positive myofibroblasts. These cells produce large amounts of extracellular matrix, leading to formation of a plaque in the penile tunica albuginea (TA), causing pain, penile curvature, and erectile dysfunction. We have used primary fibroblasts derived from the TA of PD patients to explore the role of transforming growth factor beta 1 (TGF-β1), a key signalling factor in this process. TGF-β1 treatment elicited a range of responses from the myofibroblasts: (i) they secreted extracellular vesicles (EVs) that were more numerous and differed in size and shape from those secreted by fibroblasts, (ii) these EVs prevented TGF-β1-induced transformation of fibroblasts in a manner that was dependent on vesicle uptake and (iii) they prevented phosphorylation of Erk1/2, a critical component in modulating fibrogenic phenotypic responses, but did not affect TGF-β1-induced Smad-signalling. We posit that this effect could be linked to enrichment of TSG-6 in myofibroblast-derived EVs. The ability of myofibroblast-derived vesicles to prevent further myofibroblast transformation may establish them as part of an anti-fibrotic negative feedback loop, with potential to be exploited for future therapeutic approaches.

Multifunctional polypeptide-based hydrogel bio-adhesives with pro-healing activities and their working principles

Wound healing is a complex physiological process involving hemostasis, inflammation, proliferation, and tissue remodeling. Therefore, there is an urgent need for suitable wound dressings for effective and systematical wound management. Polypeptide-based hydrogel bio-adhesives offer unique advantages and are ideal candidates. However, comprehensive reviews on polypeptide-based hydrogel bio-adhesives for wound healing are still lacking. In this review, the physiological mechanisms and evaluation parameters of wound healing were first described in detail. Then, the working principles of hydrogel bio-adhesives were summarized. Recent advances made in multifunctional polypeptide-based hydrogel bio-adhesives involving gelatin, silk fibroin, fibrin, keratin, poly-γ-glutamic acid, ɛ-poly-lysine, serum albumin, and elastin with pro-healing activities in wound healing and tissue repair were reviewed. Finally, the current status, challenges, developments, and future trends of polypeptide-based hydrogel bio-adhesives were discussed, hoping that further developments would be stimulated to meet the growing needs of their clinical applications.

Exploring Extracellular Matrix Crosslinking as a Therapeutic Approach to Fibrosis

The extracellular matrix (ECM) provides structural support for tissues and regulatory signals for resident cells. ECM requires a careful balance between protein accumulation and degradation for homeostasis. Disruption of this balance can lead to pathological processes such as fibrosis in organs across the body. Post-translational crosslinking modifications to ECM proteins such as collagens alter ECM structure and function. Dysregulation of crosslinking enzymes as well as changes in crosslinking composition are prevalent in fibrosis. Because of the crucial roles these ECM crosslinking pathways play in disease, the enzymes that govern crosslinking events are being explored as therapeutic targets for fibrosis. Here, we review in depth the molecular mechanisms underlying ECM crosslinking, how ECM crosslinking contributes to fibrosis, and the therapeutic strategies being explored to target ECM crosslinking in fibrosis to restore normal tissue structure and function.

Cocktail Cell-Reprogrammed Hydrogel Microspheres Achieving Scarless Hair Follicle Regeneration

The scar repair inevitably causes damage of skin function and loss of skin appendages such as hair follicles (HF). It is of great challenge in wound repair that how to intervene in scar formation while simultaneously remodeling HF niche and inducing in situ HF regeneration. Here, chemical reprogramming techniques are used to identify a clinically chemical cocktail (Tideglusib and Tamibarotene) that can drive fibroblasts toward dermal papilla cell (DPC) fate. Considering the advantage of biomaterials in tissue repair and their regulation in cell behavior that may contributes to cellular reprogramming, the artificial HF seeding (AHFS) hydrogel microspheres, inspired by the natural processes of "seeding and harvest", are constructed via using a combination of liposome nanoparticle drug delivery system, photoresponsive hydrogel shell, positively charged polyamide modification, microfluidic and photocrosslinking techniques. The identified chemical cocktail is as the core nucleus of AHFS. In vitro and in vivo studies show that AHFS can regulate fibroblast fate, induce fibroblast-to-DPC reprogramming by activating the PI3K/AKT pathway, finally promoting wound healing and in situ HF regeneration while inhibiting scar formation in a two-pronged translational approach. In conclusion, AHFS provides a new and effective strategy for functional repair of skin wounds.

Role of platelet factor 4 in arteriovenous fistula maturation failure: What do we know so far?

The rate of arteriovenous fistula (AVF) maturation failure remains unacceptably high despite continuous efforts on technique improvement and careful pre-surgery planning. In fact, half of all newly created AVFs are unable to be used for hemodialysis (HD) without a salvage procedure. While vascular stenosis in the venous limb of the access is the culprit, the underlying factors leading to vascular narrowing and AVF maturation failure are yet to be determined. We have recently demonstrated that AVF non-maturation is associated with post-operative medial fibrosis and fibrotic stenosis, and post-operative intimal hyperplasia (IH) exacerbates the situation. Multiple pathological processes and signaling pathways are underlying the stenotic remodeling of the AVF. Our group has recently indicated that a pro-inflammatory cytokine platelet factor 4 (PF4/CXCL4) is upregulated in veins that fail to mature after AVF creation. Platelet factor 4 is a fibrosis marker and can be detected in vascular stenosis tissue, suggesting that it may contribute to AVF maturation failure through stimulation of fibrosis and development of fibrotic stenosis. Here, we present an overview of the how PF4-mediated fibrosis determines AVF maturation failure.

Characterization of cardiac fibroblast-extracellular matrix crosstalk across developmental ages provides insight into age-related changes in cardiac repair

Heart failure afflicts an estimated 6.5 million people in the United States, driven largely by incidents of coronary heart disease (CHD). CHD leads to heart failure due to the inability of adult myocardial tissue to regenerate after myocardial infarction (MI). Instead, immune cells and resident cardiac fibroblasts (CFs), the cells responsible for the maintenance of the cardiac extracellular matrix (cECM), drive an inflammatory wound healing response, which leads to fibrotic scar tissue. However, fibrosis is reduced in fetal and early (<1-week-old) neonatal mammals, which exhibit a transient capability for regenerative tissue remodeling. Recent work by our laboratory and others suggests this is in part due to compositional differences in the cECM and functional differences in CFs with respect to developmental age. Specifically, fetal cECM and CFs appear to mitigate functional loss in MI models and engineered cardiac tissues, compared to adult CFs and cECM. We conducted 2D studies of CFs on solubilized fetal and adult cECM to investigate whether these age-specific functional differences are synergistic with respect to their impact on CF phenotype and, therefore, cardiac wound healing. We found that the CF migration rate and stiffness vary with respect to cell and cECM developmental age and that CF transition to a fibrotic phenotype can be partially attenuated in the fetal cECM. However, this effect was not observed when cells were treated with cytokine TGF-β1, suggesting that inflammatory signaling factors are the dominant driver of the fibroblast phenotype. This information may be valuable for targeted therapies aimed at modifying the CF wound healing response and is broadly applicable to age-related studies of cardiac remodeling.

Spider-Silk-like Fiber Mat-Covered Polypropylene Warp-Knitted Hernia Mesh for Inhibition of Fibrosis under Dynamic Environment

Hernia surgery is a widely performed procedure, and the use of a polypropylene mesh is considered the standard approach. However, the mesh often leads to complications, including the development of scar tissue that wraps around the mesh and causes it to shrink. Consequently, there is a need to investigate the relationship between the mesh and scar formation as well as to develop a hernia mesh that can prevent fibrosis. In this study, three different commercial polypropylene hernia meshes were examined to explore the connection between the fabric structure and mechanical properties. In vitro dynamic culture was used to investigate the mechanism by which the mechanical properties of the mesh in a dynamic environment affect cell differentiation. Additionally, electrospinning was employed to create polycaprolactone spider-silk-like fiber mats to achieve mechanical energy dissipation in dynamic conditions. These fiber mats were then combined with the preferred hernia mesh. The results demonstrated that the composite mesh could reduce the activation of fibroblast mechanical signaling pathways and inhibit its differentiation into myofibroblasts in dynamic environments.

Linking NLRP3 inflammasome and pulmonary fibrosis: mechanistic insights and promising therapeutic avenues

Pulmonary fibrosis is a devastating disorder distinguished by redundant inflammation and matrix accumulation in the lung interstitium. The early inflammatory cascade coupled with recurring tissue injury orchestrates a set of events marked by perturbed matrix hemostasis, deposition of matrix proteins, and remodeling in lung tissue. Numerous investigations have corroborated a direct correlation between the NLR family pyrin domain-containing 3 (NLRP3) activation and the development of pulmonary fibrosis. Dysregulated activation of NLRP3 within the pulmonary microenvironment exacerbates inflammation and may incite fibrogenic responses. Nevertheless, the precise mechanisms through which the NLRP3 inflammasome elicits pro-fibrogenic responses remain inadequately defined. Contemporary findings suggest that the pro-fibrotic consequences stemming from NLRP3 signaling primarily hinge on the action of interleukin-1β (IL-1β). IL-1β instigates IL-1 receptor signaling, potentiating the activity of transforming growth factor-beta (TGF-β). This signaling cascade, in turn, exerts influence over various transcription factors, including SNAIL, TWIST, and zinc finger E-box-binding homeobox 1 (ZEB 1/2), which collectively foster myofibroblast activation and consequent lung fibrosis. Here, we have connected the dots to illustrate how the NLRP3 inflammasome orchestrates a multitude of signaling events, including the activation of transcription factors that facilitate myofibroblast activation and subsequent lung remodeling. In addition, we have highlighted the prominent role played by various cells in the formation of myofibroblasts, the primary culprit in lung fibrosis. We also provided a concise overview of various compounds that hold the potential to impede NLRP3 inflammasome signaling, thus offering a promising avenue for the treatment of pulmonary fibrosis.

Hydrogel Loaded with Components for Therapeutic Applications in Hypertrophic Scars and Keloids

Hypertrophic scars and keloids are common fibroproliferative diseases following injury. Patients with pathologic scars suffer from impaired quality of life and psychological health due to appearance disfiguration, itch, pain, and movement disorders. Recently, the advancement of hydrogels in biomedical fields has brought a variety of novel materials, methods and therapeutic targets for treating hypertrophic scars and keloids, which exhibit broad prospects. This review has summarized current research on hydrogels and loaded components used in preventing and treating hypertrophic scars and keloids. These hydrogels attenuate keloid and hypertrophic scar formation and progression by loading organic chemicals, drugs, or bioactive molecules (such as growth factors, genes, proteins/peptides, and stem cells/exosomes). Among them, smart hydrogels (a very promising method for loading many types of bioactive components) are currently favoured by researchers. In addition, combining hydrogels and current therapy (such as laser or radiation therapy, etc.) could improve the treatment of hypertrophic scars and keloids. Then, the difficulties and limitations of the current research and possible suggestions for improvement are listed. Moreover, we also propose novel strategies for facilitating the construction of target multifunctional hydrogels in the future.

Macrophage-derived MMP12 promotes fibrosis through sustained damage to endothelial cells

Macrophages are essential for the maintenance of endothelial cell function. However, the potential impact and mechanisms of crosstalk between macrophages and endothelial cells during silicosis progression remain unexplored. To fill this knowledge gap, a mouse model of silicosis was established. Single cell sequencing, spatial transcriptome sequencing, western blotting, immunofluorescence staining, tube-forming and wound healing assays were used to explore the effects of silicon dioxide on macrophage-endothelial interactions. To investigate the mechanism of macrophage-mediated fibrosis, MMP12 was specifically inactivated using siRNA and pharmacological approaches, and macrophages were depleted using disodium chlorophosphite liposomes. Compared to the normal saline group, the silica dust group showed altered macrophage-endothelial interactions. Matrix metalloproteinase family member MMP12 was identified as a key mediator of the altered function of macrophage-endothelial interactions after silica exposure, which was accompanied by pro-inflammatory macrophage activation and fibrotic progression. By using ablation strategies, macrophage-derived MMP12 was shown to mediate endothelial cell dysfunction by accumulating on the extracellular matrix. During the inflammatory phase of silicosis, MMP12 secreted by pro-inflammatory macrophages caused decreased endothelial cell viability, reduced migration, decreased trans-endothelial resistance and increased permeability; while during the fibrotic phase, macrophage-derived MMP12 sustained endothelial cell injury through accumulation on the extracellular matrix.

Inhibition of phosphatidylinositol 3-kinase catalytic subunit alpha by miR-203a-3p reduces hypertrophic scar formation via phosphatidylinositol 3-kinase/AKT/mTOR signaling pathway

Background

Hypertrophic scar (HS) is a common fibroproliferative skin disease that currently has no truly effective therapy. Given the importance of phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) in hypertrophic scar formation, the development of therapeutic strategies for endogenous inhibitors against PIK3CA is of great interest. Here, we explored the molecular mechanisms underlying the protective effects of miR-203a-3p (PIK3CA inhibitor) against excessive scar.

Methods

Bioinformatic analysis, immunohistochemistry, immunofluorescence, miRNA screening and fluorescence in situ hybridization assays were used to identify the possible pathways and target molecules mediating HS formation. A series of in vitro and in vivo experiments were used to clarify the role of PIK3CA and miR-203a-3p in HS. Mechanistically, transcriptomic sequencing, immunoblotting, dual-luciferase assay and rescue experiments were executed.

Results

Herein, we found that PIK3CA and the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway were upregulated in scar tissues and positively correlated with fibrosis. We then identified miR-203a-3p as the most suitable endogenous inhibitor of PIK3CA. miR-203a-3p suppressed the proliferation, migration, collagen synthesis and contractility as well as the transdifferentiation of fibroblasts into myofibroblasts in vitro, and improved the morphology and histology of scars in vivo. Mechanistically, miR-203a-3p attenuated fibrosis by inactivating the PI3K/AKT/mTOR pathway by directly targeting PIK3CA.

Conclusions

PIK3CA and the PI3K/AKT/mTOR pathway are actively involved in scar fibrosis and miR-203a-3p might serve as a potential strategy for hypertrophic scar therapy through targeting PIK3CA and inactivating the PI3K/AKT/mTOR pathway.

Models for Implant-Induced Capsular Contracture Post Breast Cancer Surgery

Capsular contracture is a painful deformation of scar-tissue that may form around an implant in post-breast cancer reconstruction or cosmetic surgery. Inflammation due to surgical trauma or contamination in the tissue around the implant could account for recruitment of immune cells, and transdifferentiation of resident fibroblasts into cells that deposit abnormally thick collagen. Here we examine this hypothesis using a mathematical model for interacting macrophages, fibroblasts, myofibroblasts, and collagen. Our model demonstrates that cellular response can, together with inflammatory cell recruitment, account for prognoses.

M2-Macrophage-Induced Chronic Inflammation Promotes Reversible Mesenchymal Stromal Cell Senescence and Reduces Their Anti-Fibrotic Properties

Fibrosis and the associated decline in organ functionality lead to an almost 50% mortality rate in developed countries. Multipotent mesenchymal stromal cells (MSC) were shown to suppress the development and progression of fibrosis through secreted factors including specific non-coding RNAs transferred within extracellular vesicles (EV). However, age-associated chronic inflammation can provoke MSC senescence and change secretome composition, thereby affecting their antifibrotic properties. Alternatively activated macrophages (M2-type) are key players in chronic inflammation that may interact with MSC through paracrine mechanisms and decrease their antifibrotic functions. To confirm this hypothesis, we evaluated the M2-macrophage conditioned medium (CM-M2) effect on human adipose-tissue-derived MSC senescence in vitro. We found that CM-M2, as well as a pro-senescence agent, hydrogen peroxide (H2O2), increased p21+-MSC number and secretion of IL-6 and MCP-1, which are considered main senescence-associated secretory phenotype (SASP) components. Thus, both exposures led to the senescent phenotype acquisition of MSC. EV from both CM-M2 and H2O2-exposed MSC, which showed a decreased effect on the suppression of TGFβ-induced fibroblast-to-myofibroblast differentiation compared to EV from control MSC according to αSMA level and the αSMA+-stress fiber reduction. After two weeks of subsequent cultivation under standard conditions, MSC demonstrated a decrease in senescence hallmarks and fibroblast differentiation suppression via EV. These results suggest that M2-macrophage-induced chronic inflammation can reversibly induce MSC senescence, which reduces the MSC's ability to inhibit fibroblast-to-myofibroblast differentiation.

Development of accessible platforms to promote myofibroblast differentiation by playing on hydrogel scaffold composition

Mechanomimetic materials are particularly attractive for modeling in vitro fibroblast to myofibroblast (Myof) transition, a key process in the physiological repair of damaged tissue, and recognized as the core cellular mechanism of pathological fibrosis in different organs. In vivo, mechanical stimuli from the extracellular matrix (ECM) are crucial, together with cell-cell contacts and the pro-fibrotic transforming growth factor (TGF)-β1, in promoting fibroblast differentiation. Here, we explore the impact of hydrogels made by polyacrylamide with different composition on fibroblast behavior. By appropriate modulation of the hydrogel composition (e.g. adjusting the crosslinker content), we produce and fully characterize three kinds of scaffolds with different Young modulus (E). We observe that soft hydrogels (E < 1 kPa) induced fibroblast differentiation better than stiffer ones, also in the absence of TGF-β1. This study provides a readily accessible biomaterial platform to promote Myof generation. The easy approach used and the commercial availability of the monomers make these hydrogels suitable to a wide range of biomedical applications combined with high reproducibility and simple preparation protocols.

Cobweb-Inspired Micro/Nanostructured Scaffolds for Soft Tissue Regeneration with Inhibition Effect of Fibrosis under Dynamic Environment

In soft tissue repair, fibrosis can lead to repair failure and long-term chronic pain in patients. Excessive mechanical stimulation of fibroblasts is one of the causes of fibrosis during abdominal wall regeneration. Inspired by the cobweb, a polycaprolactone beaded fiber is prepared by electrospinning. The cobweb-inspired structure attenuates the mechanical stimulation of cells under a dynamic environment. Nano-protrusions are introduced into the scaffold for further inhibition of fibrosis by self-induced crystallization. A machine is built for in vitro dynamic culture and rat abdominal subcutaneous embedding experiments are performed to verify the inhibiting effect of fibrosis in a dynamic environment in vivo. Results show that the expression of integrin β1 and α-smooth muscle actin is inhibited by the cobweb-inspired structure under dynamic culture. The results of hematoxylin and eosin and Masson's trichrome indicate that the cobweb-inspired structure has a good inhibitory effect on fibrosis in a dynamic environment in vivo. In general, the cobweb-inspired scaffold with nano-protrusions has a good ability to inhibit fibrosis under both static and dynamic environments. It is believed that the scaffold has promising applications in the field of inhibiting fibrosis caused by mechanical stimulation.

Novel roles for cooperating collagen receptor families in fibrotic niches

Recent data indicate that integrin and non-integrin collagen receptors cooperate in the fibrosis-specific microenvironment (i.e., the fibrotic niche). In certain tumor types, DDR1 can regulate the interaction with collagen III to regulate dormancy and metastasis, whereas in other tumor types, DDR1 can be shed and used to reorganize collagen. DDR1 expressed on tumor cells, together with DDR2 and α11β1 integrin expressed on cancer-associated fibroblasts, can increase tumor tissue stiffness. Integrin α1β1 and α2β1 are present on immune cells where they together with the immunosuppressive collagen receptor LAIR-1 can mediate binding to intratumor collagens. In summary, collagen-binding integrins together with DDRs, can create fibrillar collagen niches that act as traps to hinder immune cell trafficking into the tumor cell mass. Binding of collagens via LAIR-1 on immune cells in turn results in CD8+T-cell exhaustion. Continued studies of these complex interactions are needed for successful new stroma-based therapeutic interventions. In the current review, we will summarize recent data on collagen receptors with a special focus on their potential role in tumor fibrosis and highlight their collaborative roles in tumor fibrotic niches.

Macrophages Serve as Bidirectional Regulators and Potential Therapeutic Targets for Liver Fibrosis

Liver fibrosis is a dynamic pathological process in which the structure and function of the liver abnormally change due to long-term complex inflammatory reactions and chronic liver injury caused by multiple internal and external factors. Previous studies believed that the activation of hepatic stellate cells is a critical part of the occurrence and development of liver fibrosis. However, an increasing number of studies have indicated that the macrophage plays an important role as a central regulator in liver fibrosis, and it directly affects the development and recovery of liver fibrosis. Studies of macrophages and liver fibrosis in the recent 10 years will be reviewed in this paper. This review will not only clarify the molecular mechanism of liver fibrosis regulated by macrophages but also provide new strategies and methods for ameliorating and treating liver fibrosis.

Macrophage phenotypes and functions: resolving inflammation and restoring homeostasis

Inflammation must be tightly regulated to both defend against pathogens and restore tissue homeostasis. The resolution of inflammatory responses is a dynamic process orchestrated by cells of the immune system. Macrophages, tissue-resident innate immune cells, are key players in modulating inflammation. Here, we review recent work highlighting the importance of macrophages in tissue resolution and the return to homeostasis. We propose that enhancing macrophage pro-resolution functions represents a novel and widely applicable therapeutic strategy to dampen inflammation, promote repair, and restore tissue integrity and function.

The formin DAAM1 regulates the deubiquitinase activity of USP10 and integrin homeostasis

The differentiation of fibroblasts into pathological myofibroblasts during wound healing is characterized by increased cell surface expression of αv-integrins. Our previous studies found that the deubiquitinase (DUB) USP10 removes ubiquitin from αv-integrins, leading to cell surface integrin accumulation, subsequent TGFβ1 activation, and pathological myofibroblast differentiation. In this study, a yeast two-hybrid screen revealed a novel binding partner for USP10, the formin, DAAM1. We found that DAAM1 binds to and inhibits USP10's DUB activity through the FH2 domain of DAAM1 independent of its actin functions. The USP10/DAAM1 interaction was also supported by proximity ligation assay (PLA) in primary human corneal fibroblasts. Treatment with TGFβ1 significantly increased USP10 and DAAM1 protein expression, PLA signal, and co-localization to actin stress fibers. DAAM1 siRNA knockdown significantly reduced co-precipitation of USP10 and DAAM1 on purified actin stress fibers, and β1- and β5-integrin ubiquitination. This resulted in increased αv-, β1-, and β5-integrin total protein levels, αv-integrin recycling, and extracellular fibronectin (FN) deposition. Together, our data demonstrate that DAAM1 inhibits USP10's DUB activity on integrins subsequently regulating cell surface αv-integrin localization and FN accumulation.

High-Fidelity Extrusion Bioprinting of Low-Printability Polymers Using Carbopol as a Rheology Modifier

Extrusion three-dimensional (3D) bioprinting is a promising technology with many applications in the biomedical and tissue engineering fields. One of the key limitations for the widespread use of this technology is the narrow window of printability that results from the need to have bioinks with rheological properties that allow the extrusion of continuous filaments while maintaining high cell viability within the materials during and after printing. In this work, we use Carbopol (CBP) as rheology modifier for extrusion printing of biomaterials that are typically nonextrudable or present low printability. We show that low concentrations of CBP can introduce the desired rheological properties for a wide range of formulations, allowing the use of polymers with different cross-linking mechanisms and the introduction of additives and cells. To explore the opportunities and limitations of CBP as a rheology modifier, we used ink formulations based on poly(ethylene glycol)diacrylate with extrusion 3D printing to produce soft, yet stable, hydrogels with tunable mechanical properties. Cell-laden constructs made with such inks presented high viability for cells seeded on top of cross-linked materials and cells incorporated within the bioink during printing, showing that the materials are noncytotoxic and the printed structures do not degrade for up to 14 days. To our knowledge, this is the first report of the use of CBP-containing bioinks to 3D-print complex cell-laden structures that are stable for days and present high cell viability. The use of CBP to obtain highly printable inks can accelerate the evolution of extrusion 3D bioprinting by guaranteeing the required rheological properties and expanding the number of materials that can be successfully printed. This will allow researchers to develop and optimize new bioinks focusing on the biochemical, cellular, and mechanical requirements of the targeted applications rather than the rheology needed to achieve good printability.

Fibroblast Activation Protein Alpha (FAPα) in Fibrosis: Beyond a Perspective Marker for Activated Stromal Cells?

The development of tissue fibrosis is a complex process involving the interaction of multiple cell types, which makes the search for antifibrotic agents rather challenging. So far, myofibroblasts have been considered the key cell type that mediated the development of fibrosis and thus was the main target for therapy. However, current strategies aimed at inhibiting myofibroblast function or eliminating them fail to demonstrate sufficient effectiveness in clinical practice. Therefore, today, there is an unmet need to search for more reliable cellular targets to contribute to fibrosis resolution or the inhibition of its progression. Activated stromal cells, capable of active proliferation and invasive growth into healthy tissue, appear to be such a target population due to their more accessible localization in the tissue and their high susceptibility to various regulatory signals. This subpopulation is marked by fibroblast activation protein alpha (FAPα). For a long time, FAPα was considered exclusively a marker of cancer-associated fibroblasts. However, accumulating data are emerging on the diverse functions of FAPα, which suggests that this protein is not only a marker but also plays an important role in fibrosis development and progression. This review aims to summarize the current data on the expression, regulation, and function of FAPα regarding fibrosis development and identify promising advances in the area.

Alpha-1 adrenergic signaling drives cardiac regeneration via extracellular matrix remodeling transcriptional program in zebrafish macrophages

The autonomic nervous system plays a pivotal role in cardiac repair. Here, we describe the mechanistic underpinning of adrenergic signaling in fibrotic and regenerative response of the heart to be dependent on immunomodulation. A pharmacological approach identified adrenergic receptor alpha-1 as a key regulator of macrophage phenotypic diversification following myocardial damage in zebrafish. Genetic manipulation and single-cell transcriptomics showed that the receptor signals activation of an "extracellular matrix remodeling" transcriptional program in a macrophage subset, which serves as a key regulator of matrix composition and turnover. Mechanistically, adrenergic receptor alpha-1-activated macrophages determine activation of collagen-12-expressing fibroblasts, a cellular determinant of cardiac regenerative niche, through midkine-mediated paracrine crosstalk, allowing lymphatic and blood vessel growth and cardiomyocyte proliferation at the lesion site. These findings identify the mechanism of adrenergic signaling in macrophage phenotypic and functional determination and highlight the potential of neural modulation for regulation of fibrosis and coordination of myocardial regenerative response.

The pathogenesis of organ fibrosis: Focus on necroptosis

Fibrosis is a common process of tissue repair response to multiple injuries in all chronic progressive diseases, which features with excessive deposition of extracellular matrix. Fibrosis can occur in all organs and tends to be nonreversible with the progress of the disease. Different cells types in different organs are involved in the occurrence and development of fibrosis, that is, hepatic stellate cells, pancreatic stellate cells, fibroblasts and myofibroblasts. Various types of programmed cell death, including apoptosis, autophagy, ferroptosis and necroptosis, are closely related to organ fibrosis. Among these programmed cell death types, necroptosis, an emerging regulated cell death type, is regarded as a huge potential target to ameliorate organ fibrosis. In this review, we summarize the role of necroptosis signalling in organ fibrosis and collate the small molecule compounds targeting necroptosis. In addition, we discuss the potential challenges, opportunities and open questions in using necroptosis signalling as a potential target for antifibrotic therapies. LINKED ARTICLES: This article is part of a themed issue on Translational Advances in Fibrosis as a Therapeutic Target. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.22/issuetoc.

A biomimetic renal fibrosis progression model on-chip evaluates anti-fibrotic effects longitudinally in a dynamic fibrogenic niche

Although renal fibrosis can advance chronic kidney disease and progressively lead to end-stage renal failure, no effective anti-fibrotic drugs have been clinically approved. To aid drug development, we developed a biomimetic renal fibrosis progression model on-chip to evaluate anti-fibrotic effects of natural killer cell-derived extracellular vesicles and pirfenidone (PFD) across different fibrotic stages. First, the dynamic interplay between fibroblasts and kidney-derived extracellular matrix (ECM) resembling the fibrogenic niche on-chip demonstrated that myofibroblasts induced by stiff ECM in 3 days were reversed to fibroblasts by switching to soft ECM, which was within 2, but not 7 days. Second, PFD significantly down-regulated the expression of α-SMA in NRK-49F in medium ECM, as opposed to stiff ECM. Third, a study in rats showed that early administration of PFD significantly inhibited renal fibrosis in terms of the expression levels of α-SMA and YAP. Taken together, both on-chip and animal models indicate the importance of early anti-fibrotic intervention for checking the progression of renal fibrosis. Therefore, this renal fibrosis progression on-chip with a feature of recapitulating dynamic biochemical and biophysical cues can be readily used to assess anti-fibrotic candidates and to explore the tipping point when the fibrotic fate can be rescued for better medical intervention.

Macrophage polarization in tissue fibrosis

Fibrosis can occur in all major organs with relentless progress, ultimately leading to organ failure and potentially death. Unfortunately, current clinical treatments cannot prevent or reverse tissue fibrosis. Thus, new and effective antifibrotic therapeutics are urgently needed. In recent years, a growing body of research shows that macrophages are involved in fibrosis. Macrophages are highly heterogeneous, polarizing into different phenotypes. Some studies have found that regulating macrophage polarization can inhibit the development of inflammation and cancer. However, the exact mechanism of macrophage polarization in different tissue fibrosis has not been fully elucidated. This review will discuss the major signaling pathways relevant to macrophage-driven fibrosis and profibrotic macrophage polarization, the role of macrophage polarization in fibrosis of lung, kidney, liver, skin, and heart, potential therapeutics targets, and investigational drugs currently in development, and hopefully, provide a useful review for the future treatment of fibrosis.

Tissue fibrosis induced by radiotherapy: current understanding of the molecular mechanisms, diagnosis and therapeutic advances

Cancer remains the leading cause of death around the world. In cancer treatment, over 50% of cancer patients receive radiotherapy alone or in multimodal combinations with other therapies. One of the adverse consequences after radiation exposure is the occurrence of radiation-induced tissue fibrosis (RIF), which is characterized by the abnormal activation of myofibroblasts and the excessive accumulation of extracellular matrix. This phenotype can manifest in multiple organs, such as lung, skin, liver and kidney. In-depth studies on the mechanisms of radiation-induced fibrosis have shown that a variety of extracellular signals such as immune cells and abnormal release of cytokines, and intracellular signals such as cGAS/STING, oxidative stress response, metabolic reprogramming and proteasome pathway activation are involved in the activation of myofibroblasts. Tissue fibrosis is extremely harmful to patients' health and requires early diagnosis. In addition to traditional serum markers, histologic and imaging tests, the diagnostic potential of nuclear medicine techniques is emerging. Anti-inflammatory and antioxidant therapies are the traditional treatments for radiation-induced fibrosis. Recently, some promising therapeutic strategies have emerged, such as stem cell therapy and targeted therapies. However, incomplete knowledge of the mechanisms hinders the treatment of this disease. Here, we also highlight the potential mechanistic, diagnostic and therapeutic directions of radiation-induced fibrosis.

Novel approaches to target fibroblast mechanotransduction in fibroproliferative diseases

The ability of cells to sense and respond to changes in mechanical environment is vital in conditions of organ injury when the architecture of normal tissues is disturbed or lost. Among the various cellular players that respond to injury, fibroblasts take center stage in re-establishing tissue integrity by secreting and organizing extracellular matrix into stabilizing scar tissue. Activation, activity, survival, and death of scar-forming fibroblasts are tightly controlled by mechanical environment and proper mechanotransduction ensures that fibroblast activities cease after completion of the tissue repair process. Conversely, dysregulated mechanotransduction often results in fibroblast over-activation or persistence beyond the state of normal repair. The resulting pathological accumulation of extracellular matrix is called fibrosis, a condition that has been associated with over 40% of all deaths in the industrialized countries. Consequently, elements in fibroblast mechanotransduction are scrutinized for their suitability as anti-fibrotic therapeutic targets. We review the current knowledge on mechanically relevant factors in the fibroblast extracellular environment, cell-matrix and cell-cell adhesion structures, stretch-activated membrane channels, stress-regulated cytoskeletal structures, and co-transcription factors. We critically discuss the targetability of these elements in therapeutic approaches and their progress in pre-clinical and/or clinical trials to treat organ fibrosis.

MiR-148a-3p within HucMSC-Derived Extracellular Vesicles Suppresses Hsp90b1 to Prevent Fibroblast Collagen Synthesis and Secretion in Silica-Induced Pulmonary Fibrosis

Silicosis is a fatal occupational respiratory disease caused by the prolonged inhalation of respirable silica. The core event of silicosis is the heightened activity of fibroblasts, which excessively synthesize extracellular matrix (ECM) proteins. Our previous studies have highlighted that human umbilical cord mesenchymal stem cell-derived extracellular vesicles (hucMSC-EVs) hold promise in mitigating silicosis and the significant role played by microRNAs (miRNAs) in this process. Delving deeper into this mechanism, we found that miR-148a-3p was the most abundant miRNA of the differential miRNAs in hucMSC-EVs, with the gene heat shock protein 90 beta family member 1 (Hsp90b1) as a potential target. Notably, miR-148a-3p's expression was downregulated during the progression of silica-induced pulmonary fibrosis both in vitro and in vivo, but was restored after hucMSC-EVs treatment (p < 0.05). Introducing miR-148a-3p mimics effectively hindered the collagen synthesis and secretion of fibroblasts induced by transforming growth factor-β1 (TGF-β1) (p < 0.05). Confirming our hypothesis, Hsp90b1 was indeed targeted by miR-148a-3p, with significantly reduced collagen activity in TGF-β1-treated fibroblasts upon Hsp90b1 inhibition (p < 0.05). Collectively, our findings provide compelling evidence that links miR-148a-3p present in hucMSC-EVs with the amelioration of silicosis, suggesting its therapeutic potential by specifically targeting Hsp90b1, thereby inhibiting fibroblast collagen activities. This study sheds light on the role of miR-148a-3p in hucMSC-EVs, opening avenues for innovative therapeutic interventions targeting molecular pathways in pulmonary fibrosis.

Inflammation-related signaling pathways in tendinopathy

Tendon is a connective tissue that produces movement by transmitting the force produced by muscle contraction to the bones. Most tendinopathy is caused by prolonged overloading of the tendon, leading to degenerative disease of the tendon. When overloaded, the oxygen demand of tenocytes increases, and the tendon structure is special and lacks blood supply, which makes it easier to form an oxygen-deficient environment in tenocytes. The production of reactive oxygen species due to hypoxia causes elevation of inflammatory markers in the tendon, including PGE2, IL-1β, and TNF-α. In the process of tendon healing, inflammation is also a necessary stage. The inflammatory environment formed by cytokines and various immune cells play an important role in the clearance of necrotic material, the proliferation of tenocytes, and the production of collagen fibers. However, excessive inflammation can lead to tendon adhesions and hinder tendon healing. Some important and diverse biological functions of the body originate from intercellular signal transduction, among which cytokine mediation is an important way of signal transduction. In particular, NF-κB, NLRP3, p38/MAPK, and signal transducer and activator of transcription 3, four common signaling pathways in tendinopathy inflammatory response, play a crucial role in the regulation and transcription of inflammatory factors. Therefore, summarizing the specific mechanisms of inflammatory signaling pathways in tendinopathy is of great significance for an in-depth understanding of the inflammatory response process and exploring how to inhibit the harmful part of the inflammatory response and promote the beneficial part to improve the healing effect of the tendon.

Growth factors in the treatment of Achilles tendon injury

Achilles tendon (AT) injury is one of the most common tendon injuries, especially in athletes, the elderly, and working-age people. In AT injury, the biomechanical properties of the tendon are severely affected, leading to abnormal function. In recent years, many efforts have been underway to develop effective treatments for AT injuries to enable patients to return to sports faster. For instance, several new techniques for tissue-engineered biological augmentation for tendon healing, growth factors (GFs), gene therapy, and mesenchymal stem cells were introduced. Increasing evidence has suggested that GFs can reduce inflammation, promote extracellular matrix production, and accelerate AT repair. In this review, we highlighted some recent investigations regarding the role of GFs, such as transforming GF-β(TGF-β), bone morphogenetic proteins (BMP), fibroblast GF (FGF), vascular endothelial GF (VEGF), platelet-derived GF (PDGF), and insulin-like GF (IGF), in tendon healing. In addition, we summarized the clinical trials and animal experiments on the efficacy of GFs in AT repair. We also highlighted the advantages and disadvantages of the different isoforms of TGF-β and BMPs, including GFs combined with stem cells, scaffolds, or other GFs. The strategies discussed in this review are currently in the early stages of development. It is noteworthy that although these emerging technologies may potentially develop into substantial clinical treatment options for AT injury, definitive conclusions on the use of these techniques for routine management of tendon ailments could not be drawn due to the lack of data.

Novel bioprinted 3D model to human fibrosis investigation

Fibrosis is shared in multiple diseases with progressive tissue stiffening, organ failure and limited therapeutic options. This unmet need is also due to the lack of adequate pre-clinical models to mimic fibrosis and to be challenged novel by anti-fibrotic therapeutic venues. Here using bioprinting, we designed a novel 3D model where normal human healthy fibroblasts have been encapsulated in type I collagen. After stimulation by Transforming Growth factor beta (TGFβ), embedded cells differentiated into myofibroblasts and enhanced the contractile activity, as confirmed by the high level of α - smooth muscle actin (αSMA) and F-actin expression. As functional assays, SEM analysis revealed that after TGFβ stimulus the 3D microarchitecture of the scaffold was dramatically remolded with an increased fibronectin deposition with an abnormal collagen fibrillar pattern. Picrius Sirius Red staining additionally revealed that TGFβ stimulation enhanced of two logarithm the collagen fibrils neoformation in comparison with control. These data indicate that by bioprinting technology, it is possible to generate a reproducible and functional 3D platform to mimic fibrosis as key tool for drug discovery and impacting on animal experimentation and reducing costs and time in addressing fibrosis.

Nonmyocytes as electrophysiological contributors to cardiac excitation and conduction

Although cardiac action potential (AP) generation and propagation have traditionally been attributed exclusively to cardiomyocytes (CM), other cell types in the heart are also capable of forming electrically conducting junctions. Interactions between CM and nonmyocytes (NM) enable and modulate each other's activity. This review provides an overview of the current understanding of heterocellular electrical communication in the heart. Although cardiac fibroblasts were initially thought to be electrical insulators, recent studies have demonstrated that they form functional electrical connections with CM in situ. Other NM, such as macrophages, have also been recognized as contributing to cardiac electrophysiology and arrhythmogenesis. Novel experimental tools have enabled the investigation of cell-specific activity patterns in native cardiac tissue, which is expected to yield exciting new insights into the development of novel or improved diagnostic and therapeutic strategies.

Angiogenin as a Possible Mediator of Macrophage-Mediated Regulation of Fibroblast Functions

We studied angiogenin production by human macrophages and evaluated the role of this factor in the macrophage-mediated regulation of fibroblasts. All macrophage subtypes, and especially the efferocytosis-polarized macrophages, M2(LS), actively produced angiogenin. Exogenous recombinant angiogenin dose-dependently enhanced the proliferation and differentiation of dermal fibroblasts. The addition of the angiogenin inhibitor to fibroblasts cultures suppressed the stimulating effect of exogenous angiogenin or M2(LS) conditioned media. These findings indicate the involvement of angiogenin in the macrophage-mediated paracrine regulation of skin fibroblasts.

Recent advances in strategies to target the behavior of macrophages in wound healing

Chronic wounds and scar formation are widespread due to limited suitable remedies. The macrophage is a crucial regulator in wound healing, controlling the onset and termination of inflammation and regulating other processes related to wound healing. The current breakthroughs in developing new medications and drug delivery methods have enabled the accurate targeting of macrophages in oncology and rheumatic disease therapies through clinical trials. These successes have cleared the way to utilize drugs targeting macrophages in various disorders. This review thus summarizes macrophage involvement in normal and pathologic wound healing. It further details the targets available for macrophage intervention and therapeutic strategies for targeting the behavior of macrophages in tissue repair and regeneration.

Multifunctional silk vinyl sulfone-based hydrogel scaffolds for dynamic material-cell interactions

Biochemical and mechanical interactions between cells and the surrounding extracellular matrix influence cell behavior and fate. Mimicking these features in vitro has prompted the design and development of biomaterials, with continuing efforts to improve tailorable systems that also incorporate dynamic chemical functionalities. The majority of these chemistries have been incorporated into synthetic biomaterials, here we focus on modifications of silk protein with dynamic features achieved via enzymatic, "click", and photo-chemistries. The one-pot synthesis of vinyl sulfone modified silk (SilkVS) can be tuned to manipulate the degree of functionalization. The resultant modified protein-based material undergoes three different gelation mechanisms, enzymatic, "click", and light-induced, to generate hydrogels for in vitro cell culture. Further, the versatility of this chemical functionality is exploited to mimic cell-ECM interactions via the incorporation of bioactive peptides and proteins or by altering the mechanical properties of the material to guide cell behavior. SilkVS is well-suited for use in in vitro culture, providing a natural protein with both tunable biochemistry and mechanics.

Human Macrophages Polarized by Interaction with Apoptotic Cells Produce Fibrosis-Associated Mediators and Enhance Pro-Fibrotic Activity of Dermal Fibroblasts In Vitro

Apoptosis and subsequent removal of dead cells are an essential part of wound healing. Macrophages phagocytize apoptotic cells (efferocytosis) and contribute to the resolution of inflammation. However, their participation in fibrogenesis and the mechanisms of influence on this process remain unclear. In the present study, we focused on the fibrogenic properties of human monocyte-derived macrophages polarized in the M2 direction by interaction with apoptotic cells. We studied their influence on the proliferation ([3H]-thymidine incorporation), differentiation (by the expression of α-SMA, a myofibroblast marker) and collagen-producing activity (ELISA) of dermal fibroblasts compared to classically (LPS) and alternatively (IL-4) activated macrophages. Macrophages polarized by the interaction with apoptotic cells had a unique phenotype and profile of produced factors and differed from the compared macrophage subtypes. Their conditioned media promoted the proliferation of dermal fibroblasts and the expression of α-SMA in them at the level of macrophages stimulated by IL-4, while the stimulating effect on the collagen-producing activity was more pronounced compared to that of the other macrophage subtypes. Moreover, they are characterized by the high level of production of pro-fibrotic factors such as TIMP-1, TGF-β1 and angiogenin. Taken together, M2-like macrophages polarized by efferocytosis demonstrate in vitro pro-fibrotic activity by promoting the functional activity of dermal fibroblasts and producing pro-fibrotic and pro-angiogenic factors.