Expression of α-Smooth Muscle Actin Determines the Fate of Mesenchymal Stromal Cells

Silencing of Nesprin-2 inhibits the differentiation of myofibroblasts from fibroblasts induced by mechanical stretch

Mechanical force plays a pivotal role in the pathogenesis of hypertrophic scar (HTS). Dermal fibroblasts and myofibroblasts are the key cells involved in HTS. Myofibroblasts in HTS possess different biochemical and biophysical characteristics by which myofibroblasts are often distinguished from fibroblasts. The role of mechanotransducers outside the nucleus in the pathogenesis of HTS has been reported in many studies. However, the role of Nesprin‐2 in HTS is not clear. Hence, we aim to construct a cell model of HTS and explore the role of Nesprin‐2 in this process. Myofibroblasts and fibroblasts were isolated from HTS and healthy skin tissues of the same patient. Fibroblasts were exposed to cyclic stretch with 10% magnitude and a frequency of 0.1 Hz for 3 days, 5 days, and 7 days, respectively. After the cell model was confirmed, fibroblasts transfected with siRNA targeting human Nesprin‐2 were exposed to cyclic stretch. The mechanical behaviour and biochemical reaction of the dermal fibroblasts were analysed. The stretched fibroblasts at day 5 showed the same mechanotransductive and biochemical features as unstretched myofibroblasts. Mechanical strain could induce the myofibroblasts differentiation and a cell model of HTS was established successfully at day 5. The expressions of lamin A/C, alpha‐smooth muscle actin, transforming growth factor beta 1, and collagen type I in fibroblasts were reduced by the silencing of Nesprin‐2. Mechanical strain could induce the myofibroblasts differentiation and silencing of Nesprin‐2 could block the mechanical stimulation of terminal myofibroblasts differentiation. Nesprin‐2 might be a potential target to treat the HTS.

Mechanotransductive Differentiation of Hair Follicle Stem Cells Derived from Aged Eyelid Skin into Corneal Endothelial-Like Cells

Corneal endothelial insufficiency is one of the leading causes of blindness. The main contemporary treatment for corneal blindness is endothelial keratoplasty, which, however, is unsatisfactory as a medical therapy due to the lack of donor corneas and graft rejection. Therefore, autologous stem cell-based corneal endothelial tissue substitutes may be a promising alternative to conventional grafts in the future. To address the age of most patients suffering from corneal endothelial deficiencies, we investigated the presence and potential of hair-derived stem cells from older tissue donors. Our studies revealed the presence of pluripotency- and neural crest-associated markers in tissue sections from blepharoplasty patients aged 50 to 80 years. In vitro outgrowths from eyelid hair follicles on collagen-coated tissue culture plates revealed a weak decrease in stem-cell potency. In contrast, cells within the spheres that spontaneously formed from the adherent cell layer retained full stem-cell potency and could be differentiated into cells of the ecto- meso and endodermal lineages. Although these highly potent hair follicle derived stem cells (HFSC) were only very slightly expandable, they were able to recognize the biomimicry of the Descemet’s-like topography and differentiate into corneal endothelial-like cells. In conclusion, HFSCs derived from epidermal skin of eyelid biopsies are a promising cell source to provide autologous corneal endothelial replacement for any age group of patients.

Implant Fibrosis and the Underappreciated Role of Myofibroblasts in the Foreign Body Reaction

Body implants and implantable medical devices have dramatically improved and prolonged the life of countless patients. However, our body repair mechanisms have evolved to isolate, reject, or destroy any object that is recognized as foreign to the organism and inevitably mounts a foreign body reaction (FBR). Depending on its severity and chronicity, the FBR can impair implant performance or create severe clinical complications that will require surgical removal and/or replacement of the faulty device. The number of review articles discussing the FBR seems to be proportional to the number of different implant materials and clinical applications and one wonders, what else is there to tell? We will here take the position of a fibrosis researcher (which, coincidentally, we are) to elaborate similarities and differences between the FBR, normal wound healing, and chronic healing conditions that result in the development of peri-implant fibrosis. After giving credit to macrophages in the inflammatory phase of the FBR, we will mainly focus on the activation of fibroblastic cells into matrix-producing and highly contractile myofibroblasts. While fibrosis has been discussed to be a consequence of the disturbed and chronic inflammatory milieu in the FBR, direct activation of myofibroblasts at the implant surface is less commonly considered. Thus, we will provide a perspective how physical properties of the implant surface control myofibroblast actions and accumulation of stiff scar tissue. Because formation of scar tissue at the surface and around implant materials is a major reason for device failure and extraction surgeries, providing implant surfaces with myofibroblast-suppressing features is a first step to enhance implant acceptance and functional lifetime. Alternative therapeutic targets are elements of the myofibroblast mechanotransduction and contractile machinery and we will end with a brief overview on such targets that are considered for the treatment of other organ fibroses.

Functions of Matricellular Proteins in Dental Tissues and Their Emerging Roles in Orofacial Tissue Development, Maintenance, and Disease

Matricellular proteins (MCPs) are defined as extracellular matrix (ECM) associated proteins that are important regulators and integrators of microenvironmental signals, contributing to the dynamic nature of ECM signalling. There is a growing understanding of the role of matricellular proteins in cellular processes governing tissue development as well as in disease pathogenesis. In this review, the expression and functions of different MP family members (periostin, CCNs, TSPs, SIBLINGs and others) are presented, specifically in relation to craniofacial development and the maintenance of orofacial tissues, including bone, gingiva, oral mucosa, palate and the dental pulp. As will be discussed, each MP family member has been shown to have non-redundant roles in development, tissue homeostasis, wound healing, pathology and tumorigenesis of orofacial and dental tissues.

Systemic sclerosis skin is a primed microenvironment for soft tissue calcification-a hypothesis

Calcinosis cutis, defined as sub-epidermal deposition of calcium salts, is a major clinical problem in patients with SSc, affecting 20-40% of patients. A number of recognized factors associated with calcinosis have been identified, including disease duration, digital ischaemia and acro-osteolysis. Yet, to date, the pathogenesis of SSc-related calcinosis remains unknown, and currently there is no effective disease-modifying pharmacotherapy. Following onset of SSc, there are marked changes in the extracellular matrix (ECM) of the skin, notably a breakdown in the microfibrillar network and accumulation of type I collagen. Our hypothesis is that these pathological changes reflect a changing cellular phenotype and result in a primed microenvironment for soft tissue calcification, with SSc fibroblasts adopting a pro-osteogenic profile, and specific driving forces promoting tissue mineralization. Considering the role of the ECM in disease progression may help elucidate the mechanism(s) behind SSc-related calcinosis and inform the development of future therapeutic interventions.

Novel factors that activate and deactivate cardiac fibroblasts: A new perspective for treatment of cardiac fibrosis

Heart disease with attendant cardiac fibrosis kills more patients in developed countries than any other disease, including cancer. We highlight the recent literature on factors that activate and also deactivate cardiac fibroblasts. Activation of cardiac fibroblasts results in myofibroblasts phenotype which incorporates aSMA to stress fibres, express ED-A fibronectin, elevated PDGFRα and are hypersecretory ECM components. These cells facilitate both acute wound healing (infarct site) and chronic cardiac fibrosis. Quiescent fibroblasts are associated with normal myocardial tissue and provide relatively slow turnover of the ECM. Deactivation of activated myofibroblasts is a much less studied phenomenon. In this context, SKI is a known negative regulator of TGFb₁ /Smad signalling, and thus may share functional similarity to PPARγ activation. The discovery of SKI's potent anti-fibrotic role, and its ability to deactivate and/or myofibroblasts is featured and contrasted with PPARγ. While myofibroblasts are typically recruited from pools of potential precursor cells in a variety of organs, the importance of activation of resident cardiac fibroblasts has been recently emphasised. Myofibroblasts deposit ECM components at an elevated rate and contribute to both systolic and diastolic dysfunction with attendant cardiac fibrosis. A major knowledge gap exists as to specific proteins that may signal for fibroblast deactivation. As SKI may be a functionally pluripotent protein, we suggest that it serves as a scaffold to proteins other than R-Smads and associated Smad signal proteins, and thus its anti-fibrotic effects may extend beyond binding R-Smads. While cardiac fibrosis is causal to heart failure, the treatment of cardiac fibrosis is hampered by the lack of availability of effective pharmacological anti-fibrotic agents. The current review will provide an overview of work highlighting novel factors which cause fibroblast activation and deactivation to underscore putative therapeutic avenues for improving disease outcomes in cardiac patients with fibrosed hearts.

Decreased Substrate Stiffness Promotes a Hypofibrotic Phenotype in Cardiac Fibroblasts

A hypofibrotic phenotype has been observed in cardiac fibroblasts (CFs) isolated from a volume overload heart failure model, aortocaval fistula (ACF). This paradoxical phenotype results in decreased ECM synthesis despite increased TGF-β presence. Since ACF results in decreased tissue stiffness relative to control (sham) hearts, this study investigates whether the effects of substrate stiffness could account for the observed hypofibrotic phenotype in CFs isolated from ACF. CFs isolated from ACF and sham hearts were plated on polyacrylamide gels of a range of stiffness (2 kPa to 50 kPa). Markers related to cytoskeletal and fibrotic proteins were measured. Aspects of the hypofibrotic phenotype observed in ACF CFs were recapitulated by sham CFs on soft substrates. For instance, sham CFs on the softest gels compared to ACF CFs on the stiffest gels results in similar CTGF (0.80 vs. 0.76) and transgelin (0.44 vs. 0.57) mRNA expression. The changes due to stiffness may be explained by the observed decreased nuclear translocation of transcriptional regulators, MRTF-A and YAP. ACF CFs appear to have a mechanical memory of a softer environment, supported by a hypofibrotic phenotype overall compared to sham with less YAP detected in the nucleus, and less CTGF and transgelin on all stiffnesses.

Stabilization of Damaged Articular Cartilage with Hydrogel-Mediated Reinforcement and Sealing

Cartilage injuries and subsequent tissue deterioration impact millions of patients. Since the regeneration of functional hyaline cartilage remains elusive, methods to stabilize the remaining tissue, and prevent further deterioration, would be of significant clinical utility and prolong joint function. Finite element modeling shows that fortification of the degenerate cartilage (Reinforcement) and reestablishment of a superficial zone (Sealing) are both required to restore fluid pressurization within the tissue and restrict fluid flow and matrix loss from the defect surface. Here, a hyaluronic acid (HA) hydrogel system is designed to both interdigitate with and promote the sealing of the degenerated cartilage. Interdigitating fortification restores both bulk and local pericellular tissue mechanics, reestablishing the homeostatic mechanotransduction of endogenous chondrocytes within the tissue. This HA therapy is further functionalized to present chemo mechanical cues that improve the attachment and direct the response of mesenchymal stem/stromal cells at the defect site, guiding localized extracellular matrix deposition to "seal" the defect. Together, these results support the therapeutic potential, across cell and tissue length scales, of an innovative hydrogel therapy for the treatment of damaged cartilage.

A single-cell atlas of human teeth

Teeth exert fundamental functions related to mastication and speech. Despite their great biomedical importance, an overall picture of their cellular and molecular composition is still missing. In this study, we have mapped the transcriptional landscape of the various cell populations that compose human teeth at single-cell resolution, and we analyzed in deeper detail their stem cell populations and their microenvironment. Our study identified great cellular heterogeneity in the dental pulp and the periodontium. Unexpectedly, we found that the molecular signatures of the stem cell populations were very similar, while their respective microenvironments strongly diverged. Our findings suggest that the microenvironmental specificity is a potential source for functional differences between highly similar stem cells located in the various tooth compartments and open new perspectives toward cell-based dental therapeutic approaches.

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Dental atlas of the pulp and periodontal tissues of human teeth

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Identification of three common MSC subclusters between dental pulp and periodontium

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Dental pulp and periodontal MSCs are similar, and their niches diverge

SKI activates the Hippo pathway via LIMD1 to inhibit cardiac fibroblast activation

We have previously shown that overexpression of SKI, an endogenous TGF-β₁ repressor, deactivates the pro-fibrotic myofibroblast phenotype in the heart. We now show that SKI also functions independently of SMAD/TGF-β signaling, by activating the Hippo tumor-suppressor pathway and inhibiting the Transcriptional co-Activator with PDZ-binding motif (TAZ or WWTR1). The mechanism(s) by which SKI targets TAZ to inhibit cardiac fibroblast activation and fibrogenesis remain undefined. A rat model of post-myocardial infarction was used to examine the expression of TAZ during acute fibrogenesis and chronic heart failure. Results were then corroborated with primary rat cardiac fibroblast cell culture performed both on plastic and on inert elastic substrates, along with the use of siRNA and adenoviral expression vectors for active forms of SKI, YAP, and TAZ. Gene expression was examined by qPCR and luciferase assays, while protein expression was examined by immunoblotting and fluorescence microscopy. Cell phenotype was further assessed by functional assays. Finally, to elucidate SKI’s effects on Hippo signaling, the SKI and TAZ interactomes were captured in human cardiac fibroblasts using BioID2 and mass spectrometry. Potential interactors were investigated in vitro to reveal novel mechanisms of action for SKI. In vitro assays on elastic substrates revealed the ability of TAZ to overcome environmental stimuli and induce the activation of hypersynthetic cardiac myofibroblasts. Further cell-based assays demonstrated that SKI causes specific proteasomal degradation of TAZ, but not YAP, and shifts actin cytoskeleton dynamics to inhibit myofibroblast activation. These findings were supported by identifying the bi-phasic expression of TAZ in vivo during post-MI remodeling and fibrosis. BioID2-based interactomics in human cardiac fibroblasts suggest that SKI interacts with actin-modifying proteins and with LIM Domain-containing protein 1 (LIMD1), a negative regulator of Hippo signaling. Furthermore, we found that LATS2 interacts with TAZ, whereas LATS1 does not, and that LATS2 knockdown prevented TAZ downregulation with SKI overexpression. Our findings indicate that SKI’s capacity to regulate cardiac fibroblast activation is mediated, in part, by Hippo signaling. We postulate that the interaction between SKI and TAZ in cardiac fibroblasts is arbitrated by LIMD1, an important intermediary in focal adhesion-associated signaling pathways. This study contributes to the understanding of the unique physiology of cardiac fibroblasts, and of the relationship between SKI expression and cell phenotype.

Excess TGF-β1 Drives Cardiac Mesenchymal Stromal Cells to a Pro-Fibrotic Commitment in Arrhythmogenic Cardiomyopathy

Arrhythmogenic Cardiomyopathy (ACM) is characterized by the replacement of the myocardium with fibrotic or fibro-fatty tissue and inflammatory infiltrates in the heart. To date, while ACM adipogenesis is a well-investigated differentiation program, ACM-related fibrosis remains a scientific gap of knowledge. In this study, we analyze the fibrotic process occurring during ACM pathogenesis focusing on the role of cardiac mesenchymal stromal cells (C-MSC) as a source of myofibroblasts. We performed the ex vivo studies on plasma and right ventricular endomyocardial bioptic samples collected from ACM patients and healthy control donors (HC). In vitro studies were performed on C-MSC isolated from endomyocardial biopsies of both groups. Our results revealed that circulating TGF-β1 levels are significantly higher in the ACM cohort than in HC. Accordingly, fibrotic markers are increased in ACM patient-derived cardiac biopsies compared to HC ones. This difference is not evident in isolated C-MSC. Nevertheless, ACM C-MSC are more responsive than HC ones to TGF-β1 treatment, in terms of pro-fibrotic differentiation and higher activation of the SMAD2/3 signaling pathway. These results provide the novel evidence that C-MSC are a source of myofibroblasts and participate in ACM fibrotic remodeling, being highly responsive to ACM-characteristic excess TGF-β1.

Hypoxia Mesenchymal Stem Cells Accelerate Wound Closure Improvement by Controlling α-smooth Muscle actin Expression in the Full-thickness Animal Model

BACKGROUND: The active myofibroblast producing extracellular matrix deposition regarding wound closure is characterized by alpha-smooth muscle actin (α-SMA) expression. However, the persistence of α-SMA expression due to prolonged inflammation may trigger scar formation. A new strategy to control α-SMA expression in line with wound closure improvement uses hypoxic mesenchymal stem cells (HMSCs) due to their ability to firmly control inflammation for early initiating cell proliferation, including the regulation of α-SMA expression associated with wound closure acceleration. AIM: This study aimed to explore the role of HMSCs in accelerating the optimum wound closure percentages through controlling the α-SMA expression. MATERIALS AND METHODS: Twenty-four full-thickness rats wound model were randomly divided into four groups: Sham (Sh), Control (C) by NaCl administration only, and two treatment groups by HMSCs at doses of 1.5×106 cells (T1) and HMSCs at doses of 3×106 cells (T2). HMSCs were incubated under hypoxic conditions. The α-SMA expression was analyzed under immunohistochemistry staining assay, and the wound closure percentage was analyzed by ImageJ software. RESULTS: This study showed a significant increase in wound closure percentage in all treatment groups that gradually initiated on days 6 and 9 (p < 0.05). In line with the increase of wound closure percentages on day 9, there was also a significant decrease in α-SMA expression in all treatment groups (p < 0.05), indicating the optimum wound healing has preceded. CONCLUSION: HMSCs have a robust ability to accelerated wound closure improvement to the optimum wound healing by controlling α-SMA expression depending on wound healing phases.

Keloid disorder: Fibroblast differentiation and gene expression profile in fibrotic skin diseases

Keloid disorder, a group of fibroproliferative skin diseases, is characterized by unremitting accumulation of the extracellular matrix (ECM) of connective tissue, primarily collagen, to develop cutaneous tumors on the predilection sites of skin. There is a strong genetic predisposition for keloid formation, and individuals of African and Asian ancestry are particularly prone. The principal cell type responsible for ECM accumulation is the myofibroblast derived from quiescent resident skin fibroblasts either through trans-differentiation or from keloid progenitor stem cells with capacity for multi-lineage differentiation and self-renewal. The biosynthetic pathways leading to ECM accumulation are activated by several cytokines, but particularly by TGF-β signalling. The mechanical properties of the cellular microenvironment also play a critical role in the cell's response to TGF-β, as demonstrated by culturing of fibroblasts derived from keloids and control skin on substrata with different degrees of stiffness. These studies also demonstrated that culturing of fibroblasts on tissue culture plastic in vitro does not reflect their biosynthetic capacity in vivo. Collectively, our current understanding of the pathogenesis of keloids suggests a complex network of interacting cellular, molecular and mechanical factors, with distinct pathways leading to myofibroblast differentiation and activation. Keloids can serve as a model system of fibrotic diseases, a group of currently intractable disorders, and deciphering of the critical pathogenetic steps leading to ECM accumulation is expected to identify targets for pharmacologic intervention, not only for keloids but also for a number of other, both genetic and acquired, fibrotic diseases.

miR-127-3p Is an Epigenetic Activator of Myofibroblast Senescence Situated within the MicroRNA-Enriched Dlk1-Dio3‒Imprinted Domain on Mouse Chromosome 12

During wound healing, fibroblasts differentiate into nonproliferative contractile myofibroblasts, contribute to skin repair, and eventually undergo apoptosis or become senescent. MicroRNAs are post-transcriptional regulators of gene expression networks that control cell fate and survival and may also regulate senescence. In this study, we determined the regulated microRNAs in myofibroblasts isolated from wounds and analyzed their role in senescent myofibroblast formation. Transcriptome profiling showed that a 200 kilobase pair region of the Dlk1-Dio3‒imprinted domain on mouse chromosome 12 encodes for most of the upregulated microRNAs in the entire genome of mouse myofibroblasts. Among those, miR-127-3p induced a myofibroblast-like phenotype associated with a block in proliferation. Molecular analysis revealed that miR-127-3p induced a prolonged cell cycle arrest with unique molecular features of senescence, including the activation of the senescence-associated β-galactosidase, increase in p53 and p21 levels, inhibition of lamin B1, proliferation factors, and the production of senescence-associated inflammatory and extracellular matrix‒remodeling components. Hence, miR-127-3p emerges as an epigenetic activator regulating the transition from repair to remodeling during skin wound healing but may also induce age-related defects, pathological scarring, and fibrosis, all linked to myofibroblast senescence.

Isolation and characterization of mesenchymal stem cells in orthopaedics and the emergence of compact bone mesenchymal stem cells as a promising surgical adjunct

The potential clinical and economic impact of mesenchymal stem cell (MSC) therapy is immense. MSCs act through multiple pathways: (1) as “trophic” cells, secreting various factors that are immunomodulatory, anti-inflammatory, anti-apoptotic, proangiogenic, proliferative, and chemoattractive; (2) in conjunction with cells native to the tissue they reside in to enhance differentiation of surrounding cells to facilitate tissue regrowth. Researchers have developed methods for the extraction and expansion of MSCs from animal and human tissues. While many sources of MSCs exist, including adipose tissue and iliac crest bone graft, compact bone (CB) MSCs have shown great potential for use in orthopaedic surgery. CB MSCs exert powerful immunomodulatory effects in addition to demonstrating excellent regenerative capacity for use in filling boney defects. CB MSCs have been shown to have enhanced response to hypoxic conditions when compared with other forms of MSCs. More work is needed to continue to characterize the potential applications for CB MSCs in orthopaedic trauma.

Steering cell behavior through mechanobiology in 3D: A regenerative medicine perspective

Mechanobiology, translating mechanical signals into biological ones, greatly affects cellular behavior. Steering cellular behavior for cell-based regenerative medicine approaches requires a thorough understanding of the orchestrating molecular mechanisms, among which mechanotransducive ones are being more and more elucidated. Because of their wide use and highly mechanotransduction dependent differentiation, this review focuses on mesenchymal stromal cells (MSCs), while also briefly relating the discussed results to other cell types. While the mechanotransduction pathways are relatively well-studied in 2D, much remains unknown of the role and regulation of these pathways in 3D. Ultimately, cells need to be cultured in a 3D environment to create functional de novo tissue. In this review, we explore the literature on the roles of different material properties on cellular behavior and mechanobiology in 2D and 3D. For example, while stiffness plays a dominant role in 2D MSCs differentiation, it seems to be of subordinate importance in 3D MSCs differentiation, where matrix remodeling seems to be key. Also, the role and regulation of some of the main mechanotransduction players are discussed, focusing on MSCs. We have only just begun to fundamentally understand MSCs and other stem cells behavior in 3D and more fundamental research is required to advance biomaterials able to replicate the stem cell niche and control cell activity. This better understanding will contribute to smarter tissue engineering scaffold design and the advancement of regenerative medicine.

High Mannose N-Glycans Promote Migration of Bone-Marrow-Derived Mesenchymal Stromal Cells

For hundreds of indications, mesenchymal stromal cells (MSCs) have not achieved the expected therapeutic efficacy due to an inability of the cells to reach target tissues. We show that inducing high mannose N-glycans either chemically, using the mannosidase I inhibitor Kifunensine, or genetically, using an shRNA to silence the expression of mannosidase I A1 (MAN1A1), strongly increases the motility of MSCs. We show that treatment of MSCs with Kifunensine increases cell migration toward bone fracture sites after percutaneous injection, and toward lungs after intravenous injection. Mechanistically, high mannose N-glycans reduce the contact area of cells with its substrate. Silencing MAN1A1 also makes cells softer, suggesting that an increase of high mannose N-glycoforms may change the physical properties of the cell membrane. To determine if treatment with Kifunensine is feasible for future clinical studies, we used mass spectrometry to analyze the N-glycan profile of MSCs over time and demonstrate that the effect of Kifunensine is both transitory and at the expense of specific N-glycoforms, including fucosylations. Finally, we also investigated the effect of Kifunensine on cell proliferation, differentiation, and the secretion profile of MSCs. Our results support the notion of inducing high mannose N-glycans in MSCs in order to enhance their migration potential.

Extracellular matrix stiffness determines DNA repair efficiency and cellular sensitivity to genotoxic agents

DNA double-strand breaks (DSBs) are highly toxic lesions that can drive genetic instability. These lesions also contribute to the efficacy of radiotherapy and many cancer chemotherapeutics. DNA repair efficiency is regulated by both intracellular and extracellular chemical signals. However, it is largely unknown whether this process is regulated by physical stimuli such as extracellular mechanical signals. Here, we report that DSB repair is regulated by extracellular mechanical signals. Low extracellular matrix (ECM) stiffness impairs DSB repair and renders cells sensitive to genotoxic agents. Mechanistically, we found that the MAP4K4/6/7 kinases are activated and phosphorylate ubiquitin in cells at low stiffness. Phosphorylated ubiquitin impairs RNF8-mediated ubiquitin signaling at DSB sites, leading to DSB repair deficiency. Our results thus demonstrate that ECM stiffness regulates DSB repair efficiency and genotoxic sensitivity through MAP4K4/6/7 kinase-mediated ubiquitin phosphorylation, providing a previously unidentified regulation in DSB-induced ubiquitin signaling.

Adipose stem cells exhibit mechanical memory and reduce fibrotic contracture in a rat elbow injury model

Fibrosis is driven by a misdirected cell response causing the overproduction of extracellular matrix and tissue dysfunction. Numerous pharmacological strategies have attempted to prevent fibrosis but have attained limited efficacy with some detrimental side effects. While stem cell treatments have provided more encouraging results, they have exhibited high variability and have not always improved tissue function. To enhance stem cell efficacy, we evaluated whether mechanical memory could direct cell response. We hypothesized that mechanically pre-conditioning on a soft matrix (soft priming) will delay adipose-derived stem cell (ASC) transition to a pro-fibrotic phenotype, expanding their regenerative potential, and improving healing in a complex tissue environment. Primary ASCs isolated from rat and human subcutaneous fat exhibited mechanical memory, demonstrated by a delayed cell response to stiffness following two weeks of soft priming including decreased cell area, actin coherency, and extracellular matrix production compared to cells on stiff substrates. Soft primed ASCs injected into our rat model of post-traumatic elbow contracture decreased histological evidence of anterior capsule fibrosis and increased elbow range-of-motion when evaluated by joint mechanics. These findings suggest that exploiting mechanical memory by strategically controlling the culture environment during cell expansion may improve the efficacy of stem cell-based therapies targeting fibrosis.

A Complex and Evolutive Character: Two Face Aspects of ECM in Tumor Progression

Tumor microenvironment, including extracellular matrix (ECM) and stromal cells, is a key player during tumor development, from initiation, growth and progression to metastasis. During all of these steps, remodeling of matrix components occurs, changing its biochemical and physical properties. The global and basic cancer ECM model is that tumors are surrounded by activated stromal cells, that remodel physiological ECM to evolve into a stiffer and more crosslinked ECM than in normal conditions, thereby increasing invasive capacities of cancer cells. In this review, we show that this too simple model does not consider the complexity, specificity and heterogeneity of each organ and tumor. First, we describe the general ECM in context of cancer. Then, we go through five invasive and most frequent cancers from different origins (breast, liver, pancreas, colon, and skin), and show that each cancer has its own specific matrix, with different stromal cells, ECM components, biochemical properties and activated signaling pathways. Furthermore, in these five cancers, we describe the dual role of tumor ECM: as a protective barrier against tumor cell proliferation and invasion, and as a major player in tumor progression. Indeed, crosstalk between tumor and stromal cells induce changes in matrix organization by remodeling ECM through invadosome formation in order to degrade it, promoting tumor progression and cell invasion. To sum up, in this review, we highlight the specificities of matrix composition in five cancers and the necessity not to consider the ECM as one general and simple entity, but one complex, dynamic and specific entity for each cancer type and subtype.

Bone marrow mesenchymal stem cells in microenvironment transform into cancer-associated fibroblasts to promote the progression of B-cell acute lymphoblastic leukemia

Bone marrow microenvironment is essential for leukemia cells to survive and escape the killing effect of chemotherapeutics. Cancer-associated fibroblasts (CAFs) are the dominant stromal cells in tumor microenvironment (TME), but their role in B-cell acute lymphoblastic leukemia (B-ALL) remains unclear. Here, RT-PCR and Western blotting in bone marrow mononuclear cells revealed higher proportions of CAFs markers α-SMA and FAP in the newly diagnosed and relapsed B-ALL patients. In vitro experiments, bone marrow mesenchymal stem cells (BM-MSCs) acquired a CAFs phenotype after co-culture with leukemia cells, which produced high level of tumor-promoting growth factors and reduced the daunorubicin (DNR)-induced damage to B-ALL cells. As for its mechanism, CAFs activation was mediated by TGF-β up-regulation in the co-culture system, and TGF-β triggered MSCs conversion into CAFs relying on the SDF-1/CXCR4 pathway. Further LY2109761 and AMD3100 effectively decreased the activation of CAFs through inhibiting TGF-β receptor and CXCR4. Comparative experiments with MSCs and transformed CAFs prompted that CAFs had more obvious effect than MSCs on stimulating leukemia progression through accelerating leukemia cell migration and invasion. These results clarified the important role of CAFs in B-ALL progression and the possible mechanisms of CAFs activation in leukemia microenvironment, which might provide a theoretical basis for B-ALL patients to find more effective targeted therapies targeting the bone marrow microenvironment.

Periostin and matrix stiffness combine to regulate myofibroblast differentiation and fibronectin synthesis during palatal healing

Although the matricellular protein periostin is prominently upregulated in skin and gingival healing, it plays contrasting roles in myofibroblast differentiation and matrix synthesis respectively. Palatal healing is associated with scarring that can alter or restrict maxilla growth, but the expression pattern and contribution of periostin in palatal healing is unknown. Using periostin-knockout (Postn^-/-) and wild-type (WT) mice, the contribution of periostin to palatal healing was investigated through 1.5 mm full-thickness excisional wounds in the hard palate. In WT mice, periostin was upregulated 6 days post-wounding, with mRNA levels peaking at day 12. Genetic deletion of periostin significantly reduced wound closure rates compared to WT mice. Absence of periostin reduced mRNA levels of pivotal genes in wound repair, including α-SMA/acta2, fibronectin and βigh3. Recruitment of fibroblasts and inflammatory cells, as visualized by immunofluorescent staining for fibroblast specific factor-1, vimentin, and macrophages markers Arginase-1 and iNOS was also impaired in Postn^-/-, but not WT mice. Palatal fibroblasts isolated from the hard palate of mice were cultured on collagen gels and prefabricated silicon substrates with varying stiffness. Postn^-/- fibroblasts showed a significantly reduced ability to contract a collagen gel, which was rescued by the exogenous addition of recombinant periostin. As the stiffness increased, Postn^-/- fibroblasts increasingly differentiated into myofibroblasts, but not to the same degree as the WT. Pharmacological inhibition of Rac rescued the deficient myofibroblastic phenotype of Postn^-/- cells. Low stiffness substrates (0.2 kPa) resulted in upregulation of fibronectin in WT cells, an effect which was significantly reduced in Postn^-/- cells. Quantification of immunostaining for vinculin and integrinβ1 adhesions revealed that Periostin is required for the formation of focal and fibrillar adhesions in mPFBs. Our results suggest that periostin modulates myofibroblast differentiation and contraction via integrinβ1/RhoA pathway, and fibronectin synthesis in an ECM stiffness dependent manner in palatal healing.

Characterization of rodent Sertoli cell primary cultures

Sertoli cells play a vital role in spermatogenesis by offering physical and nutritional support to the differentiating male germ cells. They form the blood-testis barrier and secrete growth factors essential for germ cell differentiation. Sertoli cell primary cultures are critical for understanding the regulation of spermatogenesis; however, obtaining pure cultures has been a challenge. Rodent Sertoli cell isolation protocols do not rule out contamination by the interstitial or connective tissue cells. Sertoli cell-specific markers could be helpful, but there is no consensus. Vimentin, the most commonly used marker, is not specific for Sertoli cells since its expression has been reported in peritubular myoid cells, mesenchymal stem cells, fibroblasts, macrophages, and endothelial cells, which contaminate Sertoli cell preparations. Markers based on transcription and growth factors also have limitations. Thus, the impediment to obtaining pure Sertoli cell cultures pertains to both the method of isolation and marker usage. The aim of this review is to discuss improvements to current methods of rodent Sertoli cell primary cultures, assess the properties of prepubertal versus mature Sertoli cell cultures, and propose steps to improve cellular characterization. Potential benefits of using contemporary approaches, including lineage tracing, specific cell ablation, and RNA-seq for obtaining Sertoli-specific transcript markers are discussed. Evaluating the specificity and applicability of these markers at the protein level to characterize Sertoli cells in culture would be critical. This review is expected to positively impact future work using primary cultures of rodent Sertoli cells.

Cancer-associated fibroblasts mediate cancer progression and remodel the tumouroid stroma

Background

Cancer-associated fibroblasts (CAFs) are highly differentiated and heterogeneous cancer-stromal cells that promote tumour growth, angiogenesis and matrix remodelling.

Methods

We utilised an adapted version of a previously developed 3D in vitro model of colorectal cancer, composed of a cancer mass and the surrounding stromal compartment. We compared cancer invasion with an acellular stromal surround, a “healthy” or normal cellular stroma and a cancerous stroma. For the cancerous stroma, we incorporated six patient-derived CAF samples to study their differential effects on cancer growth, vascular network formation and remodelling.

Results

CAFs enhanced the distance and surface area of the invasive cancer mass whilst inhibiting vascular-like network formation. These processes correlated with the upregulation of hepatocyte growth factor (HGF), metallopeptidase inhibitor 1 (TIMP1) and fibulin-5 (FBLN5). Vascular remodelling of previously formed endothelial structures occurred through the disruption of complex networks, and was associated with the upregulation of vascular endothelial growth factor (VEGFA) and downregulation in vascular endothelial cadherin (VE-Cadherin).

Conclusions

These results support, within a biomimetic 3D, in vitro framework, the direct role of CAFs in promoting cancer invasion, and their key function in driving vasculogenesis and angiogenesis.

Inflammation Differentially Modulates the Biological Features of Adult Derived Human Liver Stem/Progenitor Cells

The progression of mesenchymal stem cell-based therapy from concept to cure closely depends on the optimization of conditions that allow a better survival and favor the cells to achieve efficient liver regeneration. We have previously demonstrated that adult-derived human liver stem/progenitor cells (ADHLSC) display significant features that support their clinical development. The current work aims at studying the impact of a sustained pro-inflammatory environment on the principal biological features of ADHLSC in vitro. METHODS: ADHLSC from passages 4–7 were exposed to a cocktail of inflammatory cytokines for 24 h and 9 days and subsequently analyzed for their viability, expression, and secretion profiles by using flow cytometry, RT-qPCR, and antibody array assay. The impact of inflammation on the hepatocytic differentiation potential of ADHLSC was also evaluated. RESULTS: ADHLSC treated with a pro-inflammatory cocktail displayed significant decrease of cell yield at both times of treatment while cell mortality was observed at 9 days post-priming. After 24 h, no significant changes in the immuno-phenotype of ADHLSC expression profile could be noticed while after 9 days, the expression profile of relevant markers has changed both in the basal conditions and after inflammation treatment. Inflammation cocktail enhanced the release of IL-6, IL-8, CCL5, monocyte-chemo-attractant protein-2 and 3, CXCL1/GRO, and CXCL5/ENA78. Furthermore, while IP-10 secretion was increased after 24 h priming, granulocyte macrophage colony-stimulating factor enhanced secretion was noticed after 9 days treatment. Finally, priming of ADHLSC did not affect their potential to differentiate into hepatocyte-like cells. CONCLUSION: These results indicate that ADHLSCs are highly sensitive to inflammation and respond to such signals by adjusting their gene and protein expression. Accordingly, monitoring the inflammatory status of patients at the time of cell transplantation, will certainly help in enhancing ADHLSC safety and efficiency.

miR-1323 suppresses bone mesenchymal stromal cell osteogenesis and fracture healing via inhibiting BMP4/SMAD4 signaling

Background

Atrophic non-union fractures show no radiological evidence of callus formation within 3 months of fracture. microRNA dysregulation may underlie the dysfunctional osteogenesis in atrophic non-union fractures. Here, we aimed to analyze miR-1323 expression in human atrophic non-union fractures and examine miR-1323’s underlying mechanism of action in human mesenchymal stromal cells.

Methods

Human atrophic non-union and standard healing fracture specimens were examined using H&E and Alcian Blue staining, immunohistochemistry, qRT-PCR, immunoblotting, and ALP activity assays. The effects of miR-1323 mimics or inhibition on BMP4, SMAD4, osteogenesis-related proteins, ALP activity, and bone mineralization were analyzed in human mesenchymal stromal cells. Luciferase reporter assays were utilized to assay miR-1323’s binding to the 3'UTRs of BMP4 and SMAD4. The effects of miR-1323, BMP4, and SMAD4 were analyzed by siRNA and overexpression vectors. A rat femur fracture model was established to analyze the in vivo effects of antagomiR-1323 treatment.

Results

miR-1323 was upregulated in human atrophic non-union fractures. Atrophic non-union was associated with downregulation of BMP4 and SMAD4 as well as the osteogenic markers ALP, collagen I, and RUNX2. In vitro, miR-1323 suppressed BMP4 and SMAD4 expression by binding to the 3'UTRs of BMP4 and SMAD4. Moreover, miR-1323’s inhibition of BMP4 and SMAD4 inhibited mesenchymal stromal cell osteogenic differentiation via modulating the nuclear translocation of the transcriptional co-activator TAZ. In vivo, antagomiR-1323 therapy facilitated the healing of fractures in a rat model of femoral fracture.

Conclusions

This evidence supports the miR-1323/BMP4 and miR-1323/SMAD4 axes as novel therapeutic targets for atrophic non-union fractures.

Drebrin is induced during myofibroblast differentiation and enhances the production of fibrosis-related genes

Fibrosis is attributed to excess deposition of extracellular matrix (ECM) proteins including collagen and is associated with various organ dysfunction. This excessive ECM is produced by myofibroblasts, which are differentiated from various cells by a variety of stimuli, represented by TGF-β. However, molecular mechanisms for the regulation of ECM production in myofibroblasts remain obscure. In this study, we demonstrate that the expression of drebrin, which binds to and increases the stability of actin filament in neurons, is increased in mouse hearts and lungs upon fibrosis. Drebrin is mainly expressed in myofibroblasts in the fibrotic hearts and lungs and promotes the expression of fibrosis-related genes, such as Acta2 and Col1a1. Taken together, our study identifies drebrin as a molecule that promotes the production of fibrosis-related genes in myofibroblasts.

Collagen microarchitecture mechanically controls myofibroblast differentiation

Altered microarchitecture of collagen type I is a hallmark of wound healing and cancer that is commonly attributed to myofibroblasts. However, it remains unknown which effect collagen microarchitecture has on myofibroblast differentiation. Here, we combined experimental and computational approaches to investigate the hypothesis that the microarchitecture of fibrillar collagen networks mechanically regulates myofibroblast differentiation of adipose stromal cells (ASCs) independent of bulk stiffness. Collagen gels with controlled fiber thickness and pore size were microfabricated by adjusting the gelation temperature while keeping their concentration constant. Rheological characterization and simulation data indicated that networks with thicker fibers and larger pores exhibited increased strain-stiffening relative to networks with thinner fibers and smaller pores. Accordingly, ASCs cultured in scaffolds with thicker fibers were more contractile, expressed myofibroblast markers, and deposited more extended fibronectin fibers. Consistent with elevated myofibroblast differentiation, ASCs in scaffolds with thicker fibers exhibited a more proangiogenic phenotype that promoted endothelial sprouting in a contractility-dependent manner. Our findings suggest that changes of collagen microarchitecture regulate myofibroblast differentiation and fibrosis independent of collagen quantity and bulk stiffness by locally modulating cellular mechanosignaling. These findings have implications for regenerative medicine and anticancer treatments.

Human umbilical cord mesenchymal stem cell-derived exosomes suppress dermal fibroblasts-myofibroblats transition via inhibiting the TGF-β1/Smad 2/3 signaling pathway

OBJECTIVE

Exosomes originated from mesenchymal stem cells (MSCs) benefit wound healing. This study investigated effects of exosomes originated from human umbilical cord MSCs (hUC-MSCs) on dermal fibroblasts-myofibroblasts transition via the TGF-β1/Smad2/3 signaling pathway.

METHODS

Firstly, hUC-MSCs were collected and identified. Alizarin red, oil red O staining and toluidine blue staining were used to determine the osteogenic, adipogenic and chondrogenic differentiation abilities of hUC-MSCs. Then exosomes from hUC-MSCs were extracted and identified. To figure out the roles of exosomes and TGF-β1 in dermal fibroblasts-myofibroblasts transition, dermal fibroblasts were treated with TGF-β1 or/and exosomes at different concentrations. RT-qPCR, Western blot analyses were employed to examine levels of Collagen I, Collagen III, α-smooth muscle actin (α-SMA), and Smad2/3 phosphorylation, and immunofluorescence was employed to test α-SMA content and the localization and nucleation of Smad2/3 protein in cells.

RESULTS

hUC-MSCs and exosomes were successfully cultured and extracted. Levels of Collagen I, Collagen III, α-SMA, and Smad2/3, and Smad2/3 phosphorylation in fibroblasts treated with exosomes decreased markedly. After treatment with exosomes and TGF-β1 together, levels of Collagen I, Collagen III, α-SMA, and Smad2/3, and Smad2/3 phosphorylation in fibroblasts decreased significantly as compared to TGF-β1-treated fibroblasts. Exosome treatment reduced the entry of Smad2/3 into fibroblasts.

CONCLUSION

Our data suggested that hUC-MSCs-derived exosomes could inhibit dermal fibroblasts-myofibroblasts transition by inhibiting the TGF-β1/Smad2/3 signaling pathway.

Efficient differentiation of vascular smooth muscle cells from Wharton’s Jelly mesenchymal stromal cells using human platelet lysate: A potential cell source for small blood vessel engineering

BACKGROUND

The development of fully functional small diameter vascular grafts requires both a properly defined vessel conduit and tissue-specific cellular populations. Mesenchymal stromal cells (MSCs) derived from the Wharton’s Jelly (WJ) tissue can be used as a source for obtaining vascular smooth muscle cells (VSMCs), while the human umbilical arteries (hUAs) can serve as a scaffold for blood vessel engineering.

AIM

To develop VSMCs from WJ-MSCs utilizing umbilical cord blood platelet lysate.

METHODS

WJ-MSCs were isolated and expanded until passage (P) 4. WJ-MSCs were properly defined according to the criteria of the International Society for Cell and Gene Therapy. Then, these cells were differentiated into VSMCs with the use of platelet lysate from umbilical cord blood in combination with ascorbic acid, followed by evaluation at the gene and protein levels. Specifically, gene expression profile analysis of VSMCs for ACTA2, MYH11, TGLN, MYOCD, SOX9, NANOG homeobox, OCT4 and GAPDH, was performed. In addition, immunofluorescence against ACTA2 and MYH11 in combination with DAPI staining was also performed in VSMCs. HUAs were decellularized and served as scaffolds for possible repopulation by VSMCs. Histological and biochemical analyses were performed in repopulated hUAs.

RESULTS

WJ-MSCs exhibited fibroblastic morphology, successfully differentiating into “osteocytes”, “adipocytes” and “chondrocytes”, and were characterized by positive expression (> 90%) of CD90, CD73 and CD105. In addition, WJ-MSCs were successfully differentiated into VSMCs with the proposed differentiation protocol. VSMCs successfully expressed ACTA2, MYH11, MYOCD, TGLN and SOX9. Immunofluorescence results indicated the expression of ACTA2 and MYH11 in VSMCs. In order to determine the functionality of VSMCs, hUAs were isolated and decellularized. Based on histological analysis, decellularized hUAs were free of any cellular or nuclear materials, while their extracellular matrix retained intact. Then, repopulation of decellularized hUAs with VSMCs was performed for 3 wk. Decellularized hUAs were repopulated efficiently by the VSMCs. Biochemical analysis revealed the increase of total hydroyproline and sGAG contents in repopulated hUAs with VSMCs. Specifically, total hydroxyproline and sGAG content after the 1^st, 2^nd and 3^rd wk was 71 ± 10, 74 ± 9 and 86 ± 8 μg hydroxyproline/mg of dry tissue weight and 2 ± 1, 3 ± 1 and 3 ± 1 μg sGAG/mg of dry tissue weight, respectively. Statistically significant differences were observed between all study groups (P < 0.05).

CONCLUSION

VSMCs were successfully obtained from WJ-MSCs with the proposed differentiation protocol. Furthermore, hUAs were efficiently repopulated by VSMCs. Differentiated VSMCs from WJ-MSCs could provide an alternative source of cells for vascular tissue engineering.

Cell immaturity and white/beige adipocyte potential of primary human adipose-derived stromal cells are restrained by culture-medium TGFβ1

Human adipose-derived stem/stromal cells (hASCs) can differentiate into specialized cell types and thereby contribute to tissue regeneration. As such, hASCs have drawn increasing attention in cell therapy and regenerative medicine, not to mention the ease to isolate them from donors. Culture conditions are critical for expanding hASCs while maintaining optimal therapeutic capabilities. Here, we identified a role for transforming growth factor β1 (TGFβ1) in culture medium in influencing the fate of hASCs during in vitro cell expansion. Human ASCs obtained after expansion in standard culture medium (Standard-hASCs) and in endothelial cell growth medium 2 (EGM2-hASCs) were characterized by high-throughput transcriptional studies, gene set enrichment analysis and functional properties. EGM2-hASCs exhibited enhanced multipotency capabilities and an immature phenotype compared with Standard-hASCs. Moreover, the adipogenic potential of EGM2-hASCs was enhanced, including toward beige adipogenesis, compared with Standard-hASCs. In these conditions, TGFβ1 acts as a critical factor affecting the immaturity and multipotency of Standard-hASCs, as suggested by small mother of decapentaplegic homolog 3 (SMAD3) nuclear localization and phosphorylation in Standard-hASCs vs EGM2-hASCs. Finally, the typical priming of Standard-hASCs into osteoblast, chondroblast, and vascular smooth muscle cell (VSMC) lineages was counteracted by pharmacological inhibition of the TGFβ1 receptor, which allowed retention of SMAD3 into the cytoplasm and a decrease in expression of osteoblast and VSMC lineage markers. Overall, the TGFβ1 pathway appears critical in influencing the commitment of hASCs toward osteoblast, chondroblast, and VSMC lineages, thus reducing their adipogenic potential. These effects can be counteracted by using EGM2 culture medium or chemical inhibition of the TGFβ1 pathway.

Canine Corneal Stromal Cells Have Multipotent Mesenchymal Stromal Cell Properties In Vitro

The objective of this study was to determine whether corneal stromal cells (CSCs) from the limbal and central corneal stroma in dogs have multipotent mesenchymal stem/stromal cell (MSC) properties, and whether this cell population can be differentiated into keratocyte-like cells (KDCs). Normal, donated, mesocephalic dog corneas were used to isolate CSC in vitro. Immunohistochemistry demonstrated a distinct population of CD90 expressing cells in the anterior stroma throughout the limbal and central cornea. CSC could be cultured from both the limbal and central cornea and the culture kinetics showed a progenitor cell profile. The CSC expressed stem cell markers CD90, CD73, CD105, N-cadherin, and Pax6, while CD34 was negative. Limbal and central CSC differentiated into osteoblasts, chondrocytes, and adipocytes confirming their multipotency. Coculturing allogeneic peripheral blood mononuclear cells (PBMCs) with limbal CSCs did not affect baseline PBMC proliferation indicating a degree of innate immune privilege. Limbal CSC could be differentiated into KDCs that expressed Keratocan, Lumican, and ALDH1A3 and downregulated Pax6 and N-cadherin. In conclusion, canine CSCs have multipotent MSC properties similarly described in humans and could serve as a source of cells for cell therapy and studying corneal diseases.

Effects of Physical, Chemical, and Biological Stimulus on h-MSC Expansion and Their Functional Characteristics

Human adult mesenchymal stem or stromal cells (h-MSC) therapy has gained considerable attention due to the potential to treat or cure diseases given their immunosuppressive properties and tissue regeneration capabilities. Researchers have explored diverse strategies to promote high h-MSC production without losing functional characteristics or properties. Physical stimulus including stiffness, geometry, and topography, chemical stimulus, like varying the surface chemistry, and biochemical stimuli such as cytokines, hormones, small molecules, and herbal extracts have been studied but have yet to be translated to industrial manufacturing practice. In this review, we describe the role of those stimuli on h-MSC manufacturing, and how these stimuli positively promote h-MSC properties, impacting the cell manufacturing field for cell-based therapies. In addition, we discuss other process considerations such as bioreactor design, good manufacturing practice, and the importance of the cell donor and ethics factors for manufacturing potent h-MSC.

Towards extracellular matrix normalization for improved treatment of solid tumors

It is currently challenging to eradicate cancer. In the case of solid tumors, the dense and aberrant extracellular matrix (ECM) is a major contributor to the heterogeneous distribution of small molecule drugs and nano-formulations, which makes certain areas of the tumor difficult to treat. As such, much research is devoted to characterizing this matrix and devising strategies to modify its properties as a means to facilitate the improved penetration of drugs and their nano-formulations. This contribution presents the current state of knowledge on the composition of normal ECM and changes to ECM that occur during the pathological progression of cancer. It also includes discussion of strategies designed to modify the composition/properties of the ECM as a means to enhance the penetration and transport of drugs and nano-formulations within solid tumors. Moreover, a discussion of approaches to image the ECM, as well as ways to monitor changes in the ECM as a function of time are presented, as these are important for the implementation of ECM-modifying strategies within therapeutic interventions. Overall, considering the complexity of the ECM, its variability within different tissues, and the multiple pathways by which homeostasis is maintained (both in normal and malignant tissues), the available literature - while promising - suggests that improved monitoring of ECM remodeling in vivo is needed to harness the described strategies to their full potential, and match them with an appropriate chemotherapy regimen.

Specific Overexpression of Mitofusin-2 in Hepatic Stellate Cells Ameliorates Liver Fibrosis in Mice Model

Liver fibrosis is a chronic liver disease that could further develop to cirrhosis and liver carcinoma. Hepatic stellate cells (HSCs) are primary effector cells to initiate liver fibrosis. We aimed to explore the function and underlying mechanisms of mitochondrial fusion protein Mitofusin-2 (MFN2) in liver fibrosis. First, we utilized an alpha-smooth muscle actin promoter to overexpress MFN2 specifically in HSCs using adeno-associated virus (AAV) vector (AAV-MFN2). Overexpression of MFN2 was specifically achieved in HSC-T6 cells, but not in murine bone marrow-derived macrophages or hepatocyte AML-12 cells. We found that high expression of MFN2 induced apoptosis of HSC-T6 cells. Mechanistically, we demonstrated that high level of MFN2 inhibited TGF-β1/Smad signaling pathway, triggered downregulation of type I, type III, and type IV collagen, and antagonized the formation of factors associated with liver fibrosis. Furthermore, we found that overexpression of MFN2 using AAV-MFN2 ameliorated CCl₄-induced liver fibrosis in vivo with significantly decreased immune cell infiltration. Taken together, our findings indicate that MFN2 is critical in regulating apoptosis and liver fibrosis in HSCs, which might be a useful therapeutic target to treat liver fibrosis.

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.

Biological approaches for hypertrophic scars

Scar formation is usually the pathological consequence of skin trauma. And hypertrophic scars (HSs) frequently occur in people after being injured deeply. HSs are unusually considered as the result of tissue contraction and excessive extracellular matrix component deposition. Myofibroblasts, as the effector cells, mainly differentiated from fibroblasts, play the crucial role in the pathophysiology of HSs. A number of growth factors, inflammatory cytokines involved in the process of HS occurrence. Currently, with in-depth exploration and clinical research of HSs, various creative and effective treatments budded. In here, we summarize the progress in the molecular mechanism of HSs, and review the available biotherapeutic methods for their pathophysiological characteristics. Additionally, we further prospected that the comprehensive therapy may be more suitable for HS treatment.

Yes-Associated Protein 1 Plays Major Roles in Pancreatic Stellate Cell Activation and Fibroinflammatory Responses

Background: Yes-associated protein 1 (YAP), a transcriptional co-activator and major effector of the Hippo pathway, regulates cell differentiation and morphology in many cell types and supports aberrant tumor growth. Recent studies showed that YAP is expressed in pancreas tissues in pancreatic ductal adenocarcinoma (PDAC) patients and experimental models of PDAC, with YAP largely found in cancer cells and pancreatic stellate cells (PaSC) in the stroma. Methods and Results: We studied here the role of YAP in the activated phenotype of PaSC. We found that YAP is expressed at low levels in normal mouse pancreas, but protein levels significantly increased after pancreas inflammatory damage induced by repeated cerulein administration in wild-type mice or upon initiation of neoplastic transformation of the pancreas parenchyma in Ptf1-Cre;LSL-KrasG12D/+ (KC) mice. In these animal models, YAP upregulation occurred in parallel with activation and proliferation of PaSC. Consistent with these findings, we found robust YAP expression in culture-activated mouse and human PaSC but not in quiescent, freshly isolated cells. Fully activated PaSC isolated from KC mice or PDAC patient tissues exhibited robust nuclear YAP suggesting YAP transcriptional activity. Agents that induce quiescence such as the Bromodomain and Extra-Terminal (BET) inhibitor iBET151 and the p38 MAPK inhibitor SB203580 reduced YAP levels in PaSC. Stimulation of PaSC with the potent mitogen PDGF elicited marked YAP Ser127 phosphorylation. However, unexpectedly, this effect did not diminish YAP nuclear localization, suggesting that YAP phosphorylation at this site does not govern YAP cellular localization in PaSC. siRNA-mediated knockdown of YAP reduced PDGF-induced PaSC expansion in culture and blunted the persistent activation of Akt and ERK elicited by PDGF stimulation, supporting a role for YAP in PDGF-induced cell growth. YAP knockdown also blunted fibroinflammatory gene expression responses both in unstimulated and transforming growth factor beta 1 (TGFβ1)-stimulated PaSC. Conclusion: Our data suggest a central role for YAP in sustaining the activated phenotype and fibroinflammatory responses in PaSC. Moreover, our findings indicate that a complex crosstalk between YAP, TGFβ1, and PDGF pathways regulates PaSC activity and growth.

Mesenchymal stem cell perspective: cell biology to clinical progress

The terms MSC and MSCs have become the preferred acronym to describe a cell and a cell population of multipotential stem/progenitor cells commonly referred to as mesenchymal stem cells, multipotential stromal cells, mesenchymal stromal cells, and mesenchymal progenitor cells. The MSCs can differentiate to important lineages under defined conditions in vitro and in limited situations after implantation in vivo. MSCs were isolated and described about 30 years ago and now there are over 55,000 publications on MSCs readily available. Here, we have focused on human MSCs whenever possible. The MSCs have broad anti-inflammatory and immune-modulatory properties. At present, these provide the greatest focus of human MSCs in clinical testing; however, the properties of cultured MSCs in vitro suggest they can have broader applications. The medical utility of MSCs continues to be investigated in over 950 clinical trials. There has been much progress in understanding MSCs over the years, and there is a strong foundation for future scientific research and clinical applications, but also some important questions remain to be answered. Developing further methods to understand and unlock MSC potential through intracellular and intercellular signaling, biomedical engineering, delivery methods and patient selection should all provide substantial advancements in the coming years and greater clinical opportunities. The expansive and growing field of MSC research is teaching us basic human cell biology as well as how to use this type of cell for cellular therapy in a variety of clinical settings, and while much promise is evident, careful new work is still needed.

An Improved Method of Maintaining Primary Murine Cardiac Fibroblasts in Two-Dimensional Cell Culture

Primary cardiac fibroblasts are notoriously difficult to maintain for extended periods of time in cell culture, due to the plasticity of their phenotype and sensitivity to mechanical input. In order to study cardiac fibroblast activation in vitro, we have developed cell culture conditions which promote the quiescent fibroblast phenotype in primary cells. Using elastic silicone substrata, both rat and mouse primary cardiac fibroblasts could be maintained in a quiescent state for more than 3 days after isolation and these cells showed low expression of myofibroblast markers, including fibronectin extracellular domain A, non-muscle myosin IIB, platelet-derived growth factor receptor-alpha and alpha-smooth muscle actin. Gene expression was also more fibroblast-like vs. that of myofibroblasts, as Tcf21 was significantly upregulated, while Fn1-EDA, Col1A1 and Col1A2 were markedly downregulated. Cell culture conditions (eg. serum, nutrient concentration) are critical for the control of temporal fibroblast proliferation. We propose that eliminating mechanical stimulus and limiting the nutrient content of cell culture media can extend the quiescent nature of primary cardiac fibroblasts for physiological analyses in vitro.

Induction of Fibrogenic Phenotype in Human Mesenchymal Stem Cells by Connective Tissue Growth Factor in a Hydrogel Model of Soft Connective Tissue

Scar formation is the typical endpoint of wound healing in adult mammalian tissues. An overactive or prolonged fibrogenic response following injury leads to excessive deposition of fibrotic proteins that promote tissue contraction and scar formation. Although well-defined in the dermal tissue, the progression of fibrosis is less explored in other connective tissues, such as the vocal fold. To establish a physiologically relevant 3D model of loose connective tissue fibrosis, we have developed a synthetic extracellular matrix using hyaluronic acid (HA) and peptidic building blocks carrying complementary functional groups. The resultant network was cell adhesive and protease degradable, exhibiting viscoelastic properties similar to the human vocal fold. Human mesenchymal stem cells (hMSCs) were encapsulated in the HA matrix as single cells or multicellular aggregates and cultured in pro-fibrotic media containing connective tissue growth factor (CTGF) for up to 21 days. hMSCs treated with CTGF-supplemented media exhibited an increased expression of fibrogenic markers and ECM proteins associated with scarring. Incorporation of α-smooth muscle actin into F-actin stress fibers was also observed. Furthermore, CTGF treatment increased the migratory capacity of hMSCs as compared to the CTGF-free control groups, indicative of the development of a myofibroblast phenotype. Addition of an inhibitor of the mitogen-activated protein kinase (MAPK) pathway attenuated cellular expression of fibrotic markers and related ECM proteins. Overall, this study demonstrates that CTGF promotes the development of a fibrogenic phenotype in hMSCs encapsulated within an HA matrix and that the MAPK pathway is a potential target for future therapeutic endeavors towards limiting scar formation in loose connective tissues.

A Cell Density-Dependent Reporter in the Drosophila S2 Cells

Cell density regulates many aspects of cell properties and behaviors including metabolism, growth, cytoskeletal structure and locomotion. Importantly, the responses by cultured cells to density signals also uncover key mechanisms that govern animal development and diseases in vivo. Here we characterized a density-responsive reporter system in transgenic Drosophila S2 cells. We show that the reporter genes are strongly induced in a cell density-dependent and reporter-independent fashion. The rapid and reversible induction occurs at the level of mRNA accumulation. We show that multiple DNA elements within the transgene sequences, including a metal response element from the metallothionein gene, contribute to the reporter induction. The reporter induction correlates with changes in multiple cell density and growth regulatory pathways including hypoxia, apoptosis, cell cycle and cytoskeletal organization. Potential applications of such a density-responsive reporter will be discussed.

Mechanoregulation of Cancer-Associated Fibroblast Phenotype in Three-Dimensional Interpenetrating Hydrogel Networks

Tumor stromal residing cancer-associated fibroblasts (CAFs) are significant accomplices in the growth and development of malignant neoplasms. As cancer progresses, the stroma undergoes a dramatic remodeling and stiffening of its extracellular matrix (ECM). However, exactly how these biomechanical changes influence the CAF behavior and the functional paracrine crosstalk with the neighboring tumor cells in a 3-dimensional (3D) microenvironment remains elusive. Herein, a collagen and alginate interpenetrating network (CoAl-IPN) hydrogel system was employed as a 3D in vitro surrogate of the cancerous breast tissue stromal niche. In this study, the mechanical properties of CoAl-IPN were precisely fine-tuned with Young's modulus ( E) values of ∼108 and 898 Pa. The results revealed that the 3D polymeric network mechanics and microstructure are critical biophysical determinants of the human breast CAF (b-CAF) morphology, phenotype, and paracrine dialogue with MDA-MB-231 tumoroids. A compliant hydrogel network favors b-CAF spreading, nuclear translocation of the YAP/TAZ mechanosignaling protein, and upregulation of CAF hallmark transcripts. Conversely, a rigid and highly cross-linked hydrogel network imposed a physical entrapment effect on the b-CAFs that limited their spreading and phenotype in a manner that effectively muted their pro-tumorigenic paracrine activity. Collectively, the CoAl-IPN 3D culture system has proven to be a versatile platform in defining the 3D biophysical parameters that could either promote or restrain the protumorigenic activity of b-CAFs and sheds critical mechano-mediated light onto the phenotypic plasticity and corresponding specific bioactivity of b-CAFs in the 3D microenvironment.

Primary cell-based phenotypic assays to pharmacologically and genetically study fibrotic diseases in vitro

Ongoing tissue repair and formation and deposition of collagen-rich extracellular matrix in tissues and organs finally lead to fibrotic lesions and destruction of normal tissue/organ architecture and function. In the lung, scarring is observed in asthma, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis to various degrees. At the cellular level immune cells, fibroblasts and epithelial cells are all involved in fibrotic processes. Mechanistically, fibroblast to myofibroblast transformation and epithelial to mesenchymal transition are major drivers of fibrosis. Amongst others, both processes are controlled by transforming growth factor beta-1 (TGFβ-1), a growth factor upregulated in idiopathic pulmonary fibrosis lungs. Phenotypic assays with primary human cells and complex disease-relevant readouts become increasingly important in modern drug discovery processes. We describe high-content screening based phenotypic assays with primary normal human lung fibroblasts and primary human airway epithelial cells. For both cell types, TGFβ-1 stimulation is used to induce fibrotic phenotypes in vitro, with alpha smooth muscle actin and collagen-I as readouts for FMT and E-cadherin as a readout for EMT. For each assay, a detailed image analysis protocols is described. Treatment of both cell types with TGFβ-1 and a transforming growth factor beta receptor inhibitor verifies the suitability of the assays for pharmacological interventions. In addition, the assays are compatible for siRNA and Cas9-ribonucleoprotein transfections, and thus are useful for genetic target identification/validation by modulating gene expression.

Plasticity of endometrial epithelial and stromal cells-A new approach towards the pathogenesis of equine endometrosis

Equine endometrosis, a frequent cause of subfertility, is characterized by periglandular fibrosis, and no treatment exists. Endometrial biopsies not only contain diseased glands, but also contain healthy glands and stroma. Myoepithelial (ME) and myofibroblastic (MF) markers are calponin, smooth muscle actin (SMA), desmin and glial fibrillary acidic protein (GFAP). Epithelial vimentin expression indicates epithelial to mesenchymal transition (EMT). The aim of this immunohistochemical study was to investigate whether biopsies with endometrosis express MF and ME markers and vimentin. Compared to healthy areas, significantly higher percentages of endometrotic glands were lined by calponin- and vimentin-positive epithelial cells, whereas periglandular fibrosis contained significantly higher percentages of stromal cells positive for vimentin, desmin and SMA and significantly less calponin-positive stromal cells. The rare GFAP expression was restricted to endometrotic glands. Of these, the most frequent features of endometrotic glands were higher percentages of SMA- and vimentin-positive stromal cells and the prominent epithelial calponin staining that occurred in 100%, 93% and 95% of examined biopsies. Results indicate plasticity of equine endometrial epithelial and stromal cells. Particularly, endometrotic glands show evidence for ME differentiation and EMT. The different expression of MF markers between stromal cells from healthy and endometrotic areas suggests functional differences. The characteristic changes in the expression of SMA, vimentin and calponin between endometrotic glands and healthy areas can be helpful to confirm early stages of endometrosis. The characterization of cellular differentiation may help to decipher the pathogenesis of endometrosis and could lead to therapeutic strategies.

p16INK4A-expressing mesenchymal stromal cells restore the senescence-clearance-regeneration sequence that is impaired in chronic muscle inflammation

BACKGROUND

The therapeutic benefits of mesenchymal stromal cells (MSCs) include treatment of chronic inflammation. However, given the short-lived engraftment of these cells in vivo, their therapeutic efficacy remains mysterious. Transient induction of cellular senescence contributes to activation of immune cells, which promotes clearance of damaged cells during tissue remodelling. This may occur in tissue-resident mesenchymal progenitor cells during regeneration. Elucidation of the role of senescence in tissue-resident mesenchymal progenitor cells during regeneration would provide insight into the profile of therapeutic MSCs for treatment of chronic inflammatory disease.

METHODS

We evaluated multipotent mesenchymal progenitor cells, termed fibro/adipogenic progenitors (FAPs), and immune cells in acute muscle injury (AMI) model mice and mice with myosin-induced experimental autoimmune myositis, a model of chronic inflammatory myopathy (CIM). Human bone marrow MSCs were optimised for the treatment of CIM using placental extract.

FINDING

FAPs in AMI transiently expressed p16^INK4A on days 1 and 2 after injury and recruited phagocytic immune cells, whereas in CIM, p16^INK4A expression in FAPs was low. Cellular senescence occurs during the natural maturation of the placenta. Therefore, we used human placental extract to induce p16^INK4A expression in therapeutic human bone marrow MSCs in culture. Treatment of CIM with p16^INK4A-expressing MSCs promoted tissue remodelling by transiently increasing the abundance of engrafted MSCs, inducing cellular senescence in innate FAPs, and recruiting phagocytic immune cells.

INTERPRETATION

MSCs may exert their effect by remodelling the chronic inflammatory environment via senescence-related regenerative processes.

Keratin scaffolds with human adipose stem cells: Physical and biological effects toward wound healing

Keratin, a natural biomaterial derived from wool or human hair, has the intrinsic ability to interact with different types of cells and the potential to serve as a controllable extracellular matrix that can be used a scaffold for tissue engineering. In this study, we demonstrated a simple and fast technique to construct 3D keratin scaffolds for accelerated wound healing using a lyophilization method based on extraction of keratin from human hair. The physical properties of the keratin scaffolds such as water uptake, pore size, and porosity can be adjusted by changing the protein concentrations during the fabrication process. The keratin scaffolds supported human adipose stem cells (hASCs) adhesion, proliferation, and differentiation. In vivo study performed on ICR mice showed that keratin scaffolds with hASCs shortened skin wound healing time, accelerated epithelialization, and promoted wound remodeling. Therefore, keratin scaffolds alone or together with hASCs may serve as therapeutic agents for repairing wounded tissue.

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.

Substrate mechanics controls adipogenesis through YAP phosphorylation by dictating cell spreading

The mechanoregulated proteins YAP/TAZ are involved in the adipogenic/osteogenic switch of mesenchymal stem cells (MSCs). MSC fate decision can be unbalanced by controlling substrate mechanics, in turn altering the transmission of tension through cell cytoskeleton. MSCs have been proposed for orthopedic and reconstructive surgery applications. Thus, a tight control of their adipogenic potential is required in order to avoid their drifting towards fat tissue. Substrate mechanics has been shown to drive MSC commitment and to regulate YAP/TAZ protein shuttling and turnover. The mechanism by which YAP/TAZ co-transcriptional activity is mechanically regulated during MSC fate acquisition is still debated. Here, we design few bioengineering tools suited to disentangle the contribution of mechanical from biological stimuli to MSC adipogenesis. We demonstrate that the mechanical repression of YAP happens through its phosphorylation, is purely mediated by cell spreading downstream of substrate mechanics as dictated by dimensionality. YAP repression is sufficient to prompt MSC adipogenesis, regardless of a permissive biological environment, TEAD nuclear presence or focal adhesion stabilization. Finally, by harnessing the potential of YAP mechanical regulation, we propose a practical example of the exploitation of adipogenic transdifferentiation in tumors.