Skin progenitor cells contribute to bleomycin-induced skin fibrosis

Smooth muscle-specific deletion of cellular communication network factor 2 causes severe aorta malformation and atherosclerosis

AIMS

Cellular communication network factor 2 (CCN2) is a matricellular protein implicated in fibrotic diseases, with ongoing clinical trials evaluating anti-CCN2-based therapies. By uncovering CCN2 as abundantly expressed in non-diseased artery tissue, this study aimed to investigate the hypothesis that CCN2 plays a pivotal role in maintaining smooth muscle cell (SMC) phenotype and protection against atherosclerosis.

METHODS AND RESULTS

Global- and SMC-specific Ccn2 knockout mouse models were employed to demonstrate that Ccn2 deficiency leads to SMC de-differentiation, medial thickening, and aorta elongation under normolipidaemic conditions. Inducing hyperlipidaemia in both models resulted in severe aorta malformation and a 17-fold increase in atherosclerosis formation. Lipid-rich lesions developed at sites of the vasculature typically protected from atherosclerosis development by laminar blood flow, covering 90% of aortas and extending to other vessels, including coronary arteries. Evaluation at earlier time points revealed medial lipid accumulation as a lesion-initiating event. Fluorescently labelled LDL injection followed by confocal microscopy showed increased LDL retention in the medial layer of Ccn2 knockout aortas, likely attributed to marked proteoglycan enrichment of the medial extracellular matrix. Analyses leveraging data from the Athero-Express study cohort indicated the relevance of CCN2 in established human lesions, as CCN2 correlated with SMC marker transcripts across 654 transcriptomically profiled carotid plaques. These findings were substantiated through in situ hybridization showing CCN2 expression predominantly in the fibrous cap.

CONCLUSION

This study identifies CCN2 as a major constituent of the normal artery wall, critical in regulating SMC differentiation and aorta integrity and possessing a protective role against atherosclerosis development. These findings underscore the need for further investigation into the potential effects of anti-CCN2-based therapies on the vasculature.

F127-SE-tLAP thermosensitive hydrogel alleviates bleomycin-induced skin fibrosis via TGF-β/Smad pathway

BACKGROUND

Skin fibrosis affects the normal function of the skin. TGF-β1 is a key cytokine that affects organ fibrosis. The latency-associated peptide (LAP) is essential for TGF-β1 activation. We previously constructed and prepared truncated LAP (tLAP), and confirmed that tLAP inhibited liver fibrosis by affecting TGF-β1. SPACE peptide has both transdermal and transmembrane functions. SPACE promotes the delivery of macromolecules through the stratum corneum into the dermis. This study aimed to alleviate skin fibrosis through the delivery of tLAP by SPACE.

METHODS

The SPACE-tLAP (SE-tLAP) recombinant plasmid was constructed. SE-tLAP was purified by nickel affinity chromatography. The effects of SE-tLAP on the proliferation, migration, and expression of fibrosis-related and inflammatory factors were evaluated in TGF-β1-induced NIH-3T3 cells. F127-SE-tLAP hydrogel was constructed by using F127 as a carrier to load SE-tLAP polypeptide. The degradation, drug release, and biocompatibility of F127-SE-tLAP were evaluated. Bleomycin was used to induce skin fibrosis in mice. HE, Masson, and immunohistochemistry were used to observe the skin histological characteristics.

RESULTS

SE-tLAP inhibited the proliferation, migration, and expression of fibrosis-related and inflammatory factors in NIH-3T3 cells. F127-SE-tLAP significantly reduced ECM production, collagen deposition, and fibrotic pathological changes, thereby alleviating skin fibrosis.

CONCLUSION

F127-SE-tLAP could increase the transdermal delivery of LAP, reduce the production and deposition of ECM, inhibit the formation of dermal collagen fibers, and alleviate the progression of skin fibrosis. It may provide a new idea for the therapy of skin fibrosis.

Brown adipose tissue transplantation improves skin fibrosis in localized scleroderma

Adipose tissue transplantation shows great therapeutic potential in reversing localized scleroderma-associated skin fibrosis. Brown adipose tissue (BAT) can specifically secrete various cytokines against fibrosis, but its therapeutic potential in improving skin fibrosis has not yet been demonstrated. In this study, we have demonstrated the superior therapeutic efficacy of BAT transplantation for sclerotic skin by transplanting two distinct types of adipose tissue. In comparison to the white adipose tissue (WAT) group, mice treated with BAT transplantation exhibited a significant reduction in dermal thickness. BAT transplantation effectively reverses skin sclerosis through mechanisms involving inflammation reduction, promotion of angiogenesis, inhibition of myofibroblast accumulation, and collagen deposition. This therapeutic effect can be attributed to its unique paracrine effects. Furthermore, transcriptome sequencing (RNA-Seq) revealed upregulation of pathways associated with lipogenesis and fatty acid metabolism in BAT while downregulating pathways are related to transforming growth factor β(TGF-β), epithelial-mesenchymal transition (EMT), and inflammatory response. These findings suggest that BAT transplantation holds great promise as a novel approach for localized scleroderma treatment.

Matrix stiffness-induced α-tubulin acetylation is required for skin fibrosis formation through activation of Yes-associated protein

Skin fibrosis, a pathological process featured by fibroblast activation and extracellular matrix (ECM) deposition, makes a significant contribution to morbidity. Studies have identified biomechanics as the central element in the complex network of fibrogenesis that drives the profibrotic feedback loop. In this study, we found that the acetylation of α-tubulin at lysine 40 (K40) was augmented in fibrotic skin tissues. Further analysis showed that α-tubulin acetylation is required for fibroblast activation, including contraction, migration, and ECM deposition. More importantly, we revealed that biomechanics-induced upregulation of K40 acetylation promotes fibrosis by mediating mechanosensitive Yes-associated protein S127 dephosphorylation and its cytoplasm nucleus shuttle. Furthermore, we demonstrated that the knockdown of α-tubulin acetyltransferase 1 could rescue the K40 acetylation upregulation caused by increased matrix rigidity and ameliorate skin fibrosis both in vivo and in vitro. Herein, we highlight the critical role of α-tubulin acetylation in matrix stiffness-induced skin fibrosis and clarify a possible molecular mechanism. Our research suggests α-tubulin acetylation as a potential target for drug design and therapeutic intervention.

Adipose-derived stem cell-enriched lipotransfer reverses skin sclerosis by suppressing dermal inflammation

BACKGROUND

Scleroderma is a chronic autoimmune disease with an incidence of 2.7 per 100,000 people. Traditional lipotransfer has been used to treat atrophic sclerotic skin. Enzymatically processed cell-assisted lipotransfer (CAL) and mechanically processed stromal vascular fraction gel (SVF-gel) are fat products with abundant adipose-derived stem cells (ASCs). The present study aimed to assess whether ASC-enriched lipotransfer elicits superior therapeutic effects on scleroderma.

METHODS

Scleroderma was induced in nude mice by injections of bleomycin for 4 weeks. Human-derived Coleman fat (CF), CAL, or SVF-gel (0.1 mL) was injected into sclerotic lesions. Histologic examinations, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and expression analyses of inflammatory factors in skin lesions and transferred fat were performed at 4 weeks post-implantation.

RESULTS

Dermal thickness was lower in the CF- (339.0 ± 19.66 µm), CAL- (271.0 ± 16.15 µm), and SVF-gel- (197.8 ± 12.99 µm) injected groups than in the phosphate-buffered saline-injected group (493.3 ± 28.13 µm) (P<0.05). The numbers of TUNEL+ and Mac2+ cells in fat tissue were significantly higher in the CF-injected group than in the SVF-gel- and CAL-injected groups. Expression of monocyte chemotactic protein-1 and interleukin-6 was significantly lower in the ASC-enriched groups than in the CF group. Histologic analysis showed there were far fewer macrophages and myofibroblasts in skin lesions in the ASC-enriched groups than in the CF group.

CONCLUSION

Transplantation of SVF-gel and CAL, which contain abundant ASCs, reduces the levels of apoptotic cells and inflammation, significantly reverses skin sclerosis, and elicits superior anti-inflammatory and anti-fibrotic effects on scleroderma.

Impact of Microenvironmental Changes during Degeneration on Intervertebral Disc Progenitor Cells: A Comparison with Mesenchymal Stem Cells

Intervertebral disc (IVD) degeneration occurs with natural ageing and is linked to low back pain, a common disease. As an avascular tissue, the microenvironment inside the IVD is harsh. During degeneration, the condition becomes even more compromised, presenting a significant challenge to the survival and function of the resident cells, as well as to any regeneration attempts using cell implantation. Mesenchymal stem cells (MSCs) have been proposed as a candidate stem cell tool for IVD regeneration. Recently, endogenous IVD progenitor cells have been identified inside the IVD, highlighting their potential for self-repair. IVD progenitor cells have properties similar to MSCs, with minor differences in potency and surface marker expression. Currently, it is unclear how IVD progenitor cells react to microenvironmental factors and in what ways they possibly behave differently to MSCs. Here, we first summarized the microenvironmental factors presented in the IVD and their changes during degeneration. Then, we analyzed the available studies on the responses of IVD progenitor cells and MSCs to these factors, and made comparisons between these two types of cells, when possible, in an attempt to achieve a clear understanding of the characteristics of IVD progenitor cells when compared to MSCs; as well as, to provide possible clues to cell fate after implantation, which may facilitate future manipulation and design of IVD regeneration studies.

CCN2 (Cellular Communication Network factor 2) in the bone marrow microenvironment, normal and malignant hematopoiesis

CCN2, formerly termed Connective Tissue Growth Factor, is a protein belonging to the Cellular Communication Network (CCN)-family of secreted extracellular matrix-associated proteins. As a matricellular protein it is mainly considered to be active as a modifier of signaling activity of several different signaling pathways and as an orchestrator of their cross-talk. Furthermore, CCN2 and its fragments have been implicated in the regulation of a multitude of biological processes, including cell proliferation, differentiation, adhesion, migration, cell survival, apoptosis and the production of extracellular matrix products, as well as in more complex processes such as embryonic development, angiogenesis, chondrogenesis, osteogenesis, fibrosis, mechanotransduction and inflammation. Its function is complex and context dependent, depending on cell type, state of differentiation and microenvironmental context. CCN2 plays a role in many diseases, especially those associated with fibrosis, but has also been implicated in many different forms of cancer. In the bone marrow (BM), CCN2 is highly expressed in mesenchymal stem/stromal cells (MSCs). CCN2 is important for MSC function, supporting its proliferation, migration and differentiation. In addition, stromal CCN2 supports the maintenance and longtime survival of hematopoietic stem cells, and in the presence of interleukin 7, stimulates the differentiation of pro-B lymphocytes into pre-B lymphocytes. Overexpression of CCN2 is seen in the majority of B-acute lymphoblastic leukemias, especially in certain cytogenetic subgroups associated with poor outcome. In acute myeloid leukemia, CCN2 expression is increased in MSCs, which has been associated with leukemic engraftment in vivo. In this review, the complex function of CCN2 in the BM microenvironment and in normal as well as malignant hematopoiesis is discussed. In addition, an overview is given of data on the remaining CCN family members regarding normal and malignant hematopoiesis, having many similarities and some differences in their function.

SOX2Mediates Carbon Nanotube-Induced Fibrogenesis and Fibroblast Stem Cell Acquisition

Certain nanosized particles like carbon nanotubes (CNTs) are known to induce pulmonary fibrosis, but the underlying mechanisms are unclear, and efforts to prevent this disease are lacking. Fibroblast-associated stem cells (FSCs) have been suggested as a critical driver of fibrosis induced by CNTs by serving as a renewable source of extracellular matrix-producing cells; however, a detailed understanding of this process remains obscure. Here, we demonstrated that single-walled CNTs induced FSC acquisition and fibrogenic responses in primary human lung fibroblasts. This was indicated by increased expression of stem cell markers (e.g., CD44 and ABCG2) and fibrogenic markers (e.g., collagen and α-SMA) in CNT-exposed cells. These cells also showed increased sphere formation, anoikis resistance, and aldehyde dehydrogenase (ALDH) activities, which are characteristics of stem cells. Mechanistic studies revealed sex-determining region Y-box 2 (SOX2), a self-renewal associated transcription factor, as a key driver of FSC acquisition and fibrogenesis. Upregulation and colocalization of SOX2 and COL1 were found in the fibrotic lung tissues of CNT-exposed mice via oropharyngeal aspiration after 56 days. The knockdown of SOX2 by gene silencing abrogated the fibrogenic and FSC-inducing effects of CNTs. Chromatin immunoprecipitation assays identified SOX2-binding sites on COL1A1 and COL1A2, indicating SOX2 as a transcription factor in collagen synthesis. SOX2 was also found to play a critical role in TGF-β-induced fibrogenesis through its collagen- and FSC-inducing effects. Since many nanomaterials are known to induce TGF-β, our findings that SOX2 regulate FSCs and fibrogenesis may have broad implications on the fibrogenic mechanisms and treatment strategies of various nanomaterial-induced fibrotic disorders.

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.

Insights into Fibroblast Plasticity: Cellular Communication Network 2 Is Required for Activation of Cancer-Associated Fibroblasts in a Murine Model of Melanoma

Tumor stroma resembles a fibrotic microenvironment, being characterized by the presence of myofibroblast-like cancer-associated fibroblasts (CAFs). In wild-type mice injected with melanoma cells, we show that the stem cell transcription factor Sox2 is expressed by tumor cells and induced in CAFs derived from synthetic fibroblasts. These fibroblasts were labeled postnatally with green fluorescent protein using mice expressing a tamoxifen-dependent Cre recombinase under the control of a fibroblast-specific promoter/enhancer. Conversely, fibroblast activation was impaired in mice with a fibroblast-specific deletion of cellular communication network 2 (Ccn2), associated with reduced expression of α-smooth muscle actin and Sox2. Multipotent Sox2-expressing skin-derived precursor (SKP) spheroids were cultured from murine back skin. Using lineage tracing and flow cytometry, approximately 40% of SKPs were found to be derived from type I collagen-lineage cells and acquired multipotency in culture. Inhibition of mechanotransduction pathways prevented myofibroblast differentiation of SKPs and expression of Ccn2. In SKPs deleted for Ccn2, differentiation into a myofibroblast, but not an adipocyte or neuronal phenotype, was also impaired. In human melanoma, CCN2 expression was associated with a profibrotic integrin alpha (ITGA) 11-expressing subset of CAFs that negatively associated with survival. These results suggest that synthetic dermal fibroblasts are plastic, and that CCN2 is required for the differentiation of dermal progenitor cells into a myofibroblast/CAF phenotype and is, therefore, a therapeutic target in melanoma.

SOX2 Epidermal Overexpression Promotes Cutaneous Wound Healing via Activation of EGFR/MEK/ERK Signaling Mediated by EGFR Ligands

Oral mucosa contains a unique transcriptional network that primes oral wounds for rapid resolution in humans. Our previous work identified genes that were consistently upregulated in the oral mucosa and demonstrated that induction of one of the identified genes, transcription factor SOX2, promoted cutaneous wound healing in mice. In this study, we investigated the molecular and cellular mechanisms by which SOX2 accelerates wound healing in skin. RNA-sequencing analysis showed that SOX2 induced a proliferative and wound-activated phenotype in skin keratinocytes prior to wounding. During wound healing, SOX2 induced proliferation of epithelial and connective tissue cells and promoted angiogenesis. Chromatin immunoprecipitation assay revealed that SOX2 directly regulates expression of EGFR ligands, resulting in activation of EGFR. In vitro, skin keratinocytes overexpressing SOX2 promoted cell migration via the EGFR/MEK/ERK pathway. We conclude that induction of SOX2 in skin keratinocytes accelerates cutaneous wound healing by promoting keratinocyte migration and proliferation, and enhancement of angiogenesis via upregulation of EGFR ligands and activation of EGFR/MEK/ERK pathway. Through the identification of putative cutaneous SOX2 targets, such as HBEGF, this study opens venues to determine clinical targets for treatment of skin wounds.

Non-Canonical Regulation of Type I Collagen through Promoter Binding of SOX2 and Its Contribution to Ameliorating Pulmonary Fibrosis by Butylidenephthalide

Pulmonary fibrosis is a fatal respiratory disease that gradually leads to dyspnea, mainly accompanied by excessive collagen production in the fibroblast and myofibroblast through mechanisms such as abnormal alveolar epithelial cells remodeling and stimulation of the extracellular matrix (ECM). Our results show that a small molecule, butylidenephthalide (BP), reduces type I collagen (COL1) expression in Transforming Growth Factor beta (TGF-β)-induced lung fibroblast without altering downstream pathways of TGF-β, such as Smad phosphorylation. Treatment of BP also reduces the expression of transcription factor Sex Determining Region Y-box 2 (SOX2), and the ectopic expression of SOX2 overcomes the inhibitory actions of BP on COL1 expression. We also found that serial deletion of the SOX2 binding site on 3′COL1 promoter results in a marked reduction in luciferase activity. Moreover, chromatin immunoprecipitation, which was found on the SOX2 binding site of the COL1 promoter, decreases in BP-treated cells. In an in vivo study using a bleomycin-induced pulmonary fibrosis C57BL/6 mice model, mice treated with BP displayed reduced lung fibrosis and collagen deposition, recovering in their pulmonary ventilation function. The reduction of SOX2 expression in BP-treated lung tissues is consistent with our findings in the fibroblast. This is the first report that reveals a non-canonical regulation of COL1 promoter via SOX2 binding, and contributes to the amelioration of pulmonary fibrosis by BP treatment.

Connective tissue growth factor contributes to joint homeostasis and osteoarthritis severity by controlling the matrix sequestration and activation of latent TGFβ

OBJECTIVES

One mechanism by which cartilage responds to mechanical load is by releasing heparin-bound growth factors from the pericellular matrix (PCM). By proteomic analysis of the PCM, we identified connective tissue growth factor (CTGF) and here investigate its function and mechanism of action.

METHODS

Recombinant CTGF (rCTGF) was used to stimulate human chondrocytes for microarray analysis. Endogenous CTGF was investigated by in vitro binding assays and confocal microscopy. Its release from cut cartilage (injury CM) was analysed by Western blot under reducing and non-reducing conditions. A postnatal, conditional CtgfcKO mouse was generated for cartilage injury experiments and to explore the course of osteoarthritis (OA) by destabilisation of the medial meniscus. siRNA knockdown was performed on isolated human chondrocytes.

RESULTS

The biological responses of rCTGF were TGFβ dependent. CTGF displaced latent TGFβ from cartilage and both were released on cartilage injury. CTGF and latent TGFβ migrated as a single high molecular weight band under non-reducing conditions, suggesting that they were in a covalent (disulfide) complex. This was confirmed by immunoprecipitation. Using CtgfcKO mice, CTGF was required for sequestration of latent TGFβ in the matrix and activation of the latent complex at the cell surface through TGFβR3. In vivo deletion of CTGF increased the thickness of the articular cartilage and protected mice from OA.

CONCLUSIONS

CTGF is a latent TGFβ binding protein that controls the matrix sequestration and activation of TGFβ in cartilage. Deletion of CTGF in vivo caused a paradoxical increase in Smad2 phosphorylation resulting in thicker cartilage that was protected from OA.

β-catenin activation in hair follicle dermal stem cells induces ectopic hair outgrowth and skin fibrosis

Hair follicle dermal sheath (DS) harbors hair follicle dermal stem cells (hfDSCs), which can be recruited to replenish DS and dermal papilla (DP). Cultured DS cells can differentiate into various cell lineages in vitro. However, it is unclear how its plasticity is modulated in vivo. Wnt/β-catenin signaling plays an important role in maintaining stem cells of various lineages and is required for HF development and regeneration. Here we report that activation of β-catenin in DS generates ectopic HF outgrowth (EF) by reprogramming HF epidermal cells and DS cells themselves, and endows DS cells with hair inducing ability. Epidermal homeostasis of pre-existing HFs is disrupted. Additionally, cell-autonomous progressive skin fibrosis is prominent in dermis, where the excessive fibroblasts largely originate from DS. Gene expression analysis of purified DS cells with activated β-catenin revealed significantly increased expression of Bmp, Fgf, and Notch ligands and administration of Bmp, Fgf, or Notch signaling inhibitor attenuates EF formation. In summary, our findings advance the current knowledge of high plasticity of DS cells and provide an insight into understanding how Wnt/β-catenin signaling controls DS cell behaviors.

Aberrant SSEA-4 upregulation mediates myofibroblast activity to promote pre-cancerous oral submucous fibrosis

Oral submucous fibrosis (OSF), regarded as a precancerous condition, is characterized by juxta-epithelial inflammatory reaction followed by fibro-elastic change in the lamina properia and epithelial atrophy. The pathologic mechanisms of OSF still need to be further clarified. In the study, we investigated the functional expression of SSEA-4, which is a well-known stemness marker, in myofibroblast activity and the clinical significance in OSF tissues. The expression of SSEA-4 in OSF was evaluated by immunohistochemical staining. Functional analysis of SSEA-4 on myofibroblast activity of OSF was achieved by lentiviral silencing ST3GAL2. Immunohisitochemistry demonstrated that SSEA-4 expression was significantly higher expression in areca quid chewing-associated OSF tissues than those of normal oral mucosa tissues. From flow cytometry analysis, arecoline dose-dependently activated SSEA-4 expression in primary human normal buccal mucosal fibroblasts (BMFs). Sorted SSEA-4-positive cells from fibrotic BMFs (fBMFs) have higher colony-forming unit, collagen gel contraction, and α-smooth muscle actin (α-SMA) expression than SSEA-4-negative subset. Knockdown of ST3GAL2 in fBMFs suppressed SSEA-4 expression, collagen contraction, migration, invasiveness, and wound healing capability. Consistently, silencing ST3GAL2 was found to repress arecoline-induced myofibroblast activity in BMFs. The study highlights SSEA-4 as a critical marker for therapeutic intervention to mediate myofibroblast transdifferentiation in areca quid chewing-associated OSF.

CCN2 induces cellular senescence in fibroblasts

The expression of Ccn2 (CTGF) has been linked to fibrosis in many tissues and pathologies, although its activities in fibroblastic cells and precise mechanism of action in fibrogenesis are still controversial. Here, we showed that CCN2 can induce cellular senescence in fibroblasts both in vitro and in vivo, whereupon senescent cells express an anti-fibrotic "senescence-associated secretory phenotype" (SASP) that includes upregulation of matrix metalloproteinases and downregulation of collagen. Mechanistically, CCN2 induces fibroblast senescence through integrin α₆β₁-mediated accumulation of reactive oxygen species, leading to activation of p53 and induction of p16^INK4a. In cutaneous wound healing, Ccn2 expression is highly elevated only during the initial inflammatory phase and quickly declines thereafter to a low level during the proliferation and maturation phases of healing when myofibroblasts play a major role. Consistent with this expression kinetics, knockdown of Ccn2 has little effect on the rate of wound closure, formation of senescent cells, or collagen content of the wounds. However, application of purified CCN2 protein on cutaneous wounds leads to induction of senescent cells, expression of SASP, and reduction of collagen content. These results show that CCN2 can induce cellular senescence in fibroblasts and is capable of exerting an anti-fibrotic effect in a context-dependent manner.

Antifibrotic, Antioxidant, and Immunomodulatory Effects of Mesenchymal Stem Cells in HOCl-Induced Systemic Sclerosis

OBJECTIVE

Systemic sclerosis (SSc) is a rare intractable disease with unmet medical need and fibrosis-related mortality. Absence of efficient treatments has prompted the development of novel therapeutic strategies, among which mesenchymal stem cells/stromal cells (MSCs) or progenitor stromal cells appear to be one of the most attractive options. The purpose of this study was to use the murine model of hypochlorite-induced SSc to investigate the systemic effects of MSCs on the main features of the diffuse form of the disease: skin and lung fibrosis, autoimmunity, and oxidative status.

METHODS

We compared the effects of different doses of MSCs (2.5 × 10(5) , 5 × 10(5) , and 10(6) ) infused at different time points. Skin thickness was assessed during the experiment. At the time of euthanasia, biologic parameters were quantified in blood and tissues (by enzyme-linked immunosorbent assay, quantitative reverse transcription-polymerase chain reaction, assessment of collagen content). Assessments of histology and immunostaining were also performed.

RESULTS

A lower expression of markers of fibrosis (Col1, Col3, Tgfb1, and aSma) was observed in both skin and lung following MSC infusion, which was consistent with histologic improvement and was inversely proportional to the injected dose. Importantly, sera from treated mice exhibited lower levels of anti-Scl-70 autoantibodies and enhanced antioxidant capacity, confirming the systemic effect of MSCs. Of interest, MSC administration was efficient in both the preventive and the curative approach. We further provide evidence that MSCs exerted an antifibrotic role by normalizing extracellular matrix remodeling parameters as well as reducing proinflammatory cytokine levels and increasing antioxidant defenses.

CONCLUSION

The results of this study demonstrate the beneficial and systemic effects of MSC administration in the HOCl murine model of diffuse SSc, which is a promising finding from a clinical perspective.

β-Catenin Stabilization in Skin Fibroblasts Causes Fibrotic Lesions by Preventing Adipocyte Differentiation of the Reticular Dermis

The Wnt/β-catenin pathway plays a central role in epidermal homeostasis and regeneration, but how it affects fibroblast fate decisions is unknown. We investigated the effect of targeted β-catenin stabilization in dermal fibroblasts. Comparative gene expression profiling of stem cell antigen 1^- (Sca1^-) and Sca1⁺ neonatal fibroblasts from upper and lower dermis, respectively, confirmed that Sca1⁺ cells had a preadipocyte signature and showed differential expression of Wnt/β-catenin–associated genes. By targeting all fibroblasts or selectively targeting Dlk1⁺ lower dermal fibroblasts, we found that β-catenin stabilization between developmental stages E16.5 and P2 resulted in a reduction in the dermal adipocyte layer with a corresponding increase in dermal fibrosis and an altered hair cycle. The fibrotic phenotype correlated with a reduction in the potential of Sca1⁺ fibroblasts to undergo adipogenic differentiation ex vivo. Our findings indicate that Wnt/β-catenin signaling controls adipogenic cell fate within the lower dermis, which potentially contributes to the pathogenesis of fibrotic skin diseases.

Fibrogenesis, novel lessons from animal models

Systemic sclerosis (SSc) is a devastating chronic autoimmune connective tissue disease characterized by vasculopathy, autoimmunity with inflammation, and progressive fibrogenesis. The current paradigm of the pathogenesis of SSc is that of an unknown initial trigger, leading to a complex interaction of immune cells, endothelial cells, and fibroblasts, producing cytokines, growth and angiogenic factors, and resulting in uncontrolled and persistent tissue fibrogenesis by an altered mesenchymal cell compartment. Animal models are of utmost importance to investigate the different steps in the pathogenesis. This review will elaborate on recent findings in established and more recently developed animal models, presenting data on compounds that are in or ready to be translated into clinical trials, or provide interesting new findings in the understanding of the pathophysiology of SSc. We focus on recent findings concerning the vessel-extracellular matrix interaction, the initial triggering aggressor, the concept of autoimmunity and inflammatory changes, the effector cells and their origins, and the complex interaction of the different signaling pathways in fibrogenesis.

Markers for the identification of tendon-derived stem cells in vitro and tendon stem cells in situ - update and future development

The efficacy of tendon-derived stem cells (TDSCs) for the promotion of tendon and tendon-bone junction repair has been reported in animal studies. Modulation of the tendon stem cell niche in vivo has also been reported to influence tendon structure. There is a need to have specific and reliable markers that can define TDSCs in vitro and tendon stem cells in situ for several reasons: to understand the basic biology of TDSCs and their subpopulations in vitro; to understand the identity, niches and functions of tendon/progenitor stem cells in vivo; to meet the governmental regulatory requirements for quality of TDSCs when translating the exciting preclinical findings into clinical trial/practice; and to develop new treatment strategies for mobilizing endogenous stem/progenitor cells in tendon. TDSCs were reported to express the common mesenchymal stem cell (MSC) markers and some embryonic stem cell (ESC) markers, and there were attempts to use these markers to label tendon stem cells in situ. Are these stem cell markers useful for the identification of TDSCs in vitro and tracking of tendon stem cells in situ? This review aims to discuss the values of the panel of MSC, ESC and tendon-related markers for the identification of TDSCs in vitro. Important factors influencing marker expression by TDSCs are discussed. The usefulness and limitations of the panel of MSC, ESC and tendon-related markers for tracking stem cells in tendon, especially tendon stem cells, in situ are then reviewed. Future research directions are proposed.

Genetic Analysis of Connective Tissue Growth Factor as an Effector of Transforming Growth Factor β Signaling and Cardiac Remodeling

The matricellular secreted protein connective tissue growth factor (CTGF) is upregulated in response to cardiac injury or with transforming growth factor β (TGF-β) stimulation, where it has been suggested to function as a fibrotic effector. Here we generated transgenic mice with inducible heart-specific CTGF overexpression, mice with heart-specific expression of an activated TGF-β mutant protein, mice with heart-specific deletion of Ctgf, and mice in which Ctgf was also deleted from fibroblasts in the heart. Remarkably, neither gain nor loss of CTGF in the heart affected cardiac pathology and propensity toward early lethality due to TGF-β overactivation in the heart. Also, neither heart-specific Ctgf deletion nor CTGF overexpression altered cardiac remodeling and function with aging or after multiple acute stress stimuli. Cardiac fibrosis was also unchanged by modulation of CTGF levels in the heart with aging, pressure overload, agonist infusion, or TGF-β overexpression. However, CTGF mildly altered the overall cardiac response to TGF-β when pressure overload stimulation was applied. CTGF has been proposed to function as a critical TGF-β effector in underlying tissue remodeling and fibrosis throughout the body, although our results suggest that CTGF is of minimal importance and is an unlikely therapeutic vantage point for the heart.

Myofibroblasts in murine cutaneous fibrosis originate from adiponectin-positive intradermal progenitors

OBJECTIVE

Accumulation of myofibroblasts in fibrotic skin is a hallmark of systemic sclerosis (SSc; scleroderma), but the origins of these cells remain unknown. Because loss of intradermal adipose tissue is a consistent feature of cutaneous fibrosis, we sought to examine the hypothesis that myofibroblasts populating fibrotic dermis derive from adipocytic progenitors.

METHODS

We performed genetic fate mapping studies to investigate the loss of intradermal adipose tissue and its potential role in fibrosis in mice with bleomycin-induced scleroderma. Modulation of adipocytic phenotypes ex vivo was investigated in adipose tissue-derived cells in culture.

RESULTS

A striking loss of intradermal adipose tissue and its replacement with fibrous tissue were consistently observed in mice with bleomycin-induced fibrosis. Loss of adipose tissue and a decline in the expression of canonical adipogenic markers in lesional skin preceded the onset of dermal fibrosis and expression of fibrogenic markers. Ex vivo, subcutaneous adipocytes were driven by transforming growth factor β to preferentially undergo fibrogenic differentiation. Cell fate mapping studies in mice with the adiponectin promoter-driven Cre recombinase transgenic construct indicated that adiponectin-positive progenitors that are normally confined to the intradermal adipose tissue compartment were distributed throughout the lesional dermis over time, lost their adipocytic markers, and expressed myofibroblast markers in bleomycin-treated mice.

CONCLUSION

These observations establish a novel link between intradermal adipose tissue loss and dermal fibrosis and demonstrate that adiponectin-positive intradermal progenitors give rise to dermal myofibroblasts. Adipose tissue loss and adipocyte-myofibroblast transition might be primary events in the pathogenesis of cutaneous fibrosis that represent novel potential targets for therapeutic intervention.

CCN2 is required for recruitment of Sox2-expressing cells during cutaneous tissue repair

Connective tissue growth factor (CTGF/CCN2), a member of the CCN family of matricellular proteins is upregulated in both fibrosis as well as tissue repair. Recently, we showed that, in mice, CCN2 expression by fibroblasts was required for dermal fibrogenesis, but not for cutaneous tissue repair. Lineage tracing analysis linked the ability of CCN2 to promote fibrosis to the requirement for CCN2 to recruit cells expressing the progenitor cell marker Sox2 to fibrotic connective tissue and for differentiating these cells into myofibroblasts. Herein, we show that although loss of CCN2 expression by Sox2-expressing cells does not impair cutaneous tissue repair, CCN2 was required for recruitment of cells derived from Sox2-expressing cells to the wound area. Collectively, these results are consistent with the notion that neither CCN2 nor Sox2-expressing progenitor cells are essential for cutaneous tissue repair and that CCN2 represents a specific anti-fibrotic target.

Mesenchymal cells emerge as primary contributors to fibrosis in multiple tissues

A longstanding controversy exists regarding the cellular origin of myofibroblasts in tissue fibrosis. A recent study by Hung and colleagues (Am J Respir Crit Care Med 188(7):820-830, 2013) used genetic fate mapping of FoxD1 embryonic progenitor cells to show a major and direct contribution of mesenchymal cells to fibrogenesis in the lung. Future studies using FoxD1-specific inducible knockout models of pro-fibrotic genes such as CCN2 will be valuable for determining anti-fibrotic drug targets. The emergence of pericyte-like myofibroblast precursors also raises the question of whether mesenchymal stem cells in various niches contribute to fibrotic responses throughout the body.

CCN2 modulates hair follicle cycling in mice

Mesenchymal cells play a role in controlling the number of hair follicles. However, the precise molecules involved are unclear. Absence in mesenchymal cells of the expression of the secreted matricellular protein CTGF/CCN2 results in an increased number of hair follicles, concomitant with increased β-catenin activity.

It is critical to understand how stem cell activity is regulated during regeneration. Hair follicles constitute an important model for organ regeneration because, throughout adult life, they undergo cyclical regeneration. Hair follicle stem cells—epithelial cells located in the follicle bulge—are activated by periodic β-catenin activity, which is regulated not only by epithelial-derived Wnt, but also, through as-yet-undefined mechanisms, the surrounding dermal microenvironment. The matricellular protein connective tissue growth factor (CCN2) is secreted into the microenvironment and acts as a multifunctional signaling modifier. In adult skin, CCN2 is largely absent but is unexpectedly restricted to the dermal papillae and outer root sheath. Deletion of CCN2 in dermal papillae and the outer root sheath results in a shortened telogen-phase length and elevated number of hair follicles. Recombinant CCN2 causes decreased β-catenin stability in keratinocytes. In vivo, loss of CCN2 results in elevated numbers of K15-positive epidermal stem cells that possess elevated β-catenin levels and β-catenin–dependent reporter gene expression. These results indicate that CCN2 expression by dermal papillae cells is a physiologically relevant suppressor of hair follicle formation by destabilization of β-catenin and suggest that CCN2 normally acts to maintain stem cell quiescence.