Temporal control of PDGFRα regulates the fibroblast-to-myofibroblast transition in wound healing

Integrated-omics profiling unveils the disparities of host defense to ECM scaffolds during wound healing in aged individuals

Extracellular matrix (ECM) scaffold membranes have exhibited promising potential to better the outcomes of wound healing by creating a regenerative microenvironment around. However, when compared to the application in younger individuals, the performance of the same scaffold membrane in promoting re-epithelialization and collagen deposition was observed dissatisfying in aged mice. To comprehensively explore the mechanisms underlying this age-related disparity, we conducted the integrated analysis, combing single-cell RNA sequencing (scRNA-Seq) with spatial transcriptomics, and elucidated six functionally and spatially distinctive macrophage groups and lymphocytes surrounding the ECM scaffolds. Through intergroup comparative analysis and cell-cell communication, we characterized the dysfunction of Spp1+ macrophages in aged mice impeded the activation of the type Ⅱ immune response, thus inhibiting the repair ability of epidermal cells and fibroblasts around the ECM scaffolds. These findings contribute to a deeper understanding of biomaterial applications in varied physiological contexts, thereby paving the way for the development of precision-based biomaterials tailored specifically for aged individuals in future therapeutic strategies.

How to Keep Myofibroblasts under Control: Culture of Mouse Skin Fibroblasts on Soft Substrates

During the physiological healing of skin wounds, fibroblasts recruited from the uninjured adjacent dermis and deeper subcutaneous fascia layers are transiently activated into myofibroblasts to first secrete and then contract collagen-rich extracellular matrix into a mechanically resistant scar. Scar tissue restores skin integrity after damage but comes at the expense of poor esthetics and loss of tissue function. Stiff scar matrix also mechanically activates various precursor cells into myofibroblasts in a positive feedback loop. Persistent myofibroblast activation results in pathologic accumulation of fibrous collagen and hypertrophic scarring, called fibrosis. Consequently, the mechanisms of fibroblast-to-myofibroblast activation and persistence are studied to develop antifibrotic and prohealing treatments. Mechanistic understanding often starts in a plastic cell culture dish. This can be problematic because contact of fibroblasts with tissue culture plastic or glass surfaces invariably generates myofibroblast phenotypes in standard culture. We describe a straight-forward method to produce soft cell culture surfaces for fibroblast isolation and continued culture and highlight key advantages and limitations of the approach. Adding a layer of elastic silicone polymer tunable to the softness of normal skin and the stiffness of pathologic scars allows to control mechanical fibroblast activation while preserving the simplicity of conventional 2-dimensional cell culture.

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

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

A comprehensive exploration of hydrogel applications in multi-stage skin wound healing

Hydrogels, as an emerging biomaterial, have found extensive use in the healing of wounds due to their distinctive physicochemical structure and functional properties. Moreover, hydrogels can be made to match a range of therapeutic requirements for materials used in wound healing through specific functional modifications. This review provides a step-by-step explanation of the processes involved in cutaneous wound healing, including hemostasis, inflammation, proliferation, and reconstitution, along with an investigation of the factors that impact these processes. Furthermore, a thorough analysis is conducted on the various stages of the wound healing process at which functional hydrogels are implemented, including hemostasis, anti-infection measures, encouraging regeneration, scar reduction, and wound monitoring. Next, the latest progress of multifunctional hydrogels for wound healing and the methods to achieve these functions are discussed in depth and categorized for elucidation. Finally, perspectives and challenges associated with the clinical applications of multifunctional hydrogels are discussed.

Immunohistochemical analysis of PDGFR-α for wound age determination

Immunohistochemical analysis of platelet-derived growth factor receptor-α (PDGFR-α) was performed on human skin wounds obtained from forensic autopsy cases. Thirty human skin wounds were collected at different post-infliction intervals as follows: Group I, 4 h to 3 days (n = 16); Group II, 4 to 7 days (n = 7); Group III, 9 to 10 days (n = 3); and Group IV, 14 to 20 days (n = 4). Immunopositive reactions for PDGFR-α were not observed in the uninjured human skin specimens. In a semi-quantitative morphometrical analysis, the number of PDGFR-α-positive cells was observed increased in Group II, with the average number of PDGFR-α-positive cells being the highest in Group II. Additionally, in Group II, all specimens showed PDGFR-α-positive cells, with an average number of > 200 cells in five fields of view, suggesting a wound age of 4 to 7 days. Taken together, the immunohistochemical detection of PDGFR-α in human skin wounds can be a useful tool for wound age determination.

Early short-term hypoxia promotes epidermal cell migration by activating the CCL2-ERK1/2 pathway and epithelial-mesenchymal transition during wound healing

Background

Due to vasculature injury and increased oxygen consumption, the early wound microenvironment is typically in a hypoxic state. We observed enhanced cell migration ability under early short-term hypoxia. CCL2 belongs to the CC chemokine family and was found to be increased in early hypoxic wounds and enriched in the extracellular signal-regulated kinase (ERK)1/2 pathway in our previous study. However, the underlying mechanism through which the CCL2-ERK1/2 pathway regulates wound healing under early short-term hypoxia remains unclear. Activation of epithelial-mesenchymal transition (EMT) is a key process in cancer cell metastasis, during which epithelial cells acquire the characteristics of mesenchymal cells and enhance cell motility and migration ability. However, the relationship between epithelial cell migration and EMT under early short-term hypoxia has yet to be explored.

Methods

HaCaT cells were cultured to verify the effect of early short-term hypoxia on migration through cell scratch assays. Lentiviruses with silenced or overexpressed CCL2 were used to explore the relationship between CCL2 and migration under short-term hypoxia. An acute full-thickness cutaneous wound rat model was established with the application of an ERK inhibitor to reveal the hidden role of the ERK1/2 pathway in the early stage of wound healing. The EMT process was verified in all the above experiments through western blotting.

Results

In our study, we found that short-term hypoxia promoted cell migration. Mechanistically, hypoxia promoted cell migration through mediating CCL2. Overexpression of CCL2 via lentivirus promoted cell migration, while silencing CCL2 via lentivirus inhibited cell migration and the production of related downstream proteins. In addition, we found that CCL2 was enriched in the ERK1/2 pathway, and the application of an ERK inhibitor in vivo and in vitro verified the upstream and downstream relationships between the CCL2 pathway and ERK1/2. Western blot results both in vivo and in vitro demonstrated that early short-term hypoxia promotes epidermal cell migration by activating the CCL2-ERK1/2 pathway and EMT during wound healing.

Conclusions

Our work demonstrated that hypoxia in the early stage serves as a stimulus for triggering wound healing through activating the CCL2-ERK1/2 pathway and EMT, which promote epidermal cell migration and accelerate wound closure. These findings provide additional detailed insights into the mechanism of wound healing and new targets for clinical treatment.

Villus myofibroblasts are developmental and adult progenitors of mammalian gut lymphatic musculature

Inside the finger-like intestinal projections called villi, strands of smooth muscle cells contract to propel absorbed dietary fats through the adjacent lymphatic capillary, the lacteal, sending fats into the systemic blood circulation for energy production. Despite this vital function, mechanisms of formation, assembly alongside lacteals, and maintenance of villus smooth muscle are unknown. By combining single-cell RNA sequencing and quantitative lineage tracing of the mouse intestine, we identified a local hierarchy of subepithelial fibroblast progenitors that differentiate into mature smooth muscle fibers via intermediate contractile myofibroblasts. This continuum persists as the major mechanism for villus musculature renewal throughout adult life. The NOTCH3-DLL4 signaling axis governs the assembly of smooth muscle fibers alongside their adjacent lacteals and is required for fat absorption. Our studies identify the ontogeny and maintenance of a poorly defined class of intestinal smooth muscle, with implications for accelerated repair and recovery of digestive function following injury.

Beyond Encapsulation: Exploring Macrophage-Fibroblast Cross Talk in Implant-Induced Fibrosis

The foreign body response (FBR) and organ fibrosis are complex biological processes involving the interaction between macrophages and fibroblasts. Understanding the molecular mechanisms underlying macrophage-fibroblast cross talk is crucial for developing strategies to mitigate implant encapsulation, a major cause of implant failure. This article reviews the current knowledge on the role of macrophages and fibroblasts in the FBR and organ fibrosis, highlighting the similarities between these processes. The FBR is characterized by the formation of a fibrotic tissue capsule around the implant, leading to functional impairment. Various factors, including material properties such as surface chemistry, stiffness, and topography, influence the degree of encapsulation. Cross talk between macrophages and fibroblasts plays a critical role in both the FBR and organ fibrosis. However, the precise molecular mechanisms remain poorly understood. Macrophages secrete a wide range of cytokines that modulate fibroblast behavior such as abundant collagen deposition and myofibroblast differentiation. However, the heterogeneity of macrophages and fibroblasts and their dynamic behavior in different tissue environments add complexity to this cross talk. Experimental evidence from in vitro studies demonstrates the impact of material properties on macrophage cytokine secretion and fibroblast physiology. However, the correlation between in vitro response and in vivo encapsulation outcomes is not robust. Adverse outcome pathways (AOPs) offer a potential framework to understand and predict process complexity. AOPs describe causal relationships between measurable events leading to adverse outcomes, providing mechanistic insights for in vitro testing and predictive modeling. However, the development of an AOP for the FBR does require a comprehensive understanding of the molecular initiating events and key event relationships to identify which events are essential. In this article, we describe the current knowledge on macrophage-fibroblast cross talk in the FBR and discuss how targeted research can help build an AOP for implant-related fibrosis.

Fibroblasts and endothelial cells interplay drives hypertrophic scar formation: Insights from in vitro and in vivo models

Hypertrophic scar formation is influenced by the intricate interplay between fibroblasts and endothelial cells. In this study, we investigated this relationship using in vitro and in vivo models. Clinical observations revealed distinct morphological changes and increased vascularity at pathological scar sites. Further analysis using OCTA, immunohistochemistry, and immunofluorescence confirmed the involvement of angiogenesis in scar formation. Our indirect co-culture systems demonstrated that endothelial cells enhance the proliferation and migration of fibroblasts through the secretion of cytokines including VEGF, PDGF, bFGF, and TGF-β. Additionally, a suspended co-culture multicellular spheroid model revealed molecular-level changes associated with extracellular matrix remodeling, cellular behaviors, inflammatory response, and pro-angiogenic activity. Furthermore, KEGG pathway analysis identified the involvement of TGF-β, IL-17, Wnt, Notch, PI3K-Akt, and MAPK pathways in regulating fibroblasts activity. These findings underscore the critical role of fibroblasts-endothelial cells crosstalk in scar formation and provide potential targets for therapeutic intervention. Understanding the molecular mechanisms underlying this interplay holds promise for the development of innovative approaches to treat tissue injuries and diseases.

Therapeutic Potential and Mechanisms of Rosmarinic Acid and the Extracts of Lamiaceae Plants for the Treatment of Fibrosis of Various Organs

Fibrosis, which causes structural hardening and functional degeneration in various organs, is characterized by the excessive production and accumulation of connective tissue containing collagen, alpha-smooth muscle actin (α-SMA), etc. In traditional medicine, extracts of medicinal plants or herbal prescriptions have been used to treat various fibrotic diseases. The purpose of this narrative review is to discuss the antifibrotic effects of rosmarinic acid (RA) and plant extracts that contain RA, as observed in various experimental models. RA, as well as the extracts of Glechoma hederacea, Melissa officinalis, Elsholtzia ciliata, Lycopus lucidus, Ocimum basilicum, Prunella vulgaris, Salvia rosmarinus (Rosmarinus officinalis), Salvia miltiorrhiza, and Perilla frutescens, have been shown to attenuate fibrosis of the liver, kidneys, heart, lungs, and abdomen in experimental animal models. Their antifibrotic effects were associated with the attenuation of oxidative stress, inflammation, cell activation, epithelial-mesenchymal transition, and fibrogenic gene expression. RA treatment activated peroxisomal proliferator-activated receptor gamma (PPARγ), 5' AMP-activated protein kinase (AMPK), and nuclear factor erythroid 2-related factor 2 (NRF2) while suppressing the transforming growth factor beta (TGF-β) and Wnt signaling pathways. Interestingly, most plants that are reported to contain RA and exhibit antifibrotic activity belong to the family Lamiaceae. This suggests that RA is an active ingredient for the antifibrotic effect of Lamiaceae plants and that these plants are a useful source of RA. In conclusion, accumulating scientific evidence supports the effectiveness of RA and Lamiaceae plant extracts in alleviating fibrosis and maintaining the structural architecture and normal functions of various organs under pathological conditions.

Single-cell RNA sequencing analysis identifies one subpopulation of endothelial cells that proliferates and another that undergoes the endothelial-mesenchymal transition in regenerating pig hearts

Background: In our previous work, we demonstrated that when newborn pigs undergo apical resection (AR) on postnatal day 1 (P1), the animals' hearts were completely recover from a myocardial infarction (MI) that occurs on postnatal day 28 (P28); single-nucleus RNA sequencing (snRNAseq) data suggested that this recovery was achieved by regeneration of pig cardiomyocyte subpopulations in response to MI. However, coronary vasculature also has a key role in promoting cardiac repair. Method: Thus, in this report, we used autoencoder algorithms to analyze snRNAseq data from endothelial cells (ECs) in the hearts of the same animals. Main results: Our results identified five EC clusters, three composed of vascular ECs (VEC1-3) and two containing lymphatic ECs (LEC1-2). Cells from VEC1 expressed elevated levels of each of five cell-cyclespecific markers (Aurora Kinase B [AURKB], Marker of Proliferation Ki-67 [MKI67], Inner Centromere Protein [INCENP], Survivin [BIRC5], and Borealin [CDCA8]), as well as a number of transcription factors that promote EC proliferation, while (VEC3 was enriched for genes that regulate intercellular junctions, participate in transforming growth factor β (TGFβ), bone morphogenic protein (BMP) signaling, and promote the endothelial mesenchymal transition (EndMT). The remaining VEC2 did not appear to participate directly in the angiogenic response to MI, but trajectory analyses indicated that it may serve as a reservoir for the generation of VEC1 and VEC3 ECs in response to MI. Notably, only the VEC3 cluster was more populous in regenerating (i.e., ARP1MIP28) than non-regenerating (i.e., MIP28) hearts during the 1-week period after MI induction, which suggests that further investigation of the VEC3 cluster could identify new targets for improving myocardial recovery after MI. Histological analysis of KI67 and EndMT marker PDGFRA demonstrated that while the expression of proliferation of endothelial cells was not significantly different, expression of EndMT markers was significantly higher among endothelial cells of ARP1MIP28 hearts compared to MIP28 hearts, which were consistent with snRNAseq analysis of clusters VEC1 and VEC3. Furthermore, upregulated secrete genes by VEC3 may promote cardiomyocyte proliferation via the Pi3k-Akt and ERBB signaling pathways, which directly contribute to cardiac muscle regeneration. Conclusion: In regenerative heart, endothelial cells may express EndMT markers, and this process could contribute to regeneration via a endothelial-cardiomyocyte crosstalk that supports cardiomyocyte proliferation.

Origin and adult renewal of the gut lacteal musculature from villus myofibroblasts

Intestinal smooth muscles are the workhorse of the digestive system. Inside the millions of finger-like intestinal projections called villi, strands of smooth muscle cells contract to propel absorbed dietary fats through the adjacent lymphatic vessel, called the lacteal, sending fats into the blood circulation for energy production. Despite this vital function, how villus smooth muscles form, how they assemble alongside lacteals, and how they repair throughout life remain unknown. Here we combine single-cell RNA sequencing of the mouse intestine with quantitative lineage tracing to reveal the mechanisms of formation and differentiation of villus smooth muscle cells. Within the highly regenerative villus, we uncover a local hierarchy of subepithelial fibroblast progenitors that progress to become mature smooth muscle fibers, via an intermediate contractile myofibroblast-like phenotype. This continuum persists in the adult intestine as the major source of renewal of villus smooth muscle cells during adult life. We further found that the NOTCH3-DLL4 signaling axis governs the assembly of villus smooth muscles alongside their adjacent lacteal, and we show that this is necessary for gut absorptive function. Overall, our data shed light on the genesis of a poorly defined class of intestinal smooth muscle and pave the way for new opportunities to accelerate recovery of digestive function by stimulating muscle repair.

WAVE2 Is a Vital Regulator in Myogenic Differentiation of Progenitor Cells through the Mechanosensitive MRTFA-SRF Axis

Skeletal myogenesis is an intricate process involving the differentiation of progenitor cells into myofibers, which is regulated by actin cytoskeletal dynamics and myogenic transcription factors. Although recent studies have demonstrated the pivotal roles of actin-binding proteins (ABPs) as mechanosensors and signal transducers, the biological significance of WAVE2 (Wiskott-Aldrich syndrome protein family member 2), an ABP essential for actin polymerization, in myogenic differentiation of progenitor cells has not been investigated. Our study provides important insights into the regulatory roles played by WAVE2 in the myocardin-related transcription factor A (MRTFA)-serum response factor (SRF) signaling axis and differentiation of myoblasts. We demonstrate that WAVE2 expression is induced during myogenic differentiation and plays a pivotal role in actin cytoskeletal remodeling in C2C12 myoblasts. Knockdown of WAVE2 in C2C12 cells reduced filamentous actin levels, increased globular actin accumulation, and impaired the nuclear translocation of MRTFA. Furthermore, WAVE2 depletion in myoblasts inhibited the expression and transcriptional activity of SRF and suppressed cell proliferation in myoblasts. Consequently, WAVE2 knockdown suppressed myogenic regulatory factors (i.e., MyoD, MyoG, and SMYD1) expressions, thereby hindering the differentiation of myoblasts. Thus, this study suggests that WAVE2 is essential for myogenic differentiation of progenitor cells by modulating the mechanosensitive MRTFA-SRF axis.

Impact of a High-Fat Diet at a Young Age on Wound Healing in Mice

As the prevalence of juvenile-onset obesity rises globally, the multitude of related health consequences gain significant importance. In this context, obesity is associated with impaired cutaneous wound healing. In experimental settings, mice are the most frequently used model for investigating the effect of high-fat diet (HFD) chow on wound healing in wild-type or genetically manipulated animals, e.g., diabetic ob/ob and db/db mice. However, these studies have mainly been performed on adult animals. Thus, in the present study, we introduced a mouse model for a juvenile onset of obesity. We exposed 4-week-old mice to an investigational feeding period of 9 weeks with an HFD compared to a regular diet (RD). At a mouse age of 13 weeks, we performed excisional and incisional wounding and measured the healing rate. Wound healing was examined by serial photographs with daily wound size measurements of the excisional wounds. Histology from incisional wounds was performed to quantify granulation tissue (thickness, quality) and angiogenesis (number of blood vessels per mm2). The expression of extracellular matrix proteins (collagen types I/III/IV, fibronectin 1, elastin), inflammatory cytokines (MIF, MIF-2, IL-6, TNF-α), myofibroblast differentiation (α-SMA) and macrophage polarization (CD11c, CD301b) in the incisional wounds were evaluated by RT-qPCR and by immunohistochemistry. There was a marked delay of wound closure in the HFD group with a decrease in granulation tissue quality and thickness. Additionally, inflammatory cytokines (MIF, IL-6, TNF-α) were significantly up-regulated in HFD- when compared to RD-fed mice measured at day 3. By contrast, MIF-2 and blood vessel expression were significantly reduced in the HFD animals, starting at day 1. No significant changes were observed in macrophage polarization, collagen expression, and levels of TGF-β1 and PDGF-A. Our findings support that an early exposition to HFD resulted in juvenile obesity in mice with impaired wound repair mechanisms, which may be used as a murine model for obesity-related studies in the future.

Single-cell profiling reveals transcriptomic signatures of vascular endothelial cells in non-healing diabetic foot ulcers

Background

The treatment of diabetic foot ulcers (DFUs) poses a challenging medical problem that has long plagued individuals with diabetes. Clinically, wounds that fail to heal for more than 12 weeks after the formation of DFUs are referred to as non-healing/chronic wounds. Among various factors contributing to the non-healing of DFUs, the impairment of skin microvascular endothelial cell function caused by high glucose plays a crucial role. Our study aimed to reveal the transcriptomic signatures of non-healing DFUs endothelial cells, providing novel intervention targets for treatment strategies.

Methods

Based on the GEO dataset (GSE165816), we selected DFU-Healer, DFU-Non-healer, and healthy non-diabetic controls as research subjects. Single-cell RNA transcriptomic sequencing technology was employed to analyze the heterogeneity of endothelial cells in different skin tissue samples and identify healing-related endothelial cell subpopulations. Immunofluorescence was applied to validate the sequencing results on clinical specimens.

Results

The number of endothelial cells and vascular density showed no significant differences among the three groups of skin specimens. However, endothelial cells from non-healing DFUs exhibited apparent inhibition of angiogenesis, inflammation, and immune-related signaling pathways. The expression of CCND1, ENO1, HIF1α, and SERPINE1 was significantly downregulated at the transcriptomic and histological levels. Further analysis demonstrated that healing-related endothelial cell subpopulations in non-healing DFUs has limited connection with other cell types and weaker differentiation ability.

Conclusion

At the single-cell level, we uncovered the molecular and functional specificity of endothelial cells in non-healing DFUs and highlighted the importance of endothelial cell immune-mediated capability in angiogenesis and wound healing. This provides new insights for the treatment of DFUs.

Regulation of adipocyte dedifferentiation at the skin wound edge

Adipocytes have diverse roles in energy storage and metabolism, inflammation, and tissue repair. Mature adipocytes have been assumed to be terminally differentiated cells. However, recent evidence suggests that adipocytes retain substantial phenotypic plasticity, with potential to dedifferentiate into fibroblast-like cells under physiological and pathological conditions. Here, we develop a two-step lineage tracing approach based on the observation that fibroblasts express platelet-derived growth factor receptor alpha ( Pdgfra ) while adipocytes express Adiponectin ( Adipoq ) but not Pdgfra . Our approach specifically traces Pdgfra + cells that originate from Adipoq + adipocytes. We find many traced adipocytes and fibroblast-like cells surrounding skin wounds, but only a few traced cells localize to the wound center. In agreement with adipocyte plasticity, traced adipocytes incorporate EdU, downregulate Plin1 and PPARγ, and upregulate αSMA. We also investigate the role of potential dedifferentiation signals using constitutively active PDGFRα mutation, Pdgfra knockout, or Tgfbr2 knockout models. We find that PDGF and TGFβ signaling both promote dedifferentiation, and PDGFRα does so independently of TGFβR2. These results demonstrate an intersectional genetic approach to trace the hybrid cell phenotype of Pdgfra + adipocytes, which may be important for wound repair, regeneration and fibrosis.

Allometrically scaling tissue forces drive pathological foreign-body responses to implants via Rac2-activated myeloid cells

Small animals do not replicate the severity of the human foreign-body response (FBR) to implants. Here we show that the FBR can be driven by forces generated at the implant surface that, owing to allometric scaling, increase exponentially with body size. We found that the human FBR is mediated by immune-cell-specific RAC2 mechanotransduction signalling, independently of the chemistry and mechanical properties of the implant, and that a pathological FBR that is human-like at the molecular, cellular and tissue levels can be induced in mice via the application of human-tissue-scale forces through a vibrating silicone implant. FBRs to such elevated extrinsic forces in the mice were also mediated by the activation of Rac2 signalling in a subpopulation of mechanoresponsive myeloid cells, which could be substantially reduced via the pharmacological or genetic inhibition of Rac2. Our findings provide an explanation for the stark differences in FBRs observed in small animals and humans, and have implications for the design and safety of implantable devices.

Stricturing Crohn's Disease Single-Cell RNA Sequencing Reveals Fibroblast Heterogeneity and Intercellular Interactions

BACKGROUND & AIMS

Fibroblasts play a key role in stricture formation in Crohn's disease (CD) but understanding its pathogenesis requires a systems-level investigation to uncover new treatment targets. We studied full-thickness CD tissues to characterize fibroblast heterogeneity and function by generating the first single-cell RNA sequencing (scRNAseq) atlas of strictured bowel and providing proof of principle for therapeutic target validation.

METHODS

We performed scRNAseq of 13 fresh full-thickness CD resections containing noninvolved, inflamed nonstrictured, and strictured segments as well as 7 normal non-CD bowel segments. Each segment was separated into mucosa/submucosa or muscularis propria and analyzed separately for a total of 99 tissue samples and 409,001 cells. We validated cadherin-11 (CDH11) as a potential therapeutic target by using whole tissues, isolated intestinal cells, NanoString nCounter, next-generation sequencing, proteomics, and animal models.

RESULTS

Our integrated dataset revealed fibroblast heterogeneity in strictured CD with the majority of stricture-selective changes detected in the mucosa/submucosa, but not the muscle layer. Cell-cell interaction modeling revealed CXCL14+ as well as MMP/WNT5A+ fibroblasts displaying a central signaling role in CD strictures. CDH11, a fibroblast cell-cell adhesion molecule, was broadly expressed and up-regulated, and its profibrotic function was validated using NanoString nCounter, RNA sequencing, tissue target expression, in vitro gain- and loss-of-function experiments, proteomics, and knock-out and antibody-mediated CDH11 blockade in experimental colitis.

CONCLUSIONS

A full-thickness bowel scRNAseq atlas revealed previously unrecognized fibroblast heterogeneity and interactions in CD strictures and CDH11 was validated as a potential therapeutic target. These results provide a new resource for a better understanding of CD stricture formation and open potential therapeutic developments. This work has been posted as a preprint on Biorxiv under doi: 10.1101/2023.04.03.534781.

Radiation induces long-term muscle fibrosis and promotes a fibrotic phenotype in fibro-adipogenic progenitors

BACKGROUND

Radiation-induced muscle pathology, characterized by muscle atrophy and fibrotic tissue accumulation, is the most common debilitating late effect of therapeutic radiation exposure particularly in juvenile cancer survivors. In healthy muscle, fibro/adipogenic progenitors (FAPs) are required for muscle maintenance and regeneration, while in muscle pathology FAPs are precursors for exacerbated extracellular matrix deposition. However, the role of FAPs in radiation-induced muscle pathology has not previously been explored.

METHODS

Four-week-old Male CBA or C57Bl/6J mice received a single dose (16 Gy) of irradiation (IR) to a single hindlimb with the shielded contralateral limb (CLTR) serving as a non-IR control. Mice were sacrificed 3, 7, 14 (acute IR response), and 56 days post-IR (long-term IR response). Changes in skeletal muscle morphology, myofibre composition, muscle niche cellular dynamics, DNA damage, proliferation, mitochondrial respiration, and metabolism and changes in progenitor cell fate where assessed.

RESULTS

Juvenile radiation exposure resulted in smaller myofibre cross-sectional area, particularly in type I and IIA myofibres (P < 0.05) and reduced the proportion of type I myofibres (P < 0.05). Skeletal muscle fibrosis (P < 0.05) was evident at 56 days post-IR. The IR-limb had fewer endothelial cells (P < 0.05) and fibro-adipogenic progenitors (FAPs) (P < 0.05) at 56 days post-IR. Fewer muscle satellite (stem) cells were detected at 3 and 56 days in the IR-limb (P < 0.05). IR induced FAP senescence (P < 0.05), increased their fibrogenic differentiation (P < 0.01), and promoted their glycolytic metabolism. Further, IR altered the FAP secretome in a manner that impaired muscle satellite (stem) cell differentiation (P < 0.05) and fusion (P < 0.05).

CONCLUSIONS

Our study suggests that following juvenile radiation exposure, FAPs contribute to long-term skeletal muscle atrophy and fibrosis. These findings provide rationale for investigating FAP-targeted therapies to ameliorate the negative late effects of radiation exposure in skeletal muscle.

Progranulin inhibits fibrosis by interacting with and up-regulating DNAJC3 during mouse skin wound healing

Scars place a heavy burden on both individuals and society. Our previous study found that reduction of progranulin (PGRN) promotes fibrogenesis in mouse skin wound healing. However, the underlying mechanisms have not been elucidated. Here, we report that PGRN overexpression decreases the expression of profibrotic genes alpha-smooth muscle actin (αSMA), serum response factor (SRF), and connective tissue growth factor (CTGF), thereby inhibiting skin fibrosis during wound repair. Bioinformatics analysis suggested that the heat shock protein (Hsp) 40 superfamily C3 (DNAJC3) is a potential downstream molecule of PGRN. Further experiments showed that PGRN interacts with and upregulates DNAJC3. Moreover, this antifibrotic effect was rescued by DNAJC3 knockdown. In summary, our study suggests that PGRN inhibits fibrosis by interacting with and upregulating DNAJC3 during wound healing in mouse skin. Our study provides a mechanistic explanation of the effect of PGRN on fibrogenesis in skin wound healing.

Identifying fibrogenic cells following salivary gland obstructive injury

Fibrosis results from excess extracellular matrix accumulation, which alters normal tissue architecture and impedes function. In the salivary gland, fibrosis can be induced by irradiation treatment for cancer therapy, Sjögren's Disease, and other causes; however, it is unclear which stromal cells and signals participate in injury responses and disease progression. As hedgehog signaling has been implicated in fibrosis of the salivary gland and other organs, we examined contributions of the hedgehog effector, Gli1, to fibrotic responses in salivary glands. To experimentally induce a fibrotic response in female murine submandibular salivary glands, we performed ductal ligation surgery. We detected a progressive fibrotic response where both extracellular matrix accumulation and actively remodeled collagen significantly increased at 14 days post-ligation. Macrophages, which participate in extracellular matrix remodeling, and Gli1+ and PDGFRα+ stromal cells, which may deposit extracellular matrix, both increased with injury. Using single-cell RNA-sequencing, Gli1 + cells were not found in discrete clusters at embryonic day 16 but were found in clusters expressing the stromal genes Pdgfra and/or Pdgfrb. In adult mice, Gli1+ cells were similarly heterogeneous but more cells co-expressed PDGFRα and PDGFRβ. Using Gli1-CreERT2; ROSA26tdTomato lineage-tracing mice, we found that Gli1-derived cells expand with ductal ligation injury. Although some of the Gli1 lineage-traced tdTomato+ cells expressed vimentin and PDGFRβ following injury, there was no increase in the classic myofibroblast marker, smooth muscle alpha-actin. Additionally, there was little change in extracellular matrix area, remodeled collagen area, PDGFRα, PDGFRβ, endothelial cells, neurons, or macrophages in Gli1 null salivary glands following injury when compared with controls, suggesting that Gli1 signaling and Gli1+ cells have only a minor contribution to mechanical injury-induced fibrotic changes in the salivary gland. We used scRNA-seq to examine cell populations that expand with ligation and/or showed increased expression of matrisome genes. Some Pdgfra + /Pdgfrb + stromal cell subpopulations expanded in response to ligation, with two stromal cell subpopulations showing increased expression of Col1a1 and a greater diversity of matrisome genes, consistent with these cells being fibrogenic. However, only a few cells in these subpopulations expressed Gli1, consistent with a minor contribution of these cells to extracellular matrix production. Defining the signaling pathways driving fibrotic responses in stromal cell sub-types could reveal future therapeutic targets.

The total iridoid glycoside extract of Lamiophlomis rotata Kudo induces M2 macrophage polarization to accelerate wound healing by RAS/ p38 MAPK/NF-κB pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Lamiophlomis rotata (Benth.) Kudo (L. rotata), a Tibetan medicinal plant, is used to treat "yellow-water diseases", such as skin disease, jaundice and rheumatism. Our previous study showed that the iridoid glycoside extract of L. rotata (IGLR) is the major constituent of skin wound healing. However, the role of IGLR in the biological process of trauma repair and the probable mechanism of the action remain largely unknown.

AIM OF THE STUDY

To investigate the role of IGLR in the biological process of trauma repair and the probable mechanism of the action.

MATERIALS AND METHODS

The role of IGLR in wound healing was investigated by overall skin wound in mice with Hematoxylin and Eosin (H&E) and Masson trichrome staining. The anti-inflammatory, angiogenesis-promoting and fibril formation effects of IGLR were visualized in wound skin tissue by immunofluorescence staining, and the proinflammatory factors and growth factors were assayed by real-time polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). Macrophages, dermal fibroblasts, and endothelial cells were cultured to measure the direct/indirect interaction effects of IGLR on the proliferation and migration of cells, and flow cytometry was employed to assess the role of IGLR on macrophage phenotype. Network pharmacology combined with Western blot experiments were conducted to explore possible mechanisms of the actions.

RESULTS

IGLR increased the expression of CD206 (M2 markers) through the RAS/p38 MAPK/NF-κB signaling pathway during wound injury in vivo and in vitro. IGLR suppressed the inflammatory cytokines iNOS, IL-1β and TNF-α in the early stage of wound healing. During the proliferation step of wound repair, IGLR promoted angiogenesis and fibril formation by increasing the expression of VEGF, CD31, TGF-β and α-SMA in wound tissue, and similar results were verified by RT-PCR and ELISA. In a paracrine mechanism, the extract promoted the proliferation of dermal fibroblasts, and endothelial cells were founded by the conditioned medium (CM).

CONCLUSION

IGLR induced M2 macrophage polarization in the early stage of wound healing; in turn, IGLR played a key role in the transition from inflammation to cell proliferation during the biological process of wound healing.

A Quick Guide to CAF Subtypes in Pancreatic Cancer

Pancreatic cancer represents one of the most desmoplastic malignancies and is characterized by an extensive deposition of extracellular matrix. The latter is provided by activated cancer-associated fibroblasts (CAFs), which are abundant cells in the pancreatic tumor microenvironment. Many recent studies have made it clear that CAFs are not a singular cellular entity but represent a multitude of potentially dynamic subgroups that affect tumor biology at several levels. As mentioned before, CAFs significantly contribute to the fibrotic reaction and the biomechanical properties of the tumor, but they can also modulate the local immune environment and the response to targeted, chemo or radiotherapy. As the number of known and emerging CAF subgroups is steadily increasing, it is becoming increasingly difficult to keep up with these developments and to clearly discriminate the cellular subsets identified so far. This review aims to provide a helpful overview that enables readers to quickly familiarize themselves with field of CAF heterogeneity and to grasp the phenotypic, functional and therapeutic distinctions of the various stromal subpopulations.

Stricturing Crohn's disease single-cell RNA sequencing reveals fibroblast heterogeneity and intercellular interactions

Background

Fibroblasts play a key role in stricture formation in Crohn's disease (CD) but understanding it's pathogenesis requires a systems-level investigation to uncover new treatment targets. We studied full thickness CD tissues to characterize fibroblast heterogeneity and function by generating the first single cell RNA sequencing (scRNAseq) atlas of strictured bowel and providing proof of principle for therapeutic target validation.

Methods

We performed scRNAseq of 13 fresh full thickness CD resections containing non-involved, inflamed non-strictured, and strictured segments as well as 7 normal non-CD bowel segments. Each segment was separated into mucosa/submucosa or muscularis propria and analyzed separately for a total of 99 tissue samples and 409,001 cells. We validated cadherin-11 (CDH11) as a potential therapeutic target by using whole tissues, isolated intestinal cells, NanoString nCounter, next generation sequencing, proteomics and animal models.

Results

Our integrated dataset revealed fibroblast heterogeneity in strictured CD with the majority of stricture-selective changes detected in the mucosa/submucosa, but not the muscle layer. Cell-cell interaction modeling revealed CXCL14+ as well as MMP/WNT5A+ fibroblasts displaying a central signaling role in CD strictures. CDH11, a fibroblast cell-cell adhesion molecule, was broadly expressed and upregulated, and its pro-fibrotic function was validated by NanoString nCounter, RNA sequencing, tissue target expression, in vitro gain- and loss-of-function experiments, proteomics, and two animal models of experimental colitis.

Conclusion

A full-thickness bowel scRNAseq atlas revealed previously unrecognized fibroblast heterogeneity and interactions in CD strictures and CDH11 was validated as a potential therapeutic target. These results provide a new resource for a better understanding of CD stricture formation and opens potential therapeutic developments.

Identifying Fibrogenic Cells Following Salivary Gland Obstructive Injury

Fibrosis results from excess extracellular matrix accumulation, which alters normal tissue architecture and impedes function. In the salivary gland, fibrosis can be induced by irradiation treatment for cancer therapy, Sjögren's Disease, and other causes; however, it is unclear which stromal cells and signals participate in injury responses and disease progression. As hedgehog signaling has been implicated in fibrosis of the salivary gland and other organs, we examined contributions of the hedgehog effector, Gli1, to fibrotic responses in salivary glands. To experimentally induce a fibrotic response in female murine submandibular salivary glands, we performed ductal ligation surgery. We detected a progressive fibrotic response where both extracellular matrix accumulation and actively remodeled collagen trended upwards at 7 days and significantly increased at 14 days post- ligation. Macrophages, which participate in extracellular matrix remodeling, Gli1 + and PDGFRα + stromal cells, which may deposit extracellular matrix, both increased with injury. Using single-cell RNA-sequencing, we found that a majority of Gli1 + cells at embryonic day 16 also express Pdgfra and/or Pdgfrb. However, in adult mice, only a small subset of Gli1 + cells express PDGFRα and/or PDGFRβ at the protein level. Using lineage-tracing mice, we found that Gli1-derived cells expand with ductal ligation injury. Although some of the Gli1 lineage-traced tdTomato + cells expressed vimentin and PDGFRβ following injury, there was no increase in the classic myofibroblast marker, smooth muscle alpha-actin. Additionally, there was little change in extracellular matrix area, remodeled collagen area, PDGFRα, PDGFRβ, endothelial cells, neurons, or macrophages in Gli1 null salivary glands following injury when compared with controls, suggesting that Gli1 signaling and Gli1 + cells have only a minor contribution to mechanical injury-induced fibrotic changes in the salivary gland. We used scRNA-seq to examine cell populations that expand with ligation and/or showed increased expression of matrisome genes. Pdgfra + /Pdgfrb + stromal cell subpopulations both expanded in response to ligation, showed increased expression and a greater diversity of matrisome genes expressed, consistent with these cells being fibrogenic. Defining the signaling pathways driving fibrotic responses in stromal cell sub-types could reveal future therapeutic targets.

Fascia Layer-A Novel Target for the Application of Biomaterials in Skin Wound Healing

As the first barrier of the human body, the skin has been of great concern for its wound healing and regeneration. The healing of large, refractory wounds is difficult to be repaired by cell proliferation at the wound edges and usually requires manual intervention for treatment. Therefore, therapeutic tools such as stem cells, biomaterials, and cytokines have been applied to the treatment of skin wounds. Skin microenvironment modulation is a key technology to promote wound repair and skin regeneration. In recent years, a series of novel bioactive materials that modulate the microenvironment and cell behavior have been developed, showing the ability to efficiently facilitate wound repair and skin attachment regeneration. Meanwhile, our lab found that the fascial layer has an indispensable role in wound healing and repair, and this review summarizes the research progress of related bioactive materials and their role in wound healing.

Treatment of skin defects with PRP enriched with hyaluronic acid - histological aspects in rat model

Tissue healing is a complex, dynamic process, characterized by the replacement of devitalized and absent cell and tissue structures. This can be obtained by different methods, these being found in the "reconstructive scale", which although it is very rich does not offer a universally valid solution for closing skin wounds. In plastic surgery, platelet-rich plasma (PRP) has proven effective in the treatment of skin graft donor areas, burn wounds, skin grafts, tendons, or varicose ulcers. Also, hyaluronic acid (HA) has found its utility in different areas of medicine, other than the esthetics field, with satisfactory results after its use in various lesions. The aim of our study was to find a method of healing wounds with skin defect that shortens the time of complete epithelialization compared to native healing, which is accessible to any patient both by its simplicity and by the lowest possible costs. So, we decided to test a preparation consisting of PRP and granular HA in this type of wounds on a group of 30 Wistar rats. Corroborating the macroscopic data with the microscopic ones, an important similarity can be observed between the healing of the adjuvant-treated lesion at 14 days postoperatively and the healing of the lesion left to natural healing at 21 days, thus shortening the healing period by seven days.