Syndecan-4 independently regulates multiple small GTPases to promote fibroblast migration during wound healing

Integrins as a bridge between bacteria and cells: key targets for therapeutic wound healing

Integrins are heterodimers composed of α and β subunits that are bonded through non-covalent interactions. Integrins mediate the dynamic connection between extracellular adhesion molecules and the intracellular actin cytoskeleton. Integrins are present in various tissues and organs where these heterodimers participate in diverse physiological and pathological responses at the molecular level in living organisms. Wound healing is a crucial process in the recovery from traumatic diseases and comprises three overlapping phases: inflammation, proliferation and remodeling. Integrins are regulated during the entire wound healing process to enhance processes such as inflammation, angiogenesis and re-epithelialization. Prolonged inflammation may result in failure of wound healing, leading to conditions such as chronic wounds. Bacterial colonization of a wound is one of the primary causes of chronic wounds. Integrins facilitate the infectious effects of bacteria on the host organism, leading to chronic inflammation, bacterial colonization, and ultimately, the failure of wound healing. The present study investigated the role of integrins as bridges for bacteria-cell interactions during wound healing, evaluated the role of integrins as nodes for bacterial inhibition during chronic wound formation, and discussed the challenges and prospects of using integrins as therapeutic targets in wound healing.

Soluble vascular endothelial glycocalyx proteoglycans as potential therapeutic targets in inflammatory diseases

Reducing the activity of cytokines and leukocyte extravasation is an emerging therapeutic strategy to limit tissue-damaging inflammatory responses and restore immune homeostasis in inflammatory diseases. Proteoglycans embedded in the vascular endothelial glycocalyx, which regulate the activity of cytokines to restrict the inflammatory response in physiological conditions, are proteolytically cleaved in inflammatory diseases. Here we critically review the potential of proteolytically shed, soluble vascular endothelial glycocalyx proteoglycans to modulate pathological inflammatory responses. Soluble forms of the proteoglycans syndecan-1, syndecan-3 and biglycan exert beneficial anti-inflammatory effects by the removal of chemokines, suppression of proinflammatory cytokine expression and leukocyte migration, and induction of autophagy of proinflammatory M1 macrophages. By contrast, soluble versikine and decorin enhance proinflammatory responses by increasing inflammatory cytokine synthesis and leukocyte migration. Endogenous syndecan-2 and mimecan exert proinflammatory effects, syndecan-4 and perlecan mediate beneficial anti-inflammatory effects and glypican regulates Hh and Wnt signaling pathways involved in systemic inflammatory responses. Taken together, targeting the vascular endothelial glycocalyx-derived, soluble syndecan-1, syndecan-2, syndecan-3, syndecan-4, biglycan, versikine, mimecan, perlecan, glypican and decorin might be a potential therapeutic strategy to suppress overstimulated cytokine and leukocyte responses in inflammatory diseases.

Thy-1 (CD90)-regulated cell adhesion and migration of mesenchymal cells: insights into adhesomes, mechanical forces, and signaling pathways

Cell adhesion and migration depend on the assembly and disassembly of adhesive structures known as focal adhesions. Cells adhere to the extracellular matrix (ECM) and form these structures via receptors, such as integrins and syndecans, which initiate signal transduction pathways that bridge the ECM to the cytoskeleton, thus governing adhesion and migration processes. Integrins bind to the ECM and soluble or cell surface ligands to form integrin adhesion complexes (IAC), whose composition depends on the cellular context and cell type. Proteomic analyses of these IACs led to the curation of the term adhesome, which is a complex molecular network containing hundreds of proteins involved in signaling, adhesion, and cell movement. One of the hallmarks of these IACs is to sense mechanical cues that arise due to ECM rigidity, as well as the tension exerted by cell-cell interactions, and transduce this force by modifying the actin cytoskeleton to regulate cell migration. Among the integrin/syndecan cell surface ligands, we have described Thy-1 (CD90), a GPI-anchored protein that possesses binding domains for each of these receptors and, upon engaging them, stimulates cell adhesion and migration. In this review, we examine what is currently known about adhesomes, revise how mechanical forces have changed our view on the regulation of cell migration, and, in this context, discuss how we have contributed to the understanding of signaling mechanisms that control cell adhesion and migration.

Thy-1-Integrin Interactions in cis and Trans Mediate Distinctive Signaling

Thy-1 is a cell surface glycosylphosphatidylinositol (GPI)-anchored glycoprotein that bears a broad mosaic of biological roles across various cell types. Thy-1 displays strong physiological and pathological implications in development, cancer, immunity, and tissue fibrosis. Quite uniquely, Thy-1 is capable of mediating integrin-related signaling through direct trans- and cis-interaction with integrins. Both interaction types have shown distinctive roles, even when interacting with the same type of integrin, where binding in trans or in cis often yields divergent signaling events. In this review, we will revisit recent progress and discoveries of Thy-1–integrin interactions in trans and in cis, highlight their pathophysiological consequences and explore other potential binding partners of Thy-1 within the integrin regulation/signaling paradigm.

Pathways of integrins in the endo-lysosomal system

In this review, we present recent scientific advances about integrin trafficking in the endo-lysosomal system. In the last few years, plenty of new information has emerged about the endo-lysosomal system, integrins, and the mechanism, how exactly the intracellular trafficking of integrins is regulated. We review the internalization and recycling pathways of integrins, and we provide information about the possible ways of lysosomal degradation through the endosomal and autophagic system. The regulation of integrin internalization and recycling proved to be a complex process worth studying. Trafficking of integrins, together with the regulation of their gene expression, defines cellular adhesion and cellular migration through bidirectional signalization and ligand binding. Thus, any malfunction in this system can potentially (but not necessarily) lead to tumorigenesis or metastasis. Hence, extensive examinations of integrins in the endo-lysosomal system raise the possibility to identify potential new medical targets. Furthermore, this knowledge can also serve as a basis for further determination of integrin signaling- and adhesion-related processes.

KRAS Addiction Promotes Cancer Cell Adaptation in Harsh Microenvironment Through Macropinocytosis

KRAS is the most frequently mutated oncogene in cancer and despite intensive studies, attempts to develop effective therapies targeting KRAS or its downstream signaling have failed mostly due to the complexity of KRAS activation and function in cancer initiation and progression. Over the years, KRAS has been involved in several biological processes including cell survival, proliferation, and metabolism by promoting not only a favorable tumor environment but also a cell-microenvironment dialog to allow cancer cells to adapt to tumor microenvironment scarcity. One of the mechanisms involved in this adaption is KRAS-mediated macropinocytosis. Macropinocytosis is an evolutionarily conserved, large-scale, and nonselective form of endocytosis involving actin-driven cell membrane remodeling to engulf large amounts of extracellular fluids and proteins from the local environment. While macropinocytosis process has been known for decades, recent gain interest due to its regulation of KRAS-driven tumor growth in adverse microenvironments. By promoting extracellular protein and other macromolecules internalization, macropinocytosis provides a survival mechanism under nutrient scarce conditions and the potential for unrestricted tumor growth. Thus, a better understanding of macropinocytotic process is needed to develop alternative therapeutic strategies.

Thy-1 (CD90), Integrins and Syndecan 4 are Key Regulators of Skin Wound Healing

Acute skin wound healing is a multistage process consisting of a plethora of tightly regulated signaling events in specialized cells. The Thy-1 (CD90) glycoprotein interacts with integrins and the heparan sulfate proteoglycan syndecan 4, generating a trimolecular complex that triggers bi-directional signaling to regulate diverse aspects of the wound healing process. These proteins can act either as ligands or receptors, and they are critical for the successful progression of wound healing. The expression of Thy-1, integrins, and syndecan 4 is controlled during the healing process, and the lack of expression of any of these proteins results in delayed wound healing. Here, we review and discuss the roles and regulatory events along the stages of wound healing that support the relevance of Thy-1, integrins, and syndecan 4 as crucial regulators of skin wound healing.

Autophagy and Mitophagy-Related Pathways at the Crossroads of Genetic Pathways Involved in Familial Sarcoidosis and Host-Pathogen Interactions Induced by Coronaviruses

Sarcoidosis is a multisystem disease characterized by the development and accumulation of granulomas, the hallmark of an inflammatory process induced by environmental and/or infectious and or genetic factors. This auto-inflammatory disease mainly affects the lungs, the gateway to environmental aggressions and viral infections. We have shown previously that genetic predisposition to sarcoidosis occurring in familial cases is related to a large spectrum of pathogenic variants with, however, a clustering around mTOR (mammalian Target Of Rapamycin)-related pathways and autophagy regulation. The context of the COVID-19 pandemic led us to evaluate whether such genetic defects may increase the risk of a severe course of SARS-CoV2 infection in patients with sarcoidosis. We extended a whole exome screening to 13 families predisposed to sarcoidosis and crossed the genes sharing mutations with the list of genes involved in the SARS-CoV2 host-pathogen protein-protein interactome. A similar analysis protocol was applied to a series of 100 healthy individuals. Using ENRICH.R, a comprehensive gene set enrichment web server, we identified the functional pathways represented in the set of genes carrying deleterious mutations and confirmed the overrepresentation of autophagy- and mitophagy-related functions in familial cases of sarcoidosis. The same protocol was applied to the set of genes common to sarcoidosis and the SARS-CoV2-host interactome and found a significant enrichment of genes related to mitochondrial factors involved in autophagy, mitophagy, and RIG-I-like (Retinoic Acid Inducible Gene 1) Receptor antiviral response signaling. From these results, we discuss the hypothesis according to which sarcoidosis is a model for studying genetic abnormalities associated with host response to viral infections as a consequence of defects in autophagy and mitophagy processes.

Development of a library of laminin-mimetic peptide hydrogels for control of nucleus pulposus cell behaviors

The nucleus pulposus (NP) of the intervertebral disc plays a critical role in distributing mechanical loads to the axial skeleton. Alterations in NP cells and, consequently, NP matrix are some of the earliest changes in the development of disc degeneration. Previous studies demonstrated a role for laminin-presenting biomaterials in promoting a healthy phenotype for human NP cells from degenerated tissue. Here we investigate the use of laminin-mimetic peptides presented individually or in combination on a poly(ethylene) glycol hydrogel as a platform to modulate the behaviors of degenerative human NP cells. Data confirm that NP cells attach to select laminin-mimetic peptides that results in cell signaling downstream of integrin and syndecan binding. Furthermore, the peptide-functionalized hydrogels demonstrate an ability to promote cell behaviors that mimic that of full-length laminins. These results identify a set of peptides that can be used to regulate NP cell behaviors toward a regenerative engineering strategy.

Biologically Active TNIIIA2 Region in Tenascin-C Molecule: A Major Contributor to Elicit Aggressive Malignant Phenotypes From Tumors/Tumor Stroma

Tenascin (TN)-C is highly expressed specifically in the lesions of inflammation-related diseases, including tumors. The expression level of TN-C in tumors and the tumor stroma is positively correlated with poor prognosis. However, no drugs targeting TN-C are currently clinically available, partly because the role of TN-C in tumor progression remains controversial. TN-C harbors an alternative splicing site in its fibronectin type III repeat domain, and its splicing variants including the type III-A2 domain are frequently detected in malignant tumors. We previously identified a biologically active region termed TNIIIA2 in the fibronectin type III-A2 domain of TN-C molecule and showed that this region is involved in promoting firm and persistent cell adhesion to fibronectin. In the past decade, through the exposure of various cell lines to peptides containing the TNIIIA2 region, we have published reports demonstrating the ability of the TNIIIA2 region to modulate distinct cellular activities, including survival/growth, migration, and invasion. Recently, we reported that the signals derived from TNIIIA2-mediated β1 integrin activation might play a crucial role for inducing malignant behavior of glioblastoma (GBM). GBM cells exposed to the TNIIIA2 region showed not only exacerbation of PDGF-dependent proliferation, but also acceleration of disseminative migration. On the other hand, we also found that the pro-inflammatory phenotypic changes were promoted when macrophages are stimulated with TNIIIA2 region in relatively low concentration and resulting MMP-9 upregulation is needed to release of the TNIIIA2 region from TN-C molecule. With the contribution of TNIIIA2-stimulated macrophages, the positive feedback spiral loop, which consists of the expression of TN-C, PDGF, and β1 integrin, and TNIIIA2 release, seemed to be activated in GBM with aggressive malignancy. Actually, the growth of transplanted GBM grafts in mice was significantly suppressed via the attenuation of β1 integrin activation. In this review, we thus introduce that the TNIIIA2 region has a significant impact on malignant progression of tumors by regulating cell adhesion. Importantly, it has been demonstrated that the TNIIIA2 region exerts unique biological functions through the extremely strong activation of β1-integrins and their long-lasting duration. These findings prompt us to develop new therapeutic agents targeting the TNIIIA2 region.

Heparan Sulfate Proteoglycan Signaling in Tumor Microenvironment

In the last few decades, heparan sulfate (HS) proteoglycans (HSPGs) have been an intriguing subject of study for their complex structural characteristics, their finely regulated biosynthetic machinery, and the wide range of functions they perform in living organisms from development to adulthood. From these studies, key roles of HSPGs in tumor initiation and progression have emerged, so that they are currently being explored as potential biomarkers and therapeutic targets for cancers. The multifaceted nature of HSPG structure/activity translates in their capacity to act either as inhibitors or promoters of tumor growth and invasion depending on the tumor type. Deregulation of HSPGs resulting in malignancy may be due to either their abnormal expression levels or changes in their structure and functions as a result of the altered activity of their biosynthetic or remodeling enzymes. Indeed, in the tumor microenvironment, HSPGs undergo structural alterations, through the shedding of proteoglycan ectodomain from the cell surface or the fragmentation and/or desulfation of HS chains, affecting HSPG function with significant impact on the molecular interactions between cancer cells and their microenvironment, and tumor cell behavior. Here, we overview the structural and functional features of HSPGs and their signaling in the tumor environment which contributes to tumorigenesis and cancer progression.

Metal ions and the extracellular matrix in tumor migration

In this review, we explore the roles of divalent metal ions in structure and function within the extracellular matrix (ECM), specifically, their interaction with glycosaminoglycans (GAGs) during tumor progression. Metals and GAGs have been individually associated with physiological and pathological processes, however, their combined activities in regulating cell behavior and ECM remodeling have not been fully explored to date. During tumor progression, divalent metals and GAGs participate in central processes, such as cell migration and angiogenesis, either by modulating cell surface molecules, as well as soluble signaling factors. In addition, studies on metals and polysaccharides interactions have been of great value, as they provide structural information that can be correlated with function. Finally, we believe that understanding how metals are regulated in physiological and pathological conditions is paramount for the development of new treatment strategies, as well as diagnostic and exploratory tools.

Proteoglycans in Biomedicine: Resurgence of an Underexploited Class of ECM Molecules

Proteoglycans have emerged as biomacromolecules with important roles in matrix remodeling, homeostasis, and signaling in the past two decades. Due to their negatively charged glycosaminoglycan chains as well as distinct core protein structures, they interact with a variety of molecules, including matrix proteins, growth factors, cytokines and chemokines, pathogens, and enzymes. This led to the dawn of glycan therapies in the 20^th century, but this research was quickly overshadowed by readily available DNA and protein-based therapies. The recent development of recombinant technology and advances in our understanding of proteoglycan function have led to a resurgence of these molecules as potential therapeutics. This review focuses on the recent preclinical efforts that are bringing proteoglycan research and therapies back to the forefront. Examples of studies using proteoglycan cores and mimetics have also been included to give the readers a perspective on the wide-ranging and extensive applications of these versatile molecules. Collectively, these advances are opening new avenues for targeting diseases at a molecular level, and providing avenues for the development of new and exciting treatments in regenerative medicine.

Myoblast Migration and Directional Persistence Affected by Syndecan-4-Mediated Tiam-1 Expression and Distribution

Skeletal muscle is constantly renewed in response to injury, exercise, or muscle diseases. Muscle stem cells, also known as satellite cells, are stimulated by local damage to proliferate extensively and form myoblasts that then migrate, differentiate, and fuse to form muscle fibers. The transmembrane heparan sulfate proteoglycan syndecan-4 plays multiple roles in signal transduction processes, such as regulating the activity of the small GTPase Rac1 (Ras-related C3 botulinum toxin substrate 1) by binding and inhibiting the activity of Tiam1 (T-lymphoma invasion and metastasis-1), a guanine nucleotide exchange factor for Rac1. The Rac1-mediated actin remodeling is required for cell migration. Syndecan-4 knockout mice cannot regenerate injured muscle; however, the detailed underlying mechanism is unknown. Here, we demonstrate that shRNA-mediated knockdown of syndecan-4 decreases the random migration of mouse myoblasts during live-cell microscopy. Treatment with the Rac1 inhibitor NSC23766 did not restore the migration capacity of syndecan-4 silenced cells; in fact, it was further reduced. Syndecan-4 knockdown decreased the directional persistence of migration, abrogated the polarized, asymmetric distribution of Tiam1, and reduced the total Tiam1 level of the cells. Syndecan-4 affects myoblast migration via its role in expression and localization of Tiam1; this finding may facilitate greater understanding of the essential role of syndecan-4 in the development and regeneration of skeletal muscle.

ARHGAP18: A Flow-Responsive Gene That Regulates Endothelial Cell Alignment and Protects Against Atherosclerosis

Background

Vascular endothelial cell (EC) alignment in the direction of flow is an adaptive response that protects against aortic diseases, such as atherosclerosis. The Rho GTPases are known to regulate this alignment. Herein, we analyze the effect of ARHGAP18 on the regulation of EC alignment and examine the effect of ARHGAP18 deficiency on the development of atherosclerosis in mice.

Methods and Results

We used in vitro analysis of ECs under flow conditions together with apolipoprotein E^−/−Arhgap18^−/− double‐mutant mice to study the function of ARHGAP18 in a high‐fat diet–induced model of atherosclerosis. Depletion of ARHGAP18 inhibited the alignment of ECs in the direction of flow and promoted inflammatory phenotype, as evidenced by disrupted junctions and increased expression of nuclear factor‐κB and intercellular adhesion molecule‐1 and decreased endothelial nitric oxide synthase. Mice with double deletion in ARHGAP18 and apolipoprotein E and fed a high‐fat diet show early onset of atherosclerosis, with lesions developing in atheroprotective regions.

Conclusions

ARHGAP18 is a protective gene that maintains EC alignments in the direction of flow. Deletion of ARHGAP18 led to loss of EC ability to align and promoted atherosclerosis development.

Heparan sulfate proteoglycans: The sweet side of development turns sour in mucopolysaccharidoses

Heparan sulfate proteoglycans (HSPGs) are complex carbohydrate-modified proteins ubiquitously expressed on cell surfaces, extracellular matrix and basement membrane of mammalian tissues. Beside to serve as structural constituents, they regulate multiple cellular activities. A critical involvement of HSPGs in development has been established, and perturbations of HSPG-dependent pathways are associated with many human diseases. Recent evidence suggest a role of HSPGs in the pathogenesis of mucopolysaccharidoses (MPSs) where the accumulation of undigested HS results in the loss of cellular functions, tissue damage and organ dysfunctions accounting for clinical manifestations which include central nervous system (CNS) involvement, degenerative joint disease and reduced bone growth. Current therapies are not curative but only ameliorate the disease symptoms. Here, we highlight the link between HSPG functions in the development of CNS and musculoskeletal structures and the etiology of some MPS phenotypes, suggesting that HSPGs may represent potential targets for the therapy of such incurable diseases.

Mechanochemical Signaling of the Extracellular Matrix in Epithelial-Mesenchymal Transition

Epithelial-Mesenchymal Transition (EMT) is a critical process in embryonic development in which epithelial cells undergo a transdifferentiation into mesenchymal cells. This process is essential for tissue patterning and organization, and it has also been implicated in a wide array of pathologies. While the intracellular signaling pathways that regulate EMT are well-understood, there is increasing evidence that the mechanical properties and composition of the extracellular matrix (ECM) also play a key role in regulating EMT. In turn, EMT drives changes in the mechanics and composition of the ECM, creating a feedback loop that is tightly regulated in healthy tissues, but is often dysregulated in disease. Here we present a review that summarizes our understanding of how ECM mechanics and composition regulate EMT, and how in turn EMT alters ECM mechanics and composition.

Therapeutic strategies for enhancing angiogenesis in wound healing

The enhancement of wound healing has been a goal of medical practitioners for thousands of years. The development of chronic, non-healing wounds is a persistent medical problem that drives patient morbidity and increases healthcare costs. A key aspect of many non-healing wounds is the reduced presence of vessel growth through the process of angiogenesis. This review surveys the creation of new treatments for healing cutaneous wounds through therapeutic angiogenesis. In particular, we discuss the challenges and advancement that have been made in delivering biologic, pharmaceutical and cell-based therapies as enhancers of wound vascularity and healing.

The Small GTPase ARF6 Activates PI3K in Melanoma to Induce a Prometastatic State

Melanoma has an unusual capacity to spread in early-stage disease, prompting aggressive clinical intervention in very thin primary tumors. Despite these proactive efforts, patients with low-risk, low-stage disease can still develop metastasis, indicating the presence of permissive cues for distant spread. Here, we show that constitutive activation of the small GTPase ARF6 (ARF6^Q67L) is sufficient to accelerate metastasis in mice with BRAF^V600E/Cdkn2a^NULL melanoma at a similar incidence and severity to Pten loss, a major driver of PI3K activation and melanoma metastasis. ARF6^Q67L promoted spontaneous metastasis from significantly smaller primary tumors than PTEN^NULL, implying an enhanced ability of ARF6-GTP to drive distant spread. ARF6 activation increased lung colonization from circulating melanoma cells, suggesting that the prometastatic function of ARF6 extends to late steps in metastasis. Unexpectedly, ARF6^Q67L tumors showed upregulation of Pik3r1 expression, which encodes the p85 regulatory subunit of PI3K. Tumor cells expressing ARF6^Q67L displayed increased PI3K protein levels and activity, enhanced PI3K distribution to cellular protrusions, and increased AKT activation in invadopodia. ARF6 is necessary and sufficient for activation of both PI3K and AKT, and PI3K and AKT are necessary for ARF6-mediated invasion. We provide evidence for aberrant ARF6 activation in human melanoma samples, which is associated with reduced survival. Our work reveals a previously unknown ARF6-PI3K-AKT proinvasive pathway, it demonstrates a critical role for ARF6 in multiple steps of the metastatic cascade, and it illuminates how melanoma cells can acquire an early metastatic phenotype in patients. SIGNIFICANCE: These findings reveal a prometastatic role for ARF6 independent of tumor growth, which may help explain how melanoma spreads distantly from thin, early-stage primary tumors.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/11/2892/F1.large.jpg.

Syndecan-4 Modulates Epithelial Gut Barrier Function and Epithelial Regeneration in Experimental Colitis

BACKGROUND

The transmembrane heparan sulfate proteoglycan Syndecan-4 (Sdc4) plays an important role in the regulation of various inflammatory disorders. However, the involvement of Sdc4 in intestinal inflammation remains unknown. Therefore, we assessed the impact of Sdc4 deficiency on experimental colitis and epithelial wound healing in vitro and in vivo.

METHODS

Dextran sulfate sodium (DSS)-induced colitis was monitored in wild type and Sdc4-deficient (Sdc4-/-) mice by assessment of body weight, histology, inflammatory cellular infiltration, and colon length. Syndecan-4 expression was measured by immunohistochemistry, Western blot, and quantitative real-time PCR. Epithelial permeability was evaluated by Evans blue measurements, Western blot, and immunohistological analysis of tight junction protein expression. Impact of Sdc4 on epithelial wound healing was determined by scratch assay in vitro and by colonoscopy following mechanical wounding in vivo.

RESULTS

In Sdc4-/- mice, colitis-like symptoms including severe weight loss, shortened colon length, histological damage, and invasion of macrophages and granulocytes were markedly aggravated compared with wild type (WT) animals. Moreover, colonic epithelial permeability in Sdc4-/- mice was enhanced, while tight junction protein expression decreased. Furthermore, Sdc4-/- colonic epithelial cells had lower cell proliferation and migration rates which presented in vivo as a prolonged intestinal wound healing phenotype. Strikingly, in WT animals, Sdc4 expression was reduced during colitis and was elevated during recovery.

CONCLUSIONS

The loss of Sdc4 aggravates the course of experimental colitis, potentially through impaired epithelial cell integrity and regeneration. In view of the development of current treatment approaches involving Sdc4 inhibition for inflammatory disorders like arthritis, particular caution should be taken in case of adverse gastrointestinal side-effects.

Processed eggshell membrane powder regulates cellular functions and increase MMP-activity important in early wound healing processes

Avian eggshell membrane (ESM) is a natural biomaterial that has been used as an alternative natural bandage to cure wounds, and is available in large quantities from egg industries. We have previously demonstrated that processed eggshell membrane powder (PEP), aiming to be used in a low cost wound healing product, possesses anti-inflammatory properties. In this study, we further investigated effects of PEP on MMP activities in vitro (a dermal fibroblast cell culture system) and in vivo (a mouse skin wound healing model). Three days incubation with PEP in cell culture led to rearrangement of the actin-cytoskeleton and vinculin in focal adhesions and increased syndecan-4 shedding. In addition, we observed increased matrix metalloproteinase type 2 (MMP-2) enzyme activation, without effects on protein levels of MMP-2 or its regulators (membrane type 1 (MT1)-MMP and tissue inhibitor of matrix metalloproteinase type 2 (TIMP-2). Longer incubation (10 days) led to increased protein levels of MMP-2 and its regulators. We also observed an increased alpha-smooth muscle actin (α-SMA) production, suggesting an effect of PEP on myofibroblast differentiation. In vivo, using the mouse skin wound healing model, PEP treatment (3 days) increased MMP activity at the wound edges, along with increased MMP-2 and MMP-9 protein levels, and increased keratinocyte cell proliferation. Altogether, our data suggest PEP stimulates MMP activity, and with a positive effect on early cellular events during wound healing.

Breaking in and busting out: cell-penetrating peptides and the endosomal escape problem

Cell-penetrating peptides (CPPs) have long held great promise for the manipulation of living cells for therapeutic and research purposes. They allow a wide array of biomolecules from large, oligomeric proteins to nucleic acids and small molecules to rapidly and efficiently traverse cytoplasmic membranes. With few exceptions, if a molecule can be associated with a CPP, it can be delivered into a cell. However, a growing realization in the field is that CPP-cargo fusions largely remain trapped in endosomes and are eventually targeted for degradation or recycling rather than released into the cytoplasm or trafficked to a desired subcellular destination. This 'endosomal escape problem' has confounded efforts to develop CPP-based delivery methods for drugs, enzymes, plasmids, etc. This review provides a brief history of CPP research and discusses current issues in the field with a primary focus on the endosomal escape problem, for which several promising potential solutions have been developed. Are we on the verge of developing technologies to deliver therapeutics such as siRNA, CRISPR/Cas complexes and others that are currently failing because of an inability to get into cells, or are we just chasing after another promising but unworkable technology? We make the case for optimism.

Reduction of Syndecan Transcript Levels in the Insulin-Producing Cells Affects Glucose Homeostasis in Adult Drosophila melanogaster

Signaling by direct cell-matrix interactions has been shown to impact the transcription, secretion, and storage of insulin in mammalian β cells. However, more research is still needed in this area. Syndecans are transmembrane heparan sulfate proteoglycans that function independently and in synergy with integrin-mediated signaling to mediate cell adhesion to the extracellular matrix. In this study, we used the model organism Drosophila melanogaster to determine whether knockdown of the Syndecan (Sdc) gene expression specifically in the insulin-producing cells (IPCs) might affect insulin-like peptide (ILP) production and secretion. IPCs of adult flies produce three ILPs (ILP2, ILP3, and ILP5), which have significant homology to mammalian insulin. We report that flies with reduced Sdc expression in the IPCs did not show any difference in the expression of ilp genes compared to controls. However, they had significantly reduced levels of the circulating ILP2 protein, higher circulating carbohydrates, and were less glucose tolerant than control flies. Finally, we found that IPCs-specific Sdc knockdown led to reduced levels of head Glucose transporter1 gene expression, extracellular signal-regulated kinase phosphorylation, and reactive oxygen species. Taken together, our findings suggest a cell autonomous role for Sdc in insulin release in D. melanogaster.

Different gene response to mechanical loading during early and late phases of rat Achilles tendon healing

Mechanical loading stimulates tendon healing both when applied in the inflammatory phase and in the early remodeling phase of the process, although not necessarily via the same mechanisms. We investigated the gene response to mechanical loading in these two phases of tendon healing. The right Achilles tendon in rats was transected, and the hindlimbs were unloaded by tail suspension. The rats were exposed to 5 min of treadmill running 3 or 14 days after tendon transection. Thereafter, they were resuspended for 15 min or 3 h until euthanasia. The controls were suspended continuously. Gene analysis was first performed by microarray analysis followed by quantitative RT-PCR on selected genes, focusing on inflammation. Fifteen minutes after loading, the most important genes seemed to be the transcription factors EGR1 and C-FOS, regardless of healing phase. These transcription factors might promote tendon cell proliferation and differentiation, stimulate collagen production, and regulate inflammation. Three hours after loading on day 3, inflammation was strongly affected. Seven inflammation-related genes were upregulated according to PCR: CCL20, CCL7, IL-6, NFIL3, PTX3, SOCS1, and TLR2. These genes can be connected to macrophages, T cells, and recruitment of leukocytes. According to Ingenuity Pathway Analysis, the recruitment of leukocytes was increased by loading on day 3, which also was confirmed by histology. This inflammation-related gene response was not seen on day 14 Our results suggest that the immediate gene response after mechanical loading is similar in the early and late phases of healing but the late gene response is different.NEW & NOTEWORTHY This study investigates the direct effect of mechanical loading on gene expression during different healing phases in tendon healing. One isolated episode of mechanical loading was studied in otherwise unloaded healing tendons. This enabled us to study a time sequence, i.e., which genes were the first ones to be regulated after the loading episode.

Fibronectin on extracellular vesicles from microvascular endothelial cells is involved in the vesicle uptake into oligodendrocyte precursor cells

We previously reported transplantation of brain microvascular endothelial cells (MVECs) into cerebral white matter infarction model improved the animal's behavioral outcome by increasing the number of oligodendrocyte precursor cells (OPCs). We also revealed extracellular vesicles (EVs) derived from MVECs promoted survival and proliferation of OPCs in vitro. In this study, we investigated the mechanism how EVs derived from MVECs contribute to OPC survival and proliferation. Protein mass spectrometry and enzyme-linked immunosorbent assay revealed fibronectin was abundant on the surface of EVs from MVECs. As fibronectin has been reported to promote OPC survival and proliferation via integrin signaling pathway, we blocked the binding between fibronectin and integrins using RGD sequence mimics. Blocking the binding, however, did not attenuate the survival and proliferation promoting effect of EVs on OPCs. Flow cytometric and imaging analyses revealed fibronectin on EVs mediates their internalization into OPCs by its binding to heparan sulfate proteoglycan on OPCs. OPC survival and proliferation promoted by EVs were attenuated by blocking the internalization of EVs into OPCs. These lines of evidence suggest that fibronectin on EVs mediates their internalization into OPCs, and the cargo of EVs promotes survival and proliferation of OPCs, independent of integrin signaling pathway.

Syndecan-4 enhances PDGF-BB activity in diabetic wound healing

Non-healing ulcers are a common consequence of long-term diabetes and severe peripheral vascular disease. These non-healing wounds are a major source of morbidity in patients with diabetes and place a heavy financial burden on the healthcare system. Growth factor therapies are an attractive strategy for enhancing wound closure in non-healing wounds but have only achieved mixed results in clinical trials. Platelet derived growth factor-BB (PDGF-BB) is the only currently approved growth factor therapy for non-healing wounds. However, PDGF-BB therapy is not effective in many patients and requires high doses that increase the potential for side effects. In this work, we demonstrate that syndecan-4 delivered in a proteoliposomal formulation enhances PDGF-BB activity in diabetic wound healing. In particular, syndecan-4 proteoliposomes enhance the migration of keratinocytes derived from patients with diabetes. In addition, syndecan-4 proteoliposomes sensitize keratinocytes to PDGF-BB stimulation, enhancing the intracellular signaling response to PDGF-BB. We further demonstrated that co-therapy with syndecan-4 proteoliposomes enhanced wound closure in diabetic, hyperlipidemic ob/ob mice. Wounds treated with both syndecan-4 proteoliposomes and PDGF-BB had increased re-epithelization and angiogenesis in comparison to wounds treated with PDGF-BB alone. Moreover, the wounds treated with syndecan-4 proteoliposomes and PDGF-BB also had increased M2 macrophages and reduced M1 macrophages, suggesting syndecan-4 delivery induces immunomodulation within the healing wounds. Together our findings support that syndecan-4 proteoliposomes markedly improve PDGF-BB efficacy for wound healing and may be useful in enhancing treatments for non-healing wounds.

STATEMENT OF SIGNIFICANCE

Non-healing wounds are major healthcare issue for patients with diabetes and peripheral vascular disease. Growth factor therapies have potential for healing chronic wounds but have not been effective for many patients. PDGF-BB is currently the only approved growth factor for enhancing wound healing. However, it has not seen widespread adoption due to limited efficacy and high cost. In this work, we have developed an enhancing agent that improves the activity of PDGF-BB in promoting wound healing in animals with diabetes. This co-therapy may be useful in improving the efficacy of PDGFBB and enhance its safety through lowering the dose of growth factor needed to improve wound healing.

Syndesome Therapeutics for Enhancing Diabetic Wound Healing

Chronic wounds represent a major healthcare and economic problem worldwide. Advanced wound dressings that incorporate bioactive compounds have great potential for improving outcomes in patients with chronic wounds but significant challenges in designing treatments that are effective in long-standing, nonhealing wounds. Here, an optimized wound healing gel was developed that delivers syndecan-4 proteoliposomes ("syndesomes") with fibroblast growth factor-2 (FGF-2) to enhance diabetic wound healing. In vitro studies demonstrate that syndesomes markedly increase migration of keratinocytes and fibroblasts isolated from both nondiabetic and diabetic donors. In addition, syndesome treatment leads to increased endocytic processing of FGF-2 that includes enhanced recycling of FGF-2 to the cell surface after uptake. The optimized syndesome formulation was incorporated into an alginate wound dressing and tested in a splinted wound model in diabetic, ob/ob mice. It was found that wounds treated with syndesomes and FGF-2 have markedly enhanced wound closure in comparison to wounds treated with only FGF-2. Moreover, syndesomes have an immunomodulatory effect on wound macrophages, leading to a shift toward the M2 macrophage phenotype and alterations in the wound cytokine profile. Together, these studies show that delivery of exogenous syndecan-4 is an effective method for enhancing wound healing in the long-term diabetic diseased state.

Influence of Birch Bark Triterpenes on Keratinocytes and Fibroblasts from Diabetic and Nondiabetic Donors

Impaired wound healing is one of the main risk factors associated with diabetes mellitus. Few options are available to treat diabetic wounds, and therefore efficient remedies are urgently needed. An interesting option might be an extract of birch bark (TE) that has been clinically proven to accelerate acute wound healing. We investigated the effects of TE and its main components betulin and lupeol in cultured normal keratinocytes and dermal fibroblasts from diabetic and nondiabetic donors. These in vitro models can provide insights into possible beneficial effects in wound healing. TE and betulin treatment led to increased mRNA levels of chemokines, pro-inflammatory cytokines, and mediators important in wound healing, e.g., IL-6, TNFα, IL-8, and RANTES. We observed a pronounced upregulation of MIF, IL-8, and RANTES on the protein level. Furthermore, a shape change of the actin cytoskeleton was seen in keratinocytes and fibroblasts, and the Rho-GTPases and p38-MAPK were found to be activated in keratinocytes. On the basis of our results, TE is worthy of further study as a potential option to influence wound-healing processes under diabetic conditions. These first insights need to be confirmed by clinical studies with diabetic patients.

Syndecan-4 expression is upregulated in endometriosis and contributes to an invasive phenotype

OBJECTIVE

To study the expression and function of syndecan-4 in endometriosis.

DESIGN

Histopathological investigation of eutopic endometrium and experimental laboratory study on a cell line derived from epithelial endometriotic cells (12Z).

SETTING

University hospital laboratory.

PATIENT(S)

One hundred six women (62 controls/44 endometriosis) from the IVF center of Münster University Hospital aged 23-44 undergoing Pipelle biopsy and diagnostic exploratory laparoscopy.

INTERVENTION(S)

Eutopic endometrial tissue was investigated by immunohistochemistry for the expression of syndecan-4. The human endometriotic cell line 12Z was transiently transfected with syndecan-4 small interfering RNA and investigated for changes in cell behavior.

MAIN OUTCOME MEASURE(S)

Syndecan-4 expression in eutopic endometrium was evaluated immunohistochemically in endometrial glands and stroma. Scoring results were correlated with the stages of the menstrual cycle and presence or absence of endometriosis. Quantitative polymerase chain reaction was used to measure syndecan-4-dependent expression changes of MMP2, MMP3, MMP9, Rac1, and ATF2. Altered cell behavior was monitored by matrigel invasion assays and cell viability assays.

RESULT(S)

Syndecan-4 expression was significantly higher in the glands and stroma of patients with endometriosis compared with controls, whereas no menstrual cycle-dependent expression was observed. In 12Z cells, syndecan-4 depletion did not affect cell viability but resulted in a significantly reduced matrigel invasiveness and reduced expression of the small GTPase Rac1, the transcription factor ATF-2, and MMP3.

CONCLUSION(S)

The upregulation of syndecan-4 in the eutopic endometrium of endometriosis patients may facilitate the pathogenetic process by promoting invasive cell growth via Rac1, MMP3, and ATF-2.

Integrins in Wound Healing

Significance: Regulation of cell adhesions during tissue repair is fundamentally important for cell migration, proliferation, and protein production. All cells interact with extracellular matrix proteins with cell surface integrin receptors that convey signals from the environment into the nucleus, regulating gene expression and cell behavior. Integrins also interact with a variety of other proteins, such as growth factors, their receptors, and proteolytic enzymes. Re-epithelialization and granulation tissue formation are crucially dependent on the temporospatial function of multiple integrins. This review explains how integrins function in wound repair. Recent Advances: Certain integrins can activate latent transforming growth factor beta-1 (TGF-β1) that modulates wound inflammation and granulation tissue formation. Dysregulation of TGF-β1 function is associated with scarring and fibrotic disorders. Therefore, these integrins represent targets for therapeutic intervention in fibrosis. Critical Issues: Integrins have multifaceted functions and extensive crosstalk with other cell surface receptors and molecules. Moreover, in aberrant healing, integrins may assume different functions, further increasing the complexity of their functionality. Discovering and understanding the role that integrins play in wound healing provides an opportunity to identify the mechanisms for medical conditions, such as excessive scarring, chronic wounds, and even cancer. Future Directions: Integrin functions in acute and chronic wounds should be further addressed in models better mimicking human wounds. Application of any products in acute or chronic wounds will potentially alter integrin functions that need to be carefully considered in the design.

Syndecan 4 is required for endothelial alignment in flow and atheroprotective signaling

Atherosclerotic plaque localization correlates with regions of disturbed flow in which endothelial cells (ECs) align poorly, whereas sustained laminar flow correlates with cell alignment in the direction of flow and resistance to atherosclerosis. We now report that in hypercholesterolemic mice, deletion of syndecan 4 (S4(-/-)) drastically increased atherosclerotic plaque burden with the appearance of plaque in normally resistant locations. Strikingly, ECs from the thoracic aortas of S4(-/-) mice were poorly aligned in the direction of the flow. Depletion of S4 in human umbilical vein endothelial cells (HUVECs) using shRNA also inhibited flow-induced alignment in vitro, which was rescued by re-expression of S4. This effect was highly specific, as flow activation of VEGF receptor 2 and NF-κB was normal. S4-depleted ECs aligned in cyclic stretch and even elongated under flow, although nondirectionally. EC alignment was previously found to have a causal role in modulating activation of inflammatory versus antiinflammatory pathways by flow. Consistent with these results, S4-depleted HUVECs in long-term laminar flow showed increased activation of proinflammatory NF-κB and decreased induction of antiinflammatory kruppel-like factor (KLF) 2 and KLF4. Thus, S4 plays a critical role in sensing flow direction to promote cell alignment and inhibit atherosclerosis.

Heparan sulfate proteoglycan as a cell-surface endocytosis receptor

How various macromolecules are exchanged between cells and how they gain entry into recipient cells are fundamental questions in cell biology with important implications e.g. non-viral drug delivery, infectious disease, metabolic disorders, and cancer. The role of heparan sulfate proteoglycan (HSPG) as a cell-surface receptor of diverse macromolecular cargo has recently been manifested. Exosomes, cell penetrating peptides, polycation-nucleic acid complexes, viruses, lipoproteins, growth factors and morphogens among other ligands enter cells through HSPG-mediated endocytosis. Key questions that partially have been unraveled over recent years include the respective roles of HSPG core protein and HS chain structure specificity for macromolecular cargo endocytosis, the down-stream intracellular signaling events involved in HSPG-dependent membrane invagination and vesicle formation, and the biological significance of the HSPG transport pathway. Here, we discuss the intriguing role of HSPGs as a major entry pathway of macromolecules in mammalian cells with emphasis on recent in vitro and in vivo data that provide compelling evidence of HSPG as an autonomous endocytosis receptor.

Syndecan-4 signaling at a glance

Syndecan-4, a ubiquitous cell surface proteoglycan, mediates numerous cellular processes through signaling pathways that affect cellular proliferation, migration, mechanotransduction and endocytosis. These effects are achieved through syndecan-4 functioning as both a co-receptor for the fibroblast growth factor receptors (FGFR1-FGFR4) and its ability to independently activate signaling pathways upon ligand binding. As an FGFR co-receptor, syndecan-4 strengthens the duration and intensity of downstream signaling upon ligand binding; this is particularly evident with regard to mitogen-activated protein kinase (MAPK) signaling. In contrast, syndecan-4 also functions as an independent receptor for heparin-binding growth factors, such as fibroblast growth factors (FGFs), vascular endothelial growth factors (VEGFs) and platelet-derived growth factors (PDGFs). These signaling cascades affect canonical signaling components, such as the mammalian target of rapamycin (mTOR), AKT1 and the Rho family of GTPases. In combination with the integrin family of proteins, syndecan-4 is also able to form physical connections between the extracellular matrix (ECM) and cytoskeletal signaling proteins, and it has a key role in regulation of integrin turnover. This unique versatility of the interactions of syndecan-4 is characterized in this Cell Science at a Glance article and illustrated in the accompanying poster.

Migration of turkey muscle satellite cells is enhanced by the syndecan-4 cytoplasmic domain through the activation of RhoA

Syndecan-4 (S4) is a cell membrane-associated heparan sulfate proteoglycan that forms oligomers in muscle satellite cells. The S4 oligomers activate protein kinase Cα (PKCα) through the S4 cytoplasmic domain and may regulate the activation of ras homolog gene family member A (RhoA), a signal transduction molecule down-stream of PKCα which is thought to influence cell migration. However, little is known about the function of the S4 cytoplasmic domain in satellite cell migration and RhoA activation. The objective of the current study was to determine the function of S4 and its cytoplasmic domain in cell migration and RhoA activation. To study the objective, clones of S4 and S4 without the cytoplasmic domain (S4C) were used in overexpression studies, and small interference RNAs targeting S4 or RhoA were used in knockdown studies. Satellite cell migration was increased by S4 overexpression, but decreased by the knockdown or deletion of the S4 cytoplasmic domain. The RhoA protein was activated by the overexpression of S4, but not with the deletion of the S4 cytoplasmic domain. The treatment of Rho activator II or the knockdown of RhoA also modulated satellite cell migration. Finally, co-transfection (S4 overexpression and RhoA knockdown) and rescue (the knockdown of S4 and the treatment with Rho activator II) studies demonstrated that S4-mediated satellite cell migration was regulated through the activation of RhoA. The cytoplasmic domain of S4 is required for cell migration and RhoA activation which will affect muscle fiber formation.