The glycosaminoglycan chain of decorin plays an important role in collagen fibril formation at the early stages of fibrillogenesis

Novel Insights Into the Architecture of Macro and Microstructures in Cattle Ossa Cordis

Ossa cordis, bones located within the heart trigones, are often classified as heterotopic or ectopic bones. Despite their high prevalence in cattle and some other bovids, little is known about their structure or development. Scanning electron microscopy, X-ray microtomography, gross dissections, and measurements showed the anatomical locations, prevalence, shapes, and measurements of the cardiac bones in both Egyptian Baladi cattle and Holstein-Friesians. All cattle (n = 12) had an Ossa cordis dextrum (average = 50.70 × 20.91 × 5.40 mm). Additionally, 80% Egyptian Baladi and 57% Holstein-Friesian had a smaller Ossa cordis sinistrum (average = 24.94 × 12.75 × 4.12 mm). Egyptian Baladi Ossa cordis were smaller than observed in Holstein-Friesians. Energy-dispersive X-ray analysis showed the elemental constitution (carbon, oxygen, calcium, nitrogen, phosphorus, sodium, and magnesium) of Ossa cordis and Cartilago cordis. These imaging techniques, plus four histological stains (hematoxylin and eosin, Crossman's trichrome, Alcian blue with Van Gieson, and Sirius Red) and microscopy, demonstrated osteoblasts, osteocytes, osteoclasts, astrocytes, blood vessels, bone marrow, lamellar and woven bone, cortical bone, trabeculations with pores and canaliculi, and fibrous components including collagen in the Ossa cordis dextrum and sinistrum. Hyaline cartilage and fibrocartilage (chondrocytes and cartilage matrix) were found within and surrounding the Ossa cordis. These findings were additionally compared against other cattle breeds and species.

Acute exposure to ultraviolet radiation targets proteins involved in collagen fibrillogenesis

Introduction: Exposure to chronic, low-dose UV irradiation (UVR) can lead to premature ageing of the skin. Understanding which proteins are affected by acute UVR and photo-dynamically produced reactive oxygen species (ROS) could help to inform strategies to delay photoageing. Conventional biochemical analyses can be used to characterize UVR/ROS-induced damage on a protein-by-protein basis and we have previously shown using SDS-PAGE that collagen I and plasma fibronectin are respectively resistant and susceptible to physiological doses of UVR. The aim of this study was to screen a complex proteome for UVR-affected proteins. Methods: This study employed a sensitive mass spectrometry technique (peptide location fingerprinting: PLF) which can identify structure associated differences following trypsin digestion to characterize the impact of UVR exposure on purified collagen I and tissue fibronectin and to identify UVR-susceptible proteins in an ECM-enriched proteome. Results: Using LC/MS-MS and PLF we show that purified mature type-I collagen is resistant to UVR, whereas purified tissue fibronectin is susceptible. UV irradiation of a human dermal fibroblast-deposited ECM-enriched proteome in vitro, followed by LC/MS-MS and PLF analysis revealed two protein cluster groups of UV susceptible proteins involved in i) matrix collagen fibril assembly and ii) protein translation and motor activity. Furthermore, PLF highlighted UV susceptible domains within targeted matrix proteins, suggesting that UV damage of matrix proteins is localized. Discussion: Here we show that PLF can be used to identify protein targets of UVR and that collagen accessory proteins may be key targets in UVR exposed tissues.

Regional differences in electroactive response of the sclera

The sclera exhibits mechanical response when subjected to an external electric stimulation. The scleral electroactive response is a function of its charge density, mechanical properties, thickness, and strength of the applied electric voltage. The primary objective of the present work was to investigate the regional differences in the electroactive response of porcine sclera. To this end, we cut scleral strips in meridional directions from superior-temporal, superior-nasal, inferior-temporal, and inferior-nasal quadrants. In addition, we excised samples circumferentially from the posterior, equatorial, and anterior regions. The electroactive bending response of these samples was measured under 10 and 15 V in 0.15 M NaCl solution. The meridional samples were tested under two different configurations by clamping them either from their anterior or posterior end. It was observed that the scleral electroactive deformation increased with increasing the the electric voltage. Furthermore, regardless of the region from which meridional strips were excised, their electroactive response was considerably larger when they were clamped from their anterior end. Unlike meridional strips, the electroactive response of circumferential samples was significantly dependent on the location, that is, the average maximum bending angle of posterior samples was significantly larger than that of equatorial and anterior strips. The regionally different electroactive bending response of the sclera was discussed in terms of the variation in its biochemical and biomechanical properties throughout the eyeball.

Control of tissue homeostasis by the extracellular matrix: Synthetic heparan sulfate as a promising therapeutic for periodontal health and bone regeneration

Proteoglycans are core proteins associated with carbohydrate/sugar moieties that are highly variable in disaccharide composition, which dictates their function. These carbohydrates are named glycosaminoglycans, and they can be attached to proteoglycans or found free in tissues or on cell surfaces. Glycosaminoglycans such as hyaluronan, chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparin/heparan sulfate have multiple functions including involvement in inflammation, immunity and connective tissue structure, and integrity. Heparan sulfate is a highly sulfated polysaccharide that is abundant in the periodontium including alveolar bone. Recent evidence supports the contention that heparan sulfate is an important player in modulating interactions between damage associated molecular patterns and inflammatory receptors expressed by various cell types. The structure of heparan sulfate is reported to dictate its function, thus, the utilization of a homogenous and structurally defined heparan sulfate polysaccharide for modulation of cell function offers therapeutic potential. Recently, a chemoenzymatic approach was developed to allow production of many structurally defined heparan sulfate carbohydrates. These oligosaccharides have been studied in various pathological inflammatory conditions to better understand their function and their potential application in promoting tissue homeostasis. We have observed that specific size and sulfation patterns can modulate inflammation and promote tissue maintenance including an anabolic effect in alveolar bone. Thus, new evidence provides a strong impetus to explore heparan sulfate as a potential novel therapeutic agent to treat periodontitis, support alveolar bone maintenance, and promote bone formation.

Removal of GAGs Regulates Mechanical Properties, Collagen Fiber Formation, and Alignment in Tissue Engineered Meniscus

The complex fibrillar architecture of native meniscus is essential for proper function and difficult to recapitulate in vitro. In the native meniscus, proteoglycan content is low during the development of collagen fibers and progressively increases with aging. In vitro, fibrochondrocytes produce glycosaminoglycans (GAGs) early in culture, in contrast to native tissue, where they are deposited after collagen fibers have formed. This difference in the timing of GAG production hinders the formation of a mature fiber network in such in vitro models. In this study, we removed GAGs from collagen gel-based tissue engineered constructs using chondroitinase ABC (cABC) and evaluated the effect on the formation and alignment of collagen fibers and the subsequent effect on tensile and compressive mechanical properties. Removal of GAGs during maturation of in vitro constructs improved collagen fiber alignment in tissue engineered meniscus constructs. Additionally, removal of GAGs during maturation improved fiber alignment without compromising compressive strength, and this removal improved not only fiber alignment and formation but also tensile properties. The increased fiber organization in cABC-treated groups also appeared to influence the size, shape, and location of defects in these constructs, suggesting that treatment may prevent the propagation of large defects under loading. This data gives another method of modulating the ECM for improved collagen fiber formation and mechanical properties in tissue engineered constructs.

The role of glycans in the mechanobiology of cancer

Although cancer is a genetic disease, physical changes such as stiffening of the extracellular matrix also commonly occur in cancer. Cancer cells sense and respond to extracellular matrix stiffening through the process of mechanotransduction. Cancer cell mechanotransduction can enhance cancer-promoting cell behaviors such as survival signaling, proliferation, and migration. Glycans, carbohydrate-based polymers, have recently emerged as important mediators and/or modulators of cancer cell mechanotransduction. Stiffer tumors are characterized by increased glycan content on cancer cells and their associated extracellular matrix. Here we review the role of cancer-associated glycans in coupled mechanical and biochemical alterations during cancer progression. We discuss the recent evidence on how increased expression of different glycans, in the form of glycoproteins and proteoglycans, contributes to both mechanical changes in tumors and corresponding cancer cell responses. We conclude with a summary of emerging tools that can be used to modify glycans for future studies in cancer mechanobiology.

The factory, the antenna and the scaffold: the three-way interplay between the Golgi, cilium and extracellular matrix underlying tissue function

The growth and development of healthy tissues is dependent on the construction of a highly specialised extracellular matrix (ECM) to provide support for cell growth and migration and to determine the biomechanical properties of the tissue. These scaffolds are composed of extensively glycosylated proteins which are secreted and assembled into well-ordered structures that can hydrate, mineralise, and store growth factors as required. The proteolytic processing and glycosylation of ECM components is vital to their function. These modifications are under the control of the Golgi apparatus, an intracellular factory hosting spatially organised, protein-modifying enzymes. Regulation also requires a cellular antenna, the cilium, which integrates extracellular growth signals and mechanical cues to inform ECM production. Consequently, mutations in either Golgi or ciliary genes frequently lead to connective tissue disorders. The individual importance of each of these organelles to ECM function is well-studied. However, emerging evidence points towards a more tightly linked system of interdependence between the Golgi, cilium and ECM. This review examines how the interplay between all three compartments underpins healthy tissue. As an example, it will look at several members of the golgin family of Golgi-resident proteins whose loss is detrimental to connective tissue function. This perspective will be important for many future studies looking to dissect the cause and effect of mutations impacting tissue integrity.

Role of Decorin in the Lens and Ocular Diseases

Decorin is an archetypal member of the small leucine-rich proteoglycan gene family and is involved in various biological functions and many signaling networks, interacting with extra-cellular matrix (ECM) components, growth factors, and receptor tyrosine kinases. Decorin also modulates the growth factors, cell proliferation, migration, and angiogenesis. It has been reported to be involved in many ischemic and fibrotic eye diseases, such as congenital stromal dystrophy of the cornea, anterior subcapsular fibrosis of the lens, proliferative vitreoretinopathy, et al. Furthermore, recent evidence supports its role in secondary posterior capsule opacification (PCO) after cataract surgery. The expression of decorin mRNA in lens epithelial cells in vitro was found to decrease upon transforming growth factor (TGF)-β-2 addition and increase upon fibroblast growth factor (FGF)-2 addition. Wound healing of the injured lens in mice transgenic for lens-specific human decorin was promoted by inhibiting myofibroblastic changes. Decorin may be associated with epithelial-mesenchymal transition and PCO development in the lens. Gene therapy and decorin administration have the potential to serve as excellent therapeutic approaches for modifying impaired wound healing, PCO, and other eye diseases related to fibrosis and angiogenesis. In this review, we present findings regarding the roles of decorin in the lens and ocular diseases.

Profound Effects of Dexamethasone on the Immunological State, Synthesis and Secretion Capacity of Human Testicular Peritubular Cells

The functions of human testicular peritubular cells (HTPCs), forming a small compartment located between the seminiferous epithelium and the interstitial areas of the testis, are not fully known but go beyond intratesticular sperm transport and include immunological roles. The expression of the glucocorticoid receptor (GR) indicates that they may be regulated by glucocorticoids (GCs). Herein, we studied the consequences of the GC dexamethasone (Dex) in cultured HTPCs, which serves as a unique window into the human testis. We examined changes in cytokines, mainly by qPCR and ELISA. A holistic mass-spectrometry-based proteome analysis of cellular and secreted proteins was also performed. Dex, used in a therapeutic concentration, decreased the transcript level of proinflammatory cytokines, e.g., IL6, IL8 and MCP1. An siRNA-mediated knockdown of GR reduced the actions on IL6. Changes in IL6 were confirmed by ELISA measurements. Of note, Dex also lowered GR levels. The proteomic results revealed strong responses after 24 h (31 significantly altered cellular proteins) and more pronounced ones after 72 h of Dex exposure (30 less abundant and 42 more abundant cellular proteins). Dex also altered the composition of the secretome (33 proteins decreased, 13 increased) after 72 h. Among the regulated proteins were extracellular matrix (ECM) and basement membrane components (e.g., FBLN2, COL1A2 and COL3A1), as well as PTX3 and StAR. These results pinpoint novel, profound effects of Dex in HTPCs. If transferrable to the human testis, changes specifically in ECM and the immunological state of the testis may occur in men upon treatment with Dex for medical reasons.

The role of SLRPs and large aggregating proteoglycans in collagen fibrillogenesis, extracellular matrix assembly, and mechanical function of fibrocartilage

PURPOSE

Proteoglycans, especially small leucine rich proteoglycans (SLRPs), play major roles in facilitating the development and regulation of collagen fibers and other extracellular matrix components. However, their roles in fibrocartilage have not been widely reviewed. Here, we discuss both SLRP and large aggregating proteoglycan's roles in collagen fibrillogenesis and extracellular matrix assembly in fibrocartilage tissues such as the meniscus, annulus fibrosus (AF), and TMJ disc. We also discuss their expression levels throughout development, aging and degeneration, as well as repair.

METHODS

A review of literature discussing proteoglycans and collagen fibrillogenesis in fibrocartilage was conducted and data from these manuscripts were analyzed and grouped to discuss trends throughout the tissue's architectural zones and developmental stage.

RESULTS

The spatial collagen architecture of these fibrocartilaginous tissues is reflected in the distribution of proteoglycans expressed, suggesting that each proteoglycan plays an important role in the type of architecture presented and associated mechanical function.

CONCLUSION

The unique structure-function relationship of fibrocartilage makes the varied architectures throughout the tissues imperative for their success and understanding the functions of these proteoglycans in developing and maintaining the fiber structure could inform future work in fibrocartilage replacement using tissue engineered constructs.

Small Leucine-Rich Proteoglycans in Tendon Wound Healing

Significance: Tendon injury possesses a high morbidity rate and is difficult to achieve a satisfying prognosis with currently available treatment strategies. Current approaches used for tendon healing always lead to the formation of fibrovascular scar tissue, which significantly compromises the biomechanics of the healed tendon. Moreover, the related functional deficiency deteriorates over time with an increased injury recurrence risk. Small leucine-rich proteoglycans (SLRPs) link and interact with collagen fibrils to regulate tendon structure and biomechanics, which can provide a new and promising method in the field of tendon injury management. Recent Advances: The effect of SLRPs on tendon development has been extensively investigated. SLRP deficiency impairs tendon collagen fibril structure and biomechanic properties, while administration of SLRPs generally benefits tendon wound healing and regains better mechanical properties. Critical Issues: Current knowledge on the role of SLRPs in tendon development and regeneration mostly comes from uninjured knockout mice, and mainly focuses on the morphology description of collagen fibril profile and mechanical properties. Little is known about the regulatory mechanism on the molecular level. Future Directions: This article reviews the current knowledge in this highly translational topic and provides an evidence-based conclusion, thereby encouraging in-depth investigations of SLRPs in tendons and the development of SLRP-based treatments for desired tendon healing.

Oncosuppressive roles of decorin through regulation of multiple receptors and diverse signaling pathways

Decorin is a stromal-derived prototype member of the small leucine-rich proteoglycan gene family. In addition to its functions as a regulator of collagen fibrillogenesis and TGF-β activity soluble decorin acts as a pan-receptor tyrosine kinase (RTK) inhibitor. Decorin binds to various RTKs including EGFR HER2 HGFR/Met VEGFR2 TLR and IGFR. Although the molecular mechanism for the action of decorin on these receptors is not entirely elucidated overall decorin evokes transient activation of these receptors with suppression of downstream signaling cascades culminating in growth inhibition followed by their physical downregulation via caveosomal internalization and degradation. In the case of Met decorin leads to decreased β-catenin signaling pathway and growth suppression. As most of these RTKs are responsible for providing a growth advantage to cancer cells the result of decorin treatment is oncosuppression. Another decorin-driven mechanism to restrict cancer growth and dissemination is by impeding angiogenesis via vascular endothelial growth factor receptor 2 (VEGFR2) and the concurrent activation of protracted endothelial cell autophagy. In this review we will dissect the multiple roles of decorin in cancer biology and its potential use as a next-generation protein-based adjuvant therapy to combat cancer.

Loss of IκBζ Drives Dentin Formation via Altered H3K4me3 Status

Enforced enrichment of the active promoter marks trimethylation of histone H3 lysine 4 (H3K4me3) and acetylation of histone H3 lysine 27 (H3K27ac) by inhibiting histone demethylases and deacetylases is positively associated with hard tissue formation through the induction of osteo/odontogenic differentiation. However, the key endogenous epigenetic modulator of odontoblasts to regulate the expression of genes coding dentin extracellular matrix (ECM) proteins has not been identified. We focused on nuclear factor (NF)-κB inhibitor ζ (IκBζ), which was originally identified as the transcriptional regulator of NF-κB and recently regarded as the NF-κB-independent epigenetic modulator, and found that IκBζ null mice exhibit a thicker dentin width and narrower pulp chamber, with aged mice having more marked phenotypes. At 6 mo of age, dentin fluorescent labeling revealed significantly accelerated dentin synthesis in the incisors of IκBζ null mice. In the molars of IκBζ null mice, marked tertiary dentin formation adjacent to the pulp horn was observed. Mechanistically, the expression of COL1A2 and COL1A1 collagen genes increased more in the odontoblast-rich fraction of IκBζ null mice than in wild type in vivo, similar to human odontoblast-like cells transfected with small interfering RNA for IκBζ compared with cells transfected with control siRNA in vitro. Furthermore, the direct binding of IκBζ to the COL1A2 promoter suppressed COL1A2 expression and the local active chromatin status marked by H3K4me3. Based on whole-genome identification of H3K4me3 enrichment, ECM and ECM organization-related gene loci were selectively activated by the knockdown of IκBζ, which consistently resulted in the upregulation of these genes. Collectively, this study suggested that IκBζ is the key negative regulator of dentin formation in odontoblasts by inhibiting dentin ECM- and ECM organization-related gene expression through an altered local chromatin status marked by H3K4me3. Therefore, IκBζ is a potential target for epigenetically improving the clinical outcomes of dentin regeneration therapies such as pulp capping.

The Role of Decorin Proteoglycan in Mitophagy

Simple Summary

The eminent rise of extracellular matrix constituents, chiefly hailing from the proteoglycan gene family, has revolutionized our understanding of how intracellular catabolism is regulated at the intersection of autophagy and breast cancer. In this review, we examine the mechanisms of decorin, a small leucine-rich proteoglycan, as it relates to autophagy and mitochondrial autophagy (mitophagy). In each case, decorin signals via a unique cell surface receptor tyrosine kinase to evoke autophagy (VEGFR2) or mitophagy (MET receptor) that converges on a novel tumor suppressor gene. The downstream function of either Peg3 or mitostatin in response to decorin manifests as potent means to subdue breast cancer development and progression.

Abstract

Proteoglycans are emerging as critical regulators of intracellular catabolism. This rise in prominence has transformed our basic understanding and alerted us to the existence of non-canonical pathways, independent of nutrient deprivation, that potently control the autophagy downstream of a cell surface receptor. As a member of the small leucine-rich proteoglycan gene family, decorin has single-handedly pioneered the connection between extracellular matrix signaling and autophagy regulation. Soluble decorin evokes protracted endothelial cell autophagy via Peg3 and breast carcinoma cell mitophagy via mitostatin by interacting with VEGFR2 or the MET receptor tyrosine kinase, respectively. In this paper, we give a mechanistic perspective of the vital factors underlying the nutrient-independent, SLRP-dependent programs utilized for autophagic and/or mitophagic progression in breast cancer. Future protein therapies based on decorin (or fellow proteoglycan members) will represent a quantum leap forward in transforming autophagic progression into a powerful tool to control intracellular cell catabolism from the outside.

Supply chain logistics - the role of the Golgi complex in extracellular matrix production and maintenance

The biomechanical and biochemical properties of connective tissues are determined by the composition and quality of their extracellular matrix. This, in turn, is highly dependent on the function and organisation of the secretory pathway. The Golgi complex plays a vital role in directing matrix output by co-ordinating the post-translational modification and proteolytic processing of matrix components prior to their secretion. These modifications have broad impacts on the secretion and subsequent assembly of matrix components, as well as their function in the extracellular environment. In this Review, we highlight the role of the Golgi in the formation of an adaptable, healthy matrix, with a focus on proteoglycan and procollagen secretion as example cargoes. We then discuss the impact of Golgi dysfunction on connective tissue in the context of human disease and ageing.

Orthodontic tooth movement alters cementocyte ultrastructure and cellular cementum proteome signature

Cementum is a mineralized tissue that covers tooth roots and functions in the periodontal attachment complex. Cementocytes, resident cells of cellular cementum, share many characteristics with osteocytes, are mechanoresponsive cells that direct bone remodeling based on changes in loading. We hypothesized that cementocytes play a key role during orthodontic tooth movement (OTM). To test this hypothesis, we used 8-week-old male Wistar rats in a model of OTM for 2, 7, or 14 days (0.5 N), whereas unloaded contralateral teeth served as controls. Tissue and cell responses were analyzed by high-resolution micro-computed tomography, histology, tartrate-resistant acid phosphatase staining for odontoclasts/osteoclasts, and transmission electron microscopy. In addition, laser capture microdissection was used to collect cellular cementum, and extracted proteins were identified by liquid chromatography coupled to tandem mass spectrometry. The OTM model successfully moved first molars mesially more than 250 μm by 14 days introducing apoptosis in a small number of cementocytes and areas of root resorption on mesial and distal aspects. Cementocytes showed increased nuclear size and proportion of euchromatin suggesting cellular activity. Proteomic analysis identified 168 proteins in cellular cementum with 21 proteins found only in OTM sites and 54 proteins only present in control samples. OTM-down-regulated several extracellular matrix proteins, including decorin, biglycan, asporin, and periostin, localized to cementum and PDL by immunostaining. Furthermore, type IV collagen (COL14A1) was the protein most down-regulated (-45-fold) by OTM and immunolocalized to cells at the cementum-dentin junction. Eleven keratins were significantly increased by OTM, and a pan-keratin antibody indicated keratin localization primarily in epithelial remnants of Hertwig's epithelial root sheath. These experiments provide new insights into biological responses of cementocytes and cellular cementum to OTM.

The Beneficial Effect of Rosmarinic Acid on Benzophenone-3-Induced Alterations in Human Skin Fibroblasts

Benzophenone-3 (BP-3) is one of the most widely used chemical sunscreens. The results of many in vitro and in vivo tests confirm its high percutaneous penetration and systemic absorption, which question the safety of its wide use. The aim of our research was to assess the effect of this compound on components of the skin extracellular matrix, and to investigate whether rosmarinic acid (RA) could reduce BP-3-induced changes in human skin fibroblasts. BP-3 used at concentrations of 0.1-100 µM caused a number of unfavorable changes in the level of type I collagen, decorin, sulfated glycosaminoglycans, hyaluronic acid, elastin, and expression or activity of matrix metalloproteinases (MMP-1, MMP-2), elastase and hyaluronidase. Moreover, the intracellular retention of collagen was accompanied by changes in the expression of proteins modifying and controlling the synthesis and secretion of this protein. Most importantly, RA at a concentration of 100 µM significantly reduced or completely abolished the adverse effects of BP-3. Based on these findings, it can be concluded that this polyphenol may provide effective protection against BP-3-induced disturbances in skin cells, which may have important clinical implications.

Inherited Proteoglycan Biosynthesis Defects-Current Laboratory Tools and Bikunin as a Promising Blood Biomarker

Proteoglycans consist of proteins linked to sulfated glycosaminoglycan chains. They constitute a family of macromolecules mainly involved in the architecture of organs and tissues as major components of extracellular matrices. Some proteoglycans also act as signaling molecules involved in inflammatory response as well as cell proliferation, adhesion, and differentiation. Inborn errors of proteoglycan metabolism are a group of orphan diseases with severe and irreversible skeletal abnormalities associated with multiorgan impairments. Identifying the gene variants that cause these pathologies proves to be difficult because of unspecific clinical symptoms, hardly accessible functional laboratory tests, and a lack of convenient blood biomarkers. In this review, we summarize the molecular pathways of proteoglycan biosynthesis, the associated inherited syndromes, and the related biochemical screening techniques, and we focus especially on a circulating proteoglycan called bikunin and on its potential as a new biomarker of these diseases.

Antiwrinkle efficacy of 1-ethyl-β-N-acetylglucosaminide, an inducer of epidermal hyaluronan production

BACKGROUND

Hyaluronan (HA) has a unique hydration capacity that contributes to firmness and bounciness of the skin. Epidermal HA declines with skin aging, which may lead to clinical signs of aging including skin wrinkles and loss of hydration and elasticity. Recently, we developed a new cosmetic agent 1-ethyl-β-N-acetylglucosaminide (β-NAG2), which enhances HA production in cultured human keratinocytes. The aim of this study was to explore antiaging potential of β-NAG2 in reconstructed human epidermal models and human clinical trial.

MATERIALS AND METHODS

The amount of HA in β-NAG2-treated epidermal models by topical application was analyzed by enzyme-linked immunosorbent assay (ELISA)-like assay. A randomized, double-blind and placebo-controlled study was conducted in Japanese females (n = 33) by topically treating each side of the face with a lotion formulated with β-NAG2 or placebo for 8 weeks.

RESULTS

Topically applied β-NAG2 dose dependently increased HA production in epidermal models. Treatment with β-NAG2-formulated lotion significantly improved skin hydration and elasticity and reduced skin wrinkling in crow's foot areas when compared to the placebo formulation.

CONCLUSION

Topically applied β-NAG2 promoted epidermal HA production in vitro and showed antiwrinkle activity in vivo accompanying the improvement in skin hydration and elasticity. Our study provides a novel strategy for antiwrinkle care through β-NAG2-induced epidermal HA production.

Decorin Suppresses Invasion and EMT Phenotype of Glioma by Inducing Autophagy via c-Met/Akt/mTOR Axis

Decorin exhibits inhibitory effects in tumorigenesis in various types of cancers. The clinical characteristics of 42 patients with GBM were reviewed and analyzed. Lentiviral constructs for decorin overexpression and shRNA-mediated silencing were established for U87MG cells and T98G cells, respectively. The expressions of EMT- and autophagy-associated markers were detected in GBM cell lines. The migration and invasion of the glioma cells were assayed to reflect the malignant behavior of GBM. A mouse xenograft model was used to verify the effect of decorin on autophagy in vivo. Reduced expression of decorin in glioma tissues was associated with a poor survival of the patients. Decorin overexpression suppressed cell migration, invasion and attenuated EMT phenotype in glioma cell lines. Further study indicated that decorin inhibited EMT phenotype through the induction of autophagy. The mechanisms include inhibiting the activation of c-Met/Akt/mTOR signaling and regulating the expressions of mesenchymal markers including Slug, vimentin and Twist, and epithelial marker E-cadherin. In addition, decorin overexpression in a mice model can also suppress the GBM invasion and EMT phenotype. In conclusion, decorin suppresses invasion and EMT phenotype of glioma by inducing autophagy via c-Met/Akt/mTOR axis.

Differences in MPS I and MPS II Disease Manifestations

Mucopolysaccharidosis (MPS) type I and II are two closely related lysosomal storage diseases associated with disrupted glycosaminoglycan catabolism. In MPS II, the first step of degradation of heparan sulfate (HS) and dermatan sulfate (DS) is blocked by a deficiency in the lysosomal enzyme iduronate 2-sulfatase (IDS), while, in MPS I, blockage of the second step is caused by a deficiency in iduronidase (IDUA). The subsequent accumulation of HS and DS causes lysosomal hypertrophy and an increase in the number of lysosomes in cells, and impacts cellular functions, like cell adhesion, endocytosis, intracellular trafficking of different molecules, intracellular ionic balance, and inflammation. Characteristic phenotypical manifestations of both MPS I and II include skeletal disease, reflected in short stature, inguinal and umbilical hernias, hydrocephalus, hearing loss, coarse facial features, protruded abdomen with hepatosplenomegaly, and neurological involvement with varying functional concerns. However, a few manifestations are disease-specific, including corneal clouding in MPS I, epidermal manifestations in MPS II, and differences in the severity and nature of behavioral concerns. These phenotypic differences appear to be related to different ratios between DS and HS, and their sulfation levels. MPS I is characterized by higher DS/HS levels and lower sulfation levels, while HS levels dominate over DS levels in MPS II and sulfation levels are higher. The high presence of DS in the cornea and its involvement in the arrangement of collagen fibrils potentially causes corneal clouding to be prevalent in MPS I, but not in MPS II. The differences in neurological involvement may be due to the increased HS levels in MPS II, because of the involvement of HS in neuronal development. Current treatment options for patients with MPS II are often restricted to enzyme replacement therapy (ERT). While ERT has beneficial effects on respiratory and cardiopulmonary function and extends the lifespan of the patients, it does not significantly affect CNS manifestations, probably because the enzyme cannot pass the blood-brain barrier at sufficient levels. Many experimental therapies, therefore, aim at delivery of IDS to the CNS in an attempt to prevent neurocognitive decline in the patients.

Cyclically stretched ACL fibroblasts emigrating from spheroids adapt their cytoskeleton and ligament-related expression profile

Mechanical stress of ligaments varies; hence, ligament fibroblasts must adapt their expression profile to novel mechanomilieus to ensure tissue resilience. Activation of the mechanoreceptors leads to a specific signal transduction, the so-called mechanotransduction. However, with regard to their natural three-dimensional (3D) microenvironment cell reaction to mechanical stimuli during emigrating from a 3D spheroid culture is still unclear. This study aims to provide a deeper understanding of the reaction profile of anterior cruciate ligament (ACL)-derived fibroblasts exposed to cyclic uniaxial strain in two-dimensional (2D) monolayer culture and during emigration from 3D spheroids with respect to cell survival, cell and cytoskeletal orientation, distribution, and expression profile. Monolayers and spheroids were cultured in crosslinked polydimethyl siloxane (PDMS) elastomeric chambers and uniaxially stretched (14% at 0.3 Hz) for 48 h. Cell vitality, their distribution, nuclear shape, stress fiber orientation, focal adhesions, proliferation, expression of ECM components such as sulfated glycosaminoglycans, collagen type I, decorin, tenascin C and cell-cell communication-related gap junctional connexin (CXN) 43, tendon-related markers Mohawk and tenomodulin (myodulin) were analyzed. In contrast to unstretched cells, stretched fibroblasts showed elongation of stress fibers, cell and cytoskeletal alignment perpendicular to strain direction, less rounded cell nuclei, increased numbers of focal adhesions, proliferation, amplified CXN43, and main ECM component expression in both cultures. The applied cyclic stretch protocol evoked an anabolic response and enhanced tendon-related marker expression in ACL-derived fibroblasts emigrating from 3D spheroids and seems also promising to support in future tissue formation in ACL scaffolds seeded in vitro with spheroids.

Natural biomaterials in brain repair: A focus on collagen

Biomaterials derived from natural resources have increasingly been used for versatile applications in the central nervous system (CNS). Thanks to their biocompatibility and biodegradability, natural biomaterials offer vast possibilities for future clinical repair strategies for the CNS. These materials can be used for diverse applications such as hydrogels to fill the tissue cavities, microparticles to deliver drugs across the blood-brain barrier, and scaffolds to transplant stem cells. In this review, various uses of prominent protein and polysaccharide biomaterials, with a special focus on collagen, in repair and regenerative applications for the brain are summarized together with their individual advantages and disadvantages.

Glycosaminoglycan Modification of Decorin Depends on MMP14 Activity and Regulates Collagen Assembly

Proper processing of collagens COL1 and COL6 is required for normal function of adipose tissue and skeletal muscle. Proteoglycan decorin (DCN) regulates collagen fiber formation. The amino-terminus of DCN is modified with an O-linked glycosaminoglycan (GAG), the function of which has remained unclear. Previously, non-glycanated DCN (ngDCN) was identified as a marker of adipose stromal cells. Here, we identify MMP14 as the metalloprotease that cleaves DCN to generate ngDCN. We demonstrate that mice ubiquitously lacking DCN GAG (ngDCN mice) have reduced matrix rigidity, enlarged adipocytes, fragile skin, as well as skeletal muscle hypotrophy, fibrosis, and dysfunction. Our results indicate that DCN deglycanation results in reduced intracellular DCN—collagen binding and increased production of truncated COL6 chains, leading to aberrant procollagen processing and extracellular localization. This study reveals that the GAG of DCN functions to regulate collagen assembly in adipose tissue and skeletal muscle and uncovers a new mechanism of matrix dysfunction in obesity and aging.

Communications via the Small Leucine-rich Proteoglycans: Molecular Specificity in Inflammation and Autoimmune Diseases

Inflammation is a highly regulated biological response of the immune system that is triggered by assaulting pathogens or endogenous alarmins. It is now well established that some soluble extracellular matrix constituents, such as small leucine-rich proteoglycans (SLRPs), can act as danger signals and trigger aseptic inflammation by interacting with innate immune receptors. SLRP inflammatory signaling cascade goes far beyond its canonical function. By choosing specific innate immune receptors, coreceptors, and adaptor molecules, SLRPs promote a switch between pro- and anti-inflammatory signaling, thereby determining disease resolution or chronification. Moreover, by orchestrating signaling through various receptors, SLRPs fine-tune inflammation and, despite their structural homology, regulate inflammatory processes in a molecule-specific manner. Hence, the overarching theme of this review is to highlight the molecular and functional specificity of biglycan-, decorin-, lumican-, and fibromodulin-mediated signaling in inflammatory and autoimmune diseases.

Injectable Disc-Derived ECM Hydrogel Functionalised with Chondroitin Sulfate for Intervertebral Disc Regeneration

Low back pain resulting from intervertebral disc (IVD) degeneration is a significant socioeconomic burden. The main effect of the degeneration process involves the alteration of the nucleus pulposus (NP) via cell-mediated enzymatic breakdown of key extracellular matrix (ECM) components. Thus, the development of injectable and biomimetic biomaterials that can instruct the regenerative cell component to produce tissue-specific ECM is pivotal for IVD repair. Chondroitin sulfate (CS) and type II collagen are the primary components of NP tissue and together create the ideal environment for cells to deposit de-novo matrix. Given their high matrix synthesis capacity potential post-expansion, nasal chondrocytes (NC) have been proposed as a potential cell source to promote NP repair. The overall goal of this study was to assess the effects of CS incorporation into disc derived self-assembled ECM hydrogels on the matrix deposition of NCs. Results showed an increased sGAG production with higher amounts of CS in the gel composition and that its presence was found to be critical for the synthesis of collagen type II. Taken together, our results demonstrate how the inclusion of CS into the composition of the material aids the preservation of a rounded cell morphology for NCs in 3D culture and enhances their ability to synthesise NP-like matrix.

Treatment with Hyaluronic Acid and Collagen-Polyvinylpyrrolidone Improves Extracellular Matrix Assembly for Scarring after Tracheal Resection

Treatment of tracheal stenosis is occasionally performed in combination with wound healing modulators to manipulate new extracellular matrix (ECM) formation and prevent fibrosis. Hyaluronic acid (HA) and collagen-polyvinylpyrrolidone (collagen-PVP) decrease fibrosis in experimental tracheal healing. However, they have not been used clinically as their effect on ECM components, which modify tracheal scarring, has not been described. Objective. To evaluate the effect of the application of HA, collagen-PVP, a mixture of HA and collagen-PVP (HA+collagen-PVP), and mitomycin C on the expression of decorin, matrix metalloproteinase 1 (MMP1), and MMP9, as well as the type of collagen and deposits formed in the scar after resection and end-to-end anastomosis (REEA) of the cervical trachea using an experimental model. Materials and Methods. Thirty dogs underwent REEA of the cervical trachea and were treated with different wound healing modulators: group I (n = 6), control; group II (n = 6), HA; group III (n = 6), collagen-PVP; group IV (n = 6), HA+collagen-PVP; and group V (n = 6), mitomycin C. The dogs were evaluated clinically and endoscopically for 4 weeks. Subsequently, macroscopic and microscopic changes, expression of ECM proteins, and collagen deposition in tracheal scars were analysed. Results. Groups II, III, and IV showed reduced endoscopic, macroscopic, and microscopic inflammation, improved neovascularization, high decorin expression (p < 0.01, analysis of variance (ANOVA)), and moderate expression of MMP1 (p < 0.003, ANOVA) and type I and III collagen (p < 0.05, Kruskal–Wallis). Groups IV and V developed fewer collagen deposits (p < 0.001, ANOVA). Conclusion. Treatment with HA and collagen-PVP improved post-REEA healing by increasing neovascularization, stimulating the expression of decorin, and regulating the expression of MMP1, as well as type I and III collagen and their deposition.

The Protective Role of Decorin in Hepatic Metastasis of Colorectal Carcinoma

Decorin, the prototype member of the small leucine-rich proteoglycan gene family of extracellular matrix (ECM) proteins, acts as a powerful tumor suppressor by inducing the p21^Waf1/Cip1 cyclin-dependent kinase inhibitor, as well as through its ability to directly bind and block the action of several tyrosine kinase receptors. Our previous studies suggested that the lack of decorin promotes hepatic carcinogenesis in mice. Based on this, we set out to investigate whether excess decorin may protect against the liver metastases of colon carcinoma. We also analyzed the effect of decorin in tissue microarrays of human colon carcinoma liver metastasis and examined whether the tumor cells can directly influence the decorin production of myofibroblasts. In humans, low levels of decorin in the liver facilitated the development of colon carcinoma metastases in proportion with more aggressive phenotypes, indicating a possible antitumor action of the proteoglycan. In vitro, colon carcinoma cells inhibited decorin expression in LX2 hepatic stellate cells. Moreover, liver-targeted decorin delivery in mice effectively attenuated metastasis formation of colon cancer. Overexpressed decorin reduced the activity of multiple receptor tyrosine kinases (RTKs) including the epidermal growth factor receptor (EGFR), an important player in colorectal cancer (CRC) pathogenesis. Downstream of that, we observed weakened signaling of ERK1/2, PLCγ, Akt/mTOR, STAT and c-Jun pathways, while p38 MAPK/MSK/CREB and AMPK were upregulated culminating in enhanced p53 function. In conclusion, decorin may effectively inhibit metastatic tumor formation in the liver.

Silencing PEG3 inhibits renal fibrosis in a rat model of diabetic nephropathy by suppressing the NF-κB pathway

As paternally expressed gene 3 (PEG3), which can activate NF-κB pathway, plays an important role in the development of renal fibrosis in diabetic nephropathy (DN), the present study aimed to investigate the interaction of PEG3 and the NF-κB pathway on renal fibrosis in a DN model. Following the induction of the rat model of DN, a series of experiments were used to measure serum creatinine (Scr), blood urea nitrogen (BUN), urine protein for 24 h (UP24 h), proliferation of renal fibroblasts, positive expression of PEG3, Collagen I and Collagen II protein, the activity of NF-κB, collagen fiber expression and the FSP1⁺ cell ratio (fibroblast marker, reflecting renal fibrosis). Silencing of PEG3 or inhibition of the NF-κB pathway decreased the levels of Scr, BUN, and UP24 h, down-regulated Collagen I protein and up-regulated Collagen II protein. These treatments also down-regulated the expression of PEG3, NF-κB, Vimentin, α-SMA, FN, caspase-3 and FSP1 and the extents of IκBα, inhibitor of kappa B (IκB) kinase β (IKKβ), and NF-κB p65 phosphorylation while that of E-cadherin was up-regulated, and the ratio of FSP1⁺ cells was decreased. Taken together, these results showed that silencing of PEG3 inhibited the NF-κB pathway, thereby alleviating renal fibrosis in DN, thus presenting PEG3 as a potential therapeutic target in renal fibrosis in DN.

Biglycan in the Skeleton

Small leucine rich proteoglycans (SLRPs), including Biglycan, have key roles in many organ and tissue systems. The goal of this article is to review the function of Biglycan and other related SLRPs in mineralizing tissues of the skeleton. The review is divided into sections that include Biglycan's role in structural biology, signaling, craniofacial and long bone homeostasis, remodeled skeletal tissues, and in human genetics. While many cell types in the skeleton are now known to be affected by Biglycan, there are still unanswered questions about its mechanism of action(s).

Systematic investigation of the skin in Chst14-/- mice: A model for skin fragility in musculocontractural Ehlers-Danlos syndrome caused by CHST14 variants (mcEDS-CHST14)

Loss-of-function variants in CHST14 cause a dermatan 4-O-sulfotransferase deficiency named musculocontractural Ehlers-Danlos syndrome-CHST14 (mcEDS-CHST14), resulting in complete depletion of the dermatan sulfate moiety of decorin glycosaminoglycan (GAG) chains, which is replaced by chondroitin sulfate. Recently, we uncovered structural alteration of GAG chains in the skin of patients with mcEDS-CHST14. Here, we conducted the first systematic investigation of Chst14 gene-deleted homozygote (Chst14-/-) mice. We used skin samples of wild-type (Chst14+/+) and Chst14-/- mice. Mechanical fragility of the skin was measured with a tensile test. Pathology was observed using light microscopy, decorin immunohistochemistry and electron microscopy (EM) including cupromeronic blue (CB) staining. Quantification of chondroitin sulfate and dermatan sulfate was performed using enzymatic digestion followed by anion-exchange HPLC. In Chst14-/- mice, skin tensile strength was significantly decreased compared with that in Chst14+/+ mice. EM showed that collagen fibrils were oriented in various directions to form disorganized collagen fibers in the reticular layer. Through EM-based CB staining, rod-shaped linear GAG chains were found to be attached at one end to collagen fibrils and protruded outside of the fibrils, in contrast to them being round and wrapping the collagen fibrils in Chst14+/+ mice. A very low level of dermatan sulfate disaccharides was detected in the skin of Chst14-/- mice by anion-exchange chromatography. Chst14-/- mice, exhibiting similar abnormalities in the GAG structure of decorin and collagen networks in the skin, could be a reasonable model for skin fragility of patients with mcEDS-CHST14, shedding light on the role of dermatan sulfate in maintaining skin strength.

Alterations in extracellular matrix composition during aging and photoaging of the skin

Human skin is composed of the cell-rich epidermis, the extracellular matrix (ECM) rich dermis, and the hypodermis. Within the dermis, a dense network of ECM proteins provides structural support to the skin and regulates a wide variety of signaling pathways which govern cell proliferation and other critical processes. Both intrinsic aging, which occurs steadily over time, and extrinsic aging (photoaging), which occurs as a result of external insults such as solar radiation, cause alterations to the dermal ECM. In this study, we utilized both quantitative and global proteomics, alongside single harmonic generation (SHG) and two-photon autofluorescence (TPAF) imaging, to assess changes in dermal composition during intrinsic and extrinsic aging. We find that both intrinsic and extrinsic aging result in significant decreases in ECM-supporting proteoglycans and structural ECM integrity, evidenced by decreasing collagen abundance and increasing fibril fragmentation. Intrinsic aging also produces changes distinct from those produced by photoaging, including reductions in elastic fiber and crosslinking enzyme abundance. In contrast, photoaging is primarily defined by increases in elastic fiber-associated protein and pro-inflammatory proteases. Changes associated with photoaging are evident even in young (mid 20s) sun-exposed forearm skin, indicating that proteomic evidence of photoaging is present decades prior to clinical signs of photoaging. GO term enrichment revealed that both intrinsic aging and photoaging share common features of chronic inflammation. The proteomic data has been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD015982.

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Intrinsic aging and photoaging both decrease ECM-supporting proteoglycans and structural ECM.

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Intrinsic aging produces reductions in elastic fiber and crosslinking enzyme abundance.

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Photoaging results in increases in pro-inflammatory proteases and elastic fiber abundance.

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Intrinsic aging and photoaging share common features associated with chronic inflammation.

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Proteomic changes associated with photoaging are evident decades prior to clinical aging signs.

Growth Plate Pathology in the Mucopolysaccharidosis Type VI Rat Model-An Experimental and Computational Approach

BACKGROUND

Mucopolysaccharidoses (MPS) are a group of inherited metabolic diseases caused by impaired function or absence of lysosomal enzymes involved in degradation of glycosaminoglycans. Clinically, MPS are skeletal dysplasias, characterized by cartilage abnormalities and disturbances in the process of endochondral ossification. Histologic abnormalities of growth cartilage have been reported at advanced stages of the disease, but information regarding growth plate pathology progression either in humans or in animal models, as well as its pathophysiology, is limited.

METHODS

Histological analyses of distal femur growth plates of wild type (WT) and mucopolysaccharidosis type VI (MPS VI) rats at different stages of development were performed, including quantitative data. Experimental findings were then analyzed in a theoretical scenario.

RESULTS

Histological evaluation showed a progressive loss of histological architecture within the growth plate. Furthermore, in silico simulation suggest the abnormal cell distribution in the tissue may lead to alterations in biochemical gradients, which may be one of the factors contributing to the growth plate abnormalities observed, highlighting aspects that must be the focus of future experimental works.

CONCLUSION

The results presented shed some light on the progression of growth plate alterations observed in MPS VI and evidence the potentiality of combined theoretical and experimental approaches to better understand pathological scenarios, which is a necessary step to improve the search for novel therapeutic approaches.

Protective Role of Decorin in Primary Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) represents one of the most frequent type of primary liver cancers. Decorin, a small leucine-rich proteoglycan of the extracellular matrix, represents a powerful tumor cell growth and migration inhibitor by hindering receptor tyrosine kinases and inducing p21^WAF1/CIP1. In this study, first we tested decorin expression in HCCs utilizing in silico data, as well as formalin fixed paraffin embedded tissue samples of HCC in a tissue microarray (TMA). In silico data revealed that DCN/SMA mRNA ratio is decreased in HCC compared to normal tissues and follows the staging of the disease. Among TMA samples, 52% of HCCs were decorin negative, 33% exhibited low, and 15% high decorin levels corroborating in silico results. In addition, applying conditioned media of hepatoma cells inhibited decorin expression in LX2 stellate cells in vitro. These results raise the possibility that decorin acts as a tumor suppressor in liver cancer and that is why its expression decreased in HCCs. To further test the protective role of decorin, the proteoglycan was overexpressed in a mouse model of hepatocarcinogenesis evoked by thioacetamide (TA). After transfection, the excessive proteoglycan amount was mainly detected in hepatocytes around the central veins. Upon TA-induced hepatocarcinogenesis, the highest tumor count was observed in mice with no decorin production. Decorin gene delivery reduced tumor formation, in parallel with decreased pEGFR, increased pIGF1R levels, and with concomitant induction of pAkt (T308) and phopho-p53, suggesting a novel mechanism of action. Our results suggest the idea that decorin can be utilized as an anti-cancer agent.

Complexity of matrix phenotypes

The extracellular matrix is engaged in an ever-evolving and elegant ballet of dynamic reciprocity that directly and bi-directionally regulates cell behavior. Homeostatic and pathophysiological changes in cell-matrix signaling cascades manifest as complex matrix phenotypes. Indeed, the extracellular matrix can be implicated in virtually every known human disease, thus, making it the most critical and dynamic "organ" in the human body. The overall goal of this Special Issue is to provide an accurate and inclusive functional definition that addresses the inherent complexity of matrix phenotypes. This goal is summarily achieved via a corpus of expertly written articles, reviews and original research, focused at answering this question empirically and fundamentally via state-of-the-art methods and research strategies.

Anti-osteosarcoma property of decorin-modified titanium surface: A novel strategy to inhibit oncogenic potential of osteosarcoma cells

Osteosarcoma is the most common bone sarcoma in adolescents. Decorin (DCN) has been proposed to be a new anti-osteosarcoma therapeutic strategy. Our previous study has loaded decorin on titanium (Ti) surface by polydopamine (DOPA) as an anchor to enhance osseointegration. In this study, we investigated the effect of decorin-coated Ti substrates (TI-DOPA-DCN) on the oncogenic potential of osteosarcoma cells SAOS-2. The substrates were placed in 24-well plates for cell culture. Cell viability was determined by Cell Counting Kit-8 (CCK8) assay. Apoptosis was evaluated by DAPI staining and Annexin V-FITC/PI double staining analysis. Cell cycle was analyzed by flow cytometry. Cell migration and invasion were evaluated by Transwell assay. For co-culture, the pre-osteogenic cells MEC3T3-E1 and osteosarcoma cells SAOS-2 were stained with cell membrane fluorescent dyes, and then mixed (1:1) for co-culture. The cells were observed under a fluorescence microscope at four time points of 24, 48, 72, and 96 h. The results showed that TI-DOPA-DCN substrate can selectively inhibit cell proliferation of osteosarcoma cells but not pre-osteoblasts. However, the cell cycle of SAOS-2 was not affected by TI-DOPA-DCN substrates. Both DAPI staining and Annexin V-FITC/PI double staining analysis revealed that TI-DOPA-DCN substrates induced apoptosis of osteosarcoma cells. Transwell assay showed that TI-DOPA-DCN substrates inhibited invasion and migration of osteosarcoma cells. Moreover, TI-DOPA-DCN substrates inhibited the growth of osteosarcoma cells but promoted that of pre-osteoblasts in the coculture system. Taken together, these findings suggested that decorin coating on Ti surface simultaneously inhibited the oncogenic potential of osteosarcoma cells but enhanced cell growth of pre-osteoblasts, which could be applied to surface modification of Ti orthopedic implant.

From Translation to Protein Degradation as Mechanisms for Regulating Biological Functions: A Review on the SLRP Family in Skeletal Tissues

The extracellular matrix can trigger cellular responses through its composition and structure. Major extracellular matrix components are the proteoglycans, which are composed of a core protein associated with glycosaminoglycans, among which the small leucine-rich proteoglycans (SLRPs) are the largest family. This review highlights how the codon usage pattern can be used to modulate cellular response and discusses the biological impact of post-translational events on SLRPs, including the substitution of glycosaminoglycan moieties, glycosylation, and degradation. These modifications are listed, and their impacts on the biological activities and structural properties of SLRPs are described. We narrowed the topic to skeletal tissues undergoing dynamic remodeling.

Cell-cell junctions in developing and adult tendons

Tendons connect muscles to bones to transfer the forces necessary for movement. Cell-cell junction proteins, cadherins and connexins, may play a role in tendon development and injury. In this review, we begin by highlighting current understanding of how cell-cell junctions may regulate embryonic tendon development and differentiation. We then examine cell-cell junctions in postnatal tendon, before summarizing the role of cadherins and connexins in adult tendons. More information exists regarding the role of cell-cell junctions in the formation and homeostasis of other musculoskeletal tissues, namely cartilage and bone. Therefore, to inform future tendon studies, we include a brief survey of cadherins and connexins in chondrogenesis and osteogenesis, and summarize how cell-cell junctions are involved in some musculoskeletal tissue pathologies. An enhanced understanding of how cell-cell junctions participate in tendon development, maintenance, and disease will benefit future regenerative strategies.

Second-harmonic generation microscopy analysis reveals proteoglycan decorin is necessary for proper collagen organization in prostate

Collagen remodeling occurs in many prostate pathologies; however, the underlying structural architecture in both normal and diseased prostatic tissues is largely unexplored. Here, we use second-harmonic generation (SHG) microscopy to specifically probe the role of the proteoglycan decorin (Dcn) on collagen assembly in a wild type (wt) and Dcn null mouse (Dcn  -    /    -  ). Dcn is required for proper organization of collagen fibrils as it regulates size by forming an arch-like structure at the end of the fibril. We have utilized SHG metrics based on emission directionality (forward-backward ratio) and relative conversion efficiency, which are both related to the SHG coherence length, and found more disordered fibril organization in the Dcn  -    /    -  . We have also used image analysis readouts based on entropy, multifractal dimension, and wavelet transforms to compare the collagen fibril/fiber architecture in the two models, where all these showed that the Dcn  -    /    -   prostate comprised smaller and more disorganized collagen structures. All these SHG metrics are consistent with decreased SHG phase matching in the Dcn  -    /    -   and are further consistent with ultrastructural analysis of collagen in this model in other tissues, which show a more random distribution of fibril sizes and their packing into fibers. As Dcn is a known tumor suppressor, this work forms the basis for future studies of collagen remodeling in both malignant and benign prostate disease.

Matrix molecules and skin biology

An extracellular matrix (ECM) is a prerequisite for multicellular life. It is adapted to tissues and constantly undergoes changes to preserve microenvironmental homeostasis. The ECM acts as a structural scaffold that establishes tissue architecture and provides tensile strength. It has cell-instructive functions by serving as a reservoir and presenter of soluble agents, being directly signaling, integrating transmission of mechanical and biological cues, or serving as a co-factor potentiating signaling. The skin contains a highly developed, mechanically tough, but yet flexible ECM. The tissue-specific features of this ECM are largely attributed by minor ECM components. A large number of genetic and acquired ECM diseases with skin manifestations, provide an illustrative testament to the importance of correct assembly of the ECM for dermal homeostasis. Here, we will present the composition and features of the skin ECM during homeostasis and regeneration. We will discuss genetic and acquired ECM diseases affecting skin, and provide a short outlook to therapeutic strategies for them.

Molecular basis for governing the morphology of type-I collagen fibrils by Osteomodulin

Small leucine-rich repeat proteoglycan (SLRP) proteins have an important role in the organization of the extracellular matrix, especially in the formation of collagen fibrils. However, the mechanism governing the shape of collagen fibrils is poorly understood. Here, we report that the protein Osteomodulin (OMD) of the SLRP family is a monomeric protein in solution that interacts with type-I collagen. This interaction is dominated by weak electrostatic forces employing negatively charged residues of OMD, in particular Glu284 and Glu303, and controlled by entropic factors. The protein OMD establishes a fast-binding equilibrium with collagen, where OMD may engage not only with individual collagen molecules, but also with the growing fibrils. This weak electrostatic interaction is carefully balanced so it modulates the shape of the fibrils without compromising their viability.

Takumi Tashima and colleagues provide structural insights into how collagen fibrils are shaped by Osteomodulin. Osteomodulin keeps a fast-binding equilibrium with the collagen fibrils to slow down its growth, promoting the formation of uniform, intact collagen fibrils.

Impaired proteoglycan glycosylation, elevated TGF-β signaling, and abnormal osteoblast differentiation as the basis for bone fragility in a mouse model for gerodermia osteodysplastica

Gerodermia osteodysplastica (GO) is characterized by skin laxity and early-onset osteoporosis. GORAB, the responsible disease gene, encodes a small Golgi protein of poorly characterized function. To circumvent neonatal lethality of the Gorab^Null full knockout, Gorab was conditionally inactivated in mesenchymal progenitor cells (Prx1-cre), pre-osteoblasts (Runx2-cre), and late osteoblasts/osteocytes (Dmp1-cre), respectively. While in all three lines a reduction in trabecular bone density was evident, only Gorab^Prx1 and Gorab^Runx2 mutants showed dramatically thinned, porous cortical bone and spontaneous fractures. Collagen fibrils in the skin of Gorab^Null mutants and in bone of Gorab^Prx1 mutants were disorganized, which was also seen in a bone biopsy from a GO patient. Measurement of glycosaminoglycan contents revealed a reduction of dermatan sulfate levels in skin and cartilage from Gorab^Null mutants. In bone from Gorab^Prx1 mutants total glycosaminoglycan levels and the relative percentage of dermatan sulfate were both strongly diminished. Accordingly, the proteoglycans biglycan and decorin showed reduced glycanation. Also in cultured GORAB-deficient fibroblasts reduced decorin glycanation was evident. The Golgi compartment of these cells showed an accumulation of decorin, but reduced signals for dermatan sulfate. Moreover, we found elevated activation of TGF-β in Gorab^Prx1 bone tissue leading to enhanced downstream signalling, which was reproduced in GORAB-deficient fibroblasts. Our data suggest that the loss of Gorab primarily perturbs pre-osteoblasts. GO may be regarded as a congenital disorder of glycosylation affecting proteoglycan synthesis due to delayed transport and impaired posttranslational modification in the Golgi compartment.

Gerodermia osteodysplastica (GO) is segmental progeroid disorder affecting connective tissues and bone, leading to extreme bone fragility. The cause are loss-of-function mutations in the Golgi protein GORAB, whose function has been only partially unravelled. Using several mouse models and patient-derived primary cells we elucidate that loss of Gorab elicits a defect in proteoglycan glycanation, which is associated with collagen disorganization in dermis and bone. We also found evidence for TGF-β upregulation and enhanced downstream signalling. If these changes occur in mesenchymal stem cells or early osteoblasts they impair osteoblast differentiation resulting in cortical thinning and spontaneous fractures. We thus match GO mechanistically with also phenotypically overlapping progeroid connective tissue disorders with glycanation defects.

New developments on skin fibrosis - Essential signals emanating from the extracellular matrix for the control of myofibroblasts

Many different diseases are associated with fibrosis of the skin. The clinical symptoms can vary considerably with a broad range from isolated small areas to the involvement of the entire integument. Fibrosis is triggered by a multitude of different stimuli leading to activation of the immune and vascular system that then initiate fibroblast activation and formation of matrix depositing and remodeling myofibroblasts. Ultimately, myofibroblasts deposit excessive amounts of extracellular matrix with a pathological architecture and alterations in growth factor binding and biomechanical properties, which culminates in skin hardening and loss of mobility. Treatment depends certainly on the specific type and cause of the disease, for the autoimmune driven localized and systemic scleroderma therapeutic options are still limited, but recent research has pointed out diverse molecular targets and mechanisms that can be exploited for the development of novel antifibrotic therapy.

Decorin is a devouring proteoglycan: Remodeling of intracellular catabolism via autophagy and mitophagy

Autophagy, a fundamental and evolutionarily-conserved eukaryotic pathway, coordinates a complex balancing act for achieving both nutrient and energetic requirements for proper cellular function and homeostasis. We have discovered that soluble proteoglycans evoke autophagy in endothelial cells and mitophagy in breast carcinoma cells by directly interacting with receptor tyrosine kinases, including VEGF receptor 2 and Met. Under these circumstances, autophagic regulation is considered "non-canonical" and is epitomized by the bioactivity of the small leucine-rich proteoglycan, decorin. Soluble matrix-derived cues being transduced downstream of receptor engagement converge upon a newly-discovered nexus of autophagic machinery consisting of Peg3 for endothelial cell autophagy and mitostatin for tumor cell mitophagy. In this thematic mini-review, we will provide an overview of decorin-mediated autophagy and mitophagy and propose that regulating intracellular catabolism is the underlying molecular basis for the versatility of decorin as a potent oncosuppressive agent.

Extracellular Distribution of Collagen II and Perifibrillar Adapter Proteins in Healthy and Osteoarthritic Human Knee Joint Cartilage

Perifibrillar adapter proteins, interconnecting collagen fibrils, and linking the collagen network with the aggrecan matrix seem to play a crucial role in the pathogenesis of osteoarthritis (OA). Therefore, we examined immunohistochemically the extracellular distribution of collagen II and the main perifibrillar adapter proteins-collagen IX, decorin, cartilage oligomeric matrix protein (COMP), and matrilin-3-in human samples of healthy (n=4) and OA (n=42) knee joint cartilage. Histopathology assessment was performed using an OA score. Staining patterns were evaluated in relation to the disease stage. The perifibrillar adapter proteins were uniformly distributed in the upper zones of healthy cartilage. In moderate OA (n=8; score 14.3 ± 4.7), all proteins analyzed were locally absent in the fibrillated area or the superficial and upper mid zone. In advanced OA (n=20; score 18.9 ± 5.3), they were uniformly distributed in these zones and accumulated pericellularly. Perifibrillar adapter proteins are important for the stabilization of the collagen network in the upper zones of healthy cartilage. Their degradation might be a critical event in early OA. In advanced OA, there are indications for an increased synthesis in an attempt to regenerate the lost tissue and to protect the remaining cartilage from further destruction.

Absence of the dermatan sulfate chain of decorin does not affect mouse development

BACKGROUND

In vitro studies suggest that the multiple functions of decorin are related to both its core protein and its dermatan sulfate chain. To determine the contribution of the dermatan sulfate chain to the functional properties of decorin in vivo, a mutant mouse whose decorin lacked a dermatan sulfate chain was generated.

RESULTS

Homozygous mice expressing only the decorin core protein developed and grew in a similar manner to wild type mice. In both embryonic and postnatal mice, all connective tissues studied, including cartilage, skin and cornea, appeared to be normal upon histological examination, and their collagen fibrils were of normal diameter and organization. In addition, abdominal skin wounds healed in an identical manner in the mutant and wild type mice.

CONCLUSIONS

The absence of a dermatan sulfate chain on decorin does not appear to overtly influence its functional properties in vivo.

Decorin-inducible Peg3 Evokes Beclin 1-mediated Autophagy and Thrombospondin 1-mediated Angiostasis

We previously discovered that systemic delivery of decorin for treatment of breast carcinoma xenografts induces paternally expressed gene 3 (Peg3), an imprinted gene encoding a zinc finger transcription factor postulated to function as a tumor suppressor. Here we found that de novo expression of Peg3 increased Beclin 1 promoter activity and protein expression. This process required the full-length Peg3 as truncated mutants lacking either the N-terminal SCAN domain or the zinc fingers failed to translocate to the nucleus and promote Beclin 1 transcription. Importantly, overexpression of Peg3 in endothelial cells stimulated autophagy and concurrently inhibited endothelial cell migration and evasion from a 3D matrix. Mechanistically, we found that Peg3 induced the secretion of the powerful angiostatic glycoprotein Thrombospondin 1 independently of Beclin 1 transcriptional induction. Thus, we provide a new mechanism whereby Peg3 can simultaneously evoke autophagy in endothelial cells and attenuate angiogenesis.