SLRP interaction can protect collagen fibrils from cleavage by collagenases

Granzyme B in aging and age-related pathologies

Aging is a major risk factor for pathologies that manifest later in life. Much attention is devoted towards elucidating how prolonged environmental exposures and inflammation promote biological (accelerated) tissue aging. Granzymes, a family of serine proteases, are increasingly recognized for their emerging roles in biological aging and disease. Widely recognized as intracellular mediators of cell death, granzymes, particularly granzyme B (GzmB), also accumulate in the extracellular milieu of tissues with age, contributing to chronic tissue injury, inflammation, and impaired healing. Consequently, this has prompted the field to reconsider how GzmB regulation, accumulation, and proteolysis impact health and disease with age. While GzmB is observed in numerous age-related conditions, the current review focuses on mechanistic studies where proof-of-concept has been forwarded.

Biomimetic strategies for the deputization of proteoglycan functions

Proteoglycans (PGs), which have glycosaminoglycan chains attached to their protein cores, are essential for maintaining the morphology and function of healthy body tissues. Extracellular PGs perform various functions, classified into the following four categories: i) the modulation of tissue mechanical properties; ii) the regulation and protection of the extracellular matrix; iii) protein sequestration; and iv) the regulation of cell signaling. The depletion of PGs may significantly impair tissue function, encompassing compromised mechanical characteristics and unregulated inflammatory responses. Since PGs play critical roles in the function of healthy tissues and their synthesis is complex, the development of PG mimetic molecules that recapitulate PG functions for tissue engineering and therapeutic applications has attracted the interest of researchers for more than 20 years. These approaches have ranged from semisynthetic graft copolymers to recombinant PG domains produced by cells that have undergone genetic modifications. This review discusses some essential extracellular PG functions and approaches to mimicking these functions.

Downregulated SPESP1-driven fibroblast senescence decreases wound healing in aged mice

BACKGROUND

Human dermal fibroblasts (HDFs) are essential in the processes of skin ageing and wound healing. However, the underlying mechanism of HDFs in skin healing of the elderly has not been well defined. This study aims to elucidate the mechanisms of HDFs senescence and how senescent HDFs affect wound healing in aged skin.

METHODS

The expression and function of sperm equatorial segment protein 1 (SPESP1) in skin ageing were evaluated via in vivo and in vitro experiments. To delve into the potential molecular mechanisms by which SPESP1 influences skin ageing, a combination of techniques was employed, including proteomics, RNA sequencing, immunoprecipitation, chromatin immunoprecipitation and liquid chromatography-mass spectrometry analyses. Clearance of senescent cells by dasatinib plus quercetin (D+Q) was investigated to explore the role of SPESP1-induced senescent HDFs in wound healing.

RESULTS

Here, we define the critical role of SPESP1 in ameliorating HDFs senescence and retarding the skin ageing process. Mechanistic studies demonstrate that SPESP1 directly binds to methyl-binding protein, leading to Decorin demethylation and subsequently upregulation of its expression. Moreover, SPESP1 knockdown delays wound healing in young mice and SPESP1 overexpression induces wound healing in old mice. Notably, pharmacogenetic clearance of senescent cells by D+Q improved wound healing in SPESP1 knockdown skin.

CONCLUSIONS

Taken together, these findings reveal the critical role of SPESP1 in skin ageing and wound healing, expecting to facilitate the development of anti-ageing strategies and improve wound healing in the elderly.

Single collagen fibrils isolated from high stress and low stress tendons show differing susceptibility to enzymatic degradation by the interstitial collagenase matrix metalloproteinase-1 (MMP-1)

Bovine forelimb flexor and extensor tendons serve as a model for examining high stress, energy storing and low stress, positional tendons, respectively. Previous research has shown structural differences between the collagen fibrils of these tissues. The nanoscale collagen fibrils of flexor tendons are smaller in size, more heavily crosslinked, and respond differently to mechanical loading. Meanwhile, energy storing tendons undergo less collagen turnover compared to positional tendons and are more commonly injured. These observations raise the question of whether collagen fibril structure influences the collagen degradation processes necessary for remodelling. Atomic force microscopy was used to image dry collagen fibrils before and after 5-hour exposure to matrix metalloproteinase-1 (MMP-1) to detect changes in fibril size. Collagen fibrils from three tissue types were studied: bovine superficial digital flexor tendons, matched-pair bovine lateral digital extensor tendons, and rat tail tendons. Compared to control fibrils exposed only to buffer, a significant decrease in fibril cross-sectional area (CSA) following MMP-1 exposure was observed for bovine extensor and rat tail fibrils, with larger fibrils experiencing a greater magnitude of CSA decrease in both fibril types. Fibrils from bovine flexor tendons, on the other hand, showed no decrease in CSA when exposed to MMP-1. The result did not appear to be linked to the small size of flexor fibrils, as equivalently sized extensor fibrils were readily degraded by the enzyme. Increased proteolytic resistance of collagen fibrils from high stress tendons may help to explain the longevity of collagen within these tissues in vivo.

Engineered multi-functional, pro-angiogenic collagen-based scaffolds loaded with endothelial cells promote large deep burn wound healing

The lack of vascularization associated with deep burns delays the construction of wound beds, increases the risks of infection, and leads to the formation of hypertrophic scars or disfigurement. To address this challenge, we have fabricated a multi-functional pro-angiogenic molecule by grafting integrin αvβ3 ligand LXW7 and collagen-binding peptide (SILY) to a dermatan sulfate (DS) glycosaminoglycan backbone, named LXW7-DS-SILY (LDS), and further employed this to functionalize collagen-based Integra scaffolds. Using a large deep burn wound model in C57/BLK6 mice (8-10 weeks old, 26-32g, n = 39), we demonstrated that LDS-modified collagen-based Integra scaffolds loaded with endothelial cells (ECs) accelerate wound healing rate, re-epithelialization, vascularization, and collagen deposition. Specifically, a 2 cm × 3 cm full-thickness skin burn wound was created 48 h after the burn, and then wounds were treated with four groups of different dressing scaffolds, including Integra + ECs, Integra + LDS, and Integra + LDS + ECs with Integra-only as the control. Digital photos were taken for wound healing measurement on post-treatment days 1, 7, 14, 21, 28, and 35. Post-treatment photos revealed that treatment with the Intgera + LDS + ECs scaffold exhibited a higher wound healing rate in the proliferation phase. Histology results showed significantly increased re-epithelialization, increased collagen deposition, increased thin and mixed collagen fiber content, increased angiogenesis, and shorter wound length within the Integra + LDS + ECs group at Day 35. On Day 14, the Integra + LDS + ECs group showed the same trend. The relative proportions of collagen changed from Day 14 to Day 35 in the Integra + LDS + ECs and Integra + ECs groups demonstrated decreased thick collagen fiber deposition and greater thin and mixed collagen fiber deposition. LDS-modified Integra scaffolds represent a promising novel treatment to accelerate deep burn wound healing, thereby potentially reducing the morbidity associated with open burn wounds. These scaffolds can also potentially reduce the need for autografting and morbidity in patients with already limited areas of harvestable skin.

Noncytotoxic Roles of Granzymes in Health and Disease

Granzymes are serine proteases previously believed to play exclusive and somewhat redundant roles in lymphocyte-mediated target cell death. However, recent studies have challenged this paradigm. Distinct substrate profiles and functions have since emerged for each granzyme while their dysregulated proteolytic activities have been linked to diverse pathologies.

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.

Tyrosine-sulfated dermatopontin shares multiple binding sites and recognition determinants on triple-helical collagens with proteins implicated in cell adhesion and collagen folding, fibrillogenesis, cross-linking, and degradation

Dermatopontin (DPT), a small extracellular matrix protein that stimulates collagen fibrillogenesis, contains sulfotyrosine residues but neither its level of sulfation nor its binding sites on fibrillar collagens are known. Here, we discovered that DPT is present in a relatively high mass concentration (~ 0.02%) in porcine corneal stroma, from which we purified five DPT charge variants (A-E) containing up to six sulfations. The major variant (C), containing four sulfotyrosine residues, was used to locate binding sites for DPT on triple-helical collagens II and III using the Collagen Toolkits. DPT-binding loci included the triple helix crosslinking sites and collagenase cleavage site. We find that strong DPT-binding sites on triple-helical collagen comprise an arginine-rich, positively-charged sequence that also contains hydrophobic residues. This collagen-binding signature of DPT is similar to that of the chaperone HSP47. Thus, we propose that DPT assumes the role of HSP47 as a collagen chaperone during and after the secretion. Peptide II-44, harbouring the conserved collagenase cleavage site, shows the strongest DPT-binding of the Collagen Toolkit II peptides. Substituting any of the three arginine residues (R) with alanine in the sequence GLAGQRGIVGLOGQRGER of II-44 resulted in almost complete loss of DPT binding. Since osteogenesis imperfecta, spondyloepiphyseal dysplasia, and spondyloepimetaphyseal dysplasia congenita are associated with missense mutations that substitute the corresponding arginine residues in collagens alpha-1(I) and alpha-1(II), we suggest that disrupted DPT binding to fibrillar collagens may contribute to these connective tissue disorders. In conclusion, the present work provides a cornerstone for further elucidation of the role of DPT.

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.

Proteoglycans and proteoglycan mimetics for tissue engineering

Proteoglycans play a crucial role in proper tissue morphology and function throughout the body that is defined by a combination of their core protein and the attached glycosaminoglycan chains. Although they serve a myriad of roles, the functions of extracellular proteoglycans can be generally sorted into four categories: modulation of tissue mechanical properties, regulation and protection of the extracellular matrix, sequestering of proteins, and regulation of cell signaling. The loss of proteoglycans can result in significant tissue disfunction, ranging from poor mechanical properties to uncontrolled inflammation. Because of the key roles they play in proper tissue function and due to their complex synthesis, the past two decades have seen significant research into the development of proteoglycan mimetic molecules to recapitulate the function of proteoglycans for therapeutic and tissue engineering applications. These strategies have ranged from semisynthetic graft copolymers to recombinant proteoglycan domains synthesized by genetically engineered cells. In this review, we highlight some of the important functions of extracellular proteoglycans, as well as the strategies developed to recapitulate these functions.

Epiphycan Predicts Poor Outcomes and Promotes Metastasis in Ovarian Cancer

The small leucine-rich proteoglycan (SLRP) family is widely expressed in extracellular matrix and aggravates tumor progression. However, epiphycan (EPYC), as a member of the SLRPs family, its biological function in cancer has not been confirmed. Thus, we aimed to clarify the role of EPYC in progression of ovarian cancer (OC), and further analyze the molecular mechanisms implicated in tumorigenesis. Here, we analyzed the differential expression genes of GSE38734, including 4 matched primary OC and metastatic tissues. We obtained OC RNAseqs data from the Cancer Genome Atlas (TCGA) and analyzed the correlation between EPYC expression and OC staging, pathological grading, etc. The expression of EPYC in OC and normal ovarian tissues was compared in Oncomine website. We used siRNAs to interfere the expression of EPYC in ovarian cancer cell line SKOV3. Scratch test, transwell-matrigel chamber, CCK8 assay were used to detect the changes of SKOV3 migration, invasion and proliferation ability after EPYC was interfered. We used R software to make GO and KEGG analysis of related genes of EPYC. We used the Hitpredict website to predict interacting proteins. The results showed that the expression of EPYC in metastatic ovarian cancer was higher than primary ovarian cancer, and that in primary cancer was higher than normal ovaries. After siRNA interferes with EPYC expression, the migration, invasion and proliferation of SKOV3 cells were weakened. EPYC mainly played a role in ECM organization, and involved in PI3K/Akt, focal adhesion signaling pathways. EPYC might interact with PLCG2 and CRK, and be involved in signal transduction.

Basic Structure, Physiology, and Biochemistry of Connective Tissues and Extracellular Matrix Collagens

The physiology of connective tissues like tendons and ligaments is highly dependent upon the collagens and other such extracellular matrix molecules hierarchically organized within the tissues. By dry weight, connective tissues are mostly composed of fibrillar collagens. However, several other forms of collagens play essential roles in the regulation of fibrillar collagen organization and assembly, in the establishment of basement membrane networks that provide support for vasculature for connective tissues, and in the formation of extensive filamentous networks that allow for cell-extracellular matrix interactions as well as maintain connective tissue integrity. The structures and functions of these collagens are discussed in this chapter. Furthermore, collagen synthesis is a multi-step process that includes gene transcription, translation, post-translational modifications within the cell, triple helix formation, extracellular secretion, extracellular modifications, and then fibril assembly, fibril modifications, and fiber formation. Each step of collagen synthesis and fibril assembly is highly dependent upon the biochemical structure of the collagen molecules created and how they are modified in the cases of development and maturation. Likewise, when the biochemical structures of collagens or are compromised or these molecules are deficient in the tissues - in developmental diseases, degenerative conditions, or injuries - then the ultimate form and function of the connective tissues are impaired. In this chapter, we also review how biochemistry plays a role in each of the processes involved in collagen synthesis and assembly, and we describe differences seen by anatomical location and region within tendons. Moreover, we discuss how the structures of the molecules, fibrils, and fibers contribute to connective tissue physiology in health, and in pathology with injury and repair.

H2S signaling and extracellular matrix remodeling in cardiovascular diseases: A tale of tense relationship

Extracellular matrix (ECM) is a non-cellular three-dimensional macromolecular network that not only provides mechanical support but also transduces essential molecular signals in organ functions. ECM is constantly remodeled to control tissue homeostasis, responsible for cell adhesion, cell migration, cell-to-cell communication, and cell differentiation, etc. The dysregulation of ECM components contributes to various diseases, including cardiovascular diseases, fibrosis, cancer, and neurodegenerative diseases, etc. Aberrant ECM remodeling is initiated by various stress, such as oxidative stress, inflammation, ischemia, and mechanical stress, etc. Hydrogen sulfide (H₂S) is a gasotransmitter that exhibits a wide variety of cytoprotective and physiological functions through its anti-oxidative and anti-inflammatory actions. Amounting research shows that H₂S can attenuate aberrant ECM remodeling. In this review, we discussed the implications and mechanisms of H₂S in the regulation of ECM remodeling in cardiovascular diseases, and highlighted the potential of H₂S in the prevention and treatment of cardiovascular diseases through attenuating adverse ECM remodeling.

Stability and remineralization of proteoglycan-infused dentin substrate

OBJECTIVE

This study tested the effects of small leucine-rich proteoglycan (SLRP) proteins on phosphoric acid (PA)-treated dentin bonding overtime and the role of such SLRPs in the remineralization potential of demineralized dentin collagen.

METHODS

Coronal dentin sections of human molars were used. SLRPs were either decorin (DCN) or biglycan (BGN) in core or proteoglycan form (with glycosaminoglycans, GAGs). Groups were: No treatment (control), DCN core, DCN + GAGs, BGN core, BGN + GAGs. Samples were etched with PA for 15 s and prior to application of Adper Single Bond Plus and composite buildup an aliquot of the specific SLRPs was applied over dentin. Twenty-four hours or 6 months after the bonding procedure, samples were tested for microtensile bond strength (MTBS). Debonded beams were analyzed by scanning electron microscopy (SEM). For remineralization studies, dentin blocks were fully demineralized, infused with the SLRPs, placed in artificial saliva for 2 weeks, and evaluated by transmission electron microscopy (TEM).

RESULTS

MTBS test presented a mean of 51.4 ± 9.1 MPa in control with no statistically significant difference to DCN core (47.6 ± 8.3) and BGN core (48.3 ± 6.5). The full proteoglycan groups DCN + GAGs (27.4 ± 4.5) and BGN + GAGs (36.4 ± 13.6) showed decreased MTBS compared to control (p < 0.001). At 6 months, control or core-treated samples did not have a statistically significant difference in MTBS. However, SLRPs with GAGs showed statistically significant improvement of bonding (62.5 ± 6.0 for DCN and 52.8 ± 8.1 for BGN, p < 0.001) compared to their baseline values. SEM showed that GAGs seem to favor water retention but overtime help remineralization. TEM of demineralized dentin indicated a larger collagen fibril diameter pattern of samples treated with core proteins compared to control and a smaller diameter with DCN + GAGs in water with evidence of mineralization with DCN + GAGS, BGN core and BGN + GAGs.

SIGNIFICANCE

In conclusion, core proteins seem not to affect dentin adhesion significantly but the presence of GAGs can be detrimental to immediate bonding. However, after ageing of samples, full proteoglycans, particularly DCN, can significantly improve bonding overtime while promoting remineralization which can prove to be clinically beneficial.

Protein Levels and Microstructural Changes in Localized Regions of Early Cartilage Degeneration Compared with Adjacent Intact Cartilage

OBJECTIVE

It was hypothesized that the respective protein profiles of bovine cartilage from sites of localized mild to moderate (GI to GII) degeneration versus adjacent sites of intact tissue would vary in accordance with the tissue microstructural changes associated with a pre-osteoarthritic state.

METHODS

A total of 15 bovine patellae were obtained for this study. Paired samples of tissue were collected from the lateral region of each patella. If the patella contained a site of degeneration, a paired tissue set involved taking one sample each from the degenerated site and the intact tissue adjacent to it. Sufficient tissue was collected to facilitate 2 arms of investigation: microstructural imaging and proteome analysis. The microstructural analysis used a bespoke tissue preparation technique imaged with differential interference contrast optical microscopy to assess fibrillar scale destructuring and underlying bone spicule formation. An iTRAQ-based proteome analysis was performed using liquid chromatography-tandem mass spectrometry to identify the differential levels of proteins across the intact and degenerated cartilage and further, the results were validated with multiple reaction monitoring assay.

RESULTS

In the healthy cartilage pairs, there was no significant variation in protein profiles between 2 adjacent sample sites. In pairs of tissue that contained a sample of GI/GII tissue, there were both significant microstructural changes as well as the difference in abundance levels of 24 proteins.

CONCLUSIONS

From the known functions of the 24 proteins, found to be strongly aligned with the specific microstructural changes observed, a unique "proteins ensemble" involved in the initiation and progression of early cartilage degeneration is proposed.

Extracellular Matrix in Vascular Disease, Part 2/4: JACC Focus Seminar

Medium-sized and large arteries consist of 3 layers: the tunica intima, tunica media, and tunica adventitia. The tunica media accounts for the bulk of the vessel wall and is the chief determinant of mechanical compliance. It is primarily composed of circumferentially arranged layers of vascular smooth muscle cells that are separated by concentrically arranged elastic lamellae; a form of extracellular matrix (ECM). The tunica media is separated from the tunica intima and tunica adventitia, the innermost and outermost layers, respectively, by the internal and external elastic laminae. This second part of a 4-part JACC Focus Seminar discusses the contributions of the ECM to vascular homeostasis and pathology. Advances in genetics and proteomics approaches have fostered significant progress in our understanding of vascular ECM. This review highlights the important role of the ECM in vascular disease and the prospect of translating these discoveries into clinical disease biomarkers and potential future therapies.

Adding exogenous biglycan or decorin improves tendon formation for equine peritenon and tendon proper cells in vitro

Background

Tendon injuries amount to one of the leading causes of career-ending injuries in horses due to the inability for tendon to completely repair and the high reinjury potential. As a result, novel therapeutics are necessary to improve repair with the goal of decreasing leg lameness and potential reinjury. Small leucine-rich repeat proteoglycans (SLRPs), a class of regulatory molecules responsible for collagen organization and maturation, may be one such therapeutic to improve tendon repair. Before SLRP supplementation can occur in vivo, proper evaluation of the effect of these molecules in vitro needs to be assessed. The objective of this study was to evaluate the effectiveness of purified bovine biglycan or decorin on tendon proper and peritenon cell populations in three-dimensional tendon constructs.

Methods

Equine tendon proper or peritenon cell seeded fibrin three-dimensional constructs were supplemented with biglycan or decorin at two concentrations (5 nM or 25 nM). The functionality and ultrastructural morphology of the constructs were assessed using biomechanics, collagen content analysis, transmission electron microscopy (TEM), and gene expression by real time – quantitative polymerase chain reaction (RT-qPCR).

Results

SLRP supplementation affected both tendon proper and peritenon cells-seeded constructs. With additional SLRPs, material and tensile properties of constructs strengthened, though ultrastructural analyses indicated production of similar-sized or smaller fibrils. Overall expression of tendon markers was bolstered more in peritenon cells supplemented with either SLRP, while supplementation of SLRPs to TP cell-derived constructs demonstrated fewer changes in tendon and extracellular matrix markers. Moreover, relative to non-supplemented tendon proper cell-seeded constructs, SLRP supplementation of the peritenon cells showed increases in mechanical strength, material properties, and collagen content.

Conclusions

The SLRP-supplemented peritenon cells produced constructs with greater mechanical and material properties than tendon proper seeded constructs, as well as increased expression of matrix assembly molecules. These findings provide evidence that SLRPs should be further investigated for their potential to improve tendon formation in engineered grafts or post-injury.

Cleavage of proteoglycans, plasma proteins and the platelet-derived growth factor receptor in the hemorrhagic process induced by snake venom metalloproteinases

Envenoming by viperid snakes results in a complex pattern of tissue damage, including hemorrhage, which in severe cases may lead to permanent sequelae. Snake venom metalloproteinases (SVMPs) are main players in this pathogenesis, acting synergistically upon different mammalian proteomes. Hemorrhagic Factor 3 (HF3), a P-III class SVMP from Bothrops jararaca, induces severe local hemorrhage at pmol doses in a murine model. Our hypothesis is that in a complex scenario of tissue damage, HF3 triggers proteolytic cascades by acting on a partially known substrate repertoire. Here, we focused on the hypothesis that different proteoglycans, plasma proteins, and the platelet derived growth factor receptor (PDGFR) could be involved in the HF3-induced hemorrhagic process. In surface plasmon resonance assays, various proteoglycans were demonstrated to interact with HF3, and their incubation with HF3 showed degradation or limited proteolysis. Likewise, Western blot analysis showed in vivo degradation of biglycan, decorin, glypican, lumican and syndecan in the HF3-induced hemorrhagic process. Moreover, antithrombin III, complement components C3 and C4, factor II and plasminogen were cleaved in vitro by HF3. Notably, HF3 cleaved PDGFR (alpha and beta) and PDGF in vitro, while both receptor forms were detected as cleaved in vivo in the hemorrhagic process induced by HF3. These findings outline the multifactorial character of SVMP-induced tissue damage, including the transient activation of tissue proteinases, and underscore for the first time that endothelial glycocalyx proteoglycans and PDGFR are targets of SVMPs in the disruption of microvasculature integrity and generation of hemorrhage.

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).

A Role for Monosaccharides in Nucleation Inhibition and Transport of Collagen

Background: Collagenous tissues are composed of precisely oriented, tightly packed collagen fibril bundles to confer the maximal strength within the smallest volume. While this compact form benefits mobility, it consequentially restricts vascularity and cell density to a minimally viable level in some regions. These tissues reside in a homeostatic state with an unstable equilibrium, where perturbations to structure or molecular milieu cause descension into a long-term compromised state. Several studies have shown that glycosaminoglycans are key molecules required for healthy tissue maintenance. Our long-term goal is to determine if glycosaminoglycans serve a critical function of stabilizing soluble monomeric collagen in the interstitial fluid that bathes tissue for immediate availability in tissue development and repair in vivo. Materials and Methods: To test glycosaminoglycan and collagen interactions at the most fundamental level, we have explored the effect of the monosaccharides that populate the glycosaminoglycans of the extracellular matrix on collagen assembly kinetics, pre-established matrix stability, and collagen incorporation into a preassembled matrix. Results: Results showed that monosaccharides increased the threshold concentration required for spontaneous polymerization by at least three orders of magnitude. When the monosaccharides were introduced to a pre-existing collagen network, fibrillar dissociation was undetectable. Fluorescent-labeling studies illustrated that in the presence of the saccharide solution, soluble collagen maintains the functional capacity to integrate into a pre-existing network. Conclusion: This work demonstrates a feasible role for glycosaminoglycans in supporting tissue remodeling and highlights the potential importance of age-related deterioration of glycosaminoglycan biosynthesis in reference to the homeostasis of collagen-based tissues.

Transcriptome analyses of ovarian stroma: tunica albuginea, interstitium and theca interna

The ovary has specialised stromal compartments, including the tunica albuginea, interstitial stroma and theca interna, which develops concurrently with the follicular antrum. To characterise the molecular determinants of these compartments, stroma adjacent to preantral follicles (pre-theca), interstitium and tunica albuginea were laser microdissected (n = 4 per group) and theca interna was dissected from bovine antral follicles (n = 6). RNA microarray analysis showed minimal differences between interstitial stroma and pre-theca, and these were combined for some analyses and referred to as stroma. Genes significantly upregulated in theca interna compared to stroma included INSL3, LHCGR, HSD3B1, CYP17A1, ALDH1A1, OGN, POSTN and ASPN. Quantitative RT-PCR showed significantly greater expression of OGN and LGALS1 in interstitial stroma and theca interna versus tunica and greater expression of ACD in tunica compared to theca interna. PLN was significantly higher in interstitial stroma compared to tunica and theca. Ingenuity pathway, network and upstream regulator analyses were undertaken. Cell survival was also upregulated in theca interna. The tunica albuginea was associated with GPCR and cAMP signalling, suggesting tunica contractility. It was also associated with TGF-β signalling and increased fibrous matrix. Western immunoblotting was positive for OGN, LGALS1, ALDH1A1, ACD and PLN with PLN and OGN highly expressed in tunica and interstitial stroma (each n = 6), but not in theca interna from antral follicles (n = 24). Immunohistochemistry localised LGALS1 and POSTN to extracellular matrix and PLN to smooth muscle cells. These results have identified novel differences between the ovarian stromal compartments.

Integral Roles of Specific Proteoglycans in Hair Growth and Hair Loss: Mechanisms behind the Bioactivity of Proteoglycan Replacement Therapy with Nourkrin® with Marilex® in Pattern Hair Loss and Telogen Effluvium

Follicular proteoglycans are key players with structural, functional, and regulatory roles in the growth and cycling behaviour of the hair follicles. The expression pattern of specific proteoglycans is strongly correlated with follicular phase transitions, which further affirms their functional involvement. Research shows that bioactive proteoglycans, e.g., versican and decorin, can actively trigger follicular phase shift by their anagen-inducing, anagen-maintaining, and immunoregulatory properties. This emerging insight has led to the recognition of “dysregulated proteoglycan metabolism” as a plausible causal or mediating pathology in hair growth disorders in both men and women. In support of this, declined expression of proteoglycans has been reported in cases of anagen shortening and follicular miniaturisation. To facilitate scientific communication, we propose designating this pathology “follicular hypoglycania (FHG),” which results from an impaired ability of follicular cells to replenish and maintain a minimum relative concentration of key proteoglycans during anagen. Lasting FHG may advance to structural decay, called proteoglycan follicular atrophy (PFA). This process is suggested to be an integral pathogenetic factor in pattern hair loss (PHL) and telogen effluvium (TE). To address FHG and PFA, a proteoglycan replacement therapy (PRT) program using oral administration of a marine-derived extract (Nourkrin® with Marilex®, produced by Pharma Medico Aps, Aarhus, Denmark) containing specific proteoglycans has been developed. In clinical studies, this treatment significantly reduced hair fall, promoted hair growth, and improved quality of life in patients with male- and female-pattern hair loss. Accordingly, PRT (using Nourkrin® with Marilex®) can be recommended as an add-on treatment or monotherapy in patients with PHL and TE.

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.

The "other" 15-40%: The Role of Non-Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

Extracellular matrix (ECM) determines the physiological function of all tissues, including musculoskeletal tissues. In tendon, ECM provides overall tissue architecture, which is tailored to match the biomechanical requirements of their physiological function, that is, force transmission from muscle to bone. Tendon ECM also constitutes the microenvironment that allows tendon-resident cells to maintain their phenotype and that transmits biomechanical forces from the macro-level to the micro-level. The structure and function of adult tendons is largely determined by the hierarchical organization of collagen type I fibrils. However, non-collagenous ECM proteins such as small leucine-rich proteoglycans (SLRPs), ADAMTS proteases, and cross-linking enzymes play critical roles in collagen fibrillogenesis and guide the hierarchical bundling of collagen fibrils into tendon fascicles. Other non-collagenous ECM proteins such as the less abundant collagens, fibrillins, or elastin, contribute to tendon formation or determine some of their biomechanical properties. The interfascicular matrix or endotenon and the outer layer of tendons, the epi- and paratenon, includes collagens and non-collagenous ECM proteins, but their function is less well understood. The ECM proteins in the epi- and paratenon may provide the appropriate microenvironment to maintain the identity of distinct tendon cell populations that are thought to play a role during repair processes after injury. The aim of this review is to provide an overview of the role of non-collagenous ECM proteins and less abundant collagens in tendon development and homeostasis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:23-35, 2020.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

Expression and localization of the small proteoglycans decorin and biglycan in articular cartilage of Kashin-Beck disease and rats induced by T-2 toxin and selenium deficiency

Kashin-Beck disease (KBD) is an endemic degenerative osteoarthropathy of uncertain etiology. Our study sought to identify a correlation between small proteoglycans decorin and biglycan expression and Kashin-Beck Disease. Immunohistochemistry was used to assess the decorin and biglycan levels in cartilage specimens from both child KBD patients, and rats fed with T-2 toxin under a selenium-deficient condition. Real-time PCR and Western blot were used to assess mRNA and protein levels of decorin and biglycan in rat cartilages, as well as in C28/I2 chondrocytes stimulated by T-2 toxin and selenium in vitro. The result showed that decorin was reduced in all zones of KBD articular cartilage, while the expression of biglycan was prominently increased in KBD cartilage samples. Increased expression of biglycan and reduced expression of decorin were observed at mRNA and protein levels in the cartilage of rats fed with T-2 toxin and selenium- deficiency plus T-2 toxin diet, when compared with the normal diet group. Moreover, In vitro stimulation of C28/I2 cells with T-2 toxin resulted in an upregulation of biglycan and downregulation of decorin, T-2 toxin induction of biglycan and decorin levels were partly rescued by selenium supplement. This study highlights the focal nature of the degenerative changes that occur in KBD cartilage and may suggest that the altered expression pattern of decorin and biglycan have an important role in the onset and pathogenesis of KBD.

A structural prospective for collagen receptors such as DDR and their binding of the collagen fibril

The structure of the collagen fibril surface directly effects and possibly assists the management of collagen receptor interactions. An important class of collagen receptors, the receptor tyrosine kinases of the Discoidin Domain Receptor family (DDR1 and DDR2), are differentially activated by specific collagen types and play important roles in cell adhesion, migration, proliferation, and matrix remodeling. This review discusses their structure and function as it pertains directly to the fibrillar collagen structure with which they interact far more readily than they do with isolated molecular collagen. This prospective provides further insight into the mechanisms of activation and rational cellular control of this important class of receptors while also providing a comparison of DDR-collagen interactions with other receptors such as integrin and GPVI. When improperly regulated, DDR activation can lead to abnormal cellular proliferation activities such as in cancer. Hence how and when the DDRs associate with the major basis of mammalian tissue infrastructure, fibrillar collagen, should be of keen interest.

Catabolism of Fibromodulin in Developmental Rudiment and Pathologic Articular Cartilage Demonstrates Novel Roles for MMP-13 and ADAMTS-4 in C-terminal Processing of SLRPs

Background: Cartilage regeneration requires a balance of anabolic and catabolic processes. Aim: To examine the susceptibility of fibromodulin (FMOD) and lumican (LUM) to degradation by MMP-13, ADAMTS-4 and ADAMTS-5, the three major degradative proteinases in articular cartilage, in cartilage development and in osteoarthritis (OA). Methods: Immunolocalization of FMOD and LUM in fetal foot and adult knee cartilages using an FMOD matrix metalloprotease (MMP)-13 neoepitope antibody (TsYG11) and C-terminal anti-FMOD (PR184) and anti-LUM (PR353) antibodies. The in vitro digestion of knee cartilage with MMP-13, A Disintegrin and Metalloprotease with Thrompospondin motifs (ADAMTS)-4 and ADAMTS-5, to assess whether FMOD and LUM fragments observed in Western blots of total knee replacement specimens could be generated. Normal ovine articular cartilage explants were cultured with interleukin (IL)-1 and Oncostatin-M (OSM) ± PGE3162689, a broad spectrum MMP inhibitor, to assess FMOD, LUM and collagen degradation. Results and Discussion: FMOD and LUM were immunolocalized in metatarsal and phalangeal fetal rudiment cartilages and growth plates. Antibody TsYG11 localized MMP-13-cleaved FMOD in the hypertrophic chondrocytes of the metatarsal growth plates. FMOD was more prominently localized in the superficial cartilage of normal and fibrillated zones in OA cartilage. TsYG11-positive FMOD was located deep in the cartilage samples. Ab TsYG11 identified FMOD fragmentation in Western blots of normal and fibrillated cartilage extracts and total knee replacement cartilage. The C-terminal anti-FMOD, Ab PR-184, failed to identify FMOD fragmentation due to C-terminal processing. The C-terminal LUM, Ab PR-353, identified three LUM fragments in OA cartilages. In vitro digestion of human knee cartilage with MMP-13, ADAMTS-4 and ADAMTS-5 generated FMOD fragments of 54, 45 and 32 kDa similar to in blots of OA cartilage; LUM was less susceptible to fragmentation. Ab PR-353 detected N-terminally processed LUM fragments of 39, 38 and 22 kDa in 65–80-year-old OA knee replacement cartilage. FMOD and LUM were differentially processed in MMP-13, ADAMTS-4 and ADAMTS-5 digestions. FMOD was susceptible to degradation by MMP-13, ADAMTS-4 and to a lesser extent by ADAMTS-5; however, LUM was not. MMP-13-cleaved FMOD in metatarsal and phalangeal fetal rudiment and growth plate cartilages suggested roles in skeletogenesis and OA pathogenesis. Explant cultures of ovine cartilage stimulated with IL-1/OSM ± PGE3162689 displayed GAG loss on day 5 due to ADAMTS activity. However, by day 12, the activation of proMMPs occurred as well as the degradation of FMOD and collagen. These changes were inhibited by PGE3162689, partly explaining the FMOD fragments seen in OA and the potential therapeutic utility of PGE3162689.

Multiscale mechanisms of tendon fatigue damage progression and severity are strain and cycle dependent

Tendinopathies are common chronic injuries that occur when damage accumulation caused by sub-rupture fatigue loading outpaces repair. Studies have linked fatigue loading with various mechanical, structural, and biological changes associated with pathology. However, the multiscale progression of damage accumulation with respect to area, severity and the distinct contributions of strain level and number of cycles has not been fully elucidated. The objective of this study was to investigate multiscale mechanisms underlying fatigue damage accumulation and their effect on the cellular environment. Using an in situ model in rat tail tendon (RTT), fatigue loading was applied at various strains and cycle numbers to induce fatigue damage. Pre- and post- fatigue diagnostic mechanical testing, second harmonic generation (SHG) imaging, and transmission electron microscope (TEM) imaging were used to investigate extracellular and cellular damage modes at multiple scales. Fatigue loading at strains at or below 1.0% resulted in no significant changes in SHG damage area or severity and no changes in collagen fibril or cell morphology compared with controls. Fatigue loading at strains above 1.5% resulted in greater mechanical changes correlated with increased damage area measured by SHG and collagenous damage observed by TEM. Increased cycles at high strain further altered mechanical properties, increased structural damage severity (but not area), and altered TEM collagen rupture patterns. Cell morphology was similarly progressively affected with increased strain and cycle number. These damage mechanisms that may trigger degenerative changes characteristic of tendinopathy could be targeted as a part of prevention or therapy.

Time-dependent changes in gene expression induced in vitro by interleukin-1β in equine articular cartilage

Osteoarthritis is an inflammatory and degenerative joint disease commonly affecting horses. To identify genes of relevance for cartilage pathology in osteoarthritis we studied the time-course effects of interleukin (IL)-1β on equine articular cartilage. Articular cartilage explants from the distal third metacarpal bone were collected postmortem from three horses without evidence of joint disease. The explants were stimulated with IL-1β for 27 days and global gene expression was measured by microarray. Gene expression was compared to that of unstimulated explants at days 3, 9, 15, 21 and 27. Release of inflammatory proteins was measured using Proximity Extension Assay. Stimulation with IL-1β led to time-dependent changes in gene expression related to inflammation, the extracellular matrix (ECM), and phenotypic alterations. Gene expression and protein release of cytokines, chemokines, and matrix-degrading enzymes increased in the stimulated explants. Collagen type II was downregulated from day 15, whereas other ECM molecules were downregulated earlier. In contrast molecules involved in ECM signaling (perlecan, chondroitin sulfate proteoglycan 4, and syndecan 4) were upregulated. At the late time points, genes related to a chondrogenic phenotype were downregulated, and genes related to a hypertrophic phenotype were upregulated, suggesting a transition towards hypertrophy later in the culturing period. The data suggest that this in vitro model mimics time course events of in vivo inflammation in OA and it may be valuable as an in vitro tool to test treatments and to study disease mechanisms.

Effects of mechanical stretching on the morphology of extracellular polymers and the mRNA expression of collagens and small leucine-rich repeat proteoglycans in vaginal fibroblasts from women with pelvic organ prolapse

To determine the effect of mechanical stretching load and the efficacy of postmenopausal estrogen therapy (ET) on pelvic organ prolapse (POP), vaginal fibroblasts isolated from postmenopausal women with or without POP were subjected to 0.1-Hz uniaxial cyclic mechanical stretching (CS) with 10% elongation and 10-8 M 17-β-estradiol (E2) treatment. We investigated the morphological characteristics of extracellular polymers using scanning electron microscopy (SEM) and monitored the mRNA expression of type I collagen (COL I) and type III collagen (COL III) as well as the small leucine-rich proteoglycan (SLRP) family members decorin (DCN), biglycan (BGN), fibromodulin (FMO), and lumican (LUM), using real-time quantitative polymerase chain reaction (RT-PCR). Using SEM, certain viscoelastic polymers were found to be randomly distributed among fibroblasts, which for normal fibroblasts formed clusters of plum flower-like patterns under static-culture conditions and resembled stretched strips when stretched in culture, whereas polymers among POP fibroblasts resembled stretched strips under static-cultured conditions and presented broken networks when stretched in culture. RT-PCR revealed that COL I, DCN, BGN, FMO, and LUM mRNA expression was significantly higher in POP than in normal fibroblasts under static-culture condition. Following CS, COL I and BGN mRNA expression was significantly up-regulated in normal fibroblasts, and DCN and FMO mRNA expression was down-regulated in POP fibroblasts. Following concomitant CS and E2 treatment, significantly elevated COL I and DCN mRNA expression was observed in normal fibroblasts, and significantly elevated COL I and BGN mRNA expression was observed in POP fibroblasts. COL III mRNA expression was not significantly different between the POP and normal group, and CS did not significantly affect expression in either group, though COL III was down-regulated in normal fibroblasts concomitantly treated with E2 and CS. We conclude that the morphological distribution of extracellular polymers in POP fibroblasts exhibited higher sensitivity and lower tolerance to stretching loads than do normal fibroblasts. These mechanical properties were further reflected in the transcription of COL I. Defects in the compensatory function of BGN for DCN and LUM for FMO exist in POP fibroblasts, which further affect the structure and function of COL I in response to stretching load, ultimately resulting in abnormal reconstruction of pelvic supportive connective tissues and the occurrence of POP. ET can maintain stretching-induced elevations in COL I and DCN transcription in healthy women and improve stretching-induced COL I, DCN, BGN, and FMO transcriptional changes in POP women to prevent and improve POP. Only down-regulated COL III transcription was observed upon concomitant CS and E2 treatment in normal fibroblasts, which suggests that the tensile strength, not the elasticity, of the supportive connective tissues is damaged in POP and that the higher tensile strength induced by ET in healthy fibroblasts prevents POP. These findings confirm the role of higher sensitivity and lower tolerance to mechanical stretching in the pathogenesis of POP and further provide evidence supporting the use of ET to prevent and inhibit POP in postmenopausal women.

Extracellular matrix regulation of fibroblast function: redefining our perspective on skin aging

The dermal extracellular matrix (ECM) comprises the bulk of skin and confers strength and resiliency. In young skin, fibroblasts produce and adhere to the dermal ECM, which is composed primarily of type I collagen fibrils. Adherence allows fibroblasts to spread and exert mechanical force on the surrounding ECM. In this state, fibroblasts display a "youthful" phenotype characterized by maintenance of the composition and structural organization of the dermal ECM. During aging, fibroblast-ECM interactions become disrupted due to fragmentation of collagen fibrils. This disruption causes loss of fibroblast spreading and mechanical force, which inextricably lead to an "aged" phenotype; fibroblasts synthesize less ECM proteins and more matrix-degrading metalloproteinases. This imbalance of ECM homeostasis further drives collagen fibril fragmentation in a self-perpetuating cycle. This article summarizes age-related changes in the dermal ECM and the mechanisms by which these changes alter the interplay between fibroblasts and their extracellular matrix microenvironment that drive the aging process in human skin.

In vivo effect of opticin deficiency in cartilage in a surgically induced mouse model of osteoarthritis

The SLRP opticin (OPTC) has been demonstrated to be produced and degraded in osteoarthritic (OA) human cartilage. Here, we investigated the in vivo effect of OPTC deficiency in OA cartilage. OA was induced in 10-week-old Optc^−/− and Optc^+/+ mice. Ten weeks post-surgery, cartilage was processed for histology and immunohistochemistry. SLRP expression was determined in non-operated mouse cartilage. OA Optc^−/− demonstrated significant protection against cartilage degradation. Data revealed that in non-operated Optc^−/− cartilage, expression of SLRPs lumican and epiphycan was up-regulated at day 3 and in 10-week-olds (p ≤ 0.039), and fibromodulin down-regulated in 10-week-olds (p = 0.001). Immunohistochemistry of OA mice showed a similar pattern. In OA Optc^−/− cartilage, markers of degradation and complement factors were all down-regulated (p ≤ 0.038). In OA Optc^−/− cartilage, collagen fibers were thinner and better organized (p = 0.038) than in OA Optc^+/+ cartilage. The protective effect of OPTC deficiency during OA results from an overexpression of lumican and epiphycan, known to bind and protect collagen fibers, and a decrease in fibromodulin, contributing to a reduction in the complement activation/inflammatory process. This work suggests that the evaluation of the composition of the different SLRPs in OA cartilage could be applied as a new tool for OA prognosis classification.

Spatiotemporal variations in gene expression, histology and biomechanics in an ovine model of tendinopathy

Flexor tendinopathy is a common problem affecting humans and animals. Tendon healing is poorly understood and the outcomes of conservative and surgical management are often suboptimal. While often considered a localized injury, recent evidence indicates that in the short term, tendinopathic changes are distributed widely throughout the tendon, remote from the lesion itself. Whether these changes persist throughout healing is unknown. The aim of this study was to document gene expression, histopathological and biomechanical changes that occur throughout the superficial digital flexor tendon (SDFT) up to 16 weeks post-injury, using an ovine surgical model of tendinopathy. Partial tendon transection was associated with decreased gene expression for aggrecan, decorin, fibromodulin, tissue inhibitors of metalloproteinases (TIMPS 1, 2 and 3), collagen I and collagen II. Gene expression for collagen III, lumican and matrix metalloproteinase 13 (MMP13) increased locally around the lesion site. Expression of collagen III and MMP13 decreased with time, but compared to controls, collagen III, MMP13 and lumican expression remained regionally high throughout the study. An increase in TIMP3 was observed over time. Histologically, operated tendons had higher pathology scores than controls, especially around the injured region. A chondroid phenotype was observed with increased cellular rounding and marked proteoglycan accumulation which only partially improved with time. Biomechanically, partial tendon transection resulted in a localized decrease in elastic modulus (in compression) but only at 8 weeks postoperatively. This study improves our understanding of tendon healing, demonstrating an early ‘peak’ in pathology characterized by altered gene expression and notable histopathological changes. Many of these pathological changes become more localized to the region of injury during healing. Collagen III and MMP13 expression levels remained high close to the lesion throughout the study and may reflect the production of tendon tissue with suboptimal biomechanical properties. Further studies evaluating the long-term response of tendon to injury (6–12 months) are warranted to provide additional information on tendon healing and provide further understanding of the mechanisms underlying the pathology observed in this study.

Fibromodulin deficiency reduces collagen structural network but not glycosaminoglycan content in a syngeneic model of colon carcinoma

Tumor barrier function in carcinoma represents a major challenge to treatment and is therefore an attractive target for increasing drug delivery. Variables related to tumor barrier include aberrant blood vessels, high interstitial fluid pressure, and the composition and structure of the extracellular matrix. One of the proteins associated with dense extracellular matrices is fibromodulin, a collagen fibrillogenesis modulator expressed in tumor stroma but scarce in normal loose connective tissues. Here, we investigated the effects of fibromodulin on stroma ECM in a syngeneic murine colon carcinoma model. We show that fibromodulin deficiency decreased collagen fibril thickness but glycosaminoglycan content and composition were unchanged. Furthermore, vascular density, pericyte coverage and macrophage amount were unaffected. Fibromodulin can therefore be a unique effector of dense collagen matrix assembly in tumor stroma and, without affecting other major matrix components or the cellular composition, can function as a main agent in tumor barrier function.

Lumican delays melanoma growth in mice and drives tumor molecular assembly as well as response to matrix-targeted TAX2 therapeutic peptide

Lumican is a small leucine-rich proteoglycan (SLRP) being known as a key regulator of collagen fibrillogenesis. However, little attention has been given so far in studying its influence on tumor-associated matrix architecture. Here, we investigate the role of host lumican on tumor matrix organization as well as on disease progression considering an immunocompetent model of melanoma implanted in Lum ^-/- vs. wild type syngeneic mice. Conjointly, lumican impact on tumor response to matrix-targeted therapy was evaluated considering a previously validated peptide, namely TAX2, that targets matricellular thrombospondin-1. Analysis of available genomics and proteomics databases for melanoma first established a correlation between lumican expression and patient outcome. In the B16 melanoma allograft model, endogenous lumican inhibits tumor growth and modulates response to TAX2 peptide. Indeed, IHC analyses revealed that lumican deficiency impacts intratumoral distribution of matricellular proteins, growth factor and stromal cells. Besides, innovative imaging approaches helped demonstrating that lumican host expression drives biochemical heterogeneity of s.c. tumors, while modulating intratumoral collagen deposition as well as organization. Altogether, the results obtained present lumican as a strong endogenous inhibitor of tumor growth, while identifying for the first time this proteoglycan as a major driver of tumor matrix coherent assembly.

Regulators of Collagen Fibrillogenesis during Molar Development in the Mouse

Development of mammalian teeth and surrounding tissues includes time-space changes in the extracellular matrix composition and organization. This requires complex control mechanisms to regulate its synthesis and remodeling. Fibril-associated collagens with interrupted triple helices (FACITs) and a group of small leucine-rich proteoglycans (SLRPs) are involved in the regulation of collagen fibrillogenesis. Recently, collagen type XII and collagen type XIV, members of the FACITs family, were found in the peridental mesenchyme contributing to alveolar bone formation. This study was designed to follow temporospatial expression of collagen types XIIa and XIVa in mouse first molar and adjacent tissues from embryonic day 13, when the alveolar bone becomes morphologically apparent around the molar tooth bud, until postnatal day 22, as the posteruption stage. The patterns of decorin, biglycan, and fibromodulin, all members of the SLRPs family and interacting with collagens XIIa and XIVa, were investigated simultaneously. The situation in the tooth was related to what happens in the alveolar bone, and both were compared to the periodontal ligament. The investigation provided a complex localization of the five antigens in soft tissues, the dental pulp, and periodontal ligaments; in the mineralized tissues, predentin/dentin and alveolar bone; and junction between soft and hard tissues. The results illustrated developmentally regulated and tissue-specific changes in the balance of the two FACITs and three SLRPs.

Natural healing-inspired collagen-targeting surgical protein glue for accelerated scarless skin regeneration

Skin scarring after deep dermal injuries is a major clinical problem due to the current therapies limited to established scars with poor understanding of healing mechanisms. From investigation of aberrations within the extracellular matrix involved in pathophysiologic scarring, it was revealed that one of the main factors responsible for impaired healing is abnormal collagen reorganization. Here, inspired by the fundamental roles of decorin, a collagen-targeting proteoglycan, in collagen remodeling, we created a scar-preventive collagen-targeting glue consisting of a newly designed collagen-binding mussel adhesive protein and a specific glycosaminoglycan. The collagen-targeting glue specifically bound to type I collagen in a dose-dependent manner and regulated the rate and the degree of fibrillogenesis. In a rat skin excisional model, the collagen-targeting glue successfully accelerated initial wound regeneration as defined by effective reepithelialization, neovascularization, and rapid collagen synthesis. Moreover, the improved dermal collagen architecture was demonstrated by uniform size of collagen fibrils, their regular packing, and a restoration of healthy tissue component. Collectively, our natural healing-inspired collagen-targeting glue may be a promising therapeutic option for improving the healing rate with high-quality and effective scar inhibition.

Targeting collagen for diagnostic imaging and therapeutic delivery

As the most abundant protein in mammals and a major structural component in extracellular matrix, collagen holds a pivotal role in tissue development and maintaining the homeostasis of our body. Persistent disruption to the balance between collagen production and degradation can cause a variety of diseases, some of which can be fatal. Collagen remodeling can lead to either an overproduction of collagen which can cause excessive collagen accumulation in organs, common to fibrosis, or uncontrolled degradation of collagen seen in degenerative diseases such as arthritis. Therefore, the ability to monitor the state of collagen is crucial for determining the presence and progression of numerous diseases. This review discusses the implications of collagen remodeling and its detection methods with specific focus on targeting native collagens as well as denatured collagens. It aims to help researchers understand the pathobiology of collagen-related diseases and create novel collagen targeting therapeutics and imaging modalities for biomedical applications.

Interleukin-1α induces focal degradation of biglycan and tissue degeneration in an in-vitro ovine meniscal model

We have developed an ovine meniscal explant model where the focal degradative events leading to characteristic fragmentation patterns of biglycan in human OA of the knee and hip, and evident in animal models of knee OA and IVD degeneration are reproduced in culture. Lateral and medial menisci were dissected into outer, mid and inner zones and established in explant culture±IL-1 (10ng/ml). The biglycan species present in conditioned media samples and in GuHCl extracts of tissues were examined by Western blotting using two C-terminal antibodies PR-85 and EF-Bgn. Clear differences were evident in the biglycan species in each meniscal tissue zone with the medial outer meniscus having lower biglycan levels and major fragments of 20, 28, 33 and 36, 39kDa. Similar fragmentation was detected in articular cartilage samples, 42-45kDa core protein species were also detected. Biglycan fragmentation was not as extensive in the IL-1 stimulated meniscal cultures with 36, 39, 42 and 45kDa biglycan species evident. Thus the medial meniscus outer zone displayed the highest levels of biglycan processing in this model and correlated with a major zone of meniscal remodelling in OA in man. Significantly, enzymatic digests of meniscal tissues with MMP-13, ADAMTS-4 and ADAMTS-5 have also generated similar biglycan species in-vitro. Zymography confirmed that the medial outer zone was the region of maximal MMP activity. This model represents a convenient system to recapitulate matrix remodelling events driven by IL-1 in pathological cartilages and in animal models of joint degeneration.

Decorin inhibits the proliferation of HepG2 cells by elevating the expression of transforming growth factor-β receptor II

The aim of the present study was to investigate the effects of decorin (DCN) on the proliferation of human hepatoma HepG2 cells and the involvement of transforming growth factor-β (TGF-β) signaling pathway. A vector containing DCN was transfected into HepG2 cells with the use of Lipofectamine 2000. Cell proliferation was assessed with an MTT assay, and western blot analysis was used to detect the protein expression of TGF-β receptor I (TGF-βRI), phosphorylated TGF-βRI, p15 and TGF-βRII. In addition, small interfering RNA (siRNA) silencing was performed to knock down the target gene. The results indicated that, compared with the control group, cell proliferation was significantly decreased in HepG2 cells transfected with DCN. In addition, DCN transfection significantly increased the phosphorylation level of TGF-βRI in HepG2 cells. The expression of the downstream factor p15 was also significantly elevated in the DCN-transfected HepG2 cells. Furthermore, DCN transfection significantly elevated the expression level of TGF-βRII in HepG2 cells. By contrast, the silencing of TGF-βRII significantly decreased the phosphorylation of TGF-βRI in DCN-transfected HepG2 cells. In addition, TGF-βRII silencing abolished the effects of DCN on the proliferation of HepG2 cells. In conclusion, DCN elevated the expression level of TGF-βRII, increased the phosphorylation level of TGF-βRI, enhanced the expression of p15, and finally inhibited the proliferation of HepG2 cells. These findings may contribute to the understanding of the role of DCN in the pathogenesis of hepatic carcinoma and assist in the disease treatment.

Chronic UVB-irradiation actuates perpetuated dermal matrix remodeling in female mice: Protective role of estrogen

Chronic UVB-exposure and declined estradiol production after menopause represent important factors leading to extrinsic and intrinsic aging, respectively. Remodeling of the extracellular matrix (ECM) plays a crucial role in both responses. Whether the dermal ECM is able to recover after cessation of UVB-irradiation in dependence of estradiol is not known, however of relevance when regarding possible treatment options. Therefore, the endogenous sex hormone production was depleted by ovariectomy in female mice. Half of the mice received estradiol substitution. Mice were UVB-irradiated for 20 weeks and afterwards kept for 10 weeks without irradiation. The collagen-, hyaluronan- and proteoglycan- (versican, biglycan, lumican) matrix, collagen cleavage products and functional skin parameters were analyzed. The intrinsic aging process was characterized by increased collagen fragmentation and accumulation of biglycan. Chronic UVB-irradiation additionally augmented the lumican, versican and hyaluronan content of the dermis. In the absence of further UVB-irradiation the degradation of collagen and accumulation of biglycan in the extrinsically aged group was perpetuated in an excessive matter. Whereas estradiol increased the proteoglycan content, it reversed the effects of the perpetuated extrinsic response on collagen degradation. Suspension of the intrinsic pathway might therefore be sufficient to antagonize UVB-evoked long-term damage to the dermal ECM.

Interstitial collagen turnover during airway remodeling in acute and chronic experimental asthma

Asthma airway remodeling is characterized by the thickening of the basement membrane (BM) due to an increase in extracellular matrix (ECM) deposition, which contributes to the irreversibility of airflow obstruction. Interstitial collagens are the primary ECM components to be increased during the fibrotic process. The aim of the present study was to examine the interstitial collagen turnover during the course of acute and chronic asthma, and 1 month after the last exposure to the allergen. Guinea pigs sensitized to ovalbumin (OVA) and exposed to 3 further OVA challenges (acute model) or 12 OVA challenges (chronic model) were used as asthma experimental models. A group of animals from either model was sacrificed 1 h or 1 month after the last OVA challenge. Collagen distribution, collagen content, interstitial collagenase activity and matrix metalloproteinase (MMP)-1, MMP-13 and tissue inhibitor of metalloproteinase (TIMP)-1 protein expression levels were measured in the lung tissue samples from both experimental models. The results revealed that collagen deposit in bronchiole BM, adventitial and airway smooth muscle layers was increased in both experimental models as well as lung tissue collagen concentration. These structural changes persisted 1 month after the last OVA challenge. In the acute model, a decrease in collagenase activity and in MMP-1 concentration was observed. Collagenase activity returned to basal levels, and an increase in MMP-1 and MMP-13 expression levels along with a decrease in TIMP-1 expression levels were observed in animals sacrificed 1 month after the last OVA challenge. In the chronic model, there were no changes in collagenase activity or in MMP-13 concentration, although MMP-1 expression levels increased. One month later, an increase in collagenase activity was observed, although MMP-1 and TIMP-1 levels were not altered. The results of the present study suggest that even when the allergen challenges were discontinued, and collagenase activity and MMP-1 expression increased, fibrosis remained, contributing to the irreversibility of bronchoconstriction.