Decorin and biglycan are necessary for maintaining collagen fibril structure, fiber realignment, and mechanical properties of mature tendons

MMP-9 Expression in bone cells in the developing femur

The proteolytic functions of the matrix-degrading enzymes, such as ADAMTS (A disintegrin and metalloproteinases) and MMP (Matrix metalloproteinase), play a crucial role in development. This study investigated the proteolytic activity of different types of bone cells, focusing on the expression of MMP-9, throughout the development of the femur in rabbit embryos. The femur formed the physeal growth cartilage, which facilitated the process of endochondral bone development. Osteoblasts are situated on the outer layer of bone spicules and within the periosteum. Osteoclasts are found within the lacunae of the bone matrix, and they have also been observed in the ossification center. Osteoclasts, osteocytes, and osteoblasts all exhibit MMP-9 expression with different intensity of staining with the perichondral stem cells showing the greatest value. MMP-9 is essential in bone formation. Utilizing MMP-9 to modify the extracellular matrix could potentially serve as a favorable approach for identifying treatment targets in bone diseases.

Three-Dimensional Meltblowing as a High-Speed Fabrication Process for Tendon Tissue Engineered Scaffolds

Rotator cuff tears continue to be a critical challenge for successful repair due to the formation of fibrotic scar tissue during healing. Tendon tissue engineering seeks to improve these outcomes using nonwoven fabrication methods to produce biomimetic scaffolds. Meltblowing has several advantages over other nonwoven approaches including non-toxic fabrication processes and being high-throughput and economical, while accurately producing fiber diameters comparable to native tendon microstructure. Recently 3D meltblowing (3DMB) introduced high degrees of tunability to the core process, allowing for production of highly aligned fiber mats at anatomically relevant dimensions. Here, we evaluated 3DMB scaffolds fabricated using poly-L-lactic acid (PLA) and poly-ε-caprolactone (PCL) by characterizing scaffold properties before and after culture with human adipose stem cells (hASCs). Mechanical and fiber characterization of 3DMB scaffolds closely resembled tendon microarchitecture by exhibiting high fiber alignment and mechanical anisotropy. hASC-seeded 3DMB scaffolds after 28 days of culture proliferated and deposited aligned tendon-like extracellular matrix. Furthermore, cell culture enhanced the Young's modulus of PLA 3DMB scaffolds and improved yield stress, yield stretch, and stiffness of both 3DMB scaffolds. The proteome of cultured 3DMB scaffolds increased expression of tendon-related proteins after 28 days of culture, but polymer-dependent differences in glycoprotein composition was observed. Together, 3DMB is a promising method for tendon tissue engineering, by showing improved fiber and mechanical properties compared to meltblown scaffolds. However, while an improvement on prior iterations, continued development of this 3DMB technology is needed to better mimic the mechanical properties and biologic composition of native tendon.

Obesity and type 2 diabetes mellitus: insights from skeletal muscle extracellular matrix remodeling

Obesity and type 2 diabetes mellitus (T2DM) are metabolic diseases at epidemic proportions. The economic burden for these diseases is at an all-time high, and as such, there is an urgent need for advancements in identifying targets for treating these complex disorders. The extracellular matrix (ECM), comprising collagen, fibronectin, laminin, elastin, and proteoglycan, surrounds skeletal muscles and plays a critical role in maintaining tissue homeostasis by providing structural support and facilitating cell-to-cell communication. Disruption of the ECM signaling results in changes to its micro/macroenvironment, thereby modifying tissue homeostasis. Skeletal muscle ECM remodeling has been shown to be associated with insulin resistance, an underlying feature of obesity and T2DM. This narrative review explores the critical components of skeletal muscle ECM and its accumulation and remodeling in metabolic diseases. In addition, we discuss potential treatments to mitigate the effects of ECM remodeling in skeletal muscle. We conclude that targeting ECM remodeling in skeletal muscle represents a promising yet underexplored therapeutic avenue in the management of metabolic disorders.

Biglycan deficiency alleviates intestinal fibrosis through BMP-7-mediated Smad1/5/8 signaling

BACKGROUND

Biglycan (BGN) is a small proteoglycan rich in leucine, which plays a crucial role in the excessive production of extracellular matrix (ECM) and its association with fibrosis across various organs. Nevertheless, the precise contribution of BGN to intestinal fibrosis remains undisclosed. This study aimed to investigate the role and mechanism of BGN in intestinal fibrosis.

METHODS

Human Crohn's disease (CD) tissue samples were obtained from patients with Crohn's disease who underwent surgical resection of the intestine and were categorized as stenotic/nonstenotic regions. A dextran sodium sulfate (DSS)-induced mouse model of intestinal fibrosis was established. Bgn-/0 (BGN KO) mice and primary human intestinal fibroblasts were applied for the study of experimental fibrosis. Coimmunoprecipitation, immunofluorescence staining, western blot, and qRT-PCR were conducted to identify the regulatory effects of BGN on bone morphogenetic protein-7 (BMP-7) expression and intesinal fibrosis.

RESULTS

In both human CD samples and the DSS-induced mouse model of intestinal fibrosis, we observed a significant upregulation of BGN in areas activated by fibrosis. The genetic deletion of BGN resulted in the alleviation of intestinal fibrosis in mice administered DSS. The knockdown of BGN through siRNA significantly attenuated TGF-β1-induced ECM deposition and fibroblastic activation in primary human intestinal fibroblasts. Mechanistically, BGN directly interacted with and negatively regulated the anti-fibrotic protein BMP-7. Rescue experiments demonstrated that BGN facilitated intestinal fibrosis by modulating Smad1/5/8 phosphorylation and activating ECM deposition.

CONCLUSION

Our data indicate that BGN deficiency inhibits intestinal fibrosis through activation of the BMP-7-Smad1/5/8 signaling pathway. BGN and BMP-7 may become new biomarkers of intestinal fibrosis and novel targets for disease prevention and treatment.

The importance of biglycan, decorin and TGF-1 levels in the diagnosis of non-small cell lung cancer

BackgroundDespite Non-small cell lung cancer (NSCLC) ranks among the most deadly cancers worldwide, and currently, apart from a low percentage, targetable molecules have not been identified in its etiopathogenesis. The relationship between the proteoglycans decorin and biglycan, which are present in the extracellular matrix of cells, and transforming growth factor Beta-1 (TGF-B1), has been shown in many cancers. We investigated the significance of these molecules in NSCLC.MethodsFasting serum levels of decorin, biglycan, and TGF-B1 were obtained from 48 newly diagnosed NSCLC patients and compared with those of 48 adult control subjects matched for age and demographics. Demographic data, baseline laboratory values, and ELISA results were compared between the groups.ResultsThe median age was 65(39-83) similar in both groups. There was no relation between demographic and clinical parameters and the levels of decorin, biglycan, and TGF-B1 in the NSCLC group. However, in comparison to the control group, NSCLC patients had significantly higher levels of biglycan (42.55 ± 27.40 vs. 24.38 ± 12.05 ng/mL, p = 0.026) and TGF-B1 (15.55 ± 9.16 vs. 10.07 ± 7.8 pg/mL, p = 0.001), while decorin levels were significantly lower (6.64 ± 1.92 vs. 10.28 ± 3.13 ng/mL, p = 0.002). In the multivariate regression analysis; Decorin < 8.13 ng/mL (OR, 10.96; 95% CI: 3.440-34.958), current smoking (OR, 3.81; 95% CI: 1.320-10.998), COPD (OR, 43.6; 95% CI: 2.082-913.081), and lower BMI (OR, 1.22; 95% CI: 1.070-1.405, p = 0.003) were identified as independent predictive markers for NSCLC diagnosis.ConclusionThe decreased serum decorin level is an independent marker for NSCLC. Further studies are needed to investigate the prognostic significance of decorin on survival and its potential as a target in treatment.

Antioxidants improve the viability of diabetic bone marrow MSCs without rescuing their pro-regenerative secretome function

Bone marrow mesenchymal stem cell (BM-MSC) dysfunction and poor viability are prominent in diabetes and limit their therapeutic efficacy. A proteomic investigation was performed to assess disease associated alterations and the efficacy of antioxidants to rescue cellular function. BM-MSCs were isolated from obese diabetic mice (B6.Cg-Lepob/J) cultured in the presence or absence of N-acetylcysteine (NAC) and ascorbic acid-2phosphate (AAP). Label free Liquid Chromatography and Mass Spectrometry (LC-MS) analysis detected 5079 proteins with 251 being differentially expressed between treatment groups. NAC/AAP improved cellular growth/viability post isolation by up-regulating proteins involved in redox status, ATP synthesis, Rho-GTPase signaling and modulated the immunophenotype of BM-MSCs. Despite a single application of the secretome not providing any advantage for wound bed regeneration in full thickness excisional diabetic wounds, the intracellular proteome illustrated the potential mechanisms of action by which NAC/AAP targeted the respiratory chain and modulated the immune phenotype of BM-MSCs. Given these observations, antioxidant supplementation might be more effective as prophylactic strategy to protect MSCs against functional decline instead of using it as a restorative agent and warrants further investigation.

The Presence of Adipose Tissue in Aortic Valves Influences Inflammation and Extracellular Matrix Composition in Chronic Aortic Regurgitation

Adipose tissue is present in aortic valves (AVs). Valve interstitial cells (VICs) could differentiate into adipogenic lineages. We here characterize whether the presence of adipose tissue in the AV influences inflammation and extracellular matrix (ECM) composition in patients with aortic regurgitation (AR). A total of 144 AVs were analyzed by histological and molecular techniques. We performed discovery studies using Olink Proteomics® technology in 40 AVs (N = 16 without and N = 24 with adipose tissue). In vitro, human white adipocytes (HWAs) or VICs were cultured with adipogenic media and co-cultured with control VICs. Of Avs, 67% presented white-like adipocytes within the spongiosa. Discovery studies revealed increased levels of inflammatory and ECM molecules in AVs containing adipocytes. Interestingly, the presence of adipocytes was associated with greater AV thickness, higher inflammation, and ECM remodeling, which was characterized by increased proinflammatory molecules, collagen, fibronectin, proteoglycans, and metalloproteinases. AV thickness positively correlated with markers of adipose tissue, inflammation, and ECM. In vitro, adipocyte-like VICs expressed higher levels of adipocyte markers, increased cytokines, fibronectin, decorin, and MMP-13. Analyses of supernatants from co-cultured control VICs with HWA or adipocyte-like VICs showed higher expression of inflammatory mediators, collagen type I, proteoglycans, and metalloproteinases. AVs presenting adipocytes were thicker and exhibited changes characterized by increased inflammation accompanied by aberrant expression of collagen, proteoglycans, and metalloproteinases. VICs could differentiate into adipogenic pathway, affect neighbor VICs, and contribute to inflammation, collagen and proteoglycan accumulation, as well as to metalloproteinases secretion. In summary, the presence of adipose tissue in AV could modify its composition, favoring inflammation and remodeling with an impact on AV thickness.

Moderate- and High-Speed Treadmill Running Exercise Have Minimal Impact on Rat Achilles Tendon

Exercise influences clinical Achilles tendon health in humans, but animal models of exercise-related Achilles tendon changes are lacking. Moreover, previous investigations of the effects of treadmill running exercise on rat Achilles tendon demonstrate variable outcomes. Our objective was to assess the functional, structural, cellular, and biomechanical impacts of treadmill running exercise on rat Achilles tendon with sensitive in and ex vivo approaches. Three running levels were assessed over the course of 8 weeks: control (cage activity), moderate-speed (treadmill running at 10 m/min, no incline), and high-speed (treadmill running at 20 m/min, 10° incline). We hypothesized that moderate-speed treadmill running would beneficially impact tendon biomechanics through increased tenocyte cellularity, metabolism, and anabolism whereas high-speed treadmill running would cause a tendinopathic phenotype with compromised tendon biomechanics due to pathologic tenocyte differentiation, metabolism, and catabolism. Contrary to our hypothesis, treadmill running exercise at these speeds had a nominal effect on the rat Achilles tendon. Treadmill running modestly influenced tenocyte metabolism and nuclear aspect ratio as well as viscoelastic tendon properties but did not cause a tendinopathic phenotype. These findings highlight the need for improved models of exercise- and loading-related tendon changes that can be leveraged to develop strategies for tendinopathy prevention and treatment.

Mature murine supraspinatus tendons demonstrate regional differences in multiscale structure, function and gene expression

The hierarchical structure of tendon dictates its ability to effectively transmit loads from muscle to bone. Tendon- and site-specific differences in mechanical loading result in the establishment and remodeling of structure, as well as associated changes in composition throughout development and healing. Previous work has demonstrated region-specific differences in the response of collagen fibrils to mechanical loading within the insertion region and midsubstance regions of mouse supraspinatus tendons using atomic force microscopy. However, multiscale structure, function, and gene expression differences between the insertion and midsubstance of the supraspinatus tendon have not yet been linked together in a comprehensive study. Therefore, the purpose of this study was to elucidate site-specific hierarchical structure, function, and gene expression differences in mouse supraspinatus tendons. Supraspinatus tendons from day 150 wild-type C57BL/6 mice were harvested for regional mechanics, histology, transmission electron microscopy (TEM), and quantitative polymerase chain reaction (qPCR). Mechanical testing revealed that the midsubstance region demonstrated a greater modulus and increased collagen fiber realignment compared to the insertion region. Histological scoring demonstrated greater cellularity and more rounded cells in the insertion region. TEM analysis showed differences in collagen fibril diameter distributions between the two regions, with a shift towards smaller diameters observed at the insertion region. Gene expression analysis identified several genes that were differentially expressed between regions, with principal component analysis revealing distinct clustering based on region. These findings provide insight into the regional heterogeneity of the supraspinatus tendon and underscore the importance of considering these differences in the context of tendon injury and repair, contributing to a better understanding of tendon structure-function and guiding future studies aimed at elucidating the mechanisms underlying tendon pathology.

Extracellular matrix and pregnancy: functions and opportunities caught in the net

The extracellular matrix is a complex network of macromolecules that support the growth and homeostatic development of organisms. By conveying multiple signaling cascades, it impacts on several biological processes and influences the behaviour of numerous cell types. During the endometrial cycle and the key events necessary for a correct embryo implantation and placentation, this bioactive meshwork is substantially modified to favour endometrial receptivity and vascular adaptation, trophoblast cell migration, and immune activation as well. A correct extracellular remodeling is fundamental for the establishment of a physiological pregnancy; indeed, the occurrence of altered matrix modifications associates with gestational disorders such as preeclampsia. In the present review, we will critically evaluate the role of pivotal matrix constituents in regulating the key steps of embryo implantation and placentation, provide up-to-date information concerning their primary mechanisms of action and discuss on their potential as a novel source of biomarkers and therapeutic targets.

Loss of Cochlin drives impairments in tendon structure and function

Aging tendons undergo disruptions in homeostasis, increased susceptibility to injury, and reduced capacity for healing. Exploring the mechanisms behind this disruption in homeostasis is essential for developing therapeutics aimed at maintaining tendon health through the lifespan. We have previously identified that the extracellular matrix protein, Cochlin, which is highly expressed in healthy flexor tendon, is consistently lost during both natural aging and upon depletion of Scleraxis-lineage cells in young animals, which recapitulates many aging-associated homeostatic disruptions. Therefore, we examined the effects of Cochlin-/- on tendon maturation and hypothesized that loss of Cochlin would disrupt normal tendon maturation and recapitulate phenotypes associated with disrupted adult tendon homeostasis, including alterations in collagen fibril organization, and impaired tendon mechanics. By 3-months of age, Cochlin-/- flexor tendons exhibited altered collagen structure, with these changes persisting through at least 9-months. In addition, Cochlin -/- tendons demonstrated significant declines in structural and material properties at 6-months, and structural properties at 9-months. While Cochlin-/- did not drastically change the overall tendon proteome, consistent decreases in proteins associated with RNA metabolism, extracellular matrix production and the cytoskeleton were observed in Cochlin -/-. Interestingly, disrupted tendon maturation via Cochlin-/- did not impair the tendon healing process. Taken together, these data define a critical role for Cochlin in facilitating physiological tendon maturation.

Using load to improve tendon/ligament tissue engineering and develop novel treatments for tendinopathy

Tendon and ligament injuries are highly prevalent but heal poorly, even with proper care. Restoration of native tissue function is complicated by the fact that these tissues vary anatomically in terms of their mechanical properties, composition, and structure. These differences develop as adaptations to diverse mechanical demands; however, pathology may alter the loads placed on the tissue. Musculoskeletal loads can be generally categorized into tension, compression, and shear. Each of these regulate distinct molecular pathways that are involved in tissue remodeling, including many of the canonical tenogenic genes. In this review, we provide a perspective on the stage-specific regulation of mechanically sensitive pathways during development and maturation of tendon and ligament tissue, including scleraxis, mohawk, and others. Furthermore, we discuss structural features of healing and diseased tendon that may contribute to aberrant loading profiles, and how the associated disturbance in molecular signaling may contribute to incomplete healing or the formation of degenerative phenotypes. The perspectives provided here draw from studies spanning in vitro, animal, and human experiments of healthy and diseased tendon to propose a more targeted approach to advance rehabilitation, orthobiologics, and tissue engineering.

Pivotal roles of biglycan and decorin in regulating bone mass, water retention, and bone toughness

Proteoglycans, key components of non-collagenous proteins in the bone matrix, attract water through their negatively charged glycosaminoglycan chains. Among these proteoglycans, biglycan (Bgn) and decorin (Dcn) are major subtypes, yet their distinct roles in bone remain largely elusive. In this study, we utilized single knockout (KO) mouse models and successfully generated double KO (dKO) models despite challenges with low yield. Bgn deficiency, but not Dcn deficiency, decreased trabecular bone mass, with more pronounced bone loss in dKO mice. Low-field nuclear magnetic resonance measurements showed a marked decrease in bound water among all KO groups, especially in Bgn KO and dKO mice. Moreover, both Bgn KO and dKO mice exhibited reduced fracture toughness compared to Dcn KO mice. Dcn was significantly upregulated in Bgn KO mice, while a modest upregulation of Bgn was observed in Dcn KO mice, indicating Bgn's predominant role in bone. High resolution atomic force microscopy showed decreased in situ permanent energy dissipation and increased elastic modulus in the extrafibrillar matrix of Bgn/Dcn deficient mice, which were diminished upon dehydration. Furthermore, we found that both Bgn and Dcn are indispensable for the activation of ERK and p38 MAPK signaling pathways. Collectively, our results highlight the distinct and indispensable roles of Bgn and Dcn in maintaining bone structure, water retention, and bulk/in situ tissue properties in the bone matrix, with Bgn exerting a predominant influence.

Regulatory Role of Collagen XI in the Establishment of Mechanical Properties of Tendons and Ligaments in Mice Is Tissue Dependent

Collagen XI is ubiquitous in tissues such as joint cartilage, cancellous bone, muscles, and tendons and is an important contributor during a crucial part in fibrillogenesis. The COL11A1 gene encodes one of three alpha chains of collagen XI. The present study elucidates the role of collagen XI in the establishment of mechanical properties of tendons and ligaments. We investigated the mechanical response of three tendons and one ligament tissues from wild type and a targeted mouse model null for collagen XI: Achilles tendon (ACH), the flexor digitorum longus tendon (FDL), the supraspinatus tendon (SST), and the anterior cruciate ligament (ACL). Area was substantially lower in Col11a1ΔTen/ΔTen ACH, FDL, and SST. Maximum load and maximum stress were significantly lower in Col11a1ΔTen/ΔTen ACH and FDL. Stiffness was lower in Col11a1ΔTen/ΔTen ACH, FDL, and SST. Modulus was reduced in Col11a1ΔTen/ΔTen FDL and SST (both insertion site and midsubstance). Collagen fiber distributions were more aligned under load in both wild type group and Col11a1ΔTen/ΔTen groups. Results also revealed that the effect of collagen XI knockout on collagen fiber realignment is tendon-dependent and location-dependent (insertion versus midsubstance). In summary, this study clearly shows that the regulatory role of collagen XI on tendon and ligament is tissue specific and that joint hypermobility in type II Stickler's Syndrome may in part be due to suboptimal mechanical response of the soft tissues surrounding joints.

Transcriptional regulation of postnatal aortic development

The aorta exhibits tremendous changes in geometry, composition, and mechanical properties during postnatal development. These changes are necessarily driven by transcriptional changes, both genetically programmed and mechano-responsive, but there has not been a careful comparison of time-course changes in the transcriptional profile and biomechanical phenotype. Here, we show that the greatest period of differential gene expression in the normal postnatal mouse aorta occurs prior to weaning at three weeks of age though with important evolution of many transcripts thereafter. We identify six general temporal patterns, including transcripts that monotonically decrease to lower or increase to higher steady state values as well as those that either peak or dip prior to or near weaning. We show that diverse transcripts within individual groupings correlate well over time, and that sub-sets of these groups correlate well with the developmental progression of different biomechanical metrics that are expected to be involved in mechano-sensing. In particular, expression of genes for elastin and elastin-associated glycoproteins tend to correlate well with the ratio of systolic-to-diastolic stress whereas genes for collagen fibers correlate well with the daily rate of change of systolic stress and genes for mechano-sensing proteins tend to correlate well with the systolic stress itself. We conclude that different groupings of genes having different temporal expression patterns correlate well with different measures of the wall mechanics, hence emphasizing a need for age-dependent, gene-specific computational modeling of postnatal development.

Human Tendon-on-Chip: Unveiling the Effect of Core Compartment-T Cell Spatiotemporal Crosstalk at the Onset of Tendon Inflammation

The lack of representative in vitro models recapitulating human tendon (patho)physiology is among the major factors hindering consistent progress in the knowledge-based development of adequate therapies for tendinopathy.Here, an organotypic 3D tendon-on-chip model is designed that allows studying the spatiotemporal dynamics of its cellular and molecular mechanisms.Combining the synergistic effects of a bioactive hydrogel matrix with the biophysical cues of magnetic microfibers directly aligned on the microfluidic chip, it is possible to recreate the anisotropic architecture, cell patterns, and phenotype of tendon intrinsic (core) compartment. When incorporated with vascular-like vessels emulating the interface between its intrinsic-extrinsic compartments, crosstalk with endothelial cells are found to drive stromal tenocytes toward a reparative profile. This platform is further used to study adaptive immune cell responses at the onset of tissue inflammation, focusing on interactions between tendon compartment tenocytes and circulating T cells.The proinflammatory signature resulting from this intra/inter-cellular communication induces the recruitment of T cells into the inflamed core compartment and confirms the involvement of this cellular crosstalk in positive feedback loops leading to the amplification of tendon inflammation.Overall, the developed 3D tendon-on-chip provides a powerful new tool enabling mechanistic studies on the pathogenesis of tendinopathy as well as for assessing new therapies.

Mechanisms of assembly and remodelling of the extracellular matrix

The extracellular matrix (ECM) is the complex meshwork of proteins and glycans that forms the scaffold that surrounds and supports cells. It exerts key roles in all aspects of metazoan physiology, from conferring physical and mechanical properties on tissues and organs to modulating cellular processes such as proliferation, differentiation and migration. Understanding the mechanisms that orchestrate the assembly of the ECM scaffold is thus crucial to understand ECM functions in health and disease. This Review discusses novel insights into the compositional diversity of matrisome components and the mechanisms that lead to tissue-specific assemblies and architectures tailored to support specific functions. The Review then highlights recently discovered mechanisms, including post-translational modifications and metabolic pathways such as amino acid availability and the circadian clock, that modulate ECM secretion, assembly and remodelling in homeostasis and human diseases. Last, the Review explores the potential of 'matritherapies', that is, strategies to normalize ECM composition and architecture to achieve a therapeutic benefit.

Comparing microstructural and micromechanical deformation of the TMJ disc in two anterior disc displacement models

OBJECTIVE

Anterior disc displacement (ADD) has been used to establish temporomandibular joint disorder (TMD) models. Based on whether preserve of the retrodiscal attachment, the modelling methodologies include ADD with dissecting the retrodiscal attachment (ADDwd) and ADD without dissecting the retrodiscal attachment (ADDwod). This article aims to determine which model better matches the micromechanical and microstructural progression of TMD.

METHODS

Through meticulous microscopic observations, the microstructure and micromechanical deformation of the TMJ discs in ADDwd and ADDwod rabbit models were compared at 2 and 20 weeks.

RESULT

Scanning electron microscopy and transmission electron microscopy showed that collagen fibres became slenderized and straightened, collagen fibrils lost diameter and arrangement in the ADDwd group at 2 weeks. Meanwhile, nanoindentation and atomic electron microscopy showed that the micro- and nano- mechanical properties decreased dramatically. However, the ADDwod group exhibited no significant microstructure and micromechanical deformations at 2 weeks. Dissection of the retrodiscal attachment contribute in the acceleration of disease progression at the early stage, the devastating discal phenotype remained fundamentally the same within the two models at 20 weeks.

CONCLUSION

ADDwod models, induced stable and persistent disc deformation, therefore, can better match the progression of TMD. While ADDwd models can be considered for experiments which aim to obtain advanced phenotype in a short time.

Extracellular Matrix Components and Mechanosensing Pathways in Health and Disease

Glycosaminoglycans (GAGs) and proteoglycans (PGs) are essential components of the extracellular matrix (ECM) with pivotal roles in cellular mechanosensing pathways. GAGs, such as heparan sulfate (HS) and chondroitin sulfate (CS), interact with various cell surface receptors, including integrins and receptor tyrosine kinases, to modulate cellular responses to mechanical stimuli. PGs, comprising a core protein with covalently attached GAG chains, serve as dynamic regulators of tissue mechanics and cell behavior, thereby playing a crucial role in maintaining tissue homeostasis. Dysregulation of GAG/PG-mediated mechanosensing pathways is implicated in numerous pathological conditions, including cancer and inflammation. Understanding the intricate mechanisms by which GAGs and PGs modulate cellular responses to mechanical forces holds promise for developing novel therapeutic strategies targeting mechanotransduction pathways in disease. This comprehensive overview underscores the importance of GAGs and PGs as key mediators of mechanosensing in maintaining tissue homeostasis and their potential as therapeutic targets for mitigating mechano-driven pathologies, focusing on cancer and inflammation.

Exploring the Impact of Astaxanthin Supplementation in Conjunction with a 12-Week CrossFit Training Regimen on Selected Adipo-Myokines Levels in Obese Males

OBJECTIVE

Obesity is associated with an exacerbated metabolic condition that is mediated through impairing balance in the secretion of some adipo-myokines. Therefore, the objective of the present study was to explore the impact of astaxanthin supplementation in conjunction with a 12-week CrossFit training regimen on some selected adipo-myokines, insulin insensitivity, and serum lipid levels in obese males.

MATERIAL AND METHODS

This study is a randomized control trial design; 60 obese males were randomly divided into four groups of 15, including the control group (CG), supplement group (SG), training group (TG), and combined training and supplement group (TSG). The participants were subjected to 12 weeks of astaxanthin (AST) supplementation [20 mg/d capsule, once/d] or CrossFit training or a combination of both interventions. The training regimen comprised 36 sessions of CrossFit, each lasting 60 min, conducted three times per week. The metabolic indices, body composition, anthropometrical, cardio-respiratory, and also some plasma adipo-myokine factors, including decorin (DCN), activin A, myostatin (MST), transforming growth factor (TGF)-β1, and follistatin (FST), were examined 12 and 72 h before the initiation of the main interventional protocols, and then 72 h after the final session of the training protocol.

RESULTS

There was no significant difference in the baseline data between the groups (p > 0.05). There were significant interactions between group x time for DCN (η2 = 0.82), activin A (η2 = 0.50), FST (η2 = 0.92), MST (η2 = 0.75), and TGFB-1 (η2 = 0.67) (p < 0.001 for all the variables). Significantly changes showed for DCN in TSG compared to TG and SG and also TG compared to SG (p = 0.0001); for activin A in SG compared to TG (p = 0.01) and TSG (p = 0.002); for FST in SG compared to TG and TSG (p = 0.0001), also in TSG compared to TG (p = 0.0001); for MST in SG, TG, and TSG compared to CG (p = 0.0001) and also in TSG compared to SG (p = 0.0001) and TG (p = 0.001); for TGFB-1 in SG, TG, and TSG compared to CG (p = 0.0001) and also TSG compared to SG (p = 0.0001) and TG (p = 0.001).

CONCLUSIONS

The 12-week CrossFit training concurrent with AST supplementation reduced anthropometric and metabolic factors and also serum lipid levels while producing positive changes in body composition and cardiovascular factors. Increased FST and DCN and reduced activin A, MST, and TGF-β1 were other affirmative responses to both interventions.

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.

Chronic Adaptation of Achilles Tendon Tissues upon Injury to Rotator Cuff Tendon in Hyperlipidemic Swine

The biomechanical properties of the tendon are affected due to the changes in composition of the tendon extracellular matrix (ECM). Age, overuse, trauma and metabolic disorders are a few associated conditions that contribute to tendon abnormalities. Hyperlipidemia is one of the leading factors that contribute to the compromised biomechanical. Injury was made on infraspinatus tendon of hyperlipidemic swines. After 8 weeks (i) infraspinatus tendon from the injury site, (ii) infraspinatus tendon from the contralateral side and (iii) Achilles tendon, were collected and analyzed for ECM components that form the major part in biomechanical properties. Immunostaining of infraspinatus tendon on the injury site had higher staining collagen type-1 (COL1A1), biglycan, prolyl 4-hydroxylase and mohawk but lower staining for decorin than the control group. The Achilles tendon of the swines that had injury on infraspinatus tendon showed a chronic adaptation towards load which was evident from a more organized ECM with increased decorin, mohawk and decreased biglycan, scleraxis. The mechanism behind the collagen turnover and chronic adaptation to load need to be studied in detail with the biomechanical properties.

Collagen V haploinsufficiency in female murine patellar tendons results in altered matrix engagement and cellular density, demonstrating decreased healing

Collagen V (Col5) is a quantitatively minor component of collagen fibrils comprising tendon, however, plays a crucial role in regulation of development and dynamic healing processes. Clinically, patients with COL5a1 haploinsufficiency, known as classic Ehlers-Danlos Syndrome (cEDS), present with hyperextensible skin, joint instability and laxity, with females more likely to be affected. Previous studies in Col5-deficient mice indicated that reduced Col5a1 expression leads to a reduction in stiffness, fibril deposition, and altered fibril structure. Additionally, Col5-deficient male tendons demonstrated altered healing compared to wild-type tendons, however female mice have not yet been studied utilizing this model. Along with clinical differences between sexes in cEDS patient populations, differences in hormone physiology may be a factor influencing tendon health. Therefore, the objective of this study was to utilize a Col5a1+/ - female mouse model, to determine the effect of Col5 on tendon cell morphology, cell density, tissue composition, and mechanical properties throughout healing. We hypothesized that reduction in Col5 expression would result in an abnormal wound matrix post-injury, resulting in reduced mechanical properties compared to normal tendons. Following patellar tendon surgery, mice were euthanized at 1, 3, and 6-week post-injury. Col5-deficient tendons demonstrated altered and decreased healing compared to WT tendons. The lack of resolution in cellularity by 6-week post-injury in Col5-deficient tendons influenced the decreased mechanical properties. Stiffness did not increase post-injury in Col5-deficient mice, and collagen fiber realignment was delayed during mechanical loading. Therefore, increased Col5a1 expression post-injury is necessary to re-establish matrix engagement and cellularity throughout tendon healing.

Clearing the light path: proteoglycans and their important roles in the lens and cornea

Some of the earliest studies of glycans were performed on mammalian corneas and lenses with many of the key concepts we currently recognize as being fundamental to our understanding of basic cell biology arising from these studies. Proteoglycans and their GAG side chains are essential components of the ECM of the lens capsule. They also are present in the anterior corneal epithelial basement membrane and the posterior (Decemet's) basement membrane, and they organize collagen fiber diameters and spacing in the corneal stroma to maintain stromal clarity. Studies using genetically engineered mice and characterization of spontaneously arising mutations in genes controlling proteoglycan synthesis have generated new insight into the roles played by proteoglycans in signal transduction. We now know that proteoglycans and GAGs can regulate cell signaling and the maintenance of avascularity and immune privilege that are hallmarks of these tissues. In addition, proteoglycan-rich matrices provide the pathways for immune cells to populate the surface of the lens as a response to corneal wounding and in a model of Experimental Autoimmune Uveitis. Here we describe what is known about proteoglycans and GAGs in the cornea and lens. This knowledge has begun to provide promising leads into new proteoglycan-based treatments aimed at restoring and maintaining homeostasis in the cornea. Future studies are needed to determine how these new drugs impact the recruitment of immune cells to the lens for functions in restoring/maintaining homeostasis in the eye.

A Systems Approach to Biomechanics, Mechanobiology, and Biotransport

The human body represents a collection of interacting systems that range in scale from nanometers to meters. Investigations from a systems perspective focus on how the parts work together to enact changes across spatial scales, and further our understanding of how systems function and fail. Here, we highlight systems approaches presented at the 2022 Summer Biomechanics, Bio-engineering, and Biotransport Conference in the areas of solid mechanics; fluid mechanics; tissue and cellular engineering; biotransport; and design, dynamics, and rehabilitation; and biomechanics education. Systems approaches are yielding new insights into human biology by leveraging state-of-the-art tools, which could ultimately lead to more informed design of therapies and medical devices for preventing and treating disease as well as rehabilitating patients using strategies that are uniquely optimized for each patient. Educational approaches can also be designed to foster a foundation of systems-level thinking.

Neonatal Achilles Tendon Microstructure is Negatively Impacted by Decorin and Biglycan Knockdown After Injury and During Development

Interest in studying neonatal development and the improved healing response observed in neonates is increasing, with the goal of using this work to create better therapeutics for tendon injury. Decorin and biglycan are two small leucine-rich proteoglycans that play important roles in collagen fibrillogenesis to develop, maintain, and repair tendon structure. However, little is known about the roles of decorin and biglycan in early neonatal development and healing. The goal of this study was to determine the effects of decorin and biglycan knockdown on Achilles tendon structure and mechanics during neonatal development and recovery of these properties after injury of the neonatal tendon. We hypothesized that knockdown of decorin and biglycan would disrupt the neonatal tendon developmental process and produce tendons with impaired mechanical and structural properties. We found that knockdown of decorin and biglycan in an inducible, compound decorin/biglycan knockdown model, both during development and after injury, in neonatal mice produced tendons with reduced mechanical properties. Additionally, the collagen fibril microstructure resembled an immature tendon with a large population of small diameter fibrils and an absence of larger diameter fibrils. Overall, this study demonstrates the importance of decorin and biglycan in facilitating tendon growth and maturation during neonatal development.

Proteoglycan Dysfunction: A Common Link Between Intervertebral Disc Degeneration and Skeletal Dysplasia

Proteoglycans through their sulfated glycosaminoglycans regulate cell-matrix signaling during tissue development, regeneration, and degeneration processes. Large extracellular proteoglycans such as aggrecan, versican, and perlecan are especially important for the structural integrity of the intervertebral disc and cartilage during development. In these tissues, proteoglycans are responsible for hydration, joint flexibility, and the absorption of mechanical loads. Loss or reduction of these molecules can lead to disc degeneration and skeletal dysplasia, evident from loss of disc height or defects in skeletal development respectively. In this review, we discuss the common proteoglycans found in the disc and cartilage and elaborate on various murine models and skeletal dysplasias in humans to highlight how their absence and/or aberrant expression causes accelerated disc degeneration and developmental defects.

Genomic architecture of carcass and pork traits and their association with immune capacity

Carcass and pork traits have traditionally been considered of prime importance in pig breeding programmes. However, the changing conditions in modern farming, coupled with antimicrobial resistance issues, are raising the importance of health and robustness-related traits. Here, we explore the genetic architecture of carcass and pork traits and their relationship with immunity phenotypes in a commercial Duroc pig population. A total of nine traits related to fatness, lean content and meat pH were measured at slaughter (∼190 d of age) in 378 pigs previously phenotyped (∼70 d of age) for 36 immunity-related traits, including plasma concentrations of immunoglobulins, acute-phase proteins, leukocytes subpopulations and phagocytosis. Our study showed medium to high heritabilities and strong genetic correlations between fatness, lean content and meat pH at 24 h postmortem. Genetic correlations were found between carcass and pork traits and white blood cells. pH showed strong positive genetic correlations with leukocytes and eosinophils, and strong negative genetic correlations with haemoglobin, haematocrit and cytotoxic T cell proportion. In addition, genome-wide association studies (GWASs) pointed out four significantly associated genomic regions for lean meat percentages in different muscles, ham fat, backfat thickness, and semimembranosus pH at 24 h. The functional annotation of genes located in these regions reported a total of 14 candidate genes, with BGN, DPP10, LEPR, LEPROT, PDE4B and SLC6A8 being the strongest candidates. After performing an expression GWAS for the expression of these genes in muscle, two signals were detected in cis for the BGN and SLC6A8 genes. Our results indicate a genetic relationship between carcass fatness, lean content and meat pH with a variety of immunity-related traits that should be considered to improve immunocompetence without impairing production traits.

Type I collagen and fibromodulin enhance the tenogenic phenotype of hASCs and their potential for tendon regeneration

Our previous work demonstrated the tendon-derived extracellular matrix (ECM) extracts as vital niches to specifically direct mesenchymal stem cells towards tenogenic differentiation. This study aims to further define the effective ECM molecules capable of teno-lineage induction on human adipose-derived stem cells (hASCs) and test their function for tendon engineering. By detecting the teno-markers expression levels in hASCs exposed to various substrate coatings, collagen I (COL1) and fibromodulin (FMOD) were identified to be the key molecules as a combination and further employed to the modification of poly(L-lactide-co-ε-caprolactone) electrospun nanoyarns, which showed advantages in inducting seeded hASCs for teno-lineage specific differentiation. Under dynamic mechanical loading, modified scaffold seeded with hASCs formed neo-tendon in vitro at the histological level and formed better tendon tissue in vivo with mature histology and enhanced mechanical properties. Primary mechanistic investigation with RNA sequencing demonstrated that the inductive mechanism of these two molecules for hASCs tenogenic differentiation was directly correlated with positive regulation of peptidase activity, regulation of cell-substrate adhesion and regulation of cytoskeletal organization. These biological processes were potentially affected by LOC101929398/has-miR-197-3p/TENM4 ceRNA regulation axis. In summary, COL1 and FMOD in combination are the major bioactive molecules in tendon ECM for likely directing tenogenic phenotype of hASCs and certainly valuable for hASCs-based tendon engineering.

Biofabrication of Composite Tendon Constructs with the Fibrous Arrangement, High Cell Density, and Enhanced Cell Alignment

Current tissue-engineered tendons are mostly limited to the replication of fibrous organizations of native tendons, which lack the biomimicry of a densely packed cell arrangement. In this study, composite tendon constructs (CTCs) with fibrous arrangement, high cell density, and enhanced cell alignment were developed by integrating the electrohydrodynamic jet 3D printing (e-jetting) technique and the fabrication of tissue strands (TSs). A tubular polycaprolactone (PCL) scaffold was created using e-jetting, followed by coating a thin layer of alginate. Human mesenchymal stem cells were then microinjected into the PCL scaffolds, aggregated into TSs, and formed CTCs with a core-shell structure. Owing to the presence of TSs, CTCs demonstrated the anatomically relevant cell density and morphology, and cells migrated from the TSs onto e-jetted scaffolds. Also, the mechanical strength of CTCs approached that of native tendons due to the existence of e-jetted scaffolds (Young's modulus: ∼21 MPa, ultimate strength: ∼5 MPa). During the entire culture period, CTCs maintained high survival rates and good structural integrity without the observation of necrotic cores and disintegration of two portions. In addition, CTCs that were cultured with uniaxial cyclic stretching revealed not only the increased expression of tendon-related proteins but also the enhanced cellular orientation. The promising results demonstrated the potential of this novel biofabrication strategy for building tissue-engineered tendon constructs with the proper biological, mechanical, and histological relevance..

Investigating the temporal roles of decorin and biglycan in tendon healing

The small leucine-rich proteoglycans, decorin and biglycan, are minor components of the tendon extracellular matrix that regulate fibrillogenesis and matrix assembly. Our study objective was to define the temporal roles of decorin and biglycan during tendon healing using inducible knockout mice to include genetic knockdown at specific phases of healing: time of injury, the proliferative phase, and the remodeling phase. We hypothesized that knockdown of decorin or biglycan would adversely affect tendon healing, and that by prescribing the timing of knockdown, we could elucidate the temporal roles of these proteins during healing. Contrary to our hypothesis, decorin knockdown did not affect tendon healing. However, when biglycan was knocked down, either alone or coupled with decorin, tendon modulus was increased relative to wild-type mice, and this finding was consistent among all induction timepoints. At 6 weeks postinjury, we observed increased expression of genes associated with the extracellular matrix and growth factor signaling in the biglycan knockdown and compound decorin-biglycan knockdown tendons. Interestingly, these groups demonstrated opposing trends in gene expression as a function of knockdown-induction timepoint, highlighting distinct temporal roles for decorin and biglycan. In summary, this study finds that biglycan plays multiple functions throughout tendon healing, with the most impactful, detrimental role likely occurring during late-stage healing. Statement of clinical importance: This study helps to define the molecular factors that regulate tendon healing, which may aid in the development of new clinical therapies.

Knockdown of biglycan reveals an important role in maintenance of structural and mechanical properties during tendon aging

Biglycan, a small leucine-rich proteoglycan (SLRP), is involved in collagen fibrillogenesis and also acts as a signaling molecule. Although decorin has been considered as the primary SLRP in developing and maintaining tendon structure and mechanics, more recent work using inducible knockdown models suggests that biglycan is involved in tendon homeostasis. The purpose of the study was to determine the role of biglycan in tendon homeostasis to maintain mechanical and structural integrity in aged mice. Aged (485 days old) female Bgn+/+ control (wild type [WT], n = 16) and 16 bitransgenic conditional Bgnflox/flox mice (I-Bgn-/- , n = 16) with a tamoxifen-inducible Cre (driven by ROSA) were utilized. After biglycan knockdown, the transgenic model demonstrated effective knockdown of the target gene without any compensation from other SLRPs or type I collagen. Patellar tendon cellularity was not modified after biglycan knockdown. However, biglycan knockdown had an impact on collagen fibrillogenesis with a higher percentage of small diameter fibrils (25-45 nm) and a lower percentage of medium size fibrils (150-165 nm) in I-Bgn-/- tendons. Biglycan knockdown also induced a reduction in the midsubstance modulus and maximum stress compared to WT. Stress relaxation was reduced at 4% strain in I-Bgn-/- tendons but no changes were observed in dynamic modulus and tan delta. As in mature tendons (120 days old), this study showed significant effects of biglycan knockdown on mechanical and structural properties of aged tendons only 30 days after knockdown. These data suggest that biglycan has a major role in maintaining homeostasis in aged tendon.

Hyperprolactinemia modifies extracellular matrix components associated with collagen fibrillogenesis in harderian glands of non- and pregnant female mice

The harderian gland (HG) is a gland located at the base of the nictating membrane and fills the inferomedial aspect of the orbit in rodents. It is under the influence of the hypothalamic-pituitary-gonadal axis and, because of its hormone receptors, it is a target tissue for prolactin (PRL) and sex steroid hormones (estrogen and progesterone). In humans and murine, the anterior surface of the eyes is protected by a tear film synthesized by glands associated with the eye. In order to understand the endocrine changes caused by hyperprolactinemia in the glands responsible for the formation of the tear film, we used an animal model with metoclopramide-induced hyperprolactinemia (HPRL). Given the evidences that HPRL can lead to a process of cell death and tissue fibrosis, the protein expression of small leucine-rich proteoglycans (SLRPs) was analyzed through immunohistochemistry in the HG of the non- and the pregnant female mice with hyperprolactinemia. The SRLPs are related to collagen fibrillogenesis and they participate in pro-apoptotic signals. Our data revealed that high prolactin levels and changes in steroid hormones (estrogen and progesterone) can lead to an alteration in the amount of collagen, and in the structure of type I and III collagen fibers through changes in the amounts of lumican and decorin, which are responsible for collagen fibrillogenesis. This fact can lead to the impaired functioning of the HG by excessive apoptosis in the HG of the non- and the pregnant female mice with HPRL and especially in the HG of pregnancy-associated hyperprolactinemia.

The Degradation of Intramuscular Connective Tissue In Vitro with Purified Cathepsin L from Bovine Pancreas

To investigate the possible degradation of the intramuscular connective tissue (IMCT) with cathepsin L, isolated IMCTs were incubated with purified cathepsin L in vitro. Here, we prepared purified cathepsin L from bovine pancreas by using DEAE Sephacel, Sephacryl S-100 HR, SP Sepharose FF, and con A-Sepharose affinity chromatography in sequence. An SDS-PAGE analysis of CNBr-digested peptides showed that the degradation of collagen in IMCT could take place on terminal non-helical peptides rather than the triple helix region. Decorin (DCN) was clearly degraded at a pH of 5.0. The TP and TO of intramuscular connective tissue decreased to 41.41 °C and 43.79 °C, respectively. In the cathepsin L treatment of pH 5.0, the decreases in the TP and TO of IMCT were more sensitive than they were at pH 5.5~6.5.

The rat Achilles and patellar tendons have similar increases in mechanical properties but become transcriptionally divergent during postnatal development

The molecular events that drive post-natal tendon development are poorly characterized. In this study, we profiled morphological, mechanical, and transcriptional changes in the rat Achilles and patellar tendon before walking (P7), shortly after onset of walking (P14), and at motor maturity (P28). The Achilles and patellar tendons increased collagen content and mechanical strength similarly throughout post-natal development. However, at P28 the patellar tendon tended to display a higher maximal tensile load (MTL) (P = 0.0524) than the Achilles tendon, but a similar ultimate tensile strength (UTS; load relative to cross-sectional area) probably due to its increased cross-sectional area during development. The tendons started transcriptionally similar, with overlapping PCA clusters at P7 and P14, before becoming transcriptionally distinct at P28. In both tendons, there was an increase in extracellular matrix (ECM) gene expression and a concomitant decrease in cell cycle and mitochondrial gene expression. The transcriptional divergence at P28 suggested that STAT signalling was lower in the patellar tendon where MTL increased the most. Treating engineered human ligaments with the STAT inhibitor itacitinib increased collagen content and MTL. Our results suggest that during post-natal development, cellular resources are initially allocated towards cell proliferation before shifting towards extracellular matrix development following the onset of mechanical load and provide potential targets for improving tendon function. KEY POINTS: Little is known about mechanisms of post-natal tendon growth. We characterized morphological, mechanical, and transcriptional changes that occur before (P7), and early (P14) and late after (P28) rats begin to walk. From P7 to P28, the Achilles tendon increased in length, whereas the patellar tendon increased in cross-sectional area. Mechanical and material properties of the Achilles and patellar tendon increased from P7 to P28. From P7 to P28, the Achilles and patellar tendons increased expression of ECM genes and decreased mitochondrial and cell cycle gene expression. Ribosomal gene expression also significantly decreased in the Achilles and tended to decrease in the patellar tendon. At P28, STAT1 signalling tended to be lower in the patellar tendon which had grown by increasing cross-sectional area and inhibiting STAT activation in vitro improved mechanical properties in engineered human ligaments.

Loss of Fgfr1 and Fgfr2 in Scleraxis-lineage cells leads to enlarged bone eminences and attachment cell death

BACKGROUND

Tendons and ligaments attach to bone are essential for joint mobility and stability in vertebrates. Tendon and ligament attachments (ie, entheses) are found at bony protrusions (ie, eminences), and the shape and size of these protrusions depend on both mechanical forces and cellular cues during growth. Tendon eminences also contribute to mechanical leverage for skeletal muscle. Fibroblast growth factor receptor (FGFR) signaling plays a critical role in bone development, and Fgfr1 and Fgfr2 are highly expressed in the perichondrium and periosteum of bone where entheses can be found.

RESULTS AND CONCLUSIONS

We used transgenic mice for combinatorial knockout of Fgfr1 and/or Fgfr2 in tendon/attachment progenitors (ScxCre) and measured eminence size and shape. Conditional deletion of both, but not individual, Fgfr1 and Fgfr2 in Scx progenitors led to enlarged eminences in the postnatal skeleton and shortening of long bones. In addition, Fgfr1/Fgfr2 double conditional knockout mice had more variation collagen fibril size in tendon, decreased tibial slope, and increased cell death at ligament attachments. These findings identify a role for FGFR signaling in regulating growth and maintenance of tendon/ligament attachments and the size and shape of bony eminences.

Overload in a Rat In Vivo Model of Synergist Ablation Induces Tendon Multiscale Structural and Functional Degeneration

Tendon degeneration is typically described as an overuse injury with little distinction made between magnitude of load (overload) and number of cycles (overuse). Further, in vivo, animal models of tendon degeneration are mostly overuse models, where tendon damage is caused by a high number of load cycles. As a result, there is a lack of knowledge of how isolated overload leads to degeneration in tendons. A surgical model of synergist ablation (SynAb) overloads the target tendon, plantaris, by ablating its synergist tendon, Achilles. The objective of this study was to evaluate the structural and functional changes that occur following overload of plantaris tendon in a rat SynAb model. Tendon cross-sectional area (CSA) and shape changes were evaluated by longitudinal MR imaging up to 8 weeks postsurgery. Tissue-scale structural changes were evaluated by semiquantified histology and second harmonic generation microscopy. Fibril level changes were evaluated with serial block face scanning electron microscopy (SBF-SEM). Functional changes were evaluated using tension tests at the tissue and microscale using a custom testing system allowing both video and microscopy imaging. At 8 weeks, overloaded plantaris tendons exhibited degenerative changes including increases in CSA, cell density, collagen damage area fraction (DAF), and fibril diameter, and decreases in collagen alignment, modulus, and yield stress. To interpret the differences between overload and overuse in tendon, we introduce a new framework for tendon remodeling and degeneration that differentiates between the inputs of overload and overuse. In summary, isolated overload induces multiscale degenerative structural and functional changes in plantaris tendon.

The Contribution of Vascular Proteoglycans to Atherothrombosis: Clinical Implications

The vascular extracellular matrix (ECM) produced by endothelial and smooth muscle cells is composed of collagens and glycoproteins and plays an integral role in regulating the structure and function of the vascular wall. Alteration in the expression of these proteins is associated with endothelial dysfunction and has been implicated in the development and progression of atherosclerosis. The ECM composition of atherosclerotic plaques varies depending on plaque phenotype and vulnerability, with distinct differences observed between ruptured and erodes plaques. Moreover, the thrombi on the exposed ECM are diverse in structure and composition, suggesting that the best antithrombotic approach may differ depending on plaque phenotype. This review provides a comprehensive overview of the role of proteoglycans in atherogenesis and thrombosis. It discusses the differential expression of the proteoglycans in different plaque phenotypes and the potential impact on platelet function and thrombosis. Finally, the review highlights the importance of this concept in developing a targeted approach to antithrombotic treatments to improve clinical outcomes in cardiovascular disease.

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.

Mechanical homeostasis imbalance in hepatic stellate cells activation and hepatic fibrosis

Chronic liver disease or repeated damage to hepatocytes can give rise to hepatic fibrosis. Hepatic fibrosis (HF) is a pathological process of excessive sedimentation of extracellular matrix (ECM) proteins such as collagens, glycoproteins, and proteoglycans (PGs) in the hepatic parenchyma. Changes in the composition of the ECM lead to the stiffness of the matrix that destroys its inherent mechanical homeostasis, and a mechanical homeostasis imbalance activates hepatic stellate cells (HSCs) into myofibroblasts, which can overproliferate and secrete large amounts of ECM proteins. Excessive ECM proteins are gradually deposited in the Disse gap, and matrix regeneration fails, which further leads to changes in ECM components and an increase in stiffness, forming a vicious cycle. These processes promote the occurrence and development of hepatic fibrosis. In this review, the dynamic process of ECM remodeling of HF and the activation of HSCs into mechanotransduction signaling pathways for myofibroblasts to participate in HF are discussed. These mechanotransduction signaling pathways may have potential therapeutic targets for repairing or reversing fibrosis.

An indentation-based framework for probing the glycosaminoglycan-mediated interactions of collagen fibrils

Microscale deformation processes, such as reorientation, buckling, and sliding of collagen fibrils, determine the mechanical behavior and function of collagenous tissue. While changes in the structure and composition of tendon have been extensively studied, the deformation mechanisms that modulate the interaction of extracellular matrix (ECM) constituents are not well understood, partly due to the lack of appropriate techniques to probe the behavior. In particular, the role of glycosaminoglycans (GAGs) in modulating collagen fibril interactions has remained controversial. Some studies suggest that GAGs act as crosslinkers between the collagen fibrils, while others have not found such evidence and postulate that GAGs have other functions. Here, we introduce a new framework, relying on orientation-dependent indentation behavior of tissue and computational modeling, to evaluate the shear-mediated function of GAGs in modulating the collagen fibril interactions at a length scale more relevant to fibrils compared to bulk tests. Specifically, we use chondroitinase ABC to enzymatically deplete the GAGs in tendon; measure the orientation-dependent indentation response in transverse and longitudinal orientations; and infer the microscale deformation mechanisms and function of GAGs from a microstructural computational model and a modified shear-lag model. We validate the modeling approach experimentally and show that GAGs facilitate collagen fibril sliding with minimal crosslinking function. We suggest that the molecular reconfiguration of GAGs is a potential mechanism for their microscale, strain-dependent viscoelastic behavior. This study reveals the mechanisms that control the orientation-dependent indentation response by affecting the shear deformation and provides new insights into the mechanical function of GAGs and collagen crosslinkers in collagenous tissue.

Framing Heartaches: The Cardiac ECM and the Effects of Age

The cardiac extracellular matrix (ECM) is involved in several pathological conditions, and age itself is also associated with certain changes in the heart: it gets larger and stiffer, and it develops an increased risk of abnormal intrinsic rhythm. This, therefore, makes conditions such as atrial arrythmia more common. Many of these changes are directly related to the ECM, yet the proteomic composition of the ECM and how it changes with age is not fully resolved. The limited research progress in this field is mainly due to the intrinsic challenges in unravelling tightly bound cardiac proteomic components and also the time-consuming and costly dependency on animal models. This review aims to give an overview of the composition of the cardiac ECM, how different components aid the function of the healthy heart, how the ECM is remodelled and how it is affected by ageing.

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.

Morphological and Physiological Aspects of Mutable Collagenous Tissue at the Autotomy Plane of the Starfish Asterias rubens L. (Echinodermata, Asteroidea): An Echinoderm Paradigm

The mutable collagenous tissue (MCT) of echinoderms has the capacity to undergo changes in its tensile properties within a timescale of seconds under the control of the nervous system. All echinoderm autotomy (defensive self-detachment) mechanisms depend on the extreme destabilisation of mutable collagenous structures at the plane of separation. This review illustrates the role of MCT in autotomy by bringing together previously published and new information on the basal arm autotomy plane of the starfish Asterias rubens L. It focuses on the MCT components of breakage zones in the dorsolateral and ambulacral regions of the body wall, and details data on their structural organisation and physiology. Information is also provided on the extrinsic stomach retractor apparatus whose involvement in autotomy has not been previously recognised. We show that the arm autotomy plane of A. rubens is a tractable model system for addressing outstanding problems in MCT biology. It is amenable to in vitro pharmacological investigations using isolated preparations and provides an opportunity for the application of comparative proteomic analysis and other “-omics” methods which are aimed at the molecular profiling of different mechanical states and characterising effector cell functions.

Adipose and Bone Marrow Derived-Mesenchymal Stromal Cells Express Similar Tenogenic Expression Levels when Subjected to Mechanical Uniaxial Stretching In Vitro

The present study was conducted to determine whether adipose derived mesenchymal stromal cells (AD-MSCs) or bone marrow derived-MSCs (BM-MSCs) would provide superior tenogenic expressions when subjected to cyclical tensile loading. The results for this would indicate the best choice of MSCs source to be used for cell-based tendon repair strategies. Both AD-MSCs and BM-MSCs were obtained from ten adult donors (N = 10) and cultured in vitro. At passaged-2, cells from both groups were subjected to cyclical stretching at 1 Hz and 8% of strain. Cellular morphology, orientation, proliferation rate, protein, and gene expression levels were compared at 0, 24, and 48 hours of stretching. In both groups, mechanical stretching results in similar morphological changes, and the redirection of cell alignment is perpendicular to the direction of stretching. Loading at 8% strain did not significantly increase proliferation rates but caused an increase in total collagen expression and tenogenic gene expression levels. In both groups, these levels demonstrated no significant differences suggesting that in a similar loading environment, both cell types possess similar tenogenic potential. In conclusion, AD-MSCs and BM-MSCs both demonstrate similar tenogenic phenotypic and gene expression levels when subjected to cyclic tensile loading at 1 Hz and 8% strain, thus, suggesting that the use of either cell source may be suitable for tendon repair.

Biglycan promotes hepatic fibrosis through activating heat shock protein 47

BACKGROUND

Biglycan (BGN) is a small leucine-rich proteoglycan that participates in the production of excess extracellular matrix (ECM) and is related to fibrosis in many organs. However, the role of BGN in liver fibrosis remains poorly understood. This study aimed to investigate the role and mechanism of BGN in liver fibrosis.

METHODS

Human liver samples, Bgn-/0 (BGN KO) mice and a human LX-2 hepatic stellate cells (HSCs) model were applied for the study of experimental fibrosis. GEO data and single-cell RNA-seq data of human liver tissue were analysed as a bioinformatic approach. Coimmunoprecipitation, immunofluorescence staining, western blotting and qRT-PCR were conducted to identify the regulatory effects of BGN on heat shock protein 47 (HSP47) expression and liver fibrosis.

RESULTS

We observed that hepatic BGN expression was significantly increased in patients with fibrosis and in a mouse model of liver fibrosis. Genetic deletion of BGN disrupted TGF-β1 pathway signalling and alleviated liver fibrosis in mice administered carbon tetrachloride (CCl4 ). siRNA-mediated knockdown of BGN significantly reduced TGF-β1-induced ECM deposition and fibroblastic activation in LX-2 cells. Mechanistically, BGN directly interacted with and positively regulated the collagen synthesis chaperon protein HSP47. Rescue experiments showed that BGN promoted hepatic fibrosis by regulating ECM deposition and HSC activation by positively regulating HSP47.

CONCLUSION

Our data indicate that BGN promotes hepatic fibrosis by regulating ECM deposition and HSC activation through an HSP47-dependent mechanism. BGN may be a new biomarker of hepatic fibrosis and a novel target for disease prevention and treatment.

Differential MMP-14 targeting by biglycan, decorin, fibromodulin, and lumican unraveled by in silico approach

Small leucine-rich proteoglycans (SLRPs) are major regulators of extracellular matrix assembly and cell signaling. Lumican, a member of the SLRPs family, and its derived peptides were shown to possess antitumor activity by interacting directly with the catalytic domain of MMP-14 leading to the inhibition of its activity. The aim of the present report was to characterize by in silico three-dimensional (3D) modeling the structure and the dynamics of four SLRPs including their core protein and their specific polysaccharide chains to assess their capacity to bind to MMP-14 and to regulate its activity. Molecular docking experiments were performed to identify the specific amino acids of MMP-14 interacting with each of the four SLRPs. The inhibition of each SLRP (100 nM) on MMP-14 activity was measured and the constants of inhibition (K_i) were evaluated. The impact of the number of glycan chains, structures, and dynamics of lumican on the interaction with MMP-14 was assessed by molecular dynamics simulations. Molecular docking analysis showed that all SLRPs bind to MMP-14 through their concave face, but in different regions of the catalytic domain of MMP-14. Each SLRPs inhibited significantly the MMP-14 activity. Finally, molecular dynamics showed the role of glycan chains in interaction with MMP-14 and shielding effect of SLRPs. Altogether, the results demonstrated that each SLRP exhibited inhibition of MMP-14 activity. However, the differential targeting of MMP-14 by the SLRPs was shown to be related not only to the core protein conformation but also to the glycan chain structures and dynamics.

Regulators, functions, and mechanotransduction pathways of matrix stiffness in hepatic disease

The extracellular matrix (ECM) provides physical support and imparts significant biochemical and mechanical cues to cells. Matrix stiffening is a hallmark of liver fibrosis and is associated with many hepatic diseases, especially liver cirrhosis and carcinoma. Increased matrix stiffness is not only a consequence of liver fibrosis but is also recognized as an active driver in the progression of fibrotic hepatic disease. In this article, we provide a comprehensive view of the role of matrix stiffness in the pathological progression of hepatic disease. The regulators that modulate matrix stiffness including ECM components, MMPs, and crosslinking modifications are discussed. The latest advances of the research on the matrix mechanics in regulating intercellular signaling and cell phenotype are classified, especially for hepatic stellate cells, hepatocytes, and immunocytes. The molecular mechanism that sensing and transducing mechanical signaling is highlighted. The current progress of ECM stiffness's role in hepatic cirrhosis and liver cancer is introduced and summarized. Finally, the recent trials targeting ECM stiffness for the treatment of liver disease are detailed.

Post-injury tendon mechanics are not affected by tamoxifen treatment

PURPOSE

A growing interest in the mechanisms that govern tendon healing has resulted in the develop-ment of tools, such as the tamoxifen-inducible mouse knockdown model, to address these questions. However, tamoxifen is a selective estrogen receptor modulator and may interfere with the tendon healing process. The objective of this study was to evaluate the effects of tamoxifen on post-injury tendon mechanics in wild-type mice.

METHODS

The mice underwent treatment at the time of injury using an established mouse injury model and the injured tendons were evaluated 3 weeks post-injury. The treatment contained tamoxifen suspended in corn oil and was compared to a treatment with only corn oil, as well as mice with no treatment. Tendons were evaluated by measuring the quasi-static and viscoelastic mechanics, collagen fiber realignment, cellularity, and nuclear morphology.

RESULTS

Mechanical testing of the tendons post-injury revealed no changes to viscoelastic mechanics, quasi-static mechanics, or collagen realignment during loading after tamoxifen treatment with the dosage regimen utilized (three daily injections of 4.5 mg/40 g body weight). Additionally, histological analysis revealed no changes to cellularity or cell nuclear shape.

CONCLUSION

Overall, this study revealed that tamoxifen treatment at the time of tendon injury did not result in changes to tendon mechanics or the histological parameters at 3 weeks post-injury.

Injectable Decorin/Gellan Gum Hydrogel Encapsulating Adipose-Derived Stem Cells Enhances Anti-Inflammatory Effect in Cartilage Injury via Autophagy Signaling

Adipose-derived stem cells (ADSCs) are employed as a promising alternative in treating cartilage injury. Regulating the inflammatory "fingerprint" of ADSCs to improve their anti-inflammatory properties could enhance therapy efficiency. Herein, a novel injectable decorin/gellan gum hydrogel combined with ADSCs encapsulation for arthritis cartilage treatment is proposed. Decorin/gellan gum hydrogel was prepared according to the previous manufacturing protocol. The liquid-solid form transition of gellan gum hydrogel is perfectly suitable for intra-articular injection. Decorin-enriched matrix showing an immunomodulatory ability to enhance ADSCs anti-inflammatory phenotype under inflammation microenvironment by regulating autophagy signaling. This decorin/gellan gum/ADSCs hydrogel efficiently reverses interleukin-1β-induced cellular injury in chondrocytes. Through a mono-iodoacetate-induced arthritis mice model, the synergistic therapeutic effect of this ADSCs-loaded hydrogel, including inflammation attenuation and cartilage protection, is demonstrated. These results make the decorin/gellan gum hydrogel laden with ADSCs an ideal candidate for treating inflammatory joint disorders.