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

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.

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.

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.

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.

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.

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

BACKGROUND

Despite 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.

METHODS

Fasting 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.

RESULTS

The 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.

CONCLUSION

The 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.

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.

Mucopolysaccharidoses: Cellular Consequences of Glycosaminoglycans Accumulation and Potential Targets

Mucopolysaccharidoses (MPSs) constitute a heterogeneous group of lysosomal storage disorders characterized by the lysosomal accumulation of glycosaminoglycans (GAGs). Although lysosomal dysfunction is mainly affected, several cellular organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and their related process are also impaired, leading to the activation of pathophysiological cascades. While supplying missing enzymes is the mainstream for the treatment of MPS, including enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), or gene therapy (GT), the use of modulators available to restore affected organelles for recovering cell homeostasis may be a simultaneous approach. This review summarizes the current knowledge about the cellular consequences of the lysosomal GAGs accumulation and discusses the use of potential modulators that can reestablish normal cell function beyond ERT-, HSCT-, or GT-based alternatives.

Ex vivo study correlating the stiffness of the ovine patellar tendon to age and weight

Tendons play a crucial role in the musculoskeletal system. In humans, tendon injuries, especially chronic tendinopathy, are very common and the patellar tendon is a frequent location for tendinopathy or injuries. The biomechanical characteristics of the patellar tendon, such as elasticity and stiffness, are of paramount importance and constitute major outcome measures in research studies. We aimed to assess whether the stiffness of the healthy ovine patellar tendon changes with age and weight in a population of normal animals. Sixty-eight 'patella-patellar tendon-tibial tuberosity' units from thirty-four Ile-de-France ewes of body mass 65 to 95 kg, euthanized for reasons other than musculoskeletal diseases, underwent a tensile test providing a measure of the tendon stiffness. Animals were sorted into three categories of age (1-2 yo, 3-5 yo, 6-10 yo). We found a positive but not significant correlation between age category and stiffness (r = 0.22, p = 0.27). There was a significantly positive correlation between weight and stiffness (r = 0.39, p = 0.04). In conclusion, the study characterized biomechanical properties of healthy tendons, provided useful reference values, and established the basis for future biomechanical tests on healing tendons in sheep. The most appropriate sheep population for those future studies would be non-overweight young adults presenting with no lameness.

Altered Structure and Function of Murine Sclera in Form-Deprivation Myopia

Purpose

The sclera is believed to biomechanically influence eye size, facilitating the excessive axial elongation that occurs during myopigenesis. Here, we test the hypothesis that the sclera will be remodeled and exhibit altered biomechanics in the mouse model of form-deprivation (FD) myopia, accompanied by altered retinoid concentrations, a potential signaling molecule involved in the process.

Methods

Male C57 Bl/6J mice were subjected to unilateral FD (n = 44 eyes), leaving the contralateral eye untreated (contra; n = 44). Refractive error and ocular biometry were measured in vivo prior to and after 1 or 3 weeks of FD. Ex vivo measurements were made of scleral biomechanical properties (unconfined compression: n = 24), scleral sulfated glycosaminoglycan (sGAG) content (dimethylmethylene blue: n = 18, and immunohistochemistry: n = 22), and ocular all-trans retinoic acid (atRA) concentrations (retina and RPE + choroid + sclera, n = 24). Age-matched naïve controls were included for some outcomes (n = 32 eyes).

Results

Significant myopia developed after 1 (-2.4 ± 1.1 diopters [D], P < 0.001) and 3 weeks of FD (-4.1 ± 0.7 D, P = 0.025; mean ± standard deviation). Scleral tensile stiffness and permeability were significantly altered during myopigenesis (stiffness = -31.4 ± 12.7%, P < 0.001, and permeability = 224.4 ± 205.5%, P < 0.001). Total scleral sGAG content was not measurably altered; however, immunohistochemistry indicated a sustained decrease in chondroitin-4-sulfate and a slower decline in dermatan sulfate. The atRA increased in the retinas of eyes form-deprived for 1 week.

Conclusions

We report that biomechanics and GAG content of the mouse sclera are altered during myopigenesis. All scleral outcomes generally follow the trends found in other species and support a retina-to-sclera signaling cascade underlying mouse myopigenesis.

Achilles Tendons Display Region-Specific Transcriptomic Signatures Associated With Distinct Mechanical Properties

BACKGROUND

Previous studies have examined the transcriptomes and mechanical properties of whole tendons in different regions of the body. However, less is known about these characteristics within a single tendon.

PURPOSE

To develop a regional transcriptomic atlas and evaluate the region-specific mechanical properties of Achilles tendons.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Achilles tendons from 2-month-old male Sprague Dawley rats were used. Tendons were isolated and divided into proximal, middle, and distal thirds for RNA sequencing (n = 5). For mechanical testing, the Achilles muscle-tendon-calcaneus unit was mounted in a custom-designed materials testing system with the unit clamped over the musculotendinous junction (MTJ) and the calcaneus secured at 90° of dorsiflexion (n = 9). Tendons were stretched to 20 N at a constant speed of 0.0167 mm/s. Cross-sectional area, strain, stress, and Young modulus were determined in each tendon region.

RESULTS

An open-access, interactive transcriptional atlas was generated that revealed distinct gene expression signatures in each tendon region. The proximal and distal regions had the largest differences in gene expression, with 2596 genes significantly differentially regulated at least 1.5-fold (q < .01). The proximal tendon displayed increased expression of genes resembling a tendon phenotype and increased expression of nerve cell markers. The distal region displayed increases in genes involved in extracellular matrix synthesis and remodeling, immune cell regulation, and a phenotype similar to cartilage and bone. There was a 3.72-fold increase in Young modulus from the proximal to middle region (P < .01) and an additional 1.34-fold increase from the middle to distal region (P = .027).

CONCLUSION

Within a single tendon, there are region-specific transcriptomic signatures and mechanical properties, and there is likely a gradient in the biological and functional phenotype from the proximal origin at the MTJ to the distal insertion at the enthesis.

CLINICAL RELEVANCE

These findings improve our understanding of the underlying biological heterogeneity of tendon tissue and will help inform the future targeted use of regenerative medicine and tissue engineering strategies for patients with tendon disorders.

Advanced Gene Therapy Strategies for the Repair of ACL Injuries

The anterior cruciate ligament (ACL), the principal ligament for stabilization of the knee, is highly predisposed to injury in the human population. As a result of its poor intrinsic healing capacities, surgical intervention is generally necessary to repair ACL lesions, yet the outcomes are never fully satisfactory in terms of long-lasting, complete, and safe repair. Gene therapy, based on the transfer of therapeutic genetic sequences via a gene vector, is a potent tool to durably and adeptly enhance the processes of ACL repair and has been reported for its workability in various experimental models relevant to ACL injuries in vitro, in situ, and in vivo. As critical hurdles to the effective and safe translation of gene therapy for clinical applications still remain, including physiological barriers and host immune responses, biomaterial-guided gene therapy inspired by drug delivery systems has been further developed to protect and improve the classical procedures of gene transfer in the future treatment of ACL injuries in patients, as critically presented here.

Proteoglycans play a role in the viscoelastic behaviour of the canine cranial cruciate ligament

Proteoglycans (PGs) are minor extracellular matrix proteins, and their contributions to the mechanobiology of complex ligaments such as the cranial cruciate ligament (CCL) have not been determined to date. The CCLs are highly susceptible to injuries, and their extracellular matrix comprises higher PGs content than the other major knee ligaments. Hence these characteristics make CCLs an ideal specimen to use as a model in this study. This study addressed the hypothesis that PGs play a vital role in CCL mechanobiology by determining the biomechanical behaviour at low strain rates before and after altering PGs content. For the first time, this study qualitatively investigated the contribution of PGs to key viscoelastic characteristics, including strain rate dependency, hysteresis, creep and stress relaxation, in canine CCLs. Femur-CCL-tibia specimens (n = 6 pairs) were harvested from canine knee joints and categorised into a control group, where PGs were not depleted, and a treated group, where PGs were depleted. Specimens were preconditioned and cyclically loaded to 9.9 N at 0.1, 1 and 10%/min strain rates, followed by creep and stress relaxation tests. Low tensile loads were applied to focus on the toe-region of the stress-strain curves where the non-collagenous extracellular matrix components take significant effect. Biochemical assays were performed on the CCLs to determine PGs and water content. The PG content was ∼19% less in the treated group than in the control group. The qualitative study showed that the stress-strain curves in the treated group were strain rate dependent, similar to the control group. The CCLs in the treated group showed stiffer characteristics than the control group. Hysteresis, creep characteristics (creep strain, creep rate and creep compliance), and stress relaxation values were reduced in the treated group compared to the control group. This study suggests that altering PGs content changes the microstructural organisation of the CCLs, including water molecule contents which can lead to changes in CCL viscoelasticity. The change in mechanical properties of the CCLs may predispose to injury and lead to knee joint osteoarthritis. Future studies should focus on quantitatively identifying the effect of PG on the mechanics of intact knee ligaments across broader demography.

Biglycan has a major role in maintenance of mature tendon mechanics

Decorin and biglycan are two small leucine-rich proteoglycans (SLRPs) that regulate collagen fibrillogenesis and extracellular matrix assembly in tendon. The objective of this study was to determine the individual roles of these molecules in maintaining the structural and mechanical properties of tendon during homeostasis in mature mice. We hypothesized that knockdown of decorin in mature tendons would result in detrimental changes to tendon structure and mechanics while knockdown of biglycan would have a minor effect on these parameters. To achieve this objective, we created tamoxifen-inducible mouse knockdown models targeting decorin or biglycan inactivation. This enables the evaluation of the roles of these SLRPs in mature tendon without the abnormal tendon development caused by conventional knockout models. Contrary to our hypothesis, knockdown of decorin resulted in minor alterations to tendon structure and no changes to mechanics while knockdown of biglycan resulted in broad changes to tendon structure and mechanics. Specifically, knockdown of biglycan resulted in reduced insertion modulus, maximum stress, dynamic modulus, stress relaxation, and increased collagen fiber realignment during loading. Knockdown of decorin and biglycan produced similar changes to tendon microstructure by increasing the collagen fibril diameter relative to wild-type controls. Biglycan knockdown also decreased the cell nuclear aspect ratio, indicating a more spindle-like nuclear shape. Overall, the extensive changes to tendon structure and mechanics after knockdown of biglycan, but not decorin, provides evidence that biglycan plays a major role in the maintenance of tendon structure and mechanics in mature mice during homeostasis.

Decorin evokes reversible mitochondrial depolarization in carcinoma and vascular endothelial cells

Decorin, a small leucine-rich proteoglycan with multiple biological functions, is known to evoke autophagy and mitophagy in both endothelial and cancer cells. Here, we investigated the effects of soluble decorin on mitochondrial homeostasis using live cell imaging and ex vivo angiogenic assays. We discovered that decorin triggers mitochondrial depolarization in triple-negative breast carcinoma, HeLa, and endothelial cells. This bioactivity was mediated by the protein core in a time- and dose-dependent manner and was specific for decorin insofar as biglycan, the closest homolog, failed to trigger depolarization. Mechanistically, we found that the bioactivity of decorin to promote depolarization required the MET receptor and its tyrosine kinase. Moreover, two mitochondrial interacting proteins, mitostatin and mitofusin 2, were essential for downstream decorin effects. Finally, we found that decorin relied on the canonical mitochondrial permeability transition pore to trigger tumor cell mitochondrial depolarization. Collectively, our study implicates decorin as a soluble outside-in regulator of mitochondrial dynamics.

Collagen V deficiency during murine tendon healing results in distinct healing outcomes based on knockdown severity

Tendon function is dependent on proper organization and maintenance of the collagen I tissue matrix. Collagen V is a critical regulator of collagen I fibrils, and while prior studies have shown a negative impact of collagen V deficiency on tendon healing outcomes, these studies are confounded by collagen V deficiency through tendon development. The specific role of collagen V in regulating healing tendon properties is therefore unknown. By using inducible Col5a1 knockdown models and analyzing gene expression, fibril and histological tendon morphology, and tendon mechanical properties, this study defines the isolated role of collagen V through tendon healing. Patellar tendon injury caused large changes in tendon gene expression, and Col5a1 knockdown resulted in dysregulated expression of several genes through tendon healing. Col5a1 knockdown also impacted collagen fibril size and shape without observable changes in scar tissue formation. Surprisingly, heterozygous Col5a1 knockdown resulted in improved stiffness of healing tendons that was not observed with homozygous Col5a1 knockdown. Together, these results present an unexpected and dynamic role of collagen V deficiency on tendon healing outcomes following injury. This work suggests a model of tendon healing in which quasi-static mechanics may be improved through titration of collagen fibril size and shape with modulation of collagen V expression and activity.

Multimodal analysis of the differential effects of cyclic strain on collagen isoform composition, fibril architecture and biomechanics of tissue engineered tendon

Tendon is predominantly composed of aligned type I collagen, but additional isoforms are known to influence fibril architecture and maturation, which contribute to the tendon’s overall biomechanical performance. The role of the less well-studied collagen isoforms on fibrillogenesis in tissue engineered tendons is currently unknown, and correlating their relative abundance with biomechanical changes in response to cyclic strain is a promising method for characterising optimised bioengineered tendon grafts. In this study, human mesenchymal stem cells (MSCs) were cultured in a fibrin scaffold with 3%, 5% or 10% cyclic strain at 0.5 Hz for 3 weeks, and a comprehensive multimodal analysis comprising qPCR, western blotting, histology, mechanical testing, fluorescent probe CLSM, TEM and label-free second-harmonic imaging was performed. Molecular data indicated complex transcriptional and translational regulation of collagen isoforms I, II, III, V XI, XII and XIV in response to cyclic strain. Isoforms (XII and XIV) associated with embryonic tenogenesis were deposited in the formation of neo-tendons from hMSCs, suggesting that these engineered tendons form through some recapitulation of a developmental pathway. Tendons cultured with 3% strain had the smallest median fibril diameter but highest resistance to stress, whilst at 10% strain tendons had the highest median fibril diameter and the highest rate of stress relaxation. Second harmonic generation exposed distinct structural arrangements of collagen fibres in each strain group. Fluorescent probe images correlated increasing cyclic strain with increased fibril alignment from 40% (static strain) to 61.5% alignment (10% cyclic strain). These results indicate that cyclic strain rates stimulate differential cell responses via complex regulation of collagen isoforms which influence the structural organisation of developing fibril architectures.

The Extracellular Matrix Environment of Clear Cell Renal Cell Carcinoma

Simple Summary

The extracellular matrix (ECM) controls fundamental properties of tumors, including growth, blood vessel investment, and invasion. The ECM defines rigidity of tumor tissue and individual ECM proteins have distinct biological effects on tumor cells. This article reviews the composition and biological functions of the ECM of clear cell renal cell carcinoma (ccRCC). The most frequent initiating genetic mutation in ccRCC inactivates the VHL gene, which plays a direct role in organizing the ECM. This is predicted to result in local ECM modification, which promotes the growth of tumor cells and the invasion of blood vessels. Later in tumor growth, connective tissue cells are recruited, which are predicted to produce large amounts of ECM, affecting the growth and invasive behaviors of tumor cells. Strategies to therapeutically control the ECM are under active investigation and a better understanding of the ccRCC ECM will determine the applicability of ECM-modifying drugs to this type of cancer.

Abstract

The extracellular matrix (ECM) of tumors is a complex mix of components characteristic of the tissue of origin. In the majority of clear cell renal cell carcinomas (ccRCCs), the tumor suppressor VHL is inactivated. VHL controls matrix organization and its loss promotes a loosely organized and angiogenic matrix, predicted to be an early step in tumor formation. During tumor evolution, cancer-associated fibroblasts (CAFs) accumulate, and they are predicted to produce abundant ECM. The ccRCC ECM composition qualitatively resembles that of the healthy kidney cortex in which the tumor arises, but there are important differences. One is the quantitative difference between a healthy cortex ECM and a tumor ECM; a tumor ECM contains a higher proportion of interstitial matrix components and a lower proportion of basement membrane components. Another is the breakdown of tissue compartments in the tumor with mixing of ECM components that are physically separated in healthy kidney cortex. Numerous studies reviewed in this work reveal effects of specific ECM components on the growth and invasive behaviors of ccRCCs, and extrapolation from other work suggests an important role for ECM in controlling ccRCC tumor rigidity, which is predicted to be a key determinant of invasive behavior.

Decorin knockdown is beneficial for aged tendons in the presence of biglycan expression

Decorin and biglycan are two major small leucine-rich proteoglycans (SLRPs) present in the tendon extracellular matrix that facilitate collagen fibrillogenesis, tissue turnover, and cell signal transduction. Previously, we demonstrated that knockout of decorin prevented the decline of tendon mechanical properties that are associated with aging. The objective of this study was to determine the effects of decorin and biglycan knockdown on tendon structure and mechanics in aged tendons using tamoxifen-inducible knockdown models. We hypothesized that the knockdown of decorin and compound knockdown of decorin and biglycan would prevent age-related declines in tendon mechanics and structure compared to biglycan knockdown and wild-type controls, and that these changes would be exacerbated as the tendons progress towards geriatric ages. To achieve this objective, we created tamoxifen-inducible mouse knockdown models to target decorin and biglycan gene inactivation without the abnormal tendon development associated with traditional knockout models. Knockdown of decorin led to increased midsubstance modulus and decreased stress relaxation in aged tendons. However, these changes were not sustained in the geriatric tendons. Knockdown in biglycan led to no changes in mechanics in the aged or geriatric tendons. Contrary to our hypothesis, the compound decorin/biglycan knockdown tendons did not resemble the decorin knockdown tendons, but resulted in increased viscoelastic properties in the aged and geriatric tendons. Structurally, knockdown of SLRPs, except for the 570d I-Dcn^-/-/Bgn^-/- group, resulted in alterations to the collagen fibril diameter relative to wild-type controls. Overall, this study identified the differential roles of decorin and biglycan throughout tendon aging in the maintenance of tendon structural and mechanical properties and revealed that the compound decorin and biglycan knockdown phenotype did not resemble the single gene decorin or biglycan models and was detrimental to tendon properties throughout aging.

Impact of High-Molecular-Weight Hyaluronic Acid on Gene Expression in Rabbit Achilles Tenocytes In Vitro

(1) Background: Surgical tendon repair often leads to adhesion formation, leading to joint stiffness and a reduced range of motion. Tubular implants set around sutured tendons might help to reduce peritendinous adhesions. The lubricant hyaluronic acid (HA) is a viable option for optimizing such tubes with the goal of further enhancing the anti-adhesive effect. As the implant degrades over time and diffusion is presumed, the impact of HA on tendon cells is important to know. (2) Methods: A culture medium of rabbit Achilles tenocytes was supplemented with high-molecular-weight (HMW) HA and the growth curves of the cells were assessed. Additionally, after 3, 7 and 14 days, the gene expression of several markers was analyzed for matrix assembly, tendon differentiation, fibrosis, proliferation, matrix remodeling, pro-inflammation and resolution. (3) Results: The addition of HA decreased matrix marker genes, downregulated the fibrosis marker α-SMA for a short time and slightly increased the matrix-remodeling gene MMP-2. Of the pro-inflammatory marker genes, only IL-6 was significantly upregulated. IL-6 has to be kept in check, although IL-6 is also needed for a proper initial inflammation and efficient resolution. (4) Conclusions: The observed effects in vitro support the intended anti-adhesion effect and therefore, the use of HMW HA is promising as a biodegradable implant for tendon repair.

A decellularized flowable placental connective tissue matrix supports cellular functions of human tenocytes in vitro

Purpose

Injectable connective tissue matrices (CTMs) may promote tendon healing, given their minimally invasive properties, structural and biochemical extracellular matrix components, and capacity to fill irregular spaces. The purpose of this study is to evaluate the effects of placental CTMs on the cellular activities of human tenocytes. Decellularization, the removal of cells, cell fragments, and DNA from CTMs, has been shown to reduce the host’s inflammatory response. Therefore, the authors hypothesize that a decellularized CTM will provide a more cell-friendly matrix to support tenocyte functions.

Methods

Three human placental CTMs were selected for comparison: AmnioFill® (A-CTM), a minimally manipulated, non-viable cellular particulate, BioRenew™ (B-CTM), a liquid matrix, and Interfyl® (I-CTM), a decellularized flowable particulate. Adhesion and proliferation were evaluated using cell viability assays and tenocyte migration using a transwell migration assay. Gene expression of tenocyte markers, cytokines, growth factors, and matrix metalloprotease (MMP) in tenocytes were assessed using quantitative polymerase chain reaction.

Results

Although A-CTM supported more tenocyte adhesion, I-CTM promoted significantly more tenocyte proliferation compared with A-CTM and B-CTM. Unlike A-CTM, tenocyte migration was higher in I-CTM than the control. The presence of I-CTM also prevented the loss of tenocyte phenotype, attenuated the expression of pro-inflammatory cytokines, growth factors, and MMP, and promoted the expression of antifibrotic growth factor, TGFβ3.

Conclusion

Compared with A-CTM and B-CTM, I-CTM interacted more favorably with human tenocytes in vitro. I-CTM supported tenocyte proliferation with reduced de-differentiation and attenuation of the inflammatory response, suggesting that I-CTM may support tendon healing and regeneration in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00509-4.

Simple gene signature to assess murine fibroblast polarization

We provide an original multi-stage approach identifying a gene signature to assess murine fibroblast polarization. Prototypic polarizations (inflammatory/fibrotic) were induced by seeded mouse embryonic fibroblasts (MEFs) with TNFα or TGFß1, respectively. The transcriptomic and proteomic profiles were obtained by RNA microarray and LC-MS/MS. Gene Ontology and pathways analysis were performed among the differentially expressed genes (DEGs) and proteins (DEPs). Balb/c mice underwent daily intradermal injections of HOCl (or PBS) as an experimental murine model of inflammation-mediated fibrosis in a time-dependent manner. As results, 1456 and 2215 DEGs, and 289 and 233 DEPs were respectively found in MEFs in response to TNFα or TGFß1, respectively. Among the most significant pathways, we combined 26 representative genes to encompass the proinflammatory and profibrotic polarizations of fibroblasts. Based on principal component analysis, this signature deciphered baseline state, proinflammatory polarization, and profibrotic polarization as accurately as RNA microarray and LC-MS/MS did. Then, we assessed the gene signature on dermal fibroblasts isolated from the experimental murine model. We observed a proinflammatory polarization at day 7, and a mixture of a proinflammatory and profibrotic polarizations at day 42 in line with histological findings. Our approach provides a small-size and convenient gene signature to assess murine fibroblast polarization.

Hybrid Nanofibrous Composites with Anisotropic Mechanics and Architecture for Tendon/Ligament Repair and Regeneration

Rupture of tendons and ligaments (T/L) is a major clinical challenge due to T/L possess anisotropic mechanical properties and hierarchical structures. Here, to imitate these characteristics, an approach is presented by fabricating hybrid nanofibrous composites. First, hybrid fiber-reinforced yarns are fabricated via successively electrospinning poly(L-lactide-co-ε-caprolactone) (PLCL) and gelatin (Ge) nanofibers onto polyethylene terephthalate (PET) fibers to improve biodurability and biocompatibility. Then, by comparing different manufacturing methods, the knitted structure succeeds in simulating anisotropic mechanical properties, even being stronger than natural ligaments, and possessing comfort compliance superior to clinically used ligament advanced reinforcement system (LARS) ligament. Moreover, after inoculation with tendon-derived stem cells and transplantation in vivo, hybrid nanofibrous composites are integrated with native tendons to guide surrounding tissue ingrowth due to the highly interconnected and porous structure. The knitted hybrid nanofibrous composites are also ligamentized and remodeled in vivo to promote tendon regeneration. Specifically, after the use of optimized anisotropic hybrid nanofibrous composites to repair tendon, the deposition of tendon-associated extracellular matrix proteins is more significant. Thus, this study indicates a strategy of manufacturing anisotropic hybrid nanofibrous composites with superior mechanical properties and good histocompatibility for clinical reconstruction.