Elasticity in extracellular matrix 'shape modules' of tendon, cartilage, etc. A sliding proteoglycan-filament model

Joint Hypermobility Syndrome and Membrane Proteins: A Comprehensive Review

Ehlers-Danlos syndromes (EDSs) constitute a heterogeneous group of connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and tissue fragility. Asymptomatic EDSs, joint hypermobility without associated syndromes, EDSs, and hypermobility spectrum disorders are the commonest phenotypes associated with joint hypermobility. Joint hypermobility syndrome (JHS) is a connective tissue disorder characterized by extreme flexibility of the joints, along with pain and other symptoms. JHS can be a sign of a more serious underlying genetic condition, such as EDS, which affects the cartilage, bone, fat, and blood. The exact cause of JHS could be related to genetic changes in the proteins that add flexibility and strength to the joints, ligaments, and tendons, such as collagen. Membrane proteins are a class of proteins embedded in the cell membrane and play a crucial role in cell signaling, transport, and adhesion. Dysregulated membrane proteins have been implicated in a variety of diseases, including cancer, cardiovascular disease, and neurological disorders; recent studies have suggested that membrane proteins may also play a role in the pathogenesis of JHS. This article presents an exploration of the causative factors contributing to musculoskeletal pain in individuals with hypermobility, based on research findings. It aims to provide an understanding of JHS and its association with membrane proteins, addressing the clinical manifestations, pathogenesis, diagnosis, and management of JHS.

Collagen molecular organization preservation in human fascia lata and periosteum after tissue engineering

Large bone defect regeneration remains a major challenge for orthopedic surgeons. Tissue engineering approaches are therefore emerging in order to overcome this limitation. However, these processes can alter some of essential native tissue properties such as intermolecular crosslinks of collagen triple helices, which are known for their essential role in tissue structure and function. We assessed the persistence of extracellular matrix (ECM) properties in human fascia lata (HFL) and periosteum (HP) after tissue engineering processes such as decellularization and sterilization. Harvested from cadaveric donors (N = 3), samples from each HFL and HP were decellularized following five different chemical protocols with and without detergents (D1-D4 and D5, respectively). D1 to D4 consisted of different combinations of Triton, Sodium dodecyl sulfate and Deoxyribonuclease, while D5 is routinely used in the institutional tissue bank. Decellularized HFL tissues were further gamma-irradiated (minimum 25 kGy) in order to study the impact of sterilization on the ECM. Polarized light microscopy (PLM) was used to estimate the thickness and density of collagen fibers. Tissue hydration and content of hydroxyproline, enzymatic crosslinks, and non-enzymatic crosslinks (pentosidine) were semi-quantified with Raman spectroscopy. ELISA was also used to analyze the maintenance of the decorin (DCN), an important small leucine rich proteoglycan for fibrillogenesis. Among the decellularization protocols, detergent-free treatments tended to further disorganize HFL samples, as more thin fibers (+53.7%) and less thick ones (-32.6%) were recorded, as well as less collagen enzymatic crosslinks (-25.2%, p = 0.19) and a significant decrease of DCN (p = 0.036). GAG content was significantly reduced in both tissue types after all decellularization protocols. On the other hand, HP samples were more sensitive to the D1 detergent-based treatments, with more disrupted collagen organization and greater, though not significant loss of enzymatic crosslinks (-37.4%, p = 0.137). Irradiation of D5 HFL samples, led to a further and significant loss in the content of enzymatic crosslinks (-29.4%, p = 0.037) than what was observed with the decellularization process. Overall, the results suggest that the decellularization processes did not significantly alter the matrix. However, the addition of a gamma-irradiation is deleterious to the collagen structural integrity of the tissue.

Extracellular matrix biomechanical roles and adaptation in health and disease

Extracellular matrices (ECMs) are dynamic 3D macromolecular networks that exhibit structural characteristics and composition specific to different tissues, serving various biomechanical and regulatory functions. The interactions between ECM macromolecules such as collagen, elastin, glycosaminoglycans (GAGs), proteoglycans (PGs), fibronectin, and laminin, along with matrix effectors and water, contribute to the unique cellular and tissue functional properties during organ development, tissue homoeostasis, remodeling, disease development, and progression. Cells adapt to environmental changes by adjusting the composition and array of ECM components. ECMs, forming the 3D bioscaffolds of our body, provide mechanical support for tissues and organs and respond to the environmental variables influencing growth and final adult body shape in mammals. Different cell types display distinct adaptations to the respective ECM environments. ECMs regulate biological processes by controlling the diffusion of infections and inflammations, sensing and adapting to external stimuli and gravity from the surrounding habitat, and, in the context of cancer, interplaying with and regulating cancer cell invasion and drug resistance. Alterations in the ECM composition in pathological conditions drive adaptive responses of cells and could therefore result in abnormal cell behavior and tissue dysfunction. Understanding the biomechanical functionality, adaptation, and roles of distinct ECMs is essential for research on various pathologies, including cancer progression and multidrug resistance, which is of crucial importance for developing targeted therapies. In this Viewpoint article, we critically present and discuss specific biomechanical functions of ECMs and regulatory adaptation mechanisms in both health and disease, with a particular focus on cancer progression.

Multimodal and multiscale characterization reveals how tendon structure and mechanical response are altered by reduced loading

Tendons are collagen-based connective tissues where the composition, structure and mechanics respond and adapt to the local mechanical environment. Adaptation to prolonged inactivity can result in stiffer tendons that are more prone to injury. However, the complex relation between reduced loading, structure, and mechanical performance is still not fully understood. This study combines mechanical testing with high-resolution synchrotron X-ray imaging, scattering techniques and histology to elucidate how reduced loading affects the structural properties and mechanical response of rat Achilles tendons on multiple length scales. The results show that reduced in vivo loading leads to more crimped and less organized fibers and this structural inhomogeneity could be the reason for the altered mechanical response. Unloading also seems to change the fibril response, possibly by altering the strain partitioning between hierarchical levels, and to reduce cell density. This study elucidates the relation between in vivo loading, the Achilles tendon nano-, meso‑structure and mechanical response. The results provide fundamental insights into the mechanoregulatory mechanisms guiding the intricate biomechanics, tissue structural organization, and performance of complex collagen-based tissues. STATEMENT OF SIGNIFICANCE: Achilles tendon properties allow a dynamic interaction between muscles and tendon and influence force transmission during locomotion. Lack of physiological loading can have dramatic effects on tendon structure and mechanical properties. We have combined the use of cutting-edge high-resolution synchrotron techniques with mechanical testing to show how reduced loading affects the tendon on multiple hierarchical levels (from nanoscale up to whole organ) clarifying the relation between structural changes and mechanical performance. Our findings set the first step to address a significant healthcare challenge, such as the design of tailored rehabilitations that take into consideration structural changes after tendon immobilization.

Biomaterials and tissue engineering approaches using glycosaminoglycans for tissue repair: Lessons learned from the native extracellular matrix

Glycosaminoglycans (GAGs) are an important component of the extracellular matrix as they influence cell behavior and have been sought for tissue regeneration, biomaterials, and drug delivery applications. GAGs are known to interact with growth factors and other bioactive molecules and impact tissue mechanics. This review provides an overview of native GAGs, their structure, and properties, specifically their interaction with proteins, their effect on cell behavior, and their mechanical role in the ECM. GAGs' function in the extracellular environment is still being understood however, promising studies have led to the development of medical devices and therapies. Native GAGs, including hyaluronic acid, chondroitin sulfate, and heparin, have been widely explored in tissue engineering and biomaterial approaches for tissue repair or replacement. This review focuses on orthopaedic and wound healing applications. The use of GAGs in these applications have had significant advances leading to clinical use. Promising studies using GAG mimetics and future directions are also discussed. STATEMENT OF SIGNIFICANCE: Glycosaminoglycans (GAGs) are an important component of the native extracellular matrix and have shown promise in medical devices and therapies. This review emphasizes the structure and properties of native GAGs, their role in the ECM providing biochemical and mechanical cues that influence cell behavior, and their use in tissue regeneration and biomaterial approaches for orthopaedic and wound healing applications.

Strain-induced collagen denaturation is rate dependent in failure of cerebral arteries

While soft tissues are commonly damaged by mechanical loading, the manifestation of this damage at the microstructural level is not fully understood. Specifically, while rate-induced stiffening has been previously observed in cerebral arteries, associated changes in microstructural damage patterns following high-rate loading are largely undefined. In this study, we stretched porcine middle cerebral arteries to failure at 0.01 and >150 s^-1, both axially and circumferentially, followed by probing for denatured tropocollagen using collagen hybridizing peptide (CHP). We found that collagen fibrils aligned with the loading direction experienced less denaturation following failure tests at high than low rates. Others have demonstrated similar rate dependence in tropocollagen denaturation during soft tissue failure, but this is the first study to quantify this behavior using CHP and to report it for cerebral arteries. These findings may have significant implications for traumatic brain injury and intracranial balloon angioplasty. We additionally observed possible tropocollagen denaturation in vessel layers primarily composed of fibrils transversely aligned to the loading axis. To our knowledge, this is the first observation of collagen denaturation due to transverse loading, but further research is needed to confirm this finding. STATEMENT OF SIGNIFICANCE: Previous work shows that collagen hybridizing peptide (CHP) can be used to identify collagen molecule unfolding and denaturation in mechanically overloaded soft tissues, including the cerebral arteries. But experiments have not explored collagen damage at rates relevant to traumatic brain injury. In this work, we quantified collagen damage in cerebral arteries stretched to failure at both high and low rates. We found that the collagen molecule is less damaged at high than at low rates, suggesting that damage mechanisms of either the collagen molecule or other elements of the collagen superstructure are rate dependent. This work implies that arteries failed at high rates, such as in traumatic brain injury, will have different molecular-level damage patterns than arteries failed at low rates. Consequently, improved understanding of damage characteristics may be expanded in the future to better inform clinically relevant cases of collagen damage such as angioplasty and injury healing.

Engineering Cell-ECM-Material Interactions for Musculoskeletal Regeneration

The extracellular microenvironment regulates many of the mechanical and biochemical cues that direct musculoskeletal development and are involved in musculoskeletal disease. The extracellular matrix (ECM) is a main component of this microenvironment. Tissue engineered approaches towards regenerating muscle, cartilage, tendon, and bone target the ECM because it supplies critical signals for regenerating musculoskeletal tissues. Engineered ECM-material scaffolds that mimic key mechanical and biochemical components of the ECM are of particular interest in musculoskeletal tissue engineering. Such materials are biocompatible, can be fabricated to have desirable mechanical and biochemical properties, and can be further chemically or genetically modified to support cell differentiation or halt degenerative disease progression. In this review, we survey how engineered approaches using natural and ECM-derived materials and scaffold systems can harness the unique characteristics of the ECM to support musculoskeletal tissue regeneration, with a focus on skeletal muscle, cartilage, tendon, and bone. We summarize the strengths of current approaches and look towards a future of materials and culture systems with engineered and highly tailored cell-ECM-material interactions to drive musculoskeletal tissue restoration. The works highlighted in this review strongly support the continued exploration of ECM and other engineered materials as tools to control cell fate and make large-scale musculoskeletal regeneration a reality.

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.

Collagen Network Formation in In Vitro Models of Musculocontractural Ehlers-Danlos Syndrome

Loss-of-function mutations in carbohydrate sulfotransferase 14 (CHST14) cause musculocontractural Ehlers-Danlos syndrome-CHST14 (mcEDS-CHST14), characterized by multiple congenital malformations and progressive connective tissue fragility-related manifestations in the cutaneous, skeletal, cardiovascular, visceral and ocular system. The replacement of dermatan sulfate chains on decorin proteoglycan with chondroitin sulfate chains is proposed to lead to the disorganization of collagen networks in the skin. However, the pathogenic mechanisms of mcEDS-CHST14 are not fully understood, partly due to the lack of in vitro models of this disease. In the present study, we established in vitro models of fibroblast-mediated collagen network formation that recapacitate mcEDS-CHST14 pathology. Electron microscopy analysis of mcEDS-CHST14-mimicking collagen gels revealed an impaired fibrillar organization that resulted in weaker mechanical strength of the gels. The addition of decorin isolated from patients with mcEDS-CHST14 and Chst14^-/- mice disturbed the assembly of collagen fibrils in vitro compared to control decorin. Our study may provide useful in vitro models of mcEDS-CHST14 to elucidate the pathomechanism of this disease.

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.

An ultrastructural 3D reconstruction method for observing the arrangement of collagen fibrils and proteoglycans in the human aortic wall under mechanical load

An insight into changes of soft biological tissue ultrastructures under loading conditions is essential to understand their response to mechanical stimuli. Therefore, this study offers an approach to investigate the arrangement of collagen fibrils and proteoglycans (PGs), which are located within the mechanically loaded aortic wall. The human aortic samples were either fixed directly with glutaraldehyde in the load-free state or subjected to a planar biaxial extension test prior to fixation. The aortic ultrastructure was recorded using electron tomography. Collagen fibrils and PGs were segmented using convolutional neural networks, particularly the ESPNet model. The 3D ultrastructural reconstructions revealed a complex organization of collagen fibrils and PGs. In particular, we observed that not all PGs are attached to the collagen fibrils, but some fill the spaces between the fibrils with a clear distance to the collagen. The complex organization cannot be fully captured or can be severely misinterpreted in 2D. The approach developed opens up practical possibilities, including the quantification of the spatial relationship between collagen fibrils and PGs as a function of the mechanical load. Such quantification can also be used to compare tissues under different conditions, e.g., healthy and diseased, to improve or develop new material models. STATEMENT OF SIGNIFICANCE: The developed approach enables the 3D reconstruction of collagen fibrils and proteoglycans as they are embedded in the loaded human aortic wall. This methodological pipeline comprises the knowledge of arterial mechanics, imaging with transmission electron microscopy and electron tomography, segmentation of 3D image data sets with convolutional neural networks and finally offers a unique insight into the ultrastructural changes in the aortic tissue caused by mechanical stimuli.

Intramural Distributions of GAGs and Collagen vs. Opening Angle of the Intact Porcine Aortic Wall

The heterogeneity and contribution of collagen and elastin to residual stresses have been thoroughly studied, but more recently, glycosaminoglycans (GAGs) also emerged as potential regulators. In this study, the opening angle of aortic rings (an indicator of circumferential residual stresses) and the mural distributions of sulfated GAGs (sGAG), collagen, and elastin were quantified in the ascending, aortic arch and descending thoracic regions of 5- to 6-month-old pigs. The opening angle correlated positively with the aortic ring's mean radius and thickness, with good and moderate correlations respectively. The correlations between the sGAG, collagen, elastin, and collagen:sGAG ratio and the opening angle were evaluated to identify aortic compositional factors that could play roles in regulating circumferential residual stresses. The total collagen:sGAG ratio displayed the strongest correlation with the opening angle (r = - 0.715, p < 0.001), followed by the total sGAG content which demonstrated a good correlation (r = 0.623, p < 0.001). Additionally, the intramural gradients of collagen, sGAG and collagen:sGAG correlated moderately with the opening angle. We propose that, in addition to the individual role sGAG play through their content and intramural gradient, the interaction between collagen and sGAG should be considered when evaluating circumferential residual stresses in the aorta.

Ehlers Danlos Syndrome with Glycosaminoglycan Abnormalities

Ehlers-Danlos syndrome (EDS) is a genetically and clinically heterogeneous group of connective tissue disorders that typically present with skin hyperextensibility, joint hypermobility, and tissue fragility. The major cause of EDS appears to be impaired biosynthesis and enzymatic modification of collagen. In this chapter, we discuss two types of EDS that are associated with proteoglycan abnormalities: spondylodysplastic EDS and musculocontractural EDS. Spondylodysplastic EDS is caused by pathogenic variants in B4GALT7 or B3GALT6, both of which encode key enzymes that initiate glycosaminoglycan synthesis. Musculocontractural EDS is caused by mutations in CHST14 or DSE, both of which encode enzymes responsible for the post-translational biosynthesis of dermatan sulfate. The clinical and molecular characteristics of both types of EDS are described in this chapter.

Contribution of glycosaminoglycans to the structural and mechanical properties of tendons - A multiscale study

Tendinopathy of the Achilles tendon contributes to a large range of disorders, including mechanical damage and degenerative diseases. Glycosaminoglycans (GAGs), are thought to play a role in the mechanical strength of tendons by forming cross-links between collagen molecules and allowing the transmission of forces between fibrils. This study assessed the response of GAG-depleted tendons to damage induced by fatigue loading, investigating the mechanical damage (stiffness, hysteresis and maximum load), macrostructural changes (tenocyte morphology, fiber anisotropy and waviness) assessed by confocal imaging and nanostructural changes (fibril D-periodicity length) within the same non-viable intact tendons. Changes in fiber waviness and tenocyte shape are strongly correlated to mechanical and nano-structural (D-periodicity elongation) properties in both Control and GAG-depleted tendons. This study supports firstly, the vital role GAGs play as mechanical connectors facilitating the load transfer between the fibrils and their hydrophilic role in facilitating fibril sliding. Secondly, that observed changes in tenocyte shape and fiber waviness correlate with tendon stiffness and other mechanical profiles.

Small leucine-rich proteoglycans in physiological and biomechanical function of bone

•

Proteoglycans (PGs) and glycosaminoglycans (GAGs) play vital roles in key signaling pathways to regulate bone homeostasis.

•

The highly negatively charged GAGs are crucial in retaining bound water and modulating mechanical properties of bone.

•

Age-related changes of PGs, GAGs, and bound water contribute to deterioration of bone quality during aging.

Proteoglycans (PGs) contain long unbranched glycosaminoglycan (GAG) chains attached to core proteins. In the bone extracellular matrix, PGs represent a class of non-collagenous proteins, and have high affinity to minerals and collagen. Considering the highly negatively charged character of GAGs and their interfibrillar positioning interconnecting with collagen fibrils, PGs and GAGs play pivotal roles in maintaining hydrostatic and osmotic pressure in the matrix. In this review, we will discuss the role of PGs, especially the small leucine-rich proteoglycans, in regulating the bioactivity of multiple cytokines and growth factors, and the bone turnover process. In addition, we focus on the coupling effects of PGs and GAGs in the hydration status of bone extracellular matrix, thus modulating bone biomechanical properties under physiological and pathological conditions.

The influence of glycosaminoglycan proteoglycan side chains on tensile force transmission and the nanostructural properties of Achilles tendons

This study investigates the nanostructural mechanisms that lie behind load transmission in tendons and the role of glycosaminoglycans (GAGs) in the transmission of force in the tendon extracellular matrix. The GAGs in white New Zealand rabbit Achilles tendons were enzymatically depleted, and the tendons subjected to cyclic loading at 6% strain for up to 2 hr. A nanoscale morphometric assessment of fibril deformation under strain was linked with the decline in the tendon macroscale mechanical properties. An atomic force microscope (AFM) was employed to characterize the D-periodicity within and between fibril bundles (WFB and BFB, respectively). By the end of the second hour of the applied strain, the WFB and BFB D-periodicities had significantly increased in the GAG-depleted group (29% increase compared with 15% for the control, p < .0001). No statistically significant differences were found between WFB and BFB D-periodicities in either the control or GAG-depleted groups, suggesting that mechanical load in Achilles tendons is uniformly distributed and fairly homogenous among the WFB and BFB networks. The results of this study have provided evidence of a cycle-dependent mechanism of damage accumulation. The accurate quantification of fibril elongation (measured as the WFB and BFB D-periodicity lengths) in response to macroscopic applied strain has assisted in assessing the complex structure-function relationship in Achilles tendon.

Mechanistic Insights into the Structural Stability of Collagen-Containing Biomaterials Such as Bones and Cartilage

Structural stability of various collagen-containing biomaterials such as bones and cartilage is still a mystery. Despite the spectroscopic development of several decades, the detailed mechanism of collagen interaction with citrate in bones and glycosaminoglycans (GAGs) in the cartilage extracellular matrix (ECM) in its native state is unobservable. We present a significant advancement to probe the collagen interactions with citrate and GAGs in the ECM of native bones and cartilage along with specific/non-specific interactions inside the collagen assembly at the nanoscopic level through natural-abundance dynamic nuclear polarization-based solid-state nuclear magnetic resonance spectroscopy. The detected molecular-level interactions between citrate-collagen and GAG-collagen inside the native bone and cartilage matrices and other backbone and side-chain interactions in the collagen assembly are responsible for the structural stability and other biomechanical properties of these important classes of biomaterials.

Spatiotemporal changes in mechanical matrisome components of the human ovary from prepuberty to menopause

STUDY QUESTION

How do elastic matrisome components change during the lifetime of the human ovary?

SUMMARY ANSWER

The deposition and remodeling of mechanical matrisome components (collagen, elastin, elastin microfibril interface-located protein 1 (EMILIN-1), fibrillin-1 and glycosaminoglycans (GAGs)) that play key roles in signaling pathways related to follicle activation and development evolve in an age- and follicle stage-related manner.

WHAT IS KNOWN ALREADY

The mechanobiology of the human ovary and dynamic reciprocity that exists between ovarian cells and their microenvironment is of high importance. Indeed, while the localization of primordial follicles in the collagen-rich ovarian cortex offers a rigid physical environment that supports follicle architecture and probably plays a role in their survival, ovarian extracellular matrix (ECM) stiffness limits follicle expansion and hence oocyte maturation, maintaining follicles in their quiescent state. As growing follicles migrate to the medulla of the ovary, they encounter a softer, more pliant ECM, allowing expansion and development. Thus, changes in the rigidity of the ovarian ECM have a direct effect on follicle behavior. Evidence supporting a role for the physical environment in follicle activation was provided in clinical practice by ovarian tissue fragmentation, which promoted actin polymerization and disrupted ovarian Hippo signaling, leading to increased expression of downstream growth factors, promotion of follicle growth and generation of mature oocytes.

STUDY DESIGN, SIZE, DURATION

We investigated quantitative spatiotemporal changes in collagen, elastin, EMILIN-1, fibrillin-1 and GAGs from prepuberty to menopause, before conducting a closer analysis of the ECM surrounding follicles, from primordial to secondary stages, in both prepubertal and tissue from women of reproductive age. The study included ovarian tissue (cortex) from 68 patients of different ages: prepubertal (n = 16; mean age [±SD]=8 ± 2 years); reproductive (n = 21; mean age [±SD]=27 ± 4 years); menopausal with estrogen-based HRT (n = 7; mean age [±SD]=58 ± 4 years); and menopausal without HRT (n = 24; mean age [±SD]=61 ± 5 years).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Quantitative investigations of collagen and GAG deposition in ovarian tissue throughout a woman's lifetime were conducted by analyzing brightfield images. Characteristic features of collagen fiber content were based on polarized light microscopy, since polarized light changes with fiber thickness. To evaluate the deposition and distribution of elastin, fibrillin-1 and EMILIN-1, multiplex immunofluorescence was used on at least three sections from each patient. Image processing and tailored bioinformatic analysis were applied to enable spatiotemporal quantitative evaluation of elastic system component deposition in the human ovary over its lifetime.

MAIN RESULTS AND THE ROLE OF CHANCE

While collagen levels increased with age, fibrillin-1 and EMILIN-1 declined. Interestingly, collagen and elastin reached their peak in reproductive-age women compared to prepubertal (P < 0.01; P = 0.262) and menopausal subjects with (P = 0.706; P < 0.01) and without (P = 0.987; P = 0.610) HRT, indicating a positive impact of secreted estrogen and hormone treatment on collagen and elastin preservation. Interestingly, HRT appears to affect elastin presence in ovarian tissue, since a significantly higher (P < 0.05) proportion of elastin was detected in biopsies from menopausal women taking HRT compared to those not. Higher GAG levels were found in adult ovaries compared to prepubertal ovaries (P < 0.05), suggesting changes in tissue ultrastructure and elasticity with age. In this context, elevated GAG values are suspected to participate in hampering formation of the fibrillin-1 network (r = -0.2475; P = 0.04687), which explains its decline over time. This decline partially accounts for the decrease in EMILIN-1 (r = 0.4149; P = 0.00059). Closer examination of the ECM surrounding follicles from the primordial to the secondary stage, both before and after puberty, points to high levels of mechanical stress placed on prepubertal follicles compared to the more compliant ECM around reproductive-age follicles, as suggested by the higher collagen levels and lower elastin content detected mainly around primordial (P < 0.0001; P < 0.0001, respectively) and primary (P < 0.0001; P < 0.001, respectively) follicles. Such a stiff niche is nonpermissive to prepubertal follicle activation and growth, and is more inclined to quiescence.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

The duration and form of administered HRT were not considered when studying the menopausal patient group undergoing treatment. Moreover, we cannot exclude interference from other nongynecological medications taken by the study patients on ovarian ECM properties since there is no information in the literature describing the impact of each medication on the ECM. Finally, since the ECM is by definition a very heterogeneous meshwork of proteins, the use of two-dimensional histology could be a limitation. Single time points on fixed tissues could also present limitations, since following ovary dynamics from prepuberty to menopause in the same patient is not feasible.

WIDER IMPLICATIONS OF THE FINDINGS

From a biomechanical perspective, our study revealed important changes to ECM properties dictating the mechanical features of ovarian tissue, in line with the existing literature. Our findings pave the way for possible therapeutic targets at the ECM level in the context of female fertility and ovarian rejuvenation, such as mechanical stimulation, antifibrotic treatments, and prevention or reversion of elastic ECM degradation. Our study also sheds light on the follicle-specific ECM composition that is dependent on follicle stage and age. These data will prove very useful in designing biomimetic scaffolds and tissue-engineered models like the artificial ovary. Indeed, they emphasize the importance of encapsulating each type of isolated follicle in an appropriate biomaterial that must replicate the corresponding functional perifollicular ECM and respect ovarian tissue heterogeneity in order to guarantee its biomimicry.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS) (C.A.A. is an FRS-FNRS research associate; grant 5/4/150/5 awarded to M.M.D.) and the Université Catholique de Louvain (PhD grant 'Coopération au développement' awarded to E.O.). None of the authors have any competing interests to declare.

Proteoglycans in the periodontium: A review with emphasis on specific distributions, functions, and potential applications

Proteoglycans (PGs) are largely glycosylated proteins, consisting of a linkage sugar, core proteins, and glycosaminoglycans (GAGs). To date, more than 40 kinds of PGs have been identified, and they can be classified as intracellular, cell surface, pericellular, and extracellular PGs according to cellular locations. To illustrate, extracellular PGs are known for regulating the homeostasis of the extracellular matrix; cell-surface PGs play a role in mediating cell adhesion and binding various growth factors. In the field of periodontology, PGs are implicated in cellular proliferation, migration, adhesion, contractility, and anoikis, thereby exerting a profound influence on periodontal tissue development, wound repair, the immune response, biomechanics, and pathological process. Additionally, the expression patterns of some PGs are dynamic and cell-specific. Therefore, determining the roles and spatial-temporal expression patterns of PGs in the periodontium could shed light on treatments for wound healing, tissue regeneration, periodontitis, and gingival overgrowth. In this review, close attention is paid to the distributions, functions, and potential applications of periodontal PGs. Related genetically modified animal experiments and involved signal transduction cascades are summarized for improved understanding of periodontal PGs. To date, however, there is a large amount of speculation on this topic that requires rigorous experiments for validation.

Understanding cellular and molecular mechanisms of pathogenesis of diabetic tendinopathy

There is accumulating evidence of an increased incidence of tendon disorders in people with diabetes mellitus. Diabetic tendinopathy is an important cause of chronic pain, restricted activity, and even tendon rupture in individuals. Tenocytes and tendon stem/progenitor cells (TSPCs) are the dominant cellular components associated with tendon homeostasis, maintenance, remodeling, and repair. Some previous studies have shown alterations in tenocytes and TSPCs in high glucose or diabetic conditions that might cause structural and functional variations in diabetic tendons and even accelerate the development and progression of diabetic tendinopathy. In this review, the biomechanical properties and histopathological changes in diabetic tendons are described. Then, the cellular and molecular alterations in both tenocytes and TSPCs are summarized, and the underlying mechanisms involved are also analyzed. A better understanding of the underlying cellular and molecular pathogenesis of diabetic tendinopathy would provide new insight for the exploration and development of effective therapeutics.

A damage model for collagen fibres with an application to collagenous soft tissues

We propose a mechanical model to account for progressive damage in collagen fibres within fibrous soft tissues. The model has a similar basis to the pseudoelastic model that describes the Mullins effect in rubber but it also accounts for the effect of cross-links between collagen fibres. We show that the model is able to capture experimental data obtained from rat tail tendon fibres, and the combined effect of damage and collagen cross-links is illustrated for a simple shear test. The proposed three-dimensional framework allows a straightforward implementation in finite-element codes, which are needed to analyse more complex boundary-value problems for soft tissues under supra-physiological loading or tissues weakened by disease.

Towards extracellular matrix normalization for improved treatment of solid tumors

It is currently challenging to eradicate cancer. In the case of solid tumors, the dense and aberrant extracellular matrix (ECM) is a major contributor to the heterogeneous distribution of small molecule drugs and nano-formulations, which makes certain areas of the tumor difficult to treat. As such, much research is devoted to characterizing this matrix and devising strategies to modify its properties as a means to facilitate the improved penetration of drugs and their nano-formulations. This contribution presents the current state of knowledge on the composition of normal ECM and changes to ECM that occur during the pathological progression of cancer. It also includes discussion of strategies designed to modify the composition/properties of the ECM as a means to enhance the penetration and transport of drugs and nano-formulations within solid tumors. Moreover, a discussion of approaches to image the ECM, as well as ways to monitor changes in the ECM as a function of time are presented, as these are important for the implementation of ECM-modifying strategies within therapeutic interventions. Overall, considering the complexity of the ECM, its variability within different tissues, and the multiple pathways by which homeostasis is maintained (both in normal and malignant tissues), the available literature - while promising - suggests that improved monitoring of ECM remodeling in vivo is needed to harness the described strategies to their full potential, and match them with an appropriate chemotherapy regimen.

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

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

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

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

A microstructural model of cross-link interaction between collagen fibrils in the human cornea

We propose a simplified micromechanical model of the fibrous reinforcement of the corneal tissue. We restrict our consideration to the structural function of the collagen fibrils located in the stroma and disregard the other all-important components of the cornea. The reinforcing structure is modelled with two sets of parallel fibrils, connected by transversal bonds within the single fibril family (inter-cross-link) and across the two families (intra-cross-link). The particular design chosen for this ideal structure relies on the fact that its ability to sustain loads is dependent on the degree of the cross-link and, therefore, on the density and stiffness of the bonds. We analyse the mechanical response of the system according to the type of interlacing and on the stiffness of fibres and bonds. Results show that the weakening of transversal bonds is associated with a marked increase of the deformability of the system. In particular, the deterioration of transversal bonds due to mechanical, chemical or enzymatic reasons can justify the loss of stiffness of the stromal tissue resulting in localized thinning and bulging typically observed in keratoconus corneas. This article is part of the theme issue 'Rivlin's legacy in continuum mechanics and applied mathematics'.

Molecular-level collagen damage explains softening and failure of arterial tissues: A quantitative interpretation of CHP data with a novel elasto-damage model

The present experimental-modelling study provides a quantitative interpretation of mechanical data and damage measurements obtained from collagen hybridizing peptide (CHP) techniques on overstretched sheep cerebral arterial tissues. To this aim, a structurally-motivated constitutive model is developed in the framework of continuum damage mechanics. The model includes two internal variables for describing the effects of collagen triple-helical unfolding via interstrand delamination: one governs plastic mechanisms in collagen fibers, leading to a stress softening response of the tissue at the macroscale; the other one describes the loss of fiber structural integrity, leading to tissue final failure. The proposed model is calibrated using the obtained mechanical experimental data, showing excellent fitting capabilities. The predicted evolution of internal variables agree well with independent measurements of molecular-level CHP-based damage data, obtaining an independent a posteriori validation of damage predictions. Moreover, available data on inelastic tissue elongation following supraphysiological loads are successfully reproduced. These outcomes further the hypothesis that the accumulation of interstrand delamination is a primary cause for the evolution of inelastic mechanisms in tissues, and in particular of stress softening up to failure.

Short communication: Milk basic protein promotes proliferation and inhibits differentiation of mouse chondrogenic ATDC5 cells

It has been reported that the intake of milk basic protein (MBP) increases bone density by promoting bone formation and suppressing bone resorption. However, few studies have been done on MBP in cartilage, the tissue adjacent to bone. We therefore investigated the effect of MBP on a chondrocyte cell line, ATDC5. In a proliferative assay using the WST-1 method, the addition of 10, 100, and 1,000 µg/mL of MBP to ATDC5 cells significantly increased the cell number by about 1.2-, 1.5-, and 1.7-fold, respectively, compared with the control cells. The cell cycle analysis using flow-cytometry revealed that the proportion of S- and G₂/M-phase cells was increased but that of G₀/G₁ phase was decreased in a dose-dependent manner with MBP addition. We measured the alkaline phosphatase activity of MBP-treated ATDC5 cells to examine the differentiation stage of the cells. Alkaline phosphatase activity was suppressed in a dose-dependent manner with MBP addition and was especially drastic at higher doses of MBP (100 and 1,000 µg/mL). The Alizarin Red S staining intensity, the indicator for calcification of cells, was lower in the MBP-treated (100 µg/mL) cells than in nontreated control cells. In the reverse-transcription PCR experiment, the mRNA level of SRY-box containing gene 9 (Sox9) and type II collagen (Col2) was significantly increased in the MBP-treated cells compared with the control cells. A significant decrease of the mRNA level of runt-related transcription factor 2 (Runx2) and type X collagen (Col10) was also observed in the MBP-treated cells. These results suggested that MBP promoted the proliferation of chondrocytes by suppressing their differentiation toward calcification.

Contributions of Glycosaminoglycans to Collagen Fiber Recruitment in Constitutive Modeling of Arterial Mechanics

The contribution of glycosaminoglycans (GAGs) to the biological and mechanical functions of biological tissue has emerged as an important area of research. GAGs provide structural basis for the organization and assembly of extracellular matrix (ECM). The mechanics of tissue with low GAG content can be indirectly affected by the interaction of GAGs with collagen fibers, which have long been known to be one of the primary contributors to soft tissue mechanics. Our earlier study showed that enzymatic GAG depletion results in straighter collagen fibers that are recruited at lower levels of stretch, and a corresponding shift in earlier arterial stiffening (Mattson et al., 2016). In this study, the effect of GAGs on collagen fiber recruitment was studied through a structure-based constitutive model. The model incorporates structural information, such as fiber orientation distribution, content, and recruitment of medial elastin, medial collagen, and adventitial collagen fibers. The model was first used to study planar biaxial tensile stress-stretch behavior of porcine descending thoracic aorta. Changes in elastin and collagen fiber orientation distribution, and collagen fiber recruitment were then incorporated into the model in order to predict the stress-stretch behavior of GAG depleted tissue. Our study shows that incorporating early collagen fiber recruitment into the model predicts the stress-stretch response of GAG depleted tissue reasonably well (rms = 0.141); considering further changes of fiber orientation distribution does not improve the predicting capability (rms = 0.149). Our study suggests an important role of GAGs in arterial mechanics that should be considered in developing constitutive models.

The Impact of Post Activation Potentiation on Achilles Tendon Stiffness, Elasticity and Thickness among Basketball Players

The purpose of this study is to examine and further understand the effects of post activation potentiation on Achilles tendon (AT) thickness, elasticity and stiffness among basketball players. Basketball is one of the world’s most popular and widely viewed sports. One of the main factors which athletes depend on during their performance is elastic energy coming straight from the AT. Contractile activity increases the muscular force and is known in science as post activation potentiation (PAP). Twelve basketball players (aged 21.3 ± 2.1 years) from the first Polish league took part in this study. The PAP session consisted of single repetitions of the squat with loads corresponding to 60%, 70%, 80%, 90% and 100% of 1 repetition maximum (RM). The measurement method for AT thickness was ultrasonography and for the elasticity and stiffness was myotonometry. The measurements were taken before and immediately after PAP training session. Obtained results: AT stiffness increased significantly from the baseline post exercise, while AT thickness and elasticity decreased after the physical effort. The exercise in PAP caused significant changes in stiffness, elasticity and thickness of the AT.

Bioinspired Load-Bearing Hydrogel Based on Engineered Sea Anemone Skin-Derived Collagen-Like Protein

With the help of recombinant DNA technology, many protein candidates have been investigated and engineered for biomaterial applications. Particularly, several repeat sequences with unique secondary structures have been selected as minimal building blocks for biosynthesis to improve the mechanical properties of biomaterials. However, most of these structural proteins have been limited to silk, elastin, collagen, and resilin for decades. In the present work, new repeat sequence found in sea anemone are characterized and biosynthesized into a recombinant protein (named anegen) for potential use as a load-bearing biomaterial. Because its repeat sequence unit has a unique polyproline II structure, which is prevalently found in the triple-helix of collagen, it is assumed to be a promising structural protein candidate that can provide conformational flexibility and elasticity. Because anegen has ≈10% tyrosine residues, inspiration is taken from di-tyrosine crosslinking in the hinge structures of insects, which can be initiated by light activation. It is found that the anegen hydrogel shows higher mechanical properties than a gelatin hydrogel and endures a compression series without deformation. Moreover, the mechanical properties of the anegen hydrogel are controllable through different crosslinking conditions in a wide range of material applications. Importantly, the anegen hydrogel exhibited suitable cell retainability and cell morphology as an implantable biomaterial. Thus, based on its mechanical properties and biocompatibility, the anegen hydrogel can be used as a potential load-bearing and cell-loading scaffolding biomaterial in the tissue and biomedical engineering fields.

The effect of the carbodiimide cross-linker on the structural and biocompatibility properties of collagen-chondroitin sulfate electrospun mat

BACKGROUND

Collagen and chondroitin sulfate (CS) are an essential component of the natural extracellular matrix (ECM) of most tissues. They provide the mechanical stability to cone the compressive forces in ECM. In tissue engineering, electrospun nanofibrous scaffolds prepared by electrospinning technique have emerged as a suitable candidate to imitate natural ECM functions. Cross-linking with 1-ethyl-3-(3-dimethyl-aminopropyl)-1-carbodiimide hydrochloride/N-hydroxy succinimide can overcome the weak mechanical integrity of the engineered scaffolds in addition to the increased degradation stability under physiological conditions.

MATERIALS AND METHODS

This study has synthesized nanofibrous collagen-CS scaffolds by using the electrospinning method.

RESULTS

The results have shown that incorporation of CS in higher concentration, along with 1-ethyl-3-(3-dimethyl-aminopropyl)-1-carbodiimide hydrochloride/N-hydroxy succinimide, enhanced mechanical stability. Scaffolds showed more resistance to collagenase digestion. Fabricated scaffolds showed biocompatibility in corneal epithelial cell attachment.

CONCLUSION

These results demonstrate that cross-linked electrospun CO-CS mats exhibited a uniform nanofibrous and porous structure, especially for lower concentration of the cross-linker and may be utilized as an alternative effective substrate in tissue engineering.

Intensity-dependent effect of treadmill running on rat Achilles tendon

It is understood that mechanical loading may affect tendon properties. However, how different mechanical loading conditions may affect tendons remains unknown. The present study aimed to investigate the effect of treadmill running at various intensities on rat Achilles tendon. A total of 18 male Wistar rats were randomly assigned to one of three groups: Control (CON), medium-intensity running (MIR), and high-intensity running (HIR). Following 8 weeks of treadmill running protocols, all Achilles tendons were harvested for histological observation and gene expression analysis. Significant morphological changes were observed with regular and large diameter collagen fibrils in the MIR group, whereas irregular and small diameter collagen fibrils were observed in the HIR group. Collagen type I was significantly upregulated in the MIR group compared with the CON group, and downregulated in the HIR group compared with the CON or MIR groups (P<0.05). However, collagen type III was significantly upregulated in the HIR group in comparison with the CON or MIR groups (P<0.05). Furthermore, the expression of matrix metallopeptidase-13 was significantly increased in the MIR and HIR groups compared with the CON group (P<0.05). The expression of tissue inhibitor of metalloproteinases-1 was increased in the MIR group compared with the CON group, but decreased in the HIR group compared with the CON and MIR groups (P<0.05). Additionally, decorin expression was significantly higher in the MIR group compared with the CON group, and significantly decreased in the HIR group compared with the CON or MIR groups (P<0.05). A converse pattern of changes in biglycan expression was identified among the three groups. Aggrecan expression was significantly higher in the HIR group compared with the CON or MIR groups (P<0.05). These findings indicated that moderate exercise may induce increased collagen synthesis and organize regular and large collagen fibers, thus benefiting the Achilles tendon. However, overuse during exercise may result in collagen degradation and disturbance, which predisposes individuals to injury.

Fatigue of soft fibrous tissues: Multi-scale mechanics and constitutive modeling

In recent experimental studies a possible damage mechanism of collagenous tissues mainly caused by fatigue was disclosed. In this contribution, a multi-scale constitutive model ranging from the tropocollagen (TC) molecule level up to bundles of collagen fibers is proposed and utilized to predict the elastic and inelastic long-term tissue response. Material failure of collagen fibrils is elucidated by a permanent opening of the triple helical collagen molecule conformation, triggered either by overstretching or reaction kinetics of non-covalent bonds. This kinetics is described within a probabilistic framework of adhesive detachments of molecular linkages providing collagen fiber integrity. Both intramolecular and interfibrillar linkages are considered. The final constitutive equations are validated against recent experimental data available in literature for both uniaxial tension to failure and the evolution of fatigue in subsequent loading cycles. All material parameters of the proposed model have a clear physical interpretation.

STATEMENT OF SIGNIFICANCE

Irreversible changes take place at different length scales of soft fibrous tissues under supra-physiological loading and alter their macroscopic mechanical properties. Understanding the evolution of those histologic pathologies under loading and incorporating them into a continuum mechanical framework appears to be crucial in order to predict long-term evolution of various diseases and to support the development of tissue engineering.

Dendritic Cell Migration to Skin-Draining Lymph Nodes Is Controlled by Dermatan Sulfate and Determines Adaptive Immunity Magnitude

For full activation of naïve adaptive lymphocytes in skin-draining lymph nodes (LNs), presentation of peptide:MHC complexes by LN-resident and skin-derived dendritic cells (DCs) that encountered antigens (Ags) is an absolute prerequisite. To get to the nearest draining LN upon intradermal immunization, DCs need to migrate from the infection site to the afferent lymphatics, which can only be reached by traversing a collagen-dense network located in the dermis of the skin through the activity of proteolytic enzymes. Here, we show that mice with altered collagen fibrillogenesis resulting in thicker collagen fibers in the skin display a reduced DC migration to the draining LN upon immune challenge. Consequently, the initiation of the cellular and humoral immune response was diminished. Ag-specific CD8+ and CD4+ T cells as well as Ag-specific germinal center B cells and serum immunoglobulin levels were significantly decreased. Hence, we postulate that alterations to the production of extracellular matrix, as seen in various connective tissue disorders, may in the end affect the qualitative outcome of adaptive immunity.

Proteomic Analysis of Nucleus Pulposus Cell-derived Extracellular Matrix Niche and Its Effect on Phenotypic Alteration of Dermal Fibroblasts

Reconstituting biomimetic matrix niche in vitro and culturing cells at the cell niche interface is necessary to understand the effect and function of the specific matrix niche. Here we attempted to reconstitute a biomimetic extracellular matrix (ECM) niche by culturing nucleus pulposus cells (NPCs) in a collagen microsphere system previously established and allowing them to remodel the template matrix. The reconstituted NPC-derived complex ECM was obtained after decellularization and the composition of such niche was evaluated by proteomic analysis. Results showed that a complex acellular matrix niche consisting of ECM proteins and cytoskeletal proteins by comparing with the template collagen matrix starting material. In order to study the significance of the NPC-derived matrix niche, dermal fibroblasts were repopulated in such niche and the phenotypes of these cells were changed, gene expression of collagen type II and CA12 increased significantly. A biomimetic NPC-derived cell niche consisting of complex ECM can be reconstituted in vitro, and repopulating such matrix niche with fibroblasts resulted in changes in phenotypic markers. This work reports a 3D in vitro model to study cell niche factors, contributing to future understanding of cellular interactions at the cell-niche interface and rationalized scaffold design for tissue engineering.

Relationship between extensibility and collagen expression in immobilized rat skeletal muscle

INTRODUCTION

This study investigated longitudinal changes in muscle extension and collagen expression in an immobilized rat soleus muscle, and assessed the relationship between both elements.

METHODS

Soleus muscles of the control and immobilization groups (1, 2, 4, 8, and 12 weeks) were used for analysis of muscle extensibility and collagen expression.

RESULTS

The slope value/physiological cross-sectional area (PCSA; a parameter for muscle extensibility) and hydroxyproline (a parameter for collagen expression) were significantly higher in the immobilization group than in the control group for all experimental time points. In the immobilization group, both factors were significantly higher at 4, 8, and 12 weeks than at 1 and 2 weeks after immobilization. A significant positive correlation was observed between the slope value/PCSA and hydroxyproline expression.

DISCUSSION

The present study indicated that a decrease in muscle extensibility depended on collagen overexpression in immobilized rat soleus muscles. Muscle Nerve 57: 672-678, 2018.

Removal of dentin non-collagenous structures results in the unraveling of microfibril bundles in collagen type I

AIMS

The structural organization of collagen from mineralized tissues, such as dentin and bone, has been a topic of debate in the recent literature. Recent reports have presented novel interpretations of the complexity of collagen type I at different hierarchical levels and in different tissues. Here, we investigate the nanostructural organization of demineralized dentin collagen following the digestion of non-collagenous components with a trypsin enzyme.

MATERIALS AND METHODS

Dentin specimens were obtained from healthy third-molars, cut into small cubes, and polished down to 1 µm roughness. Samples were then demineralized with 10% citric acid for 2 min. Selected specimens were further treated with a solution containing 1 mg/ml trypsin for 48 hours at 37 °C (pH 7.9-9.0). Both untreated and trypsin digested samples were analyzed using SDS-PAGE, Field Emission Scanning Electron Microscopy (FE-SEM), and nanoindentation, where surface hardness and creep properties were compared before and after treatments.

RESULTS

FE-SEM images of demineralized dentin showed the banded morphology of D-periodical collagen type I, which upon enzymatic digestion with trypsin appeared to dissociate longitudinally, consistently unraveling ~20 nm structures (microfibril bundles). Such nanoscale structures, to the best of our knowledge, have not been characterized in dentin previously. Mechanical characterization via nanoindentation showed that the unraveling of such microfibril bundles affected the creep displacement and creep rate of demineralized dentin.

CONCLUSION

In summary, our results provide novel evidence of the organization of collagen type I from dentin, which may have important implications for the interaction of dental materials with the organic dentin matrix and the mechanical properties of mineralized tissues.

Dentin on the nanoscale: Hierarchical organization, mechanical behavior and bioinspired engineering

OBJECTIVE

Knowledge of the structural organization and mechanical properties of dentin has expanded considerably during the past two decades, especially on a nanometer scale. In this paper, we review the recent literature on the nanostructural and nanomechanical properties of dentin, with special emphasis in its hierarchical organization.

METHODS

We give particular attention to the recent literature concerning the structural and mechanical influence of collagen intrafibrillar and extrafibrillar mineral in healthy and remineralized tissues. The multilevel hierarchical structure of collagen, and the participation of non-collagenous proteins and proteoglycans in healthy and diseased dentin are also discussed. Furthermore, we provide a forward-looking perspective of emerging topics in biomaterials sciences, such as bioinspired materials design and fabrication, 3D bioprinting and microfabrication, and briefly discuss recent developments on the emerging field of organs-on-a-chip.

RESULTS

The existing literature suggests that both the inorganic and organic nanostructural components of the dentin matrix play a critical role in various mechanisms that influence tissue properties.

SIGNIFICANCE

An in-depth understanding of such nanostructural and nanomechanical mechanisms can have a direct impact in our ability to evaluate and predict the efficacy of dental materials. This knowledge will pave the way for the development of improved dental materials and treatment strategies.

CONCLUSIONS

Development of future dental materials should take into consideration the intricate hierarchical organization of dentin, and pay particular attention to their complex interaction with the dentin matrix on a nanometer scale.

Glycosaminoglycans contribute to extracellular matrix fiber recruitment and arterial wall mechanics

Elastic and collagen fibers are well known to be the major load-bearing extracellular matrix (ECM) components of the arterial wall. Studies of the structural components and mechanics of arterial ECM generally focus on elastin and collagen fibers, and glycosaminoglycans (GAGs) are often neglected. Although GAGs represent only a small component of the vessel wall ECM, they are considerably important because of their diverse functionality and their role in pathological processes. The goal of this study was to study the mechanical and structural contributions of GAGs to the arterial wall. Biaxial tensile testing was paired with multiphoton microscopic imaging of elastic and collagen fibers in order to establish the structure-function relationships of porcine thoracic aorta before and after enzymatic GAG removal. Removal of GAGs results in an earlier transition point of the nonlinear stress-strain curves [Formula: see text]. However, stiffness was not significantly different after GAG removal treatment, indicating earlier but not absolute stiffening. Multiphoton microscopy showed that when GAGs are removed, the adventitial collagen fibers are straighter, and both elastin and collagen fibers are recruited at lower levels of strain, in agreement with the mechanical change. The amount of stress relaxation also decreased in GAG-depleted arteries [Formula: see text]. These findings suggest that the interaction between GAGs and other ECM constituents plays an important role in the mechanics of the arterial wall, and GAGs should be considered in addition to elastic and collagen fibers when studying arterial function.

Ring-Mesh Model of Proteoglycan Glycosaminoglycan Chains in Tendon based on Three-dimensional Reconstruction by Focused Ion Beam Scanning Electron Microscopy

Tendons are composed of collagen fibrils and proteoglycan predominantly consisting of decorin. Decorin is located on the d-band of collagen fibrils, and its glycosaminoglycan (GAG) chains have been observed between collagen fibrils with transmission electron microscopy. GAG chains have been proposed to interact with each other or with collagen fibrils, but its three-dimensional organization remains unclear. In this report, we used focused ion beam scanning electron microscopy to examine the three-dimensional organization of the GAG chain in the Achilles tendon of mature rats embedded in epoxy resin after staining with Cupromeronic blue, which specifically stains GAG chains. We used 250 serial back-scattered electron images of longitudinal sections with a 10-nm interval for reconstruction. Three-dimensional images revealed that GAG chains form a ring mesh-like structure with each ring surrounding a collagen fibril at the d-band and fusing with adjacent rings to form the planar network. This ring mesh model of GAG chains suggests that more than two GAG chains may interact with each other around collagen fibrils, which could provide new insights into the roles of GAG chains.

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

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

Damage Models for Soft Tissues: A Survey

Damage to soft tissues in the human body has been investigated for applications in healthcare, sports, and biomedical engineering. This paper reviews and classifies damage models for soft tissues to summarize achievements, identify new directions, and facilitate finite element analysis. The main ideas of damage modeling methods are illustrated and interpreted. A few key issues related to damage models, such as experimental data curve-fitting, computational effort, connection between damage and fractures/cracks, damage model applications, and fracture/crack extension simulation, are discussed. Several new challenges in the field are identified and outlined. This review can be useful for developing more advanced damage models and extending damage modeling methods to a variety of soft tissues.