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

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.

Decorin and/or biglycan knockdown in aged mouse patellar tendon impacts fibril morphology, scar area, and mechanical properties

Small leucine-rich proteoglycans, such as decorin and biglycan, play pivotal roles in collagen fibrillogenesis during development, healing, and aging in tendon. Previous work has shown that the absence of decorin and biglycan affects fibril shape and mechanical properties during tendon healing. However, the roles of decorin and biglycan in the healing process of aged tendons are unclear. Therefore the objective of this study was to evaluate the differential roles of decorin and biglycan during healing of patellar tendon injury in aged mice. Aged (300 days old) female Dcn+/+/Bgn+/+ control (WT, n = 52), Dcnflox/flox (I-Dcn-/-, n = 36), Bgnflox/flox (I-Bgn-/-, n = 36), and compound Dcnflox/flox/Bgnflox/flox (I-Dcn-/-/Bgn-/-, n = 36) mice with a tamoxifen-inducible Cre were utilized. Targeted gene expression, collagen fibril diameter distributions, mechanical properties, and histological assays were employed to assess the effects of knockdown of decorin and/or biglycan at the time of injury. Knockdown resulted in alterations in fibril diameter distribution and scar area, but surprisingly did not lead to many differences in mechanical properties. Biglycan played a larger role in early healing stages, while decorin is more significant in later stages, particularly in scar remodeling. This study highlights some of the differential roles of biglycan and decorin in the regulation of fibril structure and scar area, as well as influencing gene expression during healing in aged mice.

Matrisome Transcriptome Dynamics during Tissue Aging

The extracellular matrix (ECM) is a complex three-dimensional network of macromolecules that provides structural support for the cells and plays a significant role in tissue homeostasis and repair. Growing evidence indicates that dysregulation of ECM remodeling contributes to various pathological conditions in the body, including age-associated diseases. In this work, gene expression data of normal human tissues obtained from the Genotype-Tissue Expression project, as well as data from MatrisomeDB 2.0, the ECM-protein knowledge database, are used to estimate the age-dependent matrisome transcriptome dynamics in the blood, heart, brain, liver, kidneys, lungs, and muscle. Differential gene expression (DE) analysis revealed dozens of matrisome genes encoding both structural elements of the ECM and ECM-associated proteins, which had a tissue-specific expression profile with age. Among common DE genes that changed expression with age in at least three tissues, COL18A1, MFAP1, IGFBP7, AEBP1, LTBP2, LTBP4, LG14, EFEMP1, PRELP, BGN, FAM20B, CTSC, CTSS, and CLEC2B were observed. The findings of the study also reveal that there are sex-specific alterations during aging in the matrisome gene expression. Taken together, the results obtained in this work may help in understanding the role of the ECM in tissue aging and might prove valuable for the future development of the field of ECM research in general.

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.

Effect of Aging on Tendon Biology, Biomechanics and Implications for Treatment Approaches

Tendon aging is associated with an increasing prevalence of tendon injuries and/or chronic tendon diseases, such as tendinopathy, which affects approximately 25% of the adult population. Aged tendons are often characterized by a reduction in the number and functionality of tendon stem/progenitor cells (TSPCs), fragmented or disorganized collagen bundles, and an increased deposition of glycosaminoglycans (GAGs), leading to pain, inflammation, and impaired mobility. Although the exact pathology is unknown, overuse and microtrauma from aging are thought to be major causative factors. Due to the hypovascular and hypocellular nature of the tendon microenvironment, healing of aged tendons and related injuries is difficult using current pain/inflammation and surgical management techniques. Therefore, there is a need for novel therapies, specifically cellular therapy such as cell rejuvenation, due to the decreased regenerative capacity during aging. To augment the therapeutic strategies for treating tendon-aging-associated diseases and injuries, a comprehensive understanding of tendon aging pathology is needed. This review summarizes age-related tendon changes, including cell behaviors, extracellular matrix (ECM) composition, biomechanical properties and healing capacity. Additionally, the impact of conventional treatments (diet, exercise, and surgery) is discussed, and recent advanced strategies (cell rejuvenation) are highlighted to address aged tendon healing. This review underscores the molecular and cellular linkages between aged tendon biomechanical properties and the healing response, and provides an overview of current and novel strategies for treating aged tendons. Understanding the underlying rationale for future basic and translational studies of tendon aging is crucial to the development of advanced therapeutics for tendon regeneration.

Equine tendon mechanical behaviour: Prospects for repair and regeneration applications

Tendons are dense connective tissues that play an important role in the biomechanical function of the musculoskeletal system. The mechanical forces have been implicated in every aspect of tendon biology. Tendon injuries are frequently occurring and their response to treatments is often unsatisfactory. A better understanding of tendon biomechanics and mechanobiology can help develop treatment options to improve clinical outcomes. Recently, tendon tissue engineering has gained more attention as an alternative treatment due to its potential to overcome the limitations of current treatments. This review first provides a summary of tendon mechanical properties, focusing on recent findings of tendon mechanobiological responses. In the next step, we highlight the biomechanical parameters of equine energy-storing and positional tendons. The final section is devoted to how mechanical loading contributes to tenogenic differentiation using bioreactor systems. This study may help develop novel strategies for tendon injury prevention or accelerate and improve tendon healing.