Osteoarthritis (OA) is a disabling condition with pathological remodeling of different joints, resulting in impaired function of the whole musculoskeletal system in vertebrates. Fibrocartilage has poor self-repair capacity after OA, leading to restricted treatment strategies and unsatisfying clinical efficacy. Recently, we constructed the spatiotemporal multiomic landscape of fibrocartilage and connective tissue in human temporomandibular joint (TMJ)-OA, observing that adjacent connective tissue could transform to fibrocartilage in TMJ-OA. We found that the COL5A1+ fibroblast population, derived from perivascular niche, contributes to fibrocartilaginous extracellular matrix (ECM) transformation. Multijoint analysis showed that integrin αV/β5 was universally activated in OA joints, which led to increased fibrocartilaginous transcription but disarranged ECM transformation in connective tissues. In OA mouse models and a TMJ-OA miniature pig model, inhibition of integrin αV/β5 activity using cilengitide facilitated the transcriptional reprogramming of Col5a1+ fibroblast and functional remodeling of the connective tissues. Our findings verified the effectiveness of cilengitide and provided a clinical route for fibrocartilage injury repair in OA.

INTRODUCTION:Condylar fibrocartilage regeneration after injury has been hindered by its poor self-repair capacity. Injection of parathyroid hormone (PTH) has been proven to effectively delay cartilage damage in osteoarthritis. In this study, we investigated the regulatory effect of PTH on the homeostasis of condylar fibrocartilage. METHODS:FCSCs were extracted and exposed to a high PTH environment from rats to analyze the transcriptional changes. The condyles of mice were cultured ex vivo and exposed to high PTH to observe changes in cartilage. Parathyroidectomy induced PTH-deficient rats were locally injected with PTH to observe its effects on cartilage homeostasis. RESULTS:High PTH environment could promote chondrogenic differentiation of FCSCs early, while weakening at late phase. The ex vivo culture of mouse condyle under PTH stimulation enhanced the proliferation of chondrocytes early, which were replaced by hypertrophic chondrocytes. The degradation of cartilage matrix also grew distinct under high PTH. PTH deficiency induced osteoarthritis-like changes in rats, characterized by cartilage layers disorder, chondrocyte reduction, and matrix degradation. Exogenous PTH could reverse fibrocartilage degeneration. CONCLUSION:The maintenance of PTH homeostasis is crucial for maintaining the function of temporomandibular condylar FCSCs. Exogenous PTH can ameliorate the characteristics associated with rat temporomandibular joint osteoarthritis.

Aim or purpose: To investigate the role of temporomandibular joint disc mural cells by comparing the changes in the extracellular matrix in normal state and ADD in human and mice. Materials and methods: Raman spectroscopy, nanoindentation test, pentachrome staining and proteomics were used to test and compare human normal and ADD TMJ disc samples to investigate the change of ECM modification in TMJ tissue. An ADD mouse model was established to investigate ECM alterations. Single-cell transcriptome sequencing was applied to analyze change in transcriptome, and subpopulations of mural cells were analyzed to explore the roles of different states of mural cells. Transgenic mice were applied to trace disc mural cell and to observe their fate after ADD. Ultimately, single-cell data were analyzed to find the cell signaling pathways that regulate these processes. Results: The results showed that the ECM of the posterior region of the human TMJ disc underwent fibrocartilage transformation in ADD, which was manifested as an increase of glycosaminoglycans; and the biomechanical modulus was significantly elevated after ADD which means that the posterior region showed functional alterations close to articular disc fibrocartilage. In contrast, a similar phenotype were found in mouse model . Lineage tracing revealed that mural cells could differentiate into a ECM transformation-associated fibroblast subpopulation. Conclusions: In the present study, we found that ECM changes of posterior disc region in the transcriptional properties and protein secretion in ADD contribute to their transformation into articular disc fibrocartilage. Mural cells participated in this process through the differentiation of specific functional fibroblasts.

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.

Interspecies comparisons of the extracellular matrix of temporomandibular joint (TMJ) condylar cartilage are necessary to elucidate the mechanisms underlying its superior mechanical properties, to guide the construction of animal models of TMJ-related diseases, and to establish standards for the engineering of TMJ condylar cartilage. Here we characterize and compare TMJ condylar cartilage from six different species from a materials science perspective, including structure, composition and mechanical properties from the macroscopic to the microscopic level. The gross morphology showed obvious interspecies differences in size and shape, which may be related to the different joint motion patterns. Although the condylar cartilage of all species can be divided histologically into a superficial fibrous layer and a deep hyaline layer, there are significant interspecies differences in the microstructure of the fibrils in the two layers, mainly in the diameter of the fibrils. Compositionally, there were no significant differences in collagen composition between species, but the content of glycosaminoglycans (GAGs) decreased progressively with increasing body size, with the same results obtained by Safranin O staining and biochemical analysis. Mechanically, the elastic modulus of mouse condylar cartilage was significantly higher than that of the other species and tended to decrease with increasing body size. This study shows that the TMJ condylar cartilage of different species has its own specific structure-composition-mechanics matching characteristics for their unique masticatory stress dissipation, and differences in fibril diameter and GAGs content may be the two ultimate factors influencing the differences in cartilage mechanical properties between species, while the condylar cartilage of pigs is most similar to that of humans, suggesting that pigs may be a suitable animal model for TMJ studies.

The musculoskeletal system is an integral part of the human body. Currently, most skeletal muscle research is conducted through conventional histological sections due to technological limitations and the structure of skeletal muscles. For studying and observing bones and muscles, there is an urgent need for three-dimensional, objective imaging technologies. Optical tissue-clearing technologies seem to offer a novel and accessible approach to research of the musculoskeletal system. Using this approach, the components which cause refraction or prevent light from penetrating into the tissue are physically and chemically eliminated; then the liquid in the tissue is replaced with high-refractive-index chemicals. This innovative method, which allows three-dimensional reconstruction at the cellular and subcellular scale, significantly improves imaging depth and resolution. Nonetheless, this technology was not originally developed to image bones or muscles. When compared with brain and nerve organs which have attracted considerable attention in this field, the musculoskeletal system contains fewer lipids and has high levels of hemoglobin, collagen fibers, and inorganic hydroxyapatite crystals. Currently, three-dimensional imaging methods are widely used in the diagnosis and treatment of skeletal and muscular illnesses. In this regard, it is vitally important to review and evaluate the optical tissue-clearing technologies currently employed in the musculoskeletal system, so that researchers may make an informed decision. In the meantime, this study offers guidelines and recommendations for expanding the use of this technology in the musculoskeletal system.

由于生物样本的不透明性,以及组织深入成像的清晰度和深度不佳,因此大型、厚组织3D成像技术的发展与创新成为近年来的研究热点.组织透明化机技术是通过各种物理或化学的方式将组织变透明,并结合荧光显微镜来实现组织或器官三维成像的新技术,因其良好的荧光保存及透明效果,在软组织领域,尤其是神经领域得到了越来越广泛的应用.近年来,各种新型的组织透明化技术不断被报道出来,本文就被动浸润法水性透明化技术、水化法水性透明化技术、水凝胶嵌入法水性透明化技术的研究进展及应用做一综述.

Revealing the true structure of tissues and organs with tissue slicing technology is difficult since images reconstructed in three dimensions are easily distorted. To address the limitations in tissue slicing technology, tissue clearing has been invented and has recently achieved significant progress in three-dimensional imaging. Currently, this technology can mainly be divided into two types: aqueous clearing methods and solvent-based clearing methods. As one of the important parts of this technology, organic solvent-based tissue clearing techniques have been widely applied because of their efficient clearing speed and high clearing intensity. This review introduces the primary organic solvent-based tissue clearing techniques and their applications.