Profiling of Stem/Progenitor Cell Regulatory Genes of the Synovial Joint by Genome-Wide RNA-Seq Analysis

Role of Wnt signaling pathway in joint development and cartilage degeneration

Osteoarthritis (OA) is a prevalent musculoskeletal disease that affects approximately 500 million people worldwide. Unfortunately, there is currently no effective treatment available to stop or delay the degenerative progression of joint disease. Wnt signaling pathways play fundamental roles in the regulation of growth, development, and homeostasis of articular cartilage. This review aims to summarize the role of Wnt pathways in joint development during embryonic stages and in cartilage maintenance throughout adult life. Specifically, we focus on aberrant mechanical loading and inflammation as major players in OA progression. Excessive mechanical load activates Wnt pathway in chondrocytes, resulting in chondrocyte apoptosis, matrix destruction and other osteoarthritis-related changes. Additionally, we discuss emerging Wnt-related modulators and present an overview of emerging treatments of OA targeting Wnt signaling. Ultimately, this review provides valuable insights towards discovering new drugs or gene therapies targeting Wnt signaling pathway for diagnosing and treating osteoarthritis and other degenerative joint diseases.

Global Trends and Future Research Directions for Temporomandibular Disorders and Stem Cells

Temporomandibular disorder (TMD) is an umbrella term used to describe various conditions that affect temporomandibular joints, masticatory muscles, and associated structures. Although the most conservative and least invasive treatment is preferable, more invasive therapies should be employed to refractory patients. Tissue engineering has been presented as a promising therapy. Our study aimed to investigate trends and point out future research directions on TMD and stem cells. A comprehensive search was carried out in the Web of Science Core Collection (WoS-CC) in October 2022. The bibliometric parameters were analyzed through descriptive statistics and graphical mapping. Thus, 125 papers, published between 1992 and 2022 in 65 journals, were selected. The period with the highest number of publications and citations was between 2012 and 2022. China has produced the most publications on the subject. The most frequently used keywords were "cartilage", "temporomandibular joint", "mesenchymal stem cells", and "osteoarthritis". Moreover, the primary type of study was in vivo. It was noticed that using stem cells to improve temporomandibular joint repair and regeneration is a significant subject of investigation. Nonetheless, a greater understanding of the biological interaction and the benefits of using these cells in patients with TMD is required.

Cartilage organoids for cartilage development and cartilage-associated disease modeling

Cartilage organoids have emerged as powerful modelling technology for recapitulation of joint embryonic events, and cartilage regeneration, as well as pathophysiology of cartilage-associated diseases. Recent breakthroughs have uncovered "mini-joint" models comprising of multicellular components and extracellular matrices of joint cartilage for development of novel disease-modifying strategies for personalized therapeutics of cartilage-associated diseases. Here, we hypothesized that LGR5-expressing embryonic joint chondroprogenitor cells are ideal stem cells for the generation of cartilage organoids as "mini-joints" ex vivo "in a dish" for embryonic joint development, cartilage repair, and cartilage-associated disease modelling as essential research models of drug screening for further personalized regenerative therapy. The pilot research data suggested that LGR5-GFP-expressing embryonic joint progenitor cells are promising for generation of cartilage organoids through gel embedding method, which may exert various preclinical and clinical applications for realization of personalized regenerative therapy in the future.

A possible connection between reactive oxygen species and the unfolded protein response in lens development: From insight to foresight

The lens is a relatively special and simple organ. It has become an ideal model to study the common developmental characteristics among different organic systems. Lens development is a complex process influenced by numerous factors, including signals from the intracellular and extracellular environment. Reactive oxygen species (ROS) are a group of highly reactive and oxygen-containing molecules that can cause endoplasmic reticulum stress in lens cells. As an adaptive response to ER stress, lens cells initiate the unfolded protein response (UPR) to maintain normal protein synthesis by selectively increasing/decreasing protein synthesis and increasing the degradation of misfolded proteins. Generally, the UPR signaling pathways have been well characterized in the context of many pathological conditions. However, recent studies have also confirmed that all three UPR signaling pathways participate in a variety of developmental processes, including those of the lens. In this review, we first briefly summarize the three stages of lens development and present the basic profiles of ROS and the UPR. We then discuss the interconnections between lens development and these two mechanisms. Additionally, the potential adoption of human pluripotent stem-cell-based lentoids in lens development research is proposed to provide a novel perspective on future developmental studies.

Implications of zonal architecture on differential gene expression profiling and altered pathway expressions in mandibular condylar cartilage

Mandibular condylar cartilage (MCC) is a multi-zonal heterogeneous fibrocartilage containing different types of cells, but the factors/mechanisms governing the phenotypic transition across the zones have not been fully understood. The reliability of molecular studies heavily rely on the procurement of pure cell populations from the heterogeneous tissue. We used a combined laser-capture microdissection and microarray analysis approach which allowed identification of differential zone-specific gene expression profiling and altered pathways in the MCC of 5-week-old rats. The bioinformatics analysis demonstrated that the MCC cells clearly exhibited distinguishable phenotypes from the articular chondrocytes. Additionally, a set of genes has been determined as potential markers to identify each MCC zone individually; Crab1 gene showed the highest enrichment while Clec3a was the most downregulated gene at the superficial layer, which consists of fibrous (FZ) and proliferative zones (PZ). Ingenuity Pathway Analysis revealed numerous altered signaling pathways; Leukocyte extravasation signaling pathway was predicted to be activated at all MCC zones, in particular mature and hypertrophic chondrocytes zones (MZ&HZ), when compared with femoral condylar cartilage (FCC). Whereas Superpathway of Cholesterol Biosynthesis showed predicted activation in both FZ and PZ as compared with deep MCC zones and FCC. Determining novel zone-specific differences of large group of potential genes, upstream regulators and pathways in healthy MCC would improve our understanding of molecular mechanisms on regional (zonal) basis, and provide new insights for future therapeutic strategies.

Neuroimmune interactions in painful TMD: Mechanisms and treatment implications

The underlying mechanisms and treatment of painful temporomandibular disorders (TMDs) are important but understudied topics in craniofacial research. As a group of musculoskeletal diseases, the onset of painful TMD is proved to be a result of disturbance of multiple systems. Recently, emerging evidence has revealed the involvement of neuroimmune interactions in painful TMD. Inflammatory factors play an important role in peripheral sensitization of temporomandibular joint (TMJ), and neurogenic inflammation in turn enhances TMJs dysfunction in TMD. Furthermore, centralized neuroimmune communications contribute to neuron excitability amplification, leading to pain sensitization, and is also responsible for chronic TMD pain and other CNS symptoms. Therapeutics targeting neuroimmune interactions may shed light on new approaches for treating TMD. In this review, we will discuss the role of neuroimmune interactions in the onset of painful TMD from the peripheral and centralized perspectives, and how understanding this mechanism could provide new treatment options. Insights into the neuroimmune interactions within TMJs and painful TMD would broaden the knowledge of mechanisms and treatments of this multifactorial disease.