Yes-associated protein nuclear translocation promotes anabolic activity in human articular chondrocytes

The Regulation of Pericellular Matrix Synthesis During Articular Cartilage Tissue Engineering

Articular cartilage, vital to the health and functioning of joints, remains challenging to regenerate. The pericellular matrix (PCM) is critical for transducing biophysical stimuli to the articular chondrocytes (ACs) that it envelops. Given the mechanobiological sensitivity of ACs, it is pivotal in maintaining the chondrogenic phenotype and the production of extracellular matrix (ECM) during articular cartilage tissue engineering. While the maintenance of the native PCM significantly improves the quality of neocartilage, current isolation methods are limited. A solution to this challenge is facilitating ACs to regenerate their PCM. However, the regulation of PCM synthesis remains poorly understood, hindering the development of effective tissue engineering strategies. This narrative review aims to provide a comprehensive analysis of the complex interplay between extracellular cues and intracellular pathways regulating PCM synthesis during articular cartilage tissue engineering. Our analysis reveals that mechanical cues, such as material stiffness and mechanical stimulation, are the primary regulators of PCM synthesis. Additionally, the use of scaffold-free techniques potentially affects the structuring of newly created PCM. Tuning these stimuli can significantly impact the quality of the formed PCM, ultimately influencing neocartilage quality. Furthermore, we highlight intracellular mechanisms involved in the transduction of these extracellular cues, including actin polymerization, yes-associated protein and transcriptional coactivator with PDZ-binding motif localization, and transforming growth factor beta-induced Smad signaling. Although the current literature suggests the involvement of these signaling pathways in regulating the synthesis of PCM components, we found that studies investigating these processes in ACs are lacking. Elucidating the relationships between extracellular stimuli, intracellular signaling, and the expression of PCM components could provide a framework for designing new cartilage tissue engineering approaches that facilitate proper PCM synthesis. Ultimately, this can improve ECM quality and advance articular cartilage regeneration.

Mechanical Signal Transduction: A Key Role of Fluid Shear Forces in the Development of Osteoarthritis

Globally, osteoarthritis is a common and highly disabling disease that places a heavy burden on society and medical systems. The role of biomechanical factors in the development of osteoarthritis has gradually received more attention. As a key biomechanical stimulus, fluid shear force is becoming the focus of research for its dual role in maintaining cartilage health and disease progression. This paper conducts an in-depth discussion on the mechanism of fluid shear force in osteoarthritis and its impact on the disease process, aiming to reveal how fluid shear stress affects the development of osteoarthritis by regulating the physiological function and signal transduction pathways of chondrocytes.

ER stress-induced YAP upregulation leads to chondrocyte phenotype loss in age-related osteoarthritis

Background

Osteoarthritis (OA) is a common degenerative joint disease, leading to pain and restricted mobility. Age-related endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of OA, but the underlying mechanisms remain unclear. This study aims to explore the relationship between age-related ER stress, YAP overexpression, and chondrocyte phenotype loss in the development of OA.

Methods

Cartilage samples were collected from patients undergoing amputation, and age-related ER stress markers and YAP expression were assessed using immunohistochemical staining and qPCR. Transgenic mice with cartilage-specific YAP overexpression (YAPOE) were created, and Pamrevlumab was administered to evaluate its therapeutic effects.

Results

Higher expression of ER stress markers and YAP were showed in aged tissues compared to younger tissues. YAP overexpression led to decreased levels of cartilage phenotype markers and increased osteogenesis-related proteins. In vivo, YAPOE mice exhibited OA-like cartilage degeneration, which was mitigated by Pamrevlumab treatment.

Conclusion

Age-related ER stress induces YAP overexpression, contributing to OA pathogenesis. Pamrevlumab effectively prevents this phenotype loss in YAPOE mice, suggesting its potential as a therapeutic agent for OA. These findings provide new insights into the molecular mechanisms of OA and highlight the importance of targeting the ER stress-YAP-CTGF signaling pathway in OA treatment and prevention.

Region partitioning of articular cartilage with streaming-potential-based parameters and indentation maps

Articular cartilage exhibits site-specific tissue inhomogeneity, for which the tissue properties may continuously vary across the articular surface. To facilitate practical applications such as studying site-specific cartilage degeneration, the inhomogeneity may be approximated with several distinct region-wise variations, with one set of tissue properties for one region. A clustering method was previously developed to partition such regions using cartilage indentation-relaxation and thickness mapping instead of simply using surface geometry. In the present study, a quantitative parameter based on streaming potential measurement was introduced as an additional feature to assess the applicability of the methodology with independent datasets. Experimental data were collected from 24 sets of femoral condyles, extracted from fresh porcine stifle joints, through streaming potential mapping, automated indentation, and needle penetration tests. K-means clustering and Elbow method were used to find optimal region partitions. Consistent with previous findings, three regions were suggested for either lateral or medial condyle regardless of left or right joint. The region shapes were approximately triangular or trapezoidal, which was similar to what was found previously. Streaming potentials were confirmed to be region-dependent, but not significantly different among joints. The cartilage was significantly thicker in the medial than lateral condyles. The region areas were consistent among joints, and comparable to that found in a previous study. The present study demonstrated the capability of region partitioning methods with different variables, which may facilitate new applications whenever site-specific tissue properties must be considered.

The role of YAP/TAZ on joint and arthritis

Osteoarthritis (OA) and rheumatoid arthritis (RA) are two common forms of arthritis with undefined etiology and pathogenesis. Yes-associated protein (YAP) and its homolog transcriptional coactivator with PDZ-binding motif (TAZ), which act as sensors for cellular mechanical and inflammatory cues, have been identified as crucial players in the regulation of joint homeostasis. Current studies also reveal a significant association between YAP/TAZ and the pathogenesis of OA and RA. The objective of this review is to elucidate the impact of YAP/TAZ on different joint tissues and to provide inspiration for further studying the potential therapeutic implications of YAP/TAZ on arthritis. Databases, such as PubMed, Cochran Library, and Embase, were searched for all available studies during the past two decades, with keywords "YAP," "TAZ," "OA," and "RA."

Osmolarity-Induced Altered Intracellular Molecular Crowding Drives Osteoarthritis Pathology

Osteoarthritis (OA) is a multifactorial degenerative joint disease of which the underlying mechanisms are yet to be fully understood. At the molecular level, multiple factors including altered signaling pathways, epigenetics, metabolic imbalance, extracellular matrix degradation, production of matrix metalloproteinases, and inflammatory cytokines, are known to play a detrimental role in OA. However, these factors do not initiate OA, but are mediators or consequences of the disease, while many other factors causing the etiology of OA are still unknown. Here, it is revealed that microenvironmental osmolarity can induce and reverse osteoarthritis-related behavior of chondrocytes via altered intracellular molecular crowding, which represents a previously unknown mechanism underlying OA pathophysiology. Decreased intracellular crowding is associated with increased sensitivity to proinflammatory triggers and decreased responsiveness to anabolic stimuli. OA-induced lowered intracellular molecular crowding could be renormalized via exposure to higher extracellular osmolarity such as those found in healthy joints, which reverse OA chondrocyte's sensitivity to catabolic stimuli as well as its glycolytic metabolism.