The potential roles of JAK/STAT signaling in the progression of osteoarthritis

Osteoarthritis (OA) is an age-related chronic progressive degenerative disease that induces persistent pain and disabilities. The development of OA is a complex process, and the risk factors are various, including aging, genetics, trauma and altered biomechanics. Inflammation and immunity play an important role in the pathogenesis of OA. JAK/STAT pathway is one of the most prominent intracellular signaling pathways, regulating cell proliferation, differentiation, and apoptosis. Inflammatory factors can act as the initiators of JAK/STAT pathway, which is implicated in the pathophysiological activity of chondrocyte. In this article, we provide a review on the importance of JAK/STAT pathway in the pathological development of OA. Potentially, JAK/STAT pathway becomes a therapeutic target for managing OA.

Noggin Inhibits IL-1β and BMP-2 Expression, and Attenuates Cartilage Degeneration and Subchondral Bone Destruction in Experimental Osteoarthritis

Osteoarthritis (OA) is a chronic inflammatory and progressive joint disease that results in cartilage degradation and subchondral bone remodeling. The proinflammatory cytokine interleukin 1 beta (IL-1β) is abundantly expressed in OA and plays a crucial role in cartilage remodeling, although its role in the activity of chondrocytes in cartilage and subchondral remodeling remains unclear. In this study, stimulating chondrogenic ATDC5 cells with IL-1β increased the levels of bone morphogenetic protein 2 (BMP-2), promoted articular cartilage degradation, and enhanced structural remodeling. Immunohistochemistry staining and microcomputed tomography imaging of the subchondral trabecular bone region in the experimental OA rat model revealed that the OA disease promotes levels of IL-1β, BMP-2, and matrix metalloproteinase 13 (MMP-13) expression in the articular cartilage and enhances subchondral bone remodeling. The intra-articular injection of Noggin protein (a BMP-2 inhibitor) attenuated subchondral bone remodeling and disease progression in OA rats. We also found that IL-1β increased BMP-2 expression by activating the mitogen-activated protein kinase (MEK), extracellular signal-regulated kinase (ERK), and specificity protein 1 (Sp1) signaling pathways. We conclude that IL-1β promotes BMP-2 expression in chondrocytes via the MEK/ERK/Sp1 signaling pathways. The administration of Noggin protein reduces the expression of IL-1β and BMP-2, which prevents cartilage degeneration and OA development.

Upregulation of microRNA-9-5p inhibits apoptosis of chondrocytes through downregulating Tnc in mice with osteoarthritis following tibial plateau fracture

Osteoarthritis (OA) is a common degenerative joint disease which is typically progressed with age, affecting smaller joints of hands, lower limbs, and the vertebral column. It has been reported that microRNAs could regulate the biological processes of OA. Therefore, the purpose of this study was to elucidate miR-9-5p's role in regulating cartilage remodeling of OA mice following tibial plateau fracture (TPF) through regulation of tenascin C (Tnc). Initially, we determined the expression of miR-9-5p and Tnc in mice with OA and then testified their relationship. The results displayed a high expression of Tnc, but a poor expression of miR-9-5p with high methylation in OA. Tnc was confirmed to be a target gene of miR-9-5p. Moreover, based on gain- and loss-function experiments, an increase of miR-9-5p and loss of Tnc had the potential to inhibit cell apoptosis, while facilitating cell proliferation, migration, invasion, and cartilage remodeling of mice with OA following TPF. This was further demonstrated by a higher expression of type II collagen, lower type X collagen, and protogenin expression. Subsequently, downregulation of miR-9-5p aggravated the pathological changes of mice, illustrated by an increase in the Mankin score. In conclusion, the present study proved that overexpression of miR-9-5p suppressed chondrocytes apoptosis and promoted cartilage remodeling through downregulating of Tnc in mice with OA.