Hypothalamic PVN Astrocytes Regulate Articular Cartilage Injury Repair Through Neuroendocrine Pathways

Articular cartilage injury refers to damage to the joint cartilage caused by trauma,aging,or pathological changes.Its characteristics include rough,layered,or torn cartilage surfaces,gradual thinning of the cartilage layer,metabolic imbalance,and decreased mechanical performance of the joint.Clinically,patients with joint cartilage injuries develop joint inflammation such as synovitis and accompanying joint pain,with up to 20%-40% of patients experiencing anxiety,depression,and other symptoms.These clinical manifestations suggest a close interaction between the joint and the central nervous system,but the underlying mechanisms are unclear.The hypothalamus is a higher center that regulates the autonomic nervous system,endocrine,emotions,and pain,while astrocytes are the largest group of glial cells that can respond immediately to stimuli and damage,participating in processes such as peripheral glucose and fat metabolism,as well as emotional and pain regulation.However,little is known about whether astrocytes have a regulatory effect on joint cartilage.Based on this,we hypothesize that hypothalamic astrocytes may respond to joint cartilage injury and regulate the repair of joint cartilage injury.Our study investigated the relationship between hypothalamic paraventricular nucleus(PVN)astrocytes and joint cartilage through induction of joint cartilage injury in mice using a microfracture(MF)surgery.Our results showed that when joint cartilage was abnormal,astrocytes in the PVN nucleus of the hypothalamus were abnormally activated,indicating a certain regulatory effect between PVN astrocytes and joint cartilage.Therefore,we found that specific inhibition of PVN astrocytes could effectively promote joint cartilage injury repair in both the MF and medial meniscus destabilization(DMM)models of joint cartilage degeneration.This inhibition reduced cartilage degradation and increased synthesis,maintaining extracellular matrix(ECM)homeostasis and protecting joint cartilage.In addition,this approach was effective in relieving joint pain caused by cartilage degeneration.Overall,inhibiting the activity of PVN astrocytes can effectively alleviate joint cartilage degeneration.We further investigated the relationship between PVN astrocytes and CRH neurons by using immunofluorescence double staining and ELISA assay.Our results showed a high contact rate between PVN astrocytes and CRH neurons,and the activation of PVN astrocytes led to a significant increase in serum CRH,while inhibiting PVN astrocytes could block the abnormal secretion of CRH.Additionally,our results showed that the expression of the CRH receptor CRHR1 in cartilage was significantly upregulated under inflammatory and pathological conditions.Knocking down Crhr1 under inflammatory conditions effectively suppressed the expression of degradation markers,efficiently promoted chondrocyte differentiation,and significantly increased chondrocyte proliferation capacity in the presence of a selective CRHR1 inhibitor.This suggests that the loss of CRHR1 can maintain the ECM homeostasis of chondrocytes,while promoting their differentiation and proliferation.To further investigate the regulatory role of CRHR1 in joint cartilage function,we used the joint cartilage injury model(MF)and the joint cartilage degeneration model(DMM),and found that the use of a CRHR1 antagonist can effectively promote joint cartilage injury repair,as well as ECM synthesis metabolism,inhibit catabolic metabolism and fibrosis,maintain joint cartilage ECM homeostasis,and alleviate joint pain.Therefore,our results suggest that CRHR1 has the potential to be a therapeutic target for the treatment of joint cartilage injuries.To validate the hypothesis that PVN astrocytes accelerate joint cartilage damage through CRH activation of CRHR1,we administered a CRHR1 antagonist into the joint cavity of mice with DMM-induced joint cartilage damage,whose PVN astrocytes were activated.Results showed that the CRHR1 antagonist effectively promoted joint cartilage damage repair after DMM surgery when PVN astrocytes were activated.In addition,an articular cartilage graft experiment with patients suffering from cartilage lesions showed that the CRHR1 antagonist was able to effectively inhibit extracellular matrix loss from the graft.Therefore,the functional loss of CRHR1 can effectively block the accelerated degeneration of joint cartilage caused by PVN astrocyte activation,maintain ECM stability,and alleviate joint pain.In summary,this study has innovatively discovered that activation of astrocytes in the hypothalamic PVN can promote CRH release from CRH neurons,which then acts on CRHR1 in joint cartilage via the bloodstream,thereby accelerating joint cartilage injury and exacerbating joint pain.We have deeply analyzed the neuroendocrine pathways by which glial cells regulate the repair of cartilage injury,providing new insights into the abnormal secretion of neurogenic factors caused by cartilage lesions.Therefore,targeting PVN astrocytes and the CRH-CRHR1 signaling pathway may provide new therapeutic strategies for treating articular cartilage injury and other degenerative joint diseases,and also provide a theoretical basis for the development of new drugs to treat cartilage injury.