Chronic Stress Exacerbates Osteoporosis in Ovariectomized Mice With Anxiety‐ and Depression‐Like Symptoms by Activating Cathepsin K and Impairing Autophagy

Chronic stress (CS) acts as both an initiating and aggravating factor for depression and osteoporosis. Cumulative evidence indicates that Cathepsin K (Cat K), a cysteine protease, is functionally linked to chronic stress and exerts critical regulatory roles in bone metabolism. Nevertheless, the molecular mechanisms whereby CS promotes osteoporosis in the background of mood-related disturbances remain poorly defined. In the present work, we established a combined mouse model of osteoporosis and chronic stress. We evaluated anxiety- and depression-like behaviors, the expression profiles of Cat K, autophagy-, apoptosis-, and inflammation-associated proteins in bone tissue, as well as vascular senescence in experimental animals. Furthermore, we investigated the biological effects of serum collected from chronically-stressed mice on MC3T3-E1 osteoblast-like cells. Following 8-week chronic stress exposure, ovariectomized (OVX) mice developed prominent anxiety- and depression-like behaviors, accompanied by deteriorated osteoporosis and aortic senescence. Meanwhile, bone tissues exhibited elevated levels of Cat K, p62, pro-inflammatory mediators, and apoptosis-related proteins, whereas the autophagy marker LC3B/A was down-regulated. Administration of E64d, a cysteine protease inhibitor, markedly reversed these pathological alterations. In vitro culture revealed that serum from chronically-stressed mice suppressed the viability of MC3T3-E1 osteoblast-like cells. Pharmacological inhibition of Cat K restored autophagic activity, mitigated the overexpression of pro-inflammatory and pro-apoptotic mediators, and rescued MC3T3-E1 cells from stress-triggered injury. Collectively, our findings demonstrate that chronic stress induces anxiety- and depression-like phenotypes in OVX mice and accelerates bone loss, at least partially via Cat K activation and autophagy suppression.