Endothelin-1/endothelin B receptor signalling mediates Prx1(+) skeletal stem cells senescence: A driver of osteoporotic bone loss.

BACKGROUND: Stem cells residing in the perivascular niche are critical for skeletal homeostasis. Vascular endothelin-1 (ET-1) controls stem cell fate in development, but its role in the exhaustion of skeletal stem cells (SSCs) and subsequent bone degeneration in osteoporosis remains poorly understood. This study aimed to determine whether ET-1 signalling drives SSCs senescence and to elucidate the underlying mechanisms. METHODS: We utilised a combination of human single-cell RNA sequencing datasets, murine models of ageing and ovariectomy (OVX), and an endothelial-specific ET-1 overexpression transgenic (TET-1) mouse model. In vitro studies on mesenchymal stem cells (MSCs) employed ET-1 challenge with and without receptor-specific antagonists (BQ123 for ET(A)R, BQ788 for ET(B)R). The mechanism was further probed using transcriptomic profiling and validated in vivo through Prx1(+) SSCs-specific ET(B)R knockout (Prx1-Cre;ET(B)R (fl/fl) ) and pharmacological inhibition with the ET(B)R antagonist BQ788. RESULTS: In aged and OVX mice, ET(B)R expression was significantly upregulated in SSCs concurrent with bone loss. Transgenic ET-1 overexpression recapitulated an aged bone phenotype, inducing SSCs senescence and accelerating bone loss. In vitro, ET-1 triggered MSCs senescence and reactive oxygen species (ROS) accumulation. Such effects were specifically abrogated by ET(B)R, but not ET(A)R. Transcriptomic analysis revealed that ET-1/ET(B)R signalling synergistically dysregulates the PI3K-AKT and p53 pathways to orchestrate senescence. Critically, both genetic knockout of ET(B)R in Prx1(+) SSCs and pharmacological inhibition with BQ788 mitigated oxidative stress, reduced cellular senescence, and preserved bone mass in OVX and aged mice. CONCLUSION: This study identified the ET-1/ET(B)R signalling axis as a critical driver of osteoporosis by promoting ROS-mediated SSCs senescence. We established a link between vascular ageing and skeletal decline. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: This study positioned ET(B)R blockade as a promising novel therapeutic strategy for osteoporosis. By targeting the upstream driver of SSCs exhaustion, ET(B)R inhibition offers a potential paradigm shift from palliative care to proactive rejuvenation of the osteogenic niche. This approach could counteract both postmenopausal and age-related bone loss by restoring the bone-forming potential of the skeleton, addressing a significant unmet clinical need.