Injury-driven stromal exhaustion disrupts intrinsic regenerative capability.

Bone marrow stromal cells, marked by leptin receptor (Lepr) and C-X-C motif chemokine ligand 12 (Cxcl12), orchestrate osteogenesis and maintain bone homeostasis. Following injury, these stromal cells directly generate reparative bone and subsequently restore the marrow microenvironment, a process widely regarded as a reliable regenerative response. However, it remains unclear whether stromal cells retain full regenerative capacity after prior injury. Here, we show that Lepr+Cxcl12+ stromal cells have limited regenerative capacity and become dysfunctional upon repeated activation, defining a state of stromal exhaustion. Lepr-Cre-labeled stromal cells progressively lose osteogenic potential after repeated injury and instead differentiate into bone marrow adipocytes. Exhausted stromal cells are distinct from aging stromal cells, exhibiting metabolic abnormalities, chronic inflammation associated with stress responses, and impaired regenerative plasticity. Furthermore, β-catenin deletion during injury repair induces adipogenesis through stromal lineage switching, whereas pharmacological and genetic activation of Wnt/β-catenin signaling partially rescues osteogenesis, indicating that dysregulated Wnt/β-catenin signaling drives stromal exhaustion and impaired regeneration. As repeated regenerative activation may occur in recurrent fractures, orthopedic surgeries, osteoporosis, and osteogenesis imperfecta, stromal exhaustion represents a critical barrier to bone regeneration and a potential therapeutic target for restoring stromal plasticity.