TSPO governs bone-lipid homeostasis by redirecting BMSC differentiation via the PI3K/AKT/β-catenin pathway

The imbalance between osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) is a central pathological feature of osteoporosis (OP). The translocator protein (TSPO) is a multifunctional protein, yet its precise role in bone metabolism remains elusive. This study aimed to investigate the role and mechanism of TSPO in OP pathogenesis.

We integrated bioinformatic analyses of human and mouse OP-related datasets and validated TSPO expression in BMSCs from osteoporotic patients and mouse models. Gain- and loss-of-function experiments in human BMSCs (h-BMSCs) assessed the impact of TSPO on proliferation, senescence, migration, and lineage differentiation. RNA sequencing and mechanistic rescue experiments were employed to identify the involved signaling pathway. The therapeutic effect of Adeno-associated virus 9 (AAV-9)-mediated TSPO silencing was evaluated in ovariectomized (OVX) mice.

TSPO was significantly upregulated in BMSCs from both OP patients and preclinical models. Functionally, TSPO overexpression suppressed h-BMSC proliferation, migration, and osteogenesis while promoting senescence and adipogenesis. Conversely, TSPO knockdown enhanced cellular fitness and osteogenic capacity. Mechanistically, TSPO functioned as a critical upstream regulator of the PI3K/AKT/GSK-3β signaling axis, suppressing the downstream phosphorylation cascade and ultimately inhibiting β-catenin-mediated osteogenic transcription. Crucially, local TSPO silencing in OVX mice effectively improved bone microarchitecture, enhanced bone formation, and reduced marrow adiposity, concomitant with the reactivation of the PI3K/AKT/GSK-3β/β-catenin pathway.

Our study identifies TSPO as a key pathogenic regulator that impairs osteogenesis by disrupting the PI3K/AKT/β-catenin pathway. Targeting TSPO presents a novel anabolic strategy for osteoporosis, potentially addressing the unmet clinical need for therapies that restore bone formation.