USP13-mediated stabilization of FOXD1 activates aerobic glycolysis to drive osteogenic differentiation and mitigate osteoporosis.

Impaired osteoblast differentiation is a central pathological event in osteoporosis. Forkhead box transcription factor D1 (FOXD1) is a key regulator of cellular metabolism, yet its precise role and upstream regulatory mechanisms during osteogenic differentiation remain poorly defined. We hypothesized that FOXD1 function might be modulated by the ubiquitin-proteasome system via the deubiquitinating enzyme USP13. Using an ovariectomy (OVX)-induced mouse osteoporosis model and MC3T3-E1 osteoprogenitor cells with Foxd1 or Usp13 knockdown/overexpression, we assessed osteogenic differentiation, glycolytic function, and the USP13-FOXD1 interaction. Results showed Foxd1 expression was upregulated during osteogenic induction. Overexpression of Foxd1 enhanced proliferation, differentiation, mineralization, and aerobic glycolysis, whereas knockdown suppressed these processes. Mechanistically, USP13 directly bound to FOXD1 and stabilized it by inhibiting proteasomal degradation via deubiquitination. Rescue experiments confirmed that FOXD1 is the critical downstream target of USP13, as Foxd1 overexpression reversed the impaired osteogenesis and suppressed glycolysis caused by Usp13 knockdown. In OVX mice, Usp13 overexpression improved bone microstructure and biomechanical strength in a FOXD1-dependent manner, while Foxd1 knockdown abolished these protective effects. This study is the first to elucidate that USP13 stabilizes FOXD1 through deubiquitination, driving aerobic glycolysis reprogramming, promoting osteogenic differentiation, and alleviating osteoporosis. This defines the "USP13-FOXD1-Glycolysis" axis as a pivotal regulatory mechanism, providing a potential therapeutic target for anti-osteoporosis strategies.