Diabetes is a chronic metabolic disease, whose incidence has continuously increased in recent years (Crowley et al., 2023). Osteoporosis is one of the most prevalent orthopedic diseases in the 21st century, affecting approximately 200 million people worldwide (Sudhakaran et al., 2023). Diabetic osteoporosis (DOP) is a secondary osteoporosis induced by diabetes, which is characterized by structural deterioration of bone tissue and bone mass loss (Priya et al., 2023a). Approximately 50–66 % of diabetic patients exhibit a decrease in bone mineral density (BMD), and about 33 % of them are diagnosed with DOP (Chen et al., 2024). Since type 2 diabetes is far more prevalent than type 1 diabetes, it is urgently required to study type 2 diabetic osteoporosis (T2DOP). Early-stage T2DOP usually has no obvious clinical manifestations and is easy to be ignored. However, patients are prone to bone pain, fatigue, skeletal deformity, or fracture as the disease progresses, which may result in disability if not timely treated, bringing a heavy economic burden to the family and society (Sheu et al., 2022). Currently, hypoglycemic and anti-osteoporosis drugs are used in combination to treat T2DOP in the clinic (Mohsin et al., 2019, Priya et al., 2024). Nevertheless, the efficacy of these drugs is limited by adverse reactions, which make them inappropriate for long-term use and large-scale application (Schacter and Leslie, 2021, Snega Priya et al., 2024). Therefore, the pathological mechanism of T2DOP needs to be further explored to develop more effective therapeutic methods and improve the prognosis of patients.

Osteoblasts and osteoclasts are respectively responsible for bone formation and resorption, and they maintain bone homeostasis and health through coordinated action (Haridevamuthu et al., 2025). The main pathological mechanism underlying the occurrence of osteoporosis is the imbalance between bone absorption and formation, which is caused by the hyperfunction of osteoclasts and decreased function of osteoblasts (Priya et al., 2023b, Snega Priya et al., 2023). Till now, various modes of osteoblast death including autophagy, apoptosis, and ferroptosis have been discovered in osteoporosis (Li et al., 2023a). Ferroptosis is a recently identified form of regulated cell death that is characterized by the iron-dependent accumulation of lipid peroxidation (Jiang et al., 2021). Recent research has revealed that ferroptosis impairs the osteogenic differentiation and mineralization of osteoblasts in the diabetic microenvironment, resulting in bone metabolism imbalance and the onset of T2DOP (Zhao et al., 2022a). Under conditions of iron overload, Fe2+ undergoes a Fenton reaction with H2O2 to produce large amounts of reactive oxygen species (ROS), leading to lipid peroxidation and oxidative stress (Kose et al., 2023). Oxidative stress not only directly induces cellular ferroptosis, but also further exacerbates osteoporosis by impairing osteoblast function (Tao et al., 2022). Therefore, inhibition of osteoblast ferroptosis is beneficial for alleviating the progression of T2DOP (Ma et al., 2024). The solute carrier family 7-member 11 (SLC7A11)-glutathione (GSH)-glutathione peroxidase 4 (GPX4) axis constitutes the main system countering ferroptosis and is regulated by the transcriptional factor Nrf2 (Koppula et al., 2021). Nrf2 plays a vital role in delaying the ferroptosis cascade by promoting the activation of its downstream antioxidant genes and enhancing the antioxidant capacity of cells (Kerins and Ooi, 2018). It has been demonstrated that activating the Nrf2/SLC7A11/GPX4 pathway is beneficial for ameliorating osteoblast ferroptosis and facilitating osteogenesis in T2DOP (Ma et al., 2020).

Polycomb Group (PcG) proteins is a family of master epigenetic regulators with multiple biological and pathological functions, including inactivating the X chromosome, controlling cell cycle, maintaining stemness, and regulating tumorigenesis (Schubert, 2019). Polycomb Repressive Complexes 1 and 2 (PRC1 and PRC2) are the best well-known PcG protein complexes, which act synergistically in repressing the transcription of hundreds of lineage-specific genes and are associated with pluripotent cell differentiation and early embryonic development (Blackledge and Klose, 2021). Chromobox 7 (CBX7) protein is a core component in PRC1, which is involved in regulating cell proliferation, apoptosis, and inflammation (Forzati et al., 2014). CBX7 knockout has been revealed to promote the regenerative capacity of various tissues or cells (van Wijnen et al., 2021). Importantly, Zhou et al. reported that deficiency of CBX7 is beneficial for osteoblast proliferation and differentiation as well as dentin and alveolar bone formation (Zhou et al., 2016). In addition, Zhang et al. suggested that CBX7 knockdown attenuated cerebral ischemia-reperfusion injury in rat models by inhibiting ferroptosis through activating the Nrf2/HO-1 signaling pathway and upregulating SLC7A11 and GPX4 expression (Zhang et al., 2022a). Jiang et al. demonstrated that interference of CBX7 protected rat cardiomyocytes H9c2 against hypoxia/reoxygenation-induced inflammation, oxidative stress, and apoptosis by curbing ferroptosis and endoplasmic reticulum stress (Jiang et al., 2024). However, the effects of CBX7 on T2DOP-related osteoblast ferroptosis have not been investigated.

In this study, we established high glucose-treated mouse pre-osteoblast MC3T3-E1 cells and high-fat diet + streptozotocin-induced T2DM rats as in vitro and in vivo models. We aimed to probe the specific role of CBX7 knockdown on ferroptosis and osteoblast differentiation during T2DOP and the underlying mechanisms. We hypothesized that CBX7 deficiency promotes osteogenic differentiation and subsequently ameliorates T2DOP progression by inhibiting ferroptosis through activating the Nrf2/SLC7A11/GPX4 pathway. Our results may provide a theoretical basis for targeting CBX7 to regulate ferroptosis for the treatment of T2DOP.