GLI1 facilitates collagen-induced arthritis in mice by collaborative regulation of DNA methyltransferases

Dnmt3a-mediated hypermethylation of FoxO3 promotes redox imbalance during osteoclastogenesis

Redox imbalance contributes to aberrant osteoclastogenesis and osteoporotic bone loss. In this study, we observed lower Forkhead box protein O3 (FoxO3), a transcription factor associated with cellular oxidative stress, enhanced osteoclastogenesis in osteoporosis (OP). Single-cell RNA sequencing (scRNA-seq) analysis on the human femoral head indicated that FoxO3 is widely expressed in macrophages. Furthermore, Lysm-Cre;FoxO3f/f OVX mice showed increased reactive oxygen species (ROS), enhanced osteoclastogenesis, and more bone loss than normal OVX mice. Mechanistically, we identified FoxO3 promoter methylation as a crucial factor contributing to decreased FoxO3, thereby influencing osteoclastogenesis and OC function. Intriguingly, we observed that Dnmt3a, highly expressed during osteoclastogenesis, played a pivotal role in regulating the methylation of the FoxO3 promoter. Knockdown of Dnmt3a promoted FoxO3 expression, inhibiting osteoclastogenesis and mitigating OP. Interestingly, we observed that Dnmt3a alleviated osteoclastogenesis by suppressing ROS via upregulating FoxO3 rather than inducing the dissociation of RANK and TRAF6. Collectively, this study elucidates the role and mechanism of FoxO3 in osteoclastogenesis and OP, providing a epigenetic target for the treatment of OP.

MTHFD2 promotes osteoclastogenesis and bone loss in rheumatoid arthritis by enhancing CKMT1-mediated oxidative phosphorylation

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by disrupted bone homeostasis. This study investigated the effect and underlying mechanisms of one-carbon metabolism enzyme methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) on osteoclast differentiation and bone loss in RA.

METHODS

The expression of MTHFD2 was examined in CD14 + monocytes and murine bone marrow-derived macrophages (BMMs). RNA-sequencing was performed to evaluate the regulatory mechanisms of MTHFD2 on osteoclastogenesis. Extracellular flux assay, JC-1 staining, and transmission electron microscopy were used to detect mitochondrial function and energy metabolism changes during osteoclast formation. Collagen-induced arthritis (CIA) mice were used to evaluate the therapeutic effect of MTHFD2 knockdown on bone loss. Bone volume and osteoclast counts were quantified by μCT and histomorphometry.

RESULTS

Elevated MTHFD2 was observed in RA patients and CIA mice with a positive correlation to bone resorption parameters. During osteoclast formation, MTHFD2 was significantly upregulated in both human CD14 + monocytes and murine BMMs. The application of MTHFD2 inhibitor and MTHFD2 knockdown suppressed osteoclastogenesis, while MTHFD2 overexpression promoted osteoclast differentiation in vitro. RNA-sequencing revealed that MTHFD2 inhibition blocked oxidative phosphorylation (OXPHOS) in osteoclasts, leading to decreased adenosine triphosphate (ATP) production and mitochondrial membrane potential without affecting mitochondrial biogenesis. Mechanistically, inhibition of MTHFD2 downregulated the expression of mitochondrial creatine kinase 1 (CKMT1), which in turn affected phosphocreatine energy shuttle and OXPHOS during osteoclastogenesis. Further, a therapeutic strategy to knock down MTHFD2 in knee joint in vivo ameliorated bone loss in CIA mice.

CONCLUSIONS

Our findings demonstrate that MTHFD2 is upregulated in RA with relation to joint destruction. MTHFD2 promotes osteoclast differentiation and arthritic bone erosion by enhancing mitochondrial energy metabolism through CKMT1. Thus, targeting MTHFD2 may provide a potential new therapeutic strategy for tackling osteoclastogenesis and bone loss in RA.

Kurarinone Mitigates LPS-Induced Inflammatory Osteolysis by Inhibiting Osteoclastogenesis Through the Reduction of ROS Levels and Suppression of the PI3K/AKT Signaling Pathway

Inflammatory bone resorption represents a pathological condition marked by an increase in bone loss, commonly associated with chronic inflammatory conditions such as rheumatoid arthritis and periodontitis. Current therapies primarily focus on anti-inflammatory drugs and bisphosphonates; however, these treatments are limited due to side effects, inadequate efficacy, and unpredictable long-term complications. Kurarinone (KR), a bioactive compound isolated from the traditional Chinese herb Sophora flavescens, exhibits a range of biological activities, including anti-inflammatory, anticancer, and cardiovascular protective effects. To address the limitations of existing therapies and enhance drug utilization, this study explores the potential of KR as a therapeutic agent for inflammatory bone resorption and delineates its underlying mechanisms. In vitro experiments reveal that KR notably inhibits osteoclastogenesis and reduces the expression of osteoclastic markers. Additionally, KR decreases the levels of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α, while downregulating NADPH oxidase 1 (NOX1) and Kelch-like ECH-associated protein 1 (Keap1) to diminish ROS production. Furthermore, KR activates the nuclear factor erythroid 2-related factor 2 (Nrf2), which enhances the activity of heme oxygenase-1 (HO-1) and catalase (CAT), facilitating the clearance of excess ROS. The compound also hinders osteoclast formation and functionality by inhibiting the PI3K/AKT/GSK-3β signaling pathway. Lentiviral knockdown of CAT can partially reverse these effects of KR. Meanwhile, in vivo experiments indicate that KR effectively mitigates bone loss in an LPS-induced inflammatory bone resorption model. In summary, KR is a promising new star in breaking through the limitations of previous drugs and treating inflammatory bone resorption.