The effect of lactate dehydrogenase B and its mediated histone lactylation on chondrocyte ferroptosis during osteoarthritis

Histone lactylation is a novel epigenetic regulator that is reported to participate in gene expression. Ferroptosis is an oxidative form of cell death and chondrocyte ferroptosis crucially impacts the development of osteoarthritis (OA). The study aimed at investigating the effect of lactate dehydrogenase B (LDHB) and its mediated histone lactylation on chondrocyte ferroptosis during OA. Our study focused on the establishment of in vivo mouse model and in vitro interleukin-1β (IL-1β)-induced chondrocytes model and administrated LDHB knockdown (siLDHB). Histopathological assessment of cartilage was conducted via HE staining, while serum levels of cartilage oligomeric matrix protein (COMP) and crosslinked C-telopeptides of type II collagen (CTX-II) were quantified using ELISA to evaluate OA severity. The matrix degradation was further examined by expression of Collagen II and Aggrecan. Levels of total iron, ferrous iron (Fe2+), and lipid reactive oxygen species (ROS) were considered measurements of ferroptosis. Assessment of cell viability and proliferation relied on cell counting kit 8 (CCK-8) together with colony formation assay. Western blotting assay served for detecting the relative expression of proteins and protein lactylation. The epigenetic regulation of ACSL4 by LDHB was determined by chromatin immunoprecipitation (ChIP) and luciferase reporter gene assay. OA mice presented remarkably elevated protein level of LDHB and H3K18 lactylation in the cartilage versus the sham group. Knockdown of LDHB downregulated the levels of COMP and CTX-II, as well as alleviated chondrocyte ferroptosis in vitro and in vivo. Results from ChIP and luciferase reporter gene assay demonstrated direct histone lactylation of ACSL promoter, and knockdown of LDHB and treatment with LDH inhibitor reduced histone lactylation and expression of ACSL4. ACSL4 overexpression could reverse the impact of LDHB depletion on chondrocyte proliferation and ferroptosis. LDHB promotes ACSL4 by histone lactylation to induce chondrocyte ferroptosis, which further contributes to OA development. The findings in the study assist in understanding the modulating mechanism of LDHB-mediated lactylation against chondrocyte ferroptosis in OA progression.