H3K56 lactylation promotes collagen Ⅱ synthesis to modulate chondrocyte metabolism in posttraumatic osteoarthritis

The accumulation of intracellular glycolytic lactate is a hallmark characteristic of chondrocytes. Histone lactylation, a post-translational modification mediated by lactate, plays a pivotal role in regulating the physiological functions of chondrocytes and contributes to the pathogenesis of posttraumatic osteoarthritis. This study was designed to investigate the role of glycolytic lactate-dependent histone H3 lysine 56 lactylation (H3K56la) in modulating the synthesis of type Ⅱ collagen in chondrocytes. Furthermore, through a combination of laboratory-based and animal experimental approaches, the study sought to uncover new insights into potential therapeutic strategies for the management of posttraumatic osteoarthritis.

In in vitro experiments, the researchers first conducted assays to inhibit and induce histone lactylation in chondrocytes, subsequently measuring changes in the expression levels of hypoxia-inducible factor 1 alpha (HIF 1α) and the type Ⅱ collagen alpha 1 chain gene (Col2a1). Next, we assessed alterations in intracellular lactylation levels and Col2a1 expression following either knockdown or overexpression of HIF 1α in chondrocytes. To further elucidate the regulatory relationship between HIF 1α and Col2a1, chromatin immunoprecipitation assays were performed to investigate the transcriptional control exerted by HIF 1α on the Col2a1 gene promoter. In addition, murine models of posttraumatic osteoarthritis were developed using anterior cruciate ligament transection surgery. Both in vivo and in vitro experiments were then carried out to explore the chondroprotective mechanisms and therapeutic potential associated with modulation of histone lactylation in chondrocytes.

Induction of histone lactylation in chondrocytes led to a significant upregulation of HIF 1α expression. Conversely, knockdown of HIF 1α resulted in a marked reduction in both H3K56 lactylation and Col2a1 expression. It was found that H3K56la and HIF 1α functioned synergistically to positively regulate collagen synthesis, with HIF 1α directly binding to the promoter region of the Col2a1 gene to enhance its transcription. Treatment with α-ketoglutarate modified the cellular redox state and contributed to increased expression of both H3K56la and Col2a1.

The glycolytic lactate/H3K56la/HIF 1α regulatory axis plays a positive regulatory role in the synthesis of type Ⅱ collagen in chondrocytes by facilitating the binding of HIF 1α to the Col2a1 gene promoter. Activation of this molecular pathway holds promise as a novel therapeutic strategy for the treatment of posttraumatic osteoarthritis.