Lactate-associated H3K18 lactylation and SYT8 in the temozolomide response of glioblastoma cells.

Lactate and histone H3K18 lactylation (H3K18la) have been linked to glioblastoma biology. We examined their relationship with synaptotagmin 8 (SYT8) and the response to temozolomide (TMZ). U251MG and U87MG cells were cultured under normoxia or hypoxia and exposed to TMZ, sodium lactate or both. H3K18la enrichment at the SYT8 promoter was assessed by chromatin immunoprecipitation. The effects of SYT8 knockdown were evaluated using CCK-8, colony formation, flow cytometry, wound healing and Transwell assays. Lactate and protein abundance were measured, including H3K18la normalized to total H3 in the four-group experiment. Endpoint tumor weight was assessed in a subcutaneous U87MG xenograft model. TMZ reduced CCK-8 signal and intracellular lactate in both cell lines, whereas lactate supplementation attenuated several effects of TMZ. H3K18la was enriched at the SYT8 promoter, and SYT8 knockdown was accompanied by lower lactate and H3K18la signals. Under TMZ treatment, SYT8-depleted cells formed fewer colonies and had a higher apoptosis fraction. Lactate partly reversed these changes and increased H3K18la/total H3 while SYT8 protein remained low. The combined SYT8-knockdown and TMZ group had the lowest endpoint tumor weight. These results link SYT8 to lactate-associated H3K18 lactylation and TMZ response in GBM cells. The reciprocal changes in SYT8, lactate and H3K18la suggest a possible feedback relationship that warrants further mechanistic study.