3-Hydroxybutyrate, A Metabolite in Sustaining Neuronal Cell Vitality: A Mendelian Randomization and in Vitro Experimentation

Background Recent research has implicated mitochondrial DNA copy number (mtDNA-CN) and Tau protein levels in the blood as potential biomarkers for early Alzheimer's disease (AD) risk assessment, correlating with metabolite profiles. However, intermediary metabolites mediating these associations remain elusive. Methods Employing a two-sample and a mediation Mendelian randomization (MR) analysis of the IEU OpenGWAS database, involving 383,476 participants from a genome-wide association study (GWAS) and an exome-wide association study (ExWAS), we identified intermediary metabolites linking mtDNA-CN and Tau.Meanwhile, the effects of mediating metabolites on HT22 cell viability and its mitochondrial morphology were also assessed in conjunction with in vitro experiments. Results Our study revealed an association of mtDNA-CN on Tau (OR = 3.102, 95% CI: 1.016-9.472, P = 0.047), as well as on other 31 metabolites such as 3-Hydroxybutyrate (3HB), Docosahexaenoic acid (DHA), Acetate, Albumin, Apolipoprotein A-I (APOA1), and so on. Notably, 3HB was further implicated in a relationship with Tau (OR = 6.030, 95% CI: 1.054-34.491, P = 0.043), acting as a mediator between mtDNA-CN and Tau. In vitro experiments demonstrated that 3HB positively sustained HT22 cell viability by MTT assay and mitigated mitochondrial swelling under low glucose conditions, as observed via HIS-SIM. Conclusions These findings underscore the potential of 3HB as a biomarker and mediator in early AD risk assessment. Moreover, 3HB's ability to enhance cell viability and preserve mitochondrial morphology in stressed conditions suggests its therapeutic potential in mitigating energy metabolism imbalances in AD brains.