Impaired ketogenesis in Leydig Cells drives testicular aging

Testicular aging commonly leads to testosterone deficiency and impaired spermatogenesis, yet the underlying mechanisms remain elusive. Here, a comprehensive analysis of senescence landscapes in mice testes during aging revealed that the Leydig cells (LCs) are particularly vulnerable to aging processes. Single-cell RNA sequencing identified the expression of Hmgcs2 (3-hydroxy-3-methylglutaryl-CoA synthetase 2), the gene encoding the rate-limiting enzyme of ketogenesis, decreased significantly in LCs from aged mice. Additionally, the concentrations of ketone bodies β-hydroxybutyric acid (BHB) and acetoacetic acid (AcAc) in the young testes were substantially higher than that in serum, but significantly diminished in aged testes. Silencing of Hmgcs2 in young LCs resulted in decreased ketone body production, which in turn drove LCs senescence and accelerated testicular aging. Mechanistically, BHB acted as an endogenous inhibitor of histone deacetylase 1 to upregulate the expression of Foxo3a by promoting histone acetylation, thereby mitigating LCs senescence and promoting testosterone production. Consistently, enhanced ketogenesis by genetic manipulation or oral BHB supplementation alleviated LCs senescence and ameliorated testicular aging in aged mice. These findings highlight defective ketogenesis as a pivotal factor in testicular aging, suggesting novel therapeutic avenues for addressing age-related testicular dysfunction.