181. SIRT6 PROTEIN IS REDUCED IN TESTES AND SPERM FROM OBESE MALE MICE

Abstract

Obesity in males is associated with altered hormone levels, reduced sperm function and increased sperm DNA damage. However, the underlying molecular mechanism has not been identified. Mammalian SIRT6 protein exhibits caloric intake dependant DNA damage repair in other tissue types. However, a possible role for SIRT6 in male obesity and subfertility has not been considered. Therefore, the aim of this study was to assess the effects of male obesity on SIRT6 in testes and mature sperm. Five week old C57BL6 male mice (n =10 per diet) were fed either a control diet (CD) (6% fat) or a high fat diet (HFD) (21% fat) for 16 weeks before collection of sperm and testes. There was no difference in Sirt6 mRNA levels as determined by qPCR in testes from HFD males. Immunohistochemistry showed SIRT6 localised to the nucleus of transitioning spermatids from late round spermatids until early elongating spermatids. SIRT6 relative fluorescence of these positive cell types was significantly decreased by 22% in males fed the HFD compared to CD (P < 0.05). This was confirmed by a decrease in total SIRT6 protein in testes from HFD males as detected by an immunoabsorbance assay (P < 0.05). Surprisingly, SIRT6 was only present in the acrosome of mature sperm. Acrosomal localisation was confirmed by the loss of SIRT6 staining after an induced acrosome reaction. SIRT6 levels in the acrosome of mature sperm was decreased by 11% in males fed the HFD (P < 0.05). This is the first study to show that SIRT6 is located to the acrosome of mature sperm, specific cells within the testes and is reduced in an obese state. Furthermore, this study suggests a possible role for SIRT6 in the acrosomal reaction and therefore potentially fertilisation, processes which are known to be reduced by male obesity.