Sirtuin 1 (SIRT1), the most conserved nicotinamide adenine dinucleotide-dependent protein deacetylase, is involved in the regulation of energy metabolism, genomic stability, and development. SIRT1 knockout (SIRT1) mice exhibit decreased energy expenditure and hypersensitivity to a high-fat diet (HFD). SIRT1 deficiency in the testis has also been shown to cause male infertility in animal models. Therefore, the present study was conducted to examine the alteration of the testicular function of SIRT1 mice on HFD. Six-week-old mice were fed ad libitum as wild type (WT) and SIRT1 male mice with either a control diet or with HFD for 32 weeks and then were sacrificed. The levels of biomarkers for hepatotoxicity, sex hormones, and cytokines were analyzed in the serum and blood-testis barrier, and the sperm morphology was examined in the testis and epididymal spermatozoa. Interestingly, an enlargement of seminal vesicles was observed in the SIRT1 mice fed with HFD. A significantly higher level of hepatotoxicity was also seen in these mice. The concentration of serum testosterone increased in HFD-fed SIRT1 mice compared to the controls. The levels of interleukin-1β and TNF-α increased in both HFD-fed WT and SIRT1 mice. In RT-PCR, the m RNA expression of tight junction protein 2 and claudin 3 significantly decreased in HFD-fed SIRT1 compared to those of the controls. Degenerative spermatocytes and spermatids were detected in the HFD-fed SIRT1 mice testicular section. Sperm motility decreased in WT and SIRT1 with HFD feeding, and sperm concentration decreased significantly in WT-HFD and SIRT1 mice with or without HFD feeding. Taken together, HFD can alter energy and steroid metabolism in SIRT1-deficient mice, which can lead to imbalances in motility and production of sperm and testosterone that can result in male reproductive disorders.

Sirtuin proteins are evolutionary conserved Sir2-related NAD+-dependent deacetylases and regulate many of cellular processes such as metabolism, inflammation, transcription, and aging. Sirtuin contains activity of either ADP-ribosyl-transferase or deacetyltranfease and their activity is dependent on the localization in cells. However, the expression pattern of Sirtuins has not been well studied. To examine the expression levels of Sirtuins, RT-PCR was performed using total RNAs from various tissues including liver, small intestine, heart, brain, kidney, lung, spleen, stomach, uterus, ovary, and testis. Sirtuins were highly expressed in most of tissues including the testis. Immunostaining assay showed that Sirt1 and Sirt6 were mainly located in the nucleus of germ cells, spermatocytes, and spermatids in the seminiferous tubules, whereas Sirt2 and Sirt5 were exclusively present in the cytoplasm of germ cells and sperma-tocytes. Our results indicate that Sirtuins may function as regulators of spermatogenesis and their activities might be dependent on their location in the seminiferous tubules.