Impact Of Dietary Organic Selenium On Female Fertility And Reproductive Efficiency Of Aging Mice: Implications Of Selenium In Ovarian Biology And Embryology

Female reproductive(ovarian)aging is distinctively characterized by a markedly reduced reproductive function due to a remarkable decline in quality and quantity of follicles and oocytes,as well as alterations in the surrounding ovarian stroma.There is an apparent dearth of clinically viable strategies aimed at either maintaining and/or ameliorating the quantity and quality of oocytes during aging.Selenium(Se)has been implicated in playing many important biological roles in male fertility and reproduction;however,its potential roles in female reproduction,particularly in aging subjects,remain poorly elucidated.Therefore,in the current study we used a murine model of female reproductive aging and elucidated how different dietary Se levels might impact the ovarian follicle reserve and reproductive efficiency in aging females.For this purpose,12-month aged mice were divided in three groups i.e.,Se-deficient(Se-D),organic Se-adequate(OSe-A),and organic Sesupplemented(OSe-S)groups and received one of the following diets: Se—Se-D: 0.08 mg Se/kg;OSe-A: 0.15 mg Se/kg;and OSe-S: Se 0.33 mg Se/kg.(1)The results showed that at the end of an 8-week dietary trial,whole-blood Se concentration and blood total antioxidant capacity(TAOC)were significantly reduced in the Se-D mice,whereas both of these biomarkers were significantly higher in the OSe-S group.Similarly,compared to the Se-D group,Se supplementation significantly ameliorated the maintenance of follicles and reduced the rate of apoptosis in ovaries.Meanwhile,the rate of in vitro-produced embryos resulting from germinal vesicle(GV)oocytes was also significantly improved in the Se-supplemented(OSe-S)group compared to the Se-D mice,in which none of the embryos developed to the hatched blastocyst stage.RT-q PCR results revealed a considerably higher m RNA expression of Gpx1,Gpx3,Gpx4 in the Sesupplemented(OSe-S)group compared to the Se-D group.Similarly,m RNA expression of Bcl-2 and p21 was significantly lower in the Se-supplemented group.Immunohistochemical assay(IHC)also revealed a significantly higher expression of GPX4 in Se-supplemented mice.(2)The m RNA expression of three ER-resident selenoproteins i.e.,Selenof,Selenok,and Selenom was also significantly higher in ovaries of mice fed a diet supplemented with organic Se(OSe-S)compared to those fed a Se-deficient diet.Similarly,immunofluorescence assay(IF)also showed that the protein signals of SELENOK were also significantly higher in the Se-supplemented group.(3)The RNA sequencing(RNA-seq)analysis was performed to see if different dietary levels of Se(Se-D vs.OSe-S)might differentially modulate the expression of nonselenoprotein genes in the ovaries of aging mice.A total of 168 genes were differentially expressed between the two groups.From these,72 and 96 differentially expressed genes(DEGs)were found to be upregulated and downregulated,respectively.Gene Ontology(GO)and pathways enrichment(KEGG)analyses revealed that these DEGs were enriched in several key GO terms and biological pathways including PI3K-Akt signaling pathway,steroid hormone biosynthesis,signaling pathways regulating pluripotency of stem cells,Hippo signaling pathway,ovarian steroidogenesis,and Wnt signaling pathway.Further filtering of RNA-seq data revealed that several DEGs such as Star,Hsd3b6,Scd1,Bmp7,Aqp8,Gas1,Fzd1,and Wwc1 were implicated in key ovarian-and fertility-related functions.In addition,some of the DEGs(Rpl26,Fbxo2,Prss35,and Fam129a)were related to ER homeostasis and/or proteostasis.These findings(DEGs)add more value to our understanding of Se modulation of ovarian functions and female fertility and will pave a way for the focused mechanistic and functional studies in this domain.Collectively,the integrated results of the present study reasonably indicate that Se deficiency(or marginal levels)can negatively impact the fertility and reproduction in females,particularly those of an advancing age,and that the dietary organic Se supplementation can substantiate ovarian function and overall reproductive efficiency in aging females.However,given the fact that the response curve of Se is U-shaped,it is essential that for future studies optimal levels of Se should be very cautiously determined.