Adult-Onset Caloric Restriction Prevents Age-Related Decline in Oocyte Yield and Quality.

Abstract

Increasing numbers of women are postponing childbearing to ages at which natural and assisted fertility attempts are often unsuccessful due to decreased ovarian follicle reserve and poor oocyte quality. While little at present can be done to prevent age-related decline in reproductive functions in humans, our recent studies in mice showed that when ad libitum (AL) feeding was resumed in females maintained on adult-onset caloric restriction (CR), fertility was sustained well beyond the age at which AL-fed control females became infertile. Importantly, fecundity and offspring survival were also maintained in aged CR-then-AL-fed females, suggesting that CR offsets age-related decline in reproductive functions in part by maintaining oocyte quantity and quality. Thus, herein we directly assessed the effects of adult-onset CR on oocyte yield, maturational stage, and on in vitro fertilization (IVF) and blastocyst developmental rates in aging female mice. Briefly, C57BL/6 female mice were kept on AL-feeding or 40% CR from 4 until 11-months-of-age at which time AL-feeding was resumed in CR cohorts. At 12 months of age, mice were superovulated with PMSG followed by hCG 46 hrs later. Oocytes were collected from the oviducts 16 hrs after hCG treatment. The number of ovulated oocytes and their maturational stage were assessed, or oocytes were fertilized and analyzed for fertilization at 24 hrs, and for development to blastocyst every 24 hrs thereafter. 3-month-old young female mice were analyzed in parallel for controls. When compared to young females, who ovulated an average of 26.3±4.6 oocytes/female (n=6), only 6.5±2.1 oocytes/female (n=12) were ovulated by 12-month-old AL-fed females. In contrast, the oocyte yield in 12-month-old CR-then-AL-fed females was nearly equal to that of young mice with an average of 25.0±3.0 oocytes/female (n=6, P < 0.05 12-month-old AL-fed vs. 12-month-old CR-then-AL-fed group). Notably, the numbers of fertilization competent MII oocytes were also maintained in 12-month-old CR-then-AL-fed females when compared to age-matched AL-fed females (15.8±3.3 vs. 4.4±1.0 MII oocytes/female, respectively, P < 0.05 vs. 12-month-old CR-then-AL-fed group) and were similar to numbers of MII oocytes obtained from young females (23.2±4.3 MII oocytes/female). Oocyte IVF rates were similar in 12-month-old AL-fed, 12-month-old CR-then-AL-fed, and young females (52.4±13.3 %, n=12; 68.0±5.2 %, n=5; and 62.4±3.6%, n=6, respectively), and comparable number of fertilized oocytes developed to blastocyst stage embryos (50±17.9 %, 54.3±14.3 %, and 44±9.4 %, respectively). Importantly, the average number of fertilized oocytes that developed to blastocyst stage per female was similar in young and 12-month-old CR-then-AL-fed females (6.2±1.1 vs. 6±1.6 blastocysts/female, respectively) and significantly higher than that was observed for 12-month-old AL-fed females (1.7±0.8 blastocysts/female, P < 0.05 vs. 12-month-old CR-then-AL-fed group). These data show that adult-onset CR is extremely efficient in preventing age-related decline in oocyte quantity and quality and substantiate our in vivo studies showing effectiveness of this regimen against age-related decline in ovarian function. Sustaining ovarian function by adult-onset CR may, in addition to oocyte quality issues, play a significant role in improving the overall quality of life of aging females normally compromised by endocrine changes associated with the loss of cyclic ovarian function. (platform)