Fat-1 Transgene Is Associated With Improved Reproductive Outcomes

Abstract

High intake of ω-3 polyunsaturated fatty acids (PUFAs) has been associated with a variety of health benefits. However, the role of ω-3 PUFAs in female reproductive function is unclear, with studies showing both positive and negative effects. The type of diet that ω-3 fatty acids are consumed with, for example, a balanced diet vs a high-fat diet (HFD), may influence how ω-3 fatty acids affect female reproductive function. To address the role of ω-3 PUFAs in female reproduction, we used the fat-1 mouse both with and without HFD exposure. Fat-1 mice constitutively express the fat-1 transgene, allowing the conversion of ω-6 to ω-3 fatty acids to yield an optimal tissue ratio of ω-6 to ω-3 fatty acids (∼1:1). In our study, at 15 weeks of age, fat-1 mice had elevated primordial follicles compared with wild-type controls with both standard chow and HFD feeding. Higher serum levels of the ω-3 docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), and eicosapentaenoic acid (EPA) were positively associated with primordial follicle numbers, whereas the ratio of the ω-6 arachidonic acid to EPA + DPA + DHA had the opposite effect. Furthermore, fat-1 mice had increased pregnancy rates and shorter time to pregnancy when fed an HFD compared with wild-type mice. In conclusion, our novel preclinical model suggests that high tissue levels of long-chain ω-3 PUFAs are associated with an improved ovarian reserve and improved reproductive outcomes. Further studies are needed to evaluate ω-3 PUFAs as a potential intervention strategy in women with diminished ovarian reserve.

Figure 1.

Optimal ω-3 to ω-6 ratio alters follicle populations across the reproductive life span. Serial ovarian sections were used to determine the number of (a) primordial, (b) primary, (c) secondary, and (d) antral follicles at 3 wk, 5 wk, 15 wk, and 1 y of age between fat-1 and WT mice. Data are presented as mean ± SEM. *P < 0.05 compared with WT mice as determined by a two-sample t test. Three-wk follicle counts: WT (n = 5), fat-1 (n = 4); 5-wk follicle counts: WT (n = 4), fat-1 (n = 4); 15-wk follicle counts: WT (n = 5), fat-1 (n = 4); 1-y follicle counts: WT (n = 5), fat-1 (n = 6).

Figure 2.

Primordial follicle numbers are positively associated with DHA, DPA, and EPA levels. Levels of serum ω PUFAs from fat-1 and WT mice aged 15 wk old were determined and Pearson correlation was performed between the average number of primordial follicles per ovary and serum levels of (a) EPA, (b) DPA, (c) DHA, and (d) the ratio of AA/EPA + DPA + DHA. Fat-1, n = 4; WT, n = 6.

Figure 3.

Optimal ω-3 to ω-6 ratio increases implantation site resorptions but does not affect litter size. An implantation study was conducted to determine if there was a difference in (a) resorptions, (b) developing pups, (c) total litter size, and (d) percentage of mice with at least one resorption site between fat-1 and WT mice. Differences in resorptions, developing pups, and total litter size were determined by a two-sample t test. Differences in prevalence of mice with resorption sites were determined by a χ² test. (a–c) Data are presented as mean ± SEM. Fat-1, n = 19; WT, n = 24. Asterisks represent statistically significant difference, P < 0.05.

Figure 4.

Optimal ω-3 to ω-6 ratio alters primordial follicle numbers in the context of HFD exposure. Serial ovarian sections were used to determine the number of (a) primordial and (b) growing follicles (primary, secondary, and antral) at 15 wk of age between fat-1 and WT mice fed HFD for 10 wk. (c) Atretic primordial and (d) growing follicles at 15 wk of age between fat-1 and WT mice fed HFD for 10 wk. A two-sample t test was used to determine differences between groups. Data are presented as mean ± SEM. *P < 0.05 compared with WT mice. WT, n = 4; fat-1, n = 5.

Figure 5.

Optimal ω-3 to ω-6 ratio decreases infiltrating ovarian macrophages in the context of HFD feeding. Macrophages were identified using the marker CD68 in HFD-fed WT (n = 5) and fat-1 (n = 5) mice. Representative images are shown for (a) WT, (b) fat-1, and (c) negative control. Quantification of macrophage-positive cells per square millimeter of ovarian section was performed and results are presented in (d) as mean ± SEM. A two-sample t test was used to compared differences between groups.

Figure 6.

Optimal ω-3 to ω-6 ratio improves pregnancy rates in the context of HFD feeding. Breeding trials were conducted from 15 wk of age until 1 y of age in fat-1 and WT mice maintained on an HFD from 5 wk of age to assess (a) average number of pups per litter per mouse, (b) average pup weight per mouse, (c) pregnancy rate, and (d) litter size over time. (a–c) Data are plotted as mean and 95% CI. ***P = 0.001 as determined by a two-sample t test. (d) Data are presented as the number of pups per litter for each month over the months observed for each mouse. (a) Fat-1, n = 7; WT, n = 11. (b, d) Fat-1, n = 8; WT, n = 11. (c) Fat-1, n = 8; WT, n = 12.

Figure 7.

Optimal ω-3 to ω-6 ratio decreases overall survival in the context of HFD feeding. Using time-to-event methods, the number of days after the start of breeding until death or euthanasia was compared between WT and fat-1 mice. Fat-1 mice were more likely to die or be euthanized earlier than WT mice (P = 0.033). WT, n = 12; fat-1, n = 8.