Impact of Dietary Fatty Acid Source on Ovarian Phosphatidylinositol-3 Kinase Signaling

The ovarian phosphatidylinositol-3 kinase (PI3K) pathway regulates follicle viability, entry of primordial follicles into the growing follicular pool and steroidogenesis via phosphorylation of AKT (pAKT). Further, ovarian intracellular signaling and function have been demonstrated to be altered by high fat diet (HFD) feeding. HFD feeding also alters gut microbiota populations in favor of an increase in gram-negative strains, which are implicated in subsequent metabolic endotoxemia (ME) and PI3K signaling. ME is characterized by increased circulating low levels of lipopolysaccharide (LPS), a component of gram-negative bacterial cell walls. LPS interacts with its receptor, toll-like receptor 4 (TLR4), at the cellular level, to initiate a signaling cascade that culminates in phosphorylation and activation of nuclear factor kappa B. LPS and TLR4 can signal via the PI3K pathway, thus, we hypothesized that HFD feeding could lead to alterations in basal ovarian intracellular signaling in swine. Using the pig as an agrimedical model, we sought to determine if HFD or dietary fatty acid composition would alter ovarian PI3K signaling. Thirty six post-pubertal gilts (56 ±6.5 kg BW) were fed one of three diets for nine weeks. The diets consisted of: 1) Low fat (LF, n=12; 20% calories coming from lard and soybean oil); 2) High fat (HF, n=12; 40% calories coming from lard and soybean oil); or 3) n-3 High fat (n3HF, n=12; 40% calories coming from menhaden fish oil, lard and soybean oil). All diets were formulated to be iso-caloric and nitrogenous and pigs were fed 2.8x maintenance and this was adjusted weekly for nine weeks. At the end of the feeding period, all pigs were euthanized and ovaries collected for quantification of proteins implicated in LPS signaling (TLR4) and follicle viability (AKT, pAKT, histone 4 lysine 5 acetylated (H4K5ac), histone 4 lysine 20 methylated (H4K20me)) by western blot. There was no treatment-induced difference in the abundance of H4K5ac, H4K20me, TLR4, or AKT. However, ovarian pAKT abundance tended to be reduced (P < 0.1) between the LF and n3HF groups compared to the HF diets. The n3HF diet also decreased (P < 0.05) the ratio of pAKT:AKT protein by 43% compared to the LF diet. These data support an influence of diet composition on ovarian PI3K that could translate to effects on follicle viability and growth activation which could, in turn, have consequences for fertility in swine fed altered dietary fatty acid sources.