Background: Obesity is associated with female reproductive abnormalities. Hyperlipidaemia might alter the embryonic micro-environment and potentially result in reduced fertility. We aimed to induce hyperlipidaemia nutritionally and investigate the consequences of hyperlipidaemic culture conditions on bovine in vitro embryo development, embryo quality and gene expression patterns.
Methods: Bovine zygotes (n = 1545) were cultured in synthetic oviductal fluid medium supplemented with serum from heifers (n = 3), each fed three successive dietary treatments: (i) control serum, following a hay-based diet, (ii) hyperlipidaemic serum, following a carbohydrate and protected palm-oil-rich diet (FatCh) or (iii) hyperlipidaemic serum, following a protected palm-oil-rich diet (Fat). Blastocysts were evaluated for development, cell count, picnotic and mitotic indexes and cryotolerance. Selected mRNA transcripts were measured by quantitative RT-PCR.
Results: FatCh and Fat diets approximately doubled the total cholesterol concentrations, compared with controls (167.1 +/- 11.9, 150.0 +/- 12.8 versus 83.4 +/- 13.7 mg/dl, respectively, P < 0.05), and fatty acid concentrations (8146.60 +/- 214.61, 6935.56 +/- 1081.04 versus 3944.0 +/- 425.07 micromol/l, respectively, P < 0.05). Supplementation of culture media with FatCh and Fat serum significantly reduced blastocyst rates, compared with controls (27.8, 23.4% versus 36.2%, respectively, P < 0.01), total cell number (103.3 +/- 30.1, 95.6 +/- 28.2 versus 146.9 +/- 34.2, respectively, P < 0.01), mitotic index (1.3 +/- 1.1, 1.7 +/- 2.4 versus 3.6 +/- 2.2%, respectively, P < 0.01) and hatching rates after vitrification (20.4, 13.8 versus 35.7%, respectively, P = 0.03). Embryos in FatCh and Fat groups exhibited significantly higher mRNA levels for genes related to apoptosis and metabolism, compared with controls.
Conclusions: This combined in vivo and in vitro model indicates that the exposure of preimplantation embryos to hyperlipidaemic conditions may result in reduced embryo quality and developmental potential, possibly resulting in poorer fertility.