Exposure of bovine oocytes and embryos to elevated non-esterified fatty acid concentrations: integration of epigenetic and transcriptomic signatures in resultant blastocysts

Abstract

BackgroundMetabolic stress associated with negative energy balance in high producing dairy cattle and obesity in women is a risk factor for decreased fertility. Non-esterified fatty acids (NEFA) are involved in this pathogenesis as they jeopardize oocyte and embryo development. Growing evidence indicates that maternal metabolic disorders can disturb epigenetic programming, such as DNA methylation, in the offspring. Oocyte maturation and early embryo development coincide with methylation changes and both are sensitive to adverse environments. Therefore, we investigated whether elevated NEFA concentrations affect establishment and maintenance of DNA methylation in oocytes and embryos, subsequently altering transcriptomic profiles and developmental competence of resultant blastocysts.ResultsBovine oocytes and embryos were exposed to different NEFA concentrations in separate experiments. In the first experiment, oocytes were matured in vitro for 24 h in medium containing: 1) physiological (“BASAL”) concentrations of oleic (OA), palmitic (PA) and stearic (SA) acid or 2) pathophysiological (“HIGH COMBI”) concentrations of OA, PA and SA. In the second experiment, zygotes were cultivated in vitro for 6.5 days under BASAL or HIGH COMBI conditions. Developmental competence was evaluated by assessing cleavage and blastocyst rate. Overall gene expression and DNA methylation of resultant blastocysts were analyzed using microarray. DNA methylation data were re-evaluated by pyrosequencing. HIGH COMBI-exposed oocytes and embryos displayed a lower competence to develop into blastocysts compared to BASAL-exposed counterparts (19.3% compared to 23.2% and 18.2% compared to 25.3%, respectively) (P < 0.05). HIGH COMBI-exposed oocytes and embryos resulted in blastocysts with altered DNA methylation and transcriptomic fingerprints, compared to BASAL-exposed counterparts. Differences in gene expression and methylation were more pronounced after exposure during culture compared to maturation suggesting that zygotes are more susceptible to adverse environments. Main gene networks affected were related to lipid and carbohydrate metabolism, cell death, immune response and metabolic disorders.ConclusionsOverall, high variation in methylation between blastocysts made it difficult to draw conclusions concerning methylation of individual genes, although a clear overview of affected pathways was obtained. This may offer clues regarding the high rate of embryonic loss and metabolic diseases during later life observed in offspring from mothers displaying lipolytic disorders.

Composing the Early Embryonic Microenvironment: Physiology and Regulation of Oviductal Secretions

“…In healthy cattle, levels of NEFAs in the tubal fluid mirror the concentrations measured in plasma [30], meaning that, in the case of lipolytic metabolism during the periconceptional period, the early embryo is likely exposed to elevated NEFAs. Elevated levels of NEFAs were shown to affect embryo DNA methylation and gene expression [103]. In addition, it has been demonstrated that elevated NEFAs affect the metabolism and barrier function of the oviduct epithelium in vitro [97], reinforcing the idea that the buffering function of the oviduct for the embryo can be compromised by maternal metabolic deflection.…”

A Comparative Analysis of Oocyte Development in Mammals

“…Exposure of bovine oocytes to a high concentration of nonesterified fatty acids during in vitro maturation can impair maturation itself, as well as subsequent fertilization and embryo development. Additionally, the resulting blastocysts display an altered pattern of gene expression and epigenetic modifications [204,205]. Cumulus cells indeed incorporate lipids from follicular fluid and store them in lipid droplets to protect the oocyte from lipo-toxicity (reviewed by [184]).…”

Reduced oxygen concentration during in vitro oocyte maturation alters global DNA methylation in the maternal pronucleus of subsequent zygotes in cattle

“…DNA methylation is also required during oocyte growth (O’Doherty, O’Shea, & Fair, ). The follicular environment can impact the establishment of methylation at imprinted loci (O’Doherty et al, ) and transcription and methylation in resultant blastocysts (Desmet et al, ).…”