Effects of NEFAs during IVM on pig embryos from granulosa cell‐cocultured oocytes

Abstract

Circulating levels of nonesterified fatty acids (NEFAs) are elevated in some females, which can impair oocyte maturation and embryo development, and may alter the phenotype of the progeny. However, the effects of NEFAs on human embryo development are not clear due to ethical limitations. Thus, we used pig as the model to investigate the impacts of NEFAs on oocyte and embryo due to their similar reproductive and metabolic physiologies to humans. In this study, porcine cumulusoocyte complexes were in vitro maturated under a pathologically high concentration of NEFAs (468 μM palmitic acid, 194 μM stearic acid, and 534 μM oleic acid) with the presence of granulosa cell monolayer, in contrast to control without NEFAs. The mature oocytes were fertilized to produce embryos for further analysis of the transcriptome and DNA methylation patterns. The elevated level of NEFAs decreased the blastocyst rate and delayed the blastocyst development. Ingenuity pathway analysis showed that the most affected gene pathways were related mainly to cell activities, metabolism, and inflammation. These findings indicated that oocytes exposed to the exogenous high level of NEFAs during in vitro maturation resulted in altered gene expression and DNA methylation of early embryos, which have detrimental impacts on blastocyst quality.

Metabolism of fatty acids in follicular cells, oocytes, and blastocysts

“…Short-term changes in NEFA levels by fasting do change the composition of NEFA in serum, FF and cumulus cells, but does not change that of oocytes nor the subsequent developmental competence ( Aardema et al 2013 ). However, elevated NEFA levels in vitro changed the FA composition profiles of all cell types and hampered oocyte quality and its developmental competence ( Vanholder et al 2006 , Valckx et al 2014 a , Van Hoeck et al 2015 , Desmet et al 2016 , Sutton-McDowall et al 2016 , Pawlak et al 2020 , Shibahara et al 2020 , Wang et al 2020 , Shi & Sirard 2021 b ). Distinctions between in vivo and in vitro studies could be explained by the different environments since the in vivo environment is more homeostatically precise and dynamic under the regulation of all the follicular cells and the FF.…”

“…Under exposure to elevated levels of saturated NEFAs, more ROS are produced and the redox regulation of cumulus cells is unable to supply enough protection to the oocyte from ROS, which was shown as the ROS accumulation in COCs and the deterioration of cumulus cells ( Lolicato et al 2015 ). Compared to blastocysts from COCs cultured without a monolayer of granulosa cells, blastocysts originated from cocultured COCs had anti-inflammatory responses to the exposure to high levels of NEFA, as demonstrated by downregulation of inflammatory factors including SP1 transcription factor (SP1), tumor necrosis factor (TNF), and nuclear factor kappa B (NFKB), and increase of anti-apoptosis factors such as BCL2 like 1 (BCL2L1) ( Shi & Sirard 2021 b ). It can be speculated that some factors originating from cocultured granulosa cells can regulate inflammation.…”