Elevated non-esterified fatty acid concentrations during bovine oocyte maturation compromise early embryo physiology

Abstract

Elevated concentrations of serum non-esterified fatty acids (NEFA), associated with maternal disorders such as obesity and type II diabetes, alter the ovarian follicular micro-environment and have been associated with subfertility arising from reduced oocyte developmental competence. We have asked whether elevated NEFA concentrations during oocyte maturation affect the development and physiology of zygotes formed from such oocytes, using the cow as a model. The zygotes were grown to blastocysts, which were evaluated for their quality in terms of cell number, apoptosis, expression of key genes, amino acid turnover and oxidative metabolism. Oocyte maturation under elevated NEFA concentrations resulted in blastocysts with significantly lower cell number, increased apoptotic cell ratio and altered mRNA abundance of DNMT3A, IGF2R and SLC2A1. In addition, the blastocysts displayed reduced oxygen, pyruvate and glucose consumption, up-regulated lactate consumption and higher amino acid metabolism. These data indicate that exposure of maturing oocytes to elevated NEFA concentrations has a negative impact on fertility not only through a reduction in oocyte developmental capacity but through compromised early embryo quality, viability and metabolism.

Figure 1. Expression patterns of key genes are altered in bovine blastocysts arising from oocytes matured in the presence of elevated NEFA.

Blastocysts were derived from oocytes matured under control, HIGH SA and HIGH COMBI conditions (n = 192; five replicates). Bars with different superscripts are significantly different between treatments with P<0.05.

Figure 2. Amino acid metabolism of blastocysts originating from NEFA-exposed oocytes is compromised.

A. Amino acid ‘turnover’ of day 7 blastocysts as calculated by summing all amino acids produced and consumed on a per-embryo basis. Comparison was done between blastocysts (n = 135; three replicates) derived from oocytes matured under control, HIGH SA and HIGH COMBI conditions. B. Overall mean profiles of individual amino acids by blastocyst in the three treatments. Bars with different superscripts are significantly different between treatments (P<0.05).

Figure 3. Key processes of ATP production are significantly altered in blastocysts arising from oocytes exposed to NEFA.

A. Mean oxygen consumption of day 7 blastocysts. Blastocysts (n = 66; three replicates) were derived from control-, HIGH SA- and HIGH COMBI-exposed oocytes. Different superscripts indicate significant differences between treatments (P<0.05). B. Mean pyruvate, glucose and lactate consumption of blastocysts. Blastocysts (n = 84; five replicates) originated from oocytes matured in control, HIGH SA and HIGH COMBI maturation medium. Different superscripts indicate significant differences between treatments (P<0.05).