Dietary omega-3 and -6 polyunsaturated fatty acids affect the composition and development of sheep granulosa cells, oocytes and embryos

Abstract

The evidence that omega-3 (n-3) and -6 (n-6) polyunsaturated fatty acids (PUFAs) have differential effects on ovarian function, oocytes and embryo quality is inconsistent. We report on the effects of n-3 versus n-6 PUFA-enriched diets fed to 36 ewes over a 6-week period, prior to ovarian stimulation and follicular aspiration, on ovarian steroidogenic parameters and embryo quality. Follicle number and size were unaltered by diet, but follicular-fluid progesterone concentrations were greater in n-3 PUFA-fed ewes than in n-6 PUFA-fed ewes. The percentage of saturated FAs (mostly stearic acid) was greater in oocytes than in either granulosa cells or plasma, indicating selective uptake and/or de novo synthesis of saturated FAs at the expense of PUFAs by oocytes. High-density lipoproteins (HDLs) fractionated from sera of these ewes increased granulosa cell proliferation and steroidogenesis relative to the FA-free BSA control during culture, but there was no differential effect of n-3 and n-6 PUFAs on either oestradiol or progesterone production. HDL was ineffective in delivering FAs to embryos during culture, although n-6 PUFA HDL reduced embryo development. All blastocysts, irrespective of the treatment, contained high levels of unsaturated FAs, in particular linoleic acid. Transcripts for HDL and low-density lipoprotein (LDL) receptors (SCARB1 and LDLR) and stearoyl-CoA desaturase (SCD) are reported in sheep embryos. HDL reduced the expression of transcripts for LDLR and SCD relative to the BSA control. The data support a differential effect of n-3 and n-6 PUFAs on ovarian steroidogenesis and pre-implantation development, the latter in the absence of a net uptake of FAs.

Effect of Linolenic acid during in vitro maturation of ovine oocytes: embryonic developmental potential and mRNA abundances of genes involved in apoptosis

“…Previous reports have shown that supplementary fatty acids have significant effects on oocyte maturation and subsequent pre-implantation development [2][3][4][5].…”

Impact of contrasting fish oil concentrations in the diet on ovine embryo development <i>in vivo</i> and of corresponding diet-specific derivative sera during <i>in vitro</i> culture

“…While the n-6/n-3 PUFA ratio of oocytes differed significantly between diets in the study of Wonnacott et al (2010), total PUFAs consistently comprised only 13% of the total fatty acid complement of the oocytes in each case, a value consistent with earlier evidence that these are much less abundant than saturated fatty acids in ruminant oocytes (McEvoy et al, 2000b). Notably, the n-6/n-3 PUFA ratio of 0.7 recorded by Wonnacott et al (2010) for oocytes from ewes given the diet with salmon oil is much closer to the 1.1 ratio we recorded previously for sheep oocytes (McEvoy et al, 2000b) than the dramatically different ratio of 8.3 associated with their sunflower oil-enriched 'n-6' diet. Consequently, although the dietary inclusion of fish oil in the present study may have influenced oocyte/embryo composition in vivo, the effects were unlikely to have dramatically altered either their PUFA complement or n-6/n-3 ratios across treatments.…”

“…In the Kuran et al (1999) study referred to just now, we found that dietary lipid was associated with significantly enhanced progesterone synthesis in primary explants of ovine luteal tissue in vitro. However, because fish oil was not the dietary lipid supplement in that instance, the recent reports by Wonnacott et al (2010) and Hughes et al (2011) are more pertinent to the current study. Among their findings, Hughes et al (2011) indicated that n-3 PUFAs specifically enhance progesterone synthesis by thecal cells of ovine follicles and that this is associated with increased StAR transcript expression, notable because the translated steroidogenic acute regulatory protein is an important facilitator of cholesterol transport to mitochondrial membranes, the rate-limiting step in progesterone biosynthesis (Stocco and Clark, 1996;Niswender, 2002).…”

“…Indeed Adamiak et al (2006) suggested there was possible follicular-level modulation of saturated:polyunsaturated fatty acid balance, achieved via selective uptake, to guard against excessive PUFA accumulation in the oocyte's immediate environment in vivo. However, Wonnacott et al (2010) did report differences in terms of the fatty acid composition of denuded oocytes from ewes fed diets enriched with either n-3 or n-6 PUFAs, the differences being achieved by provision of linseed oil (10 g/kg) plus salmon oil (35 g/kg) in the n-3 ration and sunflower oil (45 g/kg) in the n-6 ration; compared with the current study, this equated to 4.5% oil inclusion in each ration. While the n-6/n-3 PUFA ratio of oocytes differed significantly between diets in the study of Wonnacott et al (2010), total PUFAs consistently comprised only 13% of the total fatty acid complement of the oocytes in each case, a value consistent with earlier evidence that these are much less abundant than saturated fatty acids in ruminant oocytes (McEvoy et al, 2000b).…”

“…However, Wonnacott et al (2010) did report differences in terms of the fatty acid composition of denuded oocytes from ewes fed diets enriched with either n-3 or n-6 PUFAs, the differences being achieved by provision of linseed oil (10 g/kg) plus salmon oil (35 g/kg) in the n-3 ration and sunflower oil (45 g/kg) in the n-6 ration; compared with the current study, this equated to 4.5% oil inclusion in each ration. While the n-6/n-3 PUFA ratio of oocytes differed significantly between diets in the study of Wonnacott et al (2010), total PUFAs consistently comprised only 13% of the total fatty acid complement of the oocytes in each case, a value consistent with earlier evidence that these are much less abundant than saturated fatty acids in ruminant oocytes (McEvoy et al, 2000b). Notably, the n-6/n-3 PUFA ratio of 0.7 recorded by Wonnacott et al (2010) for oocytes from ewes given the diet with salmon oil is much closer to the 1.1 ratio we recorded previously for sheep oocytes (McEvoy et al, 2000b) than the dramatically different ratio of 8.3 associated with their sunflower oil-enriched 'n-6' diet.…”