Abstract
In the cow a major characteristic of metabolic stress is an elevated level of plasma free fatty acid, due to increased lipid mobilization from adipose tissue. Elevated levels of free fatty acids in blood (complexed to albumin) are associated with increased lipotoxicity in non-adipose tissue. An overview is provided on the negative impact of free fatty acids and the metabolic stress imposed on the oocyte and early embryo and thus on bovine fertility. There is increasing evidence that in vitro as well as in vivo the elevated levels of free fatty acids in blood during metabolic stress can severely hamper oocyte and embryo development. However, fatty acids do also form an essential nutrient source for the oocyte and embryo, which indicates that these good and bad effects of fatty acids should be in subtle balance to optimize the developmental competence of the oocyte and embryo.
Highlights
This manuscript presents an overview of the current knowledge of fatty acid transfer from blood to the follicle, from the follicular fluid towards the cumulus-oocyte-complex and distribution and use of fatty acids in the oocyte
It has been shown that the negative impact of saturated free fatty acids on oocytes can be compensated by mono-unsaturated oleic acid, which is present in the follicular fluid at high concentration (Aardema et al, 2013, 2015)
COCs exposed to a mixture of saturated and mono-unsaturated fatty acids solved in ethanol, demonstrated hampered oocyte developmental competence (Van Hoeck et al, 2011; Sutton-McDowall et al, 2016), whereas, in the study of Aardema et al no such negative impact of a comparable free fatty acids (FFA) mixture was observed in line with the observations after in vivo exposure of COCs to elevated levels of FFA during metabolic stress (Aardema et al, 2013)
Summary
This manuscript presents an overview of the current knowledge of fatty acid transfer from blood to the follicle, from the follicular fluid towards the cumulus-oocyte-complex and distribution and use of fatty acids in the oocyte. Cumulus cells appear to play an important role in both fatty acid transfer towards the oocyte and protection of the oocyte against elevated levels of free fatty acids during metabolic stress conditions (Aardema et al, 2013; Lolicato et al, 2015; Del Collado et al, 2017). Saturated free fatty acids appear to have a detrimental impact on oocyte developmental competence (Leroy et al, 2005; Wu et al, 2010; Aardema et al, 2011). A tight fatty acid regulation via the surrounding cumulus cells appears to be a prerequisite for good oocyte developmental competence. The protective properties of the cumulus cells surrounding the oocyte appear to be important during metabolic stress conditions when elevated levels of free fatty acids occur in the follicular fluid
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