Abstract
BackgroundOleic acid is an abundant free fatty acid present in livestock that are in a negative energy-balance state, and it may have detrimental effects on female reproduction and fertility. Oleic acid induces lipid accumulation in bovine granulosa cells, which leads to a foam cell-like morphology and reduced steroidogenesis. However, why oleic acid increases lipid accumulation but decreases steroidogenesis remains unclear. This study focused on oleic acid’s effects on lipid type and steroidogenesis.ResultsOleic acid increased the lipid accumulation in a concentration-dependent manner and mainly increased the triglyceride level and decreased the cholesterol ester level. Oleic acid also led to a decline in estradiol and progesterone production in porcine granulosa cells in vitro. In addition, oleic acid up-regulated the expression of CD36 and diacylglycerol acyltransferase 2, but down-regulated the expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, scavenger receptor class B member 1 and acetyl-Coenzyme A acetyltransferase 2, as well as steroidogenesis-related genes, including cytochrome P450 family 11 subfamily A member 1, cytochrome P450 family 19 subfamily A member 1 and 3 as well as steroidogenic acute regulatory protein at the mRNA and protein levels. An oleic acid-rich diet also enhanced the triglyceride levels and reduced the cholesterol levels in ovarian tissues of female mice, which resulted in lower estradiol levels than in control-fed mice. Compared with the control, decreases in estrus days and the numbers of antral follicles and corpora lutea, as well as an increase in the numbers of the atretic follicles, were found in the oleic acid-fed female mice.ConclusionsOleic acid changed the lipid type stored in lipid droplets of ovarian granulosa cells, and led to a decrease in steroidogenesis. These results improve our understanding of fertility decline in livestock that are in a negative energy-balance state.
Highlights
Lipid droplets (LDs) are specialized cellular organelles consisting of a neutral lipid core covered by a phospholipid monolayer embedded with various proteins [1].The LDs mainly accumulate either triglycerides (TGs) or cholesteryl esters (CEs), depending on the tissue [2]
Rat granulosa cells incubated with oleic acid and palmitic acid significantly accumulate TG in their LDs, but if loaded with HDL, they accumulate CE in their LDs [7]
The results provide new insights into the mechanisms behind the fertility decline in livestock that are in a negative energy-balance state
Summary
Lipid droplets (LDs) are specialized cellular organelles consisting of a neutral lipid core covered by a phospholipid monolayer embedded with various proteins [1].The LDs mainly accumulate either triglycerides (TGs) or cholesteryl esters (CEs), depending on the tissue [2]. The cells in some metabolic tissues, such as adipose, liver and muscle, accumulate TGs [3], whereas steroidogenic cells in some tissues, such as granulosa cells in ovaries and Leydig cells in testes, mostly accumulate CEs [4, 5]. When loaded with different substrates, the lipid type stored in LDs within cells changes. Rat granulosa cells incubated with oleic acid and palmitic acid significantly accumulate TG in their LDs, but if loaded with HDL (high-density lipoprotein), they accumulate CE in their LDs [7]. The lipid type stored in the LDs of granulosa cells changes when loaded with different substrates. Oleic acid induces lipid accumulation in bovine granulosa cells, which leads to a foam cell-like morphology and reduced steroidogenesis. This study focused on oleic acid’s effects on lipid type and steroidogenesis
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