Fatty acid elongase 5 (ELOVL5) alters the synthesis of long-chain unsaturated fatty acids in goat mammary epithelial cells

Abstract

Increased production of long-chain unsaturated fatty acids (LCUFA) can have a positive effect on the nutritional value of ruminant milk for human consumption. In nonruminant species, fatty acid elongase 5 (ELOVL5) is a key enzyme for endogenous synthesis of long-chain unsaturated fatty acids. However, whether ELOVL5 protein plays a role (if any) in ruminant mammary tissue remains unclear. In the present study, we assessed the mRNA abundance of ELOVL5 at 3 stages of lactation in goat mammary tissue. Results revealed that ELOVL5 had the lowest expression at peak lactation compared with the nonlactating and late-lactating periods. The ELOVL5 was overexpressed or knocked down to assess its role in goat mammary epithelial cells. Results revealed that ELOVL5 overexpression increased the expression of perilipin2 (PLIN2) and decreased diacylglycerolacyltransferase 2 (DGAT2) and fatty acid desaturase 2 (FADS2) mRNA, but had no effect on the expression of DGAT1, FADS1, and stearoyl-CoA desaturase 1 (SCD1). Overexpression of ELOVL5 decreased the concentration of C16:1n-7, whereas no significant change in C18:1n-7 and C18:1n-9 was observed. Knockdown of ELOVL5 decreased the expression of PLIN2 but had no effect on DGAT1, DGAT2, FADS1, FADS2, and SCD1 mRNA expression. Knockdown of ELOVL5 increased the concentration of C16:1n-7 and decreased that of C18:1n-7. The alterations of expression of genes related to lipid metabolism after overexpression or knockdown of ELOVL5 suggested a negative feedback regulation by the products of ELOVL5 activation. However, the content of triacylglycerol was not altered by knockdown or overexpression of ELOVL5 in goat mammary epithelial cells, which might have been due to the insufficient availability of substrate in vitro. Collectively, these are the first in vitro results highlighting an important role of ELOVL5 in the elongation of 16-carbon to 18-carbon unsaturated fatty acids in ruminant mammary cells.

Fatty Acid Elongase 7 (ELOVL7) Plays a Role in the Synthesis of Long-Chain Unsaturated Fatty Acids in Goat Mammary Epithelial Cells

“…This response may be caused by “complementary action” among the ELOVL isotypes. This idea is supported by the fact that C16:1 is also a substrate for ELOVL5, and that ELOVL5 had a higher expression level than ELOVL7 in GMEC [7].…”

“…The expression pattern of ELOVL7 in mammary tissue was similar to that of ELOVL5 , which also plays a role in elongating C16:1 to C18:1, indicating that the alterations of FA profiles upon knockdown of ELOVL7 might have been a negative feedback regulation by the products of ELOVL7 activation [7]. Together with the fact that ELOVL7 also catalyzes the elongation of C20, C22, and C24 FA, which are necessary for the cellular membrane composition [15], the higher expression of ELOVL7 in non-lactating mammary gland tissue suggests that ELOVL7 may participate in mammary gland development through its endogenous products.…”

“…Early in vitro studies showed that the FA elongase enzyme regulated the chain length and the degree of unsaturation of FAs [6]. Recent data in the ruminant mammary cells underscored the crucial role of some FA elongases in extending long-chain fatty acids (LCFAs) [7,8].…”

“…Previous data showed that ELOVL5, 6, and 7 were expressed in goat lactating mammary gland tissue [10]. FA profile analysis in goat epithelial mammary cells (GMEC) confirmed that ELOVL6 plays a role in the elongation of long-chain saturated FA (SFA)(C16:0 to stearate (C18:0) [8]) and ELOVL5 plays a role in the elongation of palmitoleic (C16:1n7) and oleic (C18:1n9) acid [7]. However, compared with ELOVL5 and 6, the precise role of ELOVL7 have not been determined in mammary gland tissue.…”

Effect of different exogenous fatty acids on the cytosolic triacylglycerol content in bovine mammary cells

“…Approximately 50% of total milk fatty acids (FA) are derived by de novo synthesis from acetate and butyrate ( Knutsen et al., 2018 ) within specialized mammary cells, and the other 50% by absorption from the blood. Lipids in milk are present in fat droplets formed chiefly of triacylglycerols (TAG) enclosed within a membrane derived from the secretory mammary epithelial cells ( Shi et al., 2018 ). Mammary epithelial cells are known to accumulate TAG as lipid droplets in the cytosol ( Yonezawa et al., 2004a , Yonezawa et al., 2004b ).…”