Goat FADS2 controlling fatty acid metabolism is directly regulated by SREBP1 in mammary epithelial cells

Goat milk provides benefits to human health due to its richness in bioactive components, such as polyunsaturated fatty acids (PUFAs). The fatty acid desaturase 2 (FADS2) is the first rate-limiting enzyme in PUFAs biosynthesis. However, its role and transcriptional regulation mechanisms in fatty acid metabolism in dairy goat remain unclear. Here, our study revealed that the FADS2 gene was highly expressed during the peak lactation compared with the dry period, early lactation, and late lactation. The content of triacylglycerol (TAG) was enhanced with the increasing mRNA expression of TAG synthesis genes (diacylglycerol acyltransferase 1/2, DGAT1/2) in FADS2-overexpressed goat mammary epithelial cells (GMECs). Overexpression of FADS2 was positively correlated with the elevated concentrations of dihomo-gamma-linolenic acid (DGLA) and docosahexaenoic acid (DHA) in GMECs. BODIPY staining showed that FADS2 promoted lipid droplet accumulation in GMECs. To clarify the transcriptional regulatory mechanisms of FADS2, 2,226 bp length of FADS2 promoter was obtained. Deletion mutation assays revealed that the core region of FADS2 promoter was located between the -375 and -26 region, which contained SRE1 (-361/-351) and SRE2 (-191/-181) cis-acting elements of transcription factor sterol regulatory element-binding protein 1 (SREBP1). Overexpression of SREBP1 enhanced relative luciferase activity of the single mutant of SRE1 or SRE2, vice versa, and failed to alter the relative luciferase activity of the joint mutant of SRE1 and SRE2. Chromatin immunoprecipitation (ChIP) and site-directed mutation assays further demonstrated that SREBP1 regulated the transcription of the FADS2 gene by binding to SRE sites in vivo and in vitro. In addition, the mRNA levels of FADS2 were significantly decreased by targeting SRE1 and SRE2 sites in the genome via the CRISPR interference (CRISPRi) system. These findings establish a direct role for FADS2 regulating TAG and fatty acid synthesis by SREBP1 transcriptional regulation in dairy goat, providing new insights into fatty acid metabolism in mammary gland of ruminants.