Knockout of butyrophilin subfamily 1 member A1 () alters lipid droplet formation and phospholipid composition in bovine mammary epithelial cells.

BACKGROUND

Milk lipids originate from cytoplasmic lipid droplets (LD) that are synthesized and secreted from mammary epithelial cells by a unique membrane-envelopment process. Butyrophilin 1A1 (BTN1A1) is one of the membrane proteins that surrounds LD, but its role in bovine mammary lipid droplet synthesis and secretion is not well known.

METHODS

The objective was to knockout BTN1A1 in bovine mammary epithelial cells (BMEC) via the CRISPR/Cas9 system and evaluate LD formation, abundance of lipogenic enzymes, and content of cell membrane phospholipid (PL) species. Average LD diameter was determined via Oil Red O staining, and profiling of cell membrane phospholipid species via liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Lentivirus-mediated infection of the Cas9/sgRNA expression vector into BMEC resulted in production of a homozygous clone . The LD size and content decreased following gene knockout. The mRNA abundance of fatty acid synthase () and peroxisome proliferator-activated receptor-gamma () was downregulated in the clone. Subcellular analyses indicated that BTN1A1 and LD were co-localized in the cytoplasm gene knockout increased the percentage of phosphatidylethanolamine (PE) and decreased phosphatidylcholine (PC), which resulted in a lower PC/PE ratio.

CONCLUSIONS

Results suggest that plays an important role in regulating LD synthesis via a mechanism involving membrane phospholipid composition.