Knockout of Stearoyl-CoA Desaturase 1 Decreased Milk Fat and Unsaturated Fatty Acid Contents of the Goat Model Generated by CRISPR/Cas9

Goat milk contains a rich source
of nutrients, especially unsaturated
fatty acids. However, the regulatory mechanism of milk fat and fatty
acid synthesis remains unclear. Stearoyl-CoA desaturase 1 (SCD1) is
the key enzyme catalyzing monounsaturated fatty acid synthesis and
is essential for milk lipid metabolism. To explore milk lipid synthesis
mechanism in vivo, SCD1-knockout
goats were generated through CRISPR/Cas9 technology for the first
time. SCD1 deficiency did not influence goat growth
or serum biochemistry. Plasma phosphatidylcholines increased by lipidomics
after SCD1 knockout in goats. Whole-blood RNA-seq
indicated alterations in biosynthesis of unsaturated fatty acid synthesis,
cAMP, ATPase activity, and Wnt signaling pathways. In SCD1-knockout goats, milk fat percentage and unsaturated fatty acid levels
were reduced but other milk components were unchanged. Milk lipidomics
revealed decreased triacylglycerols and diacylglycerols levels, and
the differential abundance of lipids were enriched in glycerolipid,
glycerophospholipids, and thermogenesis metabolism pathways. In milk
fat globules, the expression levels of genes related to fatty acid
and TAG synthesis including SREBP1 were reduced. ATP content and
AMPK activity were promoted, and p-p70S6K protein level was suppressed
in SCD1-knockout goat mammary epithelial cells, suggesting
that SCD1 affected milk lipid metabolism by influencing AMPK-mTORC1/p70S6K-SREBP1
pathway. The integrative analysis of gene expression levels and lipidomics
of milk revealed a crucial role of SCD1 in glycerolipids and glycerophospholipids
metabolism pathways. Our observations indicated that SCD1 regulated
the synthesis of milk fat and unsaturated fatty acid in goat by affecting
lipid metabolism gene expression and lipid metabolic pathways. These
findings would be essential for improving goat milk nutritional value
which is beneficial to human health.