Oleoyl-CoA Is the Major de NovoProduct of Stearoyl-CoA Desaturase 1 Gene Isoform and Substrate for the Biosynthesis of the Harderian Gland 1-Alkyl-2,3-diacylglycerol

Abstract

1-Alkyl-2,3-diacylglycerol (ADG) is a unique neutral lipid found in the eyeball-associated Harderian gland (HG) of the mouse and acts as a lubricant to facilitate eyelid movement. We found that the HG of the mice with a disruption in the gene for stearoyl-CoA desaturase 1 (SCD1) (SCD1؊/؊) is deficient in ADG. The amount of C20:1n-9, which is a major fatty acid of ADG, was reduced by greater than 90% despite normal elongase enzyme activity proposed to elongate it from C18:1n-9. HG from SCD1؊/؊ mice exhibited high desaturase activity toward C16:0-CoA as substrate but had very low desaturase activity toward C18:0-CoA. Feeding diets containing high levels of oleate to the SCD1؊/؊ mice did not increase the levels of C18:1n-9 or C20:1n-9 in the HG and failed to restore the ADG to the levels found in the HG of the wild-type mouse. De novo ADG synthesis as measured by the incorporation of [ 3 H]glycerol and [ 14 C]glucose was high in the SCD1؉/؉ mouse but was reduced by greater than 90% in the HG of SCD1؊/؊ mouse. The deficiencies in the levels of ADG and C20:1n-9 were not compensated for by the expression of SCD2 and SCD3 isoforms in the HG of the SCD1؊/؊ mouse. These observations demonstrate that SCD1-synthesized oleoyl-CoA is a major substrate required for the biosynthesis of normal levels of ADG and that the SCD isoforms present in the HG have different substrate specificity.

Stearoyl-CoA Desaturase 1 Gene Expression Is Necessary for Fructose-mediated Induction of Lipogenic Gene Expression by Sterol Regulatory Element-binding Protein-1c-dependent and -independent Mechanisms

“…Oleate is the major product of SCD (48). To determine whether oleate is required for the induction of SREBP-1c and lipogenic gene expression, SCD1Ϫ/Ϫ mice were fed a fructose diet supplemented with 5% triolein (18:1) for 2 or 7 days and mRNA expression of SREBP-1, FAS, and ACC were measured.…”

“…The lipid extracts were separated by TLC (hexane/diethyl ether/acetic acid, 80:20:1), and the bands were scraped from the plates, methylated, and analyzed by gas-liquid chromatography as described previously (48). Pentadecanoic acid (Sigma) was added as an internal standard for the quantitation of fatty acids.…”

Leptin-mediated changes in hepatic mitochondrial metabolism, structure, and protein levels

“…Total lipids were extracted from liver as described in previously established protocols (43) Quantification of fatty acids was done through liquid chromatography in accordance to previously published methods (44,45). For the quantification of fatty acids, pentadecanoic acid (Sigma-Aldrich) was added as an internal standard.…”

Loss of stearoyl–CoA desaturase-1 function protects mice against adiposity

“…New insights into the physiological role of the SCD1 gene and its endogenous products came from recent studies of the asebia mouse strains (ab j and ab 2j ) that have naturally occurring mutations in SCD1 (17)(18)(19) as well as a laboratory mouse model with a targeted disruption (SCD1Ϫ͞Ϫ) (6). We used these animal models to show that SCD1Ϫ͞Ϫ mice are deficient in hepatic triglycerides and cholesterol esters (7,20).…”

“…The existence of multiple SCD isoforms in mice (6,(14)(15)(16)(17)(18) and rats makes it difficult to determine the role of each isoform in lipid metabolism. New insights into the physiological role of the SCD1 gene and its endogenous products came from recent studies of the asebia mouse strains (ab j and ab 2j ) that have naturally occurring mutations in SCD1 (17)(18)(19) as well as a laboratory mouse model with a targeted disruption (SCD1Ϫ͞Ϫ) (6).…”