Identification of a novel sn-glycerol-3-phosphate acyltransferase isoform, GPAT4, as the enzyme deficient in Agpat6−/− mice

Abstract

Elucidation of the metabolic pathways of triacylglycerol (TAG) synthesis is critical to the understanding of chronic metabolic disorders such as obesity, cardiovascular disease, and diabetes. sn-Glycerol-3-phosphate acyltransferase (GPAT) and sn-1-acylglycerol-3-phosphate acyltransferase (AGPAT) catalyze the first and second steps in de novo TAG synthesis. AGPAT6 is one of eight AGPAT isoforms identified through sequence homology, but the enzyme activity for AGPAT6 has not been confirmed. We found that in liver and brown adipose tissue from Agpat6-deficient (Agpat6 2/2 ) mice, N-ethylmaleimide (NEM)-sensitive GPAT specific activity was 65% lower than in tissues from wild-type mice, but AGPAT specific activity was similar. Overexpression of Agpat6 in Cos-7 cells increased an NEM-sensitive GPAT specific activity, but AGPAT specific activity was not increased. Agpat6 and Gpat1 overexpression in Cos-7 cells increased the incorporation of [ 14 C]oleate into diacylglycerol (DAG) or into DAG and TAG, respectively, suggesting that the lysophosphatidic acid, phosphatidic acid, and DAG intermediates initiated by each of these isoforms lie in different cellular pools. Together, these data show that "Agpat6 2/2 mice" are actually deficient in a novel NEMsensitive GPAT, GPAT4, and indicate that the alterations in lipid metabolism in adipose tissue, liver, and mammary epithelium of these mice are attributable to the absence of GPAT4.-Nagle, C. A., L. Vergnes, H. DeJong, S. Wang, T. M. Lewin, K. Reue, and R. A. Coleman. Identification of a novel sn-glycerol-3-phosphate acyltransferase isoform, GPAT4, as the enzyme deficient in Agpat6 2/2 mice. J. Lipid Res. 2008. 49: 823-831.

Molecular cloning, sequence characterization, and gene expression profiling of a novel water buffalo (Bubalus bubalis) gene, AGPAT6

“…It contains 1371 nucleotides encoding a putative protein of 456 aa, 52 kDa in size, with a pI of 9.34. As in previous reports of human and mouse, the AGPAT6 protein in water buffalo also contains three hydrophobic transmembrane regions and a signal peptide of 37 aa, which implies that it is a transmembrane protein Chen et al, 2008;Nagle et al, 2008). Generally, most protein functions are regulated by phosphorylation/dephosphorylation.…”

“…As a member of the AGPAT family, AGPAT6 appears to play a key role in lipid biosynthesis (Chen et al, 2008). After careful examination of the AGPAT enzyme activity by Chen et al (2008) and Nagle et al (2008), the enzyme was recognized as another endoplasmic reticulum-localized glycerol phosphate acyltransferase (GPAT) and renamed as GPAT4. The AGPAT6 gene has recently been identified in humans, mice, cattle, and chickens (Li et al, 2003;Chen et al, 2008;Zimin et al, 2009).…”

“…It catalyzes the second step by acylating lysophosphatidic acid to phosphatidic acid (Aguado and Campbell, 1998;Coleman and Lee, 2004;Ye et al, 2005;Agarwal et al, 2006Agarwal et al, , 2007Nagle et al, 2008;Sukumaran et al, 2009). So far, eight members of the AGPAT gene family have been described in humans, which are AGPAT1-8, and each of them possesses a lysophosphatidic acid acyltransferase motif (Ye et al, 2005;Nagle et al, 2008). As a member of the AGPAT family, AGPAT6 appears to play a key role in lipid biosynthesis (Chen et al, 2008).…”

“…In both human and mouse, the AGPAT6 gene consists of 13 exons, whereas that in cattle and chicken contains 12 exons. The AGPAT6 protein contains 456 amino acids (aa) in the species mentioned above, except chicken, in which it is composed of 455 aa (Li et al, 2003;Beigneux et al, 2006;Chen et al, 2008;Nagle et al, 2008).…”

AGPAT6 polymorphism and its association with milk traits of dairy goats

“…It catalyzes the conversion of lysophosphatidic acid (LPA) to phosphatidic acid (PA) (Aguado and Campbell, 1998;Coleman and Lee, 2004;Agarwal et al, 2006Agarwal et al, , 2007Sukumaran et al, 2009). So far, eight members of the AGPAT family in human have been described, which are AGPAT1, 2, 3, 4, 5, 6, 7, and 8 (Ye et al, 2005), and all of them possess LPAAT (lysophosphatidic acid acyltransferase) motifs (Nagle et al, 2008). AGPAT6 is one of the eight AGPAT isoforms identified through sequence homology (Nagle et al, 2008).…”