Arachidonic acid (AA) is remarkably enriched in phosphatidylinositol (PI). Studies using knockout mice of lysophosphatidylinositol acyltransferase 1, which selectively incorporates AA into PI, reveal that AA-containing PI plays a crucial role in cortical lamination and neuronal migration during brain development.

Phosphatidylinositol (PI) is a component of membrane phospholipids, and it functions both as a signaling molecule and as a compartment-specific localization signal in the form of polyphosphoinositides. Arachidonic acid (AA) is the predominant fatty acid in the sn-2 position of PI in mammals. LysoPI acyltransferase (LPIAT) is thought to catalyze formation of AA-containing PI; however, the gene that encodes this enzyme has not yet been identified. In this study, we established a screening system to identify genes required for use of exogenous polyunsaturated fatty acids (PUFAs) in Caenorhabditis elegans. In C. elegans, eicosapentaenoic acid (EPA) instead of AA is the predominant fatty acid in PI. We showed that an uncharacterized gene, which we named mboa-7, is required for incorporation of PUFAs into PI. Incorporation of exogenous PUFA into PI of the living worms and LPIAT activity in the microsomes were greatly reduced in mboa-7 mutants. Furthermore, the membrane fractions of transgenic worms expressing recombinant MBOA-7 and its human homologue exhibited remarkably increased LPIAT activity. mboa-7 encodes a member of the membrane-bound O-acyltransferase family, suggesting that mboa-7 is LPIAT. Finally, mboa-7 mutants had significantly lower EPA levels in PI, and they exhibited larval arrest and egg-laying defects. INTRODUCTIONVarious kinds of fatty acids are distributed in membrane phospholipids in mammalian cells and tissues (Lands and Crawford, 1976;Holub and Kuksis, 1978;MacDonald and Sprecher, 1991). The fatty acyl residues of individual phospholipids seem to be under strict metabolic regulation. In general, saturated fatty acids are esterified at the sn-1 position, whereas polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), are commonly found at the sn-2 position. Three-fourths or more of the phosphatidylinositol (PI) fraction in rat liver and brain constitutes the 1-stearoyl-2-arachidonoyl species (Holub and Kuksis, 1971;Baker and Thompson, 1972). In contrast, the total pool of precursor phosphatidic acid (PA) in rat liver and brain has a fatty acid composition that does not resemble that of PI, showing a low AA content (Possmayer et al., 1969;Akesson et al., 1970;Baker and Thompson, 1972). Selectivity could be expressed during de novo synthesis at the level of formation of cytidine 5Ј-diphosphate (CDP)-diacylglycerol from PA and cytidine 5Ј-triphosphate or in the use of CDP-diacylglycerol in the final reaction. In fact, CDP-diacylglycerol synthase, which prefers 1-stearoyl-2-arachidonoyl PA as a substrate in vitro, has been cloned, although expression is restricted to testis, retina, and brain (Saito et al., 1997).An alternative mechanism for species selection has been proposed on the basis of turnover studies in rat brain in vivo (Baker and Thompson, 1972). [ 3 H]AA and [ 14 C]glycerol injected intracerebrally were incorporated almost exclusively into brain phospholipids. Comparison of PI and PA radioactivity suggest that the initial flux of AA into PI was independent of de novo synthesi...

Selective autophagy ensures the removal of specific soluble proteins, protein aggregates, damaged mitochondria, and invasive bacteria from cells. Defective autophagy has been directly linked to metabolic disorders. However how selective autophagy regulates metabolism remains largely uncharacterized. Here we show that a deficiency in selective autophagy is associated with suppression of lipid oxidation. Hepatic loss of Atg7 or Atg5 significantly impairs the production of ketone bodies upon fasting, due to decreased expression of enzymes involved in β-oxidation following suppression of transactivation by PPARα. Mechanistically, nuclear receptor co-repressor 1 (NCoR1), which interacts with PPARα to suppress its transactivation, binds to the autophagosomal GABARAP family proteins and is degraded by autophagy. Consequently, loss of autophagy causes accumulation of NCoR1, suppressing PPARα activity and resulting in impaired lipid oxidation. These results suggest that autophagy contributes to PPARα activation upon fasting by promoting degradation of NCoR1 and thus regulates β-oxidation and ketone bodies production.

Serine hydrolase inhibitors, which facilitate enzyme function assignment and are used to treat a range of human disorders, often act by an irreversible mechanism that involves covalent modification of the serine hydrolase catalytic nucleophile. The portion of mammalian serine hydrolases for which selective inhibitors have been developed, however, remains small. Here, we show that N-hydroxyhydantoin (NHH) carbamates are a versatile class of irreversible serine hydrolase inhibitors that can be modified on both the staying (carbamylating) and leaving (NHH) groups to optimize potency and selectivity. Synthesis and screening of a small library of NHH carbamates by competitive activity-based protein profiling furnished selective, in vivo-active inhibitors and tailored activity-based probes for multiple mammalian serine hydrolases, including palmitoyl protein thioesterease-1 (PPT1), mutations of which cause the human disease infantile neuronal ceroid lipofuscinosis.

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