Expression of fungal desaturase genes in cultured mammalian cells

Long-chain polyunsaturated fatty acids (LC-PUFA) are important components o f cellular structure and function. Most of LC-PUFA are derived from linolei c acid and a-linolenic acid. In plants and fungi, these two acids can be sy nthesized from oleic acid via the action of two enzymes, Delta 12 and Delta 15-desaturases. Due to lack of these enzymatic activities and the ability to synthesize these two essential fatty acids, animals must obtain them fro m the diet. In this report, we demonstrated the expression of a fungal Delt a 12-desaturase gene in mouse L cells incubated in serum-free medium. The r esults showed a significant increase in the amount of linoleic acid with a concomitant decrease of oleic acid in cellular lipids. Most of the newly fo rmed linoleic acid was incorporated into cellular phospholipids, particular ly phosphatidylcholine. The increase of linoleic acid provided the substrat e for the endogenous synthesis of (n-6) LC-PUFA, such as eicosadienoic acid (EDA), dihomo-gamma -linoleic acid (DGLA) and arachidonic acid (AA). Prolo nged incubation further increased the levels of linoleic acid derived from oleic acid by the action of Delta 12-desaturase, and the levels of 20:2n-6 produced from linoleic acid by the action of the endogenous elongase. Howev er, prolonged incubation suppressed significantly the formation of DGLA and AA. In a separate study, a fungal Delta6-desaturase gene has also been exp ressed in the mouse L cells incubated in serum-containing medium. The resul t shows a significant increase in levels of 20:3n-6 and 20:4n-6. These find ings demonstrate that through genetic modification, it is possible to (1) g enerate cell lines which no longer require dietary 'essential' fatty acids and (2) alter the endogenous fatty acid metabolism to enhance the productio n of LC-PUFA and their derivatives.