Functional characterization of the chicken fatty acid elongases

The health benefits of the (n-3) PUFA, EPA, and DHA have created a demand for fish and fish oil, the main sources of these PUFA. Production animals, such as poultry, are potential alternate and sustainable sources of EPA and DHA, provided these fatty acids can be synthesized from plant-derived α-linolenic acid [ALA, 18:3(n-3)]. Because elongases are potential control points in the conversion of ALA to DHA in rats, we examined the chicken elongases, ELOVL2 and ELOVL5, which had not been characterized. ELOVL2 activity was limited to C20-22 PUFA substrates and the major product of ELOVL2 metabolism of EPA was 24:5(n-3). This indicates that ELOVL2 can sequentially elongate EPA to docosapentaenoic acid [DPA, 22:5(n-3)] and then onto 24:5(n-3). ELOVL5 selectivity was broader with elongation of C18-22 PUFA substrates. The ability of chicken ELOVL5 to efficiently synthesize 24:5(n-3) is unique compared with ELOVL5 enzymes from other species. The expression of ELOVL5 was higher than ELOVL2 in livers of broiler chickens and their expression did not change when dietary ALA was increased from 0.6 to 1.3% of dietary energy for 42 d. The expression of both genes was higher than previously seen in rats. The chicken elongase enzymes are unlike those of any species studied to date, because both ELOVL2 and ELOVL5 have the ability to efficiently elongate DPA. In addition, the relative abundance of ELOVL2 and ELOVL5 in the liver suggests that chickens may be able to metabolize more DPA through to 24:5(n-3), the precursor of DHA, compared with other species such as rats.