Functional Development of Stearoyl-CoA Desaturase Gene Expression in Livestock Species
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2013 Springer Science+Business Media New York. All rights are reserved. Fatty acid composition is an important component of foods derived from livestock species, as it contributes to both the healthfulness and the functionality of beef, lamb, pork, and dairy products. The most highly regulated and most abundant fatty acid in animal tissues and dairy products is oleic acid (18:1n-9). Oleic acid is synthesized by the 9 desaturase, stearoyl-coenzyme A desaturase (SCD), which also is responsible for the conversion of trans-vaccenic acid to cis-9, trans-11 conjugated linoleic acid (CLA). In livestock species, SCD catalytic activity and gene expression are greatest in adipose tissue depots, followed by skeletal muscle, intestinal mucosa, and liver. SCD gene expression is highly up-regulated in bovine preadipocytes immediately preceding lipid filling. A single gene encodes SCD in cattle (chromosome 26), sheep (chromosome 22), and pigs (chromosome 14), although a pseudogene (SCD-5) has been identified in brain white and gray matter. While it is questionable that sufficient CLA is present in beef, lamb, or dairy products to provide significant health benefits, the quantity of oleic acid can be increased by gram quantities given appropriate production practices. In particular, dietary unsaturated fatty acids can effectively depress SCD gene expression, whereas dietary saturated fatty acids increase SCD gene expression. The effects of unsaturated fatty acids on SCD gene expression appear to be independent of PPAR and almost certainly reflect the presence of a polyunsaturated fatty acid response element that is completely conserved across livestock species. Although oleic acid strongly depresses SCD gene expression in differentiating adipocytes and myoblasts, it may act as a paracrine factor, promoting adipogenic gene expression in adjacent myoblasts.
