Conjugated linoleic acid (CLA) trans-10, cis-12 decreases ACC-α gene expression in lactating mammary gland by decreasing specific transcripts from different promoters

Abstract Text: Transcription of acetyl-CoA carboxylase alpha (ACC-α) is initiated from multiple promoters in a tissue-specific fashion and mammary expression of ACC-α is decreased during CLA-induced and diet-induced MFD. The effect of trans-10, cis-12 CLA and a low forage and high oil diet on regulation of the different ACC-α isoforms in mammary tissue was investigated. Nine mid-lactation cows were arranged in a 3 x 3 latin square design with 14 d experimental periods. Treatments were Control, 3 d i.v. infusion of trans-10, cis-12 CLA (CLA-MFD), and feeding a low forage, high oil diet (Diet-induced MFD). Milk fat yield was decreased 38% percent by the low forage and high oil diet and by 24% percent by CLA. Mammary biopsies at the end of each treatment were taken. Quantitative real-time reverse transcriptase PCR assays were developed for ACC-α specific promoters of interest. Data were analyzed using the MIXED procedure of SAS to test expression of individual ACC-α promoters I, II, III (exon 5A) and a well described splice variant (-24NT). The geometric mean of 3 housekeeping genes was calculated and used as a covariant in the model. Differences in expression of individual ACC-α promoters was declared significant at P < 0.05 and trends at P < 0.1. There was no treatment effect on expression of ACC-α transcript from promoter I. Compared to Control, ACC-α promoter II transcript were reduced 32.9% with diet-induced MFD treatment (P = 0.005) and tended to be decreased 18.5% by CLA treatment  (P = 0.06). Transcript from promoter III (exon 5A) was reduced 26.4 and 35% for CLA-induced and diet-induced MFD treatments (P = 0.0001), respectively, compared to Control. Transcript for the -24NT splice variant was reduced by 25.8% during det-induced MFD in comparison to control (P = 0.03), but CLA treatment was not different from control. Promoters II, III, and -24NT splice variant transcript of ACC-α are decreased during diet induced milk fat depression demonstrating a promoter specific role of bioactive fatty acids in ACC-α gene expression.

Keywords: Acetyl-CoA carboxylase promoters, gene expression, conjugated linoleic acid