Adipose tissue lipogenic gene networks due to lipid feeding and milk fat depression in lactating cows.

Dietary lipid supplements have been extensively evaluated for their effects on mammary tissue mRNA abundance, including the classical lipogenic genes ACACA, SCD, FASN, and the transcription regulators SREBF1, THRSP, and PPARG. Novel gene isoforms with key regulatory roles in triacylglycerol synthesis have been recently identified including LPIN1 and AGPAT6. Transcriptional networks (i.e., genes whose mRNA expression is regulated by a transcription factor or nuclear receptor) coordinate adipogenesis and lipid filling in nonruminant adipose tissue. To investigate whether long-term milk fat depression affects adipogenic networks in subcutaneous adipose tissue, we characterized mRNA expression via quantitative PCR of 20 genes in cows fed saturated and polyunsaturated lipid for 3 wk. Adipose tissue from cows fed a control diet, control with fish (10 g/kg of dry matter) and soybean oil (25 g/kg of dry matter) (FSO), or control with saturated lipid (35 g/kg, EB100; Energy Booster 100, Milk Specialties, Dundee, IL) was biopsied after 21 d of feeding. Milk production did not differ across treatments (averaged 32 kg +/- 2.8 kg/d during the 21 d) but dry matter intake (DMI) decreased in cows fed FSO versus controls (averaged 18 vs. 22 kg/d during the 21 d). Despite the decrease in DMI, FSO resulted in similar energy intake as EB100 during the last 2 wk of the study. Cows fed FSO had a gradual decline in milk fat and energy yield leading to an overall 25% decrease in milk fat yield during the study (averaged 0.90 vs. 1.2 kg/d) compared with control or EB100. Thus, during the 21-d study, FSO led to a gradual increase in intake energy available for adipose tissue deposition. Relative mRNA expression of LPL and SCD as well as ADFP (coding for a protein involved in lipid droplet formation) and LPIN1 (coding for a protein involved in diacylglycerol synthesis/transcriptional regulation) was upregulated with FSO relative to other diets. Expression of the transcription regulator THRSP tended to be greater in cows fed FSO. Overall, results suggest that long-term milk fat depression caused by feeding FSO provided additional energy as well as long-chain fatty acids that, coupled with upregulation of a subset of adipogenic genes in subcutaneous adipose tissue, might have resulted in greater tissue lipid deposition.