Pig adipose depot-specific response to a reduced protein diet in combination with n-3/n-6 polyunsaturated fatty acid intervention

The clarification of mechanisms regulating de novo fatty acid synthesis in adipose depots in pigs is an important step in designing the strategies for producing pigs with “desirable” fatty acid composition. The objective of the study was to investigate adipose depot-specific responses to dietary protein/PUFA intervention with respect to lipid metabolism-related gene expression on mRNA and protein levels and fatty acid concentrations. In total, 40 male Landrace pigs were allocated into 4 experimental groups fed diets different in protein level (19.5 vs. 15.5%) and oil supplementation (sunflower seed vs. linseed oil), and 1 control group (17.4% protein level). The pigs were fed ad libitum from 60 kg to 100 kg live weight and restricted (2.8 kg/d) until 120 kg. After slaughtering, pig adipose depots (abdominal, omental, perirenal, intestinal, and back fat) were taken for real-time quantitative PCR, western blot, and fatty acid analysis. The effects of the dietary protein/PUFA intervention were estimated by 1-way ANOVA with a fixed factor of group (group 1 to 5) using the GLM procedure of the SAS software system. n-3 PUFA vs. n-6 PUFA intervention resulted in significant changes (P < 0.05) in n-3 and n-6 PUFA concentrations in 5 different adipose depots, independent of the dietary protein level. However, the changes in n-3 and n-6 PUFA concentrations are not reflected by corresponding diet-induced alterations of ELOVL5, FADS1, FADS2, and SREBP1 mRNA and protein expression in investigated adipose depots. The mRNA expression of ELOVL5 and SREBP1 was highest in abdominal fat and FADS1 and FADS2 mRNA expression was highest in intestinal fat compared with the other pig adipose depots. Different diets did not affect the concentrations of single and sum SFA. This is in line with the ACACA and FASN gene expression, key enzymes involved in the de novo synthesis of SFA, and transcription factor SREBP-1, which was not affected by different dietary protein/PUFA intervention in all pig adipose depots, except higher protein expressions in abdominal fat of pigs fed a high-protein diet with sunflower seed oil. The gene expression of SCD, the key enzyme in the MUFA biosynthesis, was not diet affected in pig adipose depots and corresponds with the unchanged MUFA tissue concentrations. Because of the discrepancy between the highly different n-3 and n-6 PUFA concentrations and minor changes in lipogenic gene expression in pig adipose depots, alternative pathways of de novo fatty acids synthesis appear to be likely.