Metabolic Transition of Milk Triacylglycerol Synthesis in Response to Varying Levels of Three 18-Carbon Fatty Acids in Porcine Mammary Epithelial Cells.

This study aimed to examine the effects of increasing levels of three 18-carbon fatty acids (stearate, oleate and linoleate) on mammary lipogenesis, and to evaluate their effects on the milk lipogenic pathway in porcine mammary epithelial cells (pMECs). We found that increasing the three of 18-carbon fatty acids enhanced the cellular lipid synthesis in a dose-dependent manner, as reflected by the increased (triacylglycerol) TAG content and cytosolic lipid droplets in pMECs. The increased lipid synthesis by the three 18-carbon fatty acids was probably caused by the up-regulated expression of major genes associated with milk fat biosynthesis, including CD36 (long chain fatty acid uptake); GPAM, AGPAT6, DGAT1 (TAG synthesis); PLIN2 (lipid droplet formation); and PPARγ (regulation of transcription). Western blot analysis of CD36, DGAT1 and PPARγ proteins confirmed this increase with the increasing incubation of 18-carbon fatty acids. Interestingly, the mRNA expressions of ACSL3 and FABP3 (fatty acids intracellular activation and transport) were differentially affected by the three 18-carbon fatty acids. The cellular mRNA expressions of ACSL3 and FABP3 were increased by stearate, but were decreased by oleate or linoleate. However, the genes involved in fatty acid de novo synthesis (ACACA and FASN) and the regulation of transcription (SREBP1) were decreased by incubation with increasing concentrations of 18-carbon fatty acids. In conclusion, our findings provided evidence that 18-carbon fatty acids (stearate, oleate and linoleate) significantly increased cytosolic TAG accumulation in a dose-dependent manner, probably by promoting lipogenic genes and proteins that regulate the channeling of fatty acids towards milk TAG synthesis in pMECs.

Effects of Diets Differing in Composition of 18-C Fatty Acids on Adipose Tissue Thermogenic Gene Expression in Mice Fed High-Fat Diets.

Dietary fatty acids play important roles in the regulation of fat accumulation or metabolic phenotype of adipocytes, either as brown or beige fat. However, a systematic comparison of effects of diets with different composition of 18-C fatty acids on browning/beiging phenotype has not been done. In this study, we compared the effects of different dietary fats, rich in specific 18-carbon fatty acids, on thermogenesis and lipid metabolism. Male C57BL/6 mice were fed a control diet containing 5.6% kcal fat from lard and 4.4% kcal fat from soybean oil (CON) or high-fat diets (HFD) containing 25% kcal from lard and 20% kcal fat from shea butter (stearic acid-rich fat; SHB), olive oil (oleic acid-rich oil; OO), safflower oil (linoleic acid-rich oil; SFO), or soybean oil (mixed oleic, linoleic, and α-linolenic acids; SBO) ad libitum for 12 weeks, with or without a terminal 4-h norepinephrine (NE) treatment. When compared to SHB, feeding OO, SFO, and SBO resulted in lower body weight gain. The OO fed group had the highest thermogenesis level, which resulted in lower body fat accumulation and improved glucose and lipid metabolism. Feeding SFO downregulated expression of lipid oxidation-related genes and upregulated expression of lipogenic genes, perhaps due to its high n-6:n-3 ratio. In general, HFD-feeding downregulated Ucp1 expression in both subcutaneous and epididymal white adipose tissue, and suppressed NE-induced Pgc1a expression in brown adipose tissue. These results suggest that the position of double bonds in dietary fatty acids, as well as the quantity of dietary fat, may have a significant effect on the regulation of oxidative and thermogenic conditions in vivo.

Lipopolysaccharide Alters Thermogenic and Inflammatory Genes in White Adipose Tissue in Mice Fed Diets with Distinct 18-Carbon Fatty-Acid Composition.

Fatty acids are involved in the regulation of inflammatory responses in obesity. However, despite being the largest dietary fatty-acid class, effects of 18-carbon fatty acids with different degrees of saturation on inflammatory, metabolic, and thermogenic markers have not been well studied. Therefore, the objective of this study was to test if diets with different 18-carbon fatty-acid profiles differentially regulate inflammatory and metabolic genes. Male C57BL/6 mice were fed one of the four different diets: a control diet (CON) containing 5.6% kcal fat from lard and 4.4% kcal fat from soybean oil (CON) or three high-fat diets (HFD) containing 25% kcal fat from lard and 20% kcal fat from either shea butter oil (saturated fatty-acid-rich fat; shea butter [SHB]), olive oil (monounsaturated fatty-acid-rich fat; olive oil [OO]), or soybean oil (polyunsaturated fatty-acid-rich fat; soybean oil [SBO]) ad libitum for 4 weeks with or without a terminal 4-h lipopolysaccharide (LPS) treatment. Compared to CON, HFD-fed mice had higher weight gain and fat accumulation. The OO group had the highest brown adipose tissue (BAT) mass while the SBO group had higher Il6 and lower Cpt1a expression in white adipose tissue (WAT) than other HFD groups. Treatment with LPS upregulated expression of proinflammatory cytokines, and this was associated with downregulation of thermogenic gene expression. However, the diets did not have differential effects on inflammatory response to LPS. These data indicate that the saturation degree of 18-C fatty acids is not an important factor on response to LPS with regard to metabolic and inflammatory indicators.