Peroxisome proliferator activated receptor-γ controls lipogenic gene networks in goat mammary epithelial cells

Abstract Text:

In non-ruminants, peroxisome proliferator-activated receptor-γ (PPARG) plays a crucial role in fatty acid (FA) metabolism through the regulation of lipogenic gene expression. However, whether or how PPARG regulates the activity of mammary lipogenic genes in ruminant mammary cells remains largely unknown. This study explored the potential role of PPARG in regulating mRNA expression of lipogenic genes in lactating goat primary mammary epithelial cells (GMEC). Adenoviral transfection of the PPARG response element into GMEC was used in this study. The PPARG agonist rosiglitazone (ROSI) was used to study gene expression changes in response to PPARG activation. Expression of 39 genes involved in milk fat synthesis plus 3 internal control genes was measured using qPCR. Data from triplicate cultures were log-transformed and statistically analyzed using the GLM of SAS. The multiple comparisons were corrected using Tukey’s test and significance set at P<0.05. Over-expression of PPARG without (Ad-PPARG+DMSO) or with (Ad-PPARG+ROSI) ROSI markedly upregulated (P = 0.0001) the expression of PPARG compared with the control (Ad-GFP (Green fluorescent protein)+DMSO) and ROSI (Ad-GFP+ROSI) treatments. Over-expression of PPARG without ROSI up-regulated (P < 0.05) the expression of some lipogenic enzymes (ACSS2, ACSL1, SCD, DGAT1, FADS1, GPAM, LPIN1), transcription regulators (LXRα, MLXIPL, PPARG, PPARGC1B), and components of the circadian CLOCK network (CRY1, CRY2). After ROSI treatment of PPARG-overexpressing GMEC there was a further and marked increase (P < 0.05) in the mRNA expression of lipogenic enzymes (FASN, ACSS2, GPAM, LPIN1, ACSL1, SCD), transcription regulators (LXRα, PPARG, SREBF1, PPARGC1B), and components of the circadian CLOCK network (CLOCK, CRY1, CRY2). It was noteworthy that expression of RXRα , a partner of PPARG, was down-regulated in PPARG-overexpressing GMEC with or without ROSI treatment. These results provide direct evidence that PPARG plays a crucial role in regulating fatty acid metabolism in goat mammary cells and underscore the importance of PPARG in the mammary gland during lactation.

Keywords:  PPAR, nutrigenomics, milk fa synthesis