Even though recent evidence in goat mammary epithelial cells (GMEC) suggest a role of peroxisome proliferator-activated receptor delta (PPARD) in regulating lipid homeostasis, its role is not fully understood. Our hypothesis was that PPARD regulates lipid transport processes in GMEC and, thus, plays a crucial role in regulating fat formation. The PPARD was overexpressed using an adenovirus system (Ad-PPARD) with recombinant green fluorescent protein (Ad-GFP) as the control. Results revealed that overexpression of PPARD markedly upregulated the mRNA abundance of PPARD. Compared with the control (Ad-GFP+dimethyl sulfoxide), overexpression of PPARD alone had no effect on mRNA expression of CD36, SCD1, FABP4, ACSL1, and ADRP. The cultures overexpressing PPARD with the PPARD ligand GW0742 (GW) upregulated the expression of CD36, FABP3, FABP4, ACSL1, and ADRP. Overexpression of PPARD in GMEC plus GW increased the concentration of 16:1 and 18:1-trans and was associated with upregulation of SCD1. Compared with the control (Ad-GFP+dimethyl sulfoxide), the decrease of triacylglycerol concentration coupled with upregulation of genes related to lipid droplet secretion (e.g., ADRP and ACSL1) induced by PPARD overexpression suggests a role in lipid droplet (LD) secretion. Luciferase assay revealed that GW increased the ADRP promoter activity in a dose-dependent manner. Knockdown of PPARD impaired the increase of ADRP promoter activity induced by GW, whereas GW enhanced the activity of ADRP promoter in GMEC overexpressing PPARD. Data with the ADRP 5′-flanking truncated luciferase reporter suggest a core region (−1,444 to −990 bp) response element for the induction of GW. This core region contains a known PPARG response element (PPRE) at −1,003 to −990 bp. When the PPRE was mutated, the overexpression of PPARD had no effect on ADRP promoter activity. Collectively, these results reveal a novel role for PPARD in lipid homeostasis via promoting fatty acid transport and LD formation through a mechanism of direct binding to the promoter of key genes. Hence, PPARD activity may contribute to fatty acid transport and LD formation during lactation.

尽管最近在山羊乳腺上皮细胞（GMEC）中的证据表明过氧化物酶体增殖物激活受体δ（PPARD）在调节脂质稳态中的作用，但其作用尚不完全清楚。我们的假设是PPARD调节GMEC中的脂质转运过程，因此在调节脂肪形成中起关键作用。所述PPARD使用的腺病毒系统（的Ad-PPARD）用重组绿色荧光蛋白（的Ad-GFP）作为对照过表达。结果显示的过度表达PPARD显着上调的mRNA丰度的PPARD。与对照组（Ad-GFP +二甲基亚砜）相比，单独的PPARD过表达对CD36的mRNA表达没有影响，SCD1，FABP4，ACSL1和ADRP。用PPARD配体GW0742（GW）过表达PPARD的培养物上调CD36，FABP3，FABP4，ACSL1和ADRP的表达。的过表达PPARD在GMEC加GW浓度增加的16：1和18：1-反式并用的上调有关SCD1。与对照（Ad-GFP +二甲基亚砜）相比，三酰甘油浓度的降低以及与脂滴分泌相关基因（例如，ADRP和PPARD过表达诱导的ACSL1）提示在脂质滴（LD）分泌中起作用。萤光素酶测定显示，GW以剂量依赖性方式增加了ADRP启动子活性。抑制PPARD抑制了GW诱导的ADRP启动子活性的增加，而GW增强了过表达PPARD的GMEC中ADRP启动子的活性。具有ADRP 5'侧翼的截短的荧光素酶报道基因的数据表明，一个核心区域（-1,444至-990 bp）可用于诱导GW。该核心区域包含一个在-1,003至-990 bp处的已知PPARG响应元件（PPRE）。当PPRE突变，过表达PPARD有没有影响ADRP启动子活性。总体而言，这些结果揭示了PPARD通过直接结合关键基因启动子的机制促进脂肪酸转运和LD形成，从而在脂质稳态中发挥了新作用。因此，PPARD活性可能有助于泌乳过程中的脂肪酸转运和LD形成。