Department of Biology, University of Genova, Genova, Italy.
Int J Mol Med. 2010 Apr;25(4):505-12. doi: 10.3892/ijmm_00000370.
Excess energy is stored as neutral lipids in lipid droplets (LDs) whose surface is coated by PAT proteins, each playing a distinct cellular function. The adipocyte differentiation-related protein (ADRP) and tail-interacting protein (TIP47) are expressed almost ubiquitously, whereas the oxidative tissue-enriched PAT protein (OXPAT) is expressed in specific tissues, such as the liver. In rat liver, only ADRP expression has been documented. This study was aimed at identifying OXPAT and TIP47 transcripts in rat hepatocytes, and investigating how their expression is modulated by excess lipids, using fat-enriched hepatocytes to mimic different degrees of steatosis. Primary rat hepatocytes were exposed to fatty acids (FFAs) for 12, 24 and 36 h. Lipid accumulation was estimated by spectrophotometric quantification of triacylglycerol. Expression of PAT proteins as well as of PPARgamma was evaluated by real-time RT-PCR. Hepatocytes exposed to FFAs showed progressive lipid accumulation. The increase in lipid content was associated with the induction of PAT protein expression. At 12 h, OXPAT and TIP47 mRNA expression was up-regulated. At longer times, the level of OXPAT transcripts remained high, whereas that of TIP47 slowly declined. Conversely, ADRP expression showed a time-dependent increase with exposure to FFAs. This study demonstrates, for the first time, the presence of OXPAT and TIP47 transcripts in rat hepatocytes, as well as their up-regulation with lipid accumulation. The distinct time courses observed for the three PAT proteins during FFA exposure might reflect the different roles played by each protein in lipid metabolism in the hepatocyte. Up-regulation of TIP47 and OXPAT might represent an early response to excess lipids, while, in correspondence with a lipid overload, up-regulation of ADRP could address lipids towards storage.
多余的能量以中性脂质的形式储存在脂滴（LDs）中，其表面由 PAT 蛋白覆盖，每种蛋白都具有独特的细胞功能。脂肪细胞分化相关蛋白（ADRP）和尾部相互作用蛋白（TIP47）几乎普遍表达，而氧化组织丰富的 PAT 蛋白（OXPAT）则在特定组织中表达，如肝脏。在大鼠肝脏中，仅记录了 ADRP 的表达。本研究旨在鉴定大鼠肝细胞中的 OXPAT 和 TIP47 转录本，并研究其表达如何被过量脂质调节，使用富含脂肪的肝细胞来模拟不同程度的脂肪变性。原代大鼠肝细胞暴露于脂肪酸（FFAs）12、24 和 36 小时。通过分光光度法定量测定三酰甘油来估计脂质积累。通过实时 RT-PCR 评估 PAT 蛋白和 PPARγ的表达。暴露于 FFAs 的肝细胞显示出进行性脂质积累。脂质含量的增加与 PAT 蛋白表达的诱导相关。在 12 小时时，OXPAT 和 TIP47 mRNA 表达上调。在较长时间内，OXPAT 转录本的水平仍然很高，而 TIP47 的水平则缓慢下降。相反，ADRP 表达随着暴露于 FFAs 而呈现时间依赖性增加。本研究首次证明了 OXPAT 和 TIP47 转录本在大鼠肝细胞中的存在，以及它们在脂质积累时的上调。在 FFA 暴露期间，三种 PAT 蛋白的观察到的不同时间过程可能反映了每种蛋白在肝细胞中脂质代谢中的不同作用。TIP47 和 OXPAT 的上调可能代表对过量脂质的早期反应，而随着脂质过载，ADRP 的上调可能会将脂质储存起来。
