Biobehavioral Laboratory, School of Nursing, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States.
Biobehavioral Laboratory, School of Nursing, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States.
J Nutr. 2024 Apr;154(4):1109-1118. doi: 10.1016/j.tjnut.2024.02.004. Epub 2024 Feb 13.
Glycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance.
We asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur.
Mouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined.
Overexpressing GPAT1 in mouse hepatocytes impaired insulin's suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects.
These data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin's ability to suppress hepatic glucose production in primary mouse hepatocytes.
甘油-3-磷酸酰基转移酶（GPAT）的活性与肥胖和胰岛素抵抗在小鼠和人类中相关。然而，即使在体重正常的人群中也存在胰岛素抵抗，并且肥胖的个体可能代谢健康，这意味着存在复杂的病理生理机制导致胰岛素抵抗。
我们想知道 GPAT1 必须满足哪些条件才能发生肝胰岛素抵抗。
通过腺病毒感染或暴露于高或低浓度葡萄糖来过度表达小鼠肝细胞中的 GPAT。测定细胞的葡萄糖生成和细胞中的磷脂酸（PA）含量，测量 GPAT 活性，分析固醇调节元件结合蛋白 1c（SREBP1c）、碳水化合物反应元件结合蛋白（ChREBP）和 GPAT1 的相对信使 RNA 表达，并检查胰岛素信号转导。
在小鼠肝细胞中过度表达 GPAT1 会损害胰岛素对葡萄糖生成的抑制作用，同时增加 N-乙基马来酰亚胺抗性 GPAT 活性和二-16：0 PA 的含量。在过度表达 GPAT1 的肝细胞中，Akt 介导的胰岛素信号被抑制。当细胞暴露于高葡萄糖浓度时，胰岛素对葡萄糖生成的抑制作用受损，添加棕榈酸会加剧这种损伤。高葡萄糖暴露分别使 SREBP1c、ChREBP 和 GPAT1 的表达增加约 2、5 和 5.7 倍。在培养基中添加 200 mM 棕榈酸或亚油酸不会改变高葡萄糖对这些基因表达的上调。高葡萄糖暴露增加了细胞中二-16：0 PA 的含量，添加棕榈酸进一步增加了二-16：0 PA 的含量。这种作用是特异性的，因为亚油酸没有显示出这种作用。
这些数据表明，无论是通过葡萄糖暴露诱导还是通过转染获得的高 GPAT1 活性和丰富的棕榈酸都可以损害胰岛素抑制原代小鼠肝细胞葡萄糖生成的能力。
