Iron down-regulates leptin by suppressing protein O-GlcNAc modification in adipocytes, resulting in decreased levels of O-glycosylated CREB
Iron down-regulates leptin by suppressing protein O-GlcNAc modification in adipocytes, resulting in decreased levels of O-glycosylated CREB
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DOI：
10.1074/jbc.ra118.005183
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发表时间：
2019-04-05
影响因子：
4.8
通讯作者：
McClain, Donald A.
中科院分区：
文献类型：
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作者：
Gao, Yan;Liu, Jingfang;McClain, Donald A.
我们之前报道过，铁通过在瘦素基因启动子的两个位点增加磷酸化cAMP反应元件结合蛋白（pCREB）的占用来下调瘦素基因的转录。包括o - glcn酰化在内的几种营养感应途径也调节瘦素。因此，我们研究了o -糖基化是否在铁和creb介导的瘦素调节中起作用。我们发现高铁降低了培养的3T3-L1脂肪细胞和高铁饮食小鼠的o - glcn酰化蛋白，并下调了瘦素mRNA和蛋白水平。葡萄糖胺处理绕过糖基化底物合成的限速步骤，增加了O-GlcNAc和瘦素，而抑制o -糖基转移酶（OGT）则降低了O-GlcNAc和瘦素。葡萄糖胺引起的瘦素水平升高易受铁的抑制，但在OGT抑制的情况下，铁没有进一步降低瘦素。O-GlcNAcase基因缺失的小鼠，无论是通过全身杂合缺失还是通过脂肪细胞靶向纯合缺失，都表现出脂肪组织中O-GlcNAcase水平的增加和瘦素水平的增加，这些水平被铁抑制。值得注意的是，铁增加了pCREB在瘦素启动子上的占用，减少了o - glcn酰化的CREB在瘦素启动子上的占用。在我们的实验模型中观察到的这些模式表明，铁通过降低o -糖基化而不是通过增加蛋白质去糖基化来发挥其对瘦素的影响，并且O-GlcNAcase和OGT mRNA和蛋白质水平都不受铁的影响。我们得出结论，铁通过降低CREB糖基化来下调瘦素，导致CREB磷酸化增加和pCREB占用瘦素启动子。
We previously reported that iron down-regulates transcription of the leptin gene by increasing occupancy of phosphorylated cAMP response element-binding protein (pCREB) at two sites in the leptin gene promoter. Several nutrient-sensing pathways including O-GlcNAcylation also regulate leptin. We therefore investigated whether O-glycosylation plays a role in iron- and CREB-mediated regulation of leptin. We found that high iron decreases protein O-GlcNAcylation both in cultured 3T3-L1 adipocytes and in mice fed high-iron diets and down-regulates leptin mRNA and protein levels. Glucosamine treatment, which bypasses the rate-limiting step in the synthesis of substrate for glycosylation, increased both O-GlcNAc and leptin, whereas inhibition of O-glycosyltransferase (OGT) decreased O-GlcNAc and leptin. The increased leptin levels induced by glucosamine were susceptible to the inhibition by iron, but in the case of OGT inhibition, iron did not further decrease leptin. Mice with deletion of the O-GlcNAcase gene, either via whole-body heterozygous deletion or through adipocyte-targeted homozygous deletion, exhibited increased O-GlcNAc levels in adipose tissue and increased leptin levels that were inhibited by iron. Of note, iron increased the occupancy of pCREB and decreased the occupancy of O-GlcNAcylated CREB on the leptin promoter. These patterns observed in our experimental models suggest that iron exerts its effects on leptin by decreasing O-glycosylation and not by increasing protein deglycosylation and that neither O-GlcNAcase nor OGT mRNA and protein levels are affected by iron. We conclude that iron down-regulates leptin by decreasing CREB glycosylation, resulting in increased CREB phosphorylation and leptin promoter occupancy by pCREB.