Guo Hong, Foncea Rocio, O'Byrne Sheila M, Jiang Hongfeng, Zhang Yuanyuan, Deis Jessica A, Blaner William S, Bernlohr David A, Chen Xiaoli
From the Departments of Food Science and Nutrition and.
Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Twin Cities, Minnesota 55108 and.
J Biol Chem. 2016 May 20;291(21):11216-29. doi: 10.1074/jbc.M115.711556. Epub 2016 Mar 22.
We have recently characterized the role of lipocalin 2 (Lcn2) as a new adipose-derived cytokine in the regulation of adaptive thermogenesis via a non-adrenergic pathway. Herein, we explored a potential non-adrenergic mechanism by which Lcn2 regulates thermogenesis and lipid metabolism. We found that Lcn2 is a retinoic acid target gene, and retinoic acid concurrently stimulated UCP1 and Lcn2 expression in adipocytes. Lcn2 KO mice exhibited a blunted effect of all-trans-retinoic acid (ATRA) on body weight and fat mass, lipid metabolism, and retinoic acid signaling pathway activation in adipose tissue under the high fat diet-induced obese condition. We further demonstrated that Lcn2 is required for the full action of ATRA on the induction of UCP1 and PGC-1α expression in brown adipocytes and the restoration of cold intolerance in Lcn2 KO mice. Interestingly, we discovered that Lcn2 KO mice have decreased levels of retinoic acid and retinol in adipose tissue. The protein levels of STRA6 responsible for retinol uptake were significantly decreased in adipose tissue. The retinol transporter RBP4 was increased in adipose tissue but decreased in the circulation, suggesting the impairment of RBP4 secretion in Lcn2 KO adipose tissue. Moreover, Lcn2 deficiency abolished the ATRA effect on RBP4 expression in adipocytes. All the data suggest that the decreased retinoid level and action are associated with impaired retinol transport and storage in adipose tissue in Lcn2 KO mice. We conclude that Lcn2 plays a critical role in regulating metabolic homeostasis of retinoids and retinoid-mediated thermogenesis in adipose tissue.
我们最近已将脂质运载蛋白2(Lcn2)鉴定为一种新的脂肪源性细胞因子,它通过非肾上腺素能途径调节适应性产热。在此,我们探究了Lcn2调节产热和脂质代谢的潜在非肾上腺素能机制。我们发现Lcn2是视黄酸靶基因,视黄酸可同时刺激脂肪细胞中解偶联蛋白1(UCP1)和Lcn2的表达。在高脂饮食诱导的肥胖条件下,Lcn2基因敲除小鼠对全反式视黄酸(ATRA)在体重、脂肪量、脂质代谢以及脂肪组织中视黄酸信号通路激活方面的作用减弱。我们进一步证明,Lcn2是ATRA在棕色脂肪细胞中诱导UCP1和过氧化物酶体增殖物激活受体γ共激活因子1α(PGC-1α)表达以及恢复Lcn2基因敲除小鼠耐寒能力的充分作用所必需的。有趣的是,我们发现Lcn2基因敲除小鼠脂肪组织中视黄酸和视黄醇水平降低。负责视黄醇摄取的STRA6蛋白水平在脂肪组织中显著降低。视黄醇转运蛋白RBP4在脂肪组织中增加但在循环中减少,这表明Lcn2基因敲除脂肪组织中RBP4分泌受损。此外,Lcn2缺乏消除了ATRA对脂肪细胞中RBP4表达的影响。所有数据表明,视黄酸水平和作用的降低与Lcn2基因敲除小鼠脂肪组织中视黄醇转运和储存受损有关。我们得出结论,Lcn2在调节脂肪组织中视黄酸的代谢稳态和视黄酸介导的产热中起关键作用。