Department of Bioscience Technology, Chung Yuan Christian University, Chung-Li, Taiwan.
PLoS One. 2012;7(5):e36474. doi: 10.1371/journal.pone.0036474. Epub 2012 May 18.
Obesity is a complex, multifactorial disorder influenced by the interaction of genetic, epigenetic, and environmental factors. Obesity increases the risk of contracting many chronic diseases or metabolic syndrome. Researchers have established several mammalian models of obesity to study its underlying mechanism. However, a lower vertebrate model for conveniently performing drug screening against obesity remains elusive. The specific aim of this study was to create a zebrafish obesity model by over expressing the insulin signaling hub of the Akt1 gene.
METHODOLOGY/PRINCIPAL FINDINGS: Skin oncogenic transformation screening shows that a stable zebrafish transgenic of Tg(krt4Hsa.myrAkt1)(cy18) displays severely obese phenotypes at the adult stage. In Tg(krt4:Hsa.myrAkt1)(cy18), the expression of exogenous human constitutively active Akt1 (myrAkt1) can activate endogenous downstream targets of mTOR, GSK-3α/β, and 70S6K. During the embryonic to larval transitory phase, the specific over expression of myrAkt1 in skin can promote hypertrophic and hyperplastic growth. From 21 hour post-fertilization (hpf) onwards, myrAkt1 transgene was ectopically expressed in several mesenchymal derived tissues. This may be the result of the integration position effect. Tg(krt4:Hsa.myrAkt1)(cy18) caused a rapid increase of body weight, hyperplastic growth of adipocytes, abnormal accumulation of fat tissues, and blood glucose intolerance at the adult stage. Real-time RT-PCR analysis showed the majority of key genes on regulating adipogenesis, adipocytokine, and inflammation are highly upregulated in Tg(krt4:Hsa.myrAkt1)(cy18). In contrast, the myogenesis- and skeletogenesis-related gene transcripts are significantly downregulated in Tg(krt4:Hsa.myrAkt1)(cy18), suggesting that excess adipocyte differentiation occurs at the expense of other mesenchymal derived tissues.
CONCLUSION/SIGNIFICANCE: Collectively, the findings of this study provide direct evidence that Akt1 signaling plays an important role in balancing normal levels of fat tissue in vivo. The obese zebrafish examined in this study could be a new powerful model to screen novel drugs for the treatment of human obesity.
肥胖是一种复杂的多因素疾病，受遗传、表观遗传和环境因素相互作用的影响。肥胖会增加患许多慢性疾病或代谢综合征的风险。研究人员已经建立了几种哺乳动物肥胖模型来研究其潜在机制。然而，一种用于方便筛选抗肥胖药物的低等脊椎动物模型仍然难以捉摸。本研究的具体目的是通过过度表达 Akt1 基因的胰岛素信号枢纽来创建斑马鱼肥胖模型。
方法/主要发现：皮肤致癌转化筛选表明，稳定的 Tg(krt4Hsa.myrAkt1)(cy18) 斑马鱼转基因在成年期表现出严重肥胖表型。在 Tg(krt4:Hsa.myrAkt1)(cy18) 中，外源性人组成性激活 Akt1(myrAkt1)的表达可以激活 mTOR、GSK-3α/β 和 70S6K 的内源性下游靶标。在胚胎到幼虫过渡阶段，皮肤中 myrAkt1 的特异性过表达可以促进肥大和增生性生长。从受精后 21 小时（hpf）开始，myrAkt1 转基因在几个间充质衍生组织中异位表达。这可能是整合位置效应的结果。Tg(krt4:Hsa.myrAkt1)(cy18) 导致成年期体重迅速增加、脂肪细胞增生性生长、脂肪组织异常堆积和血糖不耐受。实时 RT-PCR 分析显示，调节脂肪生成、脂肪细胞因子和炎症的关键基因大多数在 Tg(krt4:Hsa.myrAkt1)(cy18) 中高度上调。相比之下，Tg(krt4:Hsa.myrAkt1)(cy18) 中的成肌和骨骼生成相关基因转录物显著下调，表明过量的脂肪细胞分化是以牺牲其他间充质衍生组织为代价的。
结论/意义：总之，本研究的结果提供了直接证据，表明 Akt1 信号在体内平衡正常脂肪组织水平方面发挥着重要作用。本研究中检查的肥胖斑马鱼可能是一种新的强大模型，可用于筛选治疗人类肥胖的新型药物。
