Brain Research Institute, School of Medicine and Health Sciences, Monash University Sunway Campus, Jalan Lagoon Selatan, Bandar Sunway, 46150 Petaling Jaya, Selangor, Malaysia.
Neuroscience. 2012 Feb 17;203:39-49. doi: 10.1016/j.neuroscience.2011.12.016. Epub 2011 Dec 19.
In addition to reproduction, gonadotropin-releasing hormone (GnRH) has been postulated to control cholesterol metabolism via cholesterol transport, which is carried out partly by the members of ATP-binding cassette (ABC) transporters G1 (ABCG1) and G4 (ABCG4). However, there is yet to be evidence demonstrating the relationship between these transporters with reference to GnRH neurons. In the present study, we cloned two ABCG1 messenger RNA (mRNA) variants and one ABCG4 mRNA and examined their expression in the brain including GnRH neurons (GnRH1, GnRH2, and GnRH3) in the cichlid tilapia (Oreochromis niloticus). Comparison of nucleotide sequences of the tilapia ABCG1 and ABCG4 with that of other fish species showed that both of these genes are evolutionarily conserved among fishes. ABCG1 and ABCG4 were shown to have high mRNA expressions in the CNS, pituitary, and gonads. In the brain, real-time polymerase chain reaction (PCR) showed that ABCG4 mRNA was higher than ABCG1a in all brain regions including the olfactory bulb (ABCG1=13.34, ABCG4=6796.35; P<0.001), dorsal telencephalon (ABCG1=8.64, ABCG4=10149.13; P=0.001), optic tectum (ABCG1=22.12, ABCG4=13931.04; P<0.01), cerebellum (ABCG1=8.68, ABCG4=12382.90; P<0.01), and preoptic area-midbrain-hypothalamus (ABCG1=21.36, ABCG4=13255.41; P=0.001). Similarly, although ABCG1 mRNA level is much higher in the pituitary compared with the brain, it was still significantly lower compared with ABCG4 (ABCG1=337.73, ABCG4=1157.87; P=0.01). The differential pattern of expression of ABCG1 and ABCG4 in the brain versus pituitary suggests that the two transporters are regulated by different mechanisms. Furthermore, ABCG1 and ABCG4 mRNA expressions were found in all three types of laser-captured GnRH neurons with highly similar percentage of expressions, suggesting that cholesterol efflux from GnRH neurons may require heterodimerization of both ABCG1 and ABCG4.
除了生殖以外，促性腺激素释放激素（GnRH）还被认为通过胆固醇转运来控制胆固醇代谢，而胆固醇转运部分由 ATP 结合盒（ABC）转运蛋白 G1（ABCG1）和 G4（ABCG4）成员执行。然而，目前还没有证据表明这些转运蛋白与 GnRH 神经元之间存在关系。在本研究中，我们克隆了两种 ABCG1 信使 RNA（mRNA）变体和一种 ABCG4 mRNA，并检测了它们在脑包括罗非鱼（Oreochromis niloticus）的 GnRH 神经元（GnRH1、GnRH2 和 GnRH3）中的表达。比较鱼类 ABCG1 和 ABCG4 的核苷酸序列与其他鱼类的序列表明，这两个基因在鱼类中是进化保守的。ABCG1 和 ABCG4 在中枢神经系统、垂体和性腺中具有高 mRNA 表达。实时聚合酶链反应（PCR）显示，ABCG4 mRNA 在包括嗅球（ABCG1=13.34，ABCG4=6796.35；P<0.001）、背侧端脑（ABCG1=8.64，ABCG4=10149.13；P=0.001）、视顶盖（ABCG1=22.12，ABCG4=13931.04；P<0.01）、小脑（ABCG1=8.68，ABCG4=12382.90；P<0.01）和视前区-中脑-下丘脑（ABCG1=21.36，ABCG4=13255.41；P=0.001）在内的所有脑区均高于 ABCG1a。同样，尽管 ABCG1 mRNA 水平在垂体中与脑相比要高得多，但与 ABCG4 相比仍显著较低（ABCG1=337.73，ABCG4=1157.87；P=0.01）。ABCG1 和 ABCG4 在脑与垂体中的表达模式的差异表明，这两种转运蛋白受不同机制的调节。此外，在所有三种类型的激光捕获 GnRH 神经元中均发现了 ABCG1 和 ABCG4 mRNA 的表达，其表达的百分比高度相似，这表明 GnRH 神经元中的胆固醇外排可能需要 ABCG1 和 ABCG4 的异二聚化。
