俄亥俄州哥倫布市一項新的研究表明,，成熟腦細胞表面的三種特定蛋白量的增加可促使細胞產生新的生長延伸,。該研究探討了小鼠腦神經細胞上的三個相關的受體蛋白：GPR3,，GPR6和GPR12,。當研究人員增加這三種蛋白的量后,，細胞生長延伸比蛋白水平正常時的神經細胞的生長大三倍,，延伸速度比對照細胞快4-8倍,。俄亥俄州立大學醫(yī)學中心的項目主持人Yoshinaga Saeki說,，“我們的研究結果顯示，這三種蛋白可能是用于治療中風,、腦和脊髓損傷及神經退行性疾病的重要靶點,。”該研究刊登在4月6日的《生物化學雜志》（Journal of Biological Chemistry）上。
這些蛋白量的增加與神經細胞cAMP內的一種重要的信號分子的水平的增加有關,。這個分子在調控神經細胞生長,、分化和生存,，以及傳輸神經沖動的軸突再生中起著關鍵作用。隨著哺乳動物神經細胞的成熟,，其細胞內的cAMP水平下降,，這可以部分解釋為什么成熟神經細胞受損的軸突不能再生。神經外科副教授,、俄亥俄州州立dardinger神經腫瘤及神經科學實驗室主管Saeki聲稱,，“我們的發(fā)現(xiàn)為cAMP在軸突生長中起著重要作用這一觀點提供了更多證據(jù)，并顯示出這些受體蛋白可能在調節(jié)神經細胞cAMP的產生中起主要作用,。”
該研究的第一作者Shigeru Tanaka是Saeki所在實驗室的一名博士后研究員,。在本項研究中，他與同事從小鼠與大鼠腦組織神經母細胞瘤中取得神經細胞,，使之在培養(yǎng)基中生長以了解更多關于這三種蛋白及其調控cAMP生長中的作用,。他們向這些細胞中注入三種基因以增加這三種蛋白的含量水平，然后用一種被稱為核糖核酸干擾的實驗室技術關閉這三種蛋白的產生,。上述三個蛋白分子中GPR3在神經細胞中最為豐富,，而GPR12刺激神經細胞延伸的作用最強。研究表明,，阻斷GPR3的產生會大大減慢神經細胞的生長速度,，研究者們通過修復GPR3或GPR12的產生扭轉了這種效應。三種蛋白質的含量水平高也與較高水平的cAMP有關,，同時GPR6和GPR12能增加兩倍到三倍的水平,。
Saeki說，“總的來說,，我們的研究結果顯示,，這三種蛋白能加快神經細胞的生長即使在抑制分子的存在下也是如此，我們迫切希望能找出可以在臨床前中風或脊髓損傷動物模型身上重現(xiàn)此結果的方法,。”
部分英文原文：
J. Biol. Chem., Vol. 282, Issue 14, 10506-10515, April 6, 2007
Neural Expression of G Protein-coupled Receptors GPR3, GPR6, and GPR12 Up-regulates Cyclic AMP Levels and Promotes Neurite Outgrowth*
Shigeru Tanaka, Ken Ishii, Kazue Kasai, Sung Ok Yoon¶, and Yoshinaga Saeki1
From the Dardinger Laboratory for Neuro-oncology and Neurosciences, Department of Neurological Surgery, ¶Department of Molecular and Cellular Biochemistry, and Center for Molecular Neurobiology, the Ohio State University, Columbus, Ohio 43210 and the Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo 160-8582, Japan
Cyclic AMP regulates multiple neuronal functions, including neurite outgrowth and axonal regeneration. GPR3, GPR6, and GPR12 make up a family of constitutively active G protein-coupled receptors (GPCRs) that share greater than 50% identity and 65% similarity at the amino acid level. They are highly expressed in the central nervous system, and their expression in various cell lines results in constitutive stimulation of cAMP production. When the constitutively active GPCRs were overexpressed in rat cerebellar granule neurons in culture, the transfected neurons exhibited significantly enhanced neurite outgrowth and overcame growth inhibition caused by myelin-associated glycoprotein. GPR12-mediated neurite outgrowth was the most prominent and was shown to depend on Gs and cAMP-dependent protein kinase. Moreover, the GPR12-mediated rescue from myelin-associated glycoprotein inhibition was attributable to cAMP-dependent protein kinase-mediated inhibition of the small GTPase, RhoA. Among the three receptors, GPR3 was revealed to be enriched in the developing rat cerebellar granule neurons. When the endogenous GPR3 was knocked down, significant reduction of neurite growth was observed, which was reversed by expression of either GPR3 or GPR12. Taken together, our results indicate that expression of the constitutively active GPCRs up-regulates cAMP production in neurons, stimulates neurite outgrowth, and counteracts myelin inhibition. Further characterization of the GPCRs in developing and injured mammalian neurons should provide insights into how basal cAMP levels are regulated in neurons and could establish a firm scientific foundation for applying receptor biology to treatment of various neurological disorders.
Received for publication, January 31, 2007
* This work was supported by National Institutes of Health Grant R21 NS44514 (to Y. S.), the Gerlach Foundation, and the Dardinger Center Fund for Neuro-oncology Research at the Arthur G. James Cancer Hospital, Ohio State University Medical Center. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The on-line version of this article (available at http://www.jbc.org) contains supplemental movies 1 and 2.
1 To whom correspondence should be addressed: Dardinger Laboratory for Neuro-oncology and Neurosciences, Dept. of Neurological Surgery, Ohio State University Medical Center, 385B Wiseman Hall-CCC, 400 West 12th Ave., Columbus, OH 43210. Tel.: 614-292-3804; Fax: 614-688-4882; E-mail: [email protected] .
