Small Kersten M, Mialet-Perez Jeanne, Seman Carrie A, Theiss Cheryl T, Brown Kari M, Liggett Stephen B
Departments of Medicine and Pharmacology and the CardioPulmonary Research Center, University of Cincinnati College of Medicine, Cincinnati, OH 45267.
Proc Natl Acad Sci U S A. 2004 Aug 31;101(35):13020-5. doi: 10.1073/pnas.0405074101. Epub 2004 Aug 19.
The presynaptic alpha2C adrenergic receptors (AR) act to inhibit norepinephrine release in cardiac and other presynaptic nerves. We have recently shown that a genetic variant in the alpha2CAR coding region (Del322-325), which renders the receptor partially uncoupled from Gi, is a risk factor for heart failure. However, variability of heart failure phenotypes and a dominance of Del322-325 in those of African descent led us to hypothesize that other regions of this gene have functional polymorphisms. In a multiethnic population, we found 20 polymorphisms within 4,625 bp of contiguous sequence of this intronless gene encompassing the promoter, 5' UTR, coding, and 3' UTR. These polymorphisms occur in 24 distinct haplotypes with complex organizations, including multiple 5'-upstream polymorphisms in regions known to direct expression, a 3' UTR substitution polymorphism within an insertion/deletion sequence, and the radical coding polymorphism that deletes four amino acids. Relatively low linkage disequilibrium between many polymorphisms, few cosmopolitan haplotypes, prevalent ethnic-specific haplotypes, and substantial genetic divergence among haplotypes was noted. The dysfunctional Del322-325 allele was partitioned into multiple haplotypes, with frequencies of 48% to 2%. The functional implications of the haplotypes were ascertained by whole-gene transfections of human neuronal cells, where haplotype was significantly related (P < 0.001) to expression levels of receptor transcript and protein. Expression varied by as much as approximately 50% by haplotype, and such studies enabled haplotype clustering by phenotypic, rather than genotypic, similarities. Thus, depending on phenotype, expression-specific haplotypes may amplify, attenuate, or dominate the cardiomyopathic effect attributed to the alpha2CDel322-325 marker.
突触前α2C肾上腺素能受体（AR）可抑制心脏及其他突触前神经中去甲肾上腺素的释放。我们最近发现，α2C AR编码区的一个基因变异（Del322 - 325）使该受体与Gi部分解偶联，是心力衰竭的一个危险因素。然而，心力衰竭表型的变异性以及Del322 - 325在非洲裔人群中的优势，促使我们推测该基因的其他区域存在功能多态性。在一个多民族人群中，我们在这个无内含子基因4625 bp的连续序列内发现了20个多态性位点，该序列涵盖启动子、5'非翻译区（UTR）、编码区和3'UTR。这些多态性位点存在于24种不同的单倍型中，其结构复杂，包括已知可指导表达区域的多个5'上游多态性位点、一个插入/缺失序列内的3'UTR替换多态性位点以及缺失四个氨基酸的激进编码多态性位点。我们注意到许多多态性位点之间的连锁不平衡相对较低、世界性单倍型较少、存在普遍的种族特异性单倍型以及单倍型之间存在显著的遗传差异。功能失调的Del322 - 325等位基因被分为多个单倍型，频率从48%到2%不等。通过对人神经细胞进行全基因转染来确定单倍型的功能影响结果显示，单倍型与受体转录本和蛋白质的表达水平显著相关（P < 0.001）。单倍型之间的表达差异高达约50%，此类研究能够根据表型相似性而非基因型相似性对单倍型进行聚类。因此，根据表型不同，表达特异性单倍型可能会增强、减弱或主导归因于α2C Del322 - 325标记的心肌病效应。
