Cardiopulmonary Genomics Program, University of Maryland, Baltimore, Maryland, United States of America.
PLoS One. 2010 Jul 29;5(7):e11819. doi: 10.1371/journal.pone.0011819.
The beta2-adrenergic receptor (beta2AR) is expressed on numerous cell-types including airway smooth muscle cells and cardiomyocytes. Drugs (agonists or antagonists) acting at these receptors for treatment of asthma, chronic obstructive pulmonary disease, and heart failure show substantial interindividual variability in response. The ADRB2 gene is polymorphic in noncoding and coding regions, but virtually all ADRB2 association studies have utilized the two common nonsynonymous coding SNPs, often reaching discrepant conclusions.
METHODOLOGY/PRINCIPAL FINDINGS: We constructed the 8 common ADRB2 haplotypes derived from 26 polymorphisms in the promoter, 5'UTR, coding, and 3'UTR of the intronless ADRB2 gene. These were cloned into an expression construct lacking a vector-based promoter, so that beta2AR expression was driven by its promoter, and steady state expression could be modified by polymorphisms throughout ADRB2 within a haplotype. "Whole-gene" transfections were performed with COS-7 cells and revealed 4 haplotypes with increased cell surface beta2AR protein expression compared to the others. Agonist-promoted downregulation of beta2AR protein expression was also haplotype-dependent, and was found to be increased for 2 haplotypes. A phylogenetic tree of the haplotypes was derived and annotated by cellular phenotypes, revealing a pattern potentially driven by expression.
CONCLUSIONS/SIGNIFICANCE: Thus for obstructive lung disease, the initial bronchodilator response from intermittent administration of beta-agonist may be influenced by certain beta2AR haplotypes (expression phenotypes), while other haplotypes may influence tachyphylaxis during the response to chronic therapy (downregulation phenotypes). An ideal clinical outcome of high expression and less downregulation was found for two haplotypes. Haplotypes may also affect heart failure antagonist therapy, where beta2AR increase inotropy and are anti-apoptotic. The haplotype-specific expression and regulation phenotypes found in this transfection-based system suggest that the density of genetic information in the form of these haplotypes, or haplotype-clusters with similar phenotypes can potentially provide greater discrimination of phenotype in human disease and pharmacogenomic association studies.
β2-肾上腺素能受体（β2AR）在包括气道平滑肌细胞和心肌细胞在内的众多细胞类型上表达。用于治疗哮喘、慢性阻塞性肺疾病和心力衰竭的作用于这些受体的药物（激动剂或拮抗剂）在反应方面表现出显著的个体间变异性。ADRB2 基因在非编码和编码区域存在多态性，但实际上所有 ADRB2 关联研究都利用了两个常见的非同义编码 SNP，经常得出不一致的结论。
方法/主要发现：我们构建了 8 个常见的 ADRB2 单倍型，这些单倍型来自 ADRB2 基因启动子、5'UTR、编码和内含子 3'UTR 中的 26 个多态性。这些单倍型被克隆到一个缺乏载体启动子的表达构建体中，因此β2AR 的表达由其启动子驱动，并且单倍型内 ADRB2 的整个基因中的多态性可以修饰稳态表达。用 COS-7 细胞进行“全基因”转染，发现与其他单倍型相比，有 4 个单倍型的细胞表面β2AR 蛋白表达增加。β2AR 蛋白表达的激动剂促进下调也依赖于单倍型，并且发现 2 个单倍型增加。通过细胞表型对单倍型进行了系统发育树的推导和注释，揭示了一种可能由表达驱动的模式。
结论/意义：因此，对于阻塞性肺疾病，间歇性给予β-激动剂的初始支气管扩张反应可能受某些β2AR 单倍型（表达表型）影响，而其他单倍型可能影响慢性治疗期间的快速耐受（下调表型）。发现两种单倍型具有高表达和较少下调的理想临床效果。单倍型也可能影响心力衰竭拮抗剂治疗，其中β2AR 增加心肌收缩力并具有抗凋亡作用。在这种基于转染的系统中发现的单倍型特异性表达和调节表型表明，这些单倍型或具有相似表型的单倍型簇形式的遗传信息密度可能为人类疾病和药物基因组关联研究中的表型提供更大的鉴别力。
