Common ADRB2 haplotypes derived from 26 polymorphic sites direct beta2-adrenergic receptor expression and regulation
Alfredo Panebra1, Wayne C Wang, Molly M Malone
1Cardiopulmonary Genomics Program, University of Maryland, Baltimore, Maryland, United States of America.
Background:
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.
Insights
Genetic variations in the beta2-adrenergic receptor (beta2AR) gene, specifically ADRB2 haplotypes, influence drug response in asthma and heart failure. Two haplotypes show ideal expression and downregulation profiles for better clinical outcomes.
Area of Science:
- Pharmacogenomics
- Molecular biology
- Genetics
Background:
- The beta2-adrenergic receptor (beta2AR) is crucial for regulating airway smooth muscle and cardiac function.
- Variability in patient response to beta2AR-targeting drugs for asthma, COPD, and heart failure is significant.
- Previous ADRB2 gene association studies often yielded conflicting results due to limited analysis of common SNPs.
Purpose of the Study:
- To investigate the functional impact of common ADRB2 haplotypes on beta2AR expression and regulation.
- To correlate specific ADRB2 haplotypes with cellular phenotypes relevant to drug response.
Main Methods:
- Constructed 8 common ADRB2 haplotypes from 26 polymorphisms across the gene.
- Cloned haplotypes into an expression vector to study promoter-driven beta2AR expression.
- Performed whole-gene transfections in COS-7 cells to assess cell surface protein expression and agonist-induced downregulation.
Main Results:
- Identified 4 out of 8 haplotypes with significantly increased cell surface beta2AR protein expression.
- Discovered that 2 haplotypes exhibited increased agonist-promoted beta2AR downregulation.
- Developed a phylogenetic tree of haplotypes annotated with cellular phenotypes, suggesting expression-driven patterns.
Conclusions:
- Specific ADRB2 haplotypes influence both initial bronchodilator response (expression) and tachyphylaxis (downregulation) in obstructive lung diseases.
- Two haplotypes demonstrated an ideal combination of high expression and low downregulation, suggesting potential for improved clinical outcomes.
- Haplotype-specific expression and regulation phenotypes may enhance discrimination in pharmacogenomic studies for conditions like heart failure and lung disease.
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