Genome-Wide Association Analysis in Asthma Subjects Identifies SPATS2L as a Novel Bronchodilator Response Gene

Bronchodilator response (BDR) is an important asthma phenotype that measures reversibility of airway obstruction by comparing lung function (i.e. FEV1) before and after the administration of a short-acting β2-agonist, the most common rescue medications used for the treatment of asthma. BDR also serves as a test of β2-agonist efficacy. BDR is a complex trait that is partly under genetic control. A genome-wide association study (GWAS) of BDR, quantified as percent change in baseline FEV1 after administration of a β2-agonist, was performed with 1,644 non-Hispanic white asthmatic subjects from six drug clinical trials: CAMP, LOCCS, LODO, a medication trial conducted by Sepracor, CARE, and ACRN. Data for 469,884 single-nucleotide polymorphisms (SNPs) were used to measure the association of SNPs with BDR using a linear regression model, while adjusting for age, sex, and height. Replication of primary P-values was attempted in 501 white subjects from SARP and 550 white subjects from DAG. Experimental evidence supporting the top gene was obtained via siRNA knockdown and Western blotting analyses. The lowest overall combined P-value was 9.7E-07 for SNP rs295137, near the SPATS2L gene. Among subjects in the primary analysis, those with rs295137 TT genotype had a median BDR of 16.0 (IQR = [6.2, 32.4]), while those with CC or TC genotypes had a median BDR of 10.9 (IQR = [5.0, 22.2]). SPATS2L mRNA knockdown resulted in increased β2-adrenergic receptor levels. Our results suggest that SPATS2L may be an important regulator of β2-adrenergic receptor down-regulation and that there is promise in gaining a better understanding of the biological mechanisms of differential response to β2-agonists through GWAS

Dose-Dependent Limitation of Arterial Enlargement by the Matrix Metalloproteinase Inhibitor RS-113,456

Background. Arterial diameter changes in response to flow. Chronic flow-mediated arterial enlargement may be mediated through metalloproteinase activity in the extracellular matrix of the arterial wall. We examined flow-mediated enlargement in the setting of increasing competitive matrix metalloproteinase (MMP) inhibition and with respect to gelatinase A and B expression and activity. Methods. Left common femoral arteriovenous fistulas (AVFs) were created in dose–response (52) and time course (34) cohorts of rats. Dose–response rats received either vehicle alone or 12.5, 25, or 37.5 mg/kg b.i.d. RS 113,456, a competitive MMP inhibitor. Heart rate, blood pressure, and weight were measured at intervals following AVF construction. Aortic and common iliac diameters were measured on postoperative day (POD) 21. Untreated time course rats were sacrificed on PODs 0 (no AVF), 3, 7, 14, and 21. Aortic diameter was measured and the vessels were harvested for tissue analysis. Equal amounts of aortic RNA underwent reverse transcription and polymerase chain reaction with primers for MMP-2, MMP-9, and GAPDH. Zymography was performed on iliac artery tissue to measure gelatinolytic activity. Results. A significant, stepwise reduction in flow-mediated aortic and left common iliac enlargement following left femoral AVF creation was noted with progressively higher doses of RS 113,456 without apparent hemodynamic or toxic effects. Right common iliac diameter was unchanged. Over 21 days following AVF creation, there was an upward trend in expression and activity for MMP-2 not evident for MMP-9. Conclusion. Flow-mediated arterial enlargement is limited by competitive MMP inhibition in a dose-dependent fashion. MMP-dependent flow-mediated enlargement may involve differential expression and activity of MMP-2 and MMP-9

Genome-Wide Association Study of Short-Acting β2-Agonists. A Novel Genome-Wide Significant Locus on Chromosome 2 near ASB3

Rationaleβ2-Agonists are the most common form of treatment of asthma, but there is significant variability in response to these medications. A significant proportion of this responsiveness may be heritable.ObjectivesTo investigate whether a genome-wide association study (GWAS) could identify novel pharmacogenetic loci in asthma.MethodsWe performed a GWAS of acute bronchodilator response (BDR) to inhaled β2-agonists. A total of 444,088 single-nucleotide polymorphisms (SNPs) were examined in 724 individuals from the SNP Health Association Resource (SHARe) Asthma Resource Project (SHARP). The top 50 SNPs were carried forward to replication in a population of 444 individuals.Measurements and main resultsThe combined P value for four SNPs reached statistical genome-wide significance aftercorrecting for multiple comparisons. Combined P values for rs350729, rs1840321, rs1384918, and rs1319797 were 2.21 × 10(-10), 5.75 × 10(-8), 9.3 × 10(-8), and 3.95 × 10(-8), respectively. The significant variants all map to a novel genetic region on chromosome 2 near the ASB3 gene, a region associated with smooth muscle proliferation. As compared with the wild type, the presence of the minor alleles reduced the degree of BDR by 20% in the original population and by a similar percentage in the confirmatory population.ConclusionsThese GWAS findings for BDR in subjects with asthma suggest that a gene associated with smooth muscle proliferation may influence a proportion of the smooth muscle relaxation that occurs in asthma

Genome-Wide Association Study of Short-Acting beta(2)-Agonists A Novel Genome-Wide Significant Locus on Chromosome 2 near ASB3

Rationale: [beta(2)-Agonists are the most common form of treatment of asthma, but there is significant variability in response to these medications. A significant proportion of this responsiveness may be heritable. Objectives: To investigate whether a genome-wide association study (GWAS) could identify novel pharmacogenetic loci in asthma. Methods: We performed a GWAS of acute bronchodilator response (BDR) to inhaled beta(2)-agonists. A total of 444,088 single-nucleotide polymorphisms (SNPs) were examined in 724 individuals from the SNP Health Association Resource (SHARe) Asthma Resource Project (SHARP). The top 50 SNPs were carried forward to replication in a population of 444 individuals. Measurements and Main Results: The combined P value for four SNPs reached statistical genome-wide significance after correcting for multiple comparisons. Combined P values for rs350729, rs1840321, rs1384918, and rs1319797 were 2:21 X 10(-10), 5.75 X 10(-8), 9.3 X 10(-8), 3.95 X 10(-8), respectively. The significant variants all map to a novel genetic region on chromosome 2 neat the ASB3 gene, a region associated with smooth muscle proliferation. As compared with the wild type, the presence of the minor alleles reduced the degree of BDR by 20% in the original population and by a similar percentage in the confirmatory population. Conclusions: These GWAS findings for BDR in subjects with asthma suggest that a gene associated with smooth muscle proliferation may influence a proportion of the smooth muscle relaxation that occurs in asthma

Primary GWAS Top Results (SNPs with Combined P-values <1e-05).

<p>CLLS = CAMP/LOCCS/LODO/Sepracor. CLLS used genotyped SNP data. CARE and ACRN used HapMap Phase 2 imputed data with Mach ratio of empirically observed dosage variance to the expected dosage variance (Rsq) values indicated.</p

Replication study of top SNPs in two independent populations (SARP and DAG).

*<p>rs295137 and rs295114 include SARP and DAG P-values. Remaining SNPs include SARP only.</p

Effect of siRNA-mediated <i>SPATS2L</i> knockdown on β₂-adrenergic receptor levels in HASM cells.

<p>(A) Knockdown efficiency of two <i>SPATS2L</i> siRNAs. Quantitative real-time PCR was done on RNAs extracted from HASM cells transfected with control non-targeting (NT) or <i>SPATS2L</i>-specific siRNAs. (B) Western blot analysis of β₂AR protein in <i>SPATS2L</i> knockdown HASM cells. Three independent experiments (siRNA transfection and Western blot analysis) were done in HASM cells. The upper panel is a representative of the three Western blots. Quantification of the β₂AR protein amount (normalized against the control β-actin protein) from three Western blots is shown in the lower panel.</p