The Functional Consequences of the 17q12 Asthma Susceptibility Locus

Brigham And Women'S Hospital, Boston MA

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Abstract

? DESCRIPTION (provided by applicant): The objective of this proposal is to identify the asthma gene that is responsible for the genetic associations on chromosome 17q12 with asthma. A common haplotype on chromosome 17q12 is the strongest, most consistently reproducible asthma-susceptibility locus to emerge from genome-wide association studies. The 17q12 asthma-risk haplotype confers regional chromatin remodeling of three neighboring genes: ORMDL3, GSDMB, and ZPBP2. However, from the available genetic data alone, it is impossible to conclude with any certainty which of these three is responsible for the genetic association. From our preliminary data, we observe that both ORDML3 and GSDMB are constitutively expressed in bronchial epithelium, and that their overexpression results in discrete molecular and cellular consequences of importance in asthma. In contrast, we find that ZPBP2 is not expressed in either bronchial epithelium or other asthma-relevant cell types. We thus hypothesize that ORMDL3 or GSDMB, but not ZPBP2, confers asthma risk. To test this hypothesis, we propose three Specific Aims. In Specific Aim 1, we will study inducible transgenic mice generated in our lab that conditionally over express ORMDL3 or GSDMB in bronchial epithelium. We will assess the effects of each gene's over expression in an established murine model of allergic asthma, examining the physiological, histological, and metabolic consequences. In Specific Aim 2, we will experimentally assess (via in vitro knockdown and over expression studies) the independent cellular consequences of ORMDL3 and GSDMB expression in human bronchial epithelial cells derived from individuals homozygous for the risk and protective 17q12 haplotypes. In Specific Aim 3, we will study the relationship of 17q12 haplotype with sphingolipid metabolism in several ways (i) we will measure sphingolipid levels in the airways & lung homogenates from our murine studies in Aim 1 to determine the in vivo effects of ORMDL3 expression; (ii) we will examine by genetic association whether the functional 17q12 regulatory variant contributes to variations in plasma sphingolipid levels in 200 asthmatics; and (iii) we will correlate these plasma sphingolipid levels with bronchodilator response to albuterol and airways hyperreactivity to methacholine. The knowledge gained through these proposed efforts will advance our understanding of this most important asthma-susceptibility locus, and will provide the requisite foundations for the development of novel asthma therapies.