Respiratory sphingolipid synthesis involved in airway hyperreactivity and viral-triggered asthma

PROJECT SUMMARY Asthma results from a complex interplay between genetic background and environmental triggers. The 17q21 asthma susceptibility locus is strongly linked to childhood asthma through ORMDL3. ORMDL3 regulates serine-palmitoyl CoA transferase (SPT), the critical enzyme for the de novo synthesis of sphingolipids. We demonstrated that decreased SPT activity leads to airway hyperreactivity. There has since been increasing evidence that sphingolipid metabolism is altered in airway epithelial cells and animal models of ORMDL3-associated asthma. We have recently shown that children with asthma have decreased sphingolipid synthesis, especially in the presence of asthma risk 17q21 genotypes. 17q21 genotypes are also linked to the risk of developing asthma following respiratory infections with human rhinovirus (HRV). This is relevant as HRV is also the most common trigger for asthma attacks. Supported by preliminary data in mice and airway epithelial cells demonstrating strong similarities in sphingolipid levels and gene expression between HRV infection and sphingolipid deficiency, we hypothesize that HRV infection can further impair sphingolipid synthesis. We propose to study the effects of HRV on sphingolipid synthesis in children with asthma and airway epithelial cells. These studies could then further solidify the central role of sphingolipids in asthma pathogenesis that has been predicted by the commonality and the strong association of 17q21 genotypes to asthma. Two specific aims are proposed to assess the overall hypothesis that the sphingolipid de novo synthesis pathway is critical not only for asthma pathogenesis but also in response to the most common trigger for asthma attacks. In Aim 1, we will determine sphingolipid synthesis in the respiratory tract in children with asthma and HRV infection. Sphingolipids will be assessed in nasal fluid, blood, and gene expression in nasal cells obtained from children during and after the resolution of HRV-triggered asthma attacks. In a subaim, we will evaluate the effects of HRV on sphingolipid metabolism and gene expression in primary human airway epithelial cells (HAEC) with homozygous for a common 17q21 asthma variation that leads to decreased blood sphingolipids in children with asthma. HAEC from an established biorepository from adult donors and nasal brushings from children all grown at air-liquid interface will be infected with HRV and RSV and evaluated for effects on sphingolipid synthesis. For Aim 2, we will test the hypothesis that the altered ratio of the sphingolipid mediator sphingosine 1-phosphate and sphinganine 1 phosphate, which we found in SPT deficiency and children with the 17q21 asthma risk genotypes, leads to airway hyperreactivity. Overall, these studies not only inform on the role of sphingolipids in the pathogenesis of asthma and the relation to its most common trigger but may lead to new therapeutic approaches involving sphingolipid metabolism.