THE ROLES OF CERAMIDE AND ORMDL3 IN ASTHMA SEVERITY

The severity of asthma, a chronic inflammatory disease of the airways, is influenced by a multitude of factors. Genomic studies offer insight into the genetic mutations that predispose individuals to this disease. Such work revealed a significant association between increased expression of ORMDL3 and susceptibility to asthma. ORMDL3 regulates de novo synthesis of sphingolipids, which proposed the involvement of sphingolipids in asthma development as well. Therefore, the focus of this research was to investigate how ceramide, the central sphingolipid metabolite, and ORMDL3 contribute to the pathology of asthma disease. Utilizing allergen mouse models that recapitulate key symptoms of human allergic asthma, we measured increased levels of ceramide in the lungs after allergen challenge. Asthmatic mice also had elevated levels of reactive oxygen species and apoptotic cell death within the lungs. Oxidative stress and apoptosis are both biological markers of asthma severity. Mitigation of lung ceramide reduced both, suggesting that allergen-induced cell death and production of reactive oxygen species are ceramide dependent. Elevated levels of ceramide species were also measured in bronchoalveolar lavage fluid from severe asthma patients, which correlated with an increase in neutrophils. In addition, ceramide induced neutrophil attachment and accumulation in mouse models. These results influenced subsequent studies, in which global overexpressing ORMDL3 transgenic mice were subjected to a Th17, neutrophil dominant model to examine the effects of ORMDL3, and its regulation of ceramide, on neutrophil infiltration. Overexpression of ORMDL3 reduced IL-17 and neutrophils in challenged mice. However, changes in ceramide for this group was inconsistent, insinuating that an alternative mechanism may be involved. Overall, this work suggests that ceramide elevation contributes to the severity of allergic asthma by apoptosis, reactive oxygen species, and neutrophil infiltration. ORMDL3 may also play a role in the Th17 neutrophil endotype, clinically associated with steroid resistant asthma patients. These findings provide promising biomarkers and strengthen the understanding of the biological processes involved in the worsening of this airway disease