Asthma affects 1 in 12 Americans. More than 50% of asthmatics (12 million) have asthma attacks each year. Asthma is a chronic inflammatory disease which has great impact on quality of life. Uncontrolled and untreated asthma leads to missed work and school, as well as high healthcare costs. There are many different types of asthma, some of which are well targeted by current therapeutics leading to disease control. However, there are some endotypes of asthma, such as TH2-low neutrophilic asthma, that do not have targeted therapies available. These endotypes are driven by inflammatory pathways that do not respond to steroids, and thus they are commonly found in steroid-resistant asthma. The premise of our proposed work is that there are additional cell types and pathways that can be identified and targeted in asthma. Hypoxia inducible factors (HIF) have been found to be master regulators of inflammation when expressed in immune cells. HIF-1? is constitutively expressed in all cells, and is important in the regulation of metabolism, cell proliferation and cell migration, in addition to regulating inflammatory pathways. HIF-2? has more limited expression, but like HIF-1? it is expressed in pulmonary endothelial cells and regulates both metabolism and inflammation. We have studied both HIF-? subunits in the setting of asthma, and have found that each regulates inflammation through myeloid cells in a pro-inflammatory manner. When either was suppressed through systemic administration of small molecule inhibitors, a more profound effect on allergic inflammation was seen, which suggests that non-myeloid cells also promote inflammation via HIF-? subunits. Pulmonary endothelial cells are the gateway to the lungs from the circulation. We hypothesize that HIF- 1? and HIF-2? play a role in activation of pulmonary endothelial cells during pulmonary inflammation, leading to expression of adhesion molecules on the vascular surface and transmigration of circulating inflammatory cells into the lungs. We propose to use pulmonary endothelial cell specific HIF-1? and HIF-2? knock-out mice to evaluate the role of HIFs in the recruitment of inflammatory cells such as eosinophils during asthma-like inflammation. Because of the heterogeneity of asthma, and the lack of therapeutic options for non-TH2 non- allergic phenotypes of asthma, we will use three immunologically disparate mouse models of asthma to evaluate the role of these HIF molecules in asthma pathogenesis. Mouse models are powerful in that they can assess for physiologic changes, and organ and system-level effects. In addition, gene knockouts in mice are a powerful tool for understanding the roles of individual proteins on disease induction and progression. However, there are differences in immune function and inflammatory responses between murine and human cells, such that murine data does not always reflect human responses. Thus, we will use human endothelial cells and human immune cells ex vivo to study the effects of suppression of HIF via small molecule inhibitors on transendothelial migration of cell types relevant to asthma: eosinophils, neutrophils, macrophages and lymphocytes in particular. We hope that the studies proposed will elucidate novel targets for drug development in asthma.
Asthma is a highly prevalent disease, affecting up to 8% of the U.S. population, with $82 billion in economic costs due to lost productivity and healthcare utilization. Veterans are affected equally to the general population, and in some cases at higher rates due to inhalation exposures. Even though we have studied asthma for years and have defined many molecular pathways involved in pathogenesis, there are many asthmatics who do not respond to current therapies. The goal of the work proposed is to look at asthma from the perspective of pulmonary endothelial cells, which act as a barrier between circulating immune cells and the lung parenchyma. We hope to identify HIF-1? or HIF-2? within pulmonary endothelial cells as new therapeutic targets for the treatment of asthma endotypes that have not been responsive to conventional treatments. Along the way we will determine how HIF-1? or HIF-2? regulate pulmonary endothelial cell function, including activation and expression of adhesion factors leading to recruitment and transmigration of leukocytes into the lungs.
