Molecular mechanisms of posttranscriptional gene regulation in asthmatic airway inflammation

Veterans Health Administration, Decatur PA

Investigators

Abstract

Asthma remains a difficult to treat disease that greatly impacts deployed military personnel and Veterans. Currently used medications either: 1) are very expensive (biologics), placing enormous burdens on the VA Healthcare System; 2) have significant side effects (oral steroids); or 3) do not work in some endotypes, e.g., steroid-resistant asthma. Due to discordance between steady-state mRNA levels and protein, transcriptomic approaches may overlook genes regulated by RNA binding proteins (RBPs). Posttranscriptional gene regulation by RBPs and microRNAs (miRNAs) is increasingly recognized as an important control mechanism for pro- inflammatory genes but understudied. RBPs, such as HuR (Elavl1), which binds to mRNA AU-rich elements (AREs), play critical roles by regulating mRNA stability and translation of key pro-inflammatory gene expression in asthma. Our recently published data indicates that HuR ablation in mice ameliorates allergen-driven lung inflammation. Furthermore, HuR is over-expressed in asthmatic CD4+ T cells and its inhibition reduces cytokine expression. Using RNA Immunoprecipitation techniques (RIP-seq) combined with genetically engineered murine models, we have demonstrated that HuR controls both Th2 and Th17 CD4+ T lineages. Without a better understanding of posttranscriptional control of inflammation, the field will continue to have a limited insight into molecular mechanisms, which likely contribute to asthma endotypes and unequal treatment responses and outcomes in patients. Our long-term goal is to understand posttranscriptional gene regulation in different endotypes of asthmatic airway inflammation. The objective of this application is to determine how HuR and TTP family members regulate key pro-inflammatory molecules produced by CD4+ T cells in different asthma endotypes. Our rationale is that investigation of HuR-driven gene expression will identify molecular mechanisms that differ between asthma endotypes, especially type 2-high vs. non-type 2-high. The central hypothesis is that the HuR-Gata3 interaction in CD4+ T cells controls airway inflammation in type 2-high asthma (driven by Gata3) and in non-type 2-high asthma (driven by Il17). We plan to test the central hypothesis and accomplish these objectives by the following three specific aims: 1) Define molecular mechanisms of HuR regulation in murine models of type 2-high airway inflammation; 2) Elucidate human CD4+ T cell gene clusters permissive for asthmatic lung inflammation and 3) Determine effects of HuR inhibition on T cell-mediated inflammation in type 2 high and non-type 2 high asthma. At the completion of the proposed research, our expected outcomes are to identify how HuR controls CD4+ T cell differentiation and function, which are critical for the development of allergic airway inflammation. These results are anticipated to have a sustained positive impact upon the field because they will further define molecular mechanisms distinguishing type 2 high from non-type 2 high asthma endotypes. The fundamentally important knowledge gained will provide opportunities to develop novel therapies to treat asthmatic lung inflammation by interfering with HuR function, including in steroid-resistant asthma.