Severe asthma accounts for only 10% of all asthma cases but is responsible for 80% of all asthma associated costs. Typified by a resistance to inhaled glucocorticoid (GC) drugs, the pathology of severe asthma includes airway remodeling, neutrophilic infiltration, and chronic inflammation. Currently, little is being done to identify the mechanisms that drive treatment resistance, with previous efforts predominantly focused on developing new GC drugs/drug combinations or attempting to sensitize patients who are resistant. With this in mind, it is vitally important to identify the mechanisms of resistance in severe asthma in order to develop new therapeutic approaches and move beyond GC treatments.
In this study we utilized an ovalbumin/chlamydia murine model to induce severe asthma in BALB/C6 mice followed by either control or dexamethasone (DMSO) treatment to mimic GC treatment. Mice were euthanized, lungs removed, and parallel shotgun proteomics and single cell RNA sequencing was performed on whole lung lobes. Single cell data was integrated with proteomics using a “deep exploration” approach focusing on validating changes to actual biology rather than high level KEGG pathway or GO term analysis.
Deep exploration revealed that when treated with DMSO, T-Cells and neutrophils both exhibited significant downregulations of almost all cell cycle checkpoint genes and cell development pathways. This was in conjunction with an upregulation of genes responsible for neutrophilic recruitment and infiltration, and a downregulation of genes responsible for neutrophilic inflammation. P53 mediated cell senescence was also upregulated in both proteomics and single cell datasets as well as a downregulation of cytokine based immune suppressors. It was also found that immune cell senescence protein and gene markers were upregulated in all other immune cell types as well.
Based on these findings, we determined that in severe asthma, treatment with steroids may cause immune cells to lose function and become senescent. These immature cells then initiate feedback loops causing increased recruitment of neutrophils and T-cells which exhibit a chronic low level inflammatory response with a loss of inflammation regulatory control. High populations of neutrophils are histologically diagnostic for severe asthma further confirming these observations. This has led us to hypothesize that the current therapeutic protocol of high dose GC drugs for severe asthma patients may cause worsening of symptoms over time necessitating further research into GC alternative therapies.