Modulation of Steroid Immunosuppression by Alveolar Efferocytosis

Pneumonia, Bacterial, Pulmonary Disease, Chronic Obstructive

Apoptosis, Bronchoscopy, Human, Mice, inbred strains, Macrophages, Alveolar, MicroRNAs, Streptococcus pneumoniae, Fluticasone

The long-term goals of this study are (a) to understand the biological underpinnings for the increased incidence of community-acquired pneumonia in patients with chronic obstructive pulmonary disease (COPD) who are treated with inhaled corticosteroids; and (b) to develop novel therapies to treated this problem using over-expression of micro-RNAs (miRNAs).

Treating chronic obstructive pulmonary disease (COPD) patients with inhaled glucocorticosteroids has been convincingly shown to increase their risk of pneumonia, but the responsible mechanisms are undefined. Work from this laboratory suggests a possible mechanism, related to the increased numbers of cells dying by apoptosis in the lungs in COPD, especially in emphysema. Uptake of apoptotic cells (efferocytosis) suppresses the ability of alveolar macrophages (AM) to fight infections. By markedly increasing AM efferocytosis, glucocorticoids plus apoptotic cells cause greater immune defects than either stimulus alone. These defects include reductions in killing of Streptococcus pneumoniae by human AM and murine AM in vitro, and in clearance of viable pneumococci from lungs of mice. This effect is called glucocorticoid augmented efferocytosis (GCAE). MicroRNAs (miRNAs) are 19-25 nucleotide-long non-coding RNAs that coordinately target large numbers of genes and reduce their protein products. Preliminary data imply that defective AM function is caused by down-regulation of specific miRNAs by GCAE (but not by apoptotic cells alone or glucocorticosteroids alone). The long-term goal of this project is to develop novel inhalational treatments based on transient over-expression of these specifically decreased miRNAs, to reverse defective AM immune function when COPD patients taking inhaled glucocorticoids present with community-acquired pneumonia. This project will use both ex vivo investigation of AM from human volunteers (never-smokers; smokers with normal spirometry; and COPD subjects who are current or former smokers), and an established murine model of pneumococcal pneumonia. Its immediate goals are to: (a) confirm that GCAE increases pneumococcal pneumonia risk and severity, and in the process, validate a murine model for testing strategies to reverse those defects; (b) define GCAE-induced AM defects functionally and by whole-transcriptome analysis, identifying genes and miRNAs uniquely regulated by the GCAE x pneumococcus interaction; (c) validate and optimize miRNA-over-expression to reverse the adverse effects of GCAE on AM defensive functions. Successful completion of this project could lead to more precisely personalized therapies and better outcomes in COPD, currently the third leading cause of death in the USA

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