Glucocorticoid receptor translational isoforms and neutrophilic airway inflammations.

Glucocorticoids are indispensable in the treatment of asthma although they are not effective in treating neutrophilic inflammation in subsets of asthma. Our long-term goal is to understand the mechanisms by which the glucocorticoid receptor (GR) mediates cell-specific functions, as this information may be useful in the development of treatments for asthma with improved efficacy/risk ratios. The goal of this proposal is to determine the role of GR translational isoforms in neutrophil glucocorticoid sensitivity. We have recently discovered that the GR has eight translational isoforms that have profoundly different effects on gene expression and cell functions. We hypothesize that selective GR translational isoforms mediate neutrophil resistance to glucocorticoid-induced apoptosis. We propose to increase the efficacy of glucocorticoids in circumventing neutrophilic inflammation by altering GR isoforms. To test our hypotheses, we will examine lenti virus-transduced human CD34+ cell-derived neutrophils, mouse bone marrow-derived neutrophils, and neutrophils in a murine asthma model. Studies in Aim 1 will determine whether the GR-A isoform will increase the sensitivity of neutrophils to glucocorticoid induced-apoptosis. We have found that primary neutrophils have predominantly the GR-D isoforms. In multiple cell types, the GR-A, but not the GR-D, isoform is proapoptotic. Our preliminary data also show that retinoic acid (RA) switches the GR-D to the -A isoform in neutrophils. If GR-A expressing neutrophils are sensitive to glucocorticoids, glucocorticoids may be effective in inhibiting neutrophilic airway inflammation. Aim 2 will determine whether translation factors such as heterogenous nuclear ribonucleoprotein L (hnRNP-L) regulate the selective expression of GR isoforms and glucocorticoid sensitivity of neutrophils. We have identified hnRNP-L as a GR-D associated translation factor. Knockdown of hnRNP-L in promyelocytic HL-60 cells switched the GR-D to -A isoform. We will test whether knockdown of hnRNP-L in neutrophils alter neutrophil glucocorticoid responses in vitro and in vivo. These studies, together with our separate clinical studies on the GR-D isoforms and glucocorticoid responses in neutrophils in refractory asthma, will improve our understanding of the role of GR translational isoforms in neutrophilc inflammation in asthma. The GR-A isoform is anticipated to increase the ability of glucocorticoids to induce neutrophil apoptosis and to inhibit components of neutrophilic inflammation.