Chromatin Remodeling in Glucocorticoid Resistance of COPD
Initial Award Abstract
Tobacco smoking is the primary risk factor for chronic obstructive pulmonary disease (COPD), an incurable lung disease characterized by airflow limitation, abnormal inflammatory response, and eventual loss of lung function. Sadly, COPD has become a global health epidemic. In fact, COPD is the most deadly tobacco-related disease. Despite its growing prevalence (which is expected to rise to the fourth leading cause of death worldwide by 2030), few effective therapies are available. Glucocorticoids are steroids with anti-inflammatory actions that are used successfully in the treatment of many diseases, including asthma (which shares many symptoms with COPD). Unfortunately, glucocorticoids have proven far less effective in COPD treatment. In order to improve therapy, it is critical to first understand why glucocorticoids fail to manage the inflammatory symptoms of COPD. Recent work suggests that chronic exposure to nicotine changes the structure of DNA packaging (called chromatin). Chromatin is essential to package approximately 1.8 meters of DNA into a small volume so that it can fit into a single cell. Changes in the structure of chromatin are used to regulate gene expression. For instance, nicotine exposure causes chromatin decondensation, which is associated with activation of the inflammatory response. I am interested in the role of chromatin structural changes, such as this decondensation, in the glucocorticoid resistance seen in COPD.
Glucocorticoids have been shown to direct a protein complex (Swi/Snf) that remodels chromatin. My preliminary data suggests that the Swi/Snf complex is necessary for normal repression of the inflammatory response by glucocorticoids. I hypothesize that in glucocorticoid-responsive systems; these steroids direct the Swi/Snf complex to alter chromatin structure in a way to help repress the inflammatory response. For instance, this might mean condensing the chromatin around inflammatory genes. Therefore, the glucocorticoid resistance that is seen in COPD could be due to defects in the Swi/Snf complex, resulting in changes in chromatin structure that fail to repress the inflammatory response.
Questions and methods:
First, I will investigate the role of the Swi/Snf complex in normal glucocorticoid regulation of the inflammatory response by studying healthy lung cells. I employ a system where I disrupt proteins within the Swi/Snf complex and use different glucocorticoid assays to determine what functions are lost. I will also mutate different domains of the proteins within the Swi/Snf complex and examine which domains are important for inflammatory response functions. Next, I will use assays that monitor chromatin structure to determine how the mechanism of chromatin remodeling changes upon glucocorticoid treatment. I will then investigate whether the observed chromatin structural changes are due to the Swi/Snf complex. These experiments will provide a baseline for normal glucocorticoid response in a system relevant to COPD. Finally, I will repeat the methods stated above in lung cells from smokers and in normal lung cells treated with nicotine to determine whether nicotine can alter the function of the Swi/Snf complex, leading to the observed chromatin decondensation associated with nicotine exposure.
Impact on COPD:
Understanding the normal role of the Swi/Snf complex in altering chromatin structure in a glucocorticoid-responsive system is an important first step to dissecting the changes that occur in COPD, which leads to glucocorticoid resistance and failure to repress the inflammatory response. This normal mechanism of action is needed before glucocorticoid therapy can be improved in COPD. Identifying defects in the Swi/Snf complex that alter the inflammatory response may provide alternative drug targets for COPD treatment. For instance, some functions of the Swi/Snf complex may need to be inhibited by drugs in order to increase the effectiveness of glucocorticoids in COPD. Therefore, this study may discover new ways to increase the effectiveness of glucocorticoids in COPD patients, providing much needed relief to COPD patients. |