Chronic obstructive pulmonary disease (COPD), already a major cause of morbidity and mortality in the U.S., is likely to become epidemic worldwide. Pulmonary emphysema, a major component of COPD, results when cigarette smoking leads to inflammatory cell recruitment with release of elastolytic proteinases in excess of inhibitors. Lung destruction coupled with inefficient repair leads to airspace enlargement that defines emphysema. We determined the relative contribution of individual proteinases in emphysema, by generating mice deficient in candidate elastases, and developing a murine model of cigarette smoke-induced emphysema in mice. Mice lacking macrophage elastase (MMP-12) were entirely protected from emphysema, and also failed to recruit macrophages in response to cigarette smoke. Impaired macrophage recruitment is not due to inability of MMP-12-/- monocytes to egress from the bloodstream, but due to lack of generation of elastin fragments by MMP-12 that are chemotactic for monocytes. Mice lacking neutrophil elastase (NE-I-) were also significantly protected from cigarette smoke-induced emphysema, developing only 42 percent as much airspace enlargement as wild-type smoke exposed littermates. These results are explained by interactions between neutrophil and macrophage elastase, with MMP-12 degrading alpha-1-antirypsin (alpha1AT). Alpha1AT deficiency, is currently the only identified genetic factor predisposing to emphysema, and it is the most common disease causing mutation in Caucasians. There remain many important unanswered questions about alpha1AT deficiency that can be addressed with an animal model and further experimentation with human tissue. We hypothesize that alpha1AT deficiency results in a complex inflammatory response with accelerated emphysema, particularly in response to cigarette smoking. This may be due in part to intracellular polymerization and aberrant effects of lung epithelial cells causing a proinflammatory state, and in part due to generation of elastin fragments that perpetuate macrophage accumulation and activation. To address these issues, we propose to:
Aim #1. Generate mice deficient in (two) alpha-1AT genes by gene targeting, and """"""""knock in"""""""" the normal human M allele, and mutant PiZ allele. We will determine the initial phenotype of alpha1AT gene targeted mice.
Aim #2. We will define the capacity of alpha1AT gene targeted mice to develop cigarette smoke-induced emphysema and bronchial disease.
Aim #3. Identify epithelial factors that initiate inflammation in PiZ subjects by performing Affymetrix expression profiling in airway epithelial cells from healthy PiZ vs PiM individuals, and we will define the inflammatory cell and proteinase profile late in alpha1AT emphysema. Completion of these studies will enhance our understanding of emphysema in general and emphysema associated with alpha1AT deficiency. In addition, these mice can be used by all interested investigators for many purposes such as fulfilling a critical need for an animal model to test gene therapy/repair approaches to correct alpha1AT deficiency.
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