COPD is associated with high mortality and there is an urgent need to develop new treatments that limit disease progression. Although much is known about how cigarette smoke (CS, the main risk factor for COPD) promotes COPD development, little is known about anti-inflammatory pathways that likely protect some cigarette smokers from developing COPD. Our novel data show that a proteinase with a disintegrin and a metalloproteinase (MP) domain-8 (Adam8) is robustly up-regulated in lung macrophages in wild type (WT) mice exposed to CS. However, CS-exposed Adam8-/- mice have higher lung macrophage counts and worse emphysema associated with decreased lung macrophage apoptosis than CS-exposed WT mice. We hypothesize that Adam8 has anti-inflammatory and protective activities in the CS-exposed murine lung by promoting macrophage apoptosis thereby reducing the half life of destructive macrophages in the lung. Although CS up-regulates anti-inflammatory Adam8 in lung macrophages in mice, ADAM8 levels are reduced in plasma and lung samples from COPD patients when compared to samples from control subjects. We hypothesize that reduced blood and plasma levels of ADAM8 in human COPD patients is linked to disease severity in human COPD via ADAM8 regulating macrophage survival in human lungs. We will test these hypotheses by pursuing the following Specific Aims:
Aim 1 : We will use a loss-of-function strategy (studies of WT vs. Adam8-/- mice in the CS exposure model) to test the hypothesis that Adam8 protects the CS-exposed murine lung from developing emphysema by promoting macrophage cell death. We will identify the mechanisms involved. We will also determine the critical cellular sources of anti-inflammatory Adam8 in the lung by generating and studying Adam8 bone marrow chimeric mice in the murine CS exposure model of emphysema.
Aim 2 : We will use gain-of-function strategies to confirm that Adam8 has anti-inflammatory activities in the CS-exposed murine lung by promoting lung macrophage apoptosis. We will generate transgenic mice that overexpress human Adam8 in an inducible fashion in lung macrophages. We will also use lentiviral vectors to selectively transduce murine lung macrophages with hADAM8 in a durable fashion. We will test whether these strategies prevent CS-induced emphysema and/or limit disease progression.
Aim 3 : We will test our hypothesis that COPD patients have reduced expression of ADAM8. We will measure ADAM8 protein and mRNA levels in blood and lung samples from COPD patients versus control subjects and correlate ADAM8 levels with disease severity, lung macrophage counts, and lung macrophage apoptosis. Significance: Our studies may provide novel insights into the mechanism(s) by which ADAM8 mediates its protective activities in the CS-exposed lung. Our studies may also identify ADAM8 as a novel target for developing therapeutic strategies to limit lung destruction and disease progression in patients with COPD.
COPD is the fourth leading cause of death in the USA, its incidence is increasing worldwide, and we have no treatments that effectively limit disease progression in most COPD patients. Our studies indicate that ADAM8 is an anti-inflammatory protein that protects the cigarette smoke-exposed lung from developing COPD. In the long term, our studies may identify ADAM8 as a novel target for developing improved treatment strategies that limit disease progression in patients with COPD.
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