PROJECT SUMMARY Abdominal aortic aneurysm (AAA) disease is a common, morbid and highly lethal disease. Importantly, there are currently no therapeutic strategies that limit the growth of aneurysms, due in large part to a lack of understanding of the mechanisms of disease and progression. In addition to advanced age, genetic predilection, and male sex, the most important risk factor for AAA is a history of tobacco use. Work from our laboratory has recently shown that subcutaneous infusion of nicotine accelerates experimental AAA formation. Furthermore, we have identified a signaling pathway whereby nicotine induces vascular oxidative stress and NF-?B activation leading to decreased miR-24. Reduced miR-24 activity releases the brake on several inflammatory genes, most notably Chi3l1. Moreover, we have shown that manipulation of this pathway can alter the course of AAA disease. We now propose to leverage this knowledge and discover whether inhaled nicotine has similar effects upon vascular redox state, inflammation, and ultimately AAA formation. The outlined studies will compare different doses of inhaled nicotine vapor and determine relative effects compared to cigarette smoke or subcutaneous delivery. In Specific Aim 1, we will define inhalation protocols that result in serum nicotine (cotinine) levels that mimic moderate-heavy smokers and determine the impact on aortic ROS production, Smad signaling, and ultimately miR-24 levels. In Specific Aim 2, we will examine the downstream impact of inhaled nicotine-induced miR-24 expression upon inflammatory gene expression focusing on Chi3l1. Finally, in Specific Aim 3, we will investigate the effects of inhaled nicotine upon AAA formation and whether there are gender differences in response. These specific aims will investigate a novel mechanism that may underlie inhaled nicotine-induced vascular inflammation and aneurysm formation as well as provide the basis for advancing future research and clinical translation.