Abstract Arterial stiffness is a hallmark of vascular aging and is related to increased cardiovascular disease events and vascular dementias. Inflammatory damage and extracellular matrix remodeling have been proposed as the major pathological causes of vascular injury and arterial stiffness. However, the molecular mechanisms that initiate and propagate aging-related pathological changes in large blood vessels remain unclear. Here, we propose to study the role of neutrophil elastase (NE), a neutrophil-specific protease, in initiating vascular leakage, inflammation and fibrosis in aged mice both with and without obesity. Neutrophils are the most abundant leukocytes, have a short lifespan, and play a critical role in initiating tissue damage and inflammation. Our data demonstrated (1) that pulse wave velocity (PWV), the primary parameter of arterial stiffness, was decreased in NE knockout (NEKO) mice compared to their wild-type littermates, and (2) that NEKO mice were resistant to aging-related inflammation, fibrosis and calcification in the aorta. We also observed that NE has potent effects on increasing vascular endothelial permeability and enhancing aortic smooth muscle cell fibrogenic and osteogenic phenotypic switch. Further, NE regulates neutrophil proinflammatory phenotype by degrading longevity regulator Sirtuin 1 (Sirt1). Based on our preliminary data, we hypothesize that pro-inflammatory neutrophils interact with blood vessels, causing vascular damage and remodeling through the release of NE. The latter contributes to the increased vascular permeability, fibrotic remodeling and calcification in the blood vessels. Thus, inhibiting NE may lead to protective effects on aging-related vascular damage, fibrotic remodeling, calcification, and subsequent arterial stiffness. The objective of this RO1 proposal is to explore how neutrophils and NE regulate inflammatory remodeling in the arterial wall during the aging process with or without feeding of an obesogenic diet. We will explore whether NE contributes to vascular aging by activating protease-activated receptor 2 (PAR2) and epithelium sodium channel (ENaC) signaling pathways in vascular endothelial cells and vascular smooth muscle cells with both in vitro and in vivo studies. Also, we will examine the role of the NE–Sirt1 signaling pathway in the regulation of neutrophil phenotype and aging-related vascular injury and remodeling in mice. Finally, we will evaluate potential therapeutic effects of a selective NE inhibitor on aging-related arterial stiffness in mice. Successful completion of this project will provide a novel therapeutic strategy for vascular aging and related diseases.