Mechanisms underlying metal nanoparticle-induced lung injury and fibrosis

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Metal nanoparticles have been widely used in cosmetics, medicine, electronics, and industry, and occupational or non-occupational exposure to metal nanoparticles is growing. In this proposal, we have selected several transition metal nanoparticles (Nano-Co, Nano-Ni, and Nano-TiO2) as `model' metal nanoparticles to examine their ability to induce pulmonary injury and fibrosis and the potential underlying mechanisms involved. An inflammasome is a multiprotein complex that serves as a platform for caspase-1-dependent proteolytic maturation and secretion of interleukin-1β (IL-1β). The central component of an inflammasome is a member of the NLRP family, and this protein associates with the adaptor protein ASC, which in turn recruits pro-inflammatory caspase precursors (such as procaspase-1). Among a number of inflammasomes, the NLRP3 inflammasome is the most extensively studied. Our working hypothesis is that exposure to metal nanoparticles will cause activation and/or dysregulation of the inflammasome and IL-1β secretion in alveolar macrophages (AMs), lung epithelial cells, and lung fibroblasts, which will cause dysregulation of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), initiating and promoting metal nanoparticle- induced pulmonary injury and fibrosis. This project will use both in vitro and in vivo systems to address the following specific aims: (1) Determine the role of inflammasome activation in IL-1β secretion induced by metal nanoparticles in vitro and in vivo. We will identify whether activation of the inflammasome is involved in metal nanoparticle-induced IL-1β secretion in alveolar macrophages (AMs), lung epithelial cells, and lung fibroblasts by: (1) using ac-YVAD-cmk, a particular inhibitor of caspase-1; (2) knocking-down one of the inflammasome components such as NLRP3, ASC, or caspase-1 by using CRISPR/Cas9 technology; and (3) using NLRP3 or ASC knock-out mice. We will then determine whether NADPH oxidase- and/or mitochondria- dependent ROS generation and potassium efflux are involved in metal nanoparticle-induced inflammasome activation and IL-1β secretion. We will also measure IL-1β secretion in mice exposed to metal nanoparticles. (2) Examine the role of IL-1β in the alteration of MMPs and TIMPs expression and activity in lung cells exposed to metal nanoparticles. While IL-1β is an inducer for MMP-2 and MMP-9 activity, it is unclear how it regulates MMPs and TIMPs with exposure to metal nanoparticles. To test the role of the inflammasome and IL- 1β in the regulation of MMPs and TIMPs, the strategies in Aim 1 will be used to inhibit inflammasome function, and strategies to inhibit IL-1 function will be applied by using: (1) the pharmacologic IL-1β inhibitor; (2) anti-IL- 1β antibody; and (3) IL-1RI-/- mice that will not respond to IL-1β. After exposure to metal nanoparticles, MMP-2, MMP-9 and TIMPs expression and activity will be determined. (3) Investigate the role of inflammasome activation in metal nanoparticle-induced lung injury and fibrosis in vivo. We will first investigate whether exposure to metal nanoparticles will cause lung fibroblasts to produce more collagen. Then the role of the inflammasome in metal nanoparticle-induced lung fibrosis will be explored by short- and long-term exposure of mice to metal nanoparticles. We will use the strategies in Aim 1 and 2 to inhibit inflammasome and IL-1β function to investigate the role of the inflammasome and IL-1β in metal nanoparticle-induced lung fibrosis.