Role of NRF2 in the Pulmonary Response to Inhaled Mine Tailing Dust

University Of Arizona, Tucson AZ

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Abstract

ABSTRACT (Project 5: Zhang, Boitano, Lantz) Chronic exposure to arsenic-containing dusts from the Iron King Mine Superfund Site, and other hardrock (metal) mining sites in arid and semi-arid climate is of public health importance worldwide. Both cancer and non-malignant lung diseases are associated with chronic arsenic exposure. While arsenic is classified as a carcinogen following either ingestion or inhalation, little data exist concerning the modes of action for development of noncancerous lung diseases from exposure to arsenic containing dusts through inhalation. Noncancerous lung diseases that have been associated with arsenic ingestion include both obstructive (chronic obstructive pulmonary disease, chronic bronchitis, emphysema, bronchiectasis) and restrictive (fibrosis) lung disease. Preliminary data from Project 4 and others suggest that inhalation of arsenic associated with particulates may be an important exposure route for lung toxicity. Collectively, data indicate that arsenic exposure compromises the barrier integrity of the airway epithelium by inducing an epithelial to mesenchymal transition (EMT). This project will examine a potential intervention to block arsenic toxicity. Nrf2 is a transcription factor that is activated by oxidative stress. Activation of the canonical Nrf2 pathway leads to expression of genes that can protect against increased oxidative stress. The Zhang team's studies (and others) indicate a protective role for Nrf2 against arsenic exposure. However, the molecular mechanisms of how Nrf2 protects airway epithelial cells, specifically, how activation of Nrf2 pathways can modulate EMT and airway epithelial barrier function, is not known. The hypothesis of Project 5 is that arsenic-containing dusts cause airway epithelial dysfunction through autophagy blockage/prolonged Nrf2 activation (non-canonical); however, intermittent induction of Nrf2 (canonical) by dietary supplementation during exposure can maintain airway epithelial barrier integrity, and thus, reduce arsenic-induced lung disease. These differential outcomes are indicative of a ?dark side? of Nrf2 that may contribute to arsenic toxicity. We will examine this hypothesis in the following three Specific Aims. In Aim 1, we will determine the protective role of Nrf2 in maintaining airway epithelial barrier integrity in response to dust particles with/without arsenic in vitro. We will then, in Aim 2, determine the molecular mechanisms of Nrf2 induction (canonical vs non-canonical) by dust particles with/without arsenic in vitro. Finally, in Aim 3, we will examine the efficacy of prophylactic canonical Nrf2 activation by dietary supplementation in maintaining airway epithelial barrier integrity and ameliorating lung damage in mice exposed to inhaled dust particles with/without arsenic. Impact: Dietary Nrf2 activation may counteract arsenic-mediated inhalation toxicity to lung epithelium, providing an intervention for populations at high risk of arsenic exposure. A detailed understanding of the mechanism of Nrf2 activation by arsenic dusts and its effects on airway epithelial cells will prove extremely valuable in the generation of preventive and therapeutic strategies for the populations at risk of exposure to arsenic, and potentially, other metal(oids).