Nicotine and nicotinic receptors in lung transitional remodeling

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DESCRIPTION (provided by applicant): Tobacco and alcohol are the two most used and abused drugs in the world. Together, they are responsible for millions of deaths each year worldwide. Despite the enormous amount of research carried out to understand how these agents affect the lung, new information leading to significant advances at the clinic has been disappointing. Because of the high prevalence of tobacco and alcohol exposure in veterans, the Roman lab is exploring the mechanisms by which these agents affect the lung. Our research revealed that both alcohol and nicotine, an alkaloid present in tobacco, promote alterations in lung matrix composition that we have termed 'transitional' remodeling, a process characterized by subtle alterations in the relatively composition of the lung extracellular matrix. Although the exact mechanisms linking these events to lung disease remain incompletely understood, we believe that transitional remodeling renders the host susceptible to lung disease, and this belief is supported by published research performed both in vitro and in vivo. Considering the above, we set out to identify the cellular/molecular mechanisms responsible for these events. Using cultured primary lung fibroblasts, we found that nicotine induces cellular proliferation and matrix expression through the activation of specific 7 nicotinic acetylcholine receptors (7 nAChRs). The importance of these receptors was confirmed in vivo showing that prenatal exposure to nicotine affects lung development and induces airway thickening and hyperreactivity in wildtype animals, but not in 7 nAChR knockout mice. Using the same culture model, we discovered that alcohol acts on lung fibroblasts via another set of nAChRs, 4 nAChRs. In rodent lungs, the expression of these receptors is increased by chronic alcohol exposure which, in turn, predisposes to acute lung injury. This work suggests that the cholinergic system plays an important role in lung homeostasis and response to injury, and points to nAChRs as potential targets for intervention. More recently, we found that nAChRs are activated through both ligand-dependent and -independent pathways. Specifically, while nicotine acts on 7 nAChRs in a traditional ligand-dependent fashion, alcohol works, at least in part, through induction of a particular form of oxidant stress (oxidation of the cysteine/cystine redox potential or Eh Cys/CySS) which, together with cysteine residues strategically located on the subunits of certain nAChR pentamers, activates nAChR signaling via ligand-independent mechanisms of action. Importantly, we have generated preliminary data to suggest that susceptibility to injury in aging might activate nAChRs through similar pathways thereby promoting transitional remodeling and increased susceptibility to lung injury. Considering the above, we propose that aging (as observed for nicotine and ethanol exposure) is associated with lung transitional remodeling via distinct nAChRs. nAChRs can be activated via ligand-dependent and -independent pathways, the latter triggered by oxidant stress induced by oxidation of the Eh Cys/CySS. Specifically, oxidant stress affects cysteines strategically located in the � subunits of nAChRs which, in turn, triggers signal transduction and promotes lung transitional remodeling and increase susceptibility to disrepair after lung injury. To test this hypothesis, we propose experiments designed to: Aim 1. Investigate the role of specific subunit cysteines in nAChR activation in lung cells and in vivo. Aim 2. Determine the role of oxidant stress, especially, oxidation of the Eh Cys/CySS in nAChR activation both in vitro and in vivo. Aim 3. Examine the role of nAChR activation in lung disease related to aging and how this is affected by tobacco and alcohol exposure.