Mitochondrial translocator protein: a target for bronchodilation

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Project Summary Effective management of asthma requires regulating airway smooth muscle (ASM) contractility to prevent or reverse bronchoconstriction. This is primarily achieved by use of direct bronchodilators (e.g., β-agonists), by anti- inflammatory agents (e.g., corticosteroids) either alone or in combination. However, effective management is lacking, as an estimated 55% of all asthmatics have suboptimal control. All current bronchodilator drugs have limitations which respect to efficacy or safety. We propose a novel approach of targeting a mitochondrial protein, the 18 kDa Translocator Protein (TSPO), as a means of bronchodilation/bronchoprotection. Our central hypothesis is that potent, efficacious agonists of TSPO can be developed and employed as effective bronchodilatory/bronchoprotection drugs. Three aims are proposed to test this hypothesis. In Aim 1, using in vitro (primary airway smooth muscle cells; ASM), ex vivo (murine and human rings and precision cut lung slices), and in vivo models (smTspo-/- mice), we will establish TSPO as a druggable target to promote relaxation of ASM. In Aim 2, we will determine the mechanistic basis of TSPO regulation of ASM contraction by assessing the roles of PKA, and mitochondrial Ca2+ and ROS, on signaling events known to regulate cross bridge cycle (regulatory myosin light chain 20 and myosin phosphatase phosphorylation) or actin polymerization state (F/G actin ratio). Lastly, in Aim 3 we will employ molecular modeling to design and synthesize new ligands for TSPO, with an emphasis on generating new drugs that demonstrate superior binding properties and improved efficacy. These will be tested in cell and tissue model systems employed in Aim 1. The proposed studies represent an innovative approach to establish an asthma management strategy that overcomes the current limitations of efficacy and safety. Moreover, the proposed mechanistic studies will provide new insight into how to optimally target the mitochondria to regulate contractile signaling and function in ASM.