Exaggerated airway narrowing and inflammation are hallmarks of clinically-important diseases such as asthma. Airway tone, largely determined by intracellular Ca2+ ([Ca2+]i) (mediated by Ca2+ influx and sarcoplasmic (SR) Ca2+ release) and Ca2+ sensitivity for force generation of airway smooth muscle (ASM), is enhanced by pro-inflammatory cytokines such as TNFa. In this regard, the role of caveolae and caveolins in the lung is an exciting and emerging area of research. Caveolae are small, uncoated flask-shaped invaginations of the plasma membrane (PM) of most cell types, and contain structural proteins called caveolins (caveolin-1, -2 and/or -3). Recent studies including our own have demonstrated that normal human ASM expresses caveolae and caveolin-1, with specific proteins involved in [Ca2+]i and force regulation co-localizing with caveolin-1. Preliminary studies show that airway inflammation (either in vitro following TNFa exposure or in vivo in a mouse model) increases caveolin-1 expression and enhances caveolar regulation of ASM contractility, suggesting that overall, caveolin-1 is associated with or promotes ASM contractility. The long term goal of the proposed studies is to understand the mechanisms by which caveolae and caveolins regulate ASM contractility under normal conditions and with airway disease. Ca2+ The overall hypothesis is that caveolae facilitate PM- SR interactions, thus influencing [Ca2+]i and force in ASM. In addition, we hypothesize that airway inflammation increases caveolae and caveolin-1 expression, and thus enhances PM-SR interactions, leading to increased [Ca2+]i and force in ASM. The novelty of our studies lies in linking previous anatomical and biochemical evidence for caveolin-1 in ASM to a physiological role in regulation of ASM contractility. Overall Approach: In vitro studies with human ASM cells and tissues in Aim 1 will examine mechanisms that can be modulated by caveolin-1 with agonist (ACh) stimulation under normal conditions, focusing on agonist receptors, second messengers (PLC/IP3, cADPR), regulation of store-operated Ca2+ entry (SOCE) by (STIM1/Orai1), and RhoA (Ca2+ sensitization). Mechanisms underlying altered caveolin-1 expression (Aim 2) and caveolin-1 contribution to enhanced ASM contractility (Aim 3) with inflammation (induced by TNFa) will then be examined, focusing on specific mechanisms (TNFR1, PTRF, MAPK, NF-?B). Finally in Aim 4, in vitro data will be integrated at the in vivo level using an ovalbumin (OVA) model of airway hyperresponsiveness in wildtype (WT) and caveolin-1 knockout (KO) mice.
The Specific Aims of this proposal are: 1) To determine mechanisms by which caveolae/caveolin-1 regulate [Ca2+]i and force responses of human ASM to agonist 2 ) To determine mechanisms by which cytokine (TNFa) stimulation alters caveolin-1 expression in human ASM 3) To determine the mechanisms by which caveolin-1 contributes to TNFa-induced enhancement of [Ca2+]i and force in human ASM;4) To determine the role of caveolin-1 in airway hyperresponsiveness in vivo.
There is increasing recognition that abnormalities in airway smooth muscle contractility (exacerbated by inflammation) contribute to exaggerated airway narrowing and accompanying shortness of breath in clinically- important diseases such as asthma and chronic bronchitis. In this regard, the potential role of cellular structures called caveolae and their constituent caveolin proteins in regulation of airway contractility is an exciting and emerging area of research. By establishing the role of caveolae and caveolins in airway narrowing with or without inflammation, the proposed studies will the foundation for better understanding of airway diseases, and potential development of new therapeutic targets.
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