Obesity increases the incidence and severity of asthma, but an incomplete understanding of the molecular mechanisms underlying obesity-related asthma make it difficult prevent and treat this phenotype. Parasympathetic nerves mediate one mechanism of airway hyperreactivity. These nerves provide dominant autonomic control of airway tone and release acetylcholine (ACh), which activates M3 muscarinic receptors on airway smooth muscle, causing contraction and bronchoconstriction. ACh release is controlled by inhibitory M2 muscarinic receptors on these nerves. Thus, airway hyperreactivity results from decreased neuronal M2 receptor function and subsequent increased ACh release. Our preliminary data show that obesity is associated with increased bronchoconstriction in response to parasympathetic nerve stimulation, with reduced neuronal M2 receptor function, and that these effects are mediated by insulin even in the absence of inflammation. Thus, our hypothesis is that increased insulin, as seen in obesity, binds to insulin receptors on airway parasympathetic nerves resulting in airway hyperreactivity by reducing M2 muscarinic function on parasympathetic nerves (thus increasing ACh release). We propose to test how insulin reduces M2 receptor expression and function, identify which insulin receptor and signaling pathways mediate neuronal M2 dysfunction and test whether manipulating insulin (with diet, oral anti-glycemic drugs and with an insulin binding antibody) protects M2 receptor function and inhibits obesity induced airway hyperreactivity. This research is significant because it has the potential to explain why obese patients with increased insulin, are more prone to asthma and identify novel strategies, including control of insulin, and M3 selective muscarinic antagonists, that may treat obesity-related asthma.
Obese asthmatics do not respond well to conventional asthma therapies, suggesting that the mechanisms underlying this phenotype are different from non-obese asthma. This study will investigate the role of insulin in obesity-related asthma and identify the mechanisms by which insulin alters nerves, smooth muscle, and inflammation in lungs to cause asthma. Our results will help to prevent and treat obesity-related asthma, benefiting millions of patients while reducing treatment costs and saving lives.
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