Cigarette smoking-related diseases claim an estimated 440,000 American lives each year, including those affected indirectly, such as babies born prematurely due to maternal smoking and victims of "secondhand" exposure to environmental cigarette smoke (ECS) from parents. Smoking is directly responsible for approximately 80-90% of COPD (emphysema and chronic bronchitis) deaths, and approximately 25% of patients with asthma are tobacco smokers. In addition, cigarette smoke is known to be associated with pulmonary hypertension (PH) in both humans and animals. Estimates based on serum cotinine concentrations for the years 1999-2002 for the USA indicate that close to 40 million children and adolescents between the ages of 3 and 9 years were exposed to ECS.
Although exposure to passive smoke from parents is associated with lung disease in children, little is known about the molecular mechanisms of early-life ECS exposure-related lung diseases. Airway hyperresponsiveness (AHR) is a key pathophysiologic event associated with asthma and COPD and appears to be related to cigarette smoke exposure, both in utero and after birth. Our recent studies suggest that pulmonary hyper-innervation increases susceptibility of mice to lung diseases. In fact, pulmonary innervation plays a key role in regulating bronchoconstriction and vasoconstriction which directly lead to lung disease symptoms. Pulmonary innervation develops rapidly during fetal and early postnatal life. Pulmonary innervation is highly susceptible to environmental insults during development, and changes in pulmonary innervation are associated with development of lung disease. We have identified P-Rex1, a Rac3 guanine nucleotide exchange factor in neurons, as an important regulator of pulmonary innervation. Importantly, the cigarette smoke-related inflammatory cytokine interleukin (IL)-6 down-regulates P-Rex1 expression, leading to excessive neurite outgrowth and extension. Our results suggest a new and exciting link between inflammation-induced P-Rex1 repression and pulmonary hyper-innervation in early-life ECS exposure increased AHR and vasoconstriction leading to the development of diseased lungs. We will integrate molecular, cellular and animal models to test the hypothesis that early-life ECS exposure leads to pulmonary hyper-innervation through down-regulation of neuronal P-Rex1, causing persistent phenotypic changes of the airways and pulmonary vasculature. These changes contribute to the development of asthma, COPD and pulmonary hypertension.
We anticipate that these studies will have a significant impact on our basic knowledge of the molecules and mechanisms involved in the development and severity of cigarette smoke-related lung disease and may have potential clinical impact by guiding development of novel therapeutics for lung disease. Furthermore, by integrating researchers in different areas within and outside Creighton in a cohesive research program, we expect to provide synergistic interactions and opportunities to improve research and extramural funding.
Our Hypothesis
Early-life environmental cigarette exposure (ECS) exposure leads to pulmonary hyper-innervation via inflammation-dependent down-regulation of neuronal P-Rex1, causing persistent phenotypic changes of the airways and pulmonary vasculature. These changes contribute to the development of asthma and pulmonary hypertension .
Project 1: To define the importance and mechanism of P-Rex1 repression in early-life ECS-increased risk of asthma.
Dr. Tuwill use P-Rex1 knockout (KO) mice as a model to determine the importance and mechanisms of P-Rex1 in regulation of early-life ECS exposure-related hyper-innervation and airway hyperresponsiveness (AHR), the pathophysiologic hallmark of asthma.These mice exhibit pulmonary hyper-innervation and increased lung resistance relative to wild-type (WT) mice. Dr. Tu will first determine the mechanism by which P-Rex1 regulates pulmonary innervation. He will then define the mechanism of cigarette smoke-related inflammatory cytokine-induced repression of neuronal P-Rex1 expression. Finally, he will use P-Rex1 KO mice as a model to determine the pathologic importance of P-Rex1 repression in a murine model of early-life ECS exposure-induced AHR. These studies will identify the aberrant signaling pathways and molecules likely to be important in the development of pulmonary hyper-innervation and AHR in patients with early-life ECS exposure-related asthma.
Project 2: To identify molecular and cellular triggers of ECS mediated pulmonary vascular dysfunction in pulmonary hypertension.
Dr. Abelwill collaborate with Dr. Tu to determine if early life ECS exposure causes an inflammation-related hyper-innervation that sensitizes the mouse pulmonary vasculature to hypoxia and other insults, causing pulmonary vascular remodeling and hyper-contraction leading to pulmonary hypertension. Dr. Abel will first determine the role of early life ECS-induced pulmonary vascular inflammation in causing pulmonary vascular remodeling and hyper-contraction. He will then collaborate with Dr. Tu and use P-Rex1 KO mice to determine whether pulmonary vascular hyper-innervation will enhance early life ECS-mediated pulmonary vascular remodeling and hyper-contraction. Drs Abel and Tu have recently found that hypoxia induces excessive vasoconstriction through down-regulation of RGS2, an important regulator of contractility of airway and vascular smooth muscle cells. They will expand this collaboration to investigate whether exposure of early-life ECS-exposed mice to a second vascular insult, such as hypoxia, in adulthood will result in hyper-contraction and pulmonary vascular remodeling that are also found in PH. Together, these studies will provide new information related to cellular and molecular mechanisms of early-life ECS exposure-induced pulmonary vascular disease.