Since Szentivanyi proposed in 1968 that asthma might be due to an inherited or acquired deficit in beta-adrenergic function, much research has focused on the beta adrenergic receptor (beta2AR) and the beta-adrenergic cascade. However, 22 years later the question is still unsettled, as research has focused largely on the leukocyte, which is a poor model of human asthma. Studies of bronchial muscle tissue from animal models of asthma and from human asthmatics obtained either at surgery or at autopsy show a very definite deficit in beta-adrenergic function. However, the intracellular events underlying this beta adrenergic deficit is unknown. We have a well characterized animal model of airway hyperresponsiveness that clearly demonstrates decreased sensitivity to beta adrenergic agonists in vivo and in vitro. We have access to human asthmatic airway tissue which shows a similar defect, and we have access to a population of well characterized human asthmatics. We hypothesize that the decreased sensitivity to beta adrenergic agonists relates to a specific defect either in generation or degradation of intracellular cAMP. To identify directly the intracellular lesion we plan to measure numbers and affinities of beta2AR and muscarinic receptor subtypes, second messengers, adenylyl cyclase and phospholipase C and their regulation by the signal transducing G proteins in the airway smooth muscle of the basenji-greyhound dog, and to understand the mechanism by which glucocorticoids modify the response. We will apply the insights gained in the animal model to similar studies with available human airway tissues. In addition, we will determine whether genetic linkage exists between inheritance of the asthma phenotype and specific beta2AR gene alleles or other genes (e.g. G proteins) involved in beta adrenergic functions, and characterize specific mutations by nucleotide sequencing. The reduced in vitro sensitivity to beta agonists in our animal model provides us with the unique opportunity of easy accessibility to large quantities of airway smooth muscle for our in vitro studies from two allergic lines of animals - one hyperresponsive and one normoresponsive, allowing us to focus on the deficit leading to hyperresponsiveness, not confounded by allergy or drug therapy. We also have the unique ability to control and manipulate environmental and genetic influences. Results from the proposed work will provide new information about the intracellular mechanisms which regulate airway smooth muscle tone in this model. We will apply this information to the limited tissues available in humans and to human asthmatics using a candidate gene approach. We think this three pronged approach, using leukocyte DNA, human airway tissue and tissue from the BG dog model of airway hyperresponsiveness will yield important new insights. Since glucocorticoids and beta agonists remain the mainstay of asthma treatment, it is critical to elucidate the molecular mechanism of reduced beta agonist sensitivity and its modulation by glucocorticoids in patients and animal models of asthma.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
1R01HL045974-01
Application #
3365083
Study Section
Special Emphasis Panel (SRC (OA))
Project Start
1990-09-30
Project End
1995-07-31
Budget Start
1990-09-30
Budget End
1991-07-31
Support Year
1
Fiscal Year
1990
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Emala, Charles W; McQuitty, Christopher K; Eleff, Scott M et al. (2002) Asthma, allergy, and airway hyperresponsiveness are not linked to the beta(2)-adrenoceptor gene. Chest 121:722-31
Schears, G; Clancy, J; Hirshman, C A et al. (1997) Chronic carbachol pretreatment decreases adenylyl cyclase activity in airway smooth muscle. Am J Physiol 273:L640-7
Emala, C W; Kuhl, J; Hirshman, C A et al. (1996) Rapid communication: cloning and sequencing of a canine beta 2-adrenergic receptor cDNA. J Anim Sci 74:2285
Emala, C W; Aryana, A; Levine, M A et al. (1995) Expression of muscarinic receptor subtypes and M2-muscarinic inhibition of adenylyl cyclase in lung. Am J Physiol 268:L101-7
Emala, C W; Aryana, A; Levine, M A et al. (1995) Basenji-greyhound dog: increased m2 muscarinic receptor expression in trachealis muscle. Am J Physiol 268:L935-40
Croxton, T L; Takahashi, M; Hirshman, C A (1994) Decreased ion transport by tracheal epithelium of the basenji-greyhound dog. J Appl Physiol 76:1489-93
McQuitty, C K; Emala, C W; Hirshman, C A et al. (1994) Polymorphism in the human beta 2 adrenergic receptor gene detected by restriction endonuclease digestion with Fnu4HI. Hum Genet 93:225
Lenox, W C; Hirshman, C A (1993) Amrinone attenuates airway constriction during halothane anesthesia. Anesthesiology 79:789-94
Sauder, R A; Lenox, W C; Tobias, J D et al. (1993) Methylprednisolone increases sensitivity to beta-adrenergic agonists within 48 hours in Basenji greyhounds. Anesthesiology 79:1278-83
Lindeman, K S; Hirshman, C A (1993) Corticosteroid withdrawal restores responses to calcium chelators and enhances cholinergic responsiveness. Am Rev Respir Dis 148:1581-5

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