The function of alveolar macrophages (AM), a very important component of lung antibacterial and antiviral defense, decreases with age. Concomitantly, the incidence and the severity of infectious lung diseases increase with age and so does the sensitivity to the acute toxicity of 03 and NO2, two important environmental pollutants, which suppress AM function. The mechanisms underlying such age-associated decline in the immune function of AM and increase in sensitivity to 03 and NO2 toxicity, however, are not clear. Glutathione (GSH), an important antioxidant, plays a critical role in maintaining the optimal function of the immune system. GSH concentration decreases with age while GSH supplementation restores or improves the immune function, especially in the elderly, suggesting a potential involvement of GSH deficiency in age-associated dysfunction of the immune system. Our previous studies further suggest that decreased expression of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo GSH synthesis, is at least partially responsible for age-associated decline in GSH content in rat tissues. However, does GSH content decrease with age in AM? If it does, what is the underlying mechanism? Most importantly, is decreased GSH content responsible for age-associated dysfunction of AM and increased susceptibility of the elderly to infectious lung diseases as well as 03 and NO2 toxicity? All these questions remain to be answered.
The specific aims of this project are 1) To determine whether the GSH content in murine AM decreases with age and the potential underlying mechanism. 2) To test the hypothesis that decreased GCS gene expression is responsible for the age-associated decline in GSH content and dysfunction of AM as well as increased sensitivity of the elderly to infectious lung diseases. Tetracycline inducible, macrophage specific GCS sense and antisense gene transgenic mouse models will be used to test this hypothesis. AM function as well as resistance of mice to pneumococci infection will be determined to see whether increasing GCS gene expression and GSH content will restore the function of AM from old mice as well as reduce their lung infection. 3) To determine whether increased sensitivity of the elderly to the acute toxicity caused by 03 or NO2 is due to a decreased GSH content and dysfunction of AM. The long-term objective of this project is to uncover the mechanism underlying dysfunction of AM and increased susceptibility to infectious lung diseases and O3/NO2 toxicity observed in the elderly and to provide therapeutic strategies for treatment of these diseases.
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