REGULATION OF PULMONARY ELASTIN PRODUCTION BY RETINOIDS

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Destructive inflammatory lung diseases lung diseases such as emphysema and bronchiectasis can irreversibly alter the elastic properties of the lung by degradation of the structural protein elastin. Since virtually all of the elastin in the normal lung is produced during early like, studying the factors which regulate elastin synthesis and deposition, and to ultimately repair the elastin network that is damaged in disease. Hypothesis: The perinatal lung contains a supply of retinoids, that it may use during the period of maximal alveolar septal elastin synthesis. Retinoids, and in particular retinoic acid (RA), may promote elastin synthesis by interstitial lung fibroblasts (LIF) and modulate the increase in elastin synthesis that is required for normal alveolar septal formation. Preliminary studies show that the quantities of RA and retinoic acid receptor-gamma mRNA and protein in neonatal rat lung fibroblasts change in a temporal pattern that suggests they could help initiate an increase in elastin synthesis by these cells. Additional studies show that RA increases elastin production by cultured neonatal LIF and acts at the level of transcription. The major goal of the proposed research is to examine the molecular mechanisms by which RA may influence elastin synthesis during normal alveolar development. The acquisition and metabolism of retinoids by lung tissue and isolated LIF will be examined to assess the utilization of endogenous pulmonary stores. The basal and RA- induced expression of the various retinoic acid receptor (RAR) and retinoid-X receptor (RXR) genes will be studied in cultured rat LIF and in LIF isolated from RAR-gamma null mice. RAR and RXR mRNA and protein will be quantitated using ribonuclease protection assays and immunoblotting, respectively. The effects of a dominant negative RAR mutation of elastin expression will be examined in cultured cells. Elastin mRNA, insoluble elastin accumulation, and alveolar growth will be studied in mice bearing gene deletions for RAR-gamma and/or RXR-alpha. The molecular details of the effects of RA on the elastin gene will be elucidated by deletional analysis and mutagenesis of two potential RA response elements (RARE) within the 5' flanking region of the rat elastin gene. Electrophorectic mobility shift assays will be used to demonstrate RA-responsive increases in the binding of nuclear proteins to these elements, in cultured LIF and in the developing lung. A ligation-mediated polymerase chain reaction will be used to evaluate binding of proteins to these putative RARE in the elastin gene in vivo during lung development, and in response to exogenous RA. Elucidation of mechanisms whereby elastin synthesis is initiated in the alveoli would provide novel information that may also be applicable to idiopathic pulmonary fibrosis and bronchopulmonary dysplasia.