Novel molecular pathologies in asthma and COPD

Both asthma and COPD are respiratory diseases and a major global health problem with increasing prevalence. Airway inflammation is a characteristic and important hallmark in both diseases and therefore, in the past, investigations focused strongly on the immunological aspect of these disorders. In recent years, it has been shown that resident cells of the airways, in particular airway smooth muscle (ASM) cells, would be pivotal in understanding the mechanisms underlying asthma, since they are able to secrete pro-inflammatory cytokines and exert a major effector function in airway constriction. Especially the abnormal expression in ASM cells in asthmatic patients of the cell cycle regulator and pro-inflammatory gene transcription factor C/EBPα may account for many asthma-specific phenotypes (increased proliferation and increased bulk of ASM cells, increased release of inflammatory mediators). In a first phase, we analyzed the translation of the CEBPA mRNA with a translation control reporter system (TCRS), which is able to monitor translation regulation of the C/EBPα. We found an impaired translation re-initiaion in ASM cells of asthmatic patients, which coincided with decreased levels of eIF4E, an important protein for translation initiation. In a second part of this thesis, we investigated the interaction of ASM cells with house dust mite extract, a potent airborne allergen. We found that HDM extract (i) reduces C/EBPα expression in ASM cells of asthma patients, (ii) enhances the release of IL-6 and (iii) induces cell proliferation. The reduction of the C/EBPα protein is achieved trough up-regulation of calreticulin, a repressor of CEBPA mRNA translation. Therefore, the direct, not immune-mediated interaction of HDM extract with the ASM cells is able to trigger an inflammatory response in these cells and to induce an enhanced proliferation, which may finally lead to the characteristic increased muscle mass observed in the airway of asthmatic patients. These findings may be of particular importance to explain non-atopic, intrinsic asthma, which affects 30% - 50% of asthmatic subjects. In the light of these findings, new therapeutic strategies targeting regulatory mechanisms of CEBPA mRNA translation should be considered in order to restore a balanced expression of the C/EBPα protein. In a third part of this thesis, we investigated the effect of cigarette smoke on the expression levels of C/EBPα and C/EBPβ in primary lung fibroblasts. Cigarette smoke affects both C/EBPα and C/EBPβ expression via translational control mechanisms in primary lung fibroblasts. In serumfree environment, cigarette smoke increased both C/EBPα and -β expression at the translational level via the uORF mechanism. In the presence of FCS, cigarette smoke increased the levels of hnRNP E2, an inhibitor of C/EBPα translation. As a consequence, both C/EBPα and -β expression decreased with increasing concentration of cigarette smoke. In both conditions, cigarette smoke had a potent antiproliferative effect on fibroblasts. Furthermore, cigarette smoke increased the release of IL-8. We postulate that the cigarette smoke-induced imbalance of proand anti-proliferative signals provides a novel mechanism to explain many pathologies of COPD and emphysema, especially the tissue destruction defined as an imbalance between tissue injury and tissue repair. Furthermore, we showed that that the direct interaction of lung fibroblast with cigarette smoke triggers the release of pro-inflammatory mediators, contributing to the inflammatory environment that characterizes COPD