93 Linking the Molecular Mechanisms of Alveolar Macrophage Cell Death Induced by Inhaled Nanoparticles with the Subsequent Pathological Outcome

Abstract

Abstract Background Carbon Nanomaterials (CNM) get released into the environment as combustion by-products and engineered materials. Our previous work has shown that inhalation of CNMs differing in shape, such as spherical carbon nanoparticles (CNPs) or fiber-shaped nanotubes (CNTs) triggers different response pattern ranging from acute and resolving to persistent and chronic lung inflammation. Furthermore, our cell and mouse data showed that, particularly rigid, multi-walled nanotubes (MWCNTs) can cell-specifically and persistently kill alveolar macrophages (AM). Here we hypothesize that the AM death pathway determines the fate of lung inflammation, as acute or chronic. Results Exposure of the murine AM cell line MH-S to MWCNT led to significant decrease of cell viability in a dose-dependent manner (IC50: 10±5 μg/ml). In comparison, CNPs showed relatively low toxicity (IC50: >200 ug/ml) to MH-S cells. Also in contrast to hardly detectable apoptosis (cleaved-Caspase3), immunoblot and -fluorescence analysis demonstrated significant induction of LC3II, a central protein in the autophagy pathway, 12h after MWCNT treatment. The MWCNT triggered cell death response from BMDM-derived AM-like cells however, did not differ between LC3B-/- and wt mice, indicating the autophagy pathway as dispensable. In contrast, inhibition of lysosomal Cathepsins via K777, rescued MWCNT induced cell death of either MH-S or AM-like cells suggesting lysosomal Cathepsins as key player in AM cell death. Conclusion Lysosomal damage with subsequent Cathepsin activity seem a central key event in MWCNT triggered AM cell death. Current studies investigate the relevance of Cathepsins for the inflammatory consequences of CNT triggered AM cell death.