|Mcgarvey, Jeffery - Jeff|
Submitted to: Cellular Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/11/2004
Publication Date: 7/20/2003
Citation: Danelishvili, L., McGarvey, J.A., Li, Y., Bermudez, L. 2003. Mycobacterium tuberculosis infection causes different levels of apoptosis and necrosis in human macrophages and alveolar epithelial cells. Cellular Microbiology. 5(9):649-660. Interpretive Summary: Mycobacterium tuberculosis is a bacterium that causes serious disease in humans as well as livestock animals. The bacterium enters the lungs of the host and infects two types of cells. The first type cell is a blood cell that normally kills bacteria that are brought into the lungs, the second type of cell are those that line the lungs. Infection by Mycobacterium tuberculosis kills both of these cells but it is unclear how these cells die. To better understand how these cells die we infected both cell types in the laboratory and examined how they died using molecular biology techniques. The results are of interest because they advance the knowledge of how bacteria can cause disease and may lead to novel therapeutic methods.
Technical Abstract: We examined the induction of apoptosis and necrosis of human macrophages and type ll/alveolar epithelial cells by virulent and attenuated Mycobacterium tuberculosis strains. Apoptosis was determined by both ELISA and TUNEL assay, necrosis was evaluated by the release of lactate dehydrogenase (LDH). Both virulent and attenuated Mycobacterium tuberculosis induced apoptosis in macrophages; however, the attenuated strain resulted in more apoptosis than the virulent strain 5 days post inoculation. The cytotoxicity of alveolar cells was the result of necrosis, not apoptosis. Although infection with Mycobacterium tuberculosis strains resulted in apoptosis of 14% of the cells on the monolayer, cell death associated the necrosis was observed in 59% of alveolar epithelial cells at 5 days post infection. Infection with Mycobacterium tuberculosis suppressed apoptosis of epithelial cells induced by the kinase inhibitor, staurosporine. Because of our findings suggest that Mycobacterium tuberculosis can modulate the apoptotic response of macrophages and epithelial cells, we performed an apoptosis pathway-specific cDNA microarray analysis of human macrophages and epithelial cells. Whereas the inhibitors of apoptosis, bcl-2 and Rb, were upregulated over 2.5-fold in infected alveolar epithelial cells, the proapoptotic genes, bad and bax, were down regulated. The opposite was observed when U937 macrophages were infected the Mycobacterium tuberculosis. Upon infection of alveolar epithelial cells with Mycobacterium tuberculosis, the generation of apoptosis, as determined by the expression of caspase-1, caspase-3 and caspase-10, was inhibition of replication of intracellular bacteria resulted in an increase in apoptosis in both cell types.