ATP-induced autophagy is associated with rapid killing of intracellular mycobacteria within human monocytes/macrophages

• Published in: BMC immunology 2008-07, Vol.9 (1), p.35-35, Article 35
• Main Authors: Biswas, Debasis, Qureshi, Omar S, Lee, Wing-Yiu, Croudace, Joanne E, Mura, Manuela, Lammas, David A
• Format: Article
• Language: English
• Subjects: Adenosine triphosphate; Adenosine Triphosphate - pharmacology; Autophagy; Calcium - metabolism; Causes of; Health aspects; Humans; Lysosomes - physiology; Macrophages - drug effects; Macrophages - immunology; Macrophages - microbiology; Macrophages - ultrastructure; Microscopy, Electron, Transmission; Monocytes - drug effects; Monocytes - immunology; Monocytes - microbiology; Mycobacterial infections; Mycobacterium; Mycobacterium bovis - drug effects; Mycobacterium bovis - immunology; Phagocytosis; Phagosomes - microbiology; Phagosomes - physiology; Phagosomes - ultrastructure; Physiological aspects; Prevention; Receptors, Purinergic P2 - metabolism; Receptors, Purinergic P2X7; Risk factors
• ISSN: 1471-2172; 1471-2172
• DOI: 10.1186/1471-2172-9-35

We have previously reported that ATP treatment of M bovis-BCG infected human macrophages induces P2X7 receptor-dependent killing of intracellular mycobacteria. The mechanism mediating this bactericidal effect has not been full characterized but is known to be Ca2+-dependent and to promote the maturation and acidification of mycobacteria-containing phagosomes. In this study we demonstrate that the ATP/P2X7-mediated, mycobactericidal effect also involves the induction of cell autophagy. We report that 3 mM ATP induces rapid cell autophagy in THP1 cells and monocyte-derived macrophages within 30 minutes post-treatment, as revealed by the expression of LC3-II bands on western blot analysis. Using Ca2+-free media and selective P2X7 agonists and antagonists, ATP-induced cell autophagy was shown to be Ca2+ and P2X7 receptor-dependent. Electron microscopy of ATP-treated, BCG-infected MDMs revealed the presence of the bacteria within characteristic double-membraned autophagosomes. Confocal analysis further confirmed that pharmacological inhibition of autophagy by wortmannin or pre-treatment of macrophages with anti-P2X7 antibody blocked ATP-induced phago-lysosomal fusion. Induction of cell autophagy with ATP was also temporally associated with a fall in intracellular mycobacterial viability, which was suppressed by treatment with wortmannin or the selective P2X7 antagonist, oxidized ATP (oATP). We provide the first evidence that ATP/P2X7-mediated killing of intracellular mycobacteria involves the induction of cell autophagy. The findings support the hypothesis that autophagy plays a key role in the control of mycobacterial infections.