Cytosolic Phospholipase A2 Participates with TNF-α in the Induction of Apoptosis of Human Macrophages Infected withMycobacterium tuberculosisH37Ra

Publisher Website
Google Scholar
Abstract
Macrophage (MΦ) apoptosis, an important innate microbial defense mechanism induced by Mycobacterium tuberculosis (Mtb) H37Ra, depends on the induction of TNF-α synthesis. When protein synthesis is blocked, both infection with Mtb and addition of TNF-α are required to induce caspase 9 activation, caspase 3 activation and apoptosis. In this study, we show that the second protein synthesis-independent signal involves activation of group IV cytosolic phospholipase A2 (cPLA2). Apoptosis of Mtb-infected MΦ and concomitant arachidonic acid release are abrogated by group IV cPLA2 inhibitors (methyl arachidonyl fluorophosphate and methyl trifluoromethyl ketone), but not by inhibitors of group VI Ca2+-independent (iPLA2 ; bromoenol lactone) or of secretory low molecular mass PLA2. In MΦ homogenates, the predominant PLA2 activity showed the same inhibitor sensitivity pattern and preferred arachidonic acid over palmitic acid in substrates, also indicating the presence of one or more group IV cPLA2 enzymes. In concordance with these findings, MΦ lysates contained transcripts and protein for group IV cPLA2-α and cPLA2-γ. Importantly, group IV cPLA2 inhibitors significantly reduced MΦ antimycobacterial activity and addition of arachidonic acid, the major product of group IV cPLA2, to infected MΦ treated with cPLA2 inhibitors completely restored the antimycobacterial activity. Importantly, addition of arachidonic acid alone to infected MΦ significantly reduced the mycobacterial burden. These findings indicate that Mtb induces MΦ apoptosis by independent signaling through at least two pathways, TNF-α and cPLA2, which are both also critical for antimycobacterial defense of the MΦ .