Bcl-x(L) mediates RIPK3-dependent necrosis in M. tuberculosis-infected macrophages

Virulent Mycobacterium tuberculosis (Mtb) triggers necrosis in host Mφ, which is essential for successful pathogenesis. Here we demonstrate that necrosis of Mtb-infected Mφ is dependent on the action of the cytosolic kinase Receptor Interacting Protein 3 (RIPK3) and the mitochondrial Bcl-2 family member protein B-cell lymphoma - extra large (Bcl-x(L)). RIPK3-deficient Mφ are able to better control bacterial growth in vitro and in vivo. Cytosolic RIPK3 translocates to the mitochondria where it promotes necrosis and blocks caspase 8-activation and apoptosis via Bcl-x(L). Furthermore, necrosis is associated with stabilization of hexokinase II on the mitochondria as well as cyclophilin D-dependent mitochondrial permeability transition (MPT). These events up-regulate the level of reactive oxygen species (ROS) to induce necrosis. Thus, in Mtb-infected Mφ mitochondria are an essential platform for induction of necrosis by activating RIPK3 function and preventing caspase 8 - activation.