New Insights into Mitochondrial Permeabilization in Apoptosis

Abstract

Mitochondria undergo dramatic changes during apoptosis, which include extensive fragmentation and the permeabilization of the outer mitochondrial membrane, which is considered a point of no return in the cell's commitment to die. These alterations are controlled by the proteins of the Bcl-2 family in collaboration with the mitochondrial machinery for fission and fusion. Despite their central role, the molecular mechanisms involved remain poorly understood. To tackle these problems, we have used a combination of advanced microscopy methods in cells and in reconstituted systems. Here we present our results with Bax, a proapoptotic protein of the Bcl-2 family involed in mitochondrial permeabilization, and Drp1, a dynamin-like protein responsible for mitochondrial division. Studies with Giant Unilamellar Vesicles show that Bax forms stable, large membrane openings, which are affected by other Bcl-2 proteins and by Dpr1. Interestingly, Drp1 has a strong effect on the organization of the membrane. Using single molecule microscopy, we have analyzed the stoichiometry of Bax oligomers in the lipid bilayer. Finally, the analysis of Bax organization at the nanoscale by superresolution microscopy in cells undergoing apoptosis reveals striking structures that seem to play a role in the mitochondrial alterations in apoptosis.View Large Image | View Hi-Res Image | Download PowerPoint Slide