Variations in the rheostat model of apoptosis: what studies of retinal ganglion cell death tell us about the functions of the Bcl2 family proteins.

Studies of the functions of members of the Bcl2 gene family suggested that apoptosis was controlled by a rheostat in which anti-apoptotic proteins like BCL2 bound and sequestered pro-apoptotic proteins like BAX. Our current understanding of these proteins suggests that this is a simplistic model. The new rheostat model predicts that BH3-only peptides act as neutralizing ligands for the anti-apoptotic proteins, thus allowing molecules like BAX to become activated and initiate mitochondrial dysfunction - a critical step in the intrinsic apoptotic program. Studies of retinal ganglion cell apoptosis indicate that a threshold of BAX expression is required for its successful activation, which is independent of the overall concentration of anti-apoptotic proteins in these cells. Copyright 2010 Elsevier Ltd. All rights reserved.