The mitochondria-shaping protein optic atrophy 1 (OPA1) has genetically 
distinguishable roles in mitochondrial morphology and apoptosis. The latter 
depends on the presenilin associated rhomboid like (PARL) protease, essential 
for the accumulation of a soluble intermembrane space form of OPA1 (IMS-OPA1). 
Here we show that OPA1 and PARL participate in the heat shock response, a 
stereotypical cellular process of adaptation to thermal stress. Upon heat shock, 
long forms of OPA1 are lost and mitochondria fragment. However, mitochondrial 
fusion is dispensable to maintain viability, whereas IMS-OPA1 is required. Upon 
conditioning-a process of mild heat shock and recovery-IMS-OPA1 accumulates, 
OPA1 oligomers increase and mitochondria release less cytochrome c, ultimately 
resulting in cellular resistance to subsequent apoptotic inducers. In Parl(-/-) 
cells accumulation of IMS-OPA1 is blunted and conditioning fails to protect from 
cytochrome c release and apoptosis. Thus, the OPA1/PARL dependent pathway of 
cristae remodeling is implicated in heat shock. This article is part of a 
Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).