1. ¹Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA, USA
2. ²Department of Biochemistry, National University of Ireland, Galway, Ireland
3. ³St Boniface General Hospital Research Center, Winnipeg, Canada

Correspondence: ÅB Gustafsson, Department of Molecular and Experimental Medicine, The Scripps Research Institute, MEM 220, 10550 N. Torrey Pines Road, CA 92037, USA. Tel: +1-858-784-9166; Fax: +1-858-784-8389; E-mail: agustafs@scripps.edu

Received 2 September 2005; Revised 20 February 2006; Accepted 13 March 2006; Published online 28 April 2006.

Abstract

Ischemia and reperfusion (I/R) injury is associated with extensive loss of cardiac myocytes. Bnip3 is a mitochondrial pro-apoptotic Bcl-2 protein which is expressed in the adult myocardium. To investigate if Bnip3 plays a role in I/R injury, we generated a TAT-fusion protein encoding the carboxyl terminal transmembrane deletion mutant of Bnip3 (TAT-Bnip3TM) which has been shown to act as a dominant negative to block Bnip3-induced cell death. Perfusion with TAT-Bnip3TM conferred protection against I/R injury, improved cardiac function, and protected mitochondrial integrity. Moreover, Bnip3 induced extensive fragmentation of the mitochondrial network and increased autophagy in HL-1 myocytes. 3D rendering of confocal images revealed fragmented mitochondria inside autophagosomes. Enhancement of autophagy by ATG5 protected against Bnip3-mediated cell death, whereas inhibition of autophagy by ATG5K130R enhanced cell death. These results suggest that Bnip3 contributes to I/R injury which triggers a protective stress response with upregulation of autophagy and removal of damaged mitochondria.