EndoG links Bnip3-induced mitochondrial damage and caspase-independent DNA fragmentation in ischemic cardiomyocytes

Abstract

Mitochondrial dysfunction, caspase activation and caspase-dependent DNA fragmentation are involved in cell damage in many tissues. However, differentiated cardiomyocytes repress the expression of the canonical apoptotic pathway and their death during ischemia is caspase-independent. The atypical BH3-only protein Bnip3 is involved in the process leading to caspase-independent DNA fragmentation in cardiomyocytes. However, the pathway by which DNA degradation ensues following Bnip3 activation is not resolved. To identify the mechanism involved, we analyzed the interdependence of Bnip3, Nix and EndoG in mitochondrial damage and DNA fragmentation during experimental ischemia in neonatal rat ventricular cardiomyocytes. Our results show that the expression of EndoG and Bnip3 increases in the heart throughout development, while the caspase-dependent machinery is silenced. TUNEL-positive DNA damage, which depends on caspase activity in other cells, is caspase-independent in ischemic cardiomyocytes and ischemia-induced DNA high and low molecular weight fragmentation is blocked by repressing EndoG expression. Ischemia-induced EndoG translocation and DNA degradation are prevented by silencing the expression of Bnip3, but not Nix, or by overexpressing Bcl-xL. These data establish a link between Bnip3 and EndoG-dependent, TUNEL-positive, DNA fragmentation in ischemic cardiomyocytes in the absence of caspases, defining an alternative cell death pathway in postmitotic cells.

The work was supported by the Ministry of Science and Innovation of Spain (SAF2005-02197 and SAF2008-02271) to DS and Programa de Suport a Grups de Recerca de Catalunya from the Government of Catalonia (AGAUR) (SGR2005-00628) and Ciberned from the Spanish Government to JXC, Instituto de Salud Carlos III -Ministerio de Sanidad y Consumo (FIS) (PI04/2537 and PS09/00140) to ML. JZ was recipient of a pre-doctoral fellowship (FPI program) from the Ministry of Education and Science of Spain and JY is recipient of a fellowship from the Universitat de Lleida. URLs: Ministry of Science and Innovation of Spain: http://www.micinn.es; AGAUR: http://www10.gencat.cat/agaur_web/AppJava/catala/index.jsp; Ministry of Education: http://www.educacion.es/portada.html; Instituto de Salud Carlos III: http://www.isciii.es/htdocs/index.jsp. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.