Detection of mitochondrial dysfunction by EPR technique in mouse model of dilated cardiomyopathy

Tg alpha q*44 mice with targeted overexpression of activated G alpha q protein in cardiomyocytes mimic many of the phenotypic characteristics of dilated cardiomyopathy in humans. However, it is not known whether the phenotype of Tg alpha q*44 mice would also involve dysfunction of cardiac mitochondria. The aim of the present work was to examine changes in EPR signals of semiquinones and iron in Fe-S clusters, as compared to classical biochemical indices of mitochondrial function in hearts from Tg alpha q*44 mice in relation to the progression of heart failure. Tg alpha q*44 mice at the age of 14 months displayed pulmonary congestion, increased heart/body ratio and impairment of cardiac function as measured in vivo by MRI. However, in hearts from Tg alpha q*44 mice already at the age of 10 months EPR signals of semiquinones, as well as cyt c oxidase activity were decreased, suggesting alterations in mitochondrial electron flow. Furthermore, in 14-months old Tg alpha q*44 mice loss of iron in Fe-S clusters, impaired citrate synthase activity, and altered mitochondrial ultrastructure were observed, supporting mitochondrial dysfunction in Tg alpha q*44 mice. In conclusion, the assessment of semiquinones content and Fe(III) analysis by EPR represents a rational approach to detect dysfunction of cardiac mitochondria. Decreased contents of semiquinones detected by EPR and a parallel decrease in cyt c oxidase activity occurs before hemodynamic decompensation of heart failure in Tg alpha q*44 mice suggesting that alterations in function of cardiac mitochondria contribute to the development of the overt heart failure in this model. (c) 2008 Elsevier Inc. All rights reserved.