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

Tgαqlow asterisk44 mice with targeted overexpression of activated Gαq protein in cardiomyocytes mimic many of the phenotypic characteristics of dilated cardiomyopathy in humans. However, it is not known whether the phenotype of Tgαqlow asterisk44 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 Tgαqlow asterisk44 mice in relation to the progression of heart failure. Tgαqlow asterisk44 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 Tgαqlow asterisk44 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 Tgαqlow asterisk44 mice loss of iron in Fe-S clusters, impaired citrate synthase activity, and altered mitochondrial ultrastructure were observed, supporting mitochondrial dysfunction in Tgαqlow asterisk44 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 Tgαqlow asterisk44 mice suggesting that alterations in function of cardiac mitochondria contribute to the development of the overt heart failure in this model.