Dilated cardiomyopathy and atrioventricular conduction blocks induced by heart-specific inactivation of mitochondrial DNA gene expression

Abstract

Mutations of mitochondrial DNA (mtDNA) cause several well-recognized human genetic syndromes with deficient oxidative phosphorylation and may also have a role in ageing and acquired diseases of old age. We report here that hallmarks of mtDNA mutation disorders can be reproduced in the mouse using a conditional mutation strategy to manipulate the expression of the gene encoding mitochondrial transcription factor A (Tfam, previously named mtTFA), which regulates transcription and replication of mtDNA. Using a loxP-flanked Tfam allele (TfamloxP) in combination with a cre-recombinase transgene under control of the muscle creatinine kinase promoter, we have disrupted Tfam in heart and muscle. Mutant animals develop a mosaic cardiac-specific progressive respiratory chain deficiency, dilated cardiomyopathy, atrioventricular heart conduction blocks and die at 2-4 weeks of age. This animal model reproduces biochemical, morphological and physiological features of the dilated cardiomyopathy of Kearns-Sayre syndrome. Furthermore, our findings provide genetic evidence that the respiratory chain is critical for normal heart function.

A switch in metabolism precedes increased mitochondrial biogenesis in respiratory chain-deficient mouse hearts

“…Hearts were collected (n ϭ 3) and prepared for isolation of DNA and RNA as described (10). RNA and DNA levels were quantified with a Fuji BAS 2000 phosphorimager and the IMAGE GAUGE 3.3 software.…”

“…Tfam loxP ͞Tfam loxP mice of mixed genetic background (10,12) were mated to heterozygous transgenic mice (ϩ͞Ckmm-NLS-cre) (15 Total RNA was isolated by using the TRIzol Reagent (GIBCO͞ BRL) and equal amounts of RNA from at least four animals were pooled for each experiment. Target preparation and hybridization to Affymetrix Mu11K Probe Arrays were performed according to the protocol supplied by Affymetrix (Santa Clara, CA).…”

“…We have previously characterized a mouse strain with tissue-specific disruption of Tfam in the heart and skeletal muscle (Tfam loxP ͞Tfam loxP ,ϩ͞Ckmm-cre) causing dilated cardiomyopathy, atrioventricular heart conduction blocks, and death at 2-4 weeks of age (10). This strain does not develop a muscle phenotype during their limited life span (10), consistent with our recent observation that it takes Ϸ4 months before TFAM protein depletion in skeletal muscle causes severely reduced MAPR (11).…”

“…Gene expression studies of respiratory chaindeficient budding yeast cells have demonstrated a variety of responses, including major reconfiguration of the metabolic pathways and induction of peroxisomal biogenesis (6). We have generated mouse models for studies of the pathogenesis of respiratory chain deficiency in vivo by using a conditional knockout strategy to disrupt the mitochondrial transcription factor A (Tfam) gene in selected cell types (7)(8)(9)(10)(11)(12). Increased cell death is a common consequence of prolonged respiratory chain deficiency, with the mechanism for cell death induction differing between affected tissues (8,9,13,14).…”

Mitochondrial DNA mutations in disease and aging

“…Also, tissue-specific knockout mice with impaired mtDNA maintenance (Wang et al, 1999;Wredenberg et al, 2002), defective mitochondrial transcription (Park et al, 2007), or impaired mitochondrial translation (Metodiev et al, 2009) have increased mitochondrial mass in affected tissues. It is generally assumed that this accumulation of mitochondria is caused by activation of mitochondrial biogenesis in response to deficient energy production.…”