Genetic modification of survival in tissue-specific knockout mice with mitochondrial cardiomyopathy

Abstract

We recently described a mouse model that reproduces important pathophysiological features of mitochondrial DNA (mtDNA) mutation diseases. The gene for mouse mitochondrial transcription factor A, Tfam (also called mtTFA), a nucleus-encoded key regulator of mtDNA expression, was targeted with loxP sites (Tfam loxP ) and disrupted in vivo by transgenic expression of cre-recombinase from the muscle creatinine kinase (Ckmm) promoter. This promoter is active from embryonic day 13, and the knockouts had normal respiratory chain function in the heart at birth and developed mitochondrial cardiomyopathy postnatally. In this paper, we describe a heart-knockout strain obtained by mating Tfam loxP mice to animals expressing cre-recombinase from the ␣-myosin heavy chain (Myhca) promoter. This promoter is active from embryonic day 8, and the knockouts had onset of mitochondrial cardiomyopathy during embryogenesis. The age of onset of cardiac respiratory chain dysfunction can thus be controlled by temporal regulation of cre-recombinase expression. Further characterization demonstrated that Ϸ75% of the knockouts died in the neonatal period, whereas, surprisingly, Ϸ25% survived for several months before dying from dilated cardiomyopathy with atrioventricular heart conduction blocks. Modifying gene(s) affect the life span of the knockouts, because Ϸ95% of the knockout offspring from an intercross of the longer-living knockouts survived the neonatal period. Thus, the tissue-specific knockouts we describe here not only reproduce important pathophysiological features of mitochondrial cardiomyopathy but also provide a powerful system by which to identify modifying genes of potential therapeutic value.

Dilated cardiomyopathy in mice deficient for the lysosomal cysteine peptidase cathepsin L

“…Furthermore, about 25% of the hearts of ctsl Ϫ/Ϫ mice had developed a severe enlargement at 12 months of age, which resulted in significantly impaired cardiac performance and led to valve insufficiencies in four of the 14 CTSL-deficient mice investigated by Doppler echocardiography. Despite these histomorphological and functional alterations, the mortality rate of adult ctsl Ϫ/Ϫ mice was not increased in mice up to 12 months of age, which contrasts with many other transgenic mouse models of DCM in which symptoms occur early in life and result in death only days or a few weeks after onset of the disease (9,10,14,16,17,36). Thus, CTSL-deficient mice represent a model of a chronic progressive DCM that is comparable to the adult form of the human disease in many respects.…”

“…Some of these lines, e.g., deletions of ␦-sarcoglycan and the actin-associated muscle LIM protein MLP or a R403N point mutation in the cardiac myosin heavy chain, resemble the phenotype of human hereditary DCM (8)(9)(10). On the other hand, multiple genetically altered mouse lines developing hereditary DCM are currently lacking human counterparts, e.g., overexpression of tumor necrosis factor ␣ or retinoic receptor ␣, inactivation of the cAMP response elementbinding protein, and deletion of the bradikinin B2 receptor and the mitochondrial transcription factor A (Tfam; [11][12][13][14][15][16][17].…”

Conditional alleles in mice: Practical considerations for tissue‐specific knockouts

“…Thus, the (Cre/ϩ; null/ϩ) mice are usually male, whereas the homozygous (floxed/floxed) mice are usually female. In this way, effort is saved for genotyping the homozygous (floxed/floxed) line that is going to be sacrificed very frequently during the course of the experi- However, this will impose greater demand for the recombinase activity, as two floxed target alleles need to be excised to achieve conditional gene inactivation in Takeda et al, 1998;Chapman et al, 1999;Sano et al, 1999;Takeda et al, 1999 Tfam (transcription factor A, mitochondrion) 10 (38.0) OE Larsson et al, 1998;Wang et al, 1999;Li et al, 2000a;Silva et al, 2000 Tgfbr2 (TGF-␤ OE 2-loxP strategy ( Fig. 2A).…”

Intracellular and Extracellular ATP Coordinately Regulate the Inverse Correlation between Osteoclast Survival and Bone Resorption

“…In addition, Tfam is absolutely required for transcription initiation at mtDNA promoters (15). In fact, disruption of the Tfam gene causes depletion of mtDNA, loss of mitochondrial transcripts, loss of mtDNA-encoded polypeptides, severe respiratory chain deficiency, and reduced ATP production (8,13,16,17).…”