Deficiency in the mouse mitochondrial adenine nucleotide translocator isoform 2 gene is associated with cardiac noncompaction

The mouse fetal and adult hearts express two adenine nucleotide translocator (ANT) isoform genes. The predominant isoform is the heart-muscle-brain ANT-isoform gene 1 (Ant1) while the other is the systemic Ant2 gene. Genetic inactivation of the Ant1 gene does not impair fetal development but results in hypertrophic cardiomyopathy in postnatal mice. Using a knockin X-linked Ant2 allele in which exons 3 and 4 are flanked by loxP sites combined in males with a protamine 1 promoter driven Cre recombinase we created females heterozygous for a null Ant2 allele. Crossing the heterozygous females with the Ant2(fl), PrmCre(+) males resulted in male and female ANT2-null embryos. These fetuses proved to be embryonic lethal by day E14.5 in association with cardiac developmental failure, immature cardiomyocytes having swollen mitochondria, cardiomyocyte hyperproliferation, and cardiac failure due to hypertrabeculation/noncompaction. ANTs have two main functions, mitochondrial-cytosol ATP/ADP exchange and modulation of the mitochondrial permeability transition pore (mtPTP). Previous studies imply that ANT2 biases the mtPTP toward closed while ANT1 biases the mtPTP toward open. It has been reported that immature cardiomyocytes have a constitutively opened mtPTP, the closure of which signals the maturation of cardiomyocytes. Therefore, we hypothesize that the developmental toxicity of the Ant2 null mutation may be the result of biasing the cardiomyocyte mtPTP to remain open thus impairing cardiomyocyte maturation and resulting in cardiomyocyte hyperproliferation and failure of trabecular maturation. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

The successful DNA typing of samples following a thermal cycler power loss

An approach for generating DNA profiles when critical samples have been consumed and a power outage occurs during the polymerase chain reaction (PCR) amplification reaction is described. This study demonstrates that a complete and accurate DNA short tandem repeat profile can be obtained: (1) when single source DNA samples are amplified for 26, 27, or 28 cycles using the Profiler Plus and COfiler Amplification Kits after an interruption in amplification, (2) from mock samples when PCR amplification has been interrupted early (after five cycles) or late (after 18 cycles) and the sample is subjected to an additional round of amplification, even after incubation of the sample at room temperature overnight, and (3) from nonprobative casework samples interrupted after approximately 18 cycles of amplification, an overnight incubation at room temperature and subjected to one or two additional rounds of PCR amplification for approximately 26 total cycles. Samples interrupted before five completed cycles and subjected to additional PCR cycles yielded variable results.

The ADP/ATP translocator is not essential for the mitochondrial permeability transition pore

A sudden increase in permeability of the inner mitochondrial membrane, the so-called mitochondrial permeability transition, is a common feature of apoptosis and is mediated by the mitochondrial permeability transition pore (mtPTP). It is thought that the mtPTP is a protein complex formed by the voltage-dependent anion channel, members of the pro- and anti-apoptotic BAX-BCL2 protein family, cyclophilin D, and the adenine nucleotide (ADP/ATP) translocators (ANTs). The latter exchange mitochondrial ATP for cytosolic ADP and have been implicated in cell death. To investigate the role of the ANTs in the mtPTP, we genetically inactivated the two isoforms of ANT in mouse liver and analysed mtPTP activation in isolated mitochondria and the induction of cell death in hepatocytes. Mitochondria lacking ANT could still be induced to undergo permeability transition, resulting in release of cytochrome c. However, more Ca2+ than usual was required to activate the mtPTP, and the pore could no longer be regulated by ANT ligands. Moreover, hepatocytes without ANT remained competent to respond to various initiators of cell death. Therefore, ANTs are non-essential structural components of the mtPTP, although they do contribute to its regulation.

Ocular pathology in mitochondrial superoxide dismutase (Sod2)-deficient mice

PURPOSE

To characterize the pathologic features in retina, optic nerve, and extraocular muscle of mitochondrial superoxide dismutase (Sod2)-deficient mice, a model of increased mitochondrial production of reactive oxygen species.

METHODS

Morphometric and ultrastructural study of eyes of 43 homozygous sod2(tm1Cje-/-) mice and wild-type control animals. For retinal morphometric analysis, 32 manganese 5,10,15,20-tetrakis (4-benzoic acid) porphyrin (MnTBAP)-treated animals aged either 9 to 10 days or 20 to 21 days were studied. Ultrastructural examination was performed on tissue from the treated animals, and 11 additional untreated mutant and control animals.

RESULTS

In treated Sod2-deficient animals, the photoreceptor layer was thinner centrally at 9 to 10 days than in control animals (mean 8.8 vs. 14.7 microm). By 20 to 21 days, all retinal layers apart from the outer nuclear layer and retinal pigment epithelium (RPE) were thinner centrally in mutant animals (total retinal thickness, 233.2 vs. 272.6 microm; combined nerve fiber layer, ganglion cell layer, and inner plexiform layer, 86.2 vs. 103.4 microm; inner nuclear layer, 51.8 vs. 60.3 microm; photoreceptors, 26.7 vs. 35.6 microm). Optic nerve cross-sectional area was less in 20- to 21-day-old treated Sod2-deficient animals than in control animals. Mitochondrial morphologic abnormalities (swelling, pale matrix, and disorganized cristae) were found predominantly in older mutant animals' (16 and 20 to 21 days) RPE and in extraocular muscle of a 16-day-old untreated mutant.

CONCLUSIONS

In sod2(tm1Cje-/-) mice, there is relative progressive retinal thinning, with particular involvement of the inner retinal layers and an early effect on the photoreceptor layer, as well as mitochondrial morphologic abnormalities, all consistent with mitochondrial disease.

Increased mitochondrial oxidative stress in the Sod2 (+/-) mouse results in the age-related decline of mitochondrial function culminating in increased apoptosis

To determine the importance of mitochondrial reactive oxygen species toxicity in aging and senescence, we analyzed changes in mitochondrial function with age in mice with partial or complete deficiencies in the mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD). Liver mitochondria from homozygous mutant mice, with a complete deficiency in MnSOD, exhibited substantial respiration inhibition and marked sensitization of the mitochondrial permeability transition pore. Mitochondria from heterozygous mice, with a partial deficiency in MnSOD, showed evidence of increased proton leak, inhibition of respiration, and early and rapid accumulation of mitochondrial oxidative damage. Furthermore, chronic oxidative stress in the heterozygous mice resulted in an increased sensitization of the mitochondrial permeability transition pore and the premature induction of apoptosis, which presumably eliminates the cells with damaged mitochondria. Mice with normal MnSOD levels show the same age-related mitochondrial decline as the heterozygotes but occurring later in life. The premature decline in mitochondrial function in the heterozygote was associated with the compensatory up-regulation of oxidative phosphorylation enzyme activity. Thus mitochondrial reactive oxygen species production, oxidative stress, functional decline, and the initiation of apoptosis appear to be central components of the aging process.

Mitochondrial oxidative stress in mice lacking the glutathione peroxidase-1 gene

Oxidative stress resulting from mitochondrially derived reactive oxygen species (ROS) has been hypothesized to damage mitochondrial oxidative phosphorylation (OXPHOS) and to be a factor in aging and degenerative disease. If this hypothesis is correct, then genetically inactivating potential mitochondrial antioxidant enzymes such as glutathione peroxidase-1 (Gpx1; EC 1.11.1.9) should increase mitochondrial ROS production and decrease OXPHOS function. To determine the expression pattern of Gpx1, isoform-specific antibodies were generated and mutant mice were prepared in which the Gpx1 protein was substituted for by beta-galactosidase, driven by the Gpx1 promoter. These experiments revealed that Gpx1 is highly expressed in both the mitochondria and the cytosol of the liver and kidney, but poorly expressed in heart and muscle. To determine the physiological importance of Gpx1, mice lacking Gpx1 were generated by targeted mutagenesis in mouse ES cells. Homozygous mutant Gpx1(tm1Mgr) mice have 20% less body weight than normal animals and increased levels of lipid peroxides in the liver. Moreover, the liver mitochondria were found to release markedly increased hydrogen peroxide, a Gpx1 substrate, and have decreased mitochondrial respiratory control ratio and power output index. Hence, genetic inactivation of Gpx1 resulted in growth retardation, presumably due in part to reduced mitochondrial energy production as a product of increased oxidative stress.