Broad AOX expression in a genetically tractable mouse model does not disturb normal physiology

Plants and many lower organisms, but not mammals, express alternative oxidases (AOXs) that branch the mitochondrial respiratory chain, transferring electrons directly from ubiquinol to oxygen without proton pumping. Thus, they maintain electron flow under conditions when the classical respiratory chain is impaired, limiting excess production of oxygen radicals and supporting redox and metabolic homeostasis. AOX from Ciona intestinalis has been used to study and mitigate mitochondrial impairments in mammalian cell lines, Drosophila disease models and, most recently, in the mouse, where multiple lentivector-AOX transgenes conferred substantial expression in specific tissues. Here, we describe a genetically tractable mouse model in which Ciona AOX has been targeted to the Rosa26 locus for ubiquitous expression. The AOX(Rosa26) mouse exhibited only subtle phenotypic effects on respiratory complex formation, oxygen consumption or the global metabolome, and showed an essentially normal physiology. AOX conferred robust resistance to inhibitors of the respiratory chain in organello; moreover, animals exposed to a systemically applied LD50 dose of cyanide did not succumb. The AOX(Rosa26) mouse is a useful tool to investigate respiratory control mechanisms and to decipher mitochondrial disease aetiology in vivo.Peer reviewe

Strategic distribution of the mitochondrial Ca2+ uniporter in cardiac mitochondria

Background: 1) Control of the mitochondrial ATP production by SR-derived Ca2+ signals includes local, nanodomain Ca2+ transfer from ryanodine receptors (RyR2) to the mitochondrial matrix (excitation-bioenergetics coupling). 2) Ca2+ crosses the inner mitochondrial membrane (IMM) via the mtCU, a low-affinity Ca2+-activated Ca2+ channel complex. 3) The surface area of cardiac IMM is extensively enhanced by cristae folding; however, mitoplast patch clamp studies showed mtCU current density the lowest amongst a range of tissues (Fieni 2012. Nat Commun)

Use of Propensity Score Matching to Identify a Strong Association Between Strategic concentration to mitochondria-SR associations of the mitochondrial Ca2+ uniporter: Ca2+ uptake hotspots in the cardiac mitochondria

Introduction: Control of the mitochondrial ATP production by SR-derived Ca2+ signals includes local, nanodomain Ca2+ transfer from ryanodine receptors (RyR2) to the mitochondrial matrix (excitation-bioenergetics coupling). Ca2+ crosses the inner mitochondrial membrane (IMM) via the mtCU, a low-affinity Ca2+-activated Ca2+ channel complex. The surface area of cardiac IMM is extensively enhanced by cristae folding; however, mitoplast patch clamp studies showed mtCU current density the lowest amongst a range of tissues (Fieni 2012. Nat Commun).https://jdc.jefferson.edu/pacbposters/1002/thumbnail.jp

Calcium uptake hotspots in the mitochondria of cardiac muscle at the interface with dyadic SR

Introduction • Control of the mitochondrial ATP production by SR-derived Ca2+ signals includes local, nanodomain Ca2+ transfer from ryanodine receptors (RyR2) to the mitochondrial matrix (excitation-bioenergetics coupling). • Ca2+ crosses the inner mitochondrial membrane (IMM) via the mtCU, a low-affinity Ca2+-activated Ca2+ channel complex. • The surface area of cardiac IMM is extensively enhanced by cristae folding; however, mitoplast patch clamp studies showed mtCU current density the lowest amongst a range of tissues (Fieni 2012. Nat Commun).https://jdc.jefferson.edu/pacbposters/1007/thumbnail.jp

Loss-of-function of human PINK1 results in mitochondrial pathology and can be rescued by parkin.

Degeneration of dopaminergic neurons in the substantia nigra is characteristic for Parkinson's disease (PD), the second most common neurodegenerative disorder. Mitochondrial dysfunction is believed to contribute to the etiology of PD. Although most cases are sporadic, recent evidence points to a number of genes involved in familial variants of PD. Among them, a loss-of-function of phosphatase and tensin homolog-induced kinase 1 (PINK1; PARK6) is associated with rare cases of autosomal recessive parkinsonism. In HeLa cells, RNA interference-mediated downregulation of PINK1 results in abnormal mitochondrial morphology and altered membrane potential. Morphological changes of mitochondria can be rescued by expression of wild-type PINK1 but not by PD-associated PINK1 mutants. Moreover, primary cells derived from patients with two different PINK1 mutants showed a similar defect in mitochondrial morphology. Human parkin but not PD-associated mutants could rescue mitochondrial pathology in human cells like wild-type PINK1. Our results may therefore suggest that PINK1 deficiency in humans results in mitochondrial abnormalities associated with cellular stress, a pathological phenotype, which can be ameliorated by enhanced expression of parkin

The spatiotemporal regulation of the Keap1–Nrf2 pathway and its importance in cellular bioenergetics

The Kelch-like ECH associated protein 1 (Keap1)-NF-E2 p45-related factor 2 (Nrf2) pathway regulates networks of proteins that protect against the cumulative damage of oxidants, electrophiles and misfolded proteins. The interaction between transcription factor Nrf2 and its main negative cytoplasmic regulator Keap1 follows a cycle whereby the protein complex sequentially adopts two conformations: 'open', in which Nrf2 binds to one monomer of Keap1, followed by 'closed', in which Nrf2 interacts with both members of the Keap1 dimer. Electrophiles and oxidants (inducers) are recognized by cysteine sensors within Keap1, disrupting its ability to target Nrf2 for ubiquitination and degradation. Consequently, the protein complex accumulates in the 'closed' conformation, free Keap1 is not regenerated and newly synthesized Nrf2 is stabilized to activate target-gene transcription. The prevailing view of the Keap1-Nrf2 pathway, for which there exists a wealth of experimental evidence, is that it lies at the heart of cellular defence, playing crucial roles in adaptation and survival under conditions of stress. More recently, the significance of Nrf2 in intermediary metabolism and mitochondrial physiology has also been recognized, adding another layer of cytoprotection to the repertoire of functions of Nrf2. One way by which Nrf2 influences mitochondrial activity is through increasing the availability of substrates (NADH and FADH&lt;inf&gt;2&lt;/inf&gt;) for respiration. Another way is through accelerating fatty acid oxidation (FAO). These findings reinforce the reciprocal relationship between oxidative phosphorylation and the cellular redox state, and highlight the key role of Nrf2 in regulating this balance.</p