Early-onset liver mtDNA depletion and late-onset proteinuric nephropathy in Mpv17 knockout mice. Hum Mol Genet

Unit of Molecular Neurogenetics - Pierfranco and Luisa Mariani Center for the Study of Mitochondrial Disorders in Children, IRCCS Foundation Neurological Institute C. Besta, Milan, Italy.
Human Molecular Genetics (Impact Factor: 6.39). 10/2008; 18(1):12-26. DOI: 10.1093/hmg/ddn309
Source: PubMed


In humans, MPV17 mutations are responsible for severe mitochondrial depletion syndrome, mainly affecting the liver and the nervous system.
To gain insight into physiopathology of MPV17-related disease, we investigated an available Mpv17 knockout animal model. We found severe mtDNA depletion in liver and, albeit to a lesser extent, in skeletal muscle, whereas hardly
any depletion was detected in brain and kidney, up to 1 year after birth. Mouse embryonic fibroblasts did show mtDNA depletion,
but only after several culturing passages, or in a serumless culturing medium. In spite of severe mtDNA depletion, only moderate
decrease in respiratory chain enzymatic activities, and mild cytoarchitectural alterations, were observed in the Mpv17−/− livers, but neither cirrhosis nor failure ever occurred in this organ at any age. The mtDNA transcription rate was markedly
increased in liver, which could contribute to compensate the severe mtDNA depletion. This phenomenon was associated with specific
downregulation of Mterf1, a negative modulator of mtDNA transcription. The most relevant clinical features involved skin,
inner ear and kidney. The coat of the Mpv17−/− mice turned gray early in adulthood, and 18-month or older mice developed focal segmental glomerulosclerosis (FSGS) with
massive proteinuria. Concomitant degeneration of cochlear sensory epithelia was reported as well. These symptoms were associated
with significantly shorter lifespan. Coincidental with the onset of FSGS, there was hardly any mtDNA left in the glomerular
tufts. These results demonstrate that Mpv17 controls mtDNA copy number by a highly tissue- and possibly cytotype-specific mechanism.

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    • "Third, other functional mechanisms may compensate MPV17 functions in dogs. The enhancement of mtDNA transcription was measured in the Mpv17-deficent mouse liver and muscle (Viscomi et al., 2009). We did not have relevant tissue material available this time from dogs to investigate this possibility. "
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    ABSTRACT: Mitochondrial DNA depletion syndromes (MDS) are often serious autosomal recessively inherited disorders characterized by tissue-specific mtDNA copy number reduction. Many genes, including MPV17, are associated with the hepatocerebral form of MDS. MPV17 encodes for a mitochondrial inner membrane protein with a poorly characterized function. Several MPV17 mutations have been reported in association with a heterogeneous group of early-onset manifestations, including liver disease and neurological problems. Mpv17-deficient mice present renal and hearing defects. We describe here a MPV17 truncation mutation in dogs. We found a 1-bp insertion in exon 4 of the MPV17 gene, resulting in a frameshift and early truncation of the encoded protein. The mutation halves MPV17 expression in the lymphocytes of the homozygous dogs and the truncated protein is not translated in transfected cells. The insertion mutation is recurrent and exists in many unrelated breeds, although is highly enriched in the Boxer breed. Unexpectedly, despite the truncation of MPV17, we could not find any common phenotypes in the genetically affected dogs. The lack of observable phenotype could be due to a late onset, mild symptoms or potential tissue-specific compensatory mechanisms. This study suggests species-specific differences in the manifestation of the MPV17 defects and establishes a novel large animal model to further study MPV17 function and role in mitochondrial biology.
    Full-text · Article · Sep 2015 · Biology Open
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    • "), and genes with poorly defined functions related to mtDNA maintenance, including, MPV17 and, interestingly, subunits of the Kreb's cycle enzyme Succinyl-CoA Synthetase, SCS (SUCLG1, SUCLA2) (Suomalainen and Isohanni, 2010). While animal models have been reported for many of these genes (Haraguchi et al., 2002; Kimura et al., 2003; Hance et al., 2005; Tyynismaa et al., 2005; Akman et al., 2008; Martinez-Azorin et al., 2008; Lopez et al., 2009; Viscomi et al., 2009), there is currently no reported animal model for SCS–dependent mtDNA depletion. SCS is the TCA cycle enzyme responsible for the conversion of succinyl-CoA to succinate in the mitochondrial matrix that is coupled to the phosphorylation of GDP or ADP, thereby providing the only " substrate level " phosphorylation in the TCA cycle. "
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    ABSTRACT: Mutations in subunits of Succinyl-CoA Synthetase/Ligase (SCS), a component of the citric acid cycle, are associated with mitochondrial encephalomyopathy, elevation of methylmalonic acid (MMA), and mitochondrial DNA (mtDNA) depletion. While performing a FACS-based retroviral-mediated gene trap mutagenesis screen in mouse embryonic stem (ES) cells for abnormal mitochondrial phenotypes, a gene trap allele of Sucla2 (Sucla2(SAβgeo)) has been isolated in mouse embryonic stem (ES) cells and used to generate transgenic animals. Sucla2 encodes the ADP-specific β subunit isoform of SCS. Sucla2(SAβgeo) homozygotes exhibit recessive lethality, with most mutants dying late in gestation (e18.5). Mutant placenta and embryonic (e17.5) brain, heart and muscle show varying degrees of mtDNA depletion (20-60%), while there is no mtDNA depletion in mutant liver, where the gene is not normally expressed. Elevated levels of MMA are observed in embryonic brain. SCS deficient mouse embryonic fibroblasts (MEFs) demonstrate a 50% reduction in mtDNA content compared to wild type MEFs. The mtDNA depletion results in reduced steady state levels of mtDNA encoded proteins and multiple respiratory chain deficiencies, while mtDNA content can be restored by reintroduction of Sucla2. This mouse model of SCS deficiency and mtDNA depletion promises to provide insights into the pathogenesis of mitochondrial diseases with mtDNA depletion and into the biology of mtDNA maintenance. In addition, this report demonstrates the power of a genetic screen that combines gene trap mutagenesis and FACS analysis in mouse ES cells to identify mitochondrial phenotypes and to develop animal models of mitochondrial dysfunction.
    Full-text · Article · Nov 2013 · Disease Models and Mechanisms
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    • "Induction prevents cardiovascular injury via anti-inflammatory effects [37], protects against platelet aggregation, and limits growth of vascular smooth muscle cells [38], effects that could contribute to I-R resistance in vivo. The function of induced Mpv17 is poorly understood, though there is evidence this inner mitochondrial membrane protein may regulate mtDNA copy number and longevity [39]. Tfrc encodes the transferrin receptor, which contributes to iron handling and could facilitate iron-dependent oxidative stress. "
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    ABSTRACT: Opioidergic SLP (sustained ligand-activated preconditioning) induced by 3-5 days of opioid receptor (OR) agonism induces persistent protection against ischemia-reperfusion (I-R) injury in young and aged hearts, and is mechanistically distinct from conventional preconditioning responses. We thus applied unbiased gene-array interrogation to identify molecular effects of SLP in pre- and post-ischemic myocardium. Male C57Bl/6 mice were implanted with 75 mg morphine or placebo pellets for 5 days. Resultant SLP did not modify cardiac function, and markedly reduced dysfunction and injury in perfused hearts subjected to 25 min ischemia/45 min reperfusion. Microarray analysis identified 14 up- and 86 down-regulated genes in normoxic hearts from SLP mice (≥1.3-fold change, FDR≤5%). Induced genes encoded sarcomeric/contractile proteins (Myh7, Mybpc3,Myom2,Des), natriuretic peptides (Nppa,Nppb) and stress-signaling elements (Csda,Ptgds). Highly repressed genes primarily encoded chemokines (Ccl2,Ccl4,Ccl7,Ccl9,Ccl13,Ccl3l3,Cxcl3), cytokines (Il1b,Il6,Tnf) and other proteins involved in inflammation/immunity (C3,Cd74,Cd83, Cd86,Hla-dbq1,Hla-drb1,Saa1,Selp,Serpina3), together with endoplasmic stress proteins (known: Dnajb1,Herpud1,Socs3; putative: Il6, Gadd45g,Rcan1) and transcriptional controllers (Egr2,Egr3, Fos,Hmox1,Nfkbid). Biological themes modified thus related to inflammation/immunity, together with cellular/cardiovascular movement and development. SLP also modified the transcriptional response to I-R (46 genes uniquely altered post-ischemia), which may influence later infarction/remodeling. This included up-regulated determinants of cellular resistance to oxidant (Mgst3,Gstm1,Gstm2) and other forms of stress (Xirp1,Ankrd1,Clu), and repression of stress-response genes (Hspa1a,Hspd1,Hsp90aa,Hsph1,Serpinh1) and Txnip. Protection via SLP is associated with transcriptional repression of inflammation/immunity, up-regulation of sarcomeric elements and natriuretic peptides, and modulation of cell stress, growth and development, while conventional protective molecules are unaltered.
    Full-text · Article · Aug 2013 · PLoS ONE
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