Project description:RNAsequencing data from POLG D257A mutant mouse iPS (induced pluripotent stem) cells. These mice accumulate random point mutations in their mitochondrial genome and manifest progeric features. The reprogramming and phenotype of the cells is described in Hämäläinen et al. 2015, Cell reports, mtDNA Mutagenesis Disrupts Pluripotent Stem Cell Function by Altering Redox Signaling. The goal of the study was to analyze altered gene expression profiles between mutant and wt iPS cells to identify altered biological pathways responsible for the stemness and proliferation defects seem in mtDNA mutator stem cells.
Project description:Somatic mitochondrial DNA (mtDNA) mutations contribute to the pathogenesis of age-related disorders, including myelodysplastic syndromes (MDS). The accumulation of mitochondria harboring mtDNA mutations in patients with these disorders suggests a failure of normal mitochondrial quality-control systems. The mtDNA-mutator mice acquire somatic mtDNA mutations via a targeted defect in the proofreading function of the mtDNA polymerase, PolgA, and develop macrocyticanemia similar to that of patients with MDS. We observed an unexpected defect in clearance of dysfunctional mitochondria at specific stages during erythroid maturation in hematopoietic cells from aged mtDNA-mutator mice. Mechanistically, aberrant activation of mechanistic target of rapamycin signaling and phosphorylation of uncoordinated 51-like kinase (ULK) 1 in mtDNA-mutator mice resulted in proteasome mediated degradation of ULK1 and inhibition of autophagy in erythroid cells. To directly evaluate the consequence of inhibiting autophagy on mitochondrial function in erythroid cells harboring mtDNA mutations in vivo, we deleted Atg7 from erythroid progenitors of wildtype and mtDNA-mutator mice. Genetic disruption of autophagy did not cause anemia in wild-type mice but accelerated the decline in mitochondrial respiration and development of macrocytic anemia in mtDNA-mutator mice. These findings highlight a pathological feedback loop that explains how dysfunctional mitochondria can escape autophagy-mediated degradation and propagate in cells predisposed to somatic mtDNA mutations, leading to disease. We used microarrays to identify expression profiles and pathways that are differentially activated or suppressed in Ter119+ bone marrow cells isolated from phlebotomized wildtype or Polg mutant mice
Project description:Somatic mitochondrial DNA (mtDNA) mutations contribute to the pathogenesis of age-related disorders, including myelodysplastic syndromes (MDS). The accumulation of mitochondria harboring mtDNA mutations in patients with these disorders suggests a failure of normal mitochondrial quality-control systems. The mtDNA-mutator mice acquire somatic mtDNA mutations via a targeted defect in the proofreading function of the mtDNA polymerase, PolgA, and develop macrocytic anemia similar to that of patients with MDS. We observed an unexpected defect in clearance of dysfunctional mitochondria at specific stages during erythroid maturation in hematopoietic cells from aged mtDNA-mutator mice. Mechanistically, aberrant activation of mechanistic target of rapamycin signaling and phosphorylation of uncoordinated 51-like kinase (ULK) 1 in mtDNA-mutator mice resulted in proteasome mediated degradation of ULK1 and inhibition of autophagy in erythroid cells. To directly evaluate the consequence of inhibiting autophagy on mitochondrial function in erythroid cells harboring mtDNA mutations in vivo, we deleted Atg7 from erythroid progenitors of wildtype and mtDNA-mutator mice. Genetic disruption of autophagy did not cause anemia in wild-type mice but accelerated the decline in mitochondrial respiration and development of macrocytic anemia in mtDNA-mutator mice. These findings highlight a pathological feedback loop that explains how dysfunctional mitochondria can escape autophagy-mediated degradation and propagate in cells predisposed to somatic mtDNA mutations, leading to disease.
Project description:Replication of mammalian mitochondrial DNA (mtDNA) is an essential process that requires high fidelity and control at multiple levels to ensure proper mitochondrial function. Mutations in the mitochondrial genome maintenance exonuclease 1 (MGME1) gene were recently reported in mitochondrial disease patients. Here, to study disease pathophysiology, we generated Mgme1 knockout mice and report that homozygous knockouts develop depletion and multiple deletions of mtDNA. The mtDNA replication stalling phenotypes vary dramatically in different tissues of Mgme1 knockout mice. Mice with MGME1 deficiency accumulate a long linear subgenomic mtDNA species, similar to the one found in mtDNA mutator mice, but do not develop progeria. This finding resolves a long-standing debate by showing that point mutations of mtDNA are the main cause of progeria in mtDNA mutator mice. We also propose a role for MGME1 in the regulation of replication and transcription termination at the end of the control region of mtDNA.
Project description:Mitochondria are vital due to their principal role in energy production via oxidative phosphorylation (OXPHOS)1. Mitochondria carry their own genome (mtDNA) encoding critical genes involved in OXPHOS, therefore, mtDNA mutations cause fatal or severely debilitating disorders with limited treatment options. 2. Clinical manifestations of mtDNA disease vary based on mutation type and heteroplasmy levels i.e. presence of mutant and normal mtDNA within each cell. 3,4. We evaluated therapeutic concepts of generating genetically corrected pluripotent stem cells for patients with mtDNA mutations. We initially generated multiple iPS cell lines from a patient with mitochondrial encephalomyopathy and stroke-like episodes (MELAS) caused by a heteroplasmic 3243A>G mutation and a patient with Leigh disease carrying a homoplasmic 8993T>G mutation (Leigh-iPS). Due to spontaneous mtDNA segregation in proliferating fibroblasts, isogenic MELAS iPS cell lines were recovered containing exclusively wild type (wt) mtDNA with normal metabolic function. As expected, all iPS cells from the patient with Leigh disease were affected. Using somatic cell nuclear transfer (SCNT; Leigh-NT1), we then simultaneously replaced mutated mtDNA and generated pluripotent stem cells from the Leigh patient fibroblasts. In addition to reversing to a normal 8993G>T, oocyte derived donor mtDNA (human haplotype D4a) in Leigh-NT1 differed from the original haplotype (F1a) at a additional 47 nucleotide sites. Leigh-NT1 cells displayed normal metabolic function compared to impaired oxygen consumption and ATP production in Leigh-iPS cells or parental fibroblasts (Leigh-fib). We conclude that natural segregation of heteroplasmic mtDNA allows the generation of iPS cells with exclusively wild type mtDNA. Moreover, SCNT offers mitochondrial gene replacement strategy for patients with homoplasmic mtDNA disease.
Project description:Exercise is a fundamental component of human health that is associated with greater life expectancy and reduced risk of chronic diseases. While the beneficial effects of endurance exercise on human health are well established, the molecular mechanisms responsible for these observations remain unclear. Endurance exercise reduces the accumulation of mitochondrial DNA (mtDNA) mutations, alleviates multisystem pathology, and increases the lifespan of the mtDNA mutator mouse model of aging, in which the proof-reading capacity of mitochondrial polymerase gamma (POLG1) is deficient. Clearly, exercise recruited a POLG1-independent mtDNA repair pathway to induce these adaptations, a novel finding as POLG1 is canonically considered to be the sole mtDNA repair enzyme. Here we investigate the identity of this pathway, and show that endurance exercise prevents mitochondrial oxidative damage, attenuates telomere erosion, and mitigates cellular senescence and apoptosis in mtDNA mutator mice. Unexpectedly, we observe translocation of tumour suppressor protein p53 to mitochondria in response to endurance exercise that facilitates mtDNA mutation repair. Indeed, endurance exercise failed to prevent mtDNA mutations, induce mitochondrial biogenesis, preserve mitochondrial morphology, reverse sarcopenia, and mitigate premature mortality in mtDNA mutator mice with muscle-specific deletion of p53. Our data establish an exciting new role for p53 in exercise-mediated maintenance of the mtDNA genome, and presents mitochondrially-targeted p53 as a novel therapeutic modality for aging-associated diseases of mitochondrial etiology. Microarray analysis of gene expression from skeletal muscle (quadriceps femoris) from Mus musculus. N=23 samples per treatment were analysed for whole transcriptiome gene expression profile using NimbleGen Arrays. The treatment groups included wild-type C57Bl/6J mice as the control group, then two treatment groups which both contained homozygous knock-in mtDNA mutator mice (PolG; PolgAD257A/D257A). Once group of these heterozygous knock out mice received regular endurance exercise sessions while the other group remained sedentraty for 6 months. The control group specimens were wild-type litter mates to the transgenic knockout mice.
Project description:Exercise is a fundamental component of human health that is associated with greater life expectancy and reduced risk of chronic diseases. While the beneficial effects of endurance exercise on human health are well established, the molecular mechanisms responsible for these observations remain unclear. Endurance exercise reduces the accumulation of mitochondrial DNA (mtDNA) mutations, alleviates multisystem pathology, and increases the lifespan of the mtDNA mutator mouse model of aging, in which the proof-reading capacity of mitochondrial polymerase gamma (POLG1) is deficient. Clearly, exercise recruited a POLG1-independent mtDNA repair pathway to induce these adaptations, a novel finding as POLG1 is canonically considered to be the sole mtDNA repair enzyme. Here we investigate the identity of this pathway, and show that endurance exercise prevents mitochondrial oxidative damage, attenuates telomere erosion, and mitigates cellular senescence and apoptosis in mtDNA mutator mice. Unexpectedly, we observe translocation of tumour suppressor protein p53 to mitochondria in response to endurance exercise that facilitates mtDNA mutation repair. Indeed, endurance exercise failed to prevent mtDNA mutations, induce mitochondrial biogenesis, preserve mitochondrial morphology, reverse sarcopenia, and mitigate premature mortality in mtDNA mutator mice with muscle-specific deletion of p53. Our data establish an exciting new role for p53 in exercise-mediated maintenance of the mtDNA genome, and presents mitochondrially-targeted p53 as a novel therapeutic modality for aging-associated diseases of mitochondrial etiology.
Project description:Accumulating evidences suggest a link between mitochondrial dysfunction and female reproduction decline. To directly and systematically figure out the influence of mitochondrial DNA (mtDNA) mutation on oocyte quality and embryo development, we used an mtDNA mutator mouse model (D257A) that harbors a proofreading-deficient version of PolgA. Here we showed that D257A mice developed a profound reduction of fertility at 19-week of age, and accumulated twofold more increase in the levels of point mutations in oocyte mtDNA. Following ovarian hyper-stimulation, we found oocyte numbers retrieved from WT and D257A mice were comparable until 19 weeks of age, while with a half reduced number of oocyte ovulated in D257A mice thereafter. We further found the oocyte quality based on mitochondrial distribution, meiotic spindle assembly, chromosomal segregation and ATP content at 19 weeks of age was identical in both group. Meanwhile, the ovulated oocytes can initiate and sustain early embryo development after in vitro fertilization, and reach the blastocyst stage with no obvious defects compared to WTs. Of note, post-implantation developmental defects were observed in D257A embryos, as revealed by fetal growth retardation and decreased ratios of pups delivered. Furthermore, genome-wide methylation analysis revealed global hypomethylation across the genome of D257A oocytes, with a dramatic reduce in genome repetitive-elements, like DNA transposon, LINEs and SINEs regions. In conclusion, our study presents the direct experimental investigation of the effect of mtDNA mutation on oocyte and embryo competence, and demonstrates altered DNA methylation in oocyte may represent a critical mechanism that mediates the phenotypic defects of mtDNA mutation in post-implantation development.