Project description:Mitochondrial DNA (mtDNA) damage is considered as a possible primary cause of Parkinson’s disease (PD). To explore the issue, mtDNA sequences from whole blood were analyzed in PD patients and controls using a resequencing chip and allelic substitutions were estimated for each nucleotide position (np) along the entire mtDNA sequence. Overall, 58 np showed a different allelic distribution in the two groups; of these, 81% showed an increase of non-reference alleles in PD patients, similar to findings reported in patients with Alzheimer’s disease, albeit in reduced proportion. These results suggest that age-related neurodegenerative diseases could share a mechanism involving mtDNA.
Project description:We report mitochondrial genome (mtDNA) sequences in purified mouse muscle stem cells at different ages. This study identifies changes in the mitochondrial genome of muscle stem cells during aging.
Project description:Generating mammalian cells with desired mtDNA sequences is enabling for studies of mitochondria, disease modeling, and potential regenerative therapies. MitoPunch, a high-throughput mitochondrial transfer device, produces cells with specific mtDNA-nDNA combinations by transferring isolated mitochondria from mouse or human cells into primary or immortal mtDNA-deficient (p0) cells. Stable isolated mitochondrial recipient (SIMR) cells isolated in restrictive media permanently retain donor mtDNA and reacquire respiration. However, SIMR fibroblasts maintain a p0-like cell metabolome and transcriptome despite growth in restrictive media. We reprogram non-immortal SIMR fibroblasts into induced pluripotent stem cells (iPSCs) with subsequent differentiation into diverse functional cell types, including mesenchymal stem cells (MSCs), adipocytes, osteoblasts, and chondrocytes. Remarkably, following reprogramming and differentiation, SIMR fibroblasts molecularly and phenotypically resemble un-manipulated control fibroblasts carried through the same protocol. Thus, our MitoPunch ‘pipeline’ enables the production of SIMR cells with unique mtDNA-nDNA combinations for additional studies and applications in multiple cell types.
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:Background: Cell free DNA (cfDNA) in plasma has received increasing attention and has been studied in a broad range of clinical conditions implicating inflammation, cancer, and aging. However, few studies have focused on mitochondrial DNA (mtDNA) in the cell free form. This study characterized the size distribution and sequence characteristics of plasma cell free mtDNA (cf mtDNA) in humans.Methods and Results: We optimized DNA isolation and next-generation sequencing library preparation protocols to better retain short DNA fragments from plasma, and applied these optimized methods to plasma samples from patients with sepsis. After massive parallel sequencing, we verified that our methods can retain substantially shorter DNA fragments than the standard isolation method, resulting in an average of 11.5 fold increase in short DNA fragments yield (DNA < 100bp). We report that cf mtDNA in plasma is highly enriched in short-size cfDNA (30 ~ 60 bp), which is much shorter than the value previously reported (~140 bp). Motivated by this unique size distribution, we size-selected short cfDNA fragments from the sequencing library, which further increased the mtDNA recovery rate by an average of 10.4 fold. Using this approach we detected mixtures of different mtDNA sequences, termed heteroplasmy, in plasma from 3 patients. In one patient who previously received bone marrow transplantation, different minor allele frequencies were observed between plasma and white blood cells (WBC) at heteroplasmic mtDNA sites, consistent with mixed-tissue origin for plasma DNA.Conclusion: mtDNA in plasma exists as very short fragments that exhibit mtDNA heteroplasmy distribution differences from that found in a single organ/tissue. This study is the first report of genome wide identification of mtDNA heteroplasmy in human plasma. Our optimized method can be used to investigate the potential utility of cf mtDNA fragments and heteroplasmy as biomarkers in various diseases.
Project description:Mammalian mitochondrial DNA (mtDNA) is coated with mitochondrial transcription factor A (TFAM) and compacted into nucleoids. TFAM is not only the main component of mitochondrial nucleoids but its levels can also control mtDNA copy number. Here we show that the TFAM-to-mtDNA ratio is critical for maintaining normal mtDNA expression in different tissues of the mouse. BAC transgenic mice with a 1.5-fold increase in TFAM protein levels maintain a normal TFAM-to-mtDNA ratio in different tissues and as a consequence mitochondrial gene expression, nucleoid distribution and whole animal metabolism are all unaltered. In contrast, mice expressing TFAM from the CAG promoter in the ROSA26 locus have 4.5-fold increase of TFAM protein levels in heart and skeletal muscle and develop pathology leading to early postnatal lethality. The TFAM-to-mtDNA ratio varies widely between tissues in these mice and is very high in skeletal muscle where it causes strong repression of mtDNA expression and deficient oxidative phosphorylation (OXPHOS) despite normal mtDNA levels. In heart, mtDNA copy number is increased leading to a near normal TFAM-to-mtDNA ratio and maintained OXPHOS capacity. In the liver, mtDNA expression is maintained despite increased TFAM levels and normal mtDNA levels. Here, tissue-specific induction of the LONP1 protease and mitochondrial RNA polymerase (POLRMT) expression counteracts the silencing effect of high TFAM levels. We conclude that the TFAM-to-mtDNA ratio has an important role in maintaining mtDNA expression in vivo. TFAM acts as a general repressor of mtDNA expression and this effect can be counterbalance by tissue-specific expression of regulatory factors.