Search

Mitochondrial dysfunction may activate innate immunity, e.g. upon abnormal handling of mitochondrial DNA in TFAM mutants or in altered mitophagy. Recent reports showed that also deletion of mitochondrial matrix peptidase ClpP in mice triggers transcriptional upregulation of inflammatory factors. Here, we studied ClpP-null mouse brain at two ages and mouse embryonal fibroblasts, to identify which signaling pathways are responsible, employing mass spectrometry, subcellular fractionation, immunoblots, and reverse transcriptase polymerase chain reaction. Several mitochondrial unfolded protein response factors showed accumulation and altered migration in blue-native gels, prominently the co-chaperone DNAJA3. Its mitochondrial dysregulation increased also its extra-mitochondrial abundance in the nucleus, a relevant observation given that DNAJA3 modulates innate immunity. Similar observations were made for STAT1, a putative DNAJA3 interactor. Elevated expression was observed not only for the transcription factorsStat1/2, but also for two interferon-stimulated genes (Ifi44,Gbp3). Inflammatory responses were strongest for the RLR pattern recognition receptors (Ddx58,Ifih1,Oasl2,Trim25) and several cytosolic nucleic acid sensors (Ifit1,Ifit3,Oas1b,Ifi204,Mnda). The consistent dysregulation of these factors from an early age might influence also human Perrault syndrome, where ClpP loss-of-function leads to early infertility and deafness, with subsequent widespread neurodegeneration.

Contributors: Anna Kosovicheva, Jeremy Wolfe. When Does Visual Search Move On? Uncovering the Dynamics of Foraging Search with Occluded Targets This experiment is a follow-up control experiment to "Foraging with Occluders (Exp 1)" - linked in the Components section below. The procedure is identical, except that the item locations are shuffled on each click.

Background Autosomal recessive mutations in the nuclear Twinkle (C10orf2) gene cause a mitochondrial DNA depletion syndrome (MDS) characterized by early onset hepatoencephalopathy. Methods We report a severe, early onset encephalopathy and multisystem failure case caused by novel recessive Twinkle gene mutations. Patient clinical, laboratory, and pathological features are reported and Twinkle-associated MDS literature reviewed. Results Typical presentation includes symptom onset before age six months, failure to thrive, psychomotor regression, epileptic encephalopathy, sensory axonal neuropathy, cholestatic liver dysfunction, and occasionally, renal tubulopathy, movement disorders, and ophthalmoplegia. Death is typical before age four years. Conclusions In the differential diagnosis of early onset encephalopathy and multisystem failure, MDS should be considered.

Background: Twinkle artifact, also known as color Doppler comet-tail artifact, occurs behind very strong, granular, and irregular reflecting interfaces such as crystals, stones, or calcification. This is visualized as a random mixture of red and blue pixels in the high-frequency shift spectrum located deep to the interface. Study results have suggested that the sonographic twinkling artifact may aid in the detection of renal stones with a variety of reference standard imaging modalities, including abdominal radiography, excretory urography, gray-scale sonography, and CT. Material and methods: Our retrospective observational study included children who had undergone abdomen/renal ultrasound for kidneys stones in our radiology department between 2013 and 2019. Presence of the twinkle artifact, and stone numbers and sizes were documented. CT examinations done

Astrocyte-specific mtDNA depletion causes spongiotic encephalopathy, aggravated by ketogenic diet or rapamycin. Astrocytes, but not neurons, drive mitochondrial integrated stress response in the CNS., Mitochondrial DNA (mtDNA) depletion syndrome (MDS) is a group of severe, tissue-specific diseases of childhood with unknown pathogenesis. Brain-specific MDS manifests as devastating spongiotic encephalopathy with no curative therapy. Here, we report cell type–specific stress responses and effects of rapamycin treatment and ketogenic diet (KD) in mice with spongiotic encephalopathy mimicking human MDS, as these interventions were reported to improve some mitochondrial disease signs or symptoms. These mice with astrocyte-specific knockout of Twnk gene encoding replicative mtDNA helicase Twinkle (TwKOastro) show wide-spread cell-autonomous astrocyte activation and mitochondrial integrated stress response (ISRmt) induction with major metabolic remodeling of the brain. Mice with neuronal-specific TwKO show no ISRmt. Both KD and rapamycin lead to rapid deterioration and weight loss of TwKOastro and premature trial termination. Although rapamycin had no robust effects on TwKOastro brain pathology, KD exacerbated spongiosis, gliosis, and ISRmt. Our evidence emphasizes that mitochondrial disease treatments and stress responses are tissue- and disease specific. Furthermore, rapamycin and KD are deleterious in MDS-linked spongiotic encephalopathy, pointing to a crucial role of diet and metabolism for mitochondrial disease progression.

Mitochondrial dysfunction manifests as different neurological diseases, but the mechanisms underlying the clinical variability remain poorly understood. To clarify whether different brain cells have differential sensitivity to mitochondrial dysfunction, we induced mitochondrial DNA (mtDNA) depletion in either neurons or astrocytes of mice, by inactivating Twinkle (TwKO), the replicative mtDNA helicase. Here we show that astrocytes, the most abundant cerebral cell type, are chronically activated upon mtDNA loss, leading to early-onset spongiotic degeneration of brain parenchyma, microgliosis and secondary neurodegeneration. Neuronal mtDNA loss does not, however, cause symptoms until 8 months of age. Findings in astrocyte-TwKO mimic neuropathology of Alpers syndrome, infantile-onset mitochondrial spongiotic encephalopathy caused by mtDNA maintenance defects. Our evidence indicates that (1) astrocytes are dependent on mtDNA integrity; (2) mitochondrial metabolism contributes to their activation; (3) chronic astrocyte activation has devastating consequences, underlying spongiotic encephalopathy; and that (4) astrocytes are a potential target for interventions., Astrocytes in the brain are metabolically dynamic. Here, Ignatenko, Chilov and colleagues delete mitochondrial DNA (mtDNA) in a cell type specific manner, and show that inactivation of mtDNA helicase Twinkle in astrocytes leads to spongiotic encephalopathy.

International audience; Objective: Mitochondrial dysfunction plays a key role in the pathophysiology of neurodegenerative disorders such as ataxia and Parkinson's disease. We describe an extended Belgian pedigree where seven individuals presented with adult-onset cerebellar ataxia, axonal peripheral ataxic neuropathy, and tremor, in variable combination with parkinsonism, seizures, cognitive decline, and ophthalmoplegia. We sought to identify the underlying molecular etiology and characterize the mitochondrial pathophysiology of this neurological syndrome. Methods: Clinical, neurophysiological, and neuroradiological evaluations were conducted. Patient muscle and cultured fibroblasts underwent extensive analyses to assess mitochondrial function. Genetic studies including genome-wide sequencing were conducted. Results: Hallmarks of mitochondrial dysfunction were present in patients' tissues including ultrastructural anomalies of mito-chondria, mosaic cytochrome c oxidase deficiency, and multiple mtDNA deletions. We identified a splice acceptor variant in POLG2, c.970-1G>C, segregating with disease in this family and associated with a concomitant decrease in levels of POLG2 protein in patient cells. Interpretation: This work extends the clinical spectrum of POLG2 deficiency to include an overwhelming, adult-onset neurological syndrome that includes cerebellar syndrome, peripheral neuropathy, tremor, and parkinsonism. We therefore suggest to include POLG2 sequencing in the evaluation of ataxia and sensory neuropathy in adults, especially when it is accompanied by tremor or parkinsonism with white matter disease. The demonstration that deletions of mtDNA resulting from autosomal-dominant POLG2 variant lead to a monogenic neurodegenerative multicompo-nent syndrome provides further evidence for a major role of mitochondrial dys-function in the pathomechanism of nonsyndromic forms of the component neurodegenerative disorders.

Mitochondria are organelles whose main function is to generate power by oxidative phosphorylation. Some of the essential genes required for this energy production are encoded by the mitochondrial genome, a small circular double stranded DNA molecule. Human mtDNA is replicated by a specialized machinery distinct from the nuclear replisome. Defects in the mitochondrial replication machinery can lead to loss of genetic information by deletion and/or depletion of the mtDNA, which subsequently may cause disturbed oxidative phosphorylation and neuromuscular symptoms in patients. We discuss here the different components of the mitochondrial replication machinery and their role in disease. We also review the mode of mammalian mtDNA replication.

Mitochondrial transcription for replication primer formation has priority over gene expression at low POLRMT levels., Mitochondria are vital in providing cellular energy via their oxidative phosphorylation system, which requires the coordinated expression of genes encoded by both the nuclear and mitochondrial genomes (mtDNA). Transcription of the circular mammalian mtDNA depends on a single mitochondrial RNA polymerase (POLRMT). Although the transcription initiation process is well understood, it is debated whether POLRMT also serves as the primase for the initiation of mtDNA replication. In the nucleus, the RNA polymerases needed for gene expression have no such role. Conditional knockout of Polrmt in the heart results in severe mitochondrial dysfunction causing dilated cardiomyopathy in young mice. We further studied the molecular consequences of different expression levels of POLRMT and found that POLRMT is essential for primer synthesis to initiate mtDNA replication in vivo. Furthermore, transcription initiation for primer formation has priority over gene expression. Surprisingly, mitochondrial transcription factor A (TFAM) exists in an mtDNA-free pool in the Polrmt knockout mice. TFAM levels remain unchanged despite strong mtDNA depletion, and TFAM is thus protected from degradation of the AAA+ Lon protease in the absence of POLRMT. Last, we report that mitochondrial transcription elongation factor may compensate for a partial depletion of POLRMT in heterozygous Polrmt knockout mice, indicating a direct regulatory role of this factor in transcription. In conclusion, we present in vivo evidence that POLRMT has a key regulatory role in the replication of mammalian mtDNA and is part of a transcriptional mechanism that provides a switch between primer formation for mtDNA replication and mitochondrial gene expression.

Genome integrity is achieved and maintained by the sum of all of the processes in the cell that ensure the faithful duplication and repair of DNA, as well as its genetic transmission from one cell division to the next. As central players in virtually all of the DNA transactions that occur in vivo, DNA helicases (molecular motors that unwind double-stranded DNA to produce single-stranded substrates) represent a crucial enzyme family that is necessary for genomic stability. Indeed, mutations in many human helicase genes are linked to a variety of diseases with symptoms that can be generally described as genomic instability, such as predispositions to cancers. This review focuses on the roles of both DNA replication helicases and recombination/repair helicases in maintaining genome integrity and provides a brief overview of the diseases related to defects in these enzymes.

Letter to the Editor

Background The Arabidopsis thaliana genome encodes a homologue of the full-length bacteriophage T7 gp4 protein, which is also homologous to the eukaryotic Twinkle protein. While the phage protein has both DNA primase and DNA helicase activities, in animal cells Twinkle is localized to mitochondria and has only DNA helicase activity due to sequence changes in the DNA primase domain. However, Arabidopsis and other plant Twinkle homologues retain sequence homology for both functional domains of the phage protein. The Arabidopsis Twinkle homologue has been shown by others to be dual targeted to mitochondria and chloroplasts. Results To determine the functional activity of the Arabidopsis protein we obtained the gene for the full-length Arabidopsis protein and expressed it in bacteria. The purified protein was shown to have both DNA primase and DNA helicase activities. Western blot and qRT-PCR analysis indicated that the Arabidopsis gene is expressed most abundantly in young leaves and shoot apex tissue, as expected if this protein plays a role in organelle DNA replication. This expression is closely correlated with the expression of organelle-localized DNA polymerase in the same tissues. Homologues from other plant species show close similarity by phylogenetic analysis. Conclusions The results presented here indicate that the Arabidopsis phage T7 gp4/Twinkle homologue has both DNA primase and DNA helicase activities and may provide these functions for organelle DNA replication.

We describe a hardware device for supporting the sieving step in integer factoring algorithms like the quadratic sieve or the number field sieve. In analogy to Bernstein's proposal for speeding up the linear algebra step, we rely on a mesh of very simple processing units. Manufacturing the device at moderate cost with current hardware technology on standard wafers with 200 mm or 300 mm diameter should not provide any major obstacle.A preliminary analysis of the parameters for factoring a 512-bit number with the number field sieve shows that the design considered here might outperform a TWINKLE device.

The current record in factoring large RSA keys is the factorization of a 465 bit (140 digit) number achieved in February 1999 by running the Number Field Sieve on hundreds of workstations for several months. This paper describes a novel factoring apparatus which can accelerate known sieve-based factoring algorithms by several orders of magnitude. It is based on a very simple handheld optoelectronic device which can analyse 100,000,000 large integers, and determine in less than 10 milliseconds which ones factor completely over a prime base consisting of the first 200,000 prime numbers. The proposed apparatus can increase the size of factorable numbers by 100 to 200 bits, and in particular can make 512 bit RSA keys (which protect 95% of today's E-commerce on the Internet) very vulnerable.