Biology subjects

Wittig, I.

Publications and source records attributed to Wittig, I..

18 recordsLinked to original sources

bioRxiv2026

Lineage-restricted dependency on an oncofetal SNHG29-IGF2BP1 RNA axis in acute megakaryoblastic leukemia

Acute megakaryoblastic leukemia (AMKL) is a rare, aggressive subtype of acute myeloid leukemia with developmental origins in early childhood. To uncover long noncoding RNAs (lncRNAs) sustaining this high-risk malignancy, we conducted CRISPR interference screens targeting lncRNAs overexpressed in primary AMKL samples. This analysis identified SNHG29 as a previously unrecognized lineage-specific dependency, whose silencing profoundly impaired leukemic proliferation and clonogenic growth in vitro and reduced leukemic burden in vivo. RNA pulldown coupled with proteomic analysis revealed that SNHG29 interacts with the oncofetal RNA-binding protein IGF2BP1, which is aberrantly expressed in AMKL. SNHG29 was required to maintain expression of IGF2BP1 target transcripts, including MYC- and E2F-driven proliferative programs, thereby reinforcing fetal transcriptional programs essential for leukemic maintenance. Pharmacologic inhibition of IGF2BP1-RNA interactions with the small-molecule BTYNB induced potent and selective cytotoxicity in patient-derived AMKL models. Together, these findings uncover a developmental co-dependency between SNHG29 and IGF2BP1 that defines a lineage-restricted oncogenic circuit and an actionable therapeutic vulnerability in AMKL.

cancer biology↗

bioRxiv2025

Human heart organoids reveal a regenerative strategy for mitochondrial disease

The human heart is among the most complex tissues to replicate in vitro, with vascular, neuronal, and immune elements shaping its development and function. Here we describe cardiomorphs, self-organising human cardiac organoids that recapitulate the cellular diversity, structural organisation, vascularisation, and innervation of the myocardium and mature along a developmental trajectory from early cardiogenesis to adult tissue. Using patient-derived cardiomorphs, we establish the first three-dimensional human tissue model of Kearns-Sayre syndrome (KSS), a rare mitochondrial disorder characterised by large-scale mtDNA deletions. KSS-cardiomorphs faithfully reproduce disease-associated metabolic, contractile, and ultrastructural hallmarks. Leveraging this platform, we identify Betaxolol, an FDA-approved selective {beta}1-adrenergic antagonist, as a modulator of mitochondrial quality control. Betaxolol increases intracellular oxygenation, selectively eliminates dysfunctional mitochondria via mitophagy, and promotes biogenesis of functional organelles, restoring contractility in KSS tissues. This dual-action, mutation-agnostic mechanism suggests a therapeutic principle with broad relevance to mitochondrial disease, cardiac pathology, and age-associated decline.

cell biology↗

bioRxiv2025

QKI ensures splicing fidelity during cardiogenesis by engaging the U6 tri-snRNP to activate splicing at weak 5' splice sites

During organogenesis, precise pre-mRNA splicing is essential to assemble tissue architecture. Many developmentally essential exons bear weak 5' splice sites (5'SS) yet are spliced with high precision, implying unknown yet active splicing fidelity mechanisms. By combining transcriptome and alternative splicing profiling with temporal eCLIP mapping of RNA interactions across development, we identify the RNA-binding protein QKI as an essential direct regulator of splicing fidelity in key cardiac transcripts. Although QKI is dispensable for cardiac specification, its loss disrupts sarcomere assembly despite intact expression of sarcomere mRNAs through exon skipping and nuclear retention of mis-spliced RNAs. QKI-dependent exons in essential cardiac genes have weak 5'SS and frequently show poor complementarity with U6 snRNA. We show that QKI directly interacts with U6 snRNA using an overlapping interface to its traditional intronic binding activity, securing U4/U6{middle dot}U5 tri-snRNP to ensure splicing fidelity. Thus, QKI exemplifies how context-aware RBPs enforce splicing fidelity at structurally vulnerable splice sites during organogenesis.

cell biology↗

bioRxiv2024

RTN4IP1 is essential for the final stages of mitochondrial complex I assembly and coenzyme Q biosynthesis

A biochemical deficiency of mitochondrial complex I (CI) underlies [~]30% of cases of primary mitochondrial disease, yet the inventory of molecular machinery required for CI assembly remains incomplete. We previously characterised patients with isolated CI deficiency caused by segregating variants in RTN4IP1, encoding a mitochondrial NAD(P)H oxidoreductase. Here, we demonstrate that RTN4IP1 deficiency causes a CI assembly defect in both patient fibroblasts and knockout cells, and report that RTN4IP1 is a bona fide CI assembly factor. Complexome profiling revealed accumulation of unincorporated ND5-module and impaired N-module production. RTN4IP1 patient fibroblasts also exhibited defective coenzyme Q biosynthesis, substantiating this emerging function of RTN4IP1. Thus, our data reveal RTN4IP1 plays an essential role in both the terminal stages of CI assembly and in coenzyme Q metabolism, and that pathogenic RTN4IP1 variants impair both functions in patients with mitochondrial disease.

cell biology↗

bioRxiv2024

The transaminase-omega-amidase pathway is a redox switch in glutamine metabolism that generates alpha-ketoglutarate

Oxidative stress is caused by short-lived molecules and metabolic changes belong to the fastest cellular responses. Here we studied how the endothelial cell metabolome reacts to acute oxidative challenges (menadione or H2O2) to identify redox-sensitive metabolic enzymes. H2O2 selectively increased -ketoglutaramate (KGM), a largely uncharacterized metabolite produced by glutamine transamination and a yet unrecognized intermediate of endothelial glutamine catabolism. The enzyme nitrilase-like 2 {omega}-amidase (NIT2) converts KGM to -ketoglutarate (KG). Reversible oxidation of specific cysteine in NIT2 by H2O2 inhibited its catalytic activity. Furthermore, a variant in the NIT2 gene that decreases its expression is associated with high plasma KGM level in humans. Endothelial-specific knockout mice of NIT2 exhibited increased levels of KGM and impaired angiogenesis. Knockout of NIT2 impaired endothelial cell proliferation and sprouting and induced senescence. In conclusion, we show that the glutamine transaminase-{omega}-amidase pathway is a metabolic switch in which NIT2 is the redox-sensitive enzyme. The pathway is modulated in humans and functionally important for endothelial glutamine metabolism.

physiology↗

bioRxiv2024

Nuclear eNOS interacts with and S-nitrosates ADAR1 to modulate type I interferon signaling and endothelial function.

BackgroundNitric oxide (NO) generated by the endothelial NO synthase (eNOS) regulates vascular tone and endothelial homeostasis to counteract vascular inflammation. Most eNOS is localized at the cell membrane or in the Golgi apparatus, but the enzyme is also present in the endothelial cell nucleus. Here we assessed the relevance of nuclear eNOS and NO signaling for endothelial cell function. MethodseNOS gain- and loss-of-function approaches were combined with confocal microscopy, biochemical, histological and multi-omics analyses. The pathophysiological relevance of the findings was assessed in murine models of atherogenesis (ApoE-/- and partial carotid ligation) as well as in samples from patients with atherosclerosis. ResultseNOS was present in the nucleus of unstimulated human and murine endothelial cells (in vitro and ex vivo) and stimulation with vascular endothelial growth factor (VEGF) enhanced its nuclear localization. Co-immunoprecipitation studies coupled with proteomics revealed the association of nuclear eNOS with 81 proteins involved in RNA binding and processing. Among the latter was double-stranded RNA-specific adenosine deaminase (ADAR1), an enzyme involved in editing double-stranded RNA (dsRNA) via the deamination of adenosine (A) to inosine (I). ADAR1 was S-nitrosated in human endothelial cells, and the knockdown of eNOS resulted in altered ADAR1-mediated A-to-I editing and an increase in dsRNA. Mitochondrial antiviral signaling protein (MAVS) was the transcript most affected by eNOS depletion, and endothelial cells lacking eNOS accumulated dsRNA as well as MAVS protein aggregates. These changes resulted in activation of the type I interferon (IFN) signaling pathway and a marked downregulation of cell cycle-related genes. ADAR1 depletion elicited similar effects on the activation of type I IFN signaling. As a result, growth factor-stimulated cell proliferation was abrogated and basal as well as stimulated cell death were increased. Endothelial dysfunction in mice as well as in subjects with atherosclerosis was accompanied by the accumulation of dsRNA and the activation of the type I IFN signaling. Preserving NO bioavailability in vivo in an eNOS gain-of-function mouse model (Tyr657Phe eNOS) prevented these effects. ConclusionsOur findings have uncovered a novel mechanism linking nuclear eNOS-derived NO with the activity of ADAR1 to maintain vascular homeostasis. Reduced NO bioavailability results in the previously unrecognized activation of a type I IFN response in the endothelium, which contributes to atherogenesis.

physiology↗

bioRxiv2024

Long non-coding RNAs direct the SWI/SNF complex to cell-specific enhancers

The coordination of chromatin remodeling is essential for DNA accessibility and gene expression control1. The highly conserved and ubiquitously expressed SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex plays a central role in cell type- and context-dependent gene expression2. Despite the absence of a defined DNA recognition motif, SWI/SNF binds lineage specific enhancers genome-wide where it actively maintains open chromatin state2-5. It does so while retaining the ability to respond dynamically to cellular signals4. However, the mechanisms that guide SWI/SNF to specific genomic targets have remained elusive. Here we demonstrate that trans-acting long non-coding RNAs (lncRNAs) direct the SWI/SNF complex to cell type-specific enhancers. SWI/SNF preferentially binds lncRNAs and these predominantly bind DNA targets in trans. Together they localize to enhancers, many of which are cell type-specific. Knockdown of SWI/SNF- and enhancer-bound lncRNAs causes the genome-wide redistribution of SWI/SNF away from enhancers and a concomitant differential expression of spatially connected target genes. These lncRNA-SWI/SNF-enhancer networks support an enhancer hub model of SWI/SNF genomic targeting. Our findings reveal a competitive recruitment of SWI/SNF by lncRNAs which provide a specific and dynamic layer of control in chromatin accessibility and gene expression.

molecular biology↗

bioRxiv2024

The aging-induced long non-coding RNA MIRIAL controls endothelial cell and mitochondrial function

AimsVascular aging is characterized by the progressive deterioration of endothelial function. Long non-coding RNAs (lncRNAs) are critical regulators of gene expression and protein function. However, their involvement in aging-related dysregulation of endothelial cell function remains largely unknown. Here, we aim to characterize the aging-regulated lncRNA MIRIAL in endothelial cells. Methods + ResultsWe identified Mirial as an aging-induced lncRNA in RNA-sequencing data of mouse cardiac endothelial cells. In human umbilical vein endothelial cells (HUVECs), gapmer-mediated knockdown of MIRIAL led to decreases in proliferation, migration and basal angiogenic sprouting. Additionally, MIRIAL knockdown led to increased mitochondrial mass, spare respiratory capacity, and vascular endothelial growth factor (VEGF)-stimulated sprouting. Mechanistically, we demonstrate that MIRIAL forms an RNA{middle dot}DNA:DNA triple helix (triplex) with a regulatory region of the quiescence-promoting Forkhead Box O1 (FOXO1) gene, thus inducing its expression. The formation of this triplex involves an Alu element within the MIRIAL transcript, representing a previously undescribed mechanism of action for a lncRNA. Further, we generated a global Mirial knockout mouse line of. Angiogenic sprouting of aortic rings from Mirial knockout mice was reduced under basal conditions, but increased after VEGF administration, validating the in vitro angiogenic phenotype. Importantly, cardiac contractile function after acute myocardial infarction is severely reduced in Mirial knockout mice, as compared to wild-type littermates. ConclusionsThe lncRNA MIRIAL is an aging-induced regulator of endothelial quiescence and metabolism. Translational PerspectiveLncRNAs often exhibit cell-type or tissue-specific expression and regulation, rendering them potentially druggable targets requiring lower doses and having fewer side effects compared to protein targets. Our current research highlights, that loss of Mirial correlates with adverse outcomes post-acute myocardial infarction in a murine model. Dysregulation of MIRIAL in various human pathological conditions, such as ischemic heart disease, abdominal aortic aneurysm, cancer, and aging, indicates its potential as a diagnostic marker. Mechanistically, MIRIAL regulates endothelial quiescence by modulating FOXO1 expression, suggesting it as a promising therapeutic target to counteract the age-related decline in endothelial cell function.

cell biology↗

bioRxiv2023

Immortalised murine R349P desmin knock-in myotubes exhibit a reduced proton leak and decreased ADP/ATP translocase levels in purified mitochondria

Desmin gene mutations cause myopathies and cardiomyopathies. Our previously characterised R349P desminopathy mice, which carry the ortholog of the common human desmin mutation R350P, showed marked alterations in mitochondrial morphology and function in muscle tissue. By isolating skeletal muscle myoblasts from offspring of R349P desminopathy and p53 knock-out mice, we established an immortalised cellular disease model. Heterozygous and homozygous R349P desmin knock-in and wild-type myoblasts could be well differentiated into multinucleated spontaneously contracting myotubes. The desminopathy myoblasts showed the characteristic disruption of the desmin cytoskeleton and desmin protein aggregation, and the desminopathy myotubes showed the characteristic myofibrillar irregularities. Long-term electrical pulse stimulation promoted myotube differentiation and markedly increased their spontaneous contraction rate. In both heterozygous and homozygous R349P desminopathy myotubes, this treatment restored a regular myofibrillar cross-striation pattern as seen in wild-type myotubes. High-resolution respirometry of mitochondria purified from myotubes by density gradient ultracentrifugation revealed normal oxidative phosphorylation capacity, but a significantly reduced proton leak in mitochondria from the homozygous R349P desmin knock-in cells. Consistent with a reduced proton flux across the inner mitochondrial membrane, our quantitative proteomic analysis of the purified mitochondria revealed significantly reduced levels of ADP/ATP translocases in the homozygous R349P desmin knock-in genotype. As this alteration was also detected in the soleus muscle of R349P desminopathy mice, which, in contrast to the mitochondria purified from cultured cells, showed a variety of other dysregulated mitochondrial proteins, we consider this finding to be an early step in the pathogenesis of secondary mitochondriopathy in desminopathy. HighlightsO_LIR349P desminopathy immortalised murine myoblasts as a cellular disease model C_LIO_LIElectrical stimulation improves myofibrillar maturation in desminopathy myotubes C_LIO_LIReduced proton leak in mitochondria of homozygous R349P desmin knock-in myotubes C_LIO_LIReduced ADP/ATP translocase levels in mitochondria of desminopathy myotubes C_LIO_LIEarly signs of secondary mitochondriopathy in desminopathy in cultured myotubes C_LI

cell biology↗

bioRxiv2023

SLP2 coordinates MICOS assembly and cristae morphogenesis via MIC13 and YME1L

The MICOS complex subunit MIC13 is essential for mitochondrial cristae organization. Mutations in MIC13 cause severe mitochondrial hepato-encephalopathy displaying defective cristae morphology and loss of the MIC10-subcomplex. Here we identified stomatin-like protein 2 (SLP2) as an interacting partner of MIC13 and decipher a critical role of SLP2 as an auxiliary MICOS subunit, modulating cristae morphology. SLP2 provides a large interaction hub for MICOS subunits and loss of SLP2 leads to drastic alterations in cristae morphology. Double deletion of SLP2 and MIC13 showed reduced assembly of core MICOS subunit, MIC60 into MICOS and dispersion of MIC60-specific puncta, demonstrating a critical role of SLP2-MIC13 in MICOS assembly and crista junction (CJ) formation. We further identified that the mitochondrial i-AAA protease YME1L in coordination either with MIC13 or SLP2 differentially regulates MICOS assembly pathways thereby interlinking MIC13-specific or scaffolding-specific role of SLP2 with quality control and assembly of the MICOS complex. YME1L- depletion in MIC13 KO could restore MIC10-subcomplex and reform the nascent CJ. Taken together, we propose seeder model for MICOS assembly and CJ formation, where SLP2- MIC13 seed the assembly of MIC60 into MICOS complex and promote the formation of CJ by regulating the quality and stability of MIC10-subcomplex.

biochemistry↗

bioRxiv2023

Ena/VASP proteins mediate endothelial cell repulsion from ephrin ligands

The interaction of Eph receptor tyrosine kinases with their transmembrane ligands; the ephrins, is important for the regulation of cell-cell communication. Ephrin-Eph signaling is probably best known for the discrimination of arterial and venous territories by repulsion of venous endothelial cells away from those with an arterial fate. Ultimately, cell repulsion is mediated by initiating the collapse of the actin cytoskeleton in membrane protrusions. Here, we investigated the role of the Ena/VASP family of actin binding proteins in endothelial cell repulsion initiated by ephrin ligands. Human endothelial cells dynamically extended sheet-like lamellipodia over ephrin-B2 coated surfaces. While lamellipodia of control siRNA transfected cells rapidly collapsed, resulting in a pronounced cell repulsion from the ephrin-B2 surfaces, the knockdown of Ena/VASP proteins impaired the cytoskeletal collapse of membrane protrusions and the cells no longer avoided the repulsive surfaces. Mechanistically, ephrin-B2 stimulation elicited the EphB-mediated tyrosine phosphorylation of VASP, which abrogated its interaction with the focal adhesion protein Zyxin. Nck2 was identified as a novel VASP binding protein, which only interacted with the tyrosine phosphorylated VASP protein. Nck links Eph-receptors to the actin cytoskeleton. Therefore, we hypothesize that Nck-Ena/VASP complex formation is required for actin reorganization and/or Eph receptor internalization downstream of ephrin-Eph interaction in endothelial cells, with implications for endothelial navigation and pathfinding.

cell biology↗

bioRxiv2022

Targeting long non-coding RNA NUDT6 enhances smooth muscle cell survival and limits vascular disease progression

Long non-coding RNAs (lncRNAs) orchestrate various biological processes and regulate the development of cardiovascular diseases. Their potential therapeutic benefit to tackle disease progression has recently been extensively explored. Our study investigates the role of lncRNA Nudix Hydrolase 6 (NUDT6) and its antisense target Fibroblast Growth Factor 2 (FGF2) in two vascular pathologies: abdominal aortic aneurysms (AAA) and carotid artery disease. Using tissue samples from both diseases, we detected a substantial increase of NUDT6, whereas FGF2 was downregulated. Targeting Nudt6 in vivo with antisense oligonucleotides in three murine and one porcine animal models of carotid artery disease and AAA limited disease progression. Restoration of FGF2 upon Nudt6 knockdown improved vessel wall morphology and fibrous cap stability. Overexpression of NUDT6 in vitro impaired smooth muscle cell (SMC) migration, while limiting their proliferation and augmenting apoptosis. By employing RNA pulldown followed by mass spectrometry as well as RNA immunoprecipitation, we identified Cysteine and Glycine Rich Protein 1 (CSRP1) as another direct NUDT6 interaction partner, regulating cell motility and SMC differentiation. Overall, the present study identifies NUDT6 as a well-conserved antisense transcript of FGF2. NUDT6 silencing triggers SMC survival and migration and could serve as a novel RNA-based therapeutic strategy in vascular diseases.

molecular biology↗

bioRxiv2022

A novel role for cystathionine gamma lyase in the control of p53: impact on endothelial senescence and metabolic reprograming

AimsAdvanced age is unequivocally linked to the development of cardiovascular disease, however, the mechanisms leading to loss of endothelial cell regenerative capacity during aging remain poorly understood. Here we aimed to investigate novel mechanisms involved in endothelial cell senescence, that impact on endothelial cell transcription and the vascular repair response upon injury Methods and resultsRNA sequencing of a unique collection of native endothelial cells from young and aged individuals, showed that aging (20 vs. 80 years) is characterized by p53- mediated reprogramming to promote the expression of senescence-associate genes. Molecular analysis revelead that p53 accumulated and acetylated in the nucleus of aged human endothelial cells to suppress glycolysis. Metabolic flux analysis identified an associated reduction in glucose uptake and ATP availability that inhibited the assembly of the telomerase complex, which was essential for proliferation. Nuclear translocation of p53 in aged endothelial cells was attributed to the loss of the vasoprotective enzyme, cystathionine {gamma}-lyase (CSE), which physically anchored p53 in the cytosol. In mice, loss of endothelial cell CSE activated p53 and arrested vascular repair upon injury, while the AAV9 mediated re-expression of an active CSE mutant retained p53 in the cytosol, maintained endothelial glucose metabolism and proliferation, and prevented endothelial cell senescence. Adenoviral overexpression of CSE in human native aged endothelial cells maintained low p53 activity and re-activated telomerase to revert endothelial cell senescence. ConclusionOur data identified the interaction between CSE and p53 as a promising target to preserve vascular regeneration during aging. Key QuestionTo identify the mechanisms that regulate endothelial cell senescence under native conditions and their impact on vascular repair in aging. Key FindingLack of a physical interaction between CSE and p53 metabolically reprogrammes endothelial cells to reduce telomerase activity and halt endothelial cell regeneration. Take home messageInterventions to increase CSE expression represent a novel therapy against p53-induced endothelial cell cycle arrest and senescense Translational perspectiveEndothelial rejuvenation strategies could serve as promising therapies against age-related cardiovascular diseases. By investigating human native endothelial cells from young and aged individuals, we identified that the age-related nuclear accumulation of p53 reprograms endothelial cell metabolism, regulates telomerase activity and inhibits endothelial cell regeneration. Nuclear localization of p53 resulted from a loss of its interaction with the cysteine catabolizing enzyme cystathionine {gamma}-lyase in the cytoplasm. Enhancing the physical interaction of p53 with CSE by gene therapy could revert endothelial cell senescence and activate endothelial reparative responses.

cell biology↗

bioRxiv2021

HIF1α-AS1 is a DNA:DNA:RNA triplex-forming lncRNA interacting with the HUSH complex

DNA:DNA:RNA triplexes that are formed through Hoogsteen base-pairing have been observed in vitro, but the extent to which these interactions occur in cells and how they impact cellular functions remains elusive. Using a combination of bioinformatic techniques, RNA/DNA pulldown and biophysical studies, we set out to identify functionally important DNA:DNA:RNA triplex-forming long non-coding RNAs (lncRNA) in human endothelial cells. The lncRNA HIF1-AS1 was retrieved as a top hit. Endogenous HIF1-AS1 reduced the expression of numerous genes, including EPH Receptor A2 and Adrenomedullin through DNA:DNA:RNA triplex formation by acting as an adapter for the repressive human silencing hub complex (HUSH). Moreover, the oxygen-sensitive HIF1-AS1 was down-regulated in pulmonary hypertension and loss-of-function approaches not only resulted in gene de-repression but also enhanced angiogenic capacity. As exemplified here with HIF1-AS1, DNA:DNA:RNA triplex formation is a functionally important mechanism of trans-acting gene expression control.

molecular biology↗

bioRxiv2020

CEDAR, an online resource for the reporting and exploration of complexome profiling data

Complexome profiling is an emerging omics approach that systematically interrogates the composition of protein complexes (the complexome) of a sample, by combining biochemical separation of native protein complexes with mass-spectrometry based quantitation proteomics. The resulting fractionation profiles hold comprehensive information on the abundance and composition of the complexome, and have a high potential for reuse by experimental and computational researchers. However, the lack of a central resource that provides access to these data, reported with adequate descriptions and an analysis tool, has limited their reuse. Therefore, we established the ComplexomE profiling DAta Resource (CEDAR, www3.cmbi.umcn.nl/cedar/), an openly accessible database for depositing and exploring mass spectrometry data from complexome profiling studies. Compatibility and reusability of the data is ensured by a standardized data and reporting format containing the "minimum information required for a complexome profiling experiment" (MIACE). The data can be accessed through a user-friendly web interface, as well as programmatically using the REST API portal. Additionally, all complexome profiles available on CEDAR can be inspected directly on the website with the profile viewer tool that allows the detection of correlated profiles and inference of potential complexes. In conclusion, CEDAR is a unique, growing and invaluable resource for the study of protein complex composition and dynamics across biological systems.

bioinformatics↗

bioRxiv2020

Msp1/ATAD1 restores mitochondrial function in Zellweger Spectrum Disease

Peroxisomal Biogenesis Disorders (PBDs) are a class of inherited metabolic disorders with profound neurological and other phenotypes. The most severe PBDs are caused by mutations in peroxin genes, which result in nonfunctional peroxisomes typically through impaired protein import. In order to better understand the molecular causes of Zellweger Spectrum Disease (ZSD) -the most severe PBDs -, we investigated the fate of peroxisomal mRNAs and proteins in ZSD model systems. We found that loss of peroxisomal import has no effect on peroxin mRNA expression or translational efficiency. Instead, peroxin proteins--still produced at high levels-- aberrantly accumulate on the mitochondrial membrane, impairing respiration and ATP generation. Finally, we rescued mitochondrial function in fibroblasts derived from human patients with ZSD by overexpressing ATAD1, an AAA-ATPase that functions in mitochondrial quality control. These findings might provide a new focus of PBD therapies in supporting quality control pathways that protect mitochondrial function.

cell biology↗

bioRxiv2020

Loss of mitochondrial protease CLPP activates type I interferon responses through the mtDNA-cGAS-STING signaling axis

Caseinolytic mitochondrial matrix peptidase proteolytic subunit, CLPP, is a serine protease that degrades damaged or misfolded mitochondrial proteins. CLPP null mice exhibit growth retardation, deafness, and sterility, resembling human Perrault syndrome (PS), but also display immune system alterations. However, the molecular mechanisms and signaling pathways underlying immunological changes in CLPP null mice remain unclear. Here we report the steady state activation of type I interferon (IFN-I) signaling and antiviral gene expression in CLPP deficient cells and tissues. Depletion of the cyclic GMP-AMP (cGAS)-Stimulator of Interferon Genes (STING) DNA sensing pathway ablates heightened IFN-I responses and abrogates the broad viral resistance phenotype of CLPP null cells. Moreover, we report that CLPP deficiency leads to mitochondrial DNA (mtDNA) instability and packaging alterations. Pharmacological and genetic approaches to deplete mtDNA or inhibit cytosolic release markedly reduce antiviral gene expression, implicating mtDNA stress as the driver of IFN-I signaling in CLPP null mice. Our work places the cGAS-STING-IFN-I innate immune pathway downstream of CLPP and may have implications for understanding myriad human diseases involving CLPP dysregulation.

immunology↗

bioRxiv2017

Hydrogen peroxide formation by Nox4 limits malignant transformation

Reactive oxygen species (ROS) can cause cellular damage and are thought to promote cancer-development. Nevertheless, under physiological conditions, all cells constantly produce ROS, either as chemical by-products or for signaling purpose. During differentiation cells induce the NADPH oxidase Nox4, which constitutively produces low amounts of H2O2. We infer that this constitutive H2O2 is unlikely to be carcinogenic and may rather maintain basal activity of cellular surveillance systems.\n\nUtilizing two different murine tumor models we demonstrate that Nox4 prevents malignant transformation and facilitated the recognition of DNA-damage. Upon DNA-damage repair is initiated as consequence of phosphorylation of H2AX ({gamma}H2AX). Repair only occurs if nuclear activity of the {gamma}H2AX-dephosphorylating phosphatase PP2A is kept sufficiently low, a task fulfilled by Nox4: Nox4 continuously oxidizes AKT, and once oxidized AKT captures PP2A in the cytosol. Absence of Nox4 facilitates nuclear PP2A translocation and dephosphorylation of {gamma}H2AX. Simultaneously the proportion of active, phosphorylated AKT is increased. Thus, DNA-damage is not recognized and the increase in AKT activity promotes proliferation. The combination of both events resulted in genomic instability and tumor initiation.\n\nWith the identification of the first cancer-protective source of reactive oxygen species, Nox4, the paradigm of reactive-oxygen species-induced initiation of malignancies should be revised.\n\nSignificanceThe stereotype of ROS produced by NADPH oxidases as cause of malignant diseases persists generalized since decades. We demonstrate that the NADPH oxidase Nox4, as constitutive source of ROS, prevents malignant transformation and that its pharmacological inhibition as currently aspired by several companies will potentially increase the risk of malignant cell transformation and eventually tumor formation.\n\nPrecisBy oxidizing AKT and keeping PP2A in the cytosol, the NADPH oxidase Nox4 allows proper DNA damage repair and averts cancer development.

cancer biology↗