Atomic vacancies of molybdenum disulfide nanoparticles stimulate mitochondrial biogenesis.

Diminished mitochondrial function underlies many rare inborn errors of energy metabolism and contributes to more common age-associated metabolic and neurodegenerative disorders. Thus, boosting mitochondrial biogenesis has been proposed as a potential therapeutic approach for these diseases; however, currently we have a limited arsenal of compounds that can stimulate mitochondrial function. In this study, we designed molybdenum disulfide (MoS2) nanoflowers with predefined atomic vacancies that are fabricated by self-assembly of individual two-dimensional MoS2 nanosheets. Treatment of mammalian cells with MoS2 nanoflowers increased mitochondrial biogenesis by induction of PGC-1α and TFAM, which resulted in increased mitochondrial DNA copy number, enhanced expression of nuclear and mitochondrial-DNA encoded genes, and increased levels of mitochondrial respiratory chain proteins. Consistent with increased mitochondrial biogenesis, treatment with MoS2 nanoflowers enhanced mitochondrial respiratory capacity and adenosine triphosphate production in multiple mammalian cell types. Taken together, this study reveals that predefined atomic vacancies in MoS2 nanoflowers stimulate mitochondrial function by upregulating the expression of genes required for mitochondrial biogenesis.

Morphine induces inflammatory responses via both TLR4 and cGAS-STING signaling pathways.

BACKGROUND: Opioid activation of the microglia or macrophage Toll-like receptor 4 (TLR4) and associated inflammatory cytokine release are implicated in opioid-induced hyperalgesia and tolerance. The cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS-STING) signaling pathway, activated by double-stranded DNA including mitochondrial DNA (mtDNA), has emerged as another key mediator of inflammatory responses. This study tested the hypothesis that morphine induces immune inflammatory responses in microglia and macrophages involving TLR4 and cGAS-STING pathway. METHODS: BV2 microglia and Raw 264.7 (Raw) macrophage cells were exposed to morphine with and without a STING inhibitor (C176) for 6 h or TLR 4 inhibitor (TAK242) for 24 h. Western blotting and RT-qPCR analyses assessed TLR4, cGAS, STING, nuclear factor-kappa B (NF-κB), and pro-inflammatory cytokine expression. Morphine-induced mitochondria dysfunction was quantified by reactive oxygen species (ROS) release using MitoSOX, mtDNA release by immunofluorescence, and RT-qPCR. Polarization of BV2 and Raw cells was assessed by inducible nitric oxide (iNOS) and CD86 expression. The role of mtDNA on morphine-related inflammation was investigated by mtDNA depletion of the cells with ethidium bromide (EtBr) or cell transfection of mtDNA extracted from morphine-treated cells. RESULTS: Morphine significantly increased the expression of TLR4, cGAS, STING, p65 NF-κB, and cytokines (IL-6 and TNF-α) in BV2 and Raw cells. Morphine-induced mitochondrial dysfunction by increased ROS and mtDNA release; the increased iNOS and CD86 evidenced inflammatory M1-like phenotype polarization. TLR4 and STING inhibitors reduced morphine-induced cytokine release in both cell types. The transfection of mtDNA activated inflammatory signaling proteins, cytokine release, and polarization. Conversely, mtDNA depletion led to the reversal of these effects. CONCLUSION: Morphine activates the cGAS-STING pathway in macrophage cell types. Inhibition of the STING pathway can be an additional method to overcome immune cell inflammation-related morphine tolerance and opioid-induced hyperalgesia.

Overactive mitochondrial DNA replication disrupts perinatal cardiac maturation.

High mitochondrial DNA (mtDNA) amount has been reported to be beneficial for resistance and recovery of metabolic stress, while increased mtDNA synthesis activity can drive aging signs. The intriguing contrast of these two mtDNA boosting outcomes prompted us to jointly elevate mtDNA amount and frequency of replication in mice. We report that high activity of mtDNA synthesis inhibits perinatal metabolic maturation of the heart. The offspring of the asymptomatic parental lines are born healthy but manifest dilated cardiomyopathy and cardiac collapse during the first days of life. The pathogenesis, further enhanced by mtDNA mutagenesis, involves prenatal upregulation of mitochondrial integrated stress response and the ferroptosis-inducer MESH1, leading to cardiac fibrosis and cardiomyocyte death after birth. Our evidence indicates that the tight control of mtDNA replication is critical for early cardiac homeostasis. Importantly, ferroptosis sensitivity is a potential targetable mechanism for infantile-onset cardiomyopathy, a common manifestation of mitochondrial diseases.

Yeast EndoG prevents genome instability by degrading extranuclear DNA species.

In metazoans mitochondrial DNA (mtDNA) or retrotransposon cDNA released to cytoplasm are degraded by nucleases to prevent sterile inflammation. It remains unknown whether degradation of these DNA also prevents nuclear genome instability. We used an amplicon sequencing-based method in yeast enabling analysis of millions of DSB repair products. In non-dividing stationary phase cells, Pol4-mediated non-homologous end-joining increases, resulting in frequent insertions of 1-3 nucleotides, and insertions of mtDNA (NUMTs) or retrotransposon cDNA. Yeast EndoG (Nuc1) nuclease limits insertion of cDNA and transfer of very long mtDNA ( >10 kb) to the nucleus, where it forms unstable circles, while promoting the formation of short NUMTs (~45-200 bp). Nuc1 also regulates transfer of extranuclear DNA to nucleus in aging or meiosis. We propose that Nuc1 preserves genome stability by degrading retrotransposon cDNA and long mtDNA, while short NUMTs originate from incompletely degraded mtDNA. This work suggests that nucleases eliminating extranuclear DNA preserve genome stability.

Crosstalk between Dysfunctional Mitochondria and Proinflammatory Responses during Viral Infections.

Mitochondria play pivotal roles in sustaining various biological functions including energy metabolism, cellular signaling transduction, and innate immune responses. Viruses exploit cellular metabolic synthesis to facilitate viral replication, potentially disrupting mitochondrial functions and subsequently eliciting a cascade of proinflammatory responses in host cells. Additionally, the disruption of mitochondrial membranes is involved in immune regulation. During viral infections, mitochondria orchestrate innate immune responses through the generation of reactive oxygen species (ROS) and the release of mitochondrial DNA, which serves as an effective defense mechanism against virus invasion. The targeting of mitochondrial damage may represent a novel approach to antiviral intervention. This review summarizes the regulatory mechanism underlying proinflammatory response induced by mitochondrial damage during viral infections, providing new insights for antiviral strategies.

Targeting PRMT3 impairs methylation and oligomerization of HSP60 to boost anti-tumor immunity by activating cGAS/STING signaling.

Immune checkpoint blockade (ICB) has emerged as a promising therapeutic option for hepatocellular carcinoma (HCC), but resistance to ICB occurs and patient responses vary. Here, we uncover protein arginine methyltransferase 3 (PRMT3) as a driver for immunotherapy resistance in HCC. We show that PRMT3 expression is induced by ICB-activated T cells via an interferon-gamma (IFNγ)-STAT1 signaling pathway, and higher PRMT3 expression levels correlate with reduced numbers of tumor-infiltrating CD8+ T cells and poorer response to ICB. Genetic depletion or pharmacological inhibition of PRMT3 elicits an influx of T cells into tumors and reduces tumor size in HCC mouse models. Mechanistically, PRMT3 methylates HSP60 at R446 to induce HSP60 oligomerization and maintain mitochondrial homeostasis. Targeting PRMT3-dependent HSP60 methylation disrupts mitochondrial integrity and increases mitochondrial DNA (mtDNA) leakage, which results in cGAS/STING-mediated anti-tumor immunity. Lastly, blocking PRMT3 functions synergize with PD-1 blockade in HCC mouse models. Our study thus identifies PRMT3 as a potential biomarker and therapeutic target to overcome immunotherapy resistance in HCC.

Mitochondrial DNA is a sensitive surrogate and oxidative stress target in oral cancer cells.

Cellular oxidative stress mediated by intrinsic and/or extrinsic reactive oxygen species (ROS) is associated with disease pathogenesis. Oxidative DNA damage can naturally be substituted by mitochondrial DNA (mtDNA), leading to base lesion/strand break formation, copy number changes, and mutations. In this study, we devised a single test for the sensitive quantification of acute mtDNA damage, repair, and copy number changes using supercoiling-sensitive quantitative PCR (ss-qPCR) and examined how oxidative stress-related mtDNA damage responses occur in oral cancer cells. We observed that exogenous hydrogen peroxide (H2O2) induced dynamic mtDNA damage responses, as reflected by early structural DNA damage, followed by DNA repair if damage did not exceed a particular threshold. However, high oxidative stress levels induced persistent mtDNA damage and caused a 5-30-fold depletion in mtDNA copy numbers over late responses. This dramatic depletion was associated with significant growth arrest and apoptosis, suggesting persistent functional consequences. Moreover, oral cancer cells responded differentially to oxidative injury when compared with normal cells, and different ROS species triggered different biological consequences under stress conditions. In conclusion, we developed a new method for the sensitive detection of mtDNA damage and copy number changes, with exogenous H2O2 inducing dynamic mtDNA damage responses associated with functional changes in stressed cancer cells. Finally, our method can help characterize oxidative DNA damage in cancer and other human diseases.

Haplotype variability in mitochondrial rRNA predisposes to metabolic syndrome.

Metabolic syndrome is a growing concern in developed societies and due to its polygenic nature, the genetic component is only slowly being elucidated. Common mitochondrial DNA sequence variants have been associated with symptoms of metabolic syndrome and may, therefore, be relevant players in the genetics of metabolic syndrome. We investigate the effect of mitochondrial sequence variation on the metabolic phenotype in conplastic rat strains with identical nuclear but unique mitochondrial genomes, challenged by high-fat diet. We find that the variation in mitochondrial rRNA sequence represents risk factor in the insulin resistance development, which is associated with diacylglycerols accumulation, induced by tissue-specific reduction of the oxidative capacity. These metabolic perturbations stem from the 12S rRNA sequence variation affecting mitochondrial ribosome assembly and translation. Our work demonstrates that physiological variation in mitochondrial rRNA might represent a relevant underlying factor in the progression of metabolic syndrome.

Differences in the Effect of Beta-Hydroxybutyrate on the Mitochondrial Biogenesis, Oxidative Stress and Inflammation Markers in Tissues from Young and Old Rats.

One of the therapeutic approaches to age-related diseases is modulation of body cell metabolism through certain diets or their pharmacological mimetics. The ketogenic diet significantly affects cell energy metabolism and functioning of mitochondria, which has been actively studied in various age-related pathologies. Here, we investigated the effect of the ketogenic diet mimetic beta-hydroxybutyrate (BHB) on the expression of genes regulating mitochondrial biogenesis (Ppargc1a, Nrf1, Tfam), quality control (Sqstm1), functioning of the antioxidant system (Nfe2l2, Gpx1, Gpx3, Srxn1, Txnrd2, Slc6a9, Slc7a11), and inflammatory response (Il1b, Tnf, Ptgs2, Gfap) in the brain, lungs, heart, liver, kidneys, and muscles of young and old rats. We also analyzed mitochondrial DNA (mtDNA) copy number, accumulation of mtDNA damage, and levels of oxidative stress based on the concentration of reduced glutathione and thiobarbituric acid-reactive substances (TBARS). In some organs, aging disrupted mitochondrial biogenesis and functioning of cell antioxidant system, which was accompanied by the increased oxidative stress and inflammation. Administration of BHB for 2 weeks had different effects on the organs of young and old rats. In particular, BHB upregulated expression of genes coding for proteins associated with the mitochondrial biogenesis and antioxidant system, especially in the liver and muscles of young (but not old) rats. At the same time, BHB contributed to the reduction of TBARS in the kidneys of old rats. Therefore, our study has shown that administration of ketone bodies significantly affected gene expression in organs, especially in young rats, by promoting mitochondrial biogenesis, improving the functioning of the antioxidant defense system, and partially reducing the level of oxidative stress. However, these changes were much less pronounced in old animals.

Multiple unfolded protein response pathways cooperate to link cytosolic dsDNA release to stimulator of interferon gene activation.

The double-stranded DNA (dsDNA) sensor STING has been increasingly implicated in responses to "sterile" endogenous threats and pathogens without nominal DNA or cyclic di-nucleotide stimuli. Previous work showed an endoplasmic reticulum (ER) stress response, known as the unfolded protein response (UPR), activates STING. Herein, we sought to determine if ER stress generated a STING ligand, and to identify the UPR pathways involved. Induction of IFN-ß expression following stimulation with the UPR inducer thapsigargin (TPG) or oxygen glucose deprivation required both STING and the dsDNA-sensing cyclic GMP-AMP synthase (cGAS). Furthermore, TPG increased cytosolic mitochondrial DNA, and immunofluorescence visualized dsDNA punctae in murine and human cells, providing a cGAS stimulus. N-acetylcysteine decreased IFN-ß induction by TPG, implicating reactive oxygen species (ROS). However, mitoTEMPO, a mitochondrial oxidative stress inhibitor did not impact TPG-induced IFN. On the other hand, inhibiting the inositol requiring enzyme 1 (IRE1) ER stress sensor and its target transcription factor XBP1 decreased the generation of cytosolic dsDNA. iNOS upregulation was XBP1-dependent, and an iNOS inhibitor decreased cytosolic dsDNA and IFN-ß, implicating ROS downstream of the IRE1-XBP1 pathway. Inhibition of the PKR-like ER kinase (PERK) pathway also attenuated cytoplasmic dsDNA release. The PERK-regulated apoptotic factor Bim was required for both dsDNA release and IFN-ß mRNA induction. Finally, XBP1 and PERK pathways contributed to cytosolic dsDNA release and IFN-induction by the RNA virus, Vesicular Stomatitis Virus (VSV). Together, our findings suggest that ER stressors, including viral pathogens without nominal STING or cGAS ligands such as RNA viruses, trigger multiple canonical UPR pathways that cooperate to activate STING and downstream IFN-ß via mitochondrial dsDNA release.

Mitochondrial Probe for Glutathione Depletion Reveals NME3 Essentiality for Mitochondrial Redox Response.

Maintenance of the mitochondrial thiol redox state is essential for cell survival. However, we lack a comprehensive understanding of the redox response to mitochondrial glutathione depletion. We developed a mitochondria-penetrating peptide, mtCDNB, to specifically deplete mitochondrial glutathione. A genome-wide CRISPR/Cas9 screen in tandem with mtCDNB treatment was employed to uncover regulators of the redox response to mitochondrial glutathione depletion. We identified nucleoside diphosphate kinase 3 (NME3) as a regulator of mitochondrial dynamics. We show that NME3 is recruited to the mitochondrial outer membrane when under redox stress. In the absence of NME3, there is impaired mitophagy, which leads to the accumulation of dysfunctional mitochondria. NME3 knockouts depleted of mitochondrial glutathione have increased mitochondrial ROS production, accumulate mtDNA lesions, and present a senescence-associated secretory phenotype. Our findings suggest a novel role for NME3 in selecting mitochondria for degradation through mitophagy under conditions of mitochondrial redox stress.

Heterogeneous brain region-specific responses to astrocytic mitochondrial DNA damage in mice.

Astrocytes display context-specific diversity in their functions and respond to noxious stimuli between brain regions. Astrocytic mitochondria have emerged as key players in governing astrocytic functional heterogeneity, given their ability to dynamically adapt their morphology to regional demands on ATP generation and Ca2+ buffering functions. Although there is reciprocal regulation between mitochondrial dynamics and mitochondrial Ca2+ signaling in astrocytes, the extent of this regulation in astrocytes from different brain regions remains unexplored. Brain-wide, experimentally induced mitochondrial DNA (mtDNA) loss in astrocytes showed that mtDNA integrity is critical for astrocyte function, however, possible diverse responses to this noxious stimulus between brain areas were not reported in these experiments. To selectively damage mtDNA in astrocytes in a brain-region-specific manner, we developed a novel adeno-associated virus (AAV)-based tool, Mito-PstI expressing the restriction enzyme PstI, specifically in astrocytic mitochondria. Here, we applied Mito-PstI to two brain regions, the dorsolateral striatum and dentate gyrus, and we show that Mito-PstI induces astrocytic mtDNA loss in vivo, but with remarkable brain-region-dependent differences on mitochondrial dynamics, Ca2+ fluxes, and astrocytic and microglial reactivity. Thus, AAV-Mito-PstI is a novel tool to explore the relationship between astrocytic mitochondrial network dynamics and astrocytic mitochondrial Ca2+ signaling in a brain-region-selective manner.

TRAP1 modulates mitochondrial biogenesis via PGC-1α/TFAM signalling pathway in colorectal cancer cells.

Metabolic rewiring promotes cancer cell adaptation to a hostile microenvironment, representing a hallmark of cancer. This process involves mitochondrial function and is mechanistically linked to the balance between mitochondrial biogenesis (MB) and mitophagy. The molecular chaperone TRAP1 is overexpressed in 60-70% of human colorectal cancers (CRC) and its over-expression correlates with poor clinical outcome, being associated with many cancer cell functions (i.e. adaptation to stress, protection from apoptosis and drug resistance, protein synthesis quality control, metabolic rewiring from glycolysis to mitochondrial respiration and vice versa). Here, the potential new role of TRAP1 in regulating mitochondrial dynamics was investigated in CRC cell lines and human CRCs. Our results revealed an inverse correlation between TRAP1 and mitochondrial-encoded respiratory chain proteins both at transcriptional and translational levels. Furthermore, TRAP1 silencing is associated with increased mitochondrial mass and mitochondrial DNA copy number (mtDNA-CN) as well as enhanced MB through PGC-1α/TFAM signalling pathway, promoting the formation of new functioning mitochondria and, likely, underlying the metabolic shift towards oxidative phosphorylation. These results suggest an involvement of TRAP1 in regulating MB process in human CRC cells. KEY MESSAGES: TRAP1 inversely correlates with protein-coding mitochondrial gene expression in CRC cells and tumours. TRAP1 silencing correlates with increased mitochondrial mass and mtDNA copy number in CRC cells. TRAP1 silencing favours mitochondrial biogenesis in CRC cells.

Blockade of the mitochondrial DNA release ameliorates hepatic ischemia-reperfusion injury through avoiding the activation of cGAS-Sting pathway.

BACKGROUND: Liver surgery during the perioperative period often leads to a significant complication known as hepatic ischemia-reperfusion (I/R) injury. Hepatic I/R injury is linked to the innate immune response. The cGAS-STING pathway triggers the activation of innate immune through the detection of DNA within cells. Nevertheless, the precise mechanism and significance of the cGAS-STING pathway in hepatic I/R injury are yet to be investigated. METHODS: Mouse model of hepatic I/R injury was used in the C57BL/6 WT mice and the STING knockout (STING-KO) mice. In addition, purified primary hepatocytes were used to construct oxygen-glucose deprivation reperfusion (OGD-Rep) treatment models. RESULTS: Our research revealed a notable increase in mRNA and protein levels of cGAS and STING in liver during I/R injury. Interestingly, the lack of STING exhibited a safeguarding impact on hepatic I/R injury by suppressing the elevation of liver enzymes, liver cell death, and inflammation. Furthermore, pharmacological cGAS and STING inhibition recapitulated these phenomena. Macrophages play a crucial role in the activation of the cGAS-STING pathway during hepatic I/R injury. The cGAS-STING pathway experiences a significant decrease in activity and hepatic I/R injury is greatly diminished following the elimination of macrophages. Significantly, we demonstrate that the activation of the cGAS-STING pathway is primarily caused by the liberation of mitochondrial DNA (mtDNA) rather than nuclear DNA (nDNA). Moreover, the safeguarding of the liver against I/R injury is also attributed to the hindrance of mtDNA release through the utilization of inhibitors targeting mPTP and VDAC oligomerization. CONCLUSIONS: The results of our study suggest that the release of mtDNA plays a significant role in causing damage to liver by activating the cGAS-STING pathway during I/R injury. Furthermore, inhibiting the release of mtDNA can provide effective protection against hepatic I/R injury.

Cocaine-derived hippuric acid activates mtDNA-STING signaling in alcoholic liver disease: Implications for alcohol and cocaine co-abuse.

The simultaneous abuse of alcohol-cocaine is known to cause stronger and more unpredictable cellular damage in the liver, heart, and brain. However, the mechanistic crosstalk between cocaine and alcohol in liver injury remains unclear. The findings revealed cocaine-induced liver injury and inflammation in both marmosets and mice. Of note, co-administration of cocaine and ethanol in mice causes more severe liver damage than individual treatment. The metabolomic analysis confirmed that hippuric acid (HA) is the most abundant metabolite in marmoset serum after cocaine consumption and that is formed in primary marmoset hepatocytes. HA, a metabolite of cocaine, increases mitochondrial DNA leakage and subsequently increases the production of proinflammatory factors via STING signaling in Kupffer cells (KCs). In addition, conditioned media of cocaine-treated KC induced hepatocellular necrosis via alcohol-induced TNFR1. Finally, disruption of STING signaling in vivo ameliorated co-administration of alcohol- and cocaine-induced liver damage and inflammation. These findings postulate intervention of HA-STING-TNFR1 axis as a novel strategy for treatment of alcohol- and cocaine-induced excessive liver damage.

Microbial genotoxin-elicited host DNA mutations related to mitochondrial dysfunction, a momentous contributor for colorectal carcinogenesis.

Gut microbe dysbiosis increases repetitive inflammatory responses, leading to an increase in the incidence of colorectal cancer. Recent studies have revealed that specific microbial species directly instigate mutations in the host nucleus DNA, thereby accelerating the progression of colorectal cancer. Given the well-established role of mitochondrial dysfunction in promoting colorectal cancer, it is reasonable to postulate that gut microbes may induce mitochondrial gene mutations, thereby inducing mitochondrial dysfunction. In this review, we focus on gut microbial genotoxins and their known and potential targets in mitochondrial genes. Consequently, we propose that targeted disruption of genotoxin transport pathways may effectively reduce the rate of mitochondrial gene mutations and yield substantial benefits for the prevention of colorectal carcinogenesis.

Exogenous expression of PGC-1α during in vitro maturation impairs the developmental competence of porcine oocytes.

Objectives of the current study were to examine the effects of exogenous expression of PGC-1α, which is a transcription factor responsive for controlling mitochondrial DNA (mtDNA) replication, mitochondria quantity control, mitochondrial biogenesis, and reactive oxygen species (ROS) maintenance, in porcine oocytes during in-vitro maturation (IVM) on the developmental competence, as well as mitochondrial quantity and function. Exogenous over-expression of PGC-1α by injection of the mRNA construct into oocytes 20 h after the start of IVM culture significantly increased the copy number of mtDNA in the oocytes, but reduced the incidences of oocytes matured to the metaphase-II stage after the IVM culture for totally 44 h and completely suppressed the early development in vitro to the blastocyst stage following parthenogenetic activation. The exogenous expression of PGC-1α also significantly induced spindle defects and chromosome misalignments. Furthermore, markedly higher ROS levels were observed in the PGC-1α-overexpressed mature oocytes, whereas mRNA level of SOD1, encoded for a ROS scavenging enzyme, was decreased. These results conclude that forced expression of PGC-1α successfully increase mtDNA copy number but led to increased ROS production, evidently by downregulation of SOD1 gene expression, inducement of spindle aberration/chromosomal misalignment, and consequently reduction in the meiotic and developmental competences of porcine oocytes.

Targeting organ-specific mitochondrial dysfunction to improve biological aging.

In an aging society, unveiling new anti-aging strategies to prevent and combat aging-related diseases is of utmost importance. Mitochondria are the primary ATP production sites and key regulators of programmed cell death. Consequently, these highly dynamic organelles play a central role in maintaining tissue function, and mitochondrial dysfunction is a pivotal factor in the progressive age-related decline in cellular homeostasis and organ function. The current review examines recent advances in understanding the interplay between mitochondrial dysfunction and organ-specific aging. Thereby, we dissect molecular mechanisms underlying mitochondrial impairment associated with the deterioration of organ function, exploring the role of mitochondrial DNA, reactive oxygen species homeostasis, metabolic activity, damage-associated molecular patterns, biogenesis, turnover, and dynamics. We also highlight emerging therapeutic strategies in preclinical and clinical tests that are supposed to rejuvenate mitochondrial function, such as antioxidants, mitochondrial biogenesis stimulators, and modulators of mitochondrial turnover and dynamics. Furthermore, we discuss potential benefits and challenges associated with the use of these interventions, emphasizing the need for organ-specific approaches given the unique mitochondrial characteristics of different tissues. In conclusion, this review highlights the therapeutic potential of addressing mitochondrial dysfunction to mitigate organ-specific aging, focusing on the skin, liver, lung, brain, skeletal muscle, and lung, as well as on the reproductive, immune, and cardiovascular systems. Based on a comprehensive understanding of the multifaceted roles of mitochondria, innovative therapeutic strategies may be developed and optimized to combat biological aging and promote healthy aging across diverse organ systems.

Metabolic regulation of the mitochondrial immune checkpoint.

Disrupting mitochondrial function in malignant cells is a promising strategy to enhance anticancer immunity. We have recently demonstrated that depriving colorectal cancer cells of serine results in mitochondrial dysfunction coupled with the cytosolic accumulation of mitochondrial DNA and consequent activation of CGAS- and STING-dependent tumor-targeting immune responses.

Loss of the DNA repair protein, polynucleotide kinase/phosphatase, activates the type 1 interferon response independent of ionizing radiation.

DNA damage has been implicated in the stimulation of the type 1 interferon (T1IFN) response. Here, we show that downregulation of the DNA repair protein, polynucleotide kinase/phosphatase (PNKP), in a variety of cell lines causes robust phosphorylation of STAT1, upregulation of interferon-stimulated genes and persistent accumulation of cytosolic DNA, all of which are indicators for the activation of the T1IFN response. Furthermore, this did not require damage induction by ionizing radiation. Instead, our data revealed that production of reactive oxygen species (ROS) synergises with PNKP loss to potentiate the T1IFN response, and that loss of PNKP significantly compromises mitochondrial DNA (mtDNA) integrity. Depletion of mtDNA or treatment of PNKP-depleted cells with ROS scavengers abrogated the T1IFN response, implicating mtDNA as a significant source of the cytosolic DNA required to potentiate the T1IFN response. The STING signalling pathway is responsible for the observed increase in the pro-inflammatory gene signature in PNKP-depleted cells. While the response was dependent on ZBP1, cGAS only contributed to the response in some cell lines. Our data have implications for cancer therapy, since PNKP inhibitors would have the potential to stimulate the immune response, and also to the neurological disorders associated with PNKP mutation.