Diesel-derived PM2.5 induces impairment of cardiac movement followed by mitochondria dysfunction in cardiomyocytes.

Particulate matter (PM) in polluted air can be exposed to the human body through inhalation, ingestion, and skin contact, accumulating in various organs throughout the body. Organ accumulation of PM is a growing health concern, particularly in the cardiovascular system. PM emissions are formed in the air by solid particles, liquid droplets, and fuel - particularly diesel - combustion. PM2.5 (size < 2.5 µm particle) is a major risk factor for approximately 200,000 premature deaths annually caused by air pollution. This study assessed the deleterious effects of diesel-derived PM2.5 exposure in HL-1 mouse cardiomyocyte cell lines. The PM2.5-induced biological changes, including ultrastructure, intracellular reactive oxygen species (ROS) generation, viability, and intracellular ATP levels, were analyzed. Moreover, we analyzed changes in transcriptomics using RNA sequencing and metabolomics using gas chromatography-tandem mass spectrometry (GC-MS/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) in PM2.5-treated HL-1 cells. Ultrastructural analysis using transmission electron microscopy revealed disruption of mitochondrial cristae structures in a PM2.5 dose-dependent manner. The elevation of ROS levels and reduction in cell viability and ATP levels were similarly observed in a PM2.5 dose-dependently. In addition, 6,005 genes were differentially expressed (fold change cut-off ± 4) from a total of 45,777 identified genes, and 20 amino acids (AAs) were differentially expressed (fold change cut-off ± 1.2) from a total of 28 identified AAs profiles. Using bioinformatic analysis with ingenuity pathway analysis (IPA) software, we found that the changes in the transcriptome and metabolome are highly related to changes in biological functions, including homeostasis of Ca2+, depolarization of mitochondria, the function of mitochondria, synthesis of ATP, and cardiomyopathy. Moreover, an integrated single omics network was constructed by combining the transcriptome and the metabolome. In silico prediction analysis with IPA predicted that upregulation of mitochondria depolarization, ROS generation, cardiomyopathy, suppression of Ca2+ homeostasis, mitochondrial function, and ATP synthesis occurred in PM2.5-treated HL-1 cells. In particular, the cardiac movement of HL-1 was significantly reduced after PM2.5 treatment. In conclusion, our results assessed the harmful effects of PM2.5 on mitochondrial function and analyzed the biological changes related to cardiac movement, which is potentially associated with cardiovascular diseases.

The Impact of Fine Particulate Matter 2.5 on the Cardiovascular System: A Review of the Invisible Killer.

Air pollution exerts several deleterious effects on the cardiovascular system, with cardiovascular disease (CVD) accounting for 80% of all premature deaths caused by air pollution. Short-term exposure to particulate matter 2.5 (PM2.5) leads to acute CVD-associated deaths and nonfatal events, whereas long-term exposure increases CVD-associated risk of death and reduces longevity. Here, we summarize published data illustrating how PM2.5 may impact the cardiovascular system to provide information on the mechanisms by which it may contribute to CVDs. We provide an overview of PM2.5, its associated health risks, global statistics, mechanistic underpinnings related to mitochondria, and hazardous biological effects. We elaborate on the association between PM2.5 exposure and CVD development and examine preventive PM2.5 exposure measures and future strategies for combating PM2.5-related adverse health effects. The insights gained can provide critical guidelines for preventing pollution-related CVDs through governmental, societal, and personal measures, thereby benefitting humanity and slowing climate change.

LDHB Deficiency Promotes Mitochondrial Dysfunction Mediated Oxidative Stress and Neurodegeneration in Adult Mouse Brain.

Age-related decline in mitochondrial function and oxidative stress plays a critical role in neurodegeneration. Lactate dehydrogenase-B (LDHB) is a glycolytic enzyme that catalyzes the conversion of lactate, an important brain energy substrate, into pyruvate. It has been reported that the LDHB pattern changes in the brain during ageing. Yet very little is known about the effect of LDHB deficiency on brain pathology. Here, we have used Ldhb knockout (Ldhb-/-) mice to test the hypothesis that LDHB deficiency plays an important role in oxidative stress-mediated neuroinflammation and neurodegeneration. LDHB knockout (Ldhb-/-) mice were generated by the ablation of the Ldhb gene using the Cre/loxP-recombination system in the C57BL/6 genetic background. The Ldhb-/- mice were treated with either osmotin (15 µg/g of the body; intraperitoneally) or vehicle twice a week for 5-weeks. After behavior assessments, the mice were sacrificed, and the cortical and hippocampal brain regions were analyzed through biochemical and morphological analysis. Ldhb-/- mice displayed enhanced reactive oxygen species (ROS) and lipid peroxidation (LPO) production, and they revealed depleted stores of cellular ATP, GSH:GSSG enzyme ratio, and downregulated expression of Nrf2 and HO-1 proteins, when compared to WT littermates. Importantly, the Ldhb-/- mice showed upregulated expression of apoptosis mediators (Bax, Cytochrome C, and caspase-3), and revealed impaired p-AMPK/SIRT1/PGC-1alpha signaling. Moreover, LDHB deficiency-induced gliosis increased the production of inflammatory mediators (TNF-α, Nf-ĸB, and NOS2), and revealed cognitive deficits. Treatment with osmotin, an adipoR1 natural agonist, significantly increased cellular ATP production by increasing mitochondrial function and attenuated oxidative stress, neuroinflammation, and neuronal apoptosis, probably, by upregulating p-AMPK/SIRT1/PGC-1alpha signaling in Ldhb-/- mice. In brief, LDHB deficiency may lead to brain oxidative stress-mediated progression of neurodegeneration via regulating p-AMPK/SIRT1/PGC-1alpha signaling, while osmotin could improve mitochondrial functions, abrogate oxidative stress and alleviate neuroinflammation and neurodegeneration in adult Ldhb-/- mice.

High levels of TFAM repress mammalian mitochondrial DNA transcription in vivo.

Mitochondrial transcription factor A (TFAM) is compacting mitochondrial DNA (dmtDNA) into nucleoids and directly controls mtDNA copy number. Here, we show that the TFAM-to-mtDNA ratio is critical for maintaining normal mtDNA expression in different mouse tissues. Moderately increased TFAM protein levels increase mtDNA copy number but a normal TFAM-to-mtDNA ratio is maintained resulting in unaltered mtDNA expression and normal whole animal metabolism. Mice ubiquitously expressing very high TFAM levels develop pathology leading to deficient oxidative phosphorylation (OXPHOS) and early postnatal lethality. The TFAM-to-mtDNA ratio varies widely between tissues in these mice and is very high in skeletal muscle leading to strong repression of mtDNA expression and OXPHOS deficiency. In the heart, increased mtDNA copy number results in a near normal TFAM-to-mtDNA ratio and maintained OXPHOS capacity. In liver, induction of LONP1 protease and mitochondrial RNA polymerase expression counteracts the silencing effect of high TFAM levels. TFAM thus acts as a general repressor of mtDNA expression and this effect can be counterbalanced by tissue-specific expression of regulatory factors.

Depletion of Adipocyte Becn1 Leads to Lipodystrophy and Metabolic Dysregulation.

Becn1/Beclin-1 is a core component of the class III phosphatidylinositol 3-kinase required for autophagosome formation and vesicular trafficking. Although Becn1 has been implicated in numerous diseases such as cancer, aging, and neurodegenerative disease, the role of Becn1 in white adipose tissue and related metabolic diseases remains elusive. In this study, we show that adipocyte-specific Becn1 knockout mice develop severe lipodystrophy, leading to adipose tissue inflammation, hepatic steatosis, and insulin resistance. Ablation of Becn1 in adipocytes stimulates programmed cell death in a cell-autonomous manner, accompanied by elevated endoplasmic reticulum (ER) stress gene expression. Furthermore, we observed that Becn1 depletion sensitized mature adipocytes to ER stress, leading to accelerated cell death. Taken together, these data suggest that adipocyte Becn1 would serve as a crucial player for adipocyte survival and adipose tissue homeostasis.

Suppressed expression of LDHB promotes age-related hearing loss via aerobic glycolysis.

Age-dependent decrease of mitochondrial energy production and cellular redox imbalance play significant roles in age-related hearing loss (ARHL). Lactate dehydrogenase B (LDHB) is a key glycolytic enzyme that catalyzes the interconversion of pyruvate and lactate. LDH activity and isoenzyme patterns are known to be changed with aging, but the role of LDHB in ARHL has not been studied yet. Here, we found that LDHB knockout mice showed hearing loss at high frequencies, which is the typical feature of ARHL. LDHB knockdown caused downregulation of mitochondrial functions in auditory cell line, University of Bristol/organ of Corti 1 (UB/OC1) with decreased NAD+ and increased hypoxia inducing factor-1α. LDHB knockdown also enhanced the death of UB/OC1 cells with ototoxic gentamicin treatment. On the contrary, the induction of LDHB expression caused enhanced mitochondrial functions, including changes in mitochondrial respiratory subunits, mitochondrial membrane potentials, ATP, and the NAD+/NADH ratio. Thus, we concluded that suppression of LDHB activity may be closely related with the early onset or progression of ARHL.

Expression of Cellular Receptors in the Ischemic Hemisphere of Mice with Increased Glucose Uptake.

Many previous studies have shown reduced glucose uptake in the ischemic brain. In contrast, in a permanent unilateral common carotid artery occlusion (UCCAO) mouse model, our pilot experiments using 18F-fluorodeoxyglucose positron emission tomography (FDG PET) revealed that a subset of mice exhibited conspicuously high uptake of glucose in the ipsilateral hemisphere at 1 week post-occlusion (asymmetric group), whereas other mice showed symmetric uptake in both hemispheres (symmetric group). Thus, we aimed to understand the discrepancy between the two groups. Cerebral blood flow and histological/metabolic changes were analyzed using laser Doppler flowmetry and immunohistochemistry/Western blotting, respectively. Contrary to the increased glucose uptake observed in the ischemic cerebral hemisphere on FDG PET (p<0.001), cerebral blood flow tended to be lower in the asymmetric group than in the symmetric group (right to left ratio [%], 36.4±21.8 vs. 58.0±24.8, p=0.059). Neuronal death was observed only in the ischemic hemisphere of the asymmetric group. In contrast, astrocytes were more activated in the asymmetric group than in the symmetric group (p<0.05). Glucose transporter-1, and monocarboxylate transporter-1 were also upregulated in the asymmetric group, compared with the symmetric group (p<0.05, respectively). These results suggest that the increased FDG uptake was associated with relatively severe ischemia, and glucose transporter-1 upregulation and astrocyte activation. Glucose metabolism may thus be a compensatory mechanism in the moderately severe ischemic brain.

Silica-coated magnetic nanoparticles induce glucose metabolic dysfunction in vitro via the generation of reactive oxygen species.

Nanoparticles are a useful material in biomedicine given their unique properties and biocompatibility; however, there is increasing concern regarding the potential toxicity of nanoparticles with respect to cell metabolism. Some evidence suggests that nanoparticles can disrupt glucose and energy homeostasis. In this study, we investigated the metabolomic, transcriptomic, and integrated effects of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate dye [MNPs@SiO2(RITC)] on glucose metabolism in human embryonic kidney 293 (HEK293) cells. Using gas chromatography-tandem mass spectrometry, we analysed the metabolite profiles of 14 organic acids (OAs), 20 amino acids (AAs), and 13 fatty acids (FAs) after treatment with 0.1 or 1.0 µg/µl MNPs@SiO2(RITC) for 12 h. The metabolic changes were highly related to reactive oxygen species (ROS) generation and glucose metabolism. Additionally, effects on the combined metabolome and transcriptome or "metabotranscriptomic network" indicated a relationship between ROS generation and glucose metabolic dysfunction. In the experimental validation, MNPs@SiO2(RITC) treatment significantly decreased the amount of glucose in cells and was associated with a reduction in glucose uptake efficiency. Decreased glucose uptake efficiency was also related to ROS generation and impaired glucose metabolism in the metabotranscriptomic network. Our results suggest that exposure to high concentrations of MNPs@SiO2(RITC) produces maladaptive alterations in glucose metabolism and specifically glucose uptake as well as related metabolomic and transcriptomic disturbances via increased ROS generation. These findings further indicate that an integrated metabotranscriptomics approach provides useful and sensitive toxicological assessment for nanoparticles.

Identification of a rare homozygous c.790C>T variation in the TFB2M gene in Korean patients with autism spectrum disorder.

Mitochondrial dysfunction and subsequent enhanced oxidative stress is implicated in the pathogenesis of autism spectrum disorder (ASD). Mitochondrial transcription factor B2 (TFB2M) is an essential protein in mitochondrial gene expression. No reports have described TFB2M mutations and variations involved in any human diseases. We identified a rare homozygous c.790C>T (His264Tyr) variation in TFB2M gene in two Korean siblings with ASD by whole-exome sequencing. The roles of the TFB2M variation in the pathogenesis of ASD were investigated. Patient fibroblasts revealed increased transcription of mitochondrial genes and mitochondrial function in terms of ATP, membrane potential, oxygen consumption, and reactive oxygen species (ROS). Overexpression of the TFB2M variant in primary-cultured fibroblasts demonstrated significantly increased transcription of mitochondrial genes and mitochondrial function compared with overexpression of wild-type TFB2M. Molecular dynamics simulation of the TFB2M variant protein suggested an increase in the rigidity of the hinge region, which may cause alterations in loading and/or unloading of TFB2M on target DNA. Our results suggest that augmentation of mitochondrial gene expression and subsequent enhancement of mitochondrial function may be associated with the pathogenesis of ASD in Korean patients.

Expanding the genetic code of Mus musculus.

Here we report the expansion of the genetic code of Mus musculus with various unnatural amino acids including Nɛ-acetyl-lysine. Stable integration of transgenes encoding an engineered Nɛ-acetyl-lysyl-tRNA synthetase (AcKRS)/tRNAPyl pair into the mouse genome enables site-specific incorporation of unnatural amino acids into a target protein in response to the amber codon. We demonstrate temporal and spatial control of protein acetylation in various organs of the transgenic mouse using a recombinant green fluorescent protein (GFPuv) as a model protein. This strategy will provide a powerful tool for systematic in vivo study of cellular proteins in the most commonly used mammalian model organism for human physiology and disease.

Cross-strand binding of TFAM to a single mtDNA molecule forms the mitochondrial nucleoid.

Mammalian mitochondrial DNA (mtDNA) is packaged by mitochondrial transcription factor A (TFAM) into mitochondrial nucleoids that are of key importance in controlling the transmission and expression of mtDNA. Nucleoid ultrastructure is poorly defined, and therefore we used a combination of biochemistry, superresolution microscopy, and electron microscopy to show that mitochondrial nucleoids have an irregular ellipsoidal shape and typically contain a single copy of mtDNA. Rotary shadowing electron microscopy revealed that nucleoid formation in vitro is a multistep process initiated by TFAM aggregation and cross-strand binding. Superresolution microscopy of cultivated cells showed that increased mtDNA copy number increases nucleoid numbers without altering their sizes. Electron cryo-tomography visualized nucleoids at high resolution in isolated mammalian mitochondria and confirmed the sizes observed by superresolution microscopy of cell lines. We conclude that the fundamental organizational unit of the mitochondrial nucleoid is a single copy of mtDNA compacted by TFAM, and we suggest a packaging mechanism.

Perturbation of NCOA6 leads to dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is a progressive heart disease characterized by left ventricular dilation and contractile dysfunction. Although many candidate genes have been identified with mouse models, few of them have been shown to be associated with DCM in humans. Germline depletion of Ncoa6, a nuclear hormone receptor coactivator, leads to embryonic lethality and heart defects. However, it is unclear whether Ncoa6 mutations cause heart diseases in adults. Here, we report that two independent mouse models of NCOA6 dysfunction develop severe DCM with impaired mitochondrial function and reduced activity of peroxisome proliferator-activated receptor δ (PPARδ), an NCOA6 target critical for normal heart function. Sequencing of NCOA6-coding regions revealed three independent nonsynonymous mutations present in 5 of 50 (10%) patients with idiopathic DCM (iDCM). These data suggest that malfunction of NCOA6 can cause DCM in humans.

Proposed cytotoxic mechanisms of the saffron carotenoids crocin and crocetin on cancer cell lines.

We investigated the cytotoxic activities of crocin and crocetin, 2 major carotenoids isolated from the stigma of Crocus sativus (saffron), on 5 human cancer cell lines and proposed their possible anticancer mechanisms. Crocetin, a glycosylated carotenoid, showed approximately 5- to 18-fold higher cytotoxicity than crocin, a carboxylic carotenoid (IC50 of 0.16-0.61 mmol/L for crocetin vs. 2.0-5.5 mmol/L for crocin). This suggests that structural differences account for the different efficacies between them. Fluorescence-activated cell sorting (FACS) analysis showed that crocetin induced a significant level of cellular reactive oxygen species (ROS) in HeLa cells, whereas crocin did not. This ROS induction supported the cytotoxicity of crocetin, but not of crocin. A significant activation of nuclear factor erythroid 2-related factor 2 (Nrf2) was observed in both HeLa cells treated with crocin and crocetin: a 3.0-fold increase by 1 mmol/L crocetin and a 1.6-fold increase by 0.8 mmol/L crocin compared to the control. Furthermore, both crocetin and crocin reduced the protein expression of lactate dehydrogenase A (LDHA), one of the targets for chemoprevention in cancer cells, by 34.2% and 10.5%, respectively, compared to the control in HeLa cells. These findings suggest that crocetin and crocin have different mechanisms for their observed cytotoxicity in cancer cell lines.

The immune-stimulating peptide WKYMVm has therapeutic effects against ulcerative colitis.

In this study, we examined the therapeutic effects of an immune-stimulating peptide, WKYMVm, in ulcerative colitis. The administration of WKYMVm to dextran sodium sulfate (DSS)-treated mice reversed decreases in body weight, bleeding score and stool score in addition to reversing DSS-induced mucosa destruction and shortened colon. The WKYMVm-induced therapeutic effect against ulcerative colitis was strongly inhibited by a formyl peptide receptor (FPR) 2 antagonist, WRWWWW, indicating the crucial role of FPR2 in this effect. Mechanistically, WKYMVm effectively decreases intestinal permeability by stimulating colon epithelial cell proliferation. WKYMVm also strongly decreases interleukin-23 and transforming growth factor-ß production in the colon of DSS-treated mice. We suggest that the potent immune-modulating peptide WKYMVm and its receptor FPR2 may be useful in the development of efficient therapeutic agents against chronic intestinal inflammatory diseases.

MTERF1 binds mtDNA to prevent transcriptional interference at the light-strand promoter but is dispensable for rRNA gene transcription regulation.

Mitochondrial transcription termination factor 1, MTERF1, has been reported to couple rRNA gene transcription initiation with termination and is therefore thought to be a key regulator of mammalian mitochondrial ribosome biogenesis. The prevailing model is based on a series of observations published over the last two decades, but no in vivo evidence exists to show that MTERF1 regulates transcription of the heavy-strand region of mtDNA containing the rRNA genes. Here, we demonstrate that knockout of Mterf1 in mice has no effect on mitochondrial rRNA levels or mitochondrial translation. Instead, loss of Mterf1 influences transcription initiation at the light-strand promoter, resulting in a decrease of de novo transcription manifested as reduced 7S RNA levels. Based on these observations, we suggest that MTERF1 does not regulate heavy-strand transcription, but rather acts to block transcription on the opposite strand of mtDNA to prevent transcription interference at the light-strand promoter.

TWINKLE is an essential mitochondrial helicase required for synthesis of nascent D-loop strands and complete mtDNA replication.

Replication of the mammalian mitochondrial DNA (mtDNA) is dependent on the minimal replisome, consisting of the heterotrimeric mtDNA polymerase (POLG), the hexameric DNA helicase TWINKLE and the tetrameric single-stranded DNA-binding protein (mtSSB). TWINKLE has been shown to unwind DNA during the replication process and many disease-causing mutations have been mapped to its gene. Patients carrying Twinkle mutations develop multiple deletions of mtDNA, deficient respiratory chain function and neuromuscular symptoms. Despite its importance in human disease, it has been unclear whether TWINKLE is the only replicative DNA helicase in mammalian mitochondria. Furthermore, a substantial portion of mtDNA replication events is prematurely terminated at the end of mitochondrial control region (D-loop) and it is unknown whether TWINKLE also has a role in this abortive replication. Here, we present a conditional mouse knockout for Twinkle and demonstrate that TWINKLE is essential for mouse embryonic development and thus is the only replicative DNA helicase in mammalian mitochondria. Conditional knockout of Twinkle results in severe and rapid mtDNA depletion in heart and skeletal muscle. No replication intermediates or deleted mtDNA molecules are observed after Twinkle knockout, suggesting that TWINKLE once loaded is very processive. We also demonstrate that TWINKLE is essential for nascent H-strand synthesis in the D-loop, thus showing that there is no separate DNA helicase responsible for replication of this region. Our data thus suggest that the relative levels of abortive D-loop synthesis versus complete mtDNA replication are regulated and may provide a mechanism to control progression to complete mtDNA replication.

MTERF3 regulates mitochondrial ribosome biogenesis in invertebrates and mammals.

Regulation of mitochondrial DNA (mtDNA) expression is critical for the control of oxidative phosphorylation in response to physiological demand, and this regulation is often impaired in disease and aging. We have previously shown that mitochondrial transcription termination factor 3 (MTERF3) is a key regulator that represses mtDNA transcription in the mouse, but its molecular mode of action has remained elusive. Based on the hypothesis that key regulatory mechanisms for mtDNA expression are conserved in metazoans, we analyzed Mterf3 knockout and knockdown flies. We demonstrate here that decreased expression of MTERF3 not only leads to activation of mtDNA transcription, but also impairs assembly of the large mitochondrial ribosomal subunit. This novel function of MTERF3 in mitochondrial ribosomal biogenesis is conserved in the mouse, thus we identify a novel and unexpected role for MTERF3 in coordinating the crosstalk between transcription and translation for the regulation of mammalian mtDNA gene expression.

LRPPRC is necessary for polyadenylation and coordination of translation of mitochondrial mRNAs.

Regulation of mtDNA expression is critical for maintaining cellular energy homeostasis and may, in principle, occur at many different levels. The leucine-rich pentatricopeptide repeat containing (LRPPRC) protein regulates mitochondrial mRNA stability and an amino-acid substitution of this protein causes the French-Canadian type of Leigh syndrome (LSFC), a neurodegenerative disorder characterized by complex IV deficiency. We have generated conditional Lrpprc knockout mice and show here that the gene is essential for embryonic development. Tissue-specific disruption of Lrpprc in heart causes mitochondrial cardiomyopathy with drastic reduction in steady-state levels of most mitochondrial mRNAs. LRPPRC forms an RNA-dependent protein complex that is necessary for maintaining a pool of non-translated mRNAs in mammalian mitochondria. Loss of LRPPRC does not only decrease mRNA stability, but also leads to loss of mRNA polyadenylation and the appearance of aberrant mitochondrial translation. The translation pattern without the presence of LRPPRC is misregulated with excessive translation of some transcripts and no translation of others. Our findings point to the existence of an elaborate machinery that regulates mammalian mtDNA expression at the post-transcriptional level.

Mitochondrial DNA mutations in disease and aging.

The small mammalian mitochondrial DNA (mtDNA) is very gene dense and encodes factors critical for oxidative phosphorylation. Mutations of mtDNA cause a variety of human mitochondrial diseases and are also heavily implicated in age-associated disease and aging. There has been considerable progress in our understanding of the role for mtDNA mutations in human pathology during the last two decades, but important mechanisms in mitochondrial genetics remain to be explained at the molecular level. In addition, mounting evidence suggests that most mtDNA mutations may be generated by replication errors and not by accumulated damage.

MTERF4 regulates translation by targeting the methyltransferase NSUN4 to the mammalian mitochondrial ribosome.

Precise control of mitochondrial DNA gene expression is critical for regulation of oxidative phosphorylation capacity in mammals. The MTERF protein family plays a key role in this process, and its members have been implicated in regulation of transcription initiation and site-specific transcription termination. We now demonstrate that a member of this family, MTERF4, directly controls mitochondrial ribosomal biogenesis and translation. MTERF4 forms a stoichiometric complex with the ribosomal RNA methyltransferase NSUN4 and is necessary for recruitment of this factor to the large ribosomal subunit. Loss of MTERF4 leads to defective ribosomal assembly and a drastic reduction in translation. Our results thus show that MTERF4 is an important regulator of translation in mammalian mitochondria.