Animal naming test is a simple and valid tool for detecting covert hepatic encephalopathy and predicting outcomes in Chinese-speaking regions: a preliminary study

BACKGROUND AND AIMS

Hepatic encephalopathy (HE) implies high morbidity and mortality. The assessment of covert HE (CHE) [i.e. minimal HE (MHE) plus grade 1 HE] is often neglected in Taiwan. Therefore, the aim was to investigate the potential of the animal naming test (ANT1 and simplified ANT1 (S-ANT1)) for assessing CHE in Chinese-speaking regions, specifically Taiwan.

METHODS

A prospective cohort study was conducted, comprising 65 cirrhotic patients and 29 healthy controls (relatives of the patients). Patients were followed up every three months and censored after two years or until death. Hospitalization for overt HE (OHE) and mortality were considered. All subjects underwent ANT1, psychometric HE score (PHES), and mini-mental state examination (MMSE). The patients underwent an electroencephalogram (EEG) to detect slowing indicative of MHE. Cut-off values for ANT1 and S-ANT1 were assessed by ROC analysis and Youden's index, considering CHE as a reference. The prognostic values for OHE and OHE-free survival were assessed.

RESULTS

Preliminary analysis confirmed that PHES ≤-4 is a good discriminant point for abnormal results. CHE was found in 29 patients: 9 had MHE (PHES ≤ -4 or altered EEG) and 20 had grade 1 HE. ANT1 and S-ANT1 were found to have diagnostic values for CHE: AUC = 0.807, 0.786; cut off: 18 and 19, respectively. ANT1 and S-ANT1 were found to have prognostic value for OHE, number of hospitalization episodes for OHE, and OHE recurrence-free survival.

CONCLUSIONS

ANT1 shows promise as a tool for CHE detection, quantification, and follow-up in Taiwan and other Chinese-speaking regions.Key messagesThe animal naming test (ANT1) is a simple and valid semantic fluency test that can be easily performed in outpatient or bedside settings in one minute and can also be used as a tool for covert hepatic encephalopathy (CHE) detection, quantification, and follow-up in Taiwan, other Chinese-speaking regions, and many other countries.The diagnostic value of ANT1 and S-ANT1 for CHE were found to be significant, with area under the receiver operating characteristic curve (AUROC) values of 0.807 and 0.786 respectively, and cut-off scores of 18 and 19.ANT1 and S-ANT1 have prognostic value for the first breakthrough of overt hepatic encephalopathy (OHE), number of hospitalization episodes for OHE, and OHE recurrence-free survival, independent of the MELD score.

Herpes Simplex Type 1 UL43 Multiple Membrane-Spanning Protein Increases Energy Metabolism in Host Cells through Interacting with ARL2

Non-essential proteins for viral replication affect host cell metabolism, while the function of the UL43 protein of herpes simplex virus 1 (HSV-1) is not clear. Herein, we performed a comprehensive microarray analysis of HUVEC cells infected with HSV-1 and its UL43-deficient mutant and found significant variation in genes associated with cellular energy metabolic pathways. The localization of UL43 protein in host cells and how it affects cellular energy metabolism pathways were further investigated. Internalization analysis showed that the UL43 protein could be endocytosis-mediated by YPLF motif (aa144-147) and localized to mitochondria. At the same time, more ATP was produced by coupling with mitochondrial small G protein ARF-like 2 (ARL2) GTPase, which triggered the phosphorylation of ANT1 (SLC25A4) to affect the opening degree of mitochondrial permeability transition pore (mPTP), and significantly promoted the aerobic oxidation and oxidative phosphorylation of glucose. Our study shows that UL43 mediates the improvement of host cell metabolism after HSV-1 infection. Additionally, UL43 protein could be a valuable ATP-stimulating factor for mammalian cells.

Identification of ADP/ATP Translocase 1 as a Novel Glycoprotein and Its Association with Parkinson's Disease

Protein glycosylation plays a crucial role in central nervous system, and abnormal glycosylation has major implications for human diseases. This study aims to evaluate an etiological implication of the variation in glycosylation for Parkinson's disease (PD), a neurodegenerative disorder. Based on a PD mouse model constructed by the intraperitoneal injection with 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine, glycosylation variation was accessed using biotinylated lectin of dolichos biflorus agglutinin (DBA) specific for the exposed N-acetylgalactosamine linked to glycoprotein. Consequently, a glycoprotein with a significantly reduced N-acetylgalactosamination was identified as ADP/ATP translocase 1 (ANT1) by lectin affinity chromatography coupled with MALDI-TOF MS/MS (mass spectrometry), and confirmed by the analysis of dual co-immunofluorescence and Western blot. A tissue-specific distribution of de-N-acetylgalactosaminated ANT1 was found to be correlated with high risk of PD. At cellular level, an obvious co-aggregation between ANT1 and DBA was only found in the MPP⁺-induced PD-like cell model using dual co-immunofluorescence. Thus, we found that ANT1 was a potential glycoprotein with terminal N-acetylgalactosamine moiety, and the variation of glycosylation in ANT1 was associated with PD. This investigation provides an innovative insight in protein glycosylation with PD pathogenesis.

Exposure to benzo(a)pyrene suppresses mitophagy via ANT1-PINK1-Parkin pathway in ovarian corpus luteum during early pregnancy

Exposure to benzo (a)pyrene (BaP) has been confirmed to interfere with embryo implantation. As the primary organ of progesterone synthesis during early pregnancy, the ovarian corpus luteum (CL) is essential for embryo implantation and pregnancy maintenance. We previously demonstrated that BaP impaired luteal function, but the molecular mechanism remains unclear. In CL cells, mitochondria are the main sites of progesterone synthesis. Mitophagy, a particular type of autophagy, regulates mitochondrial quality by degrading damaged mitochondria and ensuring the homeostasis of cell physiology. Therefore, the present study investigated the effects and the potential molecular mechanisms of BaP on ovarian mitophagy during early pregnancy. We found that BaP and its metabolite, BPDE, inhibited autophagy and PINK1/Parkin-mediated mitophagy in the pregnant ovaries and luteinized granulosa cell, KGN. Notably, adenine nucleotide translocator 1 (ANT1), a crucial mediator of PINK1-dependent mitophagy, was suppressed by BaP and BPDE both in vivo and in vitro. The inhibition of ANT1 leads to the decrease in the PINK1 bound to the outer membrane of mitochondria and consequently reduces recruitment of Parkin to the mitochondria, which is required for the subsequent clearance of mitochondria. Meanwhile, exposure to BPDE also damaged mitochondrial function, causing the reduction in mitochondrial potential and ATP production. Overexpression of ANT1 in KGN cells partially relieved the inhibition of mitophagy caused by BPDE, restored mitochondrial function and expression of hormone synthesis-associated genes. Collectively, our study firstly clarified that BaP and BPDE suppress mitophagy of CL cells via the ANT1-PINK1-Parkin pathway, which provides a new insight to explore the detailed mechanism of the BaP-induced ovarian toxicity.

Conformational change of adenine nucleotide translocase-1 mediates cisplatin resistance induced by EBV-LMP1

Adenine nucleotide translocase-1 (ANT1) is an ADP/ATP transporter protein located in the inner mitochondrial membrane. ANT1 is involved not only in the processes of ADP/ATP exchange but also in the composition of the mitochondrial membrane permeability transition pore (mPTP); and the function of ANT1 is closely related to its own conformational changes. Notably, various viral proteins can interact directly with ANT1 to influence mitochondrial membrane potential by regulating the opening of mPTP, thereby affecting tumor cell fate. The Epstein-Barr virus (EBV) encodes the key tumorigenic protein, latent membrane protein 1 (LMP1), which plays a pivotal role in promoting therapeutic resistance in related tumors. In our study, we identified a novel mechanism for EBV-LMP1-induced alteration of ANT1 conformation in cisplatin resistance in nasopharyngeal carcinoma. Here, we found that EBV-LMP1 localizes to the inner mitochondrial membrane and inhibits the opening of mPTP by binding to ANT1, thereby favoring tumor cell survival and drug resistance. The ANT1 conformational inhibitor carboxyatractyloside (CATR) in combination with cisplatin improved the chemosensitivity of EBV-LMP1-positive cells. This finding confirms that ANT1 is a novel therapeutic target for overcoming cisplatin resistance in the future.

ADP/ATP translocase 1 protects against an α-synuclein-associated neuronal cell damage in Parkinson's disease model

BACKGROUND

ADP/ATP translocase 1 (ANT1) is involved in the exchange of cytosolic ADP and mitochondrial ATP, and its defection plays an important role in mitochondrial pathogenesis. To reveal an etiological implication of ANT1 for Parkinson's disease (PD), a neurodegenerative disorder, a mouse model treated with 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine and neuroblastoma cell model induced by 1-methyl-4-pehny1-pyridine were utilized in this study.

RESULTS

The tissue-specific abundance in ANT1 in mouse brains was accessed using the analysis of Western blot and immunohistochemistry. Down-regulated soluble ANT1 was found to be correlated with PD, and ANT1 was associated with PD pathogenesis via forming protein aggregates with α-synuclein. This finding was confirmed at cellular level using neuroblastoma cell models. ANT1 supplement in neuronal cells revealed the protective roles of ANT1 against cytotoxicity caused by MPP⁺. Protein interaction assay, coupled with the analysis of LC-MS/MS, silver-stained SDS-PAGE and Western blot against anti-ANT1 antibody respectively, illustrated the interaction of ANT1 with α-synuclein using the expressed α-synuclein as a bite. Additionally, a significant increasing ROSs was detected in the MPP⁺-treated cells.

CONCLUSIONS

This study indicated that ANT1 was a potentially causative factor of PD, and led to neuropathogenic injury via promoting the formation of protein aggregates with α-synuclein. This investigation potentially promotes an innovative understanding of ANT1 on the etiology of PD and provides valuable information on developing potential drug targets in PD treatment or reliable biomarkers in PD prognostication.

Ischemia Injury induces mPTP opening by reducing Sirt3

Mitochondrial permeability transition pore (mPTP) opening is critical to mitochondrial apoptosis during ischemic injury. Sirtuin 3 (Sirt3) is a mitochondrial deacetylase known to play a major role in stress resistance and cell death. Our previous studies have shown that Sirt3 activates superoxide dismutase 2 and forkhead box O3a to reduce cellular reactive oxygen species. However, it is unclear the interaction between Sirt3 and mPTP and the roles they play in ischemic stroke. We used the middle cerebral artery occlusion (MCAO) model, a mouse model of stroke, to examine Sirt3 and mPTP-related protein levels. We then applied lentivirus packaged Sirt3 overexpression in HT22 cells, a mouse hippocampal neuronal cell line, to investigate the underlying mechanism. We found Sirt3 protein level was decreased in the penumbra area in MCAO mice, along with an increase in mPTP related proteins, namely voltage-dependent anion channel 1 (VDAC1) and adenine nucleotide translocator 1 (ANT1). Sirt3 overexpression suppressed the increase in VDAC1, ANT1 and cleaved caspase 3 that were induced by the serum and glucose deprivation (SGD) condition. Our studies suggest that ischemic injury induced mPTP opening and apoptosis by reducing Sirt3. It helps to identify new therapeutic targets for ischemic stroke.

The inner mitochondrial membrane protein ANT1 modulates IL-6 expression via the JNK pathway in macrophages

Mitochondria are increasingly associated with inflammation. Here, we focus on the relationship between inflammation and adenine nucleotide translocator type 1 (ANT1), which is localized in the mitochondrial inner membrane. ANT1 plays an important role in oxidative phosphorylation, and mutations in the ANT1 gene are responsible for mitochondrial diseases. Ample studies have demonstrated that ANT1 has a critical role in cardiomyocytes and neurons, but little has been reported on its functions in immune cells. We knocked down ANT1 expression in macrophages and examined inflammatory cytokine expression after lipopolysaccharide stimulation. ANT1 knockdown reduces the expression of IL-6. JNK, upstream of IL-6, is downregulated, but other MAP kinases and the NF-κB signaling remain unchanged. These results suggest that ANT1 modulates IL-6 expression through JNK in macrophages.

Dominance of yeast aac2R96H and aac2R252G mutations, equivalent to pathological mutations in ant1, is due to gain of function

The mitochondrial ADP/ATP carrier is a nuclear encoded protein, which catalyzes the exchange of ATP generated in mitochondria with ADP produced in the cytosol. In humans, mutations in the major ADP/ATP carrier gene, ANT1, are involved in several degenerative mitochondrial pathologies, leading to instability of mitochondrial DNA. Recessive mutations have been associated with mitochondrial myopathy and cardiomyopathy whereas dominant mutations have been associated with autosomal dominant Progressive External Ophtalmoplegia (adPEO). Recently, two de novo dominant mutations, R80H and R235G, leading to extremely severe symptoms, have been identified. In order to evaluate if the dominance is due to haploinsufficiency or to a gain of function, the two mutations have been introduced in the equivalent positions of the AAC2 gene, the yeast orthologue of human ANT1, and their dominant effect has been studied in heteroallelic strains, containing both one copy of wild type AAC2 and one copy of mutant aac2 allele. Through phenotypic characterization of these yeast models we showed that the OXPHOS phenotypes in the heteroallelic strains were more affected than in the hemiallelic strain indicating that the dominant trait of the two mutations is due to gain of function.

Two new cases of mitochondrial myopathy with exercise intolerance, hyperlactatemia and cardiomyopathy, caused by recessive SLC25A4 mutations

We report the clinical, morphological and molecular features of two patients with autosomal recessive SLC25A4 (ANT1) gene mutations. Furthermore, all previously published cases are reviewed to identify valuable features for future diagnosis. Patients present a common phenotype with exercise intolerance, hyperlactatemia, and hypertrophic cardiomyopathy. Muscle biopsies show wide sub-sarcolemmal mitochondrial aggregates, and increased activities of all respiratory chain complexes. The phenotype of recessive SLC25A4 (ANT1) mutations although rare, is homogenous and easily recognizable and could help orientate the molecular analysis in adults with exercise intolerance associated with hyperlactatemia.

Cdkal1, a type 2 diabetes susceptibility gene, regulates mitochondrial function in adipose tissue

Objectives

Understanding how loci identified by genome wide association studies (GWAS) contribute to pathogenesis requires new mechanistic insights. Variants within CDKAL1 are strongly linked to an increased risk of developing type 2 diabetes and obesity. Investigations in mouse models have focused on the function of Cdkal1 as a tRNA^Lys modifier and downstream effects of Cdkal1 loss on pro-insulin translational fidelity in pancreatic β−cells. However, Cdkal1 is broadly expressed in other metabolically relevant tissues, including adipose tissue. In addition, the Cdkal1 homolog Cdk5rap1 regulates mitochondrial protein translation and mitochondrial function in skeletal muscle. We tested whether adipocyte-specific Cdkal1 deletion alters systemic glucose homeostasis or adipose mitochondrial function independently of its effects on pro-insulin translation and insulin secretion.

Methods

We measured mRNA levels of type 2 diabetes GWAS genes, including Cdkal1, in adipose tissue from lean and obese mice. We then established a mouse model with adipocyte-specific Cdkal1 deletion. We examined the effects of adipose Cdkal1 deletion using indirect calorimetry on mice during a cold temperature challenge, as well as by measuring cellular and mitochondrial respiration in vitro. We also examined brown adipose tissue (BAT) mitochondrial morphology by electron microscopy. Utilizing co-immunoprecipitation followed by mass spectrometry, we performed interaction mapping to identify new CDKAL1 binding partners. Furthermore, we tested whether Cdkal1 loss in adipose tissue affects total protein levels or accurate Lys incorporation by tRNA^Lys using quantitative mass spectrometry.

Results

We found that Cdkal1 mRNA levels are reduced in adipose tissue of obese mice. Using adipose-specific Cdkal1 KO mice (A-KO), we demonstrated that mitochondrial function is impaired in primary differentiated brown adipocytes and in isolated mitochondria from A-KO brown adipose tissue. A-KO mice displayed decreased energy expenditure during 4 °C cold challenge. Furthermore, mitochondrial morphology was highly abnormal in A-KO BAT. Surprisingly, we found that lysine codon representation was unchanged in Cdkal1 A-KO adipose tissue. We identified novel protein interactors of CDKAL1, including SLC25A4/ANT1, an inner mitochondrial membrane ADP/ATP translocator. ANT proteins can account for the UCP1-independent basal proton leak in BAT mitochondria. Cdkal1 A-KO mice had increased ANT1 protein levels in their white adipose tissue.

Conclusions

Cdkal1 is necessary for normal mitochondrial morphology and function in adipose tissue. These results suggest that the type 2 diabetes susceptibility gene CDKAL1 has novel functions in regulating mitochondrial activity.

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Cdkal1 is a gene most strongly expressed in tissues with high mitochondrial content.

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Cdkal1 is required for normal mitochondrial morphology and function.

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Deletion of Cdkal1 in adipose tissue impairs the thermogenic response to a cold challenge.

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Cdkal1 interacts with ANT1, a mitochondrial ATP/ADP transporter.

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Loss of Cdkal1 does not affect protein translation as predicted for a tRNA modifying enzyme.

Mitochondrial ANT-1 related adPEO leading to cognitive impairment: is there a link?

ANT1 is one of the nuclear genes responsible of autosomal dominant progressive external ophthalmoplegia (adPEO) with mitochondrial DNA multiple deletions. The course of ANT1- related adPEO is relatively benign, symptoms being generally restricted to skeletal muscle. Here we report the case of an Italian 74 years old woman with ANT1-related adPEO and dementia. Further studies are needed to assess the prevalence of central neurological manifestations in ANT1 mitochondrial disease.

Mitochondrial energy deficiency leads to hyperproliferation of skeletal muscle mitochondria and enhanced insulin sensitivity

Diabetes is associated with impaired glucose metabolism in the presence of excess insulin. Glucose and fatty acids provide reducing equivalents to mitochondria to generate energy, and studies have reported mitochondrial dysfunction in type II diabetes patients. If mitochondrial dysfunction can cause diabetes, then we hypothesized that increased mitochondrial metabolism should render animals resistant to diabetes. This was confirmed in mice in which the heart-muscle-brain adenine nucleotide translocator isoform 1 (ANT1) was inactivated. ANT1-deficient animals are insulin-hypersensitive, glucose-tolerant, and resistant to high fat diet (HFD)-induced toxicity. In ANT1-deficient skeletal muscle, mitochondrial gene expression is induced in association with the hyperproliferation of mitochondria. The ANT1-deficient muscle mitochondria produce excess reactive oxygen species (ROS) and are partially uncoupled. Hence, the muscle respiration under nonphosphorylating conditions is increased. Muscle transcriptome analysis revealed the induction of mitochondrial biogenesis, down-regulation of diabetes-related genes, and increased expression of the genes encoding the myokines FGF21 and GDF15. However, FGF21 was not elevated in serum, and FGF21 and UCP1 mRNAs were not induced in liver or brown adipose tissue (BAT). Hence, increased oxidation of dietary-reducing equivalents by elevated muscle mitochondrial respiration appears to be the mechanism by which ANT1-deficient mice prevent diabetes, demonstrating that the rate of mitochondrial oxidation of calories is important in the etiology of metabolic disease.

The regulator of calcineurin 1 increases adenine nucleotide translocator 1 and leads to mitochondrial dysfunctions

The over‐expression of regulator of calcineurin 1 isoform 1 (RCAN1.1) has been implicated in mitochondrial dysfunctions of Alzheimer's disease; however, the mechanism linking RCAN1.1 over‐expression and the mitochondrial dysfunctions remains unknown. In this study, we use human neuroblastoma SH‐SY5Y cells stably expressing RCAN1.1S and rat primary neurons infected with RCAN1.1S expression lentivirus to study the association of RCAN1 with mitochondrial functions. Our study here showed that the over‐expression of RCAN1.1S remarkably up‐regulates the expression of adenine nucleotide translocator (ANT1) by stabilizing ANT1 mRNA. The increased ANT1 level leads to accelerated ATP–ADP exchange rate, more Ca²⁺‐induced mitochondrial permeability transition pore opening, increased cytochrome c release, and eventually cell apoptosis. Furthermore, knockdown of ANT1 expression brings these mitochondria perturbations caused by RCAN1.1S back to normal. The effect of RCAN1.1S on ANT1 was independent of its inhibition on calcineurin. This study elucidated a novel function of RCAN1 in mitochondria and provides a molecular basis for the RCAN1.1S over‐expression‐induced mitochondrial dysfunctions and neuronal apoptosis.

ANT1-mediated fatty acid-induced uncoupling as a target for improving myocellular insulin sensitivity

AIMS/HYPOTHESIS

Dissipating energy via mitochondrial uncoupling has been suggested to contribute to enhanced insulin sensitivity. We hypothesised that skeletal muscle mitochondria of endurance-trained athletes have increased sensitivity for fatty acid (FA)-induced uncoupling, which is driven by the mitochondrial protein adenine nucleotide translocase 1 (ANT1).

METHODS

Capacity for FA-induced uncoupling was measured in endurance-trained male athletes (T) and sedentary young men (UT) in an observational study and also in isolated skeletal muscle mitochondria from Zucker diabetic fatty (ZDF) rats and C2C12 myotubes following small interfering RNA (siRNA)-mediated gene silencing of ANT1. Thus, fuelled by glutamate/succinate (fibres) or pyruvate (mitochondria and myotubes) and in the presence of oligomycin to block ATP synthesis, increasing levels of oleate (fibres) or palmitate (mitochondria and myotubes) were automatically titrated while respiration was monitored. Insulin sensitivity was measured by hyperinsulinaemic-euglycaemic clamp in humans and via insulin-stimulated glucose uptake in myotubes.

RESULTS

Skeletal muscle from the T group displayed increased sensitivity to FA-induced uncoupling (p = 0.011) compared with muscle from the UT group, and this was associated with elevated insulin sensitivity (p = 0.034). ANT1 expression was increased in T (p = 0.013). Mitochondria from ZDF rats displayed decreased sensitivity for FA-induced uncoupling (p = 0.008). This difference disappeared in the presence of the adenine nucleotide translocator inhibitor carboxyatractyloside. Partial knockdown of ANT1 in C2C12 myotubes decreased sensitivity to the FA-induced uncoupling (p = 0.008) and insulin-stimulated glucose uptake (p = 0.025) compared with controls.

CONCLUSIONS/INTERPRETATION

Increased sensitivity to FA-induced uncoupling is associated with enhanced insulin sensitivity and is affected by ANT1 activity in skeletal muscle. FA-induced mitochondrial uncoupling may help to preserve insulin sensitivity in the face of a high supply of FAs.

TRIAL REGISTRATION

www.trialregister.nl NTR2002.

Novel phenotypes related to the breeding of purple-fruited tomatoes and effect of peel extracts on human cancer cell proliferation

The production of anthocyanins in the tomato (Solanum lycopersicum L.) fruit is normally absent or poor, but a number of mutants or introgression lines are known to increase anthocyanin levels in vegetative and reproductive tissues. Through conventional breeding, a genetic combination was obtained with the remarkable phenotype of a deep purple fruit pigmentation, due to an accumulation of anthocyanins on the peel. Such a genotype was named Sun Black (SB) as a consequence of its sensitivity to light induction. When characterized for morpho-agronomic traits, SB plants showed increased fertility. Purple fruits displayed an arrangement of the epicarp cells different from normal tomatoes, a feature that could account for different mechanical properties and shelf-life potential. The SB genotype and, to a lesser extent, its single mutant parents showed the capacity to accumulate anthocyanins in the seedling root when grown under light. This phenotype, which was greatly improved by the addition of sucrose to the germination medium, proved to be useful as selection index and gave new insights for in vitro production of anthocyanin extracts. To assess the nutraceutical potential of purple tomatoes, we tested the activity of SB skin extracts on the proliferation of two human cancer cells lines. Cell proliferation was significantly inhibited by SB extract in a dose-dependent manner. When the bioactivity of SB extracts was compared with that of other anthocyanin-containing fruits or vegetables, a significant "Extract*Line" interaction was evidenced, suggesting a crucial role for the extract composition in terms of anthocyanidins and other eventual cell growth-inhibiting compounds.