Mitochondrial Protein Synthesis Research Articles

Inhibition of Yeast Growth by Tryptamine and Recovery with Tryptophan

Background:Tryptamine, a biogenic monoamine that is present in trace levels in the mammalian central nervous system, has probable roles as a neurotransmitter and/or a neuromodulator and may be associated with various neuropsychiatric disorders. One of the ways tryptamine may affect the body is by the competitive inhibition of the attachment of tryptophan to tryptophanyl tRNA synthetases.Methods:This study has explored the effects of tryptamine on growth of six yeast species (Saccharomyces cerevisiae, Candida glabrata, C. krusei, C. dubliniensis, C. tropicalis and C. lusitaniae) in media with glucose or ethanol as the carbon source, as well as recovery of growth inhibition by the addition of tryptophan.Results:Tryptamine was found to have an inhibitory effect on respiratory growth of all yeast species when grown with ethanol as the carbon source. Tryptamine also inhibited fermentative growth of Saccharomyces cerevisiae, C. krusei and C. tropicalis with glucose as the carbon source. In most cases the inhibitory effects were reduced by added tryptophan.Conclusion:The results obtained in this study are consistent with tryptamine competing with tryptophan to bind mitochondrial and cytoplasmic tryptophanyl tRNA synthetases in yeast: effects on mitochondrial and cytoplasmic protein synthesis can be studied as a function of growth with glucose or ethanol as a carbon source. Of the yeast species tested, there is variation in the sensitivity to tryptamine and the rescue by tryptophan. The current study suggests appropriate yeast strains and approaches for further studies.

Comparative pharmacoproteomics reveals potential targets for berberine, a promising therapy for colorectal cancer

Berberine (BBR), a natural isoquinoline alkaloid, has been shown to be a promising therapeutic agent for colorectal cancer (CRC), but the molecular mechanism remains unclear. Here, we used mass spectrometry-based label-free proteomics to explore the potential targets of BBR in CRC cells. Comprehensive proteomic profiles demonstrated that of 8051 identified proteins, 503 and 277 differentially expressed proteins (DEPs) were screened out of CACO2 and LOVO cells, respectively. 83 DEPs were overlapped and most of these were down-regulated. A pathway enrichment analysis pinpointed mitochondrial translation, respiratory electron transport and the citric acid (TCA) cycle as biological effectors. The data of proteomics was subsequently confirmed by citrate synthase (CS), Tu translation elongation factor (TUFM), pentatricopeptide repeat domain 3 (PTCD3) and mitochondrial ribosomal protein L48 (MRPL 48) protein measurement. CS protein expression in CRC cells and tissues was higher than it was in normal specimens. Additionally, forcible downregulation of CS led to remarkable cell proliferation inhibition. Taken together, we concluded that the anticancer effects of BBR are attributable to mitochondrial protein synthesis, TCA and respiratory electron transport inhibition and that CS might be a useful therapeutic target in CRC treatment.

An inventory of interactors of the human HSP60/HSP10 chaperonin in the mitochondrial matrix space.

The HSP60/HSP10 chaperonin assists folding of proteins in the mitochondrial matrix space by enclosing them in its central cavity. The chaperonin forms part of the mitochondrial protein quality control system. It is essential for cellular survival and mutations in its subunits are associated with rare neurological disorders. Here we present the first survey of interactors of the human mitochondrial HSP60/HSP10 chaperonin. Using a protocol involving metabolic labeling of HEK293 cells, cross-linking, and immunoprecipitation of HSP60, we identified 323 interacting proteins. As expected, the vast majority of these proteins are localized to the mitochondrial matrix space. We find that approximately half of the proteins annotated as mitochondrial matrix proteins interact with the HSP60/HSP10 chaperonin. They cover a broad spectrum of functions and metabolic pathways including the mitochondrial protein synthesis apparatus, the respiratory chain, and mitochondrial protein quality control. Many of the genes encoding HSP60 interactors are annotated as disease genes. There is a correlation between relative cellular abundance and relative abundance in the HSP60 immunoprecipitates. Nineteen abundant matrix proteins occupy more than 60% of the HSP60/HSP10 chaperonin capacity. The reported inventory of interactors can form the basis for interrogating which proteins are especially dependent on the chaperonin.

Endurance-Type Exercise Increases Bulk and Individual Mitochondrial Protein Synthesis Rates in Rats.

Physical activity increases muscle protein synthesis rates. However, the impact of exercise on the coordinated up- and/or downregulation of individual protein synthesis rates in skeletal muscle tissue remains unclear. The authors assessed the impact of exercise on mixed muscle, myofibrillar, and mitochondrial protein synthesis rates as well as individual protein synthesis rates in vivo in rats. Adult Lewis rats either remained sedentary (n = 3) or had access to a running wheel (n = 3) for the last 2 weeks of a 3-week experimental period. Deuterated water was injected and subsequently administered in drinking water over the experimental period. Blood and soleus muscle were collected and used to assess bulk mixed muscle, myofibrillar, and mitochondrial protein synthesis rates using gas chromatography-mass spectrometry and individual muscle protein synthesis rates using liquid chromatography-mass spectrometry (i.e.,dynamic proteomic profiling). Wheel running resulted in greater myofibrillar (3.94 ± 0.26 vs. 3.03 ± 0.15%/day; p < .01) and mitochondrial (4.64 ± 0.24 vs. 3.97 ± 0.26%/day; p < .05), but not mixed muscle (2.64 ± 0.96 vs. 2.38 ± 0.62%/day; p = .71) protein synthesis rates, when compared with the sedentary condition. Exercise impacted the synthesis rates of 80 proteins, with the difference from the sedentary condition ranging between -64% and +420%. Significantly greater synthesis rates were detected for F1-ATP synthase, ATP synthase subunit alpha, hemoglobin, myosin light chain-6, and synaptopodin-2 (p < .05). The skeletal muscle protein adaptive response to endurance-type exercise involves upregulation of mitochondrial protein synthesis rates, but it is highly coordinated as reflected by the up- and downregulation of various individual proteins across different bulk subcellular protein fractions.

Effects of Highly Oxygenated Water in a Hyperuricemia Rat Model.

Recent years have seen a rapidly rising number of oxygenated water brands that claim to impart health benefits and increase athletic performance by improving oxygen availability in the body. Drinks with higher dissolved oxygen concentrations have in recent times gained popularity as potential ergogenic aids, despite the lack of evidence regarding their efficacy. The aim of this study was to characterize oxygenated water and assess the improvement in uric acid metabolism while identifying performance enhancements in animals administered oxygenated water. Oxygenated water was characterized by hydrogen and oxygen nuclear magnetic resonance (NMR) spectroscopy. Hyperuricemia in rats was induced by treatment with oxonic acid potassium salt, and the animals were given oxygenated drinking water before, during, or after oxonic acid treatment. Serum uric acid was measured to confirm the effects on uric acid metabolism. Following oxygenation, the full width at half maximum (FWHM) was reduced to 11.56 Hz and 64.16 Hz in the hydrogen and oxygen NMR spectra, respectively. Oxygenated water molecule clusters were reduced in size due to the reduction in FWHM. Oxygen concentration did not vary significantly with increased temperature. However, standing time played a critical role in the amount of oxygen dissolved in the water. The rat studies indicated that oxygenated water reduced serum uric acid levels and their rate of increase and enhanced uric acid metabolism. A significant improvement in uric acid metabolism and rate of increase in serum uric acid concentration was observed in hyperuricemic rats administered oxygenated water compared to that in rats administered regular water. High oxygen concentrations enhanced the rate of oxygen absorption, leading to increased glycolysis and mitochondrial protein synthesis. Therefore, oxygenated water is a potential adjuvant therapy or health food for treatment of hyperuricemia.

Comprehensive Analysis of the Characteristics and Differences in Adult and Newborn Brown Adipose Tissue (BAT): Newborn BAT Is a More Active/Dynamic BAT.

Brown adipose tissue (BAT) plays an essential role in maintaining body temperature and in treating obesity and diabetes. The adult BAT (aBAT) and neonatal BAT (neBAT) vary greatly in capacity, but the characteristics and differences between them on the molecular level, as well as the related features of BAT as it develops post-delivery, have not yet been fully determined. In this study, we examined the morphological features of aBAT and neBAT of mice by using hematoxylin-eosin (H&E) staining, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). We found that neBAT contains a smaller number and size of lipid droplets, as well as more abundant mitochondria, compared with aBAT. The dynamic morphological changes revealed that the number and size of lipid droplets increase, but the number of mitochondria gradually decrease during the post-delivery development, which consisted of some differences in RNA or protein expression levels, such as gradually decreased uncoupling protein 1 (UCP1) expression levels and mitochondrial genes, such as mitochondrial transcription factor A (Tfam). The adipocyte differentiation-related genes, such as transcription factor CCAAT enhancer-binding protein β (CEBPβ), were also continuously upregulated. Additionally, the different features of aBAT and neBAT were analyzed from the global transcription (RNA-Seq) level, which included messenger RNA (mRNA), microRNA, long non-coding RNA (lncRNA), circRNA, and DNA methylation, as well as proteins (proteomics). Differentially methylated region (DMR) analysis identified 383 hyper- and 503 hypo-methylated genes, as well as 1221 new circRNA in ne-BAT and 1991 new circRNA in a-BAT, with significantly higher expression of circRNA in aBAT compared with neBAT. Gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that mitochondrial activity, protein synthesis, and cell life activity levels were higher in neBAT, and pathways related to ribosomes, spliceosomes, and metabolism were significantly activated in neBAT compared to aBAT. Collectively, this study describes the dynamic changes occurring throughout post-delivery development from the morphological, molecular and omics perspectives. Our study provides information that may be utilized in improving BAT functional activity through gene regulation and/or epigenetic regulation.

Ring sideroblasts and iron metabolism

Ring sideroblasts show abnormal mitochondrial iron accumulation, and their emergence in the bone marrow is a characteristic of sideroblastic anemias (SAs). SAs are a group of heterogeneous congenital and acquired disorders. Congenital SA is a rare disease caused by gene mutations involved in heme biosynthesis, iron-sulfur cluster biosynthesis, and mitochondrial protein synthesis. SAs can also occur after exposure to certain drugs or alcohol and due to copper deficiency (secondary SA). Furthermore, SAs are associated with myelodysplastic syndrome (idiopathic SA), strongly correlating with specific somatic mutations in splicing factor 3b subunit 1 (SF3B1), which is involved in the RNA splicing machinery. Recent reports have indicated that common defects in iron/heme metabolism underlie in the mechanisms of ring sideroblast formation in congenital and acquired SAs. Current understanding of SA pathophysiology, including the mechanisms of ring sideroblast formation, is discussed in this review.

Human diseases linked to cytoplasmic aminoacyl-tRNA synthetases.

As an essential component of the translation machinery, aminoacyl-tRNA synthetases (aaRSs) are indispensable for cell viability. In complex multicellular organisms, this fundamental importance of aaRSs is further expanded by their broad regulatory functions, and reflected by their extensive human disease connections. This chapter focuses on the disease connection of the group of aaRSs supporting protein synthesis in the cytoplasm, including GlyRS and LysRS that are also used for mitochondrial translation. To date, three major disease types have been linked directly to cytoplasmic aaRSs: first, an autoimmune antisynthetase syndrome (ASS) characterized by the presence of autoantibodies targeting one of eight different aaRSs; second, a peripheral neuropathy, Charcot-Marie-Tooth disease (CMT) caused by dominant, mono-allelic mutations in six different aaRSs; and third, severe multi-organ disorders, often accompanied with developmental delays, caused by recessive, bi-allelic mutations in almost all cytoplasmic aaRSs. This chapter will cover broadly each of these types, with a lesser focus on CMT. An interesting feature of cytoplasmic aaRSs in complex organisms is the formation of a multi-synthetase complex (MSC), containing nine aaRSs and three non-enzymatic scaffold proteins. We note a general trend that MSC components are more likely to be involved in recessive diseases, whereas the freestanding aaRSs are predominantly linked to the dominant CMT disease and the autoimmune ASS. GlyRS and LysRS appear to be more susceptive to mutational impact, possibly due to their dual use for cytosolic and mitochondrial protein synthesis. Nevertheless, non-enzymatic functions of aaRSs are also linked to diseases as suggested by studies on ASS and CMT.

Expression of MTERF3 gene in breast carcinoma and the relationship with clinicopathological characteristics.

BackgroundMitochondrial transcription termination factor 3 (MTERF3) is a negative regulator of mitochondrial transcription. It is a modular factor involves in mitochondrial ribosome biogenesis and protein synthesis. However, the association between MTERF3 and breast cancers remains largely unknown. The aim of this study was to investigate the expression of MTERF3 in breast carcinoma and to analyze its clinicopathological significance, and to examine the potential prognostic value of MTERF3 in breast cancer.MethodsThe protein expression levels of MTERF3 in MCF7 (Luminal A), BT-474 (Luminal B), SKBR3 (HER2 overexpression), MDA-MB-468 (Basal like) and MCF10A cell lines were detected by Western blotting. Immunohistochemistry (IHC), Western blotting, and semiquantitative RT-PCR were performed to analyze the protein and mRNA expression levels of MTERF3 in 58 breast cancer tissues and 58 noncancerous breast tissues. The MTERF3 expression data and clinical information from breast cancer patients were downloaded from the TCGA dataset by using the R3.6.1 software. Then the relationship between the expression level of MTERF3 and clinicopathological characteristics and the prognostic value was analyzed. A Cox regression model was performed for the multivariate analysis of the factors that affected the prognosis of breast cancer. The association between the expression levels of MTERF3 and other mitochondrial regulatory genes was analyzed with GEPIA.ResultsMTERF3 is upregulated in breast cancer cell lines compared to noncancerous breast cell line. The IHC results showed that the MTERF3 protein was located in the cytoplasm, and the rate of positive expression in breast cancer tissue was significantly upregulated compared with the adjacent normal tissue. The mRNA and protein expression levels of MTERF3 in breast cancer tissues were significantly higher than that in breast tissues. Moreover, the expression of MTERF3 was significantly correlated with ER status, PR status, breast cancer molecular typing, cancer type, histological diagnosis and primary site (P<0.05). Further analysis showed MTERF3 expression was not related to prognosis. Multivariate Cox regression analysis showed that age, metastasis status and tumor type were independent prognostic factors for breast cancer patients. The expression levels of MTERF3 were positively correlated with the TFAM, TFB1M, TFB2M, MTERF1, TEFM and MFN1 genes but negatively correlated with the MTERF4 and PINK1 genes. In addition, the expression levels of MTERF3 were not correlated with the MTERF2 gene.ConclusionsMTERF3 was significantly upregulated in breast cancer cells and tissues compared with noncancerous cells and tissues. Moreover, the expression level of MTERF3 was correlated with ER status, PR status, breast cancer molecular typing, cancer type, histological diagnosis and primary site. These findings suggested that the upregulation of MTERF3 may be used as a diagnostic and therapeutic target in breast carcinoma.

Fidelity of translation initiation is required for coordinated respiratory complex assembly.

Mammalian mitochondrial ribosomes are unique molecular machines that translate 11 leaderless mRNAs; however, it is not clear how mitoribosomes initiate translation, since mitochondrial mRNAs lack untranslated regions. Mitochondrial translation initiation shares similarities with prokaryotes, such as the formation of a ternary complex of fMet-tRNAMet, mRNA and the 28S subunit, but differs in the requirements for initiation factors. Mitochondria have two initiation factors: MTIF2, which closes the decoding center and stabilizes the binding of the fMet-tRNAMet to the leaderless mRNAs, and MTIF3, whose role is not clear. We show that MTIF3 is essential for survival and that heart- and skeletal muscle-specific loss of MTIF3 causes cardiomyopathy. We identify increased but uncoordinated mitochondrial protein synthesis in mice lacking MTIF3, resulting in loss of specific respiratory complexes. Ribosome profiling shows that MTIF3 is required for recognition and regulation of translation initiation of mitochondrial mRNAs and for coordinated assembly of OXPHOS complexes in vivo.

Mouse Trmt2B protein is a dual specific mitochondrial metyltransferase responsible for m5U formation in both tRNA and rRNA

ABSTRACTRNA molecules of all species contain modified nucleotides and particularly m5U residues. The vertebrate mitochondrial small subunit rRNA contains m5U nucleotide in a unique site. In this work we found an enzyme, TRMT2B, responsible for the formation of this nucleotide and m5U residues in a number of mitochondrial tRNA species. Inactivation of the Trmt2B gene leads to a reduction of the activity of respiratory chain complexes I, III and IV, containing the subunits synthesized by the mitochondrial protein synthesis apparatus. Comparative sequence analysis of m5U-specific RNA methyltransferases revealed an unusual evolutionary pathway of TRMT2B formation which includes consecutive substrate specificity switches from the large subunit rRNA to tRNA and then to the small subunit rRNA.

Mitochondrial tRNAAla 5601C>T variant may affect the clinical expression of the LHON‑related ND4 11778G>A mutation in a family.

Certain mutations in mitochondrial DNA (mtDNA) are associated with Leber's hereditary optic neuropathy (LHON). In particular, the well-known NADH dehydrogenase 4 (ND4) m.11778G>A mutation is one of the most common LHON-associated primary mutations worldwide. However, how specific mtDNA mutations, or variants, affect LHON penetrance is not fully understood. The aim of the current study was to explore the relationship between mtDNA mutations and LHON, and to provide useful information for early detection and prevention of this disease. Following the molecular characterization of a Han Chinese family with maternally inherited LHON, four out of eight matrilineal relatives demonstrated varying degrees of both visual impairment and age of onset. Through PCR amplification of mitochondrial genomes and direct Sanger sequencing analysis, a homoplasmic mitochondrial-encoded ND4 m.11778G>A mutation, alongside a set of genetic variations belonging to human mtDNA haplogroup B5b1 were identified. Among these sequence variants, alanine transfer RNA (tRNA)Ala m.5601C>T was of particular interest. This variant occurred at position 59 in the TψC loop and altered the base pairing, which led to mitochondrial RNA (mt-RNA) metabolism failure and defects in mitochondrial protein synthesis. Bioinformatics analysis suggested that the m.5601C>T variant altered tRNAAla structure. Therefore, impaired mitochondrial functions caused by the ND4 m.11778G>A mutation may be enhanced by the mt-tRNAAla m.5601C>T variant. These findings suggested that the tRNAAla m.5601C>T variant might modulate the clinical manifestation of the LHON-associated primary mutation.

Stress signaling and cellular proliferation reverse the effects of mitochondrial mistranslation.

Translation fidelity is crucial for prokaryotes and eukaryotic nuclear-encoded proteins; however, little is known about the role of mistranslation in mitochondria and its potential effects on metabolism. We generated yeast and mouse models with error-prone and hyper-accurate mitochondrial translation, and found that translation rate is more important than translational accuracy for cell function in mammals. Specifically, we found that mitochondrial mistranslation causes reduced overall mitochondrial translation and respiratory complex assembly rates. In mammals, this effect is compensated for by increased mitochondrial protein stability and upregulation of the citric acid cycle. Moreover, this induced mitochondrial stress signaling, which enables the recovery of mitochondrial translation via mitochondrial biogenesis, telomerase expression, and cell proliferation, and thereby normalizes metabolism. Conversely, we show that increased fidelity of mitochondrial translation reduces the rate of protein synthesis without eliciting a mitochondrial stress response. Consequently, the rate of translation cannot be recovered and this leads to dilated cardiomyopathy in mice. In summary, our findings reveal mammalian-specific signaling pathways that respond to changes in the fidelity of mitochondrial protein synthesis and affect metabolism.

Alteration of mitochondrial DNA homeostasis in drug-induced liver injury

Mitochondrial DNA (mtDNA) encodes for 13 proteins involved in the oxidative phosphorylation (OXPHOS) process. In liver, genetic or acquired impairment of mtDNA homeostasis can reduce ATP output but also decrease fatty acid oxidation, thus leading to different hepatic lesions including massive necrosis and microvesicular steatosis. Hence, a severe impairment of mtDNA homeostasis can lead to liver failure and death. An increasing number of investigations report that some drugs can induce mitochondrial dysfunction and drug-induced liver injury (DILI) by altering mtDNA homeostasis. Some drugs such as ciprofloxacin, antiretroviral nucleoside reverse-transcriptase inhibitors and tacrine can inhibit hepatic mtDNA replication, thus inducing mtDNA depletion. Drug-induced reduced mtDNA levels can also be the consequence of reactive oxygen species-mediated oxidative damage to mtDNA, which triggers its degradation by mitochondrial nucleases. Such mechanism is suspected for acetaminophen and troglitazone. Other pharmaceuticals such as linezolid and tetracyclines can impair mtDNA translation, thus selectively reducing the synthesis of the 13 mtDNA-encoded proteins. Lastly, some drugs might alter the mtDNA methylation status but the pathophysiological consequences of such alteration are still unclear. Drug-induced impairment of mtDNA homeostasis is probably under-recognized since preclinical and post-marketing safety studies do not classically investigate mtDNA levels, mitochondrial protein synthesis and mtDNA oxidative damage.

Mitochondrial Translation Initiation Factor 3: Structure, Functions, Interactions, and Implication in Human Health and Disease.

Mitochondria are essential organelles of eukaryotic cell that provide its respiratory function by means of the electron transfer chain. Expression of mitochondrial genes is organized in a bacterial-like manner; however multiple evolutionary differences are observed between the two systems, including translation initiation machinery. This review is dedicated to the mitochondrial translation initiation factor 3 (IF3mt), which plays a key role in the protein synthesis in mitochondria. Involvement of IF3mt in human health and disease is discussed.

TWO HITS FOR LACTIC ACIDOSIS: A STUDY IN DRUG-DRUG INTERACTION

SESSION TITLE: Wednesday Fellows Case Report Posters SESSION TYPE: Fellow Case Report Posters PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM INTRODUCTION: Tumors with high mitotic activity undergo oxidative phosphorylation for ATP synthesis. In acute myelogenous leukemia (AML) new therapies that target energy metabolism and mitochondrial protein synthesis are being studied. When these new drugs are combined with medications that also effect mitochondrial activity serious complications may occur. Particularly when side-effects from new investigation therapies are not widely known, nor available to automated electronic medical record (EMR) drug interaction checks. We present a case of life-threatening lactic acidosis due to the use of a STAT3 (signal transduction activator of transcription) inhibitor - a drug currently in clinical trials -- in a patient also receiving linezolid, in whom the risk of a life-threatening drug interaction and toxicity was not fully appreciated. CASE PRESENTATION: A 61 year-old man with a history of refractory AML in a clinical trial with a STAT 3 inhibitor presented with sepsis, but despite appropriate antibiotics his clinical status declined requiring mechanical ventilation. Lab studies showed a rapidly worsening lactic acidosis (3.9 to 18 mmol/L) over a few hours. Later it was discovered that he had completed a prolonged course of linezolid for vancomycin-resistant enterococcus bacteremia the day prior to admission. Though inputted in the medical record as an investigation study drug, the drug-drug interaction with linezolid was not registered by the EMR. Plasmapheresis and dialysis were used to remove residual linezolid and the study drug. Subsequently his lactate decreased to 2.4 and he was extubated. However, given the lack of treatment options for refractory AML the family decided to pursue comfort measures. DISCUSSION: STAT3 is a member of the STAT family of proteins involved in intracellular and extracellular signals to the nucleus, controlling gene expression. STAT3 is involved in AML cells, antiapoptosis genes, cell cycle regulators and promotes OXPHOS (oxidative phosphorylation). A major concern for the use of OXPHOS inhibitors is lactic acidosis. Similarly, linezolid decreases mitochondrial respiratory chain enzyme activity, hence disrupting cellular energy production. In our patient, it is likely that the use of two OXPHOS inhibitors resulted in severe mitochondrial toxicity and lactic acidosis. With new medications being developed that inhibit mitochondrial oxidative phosphorylation, intensive care units may see patients who are suffering from their side effects. CONCLUSIONS: This case highlights the importance of reviewing mechanisms and adverse effects of study drugs. Our case also reminds us that study drugs may not be included in the EMR or not flagged by computerized drug interaction alerts. We believe the use of STAT3 inhibitor and other new OXPHOS inhibitors warrant careful monitoring, particularly when used simultaneously with other medications that increase the risk of mitochondrial toxicity. Reference #1: Redell MS, Ruiz MJ, Alonzo TA, Gerbing RB, Tweardy DJ. Stat3 signaling in acute myeloid leukemia: ligand-dependent and -independent activation and induction of apoptosis by a novel small-molecule Stat3 inhibitor. Blood. 2011;117(21):5701-9. DISCLOSURES: No relevant relationships by Alan Gandler, source=Web Response No relevant relationships by Alexys Monoson, source=Web Response No relevant relationships by David Oxman, source=Web Response No relevant relationships by MRINALINI VENKATA SUBRAMANI, source=Web Response

Mitochondrial oxidative phosphorylation is impaired in TALLYHO mice, a new obesity and type 2 diabetes animal model

Type 2 diabetes has become an epidemic disease largely explained by the dramatic increase in obesity in recent years. Mitochondrial dysfunction is suggested as an underlying factor in obesity and type 2 diabetes. In this study, we evaluated changes in oxidative phosphorylation and mitochondrial biogenesis in a new human obesity and type 2 diabetes model, TALLYHO/Jng mice. We hypothesized that the sequence variants identified in the whole genome analysis of TALLYHO/Jng mice would affect oxidative phosphorylation and contribute to obesity and insulin resistant phenotypes. To test this hypothesis, we investigated differences in the expression and activity of oxidative phosphorylation complexes, including the transcription and translation of nuclear- and mitochondrial-encoded subunits and enzymatic activities, in the liver and kidney of TALLYHO/Jng and C57BL/6 J mice. A significant decrease was observed in the expression of nuclear- and mitochondrial-encoded subunits of complex I and IV, respectively, in TALLYHO/Jng mice, which coincided with significant reductions in their enzymatic activities. Furthermore, sequence variants were identified in oxidative phosphorylation complex subunits, a mitochondrial tRNA synthetase, and mitochondrial ribosomal proteins. Our data suggested that the lower expression and activity of oxidative phosphorylation complexes results in the diminished energy metabolism observed in TALLYHO/Jng mice. Sequence variants identified in mitochondrial proteins accentuated a defect in mitochondrial protein synthesis which also contributes to impaired biogenesis and oxidative phosphorylation in TALLYHO/Jng mice. These results demonstrated that the identification of factors contributing to mitochondrial dysfunction will allow us to improve the disease prognosis and treatment of obesity and type 2 diabetes in humans.

Characterisation of a mitochondrial iron transporter of the pathogen Trypanosoma brucei

Similar to higher eukaryotes, the protist parasite T. brucei harbours several iron-containing proteins that regulate DNA and protein processing, oxidative stress defence and mitochondrial respiration. The synthesis of these proteins occurs either in the cytoplasm or within the mitochondrion. For mitochondrial iron cluster protein synthesis, iron needs to be transported across the solute impermeable mitochondrial membrane. In T. brucei we previously identified 24 mitochondrial carrier proteins (TbMCPs) sharing conserved structural and functional features with those from higher eukaryotes. One of these carriers (TbMCP17) displayed high similarity with the iron carriers MRS3, MRS4 from yeast and mitoferrin from mammals, insects and plants. In the present study we demonstrated that TbMCP17 functions as an iron carrier by complementation studies using MRS3/4-deficient yeast. Depletion of TbMCP17 in procyclic form T. brucei resulted in growth deficiency, increased sensitivity to iron deprivation, and lowered mitochondrial iron content. Taken together our results suggest that TbMCP17 functions as a mitochondrial iron transporter in the parasite T. brucei.

Mitochondrial dysfunction generates a growth-restraining signal linked to pyruvate in Drosophila larvae

ABSTRACTThe Drosophila bang-sensitive mutant tko25t, manifesting a global deficiency in oxidative phosphorylation due to a mitochondrial protein synthesis defect, exhibits a pronounced delay in larval development. We previously identified a number of metabolic abnormalities in tko25t larvae, including elevated pyruvate and lactate, and found the larval gut to be a crucial tissue for the regulation of larval growth in the mutant. Here we established that expression of wild-type tko in any of several other tissues of tko25t also partially alleviates developmental delay. The effects appeared to be additive, whilst knockdown of tko in a variety of specific tissues phenocopied tko25t, producing developmental delay and bang-sensitivity. These findings imply the existence of a systemic signal regulating growth in response to mitochondrial dysfunction. Drugs and RNAi-targeted on pyruvate metabolism interacted with tko25t in ways that implicated pyruvate or one of its metabolic derivatives in playing a central role in generating such a signal. RNA-seq revealed that dietary pyruvate-induced changes in transcript representation were mostly non-coherent with those produced by tko25t or high-sugar, consistent with the idea that growth regulation operates primarily at the translational and/or metabolic level.

The Effect of Melatonin on Mitochondrial Function and Autophagy in In Vitro Matured Oocytes of Aged Mice.

Objective This study examined the in vitro effect of melatonin on the protein synthesis of mitochondria, as well as autophagy in matured oocytes of aged mice. Materials and Methods In this experimental study, germinal vesicles (GV) oocytes were collected from aged (with the age of six-months-old) and young mice (with age range of 6-8 weeks old) and then cultured in the in vitro culture medium (IVM) for 24 hours to each metaphase II (MII) oocytes and then supplemented with melatonin at a concentration of 10 μM. The culture medium of MII oocytes was devoid of melatonin. Afterward, the expression of the SIRT-1 and LC3 was assessed by immunocytochemistry. ATP-dependent luciferin-luciferase bioluminescence assay was employed for the measurement of the ATP contents. Intracellular reactive oxygen specious (ROS) was detected by DCFH-DA, and the total antioxidant capacity (TAC) level was determined by TAC assay. Results The expression of SIRT-1 and LC3, as well as the measurement of the ATP content, was significantly increased in oocytes treated with melatonin compared with the oocytes receiving no treatment. Moreover, TAC was considerably higher in melatonin-treated oocytes than oocytes receiving no treatment. On the other hand, the level of ROS was significantly decreased in oocytes treated with melatonin in comparison with the untreated oocytes. The results indicated that melatonin considerably improved the development of oocytes as well. ConclusionAccording to the data, melatonin increased mitochondrial function and autophagy via an increase in the expression of SIRT1 and LC3, as well as the ATP contents while it decreased the levels of ROS and increased TAC in oocytes derived from aged mice.