Deficiency In Protein Synthesis Research Articles

Loss of mitochondrial enzyme GPT2 causes early neurodegeneration in locus coeruleus

Locus coeruleus (LC) is among the first brain areas to degenerate in Alzheimer's disease and Parkinson's disease; however, the underlying causes for the vulnerability of LC neurons are not well defined. Here we report a novel mechanism of degeneration of LC neurons caused by loss of the mitochondrial enzyme glutamate pyruvate transaminase 2 (GPT2). GPT2 Deficiency is a newly-recognized childhood neurometabolic disorder. The GPT2 enzyme regulates cell growth through replenishment of tricarboxylic acid (TCA) cycle intermediates and modulation of amino acid metabolism. In Gpt2-null mice, we observe an early loss of tyrosine hydroxylase (TH)-positive neurons in LC and reduced soma size at postnatal day 18. Gpt2-null LC shows selective positive Fluoro-Jade C staining. Neuron loss is accompanied by selective, prominent microgliosis and astrogliosis in LC. We observe reduced noradrenergic projections to and norepinephrine levels in hippocampus and spinal cord. Whole cell recordings in Gpt2-null LC slices show reduced soma size and abnormal action potentials with altered firing kinetics. Strikingly, we observe early decreases in phosphorylated S6 in Gpt2-null LC, preceding prominent p62 aggregation, increased LC3B-II to LC3B-I ratio, and neuronal loss. These data are consistent with a possible mechanism involving deficiency in protein synthesis and cell growth, associated subsequently with abnormal autophagy and neurodegeneration. As compared to the few genetic animal models with LC degeneration, loss of LC neurons in Gpt2-null mice is developmentally the earliest. Early neuron loss in LC in a model of human neurometabolic disease provides important clues regarding the metabolic vulnerability of LC and may lead to new therapeutic targets.

Human mitochondrial diseases caused by lack of taurine modification in mitochondrial tRNAs

Mitochondrial DNA mutations that cause mitochondrial dysfunction are responsible for a wide spectrum of human diseases, referred to as mitochondrial diseases. Pathogenic point mutations are found frequently in genes encoding mitochondrial (mt) tRNAs, indicating that impaired functioning of mutant mt tRNAs is the primary cause of mitochondrial dysfunction. Our previous studies revealed the absence of posttranscriptional taurine modification at the anticodon wobble uridine in mutant mt tRNAs isolated from cells derived from patients with two major classes of mitochondrial diseases, MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) and MERRF (myoclonus epilepsy associated with ragged red fibers). Defective taurine modification of the mutant mt tRNAs results in a deficiency in protein synthesis as the cognate codons of the mutant mt tRNA cannot be decoded. These findings represent the first evidence of a molecular pathogenesis caused by an RNA modification disorder.

EVALUATION OF THE GENOTOXICITY OF WATER BOTTLED IN PET RECIPIENTS

The aim of this study was to establish the possible toxicological effects of chemicals released into mineral water bottled in polyethylene terephthalate (PET) bottles, preserved at room temperature and at 48oC, by Allium test. There were analyzed the growth tests, as well as chromosomal and genomic mutations. In all experimental variants the mitotic index was lower than in Control, the mitosis process being disturbed, fact correlated with growth results. There was observed a decrease in prophase percentage and an accumulation in metaphase, in both variants thermic treated. In prophase and metaphase were observed metabolic disorders, probably due to some deficiency in protein synthesis. The most frequent chromosomal aberrations were bridges, acentric fragments, ring chromosomes, but also centromere inactivation. Allium test is very sensitive, reacting to low concentrations of toxic chemicals, and thus can be used as a first alert.

Angiotensin II is Necessary for Skeletal Muscle Regeneration Following Cardiotoxin‐induced Injury

Angiotensin II (Ang II) is a pleiotropic peptide involved in vasoactivity as well as cellular growth and proliferation. We examined whether Ang II is also a mediator of muscle regeneration by administering an ACE inhibitor (captopril) following cardiotoxin (ctx)‐induced muscle injury in C57BL/6 mice. 10 days following ctx injection, captopril treated mice demonstrated a delayed response in the myogenic program evidenced by sustained expression of Pax7 and Myf5 transcripts while myogenin mRNA, a marker of differentiating myoblasts, was significantly inhibited. This delay was also evident at the myofibre level with captopril treated mice exhibiting a significant ~3.5 fold elevation in eMHC gene expression. Importantly, newly formed fibres in the captopril treated group demonstrated an impaired hypertrophic response as fibre cross‐sectional area (CSA) from day 10 to day 21 was increased by 81% in the control group and only 27% in the captopril group. This resulted in an overall difference of 25% in CSA between groups at day 21 post injury. These effects do not appear to be due to a deficiency in protein synthesis as myonuclear domain size was unchanged between groups. Rather, there appears to be a loss of satellite cell content as the captopril treated group demonstrated a ~29% decrease in Pax7+ cells by day 21 post injury. This research was supported by NSERC.

Thrombopoietin serum levels do not correlate with thrombocytopenia in hepatic schistosomiasis.

In severe forms of cirrhosis reduced liver synthesis of thrombopoietin (Tpo) can contribute to thrombocytopenia. In the hepatosplenic form of schistosomiasis, portal hypertension is the most evident clinical complication, although a deficiency of protein synthesis may be detected early. Our aim was to determine, for the first time in schistosomiasis, Tpo serum concentrations in patients with chronic forms of the disease. Twenty-four patients with the pure form of schistosomiasis were studied; 13 had the hepatosplenic form (HE, with portal hypertension) and 11 had the hepatointestinal form (HI, without portal hypertension). Patients were HBsAg, anti-HBc and anti-HCV negative, and reported alcohol ingestion below 160 g/week. The Tpo serum concentration, determined in 10 healthy volunteers, varied from undetectable (< 15 pg/mL) to 489 pg/mL (median 208 pg/mL). The HE and HI groups differed (p = 0.004) in regard to the prothrombin index, thrombocytemia and gamma-glutamyltransferase but not in regard to Tpo (p = 0.622). No significant correlation was found between Tpo and the other parameters (p > 0.05). The results suggest that Tpo serum concentration does not mirror and/or has no significant participation in the mechanisms responsible for the thrombocytopenia observed in schistosomiasis patients with splenomegaly and portal hypertension.

Intramuscular delivery of rat kallikrein-binding protein gene reverses hypotension in transgenic mice expressing human tissue kallikrein.

The tissue kallikrein-kinin system has been postulated to play a role in blood pressure regulation. The activity of tissue kallikrein is controlled by a number of factors in vivo. Rat kallikrein-binding protein (RKBP) is a serine proteinase inhibitor which binds to and inhibits tissue kallikrein's activity in vitro. We have recently developed several hypotensive transgenic mouse lines which express human tissue kallikrein. In order to investigate the role of RKBP in blood pressure regulation, we delivered the RKBP to these transgenic mice by intramuscular injection. Expression of the RKBP was detected in skeletal muscle by reverse transcription-polymerase chain reaction and Southern blot analysis at 10, 20, 30, and 40 days post-injection. Immunoreactive RKBP levels in the muscle and serum of these mice were quantified by a RKBP-specific enzyme-linked immunosorbent assay and Western blot analysis. The levels of RKBP mRNA and immunoreactive protein were detectable at 10 days post-injection and increased significantly at 20 and 30 days. During this period, RKBP delivery significantly increased systemic blood pressure in the kallikrein transgenic mice to a level comparable to that of normotensive control mice. The RKBP and vector DNA delivery had no effect on the blood pressure of normotensive control mice. No serum antibodies to RKBP or its DNA were detected in the mice 40 days post injection. These results suggest that the increase of systemic blood pressure by RKBP delivery in these hypotensive transgenic mice may be mediated by inhibiting tissue kallikrein activity.

Niacin-Induced Clotting Factor Synthesis Deficiency With Coagulopathy

Although coagulopathy is a well-known complication of severe niacin-induced hepatotoxic reaction, it is not found in patients with minimal aminotransferase level elevations. Three patients with significant clotting factor synthesis deficiency and coagulopathy (prothrombin times, greater than 1.5 times control) from sustained-release niacin had only mild aminotransferase level elevations (1.5 to 2.0 times normal). In each case, protein deficiency, coagulopathy, and aminotransferase level elevation resolved promptly after withdrawal of niacin therapy. In one case, this syndrome recurred after rechallenge with sustained-release niacin, whereas the coagulopathy did not recur in a second patient rechallenged with crystalline niacin. Deficiency in protein synthesis, including coagulation factors, and coagulopathy are unrecognized complications of sustained-release niacin therapy. These cases indicate the need to measure prothrombin times routinely in patients who develop even mild aminotransferase level elevation while receiving sustained-release niacin therapy. These data are important in light of the increasing use of sustained-release niacin in the treatment of patients with lipid disorders.

Biochemistry of Deoxyribonucleic Acid-defective Amber Mutants of Bacteriophage T4: I. Ribonucleic Acid Metabolism

Abstract The relationship between DNA replication and RNA synthesis in T4 bacteriophage-infected Escherichia coli has been explored by comparing certain aspects of RNA metabolism in E. coli B infected with T4D and with five amber mutants of T4 which are unable to replicate their DNA. The following findings were made. 1. The metabolic stability of uracil-14C-labeled RNA, as determined in pulse-chase experiments, is essentially the same early and late in infection by either wild type phage or one of the mutants. 2. The rate of RNA synthesis early in infection by T4D or the amber mutants is approximately the same, but the rate decreases drastically late in infection by the amber mutants. However, the rate of RNA synthesis does not drop to zero in any case. 3. One of the mutants studied, T4 amE10, synthesizes RNA only about half as rapidly as the other mutants. A similar deficiency in protein synthesis was observed. 4. All of the RNA species formed late in infection by the amber mutants are present early in infection by T4D, as determined by competitive DNA-RNA hybridization tests. Thus, DNA replication is a necessary step for transcription of RNA species found only at late periods in normal phage development.

Studies on Agammaglobulinemia VI. Hemostasis in Patients with Agammaglobulinemia.

Summary and Conclusions1. The activity or concentration of the clotting factors recognized at the present time have been determined in 7 patients with agammaglobulinemia. Four of the patients had the congenital-hereditary form of agammaglobulinemia and three had the acquired form of the disease. 2. An elevated platelet count was observed in 5 of the 7 patients. No abnormalities in plasma clotting factors were found. 3. Data presented are consistent with the following conclusions: (a) none of the plasma coagulation factors is a gamma globulin, (b) agammaglobulinemia is probably the result of an isolated deficiency in protein synthesis, c) the deficiency of gamma globulin synthesis in these patients does not involve the liver but rather depends on an anomaly of protein metabolism existing elsewhere in the reticuloendothelial system.