A versatile proline/alanine transporter in the unicellular pathogen Leishmania donovani regulates amino acid homoeostasis and osmotic stress responses

Unlike all other organisms, parasitic protozoa of the family Trypanosomatidae maintain a large cellular pool of proline that, together with the alanine pool, serve as alternative carbon sources as well as reservoirs of organic osmolytes. These reflect adaptation to their insect vectors whose haemolymphs are exceptionally rich in the two amino acids. In the present study we identify and characterize a new neutral amino acid transporter, LdAAP24, that translocates proline and alanine across the Leishmania donovani plasma membrane. This transporter fulfils multiple functions: it is the sole supplier for the intracellular pool of proline and contributes to the alanine pool; it is essential for cell volume regulation after osmotic stress; and it regulates the transport and homoeostasis of glutamate and arginine, none of which are its substrates. Notably, we provide evidence that proline and alanine exhibit different roles in the parasitic response to hypotonic shock; alanine affects swelling, whereas proline influences the rate of volume recovery. On the basis of our data we suggest that LdAAP24 plays a key role in parasite adaptation to its varying environments in host and vector, a phenomenon essential for successful parasitism.

Unique posttranslational modifications in eukaryotic translation factors and their roles in protozoan parasite viability and pathogenesis.

Protozoan parasites are one of the major causes of diseases worldwide. The vector transmitted parasites exhibit complex life cycles involving interactions between humans, protozoa, and arthropods. In order to adapt themselves to the changing microenvironments, they have to undergo complex morphological and metabolic changes. These changes can be brought about by expressing a new pool of proteins in the cell or by modifying the existing repertoire of proteins via posttranslational modifications (PTMs). PTMs involve covalent modification and processing of proteins thereby modulating their functions. Some of these changes may involve PTMs of parasite proteins to help the parasite survive within the host and the vector. Out of many PTMs known, three are unique since they occur only on single proteins: ethanolamine phosphoglycerol (EPG) glutamate, hypusine and diphthamide. These modifications occur on eukaryotic elongation factor 1A (eEF1A), eukaryotic initiation factor 5A (eIF5A) and eukaryotic elongation factor 2 (eEF2), respectively. Interestingly, the proteins carrying these unique modifications are all involved in the elongation steps of translation. Here we review these unique PTMs, which are well conserved in protozoan parasites, and discuss their roles in viability and pathogenesis of parasites. Characterization of these modifications and studying their roles in physiology as well as pathogenesis will provide new insights in parasite biology, which may also help in developing new therapeutic interventions.

On the use of Cramér-Rao minimum variance bounds for the design of magnetic resonance spectroscopy experiments

Localized Magnetic Resonance Spectroscopy (MRS) is in widespread use for clinical brain research. Standard acquisition sequences to obtain one-dimensional spectra suffer from substantial overlap of spectral contributions from many metabolites. Therefore, specially tuned editing sequences or two-dimensional acquisition schemes are applied to extend the information content. Tuning specific acquisition parameters allows to make the sequences more efficient or more specific for certain target metabolites. Cramér-Rao bounds have been used in other fields for optimization of experiments and are now shown to be very useful as design criteria for localized MRS sequence optimization. The principle is illustrated for one- and two-dimensional MRS, in particular the 2D separation experiment, where the usual restriction to equidistant echo time spacings and equal acquisition times per echo time can be abolished. Particular emphasis is placed on optimizing experiments for quantification of GABA and glutamate. The basic principles are verified by Monte Carlo simulations and in vivo for repeated acquisitions of generalized two-dimensional separation brain spectra obtained from healthy subjects and expanded by bootstrapping for better definition of the quantification uncertainties.

Brain metabolite composition during early human brain development as measured by quantitative in vivo 1H magnetic resonance spectroscopy

Biochemical maturation of the brain can be studied noninvasively by (1)H magnetic resonance spectroscopy (MRS) in human infants. Detailed time courses of cerebral tissue contents are known for the most abundant metabolites only, and whether or not premature birth affects biochemical maturation of the brain is disputed. Hence, the last trimester of gestation was observed in infants born prematurely, and their cerebral metabolite contents at birth and at expected term were compared with those of fullterm infants. Successful quantitative short-TE (1)H MRS was performed in three cerebral locations in 21 infants in 28 sessions (gestational age 32-43 weeks). The spectra were analyzed with linear combination model fitting, considerably extending the range of observable metabolites to include acetate, alanine, aspartate, cholines, creatines, gamma-aminobutyrate, glucose, glutamine, glutamate, glutathione, glycine, lactate, myo-inositol, macromolecular contributions, N-acetylaspartate, N-acetylaspartylglutamate, o-phosphoethanolamine, scyllo-inositol, taurine, and threonine. Significant effects of age and location were found for many metabolites, including the previously observed neuronal maturation reflected by an increase in N-acetylaspartate. Absolute brain metabolite content in premature infants at term was not considerably different from that in fullterm infants, indicating that prematurity did not affect biochemical brain maturation substantially in the studied population, which did not include infants of extremely low birthweight.

Genetic testing for TMEM154 mutations associated with lentivirus susceptibility in sheep.

In sheep, small ruminant lentiviruses cause an incurable, progressive, lymphoproliferative disease that affects millions of animals worldwide. Known as ovine progressive pneumonia virus (OPPV) in the U.S., and Visna/Maedi virus (VMV) elsewhere, these viruses reduce an animal's health, productivity, and lifespan. Genetic variation in the ovine transmembrane protein 154 gene (TMEM154) has been previously associated with OPPV infection in U.S. sheep. Sheep with the ancestral TMEM154 haplotype encoding glutamate (E) at position 35, and either form of an N70I variant, were highly-susceptible compared to sheep homozygous for the K35 missense mutation. Our current overall aim was to characterize TMEM154 in sheep from around the world to develop an efficient genetic test for reduced susceptibility. The average frequency of TMEM154 E35 among 74 breeds was 0.51 and indicated that highly-susceptible alleles were present in most breeds around the world. Analysis of whole genome sequences from an international panel of 75 sheep revealed more than 1,300 previously unreported polymorphisms in a 62 kb region containing TMEM154 and confirmed that the most susceptible haplotypes were distributed worldwide. Novel missense mutations were discovered in the signal peptide (A13V) and the extracellular domains (E31Q, I74F, and I102T) of TMEM154. A matrix-assisted laser desorption/ionization-time-of flight mass spectrometry (MALDI-TOF MS) assay was developed to detect these and six previously reported missense and two deletion mutations in TMEM154. In blinded trials, the call rate for the eight most common coding polymorphisms was 99.4% for 499 sheep tested and 96.0% of the animals were assigned paired TMEM154 haplotypes (i.e., diplotypes). The widespread distribution of highly-susceptible TMEM154 alleles suggests that genetic testing and selection may improve the health and productivity of infected flocks.

Brain-derived neurotrophic factor protects against multiple forms of brain injury in bacterial meningitis

BACKGROUND Brain-derived neurotrophic factor (BDNF) blocks activation of caspase-3, reduces translocation of apoptosis-inducing factor (AIF), attenuates excitotoxicity of glutamate, and increases antioxidant enzyme activities. The mechanisms of neuroprotection suggest that BDNF may be beneficial in bacterial meningitis. METHODS To assess a potentially beneficial effect of adjuvant treatment with BDNF in bacterial meningitis, 11-day-old infant rats with experimental meningitis due to Streptococcus pneumoniae or group B streptococci (GBS) were randomly assigned to receive intracisternal injections with either BDNF (3 mg/kg) or equal volumes (10 mu L) of saline. Twenty-two hours after infection, brains were analyzed, by histomorphometrical examination, for the extent of cortical and hippocampal neuronal injury. RESULTS Compared with treatment with saline, treatment with BDNF significantly reduced the extent of 3 distinct forms of brain cell injury in this disease model: cortical necrosis in meningitis due to GBS (median, 0.0% [range, 0.0%-33.7%] vs. 21.3% [range, 0.0%-55.3%]; P<.03), caspase-3-dependent cell death in meningitis due to S. pneumoniae (median score, 0.33 [range, 0.0-1.0] vs. 1.10 [0.10-1.56]; P<.05), and caspase-3-independent hippocampal cell death in meningitis due to GBS (median score, 0 [range, 0-2] vs. 0.88 [range, 0-3.25]; P<.02). The last form of injury was associated with nuclear translocation of AIF. CONCLUSION BDNF efficiently reduces multiple forms of neuronal injury in bacterial meningitis and may hold promise as adjunctive therapy for this disease.

Norepinephrine drives persistent activity in prefrontal cortex via synergistic α1 and α2 adrenoceptors

Optimal norepinephrine levels in the prefrontal cortex (PFC) increase delay-related firing and enhance working memory, whereas stress-related or pathologically high levels of norepinephrine are believed to inhibit working memory via α1 adrenoceptors. However, it has been shown that activation of Gq-coupled and phospholipase C-linked receptors can induce persistent firing, a cellular correlate of working memory, in cortical pyramidal neurons. Therefore, despite its importance in stress and cognition, the exact role of norepinephrine in modulating PFC activity remains elusive. Using electrophysiology and optogenetics, we report here that norepinephrine induces persistent firing in pyramidal neurons of the PFC independent of recurrent fast synaptic excitation. This persistent excitatory effect involves presynaptic α1 adrenoceptors facilitating glutamate release and subsequent activation of postsynaptic mGluR5 receptors, and is enhanced by postsynaptic α2 adrenoceptors inhibiting HCN channel activity. Activation of α2 adrenoceptors or inhibition of HCN channels also enhances cholinergic persistent responses in pyramidal neurons, providing a mechanism of crosstalk between noradrenergic and cholinergic inputs. The present study describes a novel cellular basis for the noradrenergic control of cortical information processing and supports a synergistic combination of intrinsic and network mechanisms for the expression of mnemonic properties in pyramidal neurons.

Reelin immunoreactivity in dissociated cultures of the postnatal hippocampus

Reelin is an extracellular matrix glycoprotein expressed in different nerve cell populations in the developing, early postnatal and adult central nervous system. During histogenesis of the neocortex and hippocampus, reelin is present in Cajal-Retzius cells and other early neurons and contributes to correct layering of these regions. During early postnatal life, pioneer neurons disappear and reelin expression establishes in a subpopulation of cortical and hippocampal GABAergic interneurons, where it is maintained throughout adult life. We studied the developmental distribution pattern of reelin in dissociated cultures obtained from the early postnatal hippocampus to verify whether or not such a maturation phenomenon is maintained in vitro. Reelin is expressed both in Cajal-Retzius cells and multipolar and pyramidal neurons in younger cultures. The density of reelin-positive Cajal-Retzius cells dropped drastically by about 84% in 4-week-old cultures. Multipolar and pyramidal neurons containing reelin represented 12% of the total cell population in younger cultures and decreased by about 25% after 3 to 4 weeks of cultivation. Their density was significantly lower in cultures of the same age treated with glutamate receptor antagonists. These reelin-positive multipolar and pyramidal neurons were heterogeneous, including a larger amount of non-GABAergic, and 30-40% of GABAergic neurons. Cells double labeled for reelin and the GABA synthesizing enzyme glutamic acid decarboxylase represented about 4% of the total neuron population in culture and their density remained constant with age. It is thus possible that the decrease in the total reelin population may selectively be of importance to the larger non-GABAergic fraction of reelin cells. This study shows that reelin-expressing neurons are maintained in dissociated cultures of the neonatal hippocampus and their distribution and age-dependent changes in density resemble those of the early postnatal hippocampus in vivo.

1H HR-MAS NMR Based Metabolic Profiling of Cells in Response to Treatment with a Hexacationic Ruthenium Metallaprism as Potential Anticancer Drug.

1H high resolution magic angle spinning (HR-MAS) NMR spectroscopy was applied in combination with multivariate statistical analyses to study the metabolic response of whole cells to the treatment with a hexacationic ruthenium metallaprism [1]6+ as potential anticancer drug. Human ovarian cancer cells (A2780), the corresponding cisplatin resistant cells (A2780cisR), and human embryonic kidney cells (HEK-293) were each incubated for 24 h and 72 h with [1]6+ and compared to untreated cells. Different responses were obtained depending on the cell type and incubation time. Most pronounced changes were found for lipids, choline containing compounds, glutamate and glutathione, nucleotide sugars, lactate, and some amino acids. Possible contributions of these metabolites to physiologic processes are discussed. The time-dependent metabolic response patterns suggest that A2780 cells on one hand and HEK-293 cells and A2780cisR cells on the other hand may follow different cell death pathways and exist in different temporal stages thereof.

The transporter GAT1 plays an important role in GABA-mediated carbon-nitrogen interactions in Arabidopsis

Glutamate derived γ-aminobutyric acid (GABA) is synthetized in the cytosol prior to delivery to the mitochondria where it is catabolized via the TCA cycle. GABA accumulates under various environmental conditions, but an increasing number of studies show its involvement at the crossroad between C and N metabolism. To assess the role of GABA in modulating cellular metabolism, we exposed seedlings of A. thaliana GABA transporter gat1 mutant to full nutrition medium and media deficient in C and N combined with feeding of different concentrations (0.5 and 1 mM) of exogenous GABA. GC-MS based metabolite profiling showed an expected effect of medium composition on the seedlings metabolism of mutant and wild type alike. That being said, a significant interaction between GAT1 deficiency and medium composition was determined with respect to magnitude of change in relative amino acid levels. The effect of exogenous GABA treatment on metabolism was contingent on both the medium and the genotype, leading for instance to a drop in asparagine under full nutrition and low C conditions and glucose under all tested media, but not to changes in GABA content. We additionally assessed the effect of GAT1 deficiency on the expression of glutamate metabolism related genes and genes involved in abiotic stress responses. These results suggest a role for GAT1 in GABA-mediated metabolic alterations in the context of the C-N equilibrium of plant cells.

Biochemical changes in barley plants after excessive supply of copper and manganese

The present study was undertaken to identify changes in some important proteins involved in CO2 fixation (Rubisco, Rubisco activase (RA), Rubisco binding protein (RBP)), NH4+ assimilation (glutamine synthetase (GS) and glutamate synthase (GOGAT)), using immunoblotting, and in the antioxidative defense as a result of Cu or Mn excess in barley leaves (Hordeum vulgare L. cv. Obzor). Activities and isoenzyme patterns of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase (CAT), as well as the levels of ascorbate (ASC), non-protein sulfhydryl groups, hydrogen peroxide and oxidative damage to proteins were determined. Data were correlated to the accumulation of Cu or Mn in the leaves after 5 days supply of heavy metal (HM) excess in the nutrient solution. In the highest Cu excess (1500 μM), Rubisco LS and SS were reduced considerably whereas under the highest Mn concentrations (18,300 μM) only minor changes in Rubisco subunits were detected. The RBP was diminished under the highest concentrations of both Cu or Mn. The bands of RA changed differently comparing Cu and Mn toxicity. GS decreased and GOGAT was absent under the highest concentration of Cu. At Mn excess Fd-GOGAT diminished whereas GS was not apparently changed. The development of toxicity symptoms corresponded to an accumulation of Cu or Mn in the leaves and to a gradual increase in protein carbonylation, a lower SOD activity and elevated CAT and GPX activities. APX activity was diminished under Mn toxicity and was not changed under Cu excess. Generally, changes in the isoenzyme profiles were similar under both toxicities. An accumulation of H2O2 was observed only at Mn excess. Contrasting changes in the low-molecular antioxidants were detected when comparing both toxicities. Cu excess affected mainly the non-protein SH groups, while Mn influenced the ASC content. Oxidative stress under Cu or Mn toxicity was most probably the consequence of depletion in low-molecular antioxidants as a result of their involvement in detoxification processes and disbalance in antioxidative enzymes. The link between heavy metal accumulation in leaves, leading to different display of oxidative stress, and changes in individual chloroplast proteins is discussed in the article.

Aberrant association of misfolded SOD1 with Na+/K+ATPase-α3 impairs its activity and contributes to motor neuron vulnerability in ALS.

Amyotrophic lateral sclerosis (ALS) is an adult onset progressive motor neuron disease with no cure. Transgenic mice overexpressing familial ALS associated human mutant SOD1 are a commonly used model for examining disease mechanisms. Presently, it is well accepted that alterations in motor neuron excitability and spinal circuits are pathological hallmarks of ALS, but the underlying molecular mechanisms remain unresolved. Here, we sought to understand whether the expression of mutant SOD1 protein could contribute to altering processes governing motor neuron excitability. We used the conformation specific antibody B8H10 which recognizes a misfolded state of SOD1 (misfSOD1) to longitudinally identify its interactome during early disease stage in SOD1G93A mice. This strategy identified a direct isozyme-specific association of misfSOD1 with Na+/K+ATPase-α3 leading to the premature impairment of its ATPase activity. Pharmacological inhibition of Na+/K+ATPase-α3 altered glutamate receptor 2 expression, modified cholinergic inputs and accelerated disease pathology. After mapping the site of direct association of misfSOD1 with Na+/K+ATPase-α3 onto a 10 amino acid stretch that is unique to Na+/K+ATPase-α3 but not found in the closely related Na+/K+ATPase-α1 isozyme, we generated a misfSOD1 binding deficient, but fully functional Na+/K+ATPase-α3 pump. Adeno associated virus (AAV)-mediated expression of this chimeric Na+/K+ATPase-α3 restored Na+/K+ATPase-α3 activity in the spinal cord, delayed pathological alterations and prolonged survival of SOD1G93A mice. Additionally, altered Na+/K+ATPase-α3 expression was observed in the spinal cord of individuals with sporadic and familial ALS. A fraction of sporadic ALS cases also presented B8H10 positive misfSOD1 immunoreactivity, suggesting that similar mechanism might contribute to the pathology.

CO2, light and temperature influence senescence and protein degradation in wheat leaf segments

Effects of environmental conditions influencing photosynthesis and photorespiration on senescence and net protein degradation were investigated in segments from the first leaf of young wheat (Triticum aestivum L. cv. Arina) plants. The segments were floated on H2O at 25, 30 or 35°C in continuous light (PAR: 50 or 150 µmol m−2 s−1) in ambient air and in CO2-depleted air. Stromal enzymes, including phosphoglycolate phosphatase, glutamine synthetase, ferredoxin-dependent glutamate synthase, phosphoribulokinase, and the peroxisomal enzyme, glycolate oxidase, were detected by SDS-PAGE followed by immunoblotting with specific antibodies. In general, the net degradation of proteins and chlorophylls was delayed in CO2-depleted air. However, little effect of CO2 on protein degradation was observed at 25°C under the lower level of irradiance. The senescence retardation by the removal of CO2 was most pronounced at 30°C and at the higher irradiance. The stromal enzymes declined in a coordinated manner. Immunoreactive fragments from the degraded polypeptides were in most cases not detectable. However, an insolubilized fragment of glycolate oxidase accumulated in vivo, especially at 25°C in the presence of CO2. Detection of this fragment was minimal after incubation at 30°C and completely absent on blots from segments kept at 35°C. In CO2-depleted air, the fragment was only weakly detectable after incubation at 25°C. The results from these investigations indicate that environmental conditions that influence photosynthesis may interfere with senescence and protein catabolism in wheat leaves.

Light-independent degradation of stromal proteins in intact chloroplasts isolated from Pisum sativum L. leaves: requirement for divalent cations

Intact chloroplasts were isolated from mature pea (Pisum sativum L.) leaves in order to study the degradation of several stromal proteins in organello. Changes in the abundances of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), phosphoribulokinase (EC 2.7.1.19), glutamine synthetase (EC 6.3.1.2) and ferredoxin-dependent glutamine:α-ketoglutarate aminotransferase (glutamate synthase; EC 1.4.7.1) were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Coomassie-staining of the gels or immunoblotting using specific antibodies for the different enzymes. Degradation of several stromal proteins was strongly stimulated when intact chloroplasts were incubated in the light in the presence of dithiothreitol. Since free radicals may artificially accumulate in the chloroplast under such conditions and interfere with the stability of stromal proteins, the general relevance of these processes remains questionable. In the absence of light, proteolysis proceeded slowly in isolated chloroplasts and was not stimulated by dithiothreitol. Inhibition by ethylenediaminetetraacetic acid (EDTA), 1,10-phenanthroline or excess zinc ions as well as the requirement for divalent cations suggested that a zinc-containing metalloprotease participated in this process. Furthermore, light-independent degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoribulokinase was enhanced in chloroplasts isolated from leaves in which senescence was accelerated by nitrogen starvation. Our results indicate that light-independent stromal protein degradation in intact chloroplasts may be analogous to proteolysis that occurs in intact leaves during senescence.

Low-cost disposable ALT electrochemical microsensors for in-vitro hepatotoxic assessment

Liver-on-chip systems are widely seen as having the potential to replace animal testing for long-term liver toxicity assessments. However, such systems necessitate solutions, such as electrochemical microsensors, to provide information about the cells exposed to chemical compounds in a confined space. This study describes the development of microsensors for the detection of alanine-aminotransferase (ALT), an intracellular enzyme found in hepatocytes, for monitoring the viability of in-vitro hepatic cell cultures. The electrochemical sensors were developed by using screen printed electrodes functionalized by drop-casting. These technologies are intended to produce disposable and low-cost sensors that can easily be exchanged once their performance is degraded. The sensors are capable of measuring ALT in a microfluidic environment through the detection of changes in glutamate concentration. The microsensors were found to be stable for more than 60 days and were successfully tested using hepatocellular lysates to assess their capability to quantify ALT activity in a hepatic cell culture. These results open the way to their integration in liver bioreactors to assess hepatocellular toxicity in-vitro.