Coarse-Grained Parameters for Divalent Cations within the SIRAH Force Field.

Although molecular dynamics simulations allow for the study of interactions among virtually all biomolecular entities, metal ions still pose significant challenges in achieving an accurate structural and dynamical description of many biological assemblies, particularly to coarse-grained (CG) models. Although the reduced computational cost of CG methods often makes them the technique of choice for the study of large biomolecular systems, the parameterization of metal ions is still very crude or not available for the vast majority of CG force fields. Here, we show that incorporating statistical data retrieved from the Protein Data Bank (PDB) to set specific Lennard-Jones interactions can produce structurally accurate CG molecular dynamics simulations using the SIRAH force field. We provide a set of interaction parameters for calcium, magnesium, and zinc ions, which cover more than 80% of the metal-bound structures reported in the PDB. Simulations performed on several proteins and DNA systems show that it is possible to preclude the use of topological constraints by modifying specific Lennard-Jones interactions.

Pentameric Ligand-Gated Ion Channels as Pharmacological Targets Against Chronic Pain.

Chronic pain is a common detrimental condition that affects around 20% of the world population. The current drugs to treat chronic pain states, especially neuropathic pain, have a limited clinical efficiency and present significant adverse effects that complicates their regular use. Recent studies have proposed new therapeutic strategies focused on the pharmacological modulation of G-protein-coupled receptors, transporters, enzymes, and ion channels expressed on the nociceptive pathways. The present work intends to summarize recent advances on the pharmacological modulation of pentameric ligand-gated ion channels, which plays a key role in pain processing. Experimental data have shown that novel allosteric modulators targeting the excitatory nicotinic acetylcholine receptor, as well as the inhibitory GABAA and glycine receptors, reverse chronic pain-related behaviors in preclinical assays. Collectively, these evidences strongly suggest the pharmacological modulation of pentameric ligand-gated ion channels is a promising strategy towards the development of novel therapeutics to treat chronic pain states in humans.

Altered lactate metabolism in Huntington's disease is dependent on GLUT3 expression.

AIMS: Huntington's disease (HD) is a neurodegenerative disorder characterized by progressive abnormalities in cognitive function, mental state, and motor control. HD is characterized by a failure in brain energy metabolism. It has been proposed that monocarboxylates, such as lactate, support brain activity. During neuronal synaptic activity, ascorbic acid released from glial cells stimulates lactate and inhibits glucose transport. The aim of this study was to evaluate the expression and function of monocarboxylate transporters (MCTs) in two HD models. METHODS: Using immunofluorescence, qPCR, and Western blot analyses, we explored mRNA and protein levels of MCTs in the striatum of R6/2 animals and HdhQ7/111 cells. We also evaluated MCT function in HdhQ7/111 cells using radioactive tracers and the fluorescent lactate sensor Laconic. RESULTS: We found no significant differences in the mRNA or protein levels of neuronal MCTs. Functional analyses revealed that neuronal MCT2 had a high catalytic efficiency in HD cells. Ascorbic acid did not stimulate lactate uptake in HD cells. Ascorbic acid was also unable to inhibit glucose transport in HD cells because they exhibit decreased expression of the neuronal glucose transporter GLUT3. CONCLUSION: We demonstrate that stimulation of lactate uptake by ascorbic acid is a consequence of inhibiting glucose transport. Supporting this, lactate transport stimulation by ascorbic acid in HD cells was completely restored by overexpressing GLUT3. Therefore, alterations in GLUT3 expression could be responsible for inefficient use of lactate in HD neurons, contributing to the metabolic failure observed in HD.

The presence of glia stimulates the appearance of glycinergic synaptic transmission in spinal cord neurons.

Previous studies, using electrophysiological and fluorimetric analysis with a calcium sensitive dye, have shown that 5-7 DIV developing spinal cord neurons displayed high levels of glycinergic transmission. GABAergic and AMPAergic neurotransmission contributed much less to the overall transmission. Here, we show that culturing neurons in absence of a glia cell monolayer reduced the frequency of glycinergic spontaneous IPSCs (0.1 +/- 0.01 Hz), without altering the level of overall transmission (3 +/- 1.1 Hz). The predominant transmission was mediated by GABA(A) receptors (72% of total synaptic events). In addition, combination of bicuculline and CNQX blocked synaptically mediated calcium transients recorded with fluo-3. Furthermore, application of glycine revealed the presence of extrasynaptic receptors in these neurons (25 +/- 6 pA/pF). Culturing neurons on a glial cell monolayer increased the frequency of glycinergic currents (0.4 +/- 0.02 Hz), without changing the amplitude of the current (20 +/- 4 pA). The use of a glia-conditioned media reversed the effect of growing the neurons in a glia-deprived condition. These results indicate that the establishment of glycinergic transmission is dependent on the presence of a glia derived soluble factor. However, functional GlyRs were still able to insert in the neuronal membrane in a glia-independent manner.

Changes on the properties of glycine receptors during neuronal development.

Glycine receptors (GlyRs) play a major role in the excitability of spinal cord and brain stem neurons. During development, several properties of these receptors undergo significant changes resulting in major modifications of their physiological functions. For example, the receptor structure switches from a monomeric alpha or heteromeric alpha 2 beta in immature neurons to an alpha 1 beta receptor type in mature neurons. Together with these changes in receptor subunits, the postsynaptic cluster size increases with development. Parallel to these modifications, the apparent receptor affinity to glycine and strychnine, as well as that of Zn(2+) and ethanol increases with time. The mature receptor is characterized by a slow desensitizing current and high sensitivity to modulation by protein kinase C. Also, the high level of glycinergic transmission in immature spinal neurons modulates neuronal excitability causing membrane depolarization and changes in intracellular calcium. Due to these properties, chronic inhibition of glycinergic transmission affects neurite outgrowth and produces changes in the level of synaptic transmission induced by GABA(A) and AMPA receptors. Finally, the high level of plasticity found in immature GlyRs is likely associated to changes in cytoskeleton dynamics.