ARTICLE | doi:10.20944/preprints202105.0293.v1
Subject: Materials Science, Biomaterials Keywords: mineralization; polyelectrolyte brushes; poly(amino acids); poly-(α,L-glutamic acid); poly-(α,L-aspartic acid); cellulose; molecular dynamics simulation.
Online: 13 May 2021 (13:09:40 CEST)
We used atomistic molecular dynamics (MD) simulations to study polyelectrolyte brushes based on anionic α-L-glutamic acid and α-L-aspartic acid grafted on cellulose in the presence of divalent CaCl2 salt at different concentrations. The motivation is the search of the ways to control properties such as sorption capacity and the structural response of the brush to multivalent salts. For this detailed understanding of the role of side chain length, chemical structure and their interplay is required. It was found that in the case of glutamic acid oligomers, the longer side chains facilitate attractive interactions with the cellulose surface, which forces the grafted chains to lie down on the surface. The additional methylene group in the side chain enables side chain rotation enhancing this effect. On the other hand, the shorter and more restricted side chains of aspartic acid oligomers prevent attractive interactions to a large degree and push the grafted chains away from the surface. The difference in side chain length also leads to differences in other properties of the brush in divalent salt solutions. At a low grafting density, the longer side chains of glutamic acid allow the adsorbed cations to be spatially distributed inside the brush resulting in a charge inversion. With an increase in grafting density, the difference in the total charge of the aspartic and glutamine brushes disappears, but new structural features appear. The longer sides allow for ion bridging between the grafted chains and the cellulose surface without a significant change in main chain conformation. This leads to the brush structure being less sensitive to changes in salt concentration.
ARTICLE | doi:10.20944/preprints202208.0351.v1
Subject: Medicine & Pharmacology, General Medical Research Keywords: astrocytes; hypoglycemia; diabetes mellitus, type 1; mitochondria; glycemic control; hypothalamus; glutamic acid.
Online: 18 August 2022 (14:24:35 CEST)
Recurrent hypoglycaemia, a common side-effect of insulin therapy in the treatment of type 1 diabetes, induces impaired glucose-sensing. Better understanding of how astrocytes, important non-neuronal cells in the brain, function in low glucose environments may improve our understanding of recurrent hypoglycaemia-induced defective counterregulation. Astrocytes contribute to glutamatergic signalling, which is required for hypoglycaemia counterregulation and is impaired by recurrent insulin-induced hypoglcyaemia. This study examined the glutamate response of astrocytes when challenged with acute and recurrent low glucose (RLG) exposure. The metabolic responses of cortical (CRTAS) and hypothalamic (HTAS) primary rat astrocytes were measured in acute and recurrent low glucose using extracellular flux analyses. RLG caused mitochondrial adaptations in both HTAS and CRTAS, many of which were attenuated by glutamate exposure during low glucose treatments. We observed an increase in capacity of HTAS to metabolise glutamine after RLG exposure. Demonstrating astrocytic heterogeneity in the response to LG, CRTAS increased cellular acidification, a marker of glycolysis in LG, whereas this decreased in HTAS. The directional change in intracellular Ca2+ levels of each cell type, correlated with the change in extracellular acidification rate (ECAR) during LG. Further examination of glutamate-induced Ca2+ responses in low glucose treated CRTAS and HTAS identified sub-populations of glucose-excited- and glucose-inhibited-like cells with differing responses to glutamate. Lastly, release of the gliotransmitter ATP by HTAS was elevated by RLG, both with and without concurrent glutamate exposure. Therefore, hypothalamic astrocytes adapt to RLG by increasing glutamate uptake and oxidation in a manner that attenuates RLG-induced mitochondrial adaptations.
REVIEW | doi:10.20944/preprints202112.0469.v1
Subject: Medicine & Pharmacology, General Medical Research Keywords: astrocyte; gamma-amino butyric acid (GABA); GABA transporter (GAT); GABAA receptor; glutamic acid decarboxylase (GAD); glycine; glycine receptor; glycine transporter (GlyT); K+-Cl- co-transporter 2 (KCC2); vesicular GABA transporter (VGAT)
Online: 29 December 2021 (14:27:41 CET)
Gamma-aminobutyric acid (GABA) and glycine act as inhibitory neurotransmitters. Three types of inhibitory neurons and terminals, GABAergic, GABA/glycine co-releasing, and glycinergic, are orchestrated in the spinal cord neural circuits and play key roles in the regulation of pain, locomotive movement, and respiratory rhythms. Herein, we first describe GABAergic and glycinergic transmission and inhibitory networks, which consist of three types of terminals, in the mature mouse spinal cord. Second, we describe the developmental formation of GABAergic and glycinergic networks, with specific focus on the differentiation of neurons, formation of synapses, maturation of removal systems, and changes in their action. GABAergic and glycinergic neurons are derived from the same domains of the ventricular zone. Initially, GABAergic neurons are differentiated and their axons form synapses. Some of these neurons remain GABAergic in lamina I and II. Many of GABAergic neurons convert to co-releasing state. The co-releasing neurons and terminals remain in the dorsal horn, whereas many of co-releasing ones ultimately become glycinergic in the ventral horn. During the development of terminals and the transformation from radial glia to astrocytes, GABA and glycine receptor subunit compositions markedly change, removal systems mature, and GABAergic and glycinergic action shifts from excitatory to inhibitory.