Possible Existence of the Hypothalamic-Pituitary-Hippocampal (HPH) Axis: A Reciprocal Relationship Between Hippocampal Specific Neuroestradiol Synthesis and Neuroblastosis in Ageing Brains with Special Reference to Menopause and Neurocognitive Disorders

The hippocampus-derived neuroestradiol plays a major role in neuroplasticity, independent of circulating estradiol that originates from gonads. The response of hypothalamus-pituitary regions towards the synthesis of neuroestradiol in the hippocampus is an emerging scientific concept in cognitive neuroscience. Hippocampal plasticity has been proposed to be regulated via neuroblasts, a major cellular determinant of functional neurogenesis in the adult brain. Defects in differentiation, integration and survival of neuroblasts in the hippocampus appear to be an underlying cause of neurocognitive disorders. Gonadotropin receptors and steroidogenic enzymes have been found to be expressed in neuroblasts in the hippocampus of the brain. However, the reciprocal relationship between hippocampal-specific neuroestradiol synthesis along neuroblastosis and response of pituitary based feedback regulation towards regulation of estradiol level in the hippocampus have not completely been ascertained. Therefore, this conceptual article revisits (1) the cellular basis of neuroestradiol synthesis (2) a potential relationship between neuroestradiol synthesis and neuroblastosis in the hippocampus (3) the possible involvement of aberrant neuroestradiol production with mitochondrial dysfunctions and dyslipidemia in menopause and adult-onset neurodegenerative disorders and (4) provides a hypothesis for the possible existence of the hypothalamic-pituitary-hippocampal (HPH) axis in the adult brain. Eventually, understanding the regulation of hippocampal neurogenesis by abnormal levels of neuroestradiol concentration in association with the feedback regulation of HPH axis might provide additional cues to establish a neuroregenerative therapeutic management for mood swings, depression and cognitive decline in menopause and neurocognitive disorders.

     

Molecular docking analysis of phytocompounds from Andrographis paniculata binding with proteins in the notch-signaling pathway

It is of interest to document the molecular docking analysis of phytocompounds from Andrographis paniculata binding with protein NOTCH1 in the Notch-signaling pathway in the context of cancer. Hence, we document the binding features of neoandrographolide, 14-deoxyandrographolide, androgapholide and andrograpanin with proteins in the notch-signaling pathway for further consideration.     

Subtype-dependent N-Methyl-d-aspartate Receptor Amino-terminal Domain Conformations and Modulation by Spermine

The N-methyl-d-aspartate (NMDA) subtype of the ionotropic glutamate receptors is the primary mediator of calcium-permeable excitatory neurotransmission in the central nervous system. Subunit composition and binding of allosteric modulators to the amino-terminal domain determine the open probability of the channel. By using luminescence resonance energy transfer with functional receptors expressed in CHO cells, we show that the cleft of the amino-terminal domain of the GluN2B subunit, which has a lower channel open probability, is on average more closed than the GluN2A subunit, which has a higher open probability. Furthermore, the GluN1 amino-terminal domain adopts a more open conformation when coassembled with GluN2A than with GluN2B. Binding of spermine, an allosteric potentiator, opens the amino-terminal domain cleft of both the GluN2B subunit and the adjacent GluN1 subunit. These studies provide direct structural evidence that the inherent conformations of the amino-terminal domains vary based on the subunit and match the reported open probabilities for the receptor.     

Assays for studying nucleated aggregation of polyglutamine proteins

The aggregation of polyglutamine containing protein sequences is implicated in a family of familial neurodegenerative diseases, the expanded CAG repeat diseases. While the cellular aggregation process undoubtedly depends on the flux and local environment of these proteins, their intrinsic physical properties and folding/aggregation propensities must also contribute to their cellular behavior. Here we describe a series of methods for determining mechanistic details of the spontaneous aggregation of polyQ-containing sequences, including the identification and structural examination of aggregation intermediates.     

14-3-3 binding and phosphorylation of neuroglobin during hypoxia modulate six-to-five heme pocket coordination and rate of nitrite reduction to nitric oxide

Neuroglobin protects neurons from hypoxia in vitro and in vivo; however, the underlying mechanisms for this effect remain poorly understood. Most of the neuroglobin is present in a hexacoordinate state with proximal and distal histidines in the heme pocket directly bound to the heme iron. At equilibrium, the concentration of the five-coordinate neuroglobin remains very low (0.1-5%). Recent studies have shown that post-translational redox regulation of neuroglobin surface thiol disulfide formation increases the open probability of the heme pocket and allows nitrite binding and reaction to form NO. We hypothesized that the equilibrium between the six- and five-coordinate states and secondary reactions with nitrite to form NO could be regulated by other hypoxia-dependent post-translational modification(s). Protein sequence models identified candidate sites for both 14-3-3 binding and phosphorylation. In both in vitro experiments and human SH-SY5Y neuronal cells exposed to hypoxia and glucose deprivation, we observed that 1) neuroglobin phosphorylation and protein-protein interactions with 14-3-3 increase during hypoxic and metabolic stress; 2) neuroglobin binding to 14-3-3 stabilizes and increases the half-life of phosphorylation; and 3) phosphorylation increases the open probability of the heme pocket, which increases ligand binding (CO and nitrite) and accelerates the rate of anaerobic nitrite reduction to form NO. These data reveal a series of hypoxia-dependent post-translational modifications to neuroglobin that regulate the six-to-five heme pocket equilibrium and heme access to ligands. Hypoxia-regulated reactions of nitrite and neuroglobin may contribute to the cellular adaptation to hypoxia.     

Human neuroglobin functions as a redox-regulated nitrite reductase

Neuroglobin is a highly conserved hemoprotein of uncertain physiological function that evolved from a common ancestor to hemoglobin and myoglobin. It possesses a six-coordinate heme geometry with proximal and distal histidines directly bound to the heme iron, although coordination of the sixth ligand is reversible. We show that deoxygenated human neuroglobin reacts with nitrite to form nitric oxide (NO). This reaction is regulated by redox-sensitive surface thiols, cysteine 55 and 46, which regulate the fraction of the five-coordinated heme, nitrite binding, and NO formation. Replacement of the distal histidine by leucine or glutamine leads to a stable five-coordinated geometry; these neuroglobin mutants reduce nitrite to NO ～2000 times faster than the wild type, whereas mutation of either Cys-55 or Cys-46 to alanine stabilizes the six-coordinate structure and slows the reaction. Using lentivirus expression systems, we show that the nitrite reductase activity of neuroglobin inhibits cellular respiration via NO binding to cytochrome c oxidase and confirm that the six-to-five-coordinate status of neuroglobin regulates intracellular hypoxic NO-signaling pathways. These studies suggest that neuroglobin may function as a physiological oxidative stress sensor and a post-translationally redox-regulated nitrite reductase that generates NO under six-to-five-coordinate heme pocket control. We hypothesize that the six-coordinate heme globin superfamily may subserve a function as primordial hypoxic and redox-regulated NO-signaling proteins.     

Hypermutation and stress adaptation in bacteria

Hypermutability is a phenotype characterized by a moderate to high elevation of spontaneous mutation rates and could result from DNA replication errors, defects in error correction mechanisms and many other causes. The elevated mutation rates are helpful to organisms to adapt to sudden and unforeseen threats to survival. At the same time hypermutability also leads to the generation of many deleterious mutations which offset its adaptive value and therefore disadvantageous. Nevertheless, it is very common in nature, especially among clinical isolates of pathogens. Hypermutability is inherited by indirect (second order) selection along with the beneficial mutations generated. At large population sizes and high mutation rates many cells in the population could concurrently acquire beneficial mutations of varying adaptive (fitness) values. These lineages compete with the ancestral cells and also among themselves for fixation. The one with the ‘fittest’ mutation gets fixed ultimately while the others are lost. This has been called ‘clonal interference’ which puts a speed limit on adaptation. The original clonal interference hypothesis has been modified recently. Nonheritable (transient) hypermtability conferring significant adaptive benefits also occur during stress response although its molecular basis remains controversial. The adaptive benefits of heritable hypermutability are discussed with emphasis on host–pathogen interactions.     

Genetic and environmental changes in SUMO homeostasis lead to nuclear mRNA retention in plants

Protein sumoylation plays an important role in plant development, flowering-time regulation, and abiotic stress response. However, the molecular role of sumoylation in these pathways is largely unknown. It was shown previously that in mutants of the inner nuclear basket nucleoporin NUA a large increase in the abundance of high-molecular weight SUMO conjugated proteins correlated with nuclear retention of bulk mRNA. Here, the connection between sumoylation and mRNA export in plants was further investigated. Both SUMO-conjugate accumulation and mRNA retention were also found in a second nucleoporin mutant that does not affect NUA, and SUMO conjugates accumulated predominantly in the nucleus. Similarly, after heat and ethanol treatment, two abiotic stress treatments known to lead to the accumulation of sumoylated proteins, nuclear mRNA was retained. To establish a causal relationship between sumoylation and mRNA export, mutations in two enzymes in the SUMO pathway were tested. Mutating either SUMO E3 ligase or SUMO isopeptidase lead to nuclear mRNA retention, indicating that both an increase and a decrease in the pool of sumoylated nuclear proteins blocks mRNA export. Together, these data show that sumoylation acts upstream of mRNA export in plants, likely through the transient sumoylation status of one or more factors involved in mRNA trafficking.     

Studies on filarial GST as a target for antifilarial drug development-in silico and in vitro inhibition of filarial GST by substituted 1,4-naphthoquinones

Eleven 1,4-naphthoquinone analogues with different amino substitutions at position 3 of the quinone ring earlier reported for macrofilaricidal activity were selected and screened against purified cytosolic GST isolated from the bovine filarial worm Setaria digitata and IC₅₀ values were determined. Of the 11 compounds tested, 8 showed good inhibition against S. digitata GST. The IC₅₀ values of the most effective macrofilaricidal compounds—11 [2-(4-methylpiperazin-1-yl)naphthalene-1,4-dione] and 9 {2-[(1,3-dimethylbutyl)amino]naphthalene -1,4-dione}—were 0.872 and 0.994 mM, respectively. Compounds 9 and 11 were further studied for type of enzyme inhibition and found to exhibit competitive and uncompetitive inhibition kinetics, respectively, with respect to substrate GSH. All 11 compounds were in agreement with Lipinski’s rule of five and passed through the FAFDrugs ADME/tox filter. Molecular docking was carried out using the modeled 3D structure of wbGST PDB ID:1SFM as receptor and substituted naphthoquinones as ligands using AutoDock 4.0. The binding energy of nine compounds varied from −9.15 to −6.58 Kcal mol⁻¹, whereas compounds 8 and 10 did not show any binding to the receptor. Among the compounds studied, compound 7 {2-[3-(diethylamino) propyl]aminonaphthalene-1,4-dione} showed maximum affinity towards wbGST as it exhibited the lowest binding energy, followed by compounds 11 and 9. However compound 7 was not macrofilaricidal while 11 and 9 exhibited macrofilaricidal activity. The results of in silico and in vitro studies with the synthesized 1,4 -naphthoquinone analogues on filarial GST and in vitro macrofilaricidal activity against adult bovine filarial worm S. digitata open up a promising biochemical target for antifilarial drug development.