Improvement in inflammation is associated with the protective effect of Gly-Pro-Glu and cycloprolylglycine against Aβ-induced depletion of the hippocampal somatostatinergic system

Glycine-proline-glutamate (GPE) is a cleaved tripeptide of IGF-I that can be processed to cycloprolylglycine (cPG) in the brain. IGF-I protects the hippocampal somatostatinergic system from β-amyloid (Aβ) insult and although neither IGF-I-derived peptides bind to IGF-I receptors, they exert protective actions in several neurological disorders. As their effects on the hippocampal somatostatinergic system remain unknown, the objective of this study was to evaluate if cPG and/or GPE prevent the deleterious effects of Aβ_25-35 infusion on this system and whether changes in intracellular-related signaling and interleukin (IL) content are involved in their protective effect. We also determined the effect of cPG or GPE co-administration with Aβ_25-35 on IL secretion in glial cultures and the influence of these ILs on signaling activation and somatostatin synthesis in neuronal cultures. cPG or GPE co-administration reduced Aβ-induced cell death and pro-inflammatory ILs, increased IL-4 and partially avoided the reduction of components of the somatostatinergic system affected by Aβ_25-35. GPE increased activation of Akt and CREB and reduced GSK3β activation and astrogliosis, whereas cPG increased phosphorylation of extracellular signal-regulated kinases. Both peptides converged in the activation of mTOR and S6 kinase. Co-administration of these peptides with Aβ_25-35 to glial cultures increased IL-4 and reduced IL-1β; this release of IL-4 could be responsible for activation of Akt and increased somatostatin in neuronal cultures. Our findings suggest that cPG and GPE exert protective effects against Aβ on the somatostatinergic system by a reduction of the inflammatory environment that may activate different pro-survival pathways in these neurons.

The isolated N terminus of Ring1B is a well-folded, monomeric fragment with native-like structure

The Polycomb group (PcG) proteins assemble into Polycomb repressive complexes (PRCs), PRC1 and PRC2, which act as general transcriptional repressors. PRC1 comprises a variety of biochemical entities endowed with histone H2A monoubiquitylation activity conferred by really interesting new gene (RING) finger E3 ubiquitin ligases Ring1A and Ring1B. All PRC1 complexes contain Ring1 proteins which are essential for Polycomb epigenetic regulation. We have been able to express the isolated N-terminal region of Ring1B, N-Ring1B, comprising the first 221 residues of the 334-residue-long Ring1B. This fragment contains the 41-residue-long RING finger motif, and flanking sequences that form an interacting platform for PcG and non-PcG proteins. We found that the N-Ring1B is a well-folded, monomeric fragment, with native-like structure which unfolds irreversibly. The protein is capable of binding to an ubiquitin-conjugase protein (with an 85% of sequence similarity to the Ring1B physiological partner) with moderate affinity.

Deciphering the binding between Nupr1 and MSL1 and their DNA-repairing activity

The stress protein Nupr1 is a highly basic, multifunctional, intrinsically disordered protein (IDP). MSL1 is a histone acetyl transferase-associated protein, known to intervene in the dosage compensation complex (DCC). In this work, we show that both Nupr1 and MSL1 proteins were recruited and formed a complex into the nucleus in response to DNA-damage, which was essential for cell survival in reply to cisplatin damage. We studied the interaction of Nupr1 and MSL1, and their binding affinities to DNA by spectroscopic and biophysical methods. The MSL1 bound to Nupr1, with a moderate affinity (2.8 µM) in an entropically-driven process. MSL1 did not bind to non-damaged DNA, but it bound to chemically-damaged-DNA with a moderate affinity (1.2 µM) also in an entropically-driven process. The Nupr1 protein bound to chemically-damaged-DNA with a slightly larger affinity (0.4 µM), but in an enthalpically-driven process. Nupr1 showed different interacting regions in the formed complexes with Nupr1 or DNA; however, they were always disordered (“fuzzy”), as shown by NMR. These results underline a stochastic description of the functionality of the Nupr1 and its other interacting partners.

Stability and binding of the phosphorylated species of the N-terminal domain of enzyme I and the histidine phosphocarrier protein from the Streptomyces coelicolor phosphoenolpyruvate:sugar phosphotransferase system

The phosphotransferase system (PTS) is involved in the use of carbon sources in bacteria. It is formed by two general proteins: enzyme I (EI) and the histidine phosphocarrier (HPr), and various sugar-specific permeases. EI is formed by two domains, with the N-terminal domain (EIN) being responsible for the binding to HPr. In low-G+C Gram-positive bacteria, HPr becomes phosphorylated not only by phosphoenolpyruvate (PEP) at the active-site histidine, but also by ATP at a serine. In this work, we have characterized: (i) the stability and binding affinities between the active-site-histidine phosphorylated species of HPr and the EIN from Streptomyces coelicolor; and (ii) the stability and binding affinities of the species involving the phosphorylation at the regulatory serine of HPr(sc). Our results show that the phosphorylated active-site species of both proteins are less stable than the unphosphorylated counterparts. Conversely, the Hpr-S47D, which mimics phosphorylation at the regulatory serine, is more stable than wild-type HPr(sc) due to helical N-capping effects, as suggested by the modeled structure of the protein. Binding among the phosphorylated and unphosphorylated species is always entropically driven, but the affinity and the enthalpy vary widely.

Non-canonical residues of the marginally stable monomeric ubiquitin conjugase from goldfish are involved in binding to the C terminus of Ring 1B

E2 ubiquitin conjugases are ~20kDa enzymes involved in ubiquitination processes in eukaryotes. The E2s are responsible for the transference of ubiquitin (Ub) to E3 enzymes, which finally transfer Ub to diverse target proteins, labelling them for degradation, localization and regulation. Although their functions are relatively well-characterized, their conformational stabilities are poorly known. In this work, we have used, as a model for our biophysical and binding studies, the E2-C from Carassius auratus (goldfish), a homologue of the human ubiquitin conjugase UbcH10. E2-C(ca) was a monomeric protein with an elongated shape; moreover, the protein was only marginally stable within a narrow pH range (from 6.0 to 8.0). We also explored the binding of E2-C(ca) towards non-canonical E3 ligases. Binding of E2-C(ca) to the C terminus of murine Ring 1B (C-Ring1B), which does not contain the RING finger of the whole Ring1B, occurred with an affinity of ~400nM, as shown by fluorescence and ITC. Furthermore, binding of E2-C(ca) to C-Ring1B did not occur at its canonical E2-loops, since residues M43 and F53, far away from those loops, were involved in binding. Thus, the C-Ring1B-interacting region of E2-C(ca) comprises the first β-strand and nearby residues.

The conformational stability and biophysical properties of the eukaryotic thioredoxins of Pisum sativum are not family-conserved

Thioredoxins (TRXs) are ubiquitous proteins involved in redox processes. About forty genes encode TRX or TRX-related proteins in plants, grouped in different families according to their subcellular localization. For instance, the h-type TRXs are located in cytoplasm or mitochondria, whereas f-type TRXs have a plastidial origin, although both types of proteins have an eukaryotic origin as opposed to other TRXs. Herein, we study the conformational and the biophysical features of TRXh1, TRXh2 and TRXf from Pisum sativum. The modelled structures of the three proteins show the well-known TRX fold. While sharing similar pH-denaturations features, the chemical and thermal stabilities are different, being PsTRXh1 (Pisum sativum thioredoxin h1) the most stable isoform; moreover, the three proteins follow a three-state denaturation model, during the chemical-denaturations. These differences in the thermal- and chemical-denaturations result from changes, in a broad sense, of the several ASAs (accessible surface areas) of the proteins. Thus, although a strong relationship can be found between the primary amino acid sequence and the structure among TRXs, that between the residue sequence and the conformational stability and biophysical properties is not. We discuss how these differences in the biophysical properties of TRXs determine their unique functions in pea, and we show how residues involved in the biophysical features described (pH-titrations, dimerizations and chemical-denaturations) belong to regions involved in interaction with other proteins. Our results suggest that the sequence demands of protein-protein function are relatively rigid, with different protein-binding pockets (some in common) for each of the three proteins, but the demands of structure and conformational stability per se (as long as there is a maintained core), are less so.

Nucleotide-induced conformational transitions in the CBS domain protein MJ0729 of Methanocaldococcus jannaschii

Nucleotide-binding cystathionine β-synthase (CBS) domains function as regulatory motifs in several proteins distributed through all kingdoms of life. This function has been proposed based on their affinity for adenosyl-derivatives, although the exact binding mechanisms remain largely unknown. The question of how CBS domains exactly work is relevant because in humans, several genetic diseases have been associated with mutations in those motifs. In this work, we describe the adenosyl-ligand (AMP, ATP, NADP and SAM) properties of the wild-type CBS domain protein MJ0729 from Methanocaldococcus jannaschii by using a combination of spectroscopic techniques (fluorescence, FTIR and FRET). The fluorescence results show that binding to AMP and ATP occurs with an apparent dissociation constant of ~10 µM, and interestingly enough, binding induces protein conformational changes, as shown by FTIR. On the other hand, fluorescence spectra (FRET and steady-state) did not change upon addition of NADP and SAM to MJ0729, suggesting that tryptophan and/or tyrosine residues were not involved in the recognition of those ligands; however, there were changes in the secondary structure of the protein upon addition of NADP and SAM, as shown by FTIR (thus, indicating binding to the nucleotide). Taken together, these results suggest that: (i) the adenosyl ligands bind to MJ0729 in different ways, and (ii) there are changes in the protein secondary structure upon binding of the nucleotides.

The CBS domain protein MJ0729 of Methanocaldococcus jannaschii binds DNA

The cystathionine beta-synthase (CBS) domains function as regulatory motifs in several proteins. Elucidating how CBS domains exactly work is relevant because several genetic human diseases have been associated with mutations in those motifs. Here, we show, for the first time, that a CBS domain binds calf-thymus DNA and E-boxes recognized by transcription factors. We have carried out the DNA-binding characterization of the CBS domain protein MJ0729 from Methanocaldococcus jannaschii by biochemical and spectroscopic techniques. Binding induces conformational changes in the protein, and involves the sole tryptophan residue. The apparent dissociation constant for the E-boxes is ∼10 μM. These results suggest that CBS domains might interact with DNA.

Evidence of non-functional redundancy between two pea h-type thioredoxins by specificity and stability studies

The largest group of plant thioredoxins (TRXs) consists of the so-called h-type; their great number raises questions about their specific or redundant roles in plant cells. Pisum sativum thioredoxin h1 (PsTRXh1) and Pisum sativum thioredoxin h2 (PsTRXh2) are both h-type TRXs from pea (Pisum sativum) previously identified and biochemically characterized. While both are involved in redox regulation and show a high-sequence identity (60%), they display different behavior during in vitro and in vivo assays. In this work, we show that these two proteins display different specificity in the capturing of protein targets in vitro, by the use of a new stringent method. PsTRXh2 interacted with classical antioxidant proteins, whereas PsTRXh1 showed a completely different pattern of targeted proteins, and was able to capture a transcription factor. We also showed that the two proteins display very different thermal and chemical stabilities. We suggest that the differences in thermal and chemical stability point to a distinct and characteristic pattern of protein specificity.

The basic helix-loop-helix region of human neurogenin 1 is a monomeric natively unfolded protein which forms a "fuzzy" complex upon DNA binding

Neuronal specification is regulated by the activity of transcription factors containing the basic helix-loop-helix motif (bHLH); these regulating proteins include, among others, the neurogenin (Ngn) family, related to the atonal family of genes. Neurogenin 1 (NGN1) is a 237-residue protein that contains a bHLH domain and is involved in neuronal differentiation. In this work, we synthesized the bHLH region of NGN1 (bHLHN) comprising residues 90-150 of the full-length NGN1. The domain is a monomeric natively unfolded protein with a pH-dependent premolten globule conformation, as shown by several spectroscopic techniques (namely, NMR, fluorescence, FTIR, and circular dichroism). The unfolded character of the domain also explains, first, the impossibility of its overexpression in several Escherichia coli strains and, second, its insolubility in aqueous buffers. To the best of our knowledge, this is the first extensive study of the conformational preferences of a bHLH domain under different solution conditions. Upon binding to two DNA E-boxes, the protein forms "fuzzy" complexes (that is, the complexes were not fully folded). The affinities of bHLHN for both DNA boxes were smaller than those of other bHLH domains, which might explain why the protein-DNA complexes were not fully folded.

Inflammatory response in Parkinsonism

Inflammatory responses have been proposed as important factors in dopaminergic neuro-degeneration in Parkinsonism. Increasing evidence suggests that the alteration of the glial microenvironment induced by neuronal degeneration could be deleterious to the remaining neurons. The activation of microglia/macrophages and reactive astrocytes may have a negative effect on the surrounding parenchyma, perpetuating the neurodegenerative process. However, this alteration may also go beyond the brain parenchyma and stimulate other inflammatory changes in other systems, inducing the release of proinflammatory cytokines and probably Acute Phase Proteins (APP) and Glucocorticoids (GC). In this work we review the latest advances in the field to provide a picture of the state of the art of studies of inflammatory responses and Parkinsonism, hopefully opening up new therapeutic perspectives for patients with Parkinson's disease.

Somatostatin and Alzheimer's disease

Alzheimer's disease (AD) is characterized by the cerebral deposition of senile plaques that are mainly composed of a set of peptides referred to as amyloid beta-peptides (Abeta). Among the numerous neuropeptides produced in intrinsic cortical and hippocampal neurons, somatostatin (SRIF) has been found to be the most consistently reduced in the brain and cerebrospinal fluid of AD patients. SRIF receptors (SSTR), which mediate the neuromodulatory signals of SRIF, are also markedly depleted in the AD brain, there being subtype-selective alterations in cortical areas. In the rat temporal cortex, we have shown that intracerebroventricular infusion of Abeta25-35 results in a decrease in SRIF-like immunoreactivity and in SRIF receptor subtype 2 (SSTR2) mRNA and protein levels, in correlation with a decrease in SSTR functionality. Insulin-like growth factor-I prevents the reduction in these parameters induced by Abeta25-35. Abeta has recently been demonstrated to be degraded primarily by a neutral endopeptidase, neprilysin, in the brain. SRIF regulates brain Abeta levels via modulation of neprilysin activity. Because SRIF expression in the brain declines upon aging in various mammals, including rodents, apes and humans, the aging-dependent reduction of SRIF has been hypothesized to trigger accumulation of Abeta in the brain by suppressing neprilysin action. Here we present an overview of recent advances on the role of SRIF in AD and its relationship with Abeta peptides.

17β-Estradiol protects depletion of rat temporal cortex somatostatinergic system by β-amyloid

Estradiol prevents amyloid-beta peptide (Abeta)-induced cell death through estrogen receptors (ERs) and modulates somatostatin (SRIF) responsiveness in the rat brain. As intracerebroventricular (ICV) Abeta25-35 administration reduces SRIFergic tone in the temporal cortex of ovariectomized (Ovx) rats, we asked whether 17beta-estradiol (E2) treatment can restore the Abeta25-35 induced changes in SRIF content, SRIF receptor density and adenylyl cyclase (AC) activity, as well as if these effects are mediated by ERs. E2 treatment did not change Abeta25-35 levels in the temporal cortex, but partially restored the SRIFergic parameters affected by Abeta insult and decreased cell death, which was correlated with Akt activation. The ER antagonist ICI 182,780 prevented the protective effect of E2 on sst2 levels, but did not modify SRIF levels. Furthermore, ICI 182,780 treatment further decreased sst2 protein and mRNA levels when administered alone to Abeta25-35-treated rats, suggesting that it may block the effects of endogenous estrogens. These findings indicate that E2 protects the temporal cortical SRIFergic system from Abeta-induced depletion independently of Abeta accumulation.

Alteration of the somatostatinergic system in the striatum of rats with acute experimental autoimmune encephalomyelitis

To date, the neurochemical basis underlying the motor and cognitive deficits described in patients with multiple sclerosis (MS) is unclear. Since the neuropeptide somatostatin (SRIF) and the striatum have been implicated in movement control and implicit memory, the aim of this study was to analyze the striatal somatostatinergic system in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). Female Lewis rats were immunized with an emulsion containing myelin basic protein (MBP) in complete Freund's adjuvant to induce the disease. The animals were decapitated when limp tail (grade 1) or severe hind limb paralysis (grade 3) was observed. Acute EAE in grade 3 did not modify striatal somatostatin-like immunoreactivity (SRIF-LI) content but decreased the overall SRIF receptor density, without affecting the apparent affinity, in the rat striatal membranes. A selective reduction in the protein levels of the SRIF receptor subtype sst2, analyzed by Western blotting, was detected in the EAE rats, which correlated with decreased sst2 mRNA levels. The expression of the receptor subtypes sst1, sst3 or sst4 was unaltered by the disease. The decrease in the SRIF receptor density was accompanied by an attenuated capacity of SRIF to inhibit both basal and forskolin-stimulated adenylyl cyclase activity. No significant changes, however, were found in the protein levels of Gi proteins (G(ialpha1), G(ialpha2) or G(ialpha3)) nor in those of the G-protein-coupled receptor kinase subtypes GRK2, GRK5 or GRK6. Acute EAE in grade 1 did not modify any of the parameters studied. In conclusion, these data demonstrate that acute EAE, in grade 3, disrupts the rat striatal SRIF receptor-effector system. These findings provide new insight into the molecular basis of EAE which might contribute to a better understanding of multiple sclerosis in humans.

Effects of single and continuous administration of amyloid beta-peptide (25-35) on adenylyl cyclase activity and the somatostatinergic system in the rat frontal and parietal cortex

It is unknown whether the amyloid beta-peptide (Abeta), a principal component found in extracellular neuritic plaques in the brain of patients with Alzheimer's disease (AD), is capable of altering adenylyl cyclase (AC) activity and the somatostatin (SRIF) receptor-effector system in the cerebral cortex of the patients. Therefore, the objective of this study was to investigate the effect of the beta fragment, beta (25-35), on AC activity and the somatostatinergic system in the rat frontoparietal cortex. A single dose of beta (25-35) (10microg) injected intracerebroventricularly significantly decreased the density of SRIF receptors (27.4%) and increased their affinity (32.2%) in the frontoparietal cortex. The inhibitory effect of SRIF on basal and forskolin (FK)-stimulated AC activity was significantly lower in the beta (25-35)-treated rats when compared with controls. beta (25-35) did not modify Gialpha1, Gialpha2 nor Gialpha3 levels in membranes from the frontoparietal cortex. Continuous infusion of the peptide induced a decrease in the SRIF receptor density in this brain area to a similar extent as that observed 14 days after the single administration of the peptide. Likewise, this treatment decreased the SRIF receptor density in the frontal cortex (15.3%) and parietal cortex (27.2%). This effect was accompanied by a decrease in the SRIF-mediated inhibition of FK-stimulated AC activity (from 41.6% to 25.6%) in the frontal cortex as well by a decrease in basal AC activity (from 36.9% to 31.6%) and FK-stimulated AC activity (from 35.6% to 27.1%) in the parietal cortex. Continuous infusion of Abeta (25-35) had no effect on Gialpha1, Gialpha2 or Gialpha3 levels in membranes from frontal and parietal cortex. However, this treatment caused a decrease in SRIF-like immunoreactivity content in the parietal (38.9%) and frontal (20.4%) cortex. These results suggest that Abeta might be involved in the alterations of somatostatinergic system reported in AD.

Protective effects of insulin-like growth factor-I on the somatostatinergic system in the temporal cortex of beta-amyloid-treated rats

Insulin-like growth factor-I (IGF-I) has protective effects against beta-amyloid (Abeta)-induced neuronal cell death. Because alterations of the somatostatinergic system have been described in Alzheimer's disease, we investigated the effects of the Abeta peptide and the possible protective role of IGF-I on the somatostatinergic system of the rat temporal cortex and on cell death and phosphorylated (p)-Akt levels in this area. Abeta25-35 was administered intracerebroventricularly to male rats via an osmotic minipump over 14 days (300 pmol/day). Another group received a subcutaneous IGF-I infusion (50 microg/kg/day), concomitant with Abeta25-35 administration, whereas a third group received IGF-I alone. Abeta25-35 significantly decreased the somatostatin (SRIF)-like immunoreactive content and the SRIF receptor density, as a result of a decrease in the levels of the SRIF receptor subtype 2. The inhibitory effect of SRIF on adenylyl cyclase activity was significantly lower after Abeta25-35 infusion, whereas the levels of the inhibitory G protein subunit Gialpha1, Gialpha2 or Gialpha3 were unaltered. Cell death was increased and p-Akt levels decreased in Abeta25-35-treated animals. IGF-I administration increased immunoreactive IGF-I levels in the temporal cortex and restored all parameters affected by Abeta25-35 to baseline values. These findings suggest that IGF-I prevents the deleterious effect of Abeta25-35 on the somatostatinergic system.

Gly-Pro-Glu protects beta-amyloid-induced somatostatin depletion in the rat cortex

The effect of Gly-Pro-Glu (GPE) on the somatostatinergic system of the temporal cortex in amyloid beta-peptide (Abeta) treated rats was investigated. Intracerebroventricular Abeta25-35 administration for 14 days (300 pmol/day) to ovariectomized rats produced a marked reduction in somatostatin (SRIF) content, SRIF receptor density and reduced the inhibitory effect of SRIF on adenylyl cyclase activity. I.p. injection of three doses (300 microg) of GPE on days 0, 6 and 12 resulted in a partial recovery of the parameters affected by Abeta25-35 administration. These results indicate that GPE may have an in vivo effect protecting the temporal cortical somatostatinergic system from Abeta insult.