Marianna Flora Tomasello

Monomeric ß-amyloid interacts with type-1 insulin-like growth factor receptors to provide energy supply to neurons

ß-amyloid (Aß1−42) is produced by proteolytic cleavage of the transmembrane type-1 protein, amyloid precursor protein. Under pathological conditions, Aß1−42self-aggregates into oligomers, which cause synaptic dysfunction and neuronal loss, and are considered the culprit of Alzheimers disease (AD). However, Aß1−42 is mainly monomeric at physiological concentrations, and the precise role of monomeric Aß1−42 in neuronal function is largely unknown. We report that the monomer of Aß1−42 activates type-1 insulin-like growth factor receptors and enhances glucose uptake in neurons and peripheral cells by promoting the translocation of the Glut3 glucose transporter from the cytosol to the plasma membrane. In neurons, activity-dependent glucose uptake was blunted after blocking endogenous Aß production, and re-established in the presence of cerebrospinal fluid Aß. APP-null neurons failed to enhance depolarization-stimulated glucose uptake unless exogenous monomeric Aß1−42 was added. These data suggest that Aß1−42 monomers were critical for maintaining neuronal glucose homeostasis. Accordingly, exogenous Aß1−42 monomers were able to rescue the low levels of glucose consumption observed in brain slices from AD mutant mice.

Copper(II) ions affect the gating dynamics of the 20S proteasome: a molecular and in cell study

Due to their altered metabolism cancer cells are more sensitive to proteasome inhibition or changes of copper levels than normal cells. Thus, the development of copper complexes endowed with proteasome inhibition features has emerged as a promising anticancer strategy. However, limited information is available about the exact mechanism by which copper inhibits proteasome. Here we show that Cu(II) ions simultaneously inhibit the three peptidase activities of isolated 20S proteasomes with potencies (IC50) in the micromolar range. Cu(II) ions, in cell-free conditions, neither catalyze red-ox reactions nor disrupt the assembly of the 20S proteasome but, rather, promote conformational changes associated to impaired channel gating. Notably, HeLa cells grown in a Cu(II)-supplemented medium exhibit decreased proteasome activity. This effect, however, was attenuated in the presence of an antioxidant. Our results suggest that if, on one hand, Cu(II)-inhibited 20S activities may be associated to conformational changes that favor the closed state of the core particle, on the other hand the complex effect induced by Cu(II) ions in cancer cells is the result of several concurring events including ROS-mediated proteasome flooding, and disassembly of the 26S proteasome into its 20S and 19S components.

On the Environmental Factors Affecting the Structural and Cytotoxic Properties of IAPP Peptides

Pancreatic islets in type 2 diabetes mellitus (T2DM) patients are characterized by reduced β-cells mass and diffuse extracellular amyloidosis. Amyloid deposition involves the islet amyloid polypeptide (IAPP), a neuropancreatic hormone cosecreted with insulin by β-cells. IAPP is physiologically involved in glucose homeostasis, but it may turn toxic to β-cells owing to its tendency to misfold giving rise to oligomers and fibrils. The process by which the unfolded IAPP starts to self-assemble and the overall factors promoting this conversion are poorly understood. Other open questions are related to the nature of the IAPP toxic species and how exactly β-cells die. Over the last decades, there has been growing consensus about the notion that early molecular assemblies, notably small hIAPP oligomers, are the culprit of β-cells decline. Numerous environmental factors might affect the conformational, aggregation, and cytotoxic properties of IAPP. Herein we review recent progress in the field, focusing on the influences that membranes, pH, and metal ions may have on the conformational conversion and cytotoxicity of full-length IAPP as well as peptide fragments thereof. Current theories proposed for the mechanisms of toxicity will be also summarized together with an outline of the underlying molecular links between IAPP and amyloid beta (Aβ) misfolding.

The Inorganic Perspective of VEGF: Interactions of Cu2 + with Peptides Encompassing a Recognition Domain of the VEGF Receptor

The vascular endothelial growth factor A (VEGF-A) is a potent angiogenic factor, its activity may be influenced by the presence of copper(II) ions. To mimic the interaction between copper(II) and VEGF (Vascular Endotelial Growth Factor), the N- and C-terminally blocked peptide fragments VEGF73-101 and VEGF84-101, owing to VEGF165 protein, have been synthesized. These protein domains represent a specific recognition site with the VEGF receptor (VEGFR). Copper(II) complexes with VEGF73-101 and VEGF84-101 were investigated by means of potentiometry and UV-Vis, ESI-MS, CD, EPR spectroscopic methods. Both peptides have three histidine residues and display a binding high affinity for copper(II) ions. The proliferative activity of the peptides in the absence and presence of copper(II) ions as well as of VEGF-165 protein was also tested on HUVEC cells (Human Umbilical Vein Endothelial Cells). The VEGF73-101 showed a dose-dependent anti-proliferative activity, while the shorter peptide VEGF84-101 did not affect HUVEC proliferation, both in the presence and in the absence of VEGF.

Porphyrin Cyclodextrin Conjugates Modulate Amyloid Beta Peptide Aggregation and Cytotoxicity

Although fibrillar amyloid beta peptide (Aβ) aggregates are one of the major hallmarks of Alzheimers disease, increasing evidence suggests that soluble Aβ oligomers are the primary toxic species. Targeting the oligomeric species could represent an effective strategy to interfere with Aβ toxicity. In this work, the biological properties of 5[4-(6-O-β-cyclodextrin)-phenyl],10,15,20-tri(4-hydroxyphenyl)-porphyrin and its zinc complex were tested, as new molecules that interact with Aβ and effectively prevent its cytotoxicity. We found that these systems can cross the cell membrane to deliver Aβ intracellularly and promote its clearance. Our results provide evidence for the use of cyclodextrin-porphyrin derivatives as a promising strategy to target amyloid aggregation.

Potential therapeutics of Alzheimer's diseases: New insights into the neuroprotective role of trehalose‐conjugated beta sheet breaker peptides

Alzheimers disease (AD) is a progressive neurodegenerative disease with no cure. The conversion of the amyloid‐β (Aβ) peptide into soluble oligomers has recently become recognized as playing a key role in AD pathogenesis. Thus, prevention and therapeutic strategies against AD focus on modulating Aβ levels aiming also at stabilizing Aβs monomeric status or inhibiting the peptides self‐assembly. Peptide‐based inhibitors may provide a reasonable alternative to chemical small molecules. We report herein further insights into the neuroprotective action of two trehalose‐conjugated peptides able to counteract the Aβs oligomers associated neuronal toxicity. In addition, the Trehalose‐Succinyl‐LPFFD‐NH2 (Th‐Succ‐LPFFD‐NH2) and Ac‐LPFFD‐Trehalose (Ac‐LPFFD‐Th) derivatives protect neuronal cells from excitotoxic insult mediated by NMDA and evoke by themselves pro‐survival signal pathways as an additional cell protective action. UHPLC‐HRMS experiments suggest that a possible step associated to the neuroprotective mechanism involves the cell uptake and/or a membrane interaction of the studied peptides.

Corrigendum to: : Ac-LPFFD-Th: A Trehalose-Conjugated Peptidomimetic as a Strong Suppressor of Amyloid-β Oligomer Formation and Cytotoxicity (ChemBioChem, (2016), 17, (1541-1549), 10.1002/cbic.201600243)

The stereochemistry of threalose given in the Table of