A Novel Ex Vivo Model to Investigate the Underlying Mechanisms in Alzheimer's Disease

The human acetylcholinesterase C-terminal T30 peptide activates neuronal growth through alpha 7 nicotinic acetylcholine receptors and the mTOR pathway

Acetylcholinesterase (AChE) is a highly conserved enzyme responsible for the regulation of acetylcholine signaling within the brain and periphery. AChE has also been shown to participate in non-enzymatic activity and contribute to cellular development and aging. In particular, enzymatic cleavage of the synaptic AChE isoform, AChE-T, is shown to generate a bioactive T30 peptide that binds to the ⍺7 nicotinic acetylcholine receptor (nAChR) at synapses. Here, we explore intracellular mechanisms of T30 signaling within the human cholinergic neural cell line SH-SY5Y using high performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS/MS). Proteomic analysis of cells exposed to (100 nM) T30 for 3-days reveals significant changes within proteins important for cell growth. Specifically, bioinformatic analysis identifies proteins that converge onto the mammalian target of rapamycin (mTOR) pathway signaling. Functional experiments confirm that T30 regulates neural cell growth via mTOR signaling and ⍺7 nAChR activation. T30 was found promote mTORC1 pro-growth signaling through an increase in phosphorylated elF4E and S6K1, and a decrease in the autophagy LC3B-II protein. These findings are corroborated in hippocampal neurons and show that T30 promotes dendritic arborization. Taken together, our findings define mTOR as a novel pathway activated by T30 interaction with the nAChR and suggest a role for this process in human disease.

AChE as a spark in the Alzheimer's blaze - Antagonizing effect of a cyclized variant

The amyloid precursor protein (APP), presenilin 1 (PS1), amyloid beta (Aβ), and GSK3 are the effectors, which are significantly associated with progression of Alzheimer's Disease (AD) and its symptoms. A significant protein, acetylcholinesterase (AChE) becomes dysfunctional as a result of cholinergic neuronal loss in AD pathology. However, certain associated peptides potentiate the release of primary neuropathological hallmarks, i.e., senile plaque and neurofibrillary tangles (NFTs), by modulating the alpha 7 acetylcholinesterase receptor (α7nAChR). The AChE variants, T30 and T14 have also been found to be elevated in AD patients and mimic the toxic actions of pathological events in patients. The manuscript discusses the significance of AChE inhibitors in AD therapeutics, by indicating the disastrous role of molecular alterations and elevation of AChE, accompanied with the downstream effects instigated by the peptide, supported by clinical evidence and investigations. The cyclized variant of AChE peptide, NBP14 has been identified as a novel candidate that reverses the harmful effects of T30, T14 and Aβ, mainly calcium influx, cell viability and AChE release. The review aims to grab the attention of neuro-researchers towards the significance of triggering effectors in propagating AD and role of AChE in regulating them, which can potentially ace the development of reliable therapeutic candidates, similar to NBP14, to mitigate neurodegeneration.

Radioiodinated 9-fluorenone derivatives for imaging α7-nicotinic acetylcholine receptors

A series of 9H-fluoren-9-one substituents were synthesized and evaluated for imaging cerebral α7-nAChRs. Meta-iodine substituted 9-fluorenone 5 with high binding affinity (K _i = 9.3 nM) and selectivity was radiolabeled with ¹²⁵I. Fully in vitro and in vivo studies of [¹²⁵I]5 have been performed. [¹²⁵I]5 exhibited well brain uptake with a peak concentration of 7.5 ± 0.9% ID/g in mice brains. Moreover, ex vivo autoradiography studies and micro single-photon emission computed tomography (micro-SPECT/CT) dynamic imaging in mice confirmed its in vivo imaging properties. Besides, molecular docking and MD studies were also performed to interpret the binding mechanisms of the two series of ligands towards α7-nAChRs. To conclude, the meta-iodine substituted 9-fluorenone [¹²⁵I]5 could be a promising tracer for imaging α7-nAChRs.

Protective and reversal actions of a novel peptidomimetic against a pivotal toxin implicated in Alzheimer's disease

Despite the many attempts to understand the aetiology of Alzheimer's disease, the basic mechanisms accounting for the progressive cycle of neuronal loss are still unknown. Previous work has suggested that the pivotal molecule mediating neurodegeneration could be an independently acting peptide cleaved from acetylcholinesterase. This previously unidentified agent acts as a signalling molecule in selectively vulnerable groups of cells where erstwhile developmental mechanisms are activated inappropriately to have a toxic effect in the context of the mature brain. We have previously shown that the toxic actions of this peptide, whose level is doubled in the Alzheimer brain, can be blocked by a cyclised variant (NBP14). However, the size and properties of NBP14 would render it unlikely as a feasible therapeutic candidate. Here therefore we test a synthetic peptidomimetic (NB-0193), modelled on the binding of NBP14 to the target alpha-7 nicotinic receptor, and benchmarked against it to screen for reversal effects using real-time optical imaging in rat brain slices. The blocking action of NB-0193 was confirmed by testing its effect against peptide-induced calcium influx in cell cultures, where it showed a dose-dependent profile over a trophic-toxic range. Moreover, NB-0193 presented promising pharmacokinetic characteristics and could therefore prompt a new therapeutic approach against Alzheimer's disease.

A Multidisciplinary Approach Reveals an Age-Dependent Expression of a Novel Bioactive Peptide, Already Involved in Neurodegeneration, in the Postnatal Rat Forebrain

The basal forebrain has received much attention due to its involvement in multiple cognitive functions, but little is known about the basic neuronal mechanisms underlying its development, nor those mediating its primary role in Alzheimer’s disease. We have previously suggested that a novel 14-mer peptide, ‘T14’, could play a pivotal role in Alzheimer’s disease, via reactivation of a developmental signaling pathway. In this study, we have characterized T14 in the context of post-natal rat brain development, using a combination of different techniques. Ex-vivo rat brain slices containing the basal forebrain, at different stages of development, were used to investigate large-scale neuronal network activity in real time with voltage-sensitive dye imaging. Subsequent Western blot analysis revealed the expression profile of endogenous T14, its target alpha7 nicotinic receptor and the familiar markers of Alzheimer’s: amyloid beta and phosphorylated Tau. Results indicated maximal neuronal activity at the earliest ages during development, reflected in a concomitant profile of T14 peptide levels and related proteins. In conclusion, these findings show that the peptide, already implicated in neurodegenerative events, has an age-dependent expression, suggesting a possible contribution to the physiological mechanisms underlying brain maturation.

Modulatory Effects of a Novel Cyclized Peptide in Reducing the Expression of Markers Linked to Alzheimer's Disease

Despite many studies attempt to identify the primary mechanisms underlying neurodegeneration in Alzheimer's disease (AD), the key events still remain elusive. We have previously shown that a peptide cleaved from the acetylcholinesterase (AChE) C-terminus (T14) can play a pivotal role as a signaling molecule in neurodegeneration, via its interaction with the α7 nicotinic acetylcholine receptor. The main goal of this study is to determine whether a cyclized variant (NBP14) of the toxic AChE-derived peptide can antagonize the effects of its linear counterpart, T14, in modulating well-known markers linked to neurodegeneration. We investigate this hypothesis applying NBP14 on ex-vivo rat brain slices containing the basal forebrain. Western blot analysis revealed an inhibitory action of NBP14 on naturally occurring T14 peptide, as well as on endogenous amyloid beta, whereas the expression of the nicotinic receptor and phosphorylated Tau was relatively unaffected. These results further confirm the neurotoxic properties of the AChE-peptide and show for the first time in an ex-vivo preparation the possible neuroprotective activity of NBP14, over a protracted period of hours, indicating that T14 pathway may offer a new prospect for therapeutic intervention in AD pathobiology.

An Alternative Approach to Study Primary Events in Neurodegeneration Using Ex Vivo Rat Brain Slices

Despite numerous studies that attempt to develop reliable animal models which reflecting the primary processes underlying neurodegeneration, very few have been widely accepted. Here, we propose a new procedure adapted from the well-known ex vivo brain slice technique, which offers a closer in vivo-like scenario than in vitro preparations, for investigating the early events triggering cell degeneration, as observed in Alzheimer's disease (AD). This variation consists of simple and easily reproducible steps, which enable preservation of the anatomical cytoarchitecture of the selected brain region and its local functionality in a physiological milieu. Different anatomical areas can be obtained from the same brain, providing the opportunity to perform multiple experiments with the treatments in question in a site-, dose-, and time-dependent manner. Potential limitations which could affect the outcomes related to this methodology are related to the conservation of the tissue, i.e., the maintenance of its anatomical integrity during the slicing and incubation steps and the section thickness, which can influence the biochemical and immunohistochemical analysis. This approach can be employed for different purposes, such as exploring molecular mechanisms involved in physiological or pathological conditions, drug screening, or dose-response assays. Finally, this protocol could also reduce the number of animals employed in behavioral studies. The application reported here has been recently described and tested for the first time on ex vivo rat brain slices containing the basal forebrain (BF), which is one of the cerebral regions primarily affected in AD. Specifically, it has been demonstrated that the administration of a toxic peptide derived from the C-terminus of acetylcholinesterase (AChE) could prompt an AD-like profile, triggering, along the antero-posterior axis of the BF, a differential expression of proteins altered in AD, such as the alpha7 nicotinic receptor (α7-nAChR), phosphorylated Tau (p-Tau), and amyloid beta (Aβ).