Involvement of calcium ions in amyloid-ß-induced lamin fragmentation.

Amyloid-ß (Aß) peptide, the main pathogenic peptide in Alzheimer's disease, has been shown to induce an increase in cytoplasmic calcium concentration (CCC). In the current study, we explored the cytotoxic signal transduction pathway in 42-amino-acid Aß (Aß42)-treated HeLa cells in relation to the increase in CCC. The increase in CCC was prominent in cells treated twice with oligomeric Aß42. We previously showed that double treatment also promoted Aß-induced lamin fragmentation (AILF), which appears to be mediated by cathepsin L. Apoptotic caspase activation was a downstream event of AILF. The Ca2+ chelator BAPTA-AM suppressed cell death, cathepsin L activation, AILF, and caspase activation in Aß-treated cells. These results indicate that Aß42 induces an increase in CCC, which is an event upstream of the cytotoxic processes. The products of AILF are different from those produced by other cell death-inducing agents, such as staurosporine, which induces caspase-6-mediated lamin fragmentation (CMLF). CMLF was unaffected by BAPTA-AM and was not detected in cells treated with Aß42, indicating that Aß42 peptide induced a specific cytotoxic pathway involving AILF via increased CCC. We confirmed that the same processes (except caspase activation) operated in Aß42-treated neuroblastoma SH-SY5Y cells.

Dihydrocapsaicin induces translational repression and stress granule through HRI-eIF2α phosphorylation axis.

Stress granules (SGs) are cytoplasmic biomolecular condensates that are formed against a variety of stress conditions when translation initiation is perturbed. SGs form through the weak protein-protein, protein-RNA, and RNA-RNA interactions, as well as through the intrinsically disordered domains and post-translation modifications within RNA binding proteins (RBPs). SGs are known to contribute to cell survivability by minimizing the stress-induced damage to the cells by delaying the activation of apoptosis. Here, we find that dihydrocapsaicin (DHC), an analogue of capsaicin, is a SG inducer that promotes polysome disassembly and reduces global protein translation via phosphorylation of eIF2α. DHC-mediated SG assembly is controlled by the phosphorylation of eIF2α at serine 51 position and is controlled by all four eIF2α stress kinases (i.e., HRI, PKR, PERK, and GCN2) with HRI showing maximal effect. We demonstrate that DHC is a bonafide compound that induces SG assembly, disassembles polysome, phosphorylates eIF2α in an HRI dependent manner, and thereby arrest global translation. Together, our results suggest that DHC is a novel SG inducer and an alternate to sodium arsenite to study SG dynamics.

Oleuropein promotes hippocampal LTP via intracellular calcium mobilization and Ca2+-permeable AMPA receptor surface recruitment.

Oleuropein (OLE), a major phenolic compound in olive oil, has been demonstrated to possess several pharmacological properties, including neuroprotection. However, the cognitive effects of OLE and its action mechanism have remained unclear. Here, we examined the effect of OLE on long-term potentiation (LTP) using field excitatory postsynaptic potential recorded in the CA1 region of both wild-type and 5XFAD mouse hippocampal slice preparations. In initial experiments with wild-type mice, 100 µM/1 h of OLE produced significant enhancements in the LTPs of Schaffer collateral synapses in the CA1 regions of treated mice, as compared to the vehicle-treated controls. As assessed by surface biotinylation and Western blot analysis, OLE caused a significant increase in protein kinase A (PKA)-mediated phosphorylation and the surface expression of GluA1 containing calcium permeable- amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (CP-AMPARs) in the hippocampus. Furthermore, we found that OLE enhanced LTP induction, while GluA1 phosphorylation occurred in an N-methyl-d-aspartate receptors (NMDARs)-independent manner. The OLE-induced CP-AMPAR trafficking resulted from elevated intracellular Ca2+ levels via regulation of phospholipase C (PLC). Consistently, we also found involvement of NMDAR-independent LTP and GluA1 phosphorylation in 5XFAD transgenic mice hippocampal slices treated with OLE. Together, our findings indicate that OLE may regulate beneficial effects on memory through the facilitation of CP-AMPAR trafficking and synaptic transmission.

Avenanthramide-C Restores Impaired Plasticity and Cognition in Alzheimer's Disease Model Mice.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline and dementia with no effective treatment. Here, we investigated a novel compound from oats named avenanthramide-C (Avn-C), on AD-related memory impairment and behavioral deficits in transgenic mouse models. Acute hippocampal slices of wild-type or AD transgenic mice were treated with Avn-C in the presence or absence of oligomeric Aß42. LTP analyses and immunoblotting were performed to assess the effect of Avn-C on Aß-induced memory impairment. To further investigate the effect of Avn-C on impaired memory and Aß pathology, two different AD transgenic mice (Tg2576 and 5XFAD) models were orally treated with either Avn-C or vehicle for 2 weeks. They were then assessed for the effect of the treatment on neuropathologies and behavioral impairments. Avn-C reversed impaired LTP in both ex vivo- and in vivo-treated AD mice hippocampus. Oral administration (6 mg/kg per day) for 2 weeks in AD mice leads to improved recognition and spatial memory, reduced caspase-3 cleavage, reversed neuroinflammation, and to accelerated glycogen synthase kinase-3ß (pS9GSK-3ß) and interleukin (IL-10) levels. Avn-C exerts its beneficial effects by binding to α1A adrenergic receptors to stimulate adenosine monophosphate-activated kinase (AMPK). All of the beneficial effects of Avn-C on LTP retrieval could be blocked by prazosin hydrochloride, a specific inhibitor of α1A adrenergic receptors. Our findings provide evidence, for the first time, that oats' Avn-C reverses the AD-related memory and behavioral impairments, and establish it as a potential candidate for Alzheimer's disease drug development.

Acute restraint stress reverses impaired LTP in the hippocampal CA1 region in mouse models of Alzheimer's disease.

Acute stress facilitates long-term potentiation (LTP) in the mouse hippocampus by modulating glucocorticoid receptors and ion channels. Here, we analysed whether this occurs in mouse models of Alzheimer's disease (AD) with impaired LTP induction. We found that a brief 30 min restraint stress protocol reversed the impaired LTP assessed with field excitatory postsynaptic potential recordings at cornu ammonis 3-1 (CA3-CA1) synapses in both Tg2576 and 5XFAD mice. This effect was accompanied by increased phosphorylation and surface expression of glutamate A1 (GluA1) -containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). Moreover, enhanced LTP induction and GluA1 phosphorylation were sustained up to 4 h after the stress. Treatment with 200 nM dexamethasone produced similar effects in the hippocampi of these mice, which supports the glucocorticoid receptor-mediated mechanism in these models. Collectively, our results demonstrated an alleviation of impaired LTP and synaptic plasticity in the hippocampal CA1 region following acute stress in the AD mouse models.

ß-Amyloid induces nuclear protease-mediated lamin fragmentation independent of caspase activation.

ß-Amyloid (Aß), a hallmark peptide of Alzheimer's disease, induces both caspase-dependent apoptosis and non-apoptotic cell death. In this study, we examined caspase-independent non-apoptotic cell death preceding caspase activation in Aß42-treated cells. We first determined the optimal treatment conditions for inducing cell death without caspase activation and selected a double-treatment method involving the incubation of cells with Aß42 for 4 and 6 h (4+6 h sample). We observed that levels of lamin A (LA) and lamin B (LB) were reduced in the 4+6 h samples. This reduction was decreased by treatment with suc-AAPF-CMK, an inhibitor of nuclear scaffold (NS) protease, but not by treatment with z-VAD-FMK, a pan-caspase inhibitor. In addition, suc-AAPF-CMK decreased the changes in nuclear morphology observed in cells in the 4+6 h samples, which were different from nuclear fragmentation observed in STS-treated cells. Furthermore, suc-AAPF-CMK inhibited cell death in the 4+6 h samples. LA and LB fragmentation occurred in the isolated nuclei and was also inhibited by suc-AAPF-CMK. Together, these data indicated that the fragmentation of LA and LB in the Aß42-treated cells was induced by an NS protease, whose identity is not clearly determined yet. A correlation between Aß42 toxicity and the lamin fragmentation by NS protease suggests that inhibition of the protease could be an effective method for controlling the pathological process of AD.

The inhibitory effects of Escherichia coli maltose binding protein on ß-amyloid aggregation and cytotoxicity.

The aggregation of ß-amyloid (Aß) peptide from its monomeric to its fibrillar form importantly contributes to the development of Alzheimer's disease. Here, we investigated the effects of Escherichia coli maltose binding protein (MBP), which has been previously used as a fusion protein, on Aß42 fibrillization, in order to improve understanding of the self-assembly process and the cytotoxic mechanism of Aß42. MBP, at a sub-stoichiometric ratio with respect to Aß42, was found to have chaperone-like inhibitory effects on ß-sheet fibril formation, due to the accumulation of Aß42 aggregates by sequestration of active Aß42 species as Aß42-MBP complexes. Furthermore, MBP increased the lag time of Aß42 polymerization, decreased the growth rate of fibril extension, and suppressed Aß42 mediated toxicity in human neuroblastoma SH-SY5Y cells. It appears that MBP decreases the active concentration of Aß42 by sequestering it as Aß42-MBP complex, and that this sequestration suppresses ongoing nucleation and retards the growth rate of Aß42 species required for fibril formation. We speculate that inhibition of the growth rate of potent Aß42 species by MBP suppresses Aß42-mediated toxicity in SH-SY5Y cells.

Keampferol-3-O-rhamnoside abrogates amyloid beta toxicity by modulating monomers and remodeling oligomers and fibrils to non-toxic aggregates.

BACKGROUND: Aggregation of soluble, monomeric ß- amyloid (Aß) to oligomeric and then insoluble fibrillar Aß is a key pathogenic feature in development of Alzheimer's disease (AD). Increasing evidence suggests that toxicity is linked to diffusible Aß oligomers, rather than to insoluble fibrils. The use of naturally occurring small molecules for inhibition of Aß aggregation has recently attracted significant interest for development of effective therapeutic strategies against the disease. A natural polyphenolic flavone, Kaempferol-3-O-rhamnoside (K-3-rh), was utilized to investigate its effects on aggregation and cytotoxic effects of Aß42 peptide. Several biochemical techniques were used to determine the conformational changes and cytotoxic effect of the peptide in the presence and absence of K-3-rh. RESULTS: K-3-rh showed a dose-dependent effect against Aß42 mediated cytotoxicity. Anti-amyloidogenic properties of K-3-rh were found to be efficient in inhibiting fibrilogenesis and secondary structural transformation of the peptide. The consequence of these inhibitions was the accumulation of oligomeric structural species. The accumulated aggregates were smaller, soluble, non-ß-sheet and non-toxic aggregates, compared to preformed toxic Aß oligomers. K-3-rh was also found to have the remodeling properties of preformed soluble oligomers and fibrils. Both of these conformers were found to remodel into non-toxic aggregates. The results showed that K-3-rh interacts with different Aß conformers, which affects fibril formation, oligomeric maturation and fibrillar stabilization. CONCLUSION: K-3-rh is an efficient molecule to hinder the self assembly and to abrogate the cytotoxic effects of Aß42 peptide. Hence, K-3-rh and small molecules with similar structure might be considered for therapeutic development against AD.