Translational control of BACE1 may go awry in Alzheimer's disease

Esculentoside A alleviates cognitive deficits and amyloid pathology through peroxisome proliferator-activated receptor γ-dependent mechanism in an Alzheimer's disease model

BACKGROUND

Alzheimer's disease (AD) is characterized clinically by cognitive deficits and pathologically by amyloid-β (Aβ) deposition and tau aggregation, as well as the brain atrophy. Esculentoside A (EsA), a neuroprotective saponin, is isolated from Phytolacca esculenta and shows potent health-promoting effects in a variety of experimental models. However, there are minimal reports on the effects of EsA on triple transgenic AD mice.

PURPOSE

The current research aimed at investigating the protective effects and underlying mechanisms of EsA on the mitigation of cognitive deficits and pathology in triple transgenic AD mice.

METHODS

Triple transgenic AD mice (3 × Tg-AD) of 8 months old received intraperitoneal treatment of 5 or 10 mg/kg EsA for 8 consecutive weeks. Morris water maze test and open field test were made to evaluate the cognitive function and degree of anxiety of the mice. Liquid chromatography with tandem mass spectrometry analysis was performed to characterize and to quantify EsA in the blood and brain of mice. Immunofluorescence assay and Western blot were adopted to measure the levels of peroxisome proliferator-activated receptor gamma (PPARγ) and key proteins in Aβ pathology, ER stress- and apoptosis-associated pathways. The combination of EsA with PPARγ were theoretically calculated by molecular docking programs and experimentally confirmed by the bio-layer interferometry technology.

RESULTS

Supplemental EsA could improve the cognitive deficits of 3 × Tg-AD mice. EsA penetrated the brain-blood barrier to exert a strong effect on AD mice, evidenced as decreasing Aβ generation, reducing the degrees of oxidative and ER stress, and mitigating neuronal apoptosis through the increase of PPARγ expression. In the culture of primary neurons, addition of PPARγ inhibitor GW9662 eliminated the effects of EsA on AD pathologies. Direct combination of EsA with PPARγ were demonstrated by molecular docking programs and bio-layer interferometry technology.

CONCLUSIONS

For the first time, these outcomes revealed that EsA could penetrate the brain-blood barrier to exert a strong effect on ameliorating cognitive deficits in 3 × Tg-AD mice and exert neuroprotective effects toward AD pathology via PPARγ-dependent mechanism.

Glucose metabolism: A link between traumatic brain injury and Alzheimer's disease

Traumatic brain injury (TBI), a growing public health problem, is a leading cause of death and disability worldwide, although its prevention measures and clinical cares are substantially improved. Increasing evidence shows that TBI may increase the risk of mood disorders and neurodegenerative diseases, including Alzheimer's disease (AD). However, the complex relationship between TBI and AD remains elusive. Metabolic dysfunction has been the common pathology in both TBI and AD. On the one hand, TBI perturbs the glucose metabolism of the brain, and causes energy crisis and subsequent hyperglycolysis. On the other hand, glucose deprivation promotes amyloidogenesis via β-site APP cleaving enzyme-1 dependent mechanism, and triggers tau pathology and synaptic function. Recent findings suggest that TBI might facilitate Alzheimer's pathogenesis by altering metabolism, which provides clues to metabolic link between TBI and AD. In this review, we will explore how TBI-induced metabolic changes contribute to the development of AD.

Effect of a Lens Protein in Low-Temperature Culture of Novel Immortalized Human Lens Epithelial Cells (iHLEC-NY2)

The prevalence of nuclear cataracts was observed to be significantly higher among residents of tropical and subtropical regions compared to those of temperate and subarctic regions. We hypothesized that elevated environmental temperatures may pose a risk of nuclear cataract development. The results of our in silico simulation revealed that in temperate and tropical regions, the human lens temperature ranges from 35.0 °C to 37.5 °C depending on the environmental temperature. The medium temperature changes during the replacement regularly in the cell culture experiment were carefully monitored using a sensor connected to a thermometer and showed a decrease of 1.9 °C, 3.0 °C, 1.7 °C, and 0.1 °C, after 5 min when setting the temperature of the heat plate device at 35.0 °C, 37.5 °C, 40.0 °C, and 42.5 °C, respectively. In the newly created immortalized human lens epithelial cell line clone NY2 (iHLEC-NY2), the amounts of RNA synthesis of αA crystallin, protein expression, and amyloid β (Aβ)1-40 secreted into the medium were increased at the culture temperature of 37.5 °C compared to 35.0 °C. In short-term culture experiments, the secretion of Aβ1-40 observed in cataracts was increased at 37.5 °C compared to 35.0 °C, suggesting that the long-term exposure to a high-temperature environment may increase the risk of cataracts.

Ferulic Acid Suppresses Amyloid β Production in the Human Lens Epithelial Cell Stimulated with Hydrogen Peroxide

It is well known that oxidative stresses induce the production of amyloid β (Aβ) in the brain, lens, and retina, leading to age-related diseases. In the present study, we investigated the effects of ferulic acid on the Aβ levels in H₂O₂-stimulated human lens epithelial (HLE) SRA 01/04 cells. Three types of Aβ peptides (Aβ_1-40, Aβ_1-42, and Aβ_1-43) were measured by ELISA, and the levels of mRNA for the expressed proteins related to Aβ production (APP, BACE1, and PS proteins) and degradation (ADAM10, NEP, and ECE1 proteins) were determined by quantitative real-time RT-PCR. H₂O₂ stimulation augmented gene expression of the proteins related to Aβ production, resulting in the production of three types of Aβ peptides. Treatment with 0.1 μM ferulic acid attenuated the augmentations of gene expression and production of the proteins related to the secretion of three types of Aβ peptides in the H₂O₂-stimulated HLE cells. These results provided evidence of antioxidative functions of ferulic acid for lens epithelial cells.

Epigallocatechin Gallate Attenuates β-Amyloid Generation and Oxidative Stress Involvement of PPARγ in N2a/APP695 Cells

The accumulation of β-amyloid (Aβ) peptide plaques is a major pathogenic event in Alzheimer's disease (AD). Aβ is a cleaved fragment of APP via BACE1, which is the rate-limiting enzyme in APP processing and Aβ generation. Nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) is considered to be a potential target for AD treatment, because of its potent antioxidant and inhibitory effects on Aβ production by negatively regulating BACE1. Epigallocatechin gallate (EGCG), a highly active catechin found in green tea, is known to enhance metabolic activity and cognitive ability in the mice model of AD. To investigate whether the therapeutic effect of EGCG is related to the PPARγ pathway, we analysed the alterations in the intracellular molecular expression of PPARγ after EGCG treatment in the N2a/APP695 cell line. In this study, we observed that EGCG attenuated Aβ generation in N2a/APP695 cells, such as the PPARγ agonist, pioglitazone, by suppressing the transcription and translation of BACE1 and that its effect was attenuated by the PPARγ inhibitor, GW9662. Intriguingly, EGCG significantly reinforced the activity of PPARγ by promoting its mRNA and protein expressions in N2a/APP695 cells. Moreover, EGCG also decreased the expression of pro-apoptotic proteins (Bax, caspase-3), reduced the activity of the anti-inflammatory agent NF-κB and inhibited the oxidative stress by decreasing the levels of ROS and MDA and increasing the expression of MnSOD. Co-administration of GW9662 also significantly decreased the EGCG-mediated neuroprotective effect evidenced by the increase in oxidative stress and inflammatory markers. The therapeutic efficacy of EGCG in AD may be derived from the up-regulation of PPARγ mRNA and protein expressions.

Excessive hydrogen peroxide enhances the attachment of amyloid β1-42 in the lens epithelium of UPL rats, a hereditary model for cataracts

Several studies have reported that hydrogen peroxide (H2O2) is related to the toxicity of amyloid β (Aβ), and that the accumulation of Aβ in the lenses of humans causes lens opacification. In this study, we investigate the accumulation of Aβ1-42 in the lenses of UPL rats, which then leads to lens opacification. In addition, we demonstrate the effect of disulfiram eye drops (DSF), a potent radical scavenger, on Aβ1-42 accumulation in the lenses of UPL rats. The H2O2 levels in 46- to 60-day-old UPL rat lenses are significantly higher than in normal rats, and the Aβ1-42 levels in 53- and 60-day-old UPL rats are also increased only in lens epithelium containing capsules (capsule-epithelium), not in the lens cortex and nucleus. However, no increases in amyloid precursor protein (APP), β- or γ-secretase mRNA were observed in lenses of the corresponding ages. It has been thought that Aβ1-42 that accumulates in the lenses of UPL rats is actually produced in another tissue containing neuronal cells, such as brain or retina. Aβ1-42 levels in the brain and retina rise with aging, and the levels of APP, β- and γ-secretase mRNA in the retinas of 53-day-old UPL rats with opaque lenses are significantly higher than in 25-day-old UPL rats with transparent lenses. In contrast to the results in retinas, the levels of APP, β- and γ-secretase mRNA in the brains of 25- and 53-day-old UPL rats are similar. On the other hand, in an in vitro study, Aβ1-42 attachment in the lens capsule-epithelium of UPL rats was found to increase in H2O2. In addition, in an in vivo study, the inhibition of H2O2 by DSF was found to attenuate the increase in Aβ1-42 in the lens capsule-epithelium of 60-day-old UPL rats. Taken together, we hypothesize that excessive H2O2 in the lens enhances the attachment of Aβ1-42 in the lens capsule-epithelium of UPL rats, and that the instillation of DSF has the ability to attenuate the attachment of Aβ1-42 by inhibiting H2O2 production in lens. These findings provide significant information that can be used to design further studies aimed at developing anti-cataract drugs.

Muscarinic activation attenuates abnormal processing of beta-amyloid precursor protein induced by cobalt chloride-mimetic hypoxia in retinal ganglion cells

beta-Amyloid peptide (Abeta), the major pathological factor in Alzheimer's disease, has recently been reported to be implicated in the development of glaucoma. In this study, we explored the effect of muscarinic activation on abnormal processing of beta-amyloid precursor protein (APP) induced by a risk factor hypoxia in retinal ganglion cells. Hypoxia mimetic compound cobalt chloride could increase the generation of Abeta via up-regulating the expression of APP as well as the expression of beta-secretase and gamma-secretase, whereas muscarinic receptor agonist pilocarpine could significantly attenuate this abnormal pathway, thereby resulting in a decreased amyloidogenic cleavage of APP. This finding may provide an insight into better understanding of pathophysiology for the retinal neurodegenerative disease and searching for its new modifying approach.

Cell biology, regulation and inhibition of beta-secretase (BACE-1)

Since the discovery of the beta-secretase responsible for initiating the Alzheimer's amyloid cascade as a novel membrane-bound aspartic proteinase, termed 'beta-site amyloid precursor protein cleaving enzyme', 'aspartyl protease-2' or 'membrane-anchored aspartic proteinase of the pepsin family-2', huge efforts have been devoted to an understanding of its biology and structure in the subsequent decade. This has paid off in many respects, as it has been cloned, its structure solved, novel physiological substrates of the enzyme discovered, and numerous inhibitors of its activity developed in a relatively short space of time. The inhibition of beta-secretase activity in vivo remains one of the most viable strategies for the treatment of Alzheimer's disease, although progress in getting inhibitors to the clinic has been slow, partly as a consequence of its aspartic proteinase character, which poses considerable problems for the production of potent, selective and brain-accessible compounds. This review reflects on the development of beta-secretase biology and chemistry to date, highlighting the diverse and innovative strategies applied to the modulation of its activity at the molecular and cellular levels.