Mitochondria-associated endoplasmic reticulum membranes: At the crossroad between familiar and sporadic Alzheimer's disease

Dual Role of NMDAR Containing NR2A and NR2B Subunits in Alzheimer's Disease

Alzheimer's disease (AD) is the main cause of dementia worldwide. Given that learning and memory are impaired in this pathology, NMDA receptors (NMDARs) appear as key players in the onset and progression of the disease. NMDARs are glutamate receptors, mainly located at the post-synapse, which regulate voltage-dependent influx of calcium into the neurons. They are heterotetramers, and there are different subunits that can be part of the receptors, which are usually composed of two obligatory GluN1 subunits plus either two NR2A or two NR2B subunits. NR2A are mostly located at the synapse, and their activation is involved in the expression of pro-survival genes. Conversely, NR2B are mainly extrasynaptic, and their activation has been related to cell death and neurodegeneration. Thus, activation of NR2A and/or inactivation of NR2B-containing NMDARS has been proposed as a therapeutic strategy to treat AD. Here, we wanted to investigate the main differences between both subunits signalling in neuronal primary cultures of the cortex and hippocampus. It has been observed that Aβ induces a significant increase in calcium release and also in MAPK phosphorylation signalling in NR2B-containing NMDAR in cortical and hippocampal neurons. However, while NR2A-containing NMDAR decreases neuronal death and favours cell viability after Aβ treatment, NR2B-containing NMDAR shows higher levels of cytotoxicity and low levels of neuronal survival. Finally, it has been detected that NMDAR has no effect on pTau axonal transport. The present results demonstrate a different role between GluNA and GluNB subunits in neurodegenerative diseases such as Alzheimer's.

Curcumin, inflammation, and neurological disorders: How are they linked?

Background

Despite the extensive research in recent years, the current treatment modalities for neurological disorders are suboptimal. Curcumin, a polyphenol found in Curcuma genus, has been shown to mitigate the pathophysiology and clinical sequalae involved in neuroinflammation and neurodegenerative diseases.

Methods

We searched PubMed database for relevant publications on curcumin and its uses in treating neurological diseases. We also reviewed relevant clinical trials which appeared on searching PubMed database using 'Curcumin and clinical trials'.

Results

This review details the pleiotropic immunomodulatory functions and neuroprotective properties of curcumin, its derivatives and formulations in various preclinical and clinical investigations. The effects of curcumin on neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), brain tumors, epilepsy, Huntington's disorder (HD), ischemia, Parkinson's disease (PD), multiple sclerosis (MS), and traumatic brain injury (TBI) with a major focus on associated signalling pathways have been thoroughly discussed.

Conclusion

This review demonstrates curcumin can suppress spinal neuroinflammation by modulating diverse astroglia mediated cascades, ensuring the treatment of neurological disorders.

Effects of intranasal dantrolene nanoparticles on brain concentration and behavior in PS19 tau transgenic mice

Background

Repurposing dantrolene as a potential disease-modifying treatment for Alzheimer's disease has been shown to be effective in amyloid transgenic mouse models but has not been examined in a model of tauopathy.

Objective

The effects of a nanoparticle intranasal formulation, the Eagle Research Formulation of Ryanodex (ERFR), in young adult and aged wild type and PS19 tau transgenic mice was investigated.

Methods

The bioavailability of intranasal ERFR was measured in 2 months and 9-12 month old C57BL/6J male mice. Mice received a single intranasal dose of ERFR and, after 20 min, blood and brain samples were collected. Dantrolene concentrations in the plasma and brain were analyzed by High Performance Liquid Chromatography. Animal behavior was examined in PS19 tau transgenic mice, with/without acrolein treatment to exacerbate cognitive deficits. Behavioral tests included cognition (cued and contextual fear conditioning, y-maze), motor function (rotarod), and olfaction (buried food test).

Results

Dantrolene concentration in the blood and brain decreased with age, though the decrease was greater in the blood resulting in a higher brain to blood concentration ratio. The behavioral assays showed no significant changes in cognition, olfaction or motor function in the PS19 mice compared to controls after chronic ERFR treatment even with acrolein treatment.

Conclusion

Our studies suggest that while we did not find PS19 mice to be a reliable Alzheimer animal model to test the therapeutic efficacy of dantrolene, the results suggest a potential for ERFR to be an effective chronic therapy for Alzheimer's disease and that further studies are indicated.

Inhibition of ferroptosis through regulating neuronal calcium homeostasis: An emerging therapeutic target for Alzheimer's disease

Alzheimer's disease (AD), a chronic and progressive neurodegenerative disease, generates a serious threat to the health of the elderly. The AD brain is microscopically characterized by amyloid plaques and neurofibrillary tangles. There are still no effective therapeutic drugs to restrain the progression of AD though much attention has been paid to exploit AD treatments. Ferroptosis, a type of programmed cell death, has been reported to promote the pathological occurrence and development of AD, and inhibition of neuronal ferroptosis can effectively improve the cognitive impairment of AD. Studies have shown that calcium (Ca²⁺) dyshomeostasis is closely related to the pathology of AD, and can drive the occurrence of ferroptosis through several pathways, such as interacting with iron, and regulating the crosstalk between endoplasmic reticulum (ER) and mitochondria. This paper mainly reviews the roles of ferroptosis and Ca²⁺ in the pathology of AD, and highlights that restraining ferroptosis through maintaining the homeostasis of Ca²⁺ may be an innovative target for the treatment of AD.

Chaperone-Dependent Mechanisms as a Pharmacological Target for Neuroprotection

Modern pharmacotherapy of neurodegenerative diseases is predominantly symptomatic and does not allow vicious circles causing disease development to break. Protein misfolding is considered the most important pathogenetic factor of neurodegenerative diseases. Physiological mechanisms related to the function of chaperones, which contribute to the restoration of native conformation of functionally important proteins, evolved evolutionarily. These mechanisms can be considered promising for pharmacological regulation. Therefore, the aim of this review was to analyze the mechanisms of endoplasmic reticulum stress (ER stress) and unfolded protein response (UPR) in the pathogenesis of neurodegenerative diseases. Data on BiP and Sigma1R chaperones in clinical and experimental studies of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease are presented. The possibility of neuroprotective effect dependent on Sigma1R ligand activation in these diseases is also demonstrated. The interaction between Sigma1R and BiP-associated signaling in the neuroprotection is discussed. The performed analysis suggests the feasibility of pharmacological regulation of chaperone function, possibility of ligand activation of Sigma1R in order to achieve a neuroprotective effect, and the need for further studies of the conjugation of cellular mechanisms controlled by Sigma1R and BiP chaperones.

Inhibition of GluN2B pathway is involved in the neuroprotective effect of silibinin on streptozotocin-induced Alzheimer's disease models

BACKGROUND

Over-activation of N-methyl-D-aspartate receptors (NMDARs) is involved in sporadic Alzheimer's disease. Silibinin, a natural flavonoid gained from the seeds of Silybum marianum, exerts neuroprotective effects on sporadic AD models, but its impacts on NMDARs remain unknown.

PURPOSE

To study silibinin's regulatory effects on NMDARs pathway in sporadic AD models.

METHODS

MTT assay, western blotting, confocal microscopy, flow cytometry, RT-PCR, and siRNA transfection etc. were used for cellular and molecular studies. The direct interactions between silibinin and NMDAR subunits were evaluated by computational molecular docking, drug affinity responsive target stability (DARTS) assay and cellular thermal shift assay (CETSA). Y maze test, novel objects recognition test and Morris water maze test were conducted to examine the learning and memory ability of rats.

RESULTS

An in vitro AD model was established by treating HT22 murine hippocampal neurons with streptozotocin (STZ), as evidenced by the amyloid β (Aβ) deposition and hyperphosphorylation of tau proteins. Silibinin shows protection of neurons against STZ-induced cell damage. It is noteworthy that STZ-induced cellular calcium influx is inhibited by silibinin-treatment, indicating the possible modulation of calcium channels. Studies on NMDARs, the most widely distributed calcium channel, by using molecular docking, DARTS and CESTA, reveal that the GluN2B subunit, but not GluN2A, is the potential target of silibinin. Further studies using the pharmacological agonist (NMDA) and the GluN2B-specific inhibitor (Ifenprodil) or siRNA, indicate that the protection by silibinin treatment from STZ-induced cytotoxicity is medicated through interference with GluN2B-containing NMDARs, followed by the upregulation of CaMKIIα/ BDNF/ TrkB signaling pathway and improved levels of synaptic proteins (SYP and PSD-95). The results in vivo using rats intracerebroventricularly injected with STZ (ICV-STZ), a well-established sporadic AD model, confirm that silibinin improves learning and memory ability in association with modulation of the GluN2B/CaMKIIα/ BDNF/TrkB signaling pathway.

CONCLUSION

Inhibiting over-activation of GluN2B-containing NMDARs is involved in the neuroprotective effect of silibinin on STZ-induced sporadic AD models.

Curcumin Inhibits Cell Damage and Apoptosis Caused by Thapsigargin-Induced Endoplasmic Reticulum Stress Involving the Recovery of Mitochondrial Function Mediated by Mitofusin-2

Endoplasmic reticulum stress (ERS) and mitochondrial dysfunction have been suggested to relate with the pathology of Alzheimer's disease (AD). However, their cross-talk is needed to investigate further. Mitofusin-2 (Mfn2) is a member of mitochondria-associated membrane (MAM), which connects endoplasmic reticulum (ER) and mitochondria. This study investigated the protective effect of curcumin on thapsigargin (TG)-induced ERS and cell apoptosis and the role of Mfn2 on mitochondrial dysfunction. The cell viability of SH-SY5Y cells was decreased and cell damage and apoptosis were increased in a concentration-dependent manner when cells were treated with TG. TG upregulated the protein levels of GRP78, pSer981-PERK, and pSer51-eIF2α. Curcumin attenuated TG-induced damage on cell viability and apoptosis and downregulated the protein levels of GRP78, pSer981-PERK, and pSer51-eIF2α. TG caused the increases in intracellular reactive oxygen species (ROS) and in the protein levels of pSer40-Nrf2 and hemoglobin oxygenase 1 (HO-1). Curcumin decreased the TG-induced intracellular ROS but did not alter the protein levels of pSer40-Nrf2 and HO-1. TG resulted in the upregulation on Mfn2 expression and mitochondrial spare respiratory capacity but the downregulation on mitochondrial basal respiration and ATP production. Curcumin attenuated the TG-induced Mfn2 expression and mitochondrial stress. When Mfn2 was silenced by shRNA interference, curcumin failed to recovery the TG-damaged mitochondrial function. In general, the TG-induced ERS trigged mitochondrial dysfunction and cell apoptosis. Curcumin attenuates TG-induced ERS and the cell damage and apoptosis. Mfn2 is required for curcumin's protection against the TG-induced damage on mitochondrial functions.

Hypothesis and Theory: Characterizing Abnormalities of Energy Metabolism Using a Cellular Platform as a Personalized Medicine Approach for Alzheimer's Disease

Sporadic or late-onset Alzheimer’s disease (LOAD) is characterized by slowly progressive deterioration and death of CNS neurons. There are currently no substantially disease-modifying therapies. LOAD pathology is closely related to changes with age and include, among others, accumulation of toxic molecules and altered metabolic, microvascular, biochemical and inflammatory processes. In addition, there is growing evidence that cellular energy deficits play a critical role in aging and LOAD pathophysiology. However, the exact mechanisms and causal relationships are largely unknown. In our studies we tested the hypothesis that altered bioenergetic and metabolic cell functions are key elements in LOAD, using a cellular platform consisting of skin fibroblasts derived from LOAD patients and AD-unaffected control individuals and therefrom generated induced pluripotent stem cells that are differentiated to brain-like cells to study LOAD pathogenic processes in context of age, disease, genetic background, cell development, and cell type. This model has revealed that LOAD cells exhibit a multitude of bioenergetic and metabolic alterations, providing evidence for an innate inefficient cellular energy management in LOAD as a prerequisite for the development of neurodegenerative disease with age. We propose that this cellular platform could ultimately be used as a conceptual basis for a personalized medicine tool to predict altered aging and risk for development of dementia, and to test or implement customized therapeutic or disease-preventive intervention strategies.