Roles and Interaction of the MAPK Signaling Cascade in Aβ25-35-Induced Neurotoxicity Using an Isolated Primary Hippocampal Cell Culture System

Hexavalent Chromium Induces Neurotoxicity by Triggering Mitochondrial Dysfunction and ROS-Mediated Signals

Hexavalent chromium (Cr (VI)), one of the most detrimental pollutants, has been ubiquitously present in the environment and causes serious toxicity to humans, such as hepatotoxicity, nephrotoxicity, pulmonary toxicity, and cardiotoxicity. However, Cr (VI)-induced neurotoxicity in primary neuron level has not been well explored yet. Herein, potassium dichromate (K2Cr2O7) was employed to examine the neurotoxicity of Cr (VI) in rat primary hippocampal neurons. MTT test was used to examine the neural viability. Mitochondrial dysfunction was assessed by the JC-1 probe and Mito-Tracker probe. DCFH-DA and Mito-SOX Red were utilized to evaluate the oxidative status. Bcl-2 family and MAPKs expression were investigated using Western blotting. The results demonstrated that Cr (VI) treatment dose- and time-dependently inhibited neural viability. Mechanism investigation found that Cr (VI) treatment causes mitochondrial dysfunction by affecting Bcl-2 family expression. Moreover, Cr (VI) treatment also induces intracellular reactive oxygen species (ROS) generation, DNA damage, and MAPKs activation in neurons. However, inhibition of ROS by glutathione (GSH) effectually balanced Bcl-2 family expression, attenuated DNA damage and the MAPKs activation, and eventually improved neural viability neurons. Collectively, these above results above suggest that Cr (VI) causes significant neurotoxicity by triggering mitochondrial dysfunction, ROS-mediated oxidative damage and MAKPs activation.

Thymidine and 2'-deoxyuridine reduce microglial activation and improve oxidative stress damage by modulating glycolytic metabolism on the Aβ25-35-induced brain injury

Alzheimer's disease (AD) is a progressive disease with a long duration and complicated pathogenesis. Thymidine (Thy) and 2'-deoxyuridine (2'-De) are pyrimidines nucleotides that are associated with nervous system diseases. However, it remains unclear whether Thy and 2'-De exert neuroprotective effects in AD. Therefore, this study was conducted to explore the interventional effects and mechanisms of Thy and 2'-De on the Aβ_25-35-induced brain injury. Donepezil (Do, 10 mg/kg/d), Thy (20 mg/kg/d), and 2'-De (20 mg/kg/d) were administered for 4 weeks after the injection of Aβ_25-35 peptides (200 μM, i.c.v.) to mice. UPLC-MS/MS method was performed to quantify Thy and 2'-De in the hippocampus of mice brain. The cognition ability, neuronal and mitochondria damage, and levels of Aβ_1-42/Aβ_1-40, p-Tau, Na⁺ K⁺-ATPase, apoptosis, oxidative stress, immune cells, and Iba 1⁺ were measured in Aβ_25-35-induced mice. The oxygen consumption (OCR) and extracellular acidification rate (ECAR) were measured using a seahorse analyzer in Aβ_25-35-induced N9 cells. Moreover, 2-Deoxy-D-glucose (2-DG), a glycolysis inhibitor, was added to explore the mechanisms underlying the effects of Thy and 2'-De on Aβ_25-35-induced N9 cells. The expression of Iba 1⁺ and levels of CD11b⁺ and reactive oxygen species (ROS) were measured after treatment with Thy (5 μM) and 2'-De (10 μM) against 2-DG (5 mM) in Aβ_25-35-induced N9 cells. The results suggested that Do, Thy, and 2'-De improved the cognition ability, attenuated the damage to hippocampus and mitochondria, downregulated the levels of Aβ_1-42/Aβ_1-40, p-Tau, Na⁺ K⁺-ATPase, apoptosis, oxidative stress, and Iba 1⁺, and regulated the immune response induced by Aβ_25-35 against the brain injury. Furthermore, Do, Thy, and 2'-De increased ATP production and inhibited glycolysis in Aβ_25-35-induced N9 cells. Moreover, 2-DG enhanced the effects of drugs, reduced microglial activation, and attenuated oxidative stress to interfere with Aβ_25-35-induced N9 cells. In conclusion, Thy and 2'-De reduced microglial activation and improved oxidative stress damage by modulating glycolytic metabolism on the Aβ_25-35-induced brain injury.

Promoter Hypomethylation of TGFBR3 as a Risk Factor of Alzheimer’s Disease: An Integrated Epigenomic-Transcriptomic Analysis

Alzheimer’s disease (AD) is characterized by the abnormal deposition of amyloid-β (Aβ) plaques and tau tangles in the brain and accompanied with cognitive impairment. However, the fundamental cause of this disease remains elusive. To elucidate the molecular processes related to AD, we carried out an integrated analysis utilizing gene expression microarrays (GSE36980 and GSE5281) and DNA methylation microarray (GSE66351) in temporal cortex of AD patients from the Gene Expression Omnibus (GEO) database. We totally discovered 409 aberrantly methylated and differentially expressed genes. These dysregulated genes were significantly enriched in biological processes including cell part morphogenesis, chemical synaptic transmission and regulation of Aβ formation. Through convergent functional genomic (CFG) analysis, expression cross-validation and clinicopathological correlation analysis, higher TGFBR3 level was observed in AD and positively correlated with Aβ accumulation. Meanwhile, the promoter methylation level of TGFBR3 was reduced in AD and negatively associated with Aβ level and advanced Braak stage. Mechanically, TGFBR3 might promote Aβ production by enhancing β- and γ-secretase activities. Further investigation revealed that TGFBR3 may exert its functions via Synaptic vesicle cycle, Calcium signaling pathway and MAPK signal pathway by regulating hub genes GNB1, GNG3, CDC5L, DYNC1H1 and FBXW7. Overall, our findings highlighted TGFBR3 as an AD risk gene and might be used as a diagnostic biomarker and therapeutic target for AD treatment.

Early Effects of the Soluble Amyloid β25-35 Peptide in Rat Cortical Neurons: Modulation of Signal Transduction Mediated by Adenosine and Group I Metabotropic Glutamate Receptors

The amyloid β peptide (Aβ) is a central player in the neuropathology of Alzheimer’s disease (AD). The alteration of Aβ homeostasis may impact the fine-tuning of cell signaling from the very beginning of the disease, when amyloid plaque is not deposited yet. For this reason, primary culture of rat cortical neurons was exposed to Aβ_25-35, a non-oligomerizable form of Aβ. Cell viability, metabotropic glutamate receptors (mGluR) and adenosine receptors (AR) expression and signalling were assessed. Aβ_25-35 increased mGluR density and affinity, mainly due to a higher gene expression and protein presence of Group I mGluR (mGluR₁ and mGluR₅) in the membrane of cortical neurons. Intriguingly, the main effector of group I mGluR, the phospholipase C β₁ isoform, was less responsive. Also, the inhibitory action of group II and group III mGluR on adenylate cyclase (AC) activity was unaltered or increased, respectively. Interestingly, pre-treatment of cortical neurons with an antagonist of group I mGluR reduced the Aβ_25-35-induced cell death. Besides, Aβ_25-35 increased the density of A₁R and A_2AR, along with an increase in their gene expression. However, while A₁R-mediated AC inhibition was increased, the A_2AR-mediated stimulation of AC remained unchanged. Therefore, one of the early events that takes place after Aβ_25-35 exposure is the up-regulation of adenosine A₁R, A_2AR, and group I mGluR, and the different impacts on their corresponding signaling pathways. These results emphasize the importance of deciphering the early events and the possible involvement of metabotropic glutamate and adenosine receptors in AD physiopathology.