Amyloid precursor protein and presenilin involvement in cell signaling

Enhanced Sensitivity of A549 Cells to Doxorubicin with WS2 and WSe2 Nanosheets via the Induction of Autophagy

The excellent physicochemical properties of two-dimensional transition-metal dichalcogenides (2D TMDCs) such as WS2 and WSe2 provide potential benefits for biomedical applications, such as drug delivery, photothermal therapy, and bioimaging. WS2 and WSe2 have recently been used as chemosensitizers; however, the detailed molecular basis underlying WS2- and WSe2-induced sensitization remains elusive. Our recent findings showed that 2D TMDCs with different thicknesses and different element compositions induced autophagy in normal human bronchial epithelial cells and mouse alveolar macrophages at sublethal concentrations. Here, we explored the mechanism by which WS2 and WSe2 act as sensitizers to increase lung cancer cell susceptibility to chemotherapeutic agents. The results showed that WS2 and WSe2 enhanced autophagy flux in A549 lung cancer cells at sublethal concentrations without causing significant cell death. Through the autophagy-specific RT2 Profiler PCR Array, we identified the genes significantly affected by WS2 and WSe2 treatment. Furthermore, the key genes that play central roles in regulating autophagy were identified by constructing a molecular interaction network. A mechanism investigation uncovered that WS2 and WSe2 activated autophagy-related signaling pathways by interacting with different cell surface proteins or cytoplasmic proteins. By utilizing this mechanism, the efficacy of the chemotherapeutic agent doxorubicin was enhanced by WS2 and WSe2 pre-treatment in A549 lung cancer cells. This study revealed a feature of WS2 and WSe2 in cancer therapy, in which they eliminate the resistance of A549 lung cancer cells against doxorubicin, at least partially, by inducing autophagy.

Induction of mTOR-dependent autophagy by WS2 nanosheets from both inside and outside of human cells

The applications of two-dimensional transition metal dichalcogenides (2D TMDCs) pose an increased risk to both the environment and human health. Due to the large surface area of 2D nanosheets, they often form multi-layered nanoclusters of various thicknesses in aqueous solution. In this work, we address the safety issue of 2D TMDCs with focus on the cellular effects of the thickness of WS2 nanosheets. At a very low and non-lethal concentration (4 cm2 mL-1 or 25 μg mL-1), 4-layered WS2 nanosheets (WS2-4) were primarily bound to the cell surface with less internalization, while 30-layered WS2 nanosheets (WS2-30) were mostly internalized by human bronchial epithelial cells. Although the cellular interactions at this low concentration caused no alterations in the cell cycle, apoptosis, necrosis and cytotoxicity, cell autophagy was induced in both cases through mTOR-dependent pathways by perturbing a number of signaling molecules, such as amyloid precursor protein (APP) and cysteine-X-cysteine chemokine receptor 4 (CXCR-4). The finding of activation of cell autophagy from both outside and inside of cells reveals a novel feature of biological perturbations by 2D nanosheets. This finding will help in the formulation of general guidelines for the safe application of 2D nanomaterials.

Remote Induction of Cell Autophagy by 2D MoS2 Nanosheets via Perturbing Cell Surface Receptors and mTOR Pathway from Outside of Cells

The ability of nanoparticles to induce adverse consequences in human cells relies on their physical shapes. In this aspect, how two-dimensional nanoparticles differ from three-dimensional nanoparticles is not well-known. To elucidate this difference, combined experimental and theoretical approaches are employed to compare MoS₂ nanosheets with 5-layer and 40-layer thicknesses for their cellular effects and the associated molecular events. At a concentration as defined by the nanosheet surface areas (10 cm²/mL), 40-layer nanosheets are internalized by cells, whereas 5-layer nanosheets mostly bind to the cell surface without internalization. Although they alter different autophagy-related genes, a common mechanism is that they both perturb cell surface protein amyloid precursor proteins and activate the mTOR signaling pathway. Our findings prove that the perturbation of cellular function without nanoparticle internalization has significant nanomedicinal and nanotoxicological significances.

APP as a Protective Factor in Acute Neuronal Insults

Despite its key role in the molecular pathology of Alzheimer’s disease (AD), the physiological function of amyloid precursor protein (APP) is unknown. Increasing evidence, however, points towards a neuroprotective role of this membrane protein in situations of metabolic stress. A key observation is the up-regulation of APP following acute (stroke, cardiac arrest) or chronic (cerebrovascular disease) hypoxic-ischemic conditions. While this mechanism may increase the risk or severity of AD, APP by itself or its soluble extracellular fragment APPsα can promote neuronal survival. Indeed, different animal models of acute hypoxia-ischemia, traumatic brain injury (TBI) and excitotoxicity have revealed protective effects of APP or APPsα. The underlying mechanisms involve APP-mediated regulation of calcium homeostasis via NMDA receptors (NMDAR), voltage-gated calcium channels (VGCC) or internal calcium stores. In addition, APP affects the expression of survival- or apoptosis-related genes as well as neurotrophic factors. In this review, we summarize the current understanding of the neuroprotective role of APP and APPsα and possible implications for future research and new therapeutic strategies.

Extensive nuclear sphere generation in the human Alzheimer's brain

Nuclear spheres are protein aggregates consisting of FE65, TIP60, BLM, and other yet unknown proteins. Generation of these structures in the cellular nucleus is putatively modulated by the amyloid precursor protein (APP), either by its cleavage or its phosphorylation. Nuclear spheres were preferentially studied in cell culture models and their existence in the human brain had not been known. Existence of nuclear spheres in the human brain was studied using immunohistochemistry. Cell culture experiments were used to study regulative mechanisms of nuclear sphere generation. The comparison of human frontal cortex brain samples from Alzheimer's disease (AD) patients to age-matched controls revealed a dramatically and highly significant enrichment of nuclear spheres in the AD brain. Costaining demonstrated that neurons are distinctly affected by nuclear spheres, but astrocytes never are. Nuclear spheres were predominantly found in neurons that were negative for threonine 668 residue in APP phosphorylation. Cell culture experiments revealed that JNK3-mediated APP phosphorylation reduces the amount of sphere-positive cells. The study suggests that nuclear spheres are a new APP-derived central hallmark of AD, which might be of crucial relevance for the molecular mechanisms in neurodegeneration.

Activin A prevents neuron-like PC12 cell apoptosis after oxygen-glucose deprivation

In this study, PC12 cells were induced to differentiate into neuron-like cells using nerve growth factor, and were subjected to oxygen-glucose deprivation. Cells were treated with 0, 10, 20, 30, 50, 100 ng/mL exogenous Activin A. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and Hoechst 33324 staining showed that the survival percentage of PC12 cells significantly decreased and the rate of apoptosis significantly increased after oxygen-glucose deprivation. Exogenous Activin A significantly increased the survival percentage of PC12 cells in a dose-dependent manner. Reverse transcription-PCR results revealed a significant increase in Activin receptor IIA, Smad3 and Smad4 mRNA levels, which are key sites in the Activin A/Smads signaling pathway, in neuron-like cells subjected to oxygen-glucose deprivation, while mRNA expression of the apoptosis-regulation gene caspase-3 decreased. Our experimental findings indicate that exogenous Activin A plays an anti-apoptotic role and protects neurons by means of activating the Activin A/Smads signaling pathway.

Neurodegeneration in Alzheimer disease: role of amyloid precursor protein and presenilin 1 intracellular signaling

Alzheimer disease (AD) is a heterogeneous neurodegenerative disorder characterized by (1) progressive loss of synapses and neurons, (2) intracellular neurofibrillary tangles, composed of hyperphosphorylated Tau protein, and (3) amyloid plaques. Genetically, AD is linked to mutations in few proteins amyloid precursor protein (APP) and presenilin 1 and 2 (PS1 and PS2). The molecular mechanisms underlying neurodegeneration in AD as well as the physiological function of APP are not yet known. A recent theory has proposed that APP and PS1 modulate intracellular signals to induce cell-cycle abnormalities responsible for neuronal death and possibly amyloid deposition. This hypothesis is supported by the presence of a complex network of proteins, clearly involved in the regulation of signal transduction mechanisms that interact with both APP and PS1. In this review we discuss the significance of novel finding related to cell-signaling events modulated by APP and PS1 in the development of neurodegeneration.

The neuronal cell cycle as a mechanism of pathogenesis in Alzheimer's disease

Differentiated neurons display specific biochemical, physiological and morphological properties that apparently prevent them from further cell division. Nevertheless, expression of cell cycle modulators persists after neuronal differentiation and is upregulated under stress conditions, such as trophic factor deprivation, oxidative stress and the presence of DNA damaging agents. This apparent reactivation of the cell cycle has been postulated as a sine qua non for neuronal death in response to those stress conditions, particularly in Alzheimer's disease. However, the physiological and pathogenic implications of a putative neuronal cell cycle are far from clear. Here, we discuss the notion of the neuronal cell cycle as a mediator of cell death, with particular emphasis on Alzheimer's disease.

Heat shock protein 90: translation from cancer to Alzheimer's disease treatment?

Both malignant transformation and neurodegeneration, as it occurs in Alzheimer's disease, are complex and lengthy multistep processes characterized by abnormal expression, post-translational modification, and processing of certain proteins. To maintain and allow the accumulation of these dysregulated processes, and to facilitate the step-wise evolution of the disease phenotype, cells must co-opt a compensatory regulatory mechanism. In cancer, this role has been attributed to heat shock protein 90 (Hsp90), a molecular chaperone that maintains the functional conformation of multiple proteins involved in cell-specific oncogenic processes. In this sense, at the phenotypic level, Hsp90 appears to serve as a biochemical buffer for the numerous cancer-specific lesions that are characteristic of diverse tumors. The current review proposes a similar role for Hsp90 in neurodegeneration. It will present experimentally demonstrated, but also hypothetical, roles that suggest Hsp90 can act as a regulator of pathogenic changes that lead to the neurodegenerative phenotype in Alzheimer's disease.

Upregulation of beta-amyloid precursor protein expression in glioblastoma multiforme

Glioma and glioblastoma multiforme constitute rapidly proliferating glial cell tumors whose pathogenic mechanisms are not well understood. This study examined proinflammatory and neurodegenerative gene expression in five American Tissue Culture Collection glioma and glioblastoma multiforme tumor cell lines and in 14 glioma and glioblastoma samples obtained from human brain biopsy. Expression of the low-abundance cyclooxygenase-1 and the high-abundance cytoskeletal element beta-actin were found not to significantly change in any cells or tissues studied and were used as internal controls. In contrast, proinflammatory cyclooxygenase-2, cytosolic phospholipase A2, IL-1beta, and beta-amyloid precursor protein expression levels were found to be significantly upregulated. These studies suggest that glioma and glioblastoma exhibit robust upregulation of proinflammatory and neurodegenerative genetic markers that may contribute to the pathobiology, phenotype, and proliferation of glial cell growth.