Overexpression of SNX3 Decreases Amyloid-ß Peptide Production by Reducing Internalization of Amyloid Precursor Protein.

BACKGROUND: Sorting nexins (SNXs) have diverse functions in protein sorting and membrane trafficking. Recently, single-nucleotide polymorphisms in SNX3 were found to be associated with Alzheimer disease. However, it remains unknown whether SNX3 participates in amyloid (A)ß peptide production. OBJECTIVE: To examine the role of SNX3 in Aß production and APP processing. METHODS: The effect of increased expression of SNX3 was studied in HEK293T cells. Aß peptides were measured by immunoassay. Protein-protein association was analyzed by a bimolecular fluorescence complementation (BiFC) assay. APP uptake was measured with an α-bungarotoxin-binding assay, and flow cytometry was used to measure cell surface APP levels. RESULTS: We found that overexpression of SNX3 in HEK293T cells decreases the levels of secreted Aß and soluble N-terminal APP fragments (sAPPß). The reduction correlated with a decreased association of APP with BACE1, as revealed by BiFC. This effect may, in part, be explained by a reduced internalization of APP; SNX3 overexpression reduced APP internalization as determined by an α-bungarotoxin-binding assay, and caused increased APP levels on the cell surface, as shown by flow cytometry. In addition, SNX3 overexpression increased the cellular levels of full-length APP. CONCLUSION: These results provide evidence that SNX3 regulates Aß production by influencing the internalization of APP.

Exercise and BDNF reduce Aß production by enhancing α-secretase processing of APP.

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by aggregation of toxic forms of amyloid ß peptide (Aß). Treatment strategies have largely been focused on inhibiting the enzymes (ß- and γ-secretases) that liberate Aß from the amyloid precursor protein (APP). While evidence suggests that individuals who exercise regularly are at reduced risk for AD and studies of animal models demonstrate that running can ameliorate brain Aß pathology and associated cognitive deficits, the underlying mechanisms are unknown. However, considerable evidence suggests that brain-derived neurotrophic factor (BDNF) mediates beneficial effects of exercise on neuroplasticity and cellular stress resistance. Here, we tested the hypothesis that BDNF promotes non-amyloidogenic APP processing. Using a transgenic mouse model of Alzheimer's disease and cultured human neural cells, we demonstrate that exercise and BDNF reduce production of toxic Aß peptides through a mechanism involving enhanced α-secretase processing of APP. This anti-amyloidogenic APP processing involves subcellular redistribution of α-secretase and an increase in intracellular neuroprotective APP peptides capable of binding and inhibiting ß-secretase. Moreover, our results suggest that BDNF's ability to promote neurite outgrowth is primarily exerted through pathways other than APP processing. Exercise and other factors that enhance BDNF signaling may therefore have both therapeutic and prophylactic value in the battle against AD. Read the Editorial Highlight for this article on page 191.

Constitutive activation of WASp leads to abnormal cytotoxic cells with increased granzyme B and degranulation response to target cells.

X-linked neutropenia (XLN) is caused by gain-of-function mutations in the actin regulator Wiskott-Aldrich Syndrome protein (WASp). XLN patients have reduced numbers of cytotoxic cells in peripheral blood; however, their capacity to kill tumor cells remains to be determined. Here, we examined NK and T cells from 2 patients with XLN harboring the activating WASpL270P mutation. XLN patient NK and T cells had increased granzyme B content and elevated degranulation and IFN-γ production when compared with healthy control cells. Murine WASpL272P NK and T cells formed stable synapses with YAC-1 tumor cells and anti-CD3/CD28-coated beads, respectively. WASpL272P mouse T cells had normal degranulation and cytokine response whereas WASpL272P NK cells showed an enhanced response. Imaging experiments revealed that while WASpL272P CD8+ T cells had increased accumulation of actin upon TCR activation, WASpL272P NK cells had normal actin accumulation at lytic synapses triggered through NKp46 signaling but had impaired response to lymphocyte function associated antigen-1 engagement. When compared with WT mice, WASpL272P mice showed reduced growth of B16 melanoma and increased capacity to reject MHC class I-deficient cells. Together, our data suggest that cytotoxic cells with constitutively active WASp have an increased capacity to respond to and kill tumor cells.

Extracellular Vesicle-Associated Aß Mediates Trans-Neuronal Bioenergetic and Ca2+-Handling Deficits in Alzheimer's Disease Models.

Alzheimer's Disease (AD) is an age-related neurodegenerative disorder in which aggregation-prone neurotoxic amyloid ß-peptide (Aß) accumulates in the brain. Extracellular vesicles (EVs) are small 50-150 nanometer membrane vesicles that have recently been implicated in the prion-like spread of self-aggregating proteins. Here we report that EVs isolated from AD patient CSF and plasma, from the plasma of two AD mouse models, and from the medium of neural cells expressing familial AD presenilin 1 mutations, destabilize neuronal Ca2+ homeostasis, impair mitochondrial function, and sensitize neurons to excitotoxicity. EVs contain a relatively low amount of Aß but have an increased Aß42/ Aß40 ratio; the majority of Aß is located on the surface of the EVs. Impairment of lysosome function results in increased generation EVs with elevated Aß42 levels. EVs may mediate transcellular spread of pathogenic Aß species and that impair neuronal Ca2+ handling and mitochondrial function, and may thereby render neurons vulnerable to excitotoxicity.