[Show abstract][Hide abstract] ABSTRACT: Amyloid precursor protein (APP) is involved in the pathogenesis of Alzheimer's disease. It is axonally transported, endocytosed and sorted to different cellular compartments where amyloid beta (Aβ) is produced. However, the mechanism of APP trafficking remains unclear. We present evidence that huntingtin associated protein 1 (HAP1) may reduce Aβ production by regulating APP trafficking to the non-amyloidogenic pathway. HAP1 and APP are highly colocalized in a number of brain regions, with similar distribution patterns in both mouse and human brains. They are associated with each other, the interacting site is the 371-599 of HAP1. APP is more retained in cis-Golgi, trans-Golgi complex, early endosome and ER-Golgi intermediate compartment in HAP1-/- neurons. HAP1 deletion significantly alters APP endocytosis and reduces the re-insertion of APP into the cytoplasmic membrane. Amyloid precursor protein-YFP(APP-YFP) vesicles in HAP1-/- neurons reveal a decreased trafficking rate and an increased number of motionless vesicles. Knock-down of HAP1 protein in cultured cortical neurons of Alzheimer's disease mouse model increases Aβ levels. Our data suggest that HAP1 regulates APP subcellular trafficking to the non-amyloidogenic pathway and may negatively regulate Aβ production in neurons.
Journal of Neurochemistry 06/2012; 122(5):1010-22. · 3.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neurons extend their dendrites and axons to build functional neural circuits, which are regulated by both positive and negative signals during development. Brain-derived neurotrophic factor (BDNF) is a positive regulator for neurite outgrowth and neuronal survival but the functions of its precursor (proBDNF) are less characterized.
Here we show that proBDNF collapses neurite outgrowth in murine dorsal root ganglion (DRG) neurons and cortical neurons by activating RhoA via the p75 neurotrophin receptor (p75NTR). We demonstrated that the receptor proteins for proBDNF, p75NTR and sortilin, were highly expressed in cultured DRG or cortical neurons. ProBDNF caused a dramatic neurite collapse in a dose-dependent manner and this effect was about 500 fold more potent than myelin-associated glycoprotein. Neutralization of endogenous proBDNF by using antibodies enhanced neurite outgrowth in vitro and in vivo, but this effect was lost in p75NTR(-/-) mice. The neurite outgrowth of cortical neurons from p75NTR deficient (p75NTR(-/-)) mice was insensitive to proBDNF. There was a time-dependent reduction of length and number of filopodia in response to proBDNF which was accompanied with a polarized RhoA activation in growth cones. Moreover, proBDNF treatment of cortical neurons resulted in a time-dependent activation of RhoA but not Cdc42 and the effect was absent in p75NTR(-/-) neurons. Rho kinase (ROCK) and the collapsin response mediator protein-2 (CRMP-2) were also involved in the proBDNF action.
proBDNF has an opposing role in neurite outgrowth to that of mature BDNF. Our observations suggest that proBDNF collapses neurites outgrowth and filopodial growth cones by activating RhoA through the p75NTR signaling pathway.
PLoS ONE 01/2012; 7(4):e35883. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Alzheimer's disease (AD), the most common form of dementia, is characterized by the deposition of amyloid plaques, accumulation of fibrillary tangles in neurons, neurite degeneration, loss of neurons, and a progressive loss of cognitive function. The pathogenesis of AD is not fully understood, and no strong disease-modifying therapies are currently available. Recent studies suggest that the pan-neurotrophin receptor, p75NTR, is a critical factor involved in the pathogenesis of AD. In this review, we have discussed the roles of p75NTR in the production of amyloid-beta (Aβ), neuronal death, neurite degeneration, tau hyperphosphorylation, cell cycle re-entry and cognition decline in AD, and proposed that p75NTR is a potential target for the development of therapeutic drugs for AD. Finally we provide perspectives in developing various therapeutic strategies targeting different aspects of AD hallmarks which relate to p75NTR functions and breaking the p75NTR-mediated positive feedback loop which promotes the cascades in the pathogenesis of AD.
[Show abstract][Hide abstract] ABSTRACT: Accumulation of toxic amyloid-β (Aβ) in the cerebral cortex and hippocampus is a major pathological feature of Alzheimer's disease (AD). The neurotrophin receptor p75NTR has been proposed to mediate Aβ-induced neurotoxicity; however, its role in the development of AD remains to be clarified. The p75NTR/ExonIII-/- mice and APPSwe/PS1dE9 mice were crossed to generate transgenic AD mice with deletion of p75NTR gene. In APPSwe/PS1dE9 transgenic mice, p75NTR expression was localized in the basal forebrain neurons and degenerative neurites in neocortex, increased with aging, and further activated by Aβ accumulation. Deletion of the p75NTR gene in APPSwe/PS1dE9 mice reduced soluble Aβ levels in the brain and serum, but increased the accumulation of insoluble Aβ and Aβ plaque formation. There was no change in the levels of amyloid precursor protein (APP) and its proteolytic derivatives, or α-, β-, and γ-secretase activities, or in levels of BACE1, neprilysin (NEP), and insulin-degrading enzyme (IDE) proteins. Aβ production by cortical neurons of APPSwe/PS1dE9 mice was reduced by deletion of p75NTR gene in vitro. Recombinant extracellular domain of p75NTR attenuated the oligomerization and fibrillation of synthetic Aβ(42) peptide in vitro, and reduced local Aβ plaques after hippocampus injection in vivo. In addition, deletion of p75NTR attenuated microgliosis but increased the microhemorrhage profiles in the brain. The deletion of p75NTR did not significantly change the cognitive function of the mice up to the age of 9 months. Our data suggest that p75NTR plays a critical role in regulating Aβ levels by both increasing Aβ production and attenuating its aggregation, and they caution that a therapeutic intervention simply reducing p75NTR may exacerbate AD pathology.
Journal of Neuroscience 02/2011; 31(6):2292-304. · 6.91 Impact Factor