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Journal of neurochemistry (1)
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Armstrong, David L. (1)
Hahm, Byoung Kwon (1)
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TrkA Gene Ablation in Basal Forebrain Results in Dysfunction of the Cholinergic Circuitry
Rubenstein, John L.
Reichardt, Louis F.
Parada, Luis F.
The Journal of Neuroscience
Dysfunction of basal forebrain cholinergic neurons (BFCNs) is an early pathological hallmark of Alzheimer's disease (AD). Numerous studies have indicated that nerve growth factor (NGF) supports survival and phenotypic differentiation of BFCNs. Consistent with a potential link to AD pathogenesis, TrkA, a NGF receptor, is expressed in cholinergic forebrain neuronal populations including those in basal forebrain (BF) and striatum, and is markedly reduced in individuals with mild cognitive impairment (MCI) without dementia and early-stage AD. To investigate the role of TrkA in the development, connectivity, and function of the BF cholinergic system and its contribution to AD pathology, we have generated a forebrain-specific conditional TrkA knockout mouse line. Our findings show a key role for TrkA signaling in establishing the BF cholinergic circuitry through the ERK pathway, and demonstrate that the normal developmental increase of choline acetyltransferase (ChAT) expression becomes critically dependent on TrkA signaling before neuronal connections are established. Moreover, the anatomical and physiological deficits caused by lack of TrkA signaling in BFCNs have selective impact on cognitive activity. These data demonstrate that TrkA loss results in cholinergic BF dysfunction and cognitive decline that is reminiscent of MCI and early AD.
Protein phosphatase 5 protects neurons against amyloid β toxicity
Hahm, Byoung Kwon
Armstrong, David L.
Journal of neurochemistry
Amyloid β (Aβ) is thought to promote neuronal cell loss in Alzheimer’s disease (AD), in part through the generation of reactive oxygen species (ROS) and subsequent activation of mitogen-activated protein kinase (MAPK) pathways. Protein phosphatase 5 (PP5) is a ubiquitously expressed serine/threonine phosphatase which has been implicated in several cell stress response pathways and shown to inactivate MAPK pathways through key dephosphorylation events. Therefore we examined whether PP5 protects dissociated embryonic rat cortical neurons in vitro from cell death evoked by Aβ. As predicted, neurons in which PP5 expression was decreased by siRNA treatment were more susceptible to Aβ toxicity. In contrast, overexpression of PP5, but not the inactive PP5 mutant, H304Q, prevented MAPK phosphorylation and neurotoxicity induced by Aβ. PP5 also prevented cell death caused by direct treatment with H2O2, but did not prevent Aβ-induced production of ROS. Thus, the neuroprotective effect of PP5 requires its phosphatase activity and lies downstream of Aβ-induced generation of ROS. In summary, our data indicate that PP5 plays a pivotal neuroprotective role against cell death induced by Aβ and oxidative stress. Consequently, PP5 might be an effective therapeutic target in AD and other neurodegenerative disorders in which oxidative stress is implicated.
PP5; protein phosphatase 5; amyloid β; Alzheimer’s disease; neuroprotection; oxidative stress
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