Altered metabolism of the amyloid beta precursor protein is associated with mitochondrial dysfunction in Down's syndrome.

Most Down's syndrome (DS) patients develop Alzheimer's disease (AD) neuropathology. Astrocyte and neuronal cultures derived from fetal DS brain show alterations in the processing of amyloid beta precursor protein (AbetaPP), including increased levels of AbetaPP and C99, reduced levels of secreted AbetaPP (AbetaPPs) and C83, and intracellular accumulation of insoluble Abeta42. This pattern of AbetaPP processing is recapitulated in normal astrocytes by inhibition of mitochondrial metabolism, consistent with impaired mitochondrial function in DS astrocytes. Intracellular Abeta42 and reduced AbetaPPs are also detected in DS and AD brains. The survival of DS neurons is markedly increased by recombinant or astrocyte-produced AbetaPPs, suggesting that AbetaPPs may be a neuronal survival factor. Thus, mitochondrial dysfunction in DS may lead to intracellular deposition of Abeta42, reduced levels of AbetaPPs, and a chronic state of increased neuronal vulnerability.

ets-2 promotes the activation of a mitochondrial death pathway in Down's syndrome neurons.

Down's syndrome (DS) is characterized by mental retardation and development of Alzheimer's disease (AD). Oxidative stress and mitochondrial dysfunction are both related to neurodegeneration in DS. Several genes in chromosome 21 have been linked to neuronal death, including the transcription factor ets-2. Cortical cultures derived from normal and DS fetal brains were used to study the role of ets-2 in DS neuronal degeneration. ets-2 was expressed in normal human cortical neurons (HCNs) and was markedly upregulated by oxidative stress. When overexpressed in normal HCNs, ets-2 induced a stereotyped sequence of apoptotic changes leading to neuronal death. DS HCNs exhibit intracellular oxidative stress and increased apoptosis after the first week in culture (Busciglio and Yankner, 1995). ets-2 levels were increased in DS HCNs, and, between 7 and 14 d in vitro, DS HCNs showed increased bax, cytoplasmic translocation of cytochrome c and apoptosis inducing factor, and active caspases 3 and 7, consistent with activation of an apoptotic mitochondrial death pathway. Degeneration of DS neurons was reduced by dominant-negative ets-2, suggesting that increased ets-2 expression promotes DS neuronal apoptosis. In the human brain, ets-2 expression was found in neurons and astrocytes. Strong ets-2 immunoreactivity was observed in DS/AD and sporadic AD brains associated with degenerative markers such as bax, intracellular Abeta, and hyperphosphorylated tau. Thus, in DS/AD and sporadic AD brains, converging pathological mechanisms leading to chronic oxidative stress and ets-2 upregulation in susceptible neurons may result in increased vulnerability by promoting the activation of a mitochondrial-dependent proapoptotic pathway of cell death.

Alzheimer's presenilin 1 mutations impair kinesin-based axonal transport.

Several lines of evidence indicate that alterations in axonal transport play a critical role in Alzheimer's disease (AD) neuropathology, but the molecular mechanisms that control this process are not understood fully. Recent work indicates that presenilin 1 (PS1) interacts with glycogen synthase kinase 3beta (GSK3beta). In vivo, GSK3beta phosphorylates kinesin light chains (KLC) and causes the release of kinesin-I from membrane-bound organelles (MBOs), leading to a reduction in kinesin-I driven motility (Morfini et al., 2002b). To characterize a potential role for PS1 in the regulation of kinesin-based axonal transport, we used PS1-/- and PS1 knock-inM146V (KIM146V) mice and cultured cells. We show that relative levels of GSK3beta activity were increased in cells either in the presence of mutant PS1 or in the absence of PS1 (PS1-/-). Concomitant with increased GSK3beta activity, relative levels of KLC phosphorylation were increased, and the amount of kinesin-I bound to MBOs was reduced. Consistent with a deficit in kinesin-I-mediated fast axonal transport, densities of synaptophysin- and syntaxin-I-containing vesicles and mitochondria were reduced in neuritic processes of KIM146V hippocampal neurons. Similarly, we found reduced levels of PS1, amyloid precursor protein, and synaptophysin in sciatic nerves of KIM146V mice. Thus PS1 appears to modulate GSK3beta activity and the release of kinesin-I from MBOs at sites of vesicle delivery and membrane insertion. These findings suggest that mutations in PS1 may compromise neuronal function by affecting GSK-3 activity and kinesin-I-based motility.

GVS-111 prevents oxidative damage and apoptosis in normal and Down's syndrome human cortical neurons.

The neuroprotective activity of a novel N-acylprolyl-containing dipeptide analog of the nootropic 2-oxo-1-pyrrolidine acetamide (Piracetam) designated as GVS-111 (DVD-111/Noopept) was tested in two in vitro models of neuronal degeneration mediated by oxidative stress: normal human cortical neurons treated with H(2)O(2), and Down's syndrome (DS) cortical neurons. Incubation of normal cortical neurons with 50 microM H(2)O(2) for 1h resulted in morphological and structural changes consistent with neuronal apoptosis and in the degeneration of more than 60% of the neurons present in the culture. GVS-111 significantly increased neuronal survival after H(2)O(2)-treatment displaying a dose-dependent neuroprotective activity from 10nM to 100 microM, and an IC(50) value of 1.21+/-0.07 microM. GVS-111 inhibited the accumulation of intracellular free radicals and lipid peroxidation damage in neurons treated with H(2)O(2) or FeSO(4), suggesting an antioxidant mechanism of action. GVS-111 exhibited significantly higher neuroprotection compared to the standard cognition enhancer Piracetam, or to the antioxidants Vitamin E, propyl gallate and N-tert-butyl-2-sulpho-phenylnitrone (s-PBN). In DS cortical cultures, chronic treatment with GVS-111 significantly reduced the appearance of degenerative changes and enhanced neuronal survival. The results suggest that the neuroprotective effect of GVS-111 against oxidative damage and its potential nootropic activity may present a valuable therapeutic combination for the treatment of mental retardation and chronic neurodegenerative disorders.

NAP and ADNF-9 protect normal and Down's syndrome cortical neurons from oxidative damage and apoptosis.

NAP (Asn-Ala-Pro-Val-Ser-Ile-Pro-Gln, single letter code: NAPVSIPQ) and ADNF-9 (activity-dependent neurotrophic factor-9; Ser-Ala-Leu-Leu-Arg-Ser-Ile-Pro-Ala; single letter code: SALLRSIPA) are peptides derived from naturally occurring glial proteins that have shown neuroprotection in rodent model systems. Here, the neuroprotective activity of ADNF-9 and NAP was tested in two human models of neuronal degeneration in culture mediated by oxidative stress: normal human cortical neurons treated with H2O2 and Down's syndrome (DS) cortical neurons. Incubation of normal cortical neurons with 50 microM H2O2 for 1 hour resulted in morphological and structural changes consistent with neuronal degeneration and loss of viability of more than 60% of the neurons present in the culture. Addition of ADNF-9 or NAP at femtomolar concentrations resulted in significant increases in survival of normal neurons treated with H2O2. Femtomolar concentrations of ADNF-9 or NAP exhibited a similar neuroprotective efficacy, comparable to the antioxidant N-tert-butyl-2-sulpho-phenylnitrone at 100 microM (s-PBN). Treatment of DS cortical neurons with ADNF-9 or NAP resulted in a significant increase in neuronal survival as well as reduction of degenerative morphological changes. The results suggest that ADNF-9 and NAP possess potent neuroprotective properties against oxidative damage in human neurons that may be useful to preserve neuronal function and prevent neuronal death associated with chronic neurodegenerative disorders.