The pattern of human tau phosphorylation is the result of priming and feedback events in primary hippocampal neurons
Département de Pathologie et Biologie Cellulaire, Université de Montréal, C.P.6128, Succursale Centre-ville, Montréal, QC H3C3J7, Canada. Neuroscience
(Impact Factor: 3.36).
06/2010; 168(2):323-34. DOI: 10.1016/j.neuroscience.2010.04.009
Tau, an axonal microtubule-associated protein, becomes hyperphosphorylated in several neurodegenerative diseases including Alzheimer disease (AD). In AD brain, tau is phosphorylated at pathological multiple-site epitopes recognized by the antibodies AT8 (S199/S202/T205), AT100 (T212/S214/T217), AT180 (T231/S235) and PHF-1 (S396/S404) and at individual sites such as S262 and S422. Although it is believed that the hyperphosphorylation of tau occurs in a precise cascade of phosphorylation events, this cascade remains to be demonstrated in mammalian neuronal cells. In the present study, human tau mutants in which disease-related sites associated with either an early (AT8, T231 and S262) or intermediate (T217) stage of tau pathology were mutated in alanine to inhibit their phosphorylation were overexpressed in primary hippocampal neurons to examine their impact on the phosphorylation of other disease-related sites. The mutation in alanine of S262 decreased the phosphorylation of the AT8 and PHF-1 epitopes and that of T217. When the sites included in the AT8 epitope were mutated in alanine, the phosphorylation of T217 and PHF-1 epitope was significantly reduced indicating that the decrease of AT8 phosphorylation was a key event in the impaired phosphorylation of T217 and PHF-1 by the S262 alanine mutant. Most interestingly, the mutation in alanine of T217 had a positive impact on the phosphorylation of the AT8 epitope, indicating the presence of a feedback loop between AT8 and T217 in rat hippocampal neurons. The phosphorylation of the AT180 epitope was increased when S262 and the sites forming the AT8 epitope were mutated in alanine. The mutation of the AT8 epitope also increased the phosphorylation of S422. All together, our data show that the sites forming the AT8 epitope could play a central role in regulating the phosphorylation of tau at disease-associated sites and that priming and feedback events take place to regulate the overall level of tau phosphorylation in rat hippocampal neurons.
Available from: Gerard Griffioen
- "Phosphorylation of TAU at the repeat domains, in particular Ser262, is required to elicit Aí µí»½-instigated neurotoxicity   , indicating that detachment from microtubules entails an important feature of AD pathogenesis. Moreover, Ser262 is one of the earliest sites phosphorylated in the course of pathogenesis  and its phosphorylation acts as a priming site for further, more extensive phosphorylation at sites that may control its signalling function . These results indicate a sequential mechanism of TAU-phosphorylation by Aí µí»½o and other AD risk factors affecting its subcellular distribution and signalling. "
[Show abstract] [Hide abstract]
ABSTRACT: Although a wide variety of genetic and nongenetic Alzheimer's disease (AD) risk factors have been identified, their role in onset and/or progression of neuronal degeneration remains elusive. Systematic analysis of AD risk factors revealed that perturbations of intraneuronal signalling pathways comprise a common mechanistic denominator in both familial and sporadic AD and that such alterations lead to increases in Aβ oligomers (Aβo) formation and phosphorylation of TAU. Conversely, Aβo and TAU impact intracellular signalling directly. This feature entails binding of Aβo to membrane receptors, whereas TAU functionally interacts with downstream transducers. Accordingly, we postulate a positive feedback mechanism in which AD risk factors or genes trigger perturbations of intraneuronal signalling leading to enhanced Aβo formation and TAU phosphorylation which in turn further derange signalling. Ultimately intraneuronal signalling becomes deregulated to the extent that neuronal function and survival cannot be sustained, whereas the resulting elevated levels of amyloidogenic Aβo and phosphorylated TAU species self-polymerizes into the AD plaques and tangles, respectively.
- "In fact, one explanation of these differences of sensitivity to amyloid peptide comes from recent study, where the authors evidenced an intrinsic specific regulation of Tau phosphorylation. Indeed, it seems that Tau phosphorylation occurred in a sequential order of events and that feedback mechanisms exist within neurons where the phosphorylation of certain sites would induce the dephosphorylation of other sites, in order to constantly maintain a phosphorylation level . Thus in our study, it could be suggested that each brain regions could be at a different stage of Tau phosphorylation, and for instance at the hippocampal level that the phosphorylation decrease observed of the AT8 epitope could be under a negative feedback loop exerted by the phosphorylation of the AT100 epitope shown in this structure 6 weeks after oAβ25–35 injection. "
[Show abstract] [Hide abstract]
ABSTRACT: Alzheimer's disease (AD) is a neurodegenerative pathology associated with aging characterized by the presence of senile plaques and neurofibrillary tangles that finally result in synaptic and neuronal loss. The major component of senile plaques is an amyloid-β protein (Aβ). Recently, we characterized the effects of a single intracerebroventricular (icv) injection of Aβ fragment (25-35) oligomers (oAβ(25-35)) for up to 3 weeks in rats and established a clear parallel with numerous relevant signs of AD. To clarify the long-term effects of oAβ(25-35) and its potential role in the pathogenesis of AD, we determined its physiological, behavioral, biochemical and morphological impacts 6 weeks after injection in rats. oAβ(25-35) was still present in the brain after 6 weeks. oAβ(25-35) injection did not affect general activity and temperature rhythms after 6 weeks, but decreased body weight, induced short- and long-term memory impairments, increased corticosterone plasma levels, brain oxidative (lipid peroxidation), mitochondrial (caspase-9 levels) and reticulum stress (caspase-12 levels), astroglial and microglial activation. It provoked cholinergic neuron loss and decreased brain-derived neurotrophic factor levels. It induced cell loss in the hippocampic CA subdivisions and decreased hippocampic neurogenesis. Moreover, oAβ(25-35) injection resulted in increased APP expression, Aβ(1-42) generation, and increased Tau phosphorylation. In conclusion, this in vivo study evidenced that the soluble oligomeric forms of short fragments of Aβ, endogenously identified in AD patient brains, not only provoked long-lasting pathological alterations comparable to the human disease, but may also directly contribute to the progressive increase in amyloid load and Tau pathology, involved in the AD physiopathology.
Available from: Linlin Yin
- "Using western blot, we observed that GRg1 pretreatment could prominently attenuate tau overphosphorylation in SK-N-SH neuroblastomas. We chose to test phosphorylation residues of tau at Ser202, because this residue was reportedly associated with tangles in the AD brains (Bertrand et al., 2010; Reynolds et al., 2000). Decreased SYN and MAP-2 expression were accompanied by elevation of phosphorylated tau and preceded significant neuronal cell death, suggesting that phosphorylation of tau and loss of synaptic proteins are early events in the process of neuronal cell death. "
[Show abstract] [Hide abstract]
ABSTRACT: In the present study we aimed to investigate the neuroprotective effect of ginsenoside Rg1 (GRg1) on neuronal damage examined in an adopted in vitro inflammatory neurodegeneration model and the involvement of p38 MAPK signal pathway.
The supernatant from Aβ(1-40)-stimulated THP-1 monocytes was used as culture medium for SK-N-SH neuroblastoma cells which was used as target neuronal cells. The cell viability of SK-N-SH cells was assessed by detecting lactate dehydrogenase (LDH) leakage; the content of pro-inflammatory cytokine was measured by radioimmunoassay; the expressions of tau phosphorylation, p-38 and synaptophysin (SYN) were evaluated by western blot assay. The microtubule associated protein-2 (MAP-2) expression was confirmed by immunostaining.
Our results showed that incubation of the supernatant from Aβ(1-40)-stimulated THP-1 cells with SK-N-SH neuroblastoma cells for 24h significantly increased LDH leakage, tau and p-38 phosphorylation in SK-N-SH cells with increased interleukin (IL)-1β release into the supernatant of THP-1 cells. Pretreatment of THP-1 cells with GRg1 (50, 100 and 150μM) for 30min before Aβ(1-40)-stimulation inhibited THP-1 cell-mediated Aβ neurotoxicity towards SK-N-SH neuroblastoma and also decreased IL-1β release into THP-1 supernatant dose-dependently. An inhibitor of p38 MAPK, SB203580, had the same effect.
These results suggested that activation of the p38 cell signal pathway may be involved in monocyte-mediated Aβ neurotoxicity towards SK-N-SH cells. Data obtained from this study demonstrated that GRg1 represented a potential treatment strategy for Alzheimer's disease (AD).
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.