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1These two authors contributed equally to this work.Abbreviations used: AD, Alzheimer's disease; AL, acetylated lysine; BSA, bovine serum albumin; GFP, Green Fluorescent Protein; HDAC, histone deacetylase 6; HEK, human embryonic kidney cells; MAPs, microtubule-associated proteins; NFTs, neurofibrillary tangles; PHFs, paired helical filaments. AbstractAnalysis of brain microtubule protein from patients with Alzheimer's disease showed decreased alpha tubulin levels along with increased acetylation of the alpha tubulin subunit, mainly in those microtubules from neurons containing neurofibrillary tau pathology. To determine the relationship of tau protein and increased tubulin acetylation, we studied the effect of tau on the acetylation-deacetylation of tubulin. Our results indicate that tau binds to the tubulin-deacetylase, histone deacetylase 6 (HDAC6), decreasing its activity with a consequent increase in tubulin acetylation. As expected, increased acetylation was also found in tubulin from wild-type mice compared with tubulin from mice lacking tau because of the tau-mediated inhibition of the deacetylase. In addition, we found that an excess of tau protein, as a HDAC6 inhibitor, prevents induction of autophagy by inhibiting proteasome function.

Alzheimer’s disease is characterized by the presence of two histopathological aberrant structures, the senile plaques and the neurofibrillary tangles. The main component of these tangles is the cytoskeletal protein tau in hyperphosphorylated form. Since a main tau kinase is glycogen synthase kinase 3 (GSK-3), the use of specific GSK-3 inhibitors, like lithium, could be a potential therapy in Alzheimer’s disease. In this short article, we have done a review on tau phosphorylation in Alzheimer’s disease and other tauopathies, and on the inhibition of kinases like GSK-3, involved in tau modification.

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a b s t r a c tLevels of tau phosphorylation are high during the developmental period of intense neurite outgrowth, but decrease later. We here investigated whether tau protein plays a role in adult neurogenesis. First we demonstrate that new neurons generated in the subgranular zone express tau in a hyperphosphorylated form. Phospho-tau expression colocalized with doublecortin but not with glial fibrillary acidic protein, Ki67 or calbindin. The same was observed in the subventricular zone. Tau knockout mice did not show a significant decrease in the number of doublecortin-positive cells, although a deficit in migration was observed. These findings suggest that basal tau phosphorylation present in adult animals is in part due to neurogenesis, and from Tau knockout mice it seems that tau is involved in normal migration of new neurons.

Dorsal hippocampal regions are involved in memory and learning processes, while ventral areas are related to emotional and anxiety processes. Hippocampal dependent memory and behaviour alterations do not always come out in neurodegenerative diseases at the same time. In this study we have tested the hypothesis that dorsal and ventral dentate gyrus (DG) regions respond in a different manner to increased glycogen synthase kinase-3β (GSK3β) levels in GSK3β transgenic mice, a genetic model of neurodegeneration. Reactive astrocytosis indicate tissue stress in dorsal DG, while ventral area does not show that marker. These changes occurred with a significant reduction of total cell number and with a significantly higher level of cell death in dorsal area than in ventral one as measured by fractin-positive cells. Biochemistry analysis showed higher levels of phosphorylated GSK3β in those residues that inactivate the enzyme in hippocampal ventral areas compared with dorsal area suggesting that the observed susceptibility is in part due to different GSK3 regulation. Previous studies carried out with this animal model had demonstrated impairment in Morris Water Maze and Object recognition tests point out to dorsal hippocampal atrophy. Here, we show that two tests used to evaluate emotional status, the light–dark box and the novelty suppressed feeding test, suggest that GSK3β mice do not show any anxiety-related disorder. Thus, our results demonstrate that in vivo overexpression of GSK3β results in dorsal but not ventral hippocampal DG neurodegeneration and suggest that both areas do not behave in a similar manner in neurodegenerative processes.

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