BackgroundThe progression of Alzheimer’s disease (AD) is associated with an increase of phosphorylated tau in the brain. One of the earliest phosphorylated sites on tau is Ser262 that is preferentially phosphorylated by microtubule affinity regulating kinase (MARK), of which four isoforms exist. Herein we investigated the expression of MARK1-4 in the hippocampus of non-demented elderly (NDE) and AD cases.ResultsIn situ hybridization revealed a uniform, neuronal distribution of all four isoform mRNAs in NDE and AD. Immunohistochemical analyses using isoform-selective antibodies demonstrated that MARK4 in a phosphorylated form colocalizes with p-tau Ser262 in granulovacuolar degeneration bodies (GVDs) that progressively accumulate in AD. In contrast MARK4 is largely absent in the neuronal cytoplasm. MARK3 was localized to a subset of the GVD-containing neurons and also had a weak general cytoplasmic neuronal staining in both NDE and AD. These results suggest that in AD, phosphorylated MARK3 and MARK4 are sequestered and proteolysed in GVDs. MARK1 and MARK2 were absent in GVDs and exhibited relatively uniform neuronal expressions with no apparent differences between NDE and AD.ConclusionWe found that the phosphorylated and fragmented forms of MARK4 and to some extent MARK3 are present in GVDs in AD, and that this expression is highly correlated with phosphorylation of tau at Ser262. This may represent a cellular defense mechanism to remove activated MARK and p-tau Ser262 from the cytosol, thereby reducing the phosphorylating effect on tau Ser262 that appears to be a critical step for subsequent neurodegeneration.

Recent reports have implicated tau-tubulin kinase 1 (TTBK1) in the pathological phosphorylation of tau that occurs in Alzheimer's disease (AD). The present study was undertaken to provide an extensive characterization of TTBK1 mRNA and protein expression in human brain from AD cases and non-demented controls so as to better understand the disease relevance of this novel kinase. In situ hybridization and immunohistochemistry revealed abundant expression of TTBK1 in the somatodendritic compartment of cortical and hippocampal neurons of both AD cases and controls. TTBK1 immunoreactivity appeared to vary with the level of phospho-tau staining, and was strong in the somatodendritic compartment of apparently healthy hippocampal neurons as well as in pre-tangle neurons where it co-localized with diffuse phospho-Ser422 tau staining. Ser422 was confirmed as a TTBK1 substrate in vitro, and an antibody towards the site, in addition to labeling AT8-positive neurofibrillary tangles (NFTs), neuritic plaques and neuropil threads, also labeled a small population of neurons that were unlabeled with AT8. These data suggest a role for TTBK1 in pre-tangle formation prior to the formation of fibrillar tau and strengthen the idea that tau is phosphorylated at Ser422 at an early/intermediate stage in NFT formation.

. Anterograde delivery of brain-derived neurotrophic factor to striatum via nigral transduction of recombinant adeno-associated virus increases neuronal death but promotes neurogenic response following stroke. European Journal of Neuroscience, 17(12), 2667-2678. DOI: 10.1046/j.1460-9568.2003 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal AbstractTo explore the role of brain-derived neurotrophic factor for survival and generation of striatal neurons after stroke, recombinant adenoassociated viral vectors carrying brain-derived neurotrophic factor or green fluorescent protein genes were injected into right rat substantia nigra 4-5 weeks prior to 30 min ipsilateral of middle cerebral artery occlusion. The brain-derived neurotrophic factorrecombinant adeno-associated viral transduction markedly increased the production of brain-derived neurotrophic factor protein by nigral cells. Brain-derived neurotrophic factor was transported anterogradely to the striatum and released in biologically active form, as revealed by the hypertrophic response of striatal neuropeptide Y-positive interneurons. Animals transduced with brain-derived neurotrophic factor-recombinant adeno-associated virus also exhibited abnormalities in body posture and movements, including tilted body to the right, choreiform movements of left forelimb and head, and spontaneous, so-called 'barrel' rotation along their long axis. The continuous delivery of brain-derived neurotrophic factor had no effect on the survival of striatal projection neurons after stroke, but exaggerated the loss of cholinergic, and parvalbumin-and neuropeptide Y-positive, g-aminobutyric acid-ergic interneurons. The high brain-derived neurotrophic factor levels in the animals subjected to stroke also gave rise to an increased number of striatal cells expressing doublecortin, a marker for migrating neuroblasts, and cells double-labelled with the mitotic marker, 5-bromo-2 0 -deoxyuridine-5 0 monophosphate, and early neuronal (Hu) or striatal neuronal (Meis2) markers. Our findings indicate that long-term anterograde delivery of high levels of brain-derived neurotrophic factor increases the vulnerability of striatal interneurons to stroke-induced damage. Concomitantly, brain-derived neurotrophic factor potentiates the stroke-induced neurogenic response, at least at early stages.

Background and Purpose-We have previously shown that delivery of brain-derived neurotrophic factor (BDNF) through direct intrahippocampal gene transduction with a viral vector suppresses the formation of new dentate granule cells triggered by global forebrain ischemia. Here, we investigated whether inhibition of endogenous BDNF alters ischemia-induced neurogenesis in the dentate gyrus. Methods-Rats were subjected to 30 minutes of global forebrain ischemia and then received intraventricular infusion of either the BDNF scavenger, TrkB-Fc fusion protein, or control Hu-Fc for 2 weeks. In parallel, all animals were injected intraperitoneally with the mitosis marker 5-bromo-2Ј-deoxyuridine-5Ј-monophosphate (BrdU). Animals were killed at 2 or 6 weeks after the ischemic insult, and neurogenesis was then assessed immunocytochemically with epifluorescence or confocal microscopy. Results-Infusion of TrkB-Fc fusion protein gave rise to elevated numbers of ischemia-generated new neurons, double-labeled with BrdU and the early neuronal marker Hu or the mature neuronal marker NeuN, in the dentate subgranular zone and granule cell layer at 2 and 6 weeks after the insult. Conclusions-Our findings provide evidence that endogenous BDNF counteracts neuronal differentiation, but not cell proliferation or survival, in ischemia-induced dentate gyrus neurogenesis. Key Words: brain-derived neurotrophic factor Ⅲ cerebral ischemia, global Ⅲ hippocampus Ⅲ neurons Ⅲ stroke Ⅲ rats I n the dentate gyrus (DG) of the adult brain, new functional granule cells are continuously formed from neural stem cells (NSCs) located in the subgranular zone (SGZ). [1][2][3] Global forebrain ischemia in rodents stimulates the proliferation of NSCs in the SGZ and leads to increased generation of granule cells. 4 -6 Because ischemic preconditioning, which protects CA1 neurons against subsequent damage, did not prevent ischemia-induced neurogenesis, it is probably not dependent on CA1 neuronal loss. 4 In accordance, stroke induced by middle cerebral artery occlusion, which causes striatal and cortical infarction but no cell loss in the hippocampus, also gives rise to a marked increase in DG neurogenesis. 7,8 Brain-derived neurotrophic factor (BDNF) plays an important role in neuronal survival and differentiation during embryonic development of the nervous system. 9 The functional effect of BDNF is mediated by interaction with its high-affinity receptor, TrkB. BDNF can significantly increase in vitro survival and differentiation of NSCs isolated from embryonic and postnatal hippocampus, 10 -13 and mutant mice lacking BDNF show increased apoptosis in the SGZ at early postnatal stages. 14 Furthermore, intraventricular infusion of BDNF protein 15,16 and overexpression of the BDNF gene in the ventricular zone 17 in intact, adult rats increase the number of new neurons in the rostral migratory stream and olfactory bulb, striatum, septum, thalamus, and hypothalamus.Global forebrain ischemia has been shown to induce increased endogenous BDNF protein levels in the rat DG...

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