The generation of new neurons from neural stem cells is restricted to two regions of the adult mammalian central nervous system: the subventricular zone of the lateral ventricle, and the subgranular zone of the hippocampal dentate gyrus. In both regions, signals provided by the microenvironment regulate the maintenance, proliferation and neuronal fate commitment of the local stem cell population. The identity of these signals is largely unknown. Here we show that adult hippocampal stem/progenitor cells (AHPs) express receptors and signalling components for Wnt proteins, which are key regulators of neural stem cell behaviour in embryonic development. We also show that the Wnt/beta-catenin pathway is active and that Wnt3 is expressed in the hippocampal neurogenic niche. Overexpression of Wnt3 is sufficient to increase neurogenesis from AHPs in vitro and in vivo. By contrast, blockade of Wnt signalling reduces neurogenesis from AHPs in vitro and abolishes neurogenesis almost completely in vivo. Our data show that Wnt signalling is a principal regulator of adult hippocampal neurogenesis and provide evidence that Wnt proteins have a role in adult hippocampal function.

The C-type lectin-like receptor 2 (CLEC-2) activates platelets through Src and Syk tyrosine kinases via a single cytoplasmic YxxL motif known as a hem immunoreceptor tyrosine-based activation motif (hemI-TAM). Here, we demonstrate using sucrose gradient ultracentrifugation and methyl-␤-cyclodextrin treatment that CLEC-2 translocates to lipid rafts upon ligand engagement and that translocation is essential for hemITAM phosphorylation and signal initiation. HemITAM phosphorylation, but not translocation, is also critically dependent on actin polymerization, Rac1 activation, and release of ADP and thromboxane A 2 (TxA 2 ). The role of ADP and TxA 2 in mediating phosphorylation is dependent on ligand engagement and rac activation but is independent of platelet aggregation. In contrast, tyrosine phosphorylation of the GPVIFcR␥-chain ITAM, which has 2 YxxL motifs, is independent of actin polymerization and secondary mediators. These results reveal a unique series of proximal events in CLEC-2 phosphorylation involving actin polymerization, secondary mediators, and Rac activation. (Blood. 2010; 115(14):2938-2946) IntroductionDectin-1, C-type lectin-like receptor 2 (CLEC-2), and CLEC-9A are C-type lectin receptors which have been shown to signal through an immunoreceptor tyrosine-based activation motif (ITAM)-like pathway via a single YxxL in their short cytoplasmic tails known as a hemITAM. [1][2][3][4] Tyrosine phosphorylation of the conserved tyrosine and both SH2 domains of the tyrosine kinase Syk have been shown to be essential for activation of Syk by CLEC-2 and dectin-1, favoring a model in which the tyrosine kinase is activated by the cross-linking of 2 receptors. 2 This is consistent with the observations that CLEC-9A is a disulphide-linked dimer and that CLEC-2 is expressed as a noncovalent dimer. 1,5 CLEC-2 is highly expressed in platelets and at lower levels in other hematopoietic cells, including neutrophils and dendritic cells. 6,7 It is a type II transmembrane protein and a nonclassical C-type lectin that lacks the conserved amino acids that mediate binding to glycans. 7 CLEC-2 was identified by affinity chromatography as a ligand for the snake venom protein rhodocytin, purified from the Malayan pit viper, Calloselasma rhodostoma. 3 Independent crystal structures of rhodocytin show that it assembles as a tetramer, which leads to the suggestion that it mediates activation of CLEC-2 through clustering. 8,9 Consistent with this clustering model of activation, whole antibodies and F(ab) 2 fragments have been reported to activate CLEC-2, whereas antibody Fab fragments were inhibitory. 3,10,11 Physiologic roles of CLEC-2 are now beginning to emerge. Recently, CLEC-2 has been implicated in tumor metastasis via its interaction with the type I sialoglycoprotein podoplanin, which is also expressed on the surface of kidney podocytes, lung type I alveolar cells, and lymphatic endothelium. 12-14 CLEC-2 has also been shown to play a role in neutrophil phagocytosis. 15 Evidence obtained using antibody depletion of CLEC-2...

Thompson et al. identify the dual specificity tyrosine-regulated kinase 1A (DYRK1A) as a new player in the control of lymphopoiesis. Loss of DYRK1A in mice results in Cyclin D3 stabilization and failure to repress E2F target genes, thus impairing cell cycle exit and proper pre–B and pre–T cell differentiation.

The dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) gene is located within the Down Syndrome (DS) critical region on chromosome 21 and is implicated in the generation of Tau and amyloid pathologies that are associated with the early onset Alzheimer's Disease (AD) observed in DS. DYRK1A is also found associated with neurofibrillary tangles in sporadic AD and phosphorylates key AD players (Tau, amyloid precursor, protein, etc). Thus, DYRK1A may be an important therapeutic target to modify the course of Tau and amyloid beta (Ab) pathologies. Here, we describe EHT 5372 (methyl 9-(2,4-dichlorophenylamino) thiazolo[5,4-f]quinazoline-2-carbimidate), a novel, highly potent (IC 50 = 0.22 nM) DYRK1A inhibitor with a high degree of selectivity over 339 kinases. Models in which inhibition of DYRK1A by siRNA reduced and DYRK1A over-expression induced Tau phosphorylation or Ab production were used. EHT 5372 inhibits DYRK1A-induced Tau phosphorylation at multiple AD-relevant sites in biochemical and cellular assays. EHT 5372 also normalizes both Ab-induced Tau phosphorylation and DYRK1A-stimulated Ab production. DYRK1A is thus as a key element of Abmediated Tau hyperphosphorylation, which links Tau and amyloid pathologies. EHT 5372 and other compounds in its class warrant in vivo investigation as a novel, high-potential therapy for AD and other Tau opathies.

Alzheimer's disease (AD) is characterized neuropathologically by the extracellular deposition of the 4 kDa b-amyloid peptide (Ab), a 39-43 amino acid peptide that is neurotoxic (Borchelt et al. 1996) and accumulates in neuritic plaques and in cerebral and meningeal microvessels (Wahrle et al. 2002). Amyloid precursor protein (APP) is the precursor of Ab and can be processed via alternative pathways. A nonamyloidogenic secretory pathway includes cleavage of APP to soluble APP (sAPPa) by a-secretases from the a disintegrin and metalloprotease (ADAM) family of proteases within the Ab peptide sequence, thus precluding the formation of Ab. In contrast, the formation of the amyloidogenic Ab peptides is regulated by the sequential action of b-and c-secretases (Checler 1995;Nunan and Small 2000). A primary strategy proposed to treat AD is to prevent the formation of Ab peptides, and their deposition as senile plaques in the brain. Recently, Postina et al. (2004) showed that activation of a-secretase significantly reduces AD-like pathology in an animal model of AD. This raises the possibility that a pharmacological approach to increase a-secretase activity and sAPPa levels, and thus reduce Ab formation may be suitable for AD treatment (Bandyopadhyay et al. 2007).This approach is consistent with the observation that profound changes occur in APP processing with aging and the development of AD. In particular, a reduction in the activity of the non-amyloidogenic pathway leading to Received February 7, 2008; revised manuscript received March 6, 2008; accepted March 28, 2008. Address correspondence and reprint requests to Laurent Désiré, Department of Neurology, Exonhit Therapeutics, 63 Bd Massena, 75013 Paris, France. E-mail: laurent.desire@exonhit.comAbbreviations used: Ab, beta amyloid; ADAM, a disintegrin and metalloprotease; AD, Alzheimer's Disease; APP, amyloid precursor protein; BACE, beta-site APP-cleaving enzyme; DAPT, N-[N-(3,5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester; IP, immunoprecipitation; LTP, long-term potentiation; PDE4, phosphodiesterase 4; PTX, picrotoxin; sAPPa, soluble APP ectodomain; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TAPI-1, TNF-a Protease Inhibitor-1. AbstractPharmacological modulation of the GABA A receptor has gained increasing attention as a potential treatment for central processes affected in Alzheimer disease (AD), including neuronal survival and cognition. The proteolytic cleavage of the amyloid precursor protein (APP) through the a-secretase pathway decreases in AD, concurrent with cognitive impairment. This APP cleavage occurs within the b-amyloid peptide (Ab) sequence, precluding formation of amyloidogenic peptides and leading to the release of the soluble N-terminal APP fragment (sAPPa) which is neurotrophic and procognitive. In this study, we show that at nanomolar-low micromolar concentrations, etazolate, a selective GABA A receptor modulator, stimulates sAPPa production in rat cortical neurons and in guinea pig brains. Etazolate (20 ...