A critical role of the amyloid precursor protein (APP) in Alzheimer's disease (AD) pathogenesis has been well established. However, the physiological function of APP remains elusive and much debated. We reported previously that the APP family of proteins is essential in mediating the developing neuromuscular synapse. In the current study, we created a conditional allele of APP and deleted APP in presynaptic motor neuron or postsynaptic muscle. Crossing these alleles onto the APP-like protein 2-null background reveals that, unexpectedly, inactivating APP in either compartment results in neuromuscular synapse defects similar to the germline deletion and that postsynaptic APP is obligatory for presynaptic targeting of the high-affinity choline transporter and synaptic transmission. Using a HEK293 and primary hippocampus mixed-culture assay, we report that expression of APP in HEK293 cells potently promotes synaptogenesis in contacting axons. This activity is dependent on neuronal APP and requires both the extracellular and intracellular domains; the latter forms a complex with Mint1 and Cask and is replaceable by the corresponding SynCAM (synaptic cell adhesion molecule) sequences. These in vitro and in vivo studies identify APP as a novel synaptic adhesion molecule. We postulate that transsynaptic APP interaction modulates its synaptic function and that perturbed APP synaptic adhesion activity may contribute to synaptic dysfunction and AD pathogenesis.

Cancer specific inhibitors reflective of unique metabolic needs, are rare. We describe a novel small molecule, Gboxin, that specifically inhibits primary mouse and human glioblastoma (GBM) cell growth but not mouse embryo fibroblasts or neonatal astrocytes. Gboxin rapidly and irreversibly compromises GBM oxygen consumption. Reliant on its positive charge, Gboxin associates with mitochondrial oxidative phosphorylation complexes in a proton gradient dependent manner and inhibits F0F1 ATP synthase activity. Gboxin resistant cells require a functional mitochondrial permeability transition pore that regulates pH impeding matrix accumulation. Administration of a pharmacologically stable Gboxin analog inhibits GBM allografts and patient derived xenografts. Gboxin toxicity extends to established human cancer cell lines of diverse organ origin and exposes the elevated proton gradient pH in cancer cell mitochondria as a new mode of action for antitumor reagent development.

Amyloidogenic processing of the amyloid precursor protein (APP) generates a large secreted ectodomain fragment (APPsβ), β-amyloid (Aβ) peptides, and an APP intracellular domain (AICD). Whereas Aβ is viewed as critical for Alzheimer's disease pathogenesis, the role of other APP processing products remains enigmatic. Of interest, the AICD has been implicated in transcriptional regulation, and N-terminal cleavage of APPsβ has been suggested to produce an active fragment that may mediate axonal pruning and neuronal cell death. We previously reported that mice deficient in APP and APP-like protein 2 ( APLP2 ) exhibit early postnatal lethality and neuromuscular synapse defects, whereas mice with neuronal conditional deletion of APP and APLP2 are viable. Using transcriptional profiling, we now identify transthyretin ( TTR ) and Klotho as APP/APLP2-dependent genes whose expression is decreased in loss-of-function states but increased in gain-of-function states. Significantly, by creating an APP knockin allele that expresses only APPsβ protein, we demonstrate that APPsβ is not normally cleaved in vivo and is fully capable of mediating the APP-dependent regulation of TTR and Klotho gene expression. Despite being an active regulator of gene expression, APPsβ did not rescue the lethality and neuromuscular synapse defects of APP and APLP2 double-KO animals. Our studies identify TTR and Klotho as physiological targets of APP that are regulated by soluble APPsβ independent of developmental APP functions. This unexpected APP-mediated signaling pathway may play an important role in maintaining TTR and Klotho levels and their respective functions in Aβ sequestration and aging.

Summary A central question in glioblastoma multiforme (GBM) research is the identity of the tumor-initiating cell, and its contribution to the malignant phenotype and genomic state. We examine the potential of adult lineage restricted progenitors to induce fully penetrant GBM using central nervous system (CNS) progenitor-specific inducible Cre mice to mutate Nf1, Trp53 and Pten. We identify two phenotypically and molecularly distinct GBM subtypes governed by identical driver mutations. We demonstrate that the two subtypes arise from functionally independent pools of adult CNS progenitors. Despite histologic identity as GBM, these tumor types are separable based on the lineage of the tumor-initiating cell. These studies point to the cell of origin as a major determinant of GBM subtype diversity.

Amyloid precursor protein (APP) has been strongly implicated in the pathogenesis of Alzheimer's disease (AD). Although impaired synaptic function is believed to be an early and causative event in AD, how APP physiologically regulates synaptic properties remains poorly understood. Here,

The key pathological features of Alzheimer's disease include synaptic dysfunction, profound changes in the cholinergic system, and deposition of ␤-amyloid peptides generated by proteolytic processing of the amyloid-␤ precursor protein (APP). However, the pathways linking APP with synaptic activity and cholinergic neuronal function are poorly understood. We report here that APP is essential in regulating the presynaptic expression and activity of the high-affinity choline transporter (CHT), a molecule that mediates the rate-limiting step of cholinergic synaptic transmission in both the neuromuscular junction and central cholinergic neurons. Loss of APP leads to aberrant localization of CHT at the neuromuscular synapses and reduced CHT activity at cholinergic projections. At the cellular level, we show that APP and CHT can be found in Rab5-positive endosomal compartments and that APP affects CHT endocytosis. Furthermore, we demonstrate that APP interacts with CHT through the C-terminal domain, providing support for a specific and direct regulation of CHT by APP through proteinprotein interactions. These results identify a physiological activity of APP in cholinergic neurons, and our data indicate that deregulation of APP function may contribute to cholinergic impairment and AD pathogenesis. neuromuscular synapse ͉ Alzheimer's disease ͉ cholinergic neurons ͉ knockout mice ͉ endocytosis G enetic and biochemical evidence establishes a pivotal role of the amyloid-␤ precursor protein (APP) in Alzheimer's disease (AD) pathogenesis. APP processing generates ␤-amyloid (A␤) peptides, which are deposited as amyloid plaques in the brains of affected individuals; point mutations or gene duplications of APP are causal for a subset of early onset familial AD (1, 2). APP is a member of a family of conserved type I membrane proteins with three mammalian homologs: APP, APP-like protein 1 (APLP1), and APLP2 (3). APP is highly expressed in neurons, where it has been shown to localize to postsynaptic densities, axons, and dendrites (4, 5). APP undergoes rapid anterograde transport (6-9) and is targeted to the synaptic sites of both the CNS and the peripheral nervous system. Despite the extensive studies on APP expression and processing, the physiological function of APP remains speculative and controversial (3).Besides the amyloid pathology, AD is correlated with synaptic dysfunction and is recognized by profound changes in the cholinergic system. These changes include the loss of basal forebrain cholinergic neurons and impaired cholinergic innervation to the cortex and hippocampus, areas that have been implicated in memory, learning, and attention (10-12). Acetylcholine (ACh) is the neurotransmitter for central and peripheral cholinergic synapses, and the latter includes the mammalian neuromuscular junction (NMJ). ACh is synthesized by choline acetyltransferase (Chat) and packaged to synaptic vesicles by vesicular acetylcholine transporter (VaChT). ACh released from presynaptic terminals binds to acetylcholine receptors (AChRs) to e...

Adult neurogenesis persists in the rodent dentate gyrus and is stimulated by chronic treatment with conventional antidepressants through BDNF/TrkB signaling. Ketamine in low doses produces both rapid and sustained antidepressant effects in patients. Previous studies have shed light on post-transcriptional synaptic NMDAR mediated mechanisms underlying the acute effect, but how ketamine acts at the cellular level to sustain this anti-depressive function for prolonged periods remains unclear. Here we report that ketamine accelerates differentiation of doublecortin-positive adult hippocampal neural progenitors into functionally mature neurons. This process requires TrkB-dependent ERK pathway activation. Genetic ablation of TrkB in neural stem/progenitor cells, or pharmacologic disruption of ERK signaling, or inhibition of adult neurogenesis, each blocks the ketamine-induced behavioral responses. Conversely, enhanced ERK activity via Nf1 gene deletion extends the response and rescues both neurogenic and behavioral deficits in mice lacking TrkB. Thus, TrkB-dependent neuronal differentiation is involved in the sustained antidepressant effects of ketamine.

No abstract