Hidenori Taru

The novel cargo Alcadein induces vesicle association of kinesin-1 motor components and activates axonal transport

Alcadeinα (Alcα) is an evolutionarily conserved type I membrane protein expressed in neurons. We show here that Alcα strongly associates with kinesin light chain (KD≈4–8 × 10−9 M) through a novel tryptophan‐ and aspartic acid‐containing sequence. Alcα can induce kinesin‐1 association with vesicles and functions as a novel cargo in axonal anterograde transport. JNK‐interacting protein 1 (JIP1), an adaptor protein for kinesin‐1, perturbs the transport of Alcα, and the kinesin‐1 motor complex dissociates from Alcα‐containing vesicles in a JIP1 concentration‐dependent manner. Alcα‐containing vesicles were transported with a velocity different from that of amyloid β‐protein precursor (APP)‐containing vesicles, which are transported by the same kinesin‐1 motor. Alcα‐ and APP‐containing vesicles comprised mostly separate populations in axons in vivo. Interactions of Alcα with kinesin‐1 blocked transport of APP‐containing vesicles and increased β‐amyloid generation. Inappropriate interactions of Alc‐ and APP‐containing vesicles with kinesin‐1 may promote aberrant APP metabolism in Alzheimers disease.

Liprin-α/SYD-2 determines the size of dense projections in presynaptic active zones in C. elegans

Liprin-α/SYD-2 activity promotes the polymerization of electron-dense projections in the presynaptic active zone through increased recruitment of ELKS-1/ELKS.

Expression and characterization of the Drosophila X11‐like/Mint protein during neural development

The X11‐like (X11L) protein was originally isolated as a protein bound to the cytoplasmic domain of the β‐amyloid precursor protein (APP), which is associated with Alzheimers disease. In mammals, X11L is believed to play an important role in the regulation of APP metabolism. Here we isolated and characterized the Drosophila X11L (dX11L) protein, also may be referred to this protein as Drosophila Mint (dMint), Lin 10 (dLin10) or X11 (dX11), is thought to be expressed in neuronal tissues from late embryonic through to the adult stages of the fly. The phosphotyrosine interaction domain of dX11L interacts with the cytoplasmic domain of the Drosophila amyloid precursor protein‐like (APPL) similar to the way human X11L (hX11L) interacts with APP. Overexpression of dX11L on post‐mitotic neurons had a lethal effect on flies and, when it was localized to the eye imaginal disc, disruption of compound eye morphology due to enhanced apoptosis of neuronal cells was observed. Overexpression of hX11L and the PDZ domain of dX11L resulted in identical eye phenotypes. The PDZ domain is highly conserved between Drosophila and human, and appears to be responsible for this phenotype. Our findings suggest that the X11L family may be involved with the regulation of apoptosis during neural cell development and that aberrant X11L function could be contribute in this way to the neuronal degeneration observed in Alzheimers disease.

Intracellular trafficking of the amyloid β-protein precursor (APP) regulated by novel function of X11-like.

Background Amyloid β (Aβ), a causative peptide of Alzheimers disease, is generated by intracellular metabolism of amyloid β-protein precursor (APP). In general, mature APP (mAPP, N- and O-glycosylated form) is subject to successive cleavages by α- or β-, and γ-secretases in the late protein secretory pathway and/or at plasma membrane, while immature APP (imAPP, N-glycosylated form) locates in the early secretory pathway such as endoplasmic reticulum or cis-Golgi, in which imAPP is not subject to metabolic cleavages. X11-like (X11L) is a neural adaptor protein composed of a phosphotyrosine-binding (PTB) and two C-terminal PDZ domains. X11L suppresses amyloidogenic cleavage of mAPP by direct binding of X11L through its PTB domain, thereby generation of Aβ lowers. X11L expresses another function in the regulation of intracellular APP trafficking. Methodology In order to analyze novel function of X11L in intracellular trafficking of APP, we performed a functional dissection of X11L. Using cells expressing various domain-deleted X11L mutants, intracellular APP trafficking was examined along with analysis of APP metabolism including maturation (O-glycosylation), processing and localization of APP. Conclusions X11L accumulates imAPP into the early secretory pathway by mediation of its C-terminal PDZ domains, without being bound to imAPP directly. With this novel function, X11L suppresses overall APP metabolism and results in further suppression of Aβ generation. Interestingly some of the accumulated imAPP in the early secretory pathway are likely to appear on plasma membrane by unidentified mechanism. Trafficking of imAPP to plasma membrane is observed in other X11 family proteins, X11 and X11L2, but not in other APP-binding partners such as FE65 and JIP1. It is herein clear that respective functional domains of X11L regulate APP metabolism at multiple steps in intracellular protein secretory pathways.

Quantitative analysis of APP axonal transport in neurons: role of JIP1 in enhanced APP anterograde transport.

APP associates with kinesin-1 via JIP1. In JIP1-decicient neurons, the fast velocity and high frequency of anterograde transport of APP cargo are impaired to reduced velocity and lower frequency, respectively. Interaction of JIP1 with KLC via two novel elements in JIP1 plays an important role in efficient APP axonal transport.

Increased amyloidogenic processing of transgenic human APP in X11-like deficient mouse brain

BackgroundX11-family proteins, including X11, X11-like (X11L) and X11-like 2 (X11L2), bind to the cytoplasmic domain of amyloid β-protein precursor (APP) and regulate APP metabolism. Both X11 and X11L are expressed specifically in brain, while X11L2 is expressed ubiquitously. X11L is predominantly expressed in excitatory neurons, in contrast to X11, which is strongly expressed in inhibitory neurons. In vivo gene-knockout studies targeting X11, X11L, or both, and studies of X11 or X11L transgenic mice have reported that X11-family proteins suppress the amyloidogenic processing of endogenous mouse APP and ectopic human APP with one exception: knockout of X11, X11L or X11L2 has been found to suppress amyloidogenic metabolism in transgenic mice overexpressing the human Swedish mutant APP (APPswe) and the mutant human PS1, which lacks exon 9 (PS1dE9). Therefore, the data on X11-family protein function in transgenic human APP metabolism in vivo are inconsistent.ResultsTo confirm the interaction of X11L with human APP ectopically expressed in mouse brain, we examined the amyloidogenic metabolism of human APP in two lines of human APP transgenic mice generated to also lack X11L. In agreement with previous reports from our lab and others, we found that the amyloidogenic metabolism of human APP increased in the absence of X11L.ConclusionX11L appears to aid in the suppression of amyloidogenic processing of human APP in brain in vivo, as has been demonstrated by previous studies using several human APP transgenic lines with various genetic backgrounds. X11L appears to regulate human APP in a manner similar to that seen in endogenous mouse APP metabolism.

Regulation of the Physiological Function and Metabolism of AβPP by AβPP Binding Proteins

Amyloid-beta protein precursor (AbetaPP) is a receptor-like, type-I membrane protein that plays a central role in the pathogenesis of Alzheimers disease. The cytoplasmic domain of AbetaPP is important for the metabolism and physiological functions of AbetaPP and contains a GYENPTY motif that interacts with proteins that contain a phosphotyrosine binding (PTB) domain such as X11/Mint, FE65, and the JIP family of proteins. X11 and X11-like proteins are neuronal adaptor proteins involved in presynaptic function and the intracellular trafficking of proteins. Recent studies in X11s knockout mice confirmed findings from in vitro studies that X11 proteins affect AbetaPP metabolism and the generation of amyloid-beta peptide. FE65 proteins are involved in transactivation in coordination with the intracellular domain fragment of AbetaPP, and/or in cellular responses to DNA damage. Neurodevelopmental defects observed in FE65s double knockout mice suggest that FE65 proteins cooperate with AbetaPP to play a role in neuronal cytoskeletal regulation. c-Jun N-terminal kinase (JNK) interacting protein-1 (JIP-1), a scaffolding protein for the JNK kinase cascade, has been suggested to mediate the intracellular trafficking of AbetaPP by molecular motor kinesin-1. This article reviews some of the recent findings regarding the regulation of physiological function and metabolism of AbetaPP by AbetaPP binding proteins.

Effects and mechanisms of prolongevity induced by Lactobacillus gasseri SBT2055 in Caenorhabditis elegans.

Lactic‐acid bacteria are widely recognized beneficial host associated groups of the microbiota of humans and animals. Some lactic‐acid bacteria have the ability to extend the lifespan of the model animals. The mechanisms behind the probiotic effects of bacteria are not entirely understood. Recently, we reported the benefit effects of Lactobacillus gasseriSBT2055 (LG2055) on animal and human health, such as preventing influenza A virus, and augmentation of IgA production. Therefore, it was preconceived that LG2055 has the beneficial effects on longevity and/or aging. We examined the effects of LG2055 on lifespan and aging of Caenorhabditis elegans and analyzed the mechanism of prolongevity. Our results demonstrated that LG2055 has the beneficial effects on longevity and anti‐aging of C. elegans. Feeding with LG2055 upregulated the expression of the skn‐1 gene and the target genes of SKN‐1, encoding the antioxidant proteins enhancing antioxidant defense responses. We found that feeding with LG2055 directly activated SKN‐1 activity via p38 MAPK pathway signaling. The oxidative stress response is elicited by mitochondrial dysfunction in aging, and we examined the influence of LG2055 feeding on the membrane potential of mitochondria. Here, the amounts of mitochondria were significantly increased by LG2055 feeding in comparison with the control. Our result suggests that feeding with LG2055 is effective to the extend lifespan in C. elegans by a strengthening of the resistance to oxidative stress and by stimulating the innate immune response signaling including p38MAPK signaling pathway and others.

SYD-1C, UNC-40 (DCC) and SAX-3 (Robo) Function Interdependently to Promote Axon Guidance by Regulating the MIG-2 GTPase

During development, axons must integrate directional information encoded by multiple guidance cues and their receptors. Axon guidance receptors, such as UNC-40 (DCC) and SAX-3 (Robo), can function individually or combinatorially with other guidance receptors to regulate downstream effectors. However, little is known about the molecular mechanisms that mediate combinatorial guidance receptor signaling. Here, we show that UNC-40, SAX-3 and the SYD-1 RhoGAP-like protein function interdependently to regulate the MIG-2 (Rac) GTPase in the HSN axon of C. elegans. We find that SYD-1 mediates an UNC-6 (netrin) independent UNC-40 activity to promote ventral axon guidance. Genetic analysis suggests that SYD-1 function in axon guidance requires both UNC-40 and SAX-3 activity. Moreover, the cytoplasmic domains of UNC-40 and SAX-3 bind to SYD-1 and SYD-1 binds to and negatively regulates the MIG-2 (Rac) GTPase. We also find that the function of SYD-1 in axon guidance is mediated by its phylogenetically conserved C isoform, indicating that the role of SYD-1 in guidance is distinct from its previously described roles in synaptogenesis and axonal specification. Our observations reveal a molecular mechanism that can allow two guidance receptors to function interdependently to regulate a common downstream effector, providing a potential means for the integration of guidance signals.

Suppression of the caspase cleavage of β‐amyloid precursor protein by its cytoplasmic phosphorylation

β‐Amyloid precursor protein (APP) is a type I transmembrane protein. Its cleavages by β‐ and γ‐secretases yield β‐amyloid, which is the main constituent of senile plaques in Alzheimers disease (AD). In apoptotic cells and AD brains, APP is alternatively cleaved by caspases in the cytoplasmic region after the Asp664 residue (with respect to the numbering conversion for the APP695 isoform). Caspase‐cleaved fragments of APP are cytotoxic and have been implicated in AD pathogenesis; however, the mechanisms regulating the cleavage have not been studied. APP is constitutively phosphorylated at Thr668 in brain. In the present study, we demonstrate that APP phosphorylated at Thr668 is less vulnerable to cytoplasmic cleavage by caspase‐3 and caspase‐8. This suggests that APP phosphorylation suppresses the generation of caspase‐cleaved fragments of APP in the brain and that perturbation of this phosphorylation may be involved in APP‐mediated neurotoxicity.