Protrudin and sphingolipid regulate neuronal function via vesicular trafficking

Protrudin and sphingolipid regulate neuronal function via vesicular trafficking

S38 Abstracts O1-G2-2 Semaphorin3A drives AMPA receptor subunit GluR2 to dendrites Naoya Yamashita, Hiroshi Usui, Sandy Chen, Yoshio Goshima Grad. S...

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S38

Abstracts

O1-G2-2 Semaphorin3A drives AMPA receptor subunit GluR2 to dendrites Naoya Yamashita, Hiroshi Usui, Sandy Chen, Yoshio Goshima Grad. Sch. Med., Yokohama City University, Yokohama, Japan Sema3A, a repulsive guidance molecule, also facilitates axodendritic transport. Here we show that Sema3A induces facilitation of axodendritic transport via electrical signals and drives AMPA receptor GluR2 to dendrites. Local application of Sema3A at axonal growth cone facilitates axodendritic transport in hippocampal neurons. This response was mediated by the activities of L-type calcium channels, ryanodine receptors, and tetrodotoxin-sensitive sodium channels. We also found that GluR2 along with GRIP1 were accumulated in neurites of Sema3A-treated hippocampal neurons. Time-lapse imaging using EGFP-GRIP1 shows that local application of Sema3A at axonal growth cone enhances the transport of GRIP1 at dendrite, suggesting that the transport of GRIP1 is induced by Sema3A signaling propagated from axonal growth cone. Concordantly, the expression level of GluR2 and GRIP1 in stratum lacunosum-moleculare was decreased in the sema3A-deficient hippocampus. Our results identify a novel mechanism and physiological roles of Sema3A-induced axodendritic transport. doi:10.1016/j.neures.2009.09.022

O1-G2-3 Mutant SOD1 impairs axonal transport of choline acetyltransferase and acetylcholine release by sequestering KAP3 Minako Tateno 1 , Ryosuke Takahashi 2 , Toshiyuki Araki 1 1

Nat. Inst. of Neuroscience, NCNP, Japan; Sch. of Med., Japan

2

Dept. of Neurol., Kyoto Univ.

Mutations in the superoxide dismutase 1 (sod1) gene cause familial amyotrophic lateral sclerosis (FALS), likely due to the toxic properties of misfolded mutant SOD1 protein. We previously reported that misfolded SOD1 species specifically associate with Kinesin-associated protein 3 (KAP3) in the spinal cord of G93A SOD1-Tg mouse, a FALS model, from the pre-onset stage. KAP3 is a Kinesin-2 subunit responsible for binding to cargos including choline acetyltransferase (ChAT), whose transport was selectively reduced in G93A SOD1-Tg motor axons prior to the disease onset. By employing a novel FALS model system in NG108-15 cells, we showed that microtubule-dependent release of acetylcholine was significantly impaired by misfolded SOD1 species. Furthermore, such impairment was normalized by KAP3 overexpression. KAP3 was incorporated into SOD1 aggregates in human FALS cases as well. These results suggest that KAP3 sequestration by misfolded SOD1 species and resultant inhibition of ChAT transport play a role in the pathogenesis of ALS. doi:10.1016/j.neures.2009.09.023

O1-G2-4 Protrudin and sphingolipid regulate neuronal function via vesicular trafficking Michiko Shirane Kyushu Univ., Japan Protrudin is a key molecule for the membrane recycling system that is required for neurite formation. Overexpression of this molecule induces process formation by directional trafficking of vesicles via Rab11-dependent vesicular recycling. Protrudin contains a FYVE domain, but the function of it has been unclear. FYVE domains are generally known to binds to PI3P, whereas protrudin-FYVE was not associated with PI3P. We have discovered that protrudin-FYVE specifically recongnizes a sphigolipid that is abundant in nervous system. Recently, a mutation of protrudin was found in a family with hereditary spastic paraplegia, AD-HSP, which is characterized by selective degeneration of motor neurons and is associated with impairment of neuronal vesicular trafficking. To investigate the physiological role of protrudin, we have generated mice deficient in protrudin, and found that the mutant mice display hindlimb weakness and subsequently show a paraplegia. The mutant mice exhibited the defects in axonal formation, axonal domain formation, and synaptosomal molecule trafficking, which seemed to be caused by the defects in membrane recycling system via the sphingolipid binding. doi:10.1016/j.neures.2009.09.024

O1-G2-5 Tubulin tyrosination is required for the maintenance of neuronal polarity Yoshiyuki Konishi, Mitsutoshi Setou Hamamatsu University School of Medicine, Japan Neurons form distinctive axonal and dendritic compartments that are important for directional signalling. The mechanisms that discriminate axons from dendrites remain elusive. The fact that the microtubule motor Kinesin-1 can recognize axons

even prior to polarization is a remarkable key for the identification of spatial cues involved in axon-dendrite differentiatio. Here, we found that amino acid substitutions in the sheet beta5-loop8 region transform truncated Kinesin-1 from the uni-destination (i.e. axon specific) to the bi-destination (i.e. axon and dendrites) state. Further, we demonstrated that tyrosinated tubulins that are abundant in somatodendrites prevent the wild-type Kinesin-1 from binding to microtubules, while the bi-destination-type Kinesin-1 overcomes this inhibition; this suggests that tubulin tyrosination sequesters Kinesin-1 from somatodendrites via beta5-loop8. Consistently, by inhibiting tubulin tyrosination in hippocampal neurons, Kinesin-1 accumulated both axon and dendrites. Further, we demonstrated that this mechanism is required for the maintenance of neuronal polarity. doi:10.1016/j.neures.2009.09.025

O1-G3-1 Generation and analysis of PS1 G183V knock-in mice as models of frontotemporal dementia Hirotaka Watanabe, Jie Shen Brigham & Women’s Hospital, Harvard Medical School, Boston, USA Mutations in the presenilin 1 (PS1) gene are involved in the pathogenesis of both early-onset familial Alzheimer disease (FAD) and familial frontotemporal dementia (FTD). Interestingly, neuropathological analysis of the Belgian FTD family carrying the G183V mutation in the PS1 gene confirmed neurodegeneration in the absence of amyloid deposition, whereas PS1 mutations associated with FAD often increase A␤42 production. To investigate how the G183V mutation causes dementia and neurodegeneration without amyloid deposition, we generated a knock-in mouse carrying this mutation. Homozygous knock-in mice are normally born, and express markedly lower levels of PS1 protein and mRNA in the brain compared to wild-type littermate controls. This PS1 reduction was caused by an aberrant spliced RNA lacking both exons 6 and 7, which was destined for nonsense-mediated mRNA decay. This aberrant splicing occurred possibly due to a transversion in the last base of exon 6 corresponding to the mutation. We will present our characterization of this knock-in mouse and discuss its implications in FTD. doi:10.1016/j.neures.2009.09.026

O1-G3-2 Microglial defects and neurodegeneration in SAMP10 mice: a model of brain aging Atsuyoshi Shimada, Sanae Ishii, Shiro Takei, Noriko Kawamura, Ayako Furukawa, Yoichi Chiba, Masanori Hosokawa Aichi Human Service Ctr. Inst. for Developmental Res., Kasugai, Japan Microglia interact with neurons via ramified processes to maintain brain homeostasis. We studied how microglial morphology changes as a function of age using SAMP10 mice (P10), a model of cerebral degeneration and SAMR1 mice (R1), normal control. Morphometric analysis of Iba-1 immunostained hippocampal microglia revealed that processes were shorter, branch points were fewer, and abnormal structures were more prominent in 3-month-old P10 than those in age-matched R1. Similar changes in microglial processes appeared in R1 at 14 months of age and older. When mice at age 3 months received kainate to induce excitotoxic hippocampal injury, microglia transformed into bottle brush-like morphology and expressed IGF-1 in R1. Microglia of P10 were defective in morphological changes and lacked IGF-1 expression. Thirty days after kainate injection, hippocampi were atrophied only in P10. Therefore, P10 microglia may play a less effective neuroprotective role, which may underlie the susceptibility to neurodegeneration. doi:10.1016/j.neures.2009.09.027

O1-G3-3 Null mutation of Drosophila yata/CG1973, which regulates trafficking of Amyloid precursor protein like, results in progressive eye vacuolization, brain volume reduction and lifespan shortening Masaki Sone 1 , Hitoshi Okazawa 1 , Yo-ichi Nabeshima 2 1

Med. Res. Inst., Tokyo Med. Dent. Univ., Japan; Univ., Japan

2

Grad. Sch. Med., Kyoto

APPL is the Drosophila orthologue of APP (amyloid precursor protein), which is involved in Alzheimer’s disease. We identified yata as a novel gene that genetically interacts with Appl. yata null mutants showed notched wing, abnormal eye morphology, progressive eye vacuolization, progressive brain volume reduction and lifespan shortening. As a candidate mechanism of the abnormalities, we found that trafficking of APPL is impaired in yata mutants. Accumulation of endogenous APPL was observed mainly in perinuclear regions, while transport of exogenously expressed APPL to synapses was also impaired. In addition, aberrant accumulation of Sec23p, a component of the COPII coat of secretory vesicles from the