CRMP2 mediates Sema3F-dependent axon pruning and dendritic spine remodeling

Regulation of axon guidance and pruning of inappropriate synapses by class 3 semaphorins are key to the development of neural circuits. Collapsin response mediator protein 2 (CRMP2) has been shown to regulate axon guidance by mediating semaphorin 3A (Sema3A) signaling;however, nothing is known about its role in synapse pruning. Here, using newly generated crmp2(-/-) mice we demonstrate that CRMP2 has a moderate effect on Sema3A-dependent axon guidance in vivo, and its deficiency leads to a mild defect in axon guidance in peripheral nerves and the corpus callosum. Surprisingly, crmp2(-/-) mice display prominent defects in stereotyped axon pruning in hippocampus and visual cortex and altered dendritic spine remodeling, which is consistent with impaired Sema3F signaling and with models of autism spectrum disorder (ASD). We demonstrate that CRMP2 mediates Sema3F signaling in primary neurons and that crmp2(-/-) mice display ASD-related social behavior changes in the early postnatal period as well as in adults. Together, we demonstrate that CRMP2 mediates Sema3F-dependent synapse pruning and its dysfunction shares histological and behavioral features of ASD

Die Trim2 Mausmutante - Ein Model für Ataxia des Zerebellums

Im Rahmen eines großangelegten Gene-Trap-Mutations-Screens mit dem Ziel, neue an der Hirnentwicklung und -funktion beteiligten Gene zu identifizieren, wurde eine Gene-Trap (GT) Maus-Linie charakterisiert, die eine postnatale Reportergen-Expression in zerebellaren Purkinje-Zellen (PZ), im Hippokampus, im Kortex und in der Ganglienzell- und inneren Körnerschicht der Retina aufweist. Die für diese Gen-Trap -Mutation homozygoten Mäuse waren bis zu einem Alter von ca. 1.5 Monaten phänotypisch nicht von ihren Wildtyp-Wurfgeschwistern unterscheidbar, wonach ein Intentionstremor gefolgt von einer Gangataxie aufzutreten begann. In späteren Stadien (um die drei Monate) waren spontane epileptische Anfälle zu beobachten. Histologisch litten die mutierten Mäuse an einer progressiven Degeneration von Purkinje-Zellen und tiefen zerebellären Kernen. Die Innervation der Purkinje-Zellen durch die Kletterfasern wurde bei den mutierten Mäusen zunächst ausgebildet, dann aber zurückgezogen und hatte eine Degeneration der Purkinje-Zellen zur Folge. In der Retina kam es zu einer Größenreduzierung in der Ganglienzell- und der inneren Körnerschicht. Die Größe der äußeren plexiformen Schicht, in der sich die Dendriten der Bipolarzellen befinden, war ebenfalls signifikant reduziert. Im Hippocampus fand sich keine Degeneration.Die GT Vektor-Insertion trat innerhalb einer RBCC/TRIM RING-finger Domäne auf, die das Gen trim2 enthält einen Bindungspartner von Myosin V. Myosin V ist, als ein Motorprotein, für den Transport des glatten endoplasmatischen Retikulums in die dendritischen Dornen der Purkinje-Zellen verantwortlich. Zudem interagiert es mit der leichten Untereinheit des Neurofilaments (NF-L) und reguliert die Neurofilament-Dichte in Axonen. Da die Dendriten in trim2 homozygoten Mäusen keinen Phänotyp aufwiesen, jedoch bereits in einerthalb-jährigen Mutanten axonale Anschwellungen sowohl in der zerebellaren weißen Substanz, als auch in der Körnerzellschicht auftraten (sogar noch vor der Degeneration der Purkinje-Zellen), nehmen wir an, daß der axonale Defekt eine Folge des zerebellären Phänotyps der trim2 Mausmutanten ist

Relative resistance of Cdk5-phosphorylated CRMP2 to dephosphorylation

Collapsin response mediator protein 2 (CRMP2) binds to microtubules and regulates axon outgrowth in neurons. This action is regulated by sequential phosphorylation by the kinases cyclin-dependent kinase 5 (Cdk5) and glycogen synthase kinase 3 (GSK3) at sites that are hyperphosphorylated in Alzheimer disease. The increased phosphorylation in Alzheimer disease could be due to increases in Cdk5 and/or GSK3 activity or, alternatively, through decreased activity of a CRMP phosphatase. Here we establish that dephosphorylation of CRMP2 at the residues targeted by GSK3 (Ser-518/Thr-514/Thr-509) is carried out by a protein phosphatase 1 family member in vitro, in neuroblastoma cells, and primary cortical neurons. Inhibition of GSK3 activity using insulin-like growth factor-1 or the highly selective inhibitor CT99021 causes rapid dephosphorylation of CRMP2 at these sites. In contrast, pharmacological inhibition of Cdk5 using purvalanol results in only a gradual and incomplete dephosphorylation of CRMP2 at the site targeted by Cdk5 (Ser-522), suggesting a distinct phosphatase targets this residue. A direct comparison of dephosphorylation at the Cdk5 versus GSK3 sites in vitro shows that the Cdk5 site is comparatively resistant to phosphatase treatment. The presence of the peptidyl-prolyl isomerase enzyme, Pin1, does not affect dephosphorylation of Ser-522 in vitro, in cells, or in Pin1 transgenic mice. Instead, the relatively high resistance of this site to phosphatase treatment is at least in part due to the presence of basic residues located nearby. Similar sequences in Tau are also highly resistant to phosphatase treatment. We propose that relative resistance to phosphatases might be a common feature of Cdk5 substrates and could contribute to the hyperphosphorylation of CRMP2 and Tau observed in Alzheimer disease

Excessive tubulin polyglutamylation causes neurodegeneration and perturbs neuronal transport

International audiencePosttranslational modifications of tubulin are emerging regulators of microtubule functions. We have shown earlier that upregulated polyglutamylation is linked to rapid degeneration of Purkinje cells in mice with a mutation in the deglutamylating enzyme CCP1. How polyglutamylation leads to degeneration, whether it affects multiple neuron types, or which physiological processes it regulates in healthy neurons has remained unknown. Here, we demonstrate that excessive polyglutamylation induces neurodegeneration in a cell-autonomous manner and can occur in many parts of the central nervous system. Degeneration of selected neurons in CCP1-deficient mice can be fully rescued by simultaneous knockout of the counteracting polyglutamylase TTLL1. Excessive polyglutamylation reduces the efficiency of neuronal transport in cultured hippocampal neurons, suggesting that impaired cargo transport plays an important role in the observed degenerative phenotypes. We thus establish polyglutamylation as a cell-autonomous mechanism for neurodegen-eration that might be therapeutically accessible through manipulation of the enzymes that control this posttranslational modification

A CRMP4‐dependent retrograde axon‐to‐soma death signal in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal non‐cell‐autonomous neurodegenerative disease characterized by the loss of motor neurons (MNs). Mutations in CRMP4 are associated with ALS in patients, and elevated levels of CRMP4 are suggested to affect MN health in the SOD1G93A‐ALS mouse model. However, the mechanism by which CRMP4 mediates toxicity in ALS MNs is poorly understood. Here, by using tissue from human patients with sporadic ALS, MNs derived from C9orf72‐mutant patients, and the SOD1G93A‐ALS mouse model, we demonstrate that subcellular changes in CRMP4 levels promote MN loss in ALS. First, we show that while expression of CRMP4 protein is increased in cell bodies of ALS‐affected MN, CRMP4 levels are decreased in the distal axons. Cellular mislocalization of CRMP4 is caused by increased interaction with the retrograde motor protein, dynein, which mediates CRMP4 transport from distal axons to the soma and thereby promotes MN loss. Blocking the CRMP4‐dynein interaction reduces MN loss in human‐derived MNs (C9orf72) and in ALS model mice. Thus, we demonstrate a novel CRMP4‐dependent retrograde death signal that underlies MN loss in ALS.SynopsisIdentification of an intracellular mechanism that mediates motor neuron (MN) death in Amyotrophic Lateral Sclerosis (ALS). CRMP4 binds the motor protein dynein and transports from distal axons to the soma where it promotes MN death. Blocking the CRMP4‐dynein interaction reduces MN death in human‐derived MNs (C9orf72) and in ALS mice.CRMP4 protein level is altered along ALS diseased motor unit.Dynein mediates CRMP4 mislocalization in motor neurons via specific CRMP4 motif.CRMP4‐dynein complexes are enhanced in ALS diseased MNs.CRMP4‐dynein complex formation facilitates selective neuronal loss in ALS.Dynein‐mediated CRMP4 redistribution from axons into the cell bodies of ALS‐affected motor neurons promotes selective neuronal toxicity in diverse ALS model‐ and patient‐derived cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/169237/1/embj2020107586.reviewer_comments.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/169237/2/embj2020107586.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/169237/3/embj2020107586-sup-0001-Appendix.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/169237/4/embj2020107586_am.pd

Pin1 has opposite effects on wild-type and P301L tau stability and tauopathy

Tau pathology is a hallmark of many neurodegenerative diseases including Alzheimer disease (AD) and frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17). Genetic tau mutations can cause FTDP-17, and mice overexpressing tau mutants such as P301L tau are used as AD models. However, since no tau mutations are found in AD, it remains unclear how appropriate tau mutant mice are as an AD model. The prolyl isomerase Pin1 binds and isomerizes tau and has been implicated in protecting against neurodegeneration, but whether such Pin1 regulation is affected by tau mutations is unknown. Consistent with earlier findings that Pin1 KO induces tauopathy, here we demonstrate that Pin1 knockdown or KO increased WT tau protein stability in vitro and in mice and that Pin1 overexpression suppressed the tauopathy phenotype in WT tau transgenic mice. Unexpectedly, Pin1 knockdown or KO decreased P301L tau protein stability and abolished its robust tauopathy phenotype in mice. In contrast, Pin1 overexpression exacerbated the tauopathy phenotype in P301L tau mice. Thus, Pin1 has opposite effects on the tauopathy phenotype depending on whether the tau is WT or a P301L mutant, indicating the need for disease-specific therapies for tauopathies