Trisomy for synaptojanin1 in Down syndrome is functionally linked to the enlargement of early endosomes.

Enlarged early endosomes have been observed in neurons and fibroblasts in Down syndrome (DS). These endosome abnormalities have been implicated in the early development of Alzheimer's disease (AD) pathology in these subjects. Here, we show the presence of enlarged endosomes in blood mononuclear cells and lymphoblastoid cell lines (LCLs) from individuals with DS using immunofluorescence and confocal microscopy. Genotype-phenotype correlations in LCLs carrying partial trisomies 21 revealed that triplication of a 2.56 Mb locus in 21q22.11 is associated with the endosomal abnormalities. This locus contains the gene encoding the phosphoinositide phosphatase synaptojanin 1 (SYNJ1), a key regulator of the signalling phospholipid phosphatidylinositol-4,5-biphosphate that has been shown to regulate clathrin-mediated endocytosis. We found that SYNJ1 transcripts are increased in LCLs from individuals with DS and that overexpression of SYNJ1 in a neuroblastoma cell line as well as in transgenic mice leads to enlarged endosomes. Moreover, the proportion of enlarged endosomes in fibroblasts from an individual with DS was reduced after silencing SYNJ1 expression with RNA interference. In LCLs carrying amyloid precursor protein (APP) microduplications causing autosomal dominant early-onset AD, enlarged endosomes were absent, suggesting that APP overexpression alone is not involved in the modification of early endosomes in this cell type. These findings provide new insights into the contribution of SYNJ1 overexpression to the endosomal changes observed in DS and suggest an attractive new target for rescuing endocytic dysfunction and lipid metabolism in DS and in AD.

[1]  D. Fremont,et al.  Dual Engagement Regulation of Protein Interactions with the AP-2 Adaptor α Appendage* , 2004, Journal of Biological Chemistry.

[2]  Kerry A. Mullaney,et al.  Alzheimer’s-related endosome dysfunction in Down syndrome is Aβ-independent but requires APP and is reversed by BACE-1 inhibition , 2009, Proceedings of the National Academy of Sciences.

[3]  D. Fremont,et al.  Dual engagement regulation of protein interactions with the AP-2 adaptor alpha appendage. , 2004, The Journal of biological chemistry.

[4]  Sang Yoon Lee,et al.  Regulation of synaptojanin 1 by cyclin-dependent kinase 5 at synapses. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[5]  P. De Camilli,et al.  Delayed reentry of recycling vesicles into the fusion-competent synaptic vesicle pool in synaptojanin 1 knockout mice , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[6]  C. Epstein.  1996 ASHG Presidential Address. Toward the 21st century. , 1997, American journal of human genetics.

[7]  Nick C Fox,et al.  Letter abstract - Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's Disease , 2009 .

[8]  J. Buxbaum,et al.  Abeta localization in abnormal endosomes: association with earliest Abeta elevations in AD and Down syndrome. , 2004, Neurobiology of aging.

[9]  R. Neve,et al.  Microarray Analysis of Hippocampal CA1 Neurons Implicates Early Endosomal Dysfunction During Alzheimer's Disease Progression , 2010, Biological Psychiatry.

[10]  E. Pasquale,et al.  EphrinB–EphB signalling regulates clathrin-mediated endocytosis through tyrosine phosphorylation of synaptojanin 1 , 2005, Nature Cell Biology.

[11]  D. Finkelstein,et al.  Mice deficient for the chromosome 21 ortholog Itsn1 exhibit vesicle-trafficking abnormalities. , 2008, Human molecular genetics.

[12]  R. Nixon,et al.  Increased Neuronal Endocytosis and Protease Delivery to Early Endosomes in Sporadic Alzheimer’s Disease: Neuropathologic Evidence for a Mechanism of Increased β-Amyloidogenesis , 1997, The Journal of Neuroscience.

[13]  P. De Camilli,et al.  Synaptojanin 1-linked phosphoinositide dyshomeostasis and cognitive deficits in mouse models of Down's syndrome , 2008, Proceedings of the National Academy of Sciences.

[14]  Kristopher L. Nazor,et al.  Probing sporadic and familial Alzheimer’s disease using induced pluripotent stem cells , 2012, Nature.

[15]  P. S. St George-Hyslop,et al.  Amyloid beta protein gene: cDNA, mRNA distribution, and genetic linkage near the Alzheimer locus. , 1987, Science.

[16]  D. McCormick,et al.  Essential Role of Phosphoinositide Metabolism in Synaptic Vesicle Recycling , 1999, Cell.

[17]  K. Micheva,et al.  Synaptojanin Forms Two Separate Complexes in the Nerve Terminal , 1997, The Journal of Biological Chemistry.

[18]  Derek Toomre,et al.  Two synaptojanin 1 isoforms are recruited to clathrin-coated pits at different stages , 2006, Proceedings of the National Academy of Sciences.

[19]  J. Buxbaum,et al.  Aβ localization in abnormal endosomes: association with earliest Aβ elevations in AD and Down syndrome , 2004, Neurobiology of Aging.

[20]  Woo-Joo Song,et al.  Overexpression of Dyrk1A Causes the Defects in Synaptic Vesicle Endocytosis , 2010, Neurosignals.

[21]  Jonathan Chabout,et al.  Prefrontal nicotinic receptors control novel social interaction between mice , 2011, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[22]  P. Camilli,et al.  Direct interaction of the 170 kDa isoform of synaptojanin 1 with clathrin and with the clathrin adaptor AP-2 , 2000, Current Biology.

[23]  J. Delabar,et al.  Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome , 1987, Science.

[24]  C. Duyckaerts,et al.  Cholesterol changes in Alzheimer's disease: methods of analysis and impact on the formation of enlarged endosomes. , 2010, Biochimica et biophysica acta.

[25]  L. Buluwela,et al.  Organization and conservation of the GART/SON/DONSON locus in mouse and human genomes. , 2000, Genomics.

[26]  L. Becker,et al.  Excessive expression of synaptojanin in brains with Down syndrome , 2002, Brain and Development.

[27]  Y. Hwang,et al.  MNB/DYRK1A phosphorylation regulates the interactions of synaptojanin 1 with endocytic accessory proteins. , 2006, Biochemical and biophysical research communications.

[28]  G. Di Paolo,et al.  Regulation of transferrin recycling kinetics by PtdIns[4,5]P2 availability , 2006, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[29]  B T Hyman,et al.  Endocytic pathway abnormalities precede amyloid beta deposition in sporadic Alzheimer's disease and Down syndrome: differential effects of APOE genotype and presenilin mutations. , 2000, The American journal of pathology.

[30]  G. Di Paolo,et al.  Cholesterol modulates ion channels via down‐regulation of phosphatidylinositol 4,5‐bisphosphate , 2010, Journal of neurochemistry.

[31]  D. Campion,et al.  APP locus duplication causes autosomal dominant early-onset Alzheimer disease with cerebral amyloid angiopathy , 2006, Nature Genetics.

[32]  R. Chan,et al.  Synaptojanin 1-mediated PI(4,5)P2 hydrolysis is modulated by membrane curvature and facilitates membrane fission. , 2011, Developmental cell.

[33]  Sang Yoon Lee,et al.  The Dual Phosphatase Activity of Synaptojanin1 Is Required for Both Efficient Synaptic Vesicle Endocytosis and Reavailability at Nerve Terminals , 2007, Neuron.

[34]  R. Neve,et al.  Down syndrome fibroblast model of Alzheimer-related endosome pathology: accelerated endocytosis promotes late endocytic defects. , 2008, The American journal of pathology.

[35]  Thomas W. Mühleisen,et al.  Genome-wide association study identifies variants at CLU and PICALM associated with Alzheimer's disease , 2013, Nature Genetics.

[36]  Kristina D. Micheva,et al.  Identification and Characterization of a Nerve Terminal-enriched Amphiphysin Isoform* , 1997, The Journal of Biological Chemistry.

[37]  T. Ijuin,et al.  Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: Challenging the gene dosage effect hypothesis (Part III) , 2003, Amino Acids.

[38]  C. Epstein,et al.  App Gene Dosage Modulates Endosomal Abnormalities of Alzheimer's Disease in a Segmental Trisomy 16 Mouse Model of Down Syndrome , 2003, The Journal of Neuroscience.

[39]  C. van Broeckhoven,et al.  Endocytic disturbances distinguish among subtypes of alzheimer's disease and related disorders , 2001, Annals of neurology.

[40]  K. Min,et al.  Upregulation of three Drosophila homologs of human chromosome 21 genes alters synaptic function: Implications for Down syndrome , 2009, Proceedings of the National Academy of Sciences.

[41]  M. Gerstein,et al.  The genetic architecture of Down syndrome phenotypes revealed by high-resolution analysis of human segmental trisomies , 2009, Proceedings of the National Academy of Sciences.

[42]  K. Grzeschik,et al.  The precursor of Alzheimer??s disease amyloid A4 protein resembles a cell-surface receptor , 1987 .

[43]  Larry Smarr.  Toward the 21st century , 1997, CACM.

[44]  S. Antonarakis,et al.  Genotype–phenotype correlations in Down syndrome identified by array CGH in 30 cases of partial trisomy and partial monosomy chromosome 21 , 2009, European Journal of Human Genetics.

[45]  E. Koo,et al.  Amyloid Precursor Protein Trafficking, Processing, and Function* , 2008, Journal of Biological Chemistry.

[46]  G. D. Paolo,et al.  Linking lipids to Alzheimer's disease: cholesterol and beyond , 2011, Nature Reviews Neuroscience.

[47]  S. Horvath,et al.  Divergence of human and mouse brain transcriptome highlights Alzheimer disease pathways , 2010, Proceedings of the National Academy of Sciences.

[48]  J M Delabar,et al.  Classification of human chromosome 21 gene-expression variations in Down syndrome: impact on disease phenotypes. , 2007, American journal of human genetics.

[49]  M. Owen,et al.  Distribution and Expression of Picalm in Alzheimer Disease , 2010, Journal of neuropathology and experimental neurology.

[50]  A. Visel,et al.  Transmembrane protein 50b (C21orf4), a candidate for Down syndrome neurophenotypes, encodes an intracellular membrane protein expressed in the rodent brain , 2008, Neuroscience.

[51]  M. Delorenzi,et al.  Natural gene-expression variation in Down syndrome modulates the outcome of gene-dosage imbalance. , 2007, American journal of human genetics.

[52]  Eric M Reiman,et al.  Functional Links Between Aβ Toxicity, Endocytic Trafficking, and Alzheimer’s Disease Risk Factors in Yeast , 2011, Science.

[53]  Nick C Fox,et al.  Common variants in ABCA7, MS4A6A/MS4A4E, EPHA1, CD33 and CD2AP are associated with Alzheimer’s disease , 2011, Nature Genetics.

[54]  D. Berman,et al.  Oligomeric amyloid-β peptide disrupts phosphatidylinositol-4,5-bisphosphate metabolism , 2008, Nature Neuroscience.

[55]  M. Yaspo,et al.  Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: Challenging the gene dosage effect hypothesis (Part I) , 2003, Amino Acids.

[56]  M. Farrer,et al.  Molecular mapping of alzheimer‐type dementia in Down's syndrome , 1998, Annals of neurology.

[57]  P. De Camilli,et al.  Assignment1 of SYNJ1 to human chromosome 21q22.2 and Synj12 to the murine homologous region on chromosome 16C3–4 by in situ hybridization , 2000, Cytogenetic and Genome Research.

[58]  Sun Young Shin,et al.  Presenilin mutations linked to familial Alzheimer's disease cause an imbalance in phosphatidylinositol 4,5-bisphosphate metabolism , 2006, Proceedings of the National Academy of Sciences.

[59]  P. De Camilli,et al.  Role of phosphorylation in regulation of the assembly of endocytic coat complexes. , 1998, Science.

[60]  M. Lerman,et al.  Characterization and chromosomal localization of a cDNA encoding brain amyloid of Alzheimer's disease. , 1987, Science.

[61]  Pietro De Camilli,et al.  Phosphoinositides in cell regulation and membrane dynamics , 2006, Nature.

[62]  R. Nixon.  Endosome function and dysfunction in Alzheimer's disease and other neurodegenerative diseases , 2005, Neurobiology of Aging.

[63]  E. Hirsch,et al.  Rescue of Mesencephalic Dopaminergic Neurons in Culture by Low-Level Stimulation of Voltage-Gated Sodium Channels , 2004, The Journal of Neuroscience.

[64]  O. Madsen,et al.  The Ectopic Expression of Pax4 in the Mouse Pancreas Converts Progenitor Cells into α and Subsequently β Cells , 2009, Cell.

[65]  Jean-Christophe Olivo-Marin,et al.  Extraction of spots in biological images using multiscale products , 2002, Pattern Recognit..

[66]  P. Stahl,et al.  Endosome fusion in living cells overexpressing GFP-rab5. , 1999, Journal of cell science.

[67]  R. Fitzsimonds,et al.  Impaired PtdIns(4,5)P2 synthesis in nerve terminals produces defects in synaptic vesicle trafficking , 2004, Nature.