ABSTRACT
Polymorphisms in the apolipoprotein E (APOE) gene affect the risk of Alzheimer disease and the amount of amyloid beta-protein (Abeta) deposited in the brain. The apoE protein reduces Abeta levels in conditioned media from cells in culture, possibly through Abeta clearance mechanisms. To explore this effect, we treated multiple neural and non-neural cell lines for 24 h with apoE at concentrations similar to those found in the cerebrospinal fluid (1-5 microg/mL). The apoE treatment reduced Abeta40 by 60-80% and Abeta42 to a lesser extent (20-30%) in the conditioned media. Surprisingly, apoE treatment resulted in an accumulation of amyloid precursor protein (APP)-C-terminal fragments in cell extracts and a marked reduction of APP intracellular domain-mediated signaling, consistent with diminished gamma-secretase processing of APP. All three isoforms of apoE, E2, E3 and E4, had similar effects on Abeta and APP-C-terminal fragments, and the effects were independent of the low-density lipoprotein receptor family. Apolipoprotein E had minimal effects on Notch cleavage and signaling in cell-based assays. These data suggest that apoE reduces gamma-secretase cleavage of APP, lowering secreted Abeta levels, with stronger effects on Abeta40. The apoE modulation of Abeta production and APP signaling is a potential mechanism affecting Alzheimer disease risk.
Subject(s)
Adaptor Proteins, Signal Transducing , Amyloid beta-Protein Precursor/metabolism , Apolipoproteins E/pharmacology , Endopeptidases/metabolism , gamma-Aminobutyric Acid/analogs & derivatives , Amyloid Precursor Protein Secretases , Amyloid beta-Peptides/chemistry , Amyloid beta-Peptides/metabolism , Animals , Apolipoprotein E3 , Apolipoprotein E4 , Aspartic Acid Endopeptidases , Blotting, Western/methods , Carrier Proteins/metabolism , Cells, Cultured , Chromatography, High Pressure Liquid/methods , Cricetinae , Cricetulus , Dose-Response Relationship, Drug , Drug Interactions , Embryo, Mammalian , Humans , Kidney , LDL-Receptor Related Protein-Associated Protein/metabolism , Lipoproteins, HDL/pharmacology , Membrane Proteins/chemistry , Membrane Proteins/metabolism , Mice , Neuroblastoma , Peptide Fragments/metabolism , Rats , Receptors, Notch , Time Factors , Transcriptional Activation/drug effects , Transfection/methods , Triglycerides/pharmacology , gamma-Aminobutyric Acid/pharmacologyABSTRACT
Lens epithelium-derived growth factor (LEDGF/p75) is a novel transcription co-activator that is critically involved in lens epithelial cell gene regulation and stress responses. Recent evidence indicates that LEDGF/p75 may play an important role in lens epithelial to fibre cell terminal differentiation. Since the lens and the brain are both ectodermally derived organs generated from epithelioid progenitor cells, we hypothesize that LEDGF/p75 is expressed and subserving similar functions in both organs. To investigate this hypothesis, we studied LEDGF/p75 expression and localization in the human brain. We detected LEDGF/p75-specific RT-PCR reaction products in both fetal and adult human brain. LEDGF/p75 mRNA expression in the brain exhibited differential developmental and regional specificity. LEDGF/p75 transcript was markedly elevated in fetal as compared to adult brain. In the adult brain, LEDGF/p75 mRNA expression was substantial in the subventricular zone (SVZ), scant in hippocampus, and undetectable elsewhere. To study LEDGF/p75 protein expression and localization, we developed and purified a new anti-LEDGF/p75 polyclonal antibody directed against a unique C-terminal region of LEDGF/p75. Western blot analysis of fetal and adult human brain revealed a approximately 75 kDa protein that demonstrated developmental and regional specificity similar to that detected by RT-PCR analysis. LEDGF/p75 protein expression was high in fetal brain and in the adult SVZ. Immunohistochemical studies of human fetal brain showed prominent LEDGF/p75-immunoreactive cells in the germinal neuroepithelium and cortical plate regions. Analysis of adult and aged human brain revealed LEDGF/p75-immunoreactive cell enrichment in the SVZ adjacent to the ventral region of the lateral ventricle at the level of the anterior commissure, a region implicated in adult neurogenesis. We utilised a primary mixed cortical cell culture system to identify LEDGF/p75 in neurons, but not astrocytes. Neuronal LEDGF/p75 exhibited a predominantly perinuclear distribution pattern. These data demonstrate that LEDGF/p75 is expressed in discrete regions and cell types within the fetal and adult human brain. Moreover, the developmental and regional expression patterns of LEDGF/p75 suggest that this transcriptional co-activator may be involved in neuroepithelial stem cell differentiation and neurogenesis.
Subject(s)
Brain/embryology , Brain/metabolism , Intercellular Signaling Peptides and Proteins/metabolism , Adult , Animals , Cells, Cultured , Gene Expression , Guinea Pigs , Humans , Intercellular Signaling Peptides and Proteins/genetics , Neurons/metabolism , RNA, Messenger/genetics , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
A recent genetic study demonstrated associations between an altered risk of Alzheimer's disease (AD) and two polymorphisms in the lipoprotein lipase (LPL) gene, Asn291Ser and Ser447Ter. LPL immunostains senile plaques, and is a ligand of the low-density lipoprotein receptor-related protein (LRP), a major apolipoprotein E (apoE) receptor. LPL increases the cellular uptake of apoE via LRP, and polymorphisms in LPL alter its ability to mediate apoE-LRP interactions, with potential implications for AD pathogenesis. Here, we tested the genetic association of LPL with AD in a case-control study. For the Asn291Ser polymorphism, we analyzed 277 individuals (141 AD, 136 control) and found no significant difference in allele frequencies between the AD and control groups. For the Ser447Ter polymorphism, we analyzed 187 individuals (108 AD, 79 control) and again found no significant difference in allele frequencies between the AD and control groups. Thus, our study does not support associations between AD and two common polymorphisms in LPL.
