|Budget Amount *help
¥3,600,000 (Direct Cost : ¥3,600,000)
Fiscal Year 1998 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Fiscal Year 1997 : ¥2,300,000 (Direct Cost : ¥2,300,000)
Apolipoprotein E (apoE) has functions in the central nervous system (CNS). Although the major site of apoE synthesis is the liver, the brain contains the second highest abundance of apoE mRNA.ApoE synthesis is dramatically increased after injury of the rat sciatic or optic nerves. In the brain, significant concentrations of apoE are detected inastrocytes, including Bergmann glia of the cerebellum, tanycytes of the third ventricle, pituicytes of then eurohypophysis, and Muller cells of the retina These indicate that- apoE may be involved in the mobilization andutilization of lipid in CNS.In humans, there are three major isoforms of apoE, designated E2 (Cysi 12 and Cys 158), E3 (Cys 112 and Argl58), and E4 (Arg 112 and Arg 158), which are products of three alleles at a single gene locus. Genetic data indicate that the e4 allele is present with increased frequency in patients with sporadic and late-onset familial Alzheimer's disease, we have isolated a human cDNA encoding a novel receptor
that binds apoE-rich beta-VLDL with high affinity and internalizes it into The cells. This new receptor, designated apoE receptor 2 (apoER2), consists of five domains that resemble those of the low density lipoprotein receptor (LDLR) and VLDL receptor.
Analysis of apoER2 transcripts in several species reveals a lost repeat in the ligand binding domain of primate apoER2.A pseudo-exon found in the primate apoER2 genes corresponds to the lost repeat but contains a crucial deletion that leads to a translational frame shift. The pseudo-exon sequence in primary transcripts of the human apoER2 gene is shown to be abolished by exon skipping due to two nucleotide substitutions at the 5'-splice donor adjacent to thepseudo-exon. These data suggest the occurrence of exon loss in the evolution of the primate apoER2 gene.
To elucidate biological roles of apoER2, we used homologous recombination in mouse embryonic stem cells to produce homozygous knockout mice that lack immunodetectable apoER2s. Homozygous mice of both sexes were viable and normally fertile. The sole abnormality detected so far was increase plasma levels of triacylglycerol. whereas those of cholesterol were unaltered. The availability of the knockout mice will allow us to determine the biological roles of apoER2.