Two Distal Downstream Enhancers Direct Expression of the Human Apolipoprotein E Gene to Astrocytes in the Brain

Abstract

Two distal downstream enhancers controlling astrocyte expression of the human apolipoprotein E (apoE) gene in the brain were identified by analysis of transgenic mice generated with various constructs of the apoE/C-I/C-IV/C-II gene cluster. In wild-type mice, the highest overall levels of apoE mRNA were found in astrocytes in the glomerular layer of olfactory bulbs and in Bergmann glia in the cerebellum. This pattern of expression was reproduced in transgenic mice expressing the entire human apoE gene cluster and also in transgenic mice expressing specific enhancer segments within the cluster. Expression of the human apoE transgene at these sites was specified by two enhancer domains: one enhancer is located 3.3 kb downstream of the apoE gene, and a duplication of this sequence is located 15 kb downstream of the apoE gene. Astrocyte enhancer activity was contained within 620 and 619 bp segments of these domains that show subtle differences in regional expression. In the absence of these distal enhancers, the apoE gene was not expressed in astrocytes. The relatively high levels of apoE expression at specific sites in the olfactory bulb and cerebellum suggest the presence of unique regulatory signals at these locations that may reflect common cellular properties and apoE gene functions. The localization of the two astrocytic enhancers reveals an unexpected complexity in the control of apoE production that is essential to understanding apoE function in the brain.

Apolipoprotein E region molecular signatures of Alzheimer's disease

“…Variant rs439401 in the APOE‐APOC1 intergenic region, which includes a specific astrocyte enhancer for the APOE gene (Grehan, Tse & Taylor, 2001), is the only variant among the 10 active expression SNPs that is active in NHAs. However, seven other variants exhibit a poised epigenetic signature in NHAs.…”

Profile and Regulation of Apolipoprotein E (ApoE) Expression in the CNS in Mice with Targeting of Green Fluorescent Protein Gene to the ApoE Locus

“…The labeled probe was purified through Micro Bio-Spin 30 chromatography columns (Bio-Rad). In situ hybridization was performed as described previously (Grehan et al, 2001b). Briefly, brain paraffin sections (7 m) were incubated with 20 g/ml proteinase K (Boehringer Mannheim, Indianapolis, IN) in 50 mM Tris-HCl, pH 8.0, 5 mM EDTA, and 150 mM NaCl for 15 min at room temperature.…”

Apolipoprotein E and Apolipoprotein E Receptors: Normal Biology and Roles in Alzheimer Disease

“…In the brain, apoE is expressed predominantly by astrocytes but also by microglia ( Fig. 2) (Pitas et al 1987;Grehan et al 2001). Under certain conditions, such as after excitotoxic injury, some neurons appear to be able to synthesize apoE (Xu et al 1999;Xu et al 2006).…”