Alpha1-chimaerin, a Rac1 GTPase-activating protein, is expressed at reduced mRNA levels in the brain of Alzheimer's disease patients

Abstract

Alpha1-chimaerin is a GTPase-activating protein (GAP) for Rac1, a member of the Rho small GTPase family, whose action leads to the inactivation of Rac1. Rac1 activity is upregulated in Alzheimer's disease, but little is known about the role of α1-chimaerin. In this study, we investigated the expression and localization of α1-chimaerin mRNA in postmortem human brains from patients with Alzheimer's disease and control subjects. In situ hybridization studies demonstrated that α1-chimaerin was expressed by neurons in the neo-cortex of the temporal lobe and the hippocampus of both controls and Alzheimer's disease cases, with the signal intensity dramatically decreased in patients with Alzheimer's disease. Real-time PCR analysis confirmed a significant reduction of α1-chimaerin mRNA expression in the temporal cortex of Alzheimer's disease cases. In contrast, α2-chimaerin mRNA levels showed no significant difference between the groups. The present study showed reduced α1-chimaerin expression in the brain of Alzheimer's disease cases, suggesting a role in the upregulation of Rac1 activity during the disease process.

Keywords: Alzheimer’s disease; In situ hybridization; Rac1; Real-time PCR; α1-chimaerin.

Fig. 1

In situ hybridization of α1-chimaerin mRNA in the temporal cortex of control subjects (A, C and D) and AD cases (B and E) using an antisense probe (A, B, D and E) or a sense probe (C). (A) and (B): positive signals were detected in the cortex of both control subjects and AD cases. (C): no signals were detected using the sense probe with the exception of nuclear staining in areas near the cortical surface of layer 1. (D) and (E): high magnification of the boxed area in layer 3 of a control (A) and an AD case (B). Positive cells appear to be neurons. Scale bar = 200 μm in A–C, and 50 μm in D and E.

Fig. 2

In situ hybridization of α1-chimaerin mRNA in the hippocampus of a control subject (A–C) and AD case (D–F). (A) and (D): at low magnification, positive signals were mainly visible in the pyramidal layers of the cornu ammonis (CA) and granular cell layer of the dentate gyrus (DG) in both control subjects and AD cases. (B) and (E): high magnification of the pyramidal layer of the CA2 region. (C) and (F): high magnification of the granular cell layer of the dentate gyrus. Signal intensity is reduced in the AD case (D–F) relative to that in controls (A–C). Scale bar = 200 μm in (A) and (D); 100 μm in (B, C, E and F).

Fig. 3

mRNA expression levels of α1-chimaerin (A) and α2-chimaerin (B) in the temporal cortex of patients with AD (n = 7) and control cases (n = 8) using real-time PCR. The mRNA expression levels of α1-chimaerin and α2-chimaerin are normalized to the ß-actin and MAP2 mRNA levels. The mRNA expression level of α1-chimaerin, but not α2-chimaerin, is significantly reduced in the temporal cortex of AD cases compared to controls. Results are presented as mean ± SEM. Statistical analysis was performed using Student's t-test: **P < 0.01 vs. control cases.