Pathological Mechanisms Linking Diabetes Mellitus and Alzheimer's Disease: the Receptor for Advanced Glycation End Products (RAGE)

Abstract

Diabetes and Alzheimer's disease (AD) place a significant burden on health care systems in the world and its aging populations. These diseases have long been regarded as separate entities; however, advanced glycation end products (AGEs) and the receptors for AGEs (RAGE) may be a link between diabetes and AD. In our study, mice injected with AGEs through stereotaxic surgery showed significant AD-like features: behavior showed decreased memory; immunofluorescence showed increased phosphorylated tau and APP. These results suggest links between diabetes and AD. Patients with diabetes are at a higher risk of developing AD, and the possible underlying molecular components of this association are now beginning to emerge.

Keywords: Alzheimer’s disease; PI3K; RAGE; advanced glycation end products; diabetes.

Figure 1

Mice injected with advanced glycation end products (AGEs) show dementia-like behavior. (A,B) Water maze experiment was performed on three groups of mice to observe the dementia-like behavior. (A) The time that the three groups of mice stayed in the target area was measured. (B) The number of times the three groups of mice crossed the platform. The criterion for judging the entry of the mouse into the target area was the entry point of the mouse torso center point. (C) Y-maze experiment measured the residence time of three groups of mice injected with BSA, AGEs, AGEs + LiCl in the brain in the new arm of the Y-maze. (D) Open-field experiment measured the length of stay of the three groups of mice in the central area time. For each group of mice, n = 5. Data are expressed as mean ± standard deviation. One-way analysis of variance (ANOVA). *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 2

Upregulation of Alzheimer’s disease (AD)-related protein expression in advanced glycation end (AGE)-injected mice. (A–C) Expression of P-tau in the hippocampus of BSA, AGEs, AGEs + LiCl treated mice. (A) P-tau in the hippocampus of three groups of mice was stained with immunofluorescence (red), and nuclei were stained with DAPI (blue). (B) qPCR was performed on the hippocampus of the three groups of mice, and the expression of tau-related proteins was measured. The expression level was normalized to the average expression level in the BSA injection group; (C,D) Western blotting was performed on the hippocampus of the three groups of mice, and the ratio of the expression levels of P-tau to tau protein in the three groups of mice was calculated and expressed as P -tau/tau value. The gray density was normalized to the average gray density of the tau protein. (E,F) APP protein expression in the hippocampus of three groups of mice. (E) APP proteins in the hippocampus of the three groups of mice were stained with immunofluorescence (green), and the nuclei were stained with DAPI (blue). (F) qPCR was performed on the hippocampus of three groups of mice to measure the expression of APP-related proteins in the hippocampus. The expression level was normalized to the average expression level of the injected BSA group. For each group of mice, n = 3. Data are expressed as mean ± standard deviation. One-way ANOVA. *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 3

AGE mouse PET image. (A) Mice injected with 18F-AV45. Green represents Aβ. (B) Mice injected with 18F-PBB3. Green represents tau.

Figure 4

The upregulation of AGEs inhibits the PI3K/SRC/ERK signaling pathway. (A,B) Western blotting detection of PI3K protein in the hippocampus of three groups of mice, normalized gray density to the average gray density of GAPDH. (C,D) Western blotting detection of SRC protein in the hippocampus of three groups of mice. Gray density was normalized to the average gray density of GAPDH. (E,F) Western blotting was performed on ERK proteins in the hippocampus of the three groups of mice, and the gray density was normalized to the average gray density of GAPDH. For each group of mice, n = 3. Data are expressed as mean ± standard deviation. One-way ANOVA. *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 5

ZDF rats show AD symptoms. (A–C) Staining rat hippocampus with RAGE antibody (red) and the nuclei with DAPI (blue). (D–F) Staining rat hippocampus with tau antibody (green) and the nuclei with DAPI (blue). (G–I) Staining rat hippocampus with APP antibody (green) and the nuclei with DAPI (blue).