The Study of Neuroinflammation and Blood-Brain Barrier Disruption in Early Stage Alzheimers Disease Animal Model with Microarray Analysis

Abstract

Alzheimers disease (AD) is the most common cause of dementia, whereas little is understood about the pathogenesis of AD. Up to date, there are no effective therapy to cure or to modify the progression of AD. Since strategy for AD has shifted to prevention, researchers started to focus on the early stage of AD. To identify genetic changes in the early stage of AD, microarray analysis of the brain from 5XFAD AD model was performed. The early stage of AD was defined by Y-maze test as the time when 5XFAD mice do not show cognitive decline. At 8 months of age, 5XFAD mice significant memory deficit than normal control. 10- and 20-weeks-old 5XFAD mice were used as AD models at early stage. Immunostaining with anti-Aβ42 antibody and Thioflavin-S staining was performed to show Aβ deposit and Aβ plaque formation, respectively (n = 2 for each group). Total 55681 mRNAs were analyzed by microarray from hippocampus of 10- and 20-week-old 5XFAD mice. Furthermore, anti-Iba1 and anti-GFAP immunostaining was performed to localize the microglia and astrocyte respect to Aβ. The disruption of Blood-brain barrier (BBB) was investigated with 111In-Cy3-albumin imaging. Deposition of Aβ was found in the brain of 5XFAD mice started from the age of 10 weeks, while Aβ plaque were detected at the age of 20 weeks. A total of 715 and 630 genes were differentially expressed between 5XFAD and wild type mice at 10 and 20 weeks or age, respectively (fold change > 2.0, p-value < 0.05). Genes that are associated with extracellular matrix (n = 20) and angiogenesis (n = 13) showed the significant downregulation in 10-week-old 5XFAD mice, compared to the wild type mice. Inflammation (n = 16) and immune response (n = 46) related genes were significantly upregulated in 20-week-old 5XFAD mice, compared to the wild type mice. Genes that showed continuous increase of expression from 10- to 20-week-old 5XFAD mice include Cst7, Ccl4, Ccl3, Itgax, and Clec7A. Immunostaining with anti-Iba1, anti-GFAP showed that microglial activation and astrogliosis were accompanied with Aβ in the 5XFAD mice from the age of 10 weeks. Moreover, penetration of 111In-Cy3-albumin into the brain parenchyma represents the disruption of BBB. Genes that constitute BBB were downregulated in the 10-week-old 5XFAD mice, while genes that are related to inflammation and immune response were upregulated in both 10- and 20-week-old 5XFAD mice. Consequently, these results show that the neuroinflammation occurs with the disruption of BBB in the early stage of AD.