Early Stage Alterations in CA1 Extracellular Region Proteins Indicate Dysregulation of IL6 and Iron Homeostasis in the 5XFAD Alzheimer’s Disease Mouse Model

Abstract

In recent years, an increasing number of research papers revealed that the compositional and volumetric alterations in the extracellular matrix are the consequences of aging and may be related to Alzheimer's disease (AD). In this study, we aimed to demonstrate the alterations in hippocampal extracellular fluid proteins in vivo using the 5XFAD mouse model. Samples were obtained from hippocampi of 5XFAD mice (n = 6) and their non-transgenic littermates by intracerebral push-pull perfusion technique at 3 months of age, representing the pre-pathological stage of the AD. Proteins in the hippocampal perfusates were analyzed by Ultra Performance Liquid Chromatography-Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (UPLC-ESI-qTOF-MS/MS). 178 proteins were identified and 19 proteins of them were found to be statistically significantly altered (p≤0.05, fold change ≥40%, unique peptide count ≥3) in the hippocampal CA1 extracellular fluid of the 5XFAD mouse model. Ingenuity pathway analysis of the protein expression results identified IL6 as an upstream regulator. The upregulation of IL6 was validated by immunohistochemical staining of the hippocampus and cortex of the 5XFAD mice prior to Aβ plaque formation. Furthermore, the iron level in the hippocampus was measured by inductively coupled plasma-mass spectrometry as IL6 is mentioned in several studies to take part in iron homeostasis and inflammation and found to be increased in 5XFAD mice hippocampus. Alterations in extracellular matrix proteins in addition to increasing amount of hippocampal IL6 and iron in the early stages of AD may reveal inflammation-mediated iron dyshomeostasis in the early stages of neurodegeneration.

Environmental Enrichment Improves Cognitive Deficits, AD Hallmarks and Epigenetic Alterations Presented in 5xFAD Mouse Model

“…Significant differences in proinflammatory chemokines secreted by astrocytes have been proved between AD patients and normal aged people (Liu et al, 2015 ). A reduction in gene expression for Il-6 and Tnf-α in 5xFAD-EE mice suggested a reduction in the inflammatory process in 5xFAD (Gurel et al, 2018 ). The lower inflammation after EE was also reinforced by a diminution in astroglial activation after EE demonstrated a significant decrease in Gfap gene expression and protein levels (Brahmachari et al, 2006 ).…”

The Dual Role of Hepcidin in Brain Iron Load and Inflammation

“…Similar to iron load, inflammation is also being recognized as an important pathogenic marker of neurodegenerative diseases. It is observed early in AD and PD, often bearing evidence of peripheral (intestinal) aberrant response to different stimuli ( Qin et al, 2016 ; Houser and Tansey, 2017 ; Raj et al, 2017 ; Gelders et al, 2018 ; Gurel et al, 2018 ; King et al, 2018 ; Steeland et al, 2018 ). This means that in AD and PD the pathogenic process is initiated and “fueled” by immunologic disturbances occurring in the gastrointestinal tract.…”

Increased expression of heme-binding protein 1 early in Alzheimer's disease is linked to neurotoxicity

“…We also observed that several inhibitors of serine proteases (serpins) appear to progressively decrease in expression during the monitoring period. Interestingly, a recent study of the hippocampal proteome in the 5 × FAD mouse model of AD also identified downregulation of serpins (Gurel et al, 2018). Protease inhibitors hold a potential as therapeutic targets since their levels in the brain can be restored through injection of recombinant protein.…”