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

Article type: Research Article

Authors: Gurel, Busra^{a; h} | Cansev, Mehmet^b | Sevinc, Cansu^b | Kelestemur, Seda^a | Ocalan, Busra^c | Cakir, Aysen^c | Aydin, Sami^b | Kahveci, Nevzat^c | Ozansoy, Mehmet^{a; d} | Taskapilioglu, Ozlem^e | Ulus, Ismail Hakki^f | Başar, Merve Karayel^h | Sahin, Betul^g | Tuzuner, Mete Bora^g | Baykal, Ahmet Tarik^{h; *}

Affiliations: [a] Regenerative and Restorative Medical Research Center, Istanbul Medipol University, Istanbul, Turkey | [b] Department of Pharmacology, Faculty of Medicine, Uludag University, Bursa, Turkey | [c] Department of Physiology, Faculty of Medicine, Uludag University, Bursa, Turkey | [d] Department of Physiology, Faculty of Medicine, Medipol University, Istanbul, Turkey | [e] Department of Neurology, Faculty of Medicine, Uludag University, Bursa, Turkey | [f] Department of Pharmacology, Faculty of Medicine, Acibadem Mehmet Ali Aydinlar University, Istanbul, Turkey | [g] Acibadem Labmed R&D Laboratory, Istanbul, Turkey | [h] Department of Medical Biochemistry, Faculty of Medicine, Acibadem Mehmet Ali Aydinlar University, Istanbul, Turkey

Correspondence: [*] Correspondence to: Assoc. Prof. Dr. Ahmet Tarik Baykal, PhD, Acibadem Mehmet Ali Aydinlar University, Department of Medical Biochemistry, School of Medicine, IcerenkoyMh. No:32, Kayisdagi Cd., 34752 Ataşehir, Istanbul, Turkey. Tel.: +902165004828; Fax: +902165443940; E-mail: tarik.baykal@acibademlabmed.com.tr.

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.

Keywords: Alzheimer’s disease, extracellular matrix, IL6, iron, neuroinflammation, proteomics

DOI: 10.3233/JAD-170329

Journal: Journal of Alzheimer's Disease, vol. 61, no. 4, pp. 1399-1410, 2018