Unit:
Τομέας Φυσιολογίας Ζώων και ΑνθρώπουLibrary of the School of Science
Dissertation committee:
Σπύρος Ευθυμιόπουλος Αναπλ.Καθηγ.(Επιβλέπων), Αικατερίνη Γαϊτανάκη Καθηγ., Διδώ Βασιλακοπούλου Αναπλ. Καθηγ.
Original Title:
Μελέτη του ρόλου της Απολιποπρωτεΐνης Ε και της χοληστερόλης στην παθογένεση της νόσου Alzheimer's σε διαγονιδιακά ποντίκια
Summary:
Alzheimer’s disease (AD) is a neurodegenerative disease that is affecting the
higher cognitive functions. It is the most common form of senile dementia and
is mainly affecting people after the age of 65. Inheritance of the ε4 allele of
Apolipoprotein E (ApoE4) is the major risk factor for the development of the
sporadic form of AD. The LDLR is one of the main APOE receptors both in the
circulation and in the CNS. In the present study the role of the LDLR was
studied in a transgenic mouse model with Alzheimer’s-like pathology (5xFAD). In
addition, the role of the peripheral-derived (non-CNS) APOE4 was analysed.
To study the role of the LDLR in the pathogenesis of Alzheimer’s disease we
have generated transgenic mice that develop an Alzheimer’s like phenotype
(5xFAD transgenic mice) and lack the endogenous Ldlr gene (Ldlr-/-). The
5XFAD;Ldlr-/- mice were analysed for amyloid deposition and APOE levels and it
was shown that amyloid plaques as well as amyloid β (Αβ) brain levels were
increased irrespectively of the presence or the absence of APOE. The guanidine
levels of APOE (plaque-associated fraction) were also increased in brain
homogenates of 5XFAD;Ldlr-/- mice. There was no difference in levels of the
total amyloid precursor protein (APP) or its carboxy-terminal fragments (CTF)
indicating that the increase in the Aβ levels is probably due to defective
clearance of amyloid. Furthermore, analysis of the inflammatory response showed
a significant decrease in astrocytosis and microgliosis in the absence of LDLR
independently of APOE.
To study the role of peripheral-derived APOE in the pathogenesis of Alzheimer’s
disease we generated transgenic mice that express the genomic human allele ε4
of ApoE under the transthyretin (TTRI) promoter (TTRI-huApoE4 transgenic mouse
model). These mice express the transgene only in the liver and macrophages and
not in the brain. The TTRI-huApoE4 transgenic mice were crossed with a mouse
model with Alzheimer-like pathology (5xFAD). Pathogenesis of the AD-like
phenotype was analysed in mice of the genotypes 5xFAD, 5xFAD;ApoE-/- and
5xFAD;TTRI-huApoE4;ApoE-/- with immunoblotting, ELISA and immunohistochemistry
methods. Histological analysis showed that 5xFAD;TTRI-huApoE4;ApoE-/- had more
hippocampal and cortical amyloid plaques than the 5xFAD;ApoE-/- mice. The 5xFAD
mice that have the endogenous ApoE, had the most abundant load of Aβ and
amyloid plaques compared to the other genotypes. Immunohistochemistry for the
Aβ peptide revealed that the 5xFAD mice had the most intense and dense pattern
of amyloid and the 5xFAD;ApoE-/- the most diffused. The
5xFAD;TTRI-huApoE4;ApoE-/- mice that express APOE4 only in the periphery and
they don’t have the endogenous ApoE had a diffused pattern like the
5xFAD;ApoE-/- mice but the spatial distribution resembled the pattern of the
5xFAD’s Aβ deposition.
Astrocytosis and microgliosis were also analysed in the aforementioned groups
of mice. It was shown that microgliosis in the 5xFAD;TTRI-huApoE4;ApoE-/- was
decreased compared to both the 5xFAD and the 5xFAD;ApoE-/- mice. In addition
the microglia/macrophages (IBA1-positive cells) surrounding the amyloid plaques
were also positive for huAPOE4 in the 5xFAD;TTRI-huApoE4;ApoE-/- mice. In order
to establish if these cells were blood-derived infiltrating
microglia/macrophages, 5xFAD;ApoE-/- mice received bone-marrow transplantation
from Tg(CAG-EGFP)10sb/J;TTRI-huApoE4;ApoE mice which express the green
fluorescent protein (GFP) in all cell types. We found that GFP-positive cells
from the periphery infiltrated the blood-brain barrier and expressed APOE4.
Also, the anti-inflammatory cytokine IL-10 was increased in the brains of
5xFAD;TTRI-huApoE4;ApoE-/- compared to the 5xFAD;ApoE-/-.
Our data demonstrate the importance of LDLR in the amyloid plaque formation and
the inflammatory response in the brain with Alzheimer-like pathology. Moreover,
this study showed that peripheral expression of huApoE4 in the
5xFAD;TTRI-huApoE4 mice results in increased amyloid deposition and reduced
microglial activation compared to the 5xFAD;ApoE-/- mice. Our proposed
mechanism is that peripheral APOE promotes Aβ aggregation by modulating the
activation of microglial cells through infiltration of huAPOE4-expressing
macrophages in the brain, thus providing an accessible target to regulate in AD
pathogenesis.
Keywords:
Apolipoprotein E, Alzheimer's disease, Low-density lipoprotein receptor, Transgenic mice, Inflammation
Number of references:
500
