Glycative Stress Research
Online edition : ISSN 2188-3610
Print edition : ISSN 2188-3602
Received : February 8, 2022
Accepted : April 17, 2022
Published online : June 30, 2022
doi:10.24659/gsr.9.2_42

Review Article

The decline of the expression of low density lipoprotein receptor-related
protein 1 (LRP1) during normal ageing and in Alzheimer's disease
Nikola Barić
Private General Practice Office, Labin, Croatia

Abstract

Considering the importance of the low-density lipoprotein receptor-related protein 1 (LRP1) as the scavenger of harmfulwaste products from the brain, especially amyloid beta (Aβ), and as the mediator in a number of signal events, LRP1 isincreasingly becoming the object of intensive researches. Alzheimer's disease (AD), as proved, is the result of the disorderedAβ intracerebral homeostasis, characterized by intensive Aβ accumulation in the brain, induced primarily by the Aβ
disordered efflux from the brain, and not by its increased production. This elevated Aβ accumulation in the brain structures
leads to the increase of the local oxidative stress with intensively harmful effects of the generated free radicals, especiallyhydroxyl radicals (*OHs). This condition is accompanied by severe oxidative damages of a number of vital brain structures,
especially endothelial cell membranes. LRP1, at the level of blood-brain barrier (BBB) endothelial cells, initiated by Aβ
binding to its ligand binding domains, especially domains II and IV, induces specific conformational changes in both receptor
domains, which causes the onset of pulling forces that, starting from the point of Aβ binding to LRP1, spread along thereceptor structure in both directions. Especially important is the spreading of these forces towards the abluminal membrane,
their passing across this membrane and entering the receptor tail region and the compound structure of its molecules. The
activation of these molecular systems leads to endocytosis, transcytosis, and exocytosis of Aβ bound to the receptor, into thecapillary blood of the BBB. The drained Aβ travels further on by the blood stream, exits from the brain, and arrives at thepositions of its degradation and elimination, liver, kidneys, spleen, and skin. Investigations have shown that generally, theexpression of LRP1 in the BBB endothelial cell system declines during normal ageing, and especially in AD. It is evident that
this phenomenon weakens the Aβ drainage from the brain. The actual question is what causes the LRP1 expression drop in
these conditions, and if it is possible to slow down this drop. In this respect, this review paper intends to explain the problemof the LRP1 expression decline, and its possible increase, i.e., the retardation of the AD pathophysiological course.

KEY WORDS: Lipoprotein receptor- related protein 1 (LRP1), intracerebral Aβ homeostasis,		Aβ drainage from the brain, blood-brain barrier (BBB)

Introduction

Oxidative stress and generation ofhydroxyl radical *OH

A whole range of compound biological and molecularinvestigations of the Alzheimer's disease (AD) pathophysiology
has shown the importance of the cell surface receptor, lowdensity lipoprotein receptor-related protein 1 (LRP1), in thedrainage of the amyloid beta (Aβ) peptide from the brain
across the blood-brain barrier (BBB) endothelial cells into thebrain capillary circulation. The accumulation of this peptide
in the brain structures, induced primarily by its disturbed
drainage, and not, according to a number of researchers by
its elevated production, leads to evident oxidative damages ofa number of important brain structures, which, as it has been
proved, are extremely important for the pathophysiologicalevents crucial in the AD development and course 1- 5).
Oxidative stress in the organism of living beings, especiallyelevated in AD, according to a number of investigations, ismostly induced by the effects of free radicals, among them
primarily by the hydroxyl radical (*OH), the neutral form of
the hydroxyl ion ( − OH). This radical is generated in the brain
during the aggregation and sedimentation of Aβ monomers
at the point of interrelated contacts of Aβ strands with thetransit of one electron ("e − hop") from the sulphur (S) of
methionine ( MetS35, nonpolar essential amino acid) on the

Corresponding to: Nikola Barić MD, PhD
Presika 153, 52220 Labin, Istria, Croatia
TEL : +385-52-285-008 e-mail: nikola.baric@pu.t-com.hr

Glycative Stress Research 2022; 9 (2) : 42-54(c) Society for Glycative Stress Research_ 42 _Glycative Stress Research

β2-strand of the incoming Aβ2, onto the ferric ion (Fe 3 + )located on the β1-strand of the earlier fixed Aβ1 (metalbinding domain, His13-His14 sequence on the β1- strand).
MetS35 on the incoming Aβ2 monomer has the reductivedonator electron function. Oxidised ferric ion ( Fe 3 + on MBD
of Aβ1) by reduction (electron gain) transforms into theredox active ferrous ion ( Fe 2 + ) that reacts with, in AD,
the abundantly present hydroxy peroxide ( H 2 O 2 ), with thegeneration of Fe 3 +, hydroxyl ion ( − OH), and the extremely
active and aggressive hydroxyl radical (*OH). These eventsare presented in the Fenton reaction: Fe 2 + + H 2 O 2 = Fe 3 + +−OH + *OH. The generated *OH oxidatively attacks thesurrounding molecules, primarily located in lipid cell
membranes ( Fig. 1, 2 ) 1, 6-13).
Redox active metal ions, for example the above mentioned
ferrous ion (Fe 2 + ), bound to the Aβ, catalyze the productionof reactive oxygen species (ROS), among them particularly
the hydroxyl radical *OH. *OH oxidatively damages thesurrounding molecules, as well as Aβ peptide itself, inducing
its conformational changes, and the decline in affinity for
LRP1. These changes result in the impairment of Aβ clearance
by LRP1. The accompanying destructive oxidation of LRP1,
with the consecutive decline of its functions, additionallycontributes to the Aβ accumulation in the brain 14, 15).

MsrA
2MetSOAn antioxidant enzymethat catalyzes the
reduction of MetSO tomethionine in proteinsand free amino acids.

Oxidant in the cells that reacts withmethionine to form methionine sulfoxide.

MetSO
Superoxide radical anion

ROS O2*‾ oxidation+
reduction

MetS35Aβ2β2
Essential nonpolar
α-amino acidstrong
antioxidant.

MetS35*+ is aggressive(toxic) by generation of free
radicals; destructive effects
on neighbouring molecular
structures by oxidation;
located on the incoming
monomer.

O
Oxidation (-e‾)
Methionine sulfide radical"e‾ hop"3++ Aβ-Fe = MetS35*+ + Aβ-Fe2+
Aβ1β1

Aβ2β2

Aβ1β1

Reduction (+e‾)

Oxidative stressoxidation Fenton reaction
Fe2+ + H2O2 = Fe3+ + ‾OH + *OH
Ferrous iron
Ferric ironHydroxyl radical, the mostreactive species of oxygen,neutral form of the hydroxideion.

Fig. 1. Aβ -mediated generation of destructive oxidation compounds.

Fig.1.
The figure presents the crucial biochemical events which result in hydroxyl radical (*OH) generation. Fenton reaction is particularly

emphasized. It is a reaction between oxidatively very reactive ferrous iron (Fe 2 + ) and hydrogen peroxide ( H2O2). Metal ions reduction(electron gain) is possible, not before the distance between MetS35 and their location on the metal binding domain (MBD, -His6,
His13, His14) on β1-strand drops below 19Å; MetS35, methionine, location on Aβ2β2-strand, reductant-electron donor; MetS35* + ,methionine sulfide cation radical of MetS35, very aggressive; − OH, hydroxyl ion; oxidation, electron loss; reduction, electron gain;"e − hop," electron crossing (without any mediator) through space from the reducing center to the acceptor; MsrA, methionine sulfide
reductase type A; MetSO, methionine sulfoxide; O 2* −, superoxide radical anion; Aβ, amyloid beta peptide; Fe 2 + , ferrous iron; Fe 3 +,ferric iron; ROS, reactive oxygen species.

_ 43 _

Drop in the LRP1 expression in Alzheimer's disease

FENTON REACTION
ferrous iron

Redox
cycle

Fe

2+

+ H2O2oxidation ferric ironFe

3+

+ *OH + ⌐OH
hydroxyl ion

LIPID PEROXIDATION

LH + *OHOXIDATIVE STRESS

initiation

PUFA

L* + H2O water

Lipid radical

L* + O2

LOO* (Lipid peroxide)

LOO* + LH

L* + LOOH

L* + O2

LOO*

Very unstable
Propagationhydroxyl radical (Very reactive and aggressive)

Very unstable
Very unstable

Lipid hydroperoxide

LOOH + L*

LOO* + LH
Very unstable

destructive cycle
Cyclic process

Fig. 2. Schematic presentation of lipid peroxidation important biochemical processes related to destructive free
radical effects on essential molecular structures.

Fig. 2.

LH, PUFAs, and hydrocarbon chains containing two or more double bonds; lipid peroxidation, oxidative degradation of lipids; during
this process free radicals (on this figure hydroxyl radical, *OH) steal electrons from the lipids in cell membranes with their consequent
destruction; between multiple PUFAs double bonds are methylene bridges (− CH 2 ) with especially reactive hydrogen atoms; brain
microvascular endothelial cells contain high proportions of PUFAs; PUFAs contain more than one double bond in their structure;
at one end these acids have a carboxyl group (COOH); oxidation, electron loss; reduction, electron gain; endothelial cell membranes
are specially vulnerable to the effects of *OH; the first step in the lipid peroxidation-production of a fatty acid radical, L* ; in lipid
peroxidation it is necessary to distinguish initiation, propagation, termination, and final products; L* is very unstable, so it reacts
readily with molecular O 2 and creates LOO* ( lipid peroxide); LOO* is also very unstable and reacts with a free LH; a new lipid
radical is produced, and the destructive cycle continues; antioxidants can inhibit lipid peroxidation; *OH can damage virtually all
types of macromolecules. It is evident that damaged endothelial cell membrane cannot effectively manage the LRP1/clathrin dependentendocytosis, transcytosis, and exocytosis; one of the final products of the lipid peroxidation is acrolein, a small aldehyde (C 3 H 4 O)
which easily binds to lysine residues of protein; protein-bound acrolein is a potential marker of oxidative and glycative stress anddamages to proteins in aging, atherosclerosis and AD; LH, non-oxidised lipids; PUFAs, polyunsaturated fatty acids; Fe 2 + , ferrous iron;Fe 3 + ferric iron; ROS, reactive oxygen species. LRP1, low density lipoprotein receptor-related protein; AD, Alzheimer's disease.

The structure and functions of the
LRP1 receptor
LRP1, the transmembrane receptor, is the memberof a great LRP receptor family. It is located on the cell
membranes of a number of brain and other body cells. In
the brain it is dominantly located on the abluminal cell
membranes of the BBB endothelial cells. As mentioned
earlier, it has the central role in the, by the transcytosis
mechanism induced, Aβ drainage across the BBB endothelial
cells into the capillary blood flow. LRP1 recognizes, binds,
and transports over 40 different ligands, among them Aβ is
the most significant. The LRP1 receptor in the human andanimal organism exists in two forms. One form is bound tothe cell membrane of a number of cells and is composed of
two components: extracellular α-chain 50-70 nm (500-700Å)
long, or magnitude of 515 kDa, and intracellular β- chain
magnitude 85 kDa. The transmembrane part is markedly
short. The receptor extracellular part consists of 31 cysteinerich modules, 22 cysteine-rich EGF repeats, and 8 YWTD
domains (β-propeller domains). All these modules areconnected with covalent bonds, except the bond between theextracellular and intracellular LRP1 part. Using the nuclear
magnetic resonance ( NMR) spectroscopy, Daly NL et al. 16),
first revealed the structure of the first cysteine-rich module(CR1) composed of 4 0 amino acids. The starting-point of
the module consists of one β-hairpin structure which isfollowed by a series of β-turns. Subsequently, undertaken_ 44 _Glycative Stress Research

crystallography analysis of the CR5 module has shown that
this module is actually a cage in which the calcium ion
stabilizes the module structure. The module consists of 6
cysteines bound by disulphide bonds. The accumulation ofnegatively charged amino acids is predominantly situated on
one module side (Asp15, Asp26, Glu30, Asp23, Asp36, Glu37,
Glu40). This paper does not address the description of the
EGF-repeats (epidermal growth factor [ EGF ]-like repeats)
and YWTD domain structures, however, it is important topresent intracellular motifs which have a crucial role in theAβ peptide drainage. Especially important are two NPXY
motifs, two di-leucine motifs, and the essential YXXL motif.
Although all these motifs have a role in the Aβ drainage
process, the most important is the YXXL motif, which isactivated by the phosphatidylinositol-binding clathrin assembly
protein ( PICALM), strongly activates endocytic andscaffold adaptors, causing the Aβ/LRP1 complex entrance
into endosomes and the consequent clathrin-dependenttranscytosis. All this indicates that the binding of Aβ to thereceptor induces conformational changes on both receptor
segments, enabling the PICALM access to the YXXL motif
and its strong activation. The other form of LRP1 is free orbound with Aβ in the spinal liquid and in the blood. This
form of receptor, sLRP1, transports Aβ to body locations
where Aβ is disintegrated. The pulling forces generated
by the binding of Aβ with the ligand binding cluster II and
IV induce the spread of the PICALM access to the YXXL
motif, their interaction, and strong YXXL motif activation.
The result is the adaptor activation with the PICALM andclathrin accumulation in the region around the receptor tailwith the beginning of PICALM/clathrin transcytosis andexocytosis. On the other hand, the NPXY and di-leucine
shift toward the abluminal cell membrane induces thedetachment of G-protein-coupled receptor (GPCR) αsegment, with the adenylate cyclase activation, transformationof adenosine triphosphate (ATP) into cyclic adenosine
monophosphate (cAMP), the activation of protein kinase A(PKA), phosphorylation of serine 76 (SE76) on the receptor
tail and a strong adaptor activation. All this has a favourable
effect on the Aβ/LRP1 transcytosis and exocytosis into thecapillary blood (Fig. 3 ) 4, 18 -20).
A number of researchers emphasize that the binding ofAβ with the negative charges of ligand binding clusters II
and IV amino acids on the extracellular segment of LRP1
induces conformational changes on the binding place, as wellas on the receptor tail structures. These changes, induced byelectrostatic forces, manifest themselves on the immediatebinding place with the approach of two included CR
modules, most probably, CR26 and CR27, with the onset ofstrong pulling forces which act from both sides of the contact
point and pull the adjoining receptor segments towards
the contact point. The pulling forces propagate with great
velocity towards the apical NH 2 end and towards the receptor
tail (COOH end). The velocity of the force propagation isincomparably greater than the velocity of activated receptor
segments. The majority of published papers related to thementioned conformational changes do not give their detailed
description. Future investigations have to describe andexplain these phenomena with exactitude (Fig. 3) 21, 22-24).
Before further analysis, it is important to emphasizethat there exist two types of AD: early onset AD (EOAD,
5 % of all cases) induced by amyloid precursor protein (APP)

gene – APP gene (chr. 21Q21), BACE1 gene (chr. 11Q23.3),
PSEN1 gene (chr. 14), and PSEN2 gene (chr. 1). Mutations in
the APP gene induce its strong production and activity witha high generation of Aβ. Mutations of BACE1, PSEN1, and
PSEN2 induce proteolysis and the fragmentation of APP
with a strong accumulation of Aβ in extracellular space. The
late onset AD (LOAD, 95% of all cases) is linked with two
genes, ADAM10 gene (chr. 15Q21.3) and allele ApoEε4 of
APOE gene (chr. 19Q13.32). Two mutations in the first geneinduce a drop in the cleaving of the APP transmembraneprotein, and the mutation in the second gene induces a dropof APOE protein lipidation and Aβ binding. In both AD
types the role of LRP1 is the same 25).
The decline of LRP1 expression in the BBB endothelium
during ageing and in AD. Following are research papers
whose authors present the mentioned expression decline
connected with life age.
Silverberg GD et al. 26, 27), based on experiments on rats,emphasize the evident capillary LRP1 expression decline
during the ageing process. This decline is inversely
proportional to the parallel expression elevation of thereceptor for advancing glycation end products (RAGE).
They emphasize that alterations in the LRP1 expression
evidently contribute to the Aβ accumulation in senescence.
This accumulation is also typical for AD. The explanation forthis phenomenon lies in the RAGE gene, where, connectedwith aging and AD, there is decreased methylation in its
promoter region. Otherwise, during the aging process and in
AD, the increased accumulation of AGEs has been found,as well as increased values of Aβ, cytokines (interleukin 1,
tumor necrosis factor), and of nuclear factor kB, which all
can decrease the promoter methylation and RAGE genetranscription. The transport of Aβ across the BBB is carriedout by LRP1 and at the same time, by the phosphoglycolate
phosphatase receptor (P-gp), which during ageing also has adecreased expression. However, the authors of the study give
preference to the LRP1 transport.
Kang DE et al. 28), by measuring the LRP 85 kDa lightchain level in the section material from the midfrontal
cortex of individuals deceased without AD signs, and bycomparing this material with the material from AD brains,
have found approximately a two-times higher LRP1 levelin brains without AD signs. In the brain of individuals nonaffected by AD, the strong inverse correlation between life
age and the LRP1 level (n = 39, r = − 0.4905, p = 0.0015 )has been found, indicating that with the rise of age the
LRP1 expression normally declines. The average expression
reduction is two times higher in the group aged 40 - 60 years
than in the group aged 85 and more. The inverse correlation
is even stronger in the bearers of alleles different from
APOEε4. In AD individuals where the disease has begun in
the later age, the authors have found greater LRP1 values,
which indicates the possibly LRP1 protective effect against
the disease.
Osgood D et al. 29), emphasize the drop of the possible
toxic metabolite clearance, linked with the changes inducedby ageing, as probably the strong factors of the Aβ and othermetabolites accumulation in the brain of the elderly and in
AD. According to these researchers, ageing is the strongest
risk factor for the AD occurrence. In the course of ageing
there is an increasing drop in LRP1 and P-glycoprotein(P-gp, besides LRP1, a very strong Aβ efflux receptor),_ 45 _

Drop in the LRP1 expression in Alzheimer's diseasepulling

EGF repeat

Direction to the CII and C1 ligand
binding clusters

EGF repeats
Ab.l.c.m.

GPCR

α
NPXY

β
active5.5Å

Di-leucine

PICALM
spreading tail

B/

.

fixed
S76
-COOH

PSD95

LAMINA RETICULARIS,
C III
Ligand binding cluster III BASEMENT MEMBRANE
Peptide bondγ
Adenyl cyclase

adaptoradaptor2 cysteine-rich EGF repeats

YXXL
activation adaptor

phosphorylation
PKA
Fe-65 [PO4]3activation

Aβ

His14

activation

LRP1 tail segment

His13

*OH

.+.+ - - 5.5ÅBinding of Aβ.+.+ - - pullingC.+
2 cysteine-rich EGF repeats
β1-strand

β2-strand
Lys16

Disabled1
attackpulling- 5.5Å Distance CR2627: 32Å to 21Å
- Ligand-binding cluster IV+
CR26
Point of pulling origin- C IV

.

Lys28
cAMP

One cysteine-rich repeat (module) is
composed of approximately 40 AA
and β-hairpin structure followed by β-turns

pulling

ATP

CR27

21Å

N

-

t1 Time scale of pulling propagation
YWTD domain

His6

β-propeller domain

A/
Arg5
LRP1 extracellular segment
The *OH attack on the abluminal
endothelial cell membrane issignificantly visible

PUFA

t2

extracellular

Lipid peroxidation

Transmembrane
PUFA Lipid peroxidation
domainintracellular*OH
Ab.l.c.m.
attackpulling

One clathrin
Membrane spanning C-terminal fragment, 85 kDa

LRP1 β-chain

PUFA

Coated pit PUFAAb.l.c.m.

*OH

AP-2

*OH

EGF repeats*OHt3
attackAP-2

NPXY motifs
5.5Å
YXXL motif
Di-leucine motifs
Passage width rises PICALM
COOH

.

S76

Tail

P

fixed

PKA

adaptors

adaptors

Direction to the luminal cell membrane

AP-2

AP-2

Clathrin scaffold

Fig. 3. Partial presentation of LRP1 (CD91) receptor molecule (CIII and C IV).

Fourth ligand-binding cluster contains 11 cysteine-rich ligand-binding repeats (blue circles); in the direction to the abluminal cellFig. 3. there are the positions of nine EGF repeats and one YWTD domain (β-propeller domain); in the tail there are visible
membrane
2 NPXY motifs, 2 di-leucine and 1 YXXL motif. Aβ binding to the LRP1 ligand binding domains II and IV (on the figure, only
domain IV is visible) induces the structural changes of both, the extracellular ligand binding domain, and receptor cytoplasmic tail.
The receptor tail has 2 NPXY motifs, 1 YXXL motif, and 2 di-leucine motifs. The binding of PICALM with YXXL motif induces
the recruitment of clathrin and AP-2 on the cell membrane at the position of coated-pit formation. PICALM /clathrin-dependenttranscytosis begins.
PICALM, phosphatidyl inositol binding clathrin assembly protein; AP-2, adaptor protein 2; EGF- repeats, epidermal growth factor( EGF ) -like repeats; Aβ, amyloid beta peptide; LRP1, low density lipoprotein receptor -related protein; GPCR, G-protein-coupled
receptor; PKA, protein kinase A; PSD95, postsynaptic density protein 95; PUFA, polyunsaturated fatty acids; ab.l.c.m,. abluminal
lipid cell membrane.

_ 46 _Glycative Stress Research

as well as the receptor expression increase in the receptor
for advanced glycation end products (AGEs). They have
proved this by measuring the mRNA LRP1, P-gp, andRAGE expression from the isolated cerebral microvessels.
In these events, the transcriptional changes connected withaging have a crucial role. Their experiments suggest thatgene transcription (in endothelial cell nucleus) is alteredby some upstream events rather than post-transcriptional
events. Transcriptional alterations of the gene expression may
occur via modification of the gene promoter or by histone
modification. Their study included a hundred male F344/BN
hybrid rats marked with similar characteristics. Histone
modifications have been observed during aging connectedwith the stimulation or destimulation of a series of related
genes. During the aging process, as well as in AD, acetylation(a reaction that includes an acetyl functional group CH 3 CO
into an organic chemical compound) has been observed, as
well as methylation (the addition of the methyl group − CH 3
on a substrate), of a histone with the consequent expression
change of the important neurotropic brain factors. The authorsof the study have also found, related to the LRP1 expression
drop, a significant decline of the PICALM expression. The
drop of the PICALM expression induces an evident decline in
the clearance of Aβ across the BBB of laboratory rats. In the
hypoxia and hypoglycemia conditions in tissue cultures, the
LRP1 mRNA level is decreased and the mRNA RAGE levelis elevated. These effects can be partially repaired by the useof Ginko biloba extract ( Fig. 4, 5 ).
Liu X et al. 30), in their review paper emphasize that
epigenetic mechanisms play a crucial role in the development
and course of AD. Among them, the most important are
the histone modifications and DNA methylation. Histone
acetylation catalyzed by histone acetyltransferase (HAT)
induces the decondensation of chromatin with the generationof euchromatine that is transcriptionally active. Condensate
chromatine type, i. e. heterochromatin, is compact andtranscriptionally inactive. This is the deacetylated type ofchromatine obtained through deacetylation catalyzed byenzyme histone deacetylase (HDAC). Otherwise, chromatin,
a nucleosome polymer, is composed of two almost
complete DNA turns wrapped around the histone octamer.
Chromatin is extremely flexible and dynamic and can exist
as heterochromatin or euchromatin. In AD, a rise of specifictypes of HDACs has been found. The decline of theirexpression induces the rise of histone acetylation and theimprovement of the AD clinical situation. The authors also
point out that the elevated level of promoter methylation ofcertain genes related to AD, and a mild cognitive impairment(MCI) are correlated with the transition from MCI to AD,
or with the deterioration of the AD clinical situation. Thislevel is markedly elevated in MCI and in AD as comparedto healthy individuals. The authors also emphasize thatthe global DNA methylation in mononuclear cells of theperiphery blood in LOAD patients shows significantly higher
values in relation to the healthy control examinees. They alsoemphasize that higher methylation levels are correlated withthe presence of ApoEε4 allele ( Fig. 5 ).
Yi SJ et al. 31), point out that the general loss of histones
and nucleosomes as the mark of ageing exists in the range
from yeast (yeast, single cell eukaryotic microorganisms) up
to humans. Here, it is necessary to present a detailed analysisof the complex process of acetylation and deacetylation of

the mentioned histone octamer, because it is certain that thesetwo processes are included in the LRP1 receptor expression.
By the HAT action, the electronegative acetyl group(CH 3 CO) is inserted onto the electropositive histone tail,and after this inclusion, the tail becomes less electropositive.
The consequence is the drop in the electrostatic attraction
between positive histone N-termini located on the tail andnegatively charged phosphate groups on the DNA strand.
Condensed chromatin (heterochromatin) transform intorelaxed euchromatin, which leads to gene transcription
increase and to an adequate protein expression. HDAC moves
the electronegative acetyl group from the positive histone
tail, leading to histone deacetylation. Following, there is arise of electrostatic interaction between histone N-termini on
the histone tail and the negative phosphate group on the DNA
strand. The level of condensed chromatin rises. Euchromatintransforms into heterochromatin that is more compact andtranscriptionally inactive, and the gene transcription declines(Fig. 5, 6 ).
Xu K et al. 32), point out the crucial characteristics ofhistone acetylation and deacetylation, the two fundamental
processes related to the AD pathophysiology. The firstprocess is catalyzed by the enzyme HAT, and the second one
by HDAC. Their experiments were performed on laboratory
rats (mouse models of AD). For tissue analyses, autopsy
material from the brain of individuals deceased from AD
was used. The histone acetylation is characterised by theinsertion of the CH 3 CO electronegative group into thehistone tail which is electropositive. The result is the decreaseof the total positivity of the tail, and consequently, to thedecrease of the interaction between the DNA phosphate andthe tail. All this induces conditions for the generation of freenoncondensed euchromatin and gene transcription. HDAC
catalyzes deacetylation, i. e. the ejection of CH 3 CO fromthe histone tail that becomes more positive. Its connection
with DNA phosphate becomes stronger, and this leads tofavourable conditions for chromatin condensation and thedrop of gene transcription. The level of histone acetylation
plays an important role in chromatin condensation andgene expression. HDAC inhibitors, presently under serious
investigations, improve the memory and cognition in mousemodels. However, their nonselective use can be inefficient,even dangerous, so their application on patients is still not
safe.
DNA methylation is catalyzed by a family of DNA
methyltransferases (Dnmts) that transfer a methyl group from
S- adenosyl methionine (SAM) to the 5 th C atom of cytosine
residue, to form 5 mC. The − CH 3 group is not a dipole. It isa nonpolar group. The role of Dnmt is to separate the methylgroup from SAM, to catalyze its transport to the C5 of thecytosine residue, and after the H deprotonation from C5,
to attach it to the empty C5 place. These events induce theconsequent decline of the DNA transcription. Recently, it
became evident that DNA methylation and demethylation
have a crucial role in epigenetic events related to geneactivity 33).
Collins BE et al. 34), emphasize that the addition of
methyl groups to the histone tails induces histone methylation.
The consequence is the generation of the condensed stateof chromatin, the heterochromatin that blocks the histonebinding to DNA phosphate and decreases the rate oftranscriptional expression. The bilaterally induced strong_ 47 _

Drop in the LRP1 expression in Alzheimer's disease

mRNA expression of LRP1 and P-gp Aβ porter genes at the BBB during aging;

Modifications of the LRP1 gene promoter and gene histone induced byacethylation / deacethylation and methylation / demethylation;

Gene transcription alterations with aging;

LRP1 and P-gp mRNA expression becomes significantly reduced and RAGE
mRNA expression significantly rises;
The LRP1 and P-gp Aβ efflux transporter expression at the BBB significantly
declines with age, and the expression of Aβ influx transporter RAGE increases;
Aβ efflux accross the BBB declines;
Aβ accumulation and aggregation in the perivascular space of BBB rises;

Fig. 4. The course of events that precede the Aβ accumulation and aggregation in the perivascular space of BBB
induced by aging.
mRNA, messenger RNA; RNA (ribonucleic acid) contains sugar ribose; ribose, monosaccharide, carbohydrate with molecular formulaC 5 H 10 O 5; P-gp, P-glycoprotein, ATP-binding cassette (ABC) transporter; gene promoter, the region of DNA where transcription ofgene is initiated; gene histone, a component of a nucleosome that is composed of two DNA turns wrapped around a histone protein
octamer, it is associated with the regulation of gene expression; gene transcription, the process of making a RNA copy of the genesequence; acetylation, chemical reaction that introduces an acetyl functional group (CH 3 - C(=) - O -); methylation, the addition of amethyl group (- CH3) on a substrate; perivascular space, crucial for Aβ drainage, intra-mural peri-arterial drainage pathway (IPAD),
on the inner side, the space is limited with endothelium and inner basement membrane of smooth muscle cells (SMCs), on the outerside the space is limited with the outer basement membrane of SMCs; vessel pia, Virchow-Robin space (pial funnel), cortical pia,
paravascular space, and astrocyte processes of glia limitans, in the region of BBB there is no perivascular space because both SMC
membranes are joined in one membrane; in this vascular segment there exist only endothelium, joined SMC membrane, and basement
membrane of glia limitans, inducing Aβ accumulation; LRP1, low density lipoprotein receptor- related protein; Aβ, amyloid beta
protein; BBB, blood-brain barrier; RAGE, receptor for advanced glycation end products. DNA, deoxyribonucleic acid; SMC, smoothmuscle cell;_ 48 _Glycative Stress Research

Chromatin is a complex of DNA and proteins (histones). HAT catalises histone acetylation indecondensated form, euchromatine, which is transcriptionally active. By HDAC euchromatintransforms into heterochromatin, which is compact and transcryptionally inactive.
Acetilation is a chemical reaction that incorporates thefunctional group CH3CO into an organic chemicalcompound. It helps the DNA transcription.

deoxyribose
Nitrogen-containing
base
Nucleosome

HAT

Deacetylation represses gene expression
by condensing the chromatin-AD.

Histone acetylation-CH3CO-CH3CO

HAT

HDAC- CH3CO..
.. . .
DNA
.
.. .
.
.. ..
.
. .. .
+ .. .
.
+. ...- .. .. .. ...
.
H-bond.
bond. .. ..+.- ... .. .. .- +... .. Hydrogen. . . . . +. . . .. Rise of.
.
.
.
Decline of attraction.+ +.. ..+-. . attraction. .. . - +. ++ ..
Nitrogen-containingbasehydrogenium. .. ...- .. . ..
. . . .. .. .. .-..
deoxyribose.
. . .
Histone tail.
.. .
. . . electropositive.
.
.. .. .
.
Linker DNA.. .. .. . Histone H1.
Histone H1
.
.
.
.
.
.
.
.
.
.
.
.
. . .. .. .. .. .. . . .. . .. .
H-bondHistone

H 2A

H 2B

H2A

Nucleosome
Histone

H 2A

H 2A

H2B

H 2B

H2B

phosphate

H

H

H

H

One strand
hydrogenium
DNA
Phosphate
Hydrogen bondelectronegative

Other strand

phosphateelectronegativehydrogenium
Hydrogen bondFig.5.
Fig. 5. Schematic presentation of the DNA with histone acetylation and deacetylation – LRP1 gene.

DNA is a complex molecule composed of two chains that coil around each other to form a double helix carrying genetic information
for the development functioning, growth, and reproduction of all known organisms and many viruses. Two DNA strands are composedof simpler monomeric units called nucleotides; Each nucleotide contains one of four nitrogen-containing nucleobases (cytosine, C,
guanine, G, adenine, A, or thymine, T). Two DNA chains are joined to one another by H-bonds; Nucleosome is a specific structurethat belongs to the cell nucleus; it is a functional unit of chromatin; lying along the DNA strand, a nucleosome is composed of eight
histone molecules and approximately two DNA turns wrapped around a set of histones. Histones associate with DNA and help the
DNA to condense into chromatin; a nucleosome height is about 6 nm; each DNA turn around the histone octamer complex has thediameter of about 2 nm; histones are positively charged proteins and strongly adhere to negatively charged DNA phosphates; histones
protect and regulate gene expression; histone tails project from the nucleosome and some residues in these tails after modification, canaffect transcription; HAT can catalyze its acetylation and as a consequence the enhanced rates of gene transcription; HDAC represses
the gene expression by condensing the chromatin; histone modifications have a crucial role in the development and course of AD;
LRP1, low density lipoprotein receptor-related protein 1; DNA, deoxyribonucleic acid; HAT, histone acetyltransferase; HDAC, histone
deacetylation catalyzed by histone deacetylase; AD, Alzheimer's disease.

_ 49 _

Drop in the LRP1 expression in Alzheimer's disease

9

Fig. 6. Presentation of the histone acetylation and deacetylation.

Due to the HAT action, the electronegative acetyl group (CH 3 CO) is inserted on the histone tail that is electropositive. After
this insertion, the tail becomes less electropositive. Consequently, there is a drop of electrostatic attraction between the positive
histone N-termini located on the tail and negatively charged phosphate groups on the DNA strand. The condensed chromatin(heterochromatin) transforms into relaxed euchromatin, resulting in the rise of gene transcription and adequate protein expression.
HDAC moves the electronegative acetyl group away from the positive histone tail, leading to histone deacetylation. The
consequence is the rise of electrostatic interaction between histone N-termini on the histone tail and the negative phosphate groupon the DNA strand. The chromatine condensation rises. Euchromatin transforms into heterochromatine which is more compact
and transcriptionally inactive. The gene transcription declines; HAT, histone acetyltransferase; HDAC, histone deacetylase; DNA,
deoxyribonucleic acid.

_ 50 _Glycative Stress Research

connection blocks the link between histone and DNA andreduces the transcriptional expression. Histone methylation
is induced by histone methyltransferases (HMTs). However,
it is found that lysine 4 on histone H3 (H3K4) methylation
activates gene expression, and lysine 27 on histone H3(H3K27) methylation represses gene expression. DNA
methylation (induced by DNA methyltransferases), locatedin the gene promoter, usually represses gene transcription.
Storck SE et al. 35), emphasize that according to theneurovascular hypothesis, the decreased expression of
LRP1 in brain capillaries of BBB contributes to neurotoxic
Aβ brain accumulation and accelerates AD pathology. In
their experiments, the authors have developed a transgenic
mouse strain on which they have investigated tamoxifeninducible selective deletion of LRP1 in the mouse brains,accompanied by a strong efflux reduction across BBB, ofthe previously injected Aβ1- 42 in the brain. Their results
show that receptor-mediated Aβ clearance can be a potential
target for the treatment and prevention of Aβ accumulationin the AD brain.
Shibata M et al. 36), in their study present experimental
results related to the intracerebral microinjections of 1251Aβ1- 40 in young and adult wild-type mice. LRP1, abundantin microvessels in young mice, was downregulated in older
experimental animals, and this downregulation correlatedwith regional Aβ accumulation in brains of Alzheimer's
units. The authors conclude that the BBB removes Aβfrom the brain largely via age-dependent LRP1-mediatedtransport that is influenced by α 2M and/or ApoE, andmay be impaired. The importance of the optimal LRP1
expression should be seen in the context of significantly
declined lipidation (covalent binding of the lipid group to
the peptide chain) of the lipoprotein APOEε4 as related tothe other two alleles, APOE2 and APOE3. The lipidationof APOE lipoprotein increases its interaction and binding
with Aβ, leading to the APOE/lipid ( LDL or HDL) Aβ
complex. The generated complex, by effects of vasomotion
and two receptors, LRP1 and ABCB1 (P-glycoprotein, ATPdependent translocase ABCB1), is promptly transported
along the perivascular space and drained in the angularneck lymphatic nodes into the venous blood. ABCB1 islocated on the the luminal and abluminal sides of the BBB
endothelial cell membranes. It is an active mediator for theAβ transport out from the brain.
APOEε4 (the dominant allele in LOAD) lipidated by
ABCA, but significantly weaker in relation to the othertwo alleles, has evidently weaker linking with Aβ, and thegenerated complex Aβ/APOEε4/HDL or LDL transport
is also weaker. The result is stronger Aβ accumulation andaggregation in the perivascular space (PVS). Otherwise, adrop of the ABCB1 and of the LRP1 expression has been
established in normal ageing, as well as in the AD patients.
All this indicates that due to the presence of APOEε4 allele(typical for LOAD) and its unfavourable effects on theperivascular drainage, the LRP1 effects would be of crucial
importance for the AD course retardation. However, thedecreased LRP1 expression, typical for the aging process
and AD, cannot adequately compensate Aβ accumulation
and aggregation, nor the accompanying oxidative stress 13).

LRP1 as a therapeutic factor in AD
Sagare AP et al. 37), point out that LRP1 is the maincell surface receptor involved in the brain and in the systemic
clearance of AD toxin Aβ. There are two forms of LRP1: theplasmatic soluble form sLRP1, which is the major transport
protein for peripheral Aβ, and the brain endothelium LRP1,
the critical factor for the drainage from the brain by clathrincoated transcytosis across BBB endothelial cells. The soluble
form sLRP1 obstructs the possible return of free plasma
Aβ into the brain. In the liver, the local LRP1 performs thedegradation and clearance of Aβ that has arrived by theblood stream. The LRP1 receptor is encoded by the genelocated on chromosome 12q13-q14. As Kang DE et al. 28),
Shibata M et al. 36), and Silverberg GD et al. 26, 27), emphasize,
the LRPI expression at the BBB is reduced duringboth, normal aging and AD. To correct the decreased
LRP1expression in the brain, Sagare AP et al. 37), suggest
three sets of actions: (a) lifestyle changes (e.g., diet, exercise,and enriched environment), (b) pharmacological agents (e.g.,
statins, plant-based active principles), and (c) gene therapy.
They emphasize that potential points of intervention are: (1)restoration and/or enhancement of BBB LRP1 expression, (2)replacement of dysfunctional sLRP1, and (3) restoration and/or enhancement of the hepatic LRP1 expression. Analyzing
the first set of actions (a), Sagare AP et al. 37), emphasize
the great importance of antioxidant nutrients ( polyphenolrich foods, vitamin A, C, and E, green tea, extra virgin oil)which could protect LRP1 from oxidative damage. Physicalactivity can improve cerebral angiogenesis in rodents andhumans. Otherwise, in AD, cerebral angiogenesis is retardedand decreased. Elevated cholesterol levels can increase therisk of AD. To reduce these levels, the optimal solution is
to use statins which are cholesterol lowering drugs. Amongthem, simvastatin and atorvastatin are especially effective inthe brain. Statins also increase the LRP1 expression in theliver. The authors point out that effective gene transfer can beachieved by viral based systems which are very effective in
mediating cell entry and transfer of genes to the target cells.
Among vectors for gene therapy, Adeno-associated virus(AVV) is frequently used as a vector for these therapies due
to its possibility to induce the long-term gene expression indifferent cells. This virus is unable to autonomously replicate,and so is not pathogenic. The AAV-2 serotype has been usedin neurological studies in mouse models of lysosomal storage
disease and Parkinson disease. The authors prefer the directtargeting of the gene transfer vector to the BBB. In the direct
approach, vector targeting is mediated by a small peptidethat has been inserted into the viral capsid sequence withthe modification of viral tropism. It is possible to enhance
the mentioned targeting by identifying molecular signature
epitopes in the cerebral endothelial cells of AD brains, andby presenting these epitopes on the capsid of AAV. It isevident that the use of AAV-2 which carries LRP1 DNA
or its smaller fragments, leads to the restoration of LRP1
expression in the brain vascular endothelial cells in AD.
Shinohara M et al. 38), emphasize that statins could reduce
the risk of AD. Fluvastatin at clinical doses significantly
reduces Aβ and amyloid precursor protein C-terminal
fragment (APP-CTF ) levels in the brain of C57BL/6 mice.
This effect is blocked by LRP1 antagonists.

_ 51 _

Drop in the LRP1 expression in Alzheimer's disease

Qosa H et al. 39), show the results of their experiments
where the elevated Aβ clearance from the wild-type micebrain across the BBB is obtained with rifampicin and caffeine.
Both preparations have induced an elevated expression of
P-glycoprotein (P-gp) in the BBB endothelium. The elevatedLRP1 expression was obtained only by rifampicin.
Tamaki C et al. 40), present the results of theirinvestigations related to the effects of insulin in the Aβ(1- 40) clearance by the liver. The portal infusion of
insulin leads to the evident rise of LRP1 expression on thehepatocyte plasma membrane. The insulin in the plasma
accelerates the LRP1 crossing from the intracellular stores
onto the liver cell membranes.

At the end of this presentation, it is necessary tomention the study by Kanekiyo T and Guojun B 5), where
they present possible therapies for AD by the use of LRP1.
Presently, a number of researchers also work on the problemof the LRP1 expression modifications in AD therapy. It isevident that the improvement of existing approaches andfinding new ones related to the mentioned modifications will
increase the LRP1 expression in AD therapy. This would be
one of the serious challenges in the elimination of AD 42, 43).

This leads to significant influx of Aβ from thecirculating blood into the hepatocytes and its adequate
degradation. This explains why the type II diabetes is anevident risk factor for AD.
Shinohara M et al. 41), in their study discuss potential
mechanisms underlying the LRP1 effects on the AD
pathogenesis through Aβ- dependent and independent
pathways, reviewing both clinical and preclinical studies.
They also discuss potential therapeutic strategies for AD
by targeting LRP1. In this respect, Fig. 3 as part of theircomprehensive presentation, shows the potential therapeutics
for AD which are mediated through LRP1. They present
pharmacological and nonpharmacological approaches
which could be promising therapeutic strategies for AD.
The pharmacological approaches include: statins (a class ofdrugs that lower cholesterol levels in the blood), Withania
somnifera ( Indian ginseng, a rejuvenating herbal drug,
important in the Indian subcontinent traditional medicine),
oleocanthol, cannabinoid, intravenous immunoglobulin (IVIG),
and α-secretase inhibitors. The nonpharmacological approach
includes environmental enrichment, electroacupuncture,and physical exercises. According to the authors, environmental
enrichment can ameliorate cognitive function and amyloid
pathology in amyloid AD mouse models. This enrichment
improves the vascular dysfunction by increasing angiogenesis
accompanied by upregulation of LRP1, ApoE, and α2macroglobulin, as well as the downregulation of RAGE,
so that this reduces Aβ deposition and restores cognitive
impairment in APPV7171 transgenic mice. At the sametime, an increase of LRP1 was found in the hippocampus.
Exercise ameliorates brain Aβ deposition and cognitive
decline in APP transgenic mice with upregulation of LRPI.
Oral administration of statins promotes Aβ clearance byincreasing cerebrovascular LRP1 in wild type mice and APPtransgenic mice. Oleocanthol (a type of natural phenolic
compound) from extra virgin olive oil upregulates LRP1 at
the BBB, and enhances Aβ clearance. Cannabinoid (naturally
occurring compounds from Cannabis sativa plant) treatment
also enhances Aβ transit at the BBB with increased LRP1
levels at the BBB. Antioxidant N-acetylcysteine combats
oxidative stress and improves the clearance of Aβ at
the BBB. It is evident that pharmacological approaches
to increase LRP1 in the cerebral vasculature are more
promising strategies for AD therapy. Statin treatment canalso upregulate LRP1 in the liver as well as in the brain.
These findings are obtained from cellular and animalmodels, so it is extremely important to carefully explore theireffects on humans.

The comprehensive analysis of the LRP1 receptor rolein Aβ drainage from the brain shows its crucial role in thisvital physiological process. Optimal Aβ homeostasis, i. e.
optimal balance between the production and elimination ofAβ from the brain structures and from the blood, is crucial
for the regular function of a range of physiological events
whose disorder leads to brain metabolic catastrophe. In
AD patients, this disorder of the mentioned homeostasis
causes the acceleration of AD rapid destructive pathology,
accompanied with the evident destruction of the patient's
personality, and at the end, the patient's complete
helplessness, and inevitable death. The LRP1 receptor
dominantly located on the BBB endothelial cell membranes,
with strong expression and activity, decelerates the courseof this chronic and lethal neurodegenerative disease, andgives justified hope that this disease could potentially beeliminated in the near future. This hope is supported bya number of cell and animal experimental models, which
reveal new diagnostic and therapeutic possibilities. In thescientific community, particularly in highly developed
countries, it is necessary to activate all available resources
with the aim to improve AD therapy, especially by thetherapeutic application of LRP1 receptors.

Conclusion

Conflicts of Interest_ 52 _

The author states that there is no conflicts of interest.

Glycative Stress Research

References
1) Mawuenyega KG, Sigurdson W, Ovod V, et al. Decreased

clearance of CNS amyloid-β in Alzheimer's disease.
Science. 2010; 330: 1774.
2) Zuroff L, Daley D, Black KL, et al. Clearance of cerebral
Aβ in Alzheimer's disease: reassessing the role of microglia
and monocytes. Cell Mol Life Sci. 2017; 742167-2201.
3) Hawkes CA, Sullivan PM, Hands S, et al. Disruption ofarterial perivascular drainage of amyloid b from the brainof mice expressing the human APOE e4 Allele. PloS One.
2012; 7(7): e41636.
4) Ramanathan A, Nelson AR, Sagare AP, et al. Impaired
vascular-mediated clearance of brain amyloid beta in
Alzheimer's disease: The role, regulation and restorationof LRP1. Front Aging Neurosci. 2015; 7: 136.
5) Kanekiyo T, Guojun B. The low-density lipoprotein
receptor- related protein 1 and amyloid-β clearance in
Alzheimer's disease. Front Aging Neurosci. 2014; 6: 93.
6) Barić N, Cetina M. Initial bonding of ferric ion ( Fe 3+)
and amyloid beta (Aβ) peptide as the precondition foroxidative stress in Alzheimer's disease. Glycative StressRes. 2017; 4: 250-265.
7) Persson T, Popescu BO, Cedazo-Minguez A. Oxidative
stress in Alzheimer's disease: Why did antioxidant therapy
fail? Oxid Med Cell Longev. 2014; 2014: 427318.
8) Huang WJ, Zhang X, Chen WW. Role of oxidative stressin Alzheimer's disease. Biomed Rep. 2016; 4: 519-522.
9) Barić N. Role of advanced glycation end products (AGEs)
on the reactive oxygen species (ROS) generation in
Alzheimer's disease amyloid plaque. Glycative Stress Res.
2015; 2: 140-155.
10) Arslan J, Jamshed H, Qureshi H. Early detection andprevention of Alzheimer's disease: Role of oxidative
markers and natural antioxidants. Front Aging Neurosci.
2020; 12: 231.
11) Misrani A, Tabassum S, Yang L. Mitochondrial dysfunction
and oxidative stress in Alzheimer's disease. Front Aging
Neurosci. 2021; 13: 617588.
12) Cioffi F, Adam RHI, Broersen K. Molecular mechanisms
and genetics of oxidative stress in Alzheimer's disease.
J Alzheimers Dis. 2019; 72: 981-1017.
13) Barić N. Pathophysiological reasons for the failure of
the cerebral perivascular drainage and progression of
Alzheimer's disease. RAD 544. Medical Sciences. 52-53.
2020; 544: 42-54.
14) Rivas-Arancibia S, Rodriguez-Martinez E, Badillo-Ramirez I,
et al. Structural changes of amyloid beta in hippocampusof rats exposed to ozone: A Ramon spectroscopy study.
Front Mol Neurosci. 2017; 10: 137.
15) Cheignon C, Tomas M, Bonnefont -Rousselot D, et al.
Oxidative stress and the amyloid beta peptide in Alzheimer's
disease. Redox Biol. 2018; 14: 450- 464.
16) Daly N L, Scanlon M J, Djordjevic J T, et al. Threedimensional structure of a cysteine-rich repeat from thelow-density lipoprotein receptor. Proc Natl Acad Sci USA.
1995; 92: 6334-6338.
17) Zlokovic BV, Deane R, Sagare AP, et al. Low-density
lipoprotein receptor-related protein 1: A serial clearance
homeostatic mechanism controlling Alzheimer's amyloid
β-peptide elimination from the brain. J Neurochem. 2010;
115: 1077-1089.

18) Barić N. The drainage mechanism of beta amyloid (Aβ)

from the intra-arterial perivascular space by LRP1
receptors of the blood brain barrier endothelial cells.
Glycative Stress Res. 2021; 8: 8-19.
19) Barić N. Conformational changes in the LRP1 receptor
related to the amyloid beta binding on the receptor's II andIV ligand binding domains. Glycative Stress Res. 2021: 8:
136 -147.
20) Zhao Z, Sagare AP, Ma Q, et al. Central role of PICALM
in amyloid-β blood-brain barrier transcytosis andclearance. Nat Neurosci. 2015; 18: 978-987.
21) De Nardis C, Lössl P, van den Biggelaar M, et al.
Recombinant expression of the full-length ectodomain
of LDL receptor-related protein 1 ( LRP1) unravels pHdependent conformational changes and stoichiometry ofbinding with receptor-associated protein (RAP). J Biol
Chem. 2017; 292: 912-924.
22) Barić N. Conformational changes in the LRP1 receptor
related to the amyloid beta binding on the receptor's II andIV ligand binding domains. Glycative Stress Res. 2021; 8:
136 -147.
23) Sheridan S, Gräter F, Daday C. How fast is too fast in forceprobe molecular dynamics simulations? J Phys Chem B.
2019; 123: 3658-3664.
24) Young HT, Edwards SA, Gräter F. How fast does a signal
propagate through proteins? PLoS One. 2013; 8(6): e64746.
25) Barić N. Role of advanced glycation end products in
Alzheimer's disease. Glycative Stress Res. 2014; 1: 68-83.
26) Silverberg GD, Messier AA, Miller MC, et al. Amyloid
efflux transporter expression at the blood-brain barrier
declines in normal aging. J Neuropathol Exp Neurol. 2010;
69: 1034 -1043.
27) Silverberg GD, Miller MC, Messier AA. Amyloid deposition
and influx transporter expression at the blood-brain barrier
increase in normal aging. J Neuropathol Exp Neurol. 2010;
69: 98-108.
28) Kang DE, Pietrzik CU, Baum L, et al. Modulation ofamyloid β-protein clearnce and Alzheimer's diseasesusceptibility by the LDL receptor-related protein pathway.
J Clin Invest. 2000; 106: 1159-1166.
29) Osgood D, Miller MC, Messier AA, et al. Aging alters
mRNA expression of amyloid transporter genes at the
blood-brain barrier. Neurobiol Aging. 2017; 57: 178-185.
30) Liu X, Jiao B, Shen L. The epigenetics of Alzheimer's
disease: Factors and therapeutic implications. Front Genet.
2018; 9: 579.
31) Yi SJ, Kim K. New insights into the role of histonechanges in aging. Int J Mol Sci. 2020; 21: 8241.
32) Xu K, Dai XL, Huang HC, et al. Targeting HDACs: A
promising therapy for Alzheimer's disease. Oxid Med Cell
Longev. 2011; 143269.
33) Moore LD, Le T, Fan G. DNA methylation and its basic
function. Neuropsychopharmacology. 2013; 38: 23-38.
34) Collins BE, Greer CB, Coleman BC, et al. Histone
H3 lysine K4 methylation and its role in learning andmemory. Epigenetics Chromatin. 2019; 12: 7.
35) Storck SE, Meister S, Nahrath J, et al. Endothelial LRP1transports amyloid-β (1-42) across the blood-brain barrier.
J Clin Invest. 2016: 126: 123-136.

_ 53 _

Drop in the LRP1 expression in Alzheimer's disease36) Shibata M, Yamada S, Kumar SR, et al. Clearance of

Alzheimer's amyloid-β1-40 peptide from brain by LDL
receptor-related protein-1 at the blood-brain barrier. J Clin
Invest. 2000; 106: 1489-1499.
37) Sagare AP, Deane R, Zlokovic BV. Low-density lipoprotein
receptor-related protein 1: A physiological AB homeostaticmechanism with multiple therapeutic opportunities.
Pharmacol Ther. 2012; 136: 94 -105.
38) Shinohara M, Sato N, Kurinami H, et al. Reduction of brain
β-amyloid (Aβ) by fluvastatin, a hydroxymethylglutarylCoA reductase inhibitor, through increase in degradationof amyloid precursor protein C-terminal fragments (APPCTFs) and Aβ clearance. J Biol Chem. 2010; 285: 2209122102.
39) Qosa H, Abuznait AH, Hill RA, et al. Enhanced brain
amyloid-β clearance by rifampicin and caffeine as apossible protective mechanism against Alzheimer's
disease. J Alzheimers Dis. 2012; 31: 151-165.
40) Tamaki C, Ohtsuki S, Terasaki T. Insulin facilitates thehepatic clearance of plasma amyloid β-peptide (1 40) byintracellular translocation of low-density lipoprotein
receptor-related protein 1 (LRP-1) to the plasma membranein hepatocytes. Mol Pharmacol. 2007; 72: 850-855.
41) Shinohara M, Tachibana M, Kanekiyo T, et al. Role of
LRP1 in the pathogenesis of Alzheimer's disease: Evidence
from clinical and preclinical studies. J Lipid Res. 2017;
58: 1267-1281.
42) Seok H, Lee M, Shin E, et al. Low-dose pioglitazone canameliorate learning and memory impairment in a mousemodel of dementia by increasing LRP1 expression in the
hippocampus. Scientific Rep. 2019; 9(1): 4414.
43) Nikolakopouloul AM, Wang Y, Ma Q, et al. Endothelial
LRP1 protects against neurodegeneration by blocking
cyclophilin A. J Exp Med. 2021; 218(4): e20202207.

_ 54 _