Scientists eliminate key Alzheimer's feature in animal model
Study suggests possible way to prevent memory-robbing disease

Date:
October 29, 2021
Source:
UT Southwestern Medical Center
Summary:
A study finds that changing the biochemistry of parts of brain
cells abolished the formation of amyloid beta plaques in a mouse
model of Alzheimer's disease. The finding might eventually lead
to treatments that prevent the memory-robbing condition in humans.



FULL STORY ==========================================================================
A study by UT Southwestern researchers finds that changing the
biochemistry of parts of brain cells abolished the formation of amyloid
beta plaques in a mouse model of Alzheimer's disease. The finding,
published in eLife, might eventually lead to treatments that prevent
the memory-robbing condition in humans.


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"We envision that drugs that act on the same protein we inhibited in
these mice could someday play a similar role in Alzheimer's disease as
statins do in heart disease, helping to prevent the condition from ever developing," said Joachim Herz, M.D., Professor of Molecular Genetics, Neurology, and Neuroscience at UTSW. Dr. Herz led the study, and graduate student Connie Wong was a co-lead author.

Nearly 6 million Americans have Alzheimer's disease, with the
vast majority developing a late-onset form that arises after age
65. Alzheimer's disease is characterized by brain cells plagued
by extracellular plaques made of a protein called amyloid beta
and intracellular tangles made of an abnormal form of a protein
called tau. Although the causes of the disease are not well defined,
scientists have long known that the most significant genetic risk factor
for late-onset Alzheimer's is apolipoprotein E4 (ApoE4), one of three
variants of a protein involved in fat metabolism in mammals. In humans,
having the ApoE4 variant reduces the average age of Alzheimer's onset by several years compared with having the most common variant, ApoE3, while
rarer ApoE2 appears to have a protective effect against this disease.

The three versions of ApoE are very similar structurally,
Ms. Wong explained: Compared with ApoE2, ApoE3 contains one amino
acid substitution, resulting in that protein having a more positive
charge. The ApoE4 variant contains two amino acid substitutions, resulting
in the highest positive charge of the three forms of ApoE protein. The mechanism by which these differences affect late- onset Alzheimer's risk
has been unknown.

In their new study, Dr. Herz, Ms. Wong, and their colleagues homed
in on early endosomes, organelles responsible for sorting proteins,
recycling them for reuse, or transporting them through the cell interior
to cellular garbage dumps called lysosomes. Previous research had shown
that early endosomes are enlarged in people and animals with ApoE4,
compared with those who carried the other two ApoE variants.

Using genetically modified mice that model Alzheimer's disease and
produce the human forms of ApoE4 and amyloid beta, the researchers
showed that the positive charges on ApoE4 caused this protein to clump
inside early endosomes because the charge of ApoE4 matches that of the environment inside endosomes. This clumping prevents these organelles
from continuing their journey through the cell to transport, recycle,
or help dispose of other proteins, including amyloid beta.

However, when the researchers used a genetic technique to turn off a
gene called NHE6in brain cells, they found that the negative effects of
ApoE4 were eliminated, and the protein was transported through the cell
without impediment. NHE6 produces a protein that acts as a pH regulator
for endosomes, exchanging acidic protons for sodium ions. When the
researchers shut off the NHE6 gene, removing its protein from the cell,
the early endosomes quickly became more acidic and that biochemical
change seemed to prevent amyloid beta aggregation.

"Inhibiting NHE6 produced the same protective effect as having ApoE2,
an effect we hope can eventually be replicated using pharmaceuticals,"
Ms. Wong said.

The team plans to continue to study this mechanism and how to inhibit
NHE6 in future studies.

Current and former UTSW researchers who contributed to this study include
co- lead authors Theresa Pohlkamp, now at Regeneron Pharmaceuticals, and
Xunde Xian, now at Peking University, as well as Murat S. Durakoglugil,
Gordon Chandler Werthmann, Bret M. Evers, Charles L. White III, Jade
Connor, and Robert E. Hammer. Takaomi C. Saido of the Riken Center for
Brain Science also contributed.

This work was supported by the National Institutes of Health (grants
R37 HL063762, R01 NS093382, R01 NS108115, and RF1 AG053391, as well as
1F31 AG067708-01 from the National Institute on Aging), the Darrell K
Royal Research Fund, the BrightFocus Foundation (A20135245, A2016396S);
the Harrington Discovery Institute; a Circle of Friends Pilot Synergy
Grant; and the Bluefield Project to Cure FTD.

Dr. Herz holds the Presbyterian Village North Foundation Distinguished
Chair in Alzheimer's Disease Therapeutic Research and the Thomas O. and
Cinda Hicks Family Distinguished Chair in Alzheimer's Disease Research.

========================================================================== Story Source: Materials provided by UT_Southwestern_Medical_Center. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Theresa Pohlkamp, Xunde Xian, Connie H Wong, Murat S Durakoglugil,
Gordon
Chandler Werthmann, Takaomi C Saido, Bret M Evers, Charles L White,
Jade Connor, Robert E Hammer, Joachim Herz. NHE6 depletion corrects
ApoE4- mediated synaptic impairments and reduces amyloid plaque
load. eLife, 2021; 10 DOI: 10.7554/eLife.72034 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211029113954.htm

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