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D-serine contributes to
β-amyloid-dependant pathophysiology in Alzheimer’s disease
J-M Billard, E Ploux, L. Gorisse, T Freret
To cite this version:
J-M Billard, E Ploux, L. Gorisse, T Freret. D-serine contributes to β-amyloid-dependant patho- physiology in Alzheimer’s disease. 11th FENS Forum of Neuroscience, Jun 2018, Berlin, Germany.
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D-SERINE CONTRIBUTES TO β-AMYLOID-DEPENDENT PATHOPHYSIOLOGY IN ALZHEIMER’S DISEASE
Billard J-M, Ploux E, Gorisse-Hussonnois L and Freret T
Normandie Univ, UNICAEN, INSERM, COMETE, 14000 Caen, France
B
fEPSP/PFV ra>o
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6
WT 5xFAD 5xFAD/SR-/-
+ D-serine
+ D-serine + D-serine
Key regulators of the structural and funcFonal brain plasFcity, the N-methyl-D- aspartate subtype of glutamate receptors (NMDARs) requires the binding of the co- agonist D-serine to be acFvated. In Alzheimer's disease (AD), soluble oligomers of the beta-amyloid pepFde (Aßo) affect NMDARs possibly through mechanisms involving changes in D-serine levels since Aßo sFmulate in vitro the producFon of the co-agonist.
In this study, we asked whether D-serine contributes in vivo to morpho-funcFonal NMDAR-related deregulaFons mediated by Aßo. Behavioral analysis combined to electrophysiological recordings at CA1/CA3 hippocampal synapses have been thus conducted in the 5xFAD transgenic mice model of amyloïdogenesis displaying marked increase in Aßo rates and compared to 5xFAD animals in which the homozygous gene of the serine racemase (SR) that synthesizes D-serine, has been jointly invalidated.
Our results therefore show that deleFon of serine racemase prevents memory-related behavioral deficits observed in mice with prominent features of amyloidogenesis as well as impairment of NMDAR-dependent funcFonal plasFcity, suggesFng a significant contribuFon of D-serine in NMDAR-dependent
β-amyloid-related pathophysiology of Alzheimer’s disease.
EXPERIMENTAL PROCEDURES
1) Behavioral analysis: 8-min spontaneous alternaFon test was performed in a Y maze apparatus to assess working memory performances in 10-12 months of aged mice. Successive entry of the three arms of the maze was considered as an alternaFon. The percentage of alternaFon was calculated as follows: number of alternaFons / (total number of arms visited – 2) x 100.
2) Electrophysiology: Hippocampal slices (400 µm thickness) were cut from two groups of WT, 5xFAD/SR+/+ and 5xFAD/SR-/- mice aged 3-4 or 10-12 months. Field excitatory postsynapFc potenFals (fEPSPs) and presynapFc fiber volley (PFV) were extracellularly recorded in CA1 stratum radiatum aner electrical sFmulaFon of Schaffer collaterals. Input/output curves of the fEPSP/PFV raFo of isolated NMDAr-mediated fEPSPs were constructed in a low magnesium medium supplemented with the non-NMDAr antagonist NBQX (10µM) before and 15 min aner addiFon of D-serine (100 µM). High frequency (HFS)-induced long-term potenFaFon (LTP) was studied in control medium aner tetanic sFmulaFon consisFng in one train at 100 Hz delivered for 1 sec. TesFng sFmulaFon was then resumed for 60 min aner HFS.
3) Semi-quanFtaFve immunoblopng analysis: Hippocampal Fssue was homogenized in protein lysis buffer. The membranes were probed with anFbodiesaginst GluN1 (1:750), GluN2A (1:2500), GluN2B (1:800), GluA2 (1:500), serine racemase (1:400) or ß-acFn (1:7000). Proteins bands of interest were analyzed by scanning densitometry and normalized to ß-acFn density.
Low frequency-induced NMDAR acFvaFon is similar in basal condiFons in all experimental groups (A) but is significantly increased by exogenous D-serine only in WT
and 5xFAD/SR-/- mice (B)
Behavioral analysis Hippocampal phenotype of the experimental groups
When in WT and SR-/- mice displayed only traces of Aßo, significant levels are found in
both 5xFADand 5xFAD/SR-/- animals
Aβ42 levels
0 0,4 0,8 1,2 1,6 2
5XFAD 5XFAD SR-/- SR-/- WT
SR expression
SR / Actin (AU)
Func>onal plas>city (HFS-induced LTP)
SR deleFon reverses LTP deficits displayed by both young (A) and aged (B) 5xFAD mice
75 100 125 150 175 200 225 250 275 300
-15 0 15 30 45 60
WT (n=11) 5xFAD (n=17) 5xFAD/SR-/- (n=9)
fEPSP slope (% of baseline)
Time (min)
3-4 month-old
75 100 125 150 175 200 225 250 275 300 325 350
-15
WT (n=11) 5xFAD (n=13) 5xFAD/SR-/- (n=11)
10-12 month-old
fEPSP slope (% of baseline)
Time (min)
0 15 30 45 60
A
B
Protein expression
1
SR Actin
SR-/- 5xFAD WT 5xFAD/SR-/-
Actin Actin GluN1
SR-/- 5xFAD WT 5xFAD/SR-/-
0 0,4 0,8 1,2 1,6 2
WT (n=4) 5XFAD (n=6) 5XFAD SR-/- (n=7)
GluN1/actin (AI)
GluN2B Actin
SR-/- WT 5xFAD SR-/-
5xFAD/SR-/- WT 5xFAD 5xFAD/SR-/- SR-/-
GluN2A Actin
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
WT (n=4) 5XFAD (n=6) 5XFAD SR-/- (n=7)
0 0,5 1 1,5 2 2,5
WT (n=4) 5XFAD (n=6) 5XFAD SR-/- (n=7)
GluN2B/actin (AI)
Total protein expression for each NMDAR subunit is not significantly affected in 5xFAD mice although it is
slightly decreased for GluN2B as compared to WT and 5xFAD/SR-/- mice
** **
NMDAR ac>va>on (isolated synap>c poten>als)
0 0,2 0,4 0,6 0,8 1 1,2 1,4
300 400 500
WT (n=15) 5xFAD (n=17)
fEPSP/PFV ra>o
S>mulus intensity (μA)
A
GluN2A/actin (AI)
20 msec 0,
2 mV
control
+ D-serine
SR deleFon reverses working memory deficits displayed by 5xFAD mice
Spontaneous alternaFon
Working memory
Y maze
0 10 20 30 40 50 60 70
WT n=13 5XFAD n=11 5XFAD/SR-/- n=14
% alternaFon
* *
