The Relation between Gingipain, TREM-2 and the Condition of

Alzheimer’s Disease

Xiaolin Ding

Hangzhou NO. 14 Middle School,

Hangzhou, Zhejiang 310005, China

Keywords: Alzheimer’s Disease, Abeta, Gingipain, TREM-1, TREM-2.

Abstract: P. gingivalis is a kind of bacterial that causes Periodontitis, and will secrete gingipain, which can help the P.

gingivalis to colonize inside the host. It is proposed that the gingipain that is secreted by P. gingivalis will

activate TREM-1, which induces the inflammation inside the brain. The inflammation inside the brain will

cause the neurodegeneration and cognitive decline, which in a way worthen the AD. Thus, it can be concluded

that TREM-1 and gingipain have influences on AD. Beyond this, we found that TREM-2 shares homology

with TREM-1, and some studies shows that TREM-2 can help to against inflammatory. In this paper, we came

up with a hypothesis that the activation of TREM-2 reduces the level of inflammation and protects neurons

from degeneration, mainwhile, P. gingivalis colonizes in the brain and exacerbates features of AD via its

gingipains.

1 INTRODUCTION

P. gingivalis is what cause the periodontitis and

secrete gingipain. For gingipain, it is essential for P.

gingivalis survival and pathogenicity, and plays

critical roles in host colonization, inactivation of host

defenses, nutrient acquisition and tissue destruction.

TREM-1’s full name is The Triggering Receptor

Expressed on Myeloid cells 1. It is a surface receptor

on immune cells that amplifies inflammatory

processes, which means that once it is being

activated, it increases the level of inflammation. This

process can be activated by bacterial infection, and

studies have shown that it is regulated by gingipain of

P. Gingivalis, inducing chronic inflammation in the

brain, leading to neurodegeneration and cognitive

decline (Haditsch, Ursula, et al. 2020). TREM-2’s full

name is Triggering Receptor Expressed on Myeloid

cells 2, it shares homology with TREM-1, encoding a

receptor expressed on immune cells such as

macrophageas and microglia (Dominy, Stephen, et al.

2019). In contrast, studies have shown that TREM-2

defends the liver against hepatocellular carcinoma

(HCC), which is a chronic liver injury involving

inflammatory and hepatic regenerative processes

(Watts, Amber, et al. 2008). Once activated by its

ligand, TREM-2 reduces the level of inflammation in

the liver, and one of the ligands of TREM-2 is A-beta

protein (Esparza-Baquer, Labiano, et al. 2021).

Figure 1: (Matsushita, Kenji & Yamada-Furukawa, Masae & Kurosawa, Mie & Shikama, Yosuke. (2020). Periodontal Disease

and Periodontal Disease-Related Bacteria Involved in the Pathogenesis of Alzheimer’s Disease. Journal of Inflammation

Research. Volume 13. 275-283. 10.2147/JIR. S255309.) It shows the process of how P. gingivalis cause the influences inside

the brain.

Ding, X.

The Relation between Gingipain, TREM-2 and the Condition of Alzheimer’s Disease.

DOI: 10.5220/0011238900003438

In Proceedings of the 1st International Conference on Health Big Data and Intelligent Healthcare (ICHIH 2022), pages 169-172

ISBN: 978-989-758-596-8

169

2 EXPERIMENTS

To prove our hypothesis, we designed experiments

follows, proven the function of gingipain, Co-

Immunoprecipitation, Gene knockout and Behavior

testing. By all these experiments, we are going to

prove that the TREM-2 can have a positive result in

AD, and it is gingipain that induces the AD (Singhrao,

Sim, and Ingar Olsen. 2019). In the first experiment

which is the proven of the function of gingipain, we

will use the following materials: Wild-type gingivalis

which normally exist in the nature, gingipain knock-

out mutant K1A which is deficient in Lys- gingipain

and E8 strains which is deficient in both Arg-

gingipain A and Arg-gingipain B (Bostanci, et al.

2016). We will first cultivate, collect, wash, and

suspend the bacterial to get enough copies for the

experiment, then, we will control environment for the

mouse and develop periodontitis inside mouse. After

five weeks, we will collect the brains of the mouse to

measure the data. We will measure the concentrations

of bacterial endotoxin in the brains and the

concentrations of A-beta protein (40 and 42) in the

brains so that we can find out whether the gingipain

works as expected (Ishida et al. 2017). In the second

experiment of Co-Immunoprecipitation, we are going

to determine the interactions between Aβ and

TREM2, the materials that will be use are the fresh

medium containing conditioning molecules and

microglia. First step of this experiment is the

preparation of cell lysates, we will cultivate bacterial

inside of a fresh medium, collect, wash, and suspend

the bacterial. After that, we will do the

immunoprecipitation, in this step, we will centrifuge

the supernatant, and aspirate the residue for use

(Maheshwari, Eslick 2015). Then, we will do the

western blot. In this step, we will run gel to get data

to prove that TREM-2 can be bound to Aβ as it will

show a similar result as Aβ is immunoprecipitated

with Aβ antibodies (Liu, Yu. 2019). In the third

experiment for gene knockout, we are going to prove

the function of TREM-1 and TREM-2. In this

experiment, we will use gingipain and mouse. The

first step is to set two LoxP sites so that it can be clear

which part of the gene is going to be knockout

(Singhrao, Sim, et al. 2015). After that, we are going

to knockout the TREM-1 gene and the TREM-2 gene

dividing by group 1 to 4 which with one only

knockout TREM-1, one only knockout TREM-2, one

knockout both and one does not knockout any gene.

Then, we will induce gingipain into the brains, and

measure the production of pro-inflammatory

cytokines by ELISA. By this experiment and the

research done by other scientists, we can conclude

that TREM-1 will increase the level of inflammation

while TREM-2 will decrease the level of

inflammation (Ishida et al. 2017).

Figure 2: (from TREM2 in Alzheimer’s Disease: Microglial Survival and Energy Metabolism) shows the process of TREM-

2 and what it caused.

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3 BEHAVIOR TESTING

After all these experiments are done, we need to know

whether the TREM-1 and TREM-2 have influence on

AD, so we designed a behavior testing. We will first

divide mouse into 4 groups with group A for the

TREM-1 knock-out, group B for TREM-2 knock-out,

group C for both knock-out, group D for the one does

not do anything. Then, we design three testing to get

the result. In the first experiment, we will design a

maze with several turns that a normal mouse can walk

out. Put each group into the maze individually to

measure the time they need for the first time to find

way out. Do the same thing for 3 times and measure

the time each group need to get out. Compare the

change in the need of time between different groups

to conclude the result. In the second experiment, we

put each group into a box with road A and B that lead

to food, if the mice pass through road A, they will

receive an electron shock of 5V. Make the mouse

empty stomach for 5 hours and put each group into

the box so that they will go for the food. Do the same

thing for 10 times and measure the time they go for

road A and B. In the third experiment, a training for

all the mouse to open the box to find food will be done

before do the surgery. After the surgery, put two

sealed boxes in two directions with two different odor

that is not related with mouse in any areas, one of the

boxes contains food. Put each group in that area to

find food for 10 times. Measure the time it takes for

mouse to know the box with which odor contains

food. The results of these experiments are that ss the

experiments above, we can assume that TREM-1 will

exacerbate inflammation during acute inflammation,

while TREM-2 will prevent chronic inflammation.

According to Naoyuki Ishida, the inflammation is

correlated with AD that when inflammation

exacerbate, it will exacerbate the symptoms of

Alzheimer's Disease (Ishida et al. 2017). So that we

can expect that the knock-out of TREM-1 will

decrease the symptoms of AD, the knock-out of

TREM-2 will exacerbate the symptoms of AD, while

knock-out of both TREM-1 and TREM-2 will cause

the deterioration of AD afterward. As the assumption

we make, we can know that group A will present the

state that AD is weakened. In group B, the present of

AD will be exacerbated. In group C, the present of

AD will be exacerbated. In group D, it is same as

group C. For the behavior testing, if our hypothesis is

correct, the result will be that in experiment 1, group

A will show an obvious decrease in the time it takes

to pass the maze as the time of trying increases. Group

B will need almost the same time during each time of

trying. Group C shows a similar result as group B.

Group D shows a constant decrease in time as the time

it passes the maze increases. In experiment 2, as the

time of the experiment increases, group A shows an

obvious decrease in the chance it goes for road A.

Group B shows a chance of about 50% that it will go

for road A. Group C shows a similar result as group

B. Group C shows a decrease in the chance it goes for

road A as the time of experiment increases. In

experiment 3, group A will show a decrease in the

time it needed to find food as the time of experiment

increases and can be concluded that group A can link

a kind of odor to food. Group B shows a similar time

each time it needed to find food as the time of

experiment increases so that it can be concluded that

group B cannot link a kind of odor with food. Group

C shows a similar result as group B. Group D shows

a decrease in time as more experiment is done and can

be concluded that group D can link a kind of odor to

food. If the hypothesis is wrong, then the result will

be that in all the experiments, the behavior of all

groups of mice are similar and the improvement in

time is almost neglectable.

Figure 3: (from Predictably irrational: assaying cognitive inflexibility in mouse models of schizophrenia) It shows some types

of behavior testing, the A and C are used in this experiment.

The Relation between Gingipain, TREM-2 and the Condition of Alzheimer’s Disease

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4 CONCLUSIONS

In this paper, it talks about the influence TREM-2

might have on Alzheimer’s Disease. After these

experiments, the hypothesis of TREM-2 and

gingipain can be proved. Though this article and the

hypothesis might be wrong, but TREM-2 and

gingipain have influences on AD by many factors in

different ways. As the Alzheimer’s disease is a very

serious disease that influence people in so many

ways, it is possible to say that the relation between

TREM-2 and Alzheimer’s disease is crucial to the

further research and the development of the treatment

in Alzheimer’s disease. This article is meant to show

a new way of seeing what influences Alzheimer’s

Disease and point out a factor that have not been

tested on. In the future, we will focus on the research

of what is the causation of Alzheimer’s Disease, what

are the factors that make it worse, and how the

symptoms Alzheimer’s Disease can be decreased.

ACKNOWLEDGEMENTS

Nicolas Chen, Priscilla Peng, Dan Wang.

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