Stress increases depression-like behaviors in Alzheimer’s disease mice

국문 초록 (Abstract)

알츠하이머성 치매 (AD) 는 인지 장애, 기억 상실, 행동 변화 및 기능적 능력 상실을 특징으로 하는 치매의 가장 흔한 질환이다. 또한, 우울증은 AD 환자에게서 흔히 나타나는 동반 질환이다. 최근 AD는 우울증과 병태생리학적으로 공통된 기전을 공유한다는 것이 밝혀졌다. 만성 스트레스는 글루코코르티코이드 (GC)의 분비를 증가시키고 글루코코르티코이드 수용체 (GR)에 결합하여 뇌의 기능을 조절한다. 많은 양의 GC 분비는 아밀로이드 전구체 단백질 (APP)의 잘못된 processing과 아밀로이드 베타 (Aβ) 생성을 유발하여 AD를 유발한다. 또한, 우울증은 스트레스와 관련된 질병으로 잘 알려져 있으며 코르티솔 수치가 우울증의 바이오마커로 사용된다. 나는 우울증과 AD의 관계를 조사하기 위해 Tg2576 마우스와 WT 마우스를 10일 동안 물 회피 스트레스 (WAS)에 노출시켰다. WAS 에 노출시킨 이후 Tg2576 WAS 마우스 를 대상으로 기억 기능 및 우울증 관련 행동실험을 진행하였다. 우울증 관련행동실험에서는 Tg2576 WAS 마우스가 WT WAS 마우스 및 Tg2576 CON 마우스보다 더 우울한 행동을 나타내는 것으로 확인하였다. 또한, Tg2576 CON 마우스는 WT CON 마우스보다 더 우울한 행동을 나타내었다. 나아가,코르티코스테론 수치와 인산화된 글루코코르티코이드 수용체 (p-GR)도 Tg2576 WAS 마우스에서 Tg2576 CON 마우스보다 더 높게 나타났다. SPNS2의 주요 기능은 S1P 를 밖으로 방출하는 역할을 한다. GEO 데이터베이스는 AD 및 우울증 환자에서 SPNS2 유전자 발현을 분석하는 데 사용되었다. 결과는 SPNS2의 유전자 발현이 AD 및 우울증과 상관관계가 있음을 보여 주었다. 다음으로 Tg2576 WAS 마우스에서 SPNS2의 발현정도를 확인하였다. Tg2576 WAS 마우스에서 SPNS2의 발현량은 Tg2576 CON 마우스와 비교하였을 때 크게 증가하였다. 또한 SPNS2 발현이 세포 내 S1P 수준을 감소시키면서 세포외 S1P level이 증가되는지를 확인하기 위해 Tg2576 WAS 마우스 의 뇌와 혈청에서 S1P level을 측정하였다. Tg2576 CON 마우스와 비교하여 뇌의 S1P level은 증가하였고 혈청에서 S1P level은 감소하였다. 또한, stress 는 뇌의 S1P 수치를 더욱 감소시켰다. 그러나 혈청 내 수치는 더욱 증가하였다. 따라서 이러한 결과는 AD와 우울증이 연관성이 있으며, 스트레스 매개 우울증이 SPNS2를 상향 조절함으로써 S1P의 방출을 통해 Tg2576 형질전환 마우스에서 더 많은 영향을 미칠 수 있음을 나타낸다.

다국어 초록 (Multilingual Abstract)

Alzheimer’s disease (AD) is the most common form of dementia characterized by cognitive impairment, loss of memory, behavioral changes and loss of functional abilities. Depression is a common co-morbidity seen in people with AD. Recent evidence suggests that AD and depression share common mechanisms of pathogenesis. Chronic stress leads to increased secretion of glucocorticoid (GC) and modify brain functions by binding glucocorticoid receptor (GR). High levels of GC secretion, triggers AD by causing the misprocess of amyloid precursor protein (APP) and the production of amyloid-beta (Aβ). Moreover, depression is well-known stress related illness and elevated levels of cortisol are used as a biomarker of depression. To investigate relationship between depression and AD, water avoidance stress (WAS) was induced for 10 days in both Tg2576 mice and wild-type (WT) mice. After WAS, memory function and depression-related test were investigated in Tg2576 WAS mice. On depression-related behavioral tests showed that Tg2576 WAS mice exhibited more depressive behaviors than WT WAS mice and Tg2576 CON mice. Tg2576 CON mice showed more depressive behaviors than WT mice. Moreover, corticosterone levels and phospho-glucocorticoid receptor (p-GR) were also higher in Tg2576 WAS mice than in Tg2576 CON mice. Sphingolipid Transporter 2 (SPNS2) is a Sphingosine-1-Phosphate (S1P) transporter. GEO database was used to analyze SPNS2 gene expression in AD and depression patients. The reults shows that SPNS2 gene expression correlates with AD and depression. Next, expression level of SPNS2 in Tg2576 WAS mice brains was measured. In Tg2576 WAS mice, SPNS2 was significantly increased compared with Tg2576 CON mice. SPNS2 was also higher in Tg2576 CON mice compared with WT CON mice. To study whether increased SPNS2 expression release more level of S1P, the S1P levels in the Tg2576 WAS mice brains and serum were measured. Compared with Tg2576 CON mice, the S1P level in the brains was decreased, but was increased in the serum. Moreover, WAS treatment further decreased S1P level in the brains. However, the level in the serum further increased. Therefore, these results indicate that AD and depression could be associated, and stress mediated depression could affect more in Tg2576 transgenic mice through the release of S1P by up-regulating SPNS2.

목차 (Table of Contents)

• Ⅰ. INTRODUCTION ······························································································1
• 1. Alzheimer’s disease ·············································································································1
• 2. Depression ·······························································································································4
• 3. Comorbidity ····························································································································7
• 4. (S1P)Sphingolipid Transporter 2 (SPNS2) ·······························································9
• 5. Sphingosine-1-phosphate ·······························································································10
• 6. Purpose of this study ······································································································11
• Ⅱ. MATERIALS AND METHODS ···················································12
• 1. Ethical statement ···············································································································12
• 2. Animal ····································································································································12
• 3. Water avoidance stress (WAS) ··················································································13
• 4. Morris Water Maze ··········································································································14
• 5. Probe test ·····························································································································14
• 6. Passive avoidance performance test ·········································································15
• 7. Novelty-suppressed feeding test ················································································16
• 8. Sucrose preference test ··································································································16
• 9. Tail suspension test ·········································································································17
• 10. Forced swimming test ··································································································17
• 11. Collection and preservation of brain tissues ······················································18
• 12. Western blot analysis ···································································································18
• 13. Serum collection and serum ELISA assay ·························································19
• 14. Measurement of sphingolipids in serum and brains ·······································19
• 15. High-Performance Liquid Chromatography Analysis ·····································20
• 16. Selection of GEO dataset ····························································································21
• 17. Gene ontology enrichment and target prediction analysis ···························21
• 18. Statistical analysis ··········································································································22
• Ⅲ. RESULTS ···············································································································26
• 1. Depression-related behavioral in stress induced Tg2576 mice ····················26
• 2. Corticosterone level of Tg2576 WAS mice brains and serum ····················30
• 3. Alzheimer’s disease related behavioral in Tg2576 WAS mice ·····················32
• 4. Protein level of Aβ in the brains of Tg2576 WAS mice ······························34
• 5. SPNS2 expression correlates with AD and depression ···································36
• 6. Expression level of SPNS2 in the brains of Tg2576 WAS mice ··············38
• 7. Levels of S1P in the brains and serum of Tg2576 WAS mice ·················40
• Ⅳ. DISCUSSION ·····································································································42
• REFERENCES ·············································································································46
• 국문초록 ····································································································································56