15-Hydroxyeicosatetraenoic acid (15-HETE)는 arachidonic acid에서 생성된 대사 산물로 15-lipoxygenase (15-LOX)에 의하여 형성된다. 지질 매개체로서 15-HETE의 생리적 역할이 보고되고 있으며, 15-HETE가 peroxisome proliferator activated receptor γ (PPARγ)에 결합하여 PPARγ를 활성화함이 규명되어 15-HETE가 PPARγ의 길항제로 작용할 수 있음이 보고되었다. 15-LOX와 15-HETE가 염증성 관절염과 암과 같은 병리 생리학적 현상에 관여함이 보고되었으나, 15-HETE의 PPARγ 길항제의 기능인 항염증 효과와 지방 분화 효과는 명확히 규명되지 않았다. 본 연구에서는 규명되지 않은 15-HETE의 항염증 효과를 검증하기 위하여 NCI-H292, 기도 상피 세포주를 이용하였으며, 지방분화에 대한 영향을 확인하기 위하여 3T3-L1 전 지방세포와 인체 골수 중간엽 줄기세포(hBMSC)를 이용하였다. NCI-H292를 이용한 연구에서는, phorbol-12-myristate-13-acetate (PMA)가 면역 자극제로 사용되었다. NCI-H292 세포가 PMA에 의해 자극을 받아 MUC5AC를 발현하였으나, 15-HETE에 의해 PMA-유도 MUC5AC의 mRNA 및 단백질 발현이 경감되었다. 또한, 15-HETE는 matrix metallopeptidase 9 (MMP-9), mitogen-activated protein kinase kinase (MEK)와 extracellular signal-regulated kinase (ERK)의 활성을 감소시켰다. 더욱이, 15-HETE는 specificity protein-1 (Sp-1) 전사인자와 nuclear factor κB (NF-κB) 세포핵으로의 전위를 억제하였다. 또한, 15-HETE에 의해 활성화된 PPARγ는 phosphatase and tensin homolog (PTEN)의 발현 증가를 통해 단백질 인산화 효소 B (PΚB/Akt)의 활성을 감소시켰다. 따라서 15-HETE가 MMP-9, MEK/ERK/Sp-1와 PPARγ/PTEN/Akt의 신호전달 경로를 조절하여 PMA에 의해 유도된 MUC5AC의 발현을 억제함을 확인하였다. 지방분화 연구로서, 3T3-L1 쥐 전 지방세포와 hBMSC의 지방세포로의 분화과정에서 15-HETE를 처리하여 15-HETE가 지방분화에 미치는 효과를 확인하였다. 3T3-L1 세포에서 15-HETE는 지방세포의 지방 축적을 증가시켰으며, PPARγ와 CCAAT/enhancer-binding protein (C/EBP) alpha와 같은 지방형성에 관여하는 인자들의 발현을 증가시켰다. 또한, 15-HETE는 지방분화를 억제하는 인자의 활성화를 감소시켰으며, 이는 5´-AMP-activated protein kinase alpha-를 통한 acetyl-CoA carboxylase 인산화의 경감으로 확인되었다. 초기지방분화에서 15-HETE는 mitotic clonal expansion에 관여하는 전사 인자인 C/EBPβ와 C/EBPδ의 발현을 증가시켰다. 더욱이, 15-HETE는 hBMSC의 지방분화를 촉진하였으며, 이는 15-HETE의 처리로 인한 지방 축적의 증가와 지방분화에 관여하는 인자들의 발현 증대로 확인되었다. 결론적으로 15-HETE가 PPARγ 길항제로서 작용하여, 전 지방세포와 중간엽 줄기세포의 지방분화를 촉진함을 확인하였다. 본 연구는 15-HETE의 신호 기전 및 기능을 조절이 천식, 만성 폐쇄성 폐 질환, 인슐린 저항성 및 비만 치료를 위한 새로운 치료 전략이 될 수 있음을 제시한다.
15-(S)Hydroxyeicosatetraenoic Acid (15-HETE) is one of the metabolites formed from arachidonic acid, catalyzed by 15-lipoxygenase (15-LOX). The characteristics of 15-HETE as lipid mediators have been researched and one of the noticeable features of 15-HETE is that 15-HETE can bind to peroxisome proliferator activated receptor γ (PPARγ) and activate it. Thus, it is possible that 15-HETE can act as a natural PPARγ agonist. Although 15-LOX and 15-HETE have been researched its roles in various pathological phenomena, such as inflammatory arthritis, anti-cancer effect, the role of 15-HETE of anti-inflammatory and adipogenic effect as a PPARγ agonist has not been determined. In order to examine anti-inflammatory effect, NCI-H292 cells, airway epithelial cells were treated with 15-HETE. On the other hand, to investigate the adipogenic effect of 15-HETE, 3T3-L1 preadipocytes and human bone marrow mesenchymal stem cells (hBMSCs) were administrated with 15-HETE during adipogenesis. In the NCI-H292 study, phorbol-12-myristate-13-acetate (PMA) was used as an immune stimulant. NCI-H292 cells were stimulated by PMA, which resulted in expression of MUC5AC, but 15-HETE inhibited PMA-induced expression of MUC5AC mRNA and secretion of MUC5AC protein. Also, 15-HETE regulated matrix metallopeptidase 9 (MMP-9), mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK). In addition, 15-HETE decreased translocation of specificity protein-1 (Sp-1) transcription factor and nuclear factor κB (NF-κB) into nuclear. Furthermore, upregulated PPARγ activity by 15-HETE relieved phosphorylation of protein kinase B (PΚB/Akt) by increasing phosphatase and tensin homolog (PTEN) expression. Therefore, 15-HETE regulated MUC5AC expression via modulating MMP-9, MEK/ERK/Sp-1 and PPARγ/PTEN/Akt signaling pathways in PMA-stimulated respiratory epithelial cells. In adipogenesis study, 3T3-L1 murine preadipocytes and human bone marrow mesenchymal stem cells (hBMSCs) were treated with 15-HETE during adipogenesis. In 3T3-L1 cells, 15-HETE promoted fat accumulation and increased adipogenic markers, such as PPARγ and CCAAT/enhancer-binding protein (C/EBP) alpha. 15-HETE decreased anti-adipogenetic factors, such as 5´-AMP-activated protein kinase alpha-mediated phosphorylation of acetyl-CoA carboxylase. In the early stage of adipogenesis, 15-HETE enhanced expression of C/EBPβ and C/EBPδ, two important transcription factors involved in mitotic clonal expansion. Finally, 15-HETE promoted adipogenesis in hBMSCs, which lipid accumulation and the expression of adipogenetic markers were increased in hBMSC treated with 15-HETE. Collectively, the results indicate that 15-HETE may function as one of the natural PPARγ agonists capable of enhancing the differentiation of preadipocytes and mesenchymal stem cells into adipocytes. This report represents the new therapeutic strategies directed at regulating 15-HETE signaling or function may be applied to care of various diseases, including asthma, chronic obstructive pulmonary disease, insulin resistance and diabetes.
Chapter 1. 15-Hydroxyeicosatetraenoic acid regulated PMA-induced MUC5AC expression in NCI-H292 bronchial epithelial cells 11.1. Abstract 11.2. Introduction 21.3. Materials and Methods 21.3.1. Cell culture and stimulation 21.3.2. Detection of MUC5AC protein 31.3.3. RNA isolation and reverse transcription polymerase chain reaction (RT-PCR) 31.3.4. Gelatin zymography 41.3.5. Immunoblot analysis 41.3.6. Nuclear and cytoplasmic fractionation 51.3.7. Immunofluorescence 51.3.8. Transcriptional activity assay 61.3.9. Statistical analysis 61.4. Results 71.4.1. Effects of 15-HETE on PMA-induced MUC5AC mRNA and protein Levels 71.4.2. Effect of 15-HETE on PMA-activated MMP-9 expression 91.4.3. Effect of 15-HETE on PMA-induced MEK/ERK signaling pathway 111.4.4. Effects of 15-HETE on PMA-induced translocation of transcription Factors 131.4.5. Effects of 15-HETE on PTEN and p-Akt expression as a PPARγ agonist 151.5. Discussion 17Chapter 2. 15-Hydroxyeicosatetraenoic acid promoted adipogenesis in 3T3-L1 murine adipocytes and human bone marrow mesenchymal stem cells 202.1. Abstract 202.2. Introduction 212.3. Material and Methods 222.3.1. Reagents 222.3.2. Cell culture and adipocyte differentiation 222.3.3. Oil Red O staining 232.3.4. Immunoblot analysis 242.3.5. RNA isolation and RT-PCR 242.3.6. Quantitative real-time PCR 252.3.7. 5-Bromo-2-deoxyuridine (BrdU) incorporation assay 252.3.8. Transcriptional activity assay 262.3.9. Statistical analysis 262.4. Results 262.4.1. 12/15-Lox expression is upregulated in differentiated 3T3-L1 cells and 15-HETE upregulates the transcriptional activity of PPARγ 262.4.2. 15-HETE promotes adipocyte differentiation in 3T3-L1 cells 292.4.3. 15-HETE promotes adipogenesis by modulating the expression of adipogenesis-related genes and proteins in 3T3-L1 cells 312.4.4. 15-HETE promotes the expression of adipogenic factors during the early stage of adipogenesis 332.4.5. 15-HETE promotes adipogenesis in human bone marrow mesenchymal stem cells 352.5. Discussion 38References 42Abstract (in Korean) 51