Deciphering the Roles of Foamy Macrophages in Atherosclerosis and Tuberculosis

Abstract

Macrophages are the myeloid immune cells which are located at whole tissue to maintain homeostasis. The immunological function of macrophages is closely related with cellular metabolic pathways. Disturbing homeostasis of metabolic pathways in macrophages induce transformation into foamy macrophages. Foamy macrophages are named by their morphological feature that is accumulation of excessive lipid bodies in their cytosolic area. These lipid-laden foamy macrophages are generated, and play important roles in the initiation and progression of atherosclerosis and tuberculosis. Therefore, the understanding of foamy macrophages is required to control the pathogenesis of atherosclerosis and tuberculosis. To investigate foamy macrophages, the lipid staining combined flow cytometry with BODIPY493/503 was established. Using this method, foamy macrophages of atherosclerosis and tuberculosis were assessed.

First, foamy macrophages of atherosclerotic lesions were dissected in vivo. Lipid-laden foamy cells were successfully detected and dissected into at least three origins including macrophages, vascular smooth muscle cells, and endothelial cells. Foamy macrophages had elevated levels of CD11b, CD11c, and Ly6c than non-foamy macrophages. Lesion size was correlated with the number of foamy macrophages in progression and alleviation of atherosclerosis.

Next, Mycobacterium tuberculosis infected foamy macrophages were analyzed in vivo and in vitro. Bacterial burdens were positively correlated with accumulated lipids in foamy macrophages. Since type Ⅰ interferon signaling is a contributor of lipid accumulation, pathogenic roles of type Ⅰ interferon on tuberculosis in metabolic pathways were investigated. Bacterial burdens and lipid accumulations were elevated by induction of type Ⅰ interferon signaling in foamy macrophages. Metabolic reprogramming was occurred to promote intracellular ceramide accumulation for supporting bacterial survival and replications by type Ⅰ interferon signaling in foamy macrophages. Blocking ceramide pathways with anti-depressants alleviates pathogenesis of tuberculosis.

Collectively, the lipid staining combined flow cytometry was developed for the investigation of foamy macrophages in atherosclerosis and tuberculosis. Using atherosclerosis models, the lipid staining combined flow cytometry was established for analyzing foamy cells. Utilization of this lipid staining combined flow cytometry, foamy macrophages was investigated for understanding of tuberculosis pathogenesis and suggesting targets of host-directed therapy.

| 큰포식세포는 전신에 존재하며 체내 항상성을 유지하는 면역세포의 하나로, 최근 큰포식세포의 면역 기능과 세포 대사 작용이 긴밀하게 연관되어 있다는 보고가 있었다. 세포 대사의 항상성이 유지되지 못하는 경우 큰포식세포는 포말성 큰포식세포로 변화되는 것으로 알려졌다. 포말성 큰포식세포는 세포질 내 과량의 지방체를 축적하는 형태적 특징에 의해 구분된다. 이러한 지질체를 가진 포말성 큰포식세포는 동맥경화와 결핵에서 생겨나고, 질병의 시작과 병변의 진행 과정에 중요한 기능을 수행하는 것으로 알려졌다. 따라서 포말성 큰포식세포에 대한 이해가 동맥경화와 결핵의 병인 기전을 조절하는 것에 필수적인 것으로 사료된다. 이에 본 연구에서는 포말성 큰포식세포를 연구하기 위해서 지질 염색을 접목한 유세포분석 방법을 확립하였다. BODIPY493/503이 포말성 큰포식세포의 지질 염색을 위해 사용되었으며, 이 방법이 동맥경화와 결핵에서 생겨나는 포말성 큰포식세포의 분석을 위해 사용되었다.

우선 동맥경화에 걸린 마우스의 혈관에서 포말성 큰포식세포를 분리하고, 지질 염색을 접목한 유세포분석 방법을 개발하여 이를 분석하였다. 동맥경화 병변에서 추출한 포말성 세포의 기원을 큰포식세포, 혈관 평활근세포, 내피세포의 3가지로 나눌 수 있었다. 포말성 큰포식세포는 다른 큰포식세포에 비해 CD11b, CD11c, Ly6c를 높게 발현하는 특징을 보였다. 동맥경화가 병변이 생겨나거나 치료를 하여 달라지는 동맥경화 병변의 크기는 혈관 내 포말성 큰포식세포의 수적 증가와 양의 상관관계를 가지는 것을 확인하였다.

다음으로 결핵균 감염 시 생겨나는 포말성 큰포식세포를 분석하였다. 결핵균 감염으로 생겨나는 포말성 큰포식세포의 세포 내 박테리아와 지질체는 양의 상관관계를 가지는 것을 확인하였다. 최근 제 1형 인터페론 신호가 지질 대사를 변화시켜 세포 내 지질의 양을 증가시키는 것이 보고되었기 때문에, 제 1형 인터페론 신호가 결핵균 감염에서 포말성 큰포식세포의 지질 대사에 미치는 영향에 대해 연구를 수행하였다. 결핵균 감염에 제 1형 인터페론 신호가 동반되는 경우 포말성 큰포식세포 내 지질체가 증가되고, 결핵균의 세포 내 성장의 증가로 이어짐을 확인하였다. 이 때 변화하는 지질 대사는 포말성 큰포식세포 내 대사체 중 세라마이드를 크게 증가시켜 결핵균의 성장이 촉진됨을 확인하였다. 이 때 세라마이드 형성을 억제할 수 있는 항우울제를 처리하면 결핵균 성장이 저해됨을 확인하였다.

총괄하여, 본 연구에서는 동맥경화와 결핵균 감염에서 생겨나는 포말성 큰포식세포를 지질 염색을 통한 유세포분석 기법을 개발하여 분석하였다. 동맥경화 모델에서 지질 염색을 통한 포말세포의 유세포분석 기법을 확립하였으며, 이 기법을 통해 결핵의 큰포식세포를 연구하여 결핵의 병인 기작의 이해와 숙주 표적 치료의 새로운 타겟을 제시하였다.; Macrophages are the myeloid immune cells which are located at whole tissue to maintain homeostasis. The immunological function of macrophages is closely related with cellular metabolic pathways. Disturbing homeostasis of metabolic pathways in macrophages induce transformation into foamy macrophages. Foamy macrophages are named by their morphological feature that is accumulation of excessive lipid bodies in their cytosolic area. These lipid-laden foamy macrophages are generated, and play important roles in the initiation and progression of atherosclerosis and tuberculosis. Therefore, the understanding of foamy macrophages is required to control the pathogenesis of atherosclerosis and tuberculosis. To investigate foamy macrophages, the lipid staining combined flow cytometry with BODIPY493/503 was established. Using this method, foamy macrophages of atherosclerosis and tuberculosis were assessed.

First, foamy macrophages of atherosclerotic lesions were dissected in vivo. Lipid-laden foamy cells were successfully detected and dissected into at least three origins including macrophages, vascular smooth muscle cells, and endothelial cells. Foamy macrophages had elevated levels of CD11b, CD11c, and Ly6c than non-foamy macrophages. Lesion size was correlated with the number of foamy macrophages in progression and alleviation of atherosclerosis.

Next, Mycobacterium tuberculosis infected foamy macrophages were analyzed in vivo and in vitro. Bacterial burdens were positively correlated with accumulated lipids in foamy macrophages. Since type Ⅰ interferon signaling is a contributor of lipid accumulation, pathogenic roles of type Ⅰ interferon on tuberculosis in metabolic pathways were investigated. Bacterial burdens and lipid accumulations were elevated by induction of type Ⅰ interferon signaling in foamy macrophages. Metabolic reprogramming was occurred to promote intracellular ceramide accumulation for supporting bacterial survival and replications by type Ⅰ interferon signaling in foamy macrophages. Blocking ceramide pathways with anti-depressants alleviates pathogenesis of tuberculosis.

Collectively, the lipid staining combined flow cytometry was developed for the investigation of foamy macrophages in atherosclerosis and tuberculosis. Using atherosclerosis models, the lipid staining combined flow cytometry was established for analyzing foamy cells. Utilization of this lipid staining combined flow cytometry, foamy macrophages was investigated for understanding of tuberculosis pathogenesis and suggesting targets of host-directed therapy.