Journal of Life Science (생명과학회지)

Korean Society of Life Science (한국생명과학회)
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Potential Role of Hedgehog Signaling in Radiation-induced Liver Fibrosis

방사선에 의한 간섬유증에서 헤지호그의 잠재적 역할

  • Wang, Sihyung (Department of Biological Science, Pusan National University) ;
  • Jung, Youngmi (Department of Biological Science, Pusan National University)
  • 왕시형 (부산대학교 자연과학대학 생명과학과) ;
  • 정영미 (부산대학교 자연과학대학 생명과학과)
  • Received : 2013.05.25
  • Accepted : 2013.05.27
  • Published : 2013.05.30
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Abstract

Radiotherapy is commonly used in treating many kinds of cancers which cannot be cured by other therapeutic strategies. However, radiotherapy also induces the damages on the normal tissues. Radiation-induced fibrosis is frequently observed in the patients undergoing radiotherapy, and becomes a major obstacle in the treatment of intrahepatic cancer. Hedgehog (Hh) that is an essential in the liver formation during embryogenesis is not detected in the healthy liver, but activated and modulates the repair process in damaged livers in adult. The expression of Hh increases with the degree of liver damage, regulating the proliferation of hepatic progenitors and hepatic stellate cells (HSC). In addition, Hh induces epithelial-to-mesencymal transition (EMT) and activation of myofibroblasts. In the irradiated livers, up-regulated expression of Hh signaling was associated with proliferation of progenitors, EMT induction, and increased fibrosis. Female-specific expression of Hh leaded to the expansion of progenitors and the accumulation of collagen in the irradiated livers of female mice, indicating that gender disparity in Hh expression may be related with radiation-susceptibility in female. Hence, Hh signaling becomes a novel object of studies for fibrogenesis induced by radiation. However, the absence of the established experimental animal models showing the similar physiopathology with human liver diseases and fibrosis-favorable microenvironment hamper the studies for the radiation-induced fibrosis, providing a few descriptive results. Therefore, further research on the association of Hh with radiation-induced fibrosis can identify the cell and tissue-specific effects of Hh and provides the basic knowledge for underlying mechanisms, contributing to developing therapies for preventing the radiation-induced fibrosis.

방사선 치료는 가장 일반적으로 사용되고 있는 항암치료로, 암 환자의 수 증가와 동반하여 방사선 활용도는 더욱 증가하고 있다. 방사선치료에 대한 환자들의 심리적 거부감과 산화적 스트레스, 저산소증, DNA 손상을 포함하여, 치료 후 나타나는 간 섬유화는 방사선 치료의 가장 큰 문제점으로 대두되고 있다. 간암의 경우 대부분의 환자들이 섬유화를 동반하고 있어서, 방사선에 의해 암세포가 제거된다 하더라도, 기존에 남아있는 손상 부위에서의 섬유화와 방사선 조사에 의한 정상조직의 섬유화는 간경변 유발 확률을 높이고 있다. 간 섬유화는 여러 간질환에서 흔히 관찰되는 증상으로, 간 섬유화 진행 기작의 규명은 만성질환으로의 진행을 억제할 수 있는 치료책 개발로 연계될 수 있지만, 아직까지 명확히 규명되지 않음에 따라, 섬유화를 억제할 수 있는 효과적인 방법이 없는 실정이다. 최근 간 섬유화 생성 및 진행에 대한 헤지호그의 역할이 밝혀지면서, 간암 및 만성질환으로의 진행을 이해하기 위한 연구대상으로 대두되고 있다. 헤지호그는 손상된 간에서 발현되어 보수과정에 기여하게 된다. 헤지호그의 발현은 간 손상 정도에 비례하여 발현되어, 간 줄기세포 및 간 성상세포의 증식을 조절한다. 또한, TGF-${\beta}1$와, EMT를 유도하고 근섬유화세포의 활성을 조절하여, 간 섬유화 진행에 중심적 역할을 한다. 방사선이 조사된 생쥐의 간에서도 헤지호그의 발현증가가 관찰되었고, 이에 따른 간 줄기세포의 증식 및 EMT 유도, 콜라겐의 축적이 관찰되었다. 또한, 방사선이 조사된 암컷 생쥐의 간에서 헤지호그의 차별적 증가는 줄기세포 및 섬유화 증대로 연결되었고, 이는 방사선 민감성에 대한 성별차이를 설명할 수 있는 생물학적 근거가 될 수 있다. 그러나, 방사선에 의해 유도된 간 섬유화에 대한 연구결과들이 헤지호그를 비롯하여, 표면적인 결과보고만 있을 뿐, 섬유화 진행에 대한 구체적 기작을 밝히지 못하고 있다. 여러 간 질환진행에서 규명된 헤지호그 작용에 대한 지식을 방사선에 의해 유도된 간 섬유화를 이해하기 위한 기초자료로 활용하고, 사람에서의 방사선 부작용과 유사한 동물모델의 정립 및 헤지호그 역할을 직접적으로 규명할 수 있는 추가적 연구을 통해서, 간 섬유화 형성 기작을 이해할 수 있는 연구결과가 기대된다.

Keywords

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