Journal of Life Science (생명과학회지)

Korean Society of Life Science (한국생명과학회)
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Expression Pattern of Kir6.2 in Skeletal Muscle Cells of Patients with Familial Hypokalemic Periodic Paralysis

가족성 저칼륨성 주기성마비 환자의 골격근 세포내 Kir6.2의 발현 및 분포 양상

  • Kim, Sung-Jo (Department of biotechnology, Hoseo University) ;
  • Yoon, Dong-Ho (Department of biotechnology, Hoseo University) ;
  • Kim, June-Bum (Department of Pediatrics, Konyang University College of Medicine)
  • 김성조 (호서대학교 생명공학과) ;
  • 윤동호 (호서대학교 생명공학과) ;
  • 김준범 (건양대학교 의과대학 소아청소년과)
  • Received : 2009.12.10
  • Accepted : 2010.03.04
  • Published : 2010.03.30
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Abstract

Familial hypokalemic periodic paralysis (HOKPP) is an autosomal dominant disorder characterized by reversible flaccid paralysis and intermittent hypokalemia. Although it has been reported that decreased activity in the $K_{ATP}$ channels of the skeletal muscle cell membrane plays a role in the pathogenesis of HOKPP, a clear mechanism has not yet been established. This study aimed to investigate the molecular biological mechanism underlying the decreased activity of $K_{ATP}$ channels in the skeletal muscles of familial HOKPP patients by studying the levels of the $K_{ATP}$ channel subunit Kir6.2. We found that when cells obtained from healthy individuals (normal cells) and HOKPP patients (patient cells) were treated with 4 mM potassium buffer, there was no quantitative change in the KCNJ11 mRNA levels and no difference in the Kir6.2 protein expression in the cytosol and cell membrane. On the other hand, when 1 mM potassium buffer was used, normal cells showed decreased expression of KCNJ11 mRNA as well as decreased expression of Kir6.2 protein in the cell membrane. However, patient cells treated with the same buffer showed no quantitative change in the levels of KCNJ11 mRNA or in the levels of Kir6.2 protein in the cytosol and cell membrane. Thus, in HOKPP patients, the Kir6.2 protein cannot be transported from the cell membrane to the cytosol, leading to closure of the $K_{ATP}$ channels, induction of depolarization, and subsequently, to the paralytic symptoms observed in the patient. Our findings thus provide new insights into the pathogenesis of HOKPP.

가족성 저칼륨성 주기성마비는 간헐적으로 발생하는 저칼륨혈증을 동반한 가역적 이완성 근육마비를 특정으로 하는 상염색체 우성 유전질환이다. 골격근 세포막에 위치한 $K_{ATP}$ 채널의 활성도 감소가 저칼륨성 주기성 마비의 발병과 관련 있는 것으로 보고되고 있으나 아직까지 명확한 기전이 밝혀져 있지 않다. 본 연구에서는 $K_{ATP}$ 채널을 구성하는 단위체인 Kir6.2를 대상으로 가족성 저칼륨성 주기성마비 환자의 골격근 세포에서 $K_{ATP}$ 채널의 활성도 감소가 발생하는 분자생물학적 기전을 알아보고자 하였다. 환자와 정상인의 골격근 세포내 Kir6.2 단위체의 유전자인 KCNJ11 의 mRNA발현 수준과 단백질 발현양상을 확인한 결과, 정상 세포외 칼륨 농도인 4mM 칼륨 완충용액에 노출된 경우 KCNJ11 mRNA와 단백질 수준의 정량적 차이는 관찰되지 않았다. 그러나 환자에서 마비를 유발할 수 있는 저칼륨 농도인 1mM의 칼륨 완충용액에 노출시킨 경우 정상세포는 KCNJ11 mRNA의 발현이 감소하였고, 그 산물인 Kir6.2 단백질의 정량적 차이를 확인한 결과 세포막에 존재하는 단백질의 양 또한 유의하게 감소하였다. 그러나 환자의 경우 1mM의 칼륨 완충용액에 노출시 KCNJ11 mRNA 발현수준에 차이가 없었고, 더불어 세포막과 세포질 상의 Kir6.2 단백질 분포에도 변화가 나타나지 않았다. 이는 환자 세포의 경우 세포막 단백질이 세포질로 회수되지 못하여 $K_{ATP}$ 채널의 폐쇄가 유지되어 탈분극이 지속되며 이로 인해 환자에서 마비 증상을 유발할 수 있음을 시사하는 결과로 본 질환의 새로운 발병 기전을 설명할 수 있는 근거로 생각된다.

Keywords

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