백서를 수유식이에서 이유식이로 전환시 간장 세포내 지방산 합성효소 증가 기전

Abstract

[한글]

본 연구는 수유식이에 있는 백서를 생후 21일에 무지방 고함수탄소 식이로 이유시켜 식이 조성이 간장 세포내 지방산 합성 효소 및 이를 합성하는 mRNA 함량 조절에 미치는 기전을 밝히고자 하였다. 이를 위하여 이유식이 투여 후 날짜별로 백서 간장 세포내 지방산 합성 효소 함량과 이 효소를 합성하는 mRNA 함량을 정량하고, 각 군의 백서 간장에서 핵을 분리하여 지방산 합성 효소의 mRNA 전사활성 및 이 효소의 mRNA efflux 활성을 정량하였다. 또한, 효소 생합성 활성을 정량하기 위하여 각 군의 백서 복강내로 [(3)**H]-leucine을 주입한 후 간장을 적출하여 세포질내 지방산 합성 효소를 정제 분리하고 방사능 동위원소 활성치를 측정하였으며, 세포질내 효소 함량과 생합성 활성치를 비교하여 다음과 같은 결과를 얻었다.

이유식이 투여 후 2일에 지방산 합성 효소 함량이 급격히 증가하여 9일까지 날짜가 경과함에 따라 증가하고, 14일에는 급격히 감소하였다. 세포질내 지방산 합성 효소의 mRNA 함량은 식이투여 후 2일에 급격히 증가하였으며 4일에는 약간 감소 현상을 보였으나, 7일

에 최고치에 달하였고 9일에는 2일군과 유사하게 유지하다가 14일에는 급격히 감소하여 이유식이 투여 전과 같은 수치를 유지하였다. 핵내에서 지방산 합성 효소의 mRNA 전사 활성은 이유식이를 투여한 후 2일에 급격히 증가하고 4일에는 약간 증가하다가 7일과 9일에 최고의 활성을 유지하였으나,14일에는 급격히 감소하여 이유식이 투여 전과 비슷하였다.

핵으로부터 지방산 합성 효소의 mRNA efflux 활성은 이유식이를 투여한 후 2일에 급격히 증가하여 7일까지 같은 활성도를 유지하였으며, 9일과 14일에는 약간 감소하였다.

또한 지방산 합성 효소 생합성 활성치는 이유식이 투여 후 2일과 4일에 각각 9%와 10%의 증가를 유지하다가 7일에 42%로 급격히 증가하였고 9일에 13% 증가된 상태를 유지하였으나, 14일에는 이유식이로 바꾸기 전의 활성치를 유지하였다.

이상과 같은 실험갈과로 미루어 간장 세포질내 지방산 합성 효소 함량은 세포질내 mRNA 함량 증가와 병행하여 증가되고, mRNA 함량 증가는 주로 mRNA 전사 활성에 의하여 조절되며, mRNA efflux 활성은 세포질내 mRNA 함량 조절에 일부 작용하는 것으로 사료된다.

이유식이 투여 후 날짜가 경과함에 따라 효소 함량이 증가되는 원인은 일차적으로 효소 생합성 증가와 밀접한 관계가 있고, 이차적으로는 합성된 효소의 축적에 의한 결과로 사료된다.

Mechanisms of increase in fatty acid synthase in the rat liver during the suckling-

weaning transition.

Soh Yeon Kim

Department of Medical Science The Graduate School, Yonsei University

(Directed by Professor Yoon Soo Kim)

This study was designed to understand the mechanisms by which fatty acid synthase

increases in the liver cytosol when the rat is weaned at day 21 of age and fed a

high carbohydrate diet. The amount of fatty acid synthase, its mRNA, mRHA

transcriptional activity and mRNA efflux activity from the nucleus of the liver

were measured at 2, 4, 7, 9 and 14 days after the weaning. In order to quantify the

rates of biosynthetic activity of fatty acid synthase, [(3)**H]-leucine was

injected into the peritoneal cavity of rats in each group. After 30 min, the liver

cytosol was extracted and the radioactivities were counted. The rate of

biosynthetic activity and the amount of the enzyme in the liver of rats in each

group were compared to understand the mechanisms of enzyme regulation.

The amount of enzyme increased rapidly at 2nd day after weaning followed by

gradual increments until 9th day after weaning then dropped rapidly at 14th day.

The amount of mRNA of fatty acid synthase within the cytosol increased rabidly at

2nd day after weaning, decreased slightly at 4th day, reached its maximum level at

7th day, showed a similar level of 2nd day at 9th day and decreased rapidly at 14th

day. The transcriptional activity of mRNA in the nucleus rose rapidly at 2nd day

after weaning, rose slightly at 4th day, maintained maximal activity at 7th and 9th

day and fell sharply at 14th day. mRNA efflux activity from the nucleus rose

sharply at 2nd day after weaning and maintained a stable rate of efflux until 7th

day then fell slightly on 9th and 14th day after weaning. The biosynthetic rate of

fatty acid synthase was increased 9% at 2nd day, 10% at 4th day, 42% at 7th day,

13% at 9th day followed by a similar level to the preweaning state at 14th day

after weaning. In conclusion, the amount of fatty acid synthase in the liver

cytosol was reflected by the amount of fatty acid synthase mRNA in the cytosol, and

the increase in the amount of mRNA in the cytosol was regulated by the

transcriptional activity together with the mRNA efflux activity that may partially

control the amount of mRNA within the cytosol. The increments in the amount of

enzyme after weaning was closely related primarily to the rate of biosynthesis of

the enzyme and secondarily to the accumulation of the enzyme.

[영문]

This study was designed to understand the mechanisms by which fatty acid synthase increases in the liver cytosol when the rat is weaned at day 21 of age and fed a high carbohydrate diet. The amount of fatty acid synthase, its mRNA, mRHA transcriptional activity and mRNA efflux activity from the nucleus of the liver

were measured at 2, 4, 7, 9 and 14 days after the weaning. In order to quantify the rates of biosynthetic activity of fatty acid synthase, [(3)**H]-leucine was injected into the peritoneal cavity of rats in each group. After 30 min, the liver cytosol was extracted and the radioactivities were counted. The rate of

biosynthetic activity and the amount of the enzyme in the liver of rats in each group were compared to understand the mechanisms of enzyme regulation.

The amount of enzyme increased rapidly at 2nd day after weaning followed by gradual increments until 9th day after weaning then dropped rapidly at 14th day.

The amount of mRNA of fatty acid synthase within the cytosol increased rabidly at 2nd day after weaning, decreased slightly at 4th day, reached its maximum level at 7th day, showed a similar level of 2nd day at 9th day and decreased rapidly at 14th day. The transcriptional activity of mRNA in the nucleus rose rapidly at 2nd day after weaning, rose slightly at 4th day, maintained maximal activity at 7th and 9th day and fell sharply at 14th day. mRNA efflux activity from the nucleus rose sharply at 2nd day after weaning and maintained a stable rate of efflux until 7th

day then fell slightly on 9th and 14th day after weaning. The biosynthetic rate of fatty acid synthase was increased 9% at 2nd day, 10% at 4th day, 42% at 7th day, 13% at 9th day followed by a similar level to the preweaning state at 14th day after weaning. In conclusion, the amount of fatty acid synthase in the liver

cytosol was reflected by the amount of fatty acid synthase mRNA in the cytosol, and the increase in the amount of mRNA in the cytosol was regulated by the transcriptional activity together with the mRNA efflux activity that may partially control the amount of mRNA within the cytosol. The increments in the amount of enzyme after weaning was closely related primarily to the rate of biosynthesis of the enzyme and secondarily to the accumulation of the enzyme.