| Co-Investigator(Kenkyū-buntansha) |
OSAME Mitsuhiro Kagoshima Univ.Faculty of Med.Professor, 医学部, 教授 (10041435)
KAMEYAMA Maski Kagoshima Univ.Faculty of Med.Professor, 医学部, 教授 (60150059)
KOBAYASHI Keiko Kagoshima Univ.Faculty of Med.Associate Professor, 医学部, 助教授 (70108869)
HORIUCHI Masahisa Kagoshima Univ.Faculty of Med.Research Associate, 医学部, 助手 (50264403)
TOMOMURA Mineko Kagoshima Univ.Faculty of Med.Research Associate, 医学部, 助手 (30217559)
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| Research Abstract |
Carnitine is an essential component for the oxidation of fatty acid in mitochondria Juvenile visceral steatosis (JVS) mice suffering from fatty liver, hyperammonemia and hypoglycaemia, discovered at Kanazawa University in 1988, were found to be carnitine-deficient. We described that the hyperammonemia is caused by the decrease of the urea cycle enzymes which results from suppressed transcription of the genes. Furthermore, we found that JVS mice show cardiac hypertrophy, too. In this study, we focused our researches on the pathogenesis and pathophysiology of JVS mice. The primary defect of JVS mice was in the transport of carnitine in the kidney, which was sodium-dependent with a high affinity for carnitine and was inhibited by carnitine analogues, D-carnitine and gamma-butyrobetaine. Large amounts of gamma-butyrobetaine were excreted in the urine of JVS mice. Since gamma-butyrobetaine is the direct precursor of carnitine biosynthesis and since the last step enzyme, gamma-butyrobetaine
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hydroxylase, was rather higher in JVS mice, we conclude that the biosynthesis pathway of carnitine is normal but secondarily defective due to defective reabsorption of the precursor in JVS mice. By the cooperative study with Kanazawa group, we mapped the jvs gene on chromosome 11, in the vicinity of microsatellite locus D11Mit31.
The suppressed expression of the urea cycle enzyme genes in JVS mice was accompanied with that of several other liver-specific enzyme or protein genes such as tyrosine aminotransferase and albumin. Those are all induced by glucocorticoid. Serum glucocorticoid levels of JVS mice were rather higher than tha controls and glucocorticoid receptor protein was abundant in the nuclear fraction. On the other hand, a nuclear transcription factor, AP-1, detected by gel-shift assay, was found to be very active in JVS mice and became activer during the weaning period. From these results, we reason that AP-1 interacts with glucocorticoid receptor and as the result, suppresses the induction by glucocorticoid of many genes. To connect the carnitine deficiency and AP-1 activation in the liver of JVS mice, we tested the effect of fatty acid and fatty acid+carnitine on the glucocorticoid induction of carbamylphosphate synthetase in the primary cultured hepatocytes. Long-chain unsaturated fatty acid, such as oleic acid and arachdonic acid, suppressed the induction of CPS by glucocorticoid. The suppression by fatty acids almost completely disappeared by the addition of carnitine, which suggests that the primary cultured hepatocytes can not metabolize long-chain fatty acid due to carnitine deficiency and mimic the situation of carnitine-deficient JVS mice. It seems that unsaturated long-chain fatty acids causes activation of AP-1. We found that some part of the cause of the cardiac hypertrophy was mediated by activation of catecholamine metabolism. The suppression of catecholamine metabolism by several inhibitors caused a partial suppression of cardiac hypertrophy. To clarify more precisely the pathophysiology of the cardiac hypertrophy, we adopted differential display for mRNAs expressed in normal and hypertrophied ventricles and found several unknown mRNA species expressed differently between the ventricles. Less
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