Alternate Galactose Pathways in GALT-Deficient Mice

半乳糖-1-磷酸尿苷转移酶(GALT)缺乏引起的人类半乳糖血症是一种谜一样的疾病。限制半乳糖饮食，虽然减轻了新生儿半乳糖毒性，但并不能预防以后的并发症、认知障碍、卵巢衰竭和神经性共济失调。饮食疗法的无效促使人们积极努力了解该病的病理生物化学基础，以开发新的治疗策略。对受影响患者的临床研究的局限性促使构建了一种“敲除”小鼠，其中GALT基因的一部分已被删除，从而消除了GALT酶的活性。然而，这些动物不会表现出人类的表型，即使喂食半乳糖也没有表现出半乳糖毒性的证据。这表明，缺乏高尔特是必要的，但不足以导致疾病。显然，GalT基因突变以外的其他因素也起着重要作用。高尔特基因敲除小鼠提供了一个有价值的体内试管，以确定为什么这些动物没有发展出人类的表型的代谢解释。这项建议的目的是研究两种可能性：第一，没有足够的代谢产物半乳糖醇的形成，它与半乳糖-1-磷酸一起是产生人类表型所必需的；第二，有一条强大的替代途径来处理半乳糖。这些将通过以下方式进行研究：1)基因操作，以构建表达人类醛糖还原酶的转基因小鼠，当与GALT缺乏的动物饲养时，将形成高水平的半乳糖醇和半乳糖-1-磷酸以及人类的表型；以及，2)利用同位素半乳糖和复杂的分析技术大力研究代谢途径。通过辨别为什么高尔特基因敲除的小鼠没有表现出人类半乳糖血症的表型，将获得对人类状况的巨大洞察力。

Human galactosemia due to deficiency of galactose-1- phosphate uridyltransferase (GALT) is an enigmatic disease. A galactose restricted diet although alleviating neonatal galactose toxicity does not prevent later complications, cognitive impairment, ovarian failure and neurologic ataxia. The inefficacy of diet therapy has mandated a vigorous effort to understand the pathobiochemical basis of the disease in order to develop new therapeutic strategies. The limitations of clinical studies of affected patients prompted the construction of a "knock-out" mouse where a portion of the GALT gene has been deleted thereby eliminating GALT enzyme activity. These animals, however, do not develop the human phenotype and show no evidence of galactose toxicity even when fed galactose. This suggests that the absence of GALT is necessary but not sufficient to produce disease. It appears obvious that factors other than the GALT gene mutation play an important role. The GALT knock-out mouse provides a valuable in vivo test tube to determine the metabolic explanation why these animals do not develop the human phenotype. The aim of this proposal is to examine two possibilities: first, that there is insufficient formation of the metabolite, galactitol, which together with galactose-1-phosphate is necessary to produce the human phenotype; and, second, that there is a robust alternate pathway for galactose disposal. These will be studied by: 1) genetic manipulation to construct a transgenic mouse which expresses human aldose reductase and, when bred with the GALT-deficient animal, will form high levels of galactitol as well as galactose- 1-phosphate and a human phenotype; and, 2) vigorous investigation of metabolic pathways employing isotopic galactose and sophisticated analytic techniques. Great insight into understanding the human condition will be gained by discerning why the GALT knock-out mouse does not exhibit the human galactosemic phenotype.