Protein Prenylation and Progeria

描述(由申请人提供)：包括Hutchinson-Gilford早衰症(HGPS)在内的几种孕激素紊乱是由于缺陷导致法尼基-前层素A在核缘堆积引起的。法尼基-前层素A的积累导致培养细胞的细胞核严重畸形。我们提出前层蛋白A的法尼化形式对细胞是有毒的，并预测抑制蛋白法尼化将减少核畸形的频率并改善疾病表型，这是我们实验室建立的两个早衰症小鼠模型，Zmpste24缺陷小鼠和HGPS杂合子小鼠(Lmna HG/+)。这些关于蛋白质法尼化重要性的预测得到了支持：法尼基转移酶抑制剂(FTI)减少了培养细胞中畸形细胞核的频率，并改善了两种早衰症小鼠模型的疾病表型。这些研究令人欣慰，因为它们表明FTI可能对治疗患有HGPS的人类有效。然而，这些研究给我们留下了关于FTI改善疾病表型的机制的重要问题。FTI治疗在改善疾病表型方面是明确有效的，但它对小鼠前层蛋白A的处理只有很小的影响。因此，如何解释疾病表型的改善？一种可能性是，对Prelamin A法尼化的极小影响足以改善疾病表型；另一种可能性是FTIs可以独立于其对Prelamin A加工的影响来改善疾病。我们的第一个目标将是通过分析其他基因靶向的小鼠模型和更好地定义FTI对体内前板层蛋白A代谢的影响来详细研究这一问题。我们的第二个目标将是进一步检验我们的HGPS小鼠的一个意想不到的发现--与Lmna HG等位基因相关的核形状异常和疾病表型可以通过减少野生型lamin A的合成(通过将Lmna HG/+小鼠中的野生型Lmna等位基因替换为“纯lamin C”等位基因)来显著减少。对这一发现的一种解释是，野生型前层蛋白A(或层蛋白A)会恶化衰老，而层蛋白C不会。在接下来的几年里，我们将通过检测Lmna HG等位基因对疾病表型和核力学的影响来详细研究这一概念，其中Lmna HG等位基因存在于“仅有lamin C”等位基因和“仅有lamin A”等位基因的存在。我们的第三个目标将探索非法尼化的前层蛋白A的生理影响。用FTI治疗早衰症将导致非法尼化的前层蛋白A的积累(来自野生型Lmna等位基因)。这种异常蛋白质的性质以及它是否表现出自己的毒性尚不清楚。我们将通过分析非法尼化前层蛋白A纯基因小鼠并检查层蛋白蛋白对细胞和组织生理学的影响来解决这个问题。公共卫生相关性拟议的研究将定义细胞核结构蛋白的突变如何导致早衰或早衰症。将建立新的小鼠模型来研究疾病的发展并测试新的治疗方法。

DESCRIPTION (provided by applicant): Several progeroid disorders, including Hutchinson-Gilford progeria syndrome (HGPS), are caused by defects that lead to the accumulation of farnesyl-prelamin A at the nuclear rim. The accumulation of farnesyl-prelamin A causes grossly misshapen nuclei in cultured cells. We proposed that the farnesylated form of prelamin A is toxic to cells and predicted that inhibiting protein farnesylation would reduce the frequency of misshapen nuclei and ameliorate disease phenotypes in a pair of progeria mouse models created in our laboratory, Zmpste24-deficient mice and mice heterozygous for a HGPS "knock-in" mutation (LmnaHG/+). These predictions regarding the importance of protein farnesylation were upheld: farnesyltransferase inhibitors (FTIs) reduced the frequency of misshapen nuclei in cultured cells and also ameliorated disease phenotypes in both of the progeria mouse models. These studies have been gratifying because they have suggested that FTIs could be efficacious for treating humans with HGPS. However, these studies left us with important questions regarding the mechanisms by which FTIs improve disease phenotypes. The FTI treatment was unequivocally efficacious in ameliorating disease phenotypes, yet it had only a small effect on prelamin A processing in mice. How, therefore, can an improvement in disease phenotypes be explained? One possibility is that an extremely small effect on prelamin A farnesylation is sufficient to ameliorate disease phenotypes; another is that FTIs could ameliorate disease independently of their effect on prelamin A processing. Our first aim will be to examine this issue in detail, by analyzing additional gene-targeted mouse models and by better defining the effects of FTIs on prelamin A metabolism in vivo. Our second aim will be to further examine an unexpected finding in our HGPS mice-that the nuclear shape abnormalities and disease phenotypes associated with the LmnaHG allele can be reduced significantly by decreasing the synthesis of wild-type lamin A (by replacing the wild-type Lmna allele in the LmnaHG/+ mice with a "lamin C-only" allele). One interpretation of this finding is that wild-type prelamin A (or lamin A) worsens progeria, while lamin C does not. During the next few years, we will examine this concept in considerable detail by examining the impact of the LmnaHG allele in the presence of both a "lamin C-only" allele and a "lamin A-only" allele on disease phenotypes and nuclear mechanics. Our third aim will explore the physiological impact of nonfarnesylated prelamin A. Treatment of progeria with an FTI will lead to the accumulation of nonfarnesylated prelamin A (from the wild-type Lmna allele). The properties of this abnormal protein and whether it exhibits its own toxicities are unknown. We will address this issue by analyzing nonfarnesylated prelamin A-only mice and examining the impact of the lamin protein on cell and tissue physiology. PUBLIC HEALTH RELEVANCE The proposed studies will define how mutations in structural proteins of the nucleus cause premature aging, or progeria. New mouse models will be created to study the development of disease and to test a new therapeutic approach.