C9ORF72 in Motor System Biology and ALS

描述（由申请人提供）：最近在相当一部分肌萎缩性侧索硬化症（ALS）患者中发现了C9ORF72的六核苷酸重复扩增。然而，这种突变是通过功能获得还是功能丧失机制起作用仍有待确定。解决这一问题对于设计和实施对抗ALS中这种突变影响的治疗方法的长期努力至关重要。作为初步数据，我们提供的证据表明，携带C9ORF72同源基因功能缺失突变的杂合子和纯合子小鼠都可以存活，存活到成年，并且最初表现出与野生型幼崽相似的运动系统功能。然而，随着杂合动物年龄的增长，我们发现它们的死亡率显着增加。杂合子动物的死亡与运动功能下降和瘫痪相关，并伴有肌肉萎缩、去神经支配和运动神经变性。纯合子突变动物表现出类似但加速和数量上更严重的表型。我们的初步研究表明，C9ORF72在哺乳动物运动系统的长期维持中起着重要的剂量依赖作用。这些发现支持了一种假设，即许多患者所携带的重复扩增导致的C9ORF72功能降低和单倍功能不全直接导致了ALS的发展。在这里，我们提出三个目标，以增加对C9ORF72在运动神经元变性生物学中所起作用的理解。首先，我们将确定携带C9ORF72同源基因功能丧失突变的小鼠的运动神经元变性特征在多大程度上与ALS中观察到的特征一致。这些研究将使我们能够确定我们所产生的小鼠在多大程度上可能作为机械和药物发现研究的小鼠模型。其次，我们将确定C9ORF72同源突变动物的运动神经元变性是通过运动神经元中的细胞自主机制发生的，还是由于突变免疫细胞的非自主影响。第三，我们将确定通过C9ORF72重复扩增在患者源性运动神经元中发现的转录变化在多大程度上可以通过C9ORF72基因产物的功能丧失来解释。如果获得资助，我们的研究将对C9ORF72基因产物的缺失在多大程度上导致运动神经元退化提供重要的见解。

DESCRIPTION (provided by applicant): A hexanucleotide repeat expansion at C9ORF72 has recently been found in a significant fraction of patients suffering from Amyotrophic Lateral Sclerosis (ALS). However, it remains to be determined whether this mutation acts through a gain of function or loss of function mechanism. Resolving this issue is essential for long term efforts to design and implement therapies that counteract the effects of this mutation in ALS. As preliminary data, we provide evidence that heterozygous and homozygous mice harboring a loss of function mutation in the ortholog of C9ORF72 are viable, survive to adulthood and initially display motor system functionality similar to their wild type littermates. However, as heterozygous animals aged, we found they displayed a significantly increased rate of mortality. Death in heterozygous animals was associated with declining motor function and paralysis that were accompanied by muscle atrophy, denervation and motor nerve degeneration. Homozygous mutant animals displayed a similar but accelerated and quantitatively more severe phenotype. Our preliminary studies suggest that C9ORF72 serves an important dose dependent function in the long-term maintenance of the mammalian motor system. These findings support the hypothesis that reduced C9ORF72 function and haploinsufficiency resulting from the repeat expansion that many patients harbor contributes directly to the development of ALS. Here we propose three aims to increase understanding of the role that C9ORF72 plays in the biology of motor neuron degeneration. First, we will determine the extent to which features of motor neuron degeneration in mice harboring a loss of function mutation in the C9ORF72 ortholog are consistent with those observed in ALS. These studies will allow us to determine to what extent the mice we have generated might have utility as a mouse model for both mechanistic and drug discovery studies. Second, we will determine whether motor neuron degeneration in C9ORF72 ortholog mutant animals occurs through cell autonomous mechanisms in motor neurons, or is due to the non-autonomous influence of mutant immune cells. Third, we will determine the extent to which transcriptional changes found in patient derived motor neurons by the C9ORF72 repeat expansion can be explained by loss of function of the C9ORF72 gene product. If funded, our studies will provide important insight into the extent to which loss of the C9ORF72 gene product contributes to motor neuron degeneration.