Development of therapies in polyglutamine diseases using hepatocyte growth factor (HGF)

脊髓和球性肌萎缩症（SBMA）是一种遗传性运动神经元疾病。SBMA的分子基础是雄激素受体（Alt）基因中编码聚谷氨酰胺（polyQ）通道的三核苷酸CAG重复序列的扩增。我们在巨细胞病毒增强子和鸡β-肌动蛋白启动子的控制下，建立了表达含有24或97个CAG重复序列的全长人AR的转基因小鼠模型（AR- 97q小鼠）。肝细胞生长因子（HGF）最初被鉴定并克隆为成熟肝细胞的有效丝裂原。随后的研究表明，HGF通过与c-Met受体酪氨酸激酶（c-Met）结合，在包括神经元在内的多种细胞中发挥多种生物学作用，包括有丝分裂、运动发生、形态发生和抗凋亡活性。HGF是最有效的体外和体内神经元存活促进因子之一。例如，HGF的神经营养作用已在培养的海马神经元和培养的胚胎脊髓运动神经元中得到证实，其在运动神经元中的抗凋亡活性与胶质细胞系来源的神经营养因子（GDNF）相当。在本研究中，我们使用过表达突变的人AR和HGF的双转基因小鼠来检测HGF对运动功能障碍的影响。我们将AR-97Q小鼠与过表达HGF的小鼠杂交。双转基因小鼠的运动功能、体重、寿命均有改善。HDF的过表达也改善了去势雄性AR-97Q小鼠的运动功能。这些发现表明，HGF过表达可改善小鼠SBMA表型。

Spinal and bulbar muscular atrophy(SBMA) is an inherited motor neuron disease. The molecular basis of SBMA is the expansion of a trinucleotide CAG repeat, which encodes the polyglutamine(polyQ) tract, in the androgen receptor(Alt) gene. We generated transgenic mouse model expressing the full-length human AR containing either 24 or 97 CAG repeats under the control of a cytomegalovirus enhancer and a chicken β-actin promoter(AR-97Q mice). Hepatocyte growth factor(HGF) was initially identified and molecularly cloned as a potent mitogen for mature hepatocytes. Subsequent studies revealed that HGF exerts multiple biological effects, including mitogenic, motogenic, morphogenic, and anti-apoptotic activities in a wide variety of cells, including neurons, by binding to the c-Met receptor tyrosine kinase(c-Met). HGF is one of the most potent in vitro and in vivo survival-promoting factors for neurons. For example, neurotrophic effects of HGF have been demonstrated in cultured hippocampal neurons and in cultured embryonic spinal motoneurons, and its anti-apoptotic activity in motoneurons is comparable to that of glial cell line-derived neurotrophic factor(GDNF). In the present study, the effects of HGF on motor dysfunction were examined using double transgenic mice overexpressing mutated human AR and HGF. We cross-bred AR-97Q mice with mice over-expressing the HGF. The double transgenic mice showed improvement of their motor function, body weight, lifespan. Overexpression of HDF also ameliorated motor function in the castrated male AR-97Q mice. These findings suggest that HGF over-expression ameliorates SBMA phenotypes in mice.