Pathogenesis informs therapy in the GM1 and GM2 Gangliosidoses

GM2神经节苷脂增多症、Tay-Sachs病和Sandhoff病分别是由于HEXA和HEXB基因突变引起的异构体溶酶体水解酶β-己氨酸酶A的酶缺陷引起的。这些常染色体隐性遗传病是从婴儿期到晚发型或成年型的连续体，表型是基于残留酶活性的量，而残留酶活性又由HEXA或HEXB基因的特定突变决定。所有亚型都以进行性神经变性为特征，婴儿形式的疾病在4-6个月起病，发育停止，然后迅速下降，12个月前出现顽固性癫痫发作，24个月后发展为植物人状态。3至6岁的死亡通常是由于吸入性肺炎。GM2神经节苷脂增多症的任何亚型都没有有效的治疗方法。 该项目旨在了解神经节苷脂储存对GM2神经节苷脂沉积症患者大脑发育的最早影响。我们推测，我们的工作将对这些破坏性疾病的治疗类型和时机产生影响。 自20世纪70年代中期以来，人们就知道，早在怀孕中期，患者大脑中就可以看到GM2的存储。然而，储存对早期大脑发育的影响还没有正式研究过。 我们对两个患有TSD的17周妊娠胎儿和年龄匹配的对照组织的4个脑区进行了Transciptome分析。我们的初步结果表明，TSD大脑缺乏神经元突触发生的转录本，这与我们之前的发现一致，即从婴儿Sandhoff病患者的iPS细胞中提取的人脑器官缺乏神经元分化。大脑器官，其表达谱对应于人类发育的前三个月，也显示出神经元增殖的差异。桑德霍夫病的细胞器明显大于正常对照的细胞器，并表现出更大程度的神经元增殖。这很有趣，因为桑德霍夫(和泰-萨克斯)的婴儿有进行性的巨脑。 利用GM2神经节苷脂沉积症动物模型(小鼠、猫和绵羊)的胎儿组织，在妊娠的特定时间点，我们计划使用一种新的技术，空间转录组学，来探索与对照组相比，特定年龄和地区的基因表达差异。 TSD婴儿早期脑发育的显著差异将对治疗的类型和时机产生明显的影响。我们的研究表明，即使在新生儿期就开始治疗，可能也不足以改变婴儿发病疾病的结果。尽管如此，针对婴儿泰-萨克斯病和桑德霍夫病的基因疗法的研究新药申请最近已经提交，试验要么正在进行中，要么在未来几个月开始登记。了解溶酶体储存对产前神经发育的影响将提高我们对疾病发病机制的理解，并可能建议替代的治疗时机或方法。

The GM2 gangliosidoses, Tay-Sachs disease and Sandhoff disease are caused by enzyme deficiency of the heteromeric lysosomal hydrolase beta-hexoaminidase A due to mutations in the HEXA and HEXB genes respectively. These autosomal recessive diseases are a continuum from infantile onset to late or adult-onset and phenotype is based on the amount of residual enzyme activity which is in turn determined by specific mutations in the HEXA or HEXB genes. All subtypes feature progressive neurodegeneration and the infantile forms of the diseases have onset of symptoms by 4-6 months with developmental arrest and then rapid decline and onset of intractable seizures before 12 months with progression to a vegetative state by 24 months. Death between 3 and 6 years is typically due to aspiration pneumonia. There are no effective therapies for any of the subtypes of the GM2 gangliosidoses. This project aims to understand the earliest impact of ganglioside storage on brain development in patients with GM2 gangliosidosis. We postulate that our work will have implications for the type and timing of therapy for these devastating disorders. It has been known since the mid-1970s that GM2 storage in the brains of affected patients can be seen as early as the second trimester of gestation. However, the impact of storage on early brain development has not been formally studied. We have performed transciptome analysis on 4 brain regions from two 17-week gestation fetuses with TSD and age-matched control tissues. Our preliminary results show that TSD brains are deficient in transcripts of neuronal synaptogenesis and align with our previous findings of lack of neuronal differentiation in human cerebral organoids derived from iPS cells from a patient with infantile Sandhoff disease. Cerebral organoids, whose expression profile corresponds to the first trimester of human development, also show differences in neuronal proliferation. Sandhoff disease organoids are significantly larger than normal control organoids and show a greater degree of neuronal proliferation. This is interesting, as Sandhoff (and Tay-Sachs) infants have progressive megalencephaly. Using fetal tissues from animal models of GM2 gangliosidosis (mice, cats, and sheep) at defined points in gestation we plan to employ a new technology, spatial transcriptomics, to probe age- and region-specific differences in gene expression compared to controls. Significant differences in early brain development of TSD infants will have obvious implications for type and timing of therapy. Our studies suggest that treatment initiated even in the newborn period may be insufficient to modify outcome in infantile onset disease. Despite this, investigational new drug applications for gene therapy for infantile Tay-Sachs and Sandhoff diseases have been recently filed and trials are either in progress or commencing enrollment in the coming months. Understanding the impact of lysosomal storage on neural development prenatally will improve our understanding of disease pathogenesis and may suggest alternative timing or approaches to therapy.