THE PERIPHERAL NERVOUS SYSTEM: A WINDOW INTO KRABBE DISEASE

Krabbe白质营养不良(KD)或球形细胞白质营养不良是一种严重的溶酶体储存 主要影响出生前几个月的婴儿的疾病，通常在几年内致命。 KD表现为易怒和运动退化，进展为全面衰退和因此而死亡 导致中枢和周围神经系统(CNS和PNS)脱髓鞘和神经变性。 KD是由于半乳糖基神经酰胺酶(GALC)的隐性突变所致，GALC是一种分解代谢的溶酶体酶 主要是髓鞘脂类、半乳糖神经酰胺和细胞毒性类神经氨酸。精神素会积聚 对髓鞘胶质细胞和神经元有毒性，导致脱髓鞘和神经变性 (精神病假说)。尽管髓鞘在KD中受到影响，但GALC存在于所有类型的细胞和其他细胞中 细胞，如神经元和巨噬细胞，可能是重要的，并参与疾病的早期。的确有 KD无法治愈，但造血干细胞移植(HSCT)可能通过以下方式改善症状 交叉校正：突变细胞摄取干细胞衍生物分泌的GALC。患者 接受HSCT最终恶化，可能是由于PNS交叉纠正不足所致。这并没有 经过实验评估，总的来说，PNS正在成为一个重要的KD组件， 并不是现有疗法的靶点。抽动症小鼠是这种疾病的自发模型 已被广泛使用，最近被用于显示造血干细胞移植、底物减少和基因治疗 有协同的有益作用，暗示了多种疾病机制。 尽管有这些进展，KD发病机制的许多基本方面仍不清楚。 例如，KD神经元和巨噬细胞是否以细胞自主的方式参与？是交叉的- 纠正有效，在体内所有类型的细胞中都会发生吗？是所有的细胞都产生精神病药，还是只有 某些细胞类型？除了精神药物毒性，还有其他机制吗？我们最近开发了 一种条件性Galc等位基因，并在中枢神经系统和三叉神经节的各种细胞类型中缺失Galc。在这 提案中，我们将使用PNS，由于其相对简单和解剖隔离，来回答 上面提出的基本问题。基于一组强有力的初步数据，我们假设交叉- 体内没有有效的纠正，髓鞘胶质细胞产生精神素，并且删除 GALC在每种细胞类型中都有细胞自主效应，可能是通过干扰溶酶体功能和 自噬。我们的结果将揭示PNS生物学的基本方面，并有助于理解 KD的发病机制和造血干细胞移植的局限性，将有助于更好地发展KD 治疗KD和其他溶酶体、神经退行性和脱髓鞘疾病。

Krabbe leukodystrophy (KD) or Globoid Cell Leukodystrophy is a severe lysosomal storage disorder that mainly affects infants in the first months of life and is usually fatal within a couple of years. KD presents with irritability and motor deterioration, which progresses to overall decline and death due to demyelination and neurodegeneration in the central and peripheral nervous system (CNS and PNS). KD is due to recessive mutations in galactosylceramidase (GALC) a lysosomal enzyme that catabolizes the major myelin lipid galactosylceramide and the cytotoxic lipid psychosine. Psychosine accumulates in patients and is toxic to myelinating glia and neurons causing demyelination and neurodegeneration (psychosine hypothesis). Although myelin is affected in KD, GALC is present in all cell types and other cells, such as neurons and macrophages, may be important and involved early in the disease. There is no cure for KD, but Hematopoietic stem cell transplantation (HSCT) improves symptoms presumably by cross-correction: the uptake by mutant cells of GALC secreted by stem cell-derivatives. Patients who receive HSCT eventually deteriorate, possibly due to insufficient PNS cross-correction. This has not been evaluated experimentally and in general the PNS is emerging as an important KD component that is not targeted by available therapies. The Twitcher mouse is a spontaneous model of the disease that has been used extensively and recently used to show that HSCT, substrate reduction and gene therapy have synergistic beneficial effects, suggesting multiple disease mechanisms. Despite these advancements, many fundamental aspects of KD pathogenesis are still unknown. For example, are KD neurons and macrophages involved in a cell autonomous manner? Is cross- correction efficient and does it occur in all cell types in vivo? Do all cells produce psychosine, or only certain cell types? Besides psychosine toxicity, are other mechanisms involved? We recently developed a conditional Galc allele and have deleted Galc in various cell types in the CNS and PNS. In this proposal, we will use the PNS, due to its relative simplicity and anatomical isolation, to answer the fundamental questions raised above. Based on a strong set of preliminary data, we postulate that cross- correction does not occur efficiently in vivo, that myelinating glia produce psychosine, and that deleting GALC has a cell autonomous effect in each cell type, likely by perturbing lysosomal function and autophagy. Our results will reveal fundamental aspects of PNS biology and help to understand the pathomechanisms of KD and the limitations of HSCT, which will allow the development of better therapies for KD and other lysosomal, neurodegenerative and demyelinating diseases.