Elucidating mechanisms involved in Lamin B1 mediated demyelination

 描述(申请人提供)：常染色体显性遗传性白血病(ADLD)是一种致命的进行性成人起病，以自主神经和运动功能障碍为特征，伴有广泛的中枢神经系统脱髓鞘。我们以前已经证明，ADLD是由lamin b1基因的复制引起的，lamin b1的表达增加是疾病过程的基础。在真核细胞中，层蛋白B1是核层的主要组成部分，核层是靠近内核膜的纤维网络。核层维持细胞核的结构完整性，并在转录、DNA复制、DNA修复和表观遗传调节等基本细胞过程中发挥作用。我们最近证实，少突胶质细胞特异性过表达lamin B1的转基因(TG)小鼠表现出严重的脊髓空泡脱髓鞘，导致与年龄相关的退行性表型，使人联想到ADLD。TG脊髓中与脂质合成有关的多个基因的表达显著减少，包括关键的生脂转录因子SREBP1和2。伴随而来的是脊髓少突胶质细胞中抑制性组蛋白标记H3K9me3和H3K27me3的整体增加。由于髓鞘由~70%的脂质组成，脂质合成缺陷可导致严重的脱髓鞘。与我们的基因表达数据一致，我们观察到脊髓白质特有的富含髓鞘的脂质显著减少。我们的结果发现，脂合成缺陷是层蛋白B1过度表达引起的脱髓鞘的主要成分，并提示层蛋白B1与脂代谢之间存在新的联系。虽然脂质失调提供了一个令人信服的框架来解释在转基因小鼠中观察到的脱髓鞘现象，但将Lamin B1过度表达与少突胶质细胞中的脂质合成联系起来的机制尚不清楚，本建议旨在确定这些途径。我们将验证Lamin B1调节抑制性组蛋白标记以下调特定靶基因表达的假设，并检查Lamin B1在少突胶质细胞中的过度表达是否会导致特定途径的失调，从而可能影响少突胶质细胞的功能。我们还将确定调节lamin B1水平如何影响疾病表型。我们提出的实验将阐明Lamin B1过度表达、脂质失调和脱髓鞘表型之间的联系机制，这些结果将对识别ADLD的治疗途径至关重要。此外，他们还将提供对少突胶质细胞功能的基本生物学的见解，这可能有助于理解其他常见的脱髓鞘疾病，如多发性硬化症。

 DESCRIPTION (provided by applicant): Autosomal Dominant Leukodystrophy (ADLD) is a fatal, progressive adult-onset disease characterized by autonomic and motor dysfunction with widespread CNS demyelination. We have previously shown that ADLD is caused by duplications of the lamin b1 gene and that increased expression of lamin B1 underlies the disease process. In eukaryotic cells, lamin B1 is a major constituent of the nuclear lamina, a fibrous meshwork adjacent to the inner nuclear membrane. The nuclear lamina maintains the structural integrity of the nucleus and has roles in essential cellular processes including transcription, DNA replication, DNA repair, and epigenetic regulation. We have recently demonstrated that transgenic (TG) mice with oligodendrocyte specific over-expression of lamin B1 exhibit severe vacuolar demyelination of the spinal cord that result in age dependent degenerative phenotypes reminiscent of ADLD. TG spinal cords showed dramatic reductions in the expression of multiple genes responsible for lipid synthesis, including the critical lipogenic transcription factors, SREBP1 and 2. This was accompanied by global increases in the repressive histone marks H3K9me3 and H3K27me3 in spinal cord oligodendrocytes. As myelin is made up of ~70% lipids, defects of lipid synthesis can result in severe demyelination. Consistent with our gene expression data, we observed a significant reduction of myelin enriched lipids that were specific to the spinal cord white matter. Our results identify lipid synthesis defects as a major component of the demyelination caused by lamin B1 over-expression and suggests a novel link between lamin B1 and lipid metabolism. While lipid dysregulation provides a cogent framework for explaining the demyelination observed in the transgenic mice, the mechanisms linking lamin B1 over-expression and lipid synthesis in oligodendrocytes are unknown and this proposal aims at identifying these pathways. We will test the hypothesis that lamin B1 modulates repressive histone marks to down regulate expression of specific target genes and examine whether lamin B1 over expression in oligodendrocytes results in the dysregulation of specific pathways that may impact oligodendrocyte function. We will also determine how modulating lamin B1 levels impacts the disease phenotype. The experiments that we have proposed will elucidate mechanisms linking lamin B1 over-expression, lipid dysregulation and the demyelination phenotype, results that will be critical in the identification of therapeutic pathways for ADLD. In addition, they will also provide insights into the basic biology of oligodendrocyte function that may help in understanding other common demyelinating diseases such as Multiple Sclerosis.