Pathogenesis of Emery-Dreifuss Muscular Dystrophy

 描述(申请人提供)：Emery-Dreifuss肌营养不良症(EDMD)是一种由几个不同基因突变引起的综合征，其中大多数基因编码核膜蛋白。骨骼肌萎缩无力、关节收缩和危及生命的心肌病是其典型的临床特征。常染色体EDMD是由LMNA突变引起的，LMNA编码A-型层粘连蛋白，即排列在内核膜上的中间丝蛋白。大多数X连锁的EDMD是由EMD的突变引起的，EMD编码内核膜的一种完整蛋白质，称为Emerin。新出现的人类遗传数据表明，编码LAP1的基因突变也会导致肌肉营养不良。LAP1是内核膜的另一种完整蛋白质，与A型板层蛋白和Emerin相互作用。根据我们以前的研究，我们提出了一个关于EDMD发病机制的假说：1)A型lamins、Emerin和LAP1在核膜中形成一个复合体，在横纹肌的维持中发挥关键作用；2)这个复合体调节MAP激酶ERK1/2，它的破坏激活了这个激酶；3)双特异性磷酸酶DUSP4将ERK1/2的激活与增强的AKT-mTOR信号联系在一起，从而损害自噬并诱导代谢缺陷，导致心脏和骨骼肌病理。使用新的小鼠和细胞模型，我们将检验这一假设。在目标1中，我们将使用A-型层粘连蛋白、Emerin和LAP1基因缺失的小鼠进行测试，以确定这些蛋白在体内横纹肌肉细胞维持中的共同功能。在目标2中，我们将使用生化和生物物理方法来表征Lamin-Emerin-LAP1复合体，并研究它与ERK1/2和DUSP4的相互作用。我们还将确定Lamin-Emerin-LAP1复合体的破坏是否激活ERK1/2。在目标3中，我们将通过将Lamin-Emerin-LAP1复合体中有变化的小鼠与缺乏DUSP4的小鼠杂交来测试我们假设的第三部分，并确定这是否会降低AKT-mTOR活性，逆转自噬缺陷，使细胞能量代谢正常化并改善病理。从公共卫生的角度来看，该项目将提供对编码核膜蛋白的不同基因突变如何导致EDMD和相关肌病的理解，并确定可能改变当前治疗范式的治疗的新靶点。

 DESCRIPTION (provided by applicant): Emery-Dreifuss muscular dystrophy (EDMD) is a syndrome that can result from mutations in several different genes, most of which encode proteins of the nuclear envelope. Skeletal muscle wasting and weakness, joint contractions and life-threatening cardiomyopathy are the classical clinical features. Autosomal EDMD results from mutations in LMNA, which encodes A-type lamins, intermediate filament proteins lining the inner nuclear membrane. Most cases of X-linked EDMD result from mutations in EMD, which encodes an integral protein of the inner nuclear membrane called emerin. Emerging human genetic data demonstrate that mutations in the gene encoding LAP1, another integral protein of the inner nuclear membrane that interacts with A-type lamins and emerin, also cause muscular dystrophy. Based on our previous research, we have devised a hypothesis regarding the pathogenesis of EDMD proposing that: 1) A-type lamins, emerin and LAP1 form a complex in the nuclear envelope that plays a critical role in striated muscle maintenance, 2) this complex regulates the MAP kinase ERK1/2 and its disruption activates this kinase and 3) the dual-specific phosphatase DUSP4 links activation of ERK1/2 to enhanced AKT-mTOR signaling, which impairs autophagy and induces metabolic defects that lead to heart and skeletal muscle pathology. Using novel murine and cellular models, we will test this hypothesis. In Aim 1, we will use mice with genetic depletions of A-type lamins, emerin and LAP1 to test to establish that these proteins function together in striated muscle cell maintenance in vivo. In Aim 2, we will use biochemical and biophysical methods to characterize the lamin-emerin-LAP1 complex and examine its interactions with ERK1/2 and DUSP4. We will also determine if disruption of the lamin-emerin-LAP1 complex activates ERK1/2. In Aim 3, we will test the third part of our hypothesis by crossing mice with alterations in the lamin-emerin-LAP1 complex to mice lacking DUSP4 and determining if this reduces AKT-mTOR activity, reverses defects in autophagy, normalizes cellular energy metabolism and ameliorates pathology. From a public health standpoint, this project will provide an understanding of how mutations in different genes encoding nuclear envelope proteins cause EDMD and related myopathies and identify novel targets for therapies that could change current treatment paradigms.