Spastic paraplegia, neurodegeneration and autism: possible role for AT-1/SLC33A1?

 描述(申请人提供)：Nε-赖氨酸乙酰化是一种重要的翻译后修饰。它调节靶蛋白的活性、分子稳定性和构象组装。四十多年来，人们一直认为赖氨酸乙酰化只能发生在胞浆和胞核中。然而，在2007年，我们报道了内质网(ER)货运蛋白的瞬时赖氨酸乙酰化。后来的研究发现，内质网有两个乙酰基转移酶(ATase1和ATase2)以及一个膜转运体(AT-1/SCL33A1)，它将乙酰化反应的乙酰基供体乙酰辅酶A转移到内质网腔内。AT-1/SCL33A1对于内质网驻留和转运蛋白的腔内乙酰化是必不可少的。乙酰辅酶A内流的变化影响内质网的乙酰化状态。在家族性痉挛截瘫患者中发现了AT-1/SCL33A1杂合突变，而在神经系统发育迟缓和过早死亡患者中发现了纯合子突变。最后，据报道，在自闭症谱系障碍和智力残疾患者中存在AT-1/SCL33A1重复。我们研究的一般假设是，AT-1严格调节乙酰辅酶A流入内质网是神经元生物学所必需的。为了验证上述假设，我们建立了(AT-1S113R/)和(AT-1Tg)乙酰辅酶A流入内质网的小鼠模型。AT-1S113R/小鼠出现免疫和神经系统缺陷。免疫系统的缺陷导致感染倾向的增加，异常的炎症反应，以及恶性倾向的增加。神经系统的缺陷会导致严重的运动障碍和周围神经系统(PNS)和中枢神经系统(CNS)的退行性改变。AT-1转基因小鼠表现为自闭症样表型，行为缺陷，LTP和LTD受损，神经元分支增加。到目前为止收集的数据表明，基于内质网的乙酰化机制调节蛋白质沿分泌途径的运输效率和ERAD(II)的诱导。具体目标1将验证S113R(与痉挛性截瘫相关)和A110P(与发育迟缓相关)突变影响AT-1结构并阻止内质网转运蛋白翻译后组装的假设。特定目标2将检验这样的假设，即Atg9A作为内质网管腔中乙酰-CoA水平的“传感器”，并调节ERAD(II)/AT-1下游自噬的诱导。总之，目标1和目标2将剖析与ER乙酰化缺陷相关的疾病的分子基础。具体目标3将测试这一假设，即在AT-1转基因小鼠的ER管腔中异常高的乙酰辅酶A流入增加了超出生理要求的分泌途径的效率，并导致神经元中蛋白质表达水平的广泛变化。这一目标将剖析与AT-1/SCL33A1重复相关的自闭症谱系障碍和智力障碍的分子基础。

 DESCRIPTION (provided by applicant): Nε-lysine acetylation is an essential post-translational modification. It regulates activity, molecular stabilization and conformational assembly of targeted proteins. For more than forty years it was assumed that lysine acetylation could only occur in the cytosol and nucleus. However, in 2007, we reported the transient lysine acetylation of endoplasmic reticulum (ER) cargo proteins. Subsequent studies revealed that the ER has two acetyltransferases (ATase1 and ATase2) as well as a membrane transporter (AT-1/SCL33A1) that translocates acetyl-CoA, donor of the acetyl group for the reaction of acetylation, into the ER lumen. AT- 1/SCL33A1 is essential for the intraluminal acetylation of ER-resident and -transiting proteins. Changes in acetyl-CoA influx affect the acetylation status of the ER. Heterozygous mutations in AT-1/SCL33A1 have been identified in patients affected by a familial form of spastic paraplegia while homozygous mutations have been identified in patients affected by developmental delay of the nervous system and premature death. Finally, a duplication of AT-1/SCL33A1 has been reported in patients with autism spectrum disorder and intellectual disability. The general hypothesis of our research is that tight regulation of acetyl-CoA influx ino the ER lumen by AT-1 is essential for neuron biology. To test the above hypothesis we have generated mouse models of reduced (AT-1S113R/+) and increased (AT-1 Tg) acetyl-CoA influx into the ER. AT-1S113R/+ mice develop deficits of both the immune and nervous system. The defects of the immune system result in increased propensity to infections, aberrant inflammatory response, and increased propensity to malignancies. The defects of the nervous system result into severe motor deficits and degenerative features of the peripheral (PNS) and central (CNS) nervous system. AT-1 Tg mice display an autistic-like phenotype with behavioral deficits, impaired LTP and LTD, and increased neuronal branching. The data collected so far suggests that the ER-based acetylation machinery regulates the efficiency of protein trafficking along the secretory pathway and the induction of ERAD(II). Specific Aim 1 will test the hypothesis that the S113R (associated with spastic paraplegia) and A110P (associated with developmental delay) mutations affect the structure of AT-1 and block post-translational assembly of the transporter in the ER membrane. Specific Aim 2 will test the hypothesis that Atg9A acts as a "sensor" of acetyl-CoA levels in the ER lumen and regulates induction of ERAD(II)/autophagy down-stream of AT-1. Together, Aim 1 and Aim 2 will dissect the molecular basis of diseases associated with deficient ER acetylation. Specific Aim 3 will test the hypothesis that abnormally high influx of acetyl-CoA into the ER lumen in AT-1 Tg mice increases the efficiency of the secretory pathway beyond physiological requirements and causes broad changes on protein expression levels in the neuron. This Aim will dissect the molecular basis of the autism spectrum disorder and intellectual disability associated with the duplication of AT-1/SCL33A1.