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

 描述（由申请人提供）：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细胞质和细胞核中。然而，在2007年，我们报道了内质网（ER）货物蛋白的瞬时赖氨酸乙酰化。随后的研究表明，ER有两个乙酰转移酶（ATase 1和ATase 2）以及一个膜转运蛋白（AT-1/SCL 33 A1），它将乙酰辅酶A（乙酰化反应的乙酰基供体）转运到ER腔中。AT- 1/SCL 33 A1是ER驻留蛋白和转运蛋白在管腔内乙酰化所必需的。乙酰辅酶A流入的变化影响ER的乙酰化状态。AT-1/SCL 33 A1的杂合突变已在家族性痉挛性截瘫患者中发现，而纯合突变已在神经系统发育迟缓和过早死亡患者中发现。最后，AT-1/SCL 33 A1的重复已在自闭症谱系障碍和智力残疾患者中报道。我们研究的一般假设是AT-1对乙酰辅酶A流入内质网腔的严格调节对于神经元生物学是必不可少的。为了检验上述假设，我们已经产生了减少的（AT-1 S113 R/+）和增加的（AT-1 Tg）乙酰辅酶A流入ER的小鼠模型。AT-1 S113 R/+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增加、异常炎症反应和恶性肿瘤倾向增加。神经系统的缺陷导致严重的运动缺陷和周围（PNS）和中枢（CNS）神经系统的退行性特征。AT-1 Tg小鼠表现出行为缺陷、LTP和LTD受损以及神经元分支增加的自闭症样表型。到目前为止收集的数据表明，ER为基础的乙酰化机制调节蛋白质运输的效率沿着分泌途径和诱导ERAD（II）。具体目标1将检验S113 R（与痉挛性截瘫相关）和A110 P（与发育迟缓相关）突变影响AT-1的结构并阻断ER膜中转运蛋白的翻译后组装的假设。具体目标2将检验Atg 9A作为ER腔中乙酰辅酶A水平的“传感器”并调节AT-1下游ERAD（II）/自噬的诱导的假设。目标1和目标2将一起剖析与ER乙酰化缺陷相关的疾病的分子基础。具体目标3将检验以下假设：AT-1 Tg小鼠中异常高的乙酰辅酶A流入ER腔增加分泌途径的效率，超出生理要求，并导致神经元中蛋白质表达水平的广泛变化。本目标将剖析与AT-1/SCL 33 A1重复相关的自闭症谱系障碍和智力残疾的分子基础。

 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.