正常的核糖体生物合成对于细胞的生存、增殖及功能至关重要,核糖体生物合成功能失常与很多疾病有关,著名的有Diamond–Blackfan贫血(DBA)、5q-综合症(5q minus (del (5q−)) syndrome)、先天性角化不良(Dyskeratosis Congenita)和Bowen-Conradi综合症等。这些疾病都含有影响核糖体生物合成的遗传突变,也具有一些相同的临床特征,因此被统称为核糖体病变(ribosomopathies)。
脊椎动物造血是一个包括造血干细胞(HSC)分化成各种谱系血细胞的进化上保守的和受高度调控的过程。斑马鱼是一类强大的研究脊椎动物循环系统的遗传和发育研究模型,尤其是研究造血功能方面,斑马鱼的造血功能与哺乳动物高度保守。其造血系统位于受精后28小时的斑马鱼腹侧壁背主动脉的一个称为主动脉 - 性腺 - 中肾(AGM)的结构中。受精后2天,AGM驱使的造血干细胞会移植到尾椎造血组织(CHT)中,这是一个类似于哺乳动物的胎肝的胚胎结构。下图为正常的野生型斑马鱼(WT)与斑马鱼突变体cas002(Mutant
cas002)间的表型对比图(KM,肾脏骨髓;T,胸腺)。
研究人员通过采用遗传作图、分子克隆等方法确定斑马鱼突变体cas002的特征,揭示出了在HSPCs的调控中,核糖体功能失常与过度自噬之间的一种新联系。cas002携带着一个隐性致死突变基因kri1l,而kri1l负责编码rRNA小亚基加工体的一个关键组件。他们证实,Kri1l是核糖体的正常生物合成、HSPCs扩增及谱系分化的必要条件。通过活体成像和生物化学研究,他们发现缺失Kri1l可导致HSPCs中错误折叠蛋白累积,及过度的PERK激活依赖性的自噬。采用自噬抑制剂(3-MA和Baf A1)或PERK抑制剂(GSK2656157)处理,或是抑制beclin1或perk均可显著恢复HSPC增殖及造血细胞分化。下图为Kri1l功能紊乱后的作用原理以及治疗方法。
作者指出,这些研究结果可能会促进一些有效的疗法的进步,使核糖体障碍罹患贫血和骨髓衰竭的患者受益。
原文标题:Mutation of kri1l causes definitive hematopoiesis failure via PERK-dependent excessive autophagy induction
摘要:Dysregulation of ribosome biogenesis causes human diseases, such as Diamond-Blackfan anemia, del (5q-) syndrome and bone marrow failure. However, the mechanisms of blood disorders in these diseases remain elusive. Through genetic mapping, molecular cloning and mechanism characterization of the zebrafish mutant cas002, we reveal a novel connection between ribosomal dysfunction and excessive autophagy in the regulation of hematopoietic stem/progenitor cells (HSPCs). cas002 carries a recessive lethal mutation in kri1l gene that encodes an essential component of rRNA small subunit processome. We show that Kri1l is required for normal ribosome biogenesis, expansion of definitive HSPCs and subsequent lineage differentiation. Through live imaging and biochemical studies, we find that loss of Kri1l causes the accumulation of misfolded proteins and excessive PERK activation-dependent autophagy in HSPCs. Blocking autophagy but not inhibiting apoptosis by Bcl2 overexpression can fully rescue hematopoietic defects, but not the lethality of kri1l cas002 embryos. Treatment with autophagy inhibitors (3-MA and Baf A1) or PERK inhibitor (GSK2656157), or knockdown of beclin1 or perk can markedly restore HSPC proliferation and definitive hematopoietic cell differentiation. These results may provide leads for effective therapeutics that benefit patients with anemia or bone marrow failure caused by ribosome disorders.