PTBP1 promotes hematopoietic stem cell maintenance and red blood cell development by ensuring sufficient availability of ribosomal constituents

Ribosomopathies constitute a range of disorders associated with defective protein synthesis mainly affecting hematopoietic stem cells (HSCs) and erythroid development. Here we demonstrate that deletion of Polypyrimidine Tract Binding Protein 1 (PTBP1) in the hematopoietic compartment led to the development of a ribosomopathy-like condition. Specifically, loss of PTBP1 was associated with decreases in HSC self-renewal, erythroid differentiation and protein synthesis. Consistent with its function as a splicing regulator, PTBP1 deficiency led to splicing defects in hundreds of genes, and we demonstrate that the up-regulation of a specific isoform of CDC42 could partly mimic the protein synthesis defect associated with loss of PTBP1. Furthermore, PTBP1 deficiency was associated with a marked defect in ribosome biogenesis and a selective reduction in the translation of mRNAs encoding ribosomal proteins. Collectively, this work identifies PTBP1 as a key integrator of ribosomal functions and highlights the broad functional repertoire of RNA binding proteins. RNA-seq transcriptomic analysis of FACS sorted bone marrow progenitors; HSC (Lin-, Sca-1+, c-kit+, CD150+, CD48-) preMegEs and pre-CFU-Es from Ptbp1 fl/fl (wt) and Ptbp1 -/- (KO) mice. Three biological replicates per genotype and population were sequenced.

核糖体病（ribosomopathies）是一类以蛋白质合成缺陷为核心特征的病症谱系，主要累及造血干细胞（hematopoietic stem cells, HSCs）与红细胞发育过程。本研究证实，在造血系统中敲除多聚嘧啶束结合蛋白1（Polypyrimidine Tract Binding Protein 1, PTBP1）可诱发类核糖体病表型。具体而言，PTBP1缺失会导致造血干细胞自我更新能力减弱、红细胞分化受阻及蛋白质合成水平下降。作为公认的剪接调控因子，PTBP1缺失会引发数百个基因的剪接异常；本研究同时证实，上调CDC42的特定剪接异构体可部分模拟PTBP1缺失所导致的蛋白质合成缺陷。此外，PTBP1缺失还会显著损伤核糖体生物发生过程，并选择性降低编码核糖体蛋白的mRNA的翻译效率。综上，本研究确立了PTBP1作为核糖体功能核心整合因子的地位，并揭示了RNA结合蛋白广泛的功能谱。本研究对来自Ptbp1 flox/flox（野生型，wt）与Ptbp1 -/-（基因敲除，KO）小鼠的荧光激活细胞分选（fluorescence-activated cell sorting, FACS）骨髓造血祖细胞开展了RNA测序转录组分析，所分选的细胞群包括造血干细胞（Lin⁻、Sca-1⁺、c-kit⁺、CD150⁺、CD48⁻）、巨核红细胞前体细胞（preMegEs）及前红细胞集落形成单位（pre-CFU-Es）。每个基因型及细胞群均设置3次生物学重复并完成测序。