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Abstract：
BACKGROUND: Hematopoietic stem cell (HSC) regeneration underlies hematopoietic recovery from myelosuppression, which is a life-threatening side effect of cytotoxicity. HSC niche is profoundly disrupted after myelosuppressive injury, while if and how the niche is reshaped and regulates HSC regeneration are poorly understood.
METHODS: A mouse model of radiation injury-induced myelosuppression was built by exposing mice to a sublethal dose of ionizing radiation. The dynamic changes in the number, distribution and functionality of HSCs and megakaryocytes were determined by flow cytometry, immunofluorescence, colony assay and bone marrow transplantation, in combination with transcriptomic analysis. The communication between HSCs and megakaryocytes was determined using a coculture system and adoptive transfer. The signaling mechanism was investigated both in vivo and in vitro, and was consolidated using megakaryocyte-specific knockout mice and transgenic mice.
RESULTS: Megakaryocytes become a predominant component of HSC niche and localize closer to HSCs after radiation injury. Meanwhile, transient insulin-like growth factor 1 (IGF1) hypersecretion is predominantly provoked in megakaryocytes after radiation injury, whereas HSCs regenerate paralleling megakaryocytic IGF1 hypersecretion. Mechanistically, HSCs are particularly susceptible to megakaryocytic IGF1 hypersecretion, and mTOR downstream of IGF1 signaling not only promotes activation including proliferation and mitochondrial oxidative metabolism of HSCs, but also inhibits ferritinophagy to restrict HSC ferroptosis. Consequently, the delicate coordination between proliferation, mitochondrial oxidative metabolism and ferroptosis ensures functional HSC expansion after radiation injury. Importantly, punctual IGF1 administration simultaneously promotes HSC regeneration and hematopoietic recovery after radiation injury, representing a superior therapeutic approach for myelosuppression.
CONCLUSIONS: Our study identifies megakaryocytes as a last line of defense against myelosuppressive injury and megakaryocytic IGF1 as a novel niche signal safeguarding HSC regeneration.
METHODS: A mouse model of radiation injury-induced myelosuppression was built by exposing mice to a sublethal dose of ionizing radiation. The dynamic changes in the number, distribution and functionality of HSCs and megakaryocytes were determined by flow cytometry, immunofluorescence, colony assay and bone marrow transplantation, in combination with transcriptomic analysis. The communication between HSCs and megakaryocytes was determined using a coculture system and adoptive transfer. The signaling mechanism was investigated both in vivo and in vitro, and was consolidated using megakaryocyte-specific knockout mice and transgenic mice.
RESULTS: Megakaryocytes become a predominant component of HSC niche and localize closer to HSCs after radiation injury. Meanwhile, transient insulin-like growth factor 1 (IGF1) hypersecretion is predominantly provoked in megakaryocytes after radiation injury, whereas HSCs regenerate paralleling megakaryocytic IGF1 hypersecretion. Mechanistically, HSCs are particularly susceptible to megakaryocytic IGF1 hypersecretion, and mTOR downstream of IGF1 signaling not only promotes activation including proliferation and mitochondrial oxidative metabolism of HSCs, but also inhibits ferritinophagy to restrict HSC ferroptosis. Consequently, the delicate coordination between proliferation, mitochondrial oxidative metabolism and ferroptosis ensures functional HSC expansion after radiation injury. Importantly, punctual IGF1 administration simultaneously promotes HSC regeneration and hematopoietic recovery after radiation injury, representing a superior therapeutic approach for myelosuppression.
CONCLUSIONS: Our study identifies megakaryocytes as a last line of defense against myelosuppressive injury and megakaryocytic IGF1 as a novel niche signal safeguarding HSC regeneration.
摘要：
背景：造血干细胞（HSC）再生是骨髓抑制造血恢复的基础，这是细胞毒性的威胁生命的副作用。骨髓抑制损伤后，HSC利基被严重破坏，虽然人们对生态位是否以及如何重塑和调节HSC再生知之甚少。
方法：通过将小鼠暴露于亚致死剂量的电离辐射，建立了辐射损伤诱导的骨髓抑制的小鼠模型。数量的动态变化，通过流式细胞术确定HSCs和巨核细胞的分布和功能，免疫荧光，集落测定和骨髓移植，结合转录组学分析。使用共培养系统和过继转移确定HSC和巨核细胞之间的通讯。在体内和体外研究了信号机制，并使用巨核细胞特异性敲除小鼠和转基因小鼠进行巩固。
结果：放射损伤后，巨核细胞成为HSC生态位的主要成分，并定位在更接近HSC的位置。同时,短暂性胰岛素样生长因子1（IGF1）的高分泌主要在辐射损伤后的巨核细胞中引起，而造血干细胞再生平行巨核细胞IGF1高分泌。机械上,HSC对巨核细胞IGF1分泌过多特别敏感,和IGF1信号下游的mTOR不仅促进HSC的激活，包括增殖和线粒体氧化代谢，但也抑制铁素吞噬限制HSC铁凋亡。因此,扩散之间的微妙协调，线粒体氧化代谢和铁凋亡确保了辐射损伤后功能性HSC的扩增。重要的是,在辐射损伤后，及时给予IGF1同时促进HSC再生和造血恢复，代表骨髓抑制的一种优越的治疗方法。
结论：我们的研究确定巨核细胞是骨髓抑制性损伤的最后一道防线，巨核细胞IGF1是保护HSC再生的新生态位信号。
方法：通过将小鼠暴露于亚致死剂量的电离辐射，建立了辐射损伤诱导的骨髓抑制的小鼠模型。数量的动态变化，通过流式细胞术确定HSCs和巨核细胞的分布和功能，免疫荧光，集落测定和骨髓移植，结合转录组学分析。使用共培养系统和过继转移确定HSC和巨核细胞之间的通讯。在体内和体外研究了信号机制，并使用巨核细胞特异性敲除小鼠和转基因小鼠进行巩固。
结果：放射损伤后，巨核细胞成为HSC生态位的主要成分，并定位在更接近HSC的位置。同时,短暂性胰岛素样生长因子1（IGF1）的高分泌主要在辐射损伤后的巨核细胞中引起，而造血干细胞再生平行巨核细胞IGF1高分泌。机械上,HSC对巨核细胞IGF1分泌过多特别敏感,和IGF1信号下游的mTOR不仅促进HSC的激活，包括增殖和线粒体氧化代谢，但也抑制铁素吞噬限制HSC铁凋亡。因此,扩散之间的微妙协调，线粒体氧化代谢和铁凋亡确保了辐射损伤后功能性HSC的扩增。重要的是,在辐射损伤后，及时给予IGF1同时促进HSC再生和造血恢复，代表骨髓抑制的一种优越的治疗方法。
结论：我们的研究确定巨核细胞是骨髓抑制性损伤的最后一道防线，巨核细胞IGF1是保护HSC再生的新生态位信号。
