Essential role of autophagy in protecting neonatal haematopoietic stem cells from oxidative stress in a p62-independent manner

Naho Nomura,Yusuke Takase,Yuko Tadokoro,Masaaki Komatsu,Masahiko Kobayashi,Atsushi Hirao,Chiaki Takahashi,Atsuko Kasahara,Susumu Kohno,Sha Si,Toru Yanagawa,Chiaki Ito,Kenta Kurayoshi,Masaya Ueno,Takako Ooshio

doi:10.1038/s41598-021-81076-z

Abstract

Autophagy is a cellular degradation system contributing to homeostasis of tissue stem cells including haematopoietic stem cells (HSCs). It plays pleiotropic roles in HSC characteristics throughout life, but its stage-specific roles in HSC self-renewal are unclear. To investigate the effects of Atg5 deletion on stage-specific HSC functions, we compared the repopulating capacity of HSCs in Atg5f/f;Vavi-cre mice from postnatal day (P) 0–7 weeks of age. Interestingly, Atg5 deficiency led to no remarkable abnormality in the HSC self-renewal capacity at P0, but significant defects at P7, followed by severe defects. Induction of Atg5 deletion at P5 by tamoxifen administration to Atg5f/f;Rosa26-Cre-ERT2 mice resulted in normal haematopoiesis, including the HSC population, until around 1 year, suggesting that Atg5 in the early neonatal period was critical for haematopoiesis in adults. Mitochondrial oxidative stress was increased by Atg5 loss in neonatal HSC/progenitor cells. Although p62 had accumulated in immature bone marrow cells of Atg5f/f;Vavi-cre mice, p62 deletion did not restore defective HSC functions, indicating that Atg5-dependent haematopoietic regulation in the developmental period was independent of p62. This study proposes a critical role of autophagy in HSC protection against harsh environments in the early neonatal stage, which is essential for healthy long-term haematopoiesis.

Highlights

Autophagy is a cellular degradation system contributing to homeostasis of tissue stem cells including haematopoietic stem cells (HSCs)
Autophagy had been originally identified as a bulk degradation pathway, selective autophagic degradation has been identified. p62, known as SQSTM1, is a major autophagic receptor that interacts with ubiquitinated substrates via the ubiquitin association domain and autophagosomes via the LC3 interaction region to intermediate selective engulfment of specific cargo into autophagosomes. p62 functions as an autophagic receptor, and in the stress response. p62 activates nuclear factor erythroid 2-related factor (Nrf2) by competitive binding to Kelch-like ECH-associated protein (Keap) 1, promoting tumourigenesis in the liver[9]
It has been demonstrated that autophagy plays a critical role in development and aging of HSCs, the importance of autophagy in perinatal HSCs, especially during the neonatal period, has not been revealed

Summary

Introduction

Autophagy is a cellular degradation system contributing to homeostasis of tissue stem cells including haematopoietic stem cells (HSCs). P62 had accumulated in immature bone marrow cells of Atg5f/f;Vavi-cre mice, p62 deletion did not restore defective HSC functions, indicating that Atg5-dependent haematopoietic regulation in the developmental period was independent of p62. Autophagy is a conserved catabolic system that degrades cellular components engulfed in autophagosomes within lysosomes This system is constitutively active to maintain cellular functions, but it is induced in response to stress condition such as oxidative stress, infection, and starvation. The Atg12–Atg5–Atg16L1 complex, which is formed through a ubiquitin-like conjugation system involving Atg[7] and Atg[10], is recruited to the autophagosome precursor/isolation membrane via PtdIns3P-binding protein WIPI2b1. The lipidation of LC3 has multiple roles in autophagy It is required for expansion of the isolation membrane and fusion of autophagosomes with lysosomes[1,3]. The relationship of the phenotype caused by autophagy deficiency and p62 accumulation remains unclear

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Results

Conclusion