Priming mobilization of hair follicle stem cells triggers permanent loss of regeneration after alkylating chemotherapy

The maintenance of genetic integrity is critical for stem cells to ensure homeostasis and regeneration. Little is known about how adult stem cells respond to irreversible DNA damage, resulting in loss of regeneration in humans. Here, we establish a permanent regeneration loss model using cycling human hair follicles treated with alkylating agents: busulfan followed by cyclophosphamide. We unravel the underlying mechanisms by which hair follicle stem cells (HFSCs) lose their pool. Contrary to immediate destructive changes in rapidly proliferating hair matrix cells, quiescent HFSCs show unexpected massive proliferation after busulfan and then undergo large-scale apoptosis following cyclophosphamide. HFSC proliferation is activated through PI3K/Akt pathway, and depletion is driven by p53/p38-induced cell death. RNA-seq analysis shows that HFSCs experience mitotic catastrophe with G2/M checkpoint activation. Our findings indicate that priming mobilization causes stem cells to lose their resistance to DNA damage, resulting in permanent loss of regeneration after alkylating chemotherapy.

遗传完整性的维持对于干细胞维持机体稳态与再生能力至关重要。目前对于成体干细胞如何应对不可逆DNA损伤、进而导致人类再生能力丧失的机制尚不明确。本研究利用经烷化剂处理（先给予白消安，随后给予环磷酰胺）的增殖期人毛囊，构建了永久再生丧失模型。我们阐明了毛囊干细胞（hair follicle stem cells, HFSCs）发生干细胞池耗竭的潜在机制：与快速增殖的毛母质细胞即刻出现破坏性变化不同，静息态HFSCs在经白消安处理后会出现意料之外的大规模增殖，随后在环磷酰胺给药后发生大规模凋亡。HFSCs的增殖通过PI3K/Akt通路被激活，而其耗竭则由p53/p38介导的细胞死亡所驱动。RNA测序（RNA-seq）分析显示，HFSCs会经历有丝分裂灾难，并伴随G2/M期检查点的激活。本研究结果表明，预激活动员会使干细胞丧失对DNA损伤的抵抗能力，最终导致烷化剂化疗后再生能力的永久丧失。