Lead exposure suppresses the Wnt3a/β-catenin signaling to increase the quiescence of hematopoietic stem cells via reducing the expression of CD70 on bone marrow-resident macrophages.

Lead (Pb) is a heavy metal highly toxic to human health in the environment. The aim of this study was to investigate the mechanism of Pb impact on the quiescence of hematopoietic stem cells (HSC). WT C57BL/6 (B6) mice treated with 1250 ppm Pb via drinking water for 8 weeks had increased the quiescence of HSC in the bone marrow (BM), which was caused by the suppressed activation of the Wnt3a/β-catenin signaling. Mechanically, a synergistic action of Pb and IFNγ on BM-resident macrophages (BM-Mφ) reduced their surface expression of CD70, which thereby dampened the Wnt3a/β-catenin signaling to suppress the proliferation of HSC in mice. In addition, a joint action of Pb and IFNγ also suppressed the expression of CD70 on human Mφ to impair the Wnt3a/β-catenin signaling and reduce the proliferation of human HSC purified from umbilical cord blood of healthy donors. Moreover, correlation analyses showed that the blood Pb concentration was or tended to be positively associated with the quiescence of HSC, and was or tended to be negatively associated with the activation of the Wnt3a/β-catenin signaling in HSC in human subjects occupationally exposed to Pb. Collectively, these data indicate that an occupationally relevant level of Pb exposure suppresses the Wnt3a/β-catenin signaling to increase the quiescence of HSC via reducing the expression of CD70 on BM-Mφ in both mice and humans.