Abstract
Haematopoietic stem cells (HSCs) reside in specialized microenvironments in the bone marrow-often referred to as 'niches'-that represent complex regulatory milieux influenced by multiple cellular constituents, including nerves(1,2). Although sympathetic nerves are known to regulate the HSC niche(3-6), the contribution of nociceptive neurons in the bone marrow remains unclear. Here we show that nociceptive nerves are required for enforced HSC mobilization and that they collaborate with sympathetic nerves to maintain HSCs in the bone marrow. Nociceptor neurons drive granulocyte colony-stimulating factor (G-CSF)-induced HSC mobilization via the secretion of calcitonin gene-related peptide (CGRP). Unlike sympathetic nerves, which regulate HSCs indirectly via the niche(3,4,6), CGRP acts directly on HSCs via receptor activity modifying protein 1 (RAMP1) and the calcitonin receptor-like receptor (CALCRL) to promote egress by activating the G alpha(s)/adenylyl cyclase/cAMP pathway. The ingestion of food containing capsaicin-a natural component of chili peppers that can trigger the activation of nociceptive neurons-significantly enhanced HSC mobilization in mice. Targeting the nociceptive nervous system could therefore represent a strategy to improve the yield of HSCs for stem cell-based therapeutic agents.