HSCs reside in bone marrow niches, closely associated with osteolineage cells, the highly innervated nestin⁺ mesenchymal stem cells (MSCs), perivascular CXCL12-abundant reticular cells, or sinusoidal lining leptin receptor⁺ cells, with overlapping regions and differing oxygen tensions. Resident macrophages provide a positive supporting factor maintaining osteolineage and mesenchymal stem cell activity, and megakaryocytes support osteolineage cells after injury through cell-to-cell contact. Similarly, HSCs making cell-to-cell contact can create signaling endosomes, enhancing osteolineage hematopoietic support, and transplanted HSCs facilitate sinusoidal endothelial repair following injury. Osteoclasts, in conjunction with osteoblasts, maintain bone formation and resorption, creating a soluble calcium gradient, which is a chemoattractant for HSCs. SNS signals regulate bone marrow niche components, and nonmyelinating Schwann cells ensheathing those neurons can directly regulate HSCs through TGF-β production.