Cellular components of the hematopoietic niche and their regulation of hematopoietic stem cell function

Purpose of review Development and functions of hematopoietic stem cells (HSC) are regulated by multiple cellular components of the hematopoietic niche. Here we review the recent advances in studying the role of three such components -- osteoblasts, osteomacs, and megakaryocytes and how they interact with each other in the hematopoietic niche to regulate HSC. Recent findings Recent advances in transgenic mice models, scRNA-seq, transcriptome profile, proteomics, and live animal imaging have revealed the location of HSC within the bone and signaling molecules required for the maintenance of the niche. Interaction between megakaryocytes, osteoblasts and osteomacs enhances hematopoietic stem and progenitor cells (HSPC) function. Studies also revealed the niche as a dynamic entity that undergoes cellular and molecular changes in response to stress. Aging, which results in reduced HSC function, is associated with a decrease in endosteal niches and osteomacs as well as reduced HSC--megakaryocyte interactions. Novel approaches to study the cellular components of the niche and their interactions to regulate HSC development and functions provided key insights about molecules involved in the maintenance of the hematopoietic system. Furthermore, these studies began to build a more comprehensive model of cellular interactions and dynamics in the hematopoietic niche.