The Dynamic Interface between Vascular Blood Vessels to Blood Forming Hematopoietic Stem Cells in Health and Disease

Adult hematopoietic stem and progenitor cells (HSPCs) reside primarily in the bone marrow (BM), a hematopoietic site where billions of mature blood cells are produced on a daily basis. In the 60’s, the concept of an HSPC-supportive BM “niche” was proposed following the observation that hematopoietic cells isolated from the BM have the exclusive capacity of long-term multipotent repopulation of the blood system. Almost two decades ago a ‘niche’ entity was identified as a BM stromal cell regulating and supporting HSPCs developmental processes. Today we know that the majority of HSPCs reside in a perivascular zone in both endosteal and central BM areas. Recently, blood vessels, and more specifically vascular blood vessel forming endothelial cells (ECs), were highlighted as more than just passive conduits for oxygen and nutrients but rather as a vigorous component of the HSPC niche. In the past few years, the vascular niche has emerged as a pivotal player in hematopoietic embryonic developmental processes, throughout adulthood, maintaining steady state and emergency hematopoiesis, and augmenting hematopoietic aging. Heterogeneous types of ECs form distinct types of niches exhibiting differential regulatory roles for hematopoiesis. In addition, the occurrence of diverse pathological insults has a profound impact on molecular cues and over the architecture of BM blood vessels, altering EC characteristics to provision the diseased phenotype at the expense of normal HSPCs. Thus, it is of high importance to gain further insights and knowledge of the vascular niche, and of the hemato-vascular interactions, to harness blood vessels as a tool for hematological manipulation in health and disease.

The aim of this Research Topic is to provide an extensive overview of the recently gained knowledge in the field of hematopoiesis about the dynamic interaction between vascular ECs and HSPCs. Multiple points of view will be provided on the subject, covering both basic scientific and clinical angles, normal steady state versus malignancy states, and recent technological advances allowing improved dissection and decryption of molecular components of the vascular niche and perivascular residents. We welcome articles following under the following topics:

• The regulatory roles of vascular ECs orchestrating hematopoiesis in the BM and other secondary hematopoietic tissues.
• Vascular dysfunction and alterations in hematological malignancies.
• Dynamic hemato-vascular interactions during embryonic developmental processes.
• Vascular and hematopoietic interactions under aging or chronic inflammation.
• Changes in the vascular niche under acute infection conditions.
• Recent technological advances in decrypting vascular heterogeneity and molecular function in regard to hematopoiesis.
• Clinical overview of the hematovascular crosstalk and of the relevant clinical trials.