Nucleosome Assembly Protein 1 (NAP‐1) determines the progenitor status of endothelial cells

Pulmonary microvascular endothelial cells (PMVECs) are enriched with a population of progenitors that enhance their growth potential. Since Nucleosome Assembly Protein‐1 (NAP‐1) expression increases endothelial cell proliferation, we sought to determine whether NAP‐1 is a key molecular determinant of an endothelial progenitor cell. PMVECs were subjected to the single cell clonogenic assay; 20% of the population was fully differentiated (i.e. did not proliferate), 30% exhibited low proliferative potential (LPP), and 50% exhibited high proliferative potential (HPP). Re‐seeding of single cells in the clonogenic assay revealed that HPPs, but not LPPs, reconstituted the entire hierarchy of growth potentials, indicating that HPPs possess the ability to self‐renew, an evidence of their intrinsic progenitor behavior. Western blot analysis demonstrated that NAP‐1 expression was increased in HPPs compared to LPPs. Stable NAP‐1 overexpression in LPPs conferred a progenitor behavior to this phenotype, where 40% of the LPP population exhibited HPP potential, with a capacity to self‐renew. Morphological and adhesive properties were similar in HPPs, LPPs, and NAP‐1‐LPP overexpressing cells, indicating that NAP‐1 regulates progenitor activity without affecting endothelial specification. Thus, NAP‐1 determines the progenitor behavior of endothelial cells. HL66299