Molecular Features of Human Bone Marrow Stem Cells

Abstract

Understanding the quality and quantity of resident bone marrow cells as well as circulating bone marrow derived cells (BMDC) are key to unlocking the complexity of their contribution to physiological hemostasis or pathological conditions such as chronic inflammation, ischemia, tumor initiation, tumor angiogenesis or tumor metastasis. Here mononuclear, hematopoietic cells that are embedded in healthy bone marrow tissues were studied. The cells were isolated from discarded human bone marrow tissue fragments and separated into hematopoietic progenitor-positive (HP+) and -negative (HP-) cell populations by removal of differentiated cells using immunomagnetic sorting after isopycnic density separation using ficoll-paque plus as a gradient centrifugation medium. The negative selection of these cells by depletion of mature cells, using a cocktail of 12 antibodies, resulted in two population cell pools distinguished by their cell granularity, complexity and molecular features. Subsequent expression analyses showed that the cell subset with smaller cells, we term bone marrow hematopoietic progenitor positive (HP+), 1-2% of the whole marrow, highly expressed stem/progenitor surface markers, such as CD34, CD45, CD123, CD133, CD90/THY-1, BST-1 as well as genes targeting endothelial cells. They exhibited a microRNAs expression profile enriched in miRs associated with cell proliferation, hematopoiesis, angiogenesis or metastasis, such as miR130b, miR155, miR92a or miR10. Furthermore, they displayed an invasive phenotype towards intact endothelial monolayers that is comparable to highly invasive cancer cells. The HP+ cell population was expanded after their isolation utilizing StemRegenin-1 (SR1), without altering their cellular and molecular phenotypes.

It is concluded that bone marrow resident hematopoietic stem/progenitor cells show an invasive behavior and can be expanded in vitro whilst maintaining their phenotype and molecular characteristics. This can provide a step forward in adult stem cell research with potential implications for bone marrow transplantation.