ABSTRACT
Adult bone marrow microenvironment is comprised of various stromal elements including, adipocytes, smooth muscle cells, reticular cells and osteoblasts (Weiss 1976). These cell populations, not only provide environmental cues to support the survival, proliferation and differentiation of hematopoietic stem cells (HSC), but also play a pivotal role in regulating skeletal tissue homeostasis. Friedenstein and colleagues were the fi rst to report the isolation of a population of stem/progenitor stromal cells located within rodent bone marrow (Friedenstein 1976). These stem/progenitor stromal cells were identifi ed by their capacity to form clonogenic adherent fi broblast clusters, containing 50 or greater cells in number when cultured in vitro, denoted as colony forming unit-fi broblasts (CFU-F) (Friedenstein 1976). Since these initial seminal fi ndings, human studies have also confi rmed that multipotential MSC or bone marrow stromal cells (BMSC) reside within the bone marrow spaces (Gronthos et al. 2003b; Pittenger et al. 1999). The developmental potential of MSC encompasses many of the stromal populations found in skeletal tissues such as osteoblasts, chondrocytes, adipocytes, myoblasts and tendon/ligament fi broblasts (Fig. 5.1).
