Osteoblast lineage cells expressing high levels of Runx2 enhance hematopoietic progenitor cell proliferation and function

Abstract

Although osteoblasts (OB) play a key role in the hematopoietic stem cell (HSC) niche, little is known as to which specific OB lineage cells are critical for the enhancement of stem and progenitor cell function. Unlike hematopoietic cells, OB cell surface phenotypic definitions are not well developed. Therefore, to determine which OB lineage cells are most important for hematopoietic progenitor cell (HPC) function, we characterized OB differentiation by gene expression and OB function, and determined whether associations existed between OB and HPC properties. OB were harvested from murine calvariae, used immediately (fresh OB) or cultured for 1, 2, or 3 weeks prior to their co-culture with Lin-Sca1+c-kit+ (LSK) cells for 1 week. OB gene expression, alkaline phosphatase activity, calcium deposition, hematopoietic cell number fold increase, CFU fold increase, and fold increase of Lin-Sca1+ cells were determined. As expected, HPC properties were enhanced when LSK cells were cultured with OB compared to being cultured alone. Initial alkaline phosphatase and calcium deposition levels were significantly and inversely associated with an increase in the number of LSK progeny. Final calcium deposition levels and OB culture duration were inversely associated with all HPC parameters, while Runx2 levels were positively associated with all HPC properties. Since calcium deposition is associated with OB maturation and high levels of Runx2 are associated with less mature OB lineage cells, these results suggest that less mature OB better promote HPC proliferation and function than do more mature OB.

Effect of diabetic osteoblasts on osteogenic differentiation of human umbilical cord mesenchymal stem cells

“…These results are similar to the view that osteoblasts can promote MSC or hematopoietic progenitor cell proliferation [22][23] . Osteoblasts can also regulate osteogenic differentiation of MSCs in stimulating osteogenesis 24 .…”

Mimicking the functional hematopoietic stem cell niche in vitro: recapitulation of marrow physiology by hydrogel-based three-dimensional cultures of mesenchymal stromal cells

“…The BM niche is known to express some important key molecules playing a critical role in the development of effective hematopoiesis: osteopontin, 18 runx-2 19 and angiopoietin-1. 20 It was, therefore, essential to quantify the expression of these genes in the 3D-MSCs at mRNA levels.…”

“…The transcripts of all these molecules were higher in the 3D-MSCs compared to those in the 2D-MSCs (Online Supplementary Figure S5B). Osteopontin-β1 [18][19][20][21] and angiopoietin-Tie-2 20 axes are known to anchor the HSCs to the niche and also to maintain their quiescence. Correspondingly, the 3D-HSCs expressed high levels of Tie-2 (Online Supplementary Figure S5D) and β1 integrin ( Figure 2C) mRNA suggesting that perhaps both axes are operative in the 3D-cultures.…”

Differential Regulation of CXCL5 by FGF2 in Osteoblastic and Endothelial Niche Cells Supports Hematopoietic Stem Cell Migration

“…Primary OBs derived from both long bone and neonatal calvariae could support and enhance hematopoietic properties [15,31]. Recently, it was reported that Runx2, a master transcription factor for OB differentiation, is important to enhance or maintain for HSC function and properties, and its expression level is high at the early stage of OB differentiation or in freshly isolated OB [16,32]. Runx2 protein was abundant in ELBOSs without any stimulation, and the primary OBs derived from long bone tissues.…”

“…2B). High levels of Runx2 in OBs are known to promote HSPC properties [16]. Conditional Bmpr1a-deficient mice that can inducibly delete Bmpr1a in bone-marrow stroma display an increased number of N-cadherin-positive OBs and HSCs [1].…”