Non‐resorbing osteoclasts induce migration and osteogenic differentiation of mesenchymal stem cells

Abstract

Osteoclast activity has traditionally been regarded as restricted to bone resorption but there is some evidence that also non-resorbing osteoclasts might influence osteoblast activity. The aim of the present study was to further investigate the hypothesis of an anabolic function of non-resorbing osteoclasts by investigating their capability to recruit mesenchymal stem cells (MSC) and to provoke their differentiation toward the osteogenic lineage. Bone-marrow-derived human MSC were exposed to conditioned media (CM) derived from non-resorbing osteoclast cultures, which were generated from human peripheral blood monocytes. Osteogenic marker genes (transcription factor Runx2, bone sialoprotein, alkaline phosphatase (AP), and osteopontin) were significantly increased. Osteogenic differentiation (OD) was also proved by von Kossa and AP staining occurred in the same range as in MSC cultures stimulated with osteogenic supplements. Chemotactic responses of MSC were measured with a modified Boyden chamber assay. CM from osteoclast cultures induced a strong migratory response in MSC, which was greatly reduced in the presence of an anti-human platelet-derived growth factor (PDGF) receptor beta antibody. Correspondingly, significantly increased PDGF-BB concentrations were measured in the CM using a PDGF-BB immunoassay. CM derived from mononuclear cell cultures did not provoke MSC differentiation and had a significantly lower migratory effect on MSC suggesting that the effects were specifically mediated by osteoclasts. In conclusion, it can be suggested that human non-resorbing osteoclasts induce migration and OD of MSC. While effects on MSC migration might be mainly due to PDGF-BB, the factors inducing OD remain to be elucidated.

Development of an osteoblast/osteoclast co-culture derived by human bone marrow stromal cells and human monocytes for biomaterials testing

“…A distinct feedback of the osteoclasts on osteoblasts is shown for the gene expression of BSP II, which is clearly most intensive for modifications III and IV -the only modifications which facilitated the formation of large C Heinemann et al Osteoblast/osteoclast co-culture for biomaterials testing multinuclear osteoclasts. Similar results have been recently published by Kreja et al whereby BSP II mRNA expression was up-regulated after stimulation of hBMSC with conditioned media collected from human osteoclasts (Kreja et al, 2010). Taking into account both the differentiation of hBMSC and hMc, modification III seems to be best-suited for cocultivation of human osteoblasts and osteoclasts in the present case.…”

Submicron-scale surface architecture of tricalcium phosphate directs osteogenesis in vitro and in vivo

“…Concerning the interspecies potency of the osteogenic factors demonstrated here, Pederson et al (2008) first reported that RAW264.7 osteoclast-like cells secrete soluble sphingosine 1 phosphate (S1P) and BMP6 which can differentiate hMSC into mineralising osteoblasts. Various other osteoclast-expressed osteogenic factors such as PDGF-BB (Kreja et al, 2010), Wnt10b (Pederson et al, 2008), other BMPs (McCullough et al, 2007, and the recently identified coupling factor CTHRC1 (Takeshita et al, 2013) may have also played a role.…”

“…Additionally, surface architecture may also impact other biological processes important for bone formation such as vasculogenesis and stem cell recruitment. Interestingly, many of the same osteogenic factors that are expressed by osteoclasts and their monocyte/macrophage precursors have also been shown to chemotactically home pre-osteoblasts (OSM, PDGF, CTHRC1) and stimulate blood vessel formation (TNF-α) (Kreja et al, 2010;Glass et al, 2011;Takeshita et al, 2013). For instance, invading macrophages signalled by the foreign body response may preferentially secrete cytokines important for both blood vessel formation and stem cell recruitment (e.g., pericytes) (Bergers and Song, 2005), followed by osteoblast/osteoclast differentiation (Fellah et al, 2010) -all in response to surface architecture.…”

“…Given no clear evidence of osteoclast resorption and depleted Ca 2+ /P i levels in the conditioned medium, we speculate that the osteogenic effects were most likely due to osteoclast-secreted trophic factors in response to the submicrostructured surface topography. In a broader biological context, it is pertinent to note that non-resorbing osteoclasts have been identified as a source of osteogenic factors in vivo (Karsdal et al, 2007;Karsdal et al, 2008;Kreja et al, 2010), emphasising that resorption is not necessary for osteogenic signalling (Fuller et al, 2010), potentially an interesting link for non-resorbable, osteoinductive materials such as microstructured titanium. Concerning the interspecies potency of the osteogenic factors demonstrated here, Pederson et al (2008) first reported that RAW264.7 osteoclast-like cells secrete soluble sphingosine 1 phosphate (S1P) and BMP6 which can differentiate hMSC into mineralising osteoblasts.…”

PDGF-BB secreted by preosteoclasts induces angiogenesis during coupling with osteogenesis

“…PDGF-BB is believed to mobilize cells of mesenchymal origin, stabilize newly formed vessels and orchestrate cellular components for osteoblast differentiation 33 . It has been reported that osteoclasts secret PDGF-BB to induce migration of MSCs or osteoblasts 34–36 .…”