CCN protein family members (CYR61, CTGF, Nov, Wisp-1, Wisp-2 and Wisp-3) have important roles in many different processes including angiogenesis, inflammation, remodelling of extracellular matrix and tumorigenesis. In bone, CCN1 increases osteoblastogenesis via Wnt3A signalling and activation of -catenin which, in turn, upregulates CCN1 expression. The exact role of CCN1, CCN2, and CCN6 in osteoclast physiology are not known but we have recently shown that recombinant human (rh)CCN1 inhibits osteoclastogenesis in vitro. The aim of this study was to determine: 1) the expressions of all six members of the CCN protein family in osteoblasts and osteoclasts; 2) the functions of recombinant human CCN2, CCN6 in osteoclastogenesis; 3) whether osteoblast-derived CCN1 may mediate the effect of CCN1 on osteoclast formation and the roles of osteoblast-derived CCN1 and/or osteoclast-derived CCN1 in osteoblast and/or osteoclast differentiation; 4) which signalling pathways are involved in the function of CCN1 in osteoclasts and osteoblasts. We found CCN1-5 but not CCN6 expressed in murine osteoclasts and osteoblasts. All six members were expressed in human OA osteoblasts but only CCN1-3 were detected in human osteoclasts using quantitative RT-PCR. rhCCN1 (in agreement with our previous observations), and also 2 and 6 inhibited human and mouse osteoclast formation in a concentration-dependent manner. We generated and validated an expression construct to specifically overexpress CCN1 in osteoblasts. Incorporation of CCN1-specific siRNA reduced CCN1 expression to between 12.5% and 50% of control osteoblast cultures. In both co-cultures with direct contact between osteoblasts and osteoclast co-cultures as well as Transwell cultures, overexpression of CCN1 in osteoblasts decreased the formation of TRAP positive multinucleated osteoclast-like cells, while siRNA mediated knockdown of CCN1 in the osteoblasts resulted in increased osteoclast-like cell formation. These data suggest that osteoblast-derived CCN1 is a secreted negative regulator of osteoclastogenesis. Moreover, overexpression or knockdown of CCN1 in osteoclast precursors inhibited or increased osteoclast differentiation whilst overexpression or knockdown CCN1 in osteoblasts increased or inhibited osteoblast mineralization respectively. Further investigation found that CCN1 increased Wnt and MAPK signalling in osteoblasts cultured in mineralization medium and inhibited Wnt and IGF-1 signalling during osteoclast differentiation. In conclusion, paracrine and autocrine effects of CCN1 have been demonstrated in osteoclasts and osteoblasts in this study and Wnt, MAPK, amd IGF-1 signalling pathways, may be involved in these effects.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:600058 |
| Date | January 2012 |
| Creators | Wang, Wen |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=204059 |
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