Figure 2.

MMP2 in bone remodelling and tumor metastasis-related bone loss. MMP2 is primarily secreted by osteocytes, osteoblasts, tumor stromal cells and tumor cells (dashed arrow). MMP2 contributes to bone loss via several pathways: 1, Degradation of collagen and osteoid seam on the bone surface; 2, recruitment of pre-osteoclasts and differentiation of osteoclasts; 3, increased VEGF activation, which promotes osteoclastogenesis; 4, inhibition of OPG expression and increase in the RANKL/OPG ratio; 5, inhibition of osteoblast differentiation; 6, activation of growth factors, such as TGF-β. CatK, cathepsin K; M-CSF, macrophage-colony-stimulating factor; MMP, matrix metalloproteinase; Naa10p, N-α-acetyltransferase 10 protein; OPG, osteoprotegerin; RANKL, receptor activator of NF-κB ligand; TRAP, tartrate-resistant acid phosphatase.