Effect of Extracellular Matrix in BMP-Induced Chondro- and Osteogenesis

骨形态发生蛋白(BMP)刺激未成熟的间充质细胞在皮下植入不溶性骨基质(IBM)，形成类似于软骨内成骨的过程。然而，通过对IBM以外的各种载体的检测，我们发现BMP诱导的细胞分化高度依赖于载体的性质。在这种情况下，我们进一步研究了使用IBM以外的至少七种不同载体的效果。这些BMP载体分为纤维型、颗粒型和块状型。(1)纤维型包括纤维胶原膜和玻璃纤维膜(FGM)。(2)颗粒型：胶原珠、羟基磷灰石多孔颗粒(PPHAP)和羟基磷灰石固体颗粒；(3)块状：羟基磷灰石多孔块和蜂窝状羟基磷灰石。重组人骨形态发生蛋白-2(rhBMP-2，山口公司赠送)以含有全部活性BMP(BMPs鸡尾酒)的部分纯化的BMP(S300组分)作为BMPs的来源。每一种骨形态发生蛋白复合载体诱导出独特的骨和软骨形成模式。举一个典型的例子，S300和FGM(纤维直径1微米，厚度0.6毫米)的组合只诱导膜内的软骨。相比之下，PPHAP/S300植入物诱导的骨形成直接跟随PPHAP毛孔内的纤维组织形成，而没有任何可检测到的软骨形成。结果表明，像PPHAP这样的连续孔结构为血管形成创造了足够的空间，而FGM(1um排除大小)的紧密网络为未成熟细胞提供了穿透膜的空间，但不能形成血管。因此，血管形成或拒绝结构是骨形态发生蛋白载体诱导骨和软骨的关键几何因素之一。

Bone morphogenetic proteins (BMPs) stimulate immature mesenchymal cells to create a process similar to endochondral ossification when they are subcutaneously implanted with insoluble bone matrix (IBM). However, by testing various carriers other than IBM,we found that BMP-induced cell-differentiation is highly dependent on the nature of carrier. This situation further led us to study the effect of the carriers using at least seven different carriers other than IBM.These BMP-carriers were classified into three types : fiber-, particle-and block-types.(1) The fiber-type includes fibrous collagen membrane and fibrous glass membrane (FGM). (2) The particle-type : collagen beads, porous particles of hydroxyapatite (PPHAP) and solid particles of hydroxyapatite, and (3) the block-type : porous blocks of hydroxyapatite and honeycomb-shaped hydroxyapatite. Recombinant human BMP-2 (rhBMP-2, a kind gift from Yamanouchi Co.) and the partially purified BMP (S300 fraction) which contains all the active BMPs (BMPs cocktail) were used as the source of BMPs. Each BMP-combined carrier induced unique pattern of bone and cartilage formation. To give typical examples, a combination of S300 and FGM (with a fiber diameter of 1mum and thickness of 0.6 mm) induced exclusively cartilage inside the membrane. In contrast, PPHAP/S300 implants induced bone formation that directly followed fibrous tissue formation within the pores of PPHAP,without any detectable cartilage formation. It was concluded that continuous pores structure such as PPHAP creates a space sufficient for vasculature, while the tight network of FGM (1 mum exclusion size) provides immature cells with space for penetrating into the membrane, but not for vascular formation. Thus, vasculature-forming or refusing structure is one of the key geometric factors of BMP-carrier for bone and cartilage induction.