Role of matrix proteins in the local regulation of bone metabolism and its abonomalities in osteoporosis

1.细胞-基质相互作用对成骨细胞分化的调控：I型胶原（COL(I)）与α 2 β 1整合素的相互作用导致成骨细胞分化和转化生长因子(TGF) - β受体下调。tgf - β受体的下调使细胞摆脱tgf - β对分化的抑制。为了阐明细胞-基质相互作用如何调节这些表型变化，我们在小鼠MC3T3-E1细胞中检测了信号通路。细胞附着在COL (I)上，刺激了局灶黏附激酶（FAK）和丝裂原活化蛋白激酶（MAPK）的酪氨酸磷酸化，并增强了MAPK的活性。herbimycin A对酪氨酸激酶的抑制、细胞松弛素D对局灶黏附的破坏或反义FAK mRNA的过表达均可阻止MAPK的激活和碱性磷酸酶（ALP）活性的增加。mapk特异性磷酸酶CL100的瞬时表达也抑制了ALP的升高。相比之下，tgf - β受体的下调不受CL100的影响，但被wortmannin（一种磷脂酰肌醇(PL) -3激酶抑制剂）所消除。这些结果表明，COL (I) -alpha2beta1整合素相互作用通过FAK-MAPK途径促进分化，并通过FAK-PI-3激酶途径下调tgf - β受体。这些信号通路可能在骨形成过程中成骨细胞的顺序分化中起重要作用。白细胞介素(IL) -11在感知加速小鼠（SAM）中的作用受损：SAM显示骨形成减少，骨密度低于正常小鼠。来自SAM的骨髓基质细胞（BMSC）含有较少的骨祖细胞，同时表现出增强的脂肪细胞分化，成骨细胞和破骨细胞的形成在SAM中受损。将IL-11添加到SAM的骨髓间充质干细胞中可抑制脂肪生成并恢复成骨细胞的形成。SAM小鼠骨髓间充质干细胞中IL-11的表达降低，而IL-11 cDNA未见异常。这些结果表明，骨髓间充质干细胞中IL-11表达不足导致SAM小鼠成骨细胞和破骨细胞形成受损。少

1.Regulation of osteoblastic differentiation by cell-matrix interactions : Interaction of type I collagen (COL(I)) with alpha2beta1 integrin causes differentiation and transforming growth factor (TGF) -beta receptor down-regulation in osteoblastic cells. The TGF-beta receptor down-regulation enables cells to escape from the inhibition of differentiation by TGF-beta. To clarify how the cell-matrix interaction regulates these phenotypic changes, signaling pathways were examined in murine MC3T3-E1 cells. Attachment of cells to COL (I) stimulated tyrosine phosphorylation of focal adhesion kinase (FAK) and mitogen-activated protein kinase (MAPK), and enhanced MAPK activity. Inhibition of tyrosine kinase by herbimycin A,destruction of focal adhesion by cytochalasin D,or overexpression of antisense FAK mRNA prevented the activation of MAPK and the increase in alkaline phosphatase (ALP) activity. Transient expression of a MAPK-specific phosphatase, CL100, also suppressed the elevation of ALP a … More ctivity. In contrast, TGF-beta receptor down-regulation was not affected by CL100, but was abrogated by wortmannin, a phosphatidyl inositol (PL) -3 kinase inhibitor. These results demonstrate that COL (I) -alpha2beta1 integrin interaction facilitates differentiation via FAK-MAPK pathway, and down-regulates TGF-beta receptors via FAK-PI-3 kinase pathway. These signaling pathways may play an important role in the sequential differentiation of osteoblasts during bone formation.2.Impaired interleukin (IL) -11 actions in sensence-accelerated mice (SAM) : SAM shows reduced bone formation with lower bone mineral density than its normal counterpart. Bone marrow stromal cells (BMSC) from SAM contain less osteoprogenitor cells while exhibiting enhanced adipocytic differentiation, and the formation of both osteoblasts and osteoclasts is impaired in SAM.Addition of IL-11 to BMSC from SAM suppressed adipogenesis and restored osteoblast formation. The expression of IL-11 was reduced in BMSC from SAM mice, whereas no abnormality was found in IL-11 cDNA from SAM mice. These results suggest that an insufficient expression of IL-11 in BMSC causes the impairment of osteoblast and osteoclast formation in SAM mice. Less