An increase in collagen type III in the matrix adsorbed to titani

An increase in collagen type III in the matrix adsorbed to titanium for instance induced an increased collagen synthesis and a decrease in alkaline phosphatase (ALP) activity and calcium phosphate deposition in rat calvarial osteoblasts, while on collagen type I the situation was reversed.15 This effect may be based on the role collagen type III plays in the early phase of intramembraneous fracture healing while collagen I only appears later and is associated with matrix mineralization.11 Collagens I, III and V all promote attachment and spreading of fibroblasts if used as coating on rigid substrates,51 on pliable substrates, though, the collagen V and I have different effects, with I promoting and V impairing fibroblast spreading.

52 Adding glycoproteins or proteoglycans instead of other collagen types is essentially of higher interest, as these multifunctional, multidomain proteins can convey a large number of ECM cell interactions. It is not very common, though; apart from fibronectin, mainly laminin and, to some extent elastin have been utilized. As they bind to a cell adhesion receptor set different from collagen, including them changes the mechanism of cell adhesion to the collagen matrix. Depending on whether collagen or collagen/FN is used, different integrin receptors are engaged and activated.15 This activates other signaling pathways, which in turn lead to other cell responses. For laminin (or laminin derived peptides) in combination with collagen, a positive effect on neuronal cell growth has been shown.

53 In human mesenchymal stem cells (hMSC) it activated an ERK dependent pathway and induced an osteogenic phenotype.54 Other ECM proteins have also been shown to influence hMSC. The cells bind to them with different integrin sets, respectively, and with varying affinities (FN > collagen I > collagen IV > vitronectin > laminin-1). Osteogenic differentiation was highest on vitronectin and collagen I, while almost none occurred on fibronectin.55 Of the two, vitronectin induced enhanced focal adhesion formation, activated FAK (focal adhesion kinase) and paxilling, and reduced the activity of ERK (extracellular signal regulated kinase) and PI3K (phosphoinositide 3 kinase) pathways. Collagen, on the other hand, reduced focal adhesion formation, reduced FAK and paxillin activation, and increased ERK and PI3K activation.

56 Collagen and vitronectin are recognized by different integrin subsets (��2��1 for collagen, ��v��3 and ��v��5 for VN), which indicates the importance these interactions may have in regulating cell behavior.57 There are only comparatively few studies that deal with collagen/proteoglycan matrices and their effect on cells. The main influence Entinostat of PGs is, unlike that of the glycoproteins, not based on the direct interaction with cell adhesion receptors, but rather with other cell surface receptors, and on their ability to bind growth factors and cytokines.

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