Attachment of human vascular smooth muscles cells to intact microfibrillar assemblies of collagen VI and fibrillin.

Human vascular smooth muscle cells have been used to assess the implied role of connective tissue microfibrils as cellular ligands. Preparations of intact high-M(r) microfibrillar assemblies of collagen VI and of fibrillin, respectively, were isolated from foetal bovine skin and used as ligands in cell attachment and spreading assays. Intact collagen VI microfibrils were capable of mediating cell attachment and partial spreading. Cell attachment assays using ligands composed of defined collagen VI fragments generated by pepsin or bacterial collagenase digestions demonstrated that both the triple-helical and non-collagenous domains of collagen VI had cell adhesion activity, although at reduced levels relative to intact microfibrils. Fibronectin was identified as a modulator of intact collagen VI microfibril-mediated cell attachment. These observations are indicative of complex multiple interactions between collagen VI microfibrils and smooth muscle cells. Purified fibrillin-containing microfibrils were also shown to support smooth muscle cell adhesion. Both pepsin-resistant and pepsin-sensitive domains of fibrillin exhibited some cell attachment activity, but at reduced levels relative to the intact fibrillin microfibrils. These data provide the first direct evidence of a physiological role for intact microfibrillar assemblies in cell-matrix interactions, and the involvement of integrin cell surface receptors containing the beta 1 subunit.