Intracellular interaction of EMILIN-1 with fibrillin-1 in human periodontal ligament cells

The elastic system fibers comprise oxytalan, elaunin and elastic fibers, differing in their relative microfibril and elastin contents. Human periodontal ligaments (PDLs) contain oxytalan fibers (pure microfibrils), which are composed mainly of fibrillin-1, the major component of microfibrils. We recently demonstrated that EMILIN-1, located at the interface between elastin and microfibrils, controls the amount of fibrillin-1 assembly in PDL fibroblast cell/matrix layers [8], although the mechanism involved was unclear. We subjected cultured PDL fibroblasts to immunofluorescence and immunoprecipitation assays in order to examine the intracellular interaction of EMILIN-1 with fibrillin-1. Immunofluorescence showed that EMILIN-1 was colocalized with fibrillin-1, both inside and outside the cells. Additionally, EMILIN-1 formed a complex with fibrillin-1 in the intracellular fraction. These results suggest that EMILIN-1 may form complexes with fibrillin-1 in cellular vesicles, thus contributing effectively to the initial assembly of pericellular fibrillin-1 during the process of oxytalan fiber formation.