Fibronectin filaments and actin microfilaments are organized into a fibronexus in Dupuytren's diseased tissue

Abstract

The fibronexus is a close transmembrane association between fibronectin filaments and actin microfilaments. It has been found at the surfaces of fibroblasts in tissue culture, as well as within contracting granulation tissue. This specialized connection has been proposed to play an important role in the adhesive properties of fibroblasts. The purpose of this study is to determine whether the fibronexus is present in other contracting tissues besides granulation tissue, specifically in Dupuytren's diseased tissue. Dupuytren's disease is a pathologic condition in which the palmar aponeurosis becomes shortened leading to irreversible flexion of the digits. Shortening of the aponeurosis is believed to be an active cellular process. Extracellular filaments and actin microfilaments form close transmembrane associations at the surfaces of actin-rich fibroblasts in Dupuytren's disease. Extracellular filaments extend from the cell surface into the surrounding tissue connecting fibroblasts with collagen fibrils and adjacent cells. In this study we have used immunoelectron microscopy to demonstrate that the extracellular filaments that participate in these close transmembrane associations contain fibronectin. High voltage electron microscopy has been used to examine the three-dimensional relationships between the cytoskeleton and fibronectin filaments in Dupuytren's diseased tissue. We propose that the fibronexus is a dominant adhesive structure at the surface of fibroblasts in Dupuytren's diseased tissue. The fibronexus, by mediating cell-to-cell and cell-to-matrix attachments, may serve to transmit contractile forces generated by actin microfilaments in these cells throughout the diseased tissue.