Location and Distribution of Non-collagenous Matrix Proteins in Musculoskeletal Tissues of Rat

The study assessed immunohistochemically the location and distribution of various non-collagenous matrix proteins (fibronectin, laminin, tenascin-C, osteocalcin, thrombospondin-1, vitronectin and undulin) in musculoskeletal tissues of rat. Fibronectin and thrombospondin-1 were found to be ubiquitous in the studied tissues. High immunoreactivity of these proteins was found in the extracellular matrix of the anatomical sites where firm bindings are needed, i.e. between muscle fibres and fibre bundles, between the collagen fibres of a tendon and at myotendinous junctions, osteotendinous junctions and articular cartilage. Tenascin-C was found in the extracellular matrix of regions where especially high forces are transmitted from one tissue component to the other, such as myotendinous junctions and osteotendinous junctions. Laminin was demonstrated in the basement membranes of the muscle cells and capillaries of the muscle–tendon units. Osteocalc in immunoreactivity concentrated in the extracellular matrix of areas of newly formed bone tissue, i.e. in the subperiosteal and subchondral regions, osteoid tissue and mineralized fibrocartilage zone of the osteotendinous junction. Mild vitronectin activity could be seen in the extracellular matrix of the osteotendinous and myotendinous junctions, and high activity around the bone marrow cells. Undulin could be demonstrated in the extracellular matrix (i.e. on the collagen fibres) of the tendon and epimysium only. However, it was co-distributed with fibronectin and tenascin-C. Together, these findings on the normal location and distribution of these non-collagenous proteins in the musculoskeletal tissues help to form the basis of knowledge against which the location and distribution of the these proteins in various pathological processes could be compared.