Galectin-3 surface expression on human adult chondrocytes: a potential substrate for collagenase-3
Abstract
Background: Galectin-3 is a lectin detected in mature and early hypertrophic chondrocytes; osteoarthritic
(OA) chondrocytes can re-express hypertrophic markers.
Objective: To investigate the synthesis and subcellular localisation of galectin-3 in adult chondrocytes as
well as the possibility of cleavage of galectin-3 by collagenase-1 and -3.
Methods: Galectin-3 was assessed by immunohistochemistry and real time polymerase chain reaction
(PCR) in normal and OA cartilage. Its localisation was investigated by subcellular fractionation,
immunocytology, and flow cytometry. Proteolysis of galectin-3 by collagenase-1 and -3 was determined
by in vitro assay.
Results: Galectin-3 expression was increased 2.4-fold as measured by reverse transcriptase (RT)-PCR
(p,0.05, n = 5) and threefold by immunohistochemistry (p,0.003 n = 6) in OA cartilage compared with
normal cartilage. In adult chondrocytes, galectin-3 was found in the cytosol and membrane enriched
fractions. Both immunocytology and flow cytometry confirmed the presence of galectin-3 at the surface of
chondrocytes. A strong correlation was found between integrin-b1 and galectin-3 expression at the
surface of chondrocytes. Moreover, collagenase-3 cleaved galectin-3 with a higher activity than
collagenase-1. The proteolysed sites generated were identical to those produced by gelatinases A and B.
Conclusion: Galectin-3 may play a part in OA, having two roles, one intracellular and not yet identified,
and another at the cell surface, possibly related to the interaction of chondrocytes and the cartilage matrix.