Human osteoarthritic knee cartilage: fingerprinting of adhesion/growth-regulatory galectins in vitro and in situ indicates differential upregulation in severe degeneration

Abstract

The apparent connection of galectin-3 to chondrocyte survival and osteoarthritis-like cartilage modifications in animal models provided incentive for the mapping of seven members of this family of adhesion/growth-regulatory proteins in human cartilage specimens. Starting with work in vitro, RT-qPCR analyses and immunocytochemistry revealed gene transcription and protein presence in cultured OA chondrocytes, especially for galectin-1, galectin-3 and galectin-8. Immunohistochemistry in clinical specimens with mild and severe cartilage degeneration detected galectins in chondrocytes-with upregulation, especially of galectin-1 in areas of severe degeneration-accompanied by α2,6-sialylation in the pericellular matrix. Given the possibility for additive/antagonistic activities between galectins, these results direct further research toward examining cellular effects of (1) these proteins (alone or in combination) on chondrocytes and (2) remodeling of the chondrocyte glycophenotype.

Galectin-1 Couples Glycobiology to Inflammation in Osteoarthritis through the Activation of an NF-κB–Regulated Gene Network

“…In previous studies, we had revealed that several members of the galectin family are expressed in vivo in osteoarthritis (10), and that specific features of the chondrocyte glycophenotype are altered during osteoarthritic conditions (8,9). In this study, we focused on Galectin-1, by immunohistochemical analysis and work with human osteoarthritic chondrocytes.…”

“…Paraffin sections of mildly and severely degenerated cartilage were stained with Safranin O (Sigma-Aldrich) (10). Thereafter, a varying number of regions (2-10 per patient, depending on availability of regions differing in degeneration) was graded according to the Mankin score (MS), as previously described (10).…”

“…Immunohistochemical staining for Galectin-1 followed recently established protocols (10). Briefly, tissue sections were incubated with rabbit polyclonal Ab against human Galectin-1 (25).…”

“…Ag-dependent staining was developed using 3,39-diaminobenzidine tetrahydrochloride hydrate (FLUKA), whereas counterstaining was performed using Mayer's hemalum solution (Merck). The percentage of Galectin-1-positive chondrocytes in the regions of interest was determined independently by two observers, as described (10).…”

“…With respect to osteoarthritis, we have characterized the human chondrocyte glycophenotype, showing that it was profoundly altered in patients suffering from cartilage degeneration (8,9). Turning to galectins by immunohistochemical screening, initial evidence had suggested that Galectin-1 was associated to the level of degeneration in human osteoarthritic cartilage (10). This lectin is known to regulate cell-tocell and cell-to-matrix communication via glycan bridging and subsequent signaling, acting as anti-inflammatory effector by inducing apoptosis of activated T cells (6).…”