Study Design. Galectin-3
expression in rat intervertebral disc
at different stages in postnatal life is evaluated.
To determine if galectin-3
expression is confined to cells of the nucleus pulposus
in the postnatal rat intervertebral disc
Summary of Background Data.
During embryonic development, the anulus fibrosus
is derived from the sclerotome, whereas the nucleus pulposus
is notochordal. Many authorities opine that in the postnatal disc, notochordal cells play a central role in controlling the development of degenerative disc disease. Surprisingly, unequivocal evidence supporting the existence of notochordal cells in the nucleus pulposus
in postnatal life has yet to be demonstrated. Since the expression of galectin-3
is commonly used to identify notochordal cells, we evaluated its expression in tissues of the rat disc and in cultured cells.
expression was studied in the nucleus pulposus
and anulus fibrosus
tissue of rat discs (2 days, 9 weeks, and 10 months old), and cultured cells using different biochemical and molecular biology methods. Rat sternal cartilage and cultured sternal chondrocytes were used as controls.
Immunohistochemical studies indicated that galectin-3
was present in the nucleus pulposus
and anulus fibrosus
. In both discal tissues and cultured cells, studies confirmed that there was a robust expression of galectin-3
messenger ribonucleic acid and protein. Protein expression patterns were similar in neonatal, young, and mature rats. There was also evidence of intracellular and membrane expression of galectin-3
in the cultured disc cells. Finally, significant levels of galectin-3
were evident in rat sternal cartilage and cultured sternal chondrocytes.
Results of the study indicate that galectin-3
is expressed in the neonatal, young, and mature rat disc, and its expression is not restricted to the cells of the nucleus pulposus
. Because of its ubiquitous expression, this protein cannot be used as a marker of notochordal cells in the postnatal rat disc.