Galectin-3 expression in the intervertebral disc: a useful marker of the notochord phenotype?
METHODS
Galectin-3 expression in rat intervertebral disc at different stages in postnatal life is evaluated.


OBJECTIVE
To determine if galectin-3 expression is confined to cells of the nucleus pulposus in the postnatal rat intervertebral disc.


BACKGROUND
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.


METHODS
Galectin-3 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.


RESULTS
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.


CONCLUSIONS
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.
Oguz
Erbil
E
Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Tsai
Tsung-Ting
TT
Di Martino
Alberto
A
Guttapalli
Asha
A
Albert
Todd J
TJ
Shapiro
Irving M
IM
Risbud
Makarand V
MV
D000375:Aging / Q000235:genetics / Q000502:physiology; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D037502:Galectin 3 / Q000096:biosynthesis* / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D007403:Intervertebral Disc / Q000254:growth & development / Q000378:metabolism*; D008297:Male; D009672:Notochord / Q000254:growth & development / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D017208:Rats, Wistar
D015415:Biomarkers; D037502:Galectin 3