Study Design. An analysis of proteoglycans of the intervertebral disc using
immunoblotting of tissue extracts.
Objectives, To investigate the changes in structure and abundance of fibrom
odulin and lumican in human intervertebral discs during aging and degenerat
ion.
Summary of Background Data. Fibromodulin and lumican are keratan sulfate pr
oteoglycan constituents of the disc's extracellular matrix, whose interacti
on with collagen fibrils may contribute to the mechanical properties of the
tissue. Changes in their abundance and/or structure that occur with aging
and degeneration therefore may have an impact on disc function.
Methods. Lumbar intervertebral discs were obtained from individuals of diff
erent ages, and extracts of anulus fibrosus and nucleus pulposus were analy
zed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immuno
blotting using antibodies specific for fibromodulin and lumican.
Results. The major changes in abundance observed with age were a decrease i
n fibromodulin in the adult nucleus pulposus and an increase in lumican in
anulus fibrosus during early juvenile development. In addition, fibromoduli
n in the anulus fibrosus exhibited a structural change with increasing age,
characterized by a shift toward the predominance of its glycoprotein form
lacking keratan sulfate. Fibromodulin was more abundant in the anulus fibro
sus than in nucleus pulposus at all ages, whereas lumican was much more abu
ndant in nucleus pulposus than in anulus fibrosus in the young juvenile; in
the adult, however, lumican was present in comparable levels in both tissu
es. With increasing degrees of degeneration, fibromodulin exhibited an incr
ease in abundance.
Conclusions. Growth, aging, and degeneration of the intervertebral disc are
associated with changes in the abundance and structure of fibromodulin and
lumican, which presumably influence the functional properties of the tissu
e.