The ground substance of the intervertebral disc consists primarily of
proteoglycans, which give the tissue its stiffness to compression and its
resiliency. To investigate the structure and composition of these
molecules, we extracted them from human infant nucleus pulposus under
associative conditions and from human infant annulus fibrosus and cartilage
end-plate under dissociative conditions. We examined the degree of
aggregation, the composition, the electron microscopic appearance, and the
dimensions of the proteoglycans of the intervertebral disc and compared
their structure and dimensions with those of the proteoglycans from bovine
hyaline cartilage. Aggregates represented 52 per cent of the proteoglycans
of the nucleus pulposus between the ages of one and ten days but only 28
per cent between the ages of six and eight months. Preparations from the
corresponding annuli contained 59 per cent aggregates at one to ten days
and 47 per cent at six months. The corresponding cartilage end-plate
preparations contained 45 and 40 per cent aggregates. The proteoglycans of
the annulus fibrosus and cartilage end-plate contained more protein and
less hexosamine than did those of the nucleus pulposus. Electron microscopy
showed that approximately two-thirds of the aggregates from nucleus
pulposus consisted of very short hyaluronate filaments with closely packed
monomers. The other third had longer hyaluronate filaments and wider
distances between monomers, and closely resembled the aggregates from the
annulus fibrosus and cartilage end-plate. Aggregated monomers consisted of
two segments: a thin segment connecting directly to the hyaluronic acid
filament and a thick segment extending peripherally from the thin segment.
The thin segment formed about 12 per cent of the total monomer length in
the samples from all three disc tissues. The lower proportion of aggregated
monomers, the lower protein content, and the smaller aggregates with
closely packed monomers suggest that the nucleus pulposus may contain less
link protein than do the annulus fibrosus and cartilage end-plate. Compared
with proteoglycan aggregates from bovine hyaline cartilage, proteoglycan
aggregates from human intervertebral disc were shorter and had fewer
monomers and wider spacing between monomers. The aggregated monomers from
the three components of the intervertebral disc had an average length of
209 +/- 90 nanometers, compared with 210 +/- 114 nanometers for monomers
from hyaline cartilage of skeletally mature cows, 250 +/- 116 nanometers
for monomers from hyaline cartilage of skeletally immature calves, and 288
+/- 108 nanometers for monomers from fetal animals.(ABSTRACT TRUNCATED AT
400 WORDS)