Secretory Cells in the Nucleus pulposus of the Adult Human Intervertebral Disc

Abstract

A light microscopical study was conducted to ascertain the type of cells in the nucleus pulposus of theadult human intervertrebral disc. Three lumbar intervertebral discs were removed from each of 15 male and femaleadults at autopsy (ages ranged from 19 to 62 years). The tissue was fixed in formalin, decalcified in formic acid, dehydrated in a graded series of ethanol, embedded in paraffin, and serially sectioned at 7–10 µm. Tissue sectionswere affixed to albuminized glass slides and stained either by hematoxylin and eosin or hematoxylin and VanGieson’s stain. The cells of the bulk of the nucleus pulposus consisted of chondrocytes and a few fibroblasts;however, the subchondral matrix of the nucleus pulposos contained numerous stellate cells with (from 1 to 8)unusually long (up to 80 µm) primary cytoplasmic porcesses that often branch into secondary processes. The cellprocesses contained cytoplasmic varicosities at various intervals along their lengths; and their endings oftenexpanded into bulbous, vesicle-filled process terminals. The surrounding extracellular matrix usually containednumerous, vesicle-filled, eosinophil matrix bodies. Morphological similarities of cytoplasmic varicosities, processterminals, and matrix bodies, as well as the apparent budding of process terminals, suggest that these previouslyunidentified cells are secreting an unknown matrix component into the subchondral matrix of the nucleus pulposusof the adult human. *

Programmed cell death in intervertebral disc degeneration

“…The other possibility is that the PCD of IVD cells is similar to chondroptosis [17,18], which is a non-classical manner of apoptosis characterized by self-destruction of chondrocytes and cellular remnants blebbing into lacunae or the interterritorial space relating to the calcification of articular cartilage ECM. Because the similar cellular remnants, called matrix bodies, have been identified by Johnson et al [83] and the electron micrograph (Fig. 1C), which showed the appearances of a IVD cell undergoing PCD, are similar to those that were used to illustrate chondroptosis by Roach et al [18] Therefore both possibilities may become new focus of interest in the research field of PCD in IVD.…”

Osteoarthritis and intervertebral disc degeneration: Quite different, quite similar

“…At birth, the human NP has a high density of notochordal cells, which are large in diameter, contain intracellular vacuoles and appear in clusters . However, they are slowly replaced by chondrocyte‐like cells after birth . There is some evidence that the cells maintain some of their notochordal characteristics, as human degenerated intervertebral disc cells express brachyury, which is a well‐established notochordal marker .…”

Regional variations in certain cellular characteristics in human lumbar intervertebral discs, including the presence of α‐smooth muscle actin

“…Groups of cells have been long reported in the IVD, especially in the NP [4,22,24,30,31,38]. They can be further divided into cell pairs and clusters containing three or more cells [23].…”

“…Pairs of chondrocytes often are contained in the same pericellular matrix. Cells in a cluster share a common intercellular matrix, sometimes called a nest [24]. A clear conclusion cannot yet be drawn as to how cell grouping in the IVD changes with age-or disease-related degeneration.…”