Review Question - QID 5838

With age the nucleus pulposus transforms its cellular phenotype, decreases cell content, decreases matrix synthesis, and decreases in size. The nucleus itself has no fibroblast-like cells; these cells are retained exclusively in the annulus fibrosus.

The aging nucleus pulposus undergoes many pathologic changes that lead to abnormal mechanics and discogenic back pain. Specifically, the disc decreases its water content, decreases its size, decreases its cellularity, and decreases its proteoglycan content. Its molecular content remains predominantly type II collagen as it ages.

Smith et. al. review intervertebral disc embryogenesis, development, and degeneration. The vertebral column develops through a complex interplay between the somites and mesoderm-derived notochord, which plays a central role in cell signaling that allows differentiation of the intervertebral disc. The disc itself it composed of a central nucleus pulposus (type II collagen) with an outer annulus fibrosus (type I collagen). The cells of the annulus adopt fibroblastic morphology, in contrast to the notochordal-like cells of the nucleus. The hallmark of the aging nucleus is its decreased cellularity. This process begins within the first 10 years of life, and eventually all notorchordal-like cells disappear and are replaced by chondrocyte-like cells with a lower metabolic rate. These cell populations are considered potential therapeutic targets for discogenic back pain.

Incorrect Answers:
Answers 1, 2, 3, 5 are all normal characteristics of the aging nucleus pulposus.