Segmental variation in the in vitro cell metabolism of nucleus pulposus cells isolated from a series of bovine caudal intervertebral discs.

摘要

STUDY DESIGN: This study focuses on the association between cell metabolism and molecular matrix composition of nucleus pulposus (NP) tissue with spine level in sequential bovine caudal intervertebral discs. OBJECTIVE: To explore the hypothesis that the molecular composition of NP tissue and corresponding cell metabolism varies with caudal spine. A secondary hypothesis is tested that potential cellular differences are maintained after monolayer culture. SUMMARY OF BACKGROUND DATA: In articular cartilage, cell metabolism and molecular matrix composition are influenced by loading history. This may also be a feature of intervertebral discs in series. METHODS: NP cells (nonpooled or level pooled) were isolated from four sequential bovine caudal intervertebral discs (levels 3-4, 4-5, 5-6, and 6-7) and cultured in alginate beads immediately or following monolayer culture. Levels of 3H-TdR (proliferation) and 35SO4 (GAG synthesis) incorporation were determined from 14 animals. In a separate set of 6 animals, total content of water, DNA, collagen (and type), GAG (and type) were also determined. RESULTS: The rate of 3H-TdR and 35SO4 incorporation in freshly isolated NP cells increased nonlinearly from level 3-4 to 6-7 (P < 0.05). Monolayer cultured cells retained level-specific differences for 35SO4 and 3H-TdR incorporation similar to that of freshly isolated cells. GAG content and chondroitin sulfate proportion decreased distally (P < 0.05); however, total collagen and Type I proportion increased distally (P < 0.05). No significant differences in water or DNA content could be determined. CONCLUSIONS: The results support the hypothesis that level-specific differences in NP cell metabolism and molecular composition are dependent on spine level potentially reflecting subtle mechanical differences between levels. Retention of level-specific differences in monolayer may suggest a certain level of cell "programming." This may be important for cellular strategies to repairspecific sites of degeneration.