Comparative expression of matrix-associated genes and inflammatory cytokines-associated genes according to disc degeneration: analysis of living human nucleus pulposus

Abstract

STUDY DESIGN: The 2 groups of living human nucleus pulposus were prospectively compared according to disc degeneration.

OBJECTIVES: This study was conducted to investigate the expressions of various genes associated with matrix synthesis and expressions of inflammatory cytokines-associated genes according to degrees of disc degeneration in human discs.

SUMMARY OF BACKGROUND DATA: Degenerated discs were obtained from 18 patients who underwent discectomy for lumbar disc herniation. Disc degeneration was graded by T2-weighted magnetic resonance imaging using Pfirrmann's grading system. Discs were allocated to 2 groups: group I (9 patients)-mildly degenerated discs (grades II and III) and group II (9 patients)-severely degenerated discs (grades IV and V).

METHODS: Cells from the nucleus pulposus were isolated and then cultured as monolayers. The mRNA expressions of aggrecan, type II collagen, Sox9, type I collagen, alkaline phosphatase, osteocalcin, tumor necrosis factor-α, and interleukin-1β in the 2 groups were compared by real-time polymerase chain reaction, and production of matrix-associate proteins (aggrecan, type II collagen, Sox9, type I collagen, alkaline phosphatase, and osteocalcin) were compared by Western blotting.

RESULTS: mRNA expressions in group I were upregulated versus group II to the following extents: 1.83 times for aggrecan, 1.82 times for type II collagen, 1.80 times for Sox9, 1.41 times for type I collagen, 1.38 times for alkaline phosphatase, and 1.80 times for osteocalcin. Furthermore, Western blotting showed that aggrecan, type II collagen, Sox9, type I collagen, alkaline phosphatase, and osteocalcin were higher in group I. However, the mRNA levels of tumor necrosis factor-α and interleukin-1β were 1.26 and 1.11-fold, respectively, upregulated in group II.

CONCLUSIONS: Mildly degenerated discs showed greater matrix, chondrogenic, and osteoblastic gene expressions than severely degenerated discs, indicating that the ability to produce matrix-associated proteins is greater for cells in mildly degenerated than in severely degenerated discs. However, inflammatory cytokine genes associated with disc degeneration were expressed at higher levels in the severely degenerated group. This study shows that a reduction in matrix synthesis and an increase of inflammatory cytokine levels occurs during disc degeneration at the same time