Disc cell gene profiles, mechanical loads and degeneration linked

Researchers compared annulus and nucleus cells' biomechanical and chemical properties.

Mechanical stimulation may regulate intervertebral disc cells’ matrix turnover via alteration of gene expression; disc degeneration may have an influence on this process.

Cornelia Neidlinger-Wilke, PhD, of Ulm, Germany, presented results of a comparison study at the 2005 Annual Congress of the Spine Society of Europe (EuroSpine 2005). The presentation won the Best Basic Science Poster Award at the meeting.

Wilke and her co-authors aimed to compare human disc annulus and nucleus cells’ gene expression in response to cyclic strain and hydrostatic pressure, the most basic mechanical loads that occur in different disc regions.

Influence of mechanical stimuli

“Dynamic loading is important for intervertebral disc physiology and prevention of disc degeneration,” she said. “[We studied] the influence of both mechanical stimuli on gene expression of anabolic and catabolic proteins of disc cells from the different disc regions.”

The researchers performed biopsies of various patients undergoing disc herniation surgery. They isolated cells from the discs' annulus and nucleus regions.

The 19 patients who underwent disc herniation surgery and donated disc cell biopsies had a mean age of 44 years. The researchers isolated the annulus and nucleus cells. They then applied cyclic strain (1% to 8%, 1 Hz) and intermittent hydrostatic pressure (0.25 Mpa, 0.1 Hz) to the cells under equal culture conditions in 3-D collagen type-I gels (300,000 cells/ml).

Next, the investigators analyzed gene expression 24 hours after mechanical stimulation ended and compared the stimulated samples to unstimulated control cultures. They used real-time reverse transcriptase-polymerase chain reaction with specific primers for anabolic (ie, collagen I, collagen II and aggrecan, or large aggregating chondroitin sulphate proteoglycan) and catabolic (MMP-2 and MMP-3) matrix proteins. They used the Wilcoxon signed-rank test to make statistical evaluations.

Cyclic strain

Cyclic strain increased collagen I expression of the annulus (A) and nucleus (N) cells (A:+30%, P=.062; N:+58%, P=.027), and aggrecan expression of annulus cells (+35%, P=.008), but decreased MMP-3 expression of both cell types (A:–38%, P=.002; N:–26%, P=.01), the researchers said.

Hydrostatic pressure increased collagen I expression of both cell types (A:+29%, P=.047; N:+23%, P=.066). It also increased aggrecan expression of nucleus cells (+24%, P=.052), but decreased MMP-3 expression of nucleus cells (–20%, P=.008).

Both mechanical stimuli gave results showing “rather big donor/donor variations with some donors being high and others low, responsive to mechanical stimulation,” researchers said.

The results suggest that mechanical stimulation has “considerable influence on disc matrix turnover via alterations of gene expression of both annulus and nucleus cells,” they wrote.

“Moderate” mechanical loading seemed to stimulate matrix formation, “whereas expression of matrix-degrading MMPs tended to decrease,” the authors said. Degrees of different donor patients’ disc tissue degeneration may influence wide variations of disc cell responses, Wilke and her co-authors added.

“Further experiments will be necessary to confirm supposable correlations between gene expression profiles and degeneration,” she said.

For more information:
Neidlinger-Wilke C, Würtz K, Liedert A, et al. Patient variations of disc cell gene expression in response to cyclic strain and hydostatic pressure — a possible influence of degeneration? Scientific poster #12. Best Basic Science Poster Award. Presented at EuroSpine 2005. Sept. 21-24, 2005. Barcelona, Spain.