The effect of capacitively coupled (CC) electrical stimulation on human disc nucleus pulposus cells and the relationship between CC and BMP-7.

Purpose: An in vitro study using human intervertebral disc nucleus pulposus cells to evaluate the effects of CC stimulation on disc-matrix macromolecule production.

Methods: Nucleus pulposus cells were cultured in alginate beads and treated with CC stimulation. The effect of BMP on CC stimulation of the cells was evaluated by applying a BMP blocker (noggin) or by applying additional BMP-7 to the culture. The mRNA levels of the disc extracellular matrix genes (collagen I, II, aggrecan) and BMPs were measured by real-time PCR. The protein levels of aggrecan, collagen II, and BMPs were determined by ELISAs and Western blots. Sulfated glycosaminoglycan (sGAG) content was assayed using the DMMB method.

Results: (1) CC stimulation upregulates the production of the disc-matrix macromolecular components: sGAG, aggrecan and collagen II; (2) CC stimulation increases the ratio of mRNA expression levels of collagen II to collagen I; (3) CC stimulation induces the expression of endogenous BMP-4 and BMP-7; (4) inhibition of BMP activity (using noggin) reduces CC-mediated upregulation of aggrecan and collagen II; (5) CC and BMP-7 act in synergy to increase the upregulation of disc-matrix macromolecules.

Conclusion: CC stimulation upregulates the production of the intervertebral disc-matrix macromolecules aggrecan, collagen II, and sGAG by a mechanism involving BMPs. CC stimulation acts in synergy with BMP-7 to increase the upregulation of these disc-matrix macromolecules.