Saturday, November 2, 2002 2:14–2:57 pm Concurrent Session 6A: Bone Morphogenic Protein: 2:14 Bone morphogenic protein–2 facilitates expression of chondrogenic not osteogenic phenotype in human intervertebral disc cells

Abstract

Purpose of study: With the introduction of growth factors and development of vector technology, it is possible to genetically modify intervertebral disc cells by transfer of growth factor genes to upregulate matrix synthesis. Bone morphogenic protein (BMP)-2 was known to play a crucial role in osteoblast differentiation and bone formation. The bone-forming potential of BMP-2 raises the research question, Can BMP-2 upregulate expression of chondrogenic phenotype rather than osteogenic phenotype in the intervertebral disc? Therefore, the objective of this in vitro study is to determine the effect of recombinant human BMP-2 (rhBMP-2) on proteoglycan synthesis and mRNA expression of matrix components, that is, aggrecan, collagen type 1, collagen type 2 and osteocalcin in human intervertebral disc cells.Methods used: We harvested cervical and lumbar disc tissue from six patients during surgical disc procedures. The disc cells were isolated from disc tissue by sequential enzymatic digestion and cultured. Then cultures were incorporated into alginate beads as described. rhBMP-2 (R&D) was administered to the cultures with various concentration. Newly synthesized proteoglycan was assessed by 35S incorporation using chromatography on Sephadex G-25 in PD-10 column. Reverse transcriptase polymerase chain reaction (RT-PCR) for expression of aggrecan, collagen type 1, collagen type 2 and osteocalcin mRNA was performed.of findings: In the rhBMP-2–treated cultures, there was increased newly synthesized proteoglycan (1.6-fold in 300 ng/ml, 3.5-fold in 1,500 ng/ml of rhBMP-2) and increased expression of aggrecan, collagen type 1 and collagen type 2 mRNA compared with untreated control in a dose-dependent manner. However, rhBMP-2 did not upregulate expression of osteocalcin mRNA in a given dose.Relationship between findings and existing knowledge: The result of this study demonstrated that the effect of BMP-2 on human intervertebral disc cells is chondrogenic rather than osteogenic. Also BMP-2 upregulates synthesis of matrix as proved by proteoglycan synthesis, mRNA expression of collagen 1, 2 and aggrecan.Overall significance of findings: In human intervertebral disc cells, rhBMP-2 clearly upregulates mRNA expression of chondrogenic component, that is, aggrecan, collagen type 1 and collagen type 2 without upregulating expression of mRNA of osteocalcin with given dose. The effect of rhBMP-2 was dose dependent in proteoglycan synthesis and mRNA expression of aggrecan, collagen type 1 and collagen type 2. In conclusion, this study raises the possibility that rhBMP-2 and BMP-2 encoding gene can be anabolic agents for regenerating matrix of the intervertebral disc.Disclosures: BMP-2: Investigational.Conflict of interest: Hwan-Mo Lee, grant research support, Brain Korea 21 Project (government).