Bone morphogenic protein (BMP-2) enhances expression of type II collagen and aggrecan in human chondrocytes in 3D alginate cultures

Background

The healing capacity of articular cartilage is very limited in the adult. Therefore, tissue engineering techniques were developed to treat cartilage lesions.

Objective

Because high expression of type II collagen is of importance for the properties of cartilage after transplantation, we investigated whether the growth factor BMP-2 may modulate the chondrogenic phenotype in monolayer cell cultures (2D) and in three-dimensional culture (3D) systems.

Methods

Chondrocytes from articular knee cartilage of five individuals were isolated and expanded under GMP conditions suitable for clinical purposes. Cells were seeded either in 2D cultures or embedded in alginate beads (3D) in the presence or absence of human recombinant BMP-2 (hr-BMP-2). Then, cells were harvested and analysis of the chondrogenic phenotype was performed using quantitative RT-PCR, immunocytochemistry and ELISA methods.

Results

Expansion of chondrocytes in primary culture (P0) or in first subculture (P1) did not yield populations enriched for dedifferentiated or hypertrophic cells, because type X collagen encoding mRNA was detectable only at very low copy numbers. Seeding P1 chondrocytes in 3D culture significantly reduced type I collagen, BMP-4 and IL-18, and induced type II collagen and BMP-2 encoding mRNA. Suppression of IL-1β and induction of IL-10 were noted but were not statistically significant. At P2, these changes were still evident. Addition of BMP-2 to 2D chondrocytes had no effect on type II collagen or IL-1β mRNA amounts. In contrast, in 3D chondrocytes BMP-2 induced type II collagen and reduced IL-1 mRNA amounts. This was also seen by ELISA and immunocytochemistry.

Conclusions

We conclude that chondrocytes during expansion for ACT may benefit from BMP-2 activation only when seeded in an appropriate 3D culture system.