Growth factor transgenes interactively regulate articular chondrocytes

Abstract

Adult articular chondrocytes lack an effective repair response to correct damage from injury or osteoarthritis. Polypeptide growth factors that stimulate articular chondrocyte proliferation and cartilage matrix synthesis may augment this response. Gene transfer is a promising approach to delivering such factors. Multiple growth factor genes regulate these cell functions, but multiple growth factor gene transfer remains unexplored. We tested the hypothesis that multiple growth factor gene transfer selectively modulates articular chondrocyte proliferation and matrix synthesis. We tested the hypothesis by delivering combinations of the transgenes encoding insulin-like growth factor I (IGF-I), fibroblast growth factor-2 (FGF-2), transforming growth factor beta1 (TGF-β1), bone morphogenetic protein-2 (BMP-2), and bone morphogenetic protien-7 (BMP-7) to articular chondrocytes and measured changes in the production of DNA, glycosaminoglycan, and collagen. The transgenes differentially regulated all these chondrocyte activities. In concert, the transgenes interacted to generate widely divergent responses from the cells. These interactions ranged from inhibitory to synergistic. The transgene pair encoding IGF-I and FGF-2 maximized cell proliferation. The three-transgene group encoding IGF-I, BMP-2, and BMP-7 maximized matrix production and also optimized the balance between cell proliferation and matrix production. These data demonstrate an approach to articular chondrocyte regulation that may be tailored to stimulate specific cell functions, and suggest that certain growth factor gene combinations have potential value for cell-based articular cartilage repair.

Figure 1

DNA content of articular chondrocytes carrying the designated growth factor transgenes. Chondrocytes were transfected with individual or multiple vectors encoding IGF-I (I1), FGF-2 (F2), TGF-β1 (T1), BMP-2 (B2), BMP-7 (B7) or empty vector (C) and cultured for 6 days. Data are expressed as DNA normalized to control ± SD for 3 independent experiments.

Figure 2

Glycosaminoglycan (GAG) (A) or collagen (B) produced by articular chondrocytes carrying the designated growth factor transgenes. Chondrocytes were transfected with individual or multiple vectors encoding IGF-I (I1), FGF-2 (F2), TGF-β1 (T1), BMP-2 (B2), BMP-7 (B7) or empty vector (C) and cultured for 6 days. GAG or collagen released into the medium and retained by the cells were measured separately. Data are expressed as GAG or collagen normalized to control ± SD for 3 independent experiments.

Figure 3

Distribution of glycosaminoglycan (GAG) (A) or collagen (B) produced by articular chondrocytes carrying the designated growth factor transgenes. Data are expressed as the ratio of cell-associated/released GAG or collagen normalized to control ± SD for 3 independent experiments.

Figure 4

Cell-associated glycosaminoglycan (GAG) (A) or collagen (B) normalized to DNA. Chondrocytes were transfected with individual or multiple vectors encoding IGF-I (I1), FGF-2 (F2), TGF-β1 (T1), BMP-2 (B2), BMP-7 (B7) or empty vector (C) and cultured for 6 days. Data are expressed as the ratio of cell-associated GAG/DNA or collagen/DNA normalized to control ± SD for 3 independent experiments.

Figure 5

Time course of released glycosaminoglycan (GAG) (A) or collagen (B) production by articular chondrocytes carrying the designated growth factor transgenes. Chondrocytes were transfected with individual or multiple vectors encoding IGF-I (I1), FGF-2 (F2), TGF-β1 (T1), BMP-2 (B2), BMP-7 (B7) or empty vector (C) and cultured for the designated time periods. GAG or collagen released into the medium was measured for each time period. Data are expressed as released GAG or collagen normalized to control for each time point ± SD for 3 independent experiments.