Transforming growth factor-beta2 suppresses collagen cleavage in cultured human osteoarthritic cartilage, reduces expression of genes associated with chondrocyte hypertrophy and degradation, and increases prostaglandin E(2) production

Abstract

Articular cartilage degeneration in osteoarthritis (OA) involves type II collagen degradation and chondrocyte differentiation (hypertrophy). Because these changes resemble growth plate remodeling, we hypothesized that collagen degradation may be inhibitable by growth factors known to suppress growth plate hypertrophy, namely transforming growth factor (TGF)-beta2, fibroblast growth factor (FGF)-2, and insulin. Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with TGF-beta2, FGF-2, and insulin in combination (growth factors) or individually. In cultured explants from five OA patients, collagenase-mediated type II collagen cleavage was significantly down-regulated by combined growth factors as measured by enzyme-linked immunosorbent assay. Individually, FGF-2 and insulin failed to inhibit collagen cleavage in some OA explants whereas TGF-beta2 reduced collagen cleavage in these 5 explants and in 19 additional explants. Moreover, TGF-beta2 effectively suppressed cleavage at low concentrations. Together or individually these growth factors did not inhibit glycosaminoglycan (primarily aggrecan) degradation while TGF-beta2 occasionally did. Semiquantitative reverse transcriptase-polymerase chain reaction of articular cartilage from six OA patients revealed that TGF-beta2 suppressed expression of matrix metalloproteinase-13 and matrix metalloproteinase-9, early (PTHrP) and late (COL10A1) differentiation-related genes, and proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha). In contrast, TGF-beta2 up-regulated PGES-1 expression and prostaglandin E(2) release. These observations show that TGF-beta2 can suppress collagen resorption and chondrocyte differentiation in OA cartilage and that this may be mediated by prostaglandin E(2). Therefore TGF-beta2 could provide therapeutic control of type II collagen degeneration in OA.

Figure 1

Inhibition of collagen cleavage by collagenase (a) and release of total proteoglycan (GAG release) in conditioned media (b) in human OA cartilage explants treated with combined growth factors (10 ng/ml TGF-β2, 10 ng/ml FGF-2, and 100 ng/ml insulin) and individually: 10 ng/ml TGF-β2, 10 ng/ml FGF-2, or 100 ng/ml insulin. The ages and sexes of patients are indicated. P value (paired t-test analysis) less than 0.05 is considered significant and is shown compared to control (*).

Figure 2

Inhibition of type II collagen cleavage by collagenase in human OA articular cartilage explants by 10 ng/ml TGF-β2 alone. P value (Mann-Whitney analysis) less than 0.05 is considered significant and is shown compared to control (*).

Figure 3

Concentration-dependent inhibition of collagen cleavage by TGF-β2 in human OA explants. The ages and sexes of patients are indicated. P value (paired t-test analysis) less than 0.05 is considered significant and is shown compared to control (*).

Figure 4

Gene expression, measured by RT-PCR in human OA articular cartilage of a 79-year-old male (A), an 82-year-old male (C), an 82-year-old female (E), a 71-year-old female (B), a 73-year-old male (D), and a 64-year-old female (F) cultured with (+) and without (−)10 ng/ml TGF-β2. 18sRNA is used as a gel loading reference.

Figure 5

PGE₂ release induced by TGF-β2 in OA articular cartilage explants. The ages and sexes of patients are indicated. P value (paired t-test analysis) less than 0.05 is considered significant and is shown compared to control (*).