TGF-beta3 stimulates and regulates collagen synthesis through TGF-beta1-dependent and independent mechanisms

In contrast to the TGF-beta1 and beta2 isoforms, TGF-beta3 has shown the ability to downregulate scarring and fibrosis in vivo under certain experimental conditions. In this study, we determined the direct effects of TGF-beta3 on cultures of human dermal fibroblasts. TGF-beta3 (0.1 to 100 pg per ml) increased DNA synthesis up to 50% (p < 0.01, r = 0.970), collagen protein synthesis up to 200% (dose range of 0.1 to 5 ng per ml, p < 0.001, r = 0.990), and increased alpha1(I) procollagen mRNA levels (r = 0.999), with maximal effects (200% of control) observed by 24 h. Collagen lattice contraction was increased by more than 50% in response to TGF-beta3 (p < 0.001), and to a similar extent as the TGF-beta1 isoform. Stimulation of collagen synthesis and of alpha1(I) procollagen mRNA levels in response to TGF-beta3 was partially blocked by a TGF-beta1-specific anti-sense oligonucleotide but was still detectable (35% greater than baseline) when TGF-beta3 was added to dermal fibroblasts from TGF-beta1 knock-out mice. In contrast with these stimulatory effects, however, downregulation of alpha1(I) procollagen, alpha1(III) procollagen, and TGF-beta1 mRNA levels toward baseline occurred when TGF-beta3 (0.1 to 5 ng per ml) was added simultaneously and in combination with TGF-beta1. We conclude that stimulation of collagen synthesis by TGF-beta3 occurs through TGF-beta1-dependent and independent pathways. By downregulating the response to TGF-beta1 and by shifting from one pathway to the other, TGF-beta3 can dampen and provide fine-tuning to the overall TGF-beta's induced program of collagen deposition.