TGF-β1-induced collagen expression in NHLF is downregulated by BMP-4. NHLF were stimulated with 5 ng/ml TGF-β1 or 100 ng/ml BMP-4 or BMP-7 alone, or with TGF-β1 in the presence of BMP-4 or BMP-7 for 24 h (A and B) or 72 h (C). Cells were harvested, RNA was extracted, reverse transcribed, and a real-time quantitative PCR for collagen type I alpha 1 chain (COL1a1, A) and collagen type IV alpha 1 chain (COL4a1, B) was performed. Results are expressed as the ratio of each transcript relative to the geometric mean of mRNA expression of the housekeeping genes UBC, SDHA, and RPL13a. Total soluble collagen release was quantified in the cell supernatants by Sircol assay (C). Data are mean ± SD of five independent experiments. *, p < 0.05, as compared to unstimulated cells and †, p < 0.05, as compared to TGF-β1-stimulated cells.