Tissue-specific and developmental regulation of transforming growth factor-β₁ expression in fetal lamb ductus arteriosus endothelial cells

We previously established that increased hyaluronan synthesis in ductus arteriosus (DA) compared with aorta (Ao) endothelial cells (EC) from early gestation fetal lambs (100-d, term = 145 d) is transforming growth factor-β (TGF-β)-dependent. We now address whether this is associated with tissue- specific and developmentally up-regulated expression of TGF-β₁ in the 100- d DA EC. Immunoprecipitation revealed TGF-β synthesis doubled in DA versus Ao EC from 100-d gestation lambs (p < 0.05). In 138-d DA EC, TGF-β protein levels were reduced (p < 0.05) and comparable to those in Ao cells. Western immunoblotting with a β₁ isoform-specific antibody confirmed these differences as being related to TGF-β₁. Northern blot analysis demonstrated that TGF-β₁ mRNA levels were slightly but not significantly increased in 100-d DA compared with Ao EC, despite its short half-life in DA (9.5 h) versus Ao EC (20 h). TGF-β₁ mRNA levels were reduced in 138-d DA and Ao EC (p < 0.05), and the mRNA half-life was comparable in DA (9 h) versus Ao (13 h). Nuclear run-on analysis confirmed increased TGF-β₁ mRNA transcription in 100-d DA versus Ao and 138-d DA EC. Thus, up-regulated TGF-β₁ expression in 100-d DA compared with Ao cells is due to increased transcription and translation of a relatively unstable mRNA, and its down-regulation in 138-d DA and Ao EC is related to reduced mRNA transcription and stability, respectively.