TISSUE-SPECIFIC AND DEVELOPMENTAL REGULATION OF TRANSFORMING GROWTH FACTOR-BETA(1) EXPRESSION IN FETAL LAMB DUCTUS-ARTERIOSUS ENDOTHELIAL-CELLS

We previously established that increased hyaluronan synthesis in ductu s arteriosus (DA) compared with aorta (Ao) endothelial cells (EC) from early gestation fetal lambs (100-d, term = 145 d) is transforming gro wth factor-beta (TGF-beta)-dependent. We now address whether this is a ssociated with tissue-specific and developmentally up-regulated expres sion of TGF-beta(1) in the 100-d DA EC. Immunoprecipitation revealed T GF-beta synthesis doubled in DA versus Ao EC from 100-d gestation lamb s (p < 0.05). In 138-d DA EC, TGF-beta protein levels were reduced (p < 0.05) and comparable to those in Ao cells. Western immunoblotting wi th a beta(1) isoform-specific antibody confirmed these differences as being related to TGF-beta(1). Northern blot analysis demonstrated that TGF-beta(1) 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-beta(1) 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-beta(1) mRNA transcription in 100-d DA versus Ao and 138-d DA EC. Thus, up-regulated TGF-beta(1) expression in 100-d DA compared with A o cells is due to increased transcription and translation of a relativ ely unstable mRNA, and its down-regulation in 138-d DA and Ao EC is re lated to reduced mRNA transcription and stability, respectively.