TGFB1 and osteogenesis imperfecta: Unlike OI fibroblasts, which did not show altered TGFβ secretion following 72 h treatment with 5 nM losartan, this same treatment significantly reduced concentrations of TGFβ secreted into the culture medium by pre-osteoblast cells and reduced phosphorylation of SMAD2 (Fig. 5C and D).