APOPTOSIS IS INDUCED BY TRANSFORMING GROWTH-FACTOR-BETA-1 WITHIN 5 HOURS IN REGRESSING LIVER WITHOUT SIGNIFICANT FRAGMENTATION OF THE DNA

In previous studies we showed that transforming growth factor-beta1 in duces apoptosis in hepatocyte cultures and regressing livers, the matu re form being more potent than the transforming growth factor-beta1 la tency-associated protein. In this study we addressed the question of w hether apoptosis can be induced within a short time after administrati on of transforming growth factor-beta1. Five hours after a single intr avenous injection of 25 mug mature transforming growth factor-beta1/kg body weight, apoptosis is augmented ninefold in the regressing rat li ver. A second preceding application induces no further augmentation. T ransforming growth factor-beta1 latency-associated protein shows no ef fect with either regimen. Morphological evaluation shows that 5 hr aft er injection of transforming growth factor-beta1 nearly all apoptotic bodies are already engulfed by their neighbor cells. After homogenizat ion of the transforming growth factor-beta1-treated livers, the conden sed apoptotic bodies are not destroyed and remain in the nuclear pelle t. No DNA fragmentation into oligosomes could be detected after purifi cation of the DNA from the nuclear pellet and application to conventio nal gel electrophoresis. Application of in situ nick translation, whic h allows detection of DNA single- and double-strand breaks in individu al apoptotic bodies, also revealed no substantial fragmentation of the DNA in apoptotic bodies. These studies show that transforming growth factor-beta1 is able to induce apoptosis within a rather short time an d also suggest that in vivo digestion of the DNA does not lead to chro matin condensation.