Bax-mediated apoptosis in the livers of rats after partial hepatectomy in the retrorsine model of hepatocellular injury.
Retrorsine is a member of the pyrrolizidine alkaloid family of compounds whose toxic effects on the liver include a long-lasting inhibition of the proliferative capacity of hepatocytes. Despite the retrorsine-induced blockade of hepatocyte proliferation, retrorsine-exposed rats are able to reconstitute completely their liver mass after surgical partial hepatectomy (PH) via the sustained proliferation of a population of small, incompletely differentiated hepatocyte-like progenitor cells (SHPCs). The extensive proliferation of SHPCs in retrorsine-injured livers is accompanied by the progressive loss of irreversibly injured megalocytes. To study the mechanism by which retrorsine-damaged hepatocytes are removed after PH, we performed TUNEL analysis to establish apoptotic indices for hepatocytes in the livers of retrorsine-exposed and control rats up to 14 days post-PH. Apoptotic indices are highest (approximately 6.0%) in the livers of retrorsine-exposed rats at 1 day post-PH, gradually declining thereafter, yet remaining significantly elevated (approximately 1%) over control rats (<0.1%) at 14 days post-PH (P <.05). After PH, levels of the proapoptotic protein Bax are increased in livers from retrorsine-exposed rats relative to the levels observed in control livers. Similarly, levels of the antiapoptotic protein Bcl-x(L) are significantly decreased (P <.05) compared with controls at t = 0 resulting in an increased (approximately 3.5-fold) Bax/Bcl-x protein ratio that is significantly elevated (P <.05) compared with controls. Finally, increased levels of Bax protein are localized to the mitochondria of retrorsine-exposed rat livers after PH during the same time that cytochrome c is released. These observations combine to suggest that retrorsine-injured hepatocytes are removed after PH via apoptotic pathways dependent on relative levels and localization of Bax and Bcl-x(L) protein.
Gordon
G J
GJ
Department of Pathology and Laboratory Medicine, Curriculum in Toxicology, UNC Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC, USA.
Coleman
W B
WB
Grisham
J W
JW
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D006498:Hepatectomy; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008099:Liver / Q000187:drug effects* / Q000473:pathology; D008297:Male; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D011763:Pyrrolizidine Alkaloids / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
C494828:Bax protein, rat; C494813:Bcl2l1 protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011763:Pyrrolizidine Alkaloids; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C003300:retrorsine