Apoptotic pathway related to oval cell proliferation.
OBJECTIVE
Oval cells, liver stem cell-derived cells, are generated from the liver periportal region and spread into the parenchyma by an autocrine signaling pathway. The mechanism behind how oval cells take their place among packed silent hepatocytes, however, is not well understood. We hypothesized that apoptosis involves a decrease in hepatocytes surrounding oval cells.


METHODS
Male Fisher rats were treated using the AAF/PH protocol to induce oval cells in the liver. Apoptosis was assessed by measuring the activity of caspase-3, -8 and -9, and apoptosis-related molecules such as caspase-3, Fas, Fas-L and Bax were also assessed by immunohistochemical analysis and reverse transcriptase-polymerase chain reaction (RT-PCR). Apoptosis was confirmed by TUNEL staining. Regarding antiapoptotic factors, nuclear factor-kappaB (NF-kappaB) DNA binding activity and proliferating cell nuclear antigen (PCNA) expression were examined.


RESULTS
NF-kappaB elevated at the early stage of oval cell proliferation. Conversely, caspase activity increased after NF-kappaB elevation. The mRNA of caspase-3, Fas, Fas-L and Bax was induced during and after AAF/PH treatment. Immunohistochemically, oval cells lacked the expression of these proteins, whereas the hepatocytes, particularly those surrounding oval cells, expressed strongly.


CONCLUSIONS
The present study suggests that the apoptosis in hepatocytes through both extrinsic and intrinsic pathways mediates oval cell proliferation.
Yano
Yoshihiko
Y
Department of Clinical Molecular Medicine, Division of Diabetes, Digestive and Kidney Diseases, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
Hayashi
Yoshitake
Y
Teramoto
Tadahisa
T
Nakaji
Miyuki
M
Nagy
Peter
P
Ninomiya
Toshiaki
T
Wada
Atsushi
A
Hirai
Midori
M
Kim
Soo Ryang
SR
Seo
Yasushi
Y
Yoon
Seitetsu
S
Kasuga
Masato
M
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D053222:Fas Ligand Protein; D022781:Hepatocytes / Q000166:cytology*; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000502:physiology*; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism
C494828:Bax protein, rat; D053222:Fas Ligand Protein; C505662:Faslg protein, rat; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D018809:Proliferating Cell Nuclear Antigen; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases