Treatment with 2-AAF blocks the small hepatocyte-like progenitor cell response in retrorsine-exposed rats

Abstract

Background/Aims-Liver regeneration after partial hepatectomy (PH) in retrorsine-exposed rats is accomplished through proliferation and differentiation of small hepatocyte-like progenitor cells (SHPCs). The cells of origin of SHPCs are not known. We investigated the possibility that SHPCs are directly derived from oval cells, a known liver progenitor cell, by combining the retrorsine/PH (RP) model with 2-acetamidofluorene (2-AAF), an anti-mitotic agent that elicits an oval cell reaction in response to liver deficit. Methods-MaleFischer 344 rats were treated with retrorsine (30 mg/kg ip) at 6 and 8 weeks of age, with PH 5 weeks after the final treatment. Seven days prior to PH, a 21 day 2-AAF (50 mg) time-release pellet was inserted subcutaneously. Livers were harvested at 3, 7, 10, 14, and 21-days post-PH.Results-Liver sections from animals treated with 2-AAF/retrorsine/PH (2-AAF/RP) contain significant numbers of proliferating oval cells, but no SHPCs at 7-days post-PH, while RP animals exhibit significant numbers of SHPCs and minimal oval cell reaction. Between 10 and 14-days post-PH, new hepatocyte clusters appear in 2-AAF/RP treated rats. Labeling of proliferating oval cells with BrdU at 6-days post-PH demonstrated that these new hepatocytes represent the progeny of differentiating oval cells.Conclusions-The observed differences in progenitor cell responses between 2-AAF/RP and RP animals strongly suggest that SHPCs are not the progeny of oval cell precursors, but represent an independent liver progenitor cell population.

Bile duct destruction by 4,4′-diaminodiphenylmethane does not block the small hepatocyte-like progenitor cell response in retrorsine-exposed rats

“…12 A definitive SHPC lineage marker does not exist, making it difficult to assess whether the regenerative responses observed in retrorsine-treated hepatitis B surface antigen transgenic mice are identical to those observed in retrorsine-exposed F344 rats. Based on data from our studies and others, 13,31 it seems likely that the hepatocyte clusters observed by Vig et al actually represent new hepatocyte progeny of oval cells rather than regenerative SHPCs. This supposition is bolstered by data in the current study that demonstrate that when oval cell-mediated regenerative responses are blocked through the use of DAPM, the SHPC-mediated regenerative response is unaffected, suggesting that oval cells are not the source of SHPCs.…”

“…However, data from our recent studies show that retrorsine-resistant SHPCs are susceptible to 2-AAF poisoning. 13 In these studies, SHPCs were never found in the livers of 2-AAFtreated retrorsine-exposed animals at any time after PH, but clustering of new hepatocytes (oval cell progeny) occurred by 14 days post-PH. 13 The cellular response in 2-AAF-treated retrorsine-exposed rats is identical to that observed in 2-AAF/PH animals (in the absence of retrorsine), suggesting that the presence of retrorsine has no effect on oval cell-mediated liver regeneration, but that 2-AAF treatment blocks the outgrowth of SHPCs.…”

“…13 In these studies, SHPCs were never found in the livers of 2-AAFtreated retrorsine-exposed animals at any time after PH, but clustering of new hepatocytes (oval cell progeny) occurred by 14 days post-PH. 13 The cellular response in 2-AAF-treated retrorsine-exposed rats is identical to that observed in 2-AAF/PH animals (in the absence of retrorsine), suggesting that the presence of retrorsine has no effect on oval cell-mediated liver regeneration, but that 2-AAF treatment blocks the outgrowth of SHPCs. 13 In addition, treatment of rats with 2-AAF 7 days after initiation of the RP protocol (at a time when SHPCs are evident) results in a blockade of SHPC proliferation.…”

“…Some evidence supports the suggestion that these cells may represent a distinct immature progenitor cell population. 1,10,11,13 A third possibility is that SHPCs represent a population of "retrorsine-resistant" mature hepatocytes. 1,10,14 In the current study, we directly investigated the possible precursor-product relationship between oval cells and SHPCs by treating retrorsine-exposed rats with the toxin DAPM (4,4Ј-diaminodiphenylmethane).…”

Activation of Inactive Hepatocytes through Histone Acetylation

“…Obviously these cells could not be responsible for functional execution, especially during the immediate days post-PH. 50 Indeed, we found that a few BrdU-positive cells emerged at day 3 after operation; however, these cells might be the progenitor cells rather than the regenerating hepatocytes since they were much smaller and showed colony-like proliferation.…”