Role of thyroid hormone in stimulating liver repopulation in the rat by transplanted hepatocytes

Abstract

Recently, we reported near-complete repopulation of the rat liver by transplanted hepatocytes using retrorsine (RS), a pyrrolizidine alkaloid that alkylates cellular DNA and blocks proliferation of resident hepatocytes, followed by transplantation of normal hepatocytes in conjunction with two-thirds partial hepatectomy (PH). Because two-thirds PH is not feasible for use in humans, in the present study, we evaluated the ability of thyroid hormone (triiodothyronine [T 3 ]), a known hepatic mitogen, to stimulate liver repopulation in the retrorsine model. Because T 3 initiates morphogenesis in amphibians through a process involving both cell proliferation and apoptosis, we also determined whether apoptosis might play a role in the mechanism of hepatocyte proliferation induced by T 3 . Following hepatocyte transplantation and repeated injections of T 3 , the number of transplanted hepatocytes in the liver of RSpretreated animals increased progressively to repopulate 60% to 80% of parenchymal cell mass in 60 days. We show further that T 3 treatment augments proliferation of normal hepatocytes, as evidenced by increased histone 3 mRNA and cyclin-dependent kinase 2 (cdk2) expression, and this is followed by apoptosis. These combined effects of T 3 lead to selective proliferation of transplanted hepatocytes in RS-pretreated rats, while endogenous hepatocytes, which are blocked in their proliferative capacity by RS, mainly undergo apoptosis. Thus, T 3 can replace PH in the RS-based rat liver repopulation model and therefore represents a significant advance in developing methods for hepatocyte transplantation. (HEPATOLOGY 1999;30:903-913.)A major problem in most hepatocyte transplantation studies to date has been the limited growth of transplanted cells in the recipient liver. [1][2][3][4][5] Efforts to solve this problem have generally used partial hepatectomy (PH) to remove a portion of the resident liver and thus provide a proliferative stimulus to transplanted cells. [3][4][5] Because host hepatocytes can also respond to this liver-regenerative stimulus, selective repopulation by transplanted cells does not occur under most circumstances. However, PH is not practical for routine use in human hepatocyte transplantation protocols, and thus, establishing alternative methods to stimulate hepatocyte proliferation in the context of cell transplantation is of great interest.Three experimental models of extensive liver repopulation have recently been described: the urokinase-type plasminogen activator (uPA) transgenic mouse, 6-8 the fumarylacetoacetate hydrolase (FAH) null mouse, 9,10 and the retrorsine (RS)/PH-treated rat. 11 In the uPA model, endogenous hepatocytes that have deleted the transgene, 6 or transplanted normal hepatocytes, 7,8 proliferate extensively because of continuous proteolytic destruction of resident hepatocytes expressing uPA. [6][7][8] Similarly, in FAH null mice, transplanted wild-type hepatocytes exhibit a growth advantage over enzymedeficient host cells, because the latter accumulate toxic intermedia...

Hepatocyte transplantation and drug-induced perturbations in liver cell compartments

“…27 Conversely, thyroxine administration to mice treated with phenytoin, rifampicin, and MCT accelerated liver repopulation, which was in agreement with the ability of thyroid hormone to stimulate hepatic DNA synthesis while promoting apoptosis in cells with genotoxic damage. 28,29 Taken together, these findings indicated that in mice exposed to phenytoin, rifampicin, and MCT, liver injury was age-dependent and gender-dependent, as shown here with 6-week-old to 8-week-old male mice. We used cell donors of 8 weeks' to 15 weeks' age for convenience; their age should have been immaterial unless aging-associated genetic lesions were to alter replication in healthy donor cells, which has not been shown.…”

Massive Liver Replacement by Transplanted Hepatocytes in the Absence of Exogenous Growth Stimuli in Rats Treated with Retrorsine

“…13,26 However, more recently we observed as high as 15 to 20% repopulation in RS-treated female rats at 6 weeks after cell transplantation, in the absence of PH or any other exogenous stimulus. 20 Interestingly, both in the latter 20 and in the present study, cell transplantation was performed at 2 weeks after the second dose of RS, whereas in the first report, 13 this interval was 4 weeks.…”

Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly

“…Important from a human standpoint, such cells can be cryopreserved for up to 20 months with no loss of repopulating activity [50]. Many studies have also examined the transplantation potential of adult hepatocytes in the DPPIV − mutant rat, combining retrorsine treatment with a mitogenic stimulus, such as partial hepatectomy or triidothyronine (T3), leading to the rapid replacement of DPPIV − cells by DPPIV + donor cells [51,52]; even in the absence of a mitogenic stimulus, near-total replacement by donor cells occurs within 12 months [53].…”