Progenitor cells in liver regeneration: molecular responses controlling their activation and expansion

Abstract

Although normally quiescent, the adult mammalian liver possesses a great capacity to regenerate after different types of injuries in order to restore the lost liver mass and ensure maintenance of the multiple liver functions. Major players in the regeneration process are mature residual cells, including hepatocytes, cholangiocytes and stromal cells. However, if the regenerative capacity of mature cells is impaired by liver-damaging agents, hepatic progenitor cells are activated and expand into the liver parenchyma. Upon transit amplification, the progenitor cells may generate new hepatocytes and biliary cells to restore liver homeostasis. In recent years, hepatic progenitor cells have been the subject of increasing interest due to their therapeutic potential in numerous liver diseases as alternative or supportive/complementary tools to liver transplantation. While the first investigations on hepatic progenitor cells have focused on their origin and phenotypic characterization, recent attention has focused on the influence of the hepatic microenvironment on their activation and proliferation. This microenvironment comprises the extracellular matrix, epithelial and non-epithelial resident liver cells, and recruited inflammatory cells as well as the variety of growth-modulating molecules produced and/or harboured by these elements. The cellular and molecular responses to different regenerative stimuli seem to depend on the injury inflicted and consequently on the molecular microenvironment created in the liver by a certain insult. This review will focus on molecular responses controlling activation and expansion of the hepatic progenitor cell niche, emphasizing similarities and differences in the microenvironments orchestrating regeneration by recruitment of progenitor cell populations or by replication of mature cells.

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

“…Oval cells are derived from the canal of Hering, and in rodents this canal barely extends beyond the limiting plate ( Figures 4, 5); in contrast, in human liver the organization of the biliary tree is different, with the canal of Hering extending to the proximate third of the lobule [68] and so apparently requiring a name change from oval cells to 'hepatic progenitor cells' (HPCs) [69]. An enormous range of markers has been used to identify ovals cells (Table 2) [70][71][72][73][74][75][76][77][78][79][80][81][82][83] and some, such as Dlk, may signal imminent hepatocyte differentiation [71]. A popular experimental procedure to elicit an oval cell response in rats is to pre-treat the animals with 2-acetylaminofluorene (2-AAF) before performing a two-thirds PH (the 2-AAF/PH protocol).…”

Effect of liver regeneration on malignant hepatic tumors

“…In the normal adult liver after injury or surgery, loss of liver parenchyma is repaired by replication of mature hepatocytes [71][72][73] . However, pre-existing liver diseases such as chronic HBV and HCV infection, alcoholic fatty liver disease, hemochromatosis and other conditions severely impair the ability of hepatocytes to replicate.…”

Thymus cell antigen-1-expressing cells in the oval cell compartment

“…OCs sprout from the putative stem cell niche (canals of Hering), forming tortuous pseudoducts and invading the liver lobule. [1][2][3][4][5][6] These pseudoducts are in close proximity to desmin-positive stellate cells. 7 Recently, we found a population of activated mesenchymal cells, thymus cell antigen-1 (Thy-1)-expressing cells, surrounding OCs.…”