The origin and liver repopulating capacity of murine oval cells

Abstract

The appearance of bipotential oval cells in chronic liver injury suggests the existence of hepatocyte progenitor͞stem cells. To study the origin and properties of this cell population, oval cell proliferation was induced in adult mouse liver by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) and a method for their isolation was developed. Transplantation into fumarylacetoacetate hydrolase (Fah) deficient mice was used to determine their capacity for liver repopulation. In competitive repopulation experiments, hepatic oval cells were at least as efficient as mature hepatocytes in repopulating the liver. In mice with chimeric livers, the oval cells were not derived from hepatocytes but from liver nonparenchymal cells. This finding supports a model in which intrahepatic progenitors differentiate into hepatocytes irreversibly. To determine whether oval cells originated from stem cells residing in the bone marrow, bone marrow transplanted wild-type mice were treated with DDC for 8 months and oval cells were then serially transferred into Fah mutants. The liver repopulating cells in these secondary transplant recipients lacked the genetic markers of the original bone marrow donor. We conclude that hepatic oval cells do not originate in bone marrow but in the liver itself, and that they have valuable properties for therapeutic liver repopulation. In mammals, hepatic cells, especially hepatocytes can rapidly proliferate after acute liver injury to repair liver damage (1). Usually, undifferentiated liver progenitors do not take part in such acute liver regeneration. However, hepatocyte progenitors are still required in some chronic injury responses, especially when the ability of differentiated hepatocytes to divide is impaired (reviewed in refs. 2 and 3). The existence of endogenous stem cells inside mammalian liver was first suggested by the observation that treatment with carcinogens results in the emergence of oval cells in the portal region of the hepatic lobule (4-9). Oval cells are Ϸ10 m in size, have a high nuclear͞ cytoplasmic ratio, and express markers of immature liver cells such as ␣-fetoprotein (AFP) (10, 11). In addition, oval cells express markers of both the biliary epithelium (CK19) and hepatocyte lineages (albumin). In vitro, these cells can be differentiated into both of these hepatic epithelial lineages under appropriate conditions.Although the anatomical location of the oval cell proliferation suggests the existence of a hepatocyte progenitor in the Canal of Hering (12), the precise origin of oval cells remains uncertain. Most studies imply the existence of an undifferentiated oval cell precursor in this location that proliferates and gives rise to oval cells (13)(14)(15)(16). In analogy to the hematopoietic system, oval cells would then represent a committed bipotential progenitor. Recent studies in both rat and human have suggested that oval cells could be derived from precursors in the bone marrow (17). Others, however, have postulated that oval cells may arise by dedifferentiation of hepatocytes,...

Bmi1promotes hepatic stem cell expansion and tumorigenicity in bothInk4a/Arf-dependent and -independent manners in Mice

“…18 Histological analyses demonstrated a drastic decrease in A6-positive oval cell numbers in 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-treated Bmi1 À/À adult liver (Supporting Fig. 3).…”

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

“…The hepatocyte potential of transplanted oval cells has been clearly demonstrated in animal models: oval cells isolated from LEC rats were transplanted into LEC/Nagase analbuminaemic double mutant rats, where they differentiated into albumin-expressing hepatocytes [90]. Oval cells can also act as transplantable hepatocyte progenitors in the Fah knockout mouse; furthermore, the fact that oval cells generated in bone marrow transplanted wild-type mice can repopulate Fah knockouts, but lack markers of the original bone marrow donor, strongly suggests that oval cells do not originate from bone marrow in this particular model [91]. Transplanted oval cells can make a modest (∼2% after 1 month, falling to 0.4% at 6 months) contribution to the hepatocyte population in the CCl 4 -damaged mouse liver [92].…”

Origine des cellules ovales hépatiques

“…Leur origine reste encore très discutée, mais il est maintenant admis que, dans leur majorité, les cellules ovales résultent de l'expansion de précurseurs qui persistent à l'état de vestige dans le foie adulte au niveau des canaux de Hering [6] (Figure 1). La dédifférenciation d'hépatocy-tes en cellules ovales semble devoir être écartée, au moins dans certains modèles expérimentaux [5]. Mais voici que l'hypothèse selon laquelle ces cellules pourrait avoir une origine extra-hépatique et dériver de cellules de la moelle osseuse [7], qui n'avait pas pu être confirmée chez le rat [8] et la souris [5], est à nouveau proposée [1].…”

“…La dédifférenciation d'hépatocy-tes en cellules ovales semble devoir être écartée, au moins dans certains modèles expérimentaux [5]. Mais voici que l'hypothèse selon laquelle ces cellules pourrait avoir une origine extra-hépatique et dériver de cellules de la moelle osseuse [7], qui n'avait pas pu être confirmée chez le rat [8] et la souris [5], est à nouveau proposée [1].…”