Insulin-like growth factor 2 is a key mitogen driving liver repopulation in mice

Hepatocyte transplantation holds great promise as an alternative to orthotopic organ transplantation in the treatment of liver diseases. However, obtaining clinically meaningful levels of liver repopulation has not been achieved because the mechanisms regulating hepatocyte proliferation in recipient livers have not yet been well characterized. In the mouse model of Hereditary Tyrosinemia Type I, the fumarylacetoacetate hydrolase-deficient (Fah^-/-) mouse, we found gradually increasing expression level of insulin-like growth factor 2 (IGF2) in the hepatocytes of host livers. Similarly, high levels of IGF2 were found in the livers of patients with deficient FAH activity. Recombinant IGF2 directly promotes proliferation of primary hepatocytes in vitro. Inhibition on IGF2 expression through the interruption of PI3K/Akt and MAPK pathways significantly reduced the level of liver repopulation in Fah^-/- mice. Interestingly, treatment with IGF2 before hepatocyte transplantation generally improved the amount of liver repopulation seen in various mice models of liver injury. Altogether, these findings underscore the underlying mechanisms of therapeutic liver repopulation in Fah^-/- mice, and indicate that IGF2 is a potential hepatocyte mitogen for liver cell transplantation therapies.