Generation of Mice with Hepatocyte-Specific Conditional Deletion of Notum.

BACKGROUND Fine tuning of the Wnt/β-catenin signaling pathway is essential for the proper development and function of the liver. Aberrant activation of this pathway is observed in 20%-40% of hepatocellular carcinomas (HCC). Notum encodes a secreted Wnt deacylase that inhibits Wnt activity and thereby restricts the zone of activation of Wnt/β-catenin signaling. An important role of NOTUM has been described in development in drosophila, planaria and zebrafish, but its role in the mammalian liver is unknown. Notum is required for spatial control of the Wnt/β-catenin signaling in several animal models and the Wnt/β-catenin pathway contributes to liver patterning involved in metabolic zonation. Therefore, Notum may be involved in the liver patterning induced by the Wnt/β-catenin signaling during the adult stage. METHODOLOGY/PRINCIPAL FINDINGS We generated a conditional Notum knockout mouse mutant to study the effect of the deletion of Notum in the liver. We show that Notum is a direct target of the Wnt/β-catenin signaling in the liver. Liver-specific deletion of Notum did not modify liver zonation, but Notum deletion had a long-term effect on mouse physiology. In particular, male mutant mice developed metabolic disorders. CONCLUSION We show that Notum is not a key actor of Wnt/β-catenin-dependent liver patterning of adult mice, but has role in liver glucose homeostasis. Male mice deficient in Notum specifically in the liver develop metabolic dysfunctions implicating Notum in the development of Type 2 diabetes.