Mice depleted for Exchange Proteins Directly Activated by cAMP (Epac) exhibit irregular liver regeneration in response to partial hepatectomy

Kathrine Sivertsen Åsrud,Lars Herfindal,Rolf Kristian Berge,Elise Aasebø,Haruna Muwonge,Line Pedersen,Stephen Jenkins,Stein Ove Døskeland,Ina Katrine Nitschke Pettersen,Marit Bakke,Frode Selheim,Reidun Aesoy,Neil Cowan Henderson,Ross Dobie

doi:10.1038/s41598-019-50219-8

Abstract

The exchange proteins directly activated by cAMP 1 and 2 (Epac1 and Epac2) are expressed in a cell specific manner in the liver, but their biological functions in this tissue are poorly understood. The current study was undertaken to begin to determine the potential roles of Epac1 and Epac2 in liver physiology and disease. Male C57BL/6J mice in which expression of Epac1 and/or Epac2 are deleted, were subjected to partial hepatectomy and the regenerating liver was analyzed with regard to lipid accumulation, cell replication and protein expression. In response to partial hepatectomy, deletion of Epac1 and/or Epac2 led to increased hepatocyte proliferation 36 h post surgery, and the transient steatosis observed in wild type mice was virtually absent in mice lacking both Epac1 and Epac2. The expression of the protein cytochrome P4504a14, which is implicated in hepatic steatosis and fibrosis, was substantially reduced upon deletion of Epac1/2, while a number of factors involved in lipid metabolism were significantly decreased. Moreover, the number of Küpffer cells was affected, and Epac2 expression was increased in the liver of wild type mice in response to partial hepatectomy, further supporting a role for these proteins in liver function. This study establishes hepatic phenotypic abnormalities in mice deleted for Epac1/2 for the first time, and introduces Epac1/2 as regulators of hepatocyte proliferation and lipid accumulation in the regenerative process.

Highlights

Diseases related to hepatic steatosis constitute an increasing health problem worldwide
Epac2C lacks the N-terminal cyclic nucleotide-binding domain found in Epac2A, which is required for insulin secretion[11], and the Dishwelled-Egl-10-pleckstrin (DEP) domain found in Epac2A, Epac2B and in exchange proteins directly activated by cAMP (Epac)[112], that is essential for membrane association[11]
We demonstrate for the first time that the cAMP binding proteins Epac1/2 are involved in regulating liver regeneration in an in vivo model

Summary

Introduction

Diseases related to hepatic steatosis constitute an increasing health problem worldwide. The effects of cAMP in the liver have been ascribed to activation of the cAMP dependent protein kinase A (PKA), but numerous observations link the exchange proteins directly activated by cAMP (Epac; known as cAMP-guanine nucleotide exchange factor, cAMP-GEF) to hepatic cellular processes[4]. It is known that hepatic stellate cells (HSC) express Epac[113], and cholangiocytes, both Epac[1] and Epac2A14, and in vitro studies link Epac1/2 to hepatic cellular processes, such as formation of canalicular networks[15], proliferation of cholangiocytes[14] and glucagon-dependent secretion of the fibroblast growth factor 21 (Fgf21) from hepatocytes[16]. We found that Epac2C expression (mRNA and protein) were increased in response to PH, and comparison of the proteome of wild type (wt) and Epac1/2−/− mice demonstrated altered expression profiles of proteins related to hepatic lipid metabolism and disease development

Methods

Results

Conclusion