Targeted expression of uncoupling protein 2 to mouse liver increases the susceptibility to lipopolysaccharide/galactosamine-induced acute liver injury

Abstract

Normal hepatocytes do not express endogenous uncoupling protein 2 (UCP2) in adult liver, although Kupffer cells do, and it is strikingly induced in hepatocytes in steatotic liver and obese conditions. However, the direct link of UCP2 with the pathogenic development of liver diseases and liver injury remains elusive. Here we report that targeted expression of UCP2 to mouse liver increases susceptibility to acute liver injury induced by lipopolysaccharide (LPS) and galactosamine (GalN). UCP2 appears to enhance proton leak, leading to mild uncoupling in a guanosine diphosphate-repressible manner. Indeed, mitochondria from the genetically manipulated mouse liver have increased state 4 respiration, lower respiratory control ratio, and reduced adenosine triphosphate (ATP) levels, which altered mitochondrial physiology. To address the underlying mechanism of how UCP2 and the reduced energy coupling efficiency enhance cell death in mouse liver, we show that the reduced ATP levels lead to activation of 5AMP-activated protein kinase (AMPK) and its downstream effector, c-Jun N-terminal kinase; thus, the increased sensitivity toward LPS/GalN-induces apoptosis. Importantly, we show that inhibition of UCP2 activity by its pharmacological inhibitor genipin prevents LPS/GalN-induced ATP reduction, AMPK activation, and apoptosis. Also, inhibition of ATP production by oligomycin promotes LPS/GalN-induced cell death both in vivo and in vitro. Conclusion: Our results clearly show that targeted expression of UCP2 in liver may result in compromised mitochondrial physiology that contributes to enhanced cell death and suggests a potential role of UCP2 in the development of liver diseases. (HEPATOLOGY 2009;50:1204-1216

Uncoupling Protein-2 Deficient Mice Are Not Protected Against Warm Ischemia/Reperfusion Injury of the Liver

“…Furthermore, we could previously demonstrate that UCP2 deficiency is protective in a murine model of endotoxemic acute liver failure [16]. In line with this, targeted expression of UCP2 to mouse liver is reported to increase the susceptibility to lipopolysaccharide/galactosamine-induced acute liver injury [25].…”

Genipin Reverses HFD-Induced Liver Damage and Inhibits UCP2-Mediated Pyroptosis in Mice

“…Moreover, overexpression of uncoupling protein-2 (UCP2) in the liver can cause acute liver injury [26]. The natural product genipin (GNP), an inhibitor of UCP2, was shown to enhance ATP production in isolated pancreatic islets and improve mitochondrial function in mice [27,28].…”

The inhibitory action of PDCD4 in lipopolysaccharide/D-galactosamine-induced acute liver injury

“…15,16 Therefore, LPS/D-GalN-induced hepatitis is a wellestablished model to mimic liver injury induced by intestinal endotoxemia in a clinical setting. [17][18][19] The present study aims to examine the in vivo role of PDCD4 in LPS/D-GalN-induced liver injury using PDCD4-deficient mice and wild-type (WT) mice. We first demonstrated that PDCD4 deficiency exacerbated LPS/DGalN-induced hepatocyte apoptosis and necrosis, and enhanced liver injury in PDCD4-deficient mice was due to an increased release of inflammatory factors induced by excessive activation of the MAPK and NF-kB pathways.…”