Abstract
Ecto-nucleotidase triphosphate diphosphohydrolase-2 (NTPDase2) is an ecto-enzyme that is expressed on portal fibroblasts in the liver that modulates P2 receptor signaling by regulating local concentrations of extracellular ATP and ADP. NTPDase2 has protective properties in liver fibrosis and may impact bile duct epithelial turnover. Here, we study the role of NTPDase2 in acute liver injury using an experimental model of acetaminophen (APAP) intoxication in mice with global deletion of NTPDase2. Acute liver toxicity was caused by administration of acetaminophen in wild type (WT) and NTPDase2-deficient (Entpd2 null) mice. The extent of liver injury was compared by histology and serum alanine transaminase (ALT). Markers of inflammation, regeneration and fibrosis were determined by qPCR). We found that Entpd2 expression is significantly upregulated after acetaminophen-induced hepatotoxicity. Entpd2 null mice showed significantly more necrosis and higher serum ALT compared to WT. Hepatic expression of IL-6 and PDGF-B are higher in Entpd2 null mice. Our data suggest inducible and protective roles of portal fibroblast-expressed NTPDase2 in acute necrotizing liver injury. Further studies should investigate the relevance of these purinergic pathways in hepatic periportal and sinusoidal biology as such advances in understanding might provide possible therapeutic targets.
Highlights
Acute liver failure afflicts patients with no pre-existing liver disease, and leads to death in up to 50% of cases [1]
Purinergic signaling responses are mediated by extracellular nucleosides and nucleotides, e.g., adenine triphosphate (ATP), adenine diphosphate (ADP), or the nucleoside derivative adenosine, which are the specific receptors together with membrane-bound ecto-enzymes that regulate the concentrations of the messenger molecules and thereby modulate the downstream effects [7]
We show that there is accentuation of APAP-induced liver injury in NTPDase2 (Entpd2 null mice), comparable to that seen in the Entpd1 null studies
Summary
Acute liver failure afflicts patients with no pre-existing liver disease, and leads to death in up to 50% of cases [1]. Purinergic signaling responses are mediated by extracellular nucleosides and nucleotides, e.g., adenine triphosphate (ATP), adenine diphosphate (ADP), or the nucleoside derivative adenosine, which are the specific receptors together with membrane-bound ecto-enzymes that regulate the concentrations of the messenger molecules and thereby modulate the downstream effects [7] This pathway has been shown to play a role in liver inflammation, immune regulation, regeneration, and development of fibrosis [8,9,10]. We observed increased mortality in Cd39 null mice intoxicated with APAP with evidence for activation of P2X7 and the inflammasome in driving liver damage Another key ecto-enzyme that regulates extracellular nucleotide concentrations is ecto-nucleotide triphosphate diphosphohydrolase-2 (ENTPD2 or NTPDase2), the second member of the CD39 family of ecto-nucleotidases. These studies have implications both for the understanding of the pathogenesis of APAP-induced hepatotoxicity as well as in translational therapeutics for acute liver injury
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