Ecto-5′-nucleotidase [cluster of differentiation 73 (CD73)] is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that converts extracellular adenosine 5′-monophosphate to adenosine. Anti-CD73 inhibitory antibodies are currently undergoing clinical testing for cancer immunotherapy. However, many protective physiological functions of CD73 need to be taken into account for new targeted therapies. This review examines CD73 functions in multiple organ systems and cell types, with a particular focus on novel findings from the last 5 years. Missense loss-of-function mutations in the CD73-encoding gene NT5E cause the rare disease “arterial calcifications due to deficiency of CD73.” Aside from direct human disease involvement, cellular and animal model studies have revealed key functions of CD73 in tissue homeostasis and pathology across multiple organ systems. In the context of the central nervous system, CD73 is antinociceptive and protects against inflammatory damage, while also contributing to age-dependent decline in cortical plasticity. CD73 preserves barrier function in multiple tissues, a role that is most evident in the respiratory system, where it inhibits endothelial permeability in an adenosine-dependent manner. CD73 has important cardioprotective functions during myocardial infarction and heart failure. Under ischemia-reperfusion injury conditions, rapid and sustained induction of CD73 confers protection in the liver and kidney. In some cases, the mechanism by which CD73 mediates tissue injury is less clear. For example, CD73 has a promoting role in liver fibrosis but is protective in lung fibrosis. Future studies that integrate CD73 regulation and function at the cellular level with physiological responses will improve its utility as a disease target.

Background & Aims Metabolic imbalance and inflammation are common features of chronic liver diseases. Molecular factors controlling these mechanisms represent potential therapeutic targets. CD73 is the major enzyme that dephosphorylates extracellular adenosine monophosphate (AMP) to form the anti-inflammatory adenosine. CD73 is expressed on pericentral hepatocytes, which are important for long-term liver homeostasis. We aimed to determine if CD73 has nonredundant hepatoprotective functions. Methods Liver-specific CD73 knockout (CD73-LKO) mice were generated by targeting the Nt5e gene in hepatocytes. The CD73-LKO mice and hepatocytes were characterized using multiple approaches. Results Deletion of hepatocyte Nt5e resulted in an approximately 70% reduction in total liver CD73 protein ( P < .0001). Male and female CD73-LKO mice developed normally during the first 21 weeks without significant liver phenotypes. Between 21 and 42 weeks, the CD73-LKO mice developed spontaneous-onset liver disease, with significant severity in male mice. Middle-aged male CD73-LKO mice showed hepatocyte swelling and ballooning ( P < .05), inflammation ( P < .01), and variable steatosis. Female CD73-LKO mice had lower serum albumin levels ( P < .05) and increased inflammatory genes ( P < .01), but did not show the spectrum of histopathologic changes in male mice, potentially owing to compensatory induction of adenosine receptors. Serum analysis and proteomic profiling of hepatocytes from male CD73-LKO mice showed significant metabolic imbalance, with increased blood urea nitrogen ( P < .0001) and impairments in major metabolic pathways, including oxidative phosphorylation and AMP-activated protein kinase (AMPK) signaling. There was significant hypophosphorylation of AMPK substrates in CD73-LKO livers ( P < .0001), while in isolated hepatocytes treated with AMP, soluble CD73 induced AMPK activation ( P < .001). Conclusions Hepatocyte CD73 supports long-term metabolic liver homeostasis through AMPK in a sex-dependent manner. These findings have implications for human liver diseases marked by CD73 dysregulation.

The purpose of this study is to compare the Hedgehog Signaling Pathway (Hh) in the acoelmorphan, Isodiametra pulchra (Ipul) and the flatworm Stenostomum virginianum (Svirg). The former occupies a primitive placement in the bilaterians, while the latter is place in a primitive position in the flatworms. Certain organisms are cilia‐dependent in their Hedgehog signaling, while others conduct signaling independently of cilia. Protostomes (Svirg), for example, have cilium‐independent signaling, whereas deuterostomes (Ipul) require cilia to conduct signaling. Proteins associated with the Hh pathway were identified from the unpublished (Univ. of Innsbruck) transcriptome for Ipul, including orthologues for Hedgehog and multiple possible orthologues for Patched. Primers have been designed and tested to verify the existence of the transcripts listed. The transcriptomic sequences of wild‐type animals (NC coast) displayed both synonymous and non‐synonymous mutations when compared to the transcriptome of the animals cultured in Innsbruck. Next, qPCR primers will be designed and tested to analyze Patched expression, since it is a marker for Hh signaling. Animals treated with cyclopamine, a Hh pathway inhibitor, should display a reduction in Patched expression; this technique will allow us to identify the correct Patched orthologue. The Hh pathway plays a critical role in development in many organisms, including humans. The importance of this study is to establish the relationship between the Hh pathway and cilia. This can ultimately lead to control of abnormalities associated with both cilia and the Hh pathway, and prevent disorders in humans. Funded by SC‐INBRE.

Background & AimsMetabolic imbalance and inflammation are common features of chronic liver diseases. Molecular factors controlling these mechanisms represent potential therapeutic targets. One promising target is CD73, the major enzyme that dephosphorylates extracellular adenosine monophosphate (AMP) to form the anti-inflammatory adenosine. In normal liver, CD73 is expressed on pericentral hepatocytes, which are important for long-term liver homeostasis. The aim of this study was to determine if CD73 has non-redundant hepatoprotective functions.Approach & ResultsWe generated mice with a targeted deletion of the CD73-encoding gene (Nt5e) in hepatocytes (CD73-LKO). Deletion of hepatocyte Nt5e resulted in approximately 70% reduction in total liver CD73 protein (p<0.0001). Male and female CD73-LKO mice developed normally during the first 21 weeks, without significant liver phenotypes. Between 21-42 weeks, the CD73-LKO mice developed spontaneous onset liver disease with significant severity in male mice. Notably, middle-aged male CD73-LKO mice displayed hepatocyte swelling and ballooning (p<0.05), inflammation (p<0.01) and variable steatosis. Female CD73-LKO mice had lower serum albumin (p<0.05) and elevated inflammatory markers (p<0.01), but did not exhibit the spectrum of histopathologic changes characteristic of the male mice, potentially due to compensatory induction of adenosine receptors. Serum analysis and proteomic profiling of hepatocytes from male CD73-LKO mice revealed significant metabolic imbalance, with elevated blood urea nitrogen (p<0.0001) and impairments in major metabolic pathways, including oxidative phosphorylation and AMP-activated protein kinase (AMPK) signaling. There was significant hypo-phosphorylation in AMPK substrate in CD73-LKO livers (p<0.0001), while in isolated hepatocytes treated with AMP, soluble CD73 induced AMPK activation (p<0.001).ConclusionsHepatocyte CD73 supports long-term metabolic liver homeostasis through AMPK in a sex-dependent manner. These findings have implications for human liver diseases marked by CD73 dysregulation.

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