The role of ecto-5'-nucleotidase in endothelial dysfunction and vascular pathologies.

Ecto-5'-nucleotidase (e5NT, CD73) is an enzyme that is highly expressed in endothelium and is involved in the extracellular nucleotide catabolism. CD73 converts AMP to adenosine that via specific subtypes of P1 receptor mediates cytoprotection involving diverse mechanisms such as vasodilatation, suppression of inflammation, inhibition of thrombosis and anti-adrenergic effect. Physiological intravascular concentration of adenosine is in nanomolar range, but could become micromolar in response to various forms of stress. Endothelium is a major site for both CD73 mediated production of adenosine and its cytoprotective effect. Nucleotides (predominantly ATP or ADP) that could be released from different cells via controlled specific of unspecific mechanisms constitute a major source of substrate for adenosine production via CD73. Direct effects of extracellular nucleotides (mediated by P2 receptors) are typically opposite to adenosine P1 mediated activities. Retention of nucleotides and decreased adenosine production due to loss of CD73 function may have negative implications and could be important cause of various pathologies. Protective role of CD73 was indicated in ectopic calcification, atherosclerosis, rejection after xenotransplantation and thrombosis. Reduced activity of CD73 due to lymphocyte contact with endothelium increases its permeability that leads to enhanced leukocyte transmigration. Upregulation of endothelial CD73 may therefore be protective in a number of cardiovascular pathologies. Such effect has been confirmed for some common drugs such as statins and it could be part of its pleiotropic portfolio. Activation of CD73 could be a new target for specific treatment strategy that in particular will enhance endothelial protection.