ADAM17‐Mediated Shedding of ACE2 in Pancreatic Beta‐Cells

Abstract

Angiotensin‐converting enzyme 2 (ACE2) hydrolyzes angiotensin II. Our laboratory has previously shown that pancreatic ACE2 levels decrease as diabetes progresses and that pancreatic ACE2 gene therapy counteracts development of hyperglycemia in diabetic animal models. As a disintegrin and metalloprotease 17 (ADAM17) is an enzyme that can cleave enzymatically active ACE2 from the cell to the extracellular environment by so‐called shedding, we hypothesize that increased levels of ADAM17 in pancreatic beta‐cells lead to reduced cellular ACE2 levels. To this end, 832/13 cells (rat insulinoma cells derived from pancreatic beta‐cells) were transfected with expression plasmids for ACE2, ADAM17, and a hydrolytically inactive E406A ADAM17 mutant. Using fluorogenic enzyme substrates, we measured shed ACE2 activity after a 24 h incubation as well as cell‐associated ACE2 and ADAM17 activities. For a wide range of ACE2 expression levels, including the ACE2 expression level observed in pancreatic islets, a 4.6‐fold increase in ADAM17 activity had the following significant effects: shed ACE2 activity was increased 2 – 2.7‐fold, cellular ACE2 activity was decreased 33‐47%, and the ratio of shed ACE2/cellular ACE2 was increased 3.4 – 4.1‐fold. Adjusting for transfection efficiency, we further determined that the cellular ACE2 activity can be described as a power function of the ADAM17 activity with exponent ‐0.29 ±0.04. We conclude that ADAM17‐mediated shedding of ACE2 has the potential to decrease cellular ACE2 levels in pancreatic beta‐cells. More studies are underway to assess the role of this mechanism in diabetes. Support: NIH: GM103424, AHA: 12EIA8030004.