Ectodomain shedding in the downregulation of cellular ACE‐2 by ER stress in lung cells (716.3)

Abstract

Previous work from this laboratory has demonstrated that angiotensin (ANG) converting enzyme‐2 (ACE‐2) protects against lung fibrosis by limiting the local accumulation of the profibrotic peptide, ANGII by converting ANGII to angiotensin 1‐7 (ANG 1‐7). However, this protective enzyme is down‐regulated in human and experimental lung fibrosis. We currently know of three ways that ACE‐2 is down‐regulated in lung cells: 1) exposure to hyperoxia in fetal lung fibroblasts, 2) treatment with proteasome inhibitors, MG132 or Clasto‐Lactacystin β‐lactone (CLBL) in alveolar epithelial cells (AECs), and 3) expressing the surfactant protein C mutation G100S (which causes lung fibrosis in people). In all of these cases, ACE‐2 was only measured in cell lysates, but not in the cell culture medium to assess “shedding”. We hypothesize that the down‐regulation of cellular ACE‐2 may be mediated by ectodomain shedding by ADAM17/TACE. Western blots of cell lysates revealed a significant decrease in immunoreactive cellular ACE‐2 with CLBL (p= < 0.01) and a potential recovery in ACE‐2 with TAPI‐2, an inhibitor of ADAM17/TACE. Contrary to our hypothesis, a similar effect was also observed in serum‐free cell culture media (p= < 0.05). From this, we can speculate that ADAMS17/TACE may play a partial role in down‐regulating ACE‐2 by degrading it, in addition to other enzymes. With this model, further research can be done to investigate alternative mechanisms that lead to the down‐regulation of cellular ACE‐2 in lung cells.Grant Funding Source: Supported by APS STRIDE Fellowship and PHS HL ‐ 45136