Evidence for an angiotensin-(1-7) neuropeptidase expressed in the brain medulla and CSF of sheep
Article first published online: 19 APR 2014
© 2014 International Society for Neurochemistry
Journal of Neurochemistry
Volume 130, Issue 2, pages 313–323, July 2014
How to Cite
J. Neurochem. (2014) 130, 313–323.
- Issue published online: 7 JUL 2014
- Article first published online: 19 APR 2014
- Accepted manuscript online: 25 MAR 2014 01:41AM EST
- Manuscript Accepted: 21 MAR 2014
- Manuscript Revised: 20 MAR 2014
- Manuscript Received: 8 FEB 2014
- National Institutes of Health. Grant Numbers: HD-047584, HD-017644, HL-51952
- Groskert Heart Fund
- Wake Forest Venture Fund
- Renin-angiotensin system
Angiotensin-(1-7) [Ang-(1-7)] is an alternative product of the brain renin-angiotensin system that exhibits central actions to lower blood pressure and improve baroreflex sensitivity. We previously identified a peptidase that metabolizes Ang-(1-7) to the inactive metabolite product Ang-(1-4) in CSF of adult sheep. This study purified the peptidase 1445-fold from sheep brain medulla and characterized this activity. The peptidase was sensitive to the chelating agents o-phenanthroline and EDTA, as well as the mercury compound p-chloromercuribenzoic acid (PCMB). Selective inhibitors to angiotensin-converting enzyme, neprilysin, neurolysin, and thimet oligopeptidase did not attenuate activity; however, the metallopeptidase agent JMV-390 was a potent inhibitor of Ang-(1-7) hydrolysis (Ki = 0.8 nM). Kinetic studies using 125I-labeled Ang-(1-7), Ang II, and Ang I revealed comparable apparent Km values (2.6, 2.8, and 4.3 μM, respectively), but a higher apparent Vmax for Ang-(1-7) (72 vs. 30 and 6 nmol/min/mg, respectively; p < 0.01). HPLC analysis of the activity confirmed the processing of unlabeled Ang-(1-7) to Ang-(1-4) by the peptidase, but revealed < 5% hydrolysis of Ang II or Ang I, and no hydrolysis of neurotensin, bradykinin or apelin-13. The unique characteristics of the purified neuropeptidase may portend a novel pathway to influence actions of Ang-(1-7) within the brain.
Angiotensin-(1-7) actions are mediated by the AT7/Mas receptor and include reduced blood pressure, decreased oxidative stress, enhanced baroreflex sensitivity, and increased nitric oxide (NO). Ang-(1-7) is directly formed from Ang I by neprilysin (NEP). We identify a new pathway for Ang-(1-7) metabolism in the brain distinct from angiotensin-converting enzyme-dependent hydrolysis. The Ang-(1-7) endopeptidase (A7-EP) degrades the peptide to Ang-(1-4) and may influence central Ang-(1-7) tone.