Evidence for an angiotensin‐(1‐7) neuropeptidase expressed in the brain medulla and CSF of sheep. (19th April 2014)

• Record Type: Journal Article
• Authors: Marshall, Allyson C.; Pirro, Nancy T.; Rose, James C.; Diz, Debra I.; Chappell, Mark C.
• Is Part Of: Journal of neurochemistry. Volume 130:Number 2(2014:Jul.)
• Page Start: 313
• Page End: 323
• Publication Date: 2014-04-19
• Subjects: Neurochemistry -- Periodicals; 616.8042
• DOI: 10.1111/jnc.12720
• Languages: English
• ISSNs: 0022-3042

Abstract

<abstract abstract-type="main" id="jnc12720-abs-0001"> <title>Abstract</title> <p>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 <sup>125</sup>I‐labeled Ang‐(1‐7), Ang II, and Ang I revealed comparable apparent <italic>K</italic><sub>m</sub> values (2.6, 2.8, and 4.3 μM, respectively), but a higher apparent <italic>V</italic><sub>max</sub> for Ang‐(1‐7) (72 vs. 30 and 6 nmol/min/mg, respectively; <italic>p</italic> < 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. <boxed-text content-type="graphic" id="jnc12720-blkfxd-0001" position="anchor" orientation="portrait"><graphic position="anchor" mimetype="image" xlink:href="ark:/27927/pghq85btnj" orientation="portrait" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /></boxed-text></p> <p>Angiotensin‐(1‐7) actions are mediated by the AT<sub>7</sub>/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.</p> </abstract>