Genetic Deletion of Carboxypeptidase N Attenuates Angiotensin II-Induced Hypertension and Target Organ Damage
Authors: White Acacia , Sriramula Srinivas 
Published: May 2024

Objectives: Kininase I transforms bradykinin and kallidin, into kinin B1 receptor (B1R) agonists des-Arg9-BK and des-Arg10-kallidin, respectively. Carboxypeptidase M (CPM) is the membrane bound isoform of kininase I and carboxypeptidase N (CPN) is the isoform located in the plasma. Activation of the B1R has been implicated in the development of hypertension, diabetes and atherosclerosis. Pharmacologic inhibition of kininase I is associated with reductions in B1R expression, inflammation, oxidative stress, and improvements in insulin resistance. B1R can interact with aminopeptidase N (CD13) or high-mobility group box 1 (HMGB1) to mediate an inflammatory response. However, the exact role of kininase I in the development of hypertension and the regulation of these B1R-mediated signaling mechanisms remains unknown. In this study, we hypothesize that gene deletion of CPN will prevent B1R activation, reduce inflammation via interfering with CD13 and HMGB1 signaling, and ultimately attenuate the progression of hypertension and target organ damage. Methods and Results: To test our hypothesis we utilized 12-week-old male and female C57BL/6NJ wild-type (WT) and CPN gene knockout (CPNKO) mice. These mice were infused angiotensin II (Ang II, 600 ng/kg/min) or saline (vehicle) via osmotic minipumps for 2 weeks. Vehicle treated CPNKO and WT mice showed no significant difference in mean arterial blood pressure (MAP) (104 ±7 vs 102 ±5 mmHg, n=5, p≤0.05). Ang II-induced elevations in MAP were significantly reduced in CPNKO mice compared to WT mice infused with Ang II (129 ±8 vs 150 ±6 mmHg, n=5, p≤0.05). Interestingly, we did not find any significant sex differences in MAP in CPNKO groups. Additionally, Ang II treatment significantly increased cardiomyocyte hypertrophy in male and female WT mice, but this effect was blunted in CPNKO mice (n=5, p≤0.05; wheat germ agglutinin staining). Ang II infusion promoted collagen deposition in the aorta of WT male and female mice, but not in CPNKO mice (n=5, p≤0.05; picrosirius red/Masson’s trichrome). In male WT mice, Ang II significantly increased the immunoreactivity of CPM in the heart, but this was abrogated in CPNKO mice infused with Ang II (n=4, p≤0.05). Similarly, B1R was also upregulated in male WT mice hearts when compared to CPNKO mice after Ang II infusions (n=3, p≤0.05). We also found that Ang II significantly increased HMGB1 and CD13 in male WT hearts and brains, but not in CPNKO mice (n=4, p≤0.05). In addition, oxidative stress levels in the brain were significantly increased by Ang II in WT mice and was attenuated in CPNKO mice (n=4, p≤0.05; dihydroethidium staining). Conclusions: Genetic deletion of CPN attenuates Ang II-induced hypertension by reducing B1R mediated reductions in CD13 and HMGB1-mediated inflammatory responses and oxidative stress. Our data suggests that targeting kininase I may be a novel therapeutic target for hypertension and target organ damage. Funding: This study was supported by NHLBI/NIH 5R01HL153115 (S. Sriramula). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.