Temporal Association Between Endoplasmic Reticulum Stress and Reactive Oxygen Species in the Subfornical Organ During Angiotensin‐II‐Mediated Hypertension
Authors: Judice Melanie L. , Hurr Chansol , Young Colin N. 
Published: June 2021

Hypertension affects one in three adults and is directly associated with diseases of the heart, kidney, and brain. While a number of factors may play a role, dysregulation in Angiotensin‐II (Ang‐II) signaling in the brain is well accepted to contribute to hypertension development. In particular, Ang‐II signaling within the subfornical organ (SFO), a forebrain circumventricular region situated outside of the blood‐brain‐barrier, plays a critical role. Ang‐II‐mediated oxidative stress and endoplasmic reticulum (ER) stress have both been implicated in Ang‐II‐dependent hypertension. However, the interplay between these key hypertensive mechanisms in the SFO remains unclear. Therefore, as a first step, we hypothesized that SFO oxidative stress and ER stress occur at the same time during the development of Ang‐II hypertension. Adult male C57B1/6 mice underwent subcutaneous implantation of osmotic mini‐pumps for continuous 2 wk delivery of Ang‐II (600 ng/kg/min) to induce hypertension, or vehicle control (BSA). At 14 days of infusion (peak hypertension), brains were collected and dihydroethidium (DHE) fluorescence staining was performed to evaluate reactive oxygen species in the SFO (n=10/group). In a separate cohort (n=4–5), immunohistochemistry for protein disulfide isomerase (PDI), an ER chaperone protein that is upregulated under conditions of ER stress, was performed. While DHE fluorescence in the SFO was minimal in control animals, 2 wk infusion of Ang‐II resulted in a robust increase in reactive oxygen species in the SFO (1.0±0.1 vs. 1.7±0.1 fold control; control vs. Ang‐II, p<0.05). Interestingly, immunohistochemistry analysis at 14 days also demonstrated marked Ang‐II‐mediated ER stress in the SFO, as indicated by upregulation of PDI (8.8±1.6 vs. 14.9±1.3 PDI density/area; control vs. Ang‐II, p<0.05). To further delineate the temporal relationship between oxidative and ER stress, in another cohort we subsequently performed PDI western blot evaluation in micropunches of the SFO at pre‐hypertensive (7 days) and established hypertension (14 days) timepoints. Importantly, we have previously shown a pre‐hypertensive (day 7) increase in SFO reactive oxygen species during Ang‐II hypertension (Young et al. AJP Cell, 2015). Following 7 day chronic infusion of Ang‐II, an ~85% increase in SFO PDI protein expression was found (1.00±0.24 vs. 1.85±0.7 fold day 0; day 0 vs. 7 day Ang‐II, p<0.05) and this ER chaperone upregulation was maintained at 14 days of Ang‐II infusion (1.58±0.16 fold day 0, p<0.05). Together, these findings indicate a close temporal relationship between Ang‐II‐induced ER stress and reactive oxygen species production in the SFO, which occurs prior to and in concert with the development of Ang‐II‐mediated hypertension.Support or Funding InformationAPS Undergraduate Summer Research Fellowship (M.J.); HL116776 (C.N.Y.)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.