Angiotensin-II impairs the cellular antioxidant defense capacity in the hypothalamic cardio regulatory nucleus of spontaneously hypertensive rats contributing to hypertension
Authors: Aitken Andrew , Mowry Francesca , Peaden Sarah , Biancardi Vinicia 
Published: May 2023

Oxidative stress is a central mechanism underlying Angiotensin II (AngII)-induced enhanced sympathetic outflow within brain cardio-regulatory nuclei in neurogenic hypertension. Yet, a causal association between AngII, Nrf2 (nuclear factor erythroid 2-related factor 2 - the master regulator of the antioxidant response), and sympathetic activity in neurogenic hypertension has not been explored. We hypothesized that increased AngII in neurogenic hypertension impairs the Nrf2 signaling pathway within the paraventricular nucleus of the hypothalamus (PVN), leading to increased oxidative stress, inflammation, and consequent sympathoexcitation. We used 12-13 week-old male hypertensive (SHRs, mean arterial pressure (MAP) 162.8±3.6mmHg; tail-cuff recording [Kent Scientific]) and normotensive Wistar Kyoto rats (WKYs, 107.8±2.1mmHg). We measured mRNA expression in PVN punches (real-time PCR) of the Nrf2 negative regulator Keap1 and Nrf2-based antioxidant defense (Gpx1 and NQO1). We found increased mRNA levels of Keap1 (2.1±0.2) and reductions in Gpx1 (0.7±0.1) and NQO1 (0.5±0.1 fold change) in SHR ( P<.05 vs. WKY), suggesting lower Nrf2 and associate antioxidant genes expression. We then measured the protein expression of Nrf2, obtained by immunofluorescence [IF], and detected by high-magnification confocal imaging in the subcellular localization of neurons and astrocytes within the PVN. The neuronal marker NeuN and the astrocytic marker GFAP were used for subcellular identification and image J analyses. Relative to WKYs, Nrf2 IF density was reduced in SHR neurons (whole cell: -43.3±4.0, nucleus: -33.3±6.7, cytosol: -63.9±6.8% vs. WKY, P<.001) and astrocytes (cell: -55.2±5.0, nucleus: -71.9±4.0, cytosol: -54.1±5.7% vs. WKY, P<.001). To dissect the cause-effect of AngII-Nrf2 dysregulation other than the MAP increase in hypertension, we treated cohorts of SHR via oral gavage with the AngII-type-1 receptor blocker Losartan (SHR-Los 20mg/kg, 4 weeks) or the vasodilator Hydralazine (SHR-Hyd 10mg/kg, 10 days). Compared to WKY, SHR-Los normalized MAP (154.9±1.7 to 103.6±2.4 mmHg, P<.001) and Nrf2 protein expression in both neurons (cell: -2.8±6.8, nucleus: -5.8±6.5, cytosol: -2.8±13.9%, P<.001) and astrocytes (cell: -3.9±9.0, nucleus:+1.2±11.9, cytosol -4.1±10.2%, P<.001). In SHR-Hyd, despite normalization of MAP (154.9±1.7 to 105.2±3.8 mmHg, P<.001), no reduction in Nrf2 protein expression was observed in neurons (cell: -39.3±3.8, nucleus: -28.4±4.2, cytosol: -61.7±5.3%) and astrocytes (cell: -51.5±4.3, nucleus: -68.4±3.8, cytosol: -5254.1±5.7%). These data support that the compromised Nrf2 dynamics observed are due to AngII signaling rather than elevations in blood pressure alone. Our ongoing studies aim to understand the Nrf2 contribution to inflammation and autonomic dysfunction in hypertension. This work was funded by AHA 953524 to VCB. This is the full abstract presented at the American Physiology Summit 2023 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.