Brain ACE2 overexpression reduces DOCA-salt hypertension independently of endoplasmic reticulum stress

Abstract

-Endoplasmic reticulum (ER) stress was previously reported to contribute to neurogenic hypertension while neuronal angiotensin-converting enzyme type 2 (ACE2) overexpression blunts the disease. To assess which brain regions are important for ACE2 beneficial effects and the contribution of ER stress to neurogenic hypertension, we first used transgenic mice harboring a floxed neuronal hACE2 transgene (SL) and tested the impact of hACE2 knockdown in the subfornical organ (SFO) and paraventricular nucleus (PVN) on deoxycorticosterone acetate (DOCA)-salt hypertension. SL and nontransgenic (NT) mice underwent DOCA-salt or sham treatment while infected with an adenoassociated virus (AAV) encoding Cre recombinase (AAV-Cre) or a control virus (AAV-green fluorescent protein) to the SFO or PVN. DOCA-salt-induced hypertension was reduced in SL mice, with hACE2 overexpression in the brain. This reduction was only partially blunted by knockdown of hACE2 in the SFO or PVN, suggesting that both regions are involved but not essential for ACE2 regulation of blood pressure (BP). DOCA-salt treatment did not increase the protein levels of ER stress and autophagy markers in NT mice, despite a significant increase in BP. In addition, these markers were not affected by hACE2 overexpression in the brain, despite a significant reduction of hypertension in SL mice. To further assess the role of ER stress in neurogenic hypertension, NT mice were infused intracerebroventricularlly with tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor, during DOCA-salt treatment. However, TUDCA infusion failed to blunt the development of hypertension in NT mice. Our data suggest that brain ER stress does not contribute to DOCA-salt hypertension and that ACE2 blunts neurogenic hypertension independently of ER stress. neurogenic hypertension; central nervous system; blood pressure; angiotensin-converting enzyme type 2; deoxycorticosterone acetate THE BRAIN RENIN-ANGIOTENSIN system (RAS) plays a critical role in the regulation of blood pressure (BP) via its actions in various brain regions, such as subfornical organ (SFO), paraventricular nucleus (PVN), rostral ventrolateral medulla (RVLM), and nucleus tractus solitarius (NTS) (17). An overactivated brain RAS leads to the development of neurogenic hypertension at least in part by increasing sympathetic outflow, blunting the baroreflex sensitivity and stimulating vasopressin secretion (17). Angiotensin-converting enzyme type 2 (ACE2), a pivotal RAS component, has been found in many regions in the bran, including SFO and PVN (8). Numerous studies have shown that ACE2 has opposite properties to that of the classic RAS via its conversion of angiotensin (ANG) II into ANG-(1-7) (20). We previously reported that overexpression of ACE2 in the brain blunts the development of hypertension in several animal models (9, 31). However, it is not clear which brain regions might be more important for the preservation of ACE2 compensatory activity.

The critical role of the central nervous system (pro)renin receptor in regulating systemic blood pressure

“…Ang-(1–7) has an effect opposite that of Ang II in that it stimulates nitric oxide (NO) release, improves baroreceptor reflexes sensitivity, and promotes vasodilation (Rabelo, Alenina, & Bader, 2011). Consistent with this, overexpression of human ACE2 in neurons or specifically in the RVLM or SFO causes a reduction in BP in Ang II-induced hypertensive mice and spontaneously hypertensive rats (SHR) (Feng, et al, 2008; Xia, et al, 2015; Yamazato, Yamazato, Sun, Diez-Freire, & Raizada, 2007). AGT in the brain is synthesized and secreted from astroglial cells (Campbell, Bouhnik, Menard, & Corvol, 1984; Deschepper, Bouhnik, & Ganong, 1986; Sernia & Mowchanuk, 1983) and neurons (G.…”

Brain Endoplasmic Reticulum Stress Mechanistically Distinguishes the Saline-Intake and Hypertensive Response to Deoxycorticosterone Acetate–Salt

“…Whereas, the absence of an effect on blood pressure is consistent with a previous report observing no changes in DOCA-salt induced blood pressure in response to TUDCA 42 , it stands in contrast to two other studies where relief of ER stress prevented the hypertensive response in Ang-II 14 and reduced blood pressure in the spontaneously hypertensive rat. 43 Assuming there are no technical limitations in both DOCA-salt studies, these results have two main implications.…”

“…However, it was recently reported that increased expression of the mRNAs encoding several ER stress biomarkers (s-XBP, ATF4, GRP78 [also known as BiP] and CHOP) was evident in the SFO and to a lesser extent the paraventricular nucleus (PVN) of DOCA-salt-treated mice. 42 However, unlike their study which surprisingly concluded that ER stress does not occur in the SFO in response to DOCA-salt, our identification of increased CHOP protein in the SFO (and SON) concomitant with ultrastructural changes consistent with ER stress, and decreased saline intake in response to SFO-targeted delivery of AdGRP78 provide compelling evidence for the induction of ER stress in the SFO in response to DOCA-salt.…”

“…CHOP and XBP1 are concomitantly induced and both were reportedly induced in the SFO in response to DOCA-salt. 42 It is well established that prolonged activation of CHOP can induce apoptosis (reviewed in 25,48 ). We have no evidence addressing if apoptosis is occurring in the brain of DOCA-salt mice and if this is worsened in regions showing evidence of ER stress, such as the SFO and SON.…”

Endoplasmic reticulum stress: a novel mechanism and therapeutic target for cardiovascular diseases

“…ERS mediated Ang II-dependent hypertension in SFO through nuclear factor (NF)-кB activation [115] . ERS also contributed to neurogenic hypertension [116] . Severe hypertension caused neuronal injury through neuronal ERS and apoptosis [117] .…”