Gerbil angiotensin II AT1 receptors are highly expressed in the hippocampus and cerebral cortex during postnatal development

Systemic Candesartan Treatment Modulates Behavior, Synaptic Protein Levels, and Neuroinflammation in Female Mice That Express Human APOE4

Evidence suggests that angiotensin receptor blockers (ARBs) could be beneficial for Alzheimer’s disease (AD) patients independent of any effects on hypertension. However, studies in rodent models directly testing the activity of ARB treatment on behavior and AD-relevent pathology including neuroinflammation, Aβ levels, and cerebrovascular function, have produced mixed results. APOE4 is a major genetic risk factor for AD and has been linked to many of the same functions as those purported to be modulated by ARB treatment. Therefore, evaluating the effects of ARB treatment on behavior and AD-relevant pathology in mice that express human APOE4 could provide important information on whether to further develop ARBs for AD therapy. In this study, we treated female and male mice that express the human APOE4 gene in the absence (E4FAD−) or presence (E4FAD+) of high Aβ levels with the ARB prodrug candesartan cilexetil for a duration of 4 months. Compared to vehicle, candesartan treatment resulted in greater memory-relevant behavior and higher hippocampal presynaptic protein levels in female, but not male, E4FAD− and E4FAD+ mice. The beneficial effects of candesartan in female E4FAD− and E4FAD+ mice occurred in tandem with lower GFAP and Iba1 levels in the hippocampus, whereas there were no effects on markers of cerebrovascular function and Aβ levels. Collectively, these data imply that the effects of ARBs on AD-relevant pathology may be modulated in part by the interaction between APOE genotype and biological sex. Thus, the further development of ARBs could provide therapeutic options for targeting neuroinflammation in female APOE4 carriers.

Ischemia-induced brain damage is enhanced in human renin and angiotensinogen double-transgenic mice

To investigate the role of brain angiotensin II (ANG II) in the pathogenesis of injury following ischemic stroke, mice overexpressing renin and angiotensinogen (R+A+) and their wild-type control animals (R-A-) were used for experimental ischemia studies. Focal brain ischemia was induced by middle cerebral artery occlusion (MCAO). The severity of ischemic injury was determined by measuring neurological deficits and histological damage at 24 and 48 h after MCAO, respectively. To exclude the influence of blood pressure and local collateral blood flow, brain slices were used for oxygen and glucose deprivation (OGD) studies. The severity of OGD-induced damage was determined by measuring indicators of tissue swelling and cell death, the intensity of the intrinsic optical signal (IOS), and the number of propidium iodide (PI) staining cells, respectively. Results showed 1) R+A+ mice showed higher neurological deficit score (3.8 +/- 0.5 and 2.5 +/- 0.3 for R+A+ and R-A-, respectively, P < 0.01) and larger infarct volume (22.2 +/- 1.6% and 14.1 +/- 1.2% for R+A+ and R-A-, respectively, P < 0.01); 2) The R+A+ brain slices showed more severe tissue swelling and cell death in the cortex (IOS: 140 +/- 6% and 114 +/- 10%; PI: 139 +/- 20 cells/field and 39 +/- 9 cells/field for R+A+ and R-A-, respectively, P < 0.01); 3) treatment with losartan (20 micromol/l) abolished OGD-induced exaggeration of cell injury seen in R+A+ mice. The data indicate that activation of ANG II/AT(1) signaling is harmful to brain exposed to ischemia.

Characterization of signal transduction pathway in neurotropic action of angiotensin II in brain neurons

Interaction of angiotensin II with the neuronal angiotensin type 1 receptor stimulates the PI3K signaling pathway. Our objective in this study was to investigate the hypothesis that the PI3K cascade regulates the neurotropic actions of angiotensin II in rat brain neurons. We followed growth associated protein-43 expression and neurite extension as markers of neurotropic activity. Angiotensin II, through its interaction with the angiotensin type 1 receptor, increased growth associated protein-43 expression and neurite extension. These effects were abolished by pretreatment of neurons with wortmannin and rapamycin, but not by PD 98059. Antisense oligonucleotides specific for p70(S6) kinase also inhibited angiotensin II-stimulated neurotropic activity. These data confirm the involvement of PI3K and p70(S6) kinase in angiotensin II-mediated neurotropic action. Further support for this was provided by the observation that angiotensin II caused a time-dependent stimulation of p70(S6) kinase by an angiotensin type 1 receptor-mediated process. We also found that the neurotropic actions of angiotensin II are mediated by plasminogen activator inhibitor-1. Evidence for this includes 1) angiotensin II-stimulated neuronal plasminogen activator inhibitor-1 gene expression, 2) potent neurotropic action of exogenous plasminogen activator inhibitor-1, and 3) inhibitory neurotropic effect of angiotensin II by antisense oligonucleotide-mediated depletion of plasminogen activator inhibitor-1. Finally, we found that the neurotropic action of plasminogen activator inhibitor-1 is not blocked by either angiotensin type 1 receptor antagonist or inhibitors of PI3K or p70(S6) kinase, indicating that the plasminogen activator inhibitor-1 step is downstream from the p70(S6) kinase. These observations demonstrate that angiotensin II is a neurotropic hormone that engages a distinct PI3K-p70(S6) kinase-plasminogen activator inhibitor-1 signaling pathway for this action.