Angiotensin IV possibly acts through PKMzeta in the hippocampus to regulate cognitive memory in rats

Acute Angiotensin II Receptor Blockade Facilitates Parahippocampal Processing During Memory Encoding in High-Trait-Anxious Individuals

Background

Angiotensin II receptor blockers (ARBs) have been associated with preventing posttraumatic stress disorder symptom development and improving memory. However, the underlying neural mechanisms are poorly understood. This study investigated ARB effects on memory encoding and hippocampal functioning that have previously been implicated in posttraumatic stress disorder development.

Methods

In a double-blind randomized design, 40 high-trait-anxious participants (33 women) received the ARB losartan (50 mg) or placebo. At drug peak level, participants encoded images of animals and landscapes before undergoing functional magnetic resonance imaging, where they viewed the encoded familiar images and unseen novel images to be memorized and classified as animals/landscapes. Memory recognition was assessed 1 hour after functional magnetic resonance imaging. To analyze neural effects, whole-brain analysis, hippocampus region-of-interest analysis, and exploratory multivariate pattern similarity analysis were employed.

Results

ARBs facilitated parahippocampal processing. In the whole-brain analysis, losartan enhanced brain activity for familiar images in the parahippocampal gyrus (PHC), anterior cingulate cortex, and caudate. For novel images, losartan enhanced brain activity in the PHC only. Pattern similarity analysis showed that losartan increased neural stability in the PHC when processing novel and familiar images. However, there were no drug effects on memory recognition or hippocampal activation.

Conclusions

Given that the hippocampus receives major input from the PHC, our findings suggest that ARBs may modulate higher-order visual processing through parahippocampal involvement, potentially preserving intact memory input. Future research needs to directly investigate whether this effect may underlie the preventive effects of ARBs in the development of posttraumatic stress disorder.

Intrathecal injections of angiotensin IV and oxytocin conjugates induce antihyperalgesia and antiallodynia in both sexes of rats

Our previous studies have established that intrathecal oxytocin (OT) and angiotensin IV (Ang IV) injections induce antihyperalgesia and antiallodynia in rodents. Ang IV, a renin-angiotensin system hexapeptide, acts as an endogenous inhibitor that inhibits the oxytocin-degrading enzyme insulin-regulated aminopeptidase (IRAP). The pain inhibitory effects by Ang IV were found to be through its inhibition on IRAP to potentiate the effect of OT. However, these effects were found to be with a significant sex difference, which could be partially due to the higher expression of IRAP at the spinal cords of female. Therefore, we synthesized Ang IV and OT conjugates connected with a peptide bond and tested for their effects on hyperalgesia and allodynia. Carrageenan-induced hyperalgesia and partial sciatic nerve ligation (PSNL) were performed using rat models. Conjugates Ang IV-OT (Ang IV at the N-terminal) and OT-Ang IV (OT at the N-terminal) were synthesized and intrathecally injected into male and female rats. Our results showed that Ang IV-OT exhibited prominent antihyperalgesia in male rats, particularly during hyperalgesia recovery, whereas OT-Ang IV was more effective during development stage. Ang IV-OT showed clear antihyperalgesia in female rats, but OT-Ang IV had no significant effect. Notably, both conjugates alleviated neuropathic allodynia in male rats; however, OT-Ang IV had no effect in female rats, whereas Ang IV-OT induced significant antiallodynia. In conclusion, Ang IV-OT has greater therapeutic potential for treating hyperalgesia and allodynia than OT-Ang IV. Its effects were not affected by sex, unlike those of OT and OT-Ang IV, extending its possible clinical applications.

Targeting brain Renin-Angiotensin System for the prevention and treatment of Alzheimer's disease: Past, present and future

Alzheimer's disease (AD) is a well-known neurodegenerative disease characterized by the presence of two main hallmarks - Tau hyperphosphorylation and Aβ deposits. Notwithstanding, in the last few years the scientific evidence about the drivers of AD have been changing and nowadays age-related vascular alterations and several cardiovascular risk factors have been shown to trigger the development of AD. In this context, drugs targeting the Renin Angiotensin System (RAS), commonly used for the treatment of hypertension, are evidencing a high potential to delay AD development due to their action on brain RAS. Indeed, the ACE 1/Ang II/AT1R axis is believed to be upregulated in AD and to be responsible for deleterious effects such as increased oxidative stress, neuroinflammation, blood-brain barrier (BBB) hyperpermeability, astrocytes dysfunction and a decrease in cerebral blood flow. In contrast, the alternative axis - ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) - seems to counterbalance the deleterious effects of the principal axis and to exert beneficial effects on memory and cognition. Accordingly, retrospective studies demonstrate a reduced risk of developing AD among people taking RAS medication as well as several in vitro and in vivo pre-clinical studies as it is herein critically reviewed. In this review, we first revise, at a glance, the pathophysiology of AD focused on its classic hallmarks. Secondly, an overview about the impact of the RAS on the pathophysiology of AD is also provided, focused on their four essential axes ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) and ACE 1/Ang II/AT1R. Finally, the therapeutic potential of available drugs targeting RAS on AD, namely angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs), is highlighted and data supporting this hope will be presented, from in vitro and in vivo pre-clinical to clinical studies.

Memory and cerebrovascular deficits recovered following angiotensin IV intervention in a mouse model of Alzheimer's disease

Angiotensin II type 1 receptor antagonists like losartan have been found to lower the incidence and progression to Alzheimer's disease (AD), as well as rescue cognitive and cerebrovascular deficits in AD mouse models. We previously found that co-administration of an angiotensin IV (AngIV) receptor (AT4R) antagonist prevented losartan's benefits, identifying AT4Rs as a possible target to counter AD pathogenesis. Therein, we investigated whether directly targeting AT4Rs could counter AD pathogenesis in a well-characterized mouse model of AD. Wild-type and human amyloid precursor protein (APP) transgenic (J20 line) mice (4.5 months old) received vehicle or AngIV (~1.3 nmol/day, 1 month) intracerebroventricularly via osmotic minipumps. AngIV restored short-term memory, spatial learning and memory in APP mice. AngIV normalized hippocampal AT4R levels, increased hippocampal subgranular zone cellular proliferation and dendritic arborization, and reduced oxidative stress. AngIV rescued whisker-evoked neurovascular coupling, endothelial- and smooth muscle cell-mediated cerebral vasodilatory responses, and cerebrovascular nitric oxide bioavailability. AngIV did not alter blood pressure, neuroinflammation or amyloid-β (Aβ) pathology. These preclinical findings identify AT4R as a promising target to counter Aβ-related cognitive and cerebrovascular deficits in AD.

Decreased behavioural and neurochemical effects of angiotensin IV following prenatal alcohol exposure in the mouse

Angiotensin IV (ang IV) is known to improve learning and memory in animal models but the mechanism is unclear. We have previously demonstrated sex differences in the pro-cognitive effects of ang IV, and that prenatal alcohol exposure (PAE) abolishes these effects. This study aimed to explore a possible mechanism underlying the sex differences and the effects of PAE in male mice. Mouse breeding harems received 5% ethanol in drinking water throughout pregnancy and lactation in a two-bottle schedule. The effects of ang IV were assessed in offspring at 4 months of age using the open field test, novel object recognition test and elevated plus maze. Aminopeptidase activity of brain insulin-regulated aminopeptidase (IRAP), a putative target of ang IV, was determined. As seen in a previous similar study, ang IV administered immediately after the second training trial significantly improved novel object recognition 24 h later in male mice but not female. PAE abolished this pro-cognitive effect in males. PAE also increased anxiety-like behaviour in male but not female offspring. Ang IV decreased the aminopeptidase activity of brain IRAP in control male, but not female, mice; PAE abolished this inhibitory effect. Ang IV improved memory consolidation in male but not female mice and PAE abolished this effect in the males. While the effects of PAE may be related to increased anxiety; ang IV decreased the aminopeptidase activity in male but not female mice and PAE abolished this inhibitory effect. The results therefore suggest that improvements in learning and memory induced by peripheral administration of ang IV correlate with a reduction of the enzyme activity of IRAP. This is the first demonstration that ang IV administered peripherally can induce long-term (24 h) changes in IRAP function which are probably not simple competitive inhibition and the first demonstration that PAE alters IRAP activity.

Cognitive benefits of angiotensin IV and angiotensin-(1-7): A systematic review of experimental studies

OBJECTIVES

To explore effects of the brain renin-angiotensin system (RAS) on cognition.

DESIGN

Systematic review of experimental (non-human) studies assessing cognitive effects of RAS peptides angiotensin-(3-8) [Ang IV] and angiotensin-(1-7) [Ang-(1-7)] and their receptors, the Ang IV receptor (AT4R) and the Mas receptor.

RESULTS

Of 450 articles identified, 32 met inclusion criteria. Seven of 11 studies of normal animals found Ang IV had beneficial effects on tests of passive or conditioned avoidance and object recognition. In models of cognitive deficit, eight of nine studies found Ang IV and its analogs (Nle¹-Ang IV, dihexa, LVV-hemorphin-7) improved performance on spatial working memory and passive avoidance tasks. Two of three studies examining Ang-(1-7) found it benefited memory. Mas receptor removal was associated with reduced fear memory in one study.

CONCLUSION

Studies of cognitive impairment show salutary effects of acute administration of Ang IV and its analogs, as well as AT4R activation. Brain RAS peptides appear most effective administered intracerebroventricularly, close to the time of learning acquisition or retention testing. Ang-(1-7) shows anti-dementia qualities.

Synaptic plasticity modulation by circulating peptides and metaplasticity: Involvement in Alzheimer's disease

Synaptic plasticity is a cellular process involved in learning and memory whose alteration in its two main forms (Long Term Depression (LTD) and Long Term Potentiation (LTP)), is observed in most brain pathologies, including neurodegenerative disorders such as Alzheimer's disease (AD). In humans, AD is associated at the cellular level with neuropathological lesions composed of extracellular deposits of β-amyloid (Aβ) protein aggregates and intracellular neurofibrillary tangles, cellular loss, neuroinflammation and a general brain homeostasis dysregulation. Thus, a dramatic synaptic environment perturbation is observed in AD patients, involving changes in brain neuropeptides, cytokines, growth factors or chemokines concentration and diffusion. Studies performed in animal models demonstrate that these circulating peptides strongly affect synaptic functions and in particular synaptic plasticity. Besides this neuromodulatory action of circulating peptides, other synaptic plasticity regulation mechanisms such as metaplasticity are altered in AD animal models. Here, we will review new insights into the study of synaptic plasticity regulatory/modulatory mechanisms which could influence the process of synaptic plasticity in the context of AD with a particular attention to the role of metaplasticity and peptide dependent neuromodulation.