Insulin-Regulated Aminopeptidase Deficiency Provides Protection against Ischemic Stroke in Mice
Howard Florey Institute, Victoria, Australia. Journal of neurotrauma
(Impact Factor: 3.71).
09/2011; 29(6):1243-8. DOI: 10.1089/neu.2011.1824
Recent studies have demonstrated that angiotensin IV (Ang IV) provides protection against brain injury caused by cerebral ischemia. Ang IV is a potent inhibitor of insulin-regulated aminopeptidase (IRAP). Therefore, we examined the effect of IRAP gene inactivation on neuroprotection following transient middle cerebral artery occlusion (MCAo) in mice. IRAP knockout mice and wild-type controls were subjected to 2 h of transient MCAo using the intraluminal filament technique. Twenty-four hours after reperfusion, neurological deficits of the stroke-induced mice were assessed and infarct volumes were measured by TTC staining. The cerebral infarct volume was significantly reduced in the IRAP knockout mice compared to wild-type littermates with corresponding improvement in neurological performance at 24 h post-ischemia. An increase in compensatory cerebral blood flow during MCAo was observed in the IRAP knockout animals with no differences in cerebral vascular anatomy detected. The current study demonstrates that deletion of the IRAP gene protects the brain from ischemic damage analogous to the effect of the IRAP inhibitor, Ang IV. This study indicates that IRAP is potentially a new therapeutic target for the development of treatment for ischemic stroke.
Available from: PubMed Central
- "This potential interest as prompted active ongoing research to identify small biologically active non-peptides molecules that, like AngIV, inhibit the catalytic domain of IRAP . Such new AT4 agonists will pave the way for innovative research for the prevention of cognitive decline, but also for stroke therapy [30,46,47]. Clearly our present findings, confirming the vascular protective effect of AngIV in type 1 diabetes mice also invite to consider AT4/IRAP as another potential target for revisited therapeutic strategies of RAAS modulation for cardiovascular disease prevention. "
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ABSTRACT: We examined the effect of chronic administration of angiotensin IV (AngIV) on the vascular alterations induced by type 1 diabetes in mice.
Diabetes was induced in adult Swiss mice with a single injection of streptozotocin (STZ). Mice were treated subcutaneously with AngIV (1.4 mg/kg/day) either immediately following diabetes induction (preventive treatment), or treated with AngIV (0.01 to 1.4 mg/kg), alone or with the AT4 receptor antagonist Divalinal or the AT2 receptor antagonist PD123319, for two weeks after 4 weeks of diabetes duration (rescue treatment). Acetylcholine-induced, endothelium-dependent relaxation (EDR) was measured in isolated aortic rings preparations. Histomorphometric measurements of the media thickness were obtained, and nitric oxide (NO) and superoxide anion production were measured by electron paramagnetic resonance in aorta and mesenteric arteries. The effect of diabetes on mesenteric vascular alterations was also examined in genetically modified mice lacking the AT2 receptor.
Induction of diabetes with STZ was associated with a progressive decrease of EDR and an increase of the aortic and mesenteric media thickness already significant after 4 weeks and peaking at week 6. Immediate treatment with AngIV fully prevented the diabetes-induced endothelial dysfunction. Rescue treatment with AngIV implemented after 4 weeks of diabetes dose-dependently restored a normal endothelial function at week 6. AngIV blunted the thickening of the aortic and mesenteric media, and reversed the diabetes-induced changes in NO and O2[bullet] - production by the vessels. The protective effect of AngIV on endothelial function was completely blunted by cotreatment with Divalinal, but not with PD123319. In contrast, both the pharmacological blockade and genetic deletion of the AT2 receptor reversed the diabetes-induced morphologic and endothelial alteration caused by diabetes.
The results suggest an opposite contribution of AT2 and AT4 receptors to the vascular alterations caused by streptozotocin-induced diabetes in mice, since chronic stimulation of AT4 by AngIV and inhibition of AT2 similarly reverse diabetes-induced endothelial dysfunction and hypertrophic remodeling, and increase NO bioavailability.
Available from: Marc de Gasparo
- "On the other hand, Ang IV binds specifically to the AT 4 receptor, which was proposed to be identical to the insulinregulated aminopeptidase (IRAP) . Indeed, the high affinity-binding site for Ang IV is absent in IRAP-KO mice , and the brains of these mice are protected against ischemic damage as Ang IV does in control animals . Cystein aminopeptidase (CysAP), also called oxytocinase or vasopressinase (EC 220.127.116.11), is considered the human variant of IRAP . "
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ABSTRACT: The model of suggests that the frontal cortex (FC) and the cardiovascular function are reciprocally and asymmetrically connected. We analyzed several angiotensinase activities in the heart left ventricle (VT) of control and captopril-treated SHR, and we search for a relationship between these activities and those determined in the left and right FC. Captopril was administered in drinking water for 4 weeks. Samples from the left VT and from the left and right FC were obtained. Soluble and membrane-bound enzymatic activities were measured fluorometrically using arylamides as substrates. The weight of heart significantly decreased after treatment with captopril, mainly, due to the reduction of the left VT weight. In the VT, no differences for soluble activities were observed between control and treated SHR. In contrast, a generalized significant reduction was observed for membrane-bound activities. The most significant correlations between FC and VT were observed in the right FC of the captopril-treated group. The other correlations, right FC versus VT and left FC versus VT in controls and left FC versus VT in the captopril group, were few and low. These results confirm that the connection between FC and cardiovascular system is asymmetrically organized.
Available from: Alexandros Nikolaou
- "Over two decades ago, angiotensin IV (Ang IV) had been identified as a bio-active fragment of angiotensin II (Swanson et al., 1992). Ang IV induces various biological effects, such as enhancement of learning and memory in mice (Gard et al., 2012) and rats (Wright et al., 1999), protection against ischemic stroke (Faure et al., 2006a; Pham et al., 2012) and against hyperglycaemia (Wong et al., 2011). The high-affinity binding site for Ang IV is the insulin-regulated aminopeptidase (IRAP, EC 18.104.22.168), a membrane-bound zinc-dependent aminopeptidase found in diverse tissues, including heart, muscle and fat (Albiston et al., 2001). "
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ABSTRACT: The hexapeptide angiotensin IV (Ang IV) induces diverse biological effects such as memory enhancement and protection against ischemic stroke. Studies on the mechanism of Ang IV however are hampered by its instability and its lack of selectivity. The high-affinity binding site for Ang IV is the insulin-regulated aminopeptidase (IRAP, EC 22.214.171.124), but Ang IV also acts as a weak agonist for the Ang II-receptor (AT(1)), implying the need for stable and highly selective Ang IV-analogues. Here we present the screening of novel Ang IV-analogues, selected on basis of high affinity for IRAP, high selectivity (compared to aminopeptidase N and the AT(1) receptor) and resistance against proteases. The selected compound IVDE77 possesses a number of advantages compared to Ang IV: (i) it has a 40 times higher affinity for IRAP (K(i) 1.71nM), (ii) it does not activate the AT(1) receptor, (iii) it is easily radiolabeled with tritium and (iv) it is resistant to proteolysis, even in human plasma. In addition, pre-treatment of intact CHO-K1 cells with IVDE77 led to a virtually complete inhibition of subsequent intracellular accumulation of [(3)H]IVDE77-IRAP complexes. IVDE77 thus represents the first Ang IV-analogue able to abolish IRAP-availability completely at the cell surface in vitro. In summary, IVDE77 is a useful tool for the detection of IRAP under physiological conditions, and may contribute to elucidating the mechanism of Ang IV to ascertain which functions are IRAP-dependent.
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