The Receptor AT1 Appears to Be Important for the Maintenance of Bone Mass and AT2 Receptor Function in Periodontal Bone Loss Appears to Be Regulated by AT1 Receptor

A large number of experimental studies has demonstrated that angiotensin II (Ang II) is involved in key events of the inflammatory process. This study aimed to evaluate the role of Ang II type 1 (AT1) and Ang II type 2 (AT2) receptors on periodontitis. Methods: Experimental periodontitis was induced by placing a 5.0 nylon thread ligature around the second upper left molar of AT1 mice, no-ligature or ligature (AT1-NL and AT1-L), AT2 (AT2-NL or AT2-L) and wild type (WT-NL or L). Alveolar bone loss was scanned using Micro-CT. Cytokines, peptides and enzymes were analyzed from gingival tissues by Elisa and RT-PCR. Results: The blockade of AT1 receptor resulted in bone loss, even in healthy animals. Ang II receptor blockades did not prevent linear bone loss. Ang II and Ang 1-7 levels were significantly increased in the AT2-L (p < 0.01) group compared to AT2-NL and AT1-L. The genic expression of the Mas receptor was significantly increased in WT-L and AT2-L compared to (WT-NL and AT2-NL, respectively) and in AT1-L. Conclusions: Our data suggest that the receptor AT1 appears to be important for the maintenance of bone mass. AT2 receptor molecular function in periodontitis appears to be regulated by AT1.

Telmisartan restricts Chikungunya virus infection in vitro and in vivo through the AT1/PPAR-γ/MAPKs pathways

Chikungunya virus (CHIKV) has re-emerged as a global public health threat. The inflammatory pathways of RAS and PPAR-γ are usually involved in viral infections. Thus, Telmisartan (TM) with known capacity to block AT1 receptor and activate PPAR-γ, was investigated against CHIKV. The anti-CHIKV effect of TM was investigated in vitro (Vero, RAW 264.7 cells and hPBMCs) and in vivo (C57BL/6 mice). TM was found to abrogate CHIKV infection efficiently (IC50 of 15.34-20.89μM in the Vero and RAW 264.7 cells respectively). Viral RNA and proteins were reduced remarkably. Additionally, TM interfered in the early and late stages of CHIKV life cycle with efficacy in both pre and post-treatment assay. Moreover, the agonist of AT1 receptor and antagonist of PPAR-γ increased CHIKV infection suggesting TM’s anti-viral potential by modulating host factors. Besides, reduced activation of all major MAPKs, NF-κB (p65) and cytokines by TM through the inflammatory axis supported the fact that the anti-CHIKV efficacy of TM is partly mediated through the AT1/PPAR-γ/MAPKs pathways. Interestingly, at the human equivalent dose, TM abrogated CHIKV infection and inflammation significantly leading to reduced clinical score and complete survival of C57BL/6 mice. Additionally, TM reduced infection in hPBMC derived monocyte-macrophage populations in vitro . Hence, TM was found to reduce CHIKV infection by targeting both viral and host factors. Considering its safety and in vivo efficacy, it can be a suitable candidate in future for repurposing against CHIKV.

Telmisartan Potentiates Insulin Secretion via Ion Channels, Independent of the AT1 Receptor and PPARγ

Angiotensin II type 1 (AT1) receptor blockers (ARBs), as antihypertensive drugs, have drawn attention for their benefits to individuals with diabetes and prediabetes. However, the direct effects of ARBs on insulin secretion remain unclear. In this study, we aimed to investigate the insulinotropic effect of ARBs and the underlying electrophysiological mechanism. We found that only telmisartan among the three ARBs (telmisartan, valsartan, and irbesartan) exhibited an insulin secretagogue role in rat islets. Independent of AT1 receptor and peroxisome proliferator-activated receptor γ (PPARγ), telmisartan exerted effects on ion channels including voltage-dependent potassium (Kv) channels and L-type voltage-gated calcium channels (VGCCs) to promote extracellular Ca2+ influx, thereby potentiating insulin secretion in a glucose-dependent manner. Furthermore, we identified that telmisartan directly inhibited Kv2.1 channel on a Chinese hamster ovary cell line with Kv2.1 channel overexpression. Acute exposure of db/db mice to a telmisartan dose equivalent to therapeutic doses in humans resulted in lower blood glucose and increased plasma insulin concentration in OGTT. We further observed the telmisartan-induced insulinotropic and electrophysiological effects on pathological pancreatic islets or β-cells isolated from db/db mice. Collectively, our results establish an important insulinotropic function of telmisartan distinct from other ARBs in the treatment of diabetes.

Stearoyl-CoA Desaturase (SCD) Induces Cardiac Dysfunction with Cardiac Lipid Overload and Angiotensin II AT1 Receptor Protein Up-Regulation

Heart failure is a major cause of death worldwide with insufficient treatment options. In the search for pathomechanisms, we found up-regulation of an enzyme, stearoyl-CoA desaturase 1 (Scd1), in different experimental models of heart failure induced by advanced atherosclerosis, chronic pressure overload, and/or volume overload. Because the pathophysiological role of Scd1/SCD in heart failure is not clear, we investigated the impact of cardiac SCD upregulation through the generation of C57BL/6-Tg(MHCSCD)Sjaa mice with myocardium-specific expression of SCD. Echocardiographic examination showed that 4.9-fold-increased SCD levels triggered cardiac hypertrophy and symptoms of heart failure at an age of eight months. Tg-SCD mice had a significantly reduced left ventricular cardiac ejection fraction of 25.7 ± 2.9% compared to 54.3 ± 4.5% of non-transgenic B6 control mice. Whole-genome gene expression profiling identified up-regulated heart-failure-related genes such as resistin, adiponectin, and fatty acid synthase, and type 1 and 3 collagens. Tg-SCD mice were characterized by cardiac lipid accumulation with 1.6- and 1.7-fold-increased cardiac contents of saturated lipids, palmitate, and stearate, respectively. In contrast, unsaturated lipids were not changed. Together with saturated lipids, apoptosis-enhancing p53 protein contents were elevated. Imaging by autoradiography revealed that the heart-failure-promoting and membrane-spanning angiotensin II AT1 receptor protein of Tg-SCD hearts was significantly up-regulated. In transfected HEK cells, the expression of SCD increased the number of cell-surface angiotensin II AT1 receptor binding sites. In addition, increased AT1 receptor protein levels were detected by fluorescence spectroscopy of fluorescent protein-labeled AT1 receptor-Cerulean. Taken together, we found that SCD promotes cardiac dysfunction with overload of cardiotoxic saturated lipids and up-regulation of the heart-failure-promoting AT1 receptor protein.

Valsartan prevented neointimal hyperplasia and inhibited SRSF1 expression and the TLR4–iNOS–ERK–AT1 receptor pathway in the balloon-injured rat aorta

Valsartan has the potential to attenuate neointimal hyperplasia and to suppress the inflammatory response. This study aimed to evaluate the role of valsartan in neointimal hyperplasia and the toll-like receptor 4 (TLR4)-nitric oxide synthase (NOS) pathway in the balloon-injured rat aorta. Forty-eight Wistar rats were randomly allocated to three groups: sham control (control), balloon-injured group (surgery), and balloon-injured+valsartan-treated group (valsartan). Rats were killed at 14 and 28 days after balloon-injury, and then the aortic tissues were collected for morphometric analysis as well as for measurements of the mRNA or protein expression of angiotensin II, angiotensin II type 1 (AT1) receptor, angiotensin II type 2 (AT2) receptor, TLR4, endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), serine/arginine-rich splicing factor 1(SRSF1) and extracellular signal regulated kinase (ERK). Valsartan at a dose of 20 mg/kg/day markedly decreased neointimal hyperplasia in the aorta of balloon-injured rats, and significantly reduced the mRNA or protein expression of TLR4, AT1 receptor, SRSF1 and phosphorylated-ERK (p-ERK) as well as the aortic levels of iNOS (all p<0.05). Moreover, valsartan increased the eNOS level and AT2 receptor mRNA and protein expression levels (all p<0.05). Valsartan prevented neointimal hyperplasia and inhibited SRSF1 expression and the TLR4-iNOS-ERK-AT1 receptor pathway in the balloon-injured rat aorta.

Angiotensin II Disrupts Neurovascular Coupling by Potentiating Calcium Increases in Astrocytic Endfeet

Background Angiotensin II (Ang II), a critical mediator of hypertension, impairs neurovascular coupling. Since astrocytes are key regulators of neurovascular coupling, we sought to investigate whether Ang II impairs neurovascular coupling through modulation of astrocytic Ca 2+ signaling. Methods and Results Using laser Doppler flowmetry, we found that Ang II attenuates cerebral blood flow elevations induced by whisker stimulation or the metabotropic glutamate receptors agonist, 1S, 3R‐1‐aminocyclopentane‐ trans ‐1,3‐dicarboxylic acid ( P <0.01). In acute brain slices, Ang II shifted the vascular response induced by 1S, 3R‐1‐aminocyclopentane‐ trans ‐1,3‐dicarboxylic acid towards vasoconstriction ( P <0.05). The resting and 1S, 3R‐1‐aminocyclopentane‐ trans ‐1,3‐dicarboxylic acid–induced Ca 2+ levels in the astrocytic endfeet were more elevated in the presence of Ang II ( P <0.01). Both effects were reversed by the AT1 receptor antagonist, candesartan ( P <0.01 for diameter and P <0.05 for calcium levels). Using photolysis of caged Ca 2+ in astrocytic endfeet or pre‐incubation of 1,2‐Bis(2‐aminophenoxy)ethane‐ N,N,N',N' ‐tetra‐acetic acid tetrakis (acetoxymethyl ester), we demonstrated the link between potentiated Ca 2+ elevation and impaired vascular response in the presence of Ang II ( P <0.001 and P <0.05, respectively). Both intracellular Ca 2+ mobilization and Ca 2+ influx through transient receptor potential vanilloid 4 mediated Ang II‐induced astrocytic Ca 2+ elevation, since blockade of these pathways significantly prevented the intracellular Ca 2+ in response to 1S, 3R‐1‐aminocyclopentane‐ trans ‐1,3‐dicarboxylic acid ( P <0.05). Conclusions These results suggest that Ang II through its AT1 receptor potentiates the astrocytic Ca 2+ responses to a level that promotes vasoconstriction over vasodilation, thus altering cerebral blood flow increases in response to neuronal activity.

The dopamine receptor D4 regulates the proliferation of pulmonary arteries smooth muscle in broilers by downregulating AT1R

The major cause of pulmonary vascular remodeling in broilers is abnormal proliferation of vascular smooth muscle cells (VSMCs), and one of the main causes of pulmonary hypertension syndrome (PHS) in broilers is pulmonary artery vascular remodeling. Forty Arbor Acres (AA) broilers were randomly divided into four groups (n = 10): a control group (deionized water, 0 g/L NaCl), a freshwater group (FW, deionized water + 1 g/L NaCl), highly salinized freshwater group 1 (H-SFW-1, deionized water + 2.5 g/L NaCl) and highly salinized freshwater group 2 (H-SFW-2, deionized water + 5 g/L NaCl). The results of in vivo experiments showed that vascular smooth muscle of the broilers could be significantly proliferated by intake of high-salinity fresh water (H-SFW-1 & H-SFW-2), which significantly increased the content of angiotensin II (Ang II) and the expression of angiotensin II type 1 (AT1) receptor protein. Meanwhile, it significantly decreased the expression of dopamine receptor D4 (DRD4) protein. The results of in vitro experiments showed that exogenous Ang II induced the proliferation of primary VSMCs in broilers, which could be significantly inhibited by DRD4 agonists (D4A, HY-101384A) and enhanced by DRD4 inhibitors (D4I, HY-B0965). In addition, the results of immunoblotting and fluorescence quantitative PCR showed that AT1 receptors could be negatively regulated by DRD4 in VSMCs of broilers, either at the transcriptional or translational level. At the same time, the expression of AT1 receptor could be increased by DRD4 inhibition by D4I and decreased by DRD4 activation by D4A. The negative regulatory effect of DRD4 on AT1 receptor occurred in a dose-dependent manner. These results indicate that long-term intake of highly salinized fresh water can cause PHS in broilers, accompanied by varying degrees of proliferation of pulmonary artery smooth muscle. This mechanism may involve response of its receptor being induced by increased Ang II, while DRD4 can negatively regulate it.

Telmisartan restricts Chikungunya virus infection in vitro and in vivo through the AT1/ PPAR-γ/MAPKs pathways

Chikungunya virus (CHIKV) has re-emerged as a global public health threat. The inflammatory pathways of RAS and PPAR-γ are usually involved in viral infections. Thus, Telmisartan (TM) with known capacity to block AT1 receptor and activate PPAR-γ, was investigated against CHIKV. The anti-CHIKV effect of TM was investigated in vitro (Vero, RAW 264.7 cells and hPBMCs) and in vivo (C57BL/6 mice). TM was found to abrogate CHIKV infection efficiently (IC50 of 15.34-20.89µM in the Vero and RAW 264.7 cells respectively). Viral RNA and proteins were reduced remarkably with the TM driven modulation of host m-TOR signaling. Additionally, TM interfered in the early and late stages of CHIKV life cycle with efficacy in both pre and post-treatment assay. Moreover, the agonist of AT1 receptor and antagonist of PPAR-γ increased CHIKV infection suggesting TM’s anti-viral potential by modulating host factors. Besides, reduced activation of all major MAPKs, NF-κB (p65) and cytokines by TM through the inflammatory axis supported the fact that the anti-CHIKV efficacy of TM is partly mediated through the AT1/PPAR-γ/MAPKs pathways. Interestingly, at the human equivalent dose, TM abrogated CHIKV infection and inflammation significantly leading to reduced clinical score and complete survival of C57BL/6 mice. Additionally, TM reduced infection in hPBMC derived monocyte-macrophage populations in vitro. Hence, TM was found to reduce CHIKV infection by targeting both viral and host factors. Considering its safety and in vivo efficacy, it can be a suitable candidate in future for repurposing against CHIKV.