Attenuation of Cuff-Induced Neointimal Formation by Overexpression of Angiotensin II Type 2 Receptor-Interacting Protein 1

Novel Pharmacology Following Heteromerization of the Angiotensin II Type 2 Receptor and the Bradykinin Type 2 Receptor

The angiotensin type 2 (AT₂) receptor and the bradykinin type 2 (B₂) receptor are G protein-coupled receptors (GPCRs) that have major roles in the cardiovascular system. The two receptors are known to functionally interact at various levels, and there is some evidence that the observed crosstalk may occur as a result of heteromerization. We investigated evidence for heteromerization of the AT₂ receptor and the B₂ receptor in HEK293FT cells using various bioluminescence resonance energy transfer (BRET)-proximity based assays, including the Receptor Heteromer Investigation Technology (Receptor-HIT) and the NanoBRET ligand-binding assay. The Receptor-HIT assay showed that Gα_q, GRK2 and β-arrestin2 recruitment proximal to AT₂ receptors only occurred upon B₂ receptor coexpression and activation, all of which is indicative of AT₂-B₂ receptor heteromerization. Additionally, we also observed specific coupling of the B₂ receptor with the Gα_z protein, and this was found only in cells coexpressing both receptors and stimulated with bradykinin. The recruitment of Gα_z, Gα_q, GRK2 and β-arrestin2 was inhibited by B₂ receptor but not AT₂ receptor antagonism, indicating the importance of B₂ receptor activation within AT₂-B₂ heteromers. The close proximity between the AT₂ receptor and B₂ receptor at the cell surface was also demonstrated with the NanoBRET ligand-binding assay. Together, our data demonstrate functional interaction between the AT₂ receptor and B₂ receptor in HEK293FT cells, resulting in novel pharmacology for both receptors with regard to Gα_q/GRK2/β-arrestin2 recruitment (AT₂ receptor) and Gα_z protein coupling (B₂ receptor). Our study has revealed a new mechanism for the enigmatic and poorly characterized AT₂ receptor to be functionally active within cells, further illustrating the role of heteromerization in the diversity of GPCR pharmacology and signaling.

Microtubule-Associated Protein ATIP3, an Emerging Target for Personalized Medicine in Breast Cancer

Breast cancer is the leading cause of death by malignancy among women worldwide. Clinical data and molecular characteristics of breast tumors are essential to guide clinician’s therapeutic decisions. In the new era of precision medicine, that aims at personalizing the treatment for each patient, there is urgent need to identify robust companion biomarkers for new targeted therapies. This review focuses on ATIP3, a potent anti-cancer protein encoded by candidate tumor suppressor gene MTUS1, whose expression levels are markedly down-regulated in breast cancer. ATIP3 is a microtubule-associated protein identified both as a prognostic biomarker of patient survival and a predictive biomarker of breast tumors response to taxane-based chemotherapy. We present here recent studies pointing out ATIP3 as an emerging anti-cancer protein and a potential companion biomarker to be combined with future personalized therapy against ATIP3-deficient breast cancer.

Recent Research Advances in Renin-Angiotensin-Aldosterone System Receptors

PURPOSE OF REVIEW

The renin-angiotensin-aldosterone system (RAAS) plays important roles in regulating blood pressure and body fluid, which contributes to the pathophysiology of hypertension and cardiovascular/renal diseases. However, accumulating evidence has further revealed the complexity of this signal transduction system, including direct interactions with other receptors and proteins. This review focuses on recent research advances in RAAS with an emphasis on its receptors.

RECENT FINDINGS

Both systemically and locally produced angiotensin II (Ang II) bind to Ang II type 1 receptor (AT1R) and elicit strong biological functions. Recent studies have shown that Ang II-induced activation of Ang II type 2 receptor (AT2R) elicits the opposite functions to those of AT1R. However, accumulating evidence has now expanded the components of RAAS, including (pro)renin receptor, angiotensin-converting enzyme 2, angiotensin 1-7, and Mas receptor. In addition, the signal transductions of AT1R and AT2R are regulated by not only Ang II but also its receptor-associated proteins such as AT1R-associated protein and AT2R-interacting protein. Recent studies have indicated that inappropriate activation of local mineralocorticoid receptor contributes to cardiovascular and renal tissue injuries through aldosterone-dependent and -independent mechanisms. Since the mechanisms of RAAS signal transduction still remain to be elucidated, further investigations are necessary to explore novel molecular mechanisms of the RAAS, which will provide alternative therapeutic agents other than existing RAAS blockers.

Microtubule associated tumor suppressor 1 interacts with mitofusins to regulate mitochondrial morphology in endothelial cells

Mitochondria are dynamic organelles that are able to change their morphology and cellular distribution by either fission or fusion. However, the molecular mechanisms controlling mitochondrial dynamics in vascular endothelial cells (ECs) remain largely unknown. In this study, we observed that knockdown of microtubule-associated tumor suppressor 1 (MTUS1) in ECs inhibited tube formation and migration, accompanied with decreased promigratory signalings. We showed that MTUS1 was localized in the outer membrane of mitochondria in ECs. Knockdown of MTUS1 disturbed the elongated mitochondrial network and induced the formation of perinuclear clusters of mitochondria. Importantly, mitochondrial motility and fusion were suppressed, whereas generation of reactive oxygen species was increased in MTUS1 knockdown ECs. Mechanistically, we showed that the N-terminal coiled-coil domain of MTUS1 interacted with the mitochondrial membrane proteins, mitofusin-1 and mitofusin-2, to maintain mitochondrial morphology in ECs. This study illustrated a novel role of MTUS1 in mitochondrial morphology and EC angiogenic responses.-Wang, Y., Huang, Y., Liu, Y., Li, J., Hao, Y., Yin, P., Liu, Z., Chen, J., Wang, Y., Wang, N., Zhang, P. Microtubule associated tumor suppressor 1 interacts with mitofusins to regulate mitochondrial morphology in endothelial cells.

Deletion of AT2 Receptor Prevents SHP-1-Induced VEGF Inhibition and Improves Blood Flow Reperfusion in Diabetic Ischemic Hindlimb

OBJECTIVE

Ischemia caused by narrowing of femoral artery is a major cause of peripheral arterial disease and morbidity affecting patients with diabetes mellitus. We have previously reported that the inhibition of the angiogenic response to VEGF (vascular endothelial growth factor) in diabetic mice was associated with the increased expression of SHP-1 (SH2 domain-containing phosphatase 1), a protein that can be activated by the AT2 (angiotensin II type 2) receptor. Deletion of AT2 receptor has been shown to promote angiogenesis within the ischemic muscle. However, the relative impact of AT2 receptor in diabetic condition remains unknown.

APPROACH AND RESULTS

Nondiabetic and diabetic AT2 null (Atgr2^-/Y) mice underwent femoral artery ligation after 2 months of diabetes mellitus. Blood perfusion was measured every week ≤4 weeks post-surgery. Expression of the VEGF, SHP-1, and renin-angiotensin pathways was evaluated. Blood flow in the ischemic muscle of diabetic Atgr2^-/Y mice recovered faster and ≤80% after 4 weeks compared with 51% recovery in diabetic control littermates. Diabetic Atgr2^-/Y had reduced apoptotic endothelial cells and elevated small vessel formation compared with diabetic Atgr2^+/Y mice, as well as increased SHP-1 expression and reduced VEGF receptor activity. In endothelial cells, high glucose levels and AT2 agonist treatment did not change SHP-1, VEGF, and VEGF receptor expression. However, the activity of SHP-1 and its association with the VEGF receptors were increased, causing inhibition of the VEGF action in endothelial cell proliferation and migration.

CONCLUSIONS

Our results suggest that the deletion of AT2 receptor reduced SHP-1 activity and restored VEGF actions, leading to an increased blood flow reperfusion after ischemia in diabetes mellitus.

MTUS1, a gene encoding angiotensin-II type 2 (AT2) receptor-interacting proteins, in health and disease, with special emphasis on its role in carcinogenesis

Loss of tumor suppressor activity is a frequent event in the formation and progression of tumors and has been listed as an important hallmark of cancers. Microtubule-Associated Scaffold Protein 1 (MTUS1) is a candidate tumor suppressor gene which is reported to be frequently down-regulated in a variety of human cancers including pancreas, colon, bladder, head-and-neck, ovarian, breast cancers, gastric, lung cancers. It is also reported to be implicated in several types of pathologies such as cardiac hypertrophy, atherosclerosis, and SLE-like lymphoproliferative diseases. Moreover, MTUS1-encoded proteins are shown to be involved in the regulation of vital cellular processes such as proliferation, differentiation, DNA repair, inflammation, vascular remodeling and senescence. However, the current knowledge is very limited about the role of this gene in human cancers as well as other type diseases. Besides, there is no literature report which summarizes and criticizes the importance of MTUS1 in the cellular processes, especially in the processes of carcinogenesis. Accordingly, in this comprehensive review, we tried to shed light on the role of tumor suppressor MTUS1/ATIP in health and disease, putting special emphasis on its role in the development and progression of human cancers as well as associated molecular mechanisms and the reasons behind MTUS1/ATIP deficiency, which have been not well documented previously.

MTUS1 silencing promotes E-selectin production through p38 MAPK-dependent CREB ubiquitination in endothelial cells

BACKGROUND

Endothelial cell activation is thought to be a key event in atherosclerosis. p38 mitogen-activated protein kinase (p38 MAPK) plays an important role in regulating pro-inflammatory cytokine production in endothelial cells (ECs), however, how p38 MAPK is controlled in EC activation remain unclear. In this study, we investigated the effect of mitochondrial tumor suppressor 1 (MTUS1) on p38 MAPK activation, cytokine induction and the underlying molecular mechanisms in ECs.

METHODS AND RESULTS

Using qPCR and ELISA methods, we found that knockdown of MTUS1 led to a marked increase in the mRNA and protein expression of E-selectin (SELE) and monocyte chemotactic protein-1 in ECs, which is accompanied with increased phosphorylation of p38 MAPK (Thr180/Tyr182), MKK3/6 (Ser 189) and IκBα (Ser 32). Using luciferase reporter assay, we found that MTUS1 silencing also activated NF-κB transcriptional activity. The inhibition of p38 MAPK and NF-κB pathway was shown to abrogate MTUS1 silencing-induced cytokine expression in ECs. Furthermore, MTUS1 silencing induced p38 MAPK-dependent ubiquitination of cAMP-response element binding protein (CREB) which potentiated CREB-binding protein-mediated NF-κB p65 acetylation and binding to the promoter of the SELE gene. Conversely, adenovirus-mediated overexpression of MTUS1 inhibited p38 MAPK activation in ECs in vitro and in vivo. Importantly, decreased expression of MTUS1 and CREB, accompanied with induced activation of p38 MAPK were observed in aortas of apoE-/- mice after high-fat diet challenge.

CONCLUSIONS

Our findings showed that MTUS1 regulates the p38 MAPK-mediated cytokine production in ECs. MTUS1 gene probably plays a protective role against pro-inflammatory response of ECs.

Identification of the Mtus1 Splice Variant as a Novel Inhibitory Factor Against Cardiac Hypertrophy

Background

In cardiac hypertrophy and failure, there is a widespread alteration in mRNA splicing, but the role of splice variants in cardiac hypertrophy has not yet been fully elucidated. In this study, we used an exon array to identify novel splice variants associated with cardiac hypertrophy.

Methods and Results

We performed genome‐wide exon array analysis and developed a splicing profile in murine hearts with hypertrophy induced by transverse aortic constriction for 8 weeks. Following global analysis of splice variants using the Mouse Exon 1.0 ST Array, we identified 46 spliced genes and narrowed our focus to 1 gene, mitochondrial tumor suppressor 1 (Mtus1), whose splice variants were registered in the NCBI RefSeq database. Notably, one of the splice variants Mtus1A was specifically upregulated, although the total expression of the Mtus1 gene remained unchanged. We showed that Mtus1A was localized in the mitochondria, and its expression level increased with the degree of cardiac hypertrophy. In cultured cardiomyocytes, Mtus1A overexpression reduced phenylephrine‐induced reactive oxygen species production and consequent ERK phosphorylation, resulting in a decrease in both cell size and protein synthesis. In vivo, cardiac‐specific Mtus1A transgenic mice showed left ventricle wall thinning and a reduced hypertrophic response to pressure overload and phenylephrine treatment.

Conclusions

We found that Mtus1 is specifically spliced in hypertrophic hearts and that the Mtus1A variant has an inhibitory effect on cardiac hypertrophy. Mtus1A is, therefore, a possible diagnostic and therapeutic target for cardiac hypertrophy and failure.

Angiotensin II Type 2 Receptor Inhibits Vascular Intimal Proliferation With Activation of PPARγ

BACKGROUND

Angiotensin II type 2 (AT2) receptor stimulation could exert beneficial effects on vascular remodeling. Previously, we reported that AT2 receptor stimulation ameliorated insulin resistance in diabetic mice accompanied by PPARγ activation which also plays a variety of crucial roles in the vasculature. Therefore, this study aimed to investigate the vascular protective effect of the AT2 receptor with activation of PPARγ involving AT2 receptor-interacting protein (ATIP).

METHODS AND RESULTS

Vascular injury was induced by polyethylene-cuff placement around the femoral artery in C57BL/6J mice. Treatment with compound 21 (C21), an AT2 receptor agonist, decreased neointimal formation, cell proliferation, and the mRNA levels of monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor (TNF)-α, and interleukin-1β, and phosphorylation of nuclear factor-kappa B, and increased PPARγ DNA-binding activity in the injured artery, whereas these inhibitory effects of C21 were attenuated by co-treatment with a PPARγ antagonist, GW9662. Treatment of vascular smooth muscle cells (VSMC) with C21 prepared from smAT2 transgenic mice, which highly express the AT2 receptor in VSMC, increased both PPARγ activity and its DNA-binding activity determined by dual-luciferase assay and electrophoresis mobility shift assay (EMSA), respectively. We observed that ATIP was involved in PPARγ complex formation, and that transfection of siRNA of ATIP1 attenuated the AT2 receptor-mediated increase in PPARγ activity in VSMC. In response to AT2 receptor stimulation, ATIP was translocated from the plasma membrane to the nucleus.

CONCLUSIONS

Our results suggest a new mechanism by which AT2 receptor stimulation activates PPARγ, thereby resulting in amelioration of vascular intimal proliferation, and that ATIP plays an important role in AT2 receptor-mediated PPARγ activation.

Low-Protein Diet-Induced Fetal Growth Restriction Leads to Exaggerated Proliferative Response to Vascular Injury in Postnatal Life

BACKGROUND

We investigated the effects of fetal growth restriction (FGR) induced by maternal protein restriction on inflammatory vascular remodeling using a cuff-induced vascular injury mouse model.

METHODS

Dams (C57BL/6J strain mice) were fed an isocaloric diet containing 20% protein (normal protein; NP) or 8% protein (low protein; LP) from 10 weeks of age until delivery. On the day of delivery, all dams were returned to the NP diet. After weaning, offspring were fed the NP diet. When offspring were 10 weeks of age, vascular injury was induced by polyethylene cuff placement around the femoral artery.

RESULTS

Birth weight in offspring from dams fed LP until delivery (LPO) was significantly lower, but body weight was the same at 2 weeks after birth compared with that in NP offspring (NPO). Arterial blood pressure at 12 weeks of age did not differ between LPO and NPO. Neointima formation was exaggerated in LPO compared with NPO and associated with an increase in cell proliferation assessed by proliferating cell nuclear antigen (PCNA) staining index. Moreover, LPO showed enhanced expression of monocyte chemotactic protein-1, interleukin (IL)-6, IL-1β, tumor necrosis factor-α, and production of superoxide anion in the injured artery. Moreover, mRNA expression of isoforms of NAD(P)H oxidase subunits such as p22phox, p40phox, p47phox, p67phox, gp91phpx, and Rac1 in the injured arteries were enhanced in LPO. Furthermore, HIF-1α expression was increased in LPO compared with that in NPO.

CONCLUSIONS

These results suggest that maternal low-protein diet-induced FGR increases susceptibility of the vasculature to postnatal injury.

An update of the role of renin angiotensin in cardiovascular homeostasis

The renin angiotensin system (RAS) is thought to be the body's main vasoconstrictor system, with physiological effects mediated via the interaction of angiotensin II with angiotensin I receptors (the "classic" RAS model). However, since the discovery of the heptapeptide angiotensin 1-7 and the development of the concept of the "alternate" RAS system, with its ability to reduce arterial blood pressure, our understanding of this physiologic system has changed dramatically. In this review, we focus on the newly discovered functions of the RAS, particularly the potential clinical significance of these developments, especially in the realm of new pharmacologic interventions for treating cardiovascular disease.

Drinking citrus fruit juice inhibits vascular remodeling in cuff-induced vascular injury mouse model

Citrus fruits are thought to have inhibitory effects on oxidative stress, thereby attenuating the onset and progression of cancer and cardiovascular disease; however, there are few reports assessing their effect on vascular remodeling. Here, we investigated the effect of drinking the juice of two different citrus fruits on vascular neointima formation using a cuff-induced vascular injury mouse model. Male C57BL6 mice were divided into five groups as follows: 1) Control (water) (C), 2) 10% Citrus unshiu (CU) juice (CU10), 3) 40% CU juice (CU40), 4) 10% Citrus iyo (CI) juice (CI10), and 5) 40% CI juice (CI40). After drinking them for 2 weeks from 8 weeks of age, cuff injury was induced by polyethylene cuff placement around the femoral artery. Neointima formation was significantly attenuated in CU40, CI10 and CI40 compared with C; however, no remarkable preventive effect was observed in CU10. The increases in levels of various inflammatory markers including cytokines such as monocyte chemotactic protein-1, interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α in response to vascular injury did not differ significantly between C, CU10 and CI10. The increases in cell proliferation and superoxide anion production were markedly attenuated in CI10, but not in CU10 compared with C. The increase in phosphorylated ERK expression was markedly attenuated both in CU10 and CI10 without significant difference between CU10 and CI10. Accumulation of immune cells did not differ between CU10 and CI10. These results indicate that drinking citrus fruit juice attenuates vascular remodeling partly via a reduction of oxidative stress. Interestingly, the preventive efficacy on neointima formation was stronger in CI than in CU at least in part due to more prominent inhibitory effects on oxidative stress by CI.

Possible Role of Angiotensin-Converting Enzyme 2 and Activation of Angiotensin II Type 2 Receptor by Angiotensin-(1–7) in Improvement of Vascular Remodeling by Angiotensin II Type 1 Receptor Blockade

Cross talk between the angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II type 1 (AT 1 ) receptor axis and the ACE2/Ang-(1–7)/Mas axis plays a role in the pathogenesis of cardiovascular remodeling. Furthermore, possible stimulation of the Ang II type 2 (AT 2 ) receptor by Ang-(1–7) has been highlighted as a new pathway. Therefore, we examined the possibility of whether the ACE2/Ang-(1–7)/Mas axis and Ang-(1–7)/AT 2 receptor axis are involved in the inhibitory effects of AT 1 receptor blockers on vascular remodeling. Wild-type, Mas-knockout, and AT 2 receptor knockout mice were used in this study. Vascular injury was induced by polyethylene-cuff placement around the mouse femoral artery. Some mice were treated with azilsartan, an AT 1 receptor blocker, or Ang-(1–7). Neointimal formation 2 weeks after cuff placement was more marked in Mas-knockout mice compared with wild-type mice. Treatment with azilsartan or Ang-(1–7) attenuated neointimal area, vascular smooth muscle cell proliferation, increases in the mRNA levels of monocyte chemoattractant protein-1, tumor necrosis factor-α, and interleukin-1β, and superoxide anion production in the injured artery; however, these inhibitory effects of azilsartan and Ang-(1–7) were less marked in Mas-knockout mice. Administration of azilsartan or Ang-(1–7) attenuated the decrease in ACE2 mRNA and increased AT 2 receptor mRNA but did not affect AT 1 receptor mRNA or the decrease in Mas mRNA. The inhibitory effect of Ang-(1–7) on neointimal formation was less marked in AT 2 receptor knockout mice compared with wild-type mice. These results suggest that blockade of the AT 1 receptor by azilsartan could enhance the activities of the ACE2/Ang-(1–7)/Mas axis and ACE2/Ang-(1–7)/AT 2 receptor axis, thereby inhibiting neointimal formation.

An animal model of atherosclerotic plaque disruption and thrombosis in rabbit using pharmacological triggering to plaques induced by perivascular collar placement

INTRODUCTION

Limited availability of suitable animal model of plaque disruption and thrombosis has hampered the study of mechanism and preclinical evaluation of plaque-stabilizing therapies. This study aims to develop an animal model of atherosclerotic plaque disruption and thrombosis in rabbit femoral artery.

METHODS

Silastic collars were placed around the bilateral femoral arteries of rabbits, which had been fed with atherogenic diet for 7 days. After 28 days on the same diet, the rabbits received pharmacological triggering by intraperitoneal injection of Russell's viper venom (RVV, 0.15 mg/kg) followed by intravenous injection of histamine (0.02 mg/kg), and the animals were then processed for imageological and histological examinations.

RESULTS

Perivascular collar placement of the femoral artery in high-cholesterol-fed rabbits for 28 days induced marked intimal hyperplasia, which was a lipid- and collagen-rich lesion that contained substantial amount of macrophages and smooth muscle cells. Subsequent histological analysis showed that the pharmacological triggering evoked plaque disruption and platelet- and fibrin-rich thrombi in the collared femoral arteries.

CONCLUSION

We demonstrated, for the first time, a rabbit model of plaque disruption and thrombosis induced by the combination of perivascular collar placement, RVV, and histamine injections. This model can be rapidly formed, easily operated, and site controlled.

Effect of angiotensin II type 2 receptor-interacting protein on adipose tissue function via modulation of macrophage polarization

We demonstrated that angiotensin II type 2 (AT₂) receptor-interacting protein (ATIP) 1 ameliorates inflammation-mediated vascular remodeling independent of the AT₂ receptor, leading us to explore the possibility of whether ATIP1 could exert anti-inflammatory effects and play a role in other pathophysiological conditions. We examined the possible anti-inflammatory effects of ATIP1 in adipose tissue associated with amelioration of insulin resistance. In mice fed a high-cholesterol diet, adipose tissue macrophage (ATM) infiltration and M1-to-M2 ratio were decreased in ATIP1 transgenic mice (ATIP1-Tg) compared with wild-type mice (WT), with decreased expression of inflammatory cytokines such as tumor necrosis factor-α and monocyte chemoattractant protein-1 in white adipose tissue (WAT), but an increase in interleukin-10, an anti-inflammatory cytokine. Moreover, 2-[³H]deoxy-d-glucose (2-[³H]DG) uptake was significantly increased in ATIP1-Tg compared with WT. Next, we examined the roles of ATIP1 in BM-derived hematopoietic cells, employing chimeric mice produced by BM transplantation into irradiated type 2 diabetic mice with obesity, KKAy, as recipients. ATM infiltration and M1-to-M2 ratio were decreased in ATIP1 chimera (ATIP1-tg as BM donor), with improvement of insulin-mediated 2-[³H]DG uptake and amelioration of inflammation in WAT. Moreover, serum adiponectin concentration in ATIP1 chimera was significantly higher than that in WT chimera (WT as BM donor) and KKAy chimera (KKAy as BM donor). These results indicate that ATIP1 could exert anti-inflammatory effects in adipose tissue via macrophage polarization associated with improvement of insulin resistance, and ATIP1 in hematopoietic cells may contribute to these beneficial effects on adipose tissue functions in type 2 diabetes.

Regulation of angiotensin II receptors beyond the classical pathway

The RAS (renin–angiotensin system) plays a role not only in the cardiovascular system, including blood pressure regulation, but also in the central nervous system. AngII (angiotensin II) binds two major receptors: the AT1 receptor (AngII type 1 receptor) and AT2 receptor (AngII type 2 receptor). It has been recognized that AT2 receptor activation not only opposes AT1 receptor actions, but also has unique effects beyond inhibitory cross-talk with AT1 receptor signalling. Novel pathways beyond the classical actions of RAS, the ACE (angiotensin-converting enzyme)/AngII/AT1 receptor axis, have been highlighted: the ACE2/Ang-(1–7) [angiotensin-(1–7)]/Mas receptor axis as a new opposing axis against the ACE/AngII/AT1 receptor axis, novel AngII-receptor-interacting proteins and various AngII-receptor-activation mechanisms including dimer formation. ATRAP (AT1-receptor-associated protein) and ATIP (AT2-receptor-interacting protein) are well-characterized AngII-receptor-associated proteins. These proteins could regulate the functions of AngII receptors and thereby influence various pathophysiological states. Moreover, the possible cross-talk between PPAR (peroxisome-proliferator-activated receptor)-γ and AngII receptor subtypes is an intriguing issue to be addressed in order to understand the roles of RAS in the metabolic syndrome, and interestingly some ARBs (AT1-receptor blockers) have been reported to have an AT1-receptor-blocking action with a partial PPAR-γ agonistic effect. These emerging concepts concerning the regulation of AngII receptors are discussed in the present review.

Angiotensin II type 2 receptor-interacting protein prevents vascular senescence

Angiotensin II type 2 (AT(2)) receptor-interacting protein (ATIP), which interacts with the C-terminal tail of the AT(2) receptor, regulates the functions of the AT(2) receptor. We have reported that AT(2) receptor stimulation attenuated vascular senescence. Therefore, we examined the possible negative role of ATIP in regulating vascular senescence. We generated ATIP-transgenic (Tg) mice, and cultured vascular smooth muscle cells (VSMCs). Persistent angiotensin II stimulation induced increases in SA-β-gal-positive cells and the level of a DNA damage marker, 8-OHdG in VSMC, whereas these effects of angiotensin II were attenuated in VSMC prepared from ATIP-Tg mice. Angiotensin II treatment also upregulated the expression of methyl methanesulfonate-sensitive 2 (MMS2), a DNA repair factor, and Src homology 2 domain-containing protein-tyrosine phosphatase 1 (SHP-1) activity, whereas these effects of angiotensin II were further enhanced in ATIP-Tg VSMC. In vivo, x-ray irradiation to mice caused increases in SA-β-gal-positive area and 8-OHdG level in the thoracic aorta; however, these effects were reduced in ATIP-Tg mice, with a significant increase in MMS2 expression. These results suggest that ATIP could inhibit VSMC senescence, involving MMS2 expression and SHP-1 activity. ATIP might be a new therapeutic molecule to treat vascular aging and age-related vascular diseases.

Microtubule associated tumor suppressor 1 deficient mice develop spontaneous heart hypertrophy and SLE-like lymphoproliferative disease

The microtubule associated tumor suppressor gene 1 (MTUS1) is a recently published tumor suppressor gene, which has also been shown to act as an early component in the growth inhibitory signaling cascade of the angiotensin II type 2 receptor (AT2R). In this study we report the generation of MTUS1 knock-out (KO) mice, which develop normally but reveal higher body weights and slightly decreased blood pressure levels. Twenty-eight percent of the studied MTUS1 KO mice also developed heart hypertrophy and 12% developed nephritis, independent of blood pressure levels. Forty-three percent of the MTUS1 KO mice revealed lymphoid hyperplasia affecting spleen (20%), kidney (37%), lung (23%), lymph nodes (17%), and liver (17%) accompanied with leukocytosis, lymphocytosis, and mild anemia. One animal (3%) developed a marginal zone B-cell lymphoma affecting submandibular salivary gland and regional lymph nodes. The symptoms of all mentioned animals are consistent with a B-cell lymphoproliferative disease with features of systemic lupus erythematosus. In addition, body weight of the MTUS1 KO mice was significantly increased and isolated skin fibroblasts showed increased cell proliferation and decreased cell size, compared to wild-type (WT) fibroblasts in response to depleted FCS concentration and lack of growth factors. In conclusion we herein report the first generation of a MTUS1 KO mouse, developing spontaneous heart hypertrophy and increased cell proliferation, confirming once more the anti-proliferative effect of MTUS1, and a SLE-like lymphoproliferative disease suggesting crucial role in regulation of inflammation. These MTUS1 KO mice can therefore serve as a model for further investigations in cardiovascular disease, autoimmune disease and carcinogenesis.

Angiotensin II, a Neuropeptide at the Frontier between Endocrinology and Neuroscience: Is There a Link between the Angiotensin II Type 2 Receptor and Alzheimer's Disease?

Amyloid-β peptide deposition, abnormal hyperphosphorylation of tau, as well as inflammation and vascular damage, are associated with the development of Alzheimer's disease (AD). Angiotensin II (Ang II) is a peripheral hormone, as well as a neuropeptide, which binds two major receptors, namely the Ang II type 1 receptor (AT1R) and the type 2 receptor (AT2R). Activation of the AT2R counteracts most of the AT1R-mediated actions, promoting vasodilation, decreasing the expression of pro-inflammatory cytokines, both in the brain and in the cardiovascular system. There is evidence that treatment with AT1R blockers (ARBs) attenuates learning and memory deficits. Studies suggest that the therapeutic effects of ARBs may reflect this unopposed activation of the AT2R in addition to the inhibition of the AT1R. Within the context of AD, modulation of AT2R signaling could improve cognitive performance not only through its action on blood flow/brain microcirculation but also through more specific effects on neurons. This review summarizes the current state of knowledge and potential therapeutic relevance of central actions of this enigmatic receptor. In particular, we highlight the possibility that selective AT2R activation by non-peptide and highly selective agonists, acting on neuronal plasticity, could represent new pharmacological tools that may help improve impaired cognitive performance in AD and other neurological cognitive disorders.

An ATIPical family of angiotensin II AT2 receptor-interacting proteins

AT2, the second subtype of angiotensin II receptors, is a major component of the renin-angiotensin system involved in cardiovascular and neuronal functions. AT2 belongs to the superfamily of G protein-coupled receptors, but its intracellular signaling pathways have long remained elusive. Over the past few years, efforts to characterize this atypical receptor have led to the identification of novel molecular scaffolds that directly bind to its intracellular tail. The present review focuses on a family of AT2 receptor-interacting proteins (ATIPs) involved in neuronal differentiation, vascular remodeling and tumor suppression. Recent findings that ATIPs and ATIP-related proteins associate with microtubules suggest that they might constitute a novel family of multifunctional proteins regulating a wide range of physiopathological functions.

Angiotensin type 2 receptor actions contribute to angiotensin type 1 receptor blocker effects on kidney fibrosis

Angiotensin type 1 (AT1) receptor blocker (ARB) ameliorates progression of chronic kidney disease. Whether this protection is due solely to blockade of AT1, or whether diversion of angiotensin II from the AT1 to the available AT2 receptor, thus potentially enhancing AT2 receptor effects, is not known. We therefore investigated the role of AT2 receptor in ARB-induced treatment effects in chronic kidney disease. Adult rats underwent 5/6 nephrectomy. Glomerulosclerosis was assessed by renal biopsy 8 wk later, and rats were divided into four groups with equivalent glomerulosclerosis: no further treatment, ARB, AT2 receptor antagonist, or combination. By week 12 after nephrectomy, systolic blood pressure was decreased in all treatment groups, but proteinuria was decreased only with ARB. Glomerulosclerosis increased significantly in AT2 receptor antagonist vs. ARB. Kidney cortical collagen content was decreased in ARB, but increased in untreated 5/6 nephrectomy, AT2 receptor antagonist, and combined groups. Glomerular cell proliferation increased in both untreated 5/6 nephrectomy and AT2 receptor antagonist vs. ARB, and phospho-Erk2 was increased by AT2 receptor antagonist. Plasminogen activator inhibitor-1 mRNA and protein were increased at 12 wk by AT2 receptor antagonist in contrast to decrease with ARB. Podocyte injury is a key component of glomerulosclerosis. We therefore assessed effects of AT1 vs. AT2 blockade on podocytes and interaction with plasminogen activator inhibitor-1. Cultured wild-type podocytes, but not plasminogen activator inhibitor-1 knockout, responded to angiotensin II with increased collagen, an effect that was completely blocked by ARB with lesser effect of AT2 receptor antagonist. We conclude that the benefical effects on glomerular injury achieved with ARB are contributed to not only by blockade of the AT1 receptor, but also by increasing angiotensin effects transduced through the AT2 receptor.