Both AT₁ and AT₂ receptors mediate proliferation and migration of porcine vascular smooth muscle cells

Interplay of Angiotensin Peptides, Vasopressin, and Insulin in the Heart: Experimental and Clinical Evidence of Altered Interactions in Obesity and Diabetes Mellitus

The present review draws attention to the specific role of angiotensin peptides [angiotensin II (Ang II), angiotensin-(1-7) (Ang-(1-7)], vasopressin (AVP), and insulin in the regulation of the coronary blood flow and cardiac contractions. The interactions of angiotensin peptides, AVP, and insulin in the heart and in the brain are also discussed. The intracardiac production and the supply of angiotensin peptides and AVP from the systemic circulation enable their easy access to the coronary vessels and the cardiomyocytes. Coronary vessels and cardiomyocytes are furnished with AT1 receptors, AT2 receptors, Ang (1-7) receptors, vasopressin V1 receptors, and insulin receptor substrates. The presence of some of these molecules in the same cells creates good conditions for their interaction at the signaling level. The broad spectrum of actions allows for the engagement of angiotensin peptides, AVP, and insulin in the regulation of the most vital cardiac processes, including (1) cardiac tissue oxygenation, energy production, and metabolism; (2) the generation of the other cardiovascular compounds, such as nitric oxide, bradykinin (Bk), and endothelin; and (3) the regulation of cardiac work by the autonomic nervous system and the cardiovascular neurons of the brain. Multiple experimental studies and clinical observations show that the interactions of Ang II, Ang(1-7), AVP, and insulin in the heart and in the brain are markedly altered during heart failure, hypertension, obesity, and diabetes mellitus, especially when these diseases coexist. A survey of the literature presented in the review provides evidence for the belief that very individualized treatment, including interactions of angiotensins and vasopressin with insulin, should be applied in patients suffering from both the cardiovascular and metabolic diseases.

Ang II-AT2R increases mesenchymal stem cell migration by signaling through the FAK and RhoA/Cdc42 pathways in vitro

Background

Mesenchymal stem cells (MSCs) migrate via the bloodstream to sites of injury and are possibly attracted by inflammatory factors. As a proinflammatory mediator, angiotensin II (Ang II) reportedly enhances the migration of various cell types by signaling via the Ang II receptor in vitro. However, few studies have focused on the effects of Ang II on MSC migration and the underlying mechanisms.

Methods

Human bone marrow MSCs migration was measured using wound healing and Boyden chamber migration assays after treatments with different concentrations of Ang II, an AT1R antagonist (Losartan), and/or an AT2R antagonist (PD-123319). To exclude the effect of proliferation on MSC migration, we measured MSC proliferation after stimulation with the same concentration of Ang II. Additionally, we employed the focal adhesion kinase (FAK) inhibitor PF-573228, RhoA inhibitor C3 transferase, Rac1 inhibitor NSC23766, or Cdc42 inhibitor ML141 to investigate the role of cell adhesion proteins and the Rho-GTPase protein family (RhoA, Rac1, and Cdc42) in Ang II-mediated MSC migration. Cell adhesion proteins (FAK, Talin, and Vinculin) were detected by western blot analysis. The Rho-GTPase family protein activities were assessed by G-LISA and F-actin levels, which reflect actin cytoskeletal organization, were detected by using immunofluorescence.

Results

Human bone marrow MSCs constitutively expressed AT1R and AT2R. Additionally, Ang II increased MSC migration in an AT2R-dependent manner. Notably, Ang II-enhanced migration was not mediated by Ang II-mediated cell proliferation. Interestingly, Ang II-enhanced migration was mediated by FAK activation, which was critical for the formation of focal contacts, as evidenced by increased Talin and Vinculin expression. Moreover, RhoA and Cdc42 were activated by FAK to increase cytoskeletal organization, thus promoting cell contraction. Furthermore, FAK, Talin, and Vinculin activation and F-actin reorganization in response to Ang II were prevented by PD-123319 but not Losartan, indicating that FAK activation and F-actin reorganization were downstream of AT2R.

Conclusions

These data indicate that Ang II-AT2R regulates human bone marrow MSC migration by signaling through the FAK and RhoA/Cdc42 pathways. This study provides insights into the mechanisms by which MSCs home to injury sites and will enable the rational design of targeted therapies to improve MSC engraftment.

Signaling mechanism underlying the promotion of keratinocyte migration by angiotensin II

Re-epithelialization begins early during skin wound healing and is regulated by various growth factors and cytokines. Angiotensin II promotes the migration of keratinocytes and thereby contributes to wound healing. We investigated the mechanism by which angiotensin II stimulates human keratinocyte migration. Angiotensin II-induced keratinocyte migration was inhibited by an angiotensin II type 1 receptor (AT1R) antagonist (candesartan) or an angiotensin II type 2 receptor (AT2R) antagonist (PD123319) as well as by depletion of AT1R or AT2R. A biased agonist for AT1R, [Sar(1),Ile(4),Ile(8)]angiotensin II, induced cell migration, whereas depletion of β-arrestin2 inhibited angiotensin II-induced migration. Angiotensin II-induced migration was blocked by neutralizing antibodies to transforming growth factor-β (TGF-β) as well as by the TGF-β receptor inhibitor SB431542. The amount of TGF-β1 was increased in the culture medium of angiotensin II-treated cells, and this effect was inhibited by candesartan or PD123319. Both angiotensin II- and TGF-β-induced cell migration were inhibited by neutralizing antibodies to the epidermal growth factor (EGF) receptor but not by those to EGF receptor ligands. Angiotensin II-induced phosphorylation of the EGF receptor, and this effect was inhibited by candesartan, PD123319, SB431542, or depletion of β-arrestin2, but not by neutralizing antibodies to heparin-binding EGF-like growth factor. Our results indicate that β-arrestin-dependent signaling downstream of AT1R as well as AT2R signaling are necessary for angiotensin II-induced keratinocyte migration, and that such signaling promotes generation of the active form of TGF-β, consequent activation of the TGF-β receptor, and transactivation of the EGF receptor by the TGF-β receptor.

The cyclic AMP response element-binding protein (CREB) mediates smooth muscle cell proliferation in response to angiotensin II

The cAMP response element-binding protein (CREB) is a transcription factor that mediates the cellular response to metabolic and mitogenic signals. Whether CREB contributes to vascular function has received little attention, especially in relation to the processes associated with atherosclerotic disease progression and restenosis. This study examined the involvement of CREB in the mitogenic actions of angiotensin II (AngII), a growth factor that promotes neointimal hyperplasia in response to vascular injury. Treatments were performed on quiescent vascular smooth muscle cells (VSMCs) obtained from a porcine explant model. Organ culture was performed on porcine hearts subjected to angioplasty ex vivo. Stimulation of VSMCs with AngII resulted in transient CREB phosphorylation. Proliferation of smooth muscle cells in response to AngII was reduced by 90 % after infection with adenovirus expressing dominant-negative killer CREB (kCREB) mutant. Likewise, expression of kCREB prevented angioplasty-induced neointimal hyperplasia. AngII-induced CREB phosphorylation was independent of cAMP activation. Examination of putative CREB kinases revealed that MSK was responsible for phosphorylating CREB. In addition, inhibition of PKC revealed that this kinase operates upstream and activates MSK. These results indicate that activation of CREB via PKC and MSK is essential for SMC proliferation in response to AngII.

Inhibition of smooth muscle cell proliferation by adiponectin requires proteolytic conversion to its globular form

Accelerated atherosclerosis is the primary cardiovascular manifestation of diabetes and correlates inversely with levels of circulating adiponectin, an anti-atherosclerotic adipokine that declines in diabetes. We therefore initiated a study to examine the mechanisms by which adiponectin, a hormone released from adipose tissue, influences the proliferation of vascular smooth muscle cells (SMCs). Addition of adiponectin to quiescent porcine coronary artery SMCs increased both protein and DNA synthesis and concurrently activated ERK1/2 and Akt. By contrast, globular adiponectin, a truncated form of this protein, exhibited anti-mitogenic properties as indicated by the inhibition of protein and DNA synthesis in SMCs stimulated with platelet-derived growth factor (PDGF). Whereas globular adiponectin did not stimulate growth-related signal transduction pathways, it was able to block the PDGF-dependent phosphorylation of eukaryotic elongation factor 2 kinase, a regulator of protein synthesis. Proteolysis of adiponectin with trypsin, which produces globular adiponectin, reversed the growth-stimulating actions of the undigested protein. As the existence of globular adiponectin remains controversial, western blotting was used to establish its presence in rat serum. We found that globular adiponectin was detectable in rat serum, but this result was not obtained with all antibodies. The contrasting properties of adiponectin and its globular form with respect to SMC proliferation suggest that protection against atherosclerosis may therefore be mediated, in part, by the level of globular adiponectin.

The effects of angiotensin peptides and angiotensin receptor antagonists on the cell growth and angiogenic activity of GH3 lactosomatotroph cells in vitro

The local renin-angiotensin system (RAS) is present in the pituitary gland, and inhibitory effects of angiotensins on the lactosomatotroph (GH3) cell growth have been revealed. The aim of this study was to examine the influence of various angiotensin peptides and angiotensin AT1, AT2, and AT4 receptors antagonists on the cell proliferation, viability, and VEGF secretion in pituitary lactosomatotroph GH3 cell culture in order to identify receptors involved in antiproliferative effects of angiotensins on GH3 tumor cells. Cell viability and proliferation using Mosmann method and BrdU incorporation during DNA synthesis, and VEGF secretion using ELISA assay were estimated. The inhibitory effects of ang II, ang IV, and ang 5-8 on the cell viability and BrdU incorporation in GH3 culture were not abolished by AT1, AT2, and AT4 receptors antagonists. Ang II, as well as ang III and ang IV at lower concentrations stimulated the secretion of VEGF in GH3 cell culture. The secretion of VEGF was inhibited by ang III and ang IV at higher concentrations. AT1 and AT2 receptors antagonists prevented the proangiogenic effects of ang II. Ang II, ang IV, and ang 5-8 decrease the cell number and proliferation in GH3 cell culture independently of the AT1, AT2, and AT4 receptors. These peptides affect also secretion of VEGF in culture examined. Both the AT1 and AT2 receptors appear to mediate the proangiogenic effects of ang II.

The involvement of angiotensin type 1 and type 2 receptors in estrogen-induced cell proliferation and vascular endothelial growth factor expression in the rat anterior pituitary

The aim of our study was to examine the involvement of renin-angiotensin system (RAS) in estrogen-induced lactotropes proliferation and vascular endothelial growth factor (VEGF) expression in rat pituitary. The study was performed on Fisher 344 rats underwent 8-day treatment with diethylstilboestrol (DES). The proliferation index (PCNA) and VEGF expression in pituitary sections were estimated using immunohistochemical methods. Treatment with DES increased the number of PCNA-positive cells, VEGF-positive cells, and VEGF-positive blood vessels in pituitary. Stimulatory effect of estrogen on cell proliferation and VEGF expression in blood vessels was attenuated by losartan, PD123319, and captopril. VEGF immunoreactivity in pituitary cells of DES-treated rats was decreased by AT1 antagonist and not changed by AT2 blocker and ACE inhibitor. Our findings suggest the involvement of RAS in DES-induced cell proliferation and VEGF expression in pituitary. Both the AT1 and AT2 receptors appear to mediate the estrogen-dependent mitogenic and proangiogenic effects in rat pituitary.

Angiotensins inhibit cell growth in GH3 lactosomatotroph pituitary tumor cell culture: a possible involvement of the p44/42 and p38 MAPK pathways

The local renin-angiotensin system is present in the pituitary. We investigated the effects of angiotensins on GH3 lactosomatotroph cells proliferation in vitro and the involvement of p44/42 and p38 MAPK inhibitors in the growth-regulatory effects of angiotensins. Materials and Methods. Cell viability using the Mosmann method and proliferation by the measurement of BrdU incorporation during DNA synthesis were estimated. Results. Ang II and ang IV decreased the viability and proliferation of GH3 cells. Inhibitor of p44/42 MAPK attenuated the effects of ang II on cell viability and proliferation but did not affect the ang 5-8-dependent actions. Inhibitor of p38 MAPK prevented the decrease in the number of GH3 cells in ang-II- and ang-IV-treated groups. Conclusions. The growth-inhibitory effect of ang II is possibly mediated by the p44/42 MAPK. The p38 MAPK appears to mediate the inhibitory effects of both ang II and ang 5-8 upon cell survival.