Endothelial nitric oxide synthase inhibits G12/13 and rho-kinase activated by the angiotensin II type-1 receptor: implication in vascular migration

Irigenin alleviates angiotensin II-induced oxidative stress and apoptosis in HUVEC cells by activating Nrf2 pathway

Endothelial dysfunction is closely related to various cardiovascular diseases. Oxidative stress and apoptosis are involved in the progress of endothelial dysfunction. Irigenin (IR) has antioxidative properties. We investigated IR as a novel therapy for angiotensin II (Ang II)-induced endothelial dysfunction and explored the potential mechanisms of IR. After human umbilical vein endothelial cell lines (HUVECs) were treated with Ang II (100, 200, 300 and 400 nmol/L) alone, IR (2.5, 5, 10, 20 and 40 μmol/L) alone or Ang II plus IR for 24 h, HUVECs viability, lactate dehydrogenase (LDH), apoptosis, oxidative stress, apoptosis-related protein and nuclear factor E2-related factor 2 (Nrf2) levels were detected by Cell Counting Kit (CCK)-8 assay, enzyme-linked immunosorbent assay, flow cytometry and western blot. Transfection rate of Nrf2 was detected by western blot. In the next rescue experiment, we used silent Nrf2 (siNrf2) to verify the previous experimental results. Different concentrations' Ang II repressed HUVECs viability and increased LDH release, and different concentrations' IR did not affect HUVECs viability or LDH release. Furthermore, IR elevated cell viability and Nrf2 level, inhibited LDH release, apoptosis, oxidative stress and apoptosis-related protein levels in Ang II-induced HUVECs. More important, siNrf2 suppressed the expression of Nrf2, and siNrf2 abrogated the protective effect of IR on Ang II-induced Nrf2 expression, cell viability, LDH activity, oxidative stress generation and apoptosis-related protein in HUVECs. IR protected HUVECs from Ang II-induced oxidative stress and apoptosis injury by activating Nrf2 pathway.

Snake venom-derived bradykinin-potentiating peptides: A promising therapy for COVID-19?

The severe acute respiratory syndrome coronavirus‐2 (SARS‐COV‐2), a novel coronavirus responsible for the recent infectious pandemic, is known to downregulate angiotensin‐converting enzyme‐2 (ACE2). Most current investigations focused on SARS‐COV‐2‐related effects on the renin–angiotensin system and especially the resultant increase in angiotensin II, neglecting its effects on the kinin–kallikrein system. SARS‐COV‐2‐induced ACE2 inhibition leads to the augmentation of bradykinin 1‐receptor effects, as ACE2 inactivates des‐Arg9‐bradykinin, a bradykinin metabolite. SARS‐COV‐2 also decreases bradykinin 2‐receptor effects as it affects bradykinin synthesis by inhibiting cathepsin L, a kininogenase present at the site of infection and involved in bradykinin production. The physiologies of both the renin–angiotensin and kinin–kallikrein system are functionally related suggesting that any intervention aiming to treat SARS‐COV‐2‐infected patients by triggering one system but ignoring the other may not be adequately effective. Interestingly, the snake‐derived bradykinin‐potentiating peptide (BPP‐10c) acts on both systems. BPP‐10c strongly decreases angiotensin II by inhibiting ACE, increasing bradykinin‐related effects on the bradykinin 2‐receptor and increasing nitric oxide‐mediated effects. Based on a narrative review of the literature, we suggest that BPP‐10c could be an optimally effective option to consider when aiming at developing an anti‐SARS‐COV‐2 drug.

Deconstructing aqueous humor outflow - The last 50 years

Herein partially summarizes one scientist-clinician's wanderings through the jungles of primate aqueous humor outflow over the past ~45 years. Totally removing the iris has no effect on outflow facility or its response to pilocarpine, whereas disinserting the ciliary muscle (CM) from the scleral spur/trabecular meshwork (TM) completely abolishes pilocarpine's effect. Epinephrine increases facility in CM disinserted eyes. Cytochalasins and latrunculins increase outflow facility, subthreshold doses of cytochalasins and epinephrine given together increase facility, and phalloidin, which has no effect on facility, partially blocks the effect of both cytochalasins and epinephrine. H-7, ML7, Y27632 and nitric oxide - donating compounds all increase facility, consistent with a mechanosensitive TM/SC. Adenosine A1 agonists increase and angiotensin II decrease facility. OCT and optical imaging techniques now permit visualization and digital recording of the distal outflow pathways in real time. Prostaglandin (PG) F2α analogues increase the synthesis and release of matrix metalloproteinases by the CM cells, causing remodeling and thinning of the interbundle extracellular matrix (ECM), thereby increasing uveoscleral outflow and reducing IOP. Combination molecules (one molecule, two or more effects) and fixed combination products (two molecules in one bottle) simplify drug regimens for patients. Gene and stem cell therapies to enhance aqueous outflow have been successful in laboratory models and may fill an unmet need in terms of patient compliance, taking the patient out of the delivery system. Functional transfer of genes inhibiting the rho cascade or decoupling actin from myosin increase facility, while genes preferentially expressed in the glaucomatous TM decrease facility. In live NHP, reporter genes are expressed for 2+ years in the TM after a single intracameral injection, with no adverse reaction. However, except for one recent report, injection of facility-effective genes in monkey organ cultured anterior segments (MOCAS) have no effect in live NHP. While intracameral injection of an FIV. BOVPGFS-myc.GFP PGF synthase vector construct reproducibly induces an ~2 mmHg reduction in IOP, the effect is much less than that of topical PGF2⍺ analogue eyedrops, and dissipates after 5 months. The turnoff mechanism has yet to be defeated, although proteasome inhibition enhances reporter gene expression in MOCAS. Intracanalicular injection might minimize off-target effects that activate turn-off mechanisms. An AD-P21 vector injected sub-tenon is effective in 'right-timing' wound healing after trabeculectomy in live laser-induced glaucomatous monkeys. In human (H)OCAS, depletion of TM cells by saponification eliminates the aqueous flow response to pressure elevation, which can be restored by either cultured TM cells or by IPSC-derived TM cells. There were many other steps along the way, but much was accomplished, biologically and therapeutically over the past half century of research and development focused on one very small but complex ocular apparatus. I am deeply grateful for this award, named for a giant in our field that none of us can live up to.

Downregulation of Brain Gα12 Attenuates Angiotensin II-Dependent Hypertension

BACKGROUND

Angiotensin II (Ang II) activates central Angiotensin II type 1 receptors to increase blood pressure via multiple pathways. However, whether central Gα proteins contribute to Ang II-induced hypertension remains unknown. We hypothesized that Angiotensin II type 1 receptors couple with Gα12 and/or Gαq to produce sympatho-excitation and increase blood pressure and downregulation of these Gα-subunit proteins will attenuate Ang II-dependent hypertension.

METHODS AND RESULTS

After chronic infusion of Ang II (s.c. 350 ng/kg/min) or vehicle for 2 weeks, Ang II evoked an increase in Gα12 expression, but not Gαq in the rostral ventrolateral medulla of Sprague-Dawley rats. In other studies, rats that received Ang II or vehicle infusion s.c. were simultaneously infused i.c.v. with a scrambled (SCR) or Gα12 oligodeoxynucleotide (ODN; 50 µg/day). Central Gα12 ODN infusion lowered mean blood pressure in Ang II infused rats compared with SCR ODN infusion (14-day peak; 133 ± 12 vs. 176 ± 11 mm Hg). Compared to the SCR ODN group, Ang II infused rats that received i.c.v. Gα12 ODN showed a greater increase in heart rate to atropine, an attenuated reduction in blood pressure to chlorisondamine, and an improved baroreflex sensitivity. In addition, central Gα12 and Gαq ODN pretreatment blunted the pressor response to an acute i.c.v. injection of Ang II (i.c.v., 200 ng).

CONCLUSIONS

These findings suggest that central Gα12 protein signaling pathways play an important role in the development of chronic Ang II-dependent hypertension in rats.

Schizandrin B attenuates angiotensin II induced endothelial to mesenchymal transition in vascular endothelium by suppressing NF-κB activation

BACKGROUND

Angiotensin II (Ang II)-induced chronic inflammation and oxidative stress often leads to irreversible vascular injury, in which the endothelial to mesenchymal transition (EndMT) in the endothelial layers are involved. Schisandrin B (Sch B), a natural product isolated from traditional Schisandra chinensis, has been reported to exert vascular protective properties with unclear mechanism.

HYPOTHESIS/PURPOSE

This study investigated the protective effects and mechanism of Sch B against Ang II-induced vascular injury.

METHODS

C57BL/6 mice were subcutaneous injected of Ang II for 4 weeks to induce irreversible vascular injury. In vitro, Ang II-induced HUVECs injury was used to study the underlying mechanism. The markers of EndMT, inflammation and oxidative stress were studied both in vitro and in vivo.

RESULTS

Pre-administration of Sch B effectively attenuated phenotypes of vascular EndMT and fibrosis in Ang II-treated animals, accompanied with decreased inflammatory cytokine and ROS. The in vitro data from HUVECs suggest that Sch B directly targets NF-κB activation to suppress Ang II-induced EndMT and vascular injury. The activation of EndMT in the presence of Ang II is regulated by the NF-κB, a common player in inflammation and oxidative stress. Ang II-induced inflammation and oxidative stress also contributed to vascular EndMT development and Sch B inhibited inflammation/ROS-mediated EndMT by suppressing NF-κB.

CONCLUSION

EndMT contributes to vascular injury in Ang II-treated mice, and it can be prevented via suppressing NF-κB activation by Sch B treatment. These results also imply that NF-κB might be a promising target to attenuate vascular remodeling induced by inflammation and oxidative stress through an EndMT mechanism.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Rho-Associated Coiled-Coil Kinase (ROCK) in Molecular Regulation of Angiogenesis

Identified as a major downstream effector of the small GTPase RhoA, Rho-associated coiled-coil kinase (ROCK) is a versatile regulator of multiple cellular processes. Angiogenesis, the process of generating new capillaries from the pre-existing ones, is required for the development of various diseases such as cancer, diabetes and rheumatoid arthritis. Recently, ROCK has attracted attention for its crucial role in angiogenesis, making it a promising target for new therapeutic approaches. In this review, we summarize recent advances in understanding the role of ROCK signaling in regulating the permeability, migration, proliferation and tubulogenesis of endothelial cells (ECs), as well as its functions in non-ECs which constitute the pro-angiogenic microenvironment. The therapeutic potential of ROCK inhibitors in angiogenesis-related diseases is also discussed.

Schisandrin B protects against angiotensin II-induced endotheliocyte deficits by targeting Keap1 and activating Nrf2 pathway

Introduction

Schisandrin B (SchB), the main active constituent in Schisandra chinensis, has antioxidant activities. Endothelial dysfunction leads to various cardiovascular diseases. Oxidative stress is a crucial pathophysiological mechanism underpinning endothelial dysfunction.

Methods

We elucidated the role and underlying mechanisms of SchB in angiotensin II-induced rat aortic endothelial-cell deficits and explored targets of SchB through siRNA analysis and molecular docking. We measured apoptosis by TUNEL and oxidative stress by dihydroethidium (DHE) and 2’,7’ –dichlorofluorescin diacetate (DCF) staining.

Results

Our results demonstrated that SchB significantly ameliorated oxidative stress, mitochondrial membrane-potential depolarization and apoptosis in angiotensin II-challenged rat aortic endothelial cells. We further discovered that these antioxidative effects of SchB were mediated through induction of Nrf2. Importantly, using molecular docking and molecular dynamic simulation, we identified that Keap1, an adaptor for the degradation of Nrf2, was a target of SchB.

Conclusion

These findings support the potential use of SchB as a Keap1 inhibitor for attenuating oxidative stress, and Keap1 might serve as a therapeutic target in the treatment of cardiovascular diseases.

CYP2J2 metabolites, epoxyeicosatrienoic acids, attenuate Ang II-induced cardiac fibrotic response by targeting Gα12/13

The arachidonic acid-cytochrome P450 2J2-epoxyeicosatrienoic acid (AA-CYP2J2-EET) metabolic pathway has been identified to be protective in the cardiovascular system. This study explored the effects of the AA-CYP2J2-EET metabolic pathway on cardiac fibrosis from the perspective of cardiac fibroblasts and underlying mechanisms. In in vivo studies, 8-week-old male CYP2J2 transgenic mice (aMHC-CYP2J2-Tr) and littermates were infused with angiotensin II (Ang II) or saline for 2 weeks. Results showed that CYP2J2 overexpression increased EET production. Meanwhile, impairment of cardiac function and fibrotic response were attenuated by CYP2J2 overexpression. The effects of CYP2J2 were associated with reduced activation of the α subunits of G12 family G proteins (Gα_12/13)/RhoA/Rho kinase (ROCK) cascade and elevation of the NO/cyclic guanosine monophosphate (cGMP) level in cardiac tissue. In in vitro studies, cardiac fibroblast activation, proliferation, migration, and collagen production induced by Ang II were associated with activation of the Gα_12/13/RhoA/ROCK pathway, which was inhibited by exogenous 11,12-EET. Moreover, silencing of Gα_12/13 or RhoA exerted similar effects as 11,12-EET. Furthermore, inhibitory effects of 11,12-EET on Gα_12/13 were blocked by NO/cGMP pathway inhibitors. Our findings indicate that enhancement of the AA-CYP2J2-EET metabolic pathway by CYP2J2 overexpression attenuates Ang II-induced cardiac dysfunction and fibrosis by reducing the fibrotic response of cardiac fibroblasts by targeting the Gα_12/13/RhoA/ROCK pathway via NO/cGMP signaling.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

Rho-Mancing to Sensitize Calcium Signaling for Contraction in the Vasculature: Role of Rho Kinase

Vascular smooth muscle contraction is an important physiological process contributing to cardiovascular homeostasis. The principal determinant of smooth muscle contraction is the intracellular free Ca²⁺ concentration, and phosphorylation of myosin light chain (MLC) by activated myosin light chain kinase (MLCK) in response to increased Ca²⁺ is the main pathway by which vasoconstrictor stimuli induce crossbridge cycling of myosin and actin filaments. A secondary pathway for vascular smooth muscle contraction that is not directly dependent on Ca²⁺ concentration, but rather mediating Ca²⁺ sensitization, is the RhoA/Rho kinase pathway. In response to contractile stimuli, the small GTPase RhoA activates its downstream effector Rho kinase which, in turn, promotes contraction via myosin light chain phosphatase (MLCP) inhibition. RhoA/Rho kinase-mediated MLCP inhibition occurs mainly by phosphorylation and inhibition of MYPT1, the regulatory subunit of MLCP, or by CPI-17-mediated inhibition of the catalytic subunit of MLCP. In this review, we describe the molecular mechanisms underlying the pivotal role exerted by Rho kinase on vascular smooth muscle contraction and discuss the main regulatory pathways for its activity.

Heterotrimeric G protein signaling in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a signalopathy of renal tubular epithelial cells caused by naturally occurring mutations in two distinct genes, polycystic kidney disease 1 (PKD1) and 2 (PKD2). Genetic variants in PKD1, which encodes the polycystin-1 (PC-1) protein, remain the predominant factor associated with the pathogenesis of nearly two-thirds of all patients diagnosed with PKD. Although the relationship between defective PC-1 with renal cystic disease initiation and progression remains to be fully elucidated, there are numerous clinical studies that have focused upon the control of effector systems involving heterotrimeric G protein regulation. A major regulator in the activation state of heterotrimeric G proteins are G protein-coupled receptors (GPCRs), which are defined by their seven transmembrane-spanning regions. PC-1 has been considered to function as an unconventional GPCR, but the mechanisms by which PC-1 controls signal processing, magnitude, or trafficking through heterotrimeric G proteins remains to be fully known. The diversity of heterotrimeric G protein signaling in PKD is further complicated by the presence of non-GPCR proteins in the membrane or cytoplasm that also modulate the functional state of heterotrimeric G proteins within the cell. Moreover, PC-1 abnormalities promote changes in hormonal systems that ultimately interact with distinct GPCRs in the kidney to potentially amplify or antagonize signaling output from PC-1. This review will focus upon the canonical and noncanonical signaling pathways that have been described in PKD with specific emphasis on which heterotrimeric G proteins are involved in the pathological reorganization of the tubular epithelial cell architecture to exacerbate renal cystogenic pathways.

Stimulation of Dopamine D3 Receptor Attenuates Renal Ischemia-Reperfusion Injury via Increased Linkage With Gα12

BACKGROUND

Renal ischemia-reperfusion (I/R) injury causes renal tubular necrosis, apoptosis, and inflammation leading to acute renal dysfunction. Recent studies have revealed that deletion of Gα12 mitigates the renal damage due to I/R injury. Our previous study showed that activation of dopamine D3 receptor (D3R) increased its linkage with Gα12, and hampered Gα12-mediated stimulation of renal sodium transport. In the present study, we used an in-vivo rat model and an in vitro study of the renal epithelial cell line (NRK52E) to investigate whether or not an increased linkage between D3R and Gα12 contributes to the protective effect of D3R on renal I/R injury.

METHODS

For in vivo studies, I/R injury was induced in a rat renal unilateral clamping model. For in vitro studies, hypoxia/reoxygenation and cold storage/rewarming injuries were performed in NRK52E cells. PD128907, a D3R agonist, or vehicle, was administered 15 minutes before clamping (or hypoxia) in both the in vivo or in vitro studies.

RESULTS

In the rat renal unilateral clamping model, pretreatment with PD128907 (0.2 mg/kg, intravenous) protected against renal I/R injury and increased survival rate during a long-term follow-up after 7 days. A decrease in the generation of reactive oxygen species, apoptosis, and inflammation may be involved in the D3R-mediated protection because pretreatment with PD128907 increased renal glutathione and superoxide dismutase levels and decreased malondialdehyde levels in the I/R group. The increase in cytokines (TNF-α, IL-1β, and IL-10) and myeloperoxidase in I/R injured kidney was also prevented with a simultaneous decrease in the apoptosis of the epithelial cells and expression of apoptosis biomarkers in kidney harvested 1 day after I/R injury. The increase in the coimmunoprecipitation between D3R and Gα12 with D3R stimulation paralleled the observed renal protection from I/R injury. Moreover, in vitro studies showed that transient overexpression of Gα12 in the NRK52E cells attenuated the protective effect of PD128907 on hypoxia/reoxygenation injury. The protective effect of PD128907 might be of significance to renal transplantation because cold storage/rewarming induced injury increased lactate dehydrogenase release and decreased cell viability in NRK52E cells. Conversely, in the presence of PD128907, the increased lactate dehydrogenase release and decreased cell viability were reversed.

CONCLUSIONS

These results suggest that activation of D3R, by decreasing Gα12-induced renal damage, may exert a protective effect from I/R injury.

Bimodal effect of oxidative stress in internal anal sphincter smooth muscle

Changes in oxidative stress may affect basal tone and relaxation of the internal anal sphincter (IAS) smooth muscle in aging. We examined this issue by investigating the effects of the oxidative stress inducer 6-anilino-5,8-quinolinedione (LY-83583) in basal as well as U-46619-stimulated tone, and nonadrenergic, noncholinergic (NANC) relaxation in rat IAS. LY-83583, which works via generation of reactive oxygen species in living cells, produced a bimodal effect in IAS tone: lower concentrations (0.1 nM to 10 μM) produced a concentration-dependent increase, while higher concentrations (50-100 μM) produced a decrease in IAS tone. An increase in IAS tone by lower concentrations was associated with an increase in RhoA/Rho kinase (ROCK) activity. This was evident by the increase in RhoA/ROCK in the particulate fractions, in ROCK activity, and in the levels of phosphorylated (p) (Thr696)-myosin phosphatase target subunit 1 and p(Thr18/Ser19)-20-kDa myosin light chain. Conversely, higher concentrations of LY-83583 produced inhibitory effects on RhoA/ROCK. Interestingly, both the excitatory and inhibitory effects of LY-83583 in the IAS were reversed by superoxide dismutase. The excitatory effects of LY-83583 were found to resemble those with neuronal nitric oxide synthase (nNOS) inhibition by l-NNA, since it produced a significant increase in the IAS tone and attenuated NANC relaxation. These effects of LY-83583 and l-NNA were reversible by l-arginine. This suggests the role of nNOS inhibition and RhoA/ROCK activation in the increase in IAS tone by LY-83583. These data have important implications in the pathophysiology and therapeutic targeting of rectoanal disorders, especially associated with IAS dysfunction.

Epidermal growth factor receptor inhibitor protects against abdominal aortic aneurysm in a mouse model

Angiotensin II (Ang II) has been implicated in the development of abdominal aortic aneurysm (AAA). In vascular smooth muscle cells (VSMC), Ang II activates epidermal growth factor receptor (EGFR) mediating growth promotion. We hypothesized that inhibition of EGFR prevents Ang II-dependent AAA. C57BL/6 mice were co-treated with Ang II and β-aminopropionitrile (BAPN) to induce AAA with or without treatment with EGFR inhibitor, erlotinib. Without erlotinib, 64.3% of mice were dead due to aortic rupture. All surviving mice had AAA associated with EGFR activation. Erlotinib-treated mice did not die and developed far fewer AAA. The maximum diameters of abdominal aortas were significantly shorter with erlotinib treatment. In contrast, both erlotinib-treated and non-treated mice developed hypertension. The erlotinib treatment of abdominal aorta was associated with lack of EGFR activation, endoplasmic reticulum (ER) stress, oxidative stress, interleukin-6 induction and matrix deposition. EGFR activation in AAA was also observed in humans. In conclusion, EGFR inhibition appears to protect mice from AAA formation induced by Ang II plus BAPN. The mechanism seems to involve suppression of vascular EGFR and ER stress.

Characterization of Angiotensin II Molecular Determinants Involved in AT1 Receptor Functional Selectivity

The octapeptide angiotensin II (AngII) exerts a variety of cardiovascular effects through the activation of the AngII type 1 receptor (AT1), a G protein-coupled receptor. The AT1 receptor engages and activates several signaling pathways, including heterotrimeric G proteins Gq and G12, as well as the extracellular signal-regulated kinases (ERK) 1/2 pathway. Additionally, following stimulation, βarrestin is recruited to the AT1 receptor, leading to receptor desensitization. It is increasingly recognized that specific ligands selectively bind and favor the activation of some signaling pathways over others, a concept termed ligand bias or functional selectivity. A better understanding of the molecular basis of functional selectivity may lead to the development of better therapeutics with fewer adverse effects. In the present study, we developed assays allowing the measurement of six different signaling modalities of the AT1 receptor. Using a series of AngII peptide analogs that were modified in positions 1, 4, and 8, we sought to better characterize the molecular determinants of AngII that underlie functional selectivity of the AT1 receptor in human embryonic kidney 293 cells. The results reveal that position 1 of AngII does not confer functional selectivity, whereas position 4 confers a bias toward ERK signaling over Gq signaling, and position 8 confers a bias toward βarrestin recruitment over ERK activation and Gq signaling. Interestingly, the analogs modified in position 8 were also partial agonists of the protein kinase C (PKC)-dependent ERK pathway via atypical PKC isoforms PKCζ and PKCι.

Critical role of exogenous nitric oxide in ROCK activity in vascular smooth muscle cells

Objective

Rho-associated kinase (ROCK) signaling pathway has been shown to mediate various cellular functions including cell proliferation, migration, adhesion, apoptosis, and contraction, all of which may be involved in pathogenesis of atherosclerosis. Endogenous nitric oxide (NO) is well known to have an anti-atherosclerotic effect, whereas the exogenous NO-mediated cardiovascular effect still remains controversial. The purpose of this study was to evaluate the effect of exogenous NO on ROCK activity in vascular smooth muscle cells (VSMCs) in vitro and in vivo.

Methods

VSMCs migration was evaluated using a modified Boyden chamber assay. ROCK activities were measured by Western blot analysis in murine and human VSMCs and aorta of mice treated with or without angiotensin II (Ang II) and/or sodium nitroprusside (SNP), an NO donor.

Results

Co-treatment with SNP inhibited the Ang II-induced cell migration and increases in ROCK activity in murine and human VSMCs. Similarly, the increased ROCK activity 2 weeks after Ang II infusion in the mouse aorta was substantially inhibited by subcutaneous injection of SNP.

Conclusions

These findings suggest that administration of exogenous NO can inhibit ROCK activity in VSMCs in vitro and in vivo.

Rho/ROCK signal cascade mediates asymmetric dimethylarginine-induced vascular smooth muscle cells migration and phenotype change

Asymmetric dimethylarginine (ADMA) induces vascular smooth muscle cells (VSMCs) migration. VSMC phenotype change is a prerequisite of migration. RhoA and Rho-kinase (ROCK) mediate migration of VSMCs. We hypothesize that ADMA induces VSMC migration via the activation of Rho/ROCK signal pathway and due to VSMCs phenotype change. ADMA activates Rho/ROCK signal pathway that interpreted by the elevation of RhoA activity and phosphorylation level of a ROCK substrate. Pretreatment with ROCK inhibitor, Y27632 completely reverses the induction of ADMA on ROCK and in turn inhibits ADMA-induced VSMCs migration. When the Rho/ROCK signal pathway has been blocked by pretreatment with Y27632, the induction of ERK signal pathway by ADMA is completely abrogated. Elimination of ADMA via overexpression of dimethylarginine dimethylaminohydrolase 2 (DDAH2) and L-arginine both blocks the effects of ADMA on the activation of Rho/ROCK and extra cellular signal-regulated kinase (ERK) in VSMCs. The expression of differentiated phenotype relative proteins was reduced and the actin cytoskeleton was disassembled by ADMA, which were blocked by Y27632, further interpreting that ADMA inducing VSMCs migration via Rho/ROCK signal pathway is due to its effect on the VSMCs phenotype change. Our present study may help to provide novel insights into the therapy and prevention of atherosclerosis.

A century old renin-angiotensin system still grows with endless possibilities: AT1 receptor signaling cascades in cardiovascular physiopathology

Ang II, the primary effector pleiotropic hormone of the renin-angiotensin system (RAS) cascade, mediates physiological control of blood pressure and electrolyte balance through its action on vascular tone, aldosterone secretion, renal sodium absorption, water intake, sympathetic activity and vasopressin release. It affects the function of most of the organs far beyond blood pressure control including heart, blood vessels, kidney and brain, thus, causing both beneficial and deleterious effects. However, the protective axis of the RAS composed of ACE2, Ang (1-7), alamandine, and Mas and MargD receptors might oppose some harmful effects of Ang II and might promote beneficial cardiovascular effects. Newly identified RAS family peptides, Ang A and angioprotectin, further extend the complexities in understanding the cardiovascular physiopathology of RAS. Most of the diverse actions of Ang II are mediated by AT1 receptors, which couple to classical Gq/11 protein and activate multiple downstream signals, including PKC, ERK1/2, Raf, tyrosine kinases, receptor tyrosine kinases (EGFR, PDGF, insulin receptor), nuclear factor κB and reactive oxygen species (ROS). Receptor activation via G12/13 stimulates Rho-kinase, which causes vascular contraction and hypertrophy. The AT1 receptor activation also stimulates G protein-independent signaling pathways such as β-arrestin-mediated MAPK activation and Src-JAK/STAT. AT1 receptor-mediated activation of NADPH oxidase releases ROS, resulting in the activation of pro-inflammatory transcription factors and stimulation of small G proteins such as Ras, Rac and RhoA. The components of the RAS and the major Ang II-induced signaling cascades of AT1 receptors are reviewed.

Caveolin 1 is critical for abdominal aortic aneurysm formation induced by angiotensin II and inhibition of lysyl oxidase

Although AngII (angiotensin II) and its receptor AT1R (AngII type 1 receptor) have been implicated in AAA (abdominal aortic aneurysm) formation, the proximal signalling events primarily responsible for AAA formation remain uncertain. Caveolae are cholesterol-rich membrane microdomains that serve as a signalling platform to facilitate the temporal and spatial localization of signal transduction events, including those stimulated by AngII. Cav1 (caveolin 1)-enriched caveolae in vascular smooth muscle cells mediate ADAM17 (a disintegrin and metalloproteinase 17)-dependent EGFR (epidermal growth factor receptor) transactivation, which is linked to vascular remodelling induced by AngII. In the present study, we have tested our hypothesis that Cav1 plays a critical role for the development of AAA at least in part via its specific alteration of AngII signalling within caveolae. Cav1-/- mice and the control wild-type mice were co-infused with AngII and β-aminopropionitrile to induce AAA. We found that Cav1-/- mice with the co-infusion did not develop AAA compared with control mice in spite of hypertension. We found an increased expression of ADAM17 and enhanced phosphorylation of EGFR in AAA. These events were markedly attenuated in Cav1-/- aortas with the co-infusion. Furthermore, aortas from Cav1-/- mice with the co-infusion showed less endoplasmic reticulum stress, oxidative stress and inflammatory responses compared with aortas from control mice. Cav1 silencing in cultured vascular smooth muscle cells prevented AngII-induced ADAM17 induction and activation. In conclusion, Cav1 appears to play a critical role in the formation of AAA and associated endoplasmic reticulum/oxidative stress, presumably through the regulation of caveolae compartmentalized signals induced by AngII.

Requirement of phosphorylatable endothelial nitric oxide synthase at Ser-1177 for vasoinhibin-mediated inhibition of endothelial cell migration and proliferation in vitro

Endothelial nitric oxide synthase (eNOS)-derived nitric oxide is a major vasorelaxing factor and a mediator of vasopermeability and angiogenesis. Vasoinhibins, a family of antiangiogenic prolactin fragments that include 16 K prolactin, block most eNOS-mediated vascular effects. Vasoinhibins activate protein phosphatase 2A, causing eNOS inactivation through dephosphorylation of eNOS at serine residue 1179 in bovine endothelial cells and thereby blocking vascular permeability. In this study, we examined whether human eNOS phosphorylation at S1177 (analogous to bovine S1179) influences other actions of vasoinhibins. Bovine umbilical vein endothelial cells were stably transfected with human wild-type eNOS (WT) or with phospho-mimetic (S1177D) or non-phosphorylatable (S1177A) eNOS mutants. Vasoinhibins inhibited the increases in eNOS activity, migration, and proliferation following the overexpression of WT eNOS but did not affect these responses in cells expressing S1177D and S1177A eNOS mutants. We conclude that eNOS inhibition by dephosphorylation of S1177 is fundamental for the inhibition of endothelial cell migration and proliferation by vasoinhibins.

The CD47-binding peptide of thrombospondin-1 induces defenestration of liver sinusoidal endothelial cells

BACKGROUND & AIMS

A fenestrated phenotype is characteristic of liver sinusoidal endothelial cells (LSECs), but liver sinusoids become defenestrated during fibrosis and other liver diseases. Thrombospondin-1 (TSP1) is a matrix glycoprotein with pro-fibrotic effects, and the CD47-binding fragment of TSP1 also has anti-angiogenic effects in endothelial cells. We hypothesized that the CD47-binding fragment of TSP1 could induce defenestration in LSECs through the Rho-Rho kinase (ROCK)-myosin pathway.

METHODS

Freshly isolated rat LSECs were treated with TSP1 or CD47-binding peptides of TSP1. LSEC fenestration was assessed with scanning electron microscopy, and myosin phosphorylation was assessed with immuno-fluorescence.

RESULTS

Treating LSECs with TSP1 caused a dose-dependent loss of fenestrae, and this effect could not be blocked by SB-431542, the TGF-β1 receptor inhibitor. A CD47-binding fragment of TSP1, p4N1, was able to induce defenestration, and a CD47-blocking antibody, B6H12, was able to suppress p4N1-induced defenestration. The p4N1 fragment also caused contraction of fenestra size, correlated with an increase in myosin activation. Pretreatment with Y-237642 (a ROCK inhibitor) prevented p4N1-induced myosin activation and fenestrae decrease. Simvastatin has also been shown to antagonize Rho-ROCK signalling, and we found that simvastatin pretreatment protected LSECs from p4N1-induced myosin activation and defenestration.

CONCLUSIONS

We conclude that CD47 signals through the Rho-ROCK-myosin pathway to induce defenestration in LSECs. In addition, our results show that simvastatin and Y-237642 have a beneficial impact on fenestration in vitro, providing an additional explanation for the efficacy of these compounds for regression of liver fibrosis.

Peach (Prunus persica) extract inhibits angiotensin II-induced signal transduction in vascular smooth muscle cells

Angiotensin II (Ang II) is a vasoactive hormone that has been implicated in cardiovascular diseases. Here, the effect of peach, Prunus persica L. Batsch, pulp extract on Ang II-induced intracellular Ca(2+) mobilization, reactive oxygen species (ROS) production and signal transduction events in cultured vascular smooth muscle cells (VSMCs) was investigated. Pretreatment of peach ethyl acetate extract inhibited Ang II-induced intracellular Ca(2+) elevation in VSMCs. Furthermore, Ang II-induced ROS generation, essential for signal transduction events, was diminished by the peach ethyl acetate extract. The peach ethyl acetate extract also attenuated the Ang II-induced phosphorylation of epidermal growth factor receptor and myosin phosphatase target subunit 1, both of which are associated with atherosclerosis and hypertension. These results suggest that peach ethyl acetate extract may have clinical potential for preventing cardiovascular diseases by interfering with Ang II-induced intracellular Ca(2+) elevation, the generation of ROS, and then blocking signal transduction events.

An extract from brown rice inhibits signal transduction of angiotensin II in vascular smooth muscle cells

BACKGROUND

Health benefits of brown rice over white rice have been described previously. However, whether the outer bran of rice contains an ingredient useful to prevent cardiovascular diseases remains unknown. The subaleurone layer of rice, which is usually lost by milling brown rice for whitening, is rich in varied nutrients, suggesting that some ingredient contained within this layer may be beneficial for the cardiovascular system.

METHODS

To assess potential benefits of the subaleurone layer toward pathological vascular remodeling, we examined the effects of the layer extracts from Japanese rice (Oryza sativa var. japonica) on angiotensin II (Ang II)-induced signal transduction and hypertrophy in cultured rat vascular smooth muscle cells (VSMCs).

RESULTS

Pretreatment of the ethyl acetate extract (100 µg/ml), but not other extracts, inhibited Ang II (100 nmol/l)-induced immediate signal transduction events. Also, the extract diminished c-Fos expression and hypertrophic protein accumulation induced by Ang II in the cells.

CONCLUSION

These data suggest that an ingredient in the ethyl acetate extract from the subaleurone layer of rice has a protective effect toward cardiovascular diseases by interfering with signal transduction induced by Ang II.

Caveolin-1 negatively regulates a metalloprotease-dependent epidermal growth factor receptor transactivation by angiotensin II

A metalloprotease, ADAM17, mediates the generation of mature ligands for the epidermal growth factor receptor (EGFR). This is the key signaling step by which angiotensin II (AngII) induces EGFR transactivation leading to hypertrophy and migration of vascular smooth muscle cells (VSMCs). However, the regulatory mechanism of ADAM17 activity remains largely unclear. Here we hypothesized that caveolin-1 (Cav1), the major structural protein of a caveolae, a membrane microdomain, is involved in the regulation of ADAM17. In cultured VSMCs, infection of adenovirus encoding Cav1 markedly inhibited AngII-induced EGFR ligand shedding, EGFR transactivation, ERK activation, hypertrophy and migration, but not intracellular Ca(2+) elevation. Methyl-β-cyclodextrin and filipin, reagents that disrupt raft structure, both stimulated an EGFR ligand shedding and EGFR transactivation in VSMCs. In addition, non-detergent sucrose gradient membrane fractionations revealed that ADAM17 cofractionated with Cav1 in lipid rafts. These results suggest that lipid rafts and perhaps caveolae provide a negative regulatory environment for EGFR transactivation linked to vascular remodeling induced by AngII. These novel findings may provide important information to target cardiovascular diseases under the enhanced renin angiotensin system.

Sphingosine kinase 1 is critically involved in nitric oxide-mediated human endothelial cell migration and tube formation

BACKGROUND AND PURPOSE

Sphingosine kinases (SKs) convert sphingosine to sphingosine 1-phosphate (S1P), which is a bioactive lipid that regulates a variety of cellular processes including proliferation, differentiation and migration.

EXPERIMENTAL APPROACH

We used the human endothelial cell line EA.hy926 to investigate the effect of nitric oxide (NO) donors on SK-1 expression, and on cell migration and tube formation.

KEY RESULTS

We showed that exposure of EA.hy926 cells to Deta-NO (125-1000 microM) resulted in a time- and concentration-dependent up-regulation of SK-1 mRNA and protein expression, and activity with a first significant effect at 250 microM of Deta-NO. The increased SK-1 mRNA expression resulted from an enhanced SK-1 promoter activity. A similar effect was also seen with various other NO donors. In mechanistic terms, the NO-triggered effect occurred independently of cGMP, but involved the classical mitogen-activated protein kinase cascade because the MEK inhibitor U0126 abolished the NO-induced SK-1 expression. The effect of NO was also markedly reduced by the thiol-reducing agent N-acetylcysteine, suggesting a redox-dependent mechanism. Functionally, Deta-NO triggered an increase in the migration of endothelial cells in an adapted Boyden chamber assay, and also increased endothelial tube formation in a Matrigel assay. These responses were both abolished in cells depleted of SK-1.

CONCLUSIONS AND IMPLICATIONS

These data show that NO donors up-regulate specifically SK-1 expression and activity in human endothelial cells, and SK-1 in turn critically contributes to the migratory capability and tube formation of endothelial cells. Thus, SK-1 may be considered an attractive novel target to interfere with pathological processes involving angiogenesis.

p63RhoGEF--a key mediator of angiotensin II-dependent signaling and processes in vascular smooth muscle cells

The purpose of our study was to investigate the role of endogenous p63RhoGEF in G(q/11)-dependent RhoA activation and signaling in rat aortic smooth muscle cells (RASMCs). Therefore, we studied the expression and subcellular localization in freshly isolated RASMCs and performed loss of function experiments to analyze its contribution to RhoGTPase activation and functional responses such as proliferation and contraction. By this, we could show that p63RhoGEF is endogenously expressed in RASMCs and acts there as the dominant mediator of the fast angiotensin II (ANG II)-dependent but not of the sphingosine-1-phosphate (S(1)P)-dependent RhoA activation. p63RhoGEF is not an activator of the concomitant Rac1 activation and functions independently of caveolae. The knockdown of endogenous p63RhoGEF significantly reduced the mitogenic response of ANG II, abolished ANG II-induced stress fiber formation and cell elongation in 2-D culture, and impaired the ANG II-driven contraction in a collagen-based 3-D model. In conclusion, our data provide for the first time evidence that p63RhoGEF is an important mediator of ANG II-dependent RhoA activation in RASMCs and therewith a leading actor in the subsequently triggered cellular processes, such as proliferation and contraction.

p21-activated kinase 1 participates in vascular remodeling in vitro and in vivo

Vascular smooth muscle cell hypertrophy, proliferation, or migration occurs in hypertension, atherosclerosis, and restenosis after angioplasty, leading to pathophysiological vascular remodeling. Angiotensin II and platelet-derived growth factor are well-known participants of vascular remodeling and activate a myriad of downstream protein kinases, including p21-activated protein kinase (PAK1). PAK1, an effector kinase of small GTPases, phosphorylates several substrates to regulate cytoskeletal reorganization. However, the exact role of PAK1 activation in vascular remodeling remains to be elucidated. Here, we have hypothesized that PAK1 is a critical target of intervention for the prevention of vascular remodeling. Adenoviral expression of dominant-negative PAK1 inhibited angiotensin II-stimulated vascular smooth muscle cell migration. It also inhibited vascular smooth muscle cell proliferation induced by platelet-derived growth factor. PAK1 was activated in neointima of the carotid artery after balloon injury in the rat. Moreover, marked inhibition of the neointima hyperplasia was observed in a dominant-negative PAK1 adenovirus-treated carotid artery after the balloon injury. Taken together, these results suggest that PAK1 is involved in both angiotensin II and platelet-derived growth factor-mediated vascular smooth muscle cell remodeling, and inactivation of PAK1 in vivo could be effective in preventing pathophysiological vascular remodeling.