Cysteinyl leukotriene 1 receptors as novel mechanosensors mediating myogenic tone together with angiotensin II type 1 receptors-brief report

Magnetogenetics as a promising tool for controlling cellular signaling pathways

Magnetogenetics emerges as a transformative approach for modulating cellular signaling pathways through the strategic application of magnetic fields and nanoparticles. This technique leverages the unique properties of magnetic nanoparticles (MNPs) to induce mechanical or thermal stimuli within cells, facilitating the activation of mechano- and thermosensitive proteins without the need for traditional ligand-receptor interactions. Unlike traditional modalities that often require invasive interventions and lack precision in targeting specific cellular functions, magnetogenetics offers a non-invasive alternative with the capacity for deep tissue penetration and the potential for targeting a broad spectrum of cellular processes. This review underscores magnetogenetics' broad applicability, from steering stem cell differentiation to manipulating neuronal activity and immune responses, highlighting its potential in regenerative medicine, neuroscience, and cancer therapy. Furthermore, the review explores the challenges and future directions of magnetogenetics, including the development of genetically programmed magnetic nanoparticles and the integration of magnetic field-sensitive cells for in vivo applications. Magnetogenetics stands at the forefront of cellular manipulation technologies, offering novel insights into cellular signaling and opening new avenues for therapeutic interventions.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Arterial myogenic response and aging

The arterial myogenic response is an inherent property of resistance arteries. Myogenic tone is crucial for maintaining a relatively constant blood flow in response to changes in intraluminal pressure and protects delicate organs from excessive blood flow. Although this fundamental physiological phenomenon has been extensively studied, the underlying molecular mechanisms are largely unknown. Recent studies identified a crucial role of mechano-activated angiotensin II type 1 receptors (AT1R) in this process. The development of myogenic response is affected by aging. In this review, we summarize recent progress made to understand the role of AT1R and other mechanosensors in the control of arterial myogenic response. We discuss age-related alterations in myogenic response and possible underlying mechanisms and implications for healthy aging.

Gq Signaling in Autophagy Control: Between Chemical and Mechanical Cues

All processes in human physiology relies on homeostatic mechanisms which require the activation of specific control circuits to adapt the changes imposed by external stimuli. One of the critical modulators of homeostatic balance is autophagy, a catabolic process that is responsible of the destruction of long-lived proteins and organelles through a lysosome degradative pathway. Identification of the mechanism underlying autophagic flux is considered of great importance as both protective and detrimental functions are linked with deregulated autophagy. At the mechanistic and regulatory levels, autophagy is activated in response to diverse stress conditions (food deprivation, hyperthermia and hypoxia), even a novel perspective highlight the potential role of physical forces in autophagy modulation. To understand the crosstalk between all these controlling mechanisms could give us new clues about the specific contribution of autophagy in a wide range of diseases including vascular disorders, inflammation and cancer. Of note, any homeostatic control critically depends in at least two additional and poorly studied interdependent components: a receptor and its downstream effectors. Addressing the selective receptors involved in autophagy regulation is an open question and represents a new area of research in this field. G-protein coupled receptors (GPCRs) represent one of the largest and druggable targets membrane receptor protein superfamily. By exerting their action through G proteins, GPCRs play fundamental roles in the control of cellular homeostasis. Novel studies have shown Gαq, a subunit of heterotrimeric G proteins, as a core modulator of mTORC1 and autophagy, suggesting a fundamental contribution of Gαq-coupled GPCRs mechanisms in the control of this homeostatic feedback loop. To address how GPCR-G proteins machinery integrates the response to different stresses including oxidative conditions and mechanical stimuli, could provide deeper insight into new signaling pathways and open potential and novel therapeutic strategies in the modulation of different pathological conditions.

Myogenic Vasoconstriction Requires Canonical Gq/11 Signaling of the Angiotensin II Type 1 Receptor

Background Blood pressure and tissue perfusion are controlled in part by the level of intrinsic (myogenic) arterial tone. However, many of the molecular determinants of this response are unknown. We previously found that mice with targeted disruption of the gene encoding the angiotensin II type 1a receptor (AT1AR) (Agtr1a), the major murine angiotensin II type 1 receptor (AT1R) isoform, showed reduced myogenic tone; however, uncontrolled genetic events (in this case, gene ablation) can lead to phenotypes that are difficult or impossible to interpret. Methods and Results We tested the mechanosensitive function of AT1R using tamoxifen-inducible smooth muscle-specific AT1aR knockout (smooth muscle-Agtr1a^-/-) mice and studied downstream signaling cascades mediated by G_q/11 and/or β-arrestins. FR900359, Sar1Ile4Ile8-angiotensin II (SII), TRV120027 and TRV120055 were used as selective G_q/11 inhibitor and biased agonists to activate noncanonical β-arrestin and canonical G_q/11 signaling of the AT1R, respectively. Myogenic and Ang II-induced constrictions were diminished in the perfused renal vasculature, mesenteric and cerebral arteries of smooth muscle-Agtr1a^-/- mice. Similar effects were observed in arteries of global mutant Agtr1a^-/- but not Agtr1b^-/- mice. FR900359 decreased myogenic tone and angiotensin II-induced constrictions whereas selective biased targeting of AT1R-β-arrestin signaling pathways had no effects. Conclusions This study demonstrates that myogenic arterial constriction requires G_q/11-dependent signaling pathways of mechanoactivated AT1R but not G protein-independent, noncanonical pathways in smooth muscle cells.

Vascular Smooth Muscle Cells Mechanosensitive Regulators and Vascular Remodeling

Blood vessels are subjected to mechanical loads of pressure and flow, inducing smooth muscle circumferential and endothelial shear stresses. The perception and response of vascular tissue and living cells to these stresses and the microenvironment they are exposed to are critical to their function and survival. These mechanical stimuli not only cause morphological changes in cells and vessel walls but also can interfere with biochemical homeostasis, leading to vascular remodeling and dysfunction. However, the mechanisms underlying how these stimuli affect tissue and cellular function, including mechanical stimulation-induced biochemical signaling and mechanical transduction that relies on cytoskeletal integrity, are unclear. This review focuses on signaling pathways that regulate multiple biochemical processes in vascular mesangial smooth muscle cells in response to circumferential stress and are involved in mechanosensitive regulatory molecules in response to mechanotransduction, including ion channels, membrane receptors, integrins, cytoskeletal proteins, nuclear structures, and cascades. Mechanoactivation of these signaling pathways is closely associated with vascular remodeling in physiological or pathophysiological states.

Calcium-Dependent Ion Channels and the Regulation of Arteriolar Myogenic Tone

Arterioles in the peripheral microcirculation regulate blood flow to and within tissues and organs, control capillary blood pressure and microvascular fluid exchange, govern peripheral vascular resistance, and contribute to the regulation of blood pressure. These important microvessels display pressure-dependent myogenic tone, the steady state level of contractile activity of vascular smooth muscle cells (VSMCs) that sets resting arteriolar internal diameter such that arterioles can both dilate and constrict to meet the blood flow and pressure needs of the tissues and organs that they perfuse. This perspective will focus on the Ca²⁺-dependent ion channels in the plasma and endoplasmic reticulum membranes of arteriolar VSMCs and endothelial cells (ECs) that regulate arteriolar tone. In VSMCs, Ca²⁺-dependent negative feedback regulation of myogenic tone is mediated by Ca²⁺-activated K⁺ (BK_Ca) channels and also Ca²⁺-dependent inactivation of voltage-gated Ca²⁺ channels (VGCC). Transient receptor potential subfamily M, member 4 channels (TRPM4); Ca²⁺-activated Cl⁻ channels (CaCCs; TMEM16A/ANO1), Ca²⁺-dependent inhibition of voltage-gated K⁺ (K_V) and ATP-sensitive K⁺ (K_ATP) channels; and Ca²⁺-induced-Ca²⁺ release through inositol 1,4,5-trisphosphate receptors (IP₃Rs) participate in Ca²⁺-dependent positive-feedback regulation of myogenic tone. Calcium release from VSMC ryanodine receptors (RyRs) provide negative-feedback through Ca²⁺-spark-mediated control of BK_Ca channel activity, or positive-feedback regulation in cooperation with IP₃Rs or CaCCs. In some arterioles, VSMC RyRs are silent. In ECs, transient receptor potential vanilloid subfamily, member 4 (TRPV4) channels produce Ca²⁺ sparklets that activate IP₃Rs and intermediate and small conductance Ca²⁺ activated K⁺ (IK_Ca and sK_Ca) channels causing membrane hyperpolarization that is conducted to overlying VSMCs producing endothelium-dependent hyperpolarization and vasodilation. Endothelial IP₃Rs produce Ca²⁺ pulsars, Ca²⁺ wavelets, Ca²⁺ waves and increased global Ca²⁺ levels activating EC sK_Ca and IK_Ca channels and causing Ca²⁺-dependent production of endothelial vasodilator autacoids such as NO, prostaglandin I₂ and epoxides of arachidonic acid that mediate negative-feedback regulation of myogenic tone. Thus, Ca²⁺-dependent ion channels importantly contribute to many aspects of the regulation of myogenic tone in arterioles in the microcirculation.

Myogenic Tone in Peripheral Resistance Arteries and Arterioles: The Pressure Is On!

Resistance arteries and downstream arterioles in the peripheral microcirculation contribute substantially to peripheral vascular resistance, control of blood pressure, the distribution of blood flow to and within tissues, capillary pressure, and microvascular fluid exchange. A hall-mark feature of these vessels is myogenic tone. This pressure-induced, steady-state level of vascular smooth muscle activity maintains arteriolar and resistance artery internal diameter at 50–80% of their maximum passive diameter providing these vessels with the ability to dilate, reducing vascular resistance, and increasing blood flow, or constrict to produce the opposite effect. Despite the central importance of resistance artery and arteriolar myogenic tone in cardiovascular physiology and pathophysiology, our understanding of signaling pathways underlying this key microvascular property remains incomplete. This brief review will present our current understanding of the multiple mechanisms that appear to underlie myogenic tone, including the roles played by G-protein-coupled receptors, a variety of ion channels, and several kinases that have been linked to pressure-induced, steady-state activity of vascular smooth muscle cells (VSMCs) in the wall of resistance arteries and arterioles. Emphasis will be placed on the portions of the signaling pathways underlying myogenic tone for which there is lack of consensus in the literature and areas where our understanding is clearly incomplete.

Regulation of blood flow in small arteries: mechanosensory events underlying myogenic vasoconstriction

As blood flow is proportional to the fourth power of the vascular radius small changes in the diameter of resistance arteries/arterioles following an increase in intraluminal pressure would be expected to substantially increase blood flow. However, arteriolar myocytes display an intrinsic ability to locally regulate blood flow according to metabolic demands by tuning the diameter of small arteries in response to local changes in he-modynamics. Critical to this, observations were made more than 100 years ago that mechanosensitive small arteries exhibit the "myogenic response" or pressure-induced vasoconstriction or vasodilation in re-sponse to increased or decreased intravascular pressure, respectively. Although cellular mechanisms underlying the myogenic response have now been studied extensively, the precise cellular mechanisms under-lying this intriguing phenomenon still remain uncertain. In particular, the biological machinery that senses changes in intravascular pressure in vascular smooth muscle cells have not been unquestionably identified and remain a significant issue in vascular biology to be fully elucidated. As such, this brief review focuses on putative mechanosensors that have been proposed to contribute to myogenic vasoreactivity. Specific attention is paid to the roles of integrins, G protein-coupled receptors, and cadherins.

Helix 8 is the essential structural motif of mechanosensitive GPCRs

G-protein coupled receptors (GPCRs) are versatile cellular sensors for chemical stimuli, but also serve as mechanosensors involved in various (patho)physiological settings like vascular regulation, cardiac hypertrophy and preeclampsia. However, the molecular mechanisms underlying mechanically induced GPCR activation have remained elusive. Here we show that mechanosensitive histamine H₁ receptors (H₁Rs) are endothelial sensors of fluid shear stress and contribute to flow-induced vasodilation. At the molecular level, we observe that H₁Rs undergo stimulus-specific patterns of conformational changes suggesting that mechanical forces and agonists induce distinct active receptor conformations. GPCRs lacking C-terminal helix 8 (H8) are not mechanosensitive, and transfer of H8 to non-responsive GPCRs confers, while removal of H8 precludes, mechanosensitivity. Moreover, disrupting H8 structural integrity by amino acid exchanges impairs mechanosensitivity. Altogether, H8 is the essential structural motif endowing GPCRs with mechanosensitivity. These findings provide a mechanistic basis for a better understanding of the roles of mechanosensitive GPCRs in (patho)physiology.

GPCRs are versatile cellular sensors for chemical stimuli but the molecular mechanisms underlying mechanically induced GPCR activation have remained elusive. Here authors identify the C-terminal helix 8 (H8) as the essential structural motif endowing H₁R and other GPCRs with mechanosensitivity.

Myogenic vasoconstriction requires G12/G13 and LARG to maintain local and systemic vascular resistance

Myogenic vasoconstriction is an autoregulatory function of small arteries. Recently, G-protein-coupled receptors have been involved in myogenic vasoconstriction, but the downstream signalling mechanisms and the in-vivo-function of this myogenic autoregulation are poorly understood. Here, we show that small arteries from mice with smooth muscle-specific loss of G₁₂/G₁₃ or the Rho guanine nucleotide exchange factor ARHGEF12 have lost myogenic vasoconstriction. This defect was accompanied by loss of RhoA activation, while vessels showed normal increases in intracellular [Ca²⁺]. In the absence of myogenic vasoconstriction, perfusion of peripheral organs was increased, systemic vascular resistance was reduced and cardiac output and left ventricular mass were increased. In addition, animals with defective myogenic vasoconstriction showed aggravated hypotension in response to endotoxin. We conclude that G₁₂/G₁₃- and Rho-mediated signaling plays a key role in myogenic vasoconstriction and that myogenic tone is required to maintain local and systemic vascular resistance under physiological and pathological condition.

Role of age, Rho-kinase 2 expression, and G protein-mediated signaling in the myogenic response in mouse small mesenteric arteries

The myogenic response (MR) and myogenic tone (MT) in resistance vessels is crucial for maintaining peripheral vascular resistance and blood flow autoregulation. Development of MT involves G protein-coupled receptors, and may be affected by aging.

AIMS

(1) to estimate the mesenteric blood flow in myogenically active small mesenteric arteries; (2) to investigate the signaling from Gαq/11 and/or Gα12 activation to MT development; (3) to investigate the role of Rho-kinase 2 and aging on MT in mesenteric resistance arteries.

METHODS

we used pressure myography, quantitative real-time PCR, and immunolocalization to study small (<200 μm) mesenteric arteries (SMA) from young, mature adult, and middle aged mice.

RESULTS

Poiseuille flow calculations indicated autoregulation of blood flow at 60-120 mm Hg arterial pressure. Gαq/11 and Gα12 were abundantly expressed at the mRNA and protein levels in SMA. The Gαq/11 inhibitor YM-254890 suppressed MT development, and the Phosholipase C inhibitors U73122 and ET-18-OCH3 robustly inhibited it. We found an age-dependent increase in ROCK2 mRNA expression, and in basal MT. The specific ROCK2 inhibitor KD025 robustly inhibited MT in SMAs in all mice with an age-dependent variation in KD025 sensitivity. The inhibitory effect of KD025 was not prevented by the L-type Ca2+ channel activator BayK 8644. KD025 reversibly inhibited MT and endothelin-1 vasoconstriction in small pial arteries from Göttingen minipigs.

CONCLUSIONS

MT development in SMAs occurs through a Gαq/11 /PLC/Ca2+ -dependent pathway, and is maintained via ROCK2-mediated Ca2+ sensitization. Increased MT at mature adulthood can be explained by increased ROCK2 expression/activity.

Deletion of the EGF receptor in vascular smooth muscle cells prevents chronic angiotensin II-induced arterial wall stiffening and media thickening

AIM

In vivo vascular smooth muscle cell (VSMC) EGF receptor (EGFR) contributes to acute angiotensin II (AII) effects on vascular tone and blood pressure. The ubiquitously expressed EGFR has been implicated in vascular remodelling preceding end-organ damage by pharmacological inhibition, and AII signalling in cultured vascular cells is partly EGFR-dependent. However, the role of VSMC-EGFR in vivo during AII-induced pathophysiological processes is not known.

METHODS

This study assesses the in vivo relevance of VSMC-EGFR during chronic AII challenge without further stressors, using a mouse model with inducible, VSMC-specific EGFR knock out (VSMC-EGFR-KO). In these mice functional and structural vascular, renal and cardiac effects or biomarkers were investigated in vivo and ex vivo.

RESULTS

Vascular smooth muscle cell-EGFR-KO prevented AII-induced media hypertrophy of mesenteric arteries, renal arterioles and the aorta, VSMC ERK1/2-phosphorylation as well as the impairment of vascular compliance. Furthermore, induction of vascular fibrosis, creatinineamia, renal interstitial fibrosis as well as the increase in fractional water excretion was prevented. AII-induced increase in systolic blood pressure was mitigated. By contrast, endothelial dysfunction, induction of vascular inflammatory marker mRNA and albuminuria were not inhibited. Cardiac and cardiomyocyte hypertrophy were also not prevented by VSMC-EGFR-KO.

CONCLUSION

Vascular smooth muscle cell-EGFRs are relevant for pathological AII action in vivo. Our data show in vivo and ex vivo the necessity of VSMC-EGFR for AII-induced structural and functional vascular remodelling, not including endothelial dysfunction. Hereby, VSMC-EGFR gains importance for complete AII-induced renal end-organ damage succeeding vascular remodelling.

Dietary canolol protects the heart against the deleterious effects induced by the association of rapeseed oil, vitamin E and coenzyme Q10 in the context of a high-fat diet

Background

Obesity progressively leads to cardiac failure. Omega-3 polyunsaturated fatty acids (PUFA) have been shown to have cardio-protective effects in numerous pathological situations. It is not known whether rapeseed oil, which contains α-linolenic acid (ALA), has a similar protective effect. Omega-3 PUFAs are sensitive to attack by reactive oxygen species (ROS), and lipid peroxidation products could damage cardiac cells. We thus tested whether dietary refined rapeseed oil (RSO) associated with or without different antioxidants (vitamin E, coenzyme Q10 and canolol) is cardio-protective in a situation of abdominal obesity.

Methods

Sixty male Wistar rats were subdivided into 5 groups. Each group was fed a specific diet for 11 weeks: a low-fat diet (3% of lipids, C diet) with compositionally-balanced PUFAs; a high-fat diet rich in palm oil (30% of lipids, PS diet); the PS diet in which 40% of lipids were replaced by RSO (R diet); the R diet supplemented with coenzyme Q10 (CoQ10) and vitamin E (RTC diet); and the RTC diet supplemented with canolol (RTCC diet). At the end of the diet period, the rats were sacrificed and the heart was collected and immediately frozen. Fatty acid composition of cardiac phospholipids was then determined. Several features of cardiac function (fibrosis, inflammation, oxidative stress, apoptosis, metabolism, mitochondrial biogenesis) were also estimated.

Results

Abdominal obesity reduced cardiac oxidative stress and apoptosis rate by increasing the proportion of arachidonic acid (AA) in membrane phospholipids. Dietary RSO had the same effect, though it normalized the proportion of AA. Adding vitamin E and CoQ10 in the RSO-rich high fat diet had a deleterious effect, increasing fibrosis by increasing angiotensin-2 receptor-1b (Ag2R-1b) mRNA expression. Overexpression of these receptors triggers coronary vasoconstriction, which probably induced ischemia. Canolol supplementation counteracted this deleterious effect by reducing coronary vasoconstriction.

Conclusion

Canolol was found to counteract the fibrotic effects of vitamin E + CoQ10 on cardiac fibrosis in the context of a high-fat diet enriched with RSO. This effect occurred through a restoration of cardiac Ag2R-1b mRNA expression and decreased ischemia.

TRPV4 (Transient Receptor Potential Vanilloid 4) Channel-Dependent Negative Feedback Mechanism Regulates Gq Protein-Coupled Receptor-Induced Vasoconstriction

OBJECTIVE

Several physiological stimuli activate smooth muscle cell (SMC) G_qPCRs (G_q protein-coupled receptors) to cause vasoconstriction. As a protective mechanism against excessive vasoconstriction, SMC G_qPCR stimulation invokes endothelial cell vasodilatory signaling. Whether Ca²⁺ influx in endothelial cells contributes to the regulation of G_qPCR-induced vasoconstriction remains unknown. Ca²⁺ influx through TRPV4 (transient receptor potential vanilloid 4) channels is a key regulator of endothelium-dependent vasodilation. We hypothesized that SMC G_qPCR stimulation engages endothelial TRPV4 channels to limit vasoconstriction.

APPROACH AND RESULTS

Using high-speed confocal microscopy to record unitary Ca²⁺ influx events through TRPV4 channels (TRPV4 sparklets), we report that activation of SMC α₁ARs (alpha₁-adrenergic receptors) with phenylephrine or thromboxane A₂ receptors with U46619 stimulated TRPV4 sparklets in the native endothelium from mesenteric arteries. Activation of endothelial TRPV4 channels did not require an increase in Ca²⁺ as indicated by the lack of effect of L-type Ca²⁺ channel activator or chelator of intracellular Ca²⁺ EGTA-AM. However, gap junction communication between SMCs and endothelial cells was required for phenylephrine activation or U46619 activation of endothelial TRPV4 channels. Lowering inositol 1,4,5-trisphosphate levels with phospholipase C inhibitor or lithium chloride suppressed phenylephrine activation of endothelial TRPV4 sparklets. Moreover, uncaging inositol 1,4,5-trisphosphate profoundly increased TRPV4 sparklet activity. In pressurized arteries, phenylephrine-induced vasoconstriction was followed by a slow, TRPV4-dependent vasodilation, reflecting activation of negative regulatory mechanism. Consistent with these data, phenylephrine induced a significantly higher increase in blood pressure in TRPV4^-/- mice.

CONCLUSIONS

These results demonstrate that SMC G_qPCR stimulation triggers inositol 1,4,5-trisphosphate-dependent activation of endothelial TRPV4 channels to limit vasoconstriction.

Angiotensin II Type 1 Receptor Mechanoactivation Involves RGS5 (Regulator of G Protein Signaling 5) in Skeletal Muscle Arteries: Impaired Trafficking of RGS5 in Hypertension

Studies suggest that arteriolar pressure-induced vasoconstriction can be initiated by GPCRs (G protein-coupled receptors), including the AT₁R (angiotensin II type 1 receptor). This raises the question, are such mechanisms regulated by negative feedback? The present studies examined whether RGS (regulators of G protein signaling) proteins in vascular smooth muscle cells are colocalized with the AT₁R when activated by mechanical stress or angiotensin II and whether this modulates AT₁R-mediated vasoconstriction. To determine whether activation of the AT₁R recruits RGS5, an in situ proximity ligation assay was performed in primary cultures of cremaster muscle arteriolar vascular smooth muscle cells treated with angiotensin II or hypotonic solution in the absence or presence of candesartan (an AT₁R blocker). Proximity ligation assay results revealed a concentration-dependent increase in trafficking/translocation of RGS5 toward the activated AT₁R, which was attenuated by candesartan. In intact arterioles, knockdown of RGS5 enhanced constriction to angiotensin II and augmented myogenic responses to increased intraluminal pressure. Myogenic constriction was attenuated to a higher degree by candesartan in RGS5 siRNA-transfected arterioles, consistent with RGS5 contributing to downregulation of AT₁R-mediated signaling. Further, translocation of RGS5 was impaired in vascular smooth muscle cells of spontaneously hypertensive rats. This is consistent with dysregulated (RGS5-mediated) AT₁R signaling that could contribute to excessive vasoconstriction in hypertension. In intact vessels, candesartan reduced myogenic vasoconstriction to a greater extent in spontaneously hypertensive rats compared with controls. Collectively, these findings suggest that AT₁R activation results in translocation of RGS5 toward the plasma membrane, limiting AT₁R-mediated vasoconstriction through its role in G_q/11 protein-dependent signaling.

Smooth muscle cell-specific Tgfbr1 deficiency promotes aortic aneurysm formation by stimulating multiple signaling events

Transforming growth factor (TGF)-β signaling disorder has emerged as a common molecular signature for aortic aneurysm development. The timing of postnatal maturation plays a key role in dictating the biological outcome of TGF-β signaling disorders in the aortic wall. In this study, we investigated the impact of deficiency of TGFβ receptors on the structural homeostasis of mature aortas. We used an inducible Cre-loxP system driven by a Myh11 promoter to delete Tgfbr1, Tgfbr2, or both in smooth muscle cells (SMCs) of adult mice. TGFBR1 deficiency resulted in rapid and severe aneurysmal degeneration, with 100% penetrance of ascending thoracic aortas, whereas TGFBR2 deletion only caused mild aortic pathology with low (26%) lesion prevalence. Removal of TGFBR2 attenuated the aortic pathology caused by TGFBR1 deletion and correlated with a reduction of early ERK phosphorylation. In addition, the production of angiotensin (Ang)-converting enzyme was upregulated in TGFBR1 deficient aortas at the early stage of aneurysmal degeneration. Inhibition of ERK phosphorylation or blockade of AngII type I receptor AT1R prevented aneurysmal degeneration of TGFBR1 deficient aortas. In conclusion, loss of SMC-Tgfbr1 triggers multiple deleterious pathways, including abnormal TGFBR2, ERK, and AngII/AT1R signals that disrupt aortic wall homeostasis to cause aortic aneurysm formation.

Mechanical activation of angiotensin II type 1 receptors causes actin remodelling and myogenic responsiveness in skeletal muscle arterioles

KEY POINTS

Candesartan, an inverse agonist of the type 1 angiotensin II receptor (AT₁ R), causes a concentration-dependent inhibition of pressure-dependent myogenic tone consistent with previous reports of mechanosensitivity of this G protein-coupled receptor. Mechanoactivation of the AT₁ R occurs independently of local angiotensin II production and the type 2 angiotensin receptor. Mechanoactivation of the AT₁ R stimulates actin polymerization by a protein kinase C-dependent mechanism, but independently of a change in intracellular Ca²⁺ . Using atomic force microscopy, changes in single vascular smooth muscle cell cortical actin are observed to remodel following mechanoactivation of the AT₁ R.

ABSTRACT

The G_q/11 protein-coupled angiotensin II type 1 receptor (AT₁ R) has been shown to be activated by mechanical stimuli. In the vascular system, evidence supports the AT₁ R being a mechanosensor that contributes to arteriolar myogenic constriction. The aim of this study was to determine if AT₁ R mechanoactivation affects myogenic constriction in skeletal muscle arterioles and to determine underlying cellular mechanisms. Using pressure myography to study rat isolated first-order cremaster muscle arterioles the AT₁ R inhibitor candesartan (10^-7 -10^-5  m) showed partial but concentration-dependent inhibition of myogenic reactivity. Inhibition was demonstrated by a rightward shift in the pressure-diameter relationship over the intraluminal pressure range, 30-110 mmHg. Pressure-induced changes in global vascular smooth muscle intracellular Ca²⁺ (using Fura-2) were similar in the absence or presence of candesartan, indicating that AT₁ R-mediated myogenic constriction relies on Ca²⁺ -independent downstream signalling. The diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) reversed the inhibitory effect of candesartan, while this rescue effect was prevented by the protein kinase C (PKC) inhibitor GF 109203X. Both candesartan and PKC inhibition caused increased G-actin levels, as determined by Western blotting of vessel lysates, supporting involvement of cytoskeletal remodelling. At the single vascular smooth muscle cell level, atomic force microscopy showed that cell swelling (stretch) with hypotonic buffer also caused thickening of cortical actin fibres and this was blocked by candesartan. Collectively, the present studies support growing evidence for novel modes of activation of the AT₁ R in arterioles and suggest that mechanically activated AT₁ R generates diacylglycerol, which in turn activates PKC which induces the actin cytoskeleton reorganization that is required for pressure-induced vasoconstriction.

Role of angiotensin II type 1a receptor in renal injury induced by deoxycorticosterone acetate-salt hypertension

The aim of this study was to investigate the in vivo role of angiotensin II type 1a (AT1a) receptor in renal damage as a result of hypertension by using transgenic mice with AT1a receptor gene disruption. Transgenic mice that express human liver-type fatty acid binding protein (L-FABP) with or without disruption of the AT1a receptor gene (L-FABP^+/− AT1a^−/−, and L-FABP^+/− AT1a^+/+, respectively) were used with urinary L-FABP as an indicator of tubulointerstitial damage. Those female mice were administered subcutaneously deoxycorticosterone acetate (DOCA)–salt tablets plus drinking water that contained 1% saline for 28 d after uninephrectomy. In L-FABP^+/− AT1a^+/+ mice that received DOCA-salt treatment, hypertension was induced and slight expansion of glomerular area, glomerular sclerosis, and tubulointerstitial damage were observed. In L-FABP^+/− AT1a^−/− mice that received DOCA-salt treatment, hypertension was similarly induced and the degree of glomerular damage was significantly more severe than in L-FABP^+/− AT1a^+/+-DOCA mice. Urinary L-FABP levels were significantly higher in L-FABP^+/− AT1a^−/−-DOCA mice compared with those in L-FABP^+/− AT1a^+/+-DOCA mice. Hydralazine treatment significantly attenuated renal damage that was found in L-FABP^+/− AT1a^−/−-DOCA mice along with a reduction in blood pressure. In summary, activation of the AT1a receptor may contribute to maintenance of the glomerular structure against hypertensive renal damage.—Hisamichi, M., Kamijo-Ikemori, A., Sugaya, T., Ichikawa, D., Natsuki, T., Hoshino, S., Kimura, K., Shibagaki, Y. Role of angiotensin II type 1a receptor in renal injury induced by deoxycorticosterone acetate–salt hypertension.

Arteriolar oxygen reactivity: where is the sensor and what is the mechanism of action?

Arterioles in the peripheral microcirculation are exquisitely sensitive to changes in PO2 in their environment: increases in PO2 cause vasoconstriction while decreases in PO2 result in vasodilatation. However, the cell type that senses O2 (the O2 sensor) and the signalling pathway that couples changes in PO2 to changes in arteriolar tone (the mechanism of action) remain unclear. Many (but not all) ex vivo studies of isolated cannulated resistance arteries and large, first-order arterioles support the hypothesis that these vessels are intrinsically sensitive to PO2 with the smooth muscle, endothelial cells, or red blood cells serving as the O2 sensor. However, in situ studies testing these hypotheses in downstream arterioles have failed to find evidence of intrinsic O2 sensitivity, and instead have supported the idea that extravascular cells sense O2 . Similarly, ex vivo studies of isolated, cannulated resistance arteries and large first-order arterioles support the hypotheses that O2 -dependent inhibition of production of vasodilator cyclooxygenase products or O2 -dependent destruction of nitric oxide mediates O2 reactivity of these upstream vessels. In contrast, most in vivo studies of downstream arterioles have disproved these hypotheses and instead have provided evidence supporting the idea that O2 -dependent production of vasoconstrictors mediates arteriolar O2 reactivity, with significant regional heterogeneity in the specific vasoconstrictor involved. Oxygen-induced vasoconstriction may serve as a protective mechanism to reduce the oxidative burden to which a tissue is exposed, a process that is superimposed on top of the local mechanisms which regulate tissue blood flow to meet a tissue's metabolic demand.

Central Role of P2Y6 UDP Receptor in Arteriolar Myogenic Tone

OBJECTIVE

Myogenic tone (MT) of resistance arteries ensures autoregulation of blood flow in organs and relies on the intrinsic property of smooth muscle to contract in response to stretch. Nucleotides released by mechanical strain on cells are responsible for pleiotropic vascular effects, including vasoconstriction. Here, we evaluated the contribution of extracellular nucleotides to MT.

APPROACH AND RESULTS

We measured MT and the associated pathway in mouse mesenteric resistance arteries using arteriography for small arteries and molecular biology. Of the P2 receptors in mouse mesenteric resistance arteries, mRNA expression of P2X1 and P2Y6 was dominant. P2Y6 fully sustained UDP/UTP-induced contraction (abrogated in P2ry6(-/-) arteries). Preventing nucleotide hydrolysis with the ectonucleotidase inhibitor ARL67156 enhanced pressure-induced MT by 20%, whereas P2Y6 receptor blockade blunted MT in mouse mesenteric resistance arteries and human subcutaneous arteries. Despite normal hemodynamic parameters, P2ry6(-/-) mice were protected against MT elevation in myocardial infarction-induced heart failure. Although both P2Y6 and P2Y2 receptors contributed to calcium mobilization, P2Y6 activation was mandatory for RhoA-GTP binding, myosin light chain, P42-P44, and c-Jun N-terminal kinase phosphorylation in arterial smooth muscle cells. In accordance with the opening of a nucleotide conduit in pressurized arteries, MT was altered by hemichannel pharmacological inhibitors and impaired in Cx43(+/-) and P2rx7(-/-) mesenteric resistance arteries.

CONCLUSIONS

Signaling through P2 nucleotide receptors contributes to MT. This mechanism encompasses the release of nucleotides coupled to specific autocrine/paracrine activation of the uracil nucleotide P2Y6 receptor and may contribute to impaired tissue perfusion in cardiovascular diseases.

Cytochrome P450 and Lipoxygenase Metabolites on Renal Function

Arachidonic acid metabolites have a myriad of biological actions including effects on the kidney to alter renal hemodynamics and tubular transport processes. Cyclooxygenase metabolites are products of an arachidonic acid enzymatic pathway that has been extensively studied in regards to renal function. Two lesser-known enzymatic pathways of arachidonic acid metabolism are the lipoxygenase (LO) and cytochrome P450 (CYP) pathways. The importance of LO and CYP metabolites to renal hemodynamics and tubular transport processes is now being recognized. LO and CYP metabolites have actions to alter renal blood flow and glomerular filtration rate. Proximal and distal tubular sodium transport and fluid and electrolyte homeostasis are also significantly influenced by renal CYP and LO levels. Metabolites of the LO and CYP pathways also have renal actions that influence renal inflammation, proliferation, and apoptotic processes at vascular and epithelial cells. These renal LO and CYP pathway actions occur through generation of specific metabolites and cell-signaling mechanisms. Even though the renal physiological importance and actions for LO and CYP metabolites are readily apparent, major gaps remain in our understanding of these lipid mediators to renal function. Future studies will be needed to fill these major gaps regarding LO and CYP metabolites on renal function.