Mechanosensitive Gq/11Protein-Coupled Receptors Mediate Myogenic Vasoconstriction

Phosphodiesterases Mediate the Augmentation of Myogenic Constriction by Inhibitory G Protein Signaling and is Negatively Modulated by the Dual Action of RGS2 and 5

G protein regulation by regulators of G protein signaling (RGS) proteins play a key role in vascular tone maintenance. The loss of Gi/o and Gq/11 regulation by RGS2 and RGS5 in non-pregnant mice is implicated in augmented vascular tone and decreased uterine blood flow (UBF). RGS2 and 5 are closely related and co-expressed in uterine arteries (UA). However, whether and how RGS2 and 5 coordinate their regulatory activities to finetune G protein signaling and regulate vascular tone are unclear. Here, we determined how the integrated activity of RGS2 and 5 modulates vascular tone to promote UBF. Using ultrasonography and pressure myography, we examined uterine hemodynamics and myogenic tone (MT) of UA of wild type (WT), Rgs2-/-, Rgs5-/-, and Rgs2/5 dbKO mice. We found that MT was reduced in Rgs5-/- relative to WT or Rgs2-/- UA. Activating Gi/o with dopamine increased, whereas exogenous cAMP decreased MT in Rgs5-/- UA to levels in WT UA. Dual deletion of Rgs2 and 5 abolished the reduced MT due to the absence of Rgs5 and enhanced dopamine-induced Gi/o effects in Rgs2/5 dbKO UA. Conversely, and as in WT UA, Gi/o inhibition with pertussis toxin or exogenous cAMP decreased MT in Rgs2/5 dbKO to levels in Rgs5-/- UA. Inhibition of phosphodiesterases (PDE) concentration-dependently decreased and normalized MT in all genotypes, and blocked dopamine-induced MT augmentation in Rgs2-/-, Rgs5-/-, and Rgs2/5 dbKO UA. We conclude that Gi/o augments UA MT in the absence of RGS2 by a novel mechanism involving PDE-mediated inhibition of cAMP-dependent vasodilatation..

Time to eRAASe chronic inflammation: current advances and future perspectives on renin-angiotensin-aldosterone-system and chronic intestinal inflammation in dogs and humans

Chronic idiopathic intestinal inflammation is an increasing worldwide problem that affects companion animals, especially dogs, and human patients. Although these disease entities have been intensely investigated recently, many questions remain, and alternative therapeutic options are needed. Diarrhea caused by dysregulation of intestinal electrolyte transport and subsequent fluid and electrolyte losses often leads to secondary consequences for the patient. Currently, it is not exactly clear which mechanisms are involved in the dysregulation of intestinal fluid absorption, but differences in intestinal electrolyte shifts between human and canine patients suggest species-specific regulatory or counterregulatory mechanisms. Several intestinal electrolyte transporters are differentially expressed in human patients with inflammatory bowel disease (IBD), whereas there are virtually no studies on electrolyte transporters and their endocrine regulation in canine chronic inflammatory enteropathy. An important mechanism involved in regulating fluid and electrolyte homeostasis is the renin-angiotensin-aldosterone-system (RAAS), which may affect intestinal Na⁺ transport. While RAAS has previously been considered a systemic regulator of blood pressure, additional complex roles of RAAS in inflammatory processes have been unraveled. These alternative RAAS pathways may pose attractive therapeutic targets to address diarrhea and, thus, electrolyte shifts in human IBD and canine chronic inflammatory enteropathy. This article comparatively summarizes the current knowledge about electrolyte transport in human IBD and canine chronic inflammatory enteropathy and the role of RAAS and offers perspectives for novel therapeutic avenues.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Selective optogenetic control of Gq signaling using human Neuropsin

G_q proteins are universally important for signal transduction in mammalian cells. The underlying kinetics and transformation from extracellular stimuli into intracellular signaling, however could not be investigated in detail so far. Here we present the human Neuropsin (hOPN5) for specific and repetitive manipulation of G_q signaling in vitro and in vivo with high spatio-temporal resolution. Properties and G protein specificity of hOPN5 are characterized by UV light induced IP₃ generation, Ca²⁺ transients and inhibition of G_IRK channel activity in HEK cells. In adult hearts from a transgenic animal model, light increases the spontaneous beating rate. In addition, we demonstrate light induced contractions in the small intestine, which are not detectable after pharmacological G_q protein block. All-optical high-throughput screening for TRPC6 inhibitors is more specific and sensitive than conventional pharmacological screening. Thus, we demonstrate specific G_q signaling of hOPN5 and unveil its potential for optogenetic applications.

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.

A Shearless Microfluidic Device Detects a Role in Mechanosensitivity for AWCON Neuron in Caenorhabditis elegans

AWC olfactory neurons are fundamental for chemotaxis toward volatile attractants in Caenorhabditis elegans. Here, it is shown that AWC^ON responds not only to chemicals but also to mechanical stimuli caused by fluid flow changes in a microfluidic device. The dynamics of calcium events are correlated with the stimulus amplitude. It is further shown that the mechanosensitivity of AWC^ON neurons has an intrinsic nature rather than a synaptic origin, and the calcium transient response is mediated by TAX-4 cGMP-gated cation channel, suggesting the involvement of one or more "odorant" receptors in AWC^ON mechano-transduction. In many cases, the responses show plateau properties resembling bistable calcium dynamics where neurons can switch from one stable state to the other. To investigate the unprecedentedly observed mechanosensitivity of AWC^ON neurons, a novel microfluidic device is designed to minimize the fluid shear flow in the arena hosting the nematodes. Animals in this device show reduced neuronal activation of AWC^ON neurons. The results observed indicate that the tangential component of the mechanical stress is the main contributor to the mechanosensitivity of AWC^ON . Furthermore, the microfluidic platform, integrating shearless perfusion and calcium imaging, provides a novel and more controlled solution for in vivo analysis both in micro-organisms and cultured cells.

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.

New insights into RhoA/Rho-kinase signaling: a key regulator of vascular contraction

While Rho-signalling controlling vascular contraction is a canonical mechanism, with the modern approaches used in research, we are advancing our understanding and details into this pathway are often uncovered. RhoA-mediated Rho-kinase is the major regulator of vascular smooth muscle cells and a key player manoeuvring other functions in these cells. The discovery of new interactions, such as oxidative stress and hydrogen sulphide with Rho signalling are emerging addition not only in the physiology of the smooth muscle, but especially in the pathophysiology of vascular diseases. Likewise, the interplay between ageing and Rho-kinase in the vasculature has been recently considered. Importantly, in smooth muscle contraction, this pathway may also be affected by sex hormones, and consequently, sex-differences. This review provides an overview of Rho signalling mediating vascular contraction and focuses on recent topics discussed in the literature affecting this pathway such as ageing, sex differences and oxidative stress.

Contribution of TRPC Channels to Intracellular Ca2 + Dyshomeostasis in Smooth Muscle From mdx Mice

Duchenne muscular dystrophy (DMD) is an irreversible muscle disease characterized by a progressive loss of muscle function, decreased ambulation, and ultimately death as a result of cardiac or respiratory failure. DMD is caused by the lack of dystrophin, a protein that is important for membrane stability and signaling in excitable cells. Although vascular smooth muscle cells (VSMCs) dysfunction occurs in many pathological conditions, little is known about vascular smooth muscle function in DMD. We have previously shown that striated muscle cells, as well as neurons isolated from dystrophic (mdx) mice have higher intracellular Ca²⁺ ([Ca²⁺]_i) and Na⁺ ([Na⁺]_i) concentrations and decreased cell viability in comparison with wild type (Wt). Experiments were carried out in isolated VSMCs from mdx (a murine model of DMD) and congenic C57BL/10SnJ Wt mice. We found elevated [Ca²⁺]_i and [Na⁺]_i in VSMCs from mdx mice compared to Wt. Exposure to 1-oleoyl-2-acetyl-sn-glycerol (OAG), a TRPC3 and TRPC6 channel activator, induced a greater elevation of [Ca²⁺]_i and [Na⁺]_i in mdx than Wt VSMCs. The OAG induced increases in [Ca²⁺]_i could be abolished by either removal of extracellular Ca²⁺ or by SAR7334, a blocker of TRPC3 and TRPC 6 channels in both genotypes. Mdx and Wt VSMCs were susceptible to muscle cell stretch-induced elevations of [Ca²⁺]_i and [Na⁺]_i which was completely inhibited by GsMTx-4, a mechanosensitive ion channel inhibitor. Western blots showed a significant upregulation of TRPC1 -3, -6 proteins in mdx VSMCs compare to age-matched Wt. The lack of dystrophin in mdx VSMCs produced a profound alteration of [Ca²⁺]_i and [Na⁺]_i homeostasis that appears to be mediated by TRPC channels. Moreover, we have been able to demonstrate pharmacologically that the enhanced stretch-induced elevation of intracellular [Ca²⁺] and concomitant cell damage in mdx VSMCs also appears to be mediated through TRPC1, -3 and -6 channel activation.

Differential expression of angiotensin II type 1 receptor subtypes within the cerebral microvasculature

Arteries and arterioles constrict in response to intraluminal pressure to generate myogenic tone, but the molecular nature of the vascular force-sensing mechanism is not fully characterized. Here, we investigated the role of angiotensin II type 1 receptors (AT1Rs) on vascular smooth muscle cells in the development of myogenic tone in cerebral parenchymal arterioles from mice. We found that pretreatment with the AT1R blocker losartan inhibited the development of myogenic tone in these vessels but did not alter the luminal diameter of arterioles with preestablished tone. Rodents express two AT1R isotypes: AT1Ra and AT1Rb. We previously demonstrated that AT1Rb is expressed at much higher levels compared with AT1Ra in cerebral pial arteries and is required for myogenic contractility in these vessels, whereas AT1Ra is unnecessary for this function. Here, we found that AT1Ra and AT1Rb are expressed at similar levels in parenchymal arterioles and that genetic knockout of AT1Ra blunted the ability of these vessels to generate myogenic tone. We also found that AT1Rb and total AT1R expression levels are much lower in parenchymal arterioles compared with pial arteries and that parenchymal arterioles are less sensitive to the vasoconstrictive effects of the endogenous AT1R ligand angiotensin II (ANG II). We conclude that 1) AT1Rs are critical for the initiation, but not the maintenance, of myogenic tone in parenchymal arterioles, and 2) lower levels of AT1Rb and total AT1R in parenchymal arterioles compared with pial arteries result in differences in myogenic and ANG II-induced vasoconstriction between these vascular segments.NEW & NOTEWORTHY Myogenic tone is critical for appropriate regulation of cerebral blood flow, but the mechanisms used by vascular smooth muscle cells to detect changes in intraluminal pressure are not fully characterized. Here, we demonstrate angiotensin II receptor type 1 (AT1R) is indispensable to initiation, but not maintenance, of myogenic tone in cerebral parenchymal arterioles. Furthermore, we demonstrate differences in AT1R expression levels lead to critical differences in contractile regulation between parenchymal arterioles and cerebral pial arteries.

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.

Loss of Vascular Myogenic Tone in miR-143/145 Knockout Mice Is Associated With Hypertension-Induced Vascular Lesions in Small Mesenteric Arteries

OBJECTIVE

Pressure-induced myogenic tone is involved in autoregulation of local blood flow and confers protection against excessive pressure levels in small arteries and capillaries. Myogenic tone is dependent on smooth muscle microRNAs (miRNAs), but the identity of these miRNAs is unclear. Furthermore, the consequences of altered myogenic tone for hypertension-induced damage to small arteries are not well understood.

APPROACH AND RESULTS

The importance of smooth muscle-enriched microRNAs, miR-143/145, for myogenic tone was evaluated in miR-143/145 knockout mice. Furthermore, hypertension-induced vascular injury was evaluated in mesenteric arteries in vivo after angiotensin II infusion. Myogenic tone was abolished in miR-143/145 knockout mesenteric arteries, whereas contraction in response to calyculin A and potassium chloride was reduced by ≈30%. Furthermore, myogenic responsiveness was potentiated by angiotensin II in wild-type but not in knockout mice. Angiotensin II administration in vivo elevated systemic blood pressure in both genotypes. Hypertensive knockout mice developed severe vascular lesions characterized by vascular inflammation, adventitial fibrosis, and neointimal hyperplasia in small mesenteric arteries. This was associated with depolymerization of actin filaments and fragmentation of the elastic laminae at the sites of vascular lesions.

CONCLUSIONS

This study demonstrates that miR-143/145 expression is essential for myogenic responsiveness. During hypertension, loss of myogenic tone results in potentially damaging levels of mechanical stress and detrimental effects on small arteries. The results presented herein provide novel insights into the pathogenesis of vascular disease and emphasize the importance of controlling mechanical factors to maintain structural integrity of the vascular wall.

Small artery mechanobiology: Roles of cellular and non-cellular elements

Small arteries and their component cellular and non-cellular elements are continually subjected to, and interact with, mechanical forces. Such interactions are key in both short- and long-term adaptation of the structure and function of the microcirculation to its local environment and metabolic requirements. Following this brief introduction is a series of papers presented as a symposium (Small Artery Mechanobiology: Roles of Cellular and Non-Cellular Elements) at the World Congress for Microcirculation, Kyoto 2015.

[Histopathologic studies on epithelial proliferation in the peripheral region of the lung with special consideration of tumorlets]

Niclosamide is an oral antihelminthic drug used to treat parasitic infections in millions of people worldwide. However recent studies have indicated that niclosamide may have broad clinical applications for the treatment of diseases other than those caused by parasites. These diseases and symptoms may include cancer, bacterial and viral infection, metabolic diseases such as Type II diabetes, NASH and NAFLD, artery constriction, endometriosis, neuropathic pain, rheumatoid arthritis, sclerodermatous graft-versus-host disease, and systemic sclerosis. Among the underlying mechanisms associated with the drug actions of niclosamide are uncoupling of oxidative phosphorylation, and modulation of Wnt/β-catenin, mTORC1, STAT3, NF-κB and Notch signaling pathways. Here we provide a brief overview of the biological activities of niclosamide, its potential clinical applications, and its challenges for use as a new therapy for systemic diseases.

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Niclosamide is an oral antihelminthic drug used to treat parasitic infections.

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Niclosamide is a multifunctional drug inhibiting multiple signaling pathways and biological processes.

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Niclosamide has biological activities potentially against systemic diseases.