PC-PLC/sphingomyelin synthase activity plays a central role in the development of myogenic tone in murine resistance arteries

Potential Drug Targets for Ceramide Metabolism in Cardiovascular Disease

Cardiovascular disease poses a significant threat to the quality of human life. Metabolic abnormalities caused by excessive caloric intake have been shown to lead to the development of cardiovascular diseases. Ceramides are structural molecules found in biological membranes; they are crucial for cell survival and lipid metabolism, as they maintain barrier function and membrane fluidity. Increasing evidence has demonstrated that ceramide has a strong correlation with cardiovascular disease progression. Nevertheless, it remains a challenge to develop sphingolipids as therapeutic targets to improve the prognosis of cardiovascular diseases. In this review, we summarize the three synthesis pathways of ceramide and other intermediates that are important in ceramide metabolism. Furthermore, mechanistic studies and therapeutic strategies, including clinical drugs and bioactive molecules based on these intermediates, are discussed.

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 Comprehensive Review on the Interplay between Neisseria spp. and Host Sphingolipid Metabolites

Sphingolipids represent a class of structural related lipids involved in membrane biology and various cellular processes including cell growth, apoptosis, inflammation and migration. Over the past decade, sphingolipids have become the focus of intensive studies regarding their involvement in infectious diseases. Pathogens can manipulate the sphingolipid metabolism resulting in cell membrane reorganization and receptor recruitment to facilitate their entry. They may recruit specific host sphingolipid metabolites to establish a favorable niche for intracellular survival and proliferation. In contrast, some sphingolipid metabolites can also act as a first line defense against bacteria based on their antimicrobial activity. In this review, we will focus on the strategies employed by pathogenic Neisseria spp. to modulate the sphingolipid metabolism and hijack the sphingolipid balance in the host to promote cellular colonization, invasion and intracellular survival. Novel techniques and innovative approaches will be highlighted that allow imaging of sphingolipid derivatives in the host cell as well as in the pathogen.

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.

Voltage-gated Ca2+ channel activity modulates smooth muscle cell calcium waves in hamster cremaster arterioles

Cremaster muscle arteriolar smooth muscle cells (SMCs) display inositol 1,4,5-trisphosphate receptor-dependent Ca²⁺ waves that contribute to global myoplasmic Ca²⁺ concentration and myogenic tone. However, the contribution made by voltage-gated Ca²⁺ channels (VGCCs) to arteriolar SMC Ca²⁺ waves is unknown. We tested the hypothesis that VGCC activity modulates SMC Ca²⁺ waves in pressurized (80 cmH₂O/59 mmHg, 34°C) hamster cremaster muscle arterioles loaded with Fluo-4 and imaged by confocal microscopy. Removal of extracellular Ca²⁺ dilated arterioles (32 ± 3 to 45 ± 3 μm, n = 15, P < 0.05) and inhibited the occurrence, amplitude, and frequency of Ca²⁺ waves ( n = 15, P < 0.05), indicating dependence of Ca²⁺ waves on Ca²⁺ influx. Blockade of VGCCs with nifedipine (1 μM) or diltiazem (10 μM) or deactivation of VGCCs by hyperpolarization of smooth muscle with the K⁺ channel agonist cromakalim (10 μM) produced similar inhibition of Ca²⁺ waves ( P < 0.05). Conversely, depolarization of SMCs with the K⁺ channel blocker tetraethylammonium (1 mM) constricted arterioles from 26 ± 3 to 14 ± 2 μm ( n = 11, P < 0.05) and increased wave occurrence (9 ± 3 to 16 ± 3 waves/SMC), amplitude (1.6 ± 0.07 to 1.9 ± 0.1), and frequency (0.5 ± 0.1 to 0.9 ± 0.2 Hz, n = 10, P < 0.05), effects that were blocked by nifedipine (1 μM, P < 0.05). Similarly, the VGCC agonist Bay K8644 (5 nM) constricted arterioles from 14 ± 1 to 8 ± 1 μm and increased wave occurrence (3 ± 1 to 10 ± 1 waves/SMC) and frequency (0.2 ± 0.1 to 0.6 ± 0.1 Hz, n = 6, P < 0.05), effects that were unaltered by ryanodine (50 μM, n = 6, P > 0.05). These data support the hypothesis that Ca²⁺ waves in arteriolar SMCs depend, in part, on the activity of VGCCs. NEW & NOTEWORTHY Arterioles that control blood flow to and within skeletal muscle depend on Ca²⁺ influx through voltage-gated Ca²⁺ channels and release of Ca²⁺ from internal stores through inositol 1,4,5-trisphosphate receptors in the form of Ca²⁺ waves to maintain pressure-induced smooth muscle tone.

STIM1 Knockout Enhances PDGF-Mediated Ca2+ Signaling through Upregulation of the PDGFR⁻PLCγ⁻STIM2 Cascade

Platelet-derived growth factor (PDGF) has mitogenic and chemotactic effects on fibroblasts. An increase in intracellular Ca²⁺ is one of the first events that occurs following the stimulation of PDGF receptors (PDGFRs). PDGF activates Ca²⁺ elevation by activating the phospholipase C gamma (PLCγ)-signaling pathway, resulting in ER Ca²⁺ release. Store-operated Ca²⁺ entry (SOCE) is the major form of extracellular Ca²⁺ influx following depletion of ER Ca²⁺ stores and stromal interaction molecule 1 (STIM1) is a key molecule in the regulation of SOCE. In this study, wild-type and STIM1 knockout mouse embryonic fibroblasts (MEF) cells were used to investigate the role of STIM1 in PDGF-induced Ca²⁺ oscillation and its functions in MEF cells. The unexpected findings suggest that STIM1 knockout enhances PDGFR–PLCγ–STIM2 signaling, which in turn increases PDGF-BB-induced Ca²⁺ elevation. Enhanced expressions of PDGFRs and PLCγ in STIM1 knockout cells induce Ca²⁺ release from the ER store through PLCγ–IP3 signaling. Moreover, STIM2 replaces STIM1 to act as the major ER Ca²⁺ sensor in activating SOCE. However, activation of PDGFRs also activate Akt, ERK, and JNK to regulate cellular functions, such as cell migration. These results suggest that alternative switchable pathways can be observed in cells, which act downstream of the growth factors that regulate Ca²⁺ signaling.

Vasoconstrictor stimulus determines the functional contribution of myoendothelial feedback to mesenteric arterial tone

KEY POINTS

In isolated resistance arteries, endothelial modulation of vasoconstrictor responses to α₁ -adrenoceptor agonists occurs via a process termed myoendothelial feedback: localized inositol trisphosphate (InsP₃ )-dependent Ca²⁺ transients activate intermediate conductance Ca²⁺ -activated K⁺ (IK_Ca ) channels, hyperpolarizing the endothelial membrane potential to limit further reductions in vessel diameter. We demonstrate that IK_Ca channel-mediated myoendothelial feedback limits responses of isolated mesenteric arteries to noradrenaline and nerve stimulation, but not to the thromboxane A₂ mimetic U46619 or to increases in intravascular pressure. In contrast, in the intact mesenteric bed, although responses to exogenous noradrenaline were limited by IK_Ca channel-mediated myoendothelial feedback, release of NO and activation of endothelial small conductance Ca²⁺ -activated K⁺ (SK_Ca ) channels in response to increases in shear stress appeared to be the primary mediators of endothelial modulation of vasoconstriction. We propose that (1) the functional contribution of myoendothelial feedback to arterial tone is determined by the nature of the vasoconstrictor stimulus, and (2) although IK_Ca channel-mediated myoendothelial feedback may contribute to local control of arterial diameter, in the intact vascular bed, increases in shear stress may be the major stimulus for engagement of the endothelium during vasoconstriction.

ABSTRACT

Constriction of isolated resistance arteries in response to α₁ -adrenoceptor agonists is limited by reciprocal engagement of inhibitory endothelial mechanisms via myoendothelial feedback. In the current model of feedback, agonist stimulation of smooth muscle cells results in localized InsP₃ -dependent Ca²⁺ transients that activate endothelial IK_Ca channels. The subsequent hyperpolarization of the endothelial membrane potential then feeds back to the smooth muscle to limit further reductions in vessel diameter. We hypothesized that the functional contribution of InsP₃ -IK_Ca channel-mediated myoendothelial feedback to limiting arterial diameter may be influenced by the nature of the vasoconstrictor stimulus. To test this hypothesis, we investigated the functional role of myoendothelial feedback in modulating responses of rat mesenteric resistance arteries to the adrenoceptor agonist noradrenaline, the thromboxane A₂ mimetic U46619, increases in intravascular pressure and stimulation of perivascular sympathetic nerves. In isolated arteries, responses to noradrenaline and stimulation of sympathetic nerves, but not to U46619 and increases in intravascular pressure, were modulated by IK_Ca channel-dependent myoendothelial feedback. In the intact mesenteric bed perfused under conditions of constant flow, responses to exogenous noradrenaline were modulated by myoendothelial feedback, but shear stress-induced release of NO and activation of endothelial SK_Ca channels appeared to be the primary mediators of endothelial modulation of vasoconstriction to agonists and nerve stimulation. Thus, we propose that myoendothelial feedback may contribute to local control of diameter within arterial segments, but at the level of the intact vascular bed, increases in shear stress may be the major stimulus for engagement of the endothelium during vasoconstriction.

Regional heterogeneity in the mechanisms of myogenic tone in hamster arterioles

Myogenic tone is an important feature of arterioles and resistance arteries, but the mechanisms responsible for this hallmark characteristic remain unclear. We used pharmacological inhibitors to compare the roles played by phospholipase C (PLC; 10 μM U73122), inositol 1,4,5-trisphosphate receptors (IP₃Rs; 100 μM 2-aminoethoxydiphenylborane), protein kinase C (10 μM bisindolylmaleimide I), angiotensin II type 1 receptors (1 μM losartan), Rho kinase (10 nM-30 μM Y27632 or 300 nM H1152), stretch-activated ion channels (10 nM-1 μM Gd³⁺ or 5 μM spider venom toxin GsMTx-4) and L-type voltage-gated Ca²⁺ channels (0.3-100 μM diltiazem) in myogenic tone of cannulated, pressurized (80 cmH₂O), second-order hamster cremaster or cheek pouch arterioles. Effective inhibition of either PLC or IP₃Rs dilated cremaster arterioles, inhibited Ca²⁺ waves, and reduced global Ca²⁺ levels. In contrast, cheek pouch arterioles did not display Ca²⁺ waves and inhibition of PLC or IP₃Rs had no effect on myogenic tone or intracellular Ca²⁺ levels. Inhibition of Rho kinase dilated both cheek pouch and cremaster arterioles with equal efficacy and potency but also reduced intracellular Ca²⁺ signals in both arterioles. Similarly, inhibition of mechanosensitive ion channels with Gd²⁺ or GsMTx-4 produced comparable dilation in both arterioles. Inhibition of L-type Ca²⁺ channels with diltiazem was more effective in dilating cremaster (86 ± 5% dilation, n = 4) than cheek pouch arterioles (54 ± 4% dilation, n = 6, P < 0.05). Thus, there are substantial differences in the mechanisms underlying myogenic tone in hamster cremaster and cheek pouch arterioles. Regional heterogeneity in myogenic mechanisms could provide new targets for drug development to improve regional blood flow in a tissue-specific manner.NEW & NOTEWORTHY Regional heterogeneity in the mechanisms of pressure-induced myogenic tone implies that resistance vessels may be able to alter myogenic signaling pathways to adapt to their environment. A better understanding of the spectrum of myogenic mechanisms could provide new targets to treat diseases that affect resistance artery and arteriolar function.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Calcium Channels in Vascular Smooth Muscle

Calcium (Ca²⁺) plays a central role in excitation, contraction, transcription, and proliferation of vascular smooth muscle cells (VSMs). Precise regulation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) is crucial for proper physiological VSM function. Studies over the last several decades have revealed that VSMs express a variety of Ca²⁺-permeable channels that orchestrate a dynamic, yet finely tuned regulation of [Ca²⁺]_i. In this review, we discuss the major Ca²⁺-permeable channels expressed in VSM and their contribution to vascular physiology and pathology.

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.

Divergent modulation of Rho-kinase and Ca(2+) influx pathways by Src family kinases and focal adhesion kinase in airway smooth muscle

Background and Purpose

The importance of tyrosine kinases in airway smooth muscle (ASM) contraction is not fully understood. The aim of this study was to investigate the role of Src‐family kinases (SrcFK) and focal adhesion kinase (FAK) in GPCR‐mediated ASM contraction and associated signalling events.

Experimental Approach

Contraction was recorded in intact or α‐toxin permeabilized rat bronchioles. Phosphorylation of SrcFK, FAK, myosin light‐chain‐20 (MLC₂₀) and myosin phosphatase targeting subunit‐1 (MYPT‐1) was evaluated in cultured human ASM cells (hASMC). [Ca²⁺]_i was evaluated in Fura‐2 loaded hASMC. Responses to carbachol (CCh) and bradykinin (BK) and the contribution of SrcFK and FAK to these responses were determined.

Key Results

Contractile responses in intact bronchioles were inhibited by antagonists of SrcFK, FAK and Rho‐kinase, while after α‐toxin permeabilization, they were sensitive to inhibition of SrcFK and Rho‐kinase, but not FAK. CCh and BK increased phosphorylation of MYPT‐1 and MLC₂₀ and auto‐phosphorylation of SrcFK and FAK. MYPT‐1 phosphorylation was sensitive to inhibition of Rho‐kinase and SrcFK, but not FAK. Contraction induced by SR Ca²⁺ depletion and equivalent [Ca²⁺]_i responses in hASMC were sensitive to inhibition of both SrcFK and FAK, while depolarization‐induced contraction was sensitive to FAK inhibition only. SrcFK auto‐phosphorylation was partially FAK‐dependent, while FAK auto‐phosphorylation was SrcFK‐independent.

Conclusions and Implications

SrcFK mediates Ca²⁺‐sensitization in ASM, while SrcFK and FAK together and individually influence multiple Ca²⁺ influx pathways. Tyrosine phosphorylation is therefore a key upstream signalling event in ASM contraction and may be a viable target for modulating ASM tone in respiratory disease.