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Nitric oxide (NO) was first described as a bioactive molecule through its ability to stimulate soluble guanylate cyclase, but the revelation that NO was the endothelium derived relaxation factor drove the field to its modern state. The wealth of research conducted over the past 30 years has provided us with a picture of how diverse NO signaling can be within the vascular wall, going beyond simple vasodilation to include such roles as signaling through protein S-nitrosation. This expanded view of NO's actions requires highly regulated and compartmentalized production. Importantly, resistance arteries house multiple proteins involved in the production and transduction of NO allowing for efficient movement of the molecule to regulate vascular tone and reactivity. In this review, we focus on the many mechanisms regulating NO production and signaling action in the vascular wall, with a focus on the control of endothelial nitric oxide synthase (eNOS), the enzyme responsible for synthesizing most of the NO within these confines. We also explore how cross talk between the endothelium and smooth muscle in the microcirculation can modulate NO signaling, illustrating that this one small molecule has the capability to produce a plethora of responses. [ABSTRACT FROM AUTHOR]

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward. [ABSTRACT FROM AUTHOR]

A vast amount of investigation has centered on how the endothelium and smooth muscle communicate. From this evidence, myoendothelial junctions have emerged as critical anatomical structures to regulate heterocellular cross talk. Indeed, there is now evidence that the myoendothelial junction serves as a signaling microdomain to organize proteins used to facilitate vascular heterocellular communication. This review highlights the evolving role of myoendothelial junctions in the context of vascular cell-cell communication. [ABSTRACT FROM AUTHOR]

Background/Aims: Myoendothelial junctions (MEJs) represent a specialized signaling domain between vascular smooth muscle cells (VSMC) and endothelial cells (EC). The functional consequences of phosphorylation state of the connexins (Cx) at the MEJ have not been explored. Methods/Results: Application of adenosine 3′,5′-cyclic monophosphate sodium (pCPT) to mouse cremasteric arterioles reduces the detection of connexin 43 (Cx43) phosphorylated at its carboxyl terminal serine 368 site (S368) at the MEJ in vivo. After single-cell microinjection of a VSMC in mouse cremaster arterioles, only in the presence of pCPT was dye transfer to EC observed. We used a vascular cell co-culture (VCCC) and applied the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (PMA) or fibroblast growth factor-2 (FGF-2) to induce phosphorylation of Cx43 S368. This phosphorylation event was associated with a significant reduction in dye transfer and calcium communication. Using a novel method to monitor increases in intracellular calcium across the in vitro MEJ, we noted that PMA and FGF-2 both inhibited movement of inositol 1,4,5-triphosphate (IP3), but to a lesser extent Ca2+. Conclusion: These data indicate that site-specific connexin phosphorylation at the MEJ can potentially regulate the movement of solutes between EC and VSMC in the vessel wall. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Within the vasculature, specialized cellular extensions from endothelium (and sometimes smooth muscle) protrude through the extracellular matrix where they interact with the opposing cell type. These structures, termed myoendothelial junctions, have been cited as a possible key element in the control of several vascular physiologies and pathologies. This review will discuss observations that have led to a focus on the myoendothelial junction as a cellular integration point in the vasculature for both homeostatic and pathological conditions and as a possible independent signaling entity. We will also highlight the need for novel approaches to studying the myoendothelial junction in order to comprehend the cellular biology associated with this structure. [ABSTRACT FROM AUTHOR]

The article discusses studies on the impact of cavernous nerve resection (CNR) on erectile function. These studies are said to have focused on determining the presence of myoendothelial junctions (MEJs) between endothelial cells (ECs). It notes the presence of MEJs in human and mouse corporal tissue that is correlated with erectile dysfunction (ED). It cites a potential key role of the said junctions in the coordinated endothelial cell-smooth muscle cell response needed for normal tumescence.

The structural changes of airway smooth muscle (ASM) that characterize airway remodeling (AR) are crucial to the pathogenesis of asthma. During AR, ASM cells dedifferentiate from a quiescent to a proliferative, migratory, and secretory phenotype. Calcium (Ca2+) is a ubiquitous second messenger that regulates many cellular processes, including proliferation, migration, contraction, and metabolism. Furthermore, mitochondria have emerged as major Ca2+ signaling organelles that buffer Ca2+ through uptake by the mitochondrial Ca2+ uniporter and extrude it through the Na+/Ca2+ exchanger (NCLX/Slc8b1). Here, we show using mitochondrial Ca2+-sensitive dyes that NCLX only partially contributes to mitochondrial Ca2+ extrusion in ASM cells. Yet, NCLX is necessary for ASM cell proliferation and migration. Through cellular imaging, RNA-Seq, and biochemical assays, we demonstrate that NCLX regulates these processes by preventing mitochondrial Ca2+ overload and supporting store-operated Ca2+ entry, activation of Ca2+/calmodulin-dependent kinase II, and transcriptional and metabolic reprogramming. Using small animal respiratory mechanic measurements and immunohistochemistry, we show that smooth muscle-specific NCLX KO mice are protected against AR, fibrosis, and hyperresponsiveness in an experimental model of asthma. Our findings support NCLX as a potential therapeutic target in the treatment of asthma. [ABSTRACT FROM AUTHOR]

Chronic hypoxia is a major driver of cardiovascular complications, including heart failure. The nitric oxide (NO) – soluble guanylyl cyclase (sGC) – cyclic guanosine monophosphate (cGMP) pathway is integral to vascular tone maintenance. Specifically , NO binds its receptor sGC within vascular smooth muscle cells (SMC) in its reduced heme (Fe2+) form to increase intracellular cGMP production, activate protein kinase G (PKG) signaling, and induce vessel relaxation. Under chronic hypoxia, oxidative stress drives oxidation of sGC heme (Fe2+→Fe3+), rendering it NO-insensitive. We previously showed that cytochrome b5 reductase 3 (CYB5R3) in SMC is a sGC reductase important for maintaining NO-dependent vasodilation and conferring resilience to systemic hypertension and sickle cell disease-associated pulmonary hypertension. To test whether CYB5R3 may be protective in the context of chronic hypoxia, we subjected SMC-specific CYB5R3 knockout mice (SMC CYB5R3 KO) to 3 weeks hypoxia and assessed vascular and cardiac function using echocardiography, pressure volume loops and wire myography. Hypoxic stress caused 1) biventricular hypertrophy in both WT and SMC CYB5R3 KO, but to a larger degree in KO mice, 2) blunted vasodilation to NO-dependent activation of sGC in coronary and pulmonary arteries of KO mice, and 3) decreased, albeit still normal, cardiac function in KO mice. Overall, these data indicate that SMC CYB5R3 deficiency potentiates bilateral ventricular hypertrophy and blunts NO-dependent vasodilation under chronic hypoxia conditions. This implicates that SMC CYB5R3 KO mice post 3-week hypoxia have early stages of cardiac remodeling and functional changes that could foretell significantly impaired cardiac function with longer exposure to hypoxia. [Display omitted] • Chronic hypoxia is an underlying cause of pulmonary hypertension and heart failure. • In chronic hypoxia, smooth muscle specific deletion of CYB5R3 increases cardiac hypertrophy. • Smooth muscle cell CYB5R3 is important for maintaining NO-dependent vasodilation under chronic hypoxic stress. [ABSTRACT FROM AUTHOR]

Aims: Pannexins (Panx) form ATP release channels and it has been proposed that they play an important role in the regulation of vascular tone. However, distribution of Panx across the arterial vasculature is not documented. Methods: We tested antibodies against Panx1, Panx2 and Panx3 on human embryonic kidney cells (which do not endogenously express Panx proteins) transfected with plasmids encoding each Panx isoform and Panx1-/- mice. Each of the Panx antibodies was found to be specific and was tested on isolated arteries using immunocytochemistry. Results: We demonstrated that Panx1 is the primary isoform detected in the arterial network. In large arteries, Panx1 is primarily in endothelial cells, whereas in small arteries and arterioles it localizes primarily to the smooth muscle cells. Panx1 was the predominant isoform expressed in coronary arteries, except in arteries less than 100 μm where Panx3 became detectable. Only Panx3 was expressed in the juxtaglomerular apparatus and cortical arterioles. The pulmonary artery and alveoli had expression of all 3 Panx isoforms. No Panx isoforms were detected at the myoendothelial junctions. Conclusion: We conclude that the specific localized expression of Panx channels throughout the vasculature points towards an important role for these channels in regulating the release of ATP throughout the arterial network. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Please cite this paper as: Billaud M, Lohman AW, Straub AC, Parpaite T, Johnstone SR, Isakson BE. Characterization of the thoracodorsal artery: morphology and reactivity. Microcirculation 19: 360-372, 2012. Abstract Objectives: In this paper, we describe the histological and contractile properties of the thoracodorsal artery (TDA), which indirectly feeds the spinotrapezius muscle. Methods: We used immunolabelling techniques to histologically characterize the TDA while the contractile properties were assessed using pressure arteriography. Results: Our results demonstrate that the TDA is composed of approximately one to two layers of smooth muscle cells, is highly innervated with adrenergic nerves, and develops spontaneous tone at intraluminal pressures above 80 mmHg. The reactivity of the TDA in response to various contractile agonists such as phenylephrine, noradrenaline, angiotensin II, serotonin, endothelin 1, and ATP, as well as vasodilators, shows that the TDA exhibits a remarkably comparable reactivity to what has been observed in mesenteric arteries. We further studied the different components of the TDA response to acetylcholine, and found that the TDA was sensitive to TRAM 34, a blocker of the intermediate conductance potassium channel, which is highly suggestive of an endothelium-dependent hyperpolarization. Conclusions: We conclude that the TDA exhibits comparable characteristics to other current vascular models, with the additional advantage of being easily manipulated for molecular and ex vivo vasoreactivity studies. [ABSTRACT FROM AUTHOR]

In resistance arteries, endothelial cells (EC) make contact with smooth muscle cells (SMC), forming myoendothelial junctions (MEJ). Endothelial nitric oxide synthase (eNOS) is present in the luminal side of the EC (apical EC) and the basal side of the EC (MEJ). To test if these eNOS pools acted in sync or separately, we co-cultured ECs and SMCs, then stimulated SMCs with phenylephrine (PE). Adrenergic activation causes inositol [1,4,5] triphosphate (IP 3 ) to move from SMC to EC through gap junctions at the MEJ. PE increases MEJ eNOS phosphorylation (eNOS-P) at S1177, but not in EC. Conversely, we used bradykinin (BK) to increase EC calcium; this increased EC eNOS-P but did not affect MEJ eNOS-P. Inhibiting gap junctions abrogated the MEJ eNOS-P after PE, but had no effect on BK eNOS-P. Differential lipid composition between apical EC and MEJ may account for the compartmentalized eNOS-P response. Indeed, DAG and phosphatidylserine are both enriched in MEJ. These lipids are cofactors for PKC activity, which was significantly increased at the MEJ after PE. Because PKC activity also relies on endoplasmic reticulum (ER) calcium release, we used thapsigargin and xestospongin C, BAPTA, and PKC inhibitors, which caused significant decreases in MEJ eNOS-P after PE. Functionally, BK inhibited leukocyte adhesion and PE caused an increase in SMC cGMP. We hypothesize that local lipid composition of the MEJ primes PKC and eNOS-P for stimulation by PE, allowing for compartmentalized function of eNOS in the blood vessel wall. [ABSTRACT FROM AUTHOR]

Epigenetic mechanisms contribute to the regulation of cell differentiation and function. Vascular smooth muscle cells (SMCs) are specialized contractile cells that retain phenotypic plasticity even after differentiation. Here, by performing selective demethylation of histone H3 lysine 4 di-methylation (H3K4me2) at SMC-specific genes, we uncovered that H3K4me2 governs SMC lineage identity. Removal of H3K4me2 via selective editing in cultured vascular SMCs and in murine arterial vasculature led to loss of differentiation and reduced contractility due to impaired recruitment of the DNA methylcytosine dioxygenase TET2. H3K4me2 editing altered SMC adaptative capacities during vascular remodeling due to loss of miR-145 expression. Finally, H3K4me2 editing induced a profound alteration of SMC lineage identity by redistributing H3K4me2 toward genes associated with stemness and developmental programs, thus exacerbating plasticity. Our studies identify the H3K4me2-TET2-miR145 axis as a central epigenetic memory mechanism controlling cell identity and function, whose alteration could contribute to various pathophysiological processes. [Display omitted] • Gene-selective epigenome editing reveals that H3K4me2 controls SMC lineage identity • H3K4me2 editing induces loss of contractility and exacerbates phenotypic plasticity • H3K4me2 interacts with TET2 and mediates TET-dependent gene activation • Loss of H3K4me2 impairs SMC-mediated vascular remodeling due to miR-145 deficiency Regulating the contractile states of smooth muscle cells (SMCs) is critical for vascular homeostasis. Liu et al. find that the H3K4me2 modification is required to maintain SMC lineage identity and contractile state, serving as a genomic footprint for TET2-mediated DNA demethylation. H3K4me2 alteration in SMCs may contribute to cardiovascular disease. [ABSTRACT FROM AUTHOR]