Female mice display sex-specific differences in cerebrovascular function and subarachnoid haemorrhage-induced injury.

BACKGROUND: In male mice, a circadian rhythm in myogenic reactivity influences the extent of brain injury following subarachnoid haemorrhage (SAH). We hypothesized that female mice have a different cerebrovascular phenotype and consequently, a distinct SAH-induced injury phenotype. METHODS: SAH was modelled by pre-chiasmatic blood injection. Olfactory cerebral resistance arteries were functionally assessed by pressure myography; these functional assessments were related to brain histology and neurobehavioral assessments. Cystic fibrosis transmembrane conductance regulator (CFTR) expression was assessed by PCR and Western blot. We compared non-ovariectomized and ovariectomized mice. FINDINGS: Cerebrovascular myogenic reactivity is not rhythmic in females and no diurnal differences in SAH-induced injury are observed; ovariectomy does not unmask a rhythmic phenotype for any endpoint. CFTR expression is rhythmic, with similar expression levels compared to male mice. CFTR inhibition studies, however, indicate that CFTR activity is lower in female arteries. Pharmacologically increasing CFTR expression in vivo (3 mg/kg lumacaftor for 2 days) reduces myogenic tone at Zeitgeber time 11, but not Zeitgeber time 23. Myogenic tone is not markedly augmented following SAH in female mice and lumacaftor loses its ability to reduce myogenic tone; nevertheless, lumacaftor confers at least some injury benefit in females with SAH. INTERPRETATION: Female mice possess a distinct cerebrovascular phenotype compared to males, putatively due to functional differences in CFTR regulation. This sex difference eliminates the CFTR-dependent cerebrovascular effects of SAH and may alter the therapeutic efficacy of lumacaftor compared to males. FUNDING: Brain Aneurysm Foundation, Heart and Stroke Foundation and Ted Rogers Centre for Heart Research.

Disrupting circadian control of peripheral myogenic reactivity mitigates cardiac injury following myocardial infarction.

AIMS: Circadian rhythms orchestrate important functions in the cardiovascular system: the contribution of microvascular rhythms to cardiovascular disease progression/severity is unknown. This study hypothesized that (i) myogenic reactivity in skeletal muscle resistance arteries is rhythmic and (ii) disrupting this rhythmicity would alter cardiac injury post-myocardial infarction (MI). METHODS AND RESULTS: Cremaster skeletal muscle resistance arteries were isolated and assessed using standard pressure myography. Circadian rhythmicity was globally disrupted with the ClockΔ19/Δ19 mutation or discretely through smooth muscle cell-specific Bmal1 deletion (Sm-Bmal1 KO). Cardiac structure and function were determined by echocardiographic, hemodynamic and histological assessments. Myogenic reactivity in cremaster muscle resistance arteries is rhythmic. This rhythm is putatively mediated by the circadian modulation of a mechanosensitive signalosome incorporating tumour necrosis factor and casein kinase 1. Following left anterior descending coronary artery ligation, myogenic responsiveness is locked at the circadian maximum, although circadian molecular clock gene expression cycles normally. Disrupting the molecular clock abolishes myogenic rhythmicity: myogenic tone is suspended at the circadian minimum and is no longer augmented by MI. The reduced myogenic tone in ClockΔ19/Δ19 mice and Sm-Bmal1 KO mice associates with reduced total peripheral resistance (TPR), improved cardiac function and reduced infarct expansion post-MI. CONCLUSIONS: Augmented microvascular constriction aggravates cardiac injury post-MI. Following MI, skeletal muscle resistance artery myogenic reactivity increases specifically within the rest phase, when TPR would normally decline. Disrupting the circadian clock interrupts the MI-induced augmentation in myogenic reactivity: therapeutics targeting the molecular clock, therefore, may be useful for improving MI outcomes.

Restoring myocardial infarction-induced long-term memory impairment by targeting the cystic fibrosis transmembrane regulator.

BACKGROUND: Cognitive impairment is a serious comorbidity in heart failure patients, but effective therapies are lacking. We investigated the mechanisms that alter hippocampal neurons following myocardial infarction (MI). METHODS: MI was induced in male C57Bl/6 mice by left anterior descending coronary artery ligation. We utilised standard procedures to measure cystic fibrosis transmembrane regulator (CFTR) protein levels, inflammatory mediator expression, neuronal structure, and hippocampal memory. Using in vitro and in vivo approaches, we assessed the role of neuroinflammation in hippocampal neuron degradation and the therapeutic potential of CFTR correction as an intervention. FINDINGS: Hippocampal dendrite length and spine density are reduced after MI, effects that associate with decreased neuronal CFTR expression and concomitant microglia activation and inflammatory cytokine expression. Conditioned medium from lipopolysaccharide-stimulated microglia (LCM) reduces neuronal cell CFTR protein expression and the mRNA expression of the synaptic regulator post-synaptic density protein 95 (PSD-95) in vitro. Blocking CFTR activity also down-regulates PSD-95 in neurons, indicating a relationship between CFTR expression and neuronal health. Pharmacologically correcting CFTR expression in vitro rescues the LCM-mediated down-regulation of PSD-95. In vivo, pharmacologically increasing hippocampal neuron CFTR expression improves MI-associated alterations in neuronal arborisation, spine density, and memory function, with a wide therapeutic time window. INTERPRETATION: Our results indicate that CFTR therapeutics improve inflammation-induced alterations in hippocampal neuronal structure and attenuate memory dysfunction following MI. FUNDING: Knut and Alice Wallenberg Foundation [F 2015/2112]; Swedish Research Council [VR; 2017-01243]; the German Research Foundation [DFG; ME 4667/2-1]; Hjärnfonden [FO2021-0112]; The Crafoord Foundation; Åke Wibergs Stiftelse [M19-0380], NMMP 2021 [V2021-2102]; the Albert Påhlsson Research Foundation; STINT [MG19-8469], Lund University; Canadian Institutes of Health Research [PJT-153269] and a Heart and Stroke Foundation of Ontario Mid-Career Investigator Award.

Circadian Rhythmicity in Cerebral Microvascular Tone Influences Subarachnoid Hemorrhage-Induced Injury.

BACKGROUND AND PURPOSE: Circadian rhythms influence the extent of brain injury following subarachnoid hemorrhage (SAH), but the mechanism is unknown. We hypothesized that cerebrovascular myogenic reactivity is rhythmic and explains the circadian variation in SAH-induced injury. METHODS: SAH was modeled in mice with prechiasmatic blood injection. Inducible, smooth muscle cell-specific Bmal1 (brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein 1) gene deletion (smooth muscle-specific Bmal1 1 knockout [sm-Bmal1 KO]) disrupted circadian rhythms within the cerebral microcirculation. Olfactory cerebral resistance arteries were functionally assessed by pressure myography in vitro; these functional assessments were related to polymerase chain reaction/Western blot data, brain histology (Fluoro-Jade/activated caspase-3), and neurobehavioral assessments (modified Garcia scores). RESULTS: Cerebrovascular myogenic vasoconstriction is rhythmic, with a peak and trough at Zeitgeber times 23 and 11 (ZT23 and ZT11), respectively. Histological and neurobehavioral assessments demonstrate that higher injury levels occur when SAH is induced at ZT23, compared with ZT11. In sm-Bmal1 KO mice, myogenic reactivity is not rhythmic. Interestingly, myogenic tone is higher at ZT11 versus ZT23 in sm-Bmal1 KO mice; accordingly, SAH-induced injury in sm-Bmal1 KO mice is more severe when SAH is induced at ZT11 compared to ZT23. We examined several myogenic signaling components and found that CFTR (cystic fibrosis transmembrane conductance regulator) expression is rhythmic in cerebral arteries. Pharmacologically stabilizing CFTR expression in vivo (3 mg/kg lumacaftor for 2 days) eliminates the rhythmicity in myogenic reactivity and abolishes the circadian variation in SAH-induced neurological injury. CONCLUSIONS: Cerebrovascular myogenic reactivity is rhythmic. The level of myogenic tone at the time of SAH ictus is a key factor influencing the extent of injury. Circadian oscillations in cerebrovascular CFTR expression appear to underlie the cerebrovascular myogenic reactivity rhythm.

The emerging significance of circadian rhythmicity in microvascular resistance.

The Earth's rotation generates environmental oscillations (e.g., in light and temperature) that have imposed unique evolutionary pressures over millions of years. Consequently, the circadian clock, a ubiquitously expressed molecular system that aligns cellular function to these environmental cues, has become an integral component of our physiology. The resulting functional rhythms optimize and economize physiological performance: perturbing these rhythms, therefore, is frequently deleterious. This perspective article focuses on circadian rhythms in resistance artery myogenic reactivity, a key mechanism governing tissue perfusion, total peripheral resistance and systemic blood pressure. Emerging evidence suggests that myogenic reactivity rhythms are locally generated in a microvascular bed-specific manner at the level of smooth muscle cells. This implies that there is a distinct interface between the molecular clock and the signalling pathways underlying myogenic reactivity in the microvascular beds of different organs. By understanding the precise nature of these molecular links, it may become possible to therapeutically manipulate microvascular tone in an organ-specific manner. This raises the prospect that interventions for vascular pathologies that are challenging to treat, such as hypertension and brain malperfusion, can be significantly improved.

Cerebral Autoregulation in Subarachnoid Hemorrhage.

Subarachnoid hemorrhage (SAH) is a devastating stroke subtype with a high rate of mortality and morbidity. The poor clinical outcome can be attributed to the biphasic course of the disease: even if the patient survives the initial bleeding emergency, delayed cerebral ischemia (DCI) frequently follows within 2 weeks time and levies additional serious brain injury. Current therapeutic interventions do not specifically target the microvascular dysfunction underlying the ischemic event and as a consequence, provide only modest improvement in clinical outcome. SAH perturbs an extensive number of microvascular processes, including the "automated" control of cerebral perfusion, termed "cerebral autoregulation." Recent evidence suggests that disrupted cerebral autoregulation is an important aspect of SAH-induced brain injury. This review presents the key clinical aspects of cerebral autoregulation and its disruption in SAH: it provides a mechanistic overview of cerebral autoregulation, describes current clinical methods for measuring autoregulation in SAH patients and reviews current and emerging therapeutic options for SAH patients. Recent advancements should fuel optimism that microvascular dysfunction and cerebral autoregulation can be rectified in SAH patients.

A Scientific Rationale for Using Cystic Fibrosis Transmembrane Conductance Regulator Therapeutics in COVID-19 Patients.

Several pathological manifestations in coronavirus disease 2019 (COVID-19), including thick mucus, poor mucociliary clearance, and bronchial wall thickening, overlap with cystic fibrosis disease patterns and may be indicative of "acquired" cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction. Indeed, tumor necrosis factor (TNF), a key cytokine driving COVID-19 pathogenesis, downregulates lung CFTR protein expression, providing a strong rationale that acquired CFTR dysfunction arises in the context of COVID-19 infection. In this perspective, we propose that CFTR therapeutics, which are safe and generally well-tolerated, may provide benefit to COVID-19 patients. Although CFTR therapeutics are currently only approved for treating cystic fibrosis, there are efforts to repurpose them for conditions with "acquired" CFTR dysfunction, for example, chronic obstructive pulmonary disease. In addition to targeting the primary lung pathology, CFTR therapeutics may possess value-added effects: their anti-inflammatory properties may dampen exaggerated immune cell responses and promote cerebrovascular dilation; the latter aspect may offer some protection against COVID-19 related stroke.

Stabilizing Cellular Barriers: Raising the Shields Against COVID-19.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its clinical manifestation (COVID-19; coronavirus disease 2019) have caused a worldwide health crisis. Disruption of epithelial and endothelial barriers is a key clinical turning point that differentiates patients who are likely to develop severe COVID-19 outcomes: it marks a significant escalation in respiratory symptoms, loss of viral containment and a progression toward multi-organ dysfunction. These barrier mechanisms are independently compromised by known COVID-19 risk factors, including diabetes, obesity and aging: thus, a synergism between these underlying conditions and SARS-CoV-2 mechanisms may explain why these risk factors correlate with more severe outcomes. This review examines the key cellular mechanisms that SARS-CoV-2 and its underlying risk factors utilize to disrupt barrier function. As an outlook, we propose that glucagon-like peptide 1 (GLP-1) may be a therapeutic intervention that can slow COVID-19 progression and improve clinical outcome following SARS-CoV-2 infection. GLP-1 signaling activates barrier-promoting processes that directly oppose the pro-inflammatory mechanisms commandeered by SARS-CoV-2 and its underlying risk factors.

Experimental Subarachnoid Hemorrhage Drives Catecholamine-Dependent Cardiac and Peripheral Microvascular Dysfunction.

Subarachnoid hemorrhage (SAH) is a devastating cerebral event caused by an aneurysmal rupture. In addition to neurological injury, SAH has significant effects on cardiac function and the peripheral microcirculation. Since these peripheral complications may exacerbate brain injury, the prevention and management of these peripheral effects are important for improving the overall clinical outcome after SAH. In this investigation, we examined the effects of SAH on cardiac function and vascular reactivity in a well-characterized blood injection model of SAH. Standard echocardiographic and blood pressure measurement procedures were utilized to assess cardiac function and hemodynamic parameters in vivo; we utilized a pressure myography approach to assess vascular reactivity in cremaster skeletal muscle resistance arteries ex vivo. We observed that elevated catecholamine levels in SAH stun the myocardium, reduce cardiac output and augment myogenic vasoconstriction in isolated cremaster arteries. These cardiac and vascular effects are driven by beta- and alpha-adrenergic receptor signaling, respectively. Clinically utilized adrenergic receptor antagonists can prevent cardiac injury and normalize vascular function. We found that tumor necrosis factor (TNF) gene deletion prevents the augmentation of myogenic reactivity in SAH: since membrane-bound TNF serves as a mechanosensor in the arteries assessed, alpha-adrenergic signaling putatively augments myogenic vasoconstriction by enhancing mechanosensor activity.

CFTR Therapeutics Normalize Cerebral Perfusion Deficits in Mouse Models of Heart Failure and Subarachnoid Hemorrhage.

Heart failure (HF) and subarachnoid hemorrhage (SAH) chronically reduce cerebral perfusion, which negatively affects clinical outcome. This work demonstrates a strong relationship between cerebral artery cystic fibrosis transmembrane conductance regulator (CFTR) expression and altered cerebrovascular reactivity in HF and SAH. In HF and SAH, CFTR corrector compounds (C18 or lumacaftor) normalize pathological alterations in cerebral artery CFTR expression, vascular reactivity, and cerebral perfusion, without affecting systemic hemodynamic parameters. This normalization correlates with reduced neuronal injury. Therefore, CFTR therapeutics have emerged as valuable clinical tools to manage cerebrovascular dysfunction, impaired cerebral perfusion, and neuronal injury.

Cerebral artery myogenic reactivity: The next frontier in developing effective interventions for subarachnoid hemorrhage.

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating cerebral event that kills or debilitates the majority of those afflicted. The blood that spills into the subarachnoid space stimulates profound cerebral artery vasoconstriction and consequently, cerebral ischemia. Thus, once the initial bleeding in SAH is appropriately managed, the clinical focus shifts to maintaining/improving cerebral perfusion. However, current therapeutic interventions largely fail to improve clinical outcome, because they do not effectively restore normal cerebral artery function. This review discusses emerging evidence that perturbed cerebrovascular "myogenic reactivity," a crucial microvascular process that potently dictates cerebral perfusion, is the critical element underlying cerebral ischemia in SAH. In fact, the myogenic mechanism could be the reason why many therapeutic interventions, including "Triple H" therapy, fail to deliver benefit to patients. Understanding the molecular basis for myogenic reactivity changes in SAH holds the key to develop more effective therapeutic interventions; indeed, promising recent advancements fuel optimism that vascular dysfunction in SAH can be corrected to improve outcome.

Constitutive smooth muscle tumour necrosis factor regulates microvascular myogenic responsiveness and systemic blood pressure.

Tumour necrosis factor (TNF) is a ubiquitously expressed cytokine with functions beyond the immune system. In several diseases, the induction of TNF expression in resistance artery smooth muscle cells enhances microvascular myogenic vasoconstriction and perturbs blood flow. This pathological role prompted our hypothesis that constitutively expressed TNF regulates myogenic signalling and systemic haemodynamics under non-pathological settings. Here we show that acutely deleting the TNF gene in smooth muscle cells or pharmacologically scavenging TNF with etanercept (ETN) reduces blood pressure and resistance artery myogenic responsiveness; the latter effect is conserved across five species, including humans. Changes in transmural pressure are transduced into intracellular signals by membrane-bound TNF (mTNF) that connect to a canonical myogenic signalling pathway. Our data positions mTNF 'reverse signalling' as an integral element of a microvascular mechanosensor; pathologic or therapeutic perturbations of TNF signalling, therefore, necessarily affect microvascular tone and systemic haemodynamics.

Tumor Necrosis Factor/Sphingosine-1-Phosphate Signaling Augments Resistance Artery Myogenic Tone in Diabetes.

Diabetes strongly associates with microvascular complications that ultimately promote multiorgan failure. Altered myogenic responsiveness compromises tissue perfusion, aggravates hypertension, and sets the stage for later permanent structural changes to the microcirculation. We demonstrate that skeletal muscle resistance arteries isolated from patients with diabetes have augmented myogenic tone, despite reasonable blood glucose control. To understand the mechanisms, we titrated a standard diabetes mouse model (high-fat diet plus streptozotocin [HFD/STZ]) to induce a mild increase in blood glucose levels. HFD/STZ treatment induced a progressive myogenic tone augmentation in mesenteric and olfactory cerebral arteries; neither HFD nor STZ alone had an effect on blood glucose or resistance artery myogenic tone. Using gene deletion models that eliminate tumor necrosis factor (TNF) or sphingosine kinase 1, we demonstrate that vascular smooth muscle cell TNF drives the elevation of myogenic tone via enhanced sphingosine-1-phosphate (S1P) signaling. Therapeutically antagonizing TNF (etanercept) or S1P (JTE013) signaling corrects this defect. Our investigation concludes that vascular smooth muscle cell TNF augments resistance artery myogenic vasoconstriction in a diabetes model that induces a small elevation of blood glucose. Our data demonstrate that microvascular reactivity is an early disease marker and advocate establishing therapies that strategically target the microcirculation.

Sphingosine-1-Phosphate Signaling Regulates Myogenic Responsiveness in Human Resistance Arteries.

We recently identified sphingosine-1-phosphate (S1P) signaling and the cystic fibrosis transmembrane conductance regulator (CFTR) as prominent regulators of myogenic responsiveness in rodent resistance arteries. However, since rodent models frequently exhibit limitations with respect to human applicability, translation is necessary to validate the relevance of this signaling network for clinical application. We therefore investigated the significance of these regulatory elements in human mesenteric and skeletal muscle resistance arteries. Mesenteric and skeletal muscle resistance arteries were isolated from patient tissue specimens collected during colonic or cardiac bypass surgery. Pressure myography assessments confirmed endothelial integrity, as well as stable phenylephrine and myogenic responses. Both human mesenteric and skeletal muscle resistance arteries (i) express critical S1P signaling elements, (ii) constrict in response to S1P and (iii) lose myogenic responsiveness following S1P receptor antagonism (JTE013). However, while human mesenteric arteries express CFTR, human skeletal muscle resistance arteries do not express detectable levels of CFTR protein. Consequently, modulating CFTR activity enhances myogenic responsiveness only in human mesenteric resistance arteries. We conclude that human mesenteric and skeletal muscle resistance arteries are a reliable and consistent model for translational studies. We demonstrate that the core elements of an S1P-dependent signaling network translate to human mesenteric resistance arteries. Clear species and vascular bed variations are evident, reinforcing the critical need for further translational study.

Therapeutically Targeting Tumor Necrosis Factor-α/Sphingosine-1-Phosphate Signaling Corrects Myogenic Reactivity in Subarachnoid Hemorrhage.

BACKGROUND AND PURPOSE: Subarachnoid hemorrhage (SAH) is a complex stroke subtype characterized by an initial brain injury, followed by delayed cerebrovascular constriction and ischemia. Current therapeutic strategies nonselectively curtail exacerbated cerebrovascular constriction, which necessarily disrupts the essential and protective process of cerebral blood flow autoregulation. This study identifies a smooth muscle cell autocrine/paracrine signaling network that augments myogenic tone in a murine model of experimental SAH: it links tumor necrosis factor-α (TNFα), the cystic fibrosis transmembrane conductance regulator, and sphingosine-1-phosphate signaling. METHODS: Mouse olfactory cerebral resistance arteries were isolated, cannulated, and pressurized for in vitro vascular reactivity assessments. Cerebral blood flow was measured by speckle flowmetry and magnetic resonance imaging. Standard Western blot, immunohistochemical techniques, and neurobehavioral assessments were also used. RESULTS: We demonstrate that targeting TNFα and sphingosine-1-phosphate signaling in vivo has potential therapeutic application in SAH. Both interventions (1) eliminate the SAH-induced myogenic tone enhancement, but otherwise leave vascular reactivity intact; (2) ameliorate SAH-induced neuronal degeneration and apoptosis; and (3) improve neurobehavioral performance in mice with SAH. Furthermore, TNFα sequestration with etanercept normalizes cerebral perfusion in SAH. CONCLUSIONS: Vascular smooth muscle cell TNFα and sphingosine-1-phosphate signaling significantly enhance cerebral artery tone in SAH; anti-TNFα and anti-sphingosine-1-phosphate treatment may significantly improve clinical outcome.

Sphingosine-1-Phosphate Is a Novel Regulator of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Activity.

The cystic fibrosis transmembrane conductance regulator (CFTR) attenuates sphingosine-1-phosphate (S1P) signaling in resistance arteries and has emerged as a prominent regulator of myogenic vasoconstriction. This investigation demonstrates that S1P inhibits CFTR activity via adenosine monophosphate-activated kinase (AMPK), establishing a potential feedback link. In Baby Hamster Kidney (BHK) cells expressing wild-type human CFTR, S1P (1µmol/L) attenuates forskolin-stimulated, CFTR-dependent iodide efflux. S1P's inhibitory effect is rapid (within 30 seconds), transient and correlates with CFTR serine residue 737 (S737) phosphorylation. Both S1P receptor antagonism (4µmol/L VPC 23019) and AMPK inhibition (80µmol/L Compound C or AMPK siRNA) attenuate S1P-stimluated (i) AMPK phosphorylation, (ii) CFTR S737 phosphorylation and (iii) CFTR activity inhibition. In BHK cells expressing the ΔF508 CFTR mutant (CFTRΔF508), the most common mutation causing cystic fibrosis, both S1P receptor antagonism and AMPK inhibition enhance CFTR activity, without instigating discernable correction. In summary, we demonstrate that S1P/AMPK signaling transiently attenuates CFTR activity. Since our previous work positions CFTR as a negative S1P signaling regulator, this signaling link may positively reinforce S1P signals. This discovery has clinical ramifications for the treatment of disease states associated with enhanced S1P signaling and/or deficient CFTR activity (e.g. cystic fibrosis, heart failure). S1P receptor/AMPK inhibition could synergistically enhance the efficacy of therapeutic strategies aiming to correct aberrant CFTR trafficking.

The role of the sphingosine-1-phosphate signaling pathway in osteocyte mechanotransduction.

Osteocytes are proposed to be the mechanosensory cells that translate mechanical loading into biochemical signals during the process of bone adaptation. The lipid mediator sphingosine-1-phosphate (S1P) has been reported to play a role in the mechanotransduction process of blood vessels and also in the dynamic control of bone mineral homeostasis. Nevertheless, the potential role of S1P in bone mechanotransduction has yet to be elucidated. In this study, we hypothesized that a S1P cascade is involved in the activation of osteocytes in response to loading-induced oscillatory fluid flow (OFF) in bone. MLO-Y4 osteocyte-like cells express the necessary components of a functional S1P cascade. To examine the involvement of S1P signaling in osteocyte mechanotransduction, we applied OFF (1 Pa, 1 Hz) to osteocyte-like MLO-Y4 cells under conditions where the S1P signaling pathway was modulated. We found that decreased endogenous S1P levels significantly suppressed the OFF-induced intracellular calcium response. Addition of extracellular S1P to MLO-Y4 cells enhanced the synthesis and release of prostaglandin E2 (PGE2) under static cells and amplified OFF-induced PGE2 release. The stimulatory effect of OFF on the gene expression levels of osteoprotegerin (OPG) and receptor activator for nuclear factor κB ligand (RANKL) was S1P dependent. Furthermore, the S1P2 receptor subtype was shown to be involved in OFF-induced PGE2 synthesis and release, as well as down-regulation of RANKL/OPG gene expression ratio. In summary, our data suggest that S1P cascade is involved in OFF-induced mechanotransduction in MLO-Y4 cells and that extracellular S1P exerts its effect partly through S1P2 receptors.

Capitalizing on diversity: an integrative approach towards the multiplicity of cellular mechanisms underlying myogenic responsiveness.

The intrinsic ability of resistance arteries to respond to transmural pressure is the single most important determinant of their function. Despite an ever-growing catalogue of signalling pathways that underlie the myogenic response, it remains an enigmatic mechanism. The myogenic response's mechanistic diversity has largely been attributed to 'hard-wired' differences across species and vascular beds; however, emerging evidence suggests that the mechanistic basis for the myogenic mechanism is, in fact, 'plastic'. This means that the myogenic response can change quantitatively (i.e. change in magnitude) and qualitatively (i.e. change in mechanistic basis) in response to environmental challenges (e.g. disease conditions). Consequently, understanding the dynamics of how the myogenic response capitalizes on its mechanistic diversity is key to unlocking clinically viable interventions. Using myogenic sphingosine-1-phosphate (S1P) signalling as an example, this review illustrates the remarkable plasticity of the myogenic response. We propose that currently unidentified 'organizational programmes' dictate the contribution of individual signalling pathways to the myogenic response and introduce the concept that certain signalling elements act as 'divergence points' (i.e. as the potential higher level regulatory sites). In the context of pressure-induced S1P signalling, the S1P-generating enzyme sphingosine kinase 1 serves as a divergence point, by orchestrating the calcium-dependent and -independent signalling pathways underlying microvascular myogenic responsiveness. By acting on divergence points, the proposed 'organizational programmes' could form the basis for the flexible recruitment and fine-tuning of separate signalling streams that underlie adaptive changes to the myogenic response and its distinctiveness across species and vascular beds.

Proximal cerebral arteries develop myogenic responsiveness in heart failure via tumor necrosis factor-α-dependent activation of sphingosine-1-phosphate signaling.

BACKGROUND: Heart failure is associated with neurological deficits, including cognitive dysfunction. However, the molecular mechanisms underlying reduced cerebral blood flow in the early stages of heart failure, particularly when blood pressure is minimally affected, are not known. METHODS AND RESULTS: Using a myocardial infarction model in mice, we demonstrate a tumor necrosis factor-α (TNFα)-dependent enhancement of posterior cerebral artery tone that reduces cerebral blood flow before any overt changes in brain structure and function. TNFα expression is increased in mouse posterior cerebral artery smooth muscle cells at 6 weeks after myocardial infarction. Coordinately, isolated posterior cerebral arteries display augmented myogenic tone, which can be fully reversed in vitro by the competitive TNFα antagonist etanercept. TNFα mediates its effect via a sphingosine-1-phosphate (S1P)-dependent mechanism, requiring sphingosine kinase 1 and the S1P(2) receptor. In vivo, sphingosine kinase 1 deletion prevents and etanercept (2-week treatment initiated 6 weeks after myocardial infarction) reverses the reduction of cerebral blood flow, without improving cardiac function. CONCLUSIONS: Cerebral artery vasoconstriction and decreased cerebral blood flow occur early in an animal model of heart failure; these perturbations are reversed by interrupting TNFα/S1P signaling. This signaling pathway may represent a potential therapeutic target to improve cognitive function in heart failure.

Tumor necrosis factor-α-mediated downregulation of the cystic fibrosis transmembrane conductance regulator drives pathological sphingosine-1-phosphate signaling in a mouse model of heart failure.

BACKGROUND: Sphingosine-1-phosphate (S1P) signaling is a central regulator of resistance artery tone. Therefore, S1P levels need to be tightly controlled through the delicate interplay of its generating enzyme sphingosine kinase 1 and its functional antagonist S1P phosphohydrolase-1. The intracellular localization of S1P phosphohydrolase-1 necessitates the import of extracellular S1P into the intracellular compartment before its degradation. The present investigation proposes that the cystic fibrosis transmembrane conductance regulator transports extracellular S1P and hence modulates microvascular S1P signaling in health and disease. METHODS AND RESULTS: In cultured murine vascular smooth muscle cells in vitro and isolated murine mesenteric and posterior cerebral resistance arteries ex vivo, the cystic fibrosis transmembrane conductance regulator (1) is critical for S1P uptake; (2) modulates S1P-dependent responses; and (3) is downregulated in vitro and in vivo by tumor necrosis factor-α, with significant functional consequences for S1P signaling and vascular tone. In heart failure, tumor necrosis factor-α downregulates the cystic fibrosis transmembrane conductance regulator across several organs, including the heart, lung, and brain, suggesting that it is a fundamental mechanism with implications for systemic S1P effects. CONCLUSIONS: We identify the cystic fibrosis transmembrane conductance regulator as a critical regulatory site for S1P signaling; its tumor necrosis factor-α-dependent downregulation in heart failure underlies an enhancement in microvascular tone. This molecular mechanism potentially represents a novel and highly strategic therapeutic target for cardiovascular conditions involving inflammation.