Sphingosine-1-phosphate-dependent activation of p38 MAPK maintains elevated peripheral resistance in heart failure through increased myogenic vasoconstriction

Characterization of the thoracodorsal artery: morphology and reactivity

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.

Controlled release of thymosin β4 from injected collagen-chitosan hydrogels promotes angiogenesis and prevents tissue loss after myocardial infarction

AIMS

Acute myocardial infarction (MI) leads to fibrosis and severe left ventricular wall thinning. Enhancing vascularization within the infarct reduces cell death and maintains a thick left ventricular wall, which is essential for proper cardiac function. Here, we evaluated the controlled delivery of thymosin β4 (Tβ4), which supports cardiomyocyte survival by inducing vascularization and upregulating Akt activity, in the treatment of MI.

MATERIALS & METHODS

We injected collagen-chitosan hydrogel with controlled release of Tβ4 into the infarct after performing left anterior descending artery ligation in rats.

RESULTS

Tβ4-encapsulated hydrogel (thymosin) significantly reduced tissue loss post-MI (13 ± 4%), compared with 58 ± 3% and 30 ± 8% tissue loss for no treatment (MI only) and Tβ4-free hydrogel (control). Significantly more Factor VIII-positive blood vessels with diameter >50 µm were in the thymosin group compared with both MI only and control (p < 0.0001), showing Tβ4-induced vascularization. Wall thickness was positively correlated with the mature blood vessel density (r = 0.9319; p < 0.0001).

CONCLUSION

Controlled release of Tβ4 within the infarct enhances angiogenesis and presence of cardiomyocytes that are necessary for cardiac repair.

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.

Emerging role of G protein-coupled receptors in microvascular myogenic tone

Blood flow autoregulation results from the ability of resistance arteries to reduce or increase their diameters in response to changes in intravascular pressure. The mechanism by which arteries maintain a constant blood flow to organs over a range of pressures relies on this myogenic response, which defines the intrinsic property of the smooth muscle to contract in response to stretch. The resistance to flow created by myogenic tone (MT) prevents tissue damage and allows the maintenance of a constant perfusion, despite fluctuations in arterial pressure. Interventions targeting MT may provide a more rational therapeutic approach in vascular disorders, such as hypertension, vasospasm, chronic heart failure, or diabetes. Despite its early description by Bayliss in 1902, the cellular and molecular mechanisms underlying MT remain poorly understood. We now appreciate that MT requires a complex mechanotransduction converting a physical stimulus (pressure) into a biological response (change in vessel diameter). Although smooth muscle cell depolarization and a rise in intracellular calcium concentration are recognized as cornerstones of the myogenic response, the role of wall strain-induced formation of vasoactive mediators is less well established. The vascular system expresses a large variety of Class 1 G protein-coupled receptors (GPCR) activated by an eclectic range of chemical entities, including peptides, lipids, nucleotides, and amines. These messengers can function in blood vessels as vasoconstrictors. This review focuses on locally generated GPCR agonists and their proposed contributions to MT. Their interplay with pivotal G(q-11) and G(12-13) protein signalling is also discussed.

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.

Post-myocardial infarct p27 fusion protein intravenous delivery averts adverse remodelling and improves heart function and survival in rodents

AIMS

P27Kip1 (p27) blocks cell proliferation through the inhibition of cyclin-dependent kinase 2 (cdk-2). Despite robust expression in the heart, little is known about the regulation and function of p27 in this terminally differentiated tissue. Previously, we demonstrated that p27 exerts anti-apoptotic and growth-inhibitory effects through interaction with casein kinase 2 (ck2) in neonatal rat cardiomyocytes. Here, we test the hypothesis that delivery of a transactivator of transcription (TAT)-p27 fusion protein (TAT.p27) will improve cardiac function and survival in a rat model of myocardial infarction (MI).

METHODS AND RESULTS

Fisher rats underwent permanent left anterior descending ligation-induced MI followed by iv injection of TAT.p27 or TAT.LacZ (20 mg/kg) on Days 1 and 7 post-MI. Delivery of TAT.p27 was evaluated by western blot (WB) and immunofluorescence microscopy. Heart function was assessed by echocardiography and pressure-volume catheter. Apoptosis, hypertrophy, and fibrosis were detected by histochemistry and morphometry. WB confirmed gradual reduction in endogenous cardiac p27 levels following MI, with immunohistochemistry demonstrating successful delivery of TAT.p27 to the heart. At 48 h post-MI, cardiac apoptosis was decreased in rats treated with TAT.p27 when compared with saline- and TAT.LacZ-treated controls. At 28 days post-MI, rats treated with TAT.p27 manifested less cardiomyocyte hypertrophy and fibrosis, less diminished cardiac function, and greater survival. Additionally, p27KO mice undergoing experimental MI suffered an early increase in apoptosis with a larger infarct size and markedly reduced survival when compared with wild-type (WT) controls.

CONCLUSION

These gain- and loss-of-function studies reveal a critical role for p27 in cardiac remodelling post-MI.

Metoprolol impairs resistance artery function in mice

Acute β-blockade with metoprolol has been associated with increased mortality by undefined mechanisms. Since metoprolol is a relatively high affinity blocker of β(2)-adrenoreceptors, we hypothesized that some of the increased mortality associated with its use may be due to its abrogation of β(2)-adrenoreceptor-mediated vasodilation of microvessels in different vascular beds. Cardiac output (CO; pressure volume loops), mean arterial pressure (MAP), relative cerebral blood flow (rCBF; laser Doppler), and microvascular brain tissue Po(2) (G2 oxyphor) were measured in anesthetized mice before and after acute treatment with metoprolol (3 mg/kg iv). The vasodilatory dose responses to β-adrenergic agonists (isoproterenol and clenbuterol), and the myogenic response, were assessed in isolated mesenteric resistance arteries (MRAs; ∼200-μm diameter) and posterior cerebral arteries (PCAs ∼150-μm diameter). Data are presented as means ± SE with statistical significance applied at P < 0.05. Metoprolol treatment did not effect MAP but reduced heart rate and stroke volume, CO, rCBF, and brain microvascular Po(2), while concurrently increasing systemic vascular resistance (P < 0.05 for all). In isolated MRAs, metoprolol did not affect basal artery tone or the myogenic response, but it did cause a dose-dependent impairment of isoproterenol- and clenbuterol-induced vasodilation. In isolated PCAs, metoprolol (50 μM) impaired maximal vasodilation in response to isoproterenol. These data support the hypothesis that acute administration of metoprolol can reduce tissue oxygen delivery by impairing the vasodilatory response to β(2)-adrenergic agonists. This mechanism may contribute to the observed increase in mortality associated with acute administration of metoprolol in perioperative patients.

Microvascular tissue perfusion is impaired in acutely decompensated heart failure and improves following standard treatment

AIMS

Acutely decompensated heart failure (ADHF) leads to neurohumoral activation potentially affecting vascular tone and organ perfusion and may be linked to unfavourable outcome. Global haemodynamic, clinical, and laboratory parameters may severely underestimate tissue hypoperfusion. Therefore, the purpose of this study was to evaluate microvascular flow index (MFI) in patients with ADHF and to assess the effect of standard pharmacological therapy using Sidestream Dark Field (SDF) imaging.

METHODS AND RESULTS

Twenty-seven patients (mean age 75.5 ± 10.1 years, 48% male) with ADHF in New York Heart Association functional class ≥III were included. Serum markers of neurohumoral activation [brain natriuretic peptide (BNP)], endothelin-1 (ET-1), noradrenaline (NA), and echocardiographic parameters of left ventricle-function were determined at hospital admission and the day before discharge. Using SDF imaging, MFI was evaluated at both time-points in semi-quantitative vessel categories (small: 10-25 μm; medium: 26-50 μm; and large: 51-100 μm). At admission, increased serum levels of BNP, NA, and ET-1 and a severely reduced MFI were observed in association with ADHF. Serum levels of BNP, NA, and ET-1 decreased significantly with standard pharmacological therapy (BNP: 2163 ± 1577 vs.1006 ± 945 pg/mL, P< 0.05; NA: 349 ± 280 to 318 ± 265 pg/mL, P< 0.05; ET-1: 5.08 ± 0.72 to 4.81 ± 0.59 pg/mL; P< 0.01). Standard pharmacological treatment also had a profound impact on tissue perfusion by significantly improving median MFI in small [2.6; inter-quartile range (IQR) 2.3-2.9 vs. 2.9; IQR 2.8-3.0; P= 0.01) and medium-sized (2.0; IQR 1.9-2.5 vs. 2.7; IQR 2.5-2.8; P< 0.01) vessels.

CONCLUSION

In patients with ADHF, microvascular tissue perfusion is impaired even when global haemodynamic or laboratory signs of hypoperfusion are absent. Effective pharmacological treatment to decrease neurohumoral activation significantly improves microflow. Hypoperfusion in ADHF is potentially linked to neurohumoral activation with increased plasma levels of vasoconstrictors and sympatho-adrenergic activity.