Minimally modified LDL upregulates endothelin type B receptors in rat coronary artery via ERK1/2 MAPK and NF-κB pathways

Tetrahydroxystilbene glucoside attenuated homocysteine-upregulated endothelin receptors in vascular smooth muscle cells via the ERK1 /2 /NF-κB signaling pathway

2,3,5,4'-Tetrahydrostilbene-2-o-β-d-glucoside (TSG) is the main active component of Polygonum multiflorum Thunb. It has effects on hypertension. However, the mechanism is unclear. Current research is devoted to exploring the mechanism of TSG improving HHcy-induced hypertension. The mice received a subcutaneous injection of Hcy in the presence or absence of TSG for 4 weeks. Blood pressure (BP) was measured using a noninvasive tail-cuff plethysmography method. Levels of plasma Hcy and endothelin-1 were measured using ELISA. Rat SMA without endothelium was cultured in a serum-free medium in the presence or absence of TSG with or without Hcy. The contractile response to sarafotoxin 6c or endothein-1 was studied using a sensitive myography. The levels of protein were detected using Western blotting. The results showed that TSG lowered HHcy-elevated BP and decreased levels of plasma Hcy and endothelin-1 in mice. Furthermore, the results showed that TSG inhibited Hcy-upregulated ET receptor expression and ET receptor-mediated contractile responses as well as the levels of p-ERK_1/2 and p-p65 in SMA. In vivo results further validate the in vitro results. In conclusion, TSG can decrease the levels of plasma Hcy and ET-1 and downregulate Hcy-upregulated ET receptors in VSMCs by inhibiting the ERK_1/2 /NF-κB/ET_B2 pathway to lower the BP.

Inhibitors of the MAPK/ NF-κB pathway attenuate the upregulation of the ETB receptor mediated by high glucose in vascular smooth muscle cells

BACKGROUND

Increased vascular smooth muscle cell (VSMC) endothelin type B (ET_B) receptor expression is involved in cardiovascular diseases. High glucose (HG) in diabetes is closely related to cardiovascular complications. Although diabetes upregulates VSMC endothelin subtype B (ET_B) receptors, its mechanism is still unclear. Our aim is to investigate the mechanism of HG-induced ET_B receptors in VSMCs.

METHODS

Rat superior mesenteric arteries (SMAs) without endothelium were cultured in medium without serum for 24 h. HG with or without mitogen-activated protein kinase (MAPK) signaling pathway inhibitors and downstream nuclear factor-kappaB (NF-κB) inhibitors was coincubated with SMAs. A sensitive myograph detected the contractile responses to sarafotoxin 6c. Western blotting and immunofluorescence staining were used to determine protein expression.

RESULTS

HG promoted the expression of VSMC ET_B receptors in rat SMAs and enhanced the ET_B receptor-induced contractile response. The results showed that HG increased vascular smooth muscle cell (VSMC) ET_B receptor expression and ET_B receptor-induced contractile responses in rat SMAs. Both extracellular signal-related kinase 1 and 2 (ERK1/2) inhibitors (U0126) and P38 inhibitors (SB203580) significantly inhibited HG-increased VSMC ET_B receptors. However, a C-jun terminal kinase (p-JNK) inhibitor (SP600125) did not affect HG- upregulated VSMC ET_B receptors. Further study showed that NF-κB using an IκB kinase inhibitor (wedelolactone) also significantly inhibited HG-increased VSMC ET_B receptors.

CONCLUSION

In conclusion, HG upregulated the VSMC ET_B receptor by activating the ERK1/2- or P38- NF-κB signaling pathway.

Minimally modified low-density lipoprotein upregulates mouse mesenteric arterial 5-HT1B receptor in vivo via activation of the JAK2/STAT3 pathway

OBJECTIVES

To explore whether minimally modified low-density lipoprotein (mmLDL) upregulates mesenteric arterial 5-hydroxytryptamine 1B (5-HT_1B) receptor expression by activating the JAK2/STAT3 signaling pathway.

METHODS

Mice were randomly divided into the following groups: the normal saline (NS), LDL, mmLDL, mmLDL+galiellactone (GL, a JAK2/STAT3 pathway inhibitor), and mmLDL+DMSO groups. The dose-response curve of mesenteric arterial ring constriction after administration of 5-carboxamidotryptamine (5-CT), an agonist of 5-HT_1B, was recorded with a microvascular tensiometer. JAK2, p-JAK2, STAT3, p-STAT3, and 5-HT_1B receptor protein expression levels were determined by Western blotting. 5-HT_1B receptor mRNA levels were measured by RT-PCR. 5-HT_1B receptor protein expression was determined by immunofluorescence.

RESULTS

Injection of mmLDL into the tail vein significantly increased the contractile dose-response curve after 5-CT stimulation, as the E_max was 82.15 ± 6.15% in the NS group and 171.88 ± 5.78% in the mmLDL group (P < 0.01); significantly elevated 5-HT_1B receptor mRNA and protein expression levels; and significantly increased p-JAK2 and p-STAT3 protein expression levels. After intraperitoneal injection of GL, the vasoconstrictive response was significantly reduced compared with that in the mmLDL group, as the E_max was decreased to 97.14 ± 1.20% (P < 0.01); 5-HT_1B receptor mRNA and protein expression levels were significantly reduced; STAT3 phosphorylation and p-JAK2 and p-STAT3 protein expression were not significantly changed; and 5-HT_1B receptor expression was altered via inhibition of p-STAT3 binding to DNA, which suppressed transcription.

CONCLUSIONS

mmLDL can upregulate 5-HT_1B receptor expression in mouse mesenteric arteries by activating the JAK2/STAT3 signaling pathway.

Minimally modified low-density lipoprotein upregulates the ETB and α1 receptors in mouse mesenteric arteries in vivo by activating the PI3K/Akt pathway

OBJECTIVES

The current study aimed to explore whether minimally modified low-density lipoprotein (mmLDL) via tail vein injection upregulates the ET_B and α₁ receptors in mouse mesenteric arteries by activating the PI3K/Akt pathway.

METHODS

The contraction curves of the mesenteric arteries caused by sarafotoxin 6c (S6c, ET_B receptor agonist) and phenylephrine (PE, α₁ receptor agonist) were measured by a myograph system. Serum oxLDL was detected using enzyme-linked immunosorbent assays. The levels of the ET_B receptor, the α₁ receptor, PI3K, p-PI3K and p-Akt were detected using real-time polymerase chain reaction and Western blot analyses.

KEY FINDINGS

Minimally modified low-density lipoprotein noticeably enhanced the contraction effect curves of S6c and PE, with significantly increased E_max values (P < 0.01), compared to those of the control group. This treatment significantly increased the mRNA expression and protein levels of the ET_B and α₁ receptors and the protein levels of p-PI3K and p-Akt in the vessel wall (P < 0.01). LY294002 inhibited the effect of mmLDL.

CONCLUSIONS

An increase in mmLDL activated the PI3K/Akt pathway, which upregulated the expression of the ET_B and α₁ receptors and enhanced the ET_B and α_1- receptor-mediated contractile function.

High glucose upregulates endothelin type B receptors in vascular smooth muscle cells via the downregulation of Sirt1

Silent information regulator family protein 1 (Sirt1) has recently gained attention for its protective effects against diabetic and cardiovascular diseases (CVDs). Vascular smooth muscle endothelin type B (ETB) receptors are involved in the pathogenesis of CVDs and diabetes. The aim of present study was to explore whether Sirt1 is involved in high glucose (HG)-mediated regulation of ETB receptors in rat superior mesenteric arteries (SMA). The rat SMA segments were cultured in the presence and absence of HG with or without the activator of Sirt1 and specific inhibitor for the extracellular signal-regulated protein kinase 1/2 (ERK1/2) for 24 h. Following organ culture, the contractile responses to sarafotoxin 6c were studied using a sensitive myograph, and the ETB receptor protein expression level was determined using western blotting. The results demonstrated that HG induced upregulation of ETB receptor expression and increased receptor-mediated vasoconstriction in SMA. Resveratrol (Res; a Sirt1 activator) concentration-dependently inhibited the HG-induced upregulation of ETB receptor expression and receptor-mediated vasoconstriction. Additionally, these effects could also be abolished by an inhibitor of the ERK1/2 signaling pathway. Furthermore, upregulation of ERK1/2 phosphorylation induced by HG was inhibited by Res. In conclusion, HG upregulated ETB receptors by downregulating Sirt1 and subsequently activating the ERK1/2 signaling pathways in the organ culture SMA.

Tail vein injection of mmLDL upregulates mouse mesenteric artery ETB receptors via activation of the ERK1/2 pathway

Minimally modified low density lipoprotein (mmLDL) is a risk factor for cardiovascular disease. This study investigated the effect of mmLDL on mouse mesenteric artery endothelin type B (ET_B) receptors and its molecular mechanism. Mice were injected with normal saline (NS group), mmLDL in the tail vein (mmLDL group), or with both mmLDL and an intraperitoneal injection of the ERK1/2 pathway-specific inhibitor U0126 (mmLDL+U0126 group). The dose-response curve of mesenteric artery contraction induced by sarafotoxin 6c (S6c), the ET_B receptor agonist, was measured using a sensitive myograph system. ELISAs, RT-PCR and Western blot were used to determine the serum concentrations of mouse oxidized low density lipoprotein (oxLDL), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) as well as the expression of ET_B receptors, ICAM-1, VCAM-1 and phosphorylated-extracellular signal-regulated kinase 1/2 (p-ERK1/2). The S6c-induced contraction dose-response curve was significantly enhanced by mmLDL treatment and showed a significantly higher E_max value than in the NS group (P<0.001), and the ET_B receptor mRNA and protein expression in the vascular wall was significantly higher than in the NS group. The serum concentration and expression of ICAM-1 and VCAM-1 were also increased by mmLDL treatment, but intraperitoneal injection of U0126 inhibited these changes as well as the increase in p-ERK1/2 protein in the vessel wall caused by mmLDL. ICAM-1 and VCAM-1 serum concentrations were positively correlated with the S6c-induced maximum contraction of blood vessels. Increased in vivo levels of mmLDL increased the serum concentrations and expression of ICAM-1 and VCAM-1 by activating the ERK1/2 pathway, resulting in the expression of ET_B receptors and the enhancement of contractile function in vascular smooth muscle. Understanding the effect of mmLDL on ET_B receptors and its mechanism can provide ideas for cardiovascular disease prevention and treatment.

Airborne fine particulate matter alters the expression of endothelin receptors in rat coronary arteries

Exposure to airborne fine particulate matter (PM_2.5) is associated with cardiovascular diseases. However, a comprehensive understanding of the underlying mechanisms by which PM_2.5 induces or aggravates these diseases is still insufficiently clear. The present study investigated whether PM_2.5 alters the expression of the endothelin subtype B (ET_B) and endothelin subtype A (ET_A) receptors in the coronary artery and examined the underlying mechanisms. Rat coronary artery segments were cultured with PM_2.5 in the presence or absence of MEK/ERK1/2, JNK, and p38 pathway inhibitors. Contractile reactivity was measured by myography. ET_B and ET_A receptor expression was evaluated using RT-PCR, western blot and immunohistochemistry. Compared with fresh arteries, the cultured coronary arteries showed a significantly enhanced contraction mediated by the ET_B receptor and an unaltered contraction mediated by the ET_A receptor. Culture with PM_2.5 significantly enhanced the contraction and the mRNA and protein expression levels of the ET_B and ET_A receptors in the coronary arteries, suggesting that PM_2.5 induces an upregulation of ET_A and ET_B receptors. In addition, the PM_2.5-induced increases in ET_B- and ET_A-mediated vasoconstriction and receptor expressions could be notably decreased by MEK1/2 inhibitor, U0126 and Raf inhibitor, SB386023, suggesting that the upregulation of ET_B and ET_A receptors is related with MEK/ERK1/2 pathway. In conclusion, PM_2.5 induces the ET_B and ET_A receptor upregulation in rat coronary arteries, and the MEK/ERK1/2 pathway may be involved in this process.

The ERK1/2 pathway participates in the upregulation of the expression of mesenteric artery α1 receptors by intravenous tail injections of mmLDL in mice

Minimally modified low density lipoprotein (mmLDL) is a risk factor for cardiovascular diseases. However, no studies examining the effect of mmLDL on vascular smooth muscle receptors have been released. The current study investigated the effect of mmLDL on the mesenteric artery α1 adrenoceptor and the molecular mechanisms. Mice were divided into the normal saline (NS), mmLDL, and mmLDL+U0126 groups. In the mmLDL+U0126 group, the animals were subjected to an intravenous tail injection of mmLDL and an intraperitoneal injection of U0126. Vascular tension caused by noradrenaline (NA) in mesenteric arteries was measured with a sensitive myograph system. The serum levels of oxLDL, TNF-α, and IL-1β were detected using enzyme-linked immunosorbent assays. The expressions of the α1 adrenoceptor, the α2 adrenoceptor, TNF-α, IL-1β, and pERK1/2 were detected using real-time polymerase chain reactions and Western blot analysis. Compared with the NS group, the mmLDL group exhibited a noticeably enhanced NA shrinkage dose-response curve and a significantly increased Emax value (P<0.01). Prazosin (α1 adrenoceptor antagonist) caused a noticeable right shift of the dose-response curve. U0126 inhibited the increases in the serum levels and vessel wall expression of IL-1β and TNF-α and enhanced the NA shrinkage dose-response curve caused by mmLDL, as observed by a significantly decreased Emax value (P<0.01). It inhibited the increased α1 adrenoceptor expression caused by mmLDL. The serum levels of IL-1β and TNF-α demonstrated a positive correlation with the NA-induced maximum shrinkage percentage. U0126 inhibited the mmLDL-induced increase in the pERK1/2 protein level in the vessel wall. In conclusion, mmLDL increased the serum levels of IL-1β and TNF-α in vivo by activating the ERK1/2 pathway, which resulted in α1 receptor-mediated vasoconstriction and an increase in the expression of α1 adrenoceptor. The results of this study may provide new ideas for the prevention and cure of cardiovascular diseases in the future.

The determination of optimal initial tension in rat coronary artery using wire myography

The aim of the present study was to determine the optimal initial tension, i.e. initial stretch for rat coronary artery when using the multi-wire myograph system. We used the normalization procedure to mimic physiological conditions and to stretch the coronary arterial segments to normalized internal circumference (IC(1)). It is determined the internal circumference when the vessel relaxed under a transmural pressure of 100 mm Hg (IC(100)), and the IC(1) is calculated by multiplying the IC(100) by a factor k. The impact of different factor k on the initial stretch and agonist-induced tension of coronary arteries were investigated. The results showed that the maximal agonist-induced tension was achieved at the factor k value of 0.90 and the initial stretch tension was given 1.16+/-0.04 mN/mm. The most appropriate factor k value was 0.90-0.95 and the most appropriate initial tension was 1.16-1.52 mN/mm. The equilibration time of the coronary artery segments should be at least 1.0 h. In the same optimal initial tension, the agonist-induced tension increased as equilibration time lengthened.

Apolipoprotein B, the villain in the drama?

Low-density lipoprotein (LDL) is the major atherogenic lipoprotein and the primary target of lipid-lowering therapy for treating ischemic cardiovascular disease. Apolipoprotein B (apoB), an important structural component of LDL, plays a key role in cholesterol transport and removal in vascular wall. On the other hand, under pathological process, apoB interacts with the arterial wall to initiate the cascade of events that leads to atherosclerosis. However, interactions between apoB and vascular wall remain to be determined. Here, we address a pathological role of apoB per se and whole LDL particle in dysfunction of vascular endothelium and smooth muscle cells i.e. decreased endothelium-dependent vasodilation and increased receptor-mediated vasoconstriction. We intend to discuss: i) how apoB is responsible for the deleterious effects of LDL in the development of ischemic cardiovascular disease; ii) why vaccine based on peptides derived from apoB-100 is a promising therapy for treating ischemic cardiovascular disease, and iii) direct inhibition of apoB production should be a better therapeutic option than simple LDL-cholesterol lowering therapy in the patients with severe hypercholesterolemia at high cardiovascular risk with statin intolerance. In conclusion, apoB, but not cholesterol, plays a major role in LDL-induced dysfunction of endothelium, suggesting that direct apoB-targeting agents might be a promising therapy for the treatment of ischemic cardiovascular disease.

Altered endothelin receptor expression and affinity in spontaneously hypertensive rat cerebral and coronary arteries

Background

Hypertension is associated with arterial hyperreactivity, and endothelin (ET) receptors are involved in vascular pathogenesis. The present study was performed to examine the hypothesis that ET receptors were altered in cerebral and coronary arteries of spontaneously hypertensive rats (SHR).

Methodology/Principal Findings

Cerebral and coronary arteries were removed from SHR. Vascular contraction was recorded using a sensitive myograph system. Real-time PCR and Western blotting were used to quantify mRNA and protein expression of receptors and essential MAPK pathway molecules. The results demonstrated that both ET_A and ET_B receptor-mediated contractile responses in SHR cerebral arteries were shifted to the left in a nonparallel manner with increased maximum contraction compared with Wistar-Kyoto (WKY) rats. In SHR coronary arteries, the ET_A receptor-mediated contraction curve was shifted to the left in parallel with an increased pEC₅₀ compared with the arteries in WKY rats. There was no significant increase in ET_B receptor-mediated contraction in SHR coronary arteries. ET_A receptor mRNA and protein expression was increased in SHR cerebral arteries compared with the arteries in WKY rats. However, ET_A receptor mRNA and protein levels in coronary arteries and ET_B receptor protein levels in cerebral and coronary arteries remained unchanged in SHR compared with WKY rats. Meanwhile, phosphorylated ERK1/2 protein was significantly increased in SHR brain and heart vessels.

Conclusions/Significance

In SHR cerebral arteries, ET_A receptor expression was upregulated. ET_A receptor affinity was increased in coronary arteries, and ET_B receptor affinity was increased in cerebral arteries. The ERK1/2 activation may be involved in the receptor alterations.

Minimally modified LDL upregulates endothelin type A receptors in rat coronary arterial smooth muscle cells

Minimally modified low-density lipoprotein (mmLDL) is a risk factor for cardiovascular disease. The present study investigated the effects of mmLDL on the expression of endothelin type A (ET_A) receptors in coronary arteries. Rat coronary arteries were organ-cultured for 24 h. The contractile responses were recorded using a myographic system. ET_A receptor mRNA and protein expressions were determined using real-time PCR and western blotting, respectively. The results showed that organ-culturing in the presence of mmLDL enhanced the arterial contractility mediated by the ET_A receptor in a concentration-dependent and time-dependent manner. Culturing with mmLDL (10 μg/mL) for 24 h shifted the concentration-contractile curves toward the left significantly with increased E_max of 228% ± 20% from control of 100% ± 10% and significantly increased ET_A receptor mRNA and protein levels. Inhibition of the protein kinase C, extracellular signal-related kinases 1 and 2 (ERK1/2), or NF-κB activities significantly attenuated the effects of mmLDL. The c-Jun N-terminal kinase inhibitor or the p38 pathway inhibitor, however, had no such effects. The results indicate that mmLDL upregulates the ET_A receptors in rat coronary arterial smooth muscle cells mainly via activating protein kinase C, ERK1/2, and the downstream transcriptional factor, NF-κB.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.