Histamine induces activation of protein kinase D that mediates tissue factor expression and activity in human aortic smooth muscle cells

Role of protein kinase D1 in vasoconstriction and haemodynamics in rats

AIMS

Protein kinase D (PKD), once considered an effector of protein kinase C (PKC), now plays many pathophysiological roles in various tissues. However, little is known about role of PKD in vascular function. We investigated the role of PKD in contraction of rat aorta and human aortic smooth muscle cells (HASMCs) and in haemodynamics in rats.

METHODS AND RESULTS

Isometric tension of rat aortic was measured to examine norepinephrine-induced contraction in the presence of PKD, PKC and Rho-kinase inhibitors. Phosphorylation of PKD1, myosin targeting subunit-1 (MYPT1), myosin light chain (MLC), CPI-17 and heat-shock protein 27 (HSP27), and actin polymerization were measured in the aorta. Phosphorylation of MYPT1 and MLC was also measured in HASMCs knocked down with specific siRNAs of PKD 1, 2 and 3. Intracellular calcium concentrations and cell shortening were measured in HASMCs. Norepinephrine-induced aortic contraction was accompanied by increased phosphorylation of PKD1, MYPT1 and MLC and actin polymerization, all of which were attenuated with PKD inhibitor CRT0066101. PKD1 phosphorylation was not inhibited by PKC inhibitor, chelerythrine or Rho kinase inhibitor, fasudil. In HASMCs, the phosphorylation of MYPT1 and MLC was attenuated by PKD1, but not PKD2, 3 knockdown. In HASMCs, CRT0066101 inhibited norepinephrine-induced cell shortening without affecting calcium concentration. Administration of CRT0066101 decreased systemic vascular resistance and blood pressure without affecting cardiac output in rats.

CONCLUSIONS

PKD1 may play roles in aorta contraction and haemodynamics via phosphorylation of MYPT1 and actin polymerization in a calcium-independent manner.

LPA1-mediated PKD2 activation promotes LPA-induced tissue factor expression via the p38α and JNK2 MAPK pathways in smooth muscle cells

Tissue factor (TF) is the principal initiator of blood coagulation and is necessary for thrombosis. We previously reported that lysophosphatidic acid (LPA), a potent bioactive lipid, highly induces TF expression at the transcriptional level in vascular smooth muscle cells. To date, however, the specific role of the LPA receptor is unknown, and the intracellular signaling pathways that lead to LPA induction of TF have been largely undetermined. In the current study, we found that LPA markedly induced protein kinase D (PKD) activation in mouse aortic smooth muscle cells (MASMCs). Small-interfering RNA-mediated knockdown of PKD2 blocked LPA-induced TF expression and activity, indicating that PKD2 is the key intracellular mediator of LPA signaling leading to the expression and cell surface activity of TF. Furthermore, our data reveal a novel finding that PKD2 mediates LPA-induced TF expression via the p38α and JNK2 MAPK signaling pathways, which are accompanied by the PKD-independent MEK1/2-ERK-JNK pathway. To identify the LPA receptor(s) responsible for LPA-induced TF expression, we isolated MASMCs from LPA receptor-knockout mice. Our results demonstrated that SMCs isolated from LPA receptor 1 (LPA₁)-deficient mice completely lost responsiveness to LPA stimulation, which mediates induction of TF expression and activation of PKD and p38/JNK MAPK, indicating that LPA₁ is responsible for PKD2-mediated activation of JNK2 and p38α. Taken together, our data reveal a new signaling mechanism in which the LPA₁-PKD2 axis mediates LPA-induced TF expression via the p38α and JNK2 pathways. This finding provides new insights into LPA signaling, the PKD2 pathway, and the mechanisms of coagulation/atherothrombosis.

Non-coding RNAs in aortic dissection: From biomarkers to therapeutic targets

Aortic dissection (AD) is the rupture of the aortic intima, causing the blood in the cavity to enter the middle of the arterial wall. Without urgent and proper treatment, the mortality rate increases to 50% within 48 hours. Most patients present with acute onset of symptoms, including sudden severe pain and complex and variable clinical manifestations, which can be easily misdiagnosed. Despite this, the molecular mechanisms underlying AD are still unknown. Recently, non‐coding RNAs have emerged as novel regulators of gene expression. Previous studies have proven that ncRNAs can regulate several cardiovascular diseases; therefore, their potential as clinical biomarkers and novel therapeutic targets for AD has aroused widespread interest. To date, several studies have reported that microRNAs are crucially involved in AD progression. Additionally, several long non‐coding RNAs and circular RNAs have been found to be differentially expressed in AD samples, suggesting their potential roles in vascular physiology and disease. In this review, we discuss the functions of ncRNAs in AD pathophysiology and highlight their potential as biomarkers and therapeutic targets for AD. Meanwhile, we present the animal models previously used for AD research, as well as the specific methods for constructing mouse or rat AD models.

Immune Factors in Deep Vein Thrombosis Initiation

Deep vein thrombosis (DVT) is a major origin of morbidity and mortality. While DVT has long been considered as blood coagulation disorder, several recent lines of evidence demonstrate that immune cells and inflammatory processes are involved in DVT initiation. Here, we discuss these mechanisms, in particular, the role of immune cells in endothelial activation, and the immune cascades leading to expression of adhesion receptors on endothelial cells. We analyze the specific recruitment and functional roles of different immune cells, such as mast cells and leukocytes, in DVT. Importantly, we also speculate how immune modulation could be used for DVT prevention with a lower risk of bleeding complications than conventional therapeutic approaches.

Differential function and regulation of orphan nuclear receptor TR3 isoforms in endothelial cells

TR3 has been reported to be an excellent target for angiogenesis therapies. We reported three TR3 transcript variant messenger RNAs (mRNAs) are expressed in human umbilical vein endothelial cell (HUVEC) and are differentially regulated by vascular endothelial growth factor (VEGF). TR3 transcript variant 1 (TR3-TV1) and variant 2 (TR3-TV2) encoding the same TR3 isoform 1 protein (TR3-iso1) that was named TR3 has been extensively studied. However, the function of TR3 isoform 2 protein (TR3-iso2) encoded by TR3 transcript variant 3 (TR3-TV3) is still not known. Here, we clone and express the novel TR3-iso2 protein and find that expression of TR3-iso2, in contrast to TR3-iso1, inhibits endothelial cell proliferation induced by VEGF-A, histamine, and phorbol-12-myristate-13-acetate (PMA). The differential function of TR3-iso2 correlates with the down-regulation of cyclin D1. However, TR3-iso2 plays similar roles in endothelial cell migration and monolayer permeability as TR3-iso1. We further demonstrate that several intracellular signaling pathways are involved in histamine-induced TR3 transcript variants, including histamine receptor H1-mediated phospholipase C (PLC)/calcium /calcineurin/protein kinase C (PKC)/protein kinase D (PKD) pathway and ERK pathway, as well as histamine receptor H3-mediated PKC-ERK pathway. Further, expressions of TR3-TV1, TR3-TV2, and TR3-TV3 by VEGF and histamine are regulated by different promoters, but not by their mRNA stability.

NPY/Y₁ receptor-mediated vasoconstrictory and proliferative effects in pulmonary hypertension

BACKGROUND AND PURPOSE

Pulmonary arteries (PAs) are innervated, but little is known about the role of neuronal axis in pulmonary hypertension (PH). Here, we have examined the role of the neuropeptide Y (NPY) and its Y₁ receptor in PH pathogenesis.

EXPERIMENTAL APPROACH

NPY was localized by immunofluorescence. Expression of NPY and Y₁ receptor were determined by quantitative PCR. Cellular response to NPY stimulation was assessed by Western blotting, thymidine incorporation and calcium imaging. Wire myography and isolated perfused mouse lung were applied to study pulmonary vasoactive effects of NPY. Selective receptor antagonists were used to assess the contribution of receptor subtypes in mediating NPY effects.

KEY RESULTS

Samples from PH patients showed increased NPYergic innervation within the PA wall and higher Y₁ receptor expression, compared with donors. However, NPY levels were unchanged in both PA and serum. In the chronic hypoxic mouse model, Y₁ receptor were up-regulated, while expression of both NPY and Y₁ receptor was increased in the lungs of monocrotaline and SU5416-hypoxia rats. On a functional level, NPY acutely increased intracellular calcium levels and enhanced vasoconstriction of lung vessels preconstricted with adrenaline. Furthermore, NPY stimulated proliferation of human pulmonary arterial smooth muscle cells and activated p38 and PKD pathways. Correspondingly, higher phosphorylation of PKD was observed in remodelled vessels from PH patients. The selective Y₁ receptor antagonist, BIBO 3304, concentration-dependently inhibited vasoconstrictive and proliferative effects of NPY.

CONCLUSIONS AND IMPLICATIONS

NPY and Y₁ receptor are possible mediators of both vasoconstriction and pulmonary vascular remodelling in PH.

The inhibitory effect of simvastatin and aspirin on histamine responsiveness in human vascular endothelial cells

Statins and aspirin deliver well-established cardiovascular benefits resulting in their increased use as combined polypills to decrease risk of stroke and heart disease. However, the direct endothelial effect of combined statin/aspirin cotreatment remains unclear. Histamine is an inflammatory mediator that increases vascular permeability, and so we examined the effect of treating human umbilical vein endothelial cells (HUVECs) for 24 h with 1 μM simvastatin and 100 μM aspirin on histamine responsiveness. Subsequent histamine (1 μM) challenge increased intracellular calcium (Ca(2+)i) concentration, an effect that was significantly inhibited by combined simvastatin/aspirin pretreatment but not when then the compounds were given separately, even at 10-fold higher concentrations. In contrast, the Ca(2+)i mobilization response to ATP challenge (10 μM) was not inhibited by combined simvastatin/aspirin pretreatment. The H1 receptor antagonist pyrilamine significantly inhibited both histamine-induced Ca(2+)i mobilization and extracellular signal-regulated kinase (ERK) activation, whereas ranitidine (H2 receptor antagonist) was without effect. However, combined simvastatin/aspirin pretreatment failed to decrease H1 receptor protein expression ruling out receptor downregulation as the mechanism of action. Histamine-induced ERK activation was also inhibited by atorvastatin pretreatment, while simvastatin further inhibited histamine-induced vascular endothelial cadherin phosphorylation as well as altered HUVEC morphology and inhibited actin polymerization. Therefore, in addition to the known therapeutic benefits of statins and aspirin, here we provide initial cellular evidence that combined statin/aspirin treatment inhibits histamine responsiveness in HUVECs.

Pro- and anti-inflammatory effects of histamine on tissue factor and TNFα expression in monocytes of human blood

BACKGROUND

Histamine is classified as an inflammatory mediator and has been reported to have anti- as well as pro-inflammatory properties. The aim of this study was to explore the role of histamine on the production of LPS-induced tissue factor (TF) activity and TNFα in monocytes of whole blood in the absence and presence of TNFα or PMA.

METHODS

Human blood anticoagulated with Fragmin was subjected to stimulation by LPS in the presence and absence of TNFα or PMA and various concentrations of histamine. Tissue factor (TF) activity was measured in lyzed cells after isolation of mononuclear cells whereas TNFα was quantified in plasma after centrifugation of cells.

RESULTS

Histamine gave a dose dependent inhibitory effect on LPS-induced TF activity in monocytes of whole blood, with a 50% reduction at 0.033 μM. A similar effect was seen when the blood cells were stimulated with the combination of LPS and TNFα although TNFα enhanced LPS-induced TF activity almost two fold. In contrast, when blood was incubated with LPS and PMA in whole blood, histamine gave a significant rise in TF activity at 0.01 μM and 0.33 μM histamine. The effect of histamine was less at 0.1 μM or higher concentrations giving a biphasic profile. Contrary to the effect of histamine on LPS plus PMA induced TF activity, histamine caused a significant reduction in TNFα albeit less than in the absence of PMA. Intake of aspirin caused a significant rise in LPS-induced TF activity that was almost abolished by histamine at 0.033 μM.

CONCLUSION

Our study shows that histamine has an anti-inflammatory effect on LPS and LPS/TNFα stimulated monocytes of whole blood. In contrast when blood cells are activated by a combination of LPS and PMA whereby PKC is activated, histamine has a procoagulant/pro-inflammatory effect through enhancement of TF activity expression.