Upregulation of vasopressin V1A receptor mRNA and protein in vascular smooth muscle cells following cyclosporin A treatment

The Biology of Vasopressin

Vasopressins are evolutionarily conserved peptide hormones. Mammalian vasopressin functions systemically as an antidiuretic and regulator of blood and cardiac flow essential for adapting to terrestrial environments. Moreover, vasopressin acts centrally as a neurohormone involved in social and parental behavior and stress response. Vasopressin synthesis in several cell types, storage in intracellular vesicles, and release in response to physiological stimuli are highly regulated and mediated by three distinct G protein coupled receptors. Other receptors may bind or cross-bind vasopressin. Vasopressin is regulated spatially and temporally through transcriptional and post-transcriptional mechanisms, sex, tissue, and cell-specific receptor expression. Anomalies of vasopressin signaling have been observed in polycystic kidney disease, chronic heart failure, and neuropsychiatric conditions. Growing knowledge of the central biological roles of vasopressin has enabled pharmacological advances to treat these conditions by targeting defective systemic or central pathways utilizing specific agonists and antagonists.

Arginine Vasopressin and Posterior Reversible Encephalopathy Syndrome Pathophysiology: the Missing Link?

Posterior reversible encephalopathy syndrome (PRES) is a clinicoradiological entity characterized by a typical brain edema. Its pathogenesis is still debated through hypoperfusion and hyperperfusion theories, which have many limitations. As PRES occurs almost exclusively in clinical situations with arginine vasopressin (AVP) hypersecretion, such as eclampsia and sepsis, we hypothesize that AVP plays a central pathophysiologic role. In this review, we discuss the genesis of PRES and its symptoms through this novel approach. We theorize that AVP axis stimulation precipitates PRES development through an increase in AVP secretion or AVP receptor density. Activation of vasopressin V_1a receptors leads to cerebral vasoconstriction, causing endothelial dysfunction and cerebral ischemia. This promotes cytotoxic edema through hydromineral transglial flux dysfunction and may increase endothelial permeability, leading to subsequent vasogenic brain edema. If our hypothesis is confirmed, it opens new perspectives for better patient monitoring and therapies targeting the AVP axis in PRES.

Vasopressin V1A receptor mediates cell proliferation through GRK2-EGFR-ERK1/2 pathway in A7r5 cells

Abnormal proliferation and hypertrophy of vascular smooth muscle (VSMC), as the main structural component of the vasculature, is an important pathological mechanism of hypertension. Recently, increased levels of arginine vasopressin (AVP) and copeptin, the C-terminal fragment of provasopressin, have been shown to correlate with the development of preeclampsia. AVP targets on the G_q-coupled vasopressin V_1A receptor and the G_s-coupled V₂ receptor in VSMC and the kidneys to regulate vascular tone and water homeostasis. However, the role of the vasopressin receptor on VSM cell proliferation during vascular remodeling is unclear. Here, we studied the effects of AVP on the proliferation of the rat VSMC-derived A7r5 cells. AVP, in a time- and concentration-dependent manner, promoted A7r5 cell proliferation as indicated by the induction of proliferating cell nuclear antigen expression, methylthiazolyldiphenyl-tetrazolium reduction and incorporation of 5'-bromodeoxyuridine into cellular DNA. These effects, coupled with the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK_1/2), were blocked by a V_1A receptor antagonist SR45059 but not by a V₂ receptor antagonist lixivaptan. Although acute activation of V_1A receptor induced ERK_1/2 phosphorylation via a protein kinase C-dependent pathway, this effect was not involved in cell proliferation. Cell proliferation and ERK_1/2 phosphorylation in response to prolonged stimulation with AVP were abolished by inhibition of G protein-coupled receptor kinase 2 (GRK2) and epidermal growth factor receptor (EGFR) using specific inhibitors or small hairpin RNA knock-down. These results suggest that activation of V_1A, but not V₂ receptor, produces a cell proliferative signal in A7r5 cells via a GRK2/EGFR/ERK_1/2-dependent mechanism.

Cyclosporine-A, but not tacrolimus significantly increases reactivity of vascular smooth muscle cells

BACKGROUND

Application of cyclosporine-A (CsA) or tacrolimus is associated with numerous side effects. One of the main reasons for restricting usage of CsA is hypertension. In tacrolimus treated subjects the frequency of these phenomena is significantly lower. The known molecular mechanism of action of tacrolimus and cyclosporine-A seems to be the same, thus we decided to compare modulatory effect of drugs on vascular smooth muscle contractility.

METHODS

Experiments were performed on isolated and perfused tail artery of Wistar rats. Contraction force was measured by increased degree of perfusion pressure with a constant flow rate.

RESULTS

Concentration-response curves for agonist in the presence CsA were significantly shifted to the left with increase in maximal responses. This effect was due to increased calcium influx from extracellular calcium stores whereas there were no significant changes in calcium influx in the presence of tacrolimus; concentration-response curve was comparable to controls.

CONCLUSION

Our results strongly support the idea that main difference between effects on smooth muscle contractility of calcineurin-dependent immunosuppressants: CsA and tacrolimus is related to the different level of extracellular calcium influx to the cytoplasm. The elucidation of these mechanisms may permit the identification of new therapeutic strategies against CsA-induced hypertension.

Cyclosporin A and atherosclerosis--cellular pathways in atherogenesis

Cyclosporin A (CsA) is an immunosuppressant drug widely used in organ transplant recipients and people with autoimmune disorders. Long term treatment with CsA is associated with many side effects including hyperlipidemia and an increased risk of atherosclerosis. While its immunosuppressive effects are closely linked to its effects on T cell activation via the inhibition of the nuclear factor of activated T cells (NFAT) pathway, the precise mechanisms underlying its cardiovascular effects appear to involve multiple pathways additional to those relevant for immunosuppression. These include inhibition of calcineurin activity and intracellular cyclophilin peptidylprolyl isomerase and chaperone activities, inhibition of pro-inflammatory extracellular cyclophilin A, and NFAT-independent transcriptional effects. CsA demonstrates complex effects on lipoprotein metabolism and bile acid production, and affects endothelial cells, smooth muscle cells and macrophages, all of which are critical to the atherosclerotic process. Interpretation of the available data is hampered as many experimental models are used to study the effects of CsA in vivo and in vitro, leading to diverse and often contradictory findings. In this review we will describe the cellular mechanisms related to CsA-induced hyperlipidemia and atherosclerosis, with a focus on identifying pro-atherogenic pathways that are distinct from those relevant to its immunosuppressant effects. The potential of CsA analogues to avoid such sequelae will be discussed.

V1a vasopressin receptor expression is modulated during myogenic differentiation

Neurohypophyseal peptides potently stimulate myogenic differentiation by acting through different receptors of the same family. Here, we show that L6C5 myogenic cells express, at a high density, a single class of V1a Arg8-vasopressin (AVP) receptor. The expression of the vasopressin receptor of type 1a (V1aR) is significantly higher in proliferating myoblasts than in differentiated myotubes. The differentiation-related decrease of V1aR expression was evident both at the mRNA and at the protein level as shown by the reduction of [(3)H]-AVP binding. However, in L6C5 cells transfected with a synthetic construct containing the luciferase gene driven by the 2 kb upstream region of V1aR, we observed a stimulation of the activity of the promoter when the cells were cultured in differentiative medium. The down-regulation of the V1aR correlated with a decreased half-life of its mRNA (half-life 5.86+/-0.74 hr in 10% fetal bovine serum [FBS] versus 3.53+/-0.72 hr in 1% FBS). Cyclosporine A and dexamethasone, but not 5'-azacytidine, treatments of cells in differentiation medium restored the V1aR level to that measured in proliferating L6C5 cells, thus confirming the role of post-transcriptional mechanisms in the modulation of V1aR expression. Taken together, these data show that mRNA stability plays a role in modulating protein expression during the myogenic differentiation process.

Disturbances in hormonal regulation of vascular tone during traumatic shock

Changes in hormonal regulation of the vascular tone in Wistar rats were studied on Cannon model of traumatic shock. The pressor response to angiotensin II decreased by 30-40% 3 h after the incidence of trauma. The reaction to vasopressin remained unchanged. However, phenylephrine in medium and high doses produced a more pronounced pressor response under these conditions. One day after trauma we revealed a decrease in vascular sensitivity not only to angiotensin II, but also to vasopressin and alpha1-adrenoceptor agonist phenylephrine. The vascular response was observed only after treatment with phenylephrine in maximum doses. Traumatic shock was accompanied by inverse response to serotonin: hypertensive effect instead of blood pressure drop. Our results show that traumatic shock is accompanied by specific changes in vascular reactivity.

Enhanced Ca2+ response to AVP in preglomerular vessels from rats with genetic hypertension during different hydration states

Exaggerated arginine vasopressin (AVP)-induced calcium signaling and renal vasoconstriction, characteristic in young spontaneously hypertensive rats (SHR) during euvolemia, are related to greater amounts of V1a receptor mRNA and V1a protein in preglomerular resistance arterioles. The present study determined whether V1a receptor density and calcium signal transduction in the renal vasculature of young SHR is regulated appropriately during physiological changes in hydration state. [3H]AVP ligand binding documented two- to threefold greater density of V1a receptors in euvolemic SHR vs. Wistar-Kyoto (WKY) rats. Parallel changes in V1a receptor density were observed in both strains during chronic water loading (plus approximately 50 fmol/mg) and during dehydration (minus approximately 50 fmol/mg). Affinity was unchanged. Real-time RT-PCR demonstrated that V1a mRNA in preglomerular arterioles was three times greater in euvolemic SHR. Dehydration decreased expression approximately 50% in renal vessels independent of rat strain; water loading increased V1a mRNA. Thus V1a receptor regulation correlated with changes in mRNA in a normal manner in response to chronic changes in AVP concentration, albeit set at a higher level in SHR. In dehydrated animals, AVP increased the cytosolic Ca2+ concentration ([Ca2+]i) by 60 +/- 5 and 112 +/- 13 nM cytosolic Ca2+ in WKY and SHR, respectively (P < 0.01), whereas in hydrated animals the [Ca2+]i increase was 168 +/- 10 and 220 +/- 18 nM, respectively (P < 0.05). In all hydration states, calcium signaling was greater in SHR compared with WKY (P < 0.05). Calcium signaling paralleled changes in the receptor density and mRNA. Mechanisms other than hydration state per se are likely to be responsible for the two- to threefold difference in the V1a receptor density between WKY and SHR in the renal vasculature at the critical age of 6 wk.

Age-dependent regulation of vasopressin V1areceptors in preglomerular vessels from the spontaneously hypertensive rat

Experiments were performed to get insight into the role of AVP receptor V1aregulation with age, i.e., during development and maintenance of high blood pressure. Previous studies showed an increased gene expression and renal vascular response to AVP in young spontaneously hypertensive rats (SHR). The age regulation of the V1areceptor was examined in preglomerular vessels from 5-, 10-, 20-, and 70-wk-old SHR using normotensive Wistar-Kyoto rats (WKY) as controls. Real-time PCR and ligand binding were used for analysis of receptor expression, and the change in cytosolic calcium concentration during stimulation of isolated preglomerular vessels with AVP was studied. Studies showed an increase of the V1areceptor protein and mRNA from 5-and 10-wk-old SHR compared with vessels from 20- and 70-wk-old SHR. In 5-wk-old SHR receptor density was 84 ± 13 fmol/mg protein, and 38 ± 11 fmol/mg protein in 70-wk-old SHR ( P < 0.05). mRNA in the 5- and 70-wk-old SHR was 15,854 ± 629 and 3,181 ± 224 V1amRNA/108 18S ribosomal RNA, respectively ( P < 0.001). Values from WKY at all ages were similar to 20- and 70-wk-old SHR. During stimulation with AVP, the change in cytosolic calcium in vessels from 5-wk-old SHR increased 234 ± 59 nM, whereas the increase was 89 ± 9 nM in 70-wk-old SHR ( P = 0.03). These results indicate that the V1areceptor is increased at protein and mRNA level during development of hypertension in SHR but is normalized when hypertension is established.

Immunosuppression and transplant vascular disease: benefits and adverse effects

Cardiac allograft vasculopathy (CAV) occurs within 5 years of transplantation surgery and represents the main cause of death in long-term heart transplant survivors. The detailed pathogenesis of CAV is unknown, but there are strong indications that immunologic mechanisms, which are regulated by nonimmunologic factors, are the major cause of this phenomenon. Cyclosporine A (CsA) is a frequently used immunosuppressive agent in transplant medicine to prevent rejection. The mechanism of action of CsA involves initial binding to cyclophilin to form a complex that then inhibits calcineurin (CN), leading to reduced interleukin (IL)-2 production as part of the signal transduction pathway for the activation of B-lymphocytes and T-lymphocytes. Based on this proposed mechanism, it was expected that CsA should be an effective strategy in attenuating the host immune response against transplanted allograft tissue; however, CsA has not changed the outcome of CAV. Several mechanisms have been suggested for the ineffectiveness of CsA in long-term prevention of CAV. For example, routine therapeutic doses of CsA may block CN incompletely (50%), whereas complete blockade requires doses that are not clinically tolerable. Another explanation is the possible activation of T-cell receptors directly (CN independent) by the immune response, which induces protein kinase C theta (PKCtheta) and leads to IL-2 production and immune rejection. Moreover, there may be a role for nonimmunologic mechanisms, such as complement, which cannot be controlled by CsA, or CsA may cause hypercholesterolemia or induce overexpression of transforming growth factor-beta (TGF-beta). This review also compares the effect of CsA with other immunosuppressants in allograft artery preservation and their clinical efficacy.

Vasopressin type 1A receptor up-regulation by cyclosporin A in vascular smooth muscle cells is mediated by superoxide

Based on our previous results, we investigated whether cyclosporin A (CsA)-induced vasopressin type 1A receptor up-regulation was mediated by free radicals. We report that CsA analogues with different affinities for cyclophilin and calcineurin were able to up-regulate vasopressin type 1A receptor and to generate free radicals in smooth muscle cells independently of calcineurin. Further, we demonstrate that the antioxidant N-acetyl-L-cysteine blocked the increase in vasopressin type 1A receptor mRNA and protein levels induced by CsA and that low concentrations of prooxidants were able to directly increase vasopressin type 1A receptor mRNA and protein levels. In addition, short exposure to CsA or pro-oxidants was sufficient to significantly increase vasopressin type 1A receptor mRNA and protein levels. Using cell-permeable forms of superoxide dismutase and catalase, we finally show that superoxide mediates the CsA-induced effects on vasopressin type 1A receptor. These results provide strong evidence that CsA-induced superoxide generation is causally involved in vasopressin type 1A receptor expression and demonstrate for the first time that low physiological concentrations of radicals, most probably superoxide, are able to directly affect cellular signaling to increase vasopressin type 1A receptor expression in rat aortic smooth muscle cells.

Science review: Vasopressin and the cardiovascular system part 1--receptor physiology

Vasopressin is emerging as a rational therapy for vasodilatory shock states. Unlike other vasoconstrictor agents, vasopressin also has vasodilatory properties. The goal of the present review is to explore the vascular actions of vasopressin. In part 1 of the review we discuss structure, signaling pathways, and tissue distributions of the classic vasopressin receptors, namely V₁ vascular, V₂ renal, V₃ pituitary and oxytocin receptors, and the P₂ class of purinoreceptors. Knowledge of the function and distribution of vasopressin receptors is key to understanding the seemingly contradictory actions of vasopressin on the vascular system. In part 2 of the review we discuss the effects of vasopressin on vascular smooth muscle and the heart, and we summarize clinical studies of vasopressin in shock states.

Portal hypertension is associated with increased mRNA levels of vasopressor G-protein-coupled receptors in human hepatic arteries

BACKGROUND

The contractile response of human splanchnic vessels to different vasoconstrictors is attenuated in cirrhosis. Functional studies indicate a cellular signalling defect upstream of the G-protein level. The aim of the present study was to analyze expression and mRNA levels of the following most relevant vasopressor receptors in the smooth musculature of human hepatic arteries: alpha1 adrenoceptor (AR) subtypes a, b and d, angiotensin II type 1 receptor (AT1), arginine vasopressin receptor type 1a (V1a), endothelin receptor type A (ETA) and B (ETB).

MATERIALS AND METHODS

Hepatic arteries were collected from 10 donors (noncirrhotic) and 14 recipients (cirrhotic) at liver transplantations. Real-time-PCR was performed to quantify steady-state levels of receptor mRNAs.

RESULTS

alpha 1aAR mRNA levels showed no significant difference between the cirrhotic arteries and the controls while the mRNA levels of the other vasoactive receptors were significantly higher in the cirrhotic hepatic arteries (alpha 1bAR: 4-fold, P = 0.013; AT1: 16-fold, P = 0.024; V1a: 23-fold, P = 0.001; ETA: 4-fold, P = 0.02; ETB: 8-fold, P = 0.008). No mRNA for the alpha 1dAR was detected either in the donor or recipient hepatic arteries.

CONCLUSION

We conclude that vascular hyporeactivity to the most relevant endogenous vasoconstrictors of cirrhotic hepatic arteries is not caused by a receptor down-regulation at mRNA levels. In contrast they were up-regulated.

Effects of immunosuppressant FTY720 on renal and hepatic hemodynamics in the rat

BACKGROUND

FTY720 is a novel immunomodulator that may provide an opportunity for a reduction in calcineurin inhibitor dosage in transplant recipients with renal/hepatic side effects. However, the effects of FTY720 on renal or hepatic hemodynamics are unknown. The aim of this study was to establish the hemodynamic and renal actions of FTY720 at therapeutically relevant dosages.

METHODS

The effects of acute and repeat oral administration of FTY720 on systemic, renal, and hepatic hemodynamics were investigated in the anesthetized male Lewis rat. Renal function and renal tubular parameters were examined in animals that received repeat high dosage of FTY720.

RESULTS

Seven-day oral administration of FTY720 did not cause any significant changes in markers of hepatocyte injury, nor did it cause any reduction in renal function (elevated urea and creatinine). Histological examination of liver and kidney from animals treated with repeat FTY720 for 1 or 3 weeks did not reveal any sclerosis, tubular changes, infiltrates, or fibrosis. Hepatocyte, vascular, and biliary structures were normal. Compared with the vehicle (saline), oral administration of FTY720 at dosages up to 5 mg/kg/day for 1 week did not have any significant effects on systemic, hepatic, or renal hemodynamics. Five min after intravenous FTY720 administration (1 mg/kg), mean arterial pressure (MAP) rose to 114+/-3.3% of baseline (P <0.01) before returning to the normal range within 30-45 min. Lower doses of FTY720 (0.3 and 0.5 mg/kg, i.v.) did not affect MAP. Renal cortical perfusion, renal artery blood flow, and renal vascular resistance were not altered by FTY720 at i.v. doses up to 1 mg/kg. Animals that received FTY720 (5 mg/kg/day) for 3 weeks showed a significant reduction in body weight (-4.8+/-1% of baseline at 3 weeks, P <0.001); however, weight-adjusted creatinine clearance, 24 h urine production, and urine osmolality were not different from those in control animals (0.71+/-0.1 vs. 0.74+/-0.1 ml/min/100 g, 2.63+/-0.2 vs. 3.12+/-0.2 ml/100 g, and 2003+/-33 vs. 1966+/-56 mOsm/kg, respectively). FTY720 at the same repeat oral dosage was, nevertheless, associated with a significantly lower 24 h sodium excretion and a significantly lower fractional excretion of sodium compared with those in control animals (223.4+/-35 vs. 304.5+/-50 micromol/100 g and 1.75+/-0.3 vs. 2.23+/-0.3%, respectively; P <0.05).

CONCLUSIONS

Our data indicate that, at least in the short term, oral FTY720 does not cause any significant adverse effects on renal or hepatic hemodynamics, nor does it cause any reduction in glomerular perfusion and thus may provide reasonable rescue/add-on therapy in calcineurin-inhibitor treated transplant recipients. At high repeat oral dosages, however, FTY720 may alter renal handling of sodium.

Calcineurin differentially regulates maintenance and growth of phenotypically distinct muscles

Adequate muscle mass is critical for human health. The molecular pathways regulating maintenance and growth of adult skeletal muscle are little understood. Calcineurin (CN) is implicated as a key signaling molecule in hypertrophy. Whether CN is involved in all forms of muscle growth or in different muscles is unknown. Here, we examine the role of CN in regulating maintenance of muscle size and growth of atrophied muscle in the soleus (slow) and plantaris (fast). The CN inhibitor cyclosporin A (CsA) differentially affects muscle growth and maintenance depending on muscle phenotype. The plantaris is more severely affected by CsA than the soleus in both growth conditions. One-week vs. 2-wk CsA treatment suggests that both CN-dependent and CN-independent growth occur in the atrophied soleus, whereas plantaris growth appears to be totally CN dependent. Our results suggest that CN regulates multiple types of muscle growth, depending both on muscle phenotype and stage of myofiber growth. Differential expression of components of the CN pathway occurs and may contribute to the differences between muscles.

Cyclosporin A-induced free radical generation is not mediated by cytochrome P-450

1. Reactive oxygen species (ROS) have been proposed to play a role in the side effects of the immunosuppressive drug cyclosporin A (CsA). 2. The aim of this study was to investigate whether cytochrome P-450 (CYP) dependent metabolism of CsA could be responsible for ROS generation since it has been suggested that CsA may influence the CYP system to produce ROS. 3. We show that CsA (1 -- 10 microM) generated antioxidant-inhibitable ROS in rat aortic smooth muscle cells (RASMC) using the fluorescent probe 2,7-dichlorofluorescin diacetate. 4. Using cytochrome c as substrate, we show that CsA (10 microM) did not inhibit NADPH cytochrome P-450 reductase in microsomes prepared from rat liver, kidney or RASMC. 5. CsA (10 microM) did not uncouple the electron flow from NADPH via NADPH cytochrome P-450 reductase to the CYP enzymes because CsA did not inhibit the metabolism of substrates selective for several CYP enzymes that do not metabolize CsA in rat liver microsomes. 6. CsA (10 microM) did not generate more radicals in CYP 3A4 expressing immortalized human liver epithelial cells (T5-3A4 cells) than in control cells that do not express CYP 3A4. 7. Neither diphenylene iodonium nor the CYP 3A inhibitor ketoconazole were able to block ROS formation in rat aortic smooth muscle or T5-3A4 cells. 8. These results demonstrate that CYP enzymes do not contribute to CsA-induced ROS formation and that CsA neither inhibits NADPH cytochrome P-450 reductase nor the electron transfer to the CYP enzymes.

Cardiovascular effects of an immunosuppressive agent cyclosporin A

Cyclosporin A (CsA) is now routinely used for transplantation of all solid organs, bone marrow transplantation, and for an increasing number of immunological diseases. However, treatment with CsA is an important iatrogenic cause of post-transplant hypertension, hyperlipidemia, and diabetes, which may contribute to the high cardiovascular morbidity in transplant recipients. Recently, the calcineurin inhibitor CsA has been employed in vivo and in vitro to examine the role of calcineurin in the signal transduction leading to cardiac hypertrophy. A cell culture study demonstrated the inhibitory effect of CsA on cytokine production by cardiac myxoma cells, the most common primary tumor of the heart. This review discusses recent data on the cardiovascular effects of CsA.