Atorvastatin inhibits angiotensin II-induced T-type Ca2+ channel expression in endothelial cells

Expression Pattern of T-Type Ca2+ Channels in Cerebellar Purkinje Cells after VEGF Treatment

T-type Ca2+ channels, generating low threshold calcium influx in neurons, play a crucial role in the function of neuronal networks and their plasticity. To further investigate their role in the complex field of research in plasticity of neurons on a molecular level, this study aimed to analyse the impact of the vascular endothelial growth factor (VEGF) on these channels. VEGF, known as a player in vasculogenesis, also shows potent influence in the central nervous system, where it elicits neuronal growth. To investigate the influence of VEGF on the three T-type Ca2+ channel isoforms, Cav3.1 (encoded by Cacna1g), Cav3.2 (encoded by Cacna1h), and Cav3.3 (encoded by Cacna1i), lasermicrodissection of in vivo-grown Purkinje cells (PCs) was performed, gene expression was analysed via qPCR and compared to in vitro-grown PCs. We investigated the VEGF receptor composition of in vivo- and in vitro-grown PCs and underlined the importance of VEGF receptor 2 for PCs. Furthermore, we performed immunostaining of T-type Ca2+ channels with in vivo- and in vitro-grown PCs and showed the distribution of T-type Ca2+ channel expression during PC development. Overall, our findings provide the first evidence that the mRNA expression of Cav3.1, Cav3.2, and Cav3.3 increases due to VEGF stimulation, which indicates an impact of VEGF on neuronal plasticity.

Deficiency of T-type Ca2+ channels Cav3.1 and Cav3.2 has no effect on angiotensin II-induced hypertension but differential effect on plasma aldosterone in mice

T-type Ca²⁺ channel Ca_v3.1 promotes microvessel contraction ex vivo. It was hypothesized that in vivo, functional deletion of Ca_v3.1, but not Ca_v3.2, protects mice against angiotensin II (ANG II)-induced hypertension. Mean arterial blood pressure (MAP) and heart rate were measured continuously with chronically indwelling catheters during infusion of ANG II (30 ng·kg^-1·min^-1, 7 days) in wild-type (WT), Ca_v3.1^-/-, and Ca_v3.2^-/- mice. Plasma aldosterone and renin concentrations were measured by radioimmunoassays. In a separate series, WT mice were infused with ANG II (100 ng·kg^-1·min^-1) with and without the mineralocorticoid receptor blocker canrenoate. Ca_v3.1^-/- and Ca_v3.2^-/- mice exhibited no baseline difference in MAP compared with WT mice, but day-night variation was blunted in both Ca_v3.1 and Ca_v3.2^-/- mice. ANG II increased significantly MAP in WT, Ca_v3.1^-/-, and Ca_v3.2^-/- mice with no differences between genotypes. Heart rate was significantly lower in Ca_v3.1^-/- and Ca_v3.2^-/- mice compared with control mice. After ANG II infusion, plasma aldosterone concentration was significantly lower in Ca_v3.1^-/- compared with Ca_v3.2^-/- mice. In response to ANG II, fibrosis was observed in heart sections from both WT and Ca_v3.1^-/- mice and while cardiac atrial natriuretic peptide mRNA was similar, the brain natriuretic peptide mRNA increase was mitigated in Ca_v3.1^-/- mice ANG II at 100 ng/kg yielded elevated pressure and an increased heart weight-to-body weight ratio in WT mice. Cardiac hypertrophy, but not hypertension, was prevented by the mineralocorticoid receptor blocker canrenoate. In conclusion, T-type channels Ca_v3.1and Ca_v3.2 do not contribute to baseline blood pressure levels and ANG II-induced hypertension. Ca_v3.1, but not Ca_v3.2, contributes to aldosterone secretion. Aldosterone promotes cardiac hypertrophy during hypertension.

Regulation of cellular communication by signaling microdomains in the blood vessel wall

It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.

T-type calcium channels blockers as new tools in cancer therapies

T-type calcium channels are involved in a multitude of cellular processes, both physiological and pathological, including cancer. T-type channels are also often aberrantly expressed in different human cancers and participate in the regulation of cell cycle progression, proliferation, migration, and survival. Here, we review the recent literature and discuss the controversies, supporting the role of T-type Ca(2+) channels in cancer cells and the proposed use of channels blockers as anticancer agents. A growing number of reports show that pharmacological inhibition or RNAi-mediated downregulation of T-type channels leads to inhibition of cancer cell proliferation and increased cancer cell death. In addition to a single agent activity, experimental results demonstrate that T-type channel blockers enhance the anticancer effects of conventional radio- and chemotherapy. At present, the detailed biological mechanism(s) underlying the anticancer activity of these channel blockers is not fully understood. Recent findings and ideas summarized here identify T-type Ca(2+) channels as a molecular target for anticancer therapy and offer new directions for the design of novel therapeutic strategies employing channels blockers. Physiological relevance: T-type calcium channels are often aberrantly expressed or deregulated in cancer cells, supporting their proliferation, survival, and resistance to treatment; therefore, T-type Ca(2+) channels could be attractive molecular targets for anticancer therapy.

Statins as a novel therapeutic strategy in acute lung injury

Acute lung injury (ALI) is a devastating clinical condition associated with pulmonary and systemic inflammation and characterized by incompetence of the pulmonary microvascular barrier culminating in noncardiogenic pulmonary edema. An understanding of the mechanisms underlying endothelial barrier dysfunction in ALI has been facilitated by study of the effects of statins in relevant cellular and animals models. Many of the pleotropic properties of these drugs, including direct effects on endothelial cell (EC) cytoskeletal rearrangement, NADPH oxidase, and nitric oxide activity, as well as effects on differential EC gene expression, are relevant to the pathobiology of ALI and suggest a potential therapeutic role for statins in this context. Moreover, results from preclinical studies and observations in relevant patient populations support the protective potential of statins in ALI, paving the way now for definitive clinical trials.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Angiotensin II regulates endothelial cell migration through calcium influx via T-type calcium channel in human umbilical vein endothelial cells

AIM

The T-type calcium channel is expressed in vascular endothelial cells, but its role in endothelial cell function is yet to be elucidated. We analysed the endothelial functional role of T-type calcium channel-dependent calcium under angiotensin II (Ang II) stimulation.

METHODS

Human umbilical vein endothelial cells were co-incubated with hormone at 10(-7) m and either Efonidipine 10(-5) m or Verapamil 10(-5) m or Mibefradil 10(-5) m or Wortmannin 10(-6) m. The contribution of Ang II receptors was evaluated using PD123319 10(-7) m and ZD 7155 10(-7) m. The calcium ion concentration was observed using Fluo-3 acetossimetil ester. The cells were observed after 3, 6, 9 and 12 h.

RESULTS

The microfluorescence method points out that Ang II induces intracellular calcium modulation in time by distinct mechanisms. AT2 receptor blockade is necessary to observe significant increase in [Ca(2+)](i) levels. Pre-treatment with Mibefradil abolishes Ang II -induced cell migration.

CONCLUSIONS

Our data show that Ang II, via AT1 receptor, modulates calcium concentration involving T-type calcium channel and L-type calcium channel but only the calcium influx via T-type calcium channels regulates endothelial cell migration which is essential for angiogenesis.

Topical atorvastatin in the treatment of diabetic wounds

BACKGROUND

Currently, it is reported that statins may be useful in the treatment of diabetes mellitus foot ulceration. The aim of this study was to evaluate treatment of the wounds in streptozotocin-induced diabetic rats with local atorvastatin.

METHODS

Two 15 x 15 mm-sized wounds were created in 28 streptozotocin-induced rats. A total of 56 diabetic wounds were studied in 8 groups (n = 7). No treatment was administered in the first and second groups, which lasted for 7 and 14 days, respectively. Third and fourth groups consisted of diabetic rats that were administered 1:1 mixture of lanolin and vaseline therapy for 7 and 14 days, respectively. One percent statin plus 1:1 mixture of lanolin and vaseline was used in the fifth and sixth groups for 7 and 14 days, respectively; and in seventh and eighth groups, 5% statin plus 1:1 mixture of lanolin and vaseline therapy was used for 7 and 14 days, respectively. On the 7th and 14th days, state of the wound healing was observed, and the percent of wound healing was determined by measuring its size and by performing a histopathologic study. The statistical analyses were performed by Mann-Whitney U test, using SPSS 14.0 software.

RESULTS

On the 14th day, the rates of wound healing in the first, second, third, and fourth groups were 14%, 40%, 96.59%, and 96.51%, respectively. This ratio was calculated by the formula healing ratio (%) = 100 x (1-wound area/initial wound area). Accordingly, in the multiple comparisons, the rates of wound healing were found to be significantly higher in the diabetic rat groups administered 1% and 5% atorvastatin compared with those administered a mixture of lanolin-vaseline and the untreated group (for comparison each one P < 0.001).

CONCLUSIONS

Local atorvastatin therapy may be useful for healing the wounds in diabetic rats. Further clinical and experimental studies are needed to confirm these results.

Angiotensin II-induced hypertension regulates AT1 receptor subtypes and extracellular matrix turnover in mouse retinal pigment epithelium

Accumulation of specific deposits and extracellular molecules under the retinal pigment epithelium (RPE) has been previously observed in eyes with age-related macular degeneration (AMD) and may play a role in the pathogenesis of AMD. Even though age is the major determinant for developing AMD, clinical studies have revealed hypertension (HTN) as another systemic risk factor. Angiotensin II (Ang II) is considered the most important hormone associated with HTN. To evaluate the relationship of Ang II to AMD, we studied whether mouse RPE expresses functional Ang II receptor subtypes and whether HTN-induced Ang II regulates expression of these receptors as well as critical ECM molecules (MMP-2 and type IV collagen) involved in ECM turnover in RPE. We used 9-month-old C57BL/6 male mice infused with Ang II alone or Ang II in combination with the AT1 receptor antagonist candesartan or the AT2 receptor antagonist PD123319 for 4 weeks to determine whether HTN-associated Ang II was important for ECM regulation in RPE. We found that mouse RPE expressed both Ang II receptor subtypes at the mRNA and protein levels. Infusion with Ang II induced HTN and elevated plasma and ocular Ang II levels. Ang II also regulated AT1a and AT1b receptor mRNA expression, the intracellular concentration of calcium [Ca(2+)](i), MMP-2 activity, and type IV collagen accumulation. Concurrent administration of Ang II with the AT1 receptor blocker prevented the increase in blood pressure and rise in ocular Ang II levels, as well as the calcium and MMP-2 responses. In contrast, the type IV collagen response to Ang II was prevented by blockade of AT2 receptors, but not AT1 receptors. Plasma Ang II levels were not modified by the AT1 or AT2 receptor blockade. Since the effects of Ang II on MMP-2 and type IV collagen require inhibition of both Ang II receptor subtypes, these receptors may play a role as a potential therapeutic targets to prevent ECM turnover dysregulation in the RPE basement membrane, suggesting a pathogenic mechanism to explain the link between HTN and AMD.

Statins in endothelial signaling and activation

The beneficial effects of statins, the most widely prescribed class of drugs in the world, are now recognized to extend well beyond their lipid-lowering properties. Through a combination of both distinct and interdependent effects on endothelial cell (EC) Rho GTPase regulation, NAPDH oxidase activity, NO bioavailability, and differential gene expression, statins confer significant protection of the vasculature. Abundant in vitro data, in addition to myriad reports relying on a range of animal models, now firmly support the idea that these drugs may serve as novel and effective therapeutic agents in a variety of disease states characterized by vascular dysfunction.

Regulation of angiotensin II receptors and extracellular matrix turnover in human retinal pigment epithelium: role of angiotensin II

The early stage of age-related macular degeneration (AMD) is characterized by the formation of subretinal pigment epithelium (RPE) deposits as a result of the dysregulation in the turnover of extracellular matrix (ECM) molecules. However, the mechanism involved remains unclear. Hypertension (HTN) is an important risk factor for AMD, and angiotensin II (ANG II) is the most important hormone associated with HTN. However, the relevance of ANG II receptors and ANG II effects on RPE have not been investigated yet. Therefore, the expression and regulation of ANG II receptors as well as the ECM turnover were studied in human RPE. ANG II receptors were expressed and upregulated by ANG II in human RPE. This regulation resulted in functional receptor expression, since an increase in intracellular concentration of calcium was observed upon ANG II stimulation. ANG II also increased matrix metalloproteinase (MMP)-2 activity and MMP-14 at the mRNA and protein levels as well as type IV collagen degradation. These ANG II effects were abolished in the presence of the ANG II receptor subtype 1 (AT1) receptor antagonist candesartan. In contrast, ANG II decreased type IV collagen via both AT1 and AT2 receptors, suggesting a synergistic effect of the two receptor subtypes. In conclusion, we have confirmed the presence of ANG II receptors in human RPE and their regulation by ANG II as well as the regulation of ECM molecules via ANG II receptors. Our data support the hypothesis that ANG II may exert biological function in RPE through ANG II receptors and that ANG II may cause dysregulation of molecules that play a major role in the turnover of ECM in RPE basement membrane and Bruch's membrane, suggesting a pathogenic mechanism to explain the link between HTN and AMD.

Regulation of neuronal T-type calcium channels

T-type calcium channels are critically important for regulating neuronal excitability, both in the central and peripheral nervous system, and are essential mediators of hormone secretion. Conversely, T-type channel hyperactivity has been linked to neurological disorders such as absence epilepsy and neuropathic pain. Hence, it is critical to understand the cellular mechanisms that control T-type channel activity, including means of altering expression patterns of the channels, activation of intracellular messenger cascades that directly affect channel activity, and the regulation of alternate splicing of T-type channel genes. Although there is substantial literature dealing with regulation of native T-type channels, the underlying molecular mechanism have only recently been addressed. Here, we highlight recent advances in our understanding of T-type channel regulation, and their implications for brain function.

Regulation of angiotensin II receptors and extracellular matrix turnover in human retinal pigment epithelium: role of angiotensin II

The early stage of age-related macular degeneration (AMD) is characterized by the formation of subretinal pigment epithelium (RPE) deposits as a result of the dysregulation in the turnover of extracellular matrix (ECM) molecules. However, the mechanism involved remains unclear. Hypertension (HTN) is an important risk factor for AMD, and angiotensin II (ANG II) is the most important hormone associated with HTN. However, the relevance of ANG II receptors and ANG II effects on RPE have not been investigated yet. Therefore, the expression and regulation of ANG II receptors as well as the ECM turnover were studied in human RPE. ANG II receptors were expressed and upregulated by ANG II in human RPE. This regulation resulted in functional receptor expression, since an increase in intracellular concentration of calcium was observed upon ANG II stimulation. ANG II also increased matrix metalloproteinase (MMP)-2 activity and MMP-14 at the mRNA and protein levels as well as type IV collagen degradation. These ANG II effects were abolished in the presence of the ANG II receptor subtype 1 (AT1) receptor antagonist candesartan. In contrast, ANG II decreased type IV collagen via both AT1 and AT2 receptors, suggesting a synergistic effect of the two receptor subtypes. In conclusion, we have confirmed the presence of ANG II receptors in human RPE and their regulation by ANG II as well as the regulation of ECM molecules via ANG II receptors. Our data support the hypothesis that ANG II may exert biological function in RPE through ANG II receptors and that ANG II may cause dysregulation of molecules that play a major role in the turnover of ECM in RPE basement membrane and Bruch's membrane, suggesting a pathogenic mechanism to explain the link between HTN and AMD.