The angiotensin–calcineurin–NFAT pathway mediates stretch-induced up-regulation of matrix metalloproteinases-2/-9 in atrial myocytes

The Progression of Pathophysiology of Moyamoya Disease

Moyamoya disease (MMD) is a chronic steno-occlusive cerebrovascular disease that often leads to hemorrhagic and ischemic strokes; however, its etiology remains elusive. Surgical revascularization by either direct or indirect bypass techniques to restore cerebral hypoperfusion is the treatment of choice to date. This review aims to provide an overview of the current advances in the pathophysiology of MMD, including the genetic, angiogenic, and inflammatory factors related to disease progression. These factors may cause MMD-related vascular stenosis and aberrant angiogenesis in complex manners. With a better understanding of the pathophysiology of MMD, nonsurgical approaches that target the pathogenesis of MMD may be able to halt or slow the progression of this disease.

Losartan impairs HTR-8/SVneo trophoblast migration through inhibition of angiotensin II-induced pro-inflammatory profile in human endometrial stromal cells

A deep interaction between the endometrium and the invading trophoblast occurs during implantation in humans, with the acquisition of uterine receptivity to the invading embryo promoted by an elevation of pro-inflammatory cytokines in the endometrium, and the invasiveness of decidualizing endometrial stromal cells, augmented by trophoblast-derived signals. Considering that usage of angiotensin II type 1 (AT1) receptor blockers, among other renin-angiotensin system (RAS) antagonists, is associated with adverse pregnancy outcomes, here we aim to analyse the involvement of AT1 receptor in the reciprocal dialogue occurring between endometrial stroma and trophoblast cells. In human endometrial stromal cells (T-HESC) pre-incubated with a decidualization cocktail, angiotensin (Ang) II increased protein expression of prolactin and FOXO1, markers of endometrial decidualization, while promoting nuclear translocation of FOXO1. In addition, Ang II treatment increased CXCL8, and matrix metalloprotease (MMP)-2 levels in T-HESC. Incubation with the AT1 receptor blocker losartan or with an NFAT signalling inhibitor, decreased Ang II-induced secretion of prolactin, CXCL8, and MMP-2 in T-HESC. In a wound healing assay, conditioned medium (CM) obtained from Ang II-treated T-HESC, but not CM from losartan-pre-incubated T-HESC, increased migration of HTR-8/SVneo trophoblasts, effect that was inhibited in the presence of a CXCL8-neutralizing antibody. An increased secretion of CXCL8 and MMP-2 was observed after treatment of T-HESC with CM obtained from HTR-8/SVneo cells, which was not observed in T-HESC pre-incubated with losartan or with the NFAT inhibitor. This study evidenced a reciprocal RAS-coded messaging between trophoblast and ESC which is affected by the AT1 receptor blocker losartan.

Effects of losartan and exercise on muscle mass and exercise endurance of old mice

This study evaluated the effects of angiotensin II type I receptor blocker (ARB) on muscle mass and exercise capacity in healthy older animals. The effects of combined ARB and exercise training were also determined. Eighty 18-month-old mice were randomized into the control group (C), exercise group (E), losartan group (L) and losartan plus exercise group (LE). Mice in the L and LE groups received losartan from drinking water every day. Mice in the E and LE groups trained on a treadmill 30 min per day, 3 days per week for 4 months. Exercise endurance and spontaneous physical activity of mice were measured at baseline and monthly for 4 months. After 4 months of intervention, serum interleukin-6 (IL-6) levels, muscle mass, and muscle fiber cross sectional area (CSA) were measured. Total antioxidant capacity (TAC), lipid peroxidation and IL-6 levels were determined in quadriceps. We found that exercise endurance only increased in the E and LE groups. Muscle TAC levels of E, L, and LE groups were greater than that in the C group. Serum IL-6 and lipid peroxidation levels were not different among groups. LE group, but not E and L groups, had greater muscle mass, larger muscle fiber CSA, and greater muscle IL-6 levels than that in the C group after 4 months of intervention. These results suggest that losartan promotes the adaptions of muscle mass with exercise training in healthy older animals.

Anemopsis californica Attenuates Photoaging by Regulating MAPK, NRF2, and NFATc1 Signaling Pathways

Long-term exposure of the skin to solar radiation causes chronic inflammation and oxidative stress, which accelerates collagen degradation. This contributes to the formation of wrinkles and dark spots, skin fragility, and even skin cancer. In this study, Anemopsis californica (AC), a herb from North America that is well known for treating microorganism infection and promoting wound healing, was investigated for its photoprotective effects. The biological effects of AC were studied on two in vitro models, namely, lipopolysaccharide (LPS)-induced macrophages and ultraviolet B (UVB)-irradiated dermal fibroblasts, to characterize its underlying molecular mechanisms. The results showed that AC decreased the mRNA levels of inflammatory mediators in sensitized macrophages, including cytokines, inducible nitric oxide synthase (iNOS), and cyclooxygenase (COX-2). Moreover, AC alleviated UVB-induced photoaging in dermal fibroblasts by restoring procollagen synthesis. This resulted from the regulation of excessive reactive oxygen species (ROS) by AC, which was mediated by the activation of the antioxidative system nuclear factor erythroid 2-related factor 2 (NRF2). AC also alleviated oxidative stress and inflammatory responses by inhibiting the phosphorylation of mitogen-activated protein kinase (MAPK) and interfering with the nuclear translocation of the immune regulator nuclear factor of activated T-cells 1 (NFATc1). In conclusion, the protective effects of AC on skin cellular components suggested that it has the potential for use in the development of drugs and cosmetics that protect the skin from UVB-induced chronic inflammation and aging.

Ginsenoside Rg1 attenuates mechanical stress-induced cardiac injury via calcium sensing receptor-related pathway

Background

Ginsenoside Rg1 (Rg1) has been well documented to be effective against various cardiovascular disease. The aim of this study is to evaluate the effect of Rg1 on mechanical stress-induced cardiac injury and its possible mechanism with a focus on the calcium sensing receptor (CaSR) signaling pathway.

Methods

Mechanical stress was implemented on rats through abdominal aortic constriction (AAC) procedure and on cardiomyocytes and cardiac fibroblasts by mechanical stretching with Bioflex Collagen I plates. The effects of Rg1 on cell hypertrophy, fibrosis, cardiac function, [Ca²⁺]_i, and the expression of CaSR and calcineurin (CaN) were assayed both on rat and cellular level.

Results

Rg1 alleviated cardiac hypertrophy and fibrosis, and improved cardiac decompensation induced by AAC in rat myocardial tissue and cultured cardiomyocytes and cardiac fibroblasts. Importantly, Rg1 treatment inhibited CaSR expression and increase of [Ca²⁺]_i, which similar to the CaSR inhibitor NPS2143. In addition, Rg1 treatment inhibited CaN and TGF-β1 pathways activation. Mechanistic analysis showed that the CaSR agonist GdCl₃ could not further increase the [Ca²⁺]_i and CaN pathway related protein expression induced by mechanical stretching in cultured cardiomyocytes. CsA, an inhibitor of CaN, inhibited cardiac hypertrophy, cardiac fibrosis, [Ca²⁺]_i and CaN signaling but had no effect on CaSR expression.

Conclusion

The activation of CaN pathway and the increase of [Ca²⁺]_i mediated by CaSR are involved in cardiac hypertrophy and fibrosis, that may be the target of cardioprotection of Rg1 against myocardial injury.

Calcineurin in the heart: New horizons for an old friend

Calcineurin, also known as PP2B or PPP3, is a member of the PPP family of protein phosphatases that also includes PP1 and PP2A. Together these three phosphatases carryout the majority of dephosphorylation events in the heart. Calcineurin is distinct in that it is activated by the binding of calcium/calmodulin (Ca2+/CaM) and therefore acts as a node for integrating Ca2+ signals with changes in phosphorylation, two fundamental intracellular signaling cascades. In the heart, calcineurin is primarily thought of in the context of pathological cardiac remodeling, acting through the Nuclear Factor of Activated T-cell (NFAT) family of transcription factors. However, calcineurin activity is also essential for normal heart development and homeostasis in the adult heart. Furthermore, it is clear that NFAT-driven changes in transcription are not the only relevant processes initiated by calcineurin in the setting of pathological remodeling. There is a growing appreciation for the diversity of calcineurin substrates that can impact cardiac function as well as the diversity of mechanisms for targeting calcineurin to specific sub-cellular domains in cardiomyocytes and other cardiac cell types. Here, we will review the basics of calcineurin structure, regulation, and function in the context of cardiac biology. Particular attention will be given to: the development of improved tools to identify and validate new calcineurin substrates; recent studies identifying new calcineurin isoforms with unique properties and targeting mechanisms; and the role of calcineurin in cardiac development and regeneration.

TRPV6 calcium channel directs homeostasis of the mammary epithelial sheets and controls epithelial mesenchymal transition

Epithelial integrity is lost upon cancer progression as cancer cells detach from the primary tumor site and start to invade to the surrounding tissues. Invasive cancers of epithelial origin often express altered levels of TRP-family cation channels. Upregulation of TRPV6 Ca2+-channel has been associated with a number of human malignancies and its high expression in breast cancer has been linked to both proliferation and invasive disease. The mechanisms behind the potential of TRPV6 to induce invasive progression have, however, not been well elucidated. Here we show that TRPV6 is connected to both E-cadherin-based adherens junctions and intracellular cytoskeletal structures. Loss of TRPV6 from normal mammary epithelial cells led to disruption of epithelial integrity and abnormal 3D-mammo sphere morphology. Furthermore, expression level of TRPV6 was tightly linked to the levels of common EMT markers, suggesting that TRPV6 may have a role in the mesenchymal invasion of breast cancer cells. Thus, either too low or too high TRPV6 levels compromise homeostasis of the mammary epithelial sheets and may promote the progression of pathophysiological conditions.

TRPV6 as A Target for Cancer Therapy

Two decades ago a class of ion channels, hitherto unsuspected, was discovered. In mammals these Transient Receptor Potential channels (TRPs) have not only expanded in number (to 26 functional channels) but also expanded the view of our interface with the physical and chemical environment. Some are heat and cold sensors while others monitor endogenous and/or exogenous chemical signals. Some TRP channels monitor osmotic potential, and others measure cell movement, stretching, and fluid flow. Many TRP channels are major players in nociception and integration of pain signals. One member of the vanilloid sub-family of channels is TRPV6. This channel is highly selective for divalent cations, particularly calcium, and plays a part in general whole-body calcium homeostasis, capturing calcium in the gut from the diet. TRPV6 can be greatly elevated in a number of cancers deriving from epithelia and considerable study has been made of its role in the cancer phenotype where calcium control is dysfunctional. This review compiles and updates recent published work on TRPV6 as a promising drug target in a number of cancers including those afflicting breast, ovarian, prostate and pancreatic tissues.

The Role of β-Arrestin Proteins in Organization of Signaling and Regulation of the AT1 Angiotensin Receptor

AT1 angiotensin receptor plays important physiological and pathophysiological roles in the cardiovascular system. Renin-angiotensin system represents a target system for drugs acting at different levels. The main effects of ATR1 stimulation involve activation of Gq proteins and subsequent IP3, DAG, and calcium signaling. It has become evident in recent years that besides the well-known G protein pathways, AT1R also activates a parallel signaling pathway through β-arrestins. β-arrestins were originally described as proteins that desensitize G protein-coupled receptors, but they can also mediate receptor internalization and G protein-independent signaling. AT1R is one of the most studied receptors, which was used to unravel the newly recognized β-arrestin-mediated pathways. β-arrestin-mediated signaling has become one of the most studied topics in recent years in molecular pharmacology and the modulation of these pathways of the AT1R might offer new therapeutic opportunities in the near future. In this paper, we review the recent advances in the field of β-arrestin signaling of the AT1R, emphasizing its role in cardiovascular regulation and heart failure.

Inhibition of Transient Receptor Potential Vanilloid 6 channel, elevated in human ovarian cancers, reduces tumour growth in a xenograft model

Background: Transient Receptor Potential Vanilloid 6 (TRPV6), a non-voltage gated calcium channel, is implicated in malignancies and correlates with Gleason scores in prostate cancer and with poor prognosis in breast cancer. Data on the TRPV6 status of ovarian malignancies has not received significant attention. The effect of inhibiting TRPV6 activity on ovarian tumour growth has never been reported.

Methods: We quantified TRPV6 mRNA and protein in biopsies of five types of ovarian cancer at different stages and grades by quantitative PCR and immunohistochemistry respectively. We verified the presence of TRPV6 in SKOV-3 cells and xenografts by Western Blotting. NOD/SCID mice bearing xenografted ovarian tumours derived from SKOV-3 were treated daily with TRPV6-antagonistic peptides (SOR-C13 and SOR-C27) at 400, 600 and 800 mg/kg delivered intraperitoneally (i.p.) over 12 days. Data from qPCR and tumour growth experiments were compared with a Student's t-test. Immunohistochemical ranking of staining were compared with Kruskall-Wallace one-way ANOVA and Dunn's Multiple Comparison post-test.

Results: TRPV6 mRNA and protein are significantly elevated at all stages and grades of 5 ovarian cancer types over normal tissue. Overall qPCR log2 values (n, mean, ± SEM) for mRNA in tumour (n = 165, 5.06 ± 0.16) were greater (p < 0.05) than normal tissues (n = 26, 0.45 ± 0.41). All stages and grades included in the biopsy arrays were significantly greater than normal tissues. Immunohistochemical staining of TRPV6 was ranked >2 (faint in most cells) in 80.5% of tumours (123) while 92% of normal tissues (23) ranked ≤ 2. Daily i.p. injection with SOR-C13 (400, 600 and 800 mg/kg) over 12 days inhibits tumour growth (59%) at the highest dose compared to non-treated controls. SOR-C27 at 800 mg/kg SOR-C27 inhibited tumour growth 55% after 12 days. Results of daily and intermittent dosing (Days 1, 2, 3 and 8, 9, 10) with SOR-C13 were indistinguishable.

Conclusion: TRPV6 mRNA and protein are elevated in biopsies of ovarian cancers compared to normal tissue. Inhibition of TRPV6 activity significantly reduces ovarian tumour growth providing evidence that TRPV6 is a feasible oncology target in ovarian cancers.

Macro- and micromechanical remodelling in the fish atrium is associated with regulation of collagen 1 alpha 3 chain expression

Numerous pathologies lead to remodelling of the mammalian ventricle, often associated with fibrosis. Recent work in fish has shown that fibrotic remodelling of the ventricle is 'reversible', changing seasonally as temperature-induced changes in blood viscosity alter haemodynamic load on the heart. The atrial response to varying haemodynamic load is less understood in mammals and completely unexplored in non-mammalian vertebrates. To investigate atrial remodelling, rainbow trout were chronically cooled (from 10 ± 1 to 5 ± 1 °C) and chronically warmed (from 10 ± 1 to 18 ± 1 °C) for a minimum of 8 weeks. We assessed the functional effects on compliance using ex vivo heart preparations and atomic force microscopy nano-indentation and found chronic cold increased passive stiffness of the whole atrium and micromechanical stiffness of tissue sections. We then performed histological, biochemical and molecular assays to probe the mechanisms underlying functional remodelling of the atrial tissue. We found cooling resulted in collagen deposition which was associated with an upregulation of collagen-promoting genes, including the fish-specific collagen I alpha 3 chain, and a reduction in gelatinase activity of collagen-degrading matrix metalloproteinases (MMPs). Finally, we found that cooling reduced mRNA expression of cardiac growth factors and hypertrophic markers. Following long-term warming, there was an opposing response to that seen with cooling; however, these changes were more moderate. Our findings suggest that chronic cooling causes atrial dilation and increased myocardial stiffness in trout atria analogous to pathological states defined by changes in preload or afterload of the mammalian atria. The reversal of this phenotype following chronic warming is particularly interesting as it suggests that typically pathological features of mammalian atrial remodelling may oscillate seasonally in the fish, revealing a more dynamic and plastic atrial remodelling response.

Poria cocos polysaccharide attenuates RANKL-induced osteoclastogenesis by suppressing NFATc1 activity and phosphorylation of ERK and STAT3

Pathological fractures caused by osteolytic lesions seriously threaten the health of patients. Osteoclasts play important roles in bone resorption whose hyperfunction are closely related to osteolytic lesions. Studies on osteoclast differentiation and function assist in the prevention of excessive bone loss associated diseases. We screened a variety of natural compounds with anti-inflammatory effect and found that poria cocos polysaccharide (PCP) inhibited RANKL-induced osteoclast formation and bone resorption via TRAcP staining, immunofluorescence, RT-PCR and western blot. PCP down-regulated phosphorylation of STAT3, P38, ERK and JNK, and thus repressed the expression of NFAcT1 and c-Fos during RANKL-induced osteoclastogenesis. Besides, the expression of bone resorption related genes such as TRAcP and CTSK was suppressed by PCP. The results suggest that PCP can be invoked as a candidate for the treatment of osteolytic diseases by inhibiting osteoclastogenesis.

Extracellular matrix remodeling and cardiac fibrosis

Cardiac fibrosis, characterized by excessive deposition of extracellular matrix (ECM) proteins in the myocardium, distorts the architecture of the myocardium, facilitates the progression of arrhythmia and cardiac dysfunction, and influences the clinical course and outcome in patients with heart failure. This review describes the composition and homeostasis in normal cardiac interstitial matrix and introduces cellular and molecular mechanisms involved in cardiac fibrosis. We also characterize the ECM alteration in the fibrotic response under diverse cardiac pathological conditions and depict the role of matricellular proteins in the pathogenesis of cardiac fibrosis. Moreover, the diagnosis of cardiac fibrosis based on imaging and biomarker detection and the therapeutic strategies are addressed. Understanding the comprehensive molecules and pathways involved in ECM homeostasis and remodeling may provide important novel potential targets for preventing and treating cardiac fibrosis.

Protective effect of dietary Alchemilla mollis on UVB-irradiated premature skin aging through regulation of transcription factor NFATc1 and Nrf2/ARE pathways

BACKGROUND

Alchemilla mollis (lady's mantle) is a common ingredient in skin care products. However, the protective mechanism of A. mollis against skin problems has not been elucidated.

PURPOSE

This study was to investigate the effects of A. mollis ethanolic extract (AM) on UVB-irradiated normal human dermal fibroblasts (NHDF) and hairless mice.

METHODS

The in vitro anti-photoaging effect of AM was performed in NHDFs. The antioxidant activities were assessed through DPPH, ABTS, and reactive oxygen species (ROS) assays. Matrix metalloproteinase 1 (MMP-1), IL-6, procollagen type I, and transforming growth factor-β1 (TGF-β1) were measured by kits. The protein levels of p-c-Jun, p-c-Fos, Nrf2, NQO-1, HO-1, nuclear NFATc1 and cytosolic p-NFATc1 were evaluated by western blotting. In in vivo, H&E and Masson's trichrome staining were carried out. Skin texture was analyzed using the roughness parameters. The expression of MMP-1, procollagen type I, TGF-β1 and elastin were measured by western blot.

RESULTS

AM included gallic acid as an active constituent. AM exhibited a strong antioxidant effect by inhibiting DPPH and ABTS free radicals, as well as ROS production. It was also found to upregulate transforming growth factor β1, type I procollagen and elastin expression, and to downregulate matrix metalloproteinase-1 and interleukin-6 expression in AM-treated NHDFs under UVB irradiation. These effects were attributed to AP-1 and Nrf2/ARE signaling pathways. Significantly, it was demonstrated that AM regulated the UVB-induced NFATc1 dephosphorylation in nucleus. Based on dietary data, AM was effective for the prevention of wrinkle formation, skin thickening, water loss, and erythema in UVB-exposed mouse skin.

CONCLUSION

Our data indicate that A. mollis provides protection from UVB exposure in both hairless mice skin in vivo and NHDFs in vitro. AM might therefore be useful as a cosmetic material and functional food for the prevention of UVB-induced human skin photoaging.

Towards a Mechanistic Understanding and Treatment of a Progressive Disease: Atrial Fibrillation

Atrial fibrosis appears to be a key factor in the genesis and/or perpetuation of atrial fibrillation (AF). The pathological distribution of atrial fibrosis is geographically consistent with the attachments between the posterior left atrium and the pericardium along the reflections where wall stiffness is increased and structural changes are found. While there is a wide range of complex etiological factors and electrophysiological mechanisms in AF, there is evidence for a common pathophysiological pathway that could account for deliberate substrate formation and progression of AF. Anatomical stresses along the atrium, mediated by the elastic modulus mismatch between atrial tissue and the pericardium, result in inflammatory and fibrotic changes which create the substrate for atrial fibrillation. This may explain the anatomical predominance of pulmonary vein triggers earlier in the development of atrial fibrillation and the increasing involvement of the atrium as the disease progresses. Ablative treatments that address the progressive nature of atrial fibrillation and fibrosis may yield improved success rates.

Serine/Threonine Phosphatases in Atrial Fibrillation

Serine/threonine protein phosphatases control dephosphorylation of numerous cardiac proteins, including a variety of ion channels and calcium-handling proteins, thereby providing precise post-translational regulation of cardiac electrophysiology and function. Accordingly, dysfunction of this regulation can contribute to the initiation, maintenance and progression of cardiac arrhythmias. Atrial fibrillation (AF) is the most common heart rhythm disorder and is characterized by electrical, autonomic, calcium-handling, contractile, and structural remodeling, which include, among other things, changes in the phosphorylation status of a wide range of proteins. Here, we review AF-associated alterations in the phosphorylation of atrial ion channels, calcium-handling and contractile proteins, and their role in AF-pathophysiology. We highlight the mechanisms controlling the phosphorylation of these proteins and focus on the role of altered dephosphorylation via local type-1, type-2A and type-2B phosphatases (PP1, PP2A, and PP2B, also known as calcineurin, respectively). Finally, we discuss the challenges for phosphatase research, potential therapeutic significance of altered phosphatase-mediated protein dephosphorylation in AF, as well as future directions.

Angiotensin II receptors and peritoneal dialysis-induced peritoneal fibrosis

The vasoactive hormone angiotensin II initiates its major hemodynamic effects through interaction with AT1 receptors, a member of the class of G protein-coupled receptors. Acting through its AT1R, angiotensin II regulates blood pressure and renal salt and water balance. Recent evidence points to additional pathological influences of activation of AT1R, in particular inflammation, fibrosis and atherosclerosis. The transcription factor nuclear factor κB, a key mediator in inflammation and atherosclerosis, can be activated by angiotensin II through a mechanism that may involve arrestin-dependent AT1 receptor internalization. Peritoneal dialysis is a therapeutic modality for treating patients with end-stage kidney disease. The effectiveness of peritoneal dialysis at removing waste from the circulation is compromised over time as a consequence of peritoneal dialysis-induced peritoneal fibrosis. The non-physiological dialysis solution used in peritoneal dialysis, i.e. highly concentrated, hyperosmotic glucose, acidic pH as well as large volumes infused into the peritoneal cavity, contributes to the development of fibrosis. Numerous trials have been conducted altering certain components of the peritoneal dialysis fluid in hopes of preventing or delaying the fibrotic response with limited success. We hypothesize that structural activation of AT1R by hyperosmotic peritoneal dialysis fluid activates the internalization process and subsequent signaling through the transcription factor nuclear factor κB, resulting in the generation of pro-fibrotic/pro-inflammatory mediators producing peritoneal fibrosis.

Autoantibodies in dilated cardiomyopathy induce vascular endothelial growth factor expression in cardiomyocytes

BACKGROUND

Autoantibodies have been identified as major predisposing factors for dilated cardiomyopathy (DCM). Patients with DCM show elevated serum levels of vascular endothelial growth factor (VEGF) whose source is unknown. Besides its well-investigated effects on angiogenesis, evidence is present that VEGF signaling is additionally involved in fibroblast proliferation and cardiomyocyte hypertrophy, hence in cardiac remodeling. Whether autoimmune effects in DCM impact cardiac VEGF signaling needs to be elucidated.

METHODS

Five DCM patients were treated by the immunoadsorption (IA) therapy on five consecutive days. The eluents from the IA columns were collected and prepared for cell culture. Cardiomyocytes from neonatal rats (NRCM) were incubated with increasing DCM-immunoglobulin-G (IgG) concentrations for 48 h. Polyclonal IgG (Venimmun N), which was used to restore IgG plasma levels in DCM patients after the IA therapy was additionally used for control cell culture purposes.

RESULTS

Elevated serum levels of VEGF decreased significantly after IA (Serum VEGF (ng/ml); DCM pre-IA: 45 ± 9.1 vs. DCM post-IA: 29 ± 6.7; P < 0.05). In cell culture, pretreatment of NRCM by DCM-IgG induced VEGF expression in a time and dose dependent manner. Biologically active VEGF that was secreted by NRCM significantly increased BNP mRNA levels in control cardiomyocytes and induced cell-proliferation of cultured cardiac fibroblast (Fibroblast proliferation; NRCM medium/HC-IgG: 1 ± 0.0 vs. NRCM medium/DCM-IgG 100 ng/ml: 5.6 ± 0.9; P < 0.05).

CONCLUSION

The present study extends the knowledge about the possible link between autoimmune signaling in DCM and VEGF induction. Whether this observation plays a considerable role in cardiac remodeling during DCM development needs to be further elucidated.

Nuclear factor of activated T cells in cancer development and treatment

Since nuclear factor of activated T cells (NFAT) was first identified as a transcription factor in T cells, various NFAT isoforms have been discovered and investigated. Accumulating studies have suggested that NFATs are involved in many aspects of cancer, including carcinogenesis, cancer cell proliferation, metastasis, drug resistance and tumor microenvironment. Different NFAT isoforms have distinct functions in different cancers. The exact function of NFAT in cancer or the tumor microenvironment is context dependent. In this review, we summarize our current knowledge of NFAT regulation and function in cancer development and treatment. NFATs have emerged as a potential target for cancer prevention and therapy.

Stimulation of Cyclooxygenase 2 Expression in Rat Peritoneal Mesothelial Cells

Objective: Since peritoneal dialysis causes peritoneal fibrosis, we examined how glucose (osmotic factor), mannitol (osmotic control), and angiotensin II (AngII) regulate proinflammatory cyclooxygenase 2 (COX-2) in primary rat peritoneal mesothelial cells. Materials and Methods: For this study, we used the following material (n = 4-8 cell lines): cells, passages 1-2; 125I-AngII receptor surface binding (AT1R antagonist losartan, AT2R antagonist PD123319; both 10 µM); intracellular calcium probe calcium-5; COX-2 immunoblotting (β-actin normalized); real-time PCR of COX-2 gene PTGS2, and NF-κB inhibitor Ro-1069920 (5 µM). Results: AngII surface receptors were predominantly AT1R (minimally AT2R). AngII and glucose increased COX-2 protein expression concentration dependently; mannitol also increased COX-2 expression. Maximal COX-2 protein expression was observed after 6 h (AngII) and 24 h (glucose, mannitol). The time course of increases in PTGS2 mRNA levels reflected that of COX-2 protein expression. At optimal exposure conditions (time/concentration), glucose was 5-fold more efficacious in stimulating COX-2 protein expression than AngII or mannitol. Losartan fully inhibited COX-2 protein responses to AngII and mannitol, but minimally inhibited responses to glucose. Ro-1069920 fully inhibited COX-2 protein responses to each effector. Conclusion: AngII, glucose, and osmotic stress (mannitol) activate COX-2; NF-κB may be an ideal site for COX-2 blockade, and COX-2 activation by osmotic stress requires AT1R, but activation by glucose is more robust and mechanistically complex. © 2014 S. Karger AG, Basel.

Olmesartan attenuates cardiac hypertrophy and improves cardiac diastolic function in spontaneously hypertensive rats through inhibition of calcineurin pathway

OBJECTIVE

To test whether olmesartan ameliorates cardiac diastolic dysfunction in spontaneously hypertensive rats (SHRs) through calcineurin pathway.

METHODS

Twenty-four male SHRs of 6 months were divided into saline- (n = 12) and olmesartan-treated (n = 12) groups. Age-matched WKY (n = 12) rats served as controls. Saline (10 mL·kg·d) or the same volume of olmesartan liquor (2.5 mg·kg·d) was administered by gavage for 3 months. Heart rate, systolic blood pressure, cardiac structure, and function and histological studies were determined. Expression of calcineurin and downstream NFAT3 were also detected.

RESULTS

Compared with age-matched Wistar Kyoto rats, SHRs of 6 months exhibited evident cardiac hypertrophy and diastolic dysfunction as demonstrated by elevated systolic blood pressure and E/E', decreased E/A and E'/A', while F, left ventricular ejection fraction and fractional shortening remained unimpaired. Treatment with olmesartan significantly decreased systolic blood pressure and ventricular hypertrophy, attenuated fibrosis, and improved diastolic function (all P < 0.05). Meanwhile, both calcineurin and NFAT3 expressions were downregulated in olmesartan group compared with the other 2 groups (both P < 0.05).

CONCLUSIONS

These data suggest the beneficial effect of olmesartan on cardiac structure and diastolic dysfunction, and it may be mediated through calcineurin pathway. This indicates a new therapeutic target for diastolic dysfunction.

NFAT as cancer target: mission possible?

The NFAT signaling pathway regulates various aspects of cellular functions; NFAT acts as a calcium sensor, integrating calcium signaling with other pathways involved in development and growth, immune response, and inflammatory response. The NFAT family of transcription factors regulates diverse cellular functions such as cell survival, proliferation, migration, invasion, and angiogenesis. The NFAT isoforms are constitutively activated and overexpressed in several cancer types wherein they transactivate downstream targets that play important roles in cancer development and progression. Though the NFAT family has been conclusively proved to be pivotal in cancer progression, the different isoforms play distinct roles in different cellular contexts. In this review, our discussion is focused on the mechanisms that drive the activation of various NFAT isoforms in cancer. Additionally, we analyze the potential of NFAT as a valid target for cancer prevention and therapy.

Myofilament dysfunction as an emerging mechanism of volume overload heart failure

Two main hemodynamic overload mechanisms [i.e., volume and pressure overload (VO and PO, respectively] result in heart failure (HF), and these two mechanisms have divergent pathologic alterations and different pathophysiological mechanisms. Extensive evidence from animal models and human studies of PO demonstrate a clear association with alterations in Ca(2+) homeostasis. By contrast, emerging evidence from animal models and patients with regurgitant valve disease and dilated cardiomyopathy point toward a more prominent role of myofilament dysfunction. With respect to VO HF, key features of excitation-contraction coupling defects, myofilament dysfunction, and extracellular matrix composition will be discussed.

The role of the NFAT signaling pathway in retinal neovascularization

PURPOSE

The purpose of the present study was to investigate the role of nuclear factor of activated T cells (NFAT), a transcription factor downstream of VEGF, in angiogenic cell behaviors of human retinal microvascular endothelial cells (HRMEC), and to assess the efficacy of NFAT signaling inhibitors in a rat model of oxygen-induced retinopathy (OIR).

METHODS

Human retinal microvascular endothelial cells were treated with VEGF in the presence or absence of the NFAT inhibitor of NFAT-calcineurin association-6 (INCA-6), and NFAT translocation was evaluated using immunocytochemistry (ICC). Human retinal microvascular endothelial cells were treated with increasing doses of INCA-6, and cell proliferation and tube formation were assessed. Rats subjected to OIR were administered increasing doses of INCA-6 or the CN inhibitor FK-506, and the retinal neovascular area was measured.

RESULTS

Nuclear factor of activated T-cells c1 was translocated to the nucleus of HRMEC treated with VEGF, and INCA-6 treatment blocked translocation. Inhibitor of NFAT-calcineurin association-6inhibited HRMEC proliferation and tube formation in a dose-dependent manner. Both INCA-6 and FK-506 treatment significantly reduced pathologic neovascularization in OIR.

CONCLUSIONS

This investigation has demonstrated that in HRMEC, NFATc1 is activated downstream of VEGF signaling and NFAT signaling plays a key role in angiogenic cell behaviors. In addition, NFAT inhibition is shown to be highly efficacious in an OIR model. These findings indicate that the NFAT signaling pathway may serve as a suitable therapeutic target for the treatment of neovascular eye disease.

Mechanical stretch increases MMP-2 production in vascular smooth muscle cells via activation of PDGFR-β/Akt signaling pathway

Increased blood pressure, leading to mechanical stress on vascular smooth muscle cells (VSMC), is a known risk factor for vascular remodeling via increased activity of matrix metalloproteinase (MMP) within the vascular wall. This study aimed to identify cell surface mechanoreceptors and intracellular signaling pathways that influence VSMC to produce MMP in response to mechanical stretch (MS). When VSMC was stimulated with MS (0–10% strain, 60 cycles/min), both production and gelatinolytic activity of MMP-2, but not MMP-9, were increased in a force-dependent manner. MS-enhanced MMP-2 expression and activity were inhibited by molecular inhibition of Akt using Akt siRNA as well as by PI3K/Akt inhibitors, LY293002 and AI, but not by MAPK inhibitors such as PD98059, SP600125 and SB203580. MS also increased Akt phosphorylation in VSMC, which was attenuated by AG1295, a PDGF receptor (PDGFR) inhibitor, but not by inhibitors for other receptor tyrosine kinase including EGF, IGF, and FGF receptors. Although MS activated PDGFR-α as well as PDGFR-β in VSMC, MS-induced Akt phosphorylation was inhibited by molecular deletion of PDGFR-β using siRNA, but not by inhibition of PDGFR-α. Collectively, our data indicate that MS induces MMP-2 production in VSMC via activation of Akt pathway, that is mediated by activation of PDGFR-β signaling pathways.

Activation of CRH receptor type 1 expressed on glutamatergic neurons increases excitability of CA1 pyramidal neurons by the modulation of voltage-gated ion channels

Corticotropin-releasing hormone (CRH) plays an important role in a substantial number of patients with stress-related mental disorders, such as anxiety disorders and depression. CRH has been shown to increase neuronal excitability in the hippocampus, but the underlying mechanisms are poorly understood. The effects of CRH on neuronal excitability were investigated in acute hippocampal brain slices. Population spikes (PS) and field excitatory postsynaptic potentials (fEPSP) were evoked by stimulating Schaffer-collaterals and recorded simultaneously from the somatic and dendritic region of CA1 pyramidal neurons. CRH was found to increase PS amplitudes (mean ± Standard error of the mean; 231.8 ± 31.2% of control; n = 10) while neither affecting fEPSPs (104.3 ± 4.2%; n = 10) nor long-term potentiation (LTP). However, when Schaffer-collaterals were excited via action potentials (APs) generated by stimulation of CA3 pyramidal neurons, CRH increased fEPSP amplitudes (119.8 ± 3.6%; n = 8) and the magnitude of LTP in the CA1 region. Experiments in slices from transgenic mice revealed that the effect on PS amplitude is mediated exclusively by CRH receptor 1 (CRHR1) expressed on glutamatergic neurons. The effects of CRH on PS were dependent on phosphatase-2B, L- and T-type calcium channels and voltage-gated potassium channels but independent on intracellular Ca²⁺-elevation. In patch-clamp experiments, CRH increased the frequency and decay times of APs and decreased currents through A-type and delayed-rectifier potassium channels. These results suggest that CRH does not affect synaptic transmission per se, but modulates voltage-gated ion currents important for the generation of APs and hence elevates by this route overall neuronal activity.

Cyclical stretch induces structural changes in atrial myocytes

Atrial fibrillation (AF) often occurs in the presence of an underlying disease. These underlying diseases cause atrial remodelling, which make the atria more susceptible to AF. Stretch is an important mediator in the remodelling process. The aim of this study was to develop an atrial cell culture model mimicking remodelling due to atrial pressure overload. Neonatal rat atrial cardiomyocytes (NRAM) were cultured and subjected to cyclical stretch on elastic membranes. Stretching with 1 Hz and 15% elongation for 30 min. resulted in increased expression of immediate early genes and phosphorylation of Erk and p38. A 24-hr stretch period resulted in hypertrophy-related changes including increased cell diameter, reinduction of the foetal gene program and cell death. No evidence of apoptosis was observed. Expression of atrial natriuretic peptide, brain natriuretic peptide and growth differentiation factor-15 was increased, and calcineurin signalling was activated. Expression of several potassium channels was decreased, suggesting electrical remodelling. Atrial stretch-induced change in skeletal α-actin expression was inhibited by pravastatin, but not by eplerenone or losartan. Stretch of NRAM results in elevation of stress markers, changes related to hypertrophy and dedifferentiation, electrical remodelling and cell death. This model can contribute to investigating the mechanisms involved in the remodelling process caused by stretch and to the testing of pharmaceutical agents.

The utility of copy number variation (CNV) in studies of hypertension-related left ventricular hypertrophy (LVH): rationale, potential and challenges

The ultimate goal of human genetics is to understand the role of genome variation in elucidating human traits and diseases. Besides single nucleotide polymorphism (SNP), copy number variation (CNV), defined as gains or losses of a DNA segment larger than 1 kb, has recently emerged as an important tool in understanding heritable source of human genomic differences. It has been shown to contribute to genetic susceptibility of various common and complex diseases. Despite a handful of publications, its role in cardiovascular diseases remains largely unknown. Here, we deliberate on the currently available technologies for CNV detection. The possible utility and the potential roles of CNV in exploring the mechanisms of cardiac remodeling in hypertension will also be addressed. Finally, we discuss the challenges for investigations of CNV in cardiovascular diseases and its possible implications in diagnosis of hypertension-related left ventricular hypertrophy (LVH).

Age-related regional differences in cardiac nerve growth factor expression

Age has been identified as an independent risk factor for cardiovascular diseases. A shift of the cardiac autonomic nervous system towards an increase in sympathetic tone has been reported in the elderly. Nerve growth factor (NGF) is the main neurotrophic factor that increases the sympathetic activity of the heart. If there is a shift of NGF expression in old compared to young cardiomyocytes and whether there are regional differences in the heart still remain unclear. Therefore, we chose a rat model of different-aged rats (3-4 days = neonatal, 6-8 weeks = young, 20-24 months = old), and isolated cardiomyocytes from the left and the right atrium (LA, RA), as well as from the left and the right ventricle (LV, RV), were used to determine NGF expression on mRNA and protein levels. In neonatal, young, and old rats, NGF amount in LA and RA was significantly lower as compared to LV and RV. In young and old rats, we found significant higher NGF protein levels in LA compared to RA. In addition, both atria showed an increase in NGF expression between age groups neonatal, young, and old. In both ventricles, we observed a significant decrease in NGF expression from neonatal to young rats and a significant increase from young to old rats. The highest NGF amount in LV and RV was observed in neonatal rats. Regarding tyrosine kinase A receptor (TrkA) expression, the main receptor for NGF signaling, both atria showed the largest expression in old rats; while in LV and RV, TrkA was expressed mainly in young rats. These results point to a contribution of nerve growth factors to the change of autonomic tone observed in elderly patients.

Calcium- and integrin-binding protein-1 and calcineurin are upregulated in the right atrial myocardium of patients with atrial fibrillation

AIMS

The aim of this study was to determine whether altered expression and distribution of calcium- and integrin-binding protein-1 (CIB1) is involved in the pathogenesis of different types of patients with atrial fibrillation (AF) associated with valvular heart disease (VHD).

METHODS AND RESULTS

Right atrial specimens obtained from 65 patients undergoing valve replacement surgery were divided into three groups: sinus rhythm group (n= 24), paroxysmal atrial fibrillation group (PaAF; n= 10), and persistent atrial fibrillation group (PeAF; AF lasting >6 month; n= 31). The expression levels of mRNA and protein content for CIB1, calcineurin B, calcineurin A, and Na(+)-Ca(2+) exchanger-1 (NCX1) were measured. We also measured the combination of CIB1 with calcineurin B, L-type Ca(2+) channel, and NCX1 using immunoprecipitation. Expression of mRNA and protein content of CIB1, calcineurin B, calcineurin A, and NCX1 was increased in the AF group. Calcium- and integrin-binding protein-1 interacted with calcineurin B and L-type Ca(2+) channel. Surprisingly, CIB1 also combined with NCX1.

CONCLUSIONS

The CIB1 and calcineurin expression was increased in AF atrial tissue and was related to the type of AF. This finding suggests that CIB1 may be involved in the pathogenesis of AF in VHD patients.

MMP-2 expression by fibroblasts is suppressed by the myofibroblast phenotype

During wound healing, fibroblasts transition from quiescence to a migratory state, then to a contractile myofibroblast state associated with wound closure. We found that the myofibroblast phenotype, characterized by the expression of high levels of contractile proteins, suppresses the expression of the pro-migratory gene, MMP-2. Fibroblasts cultured in a 3-D collagen lattice and allowed to develop tension showed increased contractile protein expression and decreased MMP-2 levels in comparison to a stress-released lattice. In 2-D cultures, factors that promote fibroblast contractility, including serum or TGF-β, down-regulated MMP-2. Pharmacologically inducing F-actin disassembly or reduced contractility increased MMP-2 expression, while conditions that promote F-actin assembly suppressed MMP-2 expression. In all cases, changes in MMP-2 levels were inversely related to changes in the contractile marker, smooth muscle α-actin. To determine if the mechanisms involved in contractile protein gene expression play a direct role in MMP-2 regulation, we used RNAi-mediated knock-down of the myocardin-like factors, MRTF-A and MRTF-B, which induced the down-regulation of contractile protein genes by fibroblasts under both serum-containing and serum-free conditions. In the presence of serum or TGF-β, MRTF-A/B knock-down resulted in the up-regulation of MMP-2; serum-free conditions prevented this increased expression. Together, these results indicate that, while MMP-2 expression is suppressed by F-actin formation, its up-regulation is not simply a consequence of contractile protein down-regulation.

Left ventricular remodeling in swine after myocardial infarction: a transcriptional genomics approach

Despite the apparent appropriateness of left ventricular (LV) remodeling following myocardial infarction (MI), it poses an independent risk factor for development of heart failure. There is a paucity of studies into the molecular mechanisms of LV remodeling in large animal species. We took an unbiased molecular approach to identify candidate transcription factors (TFs) mediating the genetic reprogramming involved in post-MI LV remodeling in swine. Left ventricular tissue was collected from remote, non-infarcted myocardium, 3 weeks after MI-induction or sham-surgery. Microarray analysis identified 285 upregulated and 278 downregulated genes (FDR < 0.05). Of these differentially expressed genes, the promoter regions of the human homologs were searched for common TF binding sites (TFBS). Eighteen TFBS were overrepresented >two-fold (p < 0.01) in upregulated and 13 in downregulated genes. Left ventricular nuclear protein extracts were assayed for DNA-binding activity by protein/DNA array. Out of 345 DNA probes, 30 showed signal intensity changes >two-fold. Five TFs were identified in both TFBS and protein/DNA array analyses, which showed matching changes for COUP-TFII and glucocorticoid receptor (GR) only. Treatment of swine with the GR antagonist mifepristone after MI reduced the post-MI increase in LV mass, but LV dilation remained unaffected. Thus, using an unbiased approach to study post-MI LV remodeling in a physiologically relevant large animal model, we identified COUP-TFII and GR as potential key mediators of post-MI remodeling.

Angiotensin II-induced MMP-2 activity and MMP-14 and basigin protein expression are mediated via the angiotensin II receptor type 1-mitogen-activated protein kinase 1 pathway in retinal pigment epithelium: implications for age-related macular degeneration

Accumulation of various lipid-rich extracellular matrix (ECM) deposits under the retinal pigment epithelium (RPE) has been observed in eyes with age-related macular degeneration (AMD). RPE-derived matrix metalloproteinase (MMP)-2, MMP-14, and basigin (BSG) are major enzymes involved in the maintenance of ECM turnover. Hypertension (HTN) is a systemic risk factor for AMD. It has previously been reported that angiotensin II (Ang II), one of the most important hormones associated with HTN, increases MMP-2 activity and its key regulator, MMP-14, in RPE, inducing breakdown of the RPE basement membrane, which may lead to progression of sub-RPE deposits. Ang II exerts most of its actions by activating the mitogen-activated protein kinase (MAPK) signaling pathway. Herein is explored the MAPK signaling pathway as a potential key intracellular modulator of Ang II-induced increase in MMP-2 activity and MMP-14 and BSG protein expression. It was observed that Ang II stimulates phosphorylation of extracellular signal-regulated kinase (ERK) and p38 MAPK in RPE cells and ERK/p38 and Jun N-terminal kinase (JNK) in mice. These effects were mediated by Ang II type 1 receptors. Blockade of ERK or p38 MAPK abrogated the increase in MMP-2 activity and MMP-14 and BSG proteins in ARPE-19 cells. A better understanding of the molecular events by which Ang II induces ECM dysregulation is of critical importance to further define its contribution to the progression of sub-RPE deposits in AMD patients with HTN.

Captopril treatment induces hyperplasia but inhibits myonuclear accretion following severe myotrauma in murine skeletal muscle

The role of ANG II in skeletal muscle and satellite cell regulation is largely unknown. Cardiotoxin (CTX) was used to investigate whether muscle injury activates a local ANG II signaling system. Following injury, immunohistochelmistry (IHC) analysis revealed a robust increase in the intensity of angiotensinogen and angiotensin type 1 (AT1) receptor expression. As regeneration proceeded, however, AT1 and angiotensinogen were downregulated. Nuclear accretion and fiber formation were also assessed during muscle regeneration in mice treated with captopril (an angiotensin-converting enzyme inhibitor). When ANG II formation was blocked through the use of captopril, we observed a significantly reduced accretion of nuclei into myofibers (−25%), while tibialis anterior total fiber number was significantly increased +37%. This phenotype appeared to be due to alterations in satellite cell differentiation kinetics; captopril treatment led to sustained mRNA expression of markers associated with quiescence and proliferation (Myf5, Pax7) and simultaneously delayed or inhibited the expression of myogenin. IHC staining supported these findings, revealing that captopril treatment resulted in a strong trend ( P = 0.06) for a decrease in the proportion of myogenin-positive myoblasts. Furthermore, these observations were associated with a delay in muscle fiber maturation; captopril treatment resulted in sustained expression of embryonic myosin heavy chain. Collectively, these findings demonstrate that localized skeletal muscle angiotensin signaling is important to muscle fiber formation, myonuclear accretion, and satellite cell function.

Electromechanical effects of the direct renin inhibitor (aliskiren) on the pulmonary vein and atrium

Activation of the atrial renin-angiotensin system plays an important role in the pathophysiology of atrial fibrillation (AF). The pulmonary vein (PV) and left atrium (LA) are important trigger and substrate for the genesis of AF. We investigate the effects of a direct renin inhibitor, aliskiren, on the PV and LA arrhythmogenic activity and the underlying electromechanical mechanisms. Conventional microelectrodes were used to record action potentials and contractility in isolated rabbit PVs and LA tissues before and after the administration of aliskiren (0.1, 1, 3 and 10 μM). By the whole-cell patch clamp and indo-1 fluorimetric ratio techniques, ionic currents and intracellular calcium transient were studied in isolated single PV and LA cardiomyocyte before and after the administration of aliskiren (3 μM). Aliskiren (0.1, 1, 3 and 10 μM) reduced PV firing rate in a concentration-dependent manner (6, 10, 14 and 17%) and decreased PV diastolic tension, which could be attenuated in the presence of 100 μM L-N(G)-Nitroarginine Methyl Ester (L-NAME). Aliskiren induced PV automatic rhythm exit block causing slow and irregular PV activity with variable pauses. Aliskiren increased PV and LA contractility, which could be abolished by pre-treating with 0.1 μM ryanodine. Aliskiren (3 μM) decreased L-type calcium currents, but increased reverse-mode of Na( + )/Ca(2+ ) exchanger currents, intracellular calcium transients, and sarcoplasmic reticulum calcium content in PV and LA cardiomyocytes. Pretreatment with renin, losartan or angiotensin II did not alter the effect of aliskiren on sarcolemmal calcium flux. In conclusion, aliskiren reduces PV arrhythmogenic activity with a direct vasodilatory property and has a positive inotropic effect on cardiomyocytes. These findings may reveal the anti-arrhythmic and anti-heart failure potentials of aliskiren.

Differential expression of MMP-2 and -9 and their inhibitors in fetal lung cells exposed to mechanical stretch: regulation by IL-10

STUDY OBJECTIVES

Abnormal remodeling of the extracellular matrix (ECM) has been implicated in the pathogenesis of bronchopulmonary dysplasia. However, the contribution of lung parenchymal cells to ECM remodeling after mechanical injury is not well defined. The objective of these studies was to investigate in vitro the release of MMP-2 and -9 and their respective inhibitors TIMP-2 and -1, and to explore potential regulation by IL-10.

DESIGN

Mouse fetal epithelial cells and fibroblasts isolated on E18-19 of gestation were exposed to 20% cyclic stretch to simulate lung injury. MMP-2 and MMP-9 activity were investigated by zymography and ELISA. TIMP-1 and TIMP-2 abundance were analyzed by Western blot.

RESULTS

We found that mechanical stretch increased MMP-2 and decreased TIMP-2 in fibroblasts, indicating that excessive stretch promotes MMP-2 activation, expressed as the MMP-2/TIMP-2 ratio. Incubation with IL-10 did not change MMP-2 activity. In contrast, mechanical stretch of epithelial cells decreased MMP-9 activity and the MMP-9/TIMP-1 ratio by 60-70%. When IL-10 was added, mechanical stretch increased the MMP-9/TIMP-1 ratio by 50%.

CONCLUSIONS

We conclude that mechanical stretch differentially affects MMP-2/9 and their inhibitors in fetal lung cells. IL-10 modulates MMP-9 activity through a combination of effects on MMP-9 and TIMP-1 levels.

Sympathetic neurons express and secrete MMP-2 and MT1-MMP to control nerve sprouting via pro-NGF conversion

Recently, we have shown that high frequency electrical field stimulation (HFES) of sympathetic neurons (SN) induces nerve sprouting by up-regulation of nerve growth factor (NGF) which targets the tyrosine kinase A receptor (TrkA) in an autocrine/paracrine manner. There is increasing evidence that matrix metalloproteinase-2 (MMP-2) is not only involved in extracellular matrix (ECM) turnover but may also exert beneficial effects during neuronal growth. Therefore, this study aimed to investigate the regulation and function of MMP-2 and its major activator membrane type 1-matrix metalloproteinase (MT1-MMP) as well its inhibitor TIMP-1 in SN under conditions of HFES. Moreover, we analyzed molecular mechanisms of the beneficial effect of losartan, an angiotensin II type I receptor (AT-1)blocker on HFES-induced nerve sprouting. Cell cultures of SN from the superior cervical ganglia (SCG) of neonatal rats were electrically stimulated for 48 h with a frequency of 5 or 50 Hz. HFES increased MMP-2 and MT1-MMP mRNA and protein expression, whereas TIMP-1 expression remained unchanged. Under conditions of HFES, we observed a shift from pro- to active-MMP-2 indicating an increase in MMP-2 enzyme activity. Specific pharmacological MMP-2 inhibition contributed to an increase in pro-NGF amount in the cell culture supernatant and significantly reduced HFES-induced neurite outgrowth. Losartan abolished HFES-induced nerve sprouting in a significant manner by preventing HFES-induced NGF, MMP-2, and MT1-MMP up-regulation. In summary, specific MMP-2 blockade prevents sympathetic nerve sprouting (SNS) by inhibition of pro-NGF conversion while losartan abolishes HFES-induced SNS by reducing total NGF, MMP-2 and MT1-MMP expression.

Angiotensin II signaling up-regulates the immediate early transcription factor ATF3 in the left but not the right atrium

The atria respond to various pathological stimuli including pressure and volume overload with remodeling and dilatation. Dilatation of the left atrium is associated with atrial fibrillation. The mechanisms involved in chamber-specific hypertrophy are largely unknown. Angiotensin II is hypothesized to take part in mediating this response. ATF3 is an immediate early gene found at the receiving end of multiple stress and growth stimuli. Here we characterize ATF3 as a direct target gene for angiotensin II. ATF3 expression is regulated by angiotensin receptor-mediated signaling in vivo and in vitro at the transcriptional level. ATF3 induction is mediated by cooperation between both the AT(1A) and AT₂ receptor subtypes. While AT₂R blocker (PD123319) efficiently blocks ATF3 induction in response to angiotensin II injection, it results in an increase in blood pressure indicating that the effect of angiotensin II on ATF3 is independent of its effect on blood pressure. In contrast to adrenergic stimulation that induces ATF3 in all heart chambers, ATF3 induction in response to angiotensin II occurs primarily in the left chambers. We hypothesize that the activation of differential signaling pathways accounts for the chamber-specific induction of ATF3 expression in response to angiotensin II stimulation. Angiotensin II injection rapidly activates the EGFR-dependent pathways including ERK and PI3K-AKT in the left but not the right atrium. EGF receptor inhibitor (Gefitinib/Iressa) as well as the AKT inhibitor (Triciribine) significantly abrogates ATF3 induction by angiotensin II in the left chambers. Collectively, our data strongly place ATF3 as a unique nuclear protein target in response to angiotensin II stimulation in the atria. The spatial expression of ATF3 may add to the understanding of the signaling pathways involved in cardiac response to neuro-hormonal stimulation, and in particular to the understanding of left atrial-generated pathology such as atrial fibrillation.

Discrepant electrophysiological characteristics and calcium homeostasis of left atrial anterior and posterior myocytes

The left atrial (LA) posterior wall has been demonstrated to have regional electrophysiological differences with a higher arrhythmogenic potential leading to atrial fibrillation (AF). However, the ionic characteristics and calcium regulation in the LA anterior and posterior myocytes have not been fully elucidated. The purpose of this study was to investigate the electrical characteristics of the LA anterior and posterior myocytes. Whole-cell patch-clamp techniques and the indo-1 fluorimetric ratio technique were used to investigate the characteristics of the ionic currents, action potentials, and intracellular calcium in single isolated rabbit myocytes in the LA anterior and posterior walls. The expression of the Na(+)-Ca(2+) exchanger (NCX) and ryanodine receptor (RyR) were evaluated by a Western blot. The LA posterior myocytes (n = 15) had a higher incidence (53 vs. 19%, P < 0.05) of delayed afterdepolarizations than the LA anterior myocytes (n = 16). The LA posterior myocytes had larger sodium currents and late sodium currents, but smaller inward rectifier potassium currents than the LA anterior myocytes. The LA posterior myocytes had larger intracellular Ca(2+) transient and sarcoplasmic reticulum Ca(2+) contents as compared with the LA anterior myocytes. However, the NCX currents in the LA posterior myocytes were smaller than those in the LA anterior myocytes. The LA posterior myocytes had a smaller protein expression of NCX, but a larger protein expression of RyR than the LA anterior myocytes. In conclusion, LA posterior myocytes contain a high arrhythmogenic potential and distinctive electrophysiological characteristics, which may contribute to the pathophysiology of AF.

Mechanisms of atrial structural changes caused by stretch occurring before and during early atrial fibrillation

Structural remodelling occurring before, due to the underlying heart disease, and during atrial fibrillation (AF) sets the stage for permanent AF. Current therapy in AF aims to maintain sinus rhythm in symptomatic patients, but outcome is unfortunately poor. Stretch of the atria is a main contributor to atrial remodelling. In this review, we describe different aspects of structural remodelling as seen in animal models and in patients with AF, including atrial enlargement, cellular hypertrophy, dedifferentiation, fibrosis, apoptosis, and loss of contractile elements. In the second part, we describe downstream signals of mechanical stretch and their contribution to AF and structural remodelling. Ultimately, knowledge of mechanisms underlying structural remodelling may help to identify new pharmacological targets for AF prevention.