Calcineurin-NFAT activation and DSCR-1 auto-inhibitory loop: how is homoeostasis regulated?

The alpha-synuclein oligomers activate nuclear factor of activated T-cell (NFAT) modulating synaptic homeostasis and apoptosis

BACKGROUND

Soluble oligomeric forms of alpha-synuclein (aSyn-O) are believed to be one of the main toxic species in Parkinson's disease (PD) leading to degeneration. aSyn-O can induce Ca2+ influx, over activating downstream pathways leading to PD phenotype. Calcineurin (CN), a phosphatase regulated by Ca2+ levels, activates NFAT transcription factors that are involved in the regulation of neuronal plasticity, growth, and survival.

METHODS

Here, using a combination of cell toxicity and gene regulation assays performed in the presence of classical inhibitors of the NFAT/CN pathway, we investigate NFAT's role in neuronal degeneration induced by aSyn-O.

RESULTS

aSyn-O are toxic to neurons leading to cell death, loss of neuron ramification and reduction of synaptic proteins which are reversed by CN inhibition with ciclosporin-A or VIVIT, a NFAT specific inhibitor. aSyn-O induce NFAT nuclear translocation and transactivation. We found that aSyn-O modulates the gene involved in the maintenance of synapses, synapsin 1 (Syn 1). Syn1 mRNA and protein and synaptic puncta are drastically reduced in cells treated with aSyn-O which are reversed by NFAT inhibition.

CONCLUSIONS

For the first time a direct role of NFAT in aSyn-O-induced toxicity and Syn1 gene regulation was demonstrated, enlarging our understanding of the pathways underpinnings synucleinopathies.

Calcium-Dependent Ion Channels and the Regulation of Arteriolar Myogenic Tone

Arterioles in the peripheral microcirculation regulate blood flow to and within tissues and organs, control capillary blood pressure and microvascular fluid exchange, govern peripheral vascular resistance, and contribute to the regulation of blood pressure. These important microvessels display pressure-dependent myogenic tone, the steady state level of contractile activity of vascular smooth muscle cells (VSMCs) that sets resting arteriolar internal diameter such that arterioles can both dilate and constrict to meet the blood flow and pressure needs of the tissues and organs that they perfuse. This perspective will focus on the Ca²⁺-dependent ion channels in the plasma and endoplasmic reticulum membranes of arteriolar VSMCs and endothelial cells (ECs) that regulate arteriolar tone. In VSMCs, Ca²⁺-dependent negative feedback regulation of myogenic tone is mediated by Ca²⁺-activated K⁺ (BK_Ca) channels and also Ca²⁺-dependent inactivation of voltage-gated Ca²⁺ channels (VGCC). Transient receptor potential subfamily M, member 4 channels (TRPM4); Ca²⁺-activated Cl⁻ channels (CaCCs; TMEM16A/ANO1), Ca²⁺-dependent inhibition of voltage-gated K⁺ (K_V) and ATP-sensitive K⁺ (K_ATP) channels; and Ca²⁺-induced-Ca²⁺ release through inositol 1,4,5-trisphosphate receptors (IP₃Rs) participate in Ca²⁺-dependent positive-feedback regulation of myogenic tone. Calcium release from VSMC ryanodine receptors (RyRs) provide negative-feedback through Ca²⁺-spark-mediated control of BK_Ca channel activity, or positive-feedback regulation in cooperation with IP₃Rs or CaCCs. In some arterioles, VSMC RyRs are silent. In ECs, transient receptor potential vanilloid subfamily, member 4 (TRPV4) channels produce Ca²⁺ sparklets that activate IP₃Rs and intermediate and small conductance Ca²⁺ activated K⁺ (IK_Ca and sK_Ca) channels causing membrane hyperpolarization that is conducted to overlying VSMCs producing endothelium-dependent hyperpolarization and vasodilation. Endothelial IP₃Rs produce Ca²⁺ pulsars, Ca²⁺ wavelets, Ca²⁺ waves and increased global Ca²⁺ levels activating EC sK_Ca and IK_Ca channels and causing Ca²⁺-dependent production of endothelial vasodilator autacoids such as NO, prostaglandin I₂ and epoxides of arachidonic acid that mediate negative-feedback regulation of myogenic tone. Thus, Ca²⁺-dependent ion channels importantly contribute to many aspects of the regulation of myogenic tone in arterioles in the microcirculation.

Calcineurin-nuclear factor for activated T cells (NFAT) signaling in pathophysiology of wound healing

Wound healing occurred with serial coordinated processes via coagulation-fibrinolysis, inflammation following to immune-activation, angiogenesis, granulation, and the final re-epithelization. Since the dermis forms critical physical and biological barriers, the repair system should be rapidly and accurately functioned to keep homeostasis in our body. The wound healing is impaired or dysregulated via an inappropriate microenvironment, which is easy to lead to several diseases, including fibrosis in multiple organs and psoriasis. Such a disease led to the dysregulation of several types of cells: immune cells, fibroblasts, mural cells, and endothelial cells. Moreover, recent progress in medical studies uncovers the significant concept. The calcium signaling, typically the following calcineurin-NFAT signaling, essentially regulates not only immune cell activations, but also various healing steps via coagulation, inflammation, and angiogenesis. In this review, we summarize the role of the NFAT activation pathway in wound healing and discuss its overall impact on future therapeutic ways.

NFAT indicates nucleocytoplasmic damped oscillation via its feedback modulator

Cell signaling and the following gene regulation are tightly regulated to keep homeostasis. NF-κB is a famous key transcription factor for inflammatory cell regulations that obtain a closed feedback loop with IκB. Similarly, we show here, NFAT is also tightly regulated via its downstream target, down syndrome critical region (DSCR)-1. In primary cultured endothelium, either shear stress or VEGF treatment revealed quick NFAT1 nuclear localization following the DSCR-1 transactivation, which in turn induced NFAT1 cytoplasm sequestration. Interestingly, both NFAT and DSCR-1 can be competitive substrates for calcineurin phosphatase and DSCR-1 is known to unstable protein, which caused NFAT1-nucleocytoplasmic damped oscillation via sustained shear stress or VEGF stimulation in endothelial cell (EC)s. To understand the molecular mechanism underlying the NFAT1 oscillation, we built a mathematical model of spatiotemporal regulation of NFAT1 combined with calcineurin and DSCR-1. Theoretically, manipulation of DSCR-1 expression in simulation predicted that DSCR-1 reduction would cause nuclear retention of dephosphorylated NFAT1 and disappearance of NFAT1 oscillation. To confirm this in ECs, DSCR-1 knockdown analysis was performed. DSCR-1 reduction indeed increased dephosphorylated NFAT1 in both the nucleus and cytoplasm, which eventually led to nuclear retention of NFAT1. Taken together, these studies suggest that DSCR-1 is a responsible critical factor for NFAT1 nucleocytoplasmic oscillation in shear stress or VEGF treated ECs. Our mathematical model successfully reproduced the experimental observations of NFAT1 dynamics. Combined mathematical and experimental approaches would provide a quantitative understanding way for the spatiotemporal NFAT1 feedback system.

Amniotic membrane matrix effects on calcineurin-NFAT-related gene expressions of SHED treated with VEGF for endothelial differentiation

The nuclear factor of activated T-cell (NFAT) signaling pathway is involved in angiogenesis following initiation by vascular endothelial growth factor (VEGF). A number of angiogenic genes have been associated with calcineurin in the NFAT pathway, forming a calcineurin-NFAT pathway. This study aims to investigate the involvement of four angiogenic genes within the calcineurin-NFAT pathway in the endothelial-like differentiation of stem cells from human exfoliated deciduous teeth (SHED) cultured on a human amniotic membrane (HAM) induced by VEGF. SHED were induced with VEGF for 24 h, then cultured on the stromal side of HAM. The cells were then further induced with VEGF until days 1 and 14. To understand the role of calcineurin, its potent inhibitor, cyclosporin A (CsA), was added into the culture. Results from SEM and H&E analyses showed SHED grew on HAM surface. Gene expression study of Cox-2 showed a drastically reduced expression with CsA treatment indicating Cox-2 involvement in the calcineurin-NFAT pathway. Meanwhile, IL-8 was probably controlled by another pathway as it showed no CsA inhibition. In contrast, high expression of ICAM-1 and RCAN1.4 by VEGF and CsA implied that these genes were not controlled by the calcineurin-NFAT-dependent pathway. In conclusion, the results of this study suggest the involvement of Cox-2 in the calcineurin-NFAT-dependent pathway while RCAN1.4 was controlled by NFAT molecule in endothelial-like differentiation of SHED cultured on HAM with VEGF induction.

Loss of Down syndrome critical region-1 leads to cholesterol metabolic dysfunction that exaggerates hypercholesterolemia in ApoE-null background

Down syndrome critical region (DSCR)-1 functions as a feedback modulator for calcineurin-nuclear factor for activated T cell (NFAT) signals, which are crucial for cell proliferation and inflammation. Stable expression of DSCR-1 inhibits pathological angiogenesis and septic inflammation. DSCR-1 also plays a critical role in vascular wall remodeling associated with aneurysm development that occurs primarily in smooth muscle cells. Besides, Dscr-1 deficiency promotes the M1-to M2-like phenotypic switch in macrophages, which correlates to the reduction of denatured cholesterol uptakes. However, the distinct roles of DSCR-1 in cholesterol and lipid metabolism are not well understood. Here, we show that loss of apolipoprotein (Apo) E in mice with chronic hypercholesterolemia induced Dscr-1 expression in the liver and aortic atheroma. In Dscr-1-null mice fed a high-fat diet, oxidative- and endoplasmic reticulum (ER) stress was induced, and sterol regulatory element-binding protein (SREBP) 2 production in hepatocytes was stimulated. This exaggerated ApoE^-/--mediated nonalcoholic fatty liver disease (NAFLD) and subsequent hypercholesterolemia. Genome-wide screening revealed that loss of both ApoE and Dscr-1 resulted in the induction of immune- and leukocyte activation-related genes in the liver compared with ApoE deficiency alone. However, expressions of inflammation-activated markers and levels of monocyte adhesion were suspended upon induction of the Dscr-1 null background in the aortic endothelium. Collectively, our study shows that the combined loss of Dscr-1 and ApoE causes metabolic dysfunction in the liver but reduces atherosclerotic plaques, thereby leading to a dramatic increase in serum cholesterol and the formation of sporadic vasculopathy.

Extracellular vesicles from human airway basal cells respond to cigarette smoke extract and affect vascular endothelial cells

The human airway epithelium lining the bronchial tree contains basal cells that proliferate, differentiate, and communicate with other components of their microenvironment. One method that cells use for intercellular communication involves the secretion of exosomes and other extracellular vesicles (EVs). We isolated exosome-enriched EVs that were produced from an immortalized human airway basal cell line (BCi-NS1.1) and found that their secretion is increased by exposure to cigarette smoke extract, suggesting that this stress stimulates release of EVs which could affect signaling to other cells. We have previously shown that primary human airway basal cells secrete vascular endothelial growth factor A (VEGFA) which can activate MAPK signaling cascades in endothelial cells via VEGF receptor-2 (VEGFR2). Here, we show that exposure of endothelial cells to exosome-enriched airway basal cell EVs promotes the survival of these cells and that this effect also involves VEGFR2 activation and is, at least in part, mediated by VEGFA present in the EVs. These observations demonstrate that EVs are involved in the intercellular signaling between airway basal cells and the endothelium which we previously reported. The downstream signaling pathways involved may be distinct and specific to the EVs, however, as increased phosphorylation of Akt, STAT3, p44/42 MAPK, and p38 MAPK was not seen following exposure of endothelial cells to airway basal cell EVs.

Calcineurin

The serine/threonine phosphatase calcineurin acts as a crucial connection between calcium signaling the phosphorylation states of numerous important substrates. These substrates include, but are not limited to, transcription factors, receptors and channels, proteins associated with mitochondria, and proteins associated with microtubules. Calcineurin is activated by increases in intracellular calcium concentrations, a process that requires the calcium sensing protein calmodulin binding to an intrinsically disordered regulatory domain in the phosphatase. Despite having been studied for around four decades, the activation of calcineurin is not fully understood. This review largely focuses on what is known about the activation process and highlights aspects that are currently not understood. Video abstract.

The role of Ca2+/NFAT in Dysfunction and Inflammation of Human Coronary Endothelial Cells induced by Sera from patients with Kawasaki disease

Ca²⁺/nuclear factor of activated T-cells (Ca²⁺/NFAT) signaling pathway may play a crucial role in the pathogenesis of Kawasaki disease (KD). We investigated the poorly understood Ca²⁺/NFAT regulation of coronary artery endothelial cells and consequent dysfunction in KD pathogenesis. Human coronary artery endothelial cells (HCAECs) stimulated with sera from patients with KD, compared with sera from healthy children, exhibited significant increases in proliferation and angiogenesis, higher levels of NFATc1 and NFATc3 and some inflammatory molecules, and increased nuclear translocation of NFATc1 and NFATc3. HCAECs stimulated with sera from patients with KD treated with cyclosporine A (CsA) showed decreased proliferation, angiogenesis, NFATc1 and inflammatory molecules levels as compared with results for untreated HCAECs. In conclusion, our data reveal that KD sera activate the Ca²⁺/NFAT in HCAECs, leading to dysfunction and inflammation of endothelial cells. CsA has cytoprotective effects by ameliorating endothelial cell homeostasis via Ca²⁺/NFAT.

Paxillin-Mediated Recruitment of Calcineurin to the Contractile Ring Is Required for the Correct Progression of Cytokinesis in Fission Yeast

Paxillin is a scaffold protein that participates in focal adhesion signaling in mammalian cells. Fission yeast paxillin ortholog, Pxl1, is required for contractile actomyosin ring (CAR) integrity and collaborates with the β-glucan synthase Bgs1 in septum formation. We show here that Pxl1's main function is to recruit calcineurin (CN) phosphatase to the actomyosin ring; and thus the absence of either Pxl1 or calcineurin causes similar cytokinesis defects. In turn, CN participates in the dephosphorylation of the Cdc15 F-BAR protein, which recruits and concentrates Pxl1 at the CAR. Our findings suggest the existence of a positive feedback loop between Pxl1 and CN and establish that Pxl1 is a crucial component of the CN signaling pathway during cytokinesis.

Decoding inflammation, its causes, genomic responses, and emerging countermeasures

Inflammation is the mechanism of diseases caused by microbial, autoimmune, allergic, metabolic and physical insults that produce distinct types of inflammatory responses. This aetiologic view of inflammation informs its classification based on a cause‐dependent mechanism as well as a cause‐directed therapy and prevention. The genomic era ushered in a new understanding of inflammation by highlighting the cell's nucleus as the centre of the inflammatory response. Exogenous or endogenous inflammatory insults evoke genomic responses in immune and non‐immune cells. These genomic responses depend on transcription factors, which switch on and off a myriad of inflammatory genes through their regulatory networks. We discuss the transcriptional paradigm of inflammation based on denying transcription factors’ access to the nucleus. We present two approaches that control proinflammatory signalling to the nucleus. The first approach constitutes a novel intracellular protein therapy with bioengineered physiologic suppressors of cytokine signalling. The second approach entails control of proinflammatory transcriptional cascades by targeting nuclear transport with a cell‐penetrating peptide that inhibits the expression of 23 out of the 26 mediators of inflammation along with the nine genes required for metabolic responses. We compare these emerging anti‐inflammatory countermeasures to current therapies. The transcriptional paradigm of inflammation offers nucleocentric strategies for microbial, autoimmune, metabolic, physical and other types of inflammation afflicting millions of people worldwide.

Coupled feedback regulation of nuclear factor of activated T-cells (NFAT) modulates activation-induced cell death of T cells

A properly functioning immune system is vital for an organism’s wellbeing. Immune tolerance is a critical feature of the immune system that allows immune cells to mount effective responses against exogenous pathogens such as viruses and bacteria, while preventing attack to self-tissues. Activation-induced cell death (AICD) in T lymphocytes, in which repeated stimulations of the T-cell receptor (TCR) lead to activation and then apoptosis of T cells, is a major mechanism for T cell homeostasis and helps maintain peripheral immune tolerance. Defects in AICD can lead to development of autoimmune diseases. Despite its importance, the regulatory mechanisms that underlie AICD remain poorly understood, particularly at an integrative network level. Here, we develop a dynamic multi-pathway model of the integrated TCR signalling network and perform model-based analysis to characterize the network-level properties of AICD. Model simulation and analysis show that amplified activation of the transcriptional factor NFAT in response to repeated TCR stimulations, a phenomenon central to AICD, is tightly modulated by a coupled positive-negative feedback mechanism. NFAT amplification is predominantly enabled by a positive feedback self-regulated by NFAT, while opposed by a NFAT-induced negative feedback via Carabin. Furthermore, model analysis predicts an optimal therapeutic window for drugs that help minimize proliferation while maximize AICD of T cells. Overall, our study provides a comprehensive mathematical model of TCR signalling and model-based analysis offers new network-level insights into the regulation of activation-induced cell death in T cells.

Arsenic Trioxide Inhibits the Metastasis of Small Cell Lung Cancer by Blocking Calcineurin-Nuclear Factor of Activated T Cells (NFAT) Signaling

BACKGROUND The inhibitory effect of arsenic trioxide (As₂O₃) on lung cancer has been reported in some preclinical studies. However, its effect on small cell lung cancer (SCLC) has been poorly explored. Calcineurin and its substrate, nuclear factor of activated T cells (NFAT), mediate the downstream signaling of VEGF, and is critical in the process endothelium activation and tumor metastasis. In this study, we aimed to evaluate whether As₂O₃ had inhibitory effects on endothelial cells activation and the metastasis of SCLC, and to explore the possible mechanisms. MATERIAL AND METHODS In vitro, human umbilical vein endothelial cells (HUVECs) were used. Cell Counting Kit-8 assay and cell migration assay were performed to determine the effect of As₂O₃ on HUVECs proliferation and migration. The level of calcineurin, NFAT, downstream factors for Down syndrome candidate region 1 (DSCR1), and the endogenous inhibitor of calcineurin, were evaluated by quantitative PCR and western blotting. In vivo, SCLC metastasis models were established by injecting NCI-H446 cells into tail veins of nude mice. Tumor-bearing mice were treated with As₂O₃ or calcineurin inhibitor for 10 days, after which tumor metastasis in target organs was evaluated. RESULTS As₂O₃ significantly inhibited the proliferation and migration of endothelial cells. Also, As₂O₃ inhibited the expression levels of calcineurin, NFAT, and the downstream target genes CXCR7 and RND1, while it upregulated the level of DSCR1. Both As₂O₃ and calcineurin inhibitor exhibited notable inhibitory effect on the metastasis of SCLC, without obvious side effects. CONCLUSIONS These findings suggested that As₂O₃ had remarkable inhibitory effects on the endothelial cell activation and SCLC metastasis, and the mechanism might be related to the blocking of calcineurin-NFAT signaling by upregulating DSCR1.

Cholecystokinin (CCK) Regulation of Pancreatic Acinar Cells: Physiological Actions and Signal Transduction Mechanisms

Pancreatic acinar cells synthesize and secrete about 20 digestive enzymes and ancillary proteins with the processes that match the supply of these enzymes to their need in digestion being regulated by a number of hormones (CCK, secretin and insulin), neurotransmitters (acetylcholine and VIP) and growth factors (EGF and IGF). Of these regulators, one of the most important and best studied is the gastrointestinal hormone, cholecystokinin (CCK). Furthermore, the acinar cell has become a model for seven transmembrane, heterotrimeric G protein coupled receptors to regulate multiple processes by distinct signal transduction cascades. In this review, we briefly describe the chemistry and physiology of CCK and then consider the major physiological effects of CCK on pancreatic acinar cells. The majority of the review is devoted to the physiologic signaling pathways activated by CCK receptors and heterotrimeric G proteins and the functions they affect. The pathways covered include the traditional second messenger pathways PLC-IP3-Ca²⁺ , DAG-PKC, and AC-cAMP-PKA/EPAC that primarily relate to secretion. Then there are the protein-protein interaction pathways Akt-mTOR-S6K, the three major MAPK pathways (ERK, JNK, and p38 MAPK), and Ca²⁺ -calcineurin-NFAT pathways that primarily regulate non-secretory processes including biosynthesis and growth, and several miscellaneous pathways that include the Rho family small G proteins, PKD, FAK, and Src that may regulate both secretory and nonsecretory processes but are not as well understood. © 2019 American Physiological Society. Compr Physiol 9:535-564, 2019.

Decreased abundance of TRESK two-pore domain potassium channels in sensory neurons underlies the pain associated with bone metastasis

Bone metastasis–associated VEGF suppresses neuronal K + channels and increases pain in rats.

Anti-angiogenic effects of Qingdu granule on breast cancer through inhibiting NFAT signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Qingdu granule (QDG), a traditional Chinese herbal prescription, had anti-tumor effect on breast cancer. However the underlying mechanism of QDG was unclear.

THE AIM OF THIS STUDY

The present study aimed to investigate whether QDG could inhibit angiogenesis of breast cancer via acting on nuclear factor of activated T-cells (NFAT) signaling pathway. This was implicated in human umbilical vein endothelial cells (HUVECs) in vitro and breast cancer xenograft model in vivo.

MATERIALS AND METHODS

The VEGF₁₆₅ (15.58 ng/mL) induced human umbilical vein endothelial cells (HUVECs) were treated with serum samples containing tamoxifen (TAM), tacrolimus (FK506), or QDG with three dosages. The migration and canalization capacities of HUVECs were evaluated by transwell migration and tube formation assay. In 72 h-cultured HUVECs, The gene expression, protein amount, and nuclear translocation of NFATc3 were measured. The anti-tumor and anti-angiogenic effects of QDG in vivo were investigated in breast cancer xenograft model. The serum VEGF levels, microvessel density, and protein expressions (immunohistochemistry and western blot) of VEGF, VEGFR2 and NFATc3 were detected.

RESULTS

The results showed that, QDG significantly inhibited HUVEC migration and tube formation. It downregulated NFATc3 gene expression, decreased NFATc3 protein amount, and reduced the ratio of NFATc3 nuclear translocation in HUVECs. In breast cancer xenograft model, QDG treatment significantly suppressed tumor growth, inhibited VEGF release, and decreased microvessel density. QDG reduced protein expressions of VEGF, VEGFR2 and NFATc3.

CONCLUSION

The results suggested that QDG showed anti-angiogenic effects of breast cancer both in vitro and in vivo. The mechanism might be partially associated with inhibiting NFAT signaling pathway.

High-Amplitude Circadian Rhythms in Drosophila Driven by Calcineurin-Mediated Post-translational Control of sarah

Post-translational control is a crucial mechanism for circadian timekeeping. Evolutionarily conserved kinases and phosphatases have been implicated in circadian phosphorylation and the degradation of clock-relevant proteins, which sustain high-amplitude rhythms with 24-hr periodicity in animal behaviors and physiology. Here, we report a novel clock function of the heterodimeric Ca²⁺/calmodulin-dependent phosphatase calcineurin and its regulator sarah (sra) in Drosophila Genomic deletion of the sra locus dampened circadian locomotor activity rhythms in free-running constant dark after entrainment in light-dark cycles. Poor rhythms in sra mutant behaviors were accompanied by lower expression of two oscillating clock proteins, PERIOD (PER) and TIMELESS (TIM), at the post-transcriptional level. RNA interference-mediated sra depletion in circadian pacemaker neurons was sufficient to phenocopy loss-of-function mutation in sra On the other hand, a constitutively active form of the catalytic calcineurin subunit, Pp2B-14D^ACT, shortened circadian periodicity in locomotor behaviors and phase-advanced PER and TIM rhythms when overexpressed in clock neurons. Heterozygous sra deletion induced behavioral arrhythmicity in Pp2B-14D^ACT flies, whereas sra overexpression rescued short periods in these animals. Finally, pharmacological inhibition of calcineurin in either wild-type flies or clock-less S2 cells decreased the levels of PER and TIM, likely by facilitating their proteasomal degradation. Taken together, these data suggest that sra negatively regulates calcineurin by cell-autonomously titrating calcineurin-dependent stabilization of PER and TIM proteins, thereby sustaining high-amplitude behavioral rhythms in Drosophila.

Boosting the signal: Endothelial inward rectifier K+ channels

Endothelial cells express a diverse array of ion channels including members of the strong inward rectifier family composed of K_IR 2 subunits. These two-membrane spanning domain channels are modulated by their lipid environment, and exist in macromolecular signaling complexes with receptors, protein kinases and other ion channels. Inward rectifier K⁺ channel (K_IR ) currents display a region of negative slope conductance at membrane potentials positive to the K⁺ equilibrium potential that allows outward current through the channels to be activated by membrane hyperpolarization, permitting K_IR to amplify hyperpolarization induced by other K⁺ channels and ion transporters. Increases in extracellular K⁺ concentration activate K_IR allowing them to sense extracellular K⁺ concentration and transduce this change into membrane hyperpolarization. These properties position K_IR to participate in the mechanism of action of hyperpolarizing vasodilators and contribute to cell-cell conduction of hyperpolarization along the wall of microvessels. The expression of K_IR in capillaries in electrically active tissues may allow K_IR to sense extracellular K⁺ , contributing to functional hyperemia. Understanding the regulation of expression and function of microvascular endothelial K_IR will improve our understanding of the control of blood flow in the microcirculation in health and disease and may provide new targets for the development of therapeutics in the future.

Endothelial Regulator of Calcineurin 1 Promotes Barrier Integrity and Modulates Histamine-Induced Barrier Dysfunction in Anaphylaxis

Anaphylaxis, the most serious and life-threatening allergic reaction, produces the release of inflammatory mediators by mast cells and basophils. Regulator of calcineurin 1 (Rcan1) is a negative regulator of mast-cell degranulation. The action of mediators leads to vasodilation and an increase in vascular permeability, causing great loss of intravascular volume in a short time. Nevertheless, the molecular basis remains unexplored on the vascular level. We investigated Rcan1 expression induced by histamine, platelet-activating factor (PAF), and epinephrine in primary human vein (HV)-/artery (HA)-derived endothelial cells (ECs) and human dermal microvascular ECs (HMVEC-D). Vascular permeability was analyzed in vitro in human ECs with forced Rcan1 expression using Transwell migration assays and in vivo using Rcan1 knockout mice. Histamine, but neither PAF nor epinephrine, induced Rcan1-4 mRNA and protein expression in primary HV-ECs, HA-ECs, and HMVEC-D through histamine receptor 1 (H1R). These effects were prevented by pharmacological inhibition of calcineurin with cyclosporine A. Moreover, intravenous histamine administration increased Rcan1 expression in lung tissues of mice undergoing experimental anaphylaxis. Functional in vitro assays showed that overexpression of Rcan1 promotes barrier integrity, suggesting a role played by this molecule in vascular permeability. Consistent with these findings, in vivo models of subcutaneous and intravenous histamine-mediated fluid extravasation showed increased response in skin, aorta, and lungs of Rcan1-deficient mice compared with wild-type animals. These findings reveal that endothelial Rcan1 is synthesized in response to histamine through a calcineurin-sensitive pathway and may reduce barrier breakdown, thus contributing to the strengthening of the endothelium and resistance to anaphylaxis. These new insights underscore its potential role as a regulator of sensitivity to anaphylaxis in humans.

Experimental Therapy of Advanced Breast Cancer: Targeting NFAT1-MDM2-p53 Pathway

Advanced breast cancer, especially advanced triple-negative breast cancer, is typically more aggressive and more difficult to treat than other breast cancer phenotypes. There is currently no curable option for breast cancer patients with advanced diseases, highlighting the urgent need for novel treatment strategies. We have recently discovered that the nuclear factor of activated T cells 1 (NFAT1) activates the murine double minute 2 (MDM2) oncogene. Both MDM2 and NFAT1 are overexpressed and constitutively activated in breast cancer, particularly in advanced breast cancer, and contribute to its initiation, progression, and metastasis. MDM2 regulates cancer cell proliferation, cell cycle progression, apoptosis, migration, and invasion through both p53-dependent and -independent mechanisms. We have proposed to target the NFAT1-MDM2-p53 pathway for the treatment of human cancers, especially breast cancer. We have recently identified NFAT1 and MDM2 dual inhibitors that have shown excellent in vitro and in vivo activities against breast cancer, including triple-negative breast cancer. Herein, we summarize recent advances made in the understanding of the oncogenic functions of MDM2 and NFAT1 in breast cancer, as well as current targeting strategies and representative inhibitors. We also propose several strategies for inhibiting the NFAT1-MDM2-p53 pathway, which could be useful for developing more specific and effective inhibitors for breast cancer therapy.

Inhibition of Calcineurin A by FK506 Suppresses Seizures and Reduces the Expression of GluN2B in Membrane Fraction

FK506, a calcineurin inhibitor, shows neuroprotective effects and has been associated with neurodegenerative diseases. Calcineurin A (CaNA), a catalytic subunit of calcineurin, mediates the dephosphorylation of various proteins. N-methyl-D-aspartate receptor (GluN) is closely related to epileptogenesis, and various phosphorylation sites of GluN2B, a regulatory subunit of the GluN complex, have different functions. Thus, we hypothesized that one of the potential anti-epileptic mechanisms of FK506 is mediated by its ability to promote the phosphorylation of GluN2B and reduce the expression of GluN2B in membrane fraction by down-regulating CaNA. CaNA expression was increased in the cortex of patients with temporal lobe epilepsy and pentylenetetrazol (PTZ)-induced epileptic models. CaNA was shown to be expressed in neurons using immunofluorescence staining. According to our behavioral observations, epileptic rats exhibited less severe seizures and were less sensitive to PTZ after a systemic injection of FK506. The levels of phosphorylated GluN2B were decreased in epileptic rats but increased after the FK506 treatment. Moreover, there was no difference in the total GluN2B levels before and after FK506 treatment. However, the expression of GluN2B in membrane fraction was suppressed after FK506 treatment. Based on these results, FK506 may reduce the severity and frequency of seizures by reducing the expression of GluN2B in membrane fraction.

Sustained inflammation after pericyte depletion induces irreversible blood-retina barrier breakdown

In the central nervous system, endothelial cells (ECs) and pericytes (PCs) of blood vessel walls cooperatively form a physical and chemical barrier to maintain neural homeostasis. However, in diabetic retinopathy (DR), the loss of PCs from vessel walls is assumed to cause breakdown of the blood-retina barrier (BRB) and subsequent vision-threatening vascular dysfunctions. Nonetheless, the lack of adequate DR animal models has precluded disease understanding and drug discovery. Here, by using an anti-PDGFRβ antibody, we show that transient inhibition of the PC recruitment to developing retinal vessels sustained EC-PC dissociations and BRB breakdown in adult mouse retinas, reproducing characteristic features of DR such as hyperpermeability, hypoperfusion, and neoangiogenesis. Notably, PC depletion directly induced inflammatory responses in ECs and perivascular infiltration of macrophages, whereby macrophage-derived VEGF and placental growth factor (PlGF) activated VEGFR1 in macrophages and VEGFR2 in ECs. Moreover, angiopoietin-2 (Angpt2) upregulation and Tie1 downregulation activated FOXO1 in PC-free ECs locally at the leaky aneurysms. This cycle of vessel damage was shut down by simultaneously blocking VEGF, PlGF, and Angpt2, thus restoring the BRB integrity. Together, our model provides new opportunities for identifying the sequential events triggered by PC deficiency, not only in DR, but also in various neurological disorders.

RCANs regulate the convergent roles of NFATc1 in bone homeostasis

Activation of calcineurin-dependent nuclear factor of activated T cells c1 (NFATc1) is convergent for normal bone homeostasis. NFATc1 regulates both osteoclastogenesis and osteoblastogenesis. Here we investigated the roles of regulator of calcineurin (RCAN) genes in bone homeostasis. RCANs function as potent physiological inhibitors of calcineurin. Overexpression of RCANs in osteoclast precursor cells attenuated osteoclast differentiation, while their overexpression in osteoblasts enhanced osteoblast differentiation and function. Intriguingly, opposing effects of RCANs in both cell types were shown by blocking activation of the calcineurin-NFATc1 pathway. Moreover, the disruption of RCAN1 or RCAN2 in mice resulted in reduced bone mass, which is associated with strongly increased osteoclast function and mildly reduced osteoblast function. Taken together, RCANs play critical roles in bone homeostasis by regulating both osteoclastogenesis and osteoblastogenesis, and they serve as inhibitors for calcineurin-NFATc1 signaling both in vivo and in vitro.

Regulator of Calcineurin 1 in Periodontal Disease

Nuclear factor of activated T-cells (NFAT) and NF-kB pathway associated processes are involved in the pathogenesis of various inflammatory disorders, for example, periodontal disease. The activation of these pathways is controlled by the regulator of calcineurin 1 (RCAN1). The aim of this study was to elucidate the role of RCAN1 in periodontal disease. Healthy and inflamed periodontal tissues were analyzed by immunohistochemistry and immunofluorescence using specific rabbit polyclonal anti-RCAN1 antibodies. For expression analysis human umbilical vein endothelial cells (HUVEC) were used. HUVEC were incubated for 2 h with Vascular Endothelial Growth Factor (VEGF) or with wild type and laboratory strains of Porphyromonas gingivalis (P. gingivalis). Expression analysis of rcan1 and cox2 was done by real time PCR using specific primers for rcan1.4 and cox2. The expression of rcan1 was found to be significantly suppressed in endothelial cells of chronically inflamed periodontal tissues compared to healthy controls. Rcan1 and cox2 were significantly induced by VEGF and wild type and laboratory P. gingivalis strains. Interestingly, the magnitude of the rcan1 and cox2 induction was strain dependent. The results of this study indicate that RCAN1 is suppressed in endothelial cells of chronically inflamed periodontal tissues. During an acute infection, however, rcan1 seems to be upregulated in endothelial cells, indicating a modulating role in immune homeostasis of periodontal tissues.

Genome-wide approaches reveal functional vascular endothelial growth factor (VEGF)-inducible nuclear factor of activated T cells (NFAT) c1 binding to angiogenesis-related genes in the endothelium

VEGF is a key regulator of endothelial cell migration, proliferation, and inflammation, which leads to activation of several signaling cascades, including the calcineurin-nuclear factor of activated T cells (NFAT) pathway. NFAT is not only important for immune responses but also for cardiovascular development and the pathogenesis of Down syndrome. By using Down syndrome model mice and clinical patient samples, we showed recently that the VEGF-calcineurin-NFAT signaling axis regulates tumor angiogenesis and tumor metastasis. However, the connection between genome-wide views of NFAT-mediated gene regulation and downstream gene function in the endothelium has not been studied extensively. Here we performed comprehensive mapping of genome-wide NFATc1 binding in VEGF-stimulated primary cultured endothelial cells and elucidated the functional consequences of VEGF-NFATc1-mediated phenotypic changes. A comparison of the NFATc1 ChIP sequence profile and epigenetic histone marks revealed that predominant NFATc1-occupied peaks overlapped with promoter-associated histone marks. Moreover, we identified two novel NFATc1 regulated genes, CXCR7 and RND1. CXCR7 knockdown abrogated SDF-1- and VEGF-mediated cell migration and tube formation. siRNA treatment of RND1 impaired vascular barrier function, caused RhoA hyperactivation, and further stimulated VEGF-mediated vascular outgrowth from aortic rings. Taken together, these findings suggest that dynamic NFATc1 binding to target genes is critical for VEGF-mediated endothelial cell activation. CXCR7 and RND1 are NFATc1 target genes with multiple functions, including regulation of cell migration, tube formation, and barrier formation in endothelial cells.