Interaction between TAK1-TAB1-TAB2 and RCAN1-calcineurin defines a signalling nodal control point

Mechanisms of Bone Morphogenetic Protein 2 in Respiratory Diseases

PURPOSE OF REVIEW

Bone morphogenetic protein 2 (BMP2) belongs to the transforming growth factor-β (TGF-β) superfamily and plays an important role in regulating embryonic development, angiogenesis, osteogenic differentiation, tissue homeostasis, and cancer invasion. Increasing studies suggest BMP2 is involved in several respiratory diseases. This study aimed to review the role and mechanisms of BMP2 in respiratory diseases.

RECENT FINDINGS

BMP2 signaling pathway includes the canonical and non-canonical signaling pathway. The canonical signaling pathway is the BMP2-SMAD pathway, and the non-canonical signaling pathway includes mitogen-activated protein kinase (MAPK) pathway and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway. The BMP2 is related to pulmonary hypertension (PH), lung cancer, pulmonary fibrosis (PF), asthma, and chronic obstructive pulmonary disease (COPD). BMP2 inhibits the proliferation of pulmonary artery smooth muscle cells (PASMCs), promotes the apoptosis of PASMCs to reduce pulmonary vascular remodeling in PH, which is closely related to the canonical and non-canonical pathway. In addition, BMP2 stimulates the proliferation and migration of cells to promote the occurrence, colonization, and metastasis of lung cancer through the canonical and the non-canonical pathway. Meanwhile, BMP2 exert anti-fibrotic function in PF through canonical signaling pathway. Moreover, BMP2 inhibits airway inflammation to maintain airway homeostasis in asthma. However, the signaling pathways involved in asthma are poorly understood. BMP2 inhibits the expression of ciliary protein and promotes squamous metaplasia of airway epithelial cells to accelerate the development of COPD. In conclusion, BMP2 may be a therapeutic target for several respiratory diseases.

Mechanical network motifs as targets for mechanomedicine

The identification and analysis of network motifs has been widely used in the functional analysis of signaling components, disease discovery and other fields. The positive feedback loop (PFL) is a simple but important network motif. The formation of a PFL is regulated by mechanical cues such as substrate stiffness, fiber stretching and cell compression in the cell microenvironment. Here, we propose a new term, 'mechanical PFL', and analyze the mechanisms of mechanical PFLs at molecular, subcellular and cellular scales. More and more therapies are being targeted against mechanosignaling pathways at the experimental and preclinical stages, and exploring mechanical PFLs as potential mechanomedicine targets could be a new direction for disease treatment.

Targeting CaN/NFAT in Alzheimer's brain degeneration

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of cognitive functions. While the exact causes of this debilitating disorder remain elusive, numerous investigations have characterized its two core pathologies: the presence of β-amyloid plaques and tau tangles. Additionally, multiple studies of postmortem brain tissue, as well as results from AD preclinical models, have consistently demonstrated the presence of a sustained inflammatory response. As the persistent immune response is associated with neurodegeneration, it became clear that it may also exacerbate other AD pathologies, providing a link between the initial deposition of β-amyloid plaques and the later development of neurofibrillary tangles. Initially discovered in T cells, the nuclear factor of activated T-cells (NFAT) is one of the main transcription factors driving the expression of inflammatory genes and thus regulating immune responses. NFAT-dependent production of inflammatory mediators is controlled by Ca2+-dependent protein phosphatase calcineurin (CaN), which dephosphorylates NFAT and promotes its transcriptional activity. A substantial body of evidence has demonstrated that aberrant CaN/NFAT signaling is linked to several pathologies observed in AD, including neuronal apoptosis, synaptic deficits, and glia activation. In view of this, the role of NFAT isoforms in AD has been linked to disease progression at different stages, some of which are paralleled to diminished cognitive status. The use of classical inhibitors of CaN/NFAT signaling, such as tacrolimus or cyclosporine, or adeno-associated viruses to specifically inhibit astrocytic NFAT activation, has alleviated some symptoms of AD by diminishing β-amyloid neurotoxicity and neuroinflammation. In this article, we discuss the recent findings related to the contribution of CaN/NFAT signaling to the progression of AD and highlight the possible benefits of targeting this pathway in AD treatment.

Ferroptosis contributes to catecholamine-induced cardiotoxicity and pathological remodeling

High levels of circulating catecholamines cause cardiac injury, pathological remodeling, and heart failure, but the underlying mechanisms remain elusive. Here we provide both in vitro and in vivo evidence that excessive β-adrenergic stimulation induces ferroptosis in cardiomyocytes, revealing a novel mechanism for catecholamine-induced cardiotoxicity and remodeling. We found that isoproterenol, a synthetic catecholamine, promoted glutathione depletion and glutathione peroxidase 4 (GPX4) degradation in cardiomyocytes, leading to GPX4 inactivation and enhanced lipid peroxidation. Isoproterenol also promoted heme oxygenase 1 (HO-1) expression by downregulating the transcription suppressor BTB and CNC homology 1 (Bach1), leading to increased labile iron accumulation through heme degradation. Moreover, isoproterenol markedly induced the accumulation of free iron and lipid reactive oxygen species (ROS) in the mitochondria, while targeted inhibition of iron overload and ROS accumulation within mitochondria effectively inhibited ferroptosis in cardiomyocytes. Importantly, isoproterenol administration markedly induced ferroptosis in the myocardium in vivo, associated with elevated non-heme iron accumulation driven by HO-1 upregulation. Strikingly, blockade of ferroptosis with ferrostatin-1 or inhibition of HO-1 activity with zinc protoporphyrin (ZnPP) effectively alleviated cardiac necrosis, pathological remodeling, and heart failure induced by isoproterenol administration. Taken together, our results reveal that catecholamine stimulation primarily induces ferroptotic cell death in cardiomyocyte through GPX4 and Bach1-HO-1 dependent signaling pathways. Targeting ferroptosis may represent a novel therapeutic strategy for catecholamine overload-induced myocardial injury and heart failure.

Oxidative stress induces mitochondrial iron overload and ferroptotic cell death

Oxidative stress has been shown to induce cell death in a wide range of human diseases including cardiac ischemia/reperfusion injury, drug induced cardiotoxicity, and heart failure. However, the mechanism of cell death induced by oxidative stress remains incompletely understood. Here we provide new evidence that oxidative stress primarily induces ferroptosis, but not apoptosis, necroptosis, or mitochondria-mediated necrosis, in cardiomyocytes. Intriguingly, oxidative stress induced by organic oxidants such as tert-butyl hydroperoxide (tBHP) and cumene hydroperoxide (CHP), but not hydrogen peroxide (H2O2), promoted glutathione depletion and glutathione peroxidase 4 (GPX4) degradation in cardiomyocytes, leading to increased lipid peroxidation. Moreover, elevated oxidative stress is also linked to labile iron overload through downregulation of the transcription suppressor BTB and CNC homology 1 (Bach1), upregulation of heme oxygenase 1 (HO-1) expression, and enhanced iron release via heme degradation. Strikingly, oxidative stress also promoted HO-1 translocation to mitochondria, leading to mitochondrial iron overload and lipid reactive oxygen species (ROS) accumulation. Targeted inhibition of mitochondrial iron overload or ROS accumulation, by overexpressing mitochondrial ferritin (FTMT) or mitochondrial catalase (mCAT), respectively, markedly inhibited oxidative stress-induced ferroptosis. The levels of mitochondrial iron and lipid peroxides were also markedly increased in cardiomyocytes subjected to simulated ischemia and reperfusion (sI/R) or the chemotherapeutic agent doxorubicin (DOX). Overexpressing FTMT or mCAT effectively prevented cardiomyocyte death induced by sI/R or DOX. Taken together, oxidative stress induced by organic oxidants but not H2O2 primarily triggers ferroptotic cell death in cardiomyocyte through GPX4 and Bach1/HO-1 dependent mechanisms. Our results also reveal mitochondrial iron overload via HO-1 mitochondrial translocation as a key mechanism as well as a potential molecular target for oxidative stress-induced ferroptosis in cardiomyocytes.

circWHSC1: A circular RNA piece in the human cancer puzzle

Circular RNAs (circRNAs) are a group of non-coding RNAs with a closed loop shape, which are transcribed via non-canonical splicing. They are mainly formed by reverse splicing of a precursor mRNA. circWHSC1 (Hsa_circ_0001387), is a cancer-related circRNA that originated from the Wolf-Hirschhorn syndrome candidate 1 (WHSC1) gene on chromosome 4. circWHSC1 has been found to be overexpressed in different neoplastic conditions. circWHSC1 acts as a sponge for many different miRNAs, including miR-195-5p, miR-532-3p, miR-646, miR-142-3p, miR-7, miR-296-3p, miR-145, miR-1182, miR-212-5p, etc. It can also moderate several signaling pathways, including FASN/AMPK/mTOR, LTBP2, NPM1, HOXA1, TAB2, AKT3, hTERT, and MUC1. Studies have shown that circWHSC1 may leads to an increase in cell growth, tumor size, cell migration, invasion, and metastasis, but a reduction in apoptosis rates. Moreover, upregulation of CircWHSC1 has been associated with reduced patient's survival in different cancers, representing the function of this circRNA as a novel prognostic marker. Nevertheless, there are no reviews focusing on the relationship between circWHSC1 and cancers. Therefore, in the current review, we will first describe the oncogenic effect of circWHSC1 in various tissues according to the evidence from in vitro, in vivo, and human studies.

The RCAN1.4 Metastasis Suppressor Is Hypermethylated at Intron 1 in Thyroid Cancer

Background: Regulator of calcineurin 1.4 (RCAN1.4) is a functionally downregulated metastasis progression suppressor (MPS) in thyroid cancer; however, the mechanisms for RCAN1.4 loss in thyroid cancer have not yet been reported. The RCAN1.4 promoter and gene contain several cytosine-guanine (CG)-rich regions, some of which are reported to be hypermethylated in nonthyroid tissues. We, therefore, hypothesized that RCAN1.4 downregulation in thyroid cancer was in part due to hypermethylation. Methods: Studies were performed in 5 thyroid cancer cell lines (TPC1, FTC133, BCPAP, C643, and 8505C) with different genetic drivers, and in 18 paired normal and thyroid cancer human thyroid cancer tissues. Basal RCAN1.4 messenger RNA (mRNA) and protein levels were assessed in all of the cell lines. Cell lines with lowest RCAN1.4 expression levels were treated with the DNA methyl transferase inhibitor, decitabine. Normal/tumor tissue pairs were analyzed for methylation of three CG-rich regions both by capture of methylated DNA by MBD2 protein and by methylation-specific polymerase chain reaction (MSPCR). Results: In all assessed cell lines, RCAN1.4 mRNA and protein levels increased after decitabine treatment. In silico analysis of the RCAN1.4 gene identified 3 CG-rich regions as possible methylation targets: 1 in the proximal promoter and 2 in intron 1. Hypermethylation of the intron 1 CG-rich regions was identified by both the capture method and MSPCR. In contrast, hypermethylation of the CG-rich region of the proximal promoter was not identified. Gene expression confirmed that hypermethylation in thyroid cancer samples in intron 1 of RCAN1.4 was associated with lower levels of RCAN1.4 mRNA. Finally, the cancer samples demonstrated increased NFE2L3 expression, a downstream marker of functional RCAN1.4 loss. Conclusions: The MPS gene, RCAN1.4, is downregulated in thyroid cancer cells and human thyroid cancer in part by hypermethylation of CG-rich regions in intron 1.

Restoration of Cardiomyogenesis in Aged Mouse Hearts by Voluntary Exercise

BACKGROUND

The human heart has limited capacity to generate new cardiomyocytes and this capacity declines with age. Because loss of cardiomyocytes may contribute to heart failure, it is crucial to explore stimuli of endogenous cardiac regeneration to favorably shift the balance between loss of cardiomyocytes and the birth of new cardiomyocytes in the aged heart. We have previously shown that cardiomyogenesis can be activated by exercise in the young adult mouse heart. Whether exercise also induces cardiomyogenesis in aged hearts, however, is still unknown. Here, we aim to investigate the effect of exercise on the generation of new cardiomyocytes in the aged heart.

METHODS

Aged (20-month-old) mice were subjected to an 8-week voluntary running protocol, and age-matched sedentary animals served as controls. Cardiomyogenesis in aged hearts was assessed on the basis of 15N-thymidine incorporation and multi-isotope imaging mass spectrometry. We analyzed 1793 cardiomyocytes from 5 aged sedentary mice and compared these with 2002 cardiomyocytes from 5 aged exercised mice, followed by advanced histology and imaging to account for ploidy and nucleation status of the cell. RNA sequencing and subsequent bioinformatic analyses were performed to investigate transcriptional changes induced by exercise specifically in aged hearts in comparison with young hearts.

RESULTS

Cardiomyogenesis was observed at a significantly higher frequency in exercised compared with sedentary aged hearts on the basis of the detection of mononucleated/diploid 15N-thymidine-labeled cardiomyocytes. No mononucleated/diploid 15N-thymidine-labeled cardiomyocyte was detected in sedentary aged mice. The annual rate of mononucleated/diploid 15N-thymidine-labeled cardiomyocytes in aged exercised mice was 2.3% per year. This compares with our previously reported annual rate of 7.5% in young exercised mice and 1.63% in young sedentary mice. Transcriptional profiling of young and aged exercised murine hearts and their sedentary controls revealed that exercise induces pathways related to circadian rhythm, irrespective of age. One known oscillating transcript, however, that was exclusively upregulated in aged exercised hearts, was isoform 1.4 of regulator of calcineurin, whose regulation and functional role were explored further.

CONCLUSIONS

Our data demonstrate that voluntary running in part restores cardiomyogenesis in aged mice and suggest that pathways associated with circadian rhythm may play a role in physiologically stimulated cardiomyogenesis.

Specific immunosuppressive role of nanodrugs targeting calcineurin in innate myeloid cells

Calcineurin (CN) inhibitors currently used to avoid transplant rejection block the activation of adaptive immune responses but also prevent the development of tolerance toward the graft, by directly inhibiting T cells. CN, through the transcription factors of the NFAT family, plays an important role also in the differentiation dendritic cells (DCs), the main cells responsible for the activation of T lymphocytes. Therefore, we hypothesized that the inhibition of CN only in DCs and not in T cells could be sufficient to prevent T cell responses, while allowing for the development of tolerance. Here, we show that inhibition of CN/NFAT pathway in innate myeloid cells, using a new nanoconjugate capable of selectively targeting phagocytes in vivo, protects against graft rejection and induces a longer graft acceptance compared to common CN inhibitors. We propose a new generation of nanoparticles-based selective immune suppressive agents for a better control of transplant acceptance.

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Calcineurin/NFATc2 pathway is required to enable DC migration to draining lymph nodes

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Calcineurin/NFATc2 pathway in DCs is required for type I immune responses activation

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Superparamagnetic iron oxide NPs can be used to efficiently target phagocytes in vivo

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Specific delivery of calcineurin inhibitor by NPs to phagocytes induce graft acceptance

RCAN1-mediated calcineurin inhibition as a target for cancer therapy

Cancer is the leading cause of mortality worldwide. Regulator of calcineurin 1 (RCAN1), as a patent endogenous inhibitor of calcineurin, plays crucial roles in the pathogenesis of cancers. Except for hypopharyngeal and laryngopharynx cancer, high expression of RCAN1 inhibits tumor progression. Molecular antitumor functions of RCAN1 are largely dependent on calcineurin. In this review, we highlight current research on RCAN1 characteristics, and the interaction between RCAN1 and calcineurin. Moreover, the dysregulation of RCAN1 in various cancers is reviewed, and the potential of targeting RCAN1 as a new therapeutic approach is discussed.

RCAN1 knockout and overexpression recapitulate an ensemble of rest-activity and circadian disruptions characteristic of Down syndrome, Alzheimer's disease, and normative aging

BACKGROUND

Regulator of calcineurin 1 (RCAN1) is overexpressed in Down syndrome (DS), but RCAN1 levels are also increased in Alzheimer's disease (AD) and normal aging. AD is highly comorbid among individuals with DS and is characterized in part by progressive neurodegeneration that resembles accelerated aging. Importantly, abnormal RCAN1 levels have been demonstrated to promote memory deficits and pathophysiology that appear symptomatic of DS, AD, and aging. Anomalous diurnal rest-activity patterns and circadian rhythm disruptions are also common in DS, AD, and aging and have been implicated in facilitating age-related cognitive decline and AD progression. However, no prior studies have assessed whether RCAN1 dysregulation may also promote the age-associated alteration of rest-activity profiles and circadian rhythms, which could in turn contribute to neurodegeneration in DS, AD, and aging.

METHODS

The present study examined the impacts of RCAN1 deficiency and overexpression on the photic entrainment, circadian periodicity, intensity and distribution, diurnal patterning, and circadian rhythmicity of wheel running in young (3-6 months old) and aged (9-14 months old) mice of both sexes.

RESULTS

We found that daily RCAN1 levels in the hippocampus and suprachiasmatic nucleus (SCN) of light-entrained young mice are generally constant and that balanced RCAN1 expression is necessary for normal circadian locomotor activity rhythms. While the light-entrained diurnal period was unaltered, RCAN1-null and RCAN1-overexpressing mice displayed lengthened endogenous (free-running) circadian periods like mouse models of AD and aging. In light-entrained young mice, RCAN1 deficiency and overexpression also recapitulated the general hypoactivity, diurnal rest-wake pattern fragmentation, and attenuated amplitudes of circadian activity rhythms reported in DS, preclinical and clinical AD, healthily aging individuals, and rodent models thereof. Under constant darkness, RCAN1-null and RCAN1-overexpressing mice displayed altered locomotor behavior indicating circadian clock dysfunction. Using the Dp(16)1Yey/+ (Dp16) mouse model for DS, which expresses three copies of Rcan1, we found reduced wheel running activity and rhythmicity in both light-entrained and free-running young Dp16 mice like young RCAN1-overexpressing mice. Critically, these diurnal and circadian deficits were rescued in part or entirely by restoring Rcan1 to two copies in Dp16 mice. We also found that RCAN1 deficiency but not RCAN1 overexpression altered protein levels of the clock gene Bmal1 in the SCN.

CONCLUSIONS

Collectively, this study's findings suggest that both loss and aberrant gain of RCAN1 precipitate anomalous light-entrained diurnal and circadian activity patterns emblematic of DS, AD, and possibly aging.

Ginsenoside Rg2 Ameliorates Myocardial Ischemia/Reperfusion Injury by Regulating TAK1 to Inhibit Necroptosis

Necroptosis contribute to the pathogenesis of myocardial ischemia/reperfusion (MI/R) injury. Ginsenoside Rg2 has been reported to have cardioprotective effects against MI/R injury; however, the underlying mechanism remains unclear. This work aimed to investigate the effect of ginsenoside Rg2 on necroptosis induced by MI/R and to explore the mechanism. In this study, hypoxia/reoxygenation (H/R) injury model was established in H9c2 cells. In vivo, male C57/BL6 mice were subjected to myocardial ischemia 30 min/reperfusion 4 h. Rg2 (50 mg/kg) or vehicle was intravenously infused 5 min before reperfusion. Cardiac function and the signaling pathway involved in necroptosis were investigated. Compared with H/R group, Rg2 significantly inhibited H/R-induced cardiomyocyte death. Rg2 treatment effectively inhibited the phosphorylation of RIP1, RIP3, and MLKL in H/R cardiomyocytes, and inhibited RIP1/RIP3 complex (necrosome) formation. In mice, Rg2 treatment manifested significantly lower ischemia/reperfusion (I/R)-induced myocardial necroptosis, as evidenced by decrease in phosphorylation of RIP1, RIP3, and MLKL, inhibited lactate dehydrogenase (LDH) release and Evans blue dye (EBD) penetration. Mechanically, an increased level of tumor necrosis factor α (TNFα), interleukin (IL)-1β, IL-6, and MCP-1 were found in MI/R hearts, and Rg2 treatment significantly inhibit the expression of these factors. We found that TNFα-induced phosphorylation of RIP1, RIP3, and MLKL was negatively correlated with transforming growth factor-activated kinase 1 (TAK1) phosphorylation, and inhibition of TAK1 phosphorylation led to necroptosis enhancement. More importantly, Rg2 treatment significantly increased TAK1 phosphorylation, enhanced TAK1 binding to RIP1 while inhibiting RIP1/RIP3 complex, ultimately reducing MI/R-induced necroptosis. These findings highlight a new mechanism of Rg2-induced cardioprotection: reducing the formation of RIP1/RIP3 necrosome by regulating TAK1 phosphorylation to block necroptosis induced by MI/R.

TAB2 deficiency induces dilated cardiomyopathy by promoting RIPK1-dependent apoptosis and necroptosis

Mutations in TGF-β-activated kinase 1 binding protein 2 (TAB2) have been implicated in the pathogenesis of dilated cardiomyopathy and/or congenital heart disease in humans, but the underlying mechanisms are currently unknown. Here, we identified an indispensable role for TAB2 in regulating myocardial homeostasis and remodeling by suppressing receptor-interacting protein kinase 1 (RIPK1) activation and RIPK1-dependent apoptosis and necroptosis. Cardiomyocyte-specific deletion of Tab2 in mice triggered dilated cardiomyopathy with massive apoptotic and necroptotic cell death. Moreover, Tab2-deficient mice were also predisposed to myocardial injury and adverse remodeling after pathological stress. In cardiomyocytes, deletion of TAB2 but not its close homolog TAB3 promoted TNF-α-induced apoptosis and necroptosis, which was rescued by forced activation of TAK1 or inhibition of RIPK1 kinase activity. Mechanistically, TAB2 critically mediates RIPK1 phosphorylation at Ser321 via a TAK1-dependent mechanism, which prevents RIPK1 kinase activation and the formation of RIPK1-FADD-caspase-8 apoptotic complex or RIPK1-RIPK3 necroptotic complex. Strikingly, genetic inactivation of RIPK1 with Ripk1-K45A knockin effectively rescued cardiac remodeling and dysfunction in Tab2-deficient mice. Together, these data demonstrated that TAB2 is a key regulator of myocardial homeostasis and remodeling by suppressing RIPK1-dependent apoptosis and necroptosis. Our results also suggest that targeting RIPK1-mediated cell death signaling may represent a promising therapeutic strategy for TAB2 deficiency-induced dilated cardiomyopathy.

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.

MAP kinase/ERK kinase 1 (MEK1) phosphorylates regulator of calcineurin 1 (RCAN1) to regulate neuronal differentiation

Regulator of calcineurin 1 (RCAN1) is located close to the Down syndrome critical region (DSCR) on human chromosome 21 and is related to the Down syndrome (DS) phenotype. To identify a novel binding partner of RCAN1, we performed yeast two-hybrid screening and identified mitogen-activated protein (MAP) kinase/extracellular signal-regulated kinase (ERK) kinase 1 (MEK1) as a partner. MEK1 was able to bind and phosphorylate RCAN1 in vitro and in vivo. MEK1-dependent RCAN1 phosphorylation caused an increase in RCAN1 expression by increasing the protein half-life. Nerve growth factor (NGF)-dependent activation of the MEK1 pathway consistently induced RCAN1 expression. Moreover, we found that RCAN1 overexpression inhibited NGF-induced neurite outgrowth and expression of neuronal marker genes, such as growth cone-associated protein 43 (GAP43) and synapsin I, via inhibition of MEK1-ERK1/2 pathways. Our findings provide evidence that MEK1-dependent RCAN1 phosphorylation acts as an important molecular mechanism in the control of neuronal differentiation.

Circular RNA WHSC1 exerts oncogenic properties by regulating miR-7/TAB2 in lung cancer

Circular RNA is a newly discovered member of non‐coding RNA (ncRNA) and regulates the target gene by acting as a micro‐RNA sponge. It plays vital roles in various diseases. However, the functions of circular RNA in non‐small cell lung cancer (NSCLC) remain still unclear. Our data showed that circ‐WHSC1 was highly expressed in NSCLC cells and tissues. Both in vitro and in vivo experiments showed that circ‐WHSC1 promoted NSCLC proliferation. circ‐WHSC1 also promoted the migration and invasion of lung cancer cells. Through bioinformatic analysis and functional experiments, we showed that circ‐WHSC1 could act as a sponge for micro‐RNA‐7 (miR‐7) and regulate the expression of TAB2 (TGF‐beta activated kinase one binding protein two). Inhibition of the circ‐WHSC1/miR‐7/TAB2 pathway could effectively attenuate lung cancer progression. In summary, this study confirmed the existence and oncogenic function of circ‐WHSC1 in NSCLC. The research suggests that the circ‐WHSC1/miR‐7/TAB2 axis might be a potential target for NSCLC therapy.

A Rare Autosomal Dominant Variant in Regulator of Calcineurin Type 1 (RCAN1) Gene Confers Enhanced Calcineurin Activity and May Cause FSGS

BACKGROUND

Podocyte dysfunction is the main pathologic mechanism driving the development of FSGS and other morphologic types of steroid-resistant nephrotic syndrome (SRNS). Despite significant progress, the genetic causes of most cases of SRNS have yet to be identified.

METHODS

Whole-genome sequencing was performed on 320 individuals from 201 families with familial and sporadic NS/FSGS with no pathogenic mutations in any known NS/FSGS genes.

RESULTS

Two variants in the gene encoding regulator of calcineurin type 1 (RCAN1) segregate with disease in two families with autosomal dominant FSGS/SRNS. In vitro, loss of RCAN1 reduced human podocyte viability due to increased calcineurin activity. Cells expressing mutant RCAN1 displayed increased calcineurin activity and NFAT activation that resulted in increased susceptibility to apoptosis compared with wild-type RCAN1. Treatment with GSK-3 inhibitors ameliorated this elevated calcineurin activity, suggesting the mutation alters the balance of RCAN1 regulation by GSK-3β, resulting in dysregulated calcineurin activity and apoptosis.

CONCLUSIONS

These data suggest mutations in RCAN1 can cause autosomal dominant FSGS. Despite the widespread use of calcineurin inhibitors in the treatment of NS, genetic mutations in a direct regulator of calcineurin have not been implicated in the etiology of NS/FSGS before this report. The findings highlight the therapeutic potential of targeting RCAN1 regulatory molecules, such as GSK-3β, in the treatment of FSGS.

Interleukin-15 response signature predicts RhCMV/SIV vaccine efficacy

Simian immunodeficiency virus (SIV) challenge of rhesus macaques (RMs) vaccinated with strain 68-1 Rhesus Cytomegalovirus (RhCMV) vectors expressing SIV proteins (RhCMV/SIV) results in a binary outcome: stringent control and subsequent clearance of highly pathogenic SIV in ~55% of vaccinated RMs with no protection in the remaining 45%. Although previous work indicates that unconventionally restricted, SIV-specific, effector-memory (EM)-biased CD8+ T cell responses are necessary for efficacy, the magnitude of these responses does not predict efficacy, and the basis of protection vs. non-protection in 68-1 RhCMV/SIV vector-vaccinated RMs has not been elucidated. Here, we report that 68-1 RhCMV/SIV vector administration strikingly alters the whole blood transcriptome of vaccinated RMs, with the sustained induction of specific immune-related pathways, including immune cell, toll-like receptor (TLR), inflammasome/cell death, and interleukin-15 (IL-15) signaling, significantly correlating with subsequent vaccine efficacy. Treatment of a separate RM cohort with IL-15 confirmed the central involvement of this cytokine in the protection signature, linking the major innate and adaptive immune gene expression networks that correlate with RhCMV/SIV vaccine efficacy. This change-from-baseline IL-15 response signature was also demonstrated to significantly correlate with vaccine efficacy in an independent validation cohort of vaccinated and challenged RMs. The differential IL-15 gene set response to vaccination strongly correlated with the pre-vaccination activity of this pathway, with reduced baseline expression of IL-15 response genes significantly correlating with higher vaccine-induced induction of IL-15 signaling and subsequent vaccine protection, suggesting that a robust de novo vaccine-induced IL-15 signaling response is needed to program vaccine efficacy. Thus, the RhCMV/SIV vaccine imparts a coordinated and persistent induction of innate and adaptive immune pathways featuring IL-15, a known regulator of CD8+ T cell function, that support the ability of vaccine-elicited unconventionally restricted CD8+ T cells to mediate protection against SIV challenge.

AAV-mediated YAP expression in cardiac fibroblasts promotes inflammation and increases fibrosis

Fibrosis is a hallmark of heart disease independent of etiology and is thought to contribute to impaired cardiac dysfunction and development of heart failure. However, the underlying mechanisms that regulate the differentiation of fibroblasts to myofibroblasts and fibrotic responses remain incompletely defined. As a result, effective treatments to mitigate excessive fibrosis are lacking. We recently demonstrated that the Hippo pathway effector Yes-associated protein (YAP) is an important mediator of myofibroblast differentiation and fibrosis in the infarcted heart. Yet, whether YAP activation in cardiac fibroblasts is sufficient to drive fibrosis, and how fibroblast YAP affects myocardial inflammation, a significant component of adverse cardiac remodeling, are largely unknown. In this study, we leveraged adeno-associated virus (AAV) to target cardiac fibroblasts and demonstrate that chronic YAP expression upregulated indices of fibrosis and inflammation in the absence of additional stress. YAP occupied the Ccl2 gene and promoted Ccl2 expression, which was associated with increased macrophage infiltration, pro-inflammatory cytokine expression, collagen deposition, and cardiac dysfunction in mice with cardiac fibroblast-targeted YAP overexpression. These results are consistent with other recent reports and extend our understanding of YAP function in modulating fibrotic and inflammatory responses in the heart.

Regulator of calcineurin 1 is a novel RNA-binding protein to regulate neuronal apoptosis

Posttranscriptional regulation of gene expression plays an important role in the maturation, transport, stability and translation of coding and noncoding RNAs. RNA-binding protein (RBP) is a key factor of the regulation. Regulator of calcineurin 1 (RCAN1) is a multifunctional protein involved in neurodegeneration, mitochondrial dysfunction, inflammation and protein glycosylation, and plays an important role in the pathogenesis of Down syndrome and Alzheimer's disease. In this report, we discovered that RCNA1 is a novel RNA-binding protein. A 23 nucleotide sequence of adenine nucleotide translocator (ANT1) mRNA was identified as the binding motif of RCAN1. Furthermore, we found that R1SR13, as the RNA aptamer of RCAN1 identified by SELEX, blocked RCAN1-induced inhibition of the nuclear factor of activated T cells (NFAT) and NF-κB signaling pathways, and reduced neuronal apoptosis. Taken together, our results demonstrate that RCAN1 is a novel RNA-binding protein and the RNA aptamer of RCAN1 plays a neuroprotective role.

FBXW5 acts as a negative regulator of pathological cardiac hypertrophy by decreasing the TAK1 signaling to pro-hypertrophic members of the MAPK signaling pathway

Pathological cardiac hypertrophy is a crucial cause of cardiac morbidity and mortality worldwide. However, the molecular mechanisms of this disease remain incompletely understood. As a member of E3 ubiquitin ligases, F-box/WD repeat-containing protein 5 (FBXW5) has been implicated in various pathophysiological processes. However, the role of FBXW5 in pathological cardiac hypertrophy remains largely unknown. In this study, decreased expression of FBXW5 was observed in both neonatal rat cardiomyocytes and mouse hearts with hypertrophic remodeling. Gain- and loss-of-function experiments were performed to study the potential function of FBXW5 in pathological cardiac hypertrophy. The in vitro results showed that FBXW5 had a protective effect against cardiac hypertrophy induced by phenylephrine (PE). FBXW5 knockout mice and mice with AAV9-mediated FBXW5 overexpression were generated. Consistent with the in vitro results, FBXW5 deficiency aggravated cardiac hypertrophy induced by pressure overload. FBXW5 overexpression protected mice from hypertrophic stimuli. Remarkably, FBXW5 ameliorated pathological cardiac hypertrophy by directly interacting with the protein transforming growth factor-beta-activated kinase 1 (TAK1) and blocking the mitogen-activated protein kinase (MAPK) signaling pathway. Furthermore, inhibition of TAK1 prevented the effects of FBXW5 on agonist- or pressure overload-induced cardiac hypertrophy. These findings imply that FBXW5 is an essential negative regulator and may be a potential therapeutic target for pathological cardiac hypertrophy.

TAK1-TABs Complex: A Central Signalosome in Inflammatory Responses

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the MAPK kinase kinase (MAPKKK) family and has been implicated in the regulation of a wide range of physiological and pathological processes. TAK1 functions through assembling with its binding partners TAK1-binding proteins (TAB1, TAB2, and TAB3) and can be activated by a variety of stimuli such as tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and toll-like receptor ligands, and they play essential roles in the activation of NF-κB and MAPKs. Numerous studies have demonstrated that post-translational modifications play important roles in properly controlling the activity, stability, and assembly of TAK1-TABs complex according to the indicated cellular environment. This review focuses on the recent advances in TAK1-TABs-mediated signaling and the regulations of TAK1-TABs complex by post-translational modifications.

NFκB promotes oxidative stress-induced necrosis and ischemia/reperfusion injury by inhibiting Nrf2-ARE pathway

In this study, we identified an unexpected pro-cell death role for NFκB in mediating oxidative stress-induced necrosis, and provide new mechanistic evidence that NFκB, in cooperation with HDAC3, negatively regulates Nrf2-ARE anti-oxidative signaling through transcriptional silencing. We showed that genetic inactivation of NFκB-p65 inhibited, whereas activation of NFκB promoted, oxidative stress-induced cell death and HMGB1 release, a biomarker of necrosis. Moreover, NFκB-luciferase activity was elevated in cardiomyocytes after simulated ischemia/reperfusion (sI/R) or doxorubicin (DOX) treatment, and inhibition of NFκB with Ad-p65-shRNA or Ad-IκBαM diminished sI/R- and DOX-induced cell death and HMGB1 release. Importantly, NFκB negatively regulated Nrf2-ARE activity and the expression of antioxidant proteins. Mechanistically, co-immunoprecipitation revealed that p65 was required for Nrf2-HDAC3 interaction and transcriptional silencing of Nrf2-ARE activity. Further, the ability of HDAC3 to repress Nrf2-ARE activity was lost in p65 deficient cells. Pharmacologic inhibition of HADCs or NFκB with trichostatin A (TSA) or BMS-345541, respectively, increased Nrf2-ARE activity and promoted cell survival after sI/R. In vivo, NFκB transcriptional activity in the mouse heart was significantly elevated after ischemia/reperfusion (I/R) injury, which was abolished by cardiomyocyte-specific deletion of p65 using p65fl/flNkx2.5-Cre mice. Moreover, genetic ablation of p65 in the mouse heart attenuated myocardial infarct size after acute I/R injury and improved cardiac remodeling and functional recovery after chronic myocardial infarction. Thus, our results identified NFκB as a key regulator of oxidative stress-induced necrosis by suppressing the Nrf2-ARE antioxidant pathway through an HDAC3-dependent mechanism. This study also revealed a new pathogenic role of NFκB in cardiac ischemic injury and pathological remodeling.

Progression and dormancy in metastatic thyroid cancer: concepts and clinical implications

Distant metastasis classically has been defined as a late-stage event in cancer progression. However, it has become clear that metastases also may occur early in the "lifetime" of a cancer and that they may remain stable at distant sites. This stability of metastatic cancer deposits has been termed "metastatic dormancy" or, as we term it, "metastatic progression dormancy" as the progression either may reflect growth of already existing metastases or new cancer spread. Biologically, dormancy is the presence of nongrowing, static metastatic cells that survive over time. Clinically, dormancy is defined by stability in tumor markers, imaging, and clinical course. Metastatic well-differentiated thyroid cancer offers an excellent tumor type to understand these processes for several reasons: (1) primary therapy often includes removal of the entire gland with ablation of residual normal tissue thereby removing one source for new metastases; (2) the presence of a sensitive biochemical and radiographic monitoring tests enabling monitoring of metastasis throughout the progression process; and (3) its tendency toward prolonged clinical dormancy that can last for years or decades be followed by progression. This latter factor provides opportunities to define therapeutic targets and/or markers of progression. In this review, we will discuss concepts of metastatic progression dormancy and the factors that drive both long-term stability and loss of dormancy with a focus on thyroid cancer.

The structure of the RCAN1:CN complex explains the inhibition of and substrate recruitment by calcineurin

Regulator of calcineurin 1 (RCAN1) is an endogenous inhibitor of the Ser/Thr phosphatase calcineurin (CN). It has been shown that excessive inhibition of CN is a critical factor for Down syndrome and Alzheimer's disease. Here, we determined RCAN1's mode of action. Using a combination of structural, biophysical, and biochemical studies, we show that RCAN1 inhibits CN via multiple routes: first, by blocking essential substrate recruitment sites and, second, by blocking the CN active site using two distinct mechanisms. We also show that phosphorylation either inhibits RCAN1-CN assembly or converts RCAN1 into a weak inhibitor, which can be reversed by CN via dephosphorylation. This highlights the interplay between posttranslational modifications in regulating CN activity. Last, this work advances our understanding of how active site inhibition of CN can be achieved in a highly specific manner. Together, these data provide the necessary road map for targeting multiple neurological disorders.

Growth hormone increases regulator of calcineurin 1-4 (Rcan1-4) mRNA through c-JUN in rat liver

Growth hormone (GH) activates multiple signal transduction pathways. To investigate these pathways, we identified novel genes whose transcription was induced by GH in the liver of hypophysectomized (HPX) rats using the suppression subtractive hybridization technique. We found that regulator of calcineurin 1 (Rcan1) mRNA was upregulated by GH administration. RCAN1 regulates the activity of calcineurin, a Ca/calmodulin-dependent phosphatase. Rcan1 encodes two major transcripts, Rcan1-1 and Rcan1-4, resulting from differential promoter use and first exon choice. We found that a single injection of GH increased the levels of Rcan1-4 mRNA and RCAN1-4 protein transiently, but did not increase Rcan1-1 mRNA in HPX rat liver. Then the molecular mechanism of GH to induce Rcan1-4 transcription was examined in rat hepatoma H4IIE cells. Experiments using inhibitors suggested that c-JUN N-terminal kinase was required for the induction of Rcan1-4 mRNA by GH. GH increased the levels of phosphorylated c-JUN protein and c-Jun mRNA in HPX rat liver. The luciferase and electrophoretic mobility shift assays showed that c-JUN upregulated Rcan1-4 mRNA by binding to the cAMP-responsive element in the upstream of Rcan1 exon 4. These results indicate that GH activates c-JUN to affect the activity of calcineurin by the induction of Rcan1-4 in rat liver.

RCAN1 Inhibits BACE2 Turnover by Attenuating Proteasome-Mediated BACE2 Degradation

Amyloid-β protein (Aβ) is the main component of neuritic plaques, the pathological hallmark of Alzheimer's disease (AD). β-site APP cleaving enzyme 1 (BACE1) is a major β-secretase contributing to Aβ generation. β-site APP cleaving enzyme 2 (BACE2), the homolog of BACE1, is not only a θ-secretase but also a conditional β-secretase. Previous studies showed that regulator of calcineurin 1 (RCAN1) is markedly increased by AD and promotes BACE1 expression. However, the role of RCAN1 in BACE2 regulation remains elusive. Here, we showed that RCAN1 increases BACE2 protein levels. Moreover, RCAN1 inhibits the turnover of BACE2 protein. Furthermore, RCAN1 attenuates proteasome-mediated BACE2 degradation, but not lysosome-mediated BACE2 degradation. Taken together, our work indicates that RCAN1 inhibits BACE2 turnover by attenuating proteasome-mediated BACE2 degradation. It advances our understanding of BACE2 regulation and provides a potential mechanism of BACE2 dysregulation in AD.

CALML6 Controls TAK1 Ubiquitination and Confers Protection against Acute Inflammation

Proper regulation of innate immune response is important for individual health. The NF-κB signaling pathway plays crucial roles in innate immunity and inflammation, and its aberrant activation is implicated in diverse diseases and disorders. In this study, we report that calmodulin-like 6 (CALML6), a member of the EF-hand protein family, is a negative regulator of the NF-κB signaling pathway. CALML6 attenuated TNF-stimulated phosphorylation of proteins downstream of TGF-β-activated kinase 1 (TAK1) and inhibited TAK1-induced NF-κB activation. Further studies showed that CALML6 interacted with TAK1 and recruited the deubiquitylating enzyme cylindromatosis to repress the K63-linked polyubiquitination of TAK1. CALML6 transgenic mice had higher tolerances to lethal LPS treatment in vivo. These findings suggest that CALML6 is a negative regulator of the NF-κB signaling pathway, which is important for maintaining the balance of the innate immune response.

Programmed delivery of cyclopeptide RA-V and antisense oligonucleotides for combination therapy on hypoxic tumors and for therapeutic self-monitoring

Chemotherapy is a dominant treatment modality for different types and stages of cancer. However, hypoxia is one of the undesirable limitations of chemotherapy, which reduces the therapeutic efficiency in cancer treatment, ultimately leading to failure of the treatment. Herein, an ideal chemosensitization system capable of attenuating the tumor hypoxia microenvironment and enhancing chemotherapy effects in tumors was designed. This system (designated as the RA/RX Liposome) uses for the first time a pH-sensitive liposome to co-deliver cyclopeptide RA-V as chemotherapeutic drugs and antisense oligonucleotides as HIF-1α inhibitors (RX-0047) for attenuating tumor hypoxia, as well as a caspase-8 activation probe for therapeutic self-monitoring. After modification with death receptor 5-specific antibodies (anti-DR5) on the surface of the liposome, the RA/RX Liposome can successfully deliver components targeting colon tumors in vivo. This work should synergistically enhance the therapeutic effects of the treatment by successfully down-regulating HIF-1α expression against tumor hypoxia during the RA-V-induced apoptotic process. More importantly, the RA/RX Liposome can be precisely applied for therapeutic self-monitoring with the light-up fluorescence of the caspase-8 probe.

Leveraging New Definitions of the LxVP SLiM To Discover Novel Calcineurin Regulators and Substrates

The Phosphoprotein Phosphatase Calcineurin (CN, PP2B, PP3) recognizes and binds to two short linear motifs (SLiMs), PxIxIT and LxVP, in its regulators and substrates. These interactions enable CN function in many key biological processes. The identification of SLiMs is difficult because of their short, degenerate sequence and often low binding affinity. Here we combine Structure Based Shape Complementarity (SBSC) analysis and proteome-wide affinity purification-mass spectrometry to identify PxIxIT and LxVP containing CN interactors to expand and thereby redefine the LxVP motif. We find that the new πφ-LxVx primary sequence defines an ensemble of binding competent confirmations and thus the binding on-rate, making it difficult to predict the LxVP binding strength from its sequence. Our analysis confirms existing and, more importantly, identifies novel CN interactors, substrates, and thus biological functions of CN.

Blockade of miR-140-3p prevents functional deterioration in afterload-enhanced engineered heart tissue

Afterload enhancement (AE) of rat engineered heart tissue (EHT) in vitro leads to a multitude of changes that in vivo are referred to as pathological cardiac hypertrophy: e.g., cardiomyocyte hypertrophy, contractile dysfunction, reactivation of fetal genes and fibrotic changes. Moreover AE induced the upregulation of 22 abundantly expressed microRNAs. Here, we aimed at evaluating the functional effect of inhibiting 7 promising microRNAs (miR-21-5p, miR-146b-5p, miR-31a-5p, miR-322-5p, miR-450a-5p, miR-140-3p and miR-132-3p) in a small-range screen. Singular transfection of locked nucleic acid (LNA)-based anti-miRs at 100 nM (before the one week AE-procedure) led to a powerful reduction of the targeted microRNAs. Pretreatment with anti-miR-146b-5p, anti-miR-322-5p or anti-miR-450a-5p did not alter the AE-induced contractile decline, while anti-miR-31a-5p-pretreatment even worsened it. Anti-miR-21-5p and anti-miR-132-3p partially attenuated the AE-effect, confirming previous reports. LNA-anti-miR against miR-140-3p, a microRNA recently identified as a prognostic biomarker of cardiovascular disease, also attenuated the AE-effect. To simplify future in vitro experiments and to create an inhibitor for in vivo applications, we designed shorter miR-140-3p-inhibitors and encountered variable efficiency. Only the inhibitor that effectively repressed miR-140-3p was also protective against the AE-induced contractile decline. In summary, in a small-range functional screen, miR-140-3p evolved as a possible new target for the attenuation of afterload-induced pathological cardiac hypertrophy.

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.

O-GlcNAc Site Mapping by Using a Combination of Chemoenzymatic Labeling, Copper-Free Click Chemistry, Reductive Cleavage, and Electron-Transfer Dissociation Mass Spectrometry

As a dynamic post-translational modification, O-linked β- N-acetylglucosamine ( O-GlcNAc) modification (i.e., O-GlcNAcylation) of proteins regulates many biological processes involving cellular metabolism and signaling. However, O-GlcNAc site mapping, a prerequisite for site-specific functional characterization, has been a challenge since its discovery. Herein we present a novel method for O-GlcNAc enrichment and site mapping. In this method, the O-GlcNAc moiety on peptides was labeled with UDP-GalNAz followed by copper-free azide-alkyne cycloaddition with a multifunctional reagent bearing a terminal cyclooctyne, a disulfide bridge, and a biotin handle. The tagged peptides were then released from NeutrAvidin beads upon reductant treatment, alkylated with (3-acrylamidopropyl)trimethylammonium chloride, and subjected to electron-transfer dissociation mass spectrometry analysis. After validation by using standard synthetic peptide gCTD and model protein α-crystallin, such an approach was applied to the site mapping of overexpressed TGF-β-activated kinase 1/MAP3K7 binding protein 2 (TAB2), with four O-GlcNAc sites unambiguously identified. Our method provides a promising tool for the site-specific characterization of O-GlcNAcylation of important proteins.

Innate Immune Signaling and Its Role in Metabolic and Cardiovascular Diseases

The innate immune system is an evolutionarily conserved system that senses and defends against infection and irritation. Innate immune signaling is a complex cascade that quickly recognizes infectious threats through multiple germline-encoded cell surface or cytoplasmic receptors and transmits signals for the deployment of proper countermeasures through adaptors, kinases, and transcription factors, resulting in the production of cytokines. As the first response of the innate immune system to pathogenic signals, inflammatory responses must be rapid and specific to establish a physical barrier against the spread of infection and must subsequently be terminated once the pathogens have been cleared. Long-lasting and low-grade chronic inflammation is a distinguishing feature of type 2 diabetes and cardiovascular diseases, which are currently major public health problems. Cardiometabolic stress-induced inflammatory responses activate innate immune signaling, which directly contributes to the development of cardiometabolic diseases. Additionally, although the innate immune elements are highly conserved in higher-order jawed vertebrates, lower-grade jawless vertebrates lack several transcription factors and inflammatory cytokine genes downstream of the Toll-like receptors (TLRs) and retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) pathways, suggesting that innate immune signaling components may additionally function in an immune-independent way. Notably, recent studies from our group and others have revealed that innate immune signaling can function as a vital regulator of cardiometabolic homeostasis independent of its immune function. Therefore, further investigation of innate immune signaling in cardiometabolic systems may facilitate the discovery of new strategies to manage the initiation and progression of cardiometabolic disorders, leading to better treatments for these diseases. In this review, we summarize the current progress in innate immune signaling studies and the regulatory function of innate immunity in cardiometabolic diseases. Notably, we highlight the immune-independent effects of innate immune signaling components on the development of cardiometabolic disorders.

Enhanced Cardiomyocyte NLRP3 Inflammasome Signaling Promotes Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is frequently associated with enhanced inflammatory response. The NLRP3 (NACHT, LRR, and PYD domain containing protein 3) inflammasome mediates caspase-1 activation and interleukin-1β release in immune cells but is not known to play a role in cardiomyocytes (CMs). Here, we assessed the role of CM NLRP3 inflammasome in AF.

METHODS

NLRP3 inflammasome activation was assessed by immunoblot in atrial whole-tissue lysates and CMs from patients with paroxysmal AF or long-standing persistent (chronic) AF. To determine whether CM-specific activation of NLPR3 is sufficient to promote AF, a CM-specific knockin mouse model expressing constitutively active NLRP3 (CM-KI) was established. In vivo electrophysiology was used to assess atrial arrhythmia vulnerability. To evaluate the mechanism of AF, electric activation pattern, Ca2+ spark frequency, atrial effective refractory period, and morphology of atria were evaluated in CM-KI mice and wild-type littermates.

RESULTS

NLRP3 inflammasome activity was increased in the atrial CMs of patients with paroxysmal AF and chronic AF. CM-KI mice developed spontaneous premature atrial contractions and inducible AF, which was attenuated by a specific NLRP3 inflammasome inhibitor, MCC950. CM-KI mice exhibited ectopic activity, abnormal sarcoplasmic reticulum Ca2+ release, atrial effective refractory period shortening, and atrial hypertrophy. Adeno-associated virus subtype-9-mediated CM-specific knockdown of Nlrp3 suppressed AF development in CM-KI mice. Finally, genetic inhibition of Nlrp3 prevented AF development in CREM transgenic mice, a well-characterized mouse model of spontaneous AF.

CONCLUSIONS

Our study establishes a novel pathophysiological role for CM NLRP3 inflammasome signaling, with a mechanistic link to the pathogenesis of AF, and establishes the inhibition of NLRP3 as a potential novel AF therapy approach.

Cyclophilin J limits inflammation through the blockage of ubiquitin chain sensing

Maintaining innate immune homeostasis is important for individual health. Npl4 zinc finger (NZF) domain-mediated ubiquitin chain sensing is reported to function in the nuclear factor-kappa B (NF-κB) signal pathway, but the regulatory mechanism remains elusive. Here we show that cyclophilin J (CYPJ), a member of the peptidylprolyl isomerase family, is induced by inflammation. CYPJ interacts with the NZF domain of transform growth factor-β activated kinase 1 binding protein 2 and 3 as well as components of the linear ubiquitin chain assembly complex to block the binding of ubiquitin-chain and negatively regulates NF-κB signaling. Mice with Cypj deficiency are susceptible to lipopolysaccharide and heat-killed Listeria monocytogenes-induced sepsis and dextran sulfate sodium-induced colitis. These findings identify CYPJ as a negative feedback regulator of the NF-κB signaling pathway, and provide insights for understanding the homeostasis of innate immunity.

Resibufogenin suppresses transforming growth factor-β-activated kinase 1-mediated nuclear factor-κB activity through protein kinase C-dependent inhibition of glycogen synthase kinase 3

Resibufogenin (RB), one of the major active compounds of the traditional Chinese medicine Chansu, has received considerable attention for its potency in cancer therapy. However, the anticancer effects and the underlying mechanisms of RB on pancreatic cancer remain elusive. Here, we found that RB inhibited the viability and induces caspase‐dependent apoptosis in human pancreatic cancer cells Panc‐1 and Aspc. Resibufogenin‐induced apoptosis was through inhibition of constitutive nuclear factor‐κB (NF‐κB) activity and its target genes’ expression, which was caused by downregulation of transforming growth factor‐β‐activated kinase 1 (TAK1) levels and suppression of IκB kinase activity in Panc‐1 and Aspc cells. This induction of TAK1‐mediated NF‐κB inactivation by RB was associated with increased glycogen synthase kinase‐3 (GSK‐3) phosphorylation and subsequent suppression of its activity. Moreover, RB‐induced GSK‐3 phosphorylation/inactivation acted through activation of protein kinase C but not Akt. Finally, RB suppressed human pancreatic tumor xenograft growth in athymic nude mice. Thus, our findings reveal a novel mechanism by which RB suppresses TAK1‐mediated NF‐κB activity through protein kinase C‐dependent inhibition of GSK‐3. Our findings provide a rationale for the potential application of RB in pancreatic cancer therapy.

Calcium-sensing receptor in nutrient sensing: an insight into the modulation of intestinal homoeostasis

The animal gut effectively prevents the entry of hazardous substances and microbes while permitting the transfer of nutrients, such as water, electrolytes, vitamins, proteins, lipids, carbohydrates, minerals and microbial metabolites, which are intimately associated with intestinal homoeostasis. The gut maintains biological functions through its nutrient-sensing receptors, including the Ca-sensing receptor (CaSR), which activates a variety of signalling pathways, depending on cellular context. CaSR coordinates food digestion and nutrient absorption, promotes cell proliferation and differentiation, regulates energy metabolism and immune response, stimulates hormone secretion, mitigates secretory diarrhoea and enhances intestinal barrier function. Thus, CaSR is crucial to the maintenance of gut homoeostasis and protection of intestinal health. In this review, we focused on the emerging roles of CaSR in the modulation of intestinal homoeostasis including related underlying mechanisms. By elucidating the relationship between CaSR and animal gut homoeostasis, effective and inexpensive methods for treating intestinal health imbalance through nutritional manipulation can be developed. This article is expected to provide experimental data of the effects of CaSR on animal or human health.

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.

Ca2+, Astrocyte Activation and Calcineurin/NFAT Signaling in Age-Related Neurodegenerative Diseases

Mounting evidence supports a fundamental role for Ca²⁺ dysregulation in astrocyte activation. Though the activated astrocyte phenotype is complex, cell-type targeting approaches have revealed a number of detrimental roles of activated astrocytes involving neuroinflammation, release of synaptotoxic factors and loss of glutamate regulation. Work from our lab and others has suggested that the Ca²⁺/calmodulin dependent protein phosphatase, calcineurin (CN), provides a critical link between Ca²⁺ dysregulation and the activated astrocyte phenotype. A proteolyzed, hyperactivated form of CN appears at high levels in activated astrocytes in both human tissue and rodent tissue around regions of amyloid and vascular pathology. Similar upregulation of the CN-dependent transcription factor nuclear factor of activated T cells (NFAT4) also appears in activated astrocytes in mouse models of Alzheimer's disease (ADs) and traumatic brain injury (TBI). Major consequences of hyperactivated CN/NFAT4 signaling in astrocytes are neuroinflammation, synapse dysfunction and glutamate dysregulation/excitotoxicity, which will be covered in this review article.

Regulator of calcineurin 1 differentially regulates TLR-dependent MyD88 and TRIF signaling pathways

Toll-like receptors (TLRs) recognize the conserved molecular patterns in microorganisms and trigger myeloid differentiation primary response 88 (MyD88) and/or TIR-domain-containing adapter-inducing interferon-β (TRIF) pathways that are critical for host defense against microbial infection. However, the molecular mechanisms that govern TLR signaling remain incompletely understood. Regulator of calcineurin-1 (RCAN1), a small evolutionarily conserved protein that inhibits calcineurin phosphatase activity, suppresses inflammation during Pseudomonas aeruginosa infection. Here, we define the roles for RCAN1 in P. aeruginosa lipopolysaccharide (LPS)-activated TLR4 signaling. We compared the effects of P. aeruginosa LPS challenge on bone marrow-derived macrophages from both wild-type and RCAN1-deficient mice and found that RCAN1 deficiency increased the MyD88-NF-κB-mediated cytokine production (IL-6, TNF and MIP-2), whereas TRIF-interferon-stimulated response elements (ISRE)-mediated cytokine production (IFNβ, RANTES and IP-10) was suppressed. RCAN1 deficiency caused increased IκBα phosphorylation and NF-κB activity in the MyD88-dependent pathway, but impaired ISRE activation and reduced IRF7 expression in the TRIF-dependent pathway. Complementary studies of a mouse model of P. aeruginosa LPS-induced acute pneumonia confirmed that RCAN1-deficient mice displayed greatly enhanced NF-κB activity and MyD88-NF-κB-mediated cytokine production, which correlated with enhanced pulmonary infiltration of neutrophils. By contrast, RCAN1 deficiency had little effect on the TRIF pathway in vivo. These findings demonstrate a novel regulatory role of RCAN1 in TLR signaling, which differentially regulates MyD88 and TRIF pathways.

Adenovirus-Mediated Small Interfering RNA Targeting TAK1 Ameliorates Joint Inflammation with Collagen-Induced Arthritis in Mice

Transforming growth factor β-activated kinase-1 (TAK1) is a key upstream kinase in cell signaling during inflammation, which regulates the expression of inflammatory mediators. Small interfering RNA (siRNA) against TAK1 offers promise as a potential therapeutic strategy in immune-mediated inflammatory disorder including rheumatoid arthritis. Here, we are to evaluate the therapeutic effects of intra-articular administration of adenoviral-mediated siRNA against TAK1 (ad-siRNA-TAK1) on collagen-induced arthritis (CIA) in mice. Ad-siRNA-TAK1 was constructed. The murine RAW 264.7 macrophages were infected with ad-siRNA-TAK1, and the silencing specificity of TAK1 was assessed by quantitative polymerase chain reaction (PCR) and western blot. DBA/1 mice were injected intra-articularly with ad-siRNA-TAK1. Development and severity of arthritis was assessed histologically. Synovial inflammation and bone destruction were determined by hematoxylin and eosin (HE) staining. Articular and serum concentrations of tumor necrosis factor-α, interleukin-1, and interleukin-6 were determined using enzyme-linked immunosorbent assay. Levels of phosphorylated p38, c-Jun N-terminal kinase (JNK), and extracellular-signal-regulated kinase (ERK) were detected by western blot. In vitro, ad--siRNA-TAK1 efficiently inhibited the expression of TAK1 at both mRNA and protein levels. In vivo, intra-articular injection of ad-siRNA-TAK1 efficiently alleviated joint inflammation, decreased the expression of pro-inflammatory mediators, and suppressed JNK pathways. Our results demonstrate the efficiency of ad--siRNA-TAK1 in controlling joint inflammation of CIA, which is associated with the suppression of the expression of pro-inflammatory cytokines and JNK activation.

RCAN1 in the inverse association between Alzheimer's disease and cancer

The inverse association between Alzheimer’s disease (AD) and cancer has been reported in several population-based studies although both of them are age-related disorders. However, molecular mechanisms of the inverse association remain elusive. Increased expression of regulator of calcineurin 1 (RCAN1) promotes the pathogenesis of AD, while it suppresses cancer growth and progression in many types of cancer. Moreover, aberrant RCAN1 expression is detected in both AD and various types of cancer. It suggests that RCAN1 may play a key role in the inverse association between AD and cancer. In this article, we aim to review the role of RCAN1 in the inverse association and discuss underlying mechanisms, providing an insight into developing a novel approach to treat AD and cancer.

BEX1 is an RNA-dependent mediator of cardiomyopathy

Regulation of mRNA splicing, processing and stability is increasingly recognized as a critical control point in dynamically altering gene expression during stress or disease. Very little is understood of this process in heart failure. Here, we show that BEX1 is a heart failure-induced gene functioning as an mRNA-associated protein that enhances expression of a subset of cardiac disease-promoting genes. Modeling the increase in BEX1 that occurs in disease, cardiac-specific BEX1 transgenic mice show worse cardiac disease with stress stimulation, whereas Bex1 gene-deleted mice are protected from heart failure-promoting insults. Proteomic and interactive screening assays show that BEX1 is part of a large ribonucleoprotein processing complex involved in regulating proinflammatory mRNA expression in the heart. Specifically, induction of BEX1 augments the stability and expression of AU-rich element containing mRNAs typically found within proinflammatory genes. Thus, BEX1 functions as an mRNA-dependent effector that augments pathology-promoting gene expression during heart failure.

Little is known about the changes in mRNA splicing, processing and stability that can alter gene expression during heart failure. Here, the authors show that BEX1 is induced during heart failure and is part of a ribonucleoprotein complex enhancing the expression and stability of proinflammatory genes.

Calcineurin Dysregulation Underlies Spinal Cord Injury-Induced K+ Channel Dysfunction in DRG Neurons

Dysfunction of the fast-inactivating Kv3.4 potassium current in dorsal root ganglion (DRG) neurons contributes to the hyperexcitability associated with persistent pain induced by spinal cord injury (SCI). However, the underlying mechanism is not known. In light of our previous work demonstrating modulation of the Kv3.4 channel by phosphorylation, we investigated the role of the phosphatase calcineurin (CaN) using electrophysiological, molecular, and imaging approaches in adult female Sprague Dawley rats. Pharmacological inhibition of CaN in small-diameter DRG neurons slowed repolarization of the somatic action potential (AP) and attenuated the Kv3.4 current. Attenuated Kv3.4 currents also exhibited slowed inactivation. We observed similar effects on the recombinant Kv3.4 channel heterologously expressed in Chinese hamster ovary cells, supporting our findings in DRG neurons. Elucidating the molecular basis of these effects, mutation of four previously characterized serines within the Kv3.4 N-terminal inactivation domain eliminated the effects of CaN inhibition on the Kv3.4 current. SCI similarly induced concurrent Kv3.4 current attenuation and slowing of inactivation. Although there was little change in CaN expression and localization after injury, SCI induced upregulation of the native regulator of CaN 1 (RCAN1) in the DRG at the transcript and protein levels. Consistent with CaN inhibition resulting from RCAN1 upregulation, overexpression of RCAN1 in naive DRG neurons recapitulated the effects of pharmacological CaN inhibition on the Kv3.4 current and the AP. Overall, these results demonstrate a novel regulatory pathway that links CaN, RCAN1, and Kv3.4 in DRG neurons. Dysregulation of this pathway might underlie a peripheral mechanism of pain sensitization induced by SCI.SIGNIFICANCE STATEMENT Pain sensitization associated with spinal cord injury (SCI) involves poorly understood maladaptive modulation of neuronal excitability. Although central mechanisms have received significant attention, recent studies have identified peripheral nerve hyperexcitability as a driver of persistent pain signaling after SCI. However, the ion channels and signaling molecules responsible for this change in primary sensory neuron excitability are still not well defined. To address this problem, this study used complementary electrophysiological and molecular methods to determine how Kv3.4, a voltage-gated K⁺ channel robustly expressed in dorsal root ganglion neurons, becomes dysfunctional upon calcineurin (CaN) inhibition. The results strongly suggest that CaN inhibition underlies SCI-induced dysfunction of Kv3.4 and the associated excitability changes through upregulation of the native regulator of CaN 1 (RCAN1).

Cardioprotective Role of Tumor Necrosis Factor Receptor-Associated Factor 2 by Suppressing Apoptosis and Necroptosis

BACKGROUND

Programmed cell death, including apoptosis, mitochondria-mediated necrosis, and necroptosis, is critically involved in ischemic cardiac injury, pathological cardiac remodeling, and heart failure progression. Whereas apoptosis and mitochondria-mediated necrosis signaling is well established, the regulatory mechanisms of necroptosis and its significance in the pathogenesis of heart failure remain elusive.

METHODS

We examined the role of tumor necrosis factor receptor-associated factor 2 (Traf2) in regulating myocardial necroptosis and remodeling using genetic mouse models. We also performed molecular and cellular biology studies to elucidate the mechanisms by which Traf2 regulates necroptosis signaling.

RESULTS

We identified a critical role for Traf2 in myocardial survival and homeostasis by suppressing necroptosis. Cardiac-specific deletion of Traf2 in mice triggered necroptotic cardiac cell death, pathological remodeling, and heart failure. Plasma tumor necrosis factor α level was significantly elevated in Traf2-deficient mice, and genetic ablation of TNFR1 largely abrogated pathological cardiac remodeling and dysfunction associated with Traf2 deletion. Mechanistically, Traf2 critically regulates receptor-interacting proteins 1 and 3 and mixed lineage kinase domain-like protein necroptotic signaling with the adaptor protein tumor necrosis factor receptor-associated protein with death domain as an upstream regulator and transforming growth factor β-activated kinase 1 as a downstream effector. It is important to note that genetic deletion of RIP3 largely rescued the cardiac phenotype triggered by Traf2 deletion, validating a critical role of necroptosis in regulating pathological remodeling and heart failure propensity.

CONCLUSIONS

These results identify an important Traf2-mediated, NFκB-independent, prosurvival pathway in the heart by suppressing necroptotic signaling, which may serve as a new therapeutic target for pathological remodeling and heart failure.

Leucine-Rich Repeat Kinase 2 (LRRK2) Stimulates IL-1β-Mediated Inflammatory Signaling through Phosphorylation of RCAN1

Leucine-rich repeat kinase 2 (LRRK2) is a Ser/Thr kinase having mixed lineage kinase-like and GTPase domains, controlling neurite outgrowth and neuronal cell death. Evidence suggests that LRRK2 is involved in innate immune response signaling, but the underlying mechanism is yet unknown. A novel protein inhibitor of phosphatase 3B, RCAN1, is known to positively regulate inflammatory signaling through modulation of several intracellular targets of interleukins in immune cells. In the present study, we report that LRRK2 phosphorylates RCAN1 (RCAN1-1S) and is markedly up-regulated during interleukin-1β (IL-1β) treatment. During IL-1β treatment, LRRK2-mediated phosphorylation of RCAN1 promoted the formation of protein complexes, including that between Tollip and RCAN1. LRRK2 decreased binding between Tollip and IRAK1, which was accompanied by increased formation of the IRAK1-TRAF6 complex. TAK1 activity was significantly enhanced by LRRK2. Furthermore, LRRK2 enhanced transcriptional activity of NF-κB and cytokine IL-8 production. These findings suggest that LRRK2 might be important in positively modulating IL-1β-mediated signaling through selective phosphorylation of RCAN1.

Calcineurin signaling in the heart: The importance of time and place

The calcium-activated protein phosphatase, calcineurin, lies at the intersection of protein phosphorylation and calcium signaling cascades, where it provides an essential nodal point for coordination between these two fundamental modes of intracellular communication. In excitatory cells, such as neurons and cardiomyocytes, that experience rapid and frequent changes in cytoplasmic calcium, calcineurin protein levels are exceptionally high, suggesting that these cells require high levels of calcineurin activity. Yet, it is widely recognized that excessive activation of calcineurin in the heart contributes to pathological hypertrophic remodeling and the progression to failure. How does a calcium activated enzyme function in the calcium-rich environment of the continuously contracting heart without pathological consequences? This review will discuss the wide range of calcineurin substrates relevant to cardiovascular health and the mechanisms calcineurin uses to find and act on appropriate substrates in the appropriate location while potentially avoiding others. Fundamental differences in calcineurin signaling in neonatal verses adult cardiomyocytes will be addressed as well as the importance of maintaining heterogeneity in calcineurin activity across the myocardium. Finally, we will discuss how circadian oscillations in calcineurin activity may facilitate integration with other essential but conflicting processes, allowing a healthy heart to reap the benefits of calcineurin signaling while avoiding the detrimental consequences of sustained calcineurin activity that can culminate in heart failure.