Dual roles of modulatory calcineurin-interacting protein 1 in cardiac hypertrophy

Cardiac reverse remodeling in a mouse model with many phenotypical features of heart failure with preserved ejection fraction: effects of modifying lifestyle

Multiple factors cause heart failure with preserved ejection fraction (HFpEF) and involve various systems. HFpEF prevalence is rapidly rising, and its prognosis remains poor after the first hospitalization. Adopting a more active lifestyle has been shown to provide beneficial clinical outcomes for patients with HFpEF. Using a two-hit HfpEF murine model, we studied cardiac reverse remodeling (RR) after stopping the causing stress and introducing voluntary exercise (VE). We checked in 2-mo-old male and female C57Bl6/J mice the heart's response to angiotensin II (ANG II; 1.5 mg/kg/day for 28 days) fed or not with a high-fat diet (HFD). Then, ANG II and/or the HFD were stopped, and VE was started for an additional 4 wk. ANG II and ANG II + HFD (metabolic-hypertensive stress, MHS) caused cardiac hypertrophy (CH) and myocardial fibrosis, left ventricular (LV) concentric remodeling, atrial enlargement, and reduced exercise capacity. HFD alone induced CH and LV concentric remodeling in female mice only. CH and LV concentric remodeling were reversed 4 wk after stopping ANG II, starting VE, and a low-fat diet. Left atrial enlargement and exercise capacity were improved but differed from controls. We performed bulk LV RNA sequencing and observed that MHS upregulated 58% of the differentially expressed genes (DEGs) compared with controls. In the RR group, compared with MHS animals, 60% of the DEGs were downregulated. In an HfpEF mouse model, we show that correcting hypertension, diet, and introducing exercise can lead to extensive cardiac reverse remodeling.NEW & NOTEWORTHY Using a two-hit murine model of heart failure with preserved ejection fraction (HfpEF), combining elevated blood pressure, obesity, and exercise intolerance in male and female animals, we showed that correction of hypertension, normalization of the diet, and introduction of voluntary exercise could help reverse the remodeling of the left ventricle and double exercise capacity. We also identify genes that escape normalization after myocardial recovery and differences between males' and females' responses to stress and recovery.

Calcineurin Is a Universal Regulator of Vessel Function-Focus on Vascular Smooth Muscle Cells

Calcineurin, a serine/threonine phosphatase regulating transcription factors like NFaT and CREB, is well known for its immune modulatory effects and role in cardiac hypertrophy. Results from experiments with calcineurin knockout animals and calcineurin inhibitors indicate that calcineurin also plays a crucial role in vascular function, especially in vascular smooth muscle cells (VSMCs). In the aorta, calcineurin stimulates the proliferation and migration of VSMCs in response to vascular injury or angiotensin II administration, leading to pathological vessel wall thickening. In the heart, calcineurin mediates coronary artery formation and VSMC differentiation, which are crucial for proper heart development. In pulmonary VSMCs, calcineurin/NFaT signaling regulates the release of Ca2+, resulting in increased vascular tone followed by pulmonary arterial hypertension. In renal VSMCs, calcineurin regulates extracellular matrix secretion promoting fibrosis development. In the mesenteric and cerebral arteries, calcineurin mediates a phenotypic switch of VSMCs leading to altered cell function. Gaining deeper insights into the underlying mechanisms of calcineurin signaling will help researchers to understand developmental and pathogenetical aspects of the vasculature. In this review, we provide an overview of the physiological function and pathophysiology of calcineurin in the vascular system with a focus on vascular smooth muscle cells in different organs. Overall, there are indications that under certain pathological settings reduced calcineurin activity seems to be beneficial for cardiovascular health.

miR-21 upregulation exacerbates pressure overload-induced cardiac hypertrophy in aged hearts

Young and aging hearts undergo different remodeling post pressure overload, but the regulator that determines responses to pressure overload at different ages remains unknown. With an angiotensin II (Ang II)-induced hypertensive model, miR-21 knockout mice (miR-21^−/−) were observed regarding the effects of miR-21 on hypertension-induced cardiac remodeling in young (12 week-old) and old (50 week-old) mice. Although the aged heart represented a more significant hypertrophy and was associated with a higher expression of miR-21, Ang II-induced cardiac hypertrophy was attenuated in miR-21^−/− mice. Upon results of cardiac-specific arrays in miR-21-overexpressing cardiomyocytes, we found a significant downregulation of S100a8. In both in vitro and in vivo models, miR-21/S100a8/NF-κB/NFAT pathway was observed to be associated with pressure overload-induced hypertrophic remodeling in aged hearts. To further investigate whether circulating miR-21 could be a biomarker reflecting the aged associated cardiac remodeling, we prospectively collected clinical and echocardiographic information of patients at young (<65 y/o) and old ages (≥65 y/o) with and without hypertension. Among 108 patients, aged subjects presented with a significantly higher expression of circulating miR-21, which was positively correlated with left ventricular wall thickness. Collectively, miR-21 was associated with a prominently hypertrophic response in aged hearts under pressure overload. Further studies should focus on therapeutic potentials of miR-21.

miR-1183 Is a Key Marker of Remodeling upon Stretch and Tachycardia in Human Myocardium

Many cardiac insults causing atrial remodeling are linked to either stretch or tachycardia, but a comparative characterization of their effects on early remodeling events in human myocardium is lacking. Here, we applied isometric stretch or sustained tachycardia at 2.5 Hz in human atrial trabeculae for 6 h followed by microarray gene expression profiling. Among largely independent expression patterns, we found a small common fraction with the microRNA miR-1183 as the highest up-regulated transcript (up to 4-fold). Both, acute stretch and tachycardia induced down-regulation of the predicted miR-1183 target genes ADAM20 and PLA2G7. Furthermore, miR-1183 was also significantly up-regulated in chronically remodeled atrial samples from patients with persistent atrial fibrillation (3-fold up-regulation versus sinus rhythm samples), and in ventricular myocardium from dilative cardiomyopathy hearts (2-fold up-regulation) as compared to non-failing controls. In sum, although stretch and tachycardia show distinct transcriptomic signatures in human atrial myocardium, both cardiac insults consistently regulate the expression of miR-1183 and its downstream targets in acute and chronic remodeling. Thus, elevated expression of miR-1183 might serve as a tissue biomarker for atrial remodeling and might be of potential functional significance in cardiac disease.

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.

When one says yes and the other says no; does calcineurin participate in physiologic cardiac hypertrophy?

Developing engaging activities that build skills for understanding and appreciating research is important for undergraduate and postgraduate science students. Comparing and contrasting opposing research studies does this, and more: it also appropriately for these cohorts challenges higher level cognitive processing. Here, we present and discuss one such scenario, that of calcineurin in the heart and its response to exercise training. This scenario is further accentuated by the existence of only two studies. The background is that regular aerobic endurance exercise training stimulates the heart to physiologically adapt to chronically increase its ability to produce a greater cardiac output to meet the increased demand for oxygenated blood in working muscles, and this happens by two main mechanisms: 1) increased cardiac contractile function and 2) physiologic hypertrophy. The major underlying mechanisms have been delineated over the last decades, but one aspect has not been resolved: the potential role of calcineurin in modulating physiologic hypertrophy. This is partly because the existing research has provided opposing and contrasting findings, one line showing that exercise training does activate cardiac calcineurin in conjunction with myocardial hypertrophy, but another line showing that exercise training does not activate cardiac calcineurin even if myocardial hypertrophy is blatantly occurring. Here, we review and present the current evidence in the field and discuss reasons for this controversy. We present real-life examples from physiology research and discuss how this may enhance student engagement and participation, widen the scope of learning, and thereby also further facilitate higher level cognitive processing.

Chronic isoprenaline/phenylephrine vs. exclusive isoprenaline stimulation in mice: critical contribution of alpha1-adrenoceptors to early cardiac stress responses

Hyperactivity of the sympathetic nervous system is a major driver of cardiac remodeling, exerting its effects through both α-, and β-adrenoceptors (α-, β-ARs). As the relative contribution of subtype α₁-AR to cardiac stress responses remains poorly investigated, we subjected mice to either subcutaneous perfusion with the β-AR agonist isoprenaline (ISO, 30 mg/kg × day) or to a combination of ISO and the stable α₁-AR agonist phenylephrine (ISO/PE, 30 mg/kg × day each). Telemetry analysis revealed similar hemodynamic responses under both ISO and ISO/PE treatment i.e., permanently increased heart rates and only transient decreases in mean blood pressure during the first 24 h. Echocardiography and single cell analysis after 1 week of exposure showed that ISO/PE-, but not ISO-treated animals established α₁-AR-mediated inotropic responsiveness to acute adrenergic stimulation. Morphologically, additional PE perfusion limited concentric cardiomyocyte growth and enhanced cardiac collagen deposition during 7 days of treatment. Time-course analysis demonstrated a diverging development in transcriptional patterns at day 4 of treatment i.e., increased expression of selected marker genes Xirp2, Nppa, Tgfb1, Col1a1, Postn under chronic ISO/PE treatment which was either less pronounced or absent in the ISO group. Transcriptome analyses at day 4 via RNA sequencing demonstrated that additional PE treatment caused a marked upregulation of genes allocated to extracellular matrix and fiber organization along with a more pronounced downregulation of genes involved in metabolic processes, muscle adaptation and cardiac electrophysiology. Consistently, transcriptome changes under ISO/PE challenge more effectively recapitulated early transcriptional alterations in pressure overload-induced experimental heart failure and in human hypertrophic 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.

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.

Inorganic arsenic induces sex-dependent pathological hypertrophy in the heart

Arsenic exposure though drinking water is widespread and well associated with adverse cardiovascular outcomes, yet the pathophysiological mechanisms by which iAS induces these effects are largely unknown. Recently, an epidemiological study in an American population with a low burden of cardiovascular risk factors found that iAS exposure was associated with altered left ventricular geometry. Considering the possibility that iAS directly induces cardiac remodeling independently of hypertension, we investigated the impact of an environmentally relevant iAS exposure on the structure and function of male and female hearts. Adult male and female C56BL/6J mice were exposed to 615 μg/L iAS for 8 wk. Males exhibited increased systolic blood pressure via tail cuff photoplethysmography, left ventricular wall thickening via transthoracic echocardiography, and increased plasma atrial natriuretic peptide via enzyme immunoassay. RT-qPCR revealed increased myocardial RNA transcripts of Acta1, Myh7, and Nppa and decreased Myh6, providing evidence of pathological hypertrophy in the male heart. Similar changes were not detected in females, and nitric oxide-dependent mechanisms of cardioprotection in the heart appeared to remain intact. Further investigation found that Rcan1 was upregulated in male hearts and that iAS activated NFAT in HEK-293 cells via luciferase assay. Interestingly, iAS induced similar hypertrophic gene expression changes in neonatal rat ventricular myocytes, which were blocked by calcineurin inhibition, suggesting that iAS may induce pathological cardiac hypertrophy in part by targeting the calcineurin-NFAT pathway. As such, these results highlight iAS exposure as an independent cardiovascular risk factor and provide biological impetus for its removal from human consumption.NEW & NOTEWORTHY This investigation provides the first mechanistic link between an environmentally relevant dose of inorganic arsenic (iAS) and pathological hypertrophy in the heart. By demonstrating that iAS exposure may cause pathological cardiac hypertrophy not only by increasing systolic blood pressure but also by potentially activating calcineurin-nuclear factor of activated T cells and inducing fetal gene expression, these results provide novel mechanistic insight into the theat of iAS exposure to the heart, which is necessary to identify targets for medical and public health intervention.

RCAN1 in cardiovascular diseases: molecular mechanisms and a potential therapeutic target

Cardiovascular diseases (CVDs) are the leading cause of mortality worldwide. Considerable efforts are needed to elucidate the underlying mechanisms for the prevention and treatment of CVDs. Regulator of calcineurin 1 (RCAN1) is involved in both development/maintenance of the cardiovascular system and the pathogenesis of CVDs. RCAN1 reduction protects against atherosclerosis by reducing the uptake of oxidized low-density lipoproteins, whereas RCAN1 has a protective effect on myocardial ischemia/reperfusion injury, myocardial hypertrophy and intramural hematoma/aortic rupture mainly mediated by maintaining mitochondrial function and inhibiting calcineurin and Rho kinase activity, respectively. In this review, the regulation and the function of RCAN1 are summarized. Moreover, the dysregulation of RCAN1 in CVDs is reviewed. In addition, the beneficial role of RCAN1 reduction in atherosclerosis and the protective role of RCAN1 in myocardial ischemia/reperfusion injury, myocardial hypertrophy and intramural hematoma /aortic rupture are discussed, as well as underlying mechanisms. Furthermore, the therapeutic potential and challenges of targeting RCAN1 for CVDs treatment are also discussed.

Regulator of Calcineurin (RCAN): Beyond Down Syndrome Critical Region

The regulator of calcineurin (RCAN) was first reported as a novel gene called DSCR1, encoded in a region termed the Down syndrome critical region (DSCR) of human chromosome 21. Genome sequence comparisons across species using bioinformatics revealed three members of the RCAN gene family, RCAN1, RCAN2, and RCAN3, present in most jawed vertebrates, with one member observed in most invertebrates and fungi. RCAN is most highly expressed in brain and striated muscles, but expression has been reported in many other tissues, as well, including the heart and kidneys. Expression levels of RCAN homologs are responsive to external stressors such as reactive oxygen species, Ca2+, amyloid β, and hormonal changes and upregulated in pathological conditions, including Alzheimer's disease, cardiac hypertrophy, diabetes, and degenerative neuropathy. RCAN binding to calcineurin, a Ca2+/calmodulin-dependent phosphatase, inhibits calcineurin activity, thereby regulating different physiological events via dephosphorylation of important substrates. Novel functions of RCANs have recently emerged, indicating involvement in mitochondria homeostasis, RNA binding, circadian rhythms, obesity, and thermogenesis, some of which are calcineurin-independent. These developments suggest that besides significant contributions to DS pathologies and calcineurin regulation, RCAN is an important participant across physiological systems, suggesting it as a favorable therapeutic target.

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.

Antihypertrophic Effects of Nebivolol on Neonatal Cardiomyocyte Hypertrophy Models

The antihypertrophic effect of nebivolol over cardioselective beta-blockers (β-blockers) is attributed to the activation of cardiac nitric oxide signaling. However, the precise role of nebivolol on hypertrophied cardiomyocytes remains unclear. In the current study, in vitro cardiomyocyte hypertrophy model was induced with isoprenaline (10 μM), angiotensin II (1 μM), and phenylephrine (20 μM) in neonatal cardiomyocytes isolated from 0- to 2-day-old Sprague-Dawley rats. In addition to hypertrophic agents, cardiomyocytes were treated with nebivolol (1 μM), metoprolol (10 μM), N(ω)-nitro-L-arginine methyl ester (L-NAME) (100 μM), KT5823 (1 μM), DETA-NONOate (1-10 μM), and BAY412272 (10 μM). After 24 hours of treatment, cardiomyocyte size and transcriptional changes in cardiac hypertrophy markers were evaluated. Cardiomyocyte size increased equally in response to all hypertrophic agents. Nebivolol reduced the enhancement in cell size in response to both isoprenaline and angiotensin II; metoprolol did not. The antihypertrophic effect of nebivolol was prevented with L-NAME blockage indicating the role of NOS signaling on cardiomyocyte hypertrophy. The increased mRNA levels of atrial natriuretic peptide induced by isoprenaline decreased with nebivolol, but both β-blockers reduced the angiotensin II-induced increase in atrial natriuretic peptide expression. Combined, these results reveal that by activating NOS signaling, nebivolol exerts antihypertrophic effects on neonatal cardiomyocytes independent from the action mechanism of hypertrophic stimulus.

Cardiomyocyte-Specific Deletion of Orai1 Reveals Its Protective Role in Angiotensin-II-Induced Pathological Cardiac Remodeling

Pathological cardiac remodeling correlates with chronic neurohumoral stimulation and abnormal Ca²⁺ signaling in cardiomyocytes. Store-operated calcium entry (SOCE) has been described in adult and neonatal murine cardiomyocytes, and Orai1 proteins act as crucial ion-conducting constituents of this calcium entry pathway that can be engaged not only by passive Ca²⁺ store depletion but also by neurohumoral stimuli such as angiotensin-II. In this study, we, therefore, analyzed the consequences of Orai1 deletion for cardiomyocyte hypertrophy in neonatal and adult cardiomyocytes as well as for other features of pathological cardiac remodeling including cardiac contractile function in vivo. Cellular hypertrophy induced by angiotensin-II in embryonic cardiomyocytes from Orai1-deficient mice was blunted in comparison to cells from litter-matched control mice. Due to lethality of mice with ubiquitous Orai1 deficiency and to selectively analyze the role of Orai1 in adult cardiomyocytes, we generated a cardiomyocyte-specific and temporally inducible Orai1 knockout mouse line (Orai1^CM–KO). Analysis of cardiac contractility by pressure-volume loops under basal conditions and of cardiac histology did not reveal differences between Orai1^CM–KO mice and controls. Moreover, deletion of Orai1 in cardiomyocytes in adult mice did not protect them from angiotensin-II-induced cardiac remodeling, but cardiomyocyte cross-sectional area and cardiac fibrosis were enhanced. These alterations in the absence of Orai1 go along with blunted angiotensin-II-induced upregulation of the expression of Myoz2 and a lack of rise in angiotensin-II-induced STIM1 and Orai3 expression. In contrast to embryonic cardiomyocytes, where Orai1 contributes to the development of cellular hypertrophy, the results obtained from deletion of Orai1 in the adult myocardium reveal a protective function of Orai1 against the development of angiotensin-II-induced cardiac remodeling, possibly involving signaling via Orai3/STIM1-calcineurin-NFAT related pathways.

Chronic activation of hexosamine biosynthesis in the heart triggers pathological cardiac remodeling

The hexosamine biosynthetic pathway (HBP) plays critical roles in nutrient sensing, stress response, and cell growth. However, its contribution to cardiac hypertrophic growth and heart failure remains incompletely understood. Here, we show that the HBP is induced in cardiomyocytes during hypertrophic growth. Overexpression of Gfat1 (glutamine:fructose-6-phosphate amidotransferase 1), the rate-limiting enzyme of HBP, promotes cardiomyocyte growth. On the other hand, Gfat1 inhibition significantly blunts phenylephrine-induced hypertrophic growth in cultured cardiomyocytes. Moreover, cardiac-specific overexpression of Gfat1 exacerbates pressure overload-induced cardiac hypertrophy, fibrosis, and cardiac dysfunction. Conversely, deletion of Gfat1 in cardiomyocytes attenuates pathological cardiac remodeling in response to pressure overload. Mechanistically, persistent upregulation of the HBP triggers decompensated hypertrophy through activation of mTOR while Gfat1 deficiency shows cardioprotection and a concomitant decrease in mTOR activity. Taken together, our results reveal that chronic upregulation of the HBP under hemodynamic stress induces pathological cardiac hypertrophy and heart failure through persistent activation of mTOR.

Metabolic remodeling plays an important role in pathological cardiac hypertrophy. Here, the authors show that hexosamine biosynthetic pathway is elevated in the heart by pressure overload, which contributes to heart failure by persistent activation of mTOR.

Elimination of fukutin reveals cellular and molecular pathomechanisms in muscular dystrophy-associated heart failure

Heart failure is the major cause of death for muscular dystrophy patients, however, the molecular pathomechanism remains unknown. Here, we show the detailed molecular pathogenesis of muscular dystrophy-associated cardiomyopathy in mice lacking the fukutin gene (Fktn), the causative gene for Fukuyama muscular dystrophy. Although cardiac Fktn elimination markedly reduced α-dystroglycan glycosylation and dystrophin-glycoprotein complex proteins in sarcolemma at all developmental stages, cardiac dysfunction was observed only in later adulthood, suggesting that membrane fragility is not the sole etiology of cardiac dysfunction. During young adulthood, Fktn-deficient mice were vulnerable to pathological hypertrophic stress with downregulation of Akt and the MEF2-histone deacetylase axis. Acute Fktn elimination caused severe cardiac dysfunction and accelerated mortality with myocyte contractile dysfunction and disordered Golgi-microtubule networks, which were ameliorated with colchicine treatment. These data reveal fukutin is crucial for maintaining myocyte physiology to prevent heart failure, and thus, the results may lead to strategies for therapeutic intervention.

Mutations in Ftkn cause Fukuyama muscular dystrophy, and heart failure is the main cause of death in thes patients. Here the authors show that acute elimination of Fktn in adult mice causes early mortality, and this is associated with myocyte dysfunction, with disorganised Golg-microtubule networks, and that the pathology can be ameliorated with colchicine treatment.

GRP78 (Glucose-Regulated Protein of 78 kDa) Promotes Cardiomyocyte Growth Through Activation of GATA4 (GATA-Binding Protein 4)

The heart manifests hypertrophic growth in response to elevation of afterload pressure. Cardiac myocyte growth involves new protein synthesis and membrane expansion, of which a number of cellular quality control machineries are stimulated to maintain function and homeostasis. The unfolded protein response is potently induced during cardiac hypertrophy to enhance protein-folding capacity and eliminate terminally misfolded proteins. However, whether the unfolded protein response directly regulates cardiac myocyte growth remains to be fully determined. Here, we show that GRP78 (glucose-regulated protein of 78 kDa)-an endoplasmic reticulum-resident chaperone and a critical unfolded protein response regulator-is induced by cardiac hypertrophy. Importantly, overexpression of GRP78 in cardiomyocytes is sufficient to potentiate hypertrophic stimulus-triggered growth. At the in vivo level, TG (transgenic) hearts overexpressing GRP78 mount elevated hypertrophic growth in response to pressure overload. We went further to show that GRP78 increases GATA4 (GATA-binding protein 4) level, which may stimulate Anf (atrial natriuretic factor) expression and promote cardiac hypertrophic growth. Silencing of GATA4 in cultured neonatal rat ventricular myocytes significantly diminishes GRP78-mediated growth response. Our results, therefore, reveal that protein-folding chaperone GRP78 may directly enhance cardiomyocyte growth by stimulating cardiac-specific transcriptional factor GATA4.

Deficiency of Cardiac Natriuretic Peptide Signaling Promotes Peripartum Cardiomyopathy-Like Remodeling in the Mouse Heart

BACKGROUND

The maternal circulatory system and hormone balance both change dynamically during pregnancy, delivery, and the postpartum period. Although atrial natriuretic peptides and brain natriuretic peptides produced in the heart control circulatory homeostasis through their common receptor, NPR1, the physiologic and pathophysiologic roles of endogenous atrial natriuretic peptide/brain natriuretic peptide in the perinatal period are not fully understood.

METHODS

To clarify the physiologic and pathophysiologic roles of the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system during the perinatal period, the phenotype of female wild-type and conventional or tissue-specific Npr1-knockout mice during the perinatal period was examined, especially focusing on maternal heart weight, blood pressure, and cardiac function.

RESULTS

In wild-type mice, lactation but not pregnancy induced reversible cardiac hypertrophy accompanied by increases in fetal cardiac gene mRNAs and ERK1/2 (extracellular signaling-regulated kinase) phosphorylation. Npr1-knockout mice exhibited significantly higher plasma aldosterone level than did wild-type mice, severe cardiac hypertrophy accompanied by fibrosis, and left ventricular dysfunction in the lactation period. Npr1-knockout mice showed a high mortality rate over consecutive pregnancy-lactation cycles. In the hearts of Npr1-knockout mice during or after the lactation period, an increase in interleukin-6 mRNA expression, phosphorylation of signal transducer and activator of transcription 3, and activation of the calcineurin-nuclear factor of the activated T cells pathway were observed. Pharmacologic inhibition of the mineralocorticoid receptor or neuron-specific deletion of the mineralocorticoid receptor gene significantly ameliorated cardiac hypertrophy in lactating Npr1-knockout mice. Anti-interleukin-6 receptor antibody administration tended to reduce cardiac hypertrophy in lactating Npr1-knockout mice.

CONCLUSIONS

These results suggest that the characteristics of lactation-induced cardiac hypertrophy in wild-type mice are different from exercise-induced cardiac hypertrophy, and that the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system plays an important role in protecting the maternal heart from interleukin-6-induced inflammation and remodeling in the lactation period, a condition mimicking peripartum cardiomyopathy.

Spliced X-box Binding Protein 1 Stimulates Adaptive Growth Through Activation of mTOR

BACKGROUND

The unfolded protein response plays versatile roles in physiology and pathophysiology. Its connection to cell growth, however, remains elusive. Here, we sought to define the role of unfolded protein response in the regulation of cardiomyocyte growth in the heart.

METHODS

We used both gain- and loss-of-function approaches to genetically manipulate XBP1s (spliced X-box binding protein 1), the most conserved signaling branch of the unfolded protein response, in the heart. In addition, primary cardiomyocyte culture was used to address the role of XBP1s in cell growth in a cell-autonomous manner.

RESULTS

We found that XBP1s expression is reduced in both human and rodent cardiac tissues under heart failure. Furthermore, deficiency of XBP1s leads to decompensation and exacerbation of heart failure progression under pressure overload. On the other hand, cardiac-restricted overexpression of XBP1s prevents the development of cardiac dysfunction. Mechanistically, we found that XBP1s stimulates adaptive cardiac growth through activation of the mechanistic target of rapamycin signaling, which is mediated via FKBP11 (FK506-binding protein 11), a novel transcriptional target of XBP1s. Moreover, silencing of FKBP11 significantly diminishes XBP1s-induced mechanistic target of rapamycin activation and adaptive cell growth.

CONCLUSIONS

Our results reveal a critical role of the XBP1s-FKBP11-mechanistic target of rapamycin axis in coupling of the unfolded protein response and cardiac cell growth regulation.

Programmed Cell Death 5 Provides Negative Feedback on Cardiac Hypertrophy Through the Stabilization of Sarco/Endoplasmic Reticulum Ca2+-ATPase 2a Protein

PDCD5 (programmed cell death 5) is ubiquitously expressed in tissues, including the heart; however, the mechanism underlying the cardiac function of PDCD5 has not been understood. We investigated the mechanisms of PDCD5 in the pathogenesis of cardiac hypertrophy. Cardiac-specific PDCD5 knockout mice developed severe cardiac hypertrophy and impaired cardiac function, whereas PDCD5 protein was significantly increased in transverse aortic constriction mouse hearts and phenylephrine-stimulated cardiomyocytes. Overexpression of PDCD5 inhibited phenylephrine-induced cardiomyocyte hypertrophy, and knockdown of PDCD5 induced cardiomyocyte hypertrophy and aggravated phenylephrine-induced hypertrophy. The expression of PDCD5 protein was regulated by NFATc2 (nuclear factor of activated T cells c2) during hypertrophy. SERCA2a (sarco/endoplasmic reticulum Ca²⁺-ATPase 2a) expression was decreased in PDCD5-deficient mouse hearts because of increased ubiquitination. PDCD5-deficient cardiomyocytes displayed decreased calcium uptake rate, slowed decay of Ca²⁺ transients, decreased calcium stores, and diastolic dysfunction. Moreover, reintroduction of PDCD5 in PDCD5-deficient mouse hearts reserved SERCA2a protein, suppressed NFATc2 protein, and rescued the hypertrophy and cardiac dysfunction. Our results revealed that PDCD5 is a novel target of NFATc2 in the hypertrophic heart and provides negative feedback to protect the heart against excessive hypertrophy via the stabilization of SERCA2a protein.

Conditional deletion of Rcan1 predisposes to hypertension-mediated intramural hematoma and subsequent aneurysm and aortic rupture

Aortic intramural hematoma (IMH) can evolve toward reabsorption, dissection or aneurysm. Hypertension is the most common predisposing factor in IMH and aneurysm patients, and the hypertensive mediator angiotensin-II induces both in mice. We have previously shown that constitutive deletion of Rcan1 isoforms prevents Angiotensin II-induced aneurysm in mice. Here we generate mice conditionally lacking each isoform or all isoforms in vascular smooth muscle cells, endothelial cells, or ubiquitously, to determine the contribution to aneurysm development of Rcan1 isoforms in vascular cells. Surprisingly, conditional Rcan1 deletion in either vascular cell-type induces a hypercontractile phenotype and aortic medial layer disorganization, predisposing to hypertension-mediated aortic rupture, IMH, and aneurysm. These processes are blocked by ROCK inhibition. We find that Rcan1 associates with GSK-3β, whose inhibition decreases myosin activation. Our results identify potential therapeutic targets for intervention in IMH and aneurysm and call for caution when interpreting phenotypes of constitutively and inducibly deficient mice.

Regulator of Calcineurin 1 helps coordinate whole-body metabolism and thermogenesis

Increasing non-shivering thermogenesis (NST), which expends calories as heat rather than storing them as fat, is championed as an effective way to combat obesity and metabolic disease. Innate mechanisms constraining the capacity for NST present a fundamental limitation to this approach, yet are not well understood. Here, we provide evidence that Regulator of Calcineurin 1 (RCAN1), a feedback inhibitor of the calcium-activated protein phosphatase calcineurin (CN), acts to suppress two distinctly different mechanisms of non-shivering thermogenesis (NST): one involving the activation of UCP1 expression in white adipose tissue, the other mediated by sarcolipin (SLN) in skeletal muscle. UCP1 generates heat at the expense of reducing ATP production, whereas SLN increases ATP consumption to generate heat. Gene expression profiles demonstrate a high correlation between Rcan1 expression and metabolic syndrome. On an evolutionary timescale, in the context of limited food resources, systemic suppression of prolonged NST by RCAN1 might have been beneficial; however, in the face of caloric abundance, RCAN1-mediated suppression of these adaptive avenues of energy expenditure may now contribute to the growing epidemic of obesity.

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.

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.

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.

RCAN1 Mutation and Functional Characterization in Children with Sporadic Congenital Heart Disease

Congenital heart disease (CHD) is the most frequent birth defect. RCAN1 (regulator of calcineurin 1) contributes to CHD in Down syndrome. However, whether RCAN1 is also associated with nonsyndromic CHD remains unclear. This study sequenced the exons and flanking region of RCAN1 in 128 sporadic CHD patients and 150 normal controls. We identified six novel heterozygous mutations in CHD patients. Functional assay showed that the g.482G>T could obviously raise the promoter activity of RCAN1.4 in vitro; However, we failed to detect the expression of RCAN1 in the right auricle, which made it confused to evaluate the pathogenicity of this mutation. In addition, we demonstrated that c.290T>C and g.1056+58C>A had no effect on the alternative splicing of RCAN1. The *196C>T, *790G>A, and *1278C>G did not influence the translation of RCAN1 post transcription. In conclusion, a novel mutation of g.482G>T in RCAN1 may be related to CHD by causing overexpression of RCAN1.4.

Regulator of calcineurin 1 modulates vascular contractility and stiffness through the upregulation of COX-2-derived prostanoids

Cyclooxygenase-2 (COX-2) derived-prostanoids participate in the altered vascular function and mechanical properties in cardiovascular diseases. We investigated whether regulator of calcineurin 1 (Rcan1) participates in vascular contractility and stiffness through the regulation of COX-2. For this, wild type (Rcan1^+/+) and Rcan1-deficient (Rcan1^-/-) mice untreated or treated with the COX-2 inhibitor rofecoxib were used. Vascular function and structure were analysed by myography. COX-2 and phospo-p65 expression were studied by western blotting and immunohistochemistry and TXA₂ production by ELISA. We found that Rcan1 deficiency increases COX-2 and IL-6 expression and NF-κB activation in arteries and vascular smooth muscle cells (VSMC). Adenoviral-mediated re-expression of Rcan1.4 in Rcan1^-/- VSMC normalized COX-2 expression. Phenylephrine-induced vasoconstrictor responses were greater in aorta from Rcan1^-/- compared to Rcan1^+/+ mice. This increased response were diminished by etoricoxib, furegrelate, SQ 29548, cyclosporine A and parthenolide, inhibitors of COX-2, TXA₂ synthase, TP receptors, calcineurin and NF-κB, respectively. Endothelial removal and NOS inhibition increased phenylephrine responses only in Rcan1^+/+ mice. TXA₂ levels were greater in Rcan1^-/- mice. In small mesenteric arteries, vascular function and structure were similar in both groups of mice; however, vessels from Rcan1^-/- mice displayed an increase in vascular stiffness that was diminished by rofecoxib. In conclusion, our results suggest that Rcan1 might act as endogenous negative modulator of COX-2 expression and activity by inhibiting calcineurin and NF-kB pathways to maintain normal contractility and vascular stiffness in aorta and small mesenteric arteries, respectively. Our results uncover a new role for Rcan1 in vascular contractility and mechanical properties.

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.

Calcium Signaling and Transcriptional Regulation in Cardiomyocytes

Calcium (Ca 2+ ) is a universal regulator of various cellular functions. In cardiomyocytes, Ca 2+ is the central element of excitation–contraction coupling, but also impacts diverse signaling cascades and influences the regulation of gene expression, referred to as excitation–transcription coupling. Disturbances in cellular Ca 2+ -handling and alterations in Ca 2+ -dependent gene expression patterns are pivotal characteristics of failing cardiomyocytes, with several excitation–transcription coupling pathways shown to be critically involved in structural and functional remodeling processes. Thus, targeting Ca 2+ -dependent transcriptional pathways might offer broad therapeutic potential. In this article, we (1) review cytosolic and nuclear Ca 2+ dynamics in cardiomyocytes with respect to their impact on Ca 2+ -dependent signaling, (2) give an overview on Ca 2+ -dependent transcriptional pathways in cardiomyocytes, and (3) discuss implications of excitation–transcription coupling in the diseased heart.

Temporal dynamics of cardiac hypertrophic growth in response to pressure overload

Hypertension is one of the most important risk factors of heart failure. In response to high blood pressure, the left ventricle manifests hypertrophic growth to ameliorate wall stress, which may progress into decompensation and trigger pathological cardiac remodeling. Despite the clinical importance, the temporal dynamics of pathological cardiac growth remain elusive. Here, we took advantage of the puromycin labeling approach to measure the relative rates of protein synthesis as a way to delineate the temporal regulation of cardiac hypertrophic growth. We first identified the optimal treatment conditions for puromycin in neonatal rat ventricular myocyte culture. We went on to demonstrate that myocyte growth reached its peak rate after 8-10 h of growth stimulation. At the in vivo level, with the use of an acute surgical model of pressure-overload stress, we observed the maximal growth rate to occur at day 7 after surgery. Moreover, RNA sequencing analysis supports that the most profound transcriptomic changes occur during the early phase of hypertrophic growth. Our results therefore suggest that cardiac myocytes mount an immediate growth response in reply to pressure overload followed by a gradual return to basal levels of protein synthesis, highlighting the temporal dynamics of pathological cardiac hypertrophic growth.NEW & NOTEWORTHY We determined the optimal conditions of puromycin incorporation in cardiac myocyte culture. We took advantage of this approach to identify the growth dynamics of cardiac myocytes in vitro. We went further to discover the protein synthesis rate in vivo, which provides novel insights about cardiac temporal growth dynamics in response to pressure overload.

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.

Down syndrome critical region 1 positively correlates with angiogenesis in hypopharyngeal cancer

Hypopharyngeal carcinoma has one of the highest mortality rates of head and neck cancer, therefore, the identification of markers associated with the pathogenesis and development of hypopharyngeal cancer is critical. Down syndrome critical region 1 (DSCR1) is associated with carcinogenesis and tumor growth in several types of malignancy. Activation of the vascular endothelial growth factor (VEGF) signaling pathway upregulates DSCR1. The aims of the present study were to determine the expression levels of DSCR1 and VEGF‑C in hypopharyngeal cancer, and investigate the association between DSCR1 and angiogenesis in the disease. Tissue samples from 94 cases of pathologically confirmed hypopharyngeal squamous cell carcinoma were collected. The mRNA levels of DSCR1 and VEGF‑C in cancerous and paracancerous tissues were examined using semi‑quantitative reverse transcription‑polymerase chain reaction. Microvessel density (MVD) was counted, according to the number of cluster of differentiation 34‑positive cells. Spearman's correlation analysis was utilized to analyze the association between DSCR1 and angiogenesis. The relative mRNA expression levels of DSCR1 and VEGF‑C, and the MVD were significantly increased in the cancerous tissue samples from the patients with hypopharyngeal cancer, compared with the paracancerous tissue samples from these patients. Higher levels of DSCR1 and increased MVD were associated with poorly differentiated tumors and lymph node metastasis. The mRNA expression levels of DSCR1 were positively correlated with the mRNA levels of VEGF‑C in the cancerous tissues. The protein expression levels of DSCR1 were also positively correlated with MVD in the cancerous tissues. The results indicated that DSCR1 is involved in tumor angiogenesis in patients with hypopharyngeal cancer, and is closely associated with the progression of the disease.

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.

Sumoylation-independent activation of Calcineurin-NFAT-signaling via SUMO2 mediates cardiomyocyte hypertrophy

The objective of this study was to identify unknown modulators of Calcineurin (Cn)-NFAT signaling. Measurement of NFAT reporter driven luciferase activity was therefore utilized to screen a human cardiac cDNA-library (~10⁷ primary clones) in C2C12 cells through serial dilutions until single clones could be identified. This extensive screening strategy culminated in the identification of SUMO2 as a most efficient Cn-NFAT activator. SUMO2-mediated activation of Cn-NFAT signaling in cardiomyocytes translated into a hypertrophic phenotype. Prohypertrophic effects were also observed in mice expressing SUMO2 in the heart using AAV9 (Adeno-associated virus), complementing the in vitro findings. In addition, increased SUMO2-mediated sumoylation in human cardiomyopathy patients and in mouse models of cardiomyopathy were observed. To decipher the underlying mechanism, we generated a sumoylation-deficient SUMO2 mutant (ΔGG). Surprisingly, ΔGG replicated Cn-NFAT-activation and the prohypertrophic effects of native SUMO2, both in vitro and in vivo, suggesting a sumoylation-independent mechanism. Finally, we discerned a direct interaction between SUMO2 and CnA, which promotes CnA nuclear localization. In conclusion, we identified SUMO2 as a novel activator of Cn-NFAT signaling in cardiomyocytes. In broader terms, these findings reveal an unexpected role for SUMO2 in cardiac hypertrophy and cardiomyopathy, which may open the possibility for therapeutic manipulation of this pathway.

Unveiling Hidden Dynamics of Hippo Signalling: A Systems Analysis

The Hippo signalling pathway has recently emerged as an important regulator of cell apoptosis and proliferation with significant implications in human diseases. In mammals, the pathway contains the core kinases MST1/2, which phosphorylate and activate LATS1/2 kinases. The pro-apoptotic function of the MST/LATS signalling axis was previously linked to the Akt and ERK MAPK pathways, demonstrating that the Hippo pathway does not act alone but crosstalks with other signalling pathways to coordinate network dynamics and cellular outcomes. These crosstalks were characterised by a multitude of complex regulatory mechanisms involving competitive protein-protein interactions and phosphorylation mediated feedback loops. However, how these different mechanisms interplay in different cellular contexts to drive the context-specific network dynamics of Hippo-ERK signalling remains elusive. Using mathematical modelling and computational analysis, we uncovered that the Hippo-ERK network can generate highly diverse dynamical profiles that can be clustered into distinct dose-response patterns. For each pattern, we offered mechanistic explanation that defines when and how the observed phenomenon can arise. We demonstrated that Akt displays opposing, dose-dependent functions towards ERK, which are mediated by the balance between the Raf-1/MST2 protein interaction module and the LATS1 mediated feedback regulation. Moreover, Ras displays a multi-functional role and drives biphasic responses of both MST2 and ERK activities; which are critically governed by the competitive protein interaction between MST2 and Raf-1. Our study represents the first in-depth and systematic analysis of the Hippo-ERK network dynamics and provides a concrete foundation for future studies.

RCAN1 deficiency protects against Salmonella intestinal infection by modulating JNK activation

OBJECTIVE

RCAN1 (regulator of calcineurin 1) has been shown to be involved in various physiological and pathological processes. However, the biological implications of RCAN1 during gastrointestinal tract infection remain unclear. In this study, we tried to determine the role of RCAN1 in acute Salmonella infectious colitis.

METHODS

Wild type and RCAN1-deficient mice or macrophages were used to characterize the impacts of RCAN1 on intestinal inflammation, inflammatory cytokines production, animal survival, and pathogen clearance following Salmonella challenge.

RESULTS

Histologic and quantitative assessments showed increased inflammation and elevated proinflammatory cytokines production in RCAN1-deficient mice. The aberrant inflammatory response was recapitulated in primary bone marrow-derived macrophages. In addition, we reveal a novel regulatory role for RCAN1 in the proinflammatory JNK signaling both in vitro and in vivo. Further analysis showed that the increased inflammation in RCAN1-deficient mice contributed to pathogen clearance and host survival.

CONCLUSIONS

The present study demonstrates that RCAN1 deficiency protects against Salmonella intestinal infection by enhancing proinflammatory JNK signaling.

Calcium signaling in skeletal muscle development, maintenance and regeneration

Skeletal muscle-specific stem cells are pivotal for tissue development and regeneration. Muscle plasticity, inherent in these processes, is also essential for daily life activities. Great advances and efforts have been made in understanding the function of the skeletal muscle-dedicated stem cells, called muscle satellite cells, and the specific signaling mechanisms that activate them for recruitment in the repair of the injured muscle. Elucidating these signaling mechanisms may contribute to devising therapies for muscular injury or disease. Here we review the studies that have contributed to our understanding of how calcium signaling regulates skeletal muscle development, homeostasis and regeneration, with a focus on the calcium dynamics and calcium-dependent effectors that participate in these processes.

Bidirectional cross-regulation between ErbB2 and β-adrenergic signalling pathways

AIMS

Despite the observation that ErbB2 regulates sensitivity of the heart to doxorubicin or ErbB2-targeted cancer therapies, mechanisms that regulate ErbB2 expression and activity have not been studied. Since isoproterenol up-regulates ErbB2 in kidney and salivary glands and β2AR and ErbB2 complex in brain and heart, we hypothesized that β-adrenergic receptors (AR) modulate ErbB2 signalling status.

METHODS AND RESULTS

ErbB2 transfection of HEK293 cells up-regulates β2AR, and β2AR transfection of HEK293 up-regulates ErbB2. Interestingly, cardiomyocytes isolated from myocyte-specific ErbB2-overexpressing (ErbB2(tg)) mice have amplified response to selective β2-agonist zinterol, and right ventricular trabeculae baseline force generation is markedly reduced with β2-antagonist ICI-118 551. Consistently, receptor binding assays and western blotting demonstrate that β2ARs levels are markedly increased in ErbB2(tg) myocardium and reduced by EGFR/ErbB2 inhibitor, lapatinib. Intriguingly, acute treatment of mice with β1- and β2-AR agonist isoproterenol resulted in myocardial ErbB2 increase, while inhibition with either β1- or β2-AR antagonist did not completely prevent isoproterenol-induced ErbB2 expression. Furthermore, inhibition of ErbB2 kinase predisposed mice hearts to injury from chronic isoproterenol treatment while significantly reducing isoproterenol-induced pAKT and pERK levels, suggesting ErbB2's role in transactivation in the heart.

CONCLUSION

Our studies show that myocardial ErbB2 and βAR signalling are linked in a feedback loop with βAR activation leading to increased ErbB2 expression and activity, and increased ErbB2 activity regulating β2AR expression. Most importantly, ErbB2 kinase activity is crucial for cardioprotection in the setting of β-adrenergic stress, suggesting that this mechanism is important in the pathophysiology and treatment of cardiomyopathy induced by ErbB2-targeting antineoplastic drugs.

Cardiac Hypertrophy Is Inhibited by a Local Pool of cAMP Regulated by Phosphodiesterase 2

RATIONALE

Chronic elevation of 3'-5'-cyclic adenosine monophosphate (cAMP) levels has been associated with cardiac remodeling and cardiac hypertrophy. However, enhancement of particular aspects of cAMP/protein kinase A signaling seems to be beneficial for the failing heart. cAMP is a pleiotropic second messenger with the ability to generate multiple functional outcomes in response to different extracellular stimuli with strict fidelity, a feature that relies on the spatial segregation of the cAMP pathway components in signaling microdomains.

OBJECTIVE

How individual cAMP microdomains affect cardiac pathophysiology remains largely to be established. The cAMP-degrading enzymes phosphodiesterases (PDEs) play a key role in shaping local changes in cAMP. Here we investigated the effect of specific inhibition of selected PDEs on cardiac myocyte hypertrophic growth.

METHODS AND RESULTS

Using pharmacological and genetic manipulation of PDE activity, we found that the rise in cAMP resulting from inhibition of PDE3 and PDE4 induces hypertrophy, whereas increasing cAMP levels via PDE2 inhibition is antihypertrophic. By real-time imaging of cAMP levels in intact myocytes and selective displacement of protein kinase A isoforms, we demonstrate that the antihypertrophic effect of PDE2 inhibition involves the generation of a local pool of cAMP and activation of a protein kinase A type II subset, leading to phosphorylation of the nuclear factor of activated T cells.

CONCLUSIONS

Different cAMP pools have opposing effects on cardiac myocyte cell size. PDE2 emerges as a novel key regulator of cardiac hypertrophy in vitro and in vivo, and its inhibition may have therapeutic applications.

Orphan Nuclear Receptor Nur77 Inhibits Cardiac Hypertrophic Response to Beta-Adrenergic Stimulation

The orphan nuclear receptor Nur77 plays critical roles in cardiovascular diseases, and its expression is markedly induced in the heart after beta-adrenergic receptor (β-AR) activation. However, the functional significance of Nur77 in β-AR signaling in the heart remains unclear. By using Northern blot, Western blot, and immunofluorescent staining assays, we showed that Nur77 expression was markedly upregulated in cardiomyocytes in response to multiple hypertrophic stimuli, including isoproterenol (ISO), phenylephrine (PE), and endothelin-1 (ET-1). In a time- and dose-dependent manner, ISO increases Nur77 expression in the nuclei of cardiomyocytes. Overexpression of Nur77 markedly inhibited ISO-induced cardiac hypertrophy by inducing nuclear translocation of Nur77 in cardiomyocytes. Furthermore, cardiac overexpression of Nur77 by intramyocardial injection of Ad-Nur77 substantially inhibited cardiac hypertrophy and ameliorated cardiac dysfunction after chronic infusion of ISO in mice. Mechanistically, we demonstrated that Nur77 functionally interacts with NFATc3 and GATA4 and inhibits their transcriptional activities, which are critical for the development of cardiac hypertrophy. These results demonstrate for the first time that Nur77 is a novel negative regulator for the β-AR-induced cardiac hypertrophy through inhibiting the NFATc3 and GATA4 transcriptional pathways. Targeting Nur77 may represent a potentially novel therapeutic strategy for preventing cardiac hypertrophy and heart failure.

Rcan1 deficiency impairs neuronal migration and causes periventricular heterotopia

Periventricular heterotopia (PH) is a cortical malformation characterized by aggregation of neurons lining the lateral ventricles due to abnormal neuronal migration. The molecular mechanism underlying the pathogenesis of PH is unclear. Here we show that Regulators of calcineurin 1 (Rcan1), a Down syndrome-related gene, plays an important role in radial migration of rat cortical neurons. Downregulation of Rcan1 by expressing shRNA impaired neural progenitor proliferation and led to defects in radial migration and PH. Two isoforms of Rcan1 (Rcan1-1 and Rcan1-4) are expressed in the rat brain. Migration defects due to downregulation of Rcan1 could be prevented by shRNA-resistant expression of Rcan1-1 but not Rcan1-4. Furthermore, we found that Rcan1 knockdown significantly decreased the expression level of Flna, an F-actin cross-linking protein essential for cytoskeleton rearrangement and cell migration, mutation of which causes the most common form of bilateral PH in humans. Finally, overexpression of FLNA in Rcan1 knockdown neurons prevented migration abnormalities. Together, these findings demonstrate that Rcan1 acts upstream from Flna in regulating radial migration and suggest that impairment of Rcan1-Flna pathway may underlie PH pathogenesis.

Myocardial Hypertrophic Preconditioning Attenuates Cardiomyocyte Hypertrophy and Slows Progression to Heart Failure Through Upregulation of S100A8/A9

BACKGROUND

Transient preceding brief ischemia provides potent cardioprotection against subsequent long ischemia, termed ischemic preconditioning. Here, we hypothesized that transient short-term hypertrophic stimulation would induce the expression of hypertrophy regression genes and render the heart resistant to subsequent hypertrophic stress, and slow the progression to heart failure, as well.

METHODS AND RESULTS

Cardiomyocyte hypertrophy was induced in mice by either transverse aortic constriction or an infusion of phenylephrine, and in neonatal rat ventricular cardiomyocytes by norepinephrine exposures. In the preconditioning groups, hypertrophic stimulation was provided for 1 to 7 days and then withdrawn for several days by either aortic debanding or discontinuing phenylephrine or norepinephrine treatment, followed by subsequent reexposure to the hypertrophic stimulus for the same period as in the control group. One or 6 weeks after transverse aortic constriction, the heart weight/body weight ratio was lower in the preconditioning group than in the control group, whereas the lung weight/body weight ratio was significantly decreased 6 weeks after transverse aortic constriction. Similar results were obtained in mice receiving phenylephrine infusion and neonatal rat ventricular cardiomyocytes stimulated with norepinephrine. Both mRNA and protein expression of S100A8 and S100A9 showed significant upregulation after the removal of hypertrophic stimulation and persisted for 6 weeks in response to reimposition of transverse aortic constriction. The treatment with recombinant S100A8/A9 inhibited norepinephrine-induced myocyte hypertrophy and reduced the expression of calcineurin and NFATc3, but the silencing of S100A8/A9 prevented such changes.

CONCLUSIONS

Preconditioning with prohypertrophic factors exerts an antihypertrophic effect and slows the progression of heart failure, indicating the existence of the phenomenon for hypertrophic preconditioning.

RCAN 1 and 3 proteins regulate thymic positive selection

Cooperation between calcineurin (CN)-NFATc and RAF-MEK-ERK signaling pathways is essential in thymocyte positive selection. It is known that the Regulators of Calcineurin (RCAN) proteins can act either facilitating or suppressing CN-dependent signaling events. Here, we show that RCAN genes are expressed in lymphoid tissues, and address the role of RCAN proteins in T cell development. Overexpression of human RCAN3 and RCAN1 can modulate T cell development by increasing positive selection-related surface markers, as well as the "Erk(hi) competence state" in double positive thymocytes, a characteristic molecular signature of positive selection, without affecting CN activity. We also found that RCAN1/3 interact with RAF kinases and CN in a non-exclusive manner. Our data suggests that the balance of RCAN interactions with CN and/or RAF kinases may influence T cell positive selection.

Carabin protects against cardiac hypertrophy by blocking calcineurin, Ras, and Ca2+/calmodulin-dependent protein kinase II signaling

BACKGROUND

Cardiac hypertrophy is an early hallmark during the clinical course of heart failure and is regulated by various signaling pathways. However, the molecular mechanisms that negatively regulate these signal transduction pathways remain poorly understood.

METHODS AND RESULTS

Here, we characterized Carabin, a protein expressed in cardiomyocytes that was downregulated in cardiac hypertrophy and human heart failure. Four weeks after transverse aortic constriction, Carabin-deficient (Carabin(-/-)) mice developed exaggerated cardiac hypertrophy and displayed a strong decrease in fractional shortening (14.6±1.6% versus 27.6±1.4% in wild type plus transverse aortic constriction mice; P<0.0001). Conversely, compensation of Carabin loss through a cardiotropic adeno-associated viral vector encoding Carabin prevented transverse aortic constriction-induced cardiac hypertrophy with preserved fractional shortening (39.9±1.2% versus 25.9±2.6% in control plus transverse aortic constriction mice; P<0.0001). Carabin also conferred protection against adrenergic receptor-induced hypertrophy in isolated cardiomyocytes. Mechanistically, Carabin carries out a tripartite suppressive function. Indeed, Carabin, through its calcineurin-interacting site and Ras/Rab GTPase-activating protein domain, functions as an endogenous inhibitor of calcineurin and Ras/extracellular signal-regulated kinase prohypertrophic signaling. Moreover, Carabin reduced Ca(2+)/calmodulin-dependent protein kinase II activation and prevented nuclear export of histone deacetylase 4 after adrenergic stimulation or myocardial pressure overload. Finally, we showed that Carabin Ras-GTPase-activating protein domain and calcineurin-interacting domain were both involved in the antihypertrophic action of Carabin.

CONCLUSIONS

Our study identifies Carabin as a negative regulator of key prohypertrophic signaling molecules, calcineurin, Ras, and Ca(2+)/calmodulin-dependent protein kinase II and implicates Carabin in the development of cardiac hypertrophy and failure.

Enzymatic and thermodynamic analysis of calcineurin inhibition by RCAN1

Calcineurin (CN) is the target of the immunophilin-immunosuppressant complex, cyclophilin/cyclosporin A (CyP/CsA). RCAN1 has recently been shown to be an endogenous regulator of CN activity. We determined the enzymatic and thermodynamic aspects of CN inhibition by RCAN1. The IC50 values of isoforms RCAN1-1L and RCAN1-4 for CN were 2.7 μM and 2.6 μM, respectively. Two deletions in the CN catalytic subunit, one a deletion of Val314 in the Loop7 domain (ΔV314) and the other in the autoinhibitory domain (CNAabc), increased the sensitivity of CN to inhibition by RCAN1-1L. The IC50s of RCAN1-1L and RCAN1-4 for CN in homogenates of mouse brain were 141 nM and 100 nM, respectively. Using isothermal titration calorimetry (ITC), we found that the RCAN1-1L/CN or CyP/CsA/CN interactions were exothermic with a dissociation constant of 0.46 μM or 0.17 μM, respectively. Our ITC results show that the interactions between CN and its two inhibitors were both characterized by a favorable binding enthalpy change. We also confirmed that overexpression of RCAN1-1L could inhibit the transcriptional activation of an NFAT-dependent promoter in response to PMA and ionomycin by inhibiting CN activity in HEK293T cells. Our data should contribute to our understanding of the regulation of CN activity by endogenous inhibitors.

Echocardiographic assessment of β-adrenoceptor stimulation-induced heart failure with reduced heart rate in mice

1. Chronic injection with the β-adrenoceptor (β-AR) agonist isoproterenol (ISO) has been commonly used as an animal model of β-AR-induced cardiac remodelling and heart failure. This ISO-treated model usually exhibits significantly decreased conscious heart rate (HR). However, the HR in treatment groups is usually adjusted to the same levels by anaesthesia to assess cardiac geometry and function. In the present study, we report a method of echocardiographic assessment that represents the true cardiac geometry and function under conditions of ISO withdrawal. 2. Briefly, C57BL/6 mice were treated with 5 mg/kg per day ISO for 12 weeks. Cardiac geometry and function were assessed by high-resolution echocardiography in vehicle (saline) - and ISO-treated mice that were either conscious or anaesthetized using different concentrations of isoflurane. 3. The cardiac β-AR response was decreased in ISO-treated mice, as evidenced by markedly decreased conscious HR. Vehicle- and ISO-treated mice did not differ in terms of cardiac geometry or function when HR was adjusted to the same level (400 b.p.m.) in both treatment groups, but cardiac geometry and function did differ when a low (1%) rather than high (1.5% or 2%) isoflurane concentration was used to adjust HR. Furthermore, 3 day ISO withdrawal eliminated the difference in conscious HR between the two groups. In addition, the groups differed in cardiac geometry and function regardless of the isoflurane concentration used. 4. In conclusion, using isoflurane to decrease the HR of treated groups to the same level may mask left ventricular dysfunction in ISO-treated mice. Withdrawal of ISO eliminated the difference in basal HR between the ISO-treated and control groups on echocardiography, allowing a more accurate assessment of cardiac pathological and functional changes.