Identification and regulation of Sprouty1, a negative inhibitor of the ERK cascade, in the human heart

Current concepts in the epigenetic regulation of cardiac fibrosis

Cardiac fibrosis is a significant driver of congestive heart failure, a syndrome that continues to affect a growing patient population globally. Cardiac fibrosis results from a constellation of complex processes at the transcription, receptor, and signaling axes levels. Various mediators and signaling cascades, such as the transformation growth factor-beta pathway, have been implicated in the pathophysiology of cardiac tissue fibrosis. Our understanding of these markers and pathways has improved in recent years as more advanced technologies and assays have been developed, allowing for better delineation of the crosstalk between specific factors. There is mounting evidence suggesting that epigenetic modulation plays a pivotal role in the progression of cardiac fibrosis. Transcriptional regulation of key pro- and antifibrotic pathways can accentuate or blunt the rate and extent of fibrosis at the tissue level. Exosomes, micro-RNAs, and long noncoding RNAs all belong to factors that can impact the epigenetic signature in cardiac fibrosis. Herein, we comprehensively review the latest literature about exosomes, their contents, and cardiac fibrosis. In doing so, we highlight the specific transcriptional factors with pro- or antifibrotic properties. We also assimilate the data supporting these mediators' potential utility as diagnostic or prognostic biomarkers. Finally, we offer insight into where further work can be done to fill existing gaps to translate preclinical findings better and improve clinical outcomes.

Biology of myocardial recovery in advanced heart failure with long-term mechanical support

Cardiac remodeling is an adaptive, compensatory biological process following an initial insult to the myocardium that gradually becomes maladaptive and causes clinical deterioration and chronic heart failure (HF). This biological process involves several pathophysiological adaptations at the genetic, molecular, cellular, and tissue levels. A growing body of clinical and translational investigations demonstrated that cardiac remodeling and chronic HF does not invariably result in a static, end-stage phenotype but can be at least partially reversed. One of the paradigms which shed some additional light on the breadth and limits of myocardial elasticity and plasticity is long term mechanical circulatory support (MCS) in advanced HF pediatric and adult patients. MCS by providing (a) ventricular mechanical unloading and (b) effective hemodynamic support to the periphery results in functional, structural, cellular and molecular changes, known as cardiac reverse remodeling. Herein, we analyze and synthesize the advances in our understanding of the biology of MCS-mediated reverse remodeling and myocardial recovery. The MCS investigational setting offers access to human tissue, providing an unparalleled opportunity in cardiovascular medicine to perform in-depth characterizations of myocardial biology and the associated molecular, cellular, and structural recovery signatures. These human tissue findings have triggered and effectively fueled a "bedside to bench and back" approach through a variety of knockout, inhibition or overexpression mechanistic investigations in vitro and in vivo using small animal models. These follow-up translational and basic science studies leveraging human tissue findings have unveiled mechanistic myocardial recovery pathways which are currently undergoing further testing for potential therapeutic drug development. Essentially, the field is advancing by extending the lessons learned from the MCS cardiac recovery investigational setting to develop therapies applicable to the greater, not end-stage, HF population. This review article focuses on the biological aspects of the MCS-mediated myocardial recovery and together with its companion review article, focused on the clinical aspects, they aim to provide a useful framework for clinicians and investigators.

miR-21 in Human Cardiomyopathies

miR-21 is a 22-nucleotide long microRNA that matches target mRNAs in a complementary base pairing fashion and regulates gene expression by repressing or degrading target mRNAs. miR-21 is involved in various cardiomyopathies, including heart failure, dilated cardiomyopathy, myocardial infarction, and diabetic cardiomyopathy. Expression levels of miR-21 notably change in both heart and circulation and provide cardiac protection after heart injury. In the meantime, miR-21 also tightly links to cardiac dysfunctions such as cardiac hypertrophy and fibrosis. This review focuses on the miR-21 expression pattern and its functions in diseased-heart and further discusses the feasibility of miR-21 as a biomarker and therapeutic target in cardiomyopathies.

Heart Failure With Targeted Cancer Therapies: Mechanisms and Cardioprotection

Oncology has seen growing use of newly developed targeted therapies. Although this has resulted in dramatic improvements in progression-free and overall survival, challenges in the management of toxicities related to longer-term treatment of these therapies have also become evident. Although a targeted approach often exploits the differences between cancer cells and noncancer cells, overlap in signaling pathways necessary for the maintenance of function and survival in multiple cell types has resulted in systemic toxicities. In particular, cardiovascular toxicities are of important concern. In this review, we highlight several targeted therapies commonly used across a variety of cancer types, including HER2 (human epidermal growth factor receptor 2)+ targeted therapies, tyrosine kinase inhibitors, immune checkpoint inhibitors, proteasome inhibitors, androgen deprivation therapies, and MEK (mitogen-activated protein kinase kinase)/BRAF (v-raf murine sarcoma viral oncogene homolog B) inhibitors. We present the oncological indications, heart failure incidence, hypothesized mechanisms of cardiotoxicity, and potential mechanistic rationale for specific cardioprotective strategies.

Exosome-Encapsulated MicroRNA-21 from Esophageal Squamous Cell Carcinoma Cells Enhances Angiogenesis of Human Umbilical Venous Endothelial Cells by Targeting SPRY1

Objective

Esophageal squamous cell carcinoma (ESCC) persists among the most prevalent cancers worldwide. Angiogenesis represents a crucial element necessitated for tumor growth and metastasis in ESCC. In this study, we aimed to study the effect of microRNA (miR)-21 on angiogenesis in ESCC and its underlying mechanism.

Materials and Methods

Initially, the expression patterns of miR-21, SPRY1, and VEGF were determined in ESCC tissues and cells. The relationship between miR-21 and SPRY1 was identified using dual-luciferase reporter assay. Exosomes were subsequently isolated from the ESCC cells, followed by co-culture with the human umbilical venous endothelial cells (HUVECs). HUVEC proliferation and angiogenesis were determined by means of CCK-8, colony formation, and microtubule formation in vitro. Chicken chorioallantoic membrane (CAM) model and mouse xenograft model of ESCC cells were established to substantiate the function of miR-21 corresponding to the angiogenesis and tumor growth of ESCC, followed by microvascular density (MVD) evaluation.

Results

Expression patterns of miR-21 and VEGF were elevated, while the SPRY1 expression pattern was repressed in ESCC tissues and cells. The downregulation of miR-21 and exosome-derived miR-21 impeded the proliferation and angiogenesis in HUVECs. Our data revealed that miR-21 could negatively target SPRY1, and positively target VEGF. The downregulation of miR-21 could evidently encumber the angiogenesis and tumor growth of ESCC in vivo, as evidenced by the decrease in number of branches of the microvessels and MVD.

Conclusion

Collectively, ESCC cell-derived exosome containing miR-21 promotes the proliferation and angiogenesis of HUVECs via SPRY1 downregulation and VEGF upregulation.

MiR-21-5p regulates extracellular matrix degradation and angiogenesis in TMJOA by targeting Spry1

BACKGROUND

Due to the lack of research on the pathological mechanism of temporomandibular joint osteoarthritis (TMJOA), there are few effective treatment measures in the clinic. In recent years, microRNAs (miRs) have been demonstrated to play an important role in the pathogenesis of osteoarthritis (OA) by regulating a variety of target genes, and the latest evidence shows that miR-21-5p is specifically overexpressed in OA. The purpose of this project was to clarify whether miR-21-5p can regulate the TMJOA process by targeting Spry1.

METHODS

TMJOA was induced by a unilateral anterior crossbite (UAC) model, and the effect of miR-21-5p knockout on TMJOA was evaluated by toluidine blue (TB), immunohistochemical (IHC) staining, Western blotting (WB) and RT-qPCR. Primary mouse condylar chondrocytes (MCCs) were isolated, cultured and transfected with a series of mimics, inhibitors, siRNA-Spry1 or cDNA Spry1. WB, RT-qPCR, IHC and TB were used to detect the effect of miR-21-5p and its target gene Spry1 on the expression of MMP-13, VEGF and p-ERK1/2 in TMJOA. The effect of miR-21-5p on angiogenesis was evaluated by chick embryo chorioallantoic membrane (CAM) assay and WB.

RESULTS

In the UAC model, the cartilage thickness and extracellular matrix of miR-21-5p knockout mice were less damaged, and miR-21-5p and UAC model were shown to affect the expression of Spry1, IL-1β, MMP-13, and VEGF. Luciferase experiments confirmed that Spry1 was the direct target of miR-21-5p. The expression levels of Spry1, MMP-13, VEGF and p-ERK1/2 in MCCs transfected with miR-21-5p mimic were higher than those in the inhibitor group. Under the simulated inflammatory environment of IL-1β, the expression levels of MMP-13, VEGF and p-ERK1/2 were positively correlated with miR-21-5p, while Spry1 was negatively correlated with miR-21-5p. Inhibition of miR-21-5p expression and overexpression of Spry1 enhanced the inhibition of MMP-13, VEGF and p-ERK1/2 expression. MiR-21-5p had a significant role in promoting angiogenesis in the chick embryo CAM assay, and this role was clearly mediated by the ERK-MAPK signalling pathway.

CONCLUSION

This study verified that miR-21-5p can promote the process of TMJOA by targeting Spry1, which provides a new direction for future research on the treatment of this disease.

Inhibition of cardiomyocyte Sprouty1 protects from cardiac ischemia-reperfusion injury

Sprouty1 (Spry1) is a negative modulator of receptor tyrosine kinase signaling, but its role in cardiomyocyte survival has not been elucidated. The aim of this study was to investigate the potential role of cardiomyocyte Spry1 in cardiac ischemia–reperfusion (I/R) injury. Infarct areas of mouse hearts showed an increase in Spry1 protein expression, which localized to cardiomyocytes. To investigate if cardiomyocyte Spry1 regulates I/R injury, 8-week-old inducible cardiomyocyte Spry1 knockout (Spry1 cKO) mice and control mice were subjected to cardiac I/R injury. Spry1 cKO mice showed reduction in release of cardiac troponin I and reduced infarct size after I/R injury compared to control mice. Similar to Spry1 knockdown in cardiomyocytes in vivo, RNAi-mediated Spry1 silencing in isolated cardiomyocytes improved cardiomyocyte survival following simulated ischemia injury. Mechanistically, Spry1 knockdown induced cardiomyocyte extracellular signal-regulated kinase (ERK) phosphorylation in healthy hearts and isolated cardiomyocytes, and enhanced ERK phosphorylation after I/R injury. Spry1-deficient cardiomyocytes showed better preserved mitochondrial membrane potential following ischemic injury and an increase in levels of phosphorylated ERK and phosphorylated glycogen synthase kinase-3β (GSK-3β) in mitochondria of hypoxic cardiomyocytes. Overexpression of constitutively active GSK-3β abrogated the protective effect of Spry1 knockdown. Moreover, pharmacological inhibition of GSK-3β protected wild-type cardiomyocytes from cell death, but did not further protect Spry1-silenced cardiomyocytes from hypoxia-induced injury. Cardiomyocyte Spry1 knockdown promotes ERK phosphorylation and offers protection from I/R injury. Our findings indicate that Spry1 is an important regulator of cardiomyocyte viability during ischemia–reperfusion injury.

Role of Sprouty1 (Spry1) in the pathogenesis of atrial fibrosis

Atrial fibrosis is the hallmark of atrial fibrillation (AF) dependent structure remodeling. Besides, sprouty 1 (Spry1) plays a key role in the process of fibrosis. In this study, we investigated whether Spry1 could regulate TGF-β1 in atrial fibrosis. Ten dogs or patients were assigned to control (n=4) and AF group (n=6). The left atrium of dogs or right atrial appendage of patients was taken. After that, cardiac fibroblasts were treated with or without angiotensin II (Ang II). Furthermore, cardiac fibroblasts were transfected with lentivirus of Spry1 over-expression vector, Spry1 shRNA or negative control (NC). And the protein expression of Spry1 and TGF-β1 was analyzed by western blot and immunohistochemistry. The results showed that TGF-β1 was highly expressed while Spry1 was lowly expressed in the models of human and canine with AF. Besides, the protein expression of TGF-β1 was up-regulated and Spry1 was down-regulated in Ang II stimulated cardiac fibroblasts. Furthermore, when Spry1 was knockdown in Ang II-induced cardiac fibroblasts, the cell proliferation and the TGF-β1 protein expression increased significantly, while Spry1 over-expression showed inverse results. Our results demonstrated that Spry1 may target TGF-β1 in regulating fibrosis. These findings may provide possible therapeutic targets in atrial fibrosis.

The developing story of Sprouty and cancer

Sprouty proteins are evolutionarily conserved modulators of MAPK/ERK pathway. Through interacting with an increasing number of effectors, mediators, and regulators with ultimate influence on multiple targets within or beyond ERK, Sprouty orchestrates a complex, multilayered regulatory system and mediates a crosstalk among different signaling pathways for a coordinated cellular response. As such, Sprouty has been implicated in various developmental and physiological processes. Evidence shows that ERK is aberrantly activated in malignant conditions. Accordingly, Sprouty deregulation has been reported in different cancer types and shown to impact cancer development, progression, and metastasis. In this article, we have tried to provide an overview of the current knowledge about the Sprouty physiology and its regulatory functions in health, as well as an updated review of the Sprouty status in cancer. Putative implications of Sprouty in cancer biology, their clinical relevance, and their proposed applications are also revisited. As a developing story, however, role of Sprouty in cancer remains to be further elucidated.

Looking into a conceptual framework of ROS-miRNA-atrial fibrillation

Atrial fibrillation (AF) has been recognized as a major cause of cardiovascular-related morbidity and mortality. MicroRNAs (miRNAs) represent recent additions to the collection of biomolecules involved in arrhythmogenesis. Reactive oxygen species (ROS) have been independently linked to both AF and miRNA regulation. However, no attempts have been made to investigate the possibility of a framework composed of ROS–miRNA–AF that is related to arrhythmia development. Therefore, this review was designed as an attempt to offer a new approach to understanding AF pathogenesis. The aim of this review was to find and to summarize possible connections that exist among AF, miRNAs and ROS to understand the interactions among the molecular entities underlying arrhythmia development in the hopes of finding unappreciated mechanisms of AF. These findings may lead us to innovative therapies for AF, which can be a life-threatening heart condition. A systemic literature review indicated that miRNAs associated with AF might be regulated by ROS, suggesting the possibility that miRNAs translate cellular stressors, such as ROS, into AF pathogenesis. Further studies with a more appropriate experimental design to either prove or disprove the existence of an ROS–miRNA–AF framework are strongly encouraged.

The expression of the Sprouty 1 protein inversely correlates with growth, proliferation, migration and invasion of ovarian cancer cells

Background

Our recent study on a panel of human ovarian cancer cells revealed that SKOV-3 cells barely express the Sprouty isoform 1 (Spry1) while 1A9 cells maintain it at a level similar to normal ovarian cells. Here we investigated the functional outcomes of induced alterations in the expression of Spry1 in the two cell lines in vitro.

Methods

Using the Spry1 specific plasmid and siRNA, the expression of Spry1 was induced and conversely silenced in SKOV-3 and 1A9 cells, respectively. The functional outcome was investigated by means of proliferation, MTT, scratch-wound, migration and invasion assays and selection of the stable clones. Mechanism of the effect was explored by Western blot.

Results

In the Spry1-transfected SKOV-3 cells, a significant reduction in growth and proliferation was evident. Stable clones of the Spry1-transfected SKOV-3 were almost undetectable after day 14. The number of migrated and invaded cells and the percentage of the scratch closure were significantly lower in the Spry1-transfected group. Spry1 silencing in 1A9 cells, on the other hand, led to a significant increase in cell growth and proliferation. The number of migrated and invaded cells and the percentage of the scratch closure significantly increased in Spry1-silenced 1A9 group. Mechanistically, overexpression of Bax, activation of caspases 3, 7, 8 and 9, cleavage of PARP and attenuation of Bcl-2 and Bcl-xl were observed along with reduced activation of Erk and Akt and increased amount and activity of PTEN in the Spry1-transfected SKOV-3 cells.

Conclusions

Here, we report the inverse correlation between the expression of Spry1 and growth, proliferation, invasion and migration of ovarian cancer cells.

Vitamin D receptor activation, left ventricular hypertrophy and myocardial fibrosis

BACKGROUND

Left ventricular hypertrophy (LVH), a common complication in chronic kidney disease (CKD), is associated with high cardiovascular mortality. The aim of this experimental study was to analyze the effect of different vitamin D receptor activators (VDRAs) on both LVH and myocardial fibrosis in chronic renal failure (CRF).

METHODS

Male Wistar rats with CRF, carried out by 7/8 nephrectomy, were treated intraperitoneally with equivalent doses of VDRAs (calcitriol, paricalcitol and alfacalcidol, 5 days per week) during 4 weeks. A placebo group (CRF + vehicle) and a Sham group with normal renal function served as controls. Biochemical, morphological, functional and molecular parameters associated with LVH were evaluated, as well as cardiac fibrosis, collagen I, transforming growth factor β1 (TGFβ1) and matrix metalloproteinase-1 (MMP1) expression.

RESULTS

All VDRAs treatment prevented LVH, with values of cardiomyocyte size, LV wall and septum thickness and heart-body weight ratio similar to those observed in the Sham group. At molecular levels, all VDRAs attenuated atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) expression compared with CRF + vehicle. The phosphorylation of ERK1/2, a signal for activating growth, was stimulated in the CRF + vehicle group; VDRAs use prevented this activation. Paricalcitol was the only VDRA used that maintained in the normal range all parameters associated with myocardial fibrosis (total collagen, collagen I, TGFβ1 and MMP1).

CONCLUSIONS

Our findings demonstrated that the three VDRAs used induced similar changes in bone metabolic parameters and LVH. In addition, paricalcitol was the only VDRA which showed a relevant beneficial effect in the reduction of myocardial fibrosis, a key factor in the myocardial dysfunction in CKD patients.

PI3K regulates branch initiation and extension of cultured mammary epithelia via Akt and Rac1 respectively

The tree-like architecture of the mammary gland is generated by branching morphogenesis, which is regulated by many signals from the microenvironment. Here we examined how signaling downstream of phosphoinositide 3-kinase (PI3K) regulates different steps of mammary branching using three-dimensional culture models of the mammary epithelial duct. We found that PI3K was required for both branch initiation and elongation. Activated Akt was enhanced at branch initiation sites where its negative regulator, PTEN, was blocked by signaling via Sprouty2 (SPRY2); inhibiting Akt prevented branch initiation. The pattern of SPRY2 expression, and thus of Akt activation and branch initiation, was controlled by mechanical signaling from endogenous cytoskeletal contractility. In contrast, activated GTP-bound Rac1 localized to the leading edge of nascent branches and was required for branch elongation. These data suggest that the PI3K network integrates mechanical and biochemical signaling to control branching morphogenesis of mammary epithelial cells.

Signaling to cardiac hypertrophy: insights from human and mouse RASopathies

Cardiac hypertrophy is the heart's response to a variety of extrinsic and intrinsic stimuli, some of which might finally lead up to a maladaptive state. An integral part of the pathogenesis of the hypertrophic cardiomyopathy disease (HCM) is the activation of the rat sarcoma (RAS)/RAF/MEK (mitogen-activated protein kinase kinase)/MAPK (mitogen-activated protein kinase) cascade. Therefore, the molecular signaling involving RAS has been the subject of intense research efforts, particularly after the identification of the RASopathies. These constitute a class of developmental disorders caused by germline mutations affecting proteins contributing to the RAS pathway. Among other phenotypic features, a subset of these syndromes is characterized by HCM, prompting researchers and clinicians to delve into the chief signaling constituents of cardiac hypertrophy. In this review, we summarize current advances in the knowledge of the molecular signaling events involved in the pathogenesis of cardiac hypertrophy through work completed on patients and on genetically manipulated animals with HCM and RASopathies. Important insights are drawn from the recognition of parallels between cardiac hypertrophy and cancer. Future research promises to further elucidate the complex molecular interactions responsible for cardiac hypertrophy, possibly pointing the way for the identification of new specific targets for the treatment of HCM.

Ablation of p21-activated kinase-1 in mice promotes isoproterenol-induced cardiac hypertrophy in association with activation of Erk1/2 and inhibition of protein phosphatase 2A

Earlier investigations in our lab indicated an anti-adrenergic effect induced by activation of p21-activated kinase (Pak-1) and protein phosphatase 2A (PP2A). Our objective was to test the hypothesis that Pak-1/PP2A is a signaling cascade controlling stress-induced cardiac growth. We determined the effects of ablation of the Pak-1 gene on the response of the myocardium to chronic stress of isoproterenol (ISO) administration. Wild-type (WT) and Pak-1-knockout (Pak-1-KO) mice were randomized into six groups to receive either ISO, saline (CTRL), or ISO and FR180204, a selective inhibitor of Erk1/2. Echocardiography revealed that hearts of the Pak-1-KO/ISO group had increased LV fractional shortening, reduced LV chamber volume in diastole and systole, increased cardiac hypertrophy, and enhanced transmitral early filling deceleration time, compared to all other groups. The changes were associated with an increase in relative Erk1/2 activation in Pak-1-KO/ISO mice versus all other groups. ISO-induced cardiac hypertrophy and Erk1/2 activation in Pak-1-KO/ISO were attenuated when the selective Erk1/2 inhibitor FR180204 was administered. Immunoprecipitation showed an association between Pak-1, PP2A, and Erk1/2. Cardiac myocytes infected with an adenoviral vector expressing constitutively active Pak-1 showed a repression of Erk1/2 activation. p38 MAPK phosphorylation was decreased in Pak-1-KO/ISO and Pak-1-KO/CTRL mice compared to WT. Levels of phosphorylated PP2A were increased in ISO-treated Pak-1-KO mice, indicating reduced phosphatase activity. Maximum Ca(2+)-activated tension in detergent-extracted bundles of papillary fibers from ISO-treated Pak-1-KO mice was higher than in all other groups. Analysis of cTnI phosphorylation indicated that compared to WT, ISO-induced phosphorylation of cTnI was blunted in Pak-1-KO mice. Active Pak-1 is a natural inhibitor of Erk1/2 and a novel anti-hypertrophic signaling molecule upstream of PP2A.

Mitogen-activated protein kinase signaling in the heart: angels versus demons in a heart-breaking tale

Among the myriad of intracellular signaling networks that govern the cardiac development and pathogenesis, mitogen-activated protein kinases (MAPKs) are prominent players that have been the focus of extensive investigations in the past decades. The four best characterized MAPK subfamilies, ERK1/2, JNK, p38, and ERK5, are the targets of pharmacological and genetic manipulations to uncover their roles in cardiac development, function, and diseases. However, information reported in the literature from these efforts has not yet resulted in a clear view about the roles of specific MAPK pathways in heart. Rather, controversies from contradictive results have led to a perception that MAPKs are ambiguous characters in heart with both protective and detrimental effects. The primary object of this review is to provide a comprehensive overview of the current progress, in an effort to highlight the areas where consensus is established verses the ones where controversy remains. MAPKs in cardiac development, cardiac hypertrophy, ischemia/reperfusion injury, and pathological remodeling are the main focuses of this review as these represent the most critical issues for evaluating MAPKs as viable targets of therapeutic development. The studies presented in this review will help to reveal the major challenges in the field and the limitations of current approaches and point to a critical need in future studies to gain better understanding of the fundamental mechanisms of MAPK function and regulation in the heart.

Targeted Sprouty1 overexpression in cardiac myocytes does not alter myocardial remodeling or function

The mitogen activated protein kinase (MAPK) signaling pathway regulates multiple events leading to heart failure including ventricular remodeling, contractility, hypertrophy, apoptosis, and fibrosis. The regulation of conserved intrinsic inhibitors of this pathway is poorly understood. We recently identified an up-regulation of Sprouty1 (Spry1) in a targeted approach for novel inhibitors of the MAPK signaling pathway in failing human hearts following reverse remodeling. The goal of this study was to test the hypothesis that up-regulated expression of Spry1 in cardiac myocytes would be sufficient to inhibit ERK1/2 activation and tissue remodeling. We established a murine model with up-regulated Spry1 expression in cardiac myocytes using the alpha-myosin heavy chain promoter (alpha-MHC). Heart weight and cardiac myocyte morphology were unchanged in adult male alpha-MHC-Spry1 mice compared to control mice. Ventricular function of alpha-MHC-Spry1 mice was unaltered at 8 weeks or 1 year of age. These findings were consistent with the lack of an effect of Spry1 on ERK1/2 activity. In summary, targeted up-regulation of Spry1 in cardiac myocytes is not sufficient to alter cell or tissue remodeling consistent with the lack of an effect on ERK1/2 activity.

Silencing of SPRY1 triggers complete regression of rhabdomyosarcoma tumors carrying a mutated RAS gene

RAS oncogenes are among the most frequently mutated genes in human cancer, but effective strategies for therapeutic inhibition of the RAS pathway have been elusive. Sprouty1 (SPRY1) is an upstream antagonist of RAS that is activated by extracellular signal-related kinase (ERK), providing a negative feedback loop for RAS signaling, and other evidence suggests that SPRY1 may have a tumor suppressor function. Studies of RAS status in the human childhood tumor rhabdomyosarcoma (RMS) indicated mutations in approximately half of the tumors of the embryonal rhabdomyosarcoma subtype (ERMS) but not the alveolar subtype (ARMS). ERMS tumors also showed overexpression of SPRY1, which was indeed upregulated by mutant RAS. However, we found that, in the presence of mutant RAS, the function of SPRY1 was changed from an antagonist to an agonist of RAS signaling. Thus, SPRY1 supported formation of activated ERK and mitogen-activated protein/ERK kinase and was essential for ERMS cell proliferation and survival. Conversely, silencing of SPRY1 in ERMS cells (but not ARMS cells) abolished their tumorigenicity in mice. Moreover, silencing of SPRY1 caused regression of established ERMS tumors (but not ARMS tumors) formed in xenograft settings. Our findings argue that SPRY1 inhibition can offer a therapeutic strategy to treat childhood RMS and possibly other tumors carrying oncogenic RAS mutations.

Intermolecular interactions of Sprouty proteins and their implications in development and disease

Receptor tyrosine kinase (RTK) signaling is spatially and temporally regulated by a number of positive and negative regulatory mechanisms. These regulatory mechanisms control the amplitude and duration of the signals initiated at the cell surface to have a normal or aberrant biological outcome in development and disease, respectively. In the past decade, the Sprouty (Spry) family of proteins has been identified as modulators of RTK signaling in normal development and disease. This review summarizes recent advances concerning the biological activities modulated by Spry family proteins, their interactions with signaling proteins, and their involvement in cardiovascular diseases and cancer. The diversity of mechanisms in the regulation of Spry expression and activity in cell systems emphasizes the crucial role of Spry proteins in development and growth across the animal kingdom.

MicroRNA-21 targets Sprouty2 and promotes cellular outgrowths

The posttranscriptional regulator, microRNA-21 (miR-21), is up-regulated in many forms of cancer, as well as during cardiac hypertrophic growth. To understand its role, we overexpressed it in cardiocytes where it revealed a unique type of cell-to-cell "linker" in the form of long slender outgrowths and branches. We subsequently confirmed that miR-21 directly targets and down-regulates the expression of Sprouty2 (SPRY2), an inhibitor of branching morphogenesis and neurite outgrowths. We found that beta-adrenergic receptor (betaAR) stimulation induces up-regulation of miR-21 and down-regulation of SPRY2 and is, likewise, associated with connecting cell branches. Knockdown of SPRY2 reproduced the branching morphology in cardiocytes, and vice versa, knockdown of miR-21 using a specific 'miRNA eraser' or overexpression of SPRY2 inhibited betaAR-induced cellular outgrowths. These structures enclose sarcomeres and connect adjacent cardiocytes through functional gap junctions. To determine how this aspect of miR-21 function translates in cancer cells, we knocked it down in colon cancer SW480 cells. This resulted in disappearance of their microvillus-like protrusions accompanied by SPRY2-dependent inhibition of cell migration. Thus, we propose that an increase in miR-21 enhances the formation of various types of cellular protrusions through directly targeting and down-regulating SPRY2.

Left ventricular assist device-induced molecular changes in the failing myocardium

PURPOSE OF REVIEW

There is considerable increase in the use of left ventricular assist devices for the treatment of severe heart failure. Traditionally viewed as a bridge to transplantation and more recently as a destination therapy, left ventricular assist device support is now recognized to offer potential for myocardial recovery through reverse remodeling, a potential that is further enhanced by combination with pharmacologic therapy. In this study, we examine the molecular changes associated with left ventricular assist device support and how these may contribute to the recovery process.

RECENT FINDINGS

Studies in both patients and experimental models have demonstrated that improved function is associated with alterations in several key pathways including cell survival, cytokine signaling, calcium handling, adrenergic receptor signaling, cytoskeletal and contractile proteins, energy metabolism, extracellular matrix, and endothelial and microvascular functions. Moreover, the unique research opportunities offered by left ventricular assist device analysis are beginning to distinguish changes associated with recovery from those of mechanical unloading alone and identify potential predictors and novel therapeutic targets capable of enhancing myocardial repair.

SUMMARY

Significant progress has been made toward revealing molecular changes associated with myocardial recovery from heart failure. These studies also offer new insight into the pathogenesis of heart failure and point to novel therapeutic strategies.

Mitogen-activated protein kinases in heart development and diseases

Mitogen-activated protein (MAP) kinases belong to a highly conserved family of Ser-Thr protein kinases in the human kinome and have diverse roles in broad physiological functions. The 4 best-characterized MAP kinase pathways, ERK1/2, JNK, p38, and ERK5, have been implicated in different aspects of cardiac regulation, from development to pathological remodeling. Recent advancements in the development of kinase-specific inhibitors and genetically engineered animal models have revealed significant new insights about MAP kinase pathways in the heart. However, this explosive body of new information also has yielded many controversies about the functional role of specific MAP kinases as either detrimental promoters or critical protectors of the heart during cardiac pathological processes. These uncertainties have raised questions on whether/how MAP kinases can be targeted to develop effective therapies against heart diseases. In this review, recent studies examining the role of MAP kinase subfamilies in cardiac development, hypertrophy, and survival are summarized.

SHP-2 is required for the maintenance of cardiac progenitors

The isolation and culturing of cardiac progenitor cells has demonstrated that growth factor signaling is required to maintain cardiac cell survival and proliferation. In this study, we demonstrate in Xenopus that SHP-2 activity is required for the maintenance of cardiac precursors in vivo. In the absence of SHP-2 signaling, cardiac progenitor cells downregulate genes associated with early heart development and fail to initiate cardiac differentiation. We further show that this requirement for SHP-2 is restricted to cardiac precursor cells undergoing active proliferation. By demonstrating that SHP-2 is phosphorylated on Y542/Y580 and that it binds to FRS-2, we place SHP-2 in the FGF pathway during early embryonic heart development. Furthermore, we demonstrate that inhibition of FGF signaling mimics the cellular and biochemical effects of SHP-2 inhibition and that these effects can be rescued by constitutively active/Noonan-syndrome-associated forms of SHP-2. Collectively, these results show that SHP-2 functions within the FGF/MAPK pathway to maintain survival of proliferating populations of cardiac progenitor cells.

LVAD-Induced Reverse Remodeling: Basic and Clinical Implications for Myocardial Recovery

BACKGROUND

With improved technology, increasing clinical experience, and expanding indications for use, left ventricular assist devices (LVADs) are assuming a greater role in the care of patients with end-stage heart failure. Early in the course of LVAD use as a bridge to transplant, it became evident that some patients exhibit substantial recovery of ventricular function, which led to the concept of reverse remodeling.

METHODS AND RESULTS

Herein we summarize and integrate insights derived from a multitude of studies that have investigated how LVAD support influences ventricular structural, cellular, extracellular matrix, molecular, biochemical, and metabolic characteristics of the end-stage failing heart. The focus includes a review of the extent and sustainability of reverse remodeling, the important advances in understanding of the pathophysiology of heart failure derived from these studies and the implications of these findings for development of new therapeutic strategies.

CONCLUSION

In brief, studies of LVAD-heart interactions have led to the understanding that although we once considered the end-stage failing heart of patients near death to be irreversibly diseased, when given sufficient mechanical unloading and restoration of more normal neurohormonal milieu, a relatively large degree of myocardial recovery is possible. Comparison of effects on right and left ventricles have provided mechanistic insights by implicating hemodynamic unloading as primarily regulating certain aspects of reverse remodeling, neurohormonal factors as regulating other aspects, and joint regulation of still other aspects. As such these observations have driven a shift of thinking of chronic heart failure as a progressive irreversible disease process to a potentially treatable entity.

Myocardial Insulin-Like Growth Factor-I Gene Expression During Recovery From Heart Failure After Combined Left Ventricular Assist Device and Clenbuterol Therapy

Background— Patients who undergo mechanical support with a left ventricular assist device (LVAD) exhibit reverse remodeling and in some cases recover from heart failure. We have developed a combination therapy using LVAD support combined with pharmacological therapy to maximize reverse remodeling, followed by the β 2 adrenergic agonist clenbuterol. We recently found that clenbuterol induces insulin-like growth factor I (IGF-I) in cardiac myocytes in vitro. The purpose of this study is to examine IGF-I expression in recovery patients after combination therapy.

Methods and Results— Myocardial mRNA levels were determined by real-time quantitative polymerase chain reaction in 12 recovery patients (at LVAD implantation, explantation, and 1 year after explantation). IGF-I mRNA was elevated at the time of LVAD explantation relative to donors, with 2 groups distinguishable: Those with low IGF-I mRNA at implantation who showed significant increase during recovery and those with high IGF-I mRNA at implantation who remained high. Levels returned to normal by 1 year after explantation. Microarray analysis of implantation and explantation samples of recovery patients further revealed elevated IGF-II and IGF binding proteins IGFBP4 and IGFBP6. IGF-I levels correlated with stromal cell-derived factor mRNA measured both in LVAD patients and in a wider cohort of heart failure patients.

Conclusions— The data suggest involvement of elevated myocardial IGF-I mRNA in recovery. IGF-I may act to limit atrophy and apoptosis during reverse remodeling and to promote repair and regeneration in concert with stromal cell derived factor.