Loss of melusin is a novel, neuronal NO synthase/FoxO3-independent master switch of unloading-induced muscle atrophy.

BACKGROUND: Unloading/disuse induces skeletal muscle atrophy in bedridden patients and aged people, who cannot prevent it by means of exercise. Because interventions against known atrophy initiators, such as oxidative stress and neuronal NO synthase (nNOS) redistribution, are only partially effective, we investigated the involvement of melusin, a muscle-specific integrin-associated protein and a recognized regulator of protein kinases and mechanotransduction in cardiomyocytes. METHODS: Muscle atrophy was induced in the rat soleus by tail suspension and in the human vastus lateralis by bed rest. Melusin expression was investigated at the protein and transcript level and after treatment of tail-suspended rats with atrophy initiator inhibitors. Myofiber size, sarcolemmal nNOS activity, FoxO3 myonuclear localization, and myofiber carbonylation of the unloaded rat soleus were studied after in vivo melusin replacement by cDNA electroporation, and muscle force, myofiber size, and atrogene expression after adeno-associated virus infection. In vivo interference of exogenous melusin with dominant-negative kinases and other atrophy attenuators (Grp94 cDNA; 7-nitroindazole) on size of unloaded rat myofibers was also explored. RESULTS: Unloading/disuse reduced muscle melusin protein levels to about 50%, already after 6 h in the tail-suspended rat (P < 0.001), and to about 35% after 8 day bed rest in humans (P < 0.05). In the unloaded rat, melusin loss occurred despite of the maintenance of ß1D integrin levels and was not abolished by treatments inhibiting mitochondrial oxidative stress, or nNOS activity and redistribution. Expression of exogenous melusin by cDNA transfection attenuated atrophy of 7 day unloaded rat myofibers (-31%), compared with controls (-48%, P = 0.001), without hampering the decrease in sarcolemmal nNOS activity and the increase in myonuclear FoxO3 and carbonylated myofibers. Infection with melusin-expressing adeno-associated virus ameliorated contractile properties of 7 day unloaded muscles (P ≤ 0.05) and relieved myofiber atrophy (-33%) by reducing Atrogin-1 and MurF-1 transcripts (P ≤ 0.002), despite of a two-fold increase in FoxO3 protein levels (P = 0.03). Atrophy attenuation by exogenous melusin did not result from rescue of Akt, ERK, or focal adhesion kinase activity, because it persisted after co-transfection with dominant-negative kinase forms (P < 0.01). Conversely, melusin cDNA transfection, combined with 7-nitroindazole treatment or with cDNA transfection of the nNOS-interacting chaperone Grp94, abolished 7 day unloaded myofiber atrophy. CONCLUSIONS: Disuse/unloading-induced loss of melusin is an early event in muscle atrophy which occurs independently from mitochondrial oxidative stress, nNOS redistribution, and FoxO3 activation. Only preservation of melusin levels and sarcolemmal nNOS localization fully prevented muscle mass loss, demonstrating that both of them act as independent, but complementary, master switches of muscle disuse atrophy.

Surface functionalization of polyurethane scaffolds mimicking the myocardial microenvironment to support cardiac primitive cells.

Scaffolds populated with human cardiac progenitor cells (CPCs) represent a therapeutic opportunity for heart regeneration after myocardial infarction. In this work, square-grid scaffolds are prepared by melt-extrusion additive manufacturing from a polyurethane (PU), further subjected to plasma treatment for acrylic acid surface grafting/polymerization and finally grafted with laminin-1 (PU-LN1) or gelatin (PU-G) by carbodiimide chemistry. LN1 is a cardiac niche extracellular matrix component and plays a key role in heart formation during embryogenesis, while G is a low-cost cell-adhesion protein, here used as a control functionalizing molecule. X-ray photoelectron spectroscopy analysis shows nitrogen percentage increase after functionalization. O1s and C1s core-level spectra and static contact angle measurements show changes associated with successful functionalization. ELISA assay confirms LN1 surface grafting. PU-G and PU-LN1 scaffolds both improve CPC adhesion, but LN1 functionalization is superior in promoting proliferation, protection from apoptosis and expression of differentiation markers for cardiomyocytes, endothelial and smooth muscle cells. PU-LN1 and PU scaffolds are biodegraded into non-cytotoxic residues. Scaffolds subcutaneously implanted in mice evoke weak inflammation and integrate with the host tissue, evidencing a significant blood vessel density around the scaffolds. PU-LN1 scaffolds show their superiority in driving CPC behavior, evidencing their promising role in myocardial regenerative medicine.

The IKK/NF-κB signaling pathway requires Morgana to drive breast cancer metastasis.

NF-κB is a transcription factor involved in the regulation of multiple physiological and pathological cellular processes, including inflammation, cell survival, proliferation, and cancer cell metastasis. NF-κB is frequently hyperactivated in several cancers, including triple-negative breast cancer. Here we show that NF-κB activation in breast cancer cells depends on the presence of the CHORDC1 gene product Morgana, a previously unknown component of the IKK complex and essential for IκBα substrate recognition. Morgana silencing blocks metastasis formation in breast cancer mouse models and this phenotype is reverted by IκBα downregulation. High Morgana expression levels in cancer cells decrease recruitment of natural killer cells in the first phases of tumor growth and induce the expression of cytokines able to attract neutrophils in the primary tumor, as well as in the pre-metastatic lungs, fueling cancer metastasis. In accordance, high Morgana levels positively correlate with NF-κB target gene expression and poor prognosis in human patients.

Morgana acts as an oncosuppressor in chronic myeloid leukemia.

We recently described morgana as an essential protein able to regulate centrosome duplication and genomic stability, by inhibiting ROCK. Here we show that morgana (+/-) mice spontaneously develop a lethal myeloproliferative disease resembling human atypical chronic myeloid leukemia (aCML), preceded by ROCK hyperactivation, centrosome amplification, and cytogenetic abnormalities in the bone marrow (BM). Moreover, we found that morgana is underexpressed in the BM of patients affected by atypical CML, a disorder of poorly understood molecular basis, characterized by nonrecurrent cytogenetic abnormalities. Morgana is also underexpressed in the BM of a portion of patients affected by Philadelphia-positive CML (Ph(+) CML) caused by the BCR-ABL oncogene, and in this condition, morgana underexpression predicts a worse response to imatinib, the standard treatment for Ph(+) CML. Thus, morgana acts as an oncosuppressor with different modalities: (1) Morgana underexpression induces centrosome amplification and cytogenetic abnormalities, and (2) in Ph(+) CML, it synergizes with BCR-ABL signaling, reducing the efficacy of imatinib treatment. Importantly, ROCK inhibition in the BM of patients underexpressing morgana restored the efficacy of imatinib to induce apoptosis, suggesting that ROCK inhibitors, combined with imatinib treatment, can overcome suboptimal responses in patients in which morgana is underexpressed.

The muscle-specific chaperone protein melusin is a potent cardioprotective agent.

Melusin is a protein selectively expressed in skeletal muscles and heart and highly conserved in vertebrates. Melusin is part of the heat shock protein 90 machinery and acts as molecular chaperone in controlling cardiomyocyte survival and adaptive hypertrophy signaling pathways in the heart in response to different stress conditions. The role of melusin has been extensively investigated in genetically modified mice over the past years disclosing an important cardioprotective function of this unique muscle-specific chaperone protein in different pathological conditions. This review highlights the findings in animal models and the molecular mechanisms underlying melusin cardioprotective function.

Endothelial podosome rosettes regulate vascular branching in tumour angiogenesis.

The mechanism by which angiogenic endothelial cells break the physical barrier of the vascular basement membrane and consequently sprout to form new vessels in mature tissues is unclear. Here, we show that the angiogenic endothelium is characterized by the presence of functional podosome rosettes. These extracellular-matrix-degrading and adhesive structures are precursors of de novo branching points and represent a key feature in the formation of new blood vessels. VEGF-A stimulation induces the formation of endothelial podosome rosettes by upregulating integrin α6ß1. In contrast, the binding of α6ß1 integrin to the laminin of the vascular basement membrane impairs the formation of podosome rosettes by restricting α6ß1 integrin to focal adhesions and hampering its translocation to podosomes. Using an ex vivo sprouting angiogenesis assay, transgenic and knockout mouse models and human tumour sample analysis, we provide evidence that endothelial podosome rosettes control blood vessel branching and are critical regulators of pathological angiogenesis.

Overexpression of the muscle-specific protein, melusin, protects from cardiac ischemia/reperfusion injury.

Melusin is a muscle-specific protein which interacts with ß1 integrin cytoplasmic domain and acts as chaperone protein. Its overexpression induces improved resistance to cardiac overload delaying left ventricle dilation and reducing the occurrence of heart failure. Here, we investigated possible protective effect of melusin overexpression against acute ischemia/reperfusion (I/R) injury with or without Postconditioning cardioprotective maneuvers. Melusin transgenic (Mel-TG) mice hearts were subjected to 30-min global ischemia followed by 60-min reperfusion. Interestingly, infarct size was reduced in Mel-TG mice hearts compared to wild-type (WT) hearts (40.3 ± 3.5 % Mel-TG vs. 59.5 ± 3.8 % WT hearts; n = 11 animals/group; P < 0.05). The melusin protective effect was also demonstrated by measuring LDH release, which was 50 % lower in Mel-TG compared to WT. Mel-TG hearts had a higher baseline level of AKT, ERK1/2 and GSK3ß phosphorylation, and displayed increased phospho-kinases level after I/R compared to WT mice. Post-ischemic Mel-TG hearts displayed also increased levels of the anti-apoptotic factor phospho-BAD. Importantly, pharmacological inhibition of PI3K/AKT (Wortmannin) and ERK1/2 (U0126) pathways abrogated the melusin protective effect. Notably, HSP90, a chaperone known to protect heart from I/R injury, showed high levels of expression in the heart of Mel-TG mice suggesting a possible collaboration of this molecule with AKT/ERK/GSK3ß pathways in the melusin-induced protection. Postconditioning, known to activate AKT/ERK/GSK3ß pathways, significantly reduced IS and LDH release in WT hearts, but had no additive protective effects in Mel-TG hearts. These findings implicate melusin as an enhancer of AKT and ERK pathways and as a novel player in cardioprotection from I/R injury.

Keep your heart in shape: molecular chaperone networks for treating heart disease.

Despite major advances in the treatment of cardiac diseases, there is still a great need for drugs capable of counteracting the deterioration of cardiac muscle function in congestive heart failure. The role of misfolded protein accumulation as a causal event in the physiopathology of common cardiac diseases is an important emerging concept. Indeed, diverse stress conditions, including mechanical stretching and oxidative stress, can induce misfolded protein accumulation, causing cardiomyocyte death. Cells react to these stress conditions by activating molecular chaperones, a class of proteins that represents an endogenous salvage machinery, essential for rescuing physiological cell functions and sustaining cell survival. Chaperones, also known as heat shock proteins (Hsps), prevent accumulation of damaged proteins by promoting either their refolding or degradation via the proteasome or the autophagosome systems. In addition, molecular chaperones play a key role in intracellular signalling by controlling conformational changes required for activation/deactivation of signalling proteins, and their assembly in specific signalosome complexes. The key role of molecular chaperones in heart function is highlighted by the fact that a number of genetic mutations in chaperone proteins result in different forms of cardiomyopathies. Moreover, a considerable amount of experimental evidence indicates that increasing expression of chaperone proteins leads to an important cardio-protective role in ischaemia/reperfusion injury, heart failure, and arrhythmia, implicating these molecules as potential innovative therapeutic agents.

Targeting myocardial remodelling to develop novel therapies for heart failure: a position paper from the Working Group on Myocardial Function of the European Society of Cardiology.

The failing heart is characterized by complex tissue remodelling involving increased cardiomyocyte death, and impairment of sarcomere function, metabolic activity, endothelial and vascular function, together with increased inflammation and interstitial fibrosis. For years, therapeutic approaches for heart failure (HF) relied on vasodilators and diuretics which relieve cardiac workload and HF symptoms. The introduction in the clinic of drugs interfering with beta-adrenergic and angiotensin signalling have ameliorated survival by interfering with the intimate mechanism of cardiac compensation. Current therapy, though, still has a limited capacity to restore muscle function fully, and the development of novel therapeutic targets is still an important medical need. Recent progress in understanding the molecular basis of myocardial dysfunction in HF is paving the way for development of new treatments capable of restoring muscle function and targeting specific pathological subsets of LV dysfunction. These include potentiating cardiomyocyte contractility, increasing cardiomyocyte survival and adaptive hypertrophy, increasing oxygen and nutrition supply by sustaining vessel formation, and reducing ventricular stiffness by favourable extracellular matrix remodelling. Here, we consider drugs such as omecamtiv mecarbil, nitroxyl donors, cyclosporin A, SERCA2a (sarcoplasmic/endoplasmic Ca(2 +) ATPase 2a), neuregulin, and bromocriptine, all of which are currently in clinical trials as potential HF therapies, and discuss novel molecular targets with potential therapeutic impact that are in the pre-clinical phases of investigation. Finally, we consider conceptual changes in basic science approaches to improve their translation into successful clinical applications.

Morgana acts as a proto-oncogene through inhibition of a ROCK-PTEN pathway.

Morgana/CHP-1 is a ubiquitously expressed protein able to inhibit ROCK II kinase activity. We have previously demonstrated that morgana haploinsufficiency leads to multiple centrosomes, genomic instability, and higher susceptibility to tumour development. While a large fraction of human cancers has shown morgana down-regulation, a small subset of tumours was shown to express high morgana levels. Here we demonstrate that high morgana expression in different breast cancer subtypes correlates with high tumour grade, mitosis number, and lymph node positivity. Moreover, morgana overexpression induces transformation in NIH-3T3 cells and strongly protects them from various apoptotic stimuli. From a mechanistic point of view, we demonstrate that morgana causes PTEN destabilization, by inhibiting ROCK activity, hence triggering the PI3K/AKT survival pathway. In turn, morgana down-regulation in breast cancer cells that express high morgana levels increases PTEN expression and leads to sensitization of cells to chemotherapy.

ESC Working Group on Myocardial Function Position Paper: how to study the right ventricle in experimental models.

The right ventricle has become an increasing focus in cardiovascular research. In this position paper, we give a brief overview of the specific pathophysiological features of the right ventricle, with particular emphasis on functional and molecular modifications as well as therapeutic strategies in chronic overload, highlighting the differences from the left ventricle. Importantly, we put together recommendations on promising topics of research in the field, experimental study design, and functional evaluation of the right ventricle in experimental models, from non-invasive methodologies to haemodynamic evaluation and ex vivo set-ups.

Melusin protects from cardiac rupture and improves functional remodelling after myocardial infarction.

AIMS: Melusin is a muscle-specific chaperone protein whose expression is required for a compensatory hypertrophy response to pressure overload. Here, we evaluated the consequences of melusin overexpression in the setting of myocardial infarction (MI) using a comprehensive multicentre approach. METHODS AND RESULTS: Mice overexpressing melusin in the heart (TG) and wild-type controls (WT) were subjected to permanent LAD ligation and both the acute response (Day 3) and subsequent remodelling (2 weeks) were examined. Mortality in wild-type mice was significant between Days 3 and 7, primarily due to cardiac rupture, but melusin's overexpression strongly reduced mortality (43.2% in wild-type vs. 27.3% in melusin-TG, P = 0.005). At Day 3 after MI, a time point preceding the mortality peak, TG hearts had increased heat shock protein 70 expression, increased ERK1/2 signalling, reduced cardiomyocyte hyper-contractility and inflammatory cell infiltrates, and increased matricellular protein expression in the infarcted area. At 2 weeks after MI, melusin overexpression conferred a favourable adaptive remodelling characterized by reduced left ventricle dilatation and better preserved contractility in the presence of a comparable degree of hypertrophy. Adaptive remodelling in melusin TG mice was characterized by reduced apoptosis and fibrosis as well as increased cardiomyocyte contractility. CONCLUSIONS: Consistent with its function as a chaperone protein, melusin overexpression exerts a dual protective action following MI reducing an array of maladaptive processes. In the early phase after MI, reduced inflammation and myocyte remodelling protect against cardiac rupture. Chronically, reduced myocyte loss and matrix remodelling, with preserved myocyte contractility, confer adaptive LV remodelling.

Key role of ERK1/2 molecular scaffolds in heart pathology.

The ability of cardiomyocytes to detect mechanical and humoral stimuli is critical for adaptation of the myocardium in response to new conditions and for sustaining the increased workload during stress. While certain stimuli mediate a beneficial adaptation to stress conditions, others result in maladaptive remodelling, ultimately leading to heart failure. Specific signalling pathways activating either adaptive or maladaptive cardiac remodelling have been identified. Paradoxically, however, in a number of cases, the transduction pathways involved in such opposing responses engage the same signalling proteins. A notable example is the Raf-MEK1/2-ERK1/2 signalling pathway that can control both adaptive and maladaptive remodelling. ERK1/2 signalling requires a signalosome complex where a scaffold protein drives the assembly of these three kinases into a linear pathway to facilitate their sequential phosphorylation, ultimately targeting specific effector molecules. Interestingly, a number of different Raf-MEK1/2-ERK1/2 scaffold proteins have been identified, and their role in determining the adaptive or maladaptive cardiac remodelling is a promising field of investigation for the development of therapeutic strategies capable of selectively potentiating the adaptive response.

Extracellular matrix, integrins, and growth factors as tailors of the stem cell niche.

It is widely acknowledged that integrins, the major receptors for the extracellular matrix (ECM) proteins, exert an extensive crosstalk with many growth factor and cytokine receptors. Among them, growth factor receptors, such as the EGFR, MET, PDGFR and VEGFR, and the IL-3 receptor have been shown to be physically and functionally associated to integrins. The connection between integrins and other transmembrane receptors is bidirectional, integrins being essential for receptor signalling, and receptors being involved in regulation of integrin expression or activation. Moreover, there is accumulating evidence for direct binding of specific growth factors and morphogens to the ECM proteins, suggesting that ECM might spatially integrate different types of signals in a specific microenvironment, facilitating integrin/transmembrane receptors connection. These interactions are crucial in controlling a variety of cell behaviours including proliferation, survival and differentiation. The increasing interest for cell therapy in regenerative medicine has recently emphasized the role of cell-ECM adhesion as stem cell determinant. The relevance of ECM, integrins and growth factor receptor network in the establishment of stem cell niche, in maintenance of stem cells and in their differentiation will be analyzed in the present review.

Morgana and melusin: two fairies chaperoning signal transduction.

Chaperones and scaffold proteins are key elements involved in controlling the assembly of molecular complexes required for coordinated signal transduction. Here we describe morgana and melusin, two phylogenetically conserved chaperones that cooperate with Hsp90 and regulate signal transduction in important physiopathological processes. While morgana is ubiquitously expressed, melusin expression is restricted to striated muscles. Despite high sequence homology, the two chaperones have distinct functions. Morgana controls genomic stability by regulating the centrosome cycle via ROCKII kinase. Melusin, however, organizes ERK signal transduction in cardiomyocytes and regulates cardiac compensatory hypertrophy in response to different stress stimuli.

ERK1/2 activation in heart is controlled by melusin, focal adhesion kinase and the scaffold protein IQGAP1.

Extracellular signal-regulated kinase 1/2 (ERK1/2) signalling is a key pathway in cardiomyocyte hypertrophy and survival in response to many different stress stimuli. We have previously characterized melusin as a muscle-specific chaperone protein capable of ERK1/2 signalling activation in the heart. Here, we show that in the heart, melusin forms a supramolecular complex with the proto-oncogene c-Raf, MEK1/2 (also known as MAPKK1/2) and ERK1/2 and that melusin-bound mitogen-activated protein kinases (MAPKs) are activated by pressure overload. Moreover, we demonstrate that both focal adhesion kinase (FAK) and IQ motif-containing GTPase activating protein 1 (IQGAP1), a scaffold protein for the ERK1/2 signalling cascade, are part of the melusin complex and are required for ERK1/2 activation in response to pressure overload. Finally, analysis of isolated neonatal cardiomyocytes indicates that both FAK and IQGAP1 regulate melusin-dependent cardiomyocyte hypertrophy and survival through ERK1/2 activation.

Towards a re-definition of 'cardiac hypertrophy' through a rational characterization of left ventricular phenotypes: a position paper of the Working Group 'Myocardial Function' of the ESC.

Many primary or secondary diseases of the myocardium are accompanied with complex remodelling of the cardiac tissue that results in increased heart mass, often identified as cardiac 'hypertrophy'. Although there have been numerous attempts at defining such 'hypertrophy', the present paper delineates the reasons as to why current definitions of cardiac hypertrophy remain unsatisfying. Based on a brief review of the underlying pathophysiology and tissue and cellular events driving myocardial remodelling with or without changes in heart dimensions, as well as current techniques to detect such changes, we propose to restrict the use of the currently popular term 'hypertrophy' to cardiac myocytes that may or may not accompany the more complex tissue rearrangements leading to changes in shape or size of the ventricles, more broadly referred to as 'remodelling'. We also discuss the great potential of genetically modified (mouse) models as tools to define the molecular pathways leading to the different forms of left ventricle remodelling. Finally, we present an algorithm for the stepwise assessment of myocardial phenotypes applicable to animal models using well-established imaging techniques and propose a list of parameters most suited for a critical evaluation of such pathophysiological phenomena in mouse models. We believe that this effort is the first step towards a much auspicated unification of the terminology between the experimental and the clinical cardiologists.

IQGAP1 regulates ERK1/2 and AKT signalling in the heart and sustains functional remodelling upon pressure overload.

AIMS: The Raf-MEK1/2-ERK1/2 (ERK1/2-extracellular signal-regulated kinases 1/2) signalling cascade is crucial in triggering cardiac responses to different stress stimuli. Scaffold proteins are key elements in coordinating signalling molecules for their appropriate spatiotemporal activation. Here, we investigated the role of IQ motif-containing GTPase-activating protein 1 (IQGAP1), a scaffold for the ERK1/2 cascade, in heart function and remodelling in response to pressure overload. METHODS AND RESULTS: IQGAP1-null mice have unaltered basal heart function. When subjected to pressure overload, IQGAP1-null mice initially develop a compensatory hypertrophy indistinguishable from that of wild-type (WT) mice. However, upon a prolonged stimulus, the hypertrophic response develops towards a thinning of left ventricular walls, chamber dilation, and a decrease in contractility, in an accelerated fashion compared with WT mice. This unfavourable cardiac remodelling is characterized by blunted reactivation of the foetal gene programme, impaired cardiomyocyte hypertrophy, and increased cardiomyocyte apoptosis. Analysis of signalling pathways revealed two temporally distinct waves of both ERK1/2 and AKT phosphorylation peaking, respectively, at 10 min and 4 days after aortic banding in WT hearts. IQGAP1-null mice show strongly impaired phosphorylation of MEK1/2-ERK1/2 and AKT following 4 days of pressure overload, but normal activation of these kinases after 10 min. Pull-down experiments indicated that IQGAP1 is able to bind the three components of the ERK cascade, namely c-Raf, MEK1/2, and ERK1/2, as well as AKT in the heart. CONCLUSION: These data demonstrate, for the first time, a key role for the scaffold protein IQGAP1 in integrating hypertrophy and survival signals in the heart and regulating long-term left ventricle remodelling upon pressure overload.