JunB-CBFbeta signaling is essential to maintain sarcomeric Z-disc structure and when defective leads to heart failure

Thallium-induced neurocardiotoxicity in zebrafish: Protective role of adaptive UPR and DNA repair

Thallium (Tl) is a hazardous heavy metal widely used in industrial applications, leading to significant environmental contamination. Tl concentrations in surface waters can reach up to 1520 μg/L, exceeding safe limits and posing risks to aquatic ecosystems and human health. Monovalent thallium [Tl(I)] is highly stable and bioaccumulative, readily accumulating in aquatic organisms, plants, and the human food chain. Exposure to Tl has been associated with neurotoxicity, kidney dysfunction, and cardiovascular diseases, particularly affecting children and pregnant women, and may increase the risk of neurodegenerative diseases and cardiac arrhythmias. However, effective strategies to mitigate Tl toxicity remain lacking. This study establishes a zebrafish embryo model to investigate the toxicological mechanisms of Tl and evaluate the protective effects of IXA4, a selective XBP1 activator. Our results show that Tl exposure increases mortality, reduces hatching rates, impairs swim bladder development, and causes pericardial edema and brain abnormalities. Transcriptomic and qPCR analyses confirm that Tl induces endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR), key pathways involved in cellular toxicity. Co-treatment with IXA4 significantly improves survival rates and developmental outcomes by upregulating DNA repair genes, particularly in the nucleotide excision repair (NER) pathway, thereby reducing cardiac and neural damage. This study provides novel insights into the mechanisms of Tl toxicity, underscores the urgent need for stricter regulatory measures, and highlights IXA4 as a potential intervention for mitigating heavy metal toxicity in aquatic ecosystems.

Loss of lims1 causes aberrant cardiac remodeling and heart failure via activating gp130/Jak1/Stat3 pathway in zebrafish

LIM zinc finger domain containing 1 (LIMS1), an evolutionally conserved LIM domain adaptor protein, is implicated in diverse pathologies, including cancer and neurological disorders. However, its roles in cardiac diseases and the underlying mechanisms remain unclear. Here, we explore the functions and mechanisms of LIMS1 in cardiac remodeling and heart failure. We identify the elevated LIMS1 expression in patients with dilated cardiomyopathy (DCM) and murine cardiomyocytes, suggesting that LIMS1 dysregulation contributes to cardiac pathology. Using CRISPR/Cas9 technology, we generate a zebrafish model of lims1 loss-of-function mutant, which exhibits severe cardiac chamber remodeling, systolic dysfunction, and premature mortality, demonstrating the essential role of lims1 in maintaining cardiac integrity. Transcriptomic profiling reveals the activation of the gp130/Jak1/Stat3 signaling in the lims1-deficient hearts. Strikingly, pharmacological inhibition of Stat3 or c-Fos partially rescues cardiomyopathy phenotypes. Our findings reveal the underlying mechanism of lims1 deficiency-caused heart failure through gp130/Jak1/Stat3 hyperactivation, offering insights into cardiac remodeling and potential therapeutic strategies.

Suppression of RBFox2 by Multiple MiRNAs in Pressure Overload-Induced Heart Failure

Heart failure is the final stage of various cardiovascular diseases and seriously threatens human health. Increasing mediators have been found to be involved in the pathogenesis of heart failure, including the RNA binding protein RBFox2. It participates in multiple aspects of the regulation of cardiac function and plays a critical role in the process of heart failure. However, how RBFox2 itself is regulated remains unclear. Here, we dissected transcriptomic signatures, including mRNAs and miRNAs, in a mouse model of heart failure after TAC surgery. A global analysis showed that an asymmetric alternation in gene expression and a large-scale upregulation of miRNAs occurred in heart failure. An association analysis revealed that the latter not only contributed to the degradation of numerous mRNA transcripts, but also suppressed the translation of key proteins such as RBFox2. With the aid of Ago2 CLIP-seq data, luciferase assays verified that RBFox2 was targeted by multiple miRNAs, including Let-7, miR-16, and miR-200b, which were significantly upregulated in heart failure. The overexpression of these miRNAs suppressed the RBFox2 protein and its downstream effects in cardiomyocytes, which was evidenced by the suppressed alternative splicing of the Enah gene and impaired E-C coupling via the repression of the Jph2 protein. The inhibition of Let-7, the most abundant miRNA family targeting RBFox2, could restore the RBFox2 protein as well as its downstream effects in dysfunctional cardiomyocytes induced by ISO treatment. In all, these findings revealed the molecular mechanism leading to RBFox2 depression in heart failure, and provided an approach to rescue RBFox2 through miRNA inhibition for the treatment of heart failure.

Spen deficiency interferes with Connexin 43 expression and leads to heart failure in zebrafish

Genome-wide association studies identified Spen as a putative modifier of cardiac function, however, the precise function of Spen in the cardiovascular system is not known yet. Here, we analyzed for the first time the in vivo role of Spen in zebrafish and found that targeted Spen inactivation led to progressive impairment of cardiac function in the zebrafish embryo. In addition to diminished cardiac contractile force, Spen-deficient zebrafish embryos developed bradycardia, atrioventricular block and heart chamber fibrillation. Assessment of cardiac-specific transcriptional profiles identified Connexin 43 (Cx43), a cardiac gap junction protein and crucial regulator of cardiomyocyte-to-cardiomyocyte communication, to be significantly diminished in Spen-deficient zebrafish embryos. Similar to the situation in Spen-deficient embryos, Morpholino-mediated knockdown of cx43 in zebrafish resulted in cardiac contractile dysfunction, bradycardia, atrioventricular block and fibrillation of the cardiac chambers. Furthermore, ectopic overexpression of cx43 in Spen deficient embryos led to the reconstitution of cardiac contractile function and suppression of cardiac arrhythmia. Additionally, sensitizing experiments by simultaneously injecting sub-phenotypic concentrations of spen- and cx43-Morpholinos into zebrafish embryos resulted in pathological supra-additive effects. In summary, our findings highlight a crucial role of Spen in controlling cx43 expression and demonstrate the Spen-Cx43 axis to be a vital regulatory cascade that is indispensable for proper heart function in vivo.

Signalosome-Regulated Serum Response Factor Phosphorylation Determining Myocyte Growth in Width Versus Length as a Therapeutic Target for Heart Failure

BACKGROUND

Concentric and eccentric cardiac hypertrophy are associated with pressure and volume overload, respectively, in cardiovascular disease both conferring an increased risk of heart failure. These contrasting forms of hypertrophy are characterized by asymmetrical growth of the cardiac myocyte in mainly width or length, respectively. The molecular mechanisms determining myocyte preferential growth in width versus length remain poorly understood. Identification of the mechanisms governing asymmetrical myocyte growth could provide new therapeutic targets for the prevention or treatment of heart failure.

METHODS

Primary adult rat ventricular myocytes, adeno-associated virus (AAV)-mediated gene delivery in mice, and human tissue samples were used to define a regulatory pathway controlling pathological myocyte hypertrophy. Chromatin immunoprecipitation assays with sequencing and precision nuclear run-on sequencing were used to define a transcriptional mechanism.

RESULTS

We report that asymmetrical cardiac myocyte hypertrophy is modulated by SRF (serum response factor) phosphorylation, constituting an epigenomic switch balancing the growth in width versus length of adult ventricular myocytes in vitro and in vivo. SRF Ser103 phosphorylation is bidirectionally regulated by RSK3 (p90 ribosomal S6 kinase type 3) and PP2A (protein phosphatase 2A) at signalosomes organized by the scaffold protein mAKAPβ (muscle A-kinase anchoring protein β), such that increased SRF phosphorylation activates AP-1 (activator protein-1)-dependent enhancers that direct myocyte growth in width. AAV are used to express in vivo mAKAPβ-derived RSK3 and PP2A anchoring disruptor peptides that block the association of the enzymes with the mAKAPβ scaffold. Inhibition of RSK3 signaling prevents concentric cardiac remodeling induced by pressure overload, while inhibition of PP2A signaling prevents eccentric cardiac remodeling induced by myocardial infarction, in each case improving cardiac function. SRF Ser103 phosphorylation is significantly decreased in dilated human hearts, supporting the notion that modulation of the mAKAPβ-SRF signalosome could be a new therapeutic approach for human heart failure.

CONCLUSIONS

We have identified a new molecular switch, namely mAKAPβ signalosome-regulated SRF phosphorylation, that controls a transcriptional program responsible for modulating changes in cardiac myocyte morphology that occur secondary to pathological stressors. Complementary AAV-based gene therapies constitute rationally-designed strategies for a new translational modality for heart failure.

Genetic compensation prevents myopathy and heart failure in an in vivo model of Bag3 deficiency

Mutations in the molecular co-chaperone Bcl2-associated athanogene 3 (BAG3) are found to cause dilated cardiomyopathy (DCM), resulting in systolic dysfunction and heart failure, as well as myofibrillar myopathy (MFM), which is characterized by protein aggregation and myofibrillar disintegration in skeletal muscle cells. Here, we generated a CRISPR/Cas9-induced Bag3 knockout zebrafish line and found the complete preservation of heart and skeletal muscle structure and function during embryonic development, in contrast to morpholino-mediated knockdown of Bag3. Intriguingly, genetic compensation, a process of transcriptional adaptation which acts independent of protein feedback loops, was found to prevent heart and skeletal muscle damage in our Bag3 knockout model. Proteomic profiling and quantitative real-time PCR analyses identified Bag2, another member of the Bag protein family, significantly upregulated on a transcript and protein level in bag3^-/- mutants. This implied that the decay of bag3 mutant mRNA in homozygous bag3^-/- embryos caused the transcriptional upregulation of bag2 expression. We further demonstrated that morpholino-mediated knockdown of Bag2 in bag3^-/- embryos evoked severe functional and structural heart and skeletal muscle defects, which are similar to Bag3 morphants. However, Bag2 knockdown in bag3^+/+ or bag3^+/- embryos did not result in (cardio-)myopathy. Finally, we found that inhibition of the nonsense-mediated mRNA decay (NMD) machinery by knockdown of upf1, an essential NMD factor, caused severe heart and skeletal muscle defects in bag3^-/- mutants due to the blockade of transcriptional adaptation of bag2 expression. Our findings provide evidence that genetic compensation might vitally influence the penetrance of disease-causing bag3 mutations in vivo.

One form of genetic compensation is described as transcriptional adaptation of gene expression triggered by deleterious gene mutations. Although the precise molecular mechanism that induces genetic compensation needs to be defined, it represents a powerful biological phenomenon that warrants genetic robustness. We find that antisense-mediated knockdown of Bag3 in zebrafish embryos causes heart failure and myopathy. By contrast, CRISPR/Cas9-induced depletion of Bag3 does not result in the abrogation of heart and skeletal muscle function in zebrafish embryos. We find here that transcriptional activation of the Bag family member bag2 is capable of restoring heart and skeletal muscle function in bag3 mutant embryos, whereas this compensatory mechanism is not present in the bag3 morphants. Furthermore, we show that nonsense-mediated decay of bag3 mRNA is the molecular trigger for the compensatory upregulation of bag2. Our study provides evidence that genetic compensation via transcriptional adaptation is a vital modulator of disease peculiarity and penetrance in bag3 mutant zebrafish and that this biological phenomenon might also be active in certain human BAG3 mutation carriers.

Natural constituents from food sources: potential therapeutic agents against muscle wasting

Skeletal muscle wasting is highly correlated with not only reduced quality of life but also higher morbidity and mortality. Although an increasing number of patients are suffering from various kinds of muscle atrophy and weakness, there is still no effective therapy available, and skeletal muscle is considered as an under-medicated organ. Food provided not only essential macronutrients but also functional substances involved in the modulation of the physiological systems of our body. Natural constituents from commonly consumed dietary plants, either extracts or compounds, have attracted more and more attention to be developed as agents for preventing and treating muscle wasting due to their safety and effectiveness, as well as structural diversity. This review provides an overview of the mechanistic aspects of muscle wasting, and summarizes the extracts and compounds from food sources as potential therapeutic agents against muscle wasting.

Loss of the novel Vcp (valosin containing protein) interactor Washc4 interferes with autophagy-mediated proteostasis in striated muscle and leads to myopathy in vivo

VCP/p97 (valosin containing protein) is a key regulator of cellular proteostasis. It orchestrates protein turnover and quality control in vivo, processes fundamental for proper cell function. In humans, mutations in VCP lead to severe myo- and neuro-degenerative disorders such as inclusion body myopathy with Paget disease of the bone and frontotemporal dementia (IBMPFD), amyotrophic lateral sclerosis (ALS) or and hereditary spastic paraplegia (HSP). We analyzed here the in vivo role of Vcp and its novel interactor Washc4/Swip (WASH complex subunit 4) in the vertebrate model zebrafish (Danio rerio). We found that targeted inactivation of either Vcp or Washc4, led to progressive impairment of cardiac and skeletal muscle function, structure and cytoarchitecture without interfering with the differentiation of both organ systems. Notably, loss of Vcp resulted in compromised protein degradation via the proteasome and the macroautophagy/autophagy machinery, whereas Washc4 deficiency did not affect the function of the ubiquitin-proteasome system (UPS) but caused ER stress and interfered with autophagy function in vivo. In summary, our findings provide novel insights into the in vivo functions of Vcp and its novel interactor Washc4 and their particular and distinct roles during proteostasis in striated muscle cells.

Acute toxic responses of embryo-larval zebrafish to zinc pyrithione (ZPT) reveal embryological and developmental toxicity

Zinc pyrithione (ZPT) is widely used in industrial and human daily life, due to its broad antimicrobial spectrum activity. Persistent accumulation of ZTP in the aquatic environment and bioaccumulation in the living organisms attracts more and more attention. However, only very limited information is available so far for the evaluation of systematic toxicity effects of ZPT on multiple organs development. This study intends to deepen our knowledge about the potential toxicity elicited by ZPT by assessing its acute effects on zebrafish (Danio rerio) through morphological, histological and molecular investigations. It has been verified that ZPT exhibits a broad spectrum of toxicity which causes growth retardation and tissue pathological and physiology alternations in heart, liver, eye, notochord, kidney and other organisms of zebrafish. The acute toxicity values of LC50 (95% CI) 96-h is calculated as 0.073 μM. Furthermore, the organ toxicity was verified due to up-regulation of expression of biomarker genes related to organ function and development. In sum, this study demonstrats systematic acute embryological and developmental toxicity of the ZPT on zebrafish embryos/larvae.

Mutation of the Na+/K+-ATPase Atp1a1a.1 causes QT interval prolongation and bradycardia in zebrafish

The genetic underpinnings that orchestrate the vertebrate heart rate are not fully understood yet, but of high clinical importance, since diseases of cardiac impulse formation and propagation are common and severe human arrhythmias. To identify novel regulators of the vertebrate heart rate, we deciphered the pathogenesis of the bradycardia in the homozygous zebrafish mutant hiphop (hip) and identified a missense-mutation (N851K) in Na⁺/K⁺-ATPase α1-subunit (atp1a1a.1). N851K affects zebrafish Na⁺/K⁺-ATPase ion transport capacity, as revealed by in vitro pump current measurements. Inhibition of the Na⁺/K⁺-ATPase in vivo indicates that hip rather acts as a hypomorph than being a null allele. Consequently, reduced Na⁺/K⁺-ATPase function leads to prolonged QT interval and refractoriness in the hip mutant heart, as shown by electrocardiogram and in vivo electrical stimulation experiments. We here demonstrate for the first time that Na⁺/K⁺-ATPase plays an essential role in heart rate regulation by prolonging myocardial repolarization.

MicroRNA 199a-5p induces apoptosis by targeting JunB

MicroRNAs participate in a variety of physiological and pathophysiological processes in various organs including the heart. Our previous work revealed that the level of miR-199a-5p was significantly higher in failing hearts than in control hearts. However, whether it is associated with the progression of heart failure (HF) and mediates cardiomyocyte apoptosis remained unclear. In the present study, we used various biochemical and molecular biological approaches to investigate the changes in miR-199a-5p levels in failing hearts in a rat model induced by acute myocardial infarction. We found that miR-199a-5p levels in the heart increased with the progression of HF, and overexpression of miR-199a-5p significantly increased apoptosis in untreated H9C2 cells and potentiated angiotensin II-induced apoptosis. Thus, our results indicate that miR-199a-5p is involved in the progression of HF and mediates cardiomyocyte apoptosis. We also confirmed that JunB, a member of the activator protein-1 transcription factor family, is one of direct targets of miR-199a-5p via a dual-luciferase reporter assay and mutagenesis on the 3' untranslated region of the JunB gene. Consistent with the above findings, overexpression of JunB in H9c2 cells suppressed cell apoptosis. Based on our findings, miR-199a-5p induces apoptosis by targeting JunB.

Paxillin and Focal Adhesion Kinase (FAK) Regulate Cardiac Contractility in the Zebrafish Heart

An orchestrated interplay of adaptor and signaling proteins at mechano-sensitive sites is essential to maintain cardiac contractility and when defective leads to heart failure. We recently showed that Integrin-linked Kinase (ILK), ß-Parvin and PINCH form the IPP-complex to grant tuned Protein Kinase B (PKB) signaling in the heart. Loss of one of the IPP-complex components results in destabilization of the whole complex, defective PKB signaling and finally heart failure. Two components of IPP, ILK and ß-Parvin directly bind to Paxillin; however, the impact of this direct interaction on the maintenance of heart function is not known yet. Here, we show that targeted gene inactivation of Paxillin results in progressive decrease of cardiac contractility and heart failure in zebrafish without affecting IPP-complex stability and PKB phosphorylation. However, we found that Paxillin deficiency leads to the destabilization of its known binding partner Focal Adhesion Kinase (FAK) and vice versa resulting in degradation of Vinculin and thereby heart failure. Our findings highlight an essential role of Paxillin and FAK in controlling cardiac contractility via the recruitment of Vinculin to mechano-sensitive sites in cardiomyocytes.

Atrogin-1 Deficiency Leads to Myopathy and Heart Failure in Zebrafish

Orchestrated protein synthesis and degradation is fundamental for proper cell function. In muscle, impairment of proteostasis often leads to severe cellular defects finally interfering with contractile function. Here, we analyze for the first time the role of Atrogin-1, a muscle-specific E3 ubiquitin ligase known to be involved in the regulation of protein degradation via the ubiquitin proteasome and the autophagy/lysosome systems, in the in vivo model system zebrafish (Danio rerio). We found that targeted inactivation of zebrafish Atrogin-1 leads to progressive impairment of heart and skeletal muscle function and disruption of muscle structure without affecting early cardiogenesis and skeletal muscle development. Autophagy is severely impaired in Atrogin-1-deficient zebrafish embryos resulting in the disturbance of the cytoarchitecture of cardiomyocytes and skeletal muscle cells. These observations are consistent with molecular and ultrastructural findings in an Atrogin-1 knockout mouse and demonstrate that the zebrafish is a suitable vertebrate model to study the molecular mechanisms of Atrogin-1-mediated autophagic muscle pathologies and to screen for novel therapeutically active substances in high-throughput in vivo small compound screens (SCS).

Junb controls lymphatic vascular development in zebrafish via miR-182

JUNB, a subunit of the AP-1 transcription factor complex, mediates gene regulation in response to a plethora of extracellular stimuli. Previously, JUNB was shown to act as a critical positive regulator of blood vessel development and homeostasis as well as a negative regulator of proliferation, inflammation and tumour growth. Here, we demonstrate that the oncogenic miR-182 is a novel JUNB target. Loss-of-function studies by morpholino-mediated knockdown and the CRISPR/Cas9 technology identify a novel function for both JUNB and its target miR-182 in lymphatic vascular development in zebrafish. Furthermore, we show that miR-182 attenuates foxo1 expression indicating that strictly balanced Foxo1 levels are required for proper lymphatic vascular development in zebrafish. In conclusion, our findings uncover with the Junb/miR-182/Foxo1 regulatory axis a novel key player in governing lymphatic vascular morphogenesis in zebrafish.

Understanding cardiac sarcomere assembly with zebrafish genetics

Mutations in sarcomere genes have been found in many inheritable human diseases, including hypertrophic cardiomyopathy. Elucidating the molecular mechanisms of sarcomere assembly shall facilitate understanding of the pathogenesis of sarcomere-based cardiac disease. Recently, biochemical and genomic studies have identified many new genes encoding proteins that localize to the sarcomere. However, their precise functions in sarcomere assembly and sarcomere-based cardiac disease are unknown. Here, we review zebrafish as an emerging vertebrate model for these studies. We summarize the techniques offered by this animal model to manipulate genes of interest, annotate gene expression, and describe the resulting phenotypes. We survey the sarcomere genes that have been investigated in zebrafish and discuss the potential of applying this in vivo model for larger-scale genetic studies.

Muscle wasting in disease: molecular mechanisms and promising therapies

Atrophy occurs in specific muscles with inactivity (for example, during plaster cast immobilization) or denervation (for example, in patients with spinal cord injuries). Muscle wasting occurs systemically in older people (a condition known as sarcopenia); as a physiological response to fasting or malnutrition; and in many diseases, including chronic obstructive pulmonary disorder, cancer-associated cachexia, diabetes, renal failure, cardiac failure, Cushing syndrome, sepsis, burns and trauma. The rapid loss of muscle mass and strength primarily results from excessive protein breakdown, which is often accompanied by reduced protein synthesis. This loss of muscle function can lead to reduced quality of life, increased morbidity and mortality. Exercise is the only accepted approach to prevent or slow atrophy. However, several promising therapeutic agents are in development, and major advances in our understanding of the cellular mechanisms that regulate the protein balance in muscle include the identification of several cytokines, particularly myostatin, and a common transcriptional programme that promotes muscle wasting. Here, we discuss these new insights and the rationally designed therapies that are emerging to combat muscle wasting.

Transcriptional networks regulating the costamere, sarcomere, and other cytoskeletal structures in striated muscle

Structural abnormalities in striated muscle have been observed in numerous transcription factor gain- and loss-of-function phenotypes in animal and cell culture model systems, indicating that transcription is important in regulating the cytoarchitecture. While most characterized cytoarchitectural defects are largely indistinguishable by histological and ultrastructural criteria, analysis of dysregulated gene expression in each mutant phenotype has yielded valuable information regarding specific structural gene programs that may be uniquely controlled by each of these transcription factors. Linking the formation and maintenance of each subcellular structure or subset of proteins within a cytoskeletal compartment to an overlapping but distinct transcription factor cohort may enable striated muscle to control cytoarchitectural function in an efficient and specific manner. Here we summarize the available evidence that connects transcription factors, those with established roles in striated muscle such as MEF2 and SRF, as well as other non-muscle transcription factors, to the regulation of a defined cytoskeletal structure. The notion that genes encoding proteins localized to the same subcellular compartment are coordinately transcriptionally regulated may prompt rationally designed approaches that target specific transcription factor pathways to correct structural defects in muscle disease.

The myosin-interacting protein SMYD1 is essential for sarcomere organization

Assembly, maintenance and renewal of sarcomeres require highly organized and balanced folding, transport, modification and degradation of sarcomeric proteins. However, the molecules that mediate these processes are largely unknown. Here, we isolated the zebrafish mutant flatline (fla), which shows disturbed sarcomere assembly exclusively in heart and fast-twitch skeletal muscle. By positional cloning we identified a nonsense mutation within the SET- and MYND-domain-containing protein 1 gene (smyd1) to be responsible for the fla phenotype. We found SMYD1 expression to be restricted to the heart and fast-twitch skeletal muscle cells. Within these cell types, SMYD1 localizes to both the sarcomeric M-line, where it physically associates with myosin, and the nucleus, where it supposedly represses transcription through its SET and MYND domains. However, although we found transcript levels of thick filament chaperones, such as Hsp90a1 and UNC-45b, to be severely upregulated in fla, its histone methyltransferase activity - mainly responsible for the nuclear function of SMYD1 - is dispensable for sarcomerogenesis. Accordingly, sarcomere assembly in fla mutant embryos can be reconstituted by ectopically expressing histone methyltransferase-deficient SMYD1. By contrast, ectopic expression of myosin-binding-deficient SMYD1 does not rescue fla mutants, implicating an essential role for the SMYD1-myosin interaction in cardiac and fast-twitch skeletal muscle thick filament assembly.

Transcriptional mechanisms regulating skeletal muscle differentiation, growth and homeostasis

Skeletal muscle is the dominant organ system in locomotion and energy metabolism. Postnatal muscle grows and adapts largely by remodelling pre-existing fibres, whereas embryonic muscle grows by the proliferation of myogenic cells. Recently, the genetic hierarchies of the myogenic transcription factors that control vertebrate muscle development - by myoblast proliferation, migration, fusion and functional adaptation into fast-twitch and slow-twitch fibres - have become clearer. The transcriptional mechanisms controlling postnatal hypertrophic growth, remodelling and functional differentiation redeploy myogenic factors in concert with serum response factor (SRF), JUNB and forkhead box protein O3A (FOXO3A). It has also emerged that there is extensive post-transcriptional regulation by microRNAs in development and postnatal remodelling.

PINCH proteins regulate cardiac contractility by modulating integrin-linked kinase-protein kinase B signaling

Integrin-linked kinase (ILK) is an essential component of the cardiac mechanical stretch sensor and is bound in a protein complex with parvin and PINCH proteins, the so-called ILK-PINCH-parvin (IPP) complex. We have recently shown that inactivation of ILK or β-parvin activity leads to heart failure in zebrafish via reduced protein kinase B (PKB/Akt) activation. Here, we show that PINCH proteins localize at sarcomeric Z disks and costameres in the zebrafish heart and skeletal muscle. To investigate the in vivo role of PINCH proteins for IPP complex stability and PKB signaling within the vertebrate heart, we inactivated PINCH1 and PINCH2 in zebrafish. Inactivation of either PINCH isoform independently leads to instability of ILK, loss of stretch-responsive anf and vegf expression, and progressive heart failure. The predominant cause of heart failure in PINCH morphants seems to be loss of PKB activity, since PKB phosphorylation at serine 473 is significantly reduced in PINCH-deficient hearts and overexpression of constitutively active PKB reconstitutes cardiac function in PINCH morphants. These findings highlight the essential function of PINCH proteins in controlling cardiac contractility by granting IPP/PKB-mediated signaling.