The RNA-binding protein QKI belongs to the hnRNP K-homology domain protein family, a well-known regulator of pre-mRNA alternative splicing and is associated with several neurodevelopmental disorders. ...Qki is found highly expressed in developing and adult hearts. By employing the human embryonic stem cell (hESC) to cardiomyocyte differentiation system and generating QKI-deficient hESCs (hESCs-QKI
) using CRISPR/Cas9 gene editing technology, we analyze the physiological role of QKI in cardiomyocyte differentiation, maturation, and contractile function. hESCs-QKI
largely maintain normal pluripotency and normal differentiation potential for the generation of early cardiogenic progenitors, but they fail to transition into functional cardiomyocytes. In this work, by using a series of transcriptomic, cell and biochemical analyses, and the Qki-deficient mouse model, we demonstrate that QKI is indispensable to cardiac sarcomerogenesis and cardiac function through its regulation of alternative splicing in genes involved in Z-disc formation and contractile physiology, suggesting that QKI is associated with the pathogenesis of certain forms of cardiomyopathies.
In vertebrate hearts, the ventricular trabecular myocardium develops as a sponge-like network of cardiomyocytes that is critical for contraction and conduction, ventricular septation, papillary ...muscle formation and wall thickening through the process of compaction
. Defective trabeculation leads to embryonic lethality
or non-compaction cardiomyopathy (NCC)
. There are divergent views on when and how trabeculation is initiated in different species. In zebrafish, trabecular cardiomyocytes extrude from compact myocardium
, whereas in chicks, chamber wall thickening occurs before overt trabeculation
. In mice, the onset of trabeculation has not been described, but is proposed to begin at embryonic day 9.0, when cardiomyocytes form radially oriented ribs
. Endocardium-myocardium communication is essential for trabeculation, and numerous signalling pathways have been identified, including Notch
and Neuregulin (NRG)
. Late disruption of the Notch pathway causes NCC
. Whereas it has been shown that mutations in the extracellular matrix (ECM) genes Has2 and Vcan prevent the formation of trabeculae in mice
and the matrix metalloprotease ADAMTS1 promotes trabecular termination
, the pathways involved in ECM dynamics and the molecular regulation of trabeculation during its early phases remain unexplored. Here we present a model of trabeculation in mice that integrates dynamic endocardial and myocardial cell behaviours and ECM remodelling, and reveal new epistatic relationships between the involved signalling pathways. NOTCH1 signalling promotes ECM degradation during the formation of endocardial projections that are critical for individualization of trabecular units, whereas NRG1 promotes myocardial ECM synthesis, which is necessary for trabecular rearrangement and growth. These systems interconnect through NRG1 control of Vegfa, but act antagonistically to establish trabecular architecture. These insights enabled the prediction of persistent ECM and cardiomyocyte growth in a mouse NCC model, providing new insights into the pathophysiology of congenital heart disease.
Ventricular trabeculation and compaction are two of the many essential steps for generating a functionally competent ventricular wall. A significant reduction in trabeculation is usually associated ...with ventricular compact zone deficiencies (hypoplastic wall), which commonly leads to embryonic heart failure and early embryonic lethality. In contrast, hypertrabeculation and lack of ventricular wall compaction (noncompaction) are closely related defects in cardiac embryogenesis associated with left ventricular noncompaction (LVNC), a genetically heterogenous disorder. Here we review recent findings through summarizing several genetically engineered mouse models that have defects in cardiac trabeculation and compaction.
Bone morphogenetic protein 10 (BMP10) is a cardiac peptide growth factor belonging to the transforming growth factor β superfamily that critically controls cardiovascular development, growth, and ...maturation. It has been shown that BMP10 elicits its intracellular signaling through a receptor complex of activin receptor-like kinase 1 with morphogenetic protein receptor type II or activin receptor type 2A. Previously, we generated and characterized a transgenic mouse line expressing BMP10 from the α-myosin heavy chain gene promoter and found that these mice have normal cardiac hypertrophic responses to both physiological and pathological stimuli. In this study, we report that these transgenic mice exhibit significantly reduced levels of cardiomyocyte apoptosis and cardiac fibrosis in response to a prolonged administration of the β-adrenoreceptor agonist isoproterenol. We further confirmed this cardioprotective function with a newly generated conditional Bmp10 transgenic mouse line, in which Bmp10 was activated in adult hearts by tamoxifen. Moreover, the intraperitoneal administration of recombinant human BMP10 was found to effectively protect hearts from injury, suggesting potential therapeutic utility of using BMP10 to prevent heart failure. Gene profiling and biochemical analyses indicated that BMP10 activates the SMAD-mediated canonical pathway and, unexpectedly, also the signal transducer and activator of transcription 3 (STAT3)–mediated signaling pathway both in vivo and in vitro. Additional findings further supported the notion that BMP10's cardioprotective function likely is due to its dual activation of SMAD- and STAT3-regulated signaling pathways, promoting cardiomyocyte survival and suppressing cardiac fibrosis.
Early human heart and brain development simultaneously occur during embryogenesis. Notably, in human newborns, congenital heart defects strongly associate with neurodevelopmental abnormalities, ...suggesting a common gene or complex underlying both cardiogenesis and neurogenesis. However, due to lack of in vivo studies, the molecular mechanisms that govern both early human heart and brain development remain elusive.
Here, we report ARID1A, a DNA-binding subunit of the SWI/SNF epigenetic complex, controls both neurogenesis and cardiogenesis from human embryonic stem cells (hESCs) through distinct mechanisms. Knockout-of-ARID1A (ARID1A
) leads to spontaneous differentiation of neural cells together with globally enhanced expression of neurogenic genes in undifferentiated hESCs. Additionally, when compared with WT hESCs, cardiac differentiation from ARID1A
hESCs is prominently suppressed, whereas neural differentiation is significantly promoted. Whole genome-wide scRNA-seq, ATAC-seq, and ChIP-seq analyses reveal that ARID1A is required to open chromatin accessibility on promoters of essential cardiogenic genes, and temporally associated with key cardiogenic transcriptional factors T and MEF2C during early cardiac development. However, during early neural development, transcription of most essential neurogenic genes is dependent on ARID1A, which can interact with a known neural restrictive silencer factor REST/NRSF.
We uncover the opposite roles by ARID1A to govern both early cardiac and neural development from pluripotent stem cells. Global chromatin accessibility on cardiogenic genes is dependent on ARID1A, whereas transcriptional activity of neurogenic genes is under control by ARID1A, possibly through ARID1A-REST/NRSF interaction.
Doxorubicin (DOX) is an effective anti-cancer therapeutic, but is associated with both acute and late-stage cardiotoxicity. Children are particularly sensitive to DOX-induced heart failure. Here, the ...impact of p53 inhibition on acute vs. late-stage DOX cardiotoxicity was examined in a juvenile model.
Two-week-old MHC-CB7 mice (which express dominant-interfering p53 in cardiomyocytes) and their non-transgenic (NON-TXG) littermates received weekly DOX injections for 5 weeks (25 mg/kg cumulative dose). One week after the last DOX treatment (acute stage), MHC-CB7 mice exhibited improved cardiac function and lower levels of cardiomyocyte apoptosis when compared with the NON-TXG mice. Surprisingly, by 13 weeks following the last DOX treatment (late stage), MHC-CB7 exhibited a progressive decrease in cardiac function and higher rates of cardiomyocyte apoptosis when compared with NON-TXG mice. p53 inhibition blocked transient DOX-induced STAT3 activation in MHC-CB7 mice, which was associated with enhanced induction of the DNA repair proteins Ku70 and Ku80. Mice with cardiomyocyte-restricted deletion of STAT3 exhibited worse cardiac function, higher levels of cardiomyocyte apoptosis, and a greater induction of Ku70 and Ku80 in response to DOX treatment during the acute stage when compared with control animals.
These data support a model wherein a p53-dependent cardioprotective pathway, mediated via STAT3 activation, mitigates DOX-induced myocardial stress during drug delivery. Furthermore, these data suggest an explanation as to how p53 inhibition can result in cardioprotection during drug treatment and, paradoxically, enhanced cardiotoxicity long after the cessation of drug treatment.
Many important signaling pathways rely on multiple ligands. It is unclear if this is a mechanism of safeguard via redundancy or if it serves other functional purposes. In this study, we report unique ...insight into this question by studying the activin receptor-like kinase 1 (ALK1) pathway. Despite its functional importance in vascular development, the physiological ligand or ligands for ALK1 remain to be determined. Using conventional knockout and specific antibodies against bone morphogenetic protein 9 (BMP9) or BMP10, we showed that BMP9 and BMP10 are the physiological, functionally equivalent ligands of ALK1 in vascular development. Timing of expression dictates the in vivo requisite role of each ligand, and concurrent expression results in redundancy. We generated mice (Bmp10 ⁹/⁹) in which the coding sequence of Bmp9 replaces that of Bmp10 . Surprisingly, analysis of Bmp10 ⁹/⁹ mice demonstrated that BMP10 has an exclusive function in cardiac development, which cannot be substituted by BMP9. Our study reveals context-dependent significance in having multiple ligands in a signaling pathway.
Glioblastomas display cellular hierarchies containing tumor-propagating glioblastoma stem cells (GSCs). STAT3 is a critical signaling node in GSC maintenance but molecular mechanisms underlying STAT3 ...activation in GSCs are poorly defined. Here we demonstrate that the bone marrow X-linked (BMX) nonreceptor tyrosine kinase activates STAT3 signaling to maintain self-renewal and tumorigenic potential of GSCs. BMX is differentially expressed in GSCs relative to nonstem cancer cells and neural progenitors. BMX knockdown potently inhibited STAT3 activation, expression of GSC transcription factors, and growth of GSC-derived intracranial tumors. Constitutively active STAT3 rescued the effects of BMX downregulation, supporting that BMX signals through STAT3 in GSCs. These data demonstrate that BMX represents a GSC therapeutic target and reinforces the importance of STAT3 signaling in stem-like cancer phenotypes.
► BMX is preferentially expressed in glioblastoma stem cells ► BMX activates STAT3 signaling specifically in glioblastoma stem cells ► BMX controls the expression of key glioblastoma stem cell transcription factors ► Targeting BMX disrupts tumorigenic potential of glioblastoma stem cells
The heterogeneity of functional cardiomyocytes arises during heart development, which is essential to the complex and highly coordinated cardiac physiological function. Yet the biological and ...physiological identities and the origin of the specialized cardiomyocyte populations have not been fully comprehended. Here we report a previously unrecognised population of cardiomyocytes expressing Dbhgene encoding dopamine beta-hydroxylase in murine heart. We determined how these myocytes are distributed across the heart by utilising advanced single-cell and spatial transcriptomic analyses, genetic fate mapping and molecular imaging with computational reconstruction. We demonstrated that they form the key functional components of the cardiac conduction system by using optogenetic electrophysiology and conditional cardiomyocyte Dbh gene deletion models. We revealed their close relationship with sympathetic innervation during cardiac conduction system formation. Our study thus provides new insights into the development and heterogeneity of the mammalian cardiac conduction system by revealing a new cardiomyocyte population with potential catecholaminergic endocrine function.
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