Ronin Governs Early Heart Development by Controlling Core Gene Expression Programs

Lpt, trr, and Hcf regulate histone mono- and dimethylation that are essential for Drosophila heart development

Mammalian KMT2C, KMT2D, and HCFC1 are expressed during heart development and have been associated with congenital heart disease, but their roles in heart development remain elusive. We found that the Drosophila Lpt and trr genes encode the N-terminal and C-terminal homologs, respectively, of mammalian KMT2C or KMT2D. Lpt and trr mutant embryos showed reduced cardiac progenitor cells. Silencing of Lpt, trr, or both simultaneously in the heart led to similar abnormal cardiac morphology, tissue fibrosis, and cardiac functional defects. Like KMT2D, Lpt and trr were found to modulate histone H3K4 mono- and dimethylation, but not trimethylation. Investigation of downstream genes regulated by mouse KMT2D in the heart showed that their fly homologs are similarly regulated by Lpt or trr in the fly heart, suggesting that Lpt and trr regulate an evolutionarily conserved transcriptional network for heart development. Moreover, we showed that cardiac silencing of Hcf, the fly homolog of mammalian HCFC1, leads to heart defects similar to those observed in Lpt and trr silencing, as well as reduced H3K4 monomethylation. Our findings suggest that Lpt and trr function together to execute the conserved function of mammalian KMT2C and KMT2D in histone H3 lysine K4 mono- and dimethylation required for heart development. Possibly aided by Hcf, which we show plays a related role in H3K4 methylation during fly heart development.

Glucosylceramide synthase inhibition protects against cardiac hypertrophy in chronic kidney disease

A significant population of patients with chronic kidney disease (CKD) develops cardiac hypertrophy, which can lead to heart failure and sudden cardiac death. Soluble klotho (sKL), the shed ectodomain of the transmembrane protein klotho, protects the heart against hypertrophic growth. We have shown that sKL protects the heart by regulating the formation and function of lipid rafts by targeting the sialic acid moiety of gangliosides, GM1/GM3. Reduction in circulating sKL contributes to an increased risk of cardiac hypertrophy in mice. sKL replacement therapy has been considered but its use is limited by the inability to mass produce the protein. Therefore, alternative methods to protect the heart are proposed. Glucosylation of ceramide catalyzed by glucosylceramide synthase is the entry step for the formation of gangliosides. Here we show that oral administration of a glucosylceramide synthase inhibitor (GCSi) reduces plasma and heart tissue glycosphingolipids, including gangliosides. Administration of GCSi is protective in two mouse models of cardiac stress-induction, one with isoproterenol overstimulation and the other with 5/6 nephrectomy-induced CKD. Treatment with GCSi does not alter the severity of renal dysfunction and hypertension in CKD. These results provide proof of principle for targeting glucosylceramide synthase to decrease gangliosides as a treatment for cardiac hypertrophy. They also support the hypothesis that sKL protects the heart by targeting gangliosides.

Mutations in Hcfc1 and Ronin result in an inborn error of cobalamin metabolism and ribosomopathy

Combined methylmalonic acidemia and homocystinuria (cblC) is the most common inborn error of intracellular cobalamin metabolism and due to mutations in Methylmalonic Aciduria type C and Homocystinuria (MMACHC). Recently, mutations in the transcriptional regulators HCFC1 and RONIN (THAP11) were shown to result in cellular phenocopies of cblC. Since HCFC1/RONIN jointly regulate MMACHC, patients with mutations in these factors suffer from reduced MMACHC expression and exhibit a cblC-like disease. However, additional de-regulated genes and the resulting pathophysiology is unknown. Therefore, we have generated mouse models of this disease. In addition to exhibiting loss of Mmachc, metabolic perturbations, and developmental defects previously observed in cblC, we uncovered reduced expression of target genes that encode ribosome protein subunits. We also identified specific phenotypes that we ascribe to deregulation of ribosome biogenesis impacting normal translation during development. These findings identify HCFC1/RONIN as transcriptional regulators of ribosome biogenesis during development and their mutation results in complex syndromes exhibiting aspects of both cblC and ribosomopathies.

Combined methylmalonic acidemia (MMA) and hyperhomocysteinemias are inborn errors of vitamin B12 metabolism, and mutations in the transcriptional regulators HCFC1 and RONIN (THAP11) underlie some forms of these disorders. Here the authors generated mouse models of a human syndrome due to mutations in RONIN (THAP11) and HCFC1, and show that this syndrome is both an inborn error of vitamin B12 metabolism and displays some features of ribosomopathy.

Ronin governs the metabolic capacity of the embryonic lineage for post-implantation development

During implantation, the murine embryo transitions from a “quiet” into an active metabolic/proliferative state, which kick‐starts the growth and morphogenesis of the post‐implantation conceptus. Such transition is also required for embryonic stem cells to be established from mouse blastocysts, but the factors regulating this process are poorly understood. Here, we show that Ronin plays a critical role in the process by enabling active energy production, and the loss of Ronin results in the establishment of a reversible quiescent state in which naïve pluripotency is promoted. In addition, Ronin fine‐tunes the expression of genes that encode ribosomal proteins and is required for proper tissue‐scale organisation of the pluripotent lineage during the transition from blastocyst to egg cylinder stage. Thus, Ronin function is essential for governing the metabolic capacity so that it can support the pluripotent lineage’s high‐energy demands for cell proliferation and morphogenesis.

The conserved long noncoding RNA CARMA regulates cardiomyocyte differentiation

AIMS

Production of functional cardiomyocytes from pluripotent stem cells requires tight control of the differentiation process. Long noncoding RNAs (lncRNAs) exert critical regulatory function in cell specification during development. In this study, we designed an integrated approach to identify lncRNAs implicated in cardiogenesis in differentiating human embryonic stem cells (ESCs).

METHODS AND RESULTS

We identified CARMA (CARdiomyocyte Maturation-Associated lncRNA), a conserved lncRNA controlling cardiomyocyte differentiation and maturation in human ESCs. CARMA is located adjacent to MIR-1-1HG, the host gene for two cardiogenic miRNAs: MIR1-1 and MIR-133a2, and transcribed in an antisense orientation. The expression of CARMA and the miRNAs is negatively correlated, and CARMA knockdown increases MIR1-1 and MIR-133a2 expression. In addition, CARMA possesses MIR-133a2 binding sites, suggesting the lncRNA could be also a target of miRNA action. Upon CARMA downregulation, MIR-133a2 target protein-coding genes are coordinately downregulated. Among those, we found RBPJ, the gene encoding the effector of the NOTCH pathway. NOTCH has been shown to control a binary cell fate decision between the mesoderm and the neuroectoderm lineages, and NOTCH inhibition leads to enhanced cardiomyocyte differentiation at the expense of neuroectodermal derivatives. Interestingly, two lncRNAs, linc1230 and linc1335, which are known repressors of neuroectodermal specification, were found upregulated upon Notch1 silencing in ESCs. Forced expression of either linc1230 or linc1335 improved ESC-derived cardiomyocyte production. These two lncRNAs were also found upregulated following CARMA knockdown in ESCs.

CONCLUSIONS

Altogether, these data suggest the existence of a network, implicating three newly identified lncRNAs, the two myomirs MIR1-1 and MIR-133a2 and the NOTCH signaling pathway, for the coordinated regulation of cardiogenic differentiation in ESCs.

TRANSLATIONAL PERSPECTIVE

Cardiac dysfunction and heart failure develop secondary to a massive loss of cardiomyocytes in the damaged myocardium. Several avenues have been evaluated to promote regeneration following injury. Cell therapy for heart disease envisages the production of functional cardiomyocytes from differentiating pluripotent stem cells prior transfer into the injured heart muscle. Here, we report the functional characterization of CARMA, a lncRNA implicated in cardiogenesis. CARMA knockdown in differentiating human embryonic stem cells (ESCs) promotes cardiogenic commitment and cardiomyocyte differentiation. CARMA represents therefore a novel target for improving human ESC-derived cardiomyocyte production, and cell-based regenerative strategies for heart disease.

Ronin overexpression induces cerebellar degeneration in a mouse model of ataxia

Spinocerebellar ataxias (SCAs) are a group of genetically heterogeneous inherited neurodegenerative disorders characterized by progressive ataxia and cerebellar degeneration. Here, we used a mouse model to test a possible connection between SCA and Ronin (Thap11), a polyglutamine-containing transcriptional regulator encoded in a region of human chromosome 16q22.1 that has been genetically linked to SCA type 4. We report that transgenic expression of Ronin in mouse cerebellar Purkinje cells leads to detrimental loss of these cells and the development of severe ataxia as early as 10 weeks after birth. Mechanistically, we find that several SCA-causing genes harbor Ronin DNA-binding motifs and are transcriptionally deregulated in transgenic animals. In addition, ectopic expression of Ronin in embryonic stem cells significantly increases the protein level of Ataxin-1, the protein encoded by Atxn1, alterations of which cause SCA type 1. This increase is also seen in the cerebellum of transgenic animals, although the latter was not statistically significant. Hence, our data provide evidence for a link between Ronin and SCAs, and suggest that Ronin may be involved in the development of other neurodegenerative diseases.

Summary: Ronin is a polyglutamine protein encoded in a region of human chromosome 16q22.1 linked to spinocerebellar ataxia type 4. Overexpression of Ronin in mouse cerebellar Purkinje cells leads to their loss and ataxia.

Oligomerization of THAP9 Transposase via Amino-Terminal Domains

Active DNA transposases like the Drosophila P element transposase (DmTNP) undergo oligomerization as a prerequisite for transposition. Human THAP9 (hTHAP9) is a catalytically active but functionally uncharacterized homologue of DmTNP. Here we report (using co-immunoprecipitation, pull down, colocalization, and proximity ligation assays) that both full length and truncated hTHAP9 (corresponding to amino-terminal DNA binding and predicted coiled coil domains) undergo homo-oligomerization, predominantly in the nuclei of HEK293T cells. Interestingly, the oligomerization is shown to be partially mediated by DNA. However, mutating the leucines (either individually or together) or deleting the predicted coiled coil region did not significantly affect oligomerization. Thus, we highlight the importance of DNA and the amino-terminal regions of hTHAP9 for their ability to form higher-order oligomeric states. We also report that Hcf-1, THAP1, THAP10, and THAP11 are possible protein interaction partners of hTHAP9. Elucidating the functional relevance of the different putative oligomeric state(s) of hTHAP9 would help answer questions about its interaction partners as well as its unknown physiological roles.

THAP11 down-regulation may contribute to cardio-protective effects of sevoflurane anesthesia: Evidence from clinical and molecular evidence

This study aimed to explore the potential target of the cardio-protective effect induced by sevoflurane anesthesia based on evidence from clinical samples and in vitro model. Forty patients undergoing mitral valve replacement were randomly allocated to receive sevoflurane or propofol-based anesthesia. Atrial muscle specimens were collected from all patients, of which 5 were used to perform transcriptomics analysis. The cTn-I concentration was tested before, at the end of, and 24 h after surgery. In in vitro study, the expression level of the identified target gene, i.e., THAP11, was studied in H9C2 cells treated with sevoflurane or propofol. Then, we studied cell viability using CCK-8 staining, apoptosis by using flow cytometry, and cell death by lactic acid dehydrogenase (LDH) detection in H9C2 cells exposed to oxygen glucose deprivation/reoxygenation (OGD/R) injury. THAP11 was the most significantly down-regulated gene in the transcriptomics analysis (P < 0.001), as confirmed in validation samples (P = 0.006). THAP11 mRNA levels in atrial muscle specimens were positively associated with cTn-I levels at 24-h postoperatively (determination coefficient = 0.564; P < 0.001). Sevoflurane treatment down-regulated THAP11 in H9C2 cell models, which promoted cell viability, inhibited cell apoptosis, and death in the OGD/R injury cell model. Up-regulation of THAP11 reduced the protective effect of sevoflurane treatment against OGD/R injury. Sevoflurane anesthesia down-regulates the expression of THAP11, which contributes to a cardio-protective effect. THAP11 down-regulation promotes cell viability, and inhibits cell apoptosis and death, thereby protecting again myocardial injury; it may therefore be a novel target for perioperative cardio-protection.

Novel exon-skipping variant disrupting the basic domain of HCFC1 causes intellectual disability without metabolic abnormalities in both male and female patients

HCFC1, a global transcriptional regulator, has been shown to associate with MMACHC expression. Pathogenic variants in HCFC1 cause X-linked combined methylmalonic acidemia and hyperhomocysteinemia, CblX type (MIM# 309541). Recent studies showed that certain variants in HCFC1 are associated with X-linked intellectual disability with mild or absent metabolic abnormalities. Here, we report five subjects (three males, two females) from the same family with a novel predicted loss of function HCFC1 variant. All five patients exhibit developmental delay or intellectual disability/learning difficulty and some dysmorphic features; findings were milder in the female as compared to male subjects. Biochemical studies in all patients did not show methylmalonic acidemia or hyperhomocysteinemia but revealed elevated vitamin B12 levels. Trio exome sequencing of the proband and his parents revealed a maternally inherited novel variant in HCFC1 designated as c.1781_1803 + 3del26insCA (NM_005334). Targeted testing confirmed the presence of the same variant in two half-siblings and maternal great uncle. In silico analysis showed that the variant is expected to reduce the quality of the splice donor site in intron 10 and causes abnormal splicing. Sequencing of proband's cDNA revealed exon 10 skipping. Further molecular studies in the two manifesting females revealed moderate and high skewing of X inactivation. Our results support previous observation that HCFC1 variants located outside the Kelch domain exhibit dissociation of the clinical and biochemical phenotype and cause milder or no metabolic changes. We also show that this novel variant can be associated with a phenotype in females, although with milder severity, but further studies are needed to understand the role of skewed X inactivation among females in this rare disorder. Our work expands the genotypes and phenotypes associated with HCFC1-related disorder.

THAP11F80L cobalamin disorder-associated mutation reveals normal and pathogenic THAP11 functions in gene expression and cell proliferation

Twelve human THAP proteins share the THAP domain, an evolutionary conserved zinc-finger DNA-binding domain. Studies of different THAP proteins have indicated roles in gene transcription, cell proliferation and development. We have analyzed this protein family, focusing on THAP7 and THAP11. We show that human THAP proteins possess differing homo- and heterodimer formation properties and interaction abilities with the transcriptional co-regulator HCF-1. HEK-293 cells lacking THAP7 were viable but proliferated more slowly. In contrast, HEK-293 cells were very sensitive to THAP11 alteration. Nevertheless, HEK-293 cells bearing a THAP11 mutation identified in a patient suffering from cobalamin disorder (THAP11F80L) were viable although proliferated more slowly. Cobalamin disorder is an inborn vitamin deficiency characterized by neurodevelopmental abnormalities, most often owing to biallelic mutations in the MMACHC gene, whose gene product MMACHC is a key enzyme in the cobalamin (vitamin B12) metabolic pathway. We show that THAP11F80L selectively affected promoter binding by THAP11, having more deleterious effects on a subset of THAP11 targets, and resulting in altered patterns of gene expression. In particular, THAP11F80L exhibited a strong effect on association with the MMACHC promoter and led to a decrease in MMACHC gene transcription, suggesting that the THAP11F80L mutation is directly responsible for the observed cobalamin disorder.

Concise Review: Genetic and Epigenetic Regulation of Cardiac Differentiation from Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs), including both embryonic stem cells and induced pluripotent stem cells, are the ideal cell sources for disease modeling, drug discovery, and regenerative medicine. In particular, regenerative therapy with hPSC-derived cardiomyocytes (CMs) is an unmet medical need for the treatment of severe heart failure. Cardiac differentiation protocols from hPSCs are made on the basis of cardiac development in vivo. However, current protocols have yet to yield 100% pure CMs, and their maturity is low. Cardiac development is regulated by the cardiac gene network, including transcription factors (TFs). According to our current understanding of cardiac development, cardiac TFs are sequentially expressed during cardiac commitment in hPSCs. Expression levels of each gene are strictly regulated by epigenetic modifications. DNA methylation, histone modification, and noncoding RNAs significantly influence cardiac differentiation. These complex circuits of genetic and epigenetic factors dynamically affect protein expression and metabolic changes in cardiac differentiation and maturation. Here, we review cardiac differentiation protocols and their molecular machinery, closing with a discussion of the future challenges for producing hPSC-derived CMs. Stem Cells 2019;37:992-1002.