Interplay of cell-cell contacts and RhoA/MRTF-A signaling regulates cardiomyocyte identity

Cell-cell and cell-matrix interactions guide organ development and homeostasis by controlling lineage specification and maintenance, but the underlying molecular principles are largely unknown. Here, we show that in human developing cardiomyocytes cell-cell contacts at the intercalated disk connect to remodeling of the actin cytoskeleton by regulating the RhoA-ROCK signaling to maintain an active MRTF/SRF transcriptional program essential for cardiomyocyte identity. Genetic perturbation of this mechanosensory pathway activates an ectopic fat gene program during cardiomyocyte differentiation, which ultimately primes the cells to switch to the brown/beige adipocyte lineage in response to adipogenesis-inducing signals. We also demonstrate by in vivo fate mapping and clonal analysis of cardiac progenitors that cardiac fat and a subset of cardiac muscle arise from a common precursor expressing Isl1 and Wt1 during heart development, suggesting related mechanisms of determination between the two lineages.

Dynamic expression of ganglion cell markers in retinal progenitors during the terminal cell cycle

The vertebrate neural retina contains seven major cell types, which arise from a common multipotent progenitor pool. During neurogenesis, these cells stop cycling, commit to a single fate, and differentiate. The mechanism and order of these steps remain unclear. The first-born type of retinal neurons, ganglion cells (RGCs), develop through the actions of Math5 (Atoh7), Brn3b (Pou4f2) and Islet1 (Isl1) factors, whereas inhibitory amacrine and horizontal precursors require Ptf1a for differentiation. We have examined the link between these markers, and the timing of their expression during the terminal cell cycle, by nucleoside pulse-chase analysis in the mouse retina. We show that G2 phase lasts 1-2 h at embryonic (E) 13.5 and E15.5 stages. Surprisingly, we found that cells expressing Brn3b and/or Isl1 were frequently co-labeled with EdU after a short chase (<1 h) in early embryos (<E14), indicating that these factors, which mark committed RGCs, can be expressed during S or G2 phases. However, during late development (>E15), Brn3b and Isl1 were exclusively expressed in post-mitotic cells, even as new RGCs are still generated. In contrast, Ptf1a and amacrine marker AP2α were detected only after terminal mitosis, at all developmental stages. Using a retroviral tracer in embryonic retinal explants (E12-E13), we identified two-cell clones containing paired ganglion cells, consistent with RGC fate commitment prior to terminal mitosis. Thus, although cell cycle exit and fate determination are temporally correlated during retinal neurogenesis, the order of these events varies according to developmental stage and final cell type.

Functional Diversification of Motor Neuron-specific Isl1 Enhancers during Evolution

Functional diversification of motor neurons has occurred in order to selectively control the movements of different body parts including head, trunk and limbs. Here we report that transcription of Isl1, a major gene necessary for motor neuron identity, is controlled by two enhancers, CREST1 (E1) and CREST2 (E2) that allow selective gene expression of Isl1 in motor neurons. Introduction of GFP reporters into the chick neural tube revealed that E1 is active in hindbrain motor neurons and spinal cord motor neurons, whereas E2 is active in the lateral motor column (LMC) of the spinal cord, which controls the limb muscles. Genome-wide ChIP-Seq analysis combined with reporter assays showed that Phox2 and the Isl1-Lhx3 complex bind to E1 and drive hindbrain and spinal cord-specific expression of Isl1, respectively. Interestingly, Lhx3 alone was sufficient to activate E1, and this may contribute to the initiation of Isl1 expression when progenitors have just developed into motor neurons. E2 was induced by onecut 1 (OC-1) factor that permits Isl1 expression in LMCm neurons. Interestingly, the core region of E1 has been conserved in evolution, even in the lamprey, a jawless vertebrate with primitive motor neurons. All E1 sequences from lamprey to mouse responded equally well to Phox2a and the Isl1-Lhx3 complex. Conversely, E2, the enhancer for limb-innervating motor neurons, was only found in tetrapod animals. This suggests that evolutionarily-conserved enhancers permit the diversification of motor neurons.

During evolution, motor neurons became specialized to control movements of different body parts including head, trunk and limbs. Here we report that two enhancers of Isl1, E1 and E2, are active together with transcription factors in motor neurons. Surprisingly, E1 and its response to transcription factors has been conserved in evolution from the lamprey to man, whereas E2 is only found in animals with limbs. Our study provides an evolutionary example of how functional diversification of motor neurons is achieved by a dynamic interplay between enhancers and transcription factors.

Statin downregulation of miR-652-3p protects endothelium from dyslipidemia by promoting ISL1 expression

BACKGROUND

Aberrant endothelial function is a major contributing factor in cardiovascular disease. Dyslipidemia leads to decreased nitric oxide (NO) bioavailability, an early sign of endothelial failure. Low insulin gene enhancer protein (ISL1) levels decrease healthy NO bioavailability. We hypothesized that the microRNA miR-652-3p negatively regulates endothelial ISL1 expression and that dyslipidemia-induced miR-652-3p upregulation induces aberrant endothelial functioning via ISL1 downregulation.

METHODS

Various in vitro experiments were conducted in human umbilical vein endothelial cells (HUVECs). Luciferase assays were performed in HEK293 cells. We constructed a high-fat diet (HFD) Apoe-/- murine model of dyslipidemia and a rat model of low-density lipoprotein (LDL)-induced dyslipidemia to conduct in vivo and ex vivo experiments.

RESULTS

Luciferase assays confirmed miR-652-3p's targeting of the ISL1 3'-untranslated region (3'-UTR). Simvastatin blocked oxidized LDL (ox-LDL)-induced increases in miR-652-3p and ox-LDL-induced decreases in ISL1 protein expression, endothelial NO synthase (eNOS) activation, and NO production. Simvastatin's effects were abrogated by miR-652-3p overexpression and phenocopied by miR-652-3p inhibition. The dyslipidemic mouse model exhibited increased miR-652-3p and decreased ISL1 protein levels in the endothelium, effects opposed by simvastatin or miR-652-3p inhibition. The impact of simvastatin in vivo was abolished by overexpressing miR-652-3p or knocking-down ISL1. The rat model of dyslipidemia exhibited a similar pattern of miR-652-3p upregulation, attenuated ISL1 protein levels, decreased eNOS activation, and decreased NO production, effects mitigated by simvastatin.

CONCLUSIONS

Dyslipidemia upregulates endothelial miR-652-3p, which decreases ISL1 protein levels, eNOS activation, and NO production. Simvastatin therapy lowers endothelial miR-652-3p expression to protect endothelial function under dyslipidemic conditions.

FHL2 regulates the resolution of tissue damage in chronic inflammatory arthritis

OBJECTIVE

We analysed the role of the adaptor molecule four-and-a-half Lin11, Isl-1 & Mec-3 (LIM) domain protein 2 (FHL2) in the activation of fibroblast-like synoviocytes in human rheumatoid arthritis (RA) and tumour necrosis factor α (TNFα)-dependent animal models of the disease.

METHODS

Synovial tissues of patients with RA and osteoarthritis (OA) as well as hind paw sections from arthritic human TNFα transgenic (hTNFtg) mice and synovial fibroblasts from these were analysed. The effects of cytokines on the expression of FHL2 and disease-relevant matrixmetalloproteases (MMPs) were determined. Analyses of human tissue specimens from patients treated with anti-TNFα as well as anti-TNFα treatment of hTNFtg mice were performed to substantiate the TNFα effects on FHL2 levels. FHL2(-/-) mice and hTNFtg mice (with constitutive or inducible transgene expression) were crossbred to generate TNFα overexpressing FHL2-deficient animals. Signalling pathways were analysed in cells from these mice and in human cells after knock down of FHL2 by western blot.

RESULTS

FHL2 levels were higher in RA than in OA and in hTNFtg than in wild-type mice. Surprisingly, while transforming growth factor (TGF)β-induced FHL2 expression, TNFα suppressed FHL2. In vivo, anti-TNFα treatment led to higher FHL2 levels both in RA patients and hTNFtg mice. The loss of FHL2 increased joint destruction in hTNFtg mice, which was accompanied by elevated MMP-13. In vitro, TNFα-mediated MMP-13 was significantly higher in FHL2(-/-) cells and after knock down of FHL2, which was caused by prolonged p38 MAPK activation.

CONCLUSIONS

These data suggest that FHL2 serves as a protective factor and that, rather than promoting the pathology, the upregulation of FHL2 in RA occurs in frame of a regenerative attempt.

Gata6 restricts Isl1 to the posterior of nascent hindlimb buds through Isl1 cis-regulatory modules

Isl1 is required for two processes during hindlimb development: initiation of the processes directing hindlimb development in the lateral plate mesoderm and configuring posterior hindlimb field in the nascent hindlimb buds. During these processes, Isl1 expression is restricted to the posterior mesenchyme of hindlimb buds. How this dynamic change in Isl1 expression is regulated remains unknown. We found that two evolutionarily conserved sequences, located 3' to the Isl1 gene, regulate LacZ transgene expression in the hindlimb-forming region in mouse embryos. Both sequences contain GATA binding motifs, and expression pattern analysis identified that Gata6 is expressed in the flank and the anterior portion of nascent hindlimb buds. Recent studies have shown that conditional inactivation of Gata6 in mice causes hindlimb-specific pre-axial polydactyly, indicating a role of Gata6 in anterior-posterior patterning of hindlimbs. We studied whether Gata6 restricts Isl1 in the nascent hindlimb bud through the cis-regulatory modules. In vitro experiments demonstrate that GATA6 binds to the conserved GATA motifs in the cis-regulatory modules. GATA6 repressed expression of a luciferase reporter that contains the cis-regulatory modules by synergizing with Zfpm2. Analyses of Gata6 mutant embryos showed that ISL1 levels are higher in the anterior of nascent hindlimb buds than in wild type. Moreover, we detected a greater number of Isl1-transcribing cells in the anterior of nascent hindlimb buds in Gata6 mutants. Our results support a model in which Gata6 contributes to repression of Isl1 expression in the anterior of nascent hindlimb buds.

ARX, PDX1, ISL1, and CDX2 Expression Distinguishes 5 Subgroups of Pancreatic Neuroendocrine Tumors With Correlations to Histology, Hormone Expression, and Outcome

Many pancreatic neuroendocrine tumors (PanNETs) fall into 2 major prognostic subtypes based on DAXX/ATRX-induced alternative lengthening of telomerase phenotype and alpha- and beta-cell-like epigenomic profiles. However, these PanNETs are still flanked by other PanNETs that do not fit into either subtype. Furthermore, despite advanced genotyping, PanNETs are generally not well-characterized in terms of their histologic and hormonal phenotypes. We aimed to identify new subgroups of PanNETs by extending the currently used transcription factor signatures and investigating their correlation with histologic, hormonal, molecular, and prognostic findings. One hundred eighty-five PanNETs (nonfunctioning 165 and functioning 20), resected between 1996 and 2023, were classified into 5 subgroups (A1, A2, B, C, and D) by cluster analysis based on ARX, PDX1, islet-1 (ISL1), and CDX2 expressions and correlated with trabecular vs solid histology, expression of insulin, glucagon, polypeptide (PP), somatostatin, serotonin, gastrin, calcitonin, adrenocorticotropic hormone (ACTH), DAXX/ATRX, MEN1, and alternative lengthening of telomerase status by fluorescence in situ hybridization, and disease-free survival. A1 (46%, ARX+/ISL1+/PDX1-/CDX2-) and A2 (15%, ARX+/ISL1+/PDX1+/CDX2-) showed trabecular histology and glucagon/PP expression, with A2 also showing gastrin expression. B (18%, PDX1+/ISL1+/ARX-/CDX2-) showed solid histology, insulin, and somatostatin expression (P < .001). It included all insulinomas and had the best outcome (P < .01). C (15%, ARX-/PDX1-/ISL1-/CDX2-) showed solid histology and frequent expression of serotonin, calcitonin, and ACTH. D (5%, PDX1+/CDX2+/ISL1-/ARX-) showed solid histology, expressed ACTH/serotonin, and was an independent poor prognosticator (P < .01). Differential expressions of ARX, PDX1, ISL1, and CDX2 stratified PanNETs into 5 subgroups with different histologies, hormone expressions, and outcomes. Subgroups A1 and A2 resembled the alpha-cell-like type, and subgroup B, the beta-cell-like type. Subgroup C with almost no transcription factor signature was unclear in cell lineage, whereas the PDX+/CDX2+ signature of subgroup D suggested a pancreatic/intestinal cell lineage. Assigning PanNETs to the subgroups may help establish the diagnosis, predict the outcome, and guide the treatment.

Transformation of jaw muscle satellite cells to cardiomyocytes

In the embryo a population of progenitor cells known as the second heart field forms not just parts of the heart but also the jaw muscles of the head. Here we show that it is possible to take skeletal muscle satellite cells from jaw muscles of the adult mouse and to direct their differentiation to become heart muscle cells (cardiomyocytes). This is done by exposing the cells to extracellular factors similar to those which heart progenitors would experience during normal embryonic development. By contrast, cardiac differentiation does not occur at all from satellite cells isolated from trunk and limb muscles, which originate from the somites of the embryo. The cardiomyocytes arising from jaw muscle satellite cells express a range of specific marker proteins, beat spontaneously, display long action potentials with appropriate responses to nifedipine, norepinephrine and carbachol, and show synchronized calcium transients. Our results show the existence of a persistent cardiac developmental competence in satellite cells of the adult jaw muscles, associated with their origin from the second heart field of the embryo, and suggest a possible method of obtaining cardiomyocytes from individual patients without the need for a heart biopsy.

Functional prediction of miR-3144-5p in human cardiac myocytes based on transcriptome sequencing and bioinformatics

BACKGROUND

RAN guanine nucleotide release factor (RANGRF) encoding protein MOG1 plays an important role in cardiac arrhythmia, so we intended to investigate the regulatory miRNA of RANGRF and explore its potential regulatory mechanism in arrhythmogenesis.

METHODS

Based on bioinformatic analysis, miR-3144-5p was predicted to be a regulatory miRNA of RANGRF, which were then validated through a dual-luciferase reporter plasmid assay. Subsequently, the expression level of miR-3144-5p in human cardiac myocytes (HCMs) was detected, followed by cell transfection with miR-3144-5p mimics. Transcriptome sequencing was then performed in HCMs with or without transfection. The sequencing results were subjected to bioinformatic analyses, including differentially expressed gene (DEG) analysis, functional enrichment analysis, protein-protein interaction (PPI) network analysis, miRNA-target gene analysis, and miRNA-transcription factor (TF)-target gene coregulatory network analysis.

RESULTS

There really existed a regulatory relation between miR-3144-5p and RANGRF. The expression level of miR-3144-5p was low in HCMs. After cell transfection, miR-3144-5p expression level significantly increased in HCMs. Bioinformatic analyses of the transcriptome sequencing results identified 300 upregulated and 271 downregulated DEGs between miR-3144-5p mimic and control group. The upregulated genes ISL1 and neuregulin 1 (NRG1) were significantly enriched in cardiac muscle cell myoblast differentiation (GO:0060379). CCL21 was one of the hub genes in the PPI network and also a target gene of miR-3144-5p. Moreover, the TF of v-Myc avian myelocytomatosis viral oncogene neuroblastoma-derived homolog (MYCN) was involved in the miR-3144-5p-TF-target gene coregulatory network and interacted with the target genes of miR-3144-5p.

CONCLUSION

ISL1, NRG1, CCL21, and MYCN were differentially expressed in the miR-3144-5p mimic group, suggesting that miR-3144-5p overexpression plays a role in HCMs by regulating these genes and TF. This study may provide new insight into the mechanisms behind the progression of cardiac arrhythmia.

Hepatoprotection in bile duct ligated mice mediated by darbepoetin-α is not caused by changes in hepatobiliary transporter expression

AIMS

Darbepoetin-α (DPO), a long-acting erythropoietin analog, has been shown to protect the liver against cholestatic injury, to exert an antifibrotic effect, and to increase the survival time in a model of common bile duct ligation. Here we evaluate whether these tissue-protective effects are caused by DPO induced regulation of hepatobiliary transporters.

MAIN METHODS

C57BL/6J mice underwent common bile duct ligation and were treated with either DPO or physiological saline. Time dependent (2, 5, 14, 28 days after bile duct ligation) protein expression of different hepatobiliary transporters which have been established to play an important role in hepatocellular (i) bile acid uptake, (ii) bile acid excretion, and (iii) retrograde bile acid efflux were assessed. mRNA and protein expression of Lhx2, an important negative regulator of hepatic stellate cell activation, was determined.

KEY FINDINGS

Saline treated cholestatic mice impress with increased mRNA expression of Lhx2 as a defense mechanism, while there is less need for such an upregulation in mice treated with DPO. Whereas Ntcp (slc10a1) protein expression is suppressed as early as 2 days after bile duct ligation to 40% in untreated animals, DPO treated mice exhibit decreased protein level not before day 5. Similarly, the steady decline of Mrp4 (abcc4) protein level during extrahepatic cholestasis in control treated animals does not occur upon DPO application.

SIGNIFICANCE

The collected data show that DPO affects expression of hepatobilliary transporters during obstructive cholestasis but do not provide sufficient evidence to demonstrate a direct correlation between this regulation and hepatoprotection by DPO.

[Expression of FHL2 during mineralization of human periodontal ligament cells in vitro]

OBJECTIVE

To investigate the expression pattern of FHL2, which is an intracellular signaling transcription molecule during mineralization in cultured human periodontal ligament cells (hPDLCs) in vitro.

METHODS

hPDLCs were cultured in vitro. Test group was cultured with mineral induction media while control group without induction media. 0, 14, 28 days after culture, alizarin red staining was used to measure the mineral nodules formation. Immunocytochemistry was used to examine the expression of FHL2 protein 0 day and 14 days after mineral induction. Meanwhile, mRNA expression level of FHL2 was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) on the 0, 14, 28 days after induction.

RESULTS

14 and 28 days after cultivation, mineral nodules formed and were stained positively with alizarin red staining in test group while no mineral nodule formed in control group. Immunocytochemical results indicated that hPDLCs in test group expressed FHL2 positively. According to RT-PCR results, 14 and 28 days after mineral induction, the expression levels of FHL2 both increased significantly when compared with 0 day (P<0.01), and the expression level at 14 days was 1.4 folds of 0 day.

CONCLUSION

FHL2 protein is found to be involved in the in vitro mineralization of hPDLCs. FHL2 protein may play a role in the differentiation and mineralization of hPDLCs.