The four and a half LIM-domain 2 controls early cardiac cell commitment and expansion via regulating β-catenin-dependent transcription

Lmpt regulates the function of Drosophila muscle by acting as a repressor of Wnt signaling

BACKGROUND

LIM domain is considered to be important in mediating protein-protein interactions, and members of the LIM protein family can co-regulate tissue-specific gene expression by interacting with different transcription factors. However, its exact function in vivo remains unclear. Our study demonstrates that the LIM protein family member Lmpt may act as a cofactor that interacts with other transcription factors to regulate cellular functions.

METHODS

In this study, we generated Lmpt knockdown Drosophila (Lmpt-KD) using the UAS-Gal4 system. We assessed the lifespan and motility of Lmpt-KD Drosophila and analyzed the expression of muscle-related and metabolism-related genes using qRT-PCR. Additionally, we utilized Western blot and Top-Flash luciferase reporter assay to evaluate the level of the Wnt signaling pathway.

RESULTS

Our study revealed that knockdown of the Lmpt gene in Drosophila resulted in a shortened lifespan and reduced motility. We also observed a significant increase in oxidative free radicals in the fly gut. Furthermore, qRT-PCR analysis indicated that knockdown of Lmpt led to decreased expression of muscle-related and metabolism-related genes in Drosophila, suggesting that Lmpt plays a crucial role in maintaining muscle and metabolic functions. Finally, we found that reduction of Lmpt significantly upregulated the expression of Wnt signaling pathway proteins.

CONCLUSION

Our results demonstrate that Lmpt is essential for motility and survival in Drosophila and acts as a repressor in Wnt signaling.

WNT/β-catenin pathway is a key regulator of cardiac function and energetic metabolism

The WNT/β-catenin pathway is a master regulator of cardiac development and growth, and its activity is low in healthy adult hearts. However, even this low activity is essential for maintaining normal heart function. Acute activation of the WNT/β-catenin signaling cascade is considered to be cardioprotective after infarction through the upregulation of prosurvival genes and reprogramming of metabolism. Chronically high WNT/β-catenin pathway activity causes profibrotic and hypertrophic effects in the adult heart. New data suggest more complex functions of β-catenin in metabolic maturation of the perinatal heart, establishing an adult pattern of glucose and fatty acid utilization. Additionally, low basal activity of the WNT/β-catenin cascade maintains oxidative metabolism in the adult heart, and this pathway is reactivated by physiological or pathological stimuli to meet the higher energy needs of the heart. This review summarizes the current state of knowledge of the organization of canonical WNT signaling and its function in cardiogenesis, heart maturation, adult heart function, and remodeling. We also discuss the role of the WNT/β-catenin pathway in cardiac glucose, lipid metabolism, and mitochondrial physiology.

Fine particulate matter induces heart defects via AHR/ROS-mediated endoplasmic reticulum stress

Accumulating body of evidence indicates that exposure to fine particulate matter (PM_2.5) is closely associated with congenital heart disease in the offspring, but the underlying molecular mechanisms remain to be elucidated. We previously reported that extractable organic matter (EOM) from PM_2.5 induces reactive oxygen species (ROS) overproduction by activating aromatic hydrocarbon receptor (AHR), leading to heart defects in zebrafish embryos. We hypothesized that endoplasmic reticulum (ER) stress might be elicited by the excessive ROS production and thereby contribute to the cardiac developmental toxicity of PM_2.5. In this study, we examined the effects of EOM on endoplasmic reticulum (ER) stress, apoptosis, and Wnt signal pathway in zebrafish embryos, and explored their roles in EOM-induced heart defects. Our results showed that 4-Phenylbutyric acid (4-PBA), a pharmaceutical inhibitor of ER stress, significantly attenuated the EOM-elevated heart malformation rates. Moreover, EOM upregulated the expression levels of ER stress marker genes including CHOP and PDI in the heart of zebrafish embryos, which were counteracted by genetic or pharmaceutical inhibition of AHR activity. The ROS scavenger N-Acetyl-l-cysteine (NAC) also abolished the EOM-induced ER stress. We further demonstrated that both 4-PBA and CHOP genetic knockdown rescued the PM_2.5-induced ROS overproduction, apoptosis and suppression of Wnt signaling. In conclusion, our results indicate that PM_2.5 induces AHR/ROS-mediated ER stress, which leads to apoptosis and Wnt signaling inhibition, ultimately resulting in heart defects.

Recent Advances in Maturation of Pluripotent Stem Cell-Derived Cardiomyocytes Promoted by Mechanical Stretch

Stem cells have significant potential use in tissue regeneration, especially for treating cardiac diseases because of their multi-directional differentiation capability. By mimicking the in vivo physiological environment of native cardiomyocytes during their development and maturation, researchers have been able to induce pluripotent stem cell-derived cardiomyocytes (PSC-CMs) at high purity. However, the phenotype of these PSC-CMs is immature compared with that of adult cardiomyocytes. Various strategies have been explored to improve the maturity of PSC-CMs, such as long-term culturing, mechanical stimuli, chemical stimuli, and combinations of these strategies. Among these strategies, mechanical stretch as a key mechanical stimulus plays an important role in PSC-CM maturation. In this review, the optimal parameters of mechanical stretch, the effects of mechanical stretch on maturation of PSC-CMs, underlying molecular mechanisms as well as existing problems are discussed. Mechanical stretch is a powerful approach to promote the maturation of SC-CMs in terms of morphology, structure, and functionality. Nonetheless, further research efforts are needed to reach a satisfactory standard for clinical applications of PSC-CMs in treating cardiac diseases.

Network-driven discovery yields new insight into Shox2-dependent cardiac rhythm control

The homeodomain transcription factor SHOX2 is involved in the development and function of the heart's primary pacemaker, the sinoatrial node (SAN), and has been associated with cardiac conduction-related diseases such as atrial fibrillation and sinus node dysfunction. To shed light on Shox2-dependent genetic processes involved in these diseases, we established a murine embryonic stem cell (ESC) cardiac differentiation model to investigate Shox2 pathways in SAN-like cardiomyocytes. Differential RNA-seq-based expression profiling of Shox2^+/+ and Shox2^-/- ESCs revealed 94 dysregulated transcripts in Shox2^-/- ESC-derived SAN-like cells. Of these, 15 putative Shox2 target genes were selected for further validation based on comparative expression analysis with SAN- and right atria-enriched genes. Network-based analyses, integrating data from the Mouse Organogenesis Cell Atlas and the Ingenuity pathways, as well as validation in mouse and zebrafish models confirmed a regulatory role for the novel identified Shox2 target genes including Cav1, Fkbp10, Igfbp5, Mcf2l and Nr2f2. Our results indicate that genetic networks involving SHOX2 may contribute to conduction traits through the regulation of these genes.

Intrauterine Programming of Diabetes Induced Cardiac Embryopathy

BACKGROUND

Maternal hyperglycemia is a well-recognized risk factor for fetal congenital heart disease. However, the underlying cellular and molecular mechanisms are not well characterized. We hypothesize that maternal hyperglycemia leading to congenital heart are linked to abnormal DNA methylation and mRNA expression at cardiac specific loci.

METHODS

Hyperglycemia was induced in normal 8-week old CD-1 female mice with a one-time intraperitoneal injection of 150 mg/kg of streptozotocin (STZ) 2 weeks prior to mating. Histological analysis of fetal cardiac morphology was evaluated for malformations on embryonic day (E) 16.5 of control pups and pups exposed to maternal hyperglycemia. We used a massively-parallel sequencing-based methylation sensitive restriction based assay to examine genome-wide cytosine methylation levels at >1.65 million loci in neonatal hearts on post-natal (P) day 0. Functional validation was performed with real time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Cardiac structural defects occurred in 28% of the pups (n=12/45) of hyperglycemic dams versus 7% (n=4/61) of controls. Notable phenotypes were hypoplastic left or right ventricle, double outlet right ventricle, ventricular septal defect, and left ventricular outflow tract obstruction. A 10-fold increase in DNA methylation of gene promoter regions was seen in many cardiac important genes in the experimental versus control P0 neonates and have corresponding decreases in gene expression in 21/32 genes functionally validated.

CONCLUSION

Maternal hyperglycemia alters DNA methylation and mRNA expression of some cardiac genes during heart development. Quantitative, genome-wide assessment of cytosine methylation can be used as a discovery platform to gain insight into the mechanisms of hyperglycemia-induced cardiac anomalies.

Microenvironmental Stiffness Regulates Dental Papilla Cell Differentiation: Implications for the Importance of Fibronectin-Paxillin-β-Catenin Axis

The mechanical stiffness of substrates is recognized to be an important physical cue in the microenvironment of local cellular residents in mammalian species due to their great capacity in regulating cell behavior. Dental papilla cells (DPCs) play an important role in the field of dental tissue engineering for their stem cell-like properties. Therefore, it is essential to provide the suitable microenvironment by combining with the physical cues of biomaterials for DPCs to carry out the function of effective tissue regeneration. However, how the substrate stiffness influences the odontogenic differentiation of DPCs is still unclear. Thus, we fabricated poly(dimethylsiloxane) substrates with varied stiffness for cell behavior. Both cell morphology and focal adhesion were shown to have significant changes in response to varied stiffness. Paxillin, an important protein adapter of focal adhesion kinase protein, was shown to interact with both ectoplasmic fibronectin and cytoplasmic β-catenin by coimmunoprecipitation. The resultant changes of β-catenin by varied stiffness were confirmed by immunofluorescent stain and western blotting. Further, the higher quantity nuclear translocation of β-catenin and the less phospho-β-catenin on the stiff substrate were detected. This nuclear translocation in the stiff substrate finally led to an increased mineralization of DPCs relative to the soft substrate detected by Von Kossa and Alizarin Red stain. Taken together, this work not only points out that the substrate stiffness can regulate the odontogenic differentiation potential of DPCs via fibronectin/paxillin/β-catenin pathway but also provides significant consequence for biomechanical control of cell behavior in cell-based tooth tissue regeneration.

De novo HAPLN1 expression hallmarks Wnt-induced stem cell and fibrogenic networks leading to aggressive human hepatocellular carcinomas

About 20% hepatocellular carcinomas (HCCs) display wild-type β-catenin, enhanced Wnt signaling, hepatocyte dedifferentiation and bad outcome, suggesting a specific impact of Wnt signals on HCC stem/progenitor cells. To study Wnt-specific molecular pathways, cell fates and clinical outcome, we fine-tuned Wnt/β-catenin signaling in liver progenitor cells, using the prototypical Wnt ligand Wnt3a. Cell biology assays and transcriptomic profiling were performed in HepaRG hepatic progenitors exposed to Wnt3a after β-catenin knockdown or Wnt inhibition with FZD8_CRD. Gene expression network, molecular pathology and survival analyses were performed on HCCs and matching non-tumor livers from 70 patients by real-time PCR and tissue micro-array-based immunohistochemistry. Wnt3a reprogrammed liver progenitors to replicating fibrogenic myofibroblast-like cells displaying stem and invasive features. Invasion was inhibited by 30 nM FZD7 and FZD8 CRDs. Translation of these data to human HCCs revealed two tight gene networks associating cell surface Wnt signaling, stem/progenitor markers and mesenchymal commitment. Both networks were linked by Hyaluronan And Proteoglycan Link Protein 1 (HAPLN1), that appeared de novo in aggressive HCCs expressing cytoplasmic β-catenin and stem cell markers. HAPLN1 was independently associated with bad overall and disease-free outcome. In vitro, HAPLN1 was expressed de novo in EPCAM¯/NCAM+ mesoderm-committed progenitors, upon spontaneous epithelial-mesenchymal transition and de-differentiation of hepatocyte-like cells to liver progenitors. In these cells, HAPLN1 knockdown downregulated key markers of mesenchymal cells, such as Snail, LGR5, collagen IV and α-SMA. In conclusion, HAPLN1 reflects a signaling network leading to stemness, mesenchymal commitment and HCC progression.

"Fibrous nests" in human hepatocellular carcinoma express a Wnt-induced gene signature associated with poor clinical outcome

Hepatocellular carcinoma (HCC) is the 3rd cause of cancer-related death worldwide. Most cases arise in a background of chronic inflammation, extracellular matrix (ECM) remodeling, severe fibrosis and stem/progenitor cell amplification. Although HCCs are soft cellular tumors, they may contain fibrous nests within the tumor mass. Thus, the aim of this study was to explore cancer cell phenotypes in fibrous nests. Combined anatomic pathology, tissue microarray and real-time PCR analyses revealed that HCCs (n=82) containing fibrous nests were poorly differentiated, expressed Wnt pathway components and target genes, as well as markers of stem/progenitor cells, such as CD44, LGR5 and SOX9. Consistently, in severe liver fibroses (n=66) and in HCCs containing fibrous nests, weighted correlation analysis revealed a gene network including the myofibroblast marker ACTA2, the basement membrane components COL4A1 and LAMC1, the Wnt pathway members FZD1; FZD7; WNT2; LEF1; DKK1 and the Secreted Frizzled Related Proteins (SFRPs) 1; 2 and 5. Moreover, unbiased random survival forest analysis of a transcriptomic dataset of 247 HCC patients revealed high DKK1, COL4A1, SFRP1 and LAMC1 to be associated with advanced tumor staging as well as with bad overall and disease-free survival. In vitro, these genes were upregulated in liver cancer stem/progenitor cells upon Wnt-induced mesenchymal commitment and myofibroblast differentiation. In conclusion, fibrous nests express Wnt target genes, as well as markers of cancer stem cells and mesenchymal commitment. Fibrous nests embody the specific microenvironment of the cancer stem cell niche and can be detected by routine anatomic pathology analyses.

Protein-protein interactions of the LIM-only protein FHL2 and functional implication of the interactions relevant in cardiovascular disease

FHL2 belongs to the LIM-domain only proteins and contains four and a half LIM domains, each of which are composed of two zinc finger structures. FHL2 exhibits specific interaction with proteins exhibiting diverse functions, including transmembrane receptors, transcription factors and transcription co-regulators, enzymes, and structural proteins. The function of these proteins is regulated by FHL2, which modulates intracellular signal transduction pathways involved in a plethora of cellular tasks. The present review summarizes the current knowledge on the protein interactome of FHL2 and provides an overview of the functional implication of these interactions in apoptosis, migration, and regulation of nuclear receptor function. FHL2 was originally identified in the heart and there is extensive literature available on the role of FHL2 in the cardiovascular system, which is also summarized in this review.

A novel genomic signature with translational significance for human idiopathic pulmonary fibrosis

The bleomycin-induced rodent lung fibrosis model is commonly used to study mechanisms of lung fibrosis and to test potential therapeutic interventions, despite the well recognized dissimilarities to human idiopathic pulmonary fibrosis (IPF). Therefore, in this study, we sought to identify genomic commonalities between the gene expression profiles from 100 IPF lungs and 108 control lungs that were obtained from the Lung Tissue Research Consortium, and rat lungs harvested at Days 3, 7, 14, 21, 28, 42, and 56 after bleomycin instillation. Surprisingly, the highest gene expression similarity between bleomycin-treated rat and IPF lungs was observed at Day 7. At this point of maximal rat-human commonality, we identified a novel set of 12 disease-relevant translational gene markers (C6, CTHRC1, CTSE, FHL2, GAL, GREM1, LCN2, MMP7, NELL1, PCSK1, PLA2G2A, and SLC2A5) that was able to separate almost all patients with IPF from control subjects in our cohort and in two additional IPF/control cohorts (GSE10667 and GSE24206). Furthermore, in combination with diffusing capacity of carbon monoxide measurements, four members of the translational gene marker set contributed to stratify patients with IPF according to disease severity. Significantly, pirfenidone attenuated the expression change of one (CTHRC1) translational gene marker in the bleomycin-induced lung fibrosis model, in transforming growth factor-β1-treated primary human lung fibroblasts and transforming growth factor-β1-treated human epithelial A549 cells. Our results suggest that a strategy focused on rodent model-human disease commonalities may identify genes that could be used to predict the pharmacological impact of therapeutic interventions, and thus facilitate the development of novel treatments for this devastating lung disease.