Connexin mutant embryonic stem cells and human diseases

Basic Research Approaches to Evaluate Cardiac Arrhythmia in Heart Failure and Beyond

Patients with heart failure often develop cardiac arrhythmias. The mechanisms and interrelations linking heart failure and arrhythmias are not fully understood. Historically, research into arrhythmias has been performed on affected individuals or in vivo (animal) models. The latter however is constrained by interspecies variation, demands to reduce animal experiments and cost. Recent developments in in vitro induced pluripotent stem cell technology and in silico modelling have expanded the number of models available for the evaluation of heart failure and arrhythmia. An agnostic approach, combining the modalities discussed here, has the potential to improve our understanding for appraising the pathology and interactions between heart failure and arrhythmia and can provide robust and validated outcomes in a variety of research settings. This review discusses the state of the art models, methodologies and techniques used in the evaluation of heart failure and arrhythmia and will highlight the benefits of using them in combination. Special consideration is paid to assessing the pivotal role calcium handling has in the development of heart failure and arrhythmia.

Connexin Gap Junctions and Hemichannels in Modulating Lens Redox Homeostasis and Oxidative Stress in Cataractogenesis

The lens is continuously exposed to oxidative stress insults, such as ultraviolet radiation and other oxidative factors, during the aging process. The lens possesses powerful oxidative stress defense systems to maintain its redox homeostasis, one of which employs connexin channels. Connexins are a family of proteins that form: (1) Hemichannels that mediate the communication between the intracellular and extracellular environments, and (2) gap junction channels that mediate cell-cell communication between adjacent cells. The avascular lens transports nutrition and metabolites through an extensive network of connexin channels, which allows the passage of small molecules, including antioxidants and oxidized wastes. Oxidative stress-induced post-translational modifications of connexins, in turn, regulates gap junction and hemichannel permeability. Recent evidence suggests that dysfunction of connexins gap junction channels and hemichannels may induce cataract formation through impaired redox homeostasis. Here, we review the recent advances in the knowledge of connexin channels in lens redox homeostasis and their response to cataract-related oxidative stress by discussing two major aspects: (1) The role of lens connexins and channels in oxidative stress and cataractogenesis, and (2) the impact and underlying mechanism of oxidative stress in regulating connexin channels.

Bisphenol S enhances gap junction intercellular communication in ovarian theca cells

Gap junction intercellular communication (GJIC) is necessary for ovarian function, and it is temporospatially regulated during follicular development and ovulation. At outermost layer of the antral follicle, theca cells provide structural, steroidogenic, and vascular support. Inter- and extra-thecal GJIC is required for intrafollicular trafficking of signaling molecules. Because GJIC can be altered by hormones and endocrine disrupting chemicals (EDCs), we tested if any of five common EDCs (bisphenol A (BPA), bisphenol S (BPS), bisphenol F (BPF), perfluorooctanesulfonic acid (PFOS), and triphenyltin chloride (TPT)) can interfere with theca cell GJIC. Since most chemicals are reported to repress GJIC, we hypothesized that all chemicals tested, within environmentally relevant human exposure concentrations, will inhibit theca cell GJICs. To evaluate this hypothesis, we used a scrape loading/dye transfer assay. BPS, but no other chemical tested, enhanced GJIC in a dose- and time-dependent manner in ovine primary theca cells. A signal-protein inhibitor approach was used to explore the GJIC-modulatory pathways involved. Phospholipase C and mitogen-activated protein kinase (MAPK) inhibitors significantly attenuated BPS-induced enhanced GJIC. Human theca cells were used to evaluate translational relevance of these findings. Human primary theca cells had a ∼40% increase in GJIC in response to BPS, which was attenuated with a MAPK inhibitor, suggestive of a conserved mechanism. Upregulation of GJIC could result in hyperplasia of the theca cell layer or prevent ovulation by holding the oocyte in meiotic arrest. Further studies are necessary to understand in vitro to in vivo translatability of these findings on follicle development and fertility outcomes.

Connexin 43 Functions as a Positive Regulator of Stem Cell Differentiation into Definitive Endoderm and Pancreatic Progenitors

Efficient stem cell differentiation into pancreatic islet cells is of critical importance for the development of cell replacement therapies for diabetes. Here, we identify the expression pattern of connexin 43 (Cx43), a gap junction (GJ) channel protein, in human embryonic stem cell (hESC)-derived definitive endoderm (DE) and primitive gut tube cells, representing early lineages for posterior foregut (PF), pancreatic progenitors (PP), pancreatic endocrine progenitors (PE), and islet cells. As the function of GJ channels is dependent on their gating status, we tested the impact of supplementing hESC-derived PP cell cultures with AAP10, a peptide that promotes Cx43 GJ channel opening. We found that this treatment promotes the expression of DE markers FoxA2 and Sox17, leads to a more efficient derivation of DE, and improves the yield of PF, PP, and PE cells. These results demonstrate a functional involvement of GJ channels in the differentiation of embryonic stem cells into pancreatic cell lineages.

Therapeutic strategies targeting connexins

The connexin family of channel-forming proteins is present in every tissue type in the human anatomy. Connexins are best known for forming clustered intercellular channels, structurally known as gap junctions, where they serve to exchange members of the metabolome between adjacent cells. In their single-membrane hemichannel form, connexins can act as conduits for the passage of small molecules in autocrine and paracrine signalling. Here, we review the roles of connexins in health and disease, focusing on the potential of connexins as therapeutic targets in acquired and inherited diseases as well as wound repair, while highlighting the associated clinical challenges.

Connexins in the Central Nervous System: Physiological Traits and Neuroprotective Targets

Cell-to-cell interaction and cell-to-extracellular environment communication are emerging as new therapeutic targets in neurodegenerative disorders. Dynamic expression of connexins leads to distinctive hemichannels and gap junctions, characterized by cell-specific conduction, exchange of stimuli or metabolites, and particular channel functions. Herein, we briefly reviewed classical physiological traits and functions of connexins, hemichannels, and gap junctions, in order to discuss the controversial role of these proteins and their mediated interactions during neuroprotection, with a particular focus on Cx43-based channels. We pointed out the contribution of connexins in neural cells populations during neurodegenerative processes to explore potential neuroprotective therapeutic applications.

The role of histone modification and a regulatory single-nucleotide polymorphism (rs2071166) in the Cx43 promoter in patients with TOF

Abnormal level of Cx43 expression could result in CHD. Epigenetic modification and disease-associated, non-coding SNPs might influence gene transcription and expression. Our study aimed to determine the role of histone modification and an rSNP (rs2071166) in the Cx43 promoter in patients with TOF. Our results indicate that H3K18ac bind to Cx43 promoter and that their levels are reduced in TOF patients relative to controls. The relationship between the non-coding SNP in the Cx43 gene and TOF patients was evaluated in 158 patients and 300 controls. The C allele of rs2071166 was confirmed to result in an increased risk of TOF (OR = 1.586, 95%CI 1.149–2.189). Individuals with the CC genotype at rs2071166 also showed a significant susceptibility to TOF (OR = 2.961, 95%CI 1.452–6.038). The mRNA level in TOF who were CC genotype was lower than that in patients with the AA/AC genotype. Functional analysis in cells and transgenic zebrafish models showed that rs2071166 decreased the activity of the promoter and could block the interaction between RXRα and RARE. This is the first study to illustrate that epigenetic modification and an rSNP in the Cx43 promoter region play a critical role in TOF by impacting the transcriptional activity and expression level of Cx43.

Role of Specificity Protein-1 and Activating Protein-2 Transcription Factors in the Regulation of the Gap Junction Protein Beta-2 Gene in the Epididymis of the Rat

In prepubertal rats, connexin 26 (GJB2) is expressed between adjacent columnar cells of the epididymis. At 28 days of age, when columnar cells differentiate into adult epithelial cell types, Gjb2 mRNA levels decrease to barely detectable levels. There is no information on the regulation of GJB2 in the epididymis. The present study characterized regulation of the Gjb2 gene promoter in the epididymis. A single transcription start site at position −3829 bp relative to the ATG was identified. Computational analysis revealed several TFAP2A, SP1, and KLF4 putative binding sites. A 1.5-kb fragment of the Gjb2 promoter was cloned into a vector containing a luciferase reporter gene. Transfection of the construct into immortalized rat caput epididymal (RCE-1) cells indicated that the promoter contained sufficient information to drive expression of the reporter gene. Deletion constructs showed that the basal activity of the promoter resides in the first −230 bp of the transcriptional start site. Two response elements necessary for GJB2 expression were identified: an overlapping TFAP2A/SP1 site (−136 to −126 bp) and an SP1 site (−50 bp). Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays confirmed that SP1 and TFAP2A were bound to the promoter. ChIP analysis of chromatin from young and pubertal rats indicated that TFAP2A and SP1 binding decreased with age. SP1 and TFAP2A knockdown indicated that SP1 is necessary for Gjb2 expression. DNA methylation did not appear to be involved in the regulation of Gjb2 expression. Results indicate that SP1 and TFAP2A regulate Gjb2 promoter activity during epididymal differentiation in rat.

[Expression of connexin 43 gene during early dental development in zebra fish]

OBJECTIVE

This study aims to investigate the expression of connexin 43 (cx43) gene during early development in zebra fish and provide a foundation for further research of cx43 gene in tooth development.

METHODS

Total RNA was extracted within 72 h after fertilization of zebra fish embryos and then reversed transcribed to generate the cDNA library. The specific fragments of the cx43 gene were then cloned and connected to the PGEMT vector. After confirming the constructed plasmid, the corresponding RNA polymerase was chosen, and the digoxin-labeled anti-sense mRNA probe of cx43 was synthesized in vitro. The cx43 gene expression of zebra fish indifferent stages was carried out by in situ hybridization. The relationship of the cx43 gene expression and anatomy of the pharyngeal teeth were compared by alizarin red staining.

RESULTS

The mRNA antisense probe of cx43 was acquired. The positive signal of sepia was observed in the different stages of zebra fish pharyngeal teeth after fertilization. After fertilization for 9 days, the expression site of cx43 in situ hybridization was overlapped in accordance with the anatomical site of the pharyngeal teeth.

CONCLUSION

cx43 gene participates in tooth development and mineralization process and plays a crucial role in later mineralization.

[Expression of connexin 43 gene during early dental development in zebra fish]

OBJECTIVE

This study aims to investigate the expression of connexin 43 (cx43) gene during early development in zebra fish and provide a foundation for further research of cx43 gene in tooth development.

METHODS

Total RNA was extracted within 72 h after fertilization of zebra fish embryos and then reversed transcribed to generate the cDNA library. The specific fragments of the cx43 gene were then cloned and connected to the PGEMT vector. After confirming the constructed plasmid, the corresponding RNA polymerase was chosen, and the digoxin-labeled anti-sense mRNA probe of cx43 was synthesized in vitro. The cx43 gene expression of zebra fish indifferent stages was carried out by in situ hybridization. The relationship of the cx43 gene expression and anatomy of the pharyngeal teeth were compared by alizarin red staining.

RESULTS

The mRNA antisense probe of cx43 was acquired. The positive signal of sepia was observed in the different stages of zebra fish pharyngeal teeth after fertilization. After fertilization for 9 days, the expression site of cx43 in situ hybridization was overlapped in accordance with the anatomical site of the pharyngeal teeth.

CONCLUSION

cx43 gene participates in tooth development and mineralization process and plays a crucial role in later mineralization.

Absence of connexin43 and connexin45 does not disturb pre- and peri-implantation development

Gap junctional intercellular communication is assumed to play an important role during pre- and peri-implantation development. In this study, we eliminated connexin43 (Cx43) and connexin45 (Cx45), major gap junctional proteins in the pre- and peri-implantation embryo. We generated Cx43−/−Cx45−/− embryos by Cx43+/−Cx45+/− intercrossing, because mice deficient in Cx43 (Cx43−/−) exhibit perinatal lethality and those deficient in Cx45 (Cx45−/−) exhibit early embryonic lethality. Wild-type, Cx43−/−, Cx45−/−, and Cx43−/−Cx45−/− blastocysts all showed similar outgrowths in in vitro culture. Moreover, Cx43−/−Cx45−/− embryos were obtained at the expected Mendelian ratio up to embryonic day 9.5, when the Cx45−/− mutation proved lethal. The Cx43−/−Cx45−/− embryos seemed to have no additional developmental abnormalities in comparison with the single knockout strains. Thus, pre- and peri-implantation development does not require Cx43 and Cx45. Other gap junctional proteins are expressed around these stages and these may compensate for the lack of Cx43 and Cx45.