Gap junctions (GJs) made of connexin-43 (Cx43) are important for the conduction of electrical impulses in the heart. Modulation of Cx43 activity may be useful in the treatment of cardiac arrhythmias and other dysfunctions. Search of novel GJ modulating agents using molecular docking approach allows to predict the binding affinities that often significantly differ from experimentally estimated their potencies. The objective of this study was to demonstrate that Quantitative Structure-Activity Relationship (QSAR) model could be used for more precise identification of potent Cx43 GJ inhibitors. Using the QSAR model and molecular docking, we evaluated the known Cx43 GJ inhibitors, suggested a new one, and tested it experimentally. Our QSAR model predicted the concentrations required to produce 50% of the maximal effect (IC50) for each of these compounds and estimated the correlation between predicted and experimental IC50ies (pIC50 and eIC50). This led to suggestion of monocyclic monoterpene d-limonene as putative Cx43 inhibitor with pIC50 = 1.07. In turn, dual whole-cell patch-clamp measurements provided eIC50=1.41. The pIC50ies of d-limonene and other Cx43 GJ inhibitors examined by our QSAR model well correlated with their eIC50ies (R = 0.88) in contrast to pIC50s obtained from molecular docking (R = 0.42). However, the molecular docking suggested that inhibitor potency may depend on their docking sites on Cx43.

Knowledge on the function of Connexin-43 on macrophages is gradually increasing and recent studies show how macrophages utilise Connexin-43. Migration, antigen-presentation and some forms of intercellular communication in macrophages are Connexin-43-dependant. Delicate processes, such as electrochemical support in conduction of the heartbeat in the AV-node, immunomodulatory regulation in the lungs and macrophage-differentiation are performed using Connexin-43 in macrophages. The relevance on pathophysiology becomes evident in inflammatory bowel disease, tumour networks and HIV in which aberrant function of Connexin-43 has been observed. Although many physiological, as well as pathophysiological functions were found to be Connexin-43-dependant, some still remain debated: the involvement of Connexin-43 in phagocytosis and polarisation, as well as its involvement in the mortality in murine sepsis are still unclear. These functions as well as further involvement in increasingly complex functions of the macrophage pose possible fields of research.

In various models of chronic kidney disease, the amount and localization of Cx43 in the nephron is known to increase, but the intracellular pathways that regulate these changes have not been identified. Therefore, we proposed that: "In the model of renal damage induced by infusion of angiotensin II (AngII), a RhoA/ROCK-dependent pathway, is activated and regulates the abundance of renal Cx43”. In rats, we evaluated: 1) the time-point where the renal damage induced by AngII is no longer reversible; and 2) the involvement of a RhoA/ROCK-dependent pathway and its relationship with the amount of Cx43 in this irreversible stage. Systolic blood pressure (SBP) and renal function (urinary protein/urinary creatinine: Uprot/UCrea) were evaluated as systemic and organ outcomes, respectively. In kidney tissue, we also evaluated: 1) oxidative stress (amount of thiobarbituric acid reactive species), 2) inflammation (immunoperoxidase detection of the inflammatory markers ED-1 and IL-1β), 3) fibrosis (immune detection of type III collagen; Col III) and 4) activity of RhoA/ROCK (amount of phosphorylated MYPT1; p-MYPT1). The ratio Uprot/UCrea, SBP, oxidative stress, inflammation, amount of Cx43 and p-MYPT1 remained high 2 weeks after suspending AngII treatment in rats treated for 4 weeks with AngII. These responses were not observed in rats treated with AngII for less than 4 weeks, in which all measurements returned spontaneously close to the control values after suspending AngII treatment. Rats treated with AngII for 6 weeks and co-treated for the last 4 weeks with Fasudil, an inhibitor of ROCK, showed high SBP but did not present renal damage or increased amount of renal Cx43. Therefore, renal damage induced by AngII correlates with the activation of RhoA/ROCK and the increase in Cx43 amounts and can be prevented by inhibitors of this pathway.

Direct intercellular communication, mediated by gap junctions formed by the connexin transmembrane protein family, is frequently dysregulated in cancer. Connexins have been described as tumour suppressors, but emerging evidence suggests that they can also act as tumour promoters. This feature is connexin- and tissue-specific and may be mediated by complex signalling pathways through gap junctions or hemichannels or by completely junction-independent events. Lung cancer is the number one cancer in terms of mortality worldwide, and novel biomarkers and therapeutic targets are urgently needed. Our objective was to gain a better understanding of connexins in this setting. We used several in silico tools to analyse TCGA data in order to compare connexin mRNA expression between healthy lung tissue and lung tumours and correlated these results with gene methylation patterns. Using Kaplan-Meier plotter tools, we analysed a microarray dataset and an RNA-seq dataset of non-small cell lung tumours in order to correlate connexin expression with patient prognosis. We found that connexin mRNA expression is frequently either upregulated or downregulated in lung tumours. This correlated with both good and poor prognosis (overall survival) in a clear connexin isoform-dependent manner. These associations were strongly influenced by the histological subtype (adenocarcinoma versus squamous cell carcinoma). We present an overview of all connexins but particularly focus on four isoforms implicated in lung cancer: Cx26, Cx30.3, Cx32 and Cx43. We further analysed the protein expression and localization of Cx43 in a series of 72 human lung tumours. We identified a subset of tumours that exhibited a unique strong nuclear Cx43 expression pattern that predicted worse overall survival (p=0.014). Upon sub-stratification, the prognostic value remained highly significant in the adenocarcinoma subtype (p=0.002) but not in the squamous carcinoma subtype (p=0.578). This finding highlights the importance of analysis of connexin expression at the protein level, particularly the subcellular localization. Elucidation of the underlying pathways regulating Cx43 localization may provide for novel therapeutic opportunities.

Cell junction that is usually associated with dynamic cytoskeletons is essential for a wide range of cellular activities such as cell migration, cell communication, barrier function and signal transduction. Real-time observation of cell junction facilitates understanding of the mechanisms by which cell junction regulate relevant cellular activities. In this study, we examined the binding capacity of a modified tridecapeptide from Cx43 to cell junction protein ZO-1 and sought to create a fluorescent peptide that could be used to label cell junction. To introduce the fluorescent peptide into the cells, a cell-penetrating peptide was linked to the modified tridecapeptide and synthesized. The binding of the modified tridecapeptide was tested using pull down and immunoprecipitation assay. The ability of the peptide to label cell junction was assessed by adding it to fixed or cultured Caco-2 cells. Testing assay revealed that the Cx43-derived peptide can bind to ZO-1. Besides, the peptide was able to label cell junction of fixed cell, although no obvious cell junction labeling was observed clearly in living cells, probably due to the inadequate affinity. These results indicate that a peptide-based strategy for labeling cell junction may be feasible, and efforts to improve its affinity are warranted in the future.

We describe a method for protein quantification and for mRNA quantification in small sample quantities of human induced pluripotent stem-cell-derived-cardiomyocytes (hiPSC-CMs). Demonstrated here is how the capillary-based protein detection system Wes^TM by ProteinSimple and the Power SYBR^TM Green Cells-to-CT^TM Kit by Invitrogen can be applied to individual samples in a 96-well microplate format and thus made compatible with high-throughput (HT) cardiomyocyte assays. As an example of the usage, we illustrate that Cx43 protein and GJA1 mRNA levels in hiPSC-CMs are enhanced when the optogenetic actuator, channelrodopsin-2 (ChR2), is genetically expressed in them. Instructions are presented for cell culture and lysate preparations from hiPSC-CMs, along with optimized parameter settings and experimental protocol steps. Strategies to optimize primary antibody concentrations as well as ways for signal normalization are discussed, i.e. antibody multiplexing and total protein assay. The sensitivity of both the Wes and Cells-to-CT kit enables protein and mRNA quantification in a HT format, which is important when dealing with precious small samples. In addition to being able to handle small cardiomyocyte samples, these streamlined and semi-automated processes enable quick mechanistic analysis.

The development of new diabetes drugs continues to be explored. Loureirin B, a flavonoid, extracted from Dracaena cochinchinensis, has been confirmed to increase insulin secretion and decrease blood glucose levels. For understanding the mechanism, a series of experiments had been employed based on computational methods and cell experiments. The insulin secretion significantly increased with the incubation of 0.01μM loureirin B for 4 hours. The viability of Ins-1 cells showed no significant difference with the treatment of loureirin B. Through computational methods, we hypothesized that loureirin B could interacts with K_ATP channels to promote insulin secretion. In cell experiments, it could be found that the current of K_ATP channel of Ins-1 cells was inhibited by the effect of loureirin B. After then, the voltage-dependent calcium channels were activated, the increase of Cx43 protein expression might mediate the Ca²⁺ to the intracellular. In summary, it could be concluded that loureirin B promoted insulin secretion mainly through inhibiting K_ATP current, the influx of Ca²⁺ to the Intracellular and the expression of Cx43.