Dye Transfer Research Articles

Expression and function of connexin 43 in human gingival wound healing and fibroblasts.

Connexins (C×s) are a family of transmembrane proteins that form hemichannels and gap junctions (GJs) on the cell membranes, and transfer small signaling molecules between the cytoplasm and extracellular space and between connecting cells, respectively. Among C×s, suppressing C×43 expression or function promotes skin wound closure and granulation tissue formation, and may alleviate scarring, but the mechanisms are not well understood. Oral mucosal gingiva is characterized by faster wound closure and scarless wound healing outcome as compared to skin wounds. Therefore, we hypothesized that C×43 function is down regulated during human gingival wound healing, which in fibroblasts promotes expression of genes conducive for fast and scarless wound healing. Cultured gingival fibroblasts expressed C×43 as their major connexin. Immunostaining of unwounded human gingiva showed that C×43 was abundantly present in the epithelium, and in connective tissue formed large C×43 plaques in fibroblasts. At the early stages of wound healing, C×43 was strongly down regulated in wound epithelial cells and fibroblasts, returning to the level of normal tissue by day 60 post-wounding. Blocking of C×43 function by C×43 mimetic peptide Gap27 suppressed GJ-mediated dye transfer, promoted migration, and caused significant changes in the expression of wound healing-associated genes in gingival fibroblasts. In particular, out of 54 genes analyzed, several MMPs and TGF-β1, involved in regulation of inflammation and extracellular matrix (ECM) turnover, and VEGF-A, involved in angiogenesis, were significantly upregulated while pro-fibrotic ECM molecules, including Collagen type I, and cell contractility-related molecules were significantly down regulated. These responses involved MAPK, GSK3α/β and TGF-β signaling pathways, and AP1 and SP1 transcription factors. Thus, suppressed function of C×43 in fibroblasts promotes their migration, and regulates expression of wound healing-associated genes via AP1, SP1, MAPK, GSK3α/β and TGF-β signaling pathways, and may promote fast and scarless wound healing in human gingiva.

Beyond Gap Junction Channel Function: the Expression of Cx43 Contributes to Aldosterone-Induced Mesangial Cell Proliferation via the ERK1/2 and PKC Pathways

Aims: This study aimed to explore the precise mechanism and signaling pathways of mesangial cell (MC) proliferation from a new point of view considering Connexin 43 (Cx43). Methods: MC proliferation was measured by the incorporation of 3H-thymidine (3H-TdR). Cx43 was over-expressed in MC cells using lipofectamine 2000, and the expression level was tested with reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses. The gap junction channel function was explored by Lucifer Yellow scrape loading and dye transfer (SLDT), and the intracellular calcium concentrations ([Ca²⁺]_i) were characterized by confocal microscopy on cells loaded with Fura-3/AM. Results: There was an inverse correlation between Cx43 expression and MC proliferation (P<0.05). SLDT studies revealed that there was no difference in the gap junction channel function between the normal and Aldosterone (Aldo)-stimulated groups (P>0.05). Our data also showed that the mineralcorticoid receptor (MR) antagonist spironolactone, ERK1/2 inhibitor PD98059 and PKC inhibitor GF109203X could attenuate the down-regulation of Cx43 expression in Aldo-induced MC proliferation; however, the PI3K inhibitor LY294002 could block MC proliferation without affecting Cx43 expression at either the mRNA or protein level. In addition, Aldo promoted MC proliferation in parallel with increasing [Ca²⁺]_i (P<0.05), suggesting that the classical PKC pathway might be activated. Conclusions: Our study provides preliminary evidence that Cx43 is an important regulator of Aldo-promoted MC proliferation. Furthermore, reduced Cx43 expression promoted MC proliferation independent of the gap junction channel function, and this process might be mediated through the ERK1/2- and PKC-dependent pathways.

Controlling cell–cell interactions using surface acoustic waves

The interactions between pairs of cells and within multicellular assemblies are critical to many biological processes such as intercellular communication, tissue and organ formation, immunological reactions, and cancer metastasis. The ability to precisely control the position of cells relative to one another and within larger cellular assemblies will enable the investigation and characterization of phenomena not currently accessible by conventional in vitro methods. We present a versatile surface acoustic wave technique that is capable of controlling the intercellular distance and spatial arrangement of cells with micrometer level resolution. This technique is, to our knowledge, among the first of its kind to marry high precision and high throughput into a single extremely versatile and wholly biocompatible technology. We demonstrated the capabilities of the system to precisely control intercellular distance, assemble cells with defined geometries, maintain cellular assemblies in suspension, and translate these suspended assemblies to adherent states, all in a contactless, biocompatible manner. As an example of the power of this system, this technology was used to quantitatively investigate the gap junctional intercellular communication in several homotypic and heterotypic populations by visualizing the transfer of fluorescent dye between cells.

Pharmacological and molecular characterization of functional P2 receptors in rat embryonic cardiomyocytes.

Purinergic receptors activated by extracellular nucleotides (adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP)) are well known to exert physiological effects on the cardiovascular system, whether nucleotides participate functionally in embryonic heart development is not clear. The responsiveness of embryonic cardiomyocytes (E) 12 to P2 receptor agonists by measuring Ca(2+) influx did not present response to ATP, but responses to P2 agonists were detected in cardiomyocytes taken from E14 and E18 rats. Photometry revealed that the responses to ATP were concentration-dependent with an EC50 of 1.32 μM and 0.18 μM for E14 and E18 cardiomyocytes, respectively. In addition, other P2 agonists were also able to induce Ca(2+) mobilization. RT-PCR showed the presence of P2X2 and P2X4 receptor transcripts on E14 cardiomyocytes with a lower expression of P2X3 and P2X7 receptors. P2X1 and a low level of P2X5 receptor messenger RNA (mRNA) were also expressed at E18. Immunofluorescence data indicated that only P2X2 and P2X4 receptor proteins were expressed in E14 cardiomyocytes while protein for all the P2X receptor subtypes was expressed in E18, except for P2X3 and P2X6. Responses mediated by agonists specific for P2Y receptors subtypes showed that P2Y receptors (P2Y1, P2Y2, P2Y4 and P2Y6) were also present in both E14 and E18 cardiomyocytes. Dye transfer experiments showed that ATP induces coupling of cells at E12, but this response is decreased at E14 and lost at E18. Conversely, UTP induced coupling with five or more cells in most cells from E12 to E18. Our results show that specific P2 receptor subtypes are present in embryonic rat cardiomyocytes, including P2X7 and P2Y4 receptors that have not been identified in adult rat cardiomyocytes. The responsiveness to ATP stimulation even before birth, suggests that ATP may be an important messenger in embryonic as well as in adult hearts.

Primary Acute Lymphoblastic Leukemia Cells Create a Drug-Resistant Niche By Tunneling Nanotube Signaling with Mesenchymal Stromal Cells

Background: Acute lymphoblastic leukemia (ALL) cells reside in the bone marrow microenvironment, which nurtures and protects cells from chemotherapeutic drugs. Bidirectional signaling between leukemic cells and their niche is shown to be essential for these processes. A major gap in our knowledge is the lack of insight into the functional mechanism regulating and controlling this crosstalk. Tunneling nanotubes (TNTs) have recently been reported as a novel mode of communication between eukaryotic cells, which can facilitate the transport of several types of cellular cargo.Objectives: This study aims to investigate the presence and functional importance of TNTs in the leukemic niche.Results: Here, we show for the first time that TNT signaling occurs between primary patient-derived leukemic cells and primary mesenchymal stromal cells using flow cytometry and time-lapse confocal microscopy. TNTs form within minutes after the start of co-culture and efficiently transfer lipophilic carbocyanine dye DiI from ALL cells towards MSCs. Dye transfer was significantly reduced when TNT signaling was inhibited using three independent experimental setups: actin inhibition, mechanical disruption through gentle shaking of cell cultures, and physical separation using a 3.0 µm pore-sized transwell system (4-fold, 5-fold and 35-fold reduction, respectively). In reciprocal experiments we also observed dye transfer via TNTs from MSCs to BCP-ALL cells, but the magnitude was strikingly less (175-fold, p ≤ 0.001). In addition, we show that leukemic cells use TNTs to modulate their microenvironment by directing non-malignant stromal cells to produce pro-survival cytokines. We observed patient-specific cytokine signatures after co-culture of primary ALL cells with different primary MSCs. For example, IP10/CXCL10 levels increased more than 1000-fold when patient ALL#1 cells were co-cultured with primary MSCs, but were undetectable in co-cultures from patient ALL#2 cells. Induction of all cytokines was dependent on TNT signaling, as TNT inhibition significantly lowered cytokine production (p ≤ 0.001). Importantly, we show that TNT signaling is functionally important for leukemic cell survival and stroma-driven drug resistance. Leukemic cell viability was assessed by flow cytometry after staining with Annexin V, Propidium Iodide and CD19. Primary leukemic cell survival significantly increased in 5-day co-cultures with primary MSCs compared to mono-culture (p ≤ 0.001). When TNT formation was prevented by shaking of these co-cultures or by transwell conditions, the cell viability reduced 3.5- and 3.6-fold, respectively (p ≤ 0.001). TNT inhibition similarly reduced the survival of primary ALL cells in co-culture with MSCs during prednisolone exposure (p ≤ 0.01). Co-culture with primary MSCs also induced resistance to prednisolone 2.5-fold compared to mono-culture in a proliferative setting, using the BCP-ALL cell line NALM6. Inhibition of TNT formation by shaking or transwell conditions significantly reduced this effect: cells in co-culture were only 1.4- and 1.1-fold more resistant compared to mono-culture, respectively (p ≤ 0.01).Conclusion: The presented study identifies TNT formation as a major regulator of interaction between ALL cells and their bone marrow niche, which facilitates signaling mainly from leukemic cells towards MSCs. This signaling drives the release of cytokines within the microenvironment. Disruption of tunneling nanotubes inhibits this release, diminishes the survival benefit that MSCs provide to primary ALL cells, and sensitizes ALL cells to the important anti-leukemic drug prednisolone. This observation gives insight into the pathogenesis of BCP-ALL and opens new avenues to develop more effective therapies that interfere with the leukemic niche. DisclosuresNo relevant conflicts of interest to declare.

Characterization of DLBCL-Derived Exosomes and Investigation of Their Biological Properties

Exosomes are membrane-bound vesicles that can be exchanged between cells and have been shown to modify the tumor microenvironment and contribute to progression of solid tumors. Little research has been done on exosomes in lymphoma and their potential biological role in tumor initiation and progression remains unknown. We characterized exosomes secreted by six DLBCL cell lines, four primary DLBCL tumors, and two normal control B cell samples. We optimized their purification and studied their nucleic acid content. We then determined that tumor-derived exosomes can be exchanged not only between tumor and immune cells, as has been shown before, but also between lymphoma cells with various biological consequences. Finally, we sequenced exosomal RNAs in order to better understand their function and role in lymphoma biology.We used serial ultracentrifugation to purify exosomes and microvesicles from six DLBCL cell lines (LY1, LY3, LY7, LY18, HBL1, TMD8). We isolated exosomes from four primary DLBCLs and two control tonsillar samples enriched for CD20+ B cells using the Total Exosome Isolation from Cell Culture Kit (Invitrogen). We found that the six DLBCL cell lines secrete large quantities of CD63+ exosomes. These exosomes also express the B-cell specific marker CD20, but not T cell marker CD3, which could enable tracing of the cell of origin and differential purification. Exosomes are known to contain small RNAs, which can be extracted with different efficiency depending on the isolation method used. We tested three approaches for nucleic acid isolation: Direct-zol™ and TRIzol® methods which were both followed by column purification, and miRCURY™ RNA isolation kit (Exiqon). We detected no traceable quantities of DNA in exosomal contents. The miRCURY™ RNA isolation kit yielded the highest amounts of RNAs of the techniques used and preserved sizes from 4-150 nucleotides (nt) in length with equal efficiency. Exosomes contained predominantly small RNAs with 6-80 nt species which constituted 9-28% of isolated RNA. We then prepared cDNA libraries using TruSeq Stranded Total kit (Illumina) and sequenced libraries using 50 bp Paired End approach on Illumina HiSeq 2000. We developed a small RNA-seq Analysis Pipeline that included QC, removing Illumina TruSeq adapters, mapping the reads, summarizing the data, and assigning reads to annotated genes. Our results indicate that exosomal RNAs contain protein coding RNAs (50-60%) and antisense RNAs (20-30%) as the most common biotypes.We also evaluated the exchange of exosomal content between DLBCL cell lines (LY1, LY3). The cells were stained with SYTO® RNASelect™ dye (Molecular Probes Inc) and cultured for 48 hours. The supernatant was collected, filtered, and cultured with unstained cells from the alternate DLBCL cell line for 48 hours. We observed uptake of LY1 exosomes by LY3 cells and LY3 exosomes by LY1 cells, as evidenced by SYTO® RNASelect™ dye transfer and CD63 positivity on FACS analysis. In addition, we tested the effect of exosomal exchange on resistance to doxorubicin, given the varied susceptibilities of LY1 and LY3 cell lines to this drug which is a part of standard frontline treatment for DLBCL. After culturing cells with filtered supernatant from the alternate cell line for 48 hours, we treated with doxorubicin and assessed for cell viability at 48 hours. We also studied the effect of exosome uptake on proliferation and cell cycle of recipient cells. Our results indicate that exosomal exchange between tumor cells and from tumor to normal B cells can modulate fundamental biological processes including drug resistance as well as cell proliferation, survival, and induction of apoptosis. We believe this is related to incorporation of exosomal RNA with resulting effects on the transcriptome of recipient cells. RNA sequencing analysis will aid in the design of additional functional studies in order to further elucidate the biological role of exosomes in DLBCL. DisclosuresNo relevant conflicts of interest to declare.

Yucca aloifolia (Asparagaceae) opts out of an obligate pollination mutualism.

• According to Cope's 'law of the unspecialized' highly dependent species interactions are 'evolutionary dead ends,' prone to extinction because reversion to more generalist interactions is thought to be unlikely. Cases of extreme specialization, such as those seen between obligate mutualists, are cast as evolutionarily inescapable, inevitably leading to extinction rather than diversification of participating species. The pollination mutualism between Yucca plants and yucca moths (Tegeticula and Parategeticula) would seem to be locked into such an obligate mutualism. Yucca aloifolia populations, however, can produce large numbers of fruit lacking moth oviposition scars. Here, we investigate the pollination ecology of Y. aloifolia, in search of the non-moth pollination of a Yucca species.• We perform pollinator exclusion studies on Yucca aloifolia and a sympatric yucca species, Y. filamentosa. We then perform postvisit exclusion treatments, an analysis of dissected fruits, and a fluorescent dye transfer experiment.• As expected, Yucca filamentosa plants set fruit only when inflorescences were exposed to crepuscular and nocturnal pollinating yucca moths. In contrast, good fruit set was observed when pollinators were excluded from Y. aloifolia inflorescences from dusk to dawn, and no fruit set was observed when pollinators were excluded during the day. Follow up experiments indicated that European honeybees (Apis mellifera) were passively yet effectively pollinating Y. aloifolia flowers.• These results indicate that even highly specialized mutualisms may not be entirely obligate interactions or evolutionary dead ends.

TMEM43 mutation p.S358L alters intercalated disc protein expression and reduces conduction velocity in arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a myocardial disease characterized by fibro-fatty replacement of myocardium in the right ventricular free wall and frequently results in life-threatening ventricular arrhythmias and sudden cardiac death. A heterozygous missense mutation in the transmembrane protein 43 (TMEM43) gene, p.S358L, has been genetically identified to cause autosomal dominant ARVC type 5 in a founder population from the island of Newfoundland, Canada. Little is known about the function of the TMEM43 protein or how it leads to the pathogenesis of ARVC. We sought to determine the distribution of TMEM43 and the effect of the p.S358L mutation on the expression and distribution of various intercalated (IC) disc proteins as well as functional effects on IC disc gap junction dye transfer and conduction velocity in cell culture. Through Western blot analysis, transmission electron microscopy (TEM), immunofluorescence (IF), and electrophysiological analysis, our results showed that the stable expression of p.S358L mutation in the HL-1 cardiac cell line resulted in decreased Zonula Occludens (ZO-1) expression and the loss of ZO-1 localization to cell-cell junctions. Junctional Plakoglobin (JUP) and α-catenin proteins were redistributed to the cytoplasm with decreased localization to cell-cell junctions. Connexin-43 (Cx43) phosphorylation was altered, and there was reduced gap junction dye transfer and conduction velocity in mutant TMEM43-transfected cells. These observations suggest that expression of the p.S358L mutant of TMEM43 found in ARVC type 5 may affect localization of proteins involved in conduction, alter gap junction function and reduce conduction velocity in cardiac tissue.

A functional assay for gap junctional examination; electroporation of adherent cells on indium-tin oxide.

In this technique, cells are cultured on a glass slide that is partly coated with indium-tin oxide (ITO), a transparent, electrically conductive material. A variety of molecules, such as peptides or oligonucleotides can be introduced into essentially 100% of the cells in a non-traumatic manner. Here, we describe how it can be used to study intercellular, gap junctional communication. Lucifer yellow penetrates into the cells when an electric pulse, applied to the conductive surface on which they are growing, causes pores to form through the cell membrane. This is electroporation. Cells growing on the nonconductive glass surface immediately adjacent to the electroporated region do not take up Lucifer yellow by electroporation but do acquire the fluorescent dye as it is passed to them via gap junctions that link them to the electroporated cells. The results of the transfer of dye from cell to cell can be observed microscopically under fluorescence illumination. This technique allows for precise quantitation of gap junctional communication. In addition, it can be used for the introduction of peptides or other non-permeant molecules, and the transfer of small electroporated peptides via gap junctions to inhibit the signal in the adjacent, non-electroporated cells is a powerful demonstration of signal inhibition.

Benzalkonium chloride suppresses rabbit corneal endothelium intercellular gap junction communication.

PurposeGap junction intercellular communication (GJIC) plays a critical role in the maintenance of corneal endothelium homeostasis. We determined if benzalkonium chloride (BAK) alters GJIC activity in the rabbit corneal endothelium since it is commonly used as a drug preservative in ocular eyedrop preparations even though it can have cytotoxic effects.MethodsThirty-six adult New Zealand albino rabbits were randomly divided into three groups. BAK at 0.01%, 0.05%, and 0.1% was applied twice daily to one eye of each of the rabbits in one of the three groups for seven days. The contralateral untreated eyes were used as controls. Corneal endothelial morphological features were observed by in vivo confocal microscopy (IVCM). Immunofluorescent staining resolved changes in gap junction integrity and localization. Western blot analysis and RT-PCR evaluated changes in levels of connexin43 (Cx43) and tight junction zonula occludens-1 (ZO-1) gene and protein expression, respectively. Cx43 and ZO-1 physical interaction was detected by immunoprecipitation (IP). Primary rabbit corneal endothelial cells were cultured in Dulbecco's Modified Eagle Medium (DMEM) containing BAK for 24 hours. The scrape-loading dye transfer technique (SLDT) was used to assess GJIC activity.ResultsTopical administration of BAK (0.05%, 0.1%) dose dependently disrupted corneal endothelial cell morphology, altered Cx43 and ZO-1 distribution and reduced Cx43 expression. BAK also markedly induced increases in Cx43 phosphorylation status concomitant with decreases in the Cx43-ZO-1 protein-protein interaction. These changes were associated with marked declines in GJIC activity.ConclusionsThe dose dependent declines in rabbit corneal endothelial GJIC activity induced by BAK are associated with less Cx43-ZO-1 interaction possibly arising from increases in Cx43 phosphorylation and declines in its protein expression. These novel changes provide additional evidence that BAK containing eyedrop preparations should be used with caution to avoid declines in corneal transparency resulting from losses in GJIC activity and endothelial function.

Cell differentiation mediated by co-culture of human umbilical cord blood stem cells with murine hepatic cells.

In the present study, purified human cord blood stem cells were co-cultivated with murine hepatic alpha mouse liver 12 (AML12) cells to compare the effect on endodermal stem cell differentiation by either direct cell-cell interaction or by soluble factors in conditioned hepatic cell medium. With that approach, we want to mimic in vitro the situation of preclinical transplantation experiments using human cells in mice. Cord blood stem cells, cultivated with hepatic conditioned medium, showed a low endodermal differentiation but an increased connexin 32 (Cx32) and Cx43, and cytokeratin 8 (CK8) and CK19 expression was monitored by reverse transcription polymerase chain reaction (RT-PCR). Microarray profiling indicated that in cultivated cord blood cells, 604 genes were upregulated 2-fold, with the highest expression for epithelial CK19 and epithelial cadherin (E-cadherin). On ultrastructural level, there were no major changes in the cellular morphology, except a higher presence of phago(ly)some-like structures observed. Direct co-culture of AML12 cells with cord blood cells led to less incisive differentiation with increased sex-determining region Y-box 17 (SOX17), Cx32 and Cx43, as well as epithelial CK8 and CK19 expressions. On ultrastructural level, tight cell contacts along the plasma membranes were revealed. FACS analysis in co-cultivated cells quantified dye exchange on low level, as also proved by time relapse video-imaging of labelled cells. Modulators of gap junction formation influenced dye transfer between the co-cultured cells, whereby retinoic acid increased and 3-heptanol reduced the dye transfer. The study indicated that the cell-co-cultured model of human umbilical cord blood cells and murine AML12 cells may be a suitable approach to study some aspects of endodermal/hepatic cell differentiation induction.

Abstract 2467: Connexin43 reduces melanoma growth within a keratinocyte microenvironment and during tumorigenesis in vivo

Abstract Gap junctions formed from connexins (Cx) have been reported to regulate proliferation, differentiation and apoptosis through formation of intercellular channels between opposing cells. Interestingly, connexins have been identified as tumor suppressors and enhancers, a distinction dependent on the type and stage of disease. In melanomas, the role of connexins during cancer onset and progression remains unclear. In the current study, we hypothesize that expression of Cx26 and Cx43 in BL6 mouse melanomas will increase gap junctional intercellular communication (GJIC) thereby decrease their tumorigenic properties. Western blots, immunofluorescence and dye coupling studies revealed that BL6 cells express low levels of Cx26 , Cx43 and are poorly coupled. When cells were engineered to express Cx26 or Cx43, dye transfer studies revealed that both Cx26- and Cx43-expressing cells were highly coupled. Interestingly, when these connexin-rich melanomas were co-cultured with Cx43-rich keratinocytes, melanoma microtumors remained functionally isolated and failed to couple to surrounding keratinocytes. Growth curve studies revealed that exogenous Cx43, but not Cx26, significantly reduced total cell numbers; that was primarily due to reduced cell proliferation. Furthermore, Cx43 expression significantly reduced anchorage-independent growth compared to controls, however, migration remained unaffected. Additionally, Cx43-expressing melanoma cells displayed a reduction in growth when co-cultured with keratinocytes, despite a lack of heterocellular GJIC. Finally, when grown in in vivo avian embryo model, primary tumor weight was reduced in tumor cells expressing Cx43 , but not in Cx26-expressing melanomas , as compared to controls. Overall, our results would suggest that Cx43 is a potent tumor suppressor in melanomas. Supported by the Canadian Institute of Health Research to DWL. Citation Format: Qing C. Shao, Mark Jake Ableser, Silvia Penuela, Dale W. Laird. Connexin43 reduces melanoma growth within a keratinocyte microenvironment and during tumorigenesis in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2467. doi:10.1158/1538-7445.AM2014-2467

Abstract 4804: Metastatic breast cancer cells induce an osteoblast-TAF-like phenotype and communicate with osteoblasts via gap junctions and exosomal crosstalk to facilitate breast cancer cell quiescence in bone

Abstract Breast cancer has a high propensity for bone colonization. Although the precise mechanism underlying preferential metastasis is unknown, bone likely provides a hospitable environment that both attracts breast cancer cells and allows them to colonize and grow. Metastatic lesions may originate from disseminated tumor cells (DTCs) shed from a primary tumor. Clinical evidence suggests that DTCs undergo a period of proliferative quiescence for ≤25 years. Despite the high prevalence of dormant tumors in humans, this area of research is poorly understood. MC3T3-E1 murine osteoblasts (OBs) were grown to early differentiation (10 days old), then MDA-MB-231 human breast cancer cells (BCCs) added at a ratio of 1 BCC to 10 OBs. Co-cultures were fixed and stained for connexin 43 expression (Cx43, representative gap junction). Cx43 expression was localized between OBs and BCCs. No Cx43 expression was seen in the control. Furthermore, a parachute assay was performed under similar conditions, where at time 48 hours, CellTracker Orange CMTMR dye transfer was seen between GFP-labeled BCCs and unlabeled OBs. Then, OBs and BCCs were grown to confluence. Individual cultures were treated with media containing exosome-free fetal bovine serum. Forty-eight hours later, culture supernatants were removed and processed through a series of ultra-centrifugation and concentration steps to purify for exosomes. Both OBs and BCCs produced exosomes, which were characterized using a Nanosight 500 System, and analyzed for microRNAs via real-time PCR. Next, OBs were grown to early differentiation (10 days), and treated with conditioned medium (CM) from BCCs. Twenty-one days later, OB-derived protein expression was assessed. When treated with BCC CM, OBs decreased their expression of alpha smooth muscle actin, but increased their expression of fibroblast activating protein and matrix metalloproteinase 13. These results are consistent with a tumor-associated fibroblast-activated myofibroblast phenotype. Finally, OBs were grown to 4 days (growth) and 10 days (early differentiation) and incubated with BCC CM. Twenty-four hours later, total RNA was collected, and ABI TaqMan qPCR cytokine arrays were used to assay for changes in OB-derived cytokine expression. OB-derived cytokines were increased in the presence of BCC CM, and included MCP-1 (CCL2), LIX (CXCL5), LIF, and NFATc2. These data imply that BCCs communicate with OBs by intercellular crosstalk via gap junctions and exosomes that creates a niche permissive for BCC dormancy in bone. This work highlights the importance of investigating OBs in the bone microenvironment as key players in BCC dormancy. Supported by the NIH; 1RC1 CA146381, 1R01NS06994, P50 CA083639 for FCM; Ruth L. Kirschstein Institutional Research Service Award (NRSA) T32 CA079448 and NIH 1 K99 CA 178177-01 for KMB. Citation Format: Karen M. Bussard, Frank C. Marini. Metastatic breast cancer cells induce an osteoblast-TAF-like phenotype and communicate with osteoblasts via gap junctions and exosomal crosstalk to facilitate breast cancer cell quiescence in bone. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4804. doi:10.1158/1538-7445.AM2014-4804

Extracellular gentamicin reduces the activity of connexin hemichannels and interferes with purinergic Ca(2+) signaling in HeLa cells.

Gap junction channels (GJCs) and hemichannels (HCs) are composed of protein subunits termed connexins (Cxs) and are permeable to ions and small molecules. In most organs, GJCs communicate the cytoplasm of adjacent cells, while HCs communicate the intra and extracellular compartments. In this way, both channel types coordinate physiological responses of cell communities. Cx mutations explain several genetic diseases, including about 50% of autosomal recessive non-syndromic hearing loss. However, the possible involvement of Cxs in the etiology of acquired hearing loss remains virtually unknown. Factors that induce post-lingual hearing loss are diverse, exposure to gentamicin an aminoglycoside antibiotic, being the most common. Gentamicin has been proposed to block GJCs, but its effect on HCs remains unknown. In this work, the effect of gentamicin on the functional state of HCs was studied and its effect on GJCs was reevaluated in HeLa cells stably transfected with Cxs. We focused on Cx26 because it is the main Cx expressed in the cochlea of mammals where it participates in purinergic signaling pathways. We found that gentamicin applied extracellularly reduces the activity of HCs, while dye transfer across GJCs was not affected. HCs were also blocked by streptomycin, another aminoglycoside antibiotic. Gentamicin also reduced the adenosine triphosphate release and the HC-dependent oscillations of cytosolic free-Ca2+ signal. Moreover, gentamicin drastically reduced the Cx26 HC-mediated membrane currents in Xenopus laevis oocytes. Therefore, the extracellular gentamicin-induced inhibition of Cx HCs may adversely affect autocrine and paracrine signaling, including the purinergic one, which might partially explain its ototoxic effects.

Investigation of connexin 43 uncoupling and prolongation of the cardiac QRS complex in preclinical and marketed drugs

Prolongation of the cardiac QRS complex is linked to increased mortality and may result from drug-induced inhibition of cardiac sodium channels (hNaV 1.5). There has been no systematic evaluation of preclinical and marketed drugs for their additional potential to cause QRS prolongation via gap junction uncoupling. Using the human cardiac gap junction connexin 43 (hCx43), a dye transfer 'parachute' assay to determine IC50 values for compound ranking was validated with compounds known to uncouple gap junctions. Uncoupling activity (and hNaV 1.5 inhibition by automated patch clamp) was determined in a set of marketed drugs and preclinical candidate drugs, each with information regarding propensity to prolong QRS. The potency of known gap junction uncouplers to uncouple hCx43 was ranked (according to IC50 ) as phorbol ester>digoxin>meclofenamic acid>carbenoxolone>heptanol. Among the drugs associated with QRS prolongation, 29% were found to uncouple hCx43 (IC50 < 50 μM), whereas no uncoupling activity was observed in drugs not associated with QRS prolongation. In preclinical candidate drugs, hCx43 and hNaV 1.5 IC50 values were similar (within threefold). No consistent margin over preclinical Cmax (free) was apparent for QRS prolongation associated with Cx43 inhibition. However, instances were found of QRS prolonging compounds that uncoupled hCx43 with significantly less activity at hNaV 1.5. These results demonstrate that off-target uncoupling activity is apparent in drug and drug-like molecules. Although the full ramifications of Cx inhibition remain to be established, screening for hCx43 off-target activity could reduce the likelihood of developing candidate drugs with a risk of causing QRS prolongation.

Electron microscopy and functional analysis of recombinant innexin gap junctions

Innexin is a molecular component of invertebrate gap junctions, which have an important role in neural and muscular electrical activity in invertebrates. Although the structure of vertebrate connexin26 was revealed by X-ray crystallography [1], the structure of innexin channels remains poorly understood. To study the structure of innexin gap junction channels, we expressed and purified Caenorhabditis elegans innexin-6 (INX-6) gap junction channels, and characterized their molecular dimensions and channel permeability using electron microscopy (EM) and a fluorescent dye transfer assay, respectively [2]. Negative-staining and thin-section EM of isolated INX-6 gap junction plaques revealed a loosely packed hexagonal lattice. We performed single particle analysis of purified INX-6 channels with negative-staining and cryo EM. Based on the negative-stain EM images, the class average of the junction form had a longitudinal height of 220 Å, a channel diameter of 110 Å in the absence of detergent micelles, and an extracellular gap space of 60 Å, whereas the class average of the hemichannels had diameters of up to 140 Å in the presence of detergent micelles. Cryo EM images revealed rotational peaks that could be related to the INX-6 subunits. Structural analysis of the reconstituted INX-6 channels with single particle analysis and electron tomography suggested that the oligomeric number of the INX-6 channel was distinct from that of the dodecameric connexin channel. Dye transfer experiments indicated that the INX-6-GFP-His channels were permeable to 3-kDa and 10-kDa dextran-conjugated tracers. These findings indicate that INX-6 channels have a characteristic oligomer component that differs from that in connexin gap junction channels.

Bioinspired Anchorable Thiol-Reactive Polymers: Synthesis and Applications Toward Surface Functionalization of Magnetic Nanoparticles

In this study, we report on the synthesis of novel thiol-reactive polymers containing a catechol moiety at their chain ends and demonstrate their application toward surface modification of magnetic nanoparticles. Poly(ethylene glycol) methyl ether acrylate (PEGMEA) based hydrophilic polymers incorporating maleimide group containing side-chains were synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization. A novel furan-protected maleimide-containing acrylate monomer was synthesized and copolymerized with hydrophilic monomers in the presence of a catechol moiety containing chain transfer unit. Removal of the furan protecting group after polymerization yields thiol-reactive polymers possessing an intact catechol unit at their chain-end for anchoring onto various surfaces. Polymers with varying composition of the masked maleimide monomer were obtained with narrow molecular weight distributions as inferred from size exclusion chromatography. Obtained polymers were characterized using proton nuclear magnetic resonance (1HNMR), infrared (IR) spectroscopy, and electrochemistry to establish their chemical composition. Oleic acid coated organo-dispersible magnetic nanoparticles were modified with the hydrophilic catechol terminated polymers to obtain water dispersible polymer-coated magnetic nanoparticles. The reactive maleimide units on the polymer-coated nanoparticles were utilized to conjugate thiol-containing hydrophobic dye using the nucleophilic Michael addition reaction to obtain water dispersible magnetic and fluorescent nanoparticles. Alternatively, it was demonstrated that radical thiol–ene reaction can also be utilized to functionalize nanoparticles coated with polymers where the maleimide group is in masked as a furan-cycloadduct. Efficient anchoring of the polymer onto nanoparticle surfaces and their subsequent functionalization was verified using various techniques such as infrared spectroscopy (IR), thermogravimetric analysis (TGA), and phase transfer studies, whereas the subsequent functionalization was evident from the organic to aqueous phase transfer of the hydrophobic fluorescent dye.

A novel ratiometric fluorescent probe through aggregation-induced emission and analyte-induced excimer dissociation

Ratiometric fluorescent sensing can minimize interfering effects and thus allow for more accurate and quantitative readouts. Ratiometric sensing can be achieved by adopting several mechanisms such as energy transfer and introduction of reference dye. Herein, we report a novel and facile approach for realizing fluorescent ratiometric sensing, which functions through aggregation-induced emission and analyte-induced excimer dissociation. For this sensing system, the fluorophore 9-anthraldehyde in its good solvent exhibits no monomer emission due to intramolecular charge transfer from anthracene moiety to aldehyde group; while in poor solvent such as water, 9-anthraldehyde molecules tend to aggregate and form excimers, which display yellow-green excimer emission. The presence of sulfite anions transforms the aldehyde groups into negatively charged ones in aqueous solution; this causes the excimers’ dissociation, makes the fluorophores exhibit blue monomer emission, and thereby realizes the ratiometric sensing for sulfite ion. The system shows a large emission wavelength separation (∼100nm) as well as highly selective and sensitive detection for sulfite with the detection limit of 3.19μM. Moreover, it can be applied to real samples such as red wine, beer and rain water.

Competitive adsorption of acid dyes from aqueous solution on diethylenetriamine‐modified chitosan beads

ABSTRACTThe interaction between two dyes (AO7 and AG25) during adsorption was studied in detail with diethylenetriamine‐modified chitosan beads (CTSN‐beads) as the adsorbent. Results indicate that the adsorption capacities and rates were directly related to the molecular size of the dye. The adsorption capacity and rate of AO7 could be greatly weakened by interaction with AG 25 during adsorption, which has a larger molecular size. The adsorption followed the pseudo‐second‐order kinetic equation and Freundlich model gave a satisfying correlation with the equilibrium data both in the single and binary component system. Adsorption could be divided into three stages, each controlled by different mechanisms. Temperature experiments showed high temperature was beneficial to the mass transfer of dyes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41168.

High glucose promotes gap junctional communication in cultured neonatal cardiac fibroblasts via AMPK activation

Cardiac fibroblasts are known to be essential for adaptiveresponses in the patho- genesis of cardiovascular diseases, and increased intercellular communication of myocardial cells and cardiac fibroblasts acts as a crucial factor in maintaining the functional integrity of the heart. AMP-activated kinase (AMPK) is a key stress signaling kinase, which plays an important role in promoting cell survival and improving cell function. However, the underlying link between AMPK and gap junctional communication (GJIC) is still poorly understood. In this study, a connection between AMPK and GJIC in high glucose-mediated neonatal cardiac fibroblasts was assessed using fibroblast migration, measurement of dye transfer and connexin43 (Cx43) expression. 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) and Compound C (CC) were used to regulate AMPK activity. The levels of cell migration and Cx43 protein expression in neonatal cardiac fibroblasts increased during high glucose treatment, accompanied by developed dye transfer. In addition, high glucose induced abundant phosphorylation of AMPK. Suppression of AMPK phosphorylation using CC reduced dye transfer, cell migration and Cx43 protein expression in neonatal cardiac fibroblasts, whereas the activation of AMPK using AICAR mimicked the high glucose-mediated cell migration, Cx43 protein expression and dye transfer enhancement. AMPK appears to participate in regulating GJIC in high-glucose-treated neonatal cardiac fibroblasts, including cell migration, dye transfer, Cx43 expression and distribution.