Gap 26

Recent findings that a high proportion of non-syndromic hereditary sensorineural hearing loss is due to mutations in the gene for connexin 26 indicate the crucial role that the gene product plays for normal functioning of the cochlea. Excluding sensory cells, most cells in the cochlea are connected via gap junctions and these gap junctions appear to play critical roles in cochlear ion homeostasis. Connexin 26 occurs in gap junctions connecting all cell classes in the cochlea. There are two independent systems of cells, which are defined by interconnecting gap junctions. The first system, the epithelial cell gap junction system, is mainly composed of all organ of Corti supporting cells, and also includes interdental cells in the spiral limbus and root cells within the spiral ligament. The second system, the connective tissue cell gap junction system, consists of strial intermediate cells, strial basal cells, fibrocytes in the spiral ligament, mesenchymal cells lining the bony otic capsule facing the scala vestibuli, mesenchymal dark cells in the supralimbal zone, and fibrocytes in the spiral limbus. One function of these gap junctional systems is the recirculation of K(+) ions from hair cells to the strial marginal cells. Interruption of this recirculation, which may be caused by the mutation in connexin 26 gene, would deprive the stria vascularis of K(+) and result in hearing loss.

Normal development, function and repair of the sensory epithelia in the inner ear are all dependent on gap junctional intercellular communication. Mutations in the connexin genes GJB2 and GJB6 (encoding CX26 and CX30) result in syndromic and non-syndromic deafness via various mechanisms. Clinical vestibular defects, however, are harder to connect with connexin dysfunction. Cx26 and Cx30 proteins are widely expressed in the epithelial and connective tissues of the cochlea, where they may form homomeric or heteromeric gap junction channels in a cell-specific and spatiotemporally complex fashion. Despite the study of mutant channels and animal models for both recessive and dominant autosomal deafness, it is still unclear why gap junctions are essential for auditory function, and why Cx26 and Cx30 do not compensate for each other in vivo. Cx26 appears to be essential for normal development of the auditory sensory epithelium, but may be dispensable during normal hearing. Cx30 appears to be essential for normal repair following sensory cell loss. The specific modes of intercellular signalling mediated by inner ear gap junction channels remain undetermined, but they are hypothesised to play essential roles in the maintenance of ionic and metabolic homeostasis in the inner ear. Recent studies have highlighted involvement of gap junctions in the transfer of essential second messengers between the non-sensory cells, and have proposed roles for hemichannels in normal hearing. Here, we summarise the current knowledge about the molecular and functional properties of inner ear gap junctions, and about tissue pathologies associated with connexin mutations.

Skeletal muscle repair/regeneration may benefit by Platelet-Rich Plasma (PRP) treatment owing to PRP pro-myogenic and anti-fibrotic effects. However, PRP anti-fibrotic action remains controversial. Here, we extended our previous researches on the inhibitory effects of PRP on in vitro transforming growth factor (TGF)-β1-induced differentiation of fibroblasts into myofibroblasts, the effector cells of fibrosis, focusing on gap junction (GJ) intercellular communication. The myofibroblastic phenotype was evaluated by cell shape analysis, confocal fluorescence microscopy and Western blotting analyses of α-smooth muscle actin and type-1 collagen expression, and electrophysiological recordings of resting membrane potential, resistance, and capacitance. PRP negatively regulated myofibroblast differentiation by modifying all the assessed parameters. Notably, myofibroblast pairs showed an increase of voltage-dependent GJ functionality paralleled by connexin (Cx) 43 expression increase. TGF-β1-treated cells, when exposed to a GJ blocker, or silenced for Cx43 expression, failed to differentiate towards myofibroblasts. Although a minority, myofibroblast pairs also showed not-voltage-dependent GJ currents and coherently Cx26 expression. PRP abolished the TGF-β1-induced voltage-dependent GJ current appearance while preventing Cx43 increase and promoting Cx26 expression. This study adds insights into molecular and functional mechanisms regulating fibroblast-myofibroblast transition and supports the anti-fibrotic potential of PRP, demonstrating the ability of this product to hamper myofibroblast generation targeting GJs.

Hereditary hearing loss affects about 1 per 1000 children. Mutations in GJB2, which encodes the connexin 26 protein (Cx26) involved in cochlear homeostasis, are found in about 50% of patients with autosomal recessive non-syndromic hearing loss. Deciphering the trafficking pathway of cochlear Cx26 in situ should represent an advance in understanding the pathogenic significance of many of these mutations. Connexins trafficking and delivery to lipid raft-associated gap junction plaques usually requires successively microtubule and actin networks. Here we show that cochlear Cx26 exhibits an unusual trafficking pathway. We observed that Cx26 assembly occurs in non-lipid raft membrane domains and that junctional plaques are devoid of actin and associated zonula occludens proteins. Using cytoskeleton-disrupting drugs in organotypic culture, we found that cochlear Cx26 gap junction assembly requires microtubules but not actin filaments. Altogether, our data provide an unexpected insight into Cx26 trafficking pathway and gap junction assembly in the cochlea.

We use cross-national data on 26 EU countries to estimate how parenthood contributes to the gender wage gap, and assess how institutional elements affect this relationship. We find that irrespective of cultural norms and policies, fathers receive a wage premium, which increases the gender gap. Motherhood gaps vary across countries. The highest gaps are seen in Eastern European countries, where policies and norms lead to long absences from work. Moderate to small penalties are found in Continental Europe, Anglo-Saxon and Nordic countries, alongside higher maternal employment. No motherhood penalties are found for Southern EU countries, where mothers return to work quickly or exit the labor market indefinitely.

Purpose:To investigate the replacement of conventional grid by air gap in axiolateral hip radiographs. The optimal air gap distance was studied with respect to radiation dose and image quality using phantom images, as well as 26 patient axiolateral hip radiographs.Methods:The CDRAD phantom, along with polymethylmethacrylate slabs with thicknesses of 10.0, 14.6, and 20.0 cm was employed. The inverse image quality index and dose area product (DAP), as well as their combination, so called figure-of-merit (FOM) parameter, were evaluated for these images, with air gaps from 20 to 50 cm in increments of 10 cm. Images were compared to those acquired using a conventional grid utilized in hip radiography. Radiation dose was measured and kept constant at the surface of the detector by using a reference dosimeter. Verbal consent was asked from 26 patients to participate to the study. Air gap distances from 20 to 50 cm and tube current-time products from 8 to 50 mAs were employed. Exposure index, DAP, as well as patient height and weight were recorded. Two radiologists evaluated the image quality of 26 hip axiolateral projection images on a 3-point nondiagnostic - good/sufficiently good - too good scale. Source-to-image distance of 200 cm and peak tube voltage of 90 kVp were used in both studies.Results and conclusion:Based on the phantom study, it is possible to reduce radiation dose by replacing conventional grid with air gap without compromising image quality. The optimal air gap distance appears to be 30 cm, based on the FOM analysis. Patient study corroborates this observation, as sufficiently good image quality was found in 24 of 26 patient radiographs, with 7 of 26 images obtained with 30 cm air gap. Thus, air gap method, with an air gap distance of 30 cm, is recommended in axiolateral hip radiography.

Cells within the vast majority of human tissues communicate directly through clustered arrays of intercellular channels called gap junctions. Gene ablation studies in mouse models have revealed that these intercellular channels are necessary for a variety of organ functions and that some of these genes are essential for survival. Molecular genetics has uncovered that germ line mutations in nearly half of the genes that encode the 21-member connexin family of gap junction proteins are linked to one or more human diseases. Frequently, these mutations are autosomal recessive, whereas in other cases, autosomal dominant mutations manifest as disease. Given the broad and overlapping distribution of connexins in a wide arrangement of tissues, it is hard to predict where connexin-linked diseases will clinically manifest. For instance, the most prevalent connexin in the human body is connexin-43 (Cx43), yet autosomal dominant mutations in the GJA1 gene, which encodes Cx43, exhibit modest developmental disorders resulting in a disease termed oculodentodigital dysplasia. Autosomal recessive mutations in the gene encoding Cx26 result in moderate to severe sensorineural hearing loss, whereas autosomal dominant mutations produce hearing loss and a wide range of skin diseases, including palmoplantar keratoderma. Here, we will focus on autosomal dominant mutations of the genes encoding Cx26 and Cx43 in relation to models that link genotypes to phenotypic outcomes with particular reference to how these approaches provide insight into human disease.

There are >120 forms of non-syndromic deafness associated with identified genetic loci. In particular, mutation of the gap junction beta 2 gene (GJB2), which encodes connexin (CX)26 protein, is the most frequent cause of hereditary deafness worldwide. We previously described an induction method to develop functional CX26 gap junction-forming cells from mouse-induced pluripotent stem cells (iPSCs) and generated in vitro models for GJB2-related deafness. However, functional CX26 gap junction-forming cells derived from human iPSCs or embryonic stem cells (ESCs) have not yet been reported. In this study, we generated human iPSC-derived functional CX26 gap junction-forming cells (iCX26GJCs), which have the characteristics of cochlear supporting cells. These iCX26GJCs had gap junction plaque-like formations at cell-cell borders and co-expressed several markers that are expressed in cochlear supporting cells. Furthermore, we generated iCX26GJCs derived from iPSCs from two patients with the most common GJB2 mutation in Asia, and these cells reproduced the pathology of GJB2-related deafness. These in vitro models may be useful for establishing optimal therapies and drug screening for various mutations in GJB2-related deafness.

Key points:A moderate increase inPCO2(55 mmHg) closes Cx26 gap junctions. This effect of CO2is independent of changes in intra- or extracellular pH. The CO2-dependent closing effect depends on the same residues (K125 and R104) that are required for the CO2-dependent opening of Cx26 hemichannels. Pathological mutations of Cx26 abolish the CO2-dependent closing of the gap junction. Elastic network modelling suggests that the effect of CO2on Cx26 hemichannels and gap junctions is mediated through changes in the lowest entropy state of the protein.Abstract:Cx26 hemichannels open in response to moderate elevations of CO2(PCO255 mmHg) via a carbamylation reaction that depends on residues K125 and R104. Here we investigate the action of CO2on Cx26 gap junctions. Using a dye transfer assay, we found that an elevatedPCO2of 55 mmHg greatly delayed the permeation of a fluorescent glucose analogue (NBDG) between HeLa cells coupled by Cx26 gap junctions. However, the mutations K125R or R104A abolished this effect of CO2. Whole cell recordings demonstrated that elevated CO2reduced the Cx26 gap junction conductance (median reduction 66.7%, 95% CI, 50.5-100.0%) but had no effect on Cx26K125Ror Cx31 gap junctions. CO2can cause intracellular acidification. Using 30 mm propionate, we found that acidification in the absence of a change inPCO2caused a median reduction in the gap junction conductance of 41.7% (95% CI, 26.6-53.7%). This effect of propionate was unaffected by the K125R mutation (median reduction 48.1%, 95% CI, 28.0-86.3%). pH-dependent and CO2-dependent closure of the gap junction are thus mechanistically independent. Mutations of Cx26 associated with the keratitis ichthyosis deafness syndrome (N14K, A40V and A88V), in combination with the mutation M151L, also abolished the CO2-dependent gap junction closure. Elastic network modelling suggests that the lowest entropy state when CO2is bound is the closed configuration for the gap junction but the open state for the hemichannel. The opposing actions of CO2on Cx26 gap junctions and hemichannels thus depend on the same residues and presumed carbamylation reaction.

The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N=1,2,…,6 S-Mo-S monolayers have been investigated by optical spectroscopy. Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure. With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 0.6 eV. This leads to a crossover to a direct-gap material in the limit of the single monolayer. Unlike the bulk material, the MoS₂ monolayer emits light strongly. The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 10⁴ compared with the bulk material.