Connexin Genes Research Articles

The genetic and molecular basis of a connexin-linked skin disease.

Erythrokeratodermia variabilis et progressiva (EKVP) is a rare hereditary skin disorder characterized by hyperkeratotic plaques and erythematous patches that progressively worsen with age. This disorder has been associated with variants in three connexin encoding genes (GJA1, GJB3, GJB4) and four unrelated genes (KRT83, KDSR, TRPM4, PERP). Most cases of connexin-linked EKVP exhibit an autosomal dominant mode of inheritance, with rare autosomal recessive cases. Collectively, evidence suggests that connexin variants associated with EKVP elicit a plethora of molecular defects including impaired gap junction (GJ) formation, dysregulated hemichannel and/or GJ channel function, cytotoxicity, dominant disruption of co-expressed connexins, and/or altered turnover kinetics. Here, we review the progress made in understanding the genetic and molecular basis of EKVP associated with connexin gene variants. We also discuss the landscape of treatment options used for this disorder and the future directions for research into this rare condition.

Mutations of the Cx43 Gene in Non-Small Cell Lung Cancer: Association with Aberrant Localization of Cx43 Protein Expression and Tumor Progression.

Background and Objectives: The Connexin43 (Cx43) gene is a suspected tumor suppressor gene, as re-expressed wild-type Cx43 genes reduce the malignancy potential of tumor cells. However, the role of Cx43 gene expression in human lung tumorigenesis remains unclear. Materials and Methods: Tumor tissues from 165 primary lung cancer patients were collected to study Cx43 protein expression and gene mutations using immunohistochemistry and direct DNA sequencing. In addition, Cx43 genes with or without mutations were transfected to CL-3 human lung cancer cells to confirm the function of these mutant forms of the Cx43 gene. Results: Aberrant localization of Cx43 protein in the nucleus and cytoplasm of tumor cells was detected in 14 out of 165 non-small cell lung cancer (NSCLC) patients. Mutations in the Cx43 gene were also found in patients with aberrant Cx43 localization, and transfection of these mutant genes into lung cancer cells enhanced their proliferation. Conclusions: To our knowledge, this is the first study to demonstrate Cx43 gene mutations in human lung neoplasm, supporting the hypothesis that Cx43 may function as a tumor suppressor in some lung cancer patients. Additionally, the findings suggest an association between aberrant localization of Cx43 protein expression and tumor progression.

Determinants of vascular impairment in type 1 diabetes–impact of sex and connexin 37 gene polymorphism: A cross-sectional study

BackgroundThe associations of risk factors with vascular impairment in type 1 diabetes patients seem more complex than that in type 2 diabetes patients. Therefore, we analyzed the associations between traditional and novel cardiovascular risk factors and vascular parameters in individuals with T1D and modifications of these associations according to sex and genetic factors.MethodsIn a cross-sectional study, we analyzed the association of risk factors in T1D individuals younger than 65 years using vascular parameters, such as ankle brachial index (ABI) and toe brachial index (TBI), duplex ultrasound, measuring the presence of plaques in carotid and femoral arteries (Belcaro score) and intima media thickness of carotid arteries (CIMT). We also used photoplethysmography, which measured the interbranch index expressed as the Oliva-Roztocil index (ORI), and analyzed renal parameters, such as urine albumin/creatinine ratio (uACR) and glomerular filtration rate (GFR). We evaluated these associations using multivariate regression analysis, including interactions with sex and the gene for connexin 37 (Cx37) polymorphism (rs1764391).ResultsIn 235 men and 227 women (mean age 43.6 ± 13.6 years; mean duration of diabetes 22.1 ± 11.3 years), pulse pressure was strongly associated with unfavorable values of most of the vascular parameters under study (ABI, TBI, Belcaro scores, uACR and ORI), whereas plasma lipids, represented by remnant cholesterol (cholesterol – LDL-HDL cholesterol), the atherogenic index of plasma (log (triglycerides/HDL cholesterol) and Lp(a), were associated primarily with renal impairment (uACR, GFR and lipoprotein (a)). Plasma non-HDL cholesterol was not associated with any vascular parameter under study. In contrast to pulse pressure, the associations of lipid factors with kidney and vascular parameters were modified by sex and the Cx37 gene.ConclusionIn addition to known information, easily obtainable risk factor, such as pulse pressure, should be considered in individuals with T1D irrespective of sex and genetic background. The associations of plasma lipids with kidney function are complex and associated with sex and genetic factors. The decision of whether pulse pressure, remnant lipoproteins, Lp(a) and other determinants of vascular damage should become treatment targets in T1D should be based on the results of future clinical trials.Graphical

Chronic dietary exposure to glyphosate-induced connexin 43 autophagic degradation contributes to blood-testis barrier disruption in roosters

Glyphosate (GLY) is the most universally used herbicide worldwide and its application has caused extensive pollution to the ecological environment. Increasing evidence has revealed the multi-organ toxicity of GLY in different species, but its male reproductive toxicity in avian species remains unknown. Thus, in vivo and in vitro studies were conducted to clarify this issue. Data firstly showed that chronic GLY exposure caused testicular pathological damage. Intriguingly, we identified and verified a marked down-regulation gap junction gene Connexin 43 (Cx43) in GLY-exposed rooster testis by transcriptome analysis. Cx43 generated by Sertoli cells acts as a key component of blood-testis barrier (BTB). To further investigate the cause of GLY-induced downregulation of Cx43 to disrupt BTB, we found that autophagy activation is revealed in GLY-exposed rooster testis and primary avian Sertoli cells. Moreover, GLY-induced Cx43 downregulation was significantly alleviated by ATG5 knockdown or CQ administration, respectively, demonstrating that GLY-induced autophagy activation contributed to Cx43 degradation. Mechanistically, GLY-induced autophagy activation and resultant Cx43 degradation was due to its direct interaction with ER-α. In summary, these findings demonstrate that chronic GLY exposure activates autophagy to induce Cx43 degradation, which causes BTB damage and resultant reproductive toxicity in roosters.

Pharmacological activation of mesenchymal stem cells increases gene expression pattern of cell adhesion molecules and fusion with neonatal cardiomyocytes.

Cellular therapy is considered a better option for the treatment of degenerative disorders. Different cell types are being used for tissue regeneration. Despite extensive research in this field, several issues remain to be addressed concerning cell transplantation. One of these issues is the survival and homing of administered cells in the injured tissue, which depends on the ability of these cells to adhere. To enhance cell adherence and survival, Rap1 GTPase was activated in mesenchymal stem cells (MSCs) as well as in cardiomyocytes (CMs) by using 8-pCPT-2'-O-Me-cAMP, and the effect on gene expression dynamics was determined through quantitative reverse transcriptase-polymerase chain reactionanalysis. Pharmacological activation of MSCs and CMsresulted in the upregulation of connexin-43 and cell adhesion genes, which increased the cell adhesion ability of MSCs and CMs, and increased the fusion of MSCs with neonatal CMs. Treating stem cells with a pharmacological agent that activates Rap1a before transplantation can enhance their fusion with CMs and increase cellular regeneration.

Gap-junction-mediated bioelectric signaling required for slow muscle development and function in zebrafish

Bioelectric signaling, intercellular communication facilitated by membrane potential and electrochemical coupling, is emerging as a key regulator of animal development. Gap junction (GJ) channels can mediate bioelectric signaling by creating a fast, direct pathway between cells for the movement of ions and other small molecules. In vertebrates, GJ channels are formed by a highly conserved transmembrane protein family called the connexins. The connexin gene family is large and complex, creating challenges in identifying specific connexins that create channels within developing and mature tissues. Using the embryonic zebrafish neuromuscular system as a model, we identify a connexin conserved across vertebrate lineages, gjd4, which encodes the Cx46.8 protein, that mediates bioelectric signaling required for slow muscle development and function. Through mutant analysis and invivo imaging, we show that gjd4/Cx46.8 creates GJ channels specifically in developing slow muscle cells. Using genetics, pharmacology, and calcium imaging, we find that spinal-cord-generated neural activity is transmitted to developing slow muscle cells, and synchronized activity spreads via gjd4/Cx46.8 GJ channels. Finally, we show that bioelectrical signal propagation within the developing neuromuscular system is required for appropriate myofiber organization and that disruption leads to defects in behavior. Our work reveals a molecular basis for GJ communication among developing muscle cells and reveals how perturbations to bioelectric signaling in the neuromuscular system may contribute to developmental myopathies. Moreover, this work underscores a critical motif of signal propagation between organ systems and highlights the pivotal role of GJ communication in coordinating bioelectric signaling during development.

Early diagnosis of Voh Winkel syndrome-inherited honeycombed hands and hearing loss

Voh-Winkel Syndrome with approximately 50 cases reported in literature is a rare inherited Palmoplantar keratoderma characterised by honeycomb like hyperkeratosis, hearing loss or ichthyosis. It also features constricting fibrous bands that develop at the base of fingers/toes and later get strangulated to cause autoamputation called pseudoainhum. It is an autosomal dominant disorder with mutations in loricrin and connexin genes leading to hearing loss and ichthyosis variants respectively and manifests in infancy and becomes apparent later in childhood or adult life. Early diagnosis of this condition and management by multiple specialities given the associated features therefore becomes an absolute necessity. An emphasis on dermatological examination to manage hyperkeratosis using topical and systemic therapy, otorhinolaryngology to manage hearing loss as well as plastic surgery to alleviate symptoms arising due to the constriction bands is mandatory for effective management of this condition. Here we report a 22-year-old female patient who came with Palmoplantar keratoderma, bilateral hearing loss and pseudo-ainhum.

Genetically engineered human embryonic kidney cells as a novel vehicle for dual patch clamp study of human gap junction channels.

Mutations in more than half of human connexin genes encoding gap junction (GJ) subunits have been linked to inherited human diseases. Functional studies of human GJ channels are essential for revealing mechanistic insights into the etiology of disease-linked connexin mutants. However, the commonly used Xenopus oocytes, N2A, HeLa, and other model cells for recombinant expression of human connexins have different and significant limitations. Here we developed a human cell line (HEK293) with each of the endogenous connexins (Cx43 and Cx45) knocked out using the CRISPR-Cas9 system. Double knockout HEK293 cells showed no background GJ coupling, were easily transfected with several human connexin genes (such as those encoding Cx46, Cx50, Cx37, Cx45, Cx26, and Cx36) which successfully formed functional GJs and were readily accessible for dual patch clamp analysis. Single knockout Cx43 or Cx45 HEK cell lines could also be used to characterize human GJ channels formed by Cx45 or Cx43, respectively, with an expression level suitable for studying macroscopic and single channel GJ channel properties. A cardiac arrhythmia linked Cx45 mutant R184G failed to form functional GJs in DKO HEK293 cells with impaired localizations. These genetically engineered HEK293 cells are well suited for patch clamp study of human GJ channels.

Modulation of the expression of connexins 37, 40, and 43 in endothelial cells in a culture.

Connexin (Cx) 37, 40, and 43 are implicated in vascular function, specifically in the electrical coupling of endothelial cells and vascular smooth-muscle cells. In the present study, we investigated whether factors implicated in vascular dysfunction can modulate the gene expression of Cx37, Cx40, and Cx43 and whether this is associated with changes in endothelial layer barrier function in human microvascular endothelial cells (HMEC-1). First, HMEC-1 were subjected to stimuli for 4 and 8h. We tested their responses to DETA-NONOate, H2O2, high glucose, and angiotensin II, none of which relevantly affected the transcription of the connexin genes. Next, we tested inflammatory factors IL-6, interferon gamma (IFNγ), and TNFα. IFNγ (10ng/mL) consistently induced Cx40 expression at 4 and 8 h to 10-20-fold when corrected for the control. TNFα and IL-6 resulted in small but significant depressions of Cx37 expression at 4h. Two JAK inhibitors, epigallocatechin-3-gallate (EGCG) (100-250μM) and AG490 (100-250μM), dose-dependently inhibited the induction of Cx40 expression by IFNγ. Subsequently, HMEC-1 were subjected to 10ng/mL IFNγ for 60h, and intercellular and transcellular impedance was monitored by electric cell-substrate impedance sensing (ECIS). In response to IFNγ, junctional-barrier impedance increased more than cellular-barrier impedance; this was prevented by AG490 (5μM). In conclusion, IFNγ can strongly induce Cx40 expression and modify the barrier properties of the endothelial cell membrane through the JAK/STAT pathway. Moreover, the Cx37, Cx40, and Cx43 expression in endothelial cells is stable and, apart from IFNγ, not affected by a number of factors implicated in endothelial dysfunction and vascular diseases.

Audiological Phenotypes of Connexin Gene Mutation Patterns: A Glance at Different GJB2/GJB6 Gene Mutation Profiles.

GJB2 mutations are the most common cause of autosomal-recessive non-syndromic sensorineural hearing loss (SNHL). The available evidence shows large phenotypic variability across different genotypes and allelic variants. The aim of this study was to investigate the clinical and audiological features of a cohort of subjects with different GJB2/GJB6 gene mutation profiles from a tertiary referral center in Northeastern Italy. We considered 57 patients with GJB2/GJB6 mutations presenting with congenital, non-syndromic SNHL, mainly coming from the Veneto region (Italy). The samples were screened for mutations in exons 1 and 2 of the GJB2 gene and for the GJB6 gene deletion del (GJB6-D13S1830). Free-field and air-conduction frequency-specific thresholds and the pure-tone average (PTA) were considered in the statistical analysis. Five patients (8.87%) had connexin gene mutations in simple heterozygosis, 15 (26.31%) in compound heterozygosis, 34 (59.64%) in homozygosis, and 3 (5.26%) with digenic patterns. The frequency-specific air-conduction thresholds showed significantly different mean values across the different genotypes (Roy's largest-root test, p = 0.0473). Despite the evidence already available on genetic SNHL, many new insights are to be expected. Further large-scale prospective studies including different populations are necessary to confirm these preliminary findings about the clinical and audiological features of patients with different GJB2/GJB6 gene mutation patterns.

P02 Erythrokeratodermia variabilis et progressiva due to a pathogenic variant in GJB3 gene

Abstract Erythrokeratodermia variabilis et progressiva (EKVP) is a clinically heterogeneous group of inherited disorders characterized by the coexistence of localized or generalized hyperkeratotic plaques and transient, stationary or migratory erythematous patches. EKPV is most often transmitted in an autosomal dominant manner. Causal pathogenic variants have been detected in the GJB3, GJB4, GJA1 KDSR and KRT83 genes encoding connexins 31, 30.3, 43, 3-ketodihydrosphingosine reductase and keratin 83, respectively. Connexins are expressed in almost all tissues and pathogenic variants in the connexin genes can cause skin diseases, cardiovascular disorders, myelin-related diseases, craniofacial disorders and hearing loss. We present a 2-year-old girl who was referred to our centre with well-demarcated hyperkeratotic plaques symmetrically distributed with a predilection for the distal extremities and buttocks as well as erythematous plaques on her cheeks. The hyperkeratotic plaques were hyperpigmented, exhibited a geographic morphology and had prominent hypertrichosis. Her trunk and upper extremities were spared and her hair, teeth and nails were normal. There was family history of mild psoriasis in her mother and mild eczema in her father. Next generation sequencing confirmed she was heterozygous for the GJB3 c.625C>T p.(Leu209Phe) pathogenic variant which is associated with erythrokeratodermia variabilis et progressiva-1 (MIM 133200) and autosomal dominant deafness-2B (MIM 612644). Erythrokeratodermia variabilis is largely a skin-limited condition however GJB3 pathogenic variants can cause haring loss and neuropathy due to its expression in peripheral nerves and the cochlea. Our patient’s hearing and development have been normal to date and will be monitored.

Hepatotoxicity of cyanotoxin microcystin-LR in human: Insights into mechanisms of action in the 3D culture model Hepoid-HepaRG

Microcystin-LR (MC-LR) is a potent hepatotoxin produced by harmful cyanobacterial blooms (CyanoHABs). MC-LR targets highly differentiated hepatocytes expressing organic anion transporting polypeptides OATP1B1 and OATP1B3 that are responsible for hepatocellular uptake of the toxin. The present study utilized an advanced 3D in vitro human liver model Hepoid-HepaRG based on the cultivation of collagen-matrix embedded multicellular spheroids composed of highly differentiated and polarized hepatocyte-like cells. 14-d-old Hepoid-HepaRG cultures showed increased expression of OATP1B1/1B3 and sensitivity to MC-LR cytotoxicity at concentrations >10 nM (48 h exposure, EC20 = 26 nM). MC-LR induced neither caspase 3/7 activity nor expression of the endoplasmic reticulum stress marker gene BiP/GRP78, but increased release of pro-inflammatory cytokine IL-8, indicating a necrotic type of cell death. Subcytotoxic (10 nM) and cytotoxic (≥100 nM) MC-LR concentrations disrupted hepatocyte functions, such as xenobiotic metabolism phase-I enzyme activities (cytochrome P450 1A/1B) and albumin secretion, along with reduced expression of CYP1A2 and ALB genes. MC-LR also decreased expression of HNF4A gene, a critical regulator of hepatocyte differentiation and function. Genes encoding hepatobiliary membrane transporters (OATP1B1, BSEP, NTCP), hepatocyte gap junctional gene connexin 32 and the epithelial cell marker E-cadherin were also downregulated. Simultaneous upregulation of connexin 43 gene, primarily expressed by liver progenitor and non-parenchymal cells, indicated a disruption of tissue homeostasis. This was associated with a shift in the expression ratio of E-cadherin to N-cadherin towards the mesenchymal cell marker, a process linked to epithelial-mesenchymal transition (EMT) and hepatocarcinogenesis. The effects observed in the human liver cell in vitro model revealed mechanisms that can potentially contribute to the MC-LR-induced promotion and progression of hepatocellular carcinoma (HCC). Hepoid-HepaRG cultures provide a robust, accessible and versatile in vitro model, capable of sensitively detecting hepatotoxic effects at toxicologically relevant concentrations, allowing for assessing hepatotoxicity mechanisms, human health hazards and impacts of environmental hepatotoxins, such as MC-LR.

The impact of duration and control of type 1 diabetes mellitus on microvascular function is strongly modified by the gene for connexin 37

Abstract Introduction Type 1 diabetes mellitus (T1DM) is almost inevitably accompanied by microvascular dysfunction. This could be responsible for cardiovascular events and is supposed to be caused mainly by long-term exposure to hyperglycemia. Nevertheless, relationship between duration and control of T1DM with microvascular complications can be modified by genetic factors; one of frequently discussed candidate genes is connexin37 (cx37), namely its rs1764391 (C1019>T (Pro319>Ser) polymorphism. We already observed sex specific association between cx37 polymorphism with macrovascular changes but also with retinopathy, neuropathy and diabetic foot. In the recent study, we analyzed if the impact of duration and control of T1DM on directly measured microvascular function is modified by cx37 gene polymorphism. Methods In 235 men and 227 women with T1DM (mean age 43.6 ± 13.6 years; mean duration of diabetes 22.1 ± 11.3 years) wide spectrum of clinical, laboratory and hemodynamic parameters was measured. Establishment of microvascular function measured by photoplethysmography (detection of blood volume changes in the microvasculature in lower extremities) and calculated as Oliva/Roztocil index (ORI), was analyzed. Cx37 gene polymorphism was measured by PCR-RFLP. The correlation (Pearson’s correlation coefficient) between duration of T1DM and ORI was calculated including analysis of potential modification by control of diabetes (HbA1c) and by cx37 gene polymorphism and standardized for potential confounders (sex, age, smoking, presence of hypertension, central obesity …) by multiple regression. The analysis was conducted separately for duration of T1DM below (n=256) and above (n=206) 20 years as the linear relationship between ORI and T1DM duration tends to change accordingly. Results In patients with T1DM, distribution of Cx37 genotypes did not differ from the already described populations (TT/CT/CC: 9.7/44.4/45.9%). In patients with satisfactory control of diabetes (HbA1c<53 mmol/mol; n=105) we detected worsening (increase) of ORI with duration of diabetes only in TT homozygotes and CT heterozygotes for duration of at least 20 years (r=0.6, p=0.006), while in patients with unsatisfactory control (HbA1c>60 mmol/mol;n=270), we detected worsening of ORI with duration of diabetes only in CC homozygotes, both for duration 0-20 years (r=0.35, p=0.03) and for duration of at least 20 years (r=0.47, p=0.03). Conclusion Microvascular function in satisfactory controlled T1DM was worsening with diabetes duration only in T allele carriers of Cx37 gene, the worsening was detected only for patients with duration longer than 20 years. However, if T1DM control was insufficient, microcirculation was worsening only in CC homozygotes.

Endocytosis and Endocytic Motifs across the Connexin Gene Family.

Proteins fated to be internalized by clathrin-mediated endocytosis require an endocytic motif, where AP-2 or another adaptor protein can bind and recruit clathrin. Tyrosine and di-leucine-based sorting signals are such canonical motifs. Connexin 43 (Cx43) has three canonical tyrosine-based endocytic motifs, two of which have been previously shown to recruit clathrin and mediate its endocytosis. In addition, di-leucine-based motifs have been characterized in the Cx32 C-terminal domain and shown to mediate its endocytosis. Here, we examined the amino acid sequences of all 21 human connexins to identify endocytic motifs across the connexin gene family. We find that although there is limited conservation of endocytic motifs between connexins, 14 of the 21 human connexins contain one or more canonical tyrosine or di-leucine-based endocytic motif in their C-terminal or intracellular loop domain. Three connexins contain non-canonical (modified) di-leucine motifs. However, four connexins (Cx25, Cx26, Cx31, and Cx40.1) do not harbor any recognizable endocytic motif. Interestingly, live cell time-lapse imaging of different GFP-tagged connexins that either contain or do not contain recognizable endocytic motifs readily undergo endocytosis, forming clearly identifiable annular gap junctions when expressed in HeLa cells. How connexins without defined endocytic motifs are endocytosed is currently not known. Our results demonstrate that an array of endocytic motifs exists in the connexin gene family. Further analysis will establish whether the sites we identified in this in silico analysis are legitimate endocytic motifs.

Inherited disease-linked arginine76/75 mutants in Cx50 and Cx45 showed impaired homotypic and heterotypic gap junction function, but not Cx43.

Connexins form intercellular communication channels, known as gap junctions (GJs), in many tissues/organs. Mutations in connexin genes are found to be linked to various inherited diseases, but the mechanisms are not fully clear. The Arg76 (R76) in Cx50 is fully conserved across the entire connexin family and is a hotspot for five connexin-linked inherited diseases, including Cx50 and Cx46-linked congenital cataract, Cx43-linked oculodentodigital dysplasia, and Cx45-linked cardiac arrhythmias. To better understand the molecular and cellular mechanism of dysfunction caused by R76/75 mutations, we examined the functional status and properties of GJs containing R76 mutations in Cx50 (R76H/C), Cx43 (R76H/S/C), and Cx45 (R75H) with an emphasis on heterotypic GJs in connexin-deficient model cells. All tested mutants showed an impairment of homotypic GJ function reflected by a decreased coupling% and conductance, except for Cx43 R76H/S. These connexin mutants also showed impaired GJ function when paired with a docking compatible connexin, such as Cx50/Cx46 or Cx45/Cx43, except for all mutants on Cx43 which formed functional heterotypic GJs with Cx45. Localization studies on fluorescent protein tagged connexin mutants revealed that Cx45 R75H and Cx43 R76C showed impaired localization. Our homology structure models indicated that mutations of R76/75 in these GJs led to a loss of intra- and/or inter-connexin non-covalent interactions (salt bridges) at the sidechain of this residue, which could contribute to the observed GJ impairments underlying diseases. It is interesting that unlike those disease-linked variants in Cx50 and Cx45, Cx43 can tolerate some variations at R76.

Multi-omics analysis of expression profile and prognostic values of connexin family in LUAD.

Our study first explored the expression differences and prognostic significance of Cx genes in pan-cancer and then focused on LUAD. Our objectives were to conducted a comprehensive analysis of the expression profile, prognostic significance, genetic alterations, potential biological functions and drug sensitivity of the Connexin gene family in LUAD. We developed a comprehensive prognostic model for LUAD by combining risk scores with clinical features and created a nomogram to predict 1-, 3-, and 5-year overall survival. Using single-cell sequencing, we examined the expression and biological functions of the identified prognostic markers. Our risk model revealed that GJB2-5 play a critical role in the prognosis of LUAD patients, associated with many biological processes such as cell cycle, DNA damage, EMT, hypoxia, invasion, and metastasis. Furthermore, the connexin gene family is linked to transcriptional mechanisms such as the extracellular matrix (ECM), migration, mobility, angiogenesis, and the epithelial-mesenchymal transition (EMT) genetic program. The risk model can be used as a potential prognostic factor for LUAD patients and may provide new insights into cancer treatment from perspective of the expression of Cx genes.

Cytomembrane Trafficking Pathways of Connexin 26, 30, and 43.

The connexin gene family is the most prevalent gene that contributes to hearing loss. Connexins 26 and 30, encoded by GJB2 and GJB6, respectively, are the most abundantly expressed connexins in the inner ear. Connexin 43, which is encoded by GJA1, appears to be widely expressed in various organs, including the heart, skin, the brain, and the inner ear. The mutations that arise in GJB2, GJB6, and GJA1 can all result in comprehensive or non-comprehensive genetic deafness in newborns. As it is predicted that connexins include at least 20 isoforms in humans, the biosynthesis, structural composition, and degradation of connexins must be precisely regulated so that the gap junctions can properly operate. Certain mutations result in connexins possessing a faulty subcellular localization, failing to transport to the cell membrane and preventing gap junction formation, ultimately leading to connexin dysfunction and hearing loss. In this review, we provide a discussion of the transport models for connexin 43, connexins 30 and 26, mutations affecting trafficking pathways of these connexins, the existing controversies in the trafficking pathways of connexins, and the molecules involved in connexin trafficking and their functions. This review can contribute to a new way of understanding the etiological principles of connexin mutations and finding therapeutic strategies for hereditary deafness.

Study of The Molecular Nature of Congenital Cataracts in Patients from The Volga–Ural Region

Hereditary cataracts are characterized by significant clinical and genetic heterogeneity, which can pose challenges for early DNA diagnosis. To comprehensively address this problem, it is essential to investigate the epidemiology of the disease, perform population studies to determine the spectrum and frequencies of mutations in the responsible genes, and examine clinical and genetic correlations. Based on modern concepts, non-syndromic hereditary cataracts are predominantly caused by genetic disease forms associated with mutations in crystallin and connexin genes. Therefore, a comprehensive approach to studying hereditary cataracts is necessary for early diagnosis and improved treatment outcomes. The crystallin (CRYAA, CRYAB, CRYGC, CRYGD, and CRYBA1) and connexin (GJA8, GJA3) genes were analyzed in 45 unrelated families from the Volga–Ural Region (VUR) with hereditary congenital cataracts. Pathogenic and probably pathogenic nucleotide variants were identified in ten unrelated families, nine of which had cataracts in an autosomal dominant pattern of inheritance. Two previously undescribed likely pathogenic missense variants were identified in the CRYAA gene: c.253C > T (p.L85F) in one family and c.291C > G (p.H97Q) in two families. The known mutation c.272_274delGAG (p.G91del) was found in the CRYBA1 gene in one family, while no pathogenic variants were found in the CRYAB, CRYGC, or CRYGD genes in the examined patients. In the GJA8 gene, the known mutation c.68G > C (p.R23T) was found in two families, and previously undescribed variants were identified in two other families: a c.133_142del deletion (p.W45Sfs*72) and a missense variant, c.179G > A (p.G60D). In one patient with a recessive form of cataract, two compound-heterozygous variants were identified—a previously undescribed likely pathogenic missense variant, c.143A > G (p.E48G), and a known variant with uncertain pathogenetic significance, c.741T > G (p.I24M). Additionally, a previously undescribed deletion, c.del1126_1139 (p.D376Qfs*69), was identified in the GJA3 gene in one family. In all families where mutations were identified, cataracts were diagnosed either immediately after birth or during the first year of life. The clinical presentation of the cataracts varied depending on the type of lens opacity, resulting in various clinical forms. This information emphasizes the importance of early diagnosis and genetic testing for hereditary congenital cataracts to guide appropriate management and improve outcomes.

Mechanisms of Diseases Associated with Mutation in GJC2/Connexin 47

Connexins are members of a family of integral membrane proteins that provide a pathway for both electrical and metabolic coupling between cells. Astroglia express connexin 30 (Cx30)-GJB6 and Cx43-GJA1, while oligodendroglia express Cx29/Cx31.3-GJC3, Cx32-GJB1, and Cx47-GJC2. Connexins organize into hexameric hemichannels (homomeric if all subunits are identical or heteromeric if one or more differs). Hemichannels from one cell then form cell-cell channels with a hemichannel from an apposed cell. (These are termed homotypic if the hemichannels are identical and heterotypic if the hemichannels differ). Oligodendrocytes couple to each other through Cx32/Cx32 or Cx47/Cx47 homotypic channels and they couple to astrocytes via Cx32/Cx30 or Cx47/Cx43 heterotypic channels. Astrocytes couple via Cx30/Cx30 and Cx43/Cx43 homotypic channels. Though Cx32 and Cx47 may be expressed in the same cells, all available data suggest that Cx32 and Cx47 cannot interact heteromerically. Animal models wherein one or in some cases two different CNS glial connexins have been deleted have helped to clarify the role of these molecules in CNS function. Mutations in a number of different CNS glial connexin genes cause human disease. Mutations in GJC2 lead to three distinct phenotypes, Pelizaeus Merzbacher like disease, hereditary spastic paraparesis (SPG44) and subclinical leukodystrophy.

Genome-wide association study of varicose veins identifies a protective missense variant in GJD3 enriched in the Finnish population

Varicose veins is the most common manifestation of chronic venous disease that displays female-biased incidence. To identify protein-inactivating variants that could guide identification of drug target genes for varicose veins and genetic evidence for the disease prevalence difference between the sexes, we conducted a genome-wide association study of varicose veins in Finns using the FinnGen dataset with 17,027 cases and 190,028 controls. We identified 50 associated genetic loci (P < 5.0 × 10−8) of which 29 were novel including one near ERG with female-specificity (rs2836405-G, OR[95% CI] = 1.09[1.05–1.13], P = 3.1 × 10−8). These also include two X-chromosomal (ARHGAP6 and SRPX) and two autosomal novel loci (TGFB2 and GJD3) with protein-coding lead variants enriched above 56-fold in Finns over non-Finnish non-Estonian Europeans. A low-frequency missense variant in GJD3 (p.Pro59Thr) is exclusively associated with a lower risk for varicose veins (OR = 0.62 [0.55–0.70], P = 1.0 × 10−14) in a phenome-wide scan of the FinnGen data. The absence of observed pleiotropy and its membership of the connexin gene family underlines GJD3 as a potential connexin-modulating therapeutic strategy for varicose veins. Our results provide insights into varicose veins etiopathology and highlight the power of isolated populations, including Finns, to discover genetic variants that inform therapeutic development.