Connexin subtype expression during oral carcinogenesis: A pilot study in patients with oral squamous cell carcinoma

Connexins in epidermal health and diseases: insights into their mutations, implications, and therapeutic solutions

The epidermis, the outermost layer of the skin, serves as a protective barrier against external factors. Epidermal differentiation, a tightly regulated process essential for epidermal homeostasis, epidermal barrier formation and skin integrity maintenance, is orchestrated by several players, including signaling molecules, calcium gradient and junctional complexes such as gap junctions (GJs). GJ proteins, known as connexins facilitate cell-to-cell communication between adjacent keratinocytes. Connexins can function as either hemichannels or GJs, depending on their interaction with other connexons from neighboring keratinocytes. These channels enable the transport of metabolites, cAMP, microRNAs, and ions, including Ca2+, across cell membranes. At least ten distinct connexins are expressed within the epidermis and mutations in at least five of them has been linked to various skin disorders. Connexin mutations may cause aberrant channel activity by altering their synthesis, their gating properties, their intracellular trafficking, and the assembly of hemichannels and GJ channels. In addition to mutations, connexin expression is dysregulated in other skin conditions including psoriasis, chronic wound and skin cancers, indicating the crucial role of connexins in skin homeostasis. Current treatment options for conditions with mutant or altered connexins are limited and primarily focus on symptom management. Several therapeutics, including non-peptide chemicals, antibodies, mimetic peptides and allele-specific small interfering RNAs are promising in treating connexin-related skin disorders. Since connexins play crucial roles in maintaining epidermal homeostasis as shown with linkage to a range of skin disorders and cancer, further investigations are warranted to decipher the molecular and cellular alterations within cells due to mutations or altered expression, leading to abnormal proliferation and differentiation. This would also help characterize the roles of each isoform in skin homeostasis, in addition to the development of innovative therapeutic interventions. This review highlights the critical functions of connexins in the epidermis and the association between connexins and skin disorders, and discusses potential therapeutic options.

Pattern Distribution of Connexins in the Ortho- and Parakeratinized Epithelium of the Lingual Mucosa in Birds

Connexins are important proteins involved in cell-to-cell communication and cytodifferentiation during renewal and cornification of the multilayered epithelia. So far, there is a lack of reports on this subject in birds' structurally different ortho- and parakeratinized epithelium of the tongue. The study aims to describe the distribution and expression profiles of the α-connexins (Cx40 and 43) and β-connexins (Cx26, 30, and 31) in those epithelia in duck, goose, and domestic turkey. Research revealed the presence of the mentioned connexins and the occurrence of interspecies differences. Connexins form gap junctions in the cell membrane or are in the cytoplasm of keratinocytes. Differences in connexin expression were noted between the basal and intermediate layers, which may determine the proliferation of keratinocytes. Cx40, 43, and Cx30 in the gap junction of the keratinocytes of the intermediate layer are related to the synchronization of the cornification process. Because of the exfoliation of cornified plaques, a lack of connexins was observed in the cornified layer of orthokeratinized epithelium. However, in parakeratinized epithelium, connexins were present in the cell membrane of keratinocytes and thus maintained cellular integrity in gradually desquamating cells. The current studies will be useful in further comparative analyses of normal and pathological epithelia of the oral cavity in birds.

Connexin Expression in Pituitary Adenomas and the Effects of Overexpression of Connexin 43 in Pituitary Tumor Cell Lines

Gap junction intercellular communication (GJIC) is considered a key mechanism in the regulation of tissue homeostasis. GJIC structures are organized in two transmembrane channels, with each channel formed by connexins (Cxs). GJIC and Cxs expression alterations are related to the process of tumorigenesis in different cell types. Pituitary neuroendocrine tumors (PitNETs) represent 15–20% of intracranial neoplasms, and usually display benign behavior. Nevertheless, some may have aggressive behavior, invading adjacent tissues, and featuring a high proliferation rate. We aimed to assess the expression and relevance of GJIC and Cxs proteins in PitNETs. We evaluated the mRNA expression levels of Cx26, 32, and 43, and the protein expression of Cx43 in a series of PitNETs. In addition, we overexpressed Cx43 in pituitary tumor cell lines. At the mRNA level, we observed variable expression of all the connexins in the tumor samples. Cx43 protein expression was absent in most of the pituitary tumor samples that were studied. Moreover, in vitro studies revealed that the overexpression of Cx43 decreases cell growth and induces apoptosis in pituitary tumor cell lines. Our results indicate that the downregulation of Cx43 protein might be involved in the tumorigenesis of most pituitary adenomas and have a potential therapeutic value for pituitary tumor therapy.

Connexin 43 reduces susceptibility to sympathetic atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia reported in clinical practice. Connexin 43 (Cx43) is a member of the connexin protein family, which serves important roles in signal transduction in vivo. The aim of the present study was to investigate the role of Cx43 in the induction and maintenance of atrial fibrillation by using an animal model of sympathomimetic atrial fibrillation. Cx43 was successfully knocked down in the myocardium with gene‑specific small interfering (si)RNA via lentiviral infection. A total of 25 dogs were randomly and evenly divided into five groups: Normal (N), rapid atrial pacing (RAP), isoproterenol (ISO) + RAP, RAP + Cx43 siRNA and ISO + RAP + Cx43 siRNA. The mRNA and protein levels, as well as the distribution of Cx43 on the cell membrane, were gradually decreased in each group compared with the N group following treatment (P<0.05). The induction rate of the atrial effective refractory period was not significantly affected in the RAP and RAP + Cx43 siRNA groups, whereas it was significantly reduced in the ISO + RAP and ISO + RAP + Cx43 siRNA groups compared with the N group (P<0.05). The induction rate of AF was gradually increased in the RAP + Cx43 siRNA, ISO + RAP and ISO + RAP + Cx43 siRNA groups compared with the N group (P<0.05). The expression of nerve growth factor (NGF) and tyrosine hydroxylase (TH) was gradually increased in the ISO + RAP and ISO + RAP + Cx43 siRNA groups compared with their respective controls (RAP and RAP + Cx43 siRNA groups, respectively). However, no significant difference in the levels of NGF and TH was observed between the RAP, RAP + Cx43 siRNA, ISO + RAP and ISO + RAP + Cx43 siRNA groups. The mitochondrial morphology in each group was notably altered compared with the N group. The mitochondrial reactive oxygen species production and apoptotic index were gradually increased in each group compared with the N group (P<0.05). The results of the present study suggest that Cx43 reduces susceptibility to AF. Downregulation of Cx43 mediates the induction and maintenance of sympathetic AF.