Connexins, Pannexins, and Their Channels in Fibroproliferative Diseases.

Cellular and molecular mechanisms of wound healing, tissue repair, and fibrogenesis are established in different organs and are essential for the maintenance of function and tissue integrity after cell injury. These mechanisms are also involved in a plethora of fibroproliferative diseases or organ-specific fibrotic disorders, all of which are associated with the excessive deposition of extracellular matrix components. Fibroblasts, which are key cells in tissue repair and fibrogenesis, rely on communicative cellular networks to ensure efficient control of these processes and to prevent abnormal accumulation of extracellular matrix into the tissue. Despite the significant impact on human health, and thus the epidemiologic relevance, there is still no effective treatment for most fibrosis-related diseases. This paper provides an overview of current concepts and mechanisms involved in the participation of cellular communication via connexin-based pores as well as pannexin-based channels in the processes of tissue repair and fibrogenesis in chronic diseases. Understanding these mechanisms may contribute to the development of new therapeutic strategies to clinically manage fibroproliferative diseases and organ-specific fibrotic disorders.

Maternal immune activation in late gestation increases neuroinflammation and aggravates experimental autoimmune encephalomyelitis in the offspring.

Multiple sclerosis (MS) is characterized by an autoimmune response against myelin antigens driven by autoreactive T cells. Several lines of evidence indicate that environmental factors, such as previous infection, can influence and trigger autoimmune responses. However, the importance of the gestational period, particularly under inflammatory conditions, on the modulation of MS and related neuroinflammation by the offspring is unknown. This study aimed to evaluate the impact of prenatal exposure to lipopolysaccharide (LPS) during late gestation on the neuroinflammatory response in primary mixed glial cultures and on the progression of experimental autoimmune encephalomyelitis (EAE, an animal model of MS) in the offspring. LPS (Escherichia coli 0127:B8, 120µg/kg) was administered intraperitoneally to pregnant C57BL/6J mice on gestational day 17, and the offspring were assigned to two experiments: (1) mixed glial cultures generated using the brain of neonates, stimulated in vitro with LPS, and (2) adult offspring immunized with MOG35-55. The EAE clinical symptoms were followed for 30days. Different sets of animals were sacrificed either during the onset (7days post-immunization [p.i.]), when spleen and lymph nodes were collected, or the peak of disease (20days p.i.), when CNS were collected for flow cytometry, cytokine production, and protein/mRNA-expression analysis. The primary CNS cultures from the LPS-treated group produced exaggerated amounts of IL-6, IL-1ß and nitrites after in vitro stimulus, while IL-10 production was lowered compared to the data of the control group. Prenatal exposure to LPS worsened EAE disease severity in adult offspring, and this worsening was linked to increased CNS-infiltrating macrophages, Th1 cells and Th17 cells at the peak of EAE severity; additionally, exacerbated gliosis was evidenced in microglia (MHC II) and astrocytes (GFAP protein level and immunoreactivity). The IL-2, IL-6 and IL-17 levels in the spleen and lymph nodes were increased in the offspring of the LPS-exposed dams. Our results indicate that maternal immune activation during late gestation predispose the offspring to increased neuroinflammation and potentiate the autoimmune response and clinical manifestation of EAE.

Electroporation transiently decreases GJB2 (connexin 26) expression in B16/BL6 melanoma cell line.

Connexins are proteins that form gap junctions. Perturbations in the cell membrane reportedly promote changes in the expression profile of connexins. Electroporation promotes destabilization by applying electrical pulses, and this procedure is used in electrochemotherapy and gene therapy, among others. This in vitro work aimed to study the interference of electroporation on the expression profile of GJB2 (Cx26 gene) and Connexin 26 in melanoma cell line B16/BL6. The techniques of immunocytochemistry, Western blot, and real-time PCR were used. After electroporation, cells showed a transient decrease in GJB2 mRNA. The immunostaining of Cx26 showed no noticeable change after electroporation at different time points. However, Western blot showed a significant reduction in Cx26 30 min after electroporation. Our results showed that electroporation interferes transiently in the expression of Connexin 26 in melanoma and are consistent with the idea that electroporation is a process of intense stress that promotes cell homeostatic imbalance and results in disruption of cell physiological processes such as transcription and translation.

Connexin and pannexin (hemi)channels in the liver.

The liver was among the first organs in which connexin proteins have been identified. Hepatocytes harbor connexin32 and connexin26, while non-parenchymal liver cells typically express connexin43. Connexins give rise to hemichannels, which dock with counterparts on adjacent cells to form gap junctions. Both hemichannels and gap junctions provide pathways for communication, via paracrine signaling or direct intercellular coupling, respectively. Over the years, hepatocellular gap junctions have been shown to regulate a number of liver-specific functions and to drive liver cell growth. In the last few years, it has become clear that connexin hemichannels are involved in liver cell death, particularly in hepatocyte apoptosis. This also holds true for hemichannels composed of pannexin1, a connexin-like protein recently identified in the liver. Moreover, pannexin1 hemichannels are key players in the regulation of hepatic inflammatory processes. The current paper provides a concise overview of the features of connexins, pannexins and their channels in the liver.

Cell proliferation and expression of connexins differ in melanotic and amelanotic canine oral melanomas.

Melanoma is a malignant neoplasm occurring in several animal species, and is the most frequently found tumor in the oral cavity in dogs. Melanomas are classified into two types: melanotic and amelanotic. Prior research suggests that human amelanotic melanomas are more aggressive than their melanotic counterparts. This study evaluates the behavior of canine melanotic and amelanotic oral cavity melanomas and quantifies cell proliferation and the expression of connexins. Twenty-five melanomas (16 melanotic and 9 amelanotic) were collected from dogs during clinical procedures at the Veterinary Hospital of the School of Veterinary Medicine and Animal Science of the University of São Paulo, Brazil. After diagnosis, dogs were followed until death or euthanasia. Histopathology confirmed the gross melanotic or amelanotic characteristics and tumors were classified according to the WHO. HMB45 or Melan A immunostainings were performed to confirm the diagnosis of amelanotic melanomas. Cell proliferation was quantified both by counting mitotic figures and PCNA positive nuclei. Expressions of connexins 26 and 43 were evaluated by immunohistochemistry, qRT-PCR and Western blot. Dogs bearing amelanotic melanomas presented a shorter lifespan in comparison to those with melanotic melanomas. Cell proliferation was significantly higher in amelanotic melanomas. Expressions of Connexins 26 and 43 were significantly reduced in amelanotic melanomas. The results presented here suggest that oral cavity melanotic and amelanotic melanomas differ regarding their behavior, cell proliferation and connexin expression in dogs, indicating a higher aggressiveness of amelanotic variants.

Chronic exposure of lung alveolar epithelial type II cells to tobacco-specific carcinogen NNK results in malignant transformation: a new in vitro lung carcinogenesis model.

Lung cancer is the leading cause of cancer-related mortality in both men and women throughout the world. This disease is strongly associated with tobacco smoking. The aim of this manuscript was to establish an in vitro model that mimics the chronic exposures of alveolar epithelial type II cells to the tobacco-specific nitrosamine carcinogen, NNK. Immortalized non-neoplastic alveolar epithelial cells type II, (E10 cells), from BALB/c mice were exposed to low concentration of NNK (100 pM) during 5, 10, 15, and 20 cycles of 48 h. NNK-transformed cells showed an increase of proliferation rate and motility. Moreover, these cells underwent epithelial-to-mesenchymal transition (EMT). Increased migratory capacity and EMT were correlated to the time of exposure to NNK. NNK-transformed cells were tested for their growth and metastatic capacity in vivo. Subcutaneous injection of cells exposed to NNK for 20 cycles (E10-NNK20 clone) into BALB/c mice led to the formation of subcutaneous tumors that arose after 40 ± 17 d in all animals, which died 95 ± 18 d after cell inoculation, with lymph nodes and lung metastasis. The morphological characteristics of tumors were compatible with metastatic undifferentiated carcinoma. Cells exposed to NNK for 5-10 cycles did not display metastatic capacity, while those exposed for 15 cycles displayed low capacity. Our results show that prolonged exposures to NNK led the cells to increasingly acquire malignant properties. The cellular model presented in this study is suitable for studying the molecular events involved in the different stages of malignant transformation.

Higher susceptibility of spontaneous and NNK-induced lung neoplasms in connexin 43 deficient CD1 × AJ F1 mice: paradoxical expression of connexin 43 during lung carcinogenesis.

Connexins (Cxs) are proteins that form the communicating gap junctions, and reportedly have a role in carcinogenesis. Here, we evaluated the importance of Connexin43 (Cx43) in spontaneous and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung carcinogenesis. Male wild-type (Cx43(+/+) ) and hemizygote (Cx43(+/-) ) CD1 × AJ F1 mice were injected with NNK or saline. After 60 weeks mice were euthanized; lung nodules were counted, measured, and fixed in formalin or snap frozen. Immunohistochemistry for Cx43 and Beta-catenin (ß-catenin) was performed and Cx43 mRNA expression was evaluated by real-time PCR. Cx43 deletion significantly increased the incidence and number of spontaneous nodules in the CD1 × AJ F1 mice and the number of gross lesions and the aggressiveness of lesions in NNK-treated mice. Cx43 mRNA increased significantly and was correlated with the aggressiveness of tumors, although lesions from Cx43(+/-) mice expressed less Cx43 RNAm than their counterparts. Lung parenchyma presented a Cx43 immunostaining pattern with points or plaques between cells. In hyperplasias and adenomas, Cx43 was found in the membrane and in cytoplasm. Malignant lesions presented increased Cx43 in cytoplasm and a few membrane spots of immunostaining. ß-catenin was weakly expressed in lung parenchyma. Though hyperplasias presented some cells with nuclear ß-catenin, NNK-induced tumors contained a higher number of this staining pattern. Also, no difference in ß-catenin occurred between both genotypes independently of the histological grade. In summary, our results indicate that Cx43 acts as a tumor suppressor gene in early lung tumorigenesis and loses this property in advanced carcinogenesis. Therefore, Cxs are better classified as conditional tumor suppressors.

Fibronectin expression is decreased in metastatic renal cell carcinoma following endostatin gene therapy.

Tumor cells induce the disruption of homeostasis between cellular and extracellular compartments to favor tumor progression. The expression of fibronectin (FN), a matrix glycoprotein, is increased in several carcinoma cell types, including renal cell carcinoma (RCC). RCC are highly vascularized tumors and are often amenable to antiangiogenic therapy. Endostatin (ES) is a fragment of collagen XVIII that possesses antiangiogenic activity. In this study, we examined the modulation of FN gene expression by ES gene therapy in a murine metastatic renal cell carcinoma (mRCC) model. Balb/C mice bearing Renca cells were treated with NIH/3T3-LXSN cells or NIH/3T3-LendSN cells. At the end of the experiment, the ES serum levels were measured, and the FN gene expression was assessed using real-time PCR. The tissue FN was evaluated by western blotting and by immunofluorescence analysis. The ES serum levels in treated mice were higher than those in the control group (P<0.05). ES treatment led to significant decreases at the FN mRNA (P<0.001) and protein levels (P<0.01). Here, we demonstrate the ES antitumor effect that is mediated by down-regulation of FN expression in mRCC.

Maternal immune activation in late gestation enhances locomotor response to acute but not chronic amphetamine treatment in male mice offspring: role of the D1 receptor.

Exposure to elevated levels of maternal cytokines can lead to functional abnormalities of the dopaminergic system in the adult offspring, including enhanced amphetamine (AMPH)-induced locomotion. Therefore, it seems reasonable to consider that offspring of challenged mothers would behave differently in models of addictive behavior, such as behavioral sensitization. Thus, we sought to evaluate the effects of prenatal exposure to lipopolysaccharide (LPS) on the locomotor response to acute and chronic AMPH treatment in male mice offspring. For this purpose, LPS (Escherichia coli 0127:B8; 120 µg/kg) was administered intraperitoneally to pregnant Swiss mice on gestational day 17. At adulthood, male offspring were studied under one of the following conditions: (1) locomotor response to acute AMPH treatment (2.5 or 5.0 mg/kg) in an open field test; (2) behavioral sensitization paradigm, which consists of a daily injection of AMPH (1.0 mg/kg) for 10 days and observation of locomotion in the open field on days 1, 5, 10 (development phase), 15 and 17 (expression phase). The LPS stimulated offspring showed enhancement of the locomotor-stimulant effect after an acute AMPH challenge in comparison to baseline and saline pre-treated mice. They also showed development of behavioral sensitization earlier than the saline pre-treated group, although no changes between saline and LPS pre-treated groups were observed on development or expression of locomotor behavioral sensitization to AMPH. Furthermore, there was up-regulation of D1 receptor protein level within striatum in the LPS-stimulated offspring which was strongly correlated with increased grooming behavior. Taken together, our results indicate that motor and dopaminergic alterations caused by maternal immune activation are restricted to the acute AMPH challenge, mostly due to up-regulation of the D1 receptor within the mesolimbic and nigrostriatal pathways, but no locomotor differences were observed for behavioral sensitization to AMPH.

Delayed osteoblastic differentiation and bone development in Cx43 knockout mice.

GJA1 gene (Connexin43, also known as Cx43) is the most abundant gap junction protein isoform in animal cells and is associated with bone development in embryos. The objective of the present work was to evaluate in vivo osteal development in GJA1-deficient fetal mice through determination of the histological and molecular alterations induced by partial or total deletion of the GJA1 gene. Heterozygous C57BL/6 mice (HT) harboring a null mutation of the GJA1 gene were mated, and pregnant females were submitted to euthanasia and Caesarean section from 12.5 to 19.5 days post coitum (dpc). HT (GJA1(+/-)) and homozygous (GJA1(-/- )) knockout (KO) mutants and wild-type (WT) fetuses were identified by polymerase chain reaction (PCR), and development curves were constructed on the basis of fetus weight and crown-rump length. Histopathological, histochemical, and real-time PCR analyses were performed in order to assess the expression of markers associated with bone development, namely, osteocalcin, osteopontin, alkaline phosphatase, RUNX2, GJA1, GJC1 (Cx45), and GJA3 (Cx46). HT and KO fetuses exhibited delays in the differentiation of osteoblasts and, consequently, in bone development in comparison with the WT group. Additionally, less deposition of mineralized and osteoid matrix was observed in GJA1-deficient fetuses. Bone development in KO fetuses was delayed through the moment of birth, but in HT animals the delay only extended until 17.5 dpc, following which development was normalized. The expression of genes coding for osteocalcin, osteopontin, alkaline phosphatise, and RUNX2 were also delayed in GJA1-deficient fetuses. Animals that exhibited a lower expression of GJA1 presented delayed expression of the GJC1 and GJA3 genes and their corresponding protein products in the bone tissue. The results of the present study contribute to our understanding of the function of GJA1 during bone development and suggest that GJC1 could play a role in restoring intercellular communication in GJA1-deficient mice.

In vitro inhibitory effect of trichostatin A on canine grade 3 mast cell tumor.

Mast cell tumor (MCT) is one of the most prevalent neoplasms that affect skin and soft tissue in dogs. Because mast cell tumors present a great variety of clinical appearance and behavior, their treatment becomes a challenge. Trichostatin A (TSA), an antifungal antibiotic, has shown inhibitory effects on the proliferation and induction of apoptosis in various types of cancer cells. In order to evaluate the potential of trichostatin A as a therapeutic drug, cells of grade 3 MCT were cultured and treated with concentrations of 1 nM to 400 nM of TSA. MTT assay and trypan blue exclusion assays were performed to estimate cell growth and cell viability, and cell cycle analysis was evaluated. TSA treatment showed a reduction in numbers of viable cells and an increase of cell death by apoptosis. The cell cycle analysis showed an increase of hypodiploid cells and a reduction of G0/G1 and G2/M -phases. According to these results, trichostatin A may be an interesting potential chemotherapeutic agent for the treatment of canine MCT.

Aberrant expression and localization of connexin43 and connexin30 in a rat glioma cell line.

Gap junctions are cellular structures which permit direct exchanges of small molecules from cytoplasm to cytoplasm in most of the cells of metazoan organisms. For four decades, it has been observed that the inhibition of this type of intercellular communication is often associated with tumorigenesis. The assumption that loss of homeostasis which characterizes tumor growth could be a consequence of a lack of gap junctional intercellular communication (GJIC) has been reinforced by strategies able to reinduce both GJIC and normalization of the phenotype. So far, no molecular data may explain clearly how gap junctions can regulate cell proliferation. It has been argued that the gap-junction tumor suppressive effect may depend specifically on the connexin type which is expressed. For instance, the transfection of connexin30 (Cx30), a gap junction protein, has been previously associated with a slower growth of rat glioma cells (9L cells). Here, we show that these cells do communicate less compared to the Cx43-expressing parental cells even if the Cx30-transfected cells do express more Cx43. This result was related to the cytoplasmic distribution of Cx43 and a nuclear localization of both the Cx30 and a 20-kDa fragment corresponding to a Cx43 signal. According to these data, it seems that cell growth regulation may depend more on the behavior of connexins than the simple establishment of GJIC.