Drop of connexin 43 in replicative senescence of human fibroblasts HEL-299 as a possible biomarker of senescence

Connexins and Aging-Associated Respiratory Disorders: The Role in Intercellular Communications

This article reviews the contemporary understanding of the functional role of connexins in intercellular communications, their involvement in maintaining cellular and tissue homeostasis, and in aging-associated respiratory disease pathogenesis. Connexins are discussed as potential therapeutic targets. The review particularly focuses on the involvement of gap junction connexins and hemichannels in the transfer of calcium ions, metabolite molecules, ATP, and mitochondria through the cell membrane. Various disorders in the regulation of intercellular communication can heavily contribute to the pathogenesis of multiple diseases, including respiratory system diseases. A deeper understanding of molecular mechanisms underlying the activities of various connexins in gap junction channels will enable the prospective development of therapeutic approaches by either inhibiting or stimulating the activities of a certain connexin, while considering its critical functions in intercellular communications on the whole.

The Molecular and Cellular Strategies of Glioblastoma and Non-Small-Cell Lung Cancer Cells Conferring Radioresistance

Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLC). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLC. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.

Mitochondria and metabolic transitions in cardiomyocytes: lessons from development for stem cell-derived cardiomyocytes

Current methods to differentiate cardiomyocytes from human pluripotent stem cells (PSCs) inadequately recapitulate complete development and result in PSC-derived cardiomyocytes (PSC-CMs) with an immature or fetal-like phenotype. Embryonic and fetal development are highly dynamic periods during which the developing embryo or fetus is exposed to changing nutrient, oxygen, and hormone levels until birth. It is becoming increasingly apparent that these metabolic changes initiate developmental processes to mature cardiomyocytes. Mitochondria are central to these changes, responding to these metabolic changes and transitioning from small, fragmented mitochondria to large organelles capable of producing enough ATP to support the contractile function of the heart. These changes in mitochondria may not simply be a response to cardiomyocyte maturation; the metabolic signals that occur throughout development may actually be central to the maturation process in cardiomyocytes. Here, we review methods to enhance maturation of PSC-CMs and highlight evidence from development indicating the key roles that mitochondria play during cardiomyocyte maturation. We evaluate metabolic transitions that occur during development and how these affect molecular nutrient sensors, discuss how regulation of nutrient sensing pathways affect mitochondrial dynamics and function, and explore how changes in mitochondrial function can affect metabolite production, the cell cycle, and epigenetics to influence maturation of cardiomyocytes.

Connexins in Cancer: Jekyll or Hyde?

The expression, localization, and function of connexins, the protein subunits that comprise gap junctions, are often altered in cancer. In addition to cell-cell coupling through gap junction channels, connexins also form hemichannels that allow communication between the cell and the extracellular space and perform non-junctional intracellular activities. Historically, connexins have been considered tumor suppressors; however, they can also serve tumor-promoting functions in some contexts. Here, we review the literature surrounding connexins in cancer cells in terms of specific connexin functions and propose that connexins function upstream of most, if not all, of the hallmarks of cancer. The development of advanced connexin targeting approaches remains an opportunity for the field to further interrogate the role of connexins in cancer phenotypes, particularly through the use of in vivo models. More specific modulators of connexin function will both help elucidate the functions of connexins in cancer and advance connexin-specific therapies in the clinic.

Where does cellular senescence belong in the pathophysiology of ovarian cancer?

Although ovarian cancer is the leading cause of death from gynecological malignancies, there are still some issues that hamper accurate interpretation of the complexity of cellular and molecular events underlying the pathophysiology of this disease. One of these is cellular senescence, which is the process whereby cells irreversibly lose their ability to divide and develop a phenotype that fuels a variety of age-related diseases, including cancer. In this review, various aspects of cellular senescence associated with intraperitoneal ovarian cancer metastasis are presented and discussed, including mechanisms of senescence in normal peritoneal mesothelial cells; the role of senescent mesothelium in ovarian cancer progression; the effect of drugs commonly used as first-line therapy in ovarian cancer patients on senescence of normal cells; mechanisms of spontaneous senescence in ovarian cancer cells; and, last but not least, other pharmacologic strategies to induce senescence in ovarian malignancies. Collectively, this study shows that cellular senescence is involved in several aspects of ovarian cancer pathobiology. Proper understanding of this phenomenon, particularly its clinical relevance, seems to be critical for oncology patients from both therapeutic and prognostic perspectives.

Mechanisms and significance of therapy-induced and spontaneous senescence of cancer cells

In contrast to the well-recognized replicative and stress-induced premature senescence of normal somatic cells, mechanisms and clinical implications of senescence of cancer cells are still elusive and uncertain from patient-oriented perspective. Moreover, recent years provided multiple pieces of evidence that cancer cells may undergo senescence not only in response to chemotherapy or ionizing radiation (the so-called therapy-induced senescence) but also spontaneously, without any external insults. Since the molecular nature of the latter process is poorly recognized, the significance of spontaneously senescent cancer cells for tumor progression, therapy effectiveness, and patient survival is purely speculative. In this review, we summarize the most up-to-date research regarding therapy-induced and spontaneous senescence of cancer cells, by delineating the most important discoveries regarding the occurrence of these phenomena in vivo and in vitro. This review provides data collected from studies on various cancer cell models, and the narration is presented from the broader perspective of the most critical findings regarding the senescence of normal somatic cells.

Connexin43 is Dispensable for Early Stage Human Mesenchymal Stem Cell Adipogenic Differentiation But is Protective against Cell Senescence

In the last couple of decades, there has been a growing optimism surrounding the potential transformative use of human mesenchymal stem cells (MSCs) and human-induced pluripotent stem cells (iPSCs) for regenerative medicine and disease treatment. In order for this to occur, it is first essential to understand the mechanisms underpinning their cell-fate specification, which includes cell signaling via gap junctional intercellular communication. Here, we investigated the role of the prototypical gap junction protein, connexin43 (Cx43), in governing the differentiation of iPSCs into MSCs and MSC differentiation along the adipogenic lineage. We found that control iPSCs, as well as iPSCs derived from oculodentodigital dysplasia patient fibroblasts harboring a GJA1 (Cx43) gene mutation, successfully and efficiently differentiated into LipidTox and perilipin-positive cells, indicating cell differentiation along the adipogenic lineage. Furthermore, the complete CRISPR-Cas9 ablation of Cx43 from iPSCs did not prevent their differentiation into bona fide MSCs or pre-adipocytes, strongly suggesting that even though Cx43 expression is upregulated during adipogenesis, it is expendable. Interestingly, late passage Cx43-ablated MSCs senesced more quickly than control cells, resulting in failure to properly differentiate in vitro. We conclude that despite being upregulated during adipogenesis, Cx43 plays no detectable role in the early stages of human iPSC-derived MSC adipogenic differentiation. However, Cx43 may play a more impactful role in protecting MSCs from premature senescence.

Senescence-related deterioration of intercellular junctions in the peritoneal mesothelium promotes the transmesothelial invasion of ovarian cancer cells

Mechanisms of transmesothelial invasion of ovarian cancer are still poorly understood. Here we examined whether this phenomenon may be determined by an expression of intercellular junctions in peritoneal mesothelial cells (PMCs). Analysis of ovarian tumors showed that cancer cells are localized below an intact layer of PMCs. The PMCs located near the invaded cancer cells displayed low expression of connexin 43, E-cadherin, occludin, and desmoglein, as well as expressed SA-β-Gal, a marker of senescence. Experiments in vitro showed that senescent PMCs exhibited decreased levels of the four tested intercellular junctions, and that the invasion of ovarian cancer cells through the PMCs increased proportionally to the admixture of senescent cells. Intervention studies showed that the expression of connexin 43, E-cadherin, occludin, and desmoglein in senescent PMCs could be restored upon the blockade of p38 MAPK, NF-κB, AKT, JNK, HGF, and TGF-β1. When these molecules were neutralized, the efficiency of the transmesothelial cancer cell invasion was diminished. Collectively, our findings show that the integrity of the peritoneal mesothelium, which is determined by the expression of junctional proteins, is critical for the invasion of ovarian cancer. They also indicate a mechanism by which senescent PMCs may promote the invasive potential of cancer cells.

Oxidative stress contributes to hepatocyte growth factor-dependent pro-senescence activity of ovarian cancer cells

The cancer-promoting activity of senescent peritoneal mesothelial cells (HPMCs) has already been well evidenced both in vitro and in vivo. Here we sought to determine if ovarian cancer cells may activate senescence in HPMCs. The study showed that conditioned medium (CM) from ovarian cancer cells (OVCAR-3, SKOV-3, A2780) inhibited growth and promoted the development of senescence phenotype (increased SA-β-Gal, γ-H2A.X, 53BP1, and decreased Cx43) in HPMCs. An analysis of tumors isolated from the peritoneum of patients with ovarian cancer revealed an abundance of senescent HPMCs in proximity to cancerous tissue. The presence of senescent HPMCs was incidental when fragments of peritoneum free from cancer were evaluated. An analysis of the cells' secretome followed by intervention studies with exogenous proteins and neutralizing antibodies revealed hepatocyte growth factor (HGF) as the mediator of the pro-senescence impact of the cancer cells. The activity of cancerous CM and HGF was associated with an induction of mitochondrial oxidative stress. Signaling pathways involved in the senescence of HPMCs elicited by the cancer-derived CM and HGF included p38 MAPK, AKT and NF-κB. HPMCs that senesced prematurely in response to the cancer-derived CM promoted adhesion of ovarian cancer cells, however this effect was effectively prevented by the cell protection against oxidative stress. Collectively, our findings indicate that ovarian cancer cells can elicit HGF-dependent senescence in HPMCs, which may contribute to the formation of a metastatic niche for these cells within the peritoneal cavity.

Hyperthermia differently affects connexin43 expression and gap junction permeability in skeletal myoblasts and HeLa cells

Stress kinases can be activated by hyperthermia and modify the expression level and properties of membranous and intercellular channels. We examined the role of c-Jun NH2-terminal kinase (JNK) in hyperthermia-induced changes of connexin43 (Cx43) expression and permeability of Cx43 gap junctions (GJs) in the rabbit skeletal myoblasts (SkMs) and Cx43-EGFP transfected HeLa cells. Hyperthermia (42°C for 6 h) enhanced the activity of JNK and its target, the transcription factor c-Jun, in both SkMs and HeLa cells. In SkMs, hyperthermia caused a 3.2-fold increase in the total Cx43 protein level and enhanced the efficacy of GJ intercellular communication (GJIC). In striking contrast, hyperthermia reduced the total amount of Cx43 protein, the number of Cx43 channels in GJ plaques, the density of hemichannels in the cell membranes, and the efficiency of GJIC in HeLa cells. Both in SkMs and HeLa cells, these changes could be prevented by XG-102, a JNK inhibitor. In HeLa cells, the changes in Cx43 expression and GJIC under hyperthermic conditions were accompanied by JNK-dependent disorganization of actin cytoskeleton stress fibers while in SkMs, the actin cytoskeleton remained intact. These findings provide an attractive model to identify the regulatory players within signalosomes, which determine the cell-dependent outcomes of hyperthermia.

AMPK-mediated downregulation of connexin43 and premature senescence of mesangial cells under high-glucose conditions

Diabetic nephropathy is associated with premature senescence. Our previous study showed that glomerular mesangial cells (GMCs) appeared to take on senescent phenotypes under high-glucose conditions in conjunction with the downregulation of connexin43 (Cx43). In this study, we investigated whether AMPK-mediated Cx43 expression and premature senescence in diabetic nephropathy are associated with mTOR activation. From in vivo and in vitro studies, we found decreased expression of Cx43 and p-AMPK but increased expression of p21 both in the glomeruli of diabetic nephropathy and in primary GMCs cultured in high glucose. Activating AMPK or inhibiting mTOR prevented the downregulation of Cx43 and reversed GMC senescence. Dominant-negative AMPK expression both reduced Cx43 expression and induced GMC senescence. Furthermore, AMPK regulated Cx43 expression and GMC senescence mainly through the inhibition of mTOR, although other pathways cannot be ruled out. This study demonstrated that AMPK signaling pathways play an important role in the regulation of the Cx43 expression that accompanies GMC senescence under high-glucose conditions.

Mesothelial cell: a multifaceted model of aging

Human peritoneal mesothelial cells (HPMCs) dominate within the peritoneal cavity and thus play a central role in a variety of intraperitoneal processes, including the transport of water and solutes, inflammation, host response, angiogenesis, and extracellular matrix remodeling. In addition, they contribute to the development of abdominal adhesions, peritonitis, endometriosis, cancer cell metastases, and peritoneal dialysis complications. For less than a decade the primary cultures of omental HPMCs have also been used as an experimental tool in studies on cellular aging. This paper provides the first comprehensive overview of the current state of art on molecular mechanisms underlying HPMC senescence in vitro. Special attention is paid to the causes of the very fast dynamics of HPMC senescence, and in particular to the role of non-telomeric DNA damage, the autocrine activity of TGF-β1, and the causative effects of oxidative stress. In addition, some clinical manifestations of HPMC senescence will be discussed, including its interplay with organismal aging, peritoneal dialysis, and cancer progression.

Age-related changes in gap junctional intercellular communication in osteoblastic cells

Aging demonstrates deleterious effects upon the skeleton which can predispose an individual to osteoporosis and related fractures. Despite the well-documented evidence that aging decreases bone formation, there remains little understanding whereby cellular aging alters skeletal homeostasis. We, and others, have previously demonstrated that gap junctions--membrane-spanning channels that allow direct cell-to-cell conductance of small signaling molecules--are critically involved in osteoblast differentiation and skeletal homeostasis. We examined whether the capacity of rat osteoblastic cells to form gap junctions and respond to known modulators of gap junction intercellular communication (GJIC) was dependent on the age of the animal from which they were isolated. We observed no effect of age upon osteoblastic Cx43 mRNA, protein or GJIC. We also examined age-related changes in PTH-stimulated GJIC. PTH demonstrated age-dependent effects upon GJIC: Osteoblastic cells from young rats increased GJIC in response to PTH, whereas there was no change in GJIC in response to PTH in osteoblastic cells from mature or old rats. PTH-stimulated GJIC occurred independently of changes in Cx43 mRNA or protein expression. Cholera toxin significantly increased GJIC in osteoblastic cells from young rats compared to those from mature and old rats. These data demonstrate an age-related impairment in the capacity of osteoblastic cells to generate functional gap junctions in response to PTH, and suggest that an age-related defect in G protein-coupled adenylate cyclase activity at least partially contributes to decreased PTH-stimulated GJIC.

Transition of kidney tubule cells to a senescent phenotype in early experimental diabetes

Diabetic nephropathy is the commonest cause of end-stage renal disease. Inordinate kidney growth and glomerular hyperfiltration at the very early stages of diabetes are putative antecedents to this disease. The kidney is the only organ that grows larger with the onset of diabetes mellitus, yet there remains confusion about the mechanism and significance of this growth. Here we show that kidney proximal tubule cells in culture transition to senescence in response to oxidative stress. We further determine the temporal expression of G(1) phase cell cycle components in rat kidney cortex at days 4 and 10 of streptozotocin diabetes to evaluate changes in this growth response. In diabetic rats we observe increases in kidney weight-to-body weight ratios correlating with increases in expression of the growth-related proteins in the kidney at day 4 after induction of diabetes. However, at day 10 we find a decrease in this profile in diabetic animals coincident with increased cyclin-dependent kinase inhibitor expressions. We observe no change in caspase-3 expression in the diabetic kidneys at these early time points; however, diabetic animals demonstrate reduced kidney connexin 43 and increased plasminogen activator inhibitor-1 expressions and increased senescence-associated beta-galactosidase activity in cortical tubules. In summary, diabetic kidneys exhibit an early temporal induction of growth phase components followed by their suppression concurrent with the induction of cyclin-dependent kinase inhibitors and markers of senescence. These data delineate a phenotypic change in cortical tubules early in the pathogenesis of diabetes that may contribute to further downstream complications of the disease.

Two new lipoaminoacids with complementary modes of action: new prospects to fight out against skin aging

The mode of action of two cosmetic active ingredients (AIs), palmitoyl glycine (PG) and cocoyl alanine (CA) was studied with cDNA array experiments and quantitative PCR confirmations, which were performed on experimentally aged human fibroblasts. These preliminary studies revealed complementary profiles. Thus, specific supplementary investigations were then carried out for each AI. Protocols used were based either on in vitro models: (i) biochemical assays, (ii) monolayer cell culture (primary human fibroblasts and keratinocytes) and (iii) the model of capillary-like tube formation by human endothelial cells or on ex vivo models, i.e. topically treated skin explants and both immunohistochemical and Chromameter(TM) investigations. New prospects are proposed to fight out against skin aging. Indeed, PG and CA showed complementary properties and thus enabled a regulation or a restoration effect on main aging-associated disorders. Thus, they can not only act on tissue architecture, cell-cell interactions and extracellular matrix protection but also on inflammation, cell longevity, skin immune system protection, skin radiance and stem cell survey. Finally, a clinical trial performed on Caucasian women confirmed AI anti-wrinkle efficacy, which was superior to that of a market reference ingredient. In the future, complementary experiments enabling a better understanding of the aging-induced decline of epidermal stem cells would be of a great interest.

Perineuronal satellite cells in mouse spinal ganglia express the gap junction protein connexin43 throughout life with decline in old age

Satellite glial cells that envelope the bodies of sensory neurons in spinal ganglia are connected to each other by gap junctions and exhibit dye coupling. These junctions may endow perineuronal satellite cells with the coordination necessary for the efficient performance of functions such as buffering of K(+) in the perineuronal microenvironment, provision of metabolic support to ganglionic neurons, and neuroprotection. Our knowledge of gap junctions has increased considerably in recent years, but little information is available on the connexins that form these junctions in spinal ganglia. In the present study we set out to determine whether the perineuronal satellite cells of mouse spinal ganglia express the connexins that are mainly present in neuroglial cells (Cx32 and Cx43). In young (3 months) mice, PCR showed the presence of both Cx32 and Cx43 transcripts. By immunocytochemistry, we localized Cx32 to axon-ensheathing Schwann cells, but not to other parts of the ganglion. We found Cx43 positivity in the perineuronal satellite cells, which were identified by their immunoreactivity to S100 protein and to glutamine synthetase. PCR showed Cx43 transcripts also in the spinal ganglia of adult (8 months) and old (24 months) animals. Cx43 immunostaining was present in satellite cells surrounding all nerve cell bodies, irrespective of size. The mean number of Cx43-immunoreactive puncta was significantly lower in the perineuronal satellite cells of aged mice compared to young and adult animals. This latter finding is consistent with observations in non-nervous tissues, and the hypothesis that a prominent decrease in Cx43 is a marker of senescence.

18alpha-glycyrrhetinic acid induces phenotypic changes of skeletal muscle cells to enter adipogenesis

The importance of connexins is implicated in proliferation and differentiation of cells. In skeletal muscle cells, connexin43 (Cx43) has been identified as the major connexin, and gap-junctional communication mediated by connexins has been shown to be required for their myogenic differentiation. In addition, inhibition of connexin function has been shown to induce transdifferentiation of osteoblasts to an adipocytic phenotype. In the present study, we examined whether the inhibition of connexin function could induce phenotypic changes in skeletal muscle cells. Treatment of skeletal muscle cells with an inhibitor of connexin function, 18alpha-glycyrrhetinic acid (AGRA), resulted in a reduction in the number of MyoD-positive cells and complete inhibition of myotube formation, concomitantly with an increase in the number of C/EBPalpha-positive cells. AGRA-treated cells cultured in adipogenic differentiation medium could give rise to mature adipocytes that express both PPARgamma and C/EBPalpha. The presence of AGRA during adipogenic differentiation did not inhibit adipogenesis of skeletal muscle cells. AGRA treatment did not affect Cx43 expression in skeletal muscle cells but reduced its phosphorylation. These results indicate that inhibition of connexin function induces phenotypic changes of skeletal muscle cells to enter adipogenesis.

Downregulation of connexin 43 expression by high glucose induces senescence in glomerular mesangial cells

Connexin 43 (Cx43) plays an important role in cell differentiation and growth control, but whether it can be regulated by high glucose and whether it can mediate in glomerular mesangial cells (GMC) the phenotype alterations that are induced by high glucose still remain to be explored. In this study, RNA interference and gene transfer techniques were used to knock down and overexpress Cx43 gene in rat GMC to determine the contribution of Cx43 to GMC senescence that was induced by high glucose. The results show that high glucose (30 mM) not only downregulated Cx43 mRNA and protein expression (P<0.05) but also increased the percentage of senescence-associated beta-galactosidase (SA-beta-gal) stained cells and expression of p21cip1 and p27kip1 (P<0.05), indicating that high glucose promoted rat GMC senescence. Knocking down Cx43 gene expression significantly increased the percentage of SA-beta-gal stained cells and p27kip1 and p21cip1 expression in GMC (P<0.05), whereas overexpression of Cx43 significantly decreased the percentage of SA-beta-gal stained cells (P<0.05). These results demonstrate for the first time that downregulation of Cx43 expression by high glucose promotes the senescence of GMC, which may be involved in the pathogenesis of diabetic nephropathy.

The role of stem cells and gap junctions as targets for cancer chemoprevention and chemotherapy

Since carcinogenesis is a multi-stage, multi-mechanism process, involving mutagenic, cell death and epigenetic mechanisms, during the "initiation/promotion/and progression" phases, chemoprevention must be based on understanding the mechanism(s) of each phase. Prevention of each phase could reduce the risk to cancer. Because reducing the initiation phase to a zero level is impossible, the most effective intervention would be at the promotion phase. Assuming the "target" cells for carcinogenesis are the pluri-potent stem cells and their early progenitor or transit cells, chemoprevention strategies for inhibiting the promotion of these two types of pre-malignant "initiated" cells will require different agents. A hypothesis will be proposed that involves stem cells, which lack gap junctional intercellular communication (GJIC-) or their early progenitor daughter cells, which express GJIC+ and are partially-differentiated, if initiated, will be promoted by agents that either inhibit secreted negative growth regulators or by inhibitors of GJIC. Chemopreventing agents to each of these two types of initiated cells must have different mechanisms of action. Assuming stem cells are target cells for carcinogenesis, an alternative method of chemoprevention would be to reduce the stem cell pool. Anti-tumor promoter chemopreventive agents, such as green tea components, resveratrol, caffeic acid phenethylene ester, that either up-regulate GJIC in stem cells or prevent the down regulation of GJIC by tumor promoters in early progenitor cells, will be provided. Human pluri-potent stem cell systems, that can be induced to form 3-dimensional "organoid" structures, will be discussed as a more realistic model system to screen for relevant chemopreventive agents.

Changes in the properties of the modulatory cerebral giant cells contribute to aging in the feeding system of Lymnaea

This study examined whether electrophysiological changes in the endogenous properties and connectivity of the modulatory serotonergic cerebral giant cells (CGCs) contributed to the age-related changes in feeding behavior of the pond snail, Lymnaea. With increasing age there was a decrease in spontaneous CGC firing rates and decreased excitability of the CGCs to both chemosensory stimulation (0.05M sucrose applied to the lips) and direct intracellular current injection. These changes could be accounted for by a decrease in the input resistance of the neuron and an increase in the amplitude and the duration of the after-hyperpolarization. Decreases were also seen in the % of CGC pairs that were electrically coupled causing asynchronous firing. Together these changes would tend to reduce the ability of the CGCs to gate and control the frequency of the feeding behavior. Part of the ability of the CGCs to gate and frequency control the feeding network is to provide a background level of excitation to the feeding motor neurons. Recordings from B1 and B4 motor neurons showed an age-related hyperpolarization of the resting membrane potential consistent with a deficit in CGC function. Increases were seen in the strength of the evoked CGC-->B1 connection, however, this increase failed to compensate for the deficits in CGC excitability. In summary, age-related changes in the properties of the CGCs were consistent with them contributing to the age-related changes in feeding behavior seen in Lymnaea.

Drop of connexins: a possible link between aging and cancer?

The incidence of cancer increases with age but we do not know why. As a working hypothesis we propose here that cells somehow initiated in vivo in the course of life and finally engaged in the aging program, which involves a drop of connexins with loss of cell-to-cell communication (equivalent to the promotion phase in the multistep process of carcinogenesis), may recover their growth potential, thus allowing cancer to progress. This is supported by evidence that: (i) connexin 43 (Cx43) acts as a tumor suppressor; (ii) cx43 and gap junction intercellular communication drop in precancerous lesions and in tumors of various origins, as well as in aging cells; (iii) telomerase is activated in cancerous somatic cells.

Cisplatin-induced premature senescence with concomitant reduction of gap junctions in human fibroblasts

To examine the role of gap junctions in cell senescence, the changes of gap junctions in cisplatin-induced premature senescence of primary cultured fibroblasts were studied and compared with the replicative senescent human fibroblasts. Dye transfer assay for gap junction function and immunofluorescent staining for connexin 43 protein distribution were done respectively. Furthermore, cytofluorimetry and DAPI fluorescence staining were performed for cell cycle and apoptosis analysis. p53 gene expression level was detected with indirect immunofluorescence. We found that cisplatin (10 mM) treatment could block cell growth cycle at G1 and induced premature senescence. The premature senescence changes included high frequency of apoptosis, elevation of p53 expression, loss of membranous gap junctions and reduction of dye-transfer capacity. These changes were comparable to the changes of replicative senescence of human fibroblasts. It was also concluded that cisplatin could induce premature senescence concomitant with inhibition of gap junctions in the fibroblasts. Loss of functional gap junctions from the cell membrane may account for the reduced intercellular communication in the premature senescent fibroblasts. The cell system we used may provide a model useful for the study of the gap junction thus promoting agents against premature senescence.

The optic nerve head region of the aged rat: an immunohistochemical investigation

PURPOSE

To study age-related changes in the rat optic nerve head.

METHODS

Eyes of young (2 months) and senescent (20 months) Wistar rats were stained with antibodies against collagen type I, III, IV, VI, laminin, glial fibrillary acidic protein (GFAP) and connexin 43.

RESULTS

In the senescent animals, an increase of collagen type I and VI, and of connexin 43 was observed in the lamina cribrosa region. In addition, connexin 43 was newly formed in the optic nerve sheath of old animals. Collagen type III and IV, laminin and GFAP did not show age-related alterations.

CONCLUSION

The described changes differ substantially from those described in the rat glaucoma model. As the rodent age-related changes are similar to those found in the human lamina cribrosa, the rat model seems to be useful for studying the influence of age on the onset of glaucoma.