A role for fibroblasts in mediating the effects of tobacco-induced epithelial cell growth and invasion

Purinergic signaling promotes premature senescence

Extracellular ATP activates P2 purinergic receptors. Whether purinergic signaling is functionally coupled to cellular senescence is largely unknown. We find that oxidative stress induced release of ATP and caused senescence in human lung fibroblasts. Inhibition of P2 receptors limited oxidative stress-induced senescence, while stimulation with exogenous ATP promoted premature senescence. Pharmacological inhibition of P2Y11 receptor (P2Y11R) inhibited premature senescence induced by either oxidative stress or ATP, while stimulation with a P2Y11R agonist was sufficient to induce cellular senescence. Our data show that both extracellular ATP and a P2Y11R agonist induced calcium (Ca++) release from the endoplasmic reticulum (ER) and that either inhibition of phospholipase C or intracellular Ca++ chelation impaired ATP-induced senescence. We also find that Ca++ that was released from the ER, following ATP-mediated activation of phospholipase C, entered mitochondria in a manner dependent on P2Y11R activation. Once in mitochondria, excessive Ca++ promoted the production of reactive oxygen species in a P2Y11R-dependent fashion, which drove development of premature senescence of lung fibroblasts. Finally, we show that conditioned medium derived from senescent lung fibroblasts, which were induced to senesce through the activation of ATP/P2Y11R-mediated signaling, promoted the proliferation of triple-negative breast cancer cells and their tumorigenic potential by secreting amphiregulin. Our study identifies the existence of a novel purinergic signaling pathway that links extracellular ATP to the development of a protumorigenic premature senescent phenotype in lung fibroblasts that is dependent on P2Y11R activation and ER-to-mitochondria calcium signaling.

Cellular senescence in skin-related research: Targeted signaling pathways and naturally occurring therapeutic agents

Despite the growing interest by researchers into cellular senescence, a hallmark of cellular aging, its role in human skin remains equivocal. The skin is the largest and most accessible human organ, reacting to the external and internal environment. Hence, it is an organ of choice to investigate cellular senescence and to target root-cause aging processes using senolytic and senomorphic agents, including naturally occurring plant-based derivatives. This review presents different aspects of skin cellular senescence, from physiology to pathology and signaling pathways. Cellular senescence can have both beneficial and detrimental effects on the skin, indicating that both prosenescent and antisenescent therapies may be desirable, based on the context. Knowledge of molecular mechanisms involved in skin cellular senescence may provide meaningful insights for developing effective therapeutics for senescence-related skin disorders, such as wound healing and cosmetic skin aging changes.

Impaired Cdc20 signaling promotes senescence in normal cells and apoptosis in non-small cell lung cancer cells

Cellular senescence is a form of irreversible growth arrest that cancer cells evade. The cell division cycle protein 20 homolog (Cdc20) is a positive regulator of cell division, but how its dysregulation may relate to senescence is unclear. Here, we find that Cdc20 mRNA and protein expression are downregulated in stress-induced premature senescent lung fibroblasts in a p53-dependent manner. Either Cdc20 downregulation or inhibition of anaphase-promoting complex/cyclosome (APC/C) is sufficient to induce premature senescence in lung fibroblasts, while APC/C activation inhibits stress-induced premature senescence. Mechanistically, we show both Cdc20 downregulation and APC/C inhibition induce premature senescence through glycogen synthase kinase (GSK)-3β-mediated phosphorylation and downregulation of securin expression. Interestingly, we determined Cdc20 expression is upregulated in human lung adenocarcinoma. We find that downregulation of Cdc20 in non-small cell lung cancer (NSCLC) cells is sufficient to inhibit cell proliferation and growth in soft agar and to promote apoptosis, but not senescence, in a manner dependent on downregulation of securin following GSK-3β-mediated securin phosphorylation. Similarly, we demonstrate securin expression is downregulated and cell viability is inhibited in NSCLC cells following inhibition of APC/C. Furthermore, we show chemotherapeutic drugs downregulate both Cdc20 and securin protein expression in NSCLC cells. Either Cdc20 downregulation by siRNA or APC/C inhibition sensitize, while securin overexpression inhibits, chemotherapeutic drug-induced NSCLC cell death. Together, our findings provide evidence that Cdc20/APC/C/securin-dependent signaling is a key regulator of cell survival, and its disruption promotes premature senescence in normal lung cells and induces apoptosis in lung cancer cells that have bypassed the senescence barrier.

Cytotoxicity, oxidative stress, and inflammatory response of smokeless tobacco extracts and cytotoxicity of combustible cigarette whole smoke in a 3D oral organotypic buccal cell model

Oral disease is frequently associated with viral and environmental exposures and oral hygiene. The use of tobacco is a risk factor in the development of oral disease. Cytotoxicity, inflammatory response, and oxidative stress have been reported to have a role in the development of oral disease. These three endpoints were evaluated in a 3D human oral buccal model, EpiOral™, following exposure to CORESTA reference smokeless tobacco products (CRPs) and cigarette whole smoke. CRPs for Swedish style snus (CRP1), moist snuff (CRP2), and dry snuff (CRP3) were each extracted in complete artificial saliva (CAS) with a ratio of 300 mg CRP to 1 mL of CAS. Each of the CRP extracts (15-300 mg/ml) were applied to the apical side of a 3D organotypic buccal cell model for 24 or 48 h continuously, then cytotoxicity (LDH), oxidative stress (8-isoprostane), and inflammatory response (IP10, IL-1α, and IL-8) were measured. Experiments with 3R4F cigarettes were conducted by exposing the buccal tissues to whole smoke for a maximum of 2.5 h. Cytotoxicity (MTT) was measured 24 h post-exposure. Exposure of buccal tissues to whole smoke from a cigarette induced a dose-dependent cytotoxic response. In contrast, the CRP extracts elicited minimal cytotoxicity (<15%) when compared to CAS (vehicle control), but time- and dose-dependent effects on oxidative stress and inflammatory response were observed. Collectively, these data demonstrate that a 3D organotypic buccal human model may be used to assess biological mechanisms (MOAs) involved in the development of oral disease following exposure to smokeless tobacco products and may be applicable for differentiation between tobacco product categories.

Extracellular Prostaglandins E1 and E2 and Inflammatory Cytokines Are Regulated by the Senescence Program in Potentially Premalignant Oral Keratinocytes

Simple Summary

The early treatment of oral cancer is a high priority, as improvements in this area could lead to greater cure rates and reduced disability due to extensive surgery. Oral cancer is very difficult to detect in over 70% of cases as it develops unseen until quite advanced, sometimes rapidly. It has become apparent that there are at least two types of epithelial cells (keratinocytes) found in oral tissue on the road to cancer (premalignant). One type secretes molecules called prostaglandins but the other does not and the former may stimulate the latter to progress to malignancy, either by stimulating their proliferation or encouraging the influx of blood vessels to feed them. Additionally, we have identified regulators of prostaglandin secretion in premalignant oral cells that could be targeted in future therapies, such as inducers of cellular senescence, drugs which kill senescent cells (senolytics), steroid metabolism, cyclo-oxygenase 2 (COX2) and p38 mitogen-activated protein kinase.

Abstract

Potentially pre-malignant oral lesions (PPOLs) are composed of keratinocytes that are either mortal (MPPOL) or immortal (IPPOL) in vitro. We report here that MPPOL, but not generally IPPOL, keratinocytes upregulate various extracellular tumor-promoting cytokines (interleukins 6 and 8) and prostaglandins E1 (ePGE1) and E2 (ePGE2) relative to normal oral keratinocytes (NOKs). ePGE upregulation in MPPOL was independent of PGE receptor status and was associated with some but not all markers of cellular senescence. Nevertheless, ePGE upregulation was dependent on the senescence program, cyclo-oxygenase 2 (COX2) and p38 mitogen-activated protein kinase and was partially regulated by hydrocortisone. Following senescence in the absence of p16^INK4A, ePGEs accumulated in parallel with a subset of tumor promoting cytokine and metalloproteinase (MMP) transcripts, all of which were ablated by ectopic telomerase. Surprisingly, ataxia telangiectasia mutated (ATM) function was not required for ePGE upregulation and was increased in expression in IPPOL keratinocytes in line with its recently reported role in telomerase function. Only ePGE1 was dependent on p53 function, suggesting that ePGEs 1 and 2 are regulated differently in oral keratinocytes. We show here that ePGE2 stimulates IPPOL keratinocyte proliferation in vitro. Therefore, we propose that MPPOL keratinocytes promote the progression of IPPOL to oral SCC in a pre-cancerous field by supplying PGEs, interleukins and MMPs in a paracrine manner. Our results suggest that the therapeutic targeting of COX-2 might be enhanced by strategies that target keratinocyte senescence.

The role of cancer stromal fibroblasts in mediating the effects of tobacco-induced cancer cell growth

Tobacco products cause a variety of cancers, nicotine and carcinogens are two major factors to link the tobacco products and various cancers. The mechanism of tobacco inducing carcinogenesis and promoting cancer progression have been studied for a long time. However, mainstream studies just focus on the mutagenic characteristics of tobacco product and its properties to induce carcinogenesis of epithelial cells. In the past decades, people began to aware of the significant role of tumor stroma in cancer development and progression. Fibroblasts, which is associated with various cancer in all stage of disease progression, are the dominant cell type in the tumor microenvironment. While only a few studies explore the crosstalk between tobacco-induced fibroblasts and surrounding epithelial cells. Our purpose is to systematically review the effects of tobacco products on fibroblasts and further discuss how these effects affect the development of cancer cells.

Breast Cancer and p16: Role in Proliferation, Malignant Transformation and Progression

The definition of new molecular biomarkers could provide a more reliable approach in predicting the prognosis of invasive breast cancers (IBC). The aim of this study is to analyze the expression of p16 protein in IBC, as well as its participation in malignant transformation. The study included 147 patients diagnosed with IBC. The presence of non-invasive lesions (NIL) was noted in each IBC and surrounding tissue. p16 expression was determined by reading the percentage of nuclear and/or cytoplasmic expression in epithelial cells of IBC and NIL, but also in stromal fibroblasts. Results showed that expression of p16 increases with the progression of cytological changes in the epithelium; it is significantly higher in IBC compared to NIL (p < 0.0005). Cytoplasmic p16 expression is more prevalent in IBC (76.6%), as opposed to nuclear staining, which is characteristic of most NIL (21.1%). There is a difference in p16 expression between different molecular subtypes of IBC (p = 0.025). In the group of p16 positive tumors, pronounced mononuclear infiltrates (p = 0.047) and increased expression of p16 in stromal fibroblasts (p = 0.044) were noted. In conclusion, p16 protein plays an important role in proliferation, malignant transformation, as well as in progression from NIL to IBC.

Overview of oral cavity squamous cell carcinoma: Risk factors, mechanisms, and diagnostics

Oral cavity squamous cell carcinoma (OCSCC) is the most common malignancy of the oral cavity. The substantial risk factors for OCSCC are the consumption of tobacco products, alcohol, betel quid, areca nut, and genetic alteration. However, technological advancements have occurred in treatment, but the survival decreases with late diagnosis; therefore, new methods are continuously being investigated for treatment. In addition, the rate of secondary tumor formation is 3-7% yearly, which is incomparable to other malignancies and can lead to the disease reoccurrence. Oral cavity cancer (OCC) arises from genetic alterations, and a complete understanding of the molecular mechanism involved in OCC is essential to develop targeted treatments. This review aims to update the researcher on oral cavity cancer, risk factors, genetic alterations, molecular mechanism, classification, diagnostic approaches, and treatment.

3D in vitro co-culture disc for spatiotemporal image analysis of cancer-stromal cell interaction

Assessing phenotypic changes in both cancer cells and surrounding cells, which construct the tumour microenvironment, is essential for understanding the role of bi-directional communication among cells in the tumorigenic process. Here, a 3D in vitro cancer-stroma co-culture system, a co-culture disc, was reported for the spatiotemporal image analysis of cancer-stromal cell interactions. Due to their centre-open disc structure, the lung cancer A549 spheroids could be co-cultured with a high concentration of fibroblasts, without gel shrinkage in the long term (>1 month). In the co-culture disc, some populations of applied normal human lung fibroblasts showed morphological and phenotypic changes into activated myofibroblasts (AMFs) with high expression of myo-fibrotic α-smooth muscle actin fibre in the cell, which is a well-known feature of cancer-associated fibroblasts. The AMFs appeared heterogeneously at the boundary of cancer spheroids, which could not be detected by standard mass analysis using a quantitative RT-qPCR system, and they led to A549 cancer cell migration. In addition, the effects of oncogenic or medicinal additives were quantitatively assessed by combining co-culture discs with image analysis. This system provides a new potential technique to analyse the complicated crosstalk among cancer tissue-constructing cells during the tumorigenic process and provides insight into applications for the quantitative evaluation of substances inducing tumorigenesis as well as drugs to prevent and inhibit cancer progression.

Cellular Senescence and Inflammaging in the Skin Microenvironment

Cellular senescence and aging result in a reduced ability to manage persistent types of inflammation. Thus, the chronic low-level inflammation associated with aging phenotype is called “inflammaging”. Inflammaging is not only related with age-associated chronic systemic diseases such as cardiovascular disease and diabetes, but also skin aging. As the largest organ of the body, skin is continuously exposed to external stressors such as UV radiation, air particulate matter, and human microbiome. In this review article, we present mechanisms for accumulation of senescence cells in different compartments of the skin based on cell types, and their association with skin resident immune cells to describe changes in cutaneous immunity during the aging process.

Long Noncoding Transcriptome in Chronic Obstructive Pulmonary Disease

Chronic airway inflammation from recurring exposures to noxious environmental stimuli results in a progressive and irreversible airflow limitation and the lung parenchymal damage that characterizes chronic obstructive pulmonary disease (COPD). The large variability observed in the onset and progression of COPD is primarily driven by complex gene-environment interactions. The transcriptomic and epigenetic memory potential of lung epithelial and innate immune cells drive responses, such as mucus hyperreactivity and airway remodeling, that are tightly regulated by various molecular mechanisms, for which several candidate susceptibility genes have been described. However, the recently described noncoding RNA species, in particular the long noncoding RNAs, may also have an important role in modulating pulmonary responses to chronic inhalation of toxic substances and the development of COPD. This review outlines the features of long noncoding RNAs that have been implicated in regulating the airway inflammatory responses to cigarette smoke exposure and their possible association with COPD pathogenesis. As COPD continues to debilitate the increasingly aging population and contribute to higher morbidity and mortality rates worldwide, the search for better biomarkers and alternative therapeutic options is pivotal.

Unmasking senescence: context-dependent effects of SASP in cancer

Cellular senescence plays a critical role in tumorigenesis. Once thought of as a tissue culture artefact by some researchers, senescence is now a major field of study. Although there are common molecular mechanisms that enforce the growth arrest that characterizes the phenotype, the impact of senescence is varied and can, in some instances, have opposite effects on tumorigenesis. It has become clearer that the cell of origin and the tissue in question dictate the impact of senescence on tumorigenesis. In this Review, we unravel this complexity by focusing on how senescence impacts tumorigenesis when it arises within incipient tumour cells versus stromal cells, and how these roles can change in different stages of disease progression. In addition, we highlight the diversity of the senescent phenotype and its functional output beyond growth arrest: the senescence-associated secretory phenotype (SASP). Fortunately, a number of new genetic and pharmacologic tools have been developed that are now allowing the senescence phenotype to be parsed further.

Dual inhibition of Akt and ERK signaling induces cell senescence in triple-negative breast cancer

Activated Akt and ERK signaling pathways are closely related to breast cancer progression, and Akt or ERK inhibition induces cell senescence. However, the crosstalk between the Akt and ERK signaling pathways in cell senescence and how to simultaneously suppress Akt and ERK signaling in triple-negative breast cancer (TNBC) are undefined. In this study, we found that norcantharidin (NCTD) effectively induced cell senescence and cell cycle arrest in TNBC in vitro, which was accompanied by a decline in phosphorylated Akt and ERK1/2 and a rise in p21 and p16. The inhibitors LY294002 and U0126 imitated the effect of NCTD when these two inhibitors were combined regardless of crosstalk between these two signaling pathways. In addition, NCTD inhibited the growth of xenografts via downregulation of phosphorylated Akt and ERK1/2 and upregulation of p21 in vivo. However, NCTD upregulated the level of soluble signaling factors of the senescence-associated secretory phenotype (SASP) in a NF-κB-independent manner. Collectively, these findings demonstrate that NCTD induced cell senescence and cell cycle arrest mainly by simultaneously blocking Akt and ERK signaling in TNBC, suggesting that NCTD may be used as a potential adjuvant therapy in TNBC.

Biomarkers of Cellular Senescence and Skin Aging

Cellular senescence is an irreversible growth arrest that occurs as a result of different damaging stimuli, including DNA damage, telomere shortening and dysfunction or oncogenic stress. Senescent cells exert a pleotropic effect on development, tissue aging and regeneration, inflammation, wound healing and tumor suppression. Strategies to remove senescent cells from aging tissues or preneoplastic lesions can delay tissue dysfunction and lead to increased healthspan. However, a significant hurdle in the aging field has been the identification of a universal biomarker that facilitates the unequivocal detection and quantification of senescent cell types in vitro and in vivo. Mammalian skin is the largest organ of the human body and consists of different cell types and compartments. Skin provides a physical barrier against harmful microbes, toxins, and protects us from ultraviolet radiation. Increasing evidence suggests that senescent cells accumulate in chronologically aged and photoaged skin; and may contribute to age-related skin changes and pathologies. Here, we highlight current biomarkers to detect senescent cells and review their utility in the context of skin aging. In particular, we discuss the efficacy of biomarkers to detect senescence within different skin compartments and cell types, and how they may contribute to myriad manifestations of skin aging and age-related skin pathologies.

The Potential Role of Senescence As a Modulator of Platelets and Tumorigenesis

In addition to thrombus formation, alterations in platelet function are frequently observed in cancer patients. Importantly, both thrombus and tumor formation are influenced by age, although the mechanisms through which physiological aging modulates these processes remain poorly understood. In this context, the potential effects of senescent cells on platelet function represent pathophysiological mechanisms that deserve further exploration. Cellular senescence has traditionally been viewed as a barrier to tumorigenesis. However, far from being passive bystanders, senescent cells are metabolically active and able to secrete a variety of soluble and insoluble factors. This feature, known as the senescence-associated secretory phenotype (SASP), may provide senescent cells with the capacity to modify the tissue environment and, paradoxically, promote proliferation and neoplastic transformation of neighboring cells. In fact, the SASP-dependent ability of senescent cells to enhance tumorigenesis has been confirmed in cellular systems involving epithelial cells and fibroblasts, leaving open the question as to whether similar interactions can be extended to other cellular contexts. In this review, we discuss the diverse functions of platelets in tumorigenesis and suggest the possibility that senescent cells might also influence tumorigenesis through their ability to modulate the functional status of platelets through the SASP.

Greater Sensitivity of Oral Fibroblasts to Smoked Versus Smokeless Tobacco

BACKGROUND

Smokers have an increased incidence and severity of periodontal disease. Although cigarette smoke contains >4,000 chemical components that could affect periodontal tissues, less is understood about the effect of smokeless tobacco. Therefore, this study compares the effects of cigarette smoke extract (CSE) and smokeless tobacco extract (STE) on cell survival and motility of periodontal ligament (PDL) and gingival fibroblasts in vitro.

METHODS

PDL and gingival fibroblasts were exposed to various concentrations of CSE, STE, or nicotine alone. Viable cells were labeled with calcein acetoxymethyl, visualized using fluorescent microscopy, and quantified using a fluorescence multi-well plate reader. In vitro wounding and collagen gel contraction assays were used to assess cell motility.

RESULTS

Both gingival and PDL fibroblasts displayed reduced cell viability with increasing concentrations of CSE and STE. Based on relative nicotine content, CSE was significantly more cytotoxic than STE. PDL fibroblasts were also more sensitive to both CSE and STE compared with gingival fibroblasts. Finally, sublethal doses of CSE reduced cell motility and gel contraction, whereas STE had less effect. Nicotine alone ≤0.5 mM had little to no effect in any of these assays.

CONCLUSIONS

Many of the underlying effects of tobacco products on periodontal tissues may be due to direct inhibition of normal fibroblast function. CSE is found to be more deleterious to the function of both PDL and gingival fibroblasts than STE. PDL fibroblasts appear to be more sensitive to CSE and STE than gingival fibroblasts. Therefore, cigarette smoke may have more profound effects than smokeless tobacco.

Programmed cell senescence: role of IL-6 in the pituitary

IL-6 is a pleiotropic cytokine with multiple pathophysiological functions. As a key factor of the senescence secretome, it can not only promote tumorigenesis and cell proliferation but also exert tumor suppressive functions, depending on the cellular context. IL-6, as do other cytokines, plays important roles in the function, growth and neuroendocrine responses of the anterior pituitary gland. The multiple actions of IL-6 on normal and adenomatous pituitary function, cell proliferation, angiogenesis and extracellular matrix remodeling indicate its importance in the regulation of the anterior pituitary. Pituitary tumors are mostly benign adenomas with low mitotic index and rarely became malignant. Premature senescence occurs in slow-growing benign tumors, like pituitary adenomas. The dual role of IL-6 in senescence and tumorigenesis is well represented in pituitary tumor development, as it has been demonstrated that effects of paracrine IL-6 may allow initial pituitary cell growth, whereas autocrine IL-6 in the same tumor triggers senescence and restrains aggressive growth and malignant transformation. IL-6 is instrumental in promotion and maintenance of the senescence program in pituitary adenomas.

Comparative systems toxicology analysis of cigarette smoke and aerosol from a candidate modified risk tobacco product in organotypic human gingival epithelial cultures: A 3-day repeated exposure study

Smoking is one of the major lifestyle-related risk factors for periodontal diseases. Modified risk tobacco products (MRTP) offer a promising alternative in the harm reduction strategy for adult smokers unable to quit. Using a systems toxicology approach, we investigated and compared the exposure effects of a reference cigarette (3R4F) and a heat-not-burn technology-based candidate MRTP, the Tobacco Heating System (THS) 2.2. Human gingival epithelial organotypic cultures were repeatedly exposed (3 days) for 28 min at two matching concentrations of cigarette smoke (CS) or THS2.2 aerosol. Results showed only minor histopathological alterations and minimal cytotoxicity upon THS2.2 aerosol exposure compared to CS (1% for THS2.2 aerosol vs. 30% for CS, at the high concentration). Among the 14 proinflammatory mediators analyzed, only 5 exhibited significant alterations with THS2.2 exposure compared with 11 upon CS exposure. Transcriptomic and metabolomic analysis indicated a general reduction of the impact in THS2.2 aerosol-exposed samples with respect to CS (∼79% lower biological impact for the high THS2.2 aerosol concentration compared to CS, and 13 metabolites significantly perturbed for THS2.2 vs. 181 for CS). This study indicates that exposure to THS2.2 aerosol had a lower impact on the pathophysiology of human gingival organotypic cultures than CS.

Telomeres and telomerase in head and neck squamous cell carcinoma: from pathogenesis to clinical implications

Strongly associated with tobacco use, heavy alcohol consumption, and with high-risk human papillomavirus (HPV) infection, head and neck squamous cell carcinoma (HNSCC) is a frequently lethal, heterogeneous disease whose pathogenesis is a multistep and multifactorial process involving genetic and epigenetic events. The majority of HNSCC patients present with locoregional advanced stage disease and are treated with combined modality strategies that can markedly impair quality of life and elicit unpredictable results. A large fraction of those who undergo locoregional treatment and achieve a complete response later develop locoregional recurrences or second field tumors. Biomarkers that are thus able to stratify risk and enable clinicians to tailor treatment plans and to personalize post-therapeutic surveillance strategies are highly desirable. To date, only HPV status is considered a reliable independent predictor of treatment response and survival in patients with HNSCC arising from the oropharyngeal site. Recent studies suggest that telomere attrition, which may be an early event in human carcinogenesis, and telomerase activation, which is detected in up to 90 % of malignancies, could be potential markers of cancer risk and disease outcome. This review examines the current state of knowledge on and discusses the implications linked to telomere dysfunction and telomerase activation in the development and clinical outcome of HNSCC.

Repeated exposure to whole cigarette smoke promotes primary human gingival epithelial cell growth and modulates keratin expression

BACKGROUND AND OBJECTIVE

The gingiva is the first oral tissue directly exposed to cigarette smoke (CS). Exposure to CS compromises the structure and function of gingival tissue. Damaging or altering the gingival epithelium leads to a compromised protective barrier of the periodontium, resulting in several diseases. The aim of this study was to assess the effect of repeated exposure to CS on gingival epithelial cell growth and on expression of apoptotic protein and keratin.

MATERIAL AND METHODS

Primary human gingival epithelial cells were seeded on a collagen scaffold for 5 d to allow growth and stratification. The cells were then exposed for 5 min to whole CS for 3, 6 and 9 d. At the end of each exposure period, cell proliferation [using (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) (MTT) and 5-bromo-2'-deoxyuridine (BrdU) assays], gene expression [by quantitative reverse transcription polymerase chain reaction (qRT-PCR)] and protein production (by western blot analysis) were investigated.

RESULTS

Higher metabolic activity was found in the CS-exposed cells than in the nonexposed cells, specifically after 3 and 6 d of exposure to CS. At 9 d there was no significant difference between CS-exposed and nonexposed cells. Metabolic activity was supported by the BrdU cell-proliferation analyses, which showed increased cell growth at 3 d compared with the control. However, at 6 and 9 d, cell proliferation in the CS-exposed culture was comparable to that in the nonexposed culture. Interestingly, the Bax/Bcl-2 protein ratios decreased with increased CS exposure, suggesting cell resistance. Moreover, protein analyses showed that CS decreased expression of keratin(K) 5 at 3, 6 and 9 d, and increased expression of K14 at 6 and 9 d. Finally, mRNA analyses showed significant decreases of K1, K6, K10 and K16 in CS-exposed cultures, correlating, at times, with a decrease of protein production.

CONCLUSION

CS was shown to increase epithelial cell proliferation, which may involve cell resistance to apoptosis. This is supported by the modulation of expression of different keratin genes and proteins. Altogether, these data may explain the hyperplasia reported in gingival tissue, as well as periodontal disease, in smokers.

Systems Toxicology Assessment of the Biological Impact of a Candidate Modified Risk Tobacco Product on Human Organotypic Oral Epithelial Cultures

Cigarette smoke (CS) has been reported to increase predisposition to oral cancer and is also recognized as a risk factor for many conditions including periodontal diseases, gingivitis, and other benign mucosal disorders. Smoking cessation remains the most effective approach for minimizing the risk of smoking-related diseases. However, reduction of harmful constituents by heating rather than combusting tobacco, without modifying the amount of nicotine, is a promising new paradigm in harm reduction. In this study, we compared effects of exposure to aerosol derived from a candidate modified risk tobacco product, the tobacco heating system (THS) 2.2, with those of CS generated from the 3R4F reference cigarette. Human organotypic oral epithelial tissue cultures (EpiOral, MatTek Corporation) were exposed for 28 min to 3R4F CS or THS2.2 aerosol, both diluted with air to comparable nicotine concentrations (0.32 or 0.51 mg nicotine/L aerosol/CS for 3R4F and 0.31 or 0.46 mg/L for THS2.2). We also tested one higher concentration (1.09 mg/L) of THS2.2. A systems toxicology approach was employed combining cellular assays (i.e., cytotoxicity and cytochrome P450 activity assays), comprehensive molecular investigations of the buccal epithelial transcriptome (mRNA and miRNA) by means of computational network biology, measurements of secreted proinflammatory markers, and histopathological analysis. We observed that the impact of 3R4F CS was greater than THS2.2 aerosol in terms of cytotoxicity, morphological tissue alterations, and secretion of inflammatory mediators. Analysis of the transcriptomic changes in the exposed oral cultures revealed significant perturbations in various network models such as apoptosis, necroptosis, senescence, xenobiotic metabolism, oxidative stress, and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2) signaling. The stress responses following THS2.2 aerosol exposure were markedly decreased, and the exposed cultures recovered more completely compared with those exposed to 3R4F CS.

Senescence in Human Mesenchymal Stem Cells: Functional Changes and Implications in Stem Cell-Based Therapy

Regenerative medicine is extensively interested in developing cell therapies using mesenchymal stem cells (MSCs), with applications to several aging-associated diseases. For successful therapies, a substantial number of cells are needed, requiring extensive ex vivo cell expansion. However, MSC proliferation is limited and it is quite likely that long-term culture evokes continuous changes in MSCs. Therefore, a substantial proportion of cells may undergo senescence. In the present review, we will first present the phenotypic characterization of senescent human MSCs (hMSCs) and their possible consequent functional alterations. The accumulation of oxidative stress and dysregulation of key differentiation regulatory factors determine decreased differentiation potential of senescent hMSCs. Senescent hMSCs also show a marked impairment in their migratory and homing ability. Finally, many factors present in the secretome of senescent hMSCs are able to exacerbate the inflammatory response at a systemic level, decreasing the immune modulation activity of hMSCs and promoting either proliferation or migration of cancer cells. Considering the deleterious effects that these changes could evoke, it would appear of primary importance to monitor the occurrence of senescent phenotype in clinically expanded hMSCs and to evaluate possible ways to prevent in vitro MSC senescence. An updated critical presentation of the possible strategies for in vitro senescence monitoring and prevention constitutes the second part of this review. Understanding the mechanisms that drive toward hMSC growth arrest and evaluating how to counteract these for preserving a functional stem cell pool is of fundamental importance for the development of efficient cell-based therapeutic approaches.

In vitro cytotoxicity of Nicotiana gossei leaves, used in the Australian Aboriginal smokeless tobacco known as pituri or mingkulpa

The Aboriginal population of Central Australia use endemic Nicotiana species to make a smokeless tobacco product known usually as pituri or mingkulpa. Nicotiana leaves are masticated with wood ash into a 'quid' that is chewed/sucked for absorption of nicotine. In addition to nicotine, smokeless tobacco products contain a spectrum of biologically active compounds that may contribute to effects on health. The objective of this study was to quantify nicotine, and related alkaloids and tobacco specific nitrosamines (TSNAs), in Nicotiana leaves used in pituri, and compare in vitro toxicity of pure nicotine with Nicotiana leaf extract at the same concentration of nicotine. An aqueous extract of dry leaves of Nicotiana gossei and a reference smokeless tobacco (CORESTA CRP2) were quantified for major pyridine alkaloids and TSNAs using HPLC-UV and LC-MS/MS. A range of extract concentrations and corresponding concentrations of nicotine standard were tested using an MTS assay to measure human lung epithelium cell (A549) survival. Cells treated for 24h with the maximum concentration of 1.5mg/ml of nicotine resulted in 77% viability. In contrast, extracts from N. gossei leaves and CRP2 containing a similar concentration of nicotine (1.3mg/ml) resulted in remarkably lower viability of 1.5 and 6%, respectively. Comparison of cytotoxicity of pure nicotine with that of the extracts revealed that nicotine was not the source of their cytotoxicity. Other biologically active compounds such as the known carcinogens NNK and NNN, derived from nicotine and nornicotine and found to be present in the smokeless tobacco extracts, may be responsible.

Cellular senescence and tumor promotion: Is aging the key?

The senescence response is a potent tumor suppressor mechanism characterized by an irreversible growth arrest in response to potentially oncogenic signals to prevent the proliferation of damaged cells. Late in life, some of the features of senescent cells seem to mediate the development of age-related pathologies, including cancer. In the present review, we present a summary of the current knowledge regarding the causes, effector pathways and cellular features of senescence. We also discuss how the senescence response, initially a tumor suppressor mechanism, turns into a tumor promoter apparently as a consequence of aging. We argue that three age-related phenomena--senescence-associated secretory phenotype (SASP) dysregulation, decline in the immune system function and genomic instability--could contribute, independently or synergistically, to deteriorate the efficacy of the senescence response in stopping cancer. As a consequence, senescent cells could be considered premalignant cells, and targeting senescent cells could be a preventive and therapeutic strategy against cancer.

Fasting protects mice from lethal DNA damage by promoting small intestinal epithelial stem cell survival

Short-term fasting protects mice from lethal doses of chemotherapy through undetermined mechanisms. Herein, we demonstrate that fasting preserves small intestinal (SI) architecture by maintaining SI stem cell viability and SI barrier function following exposure to high-dose etoposide. Nearly all SI stem cells were lost in fed mice, whereas fasting promoted sufficient SI stem cell survival to preserve SI integrity after etoposide treatment. Lineage tracing demonstrated that multiple SI stem cell populations, marked by Lgr5, Bmi1, or HopX expression, contributed to fasting-induced survival. DNA repair and DNA damage response genes were elevated in SI stem/progenitor cells of fasted etoposide-treated mice, which importantly correlated with faster resolution of DNA double-strand breaks and less apoptosis. Thus, fasting preserved SI stem cell viability as well as SI architecture and barrier function suggesting that fasting may reduce host toxicity in patients undergoing dose intensive chemotherapy.

Senescence-Derived Extracellular Molecules as Modulators of Oral Cancer Development: A Mini-Review

Oral cancers are predominantly oral squamous cell carcinomas (OSCCs) derived from keratinocytes, and there is now very detailed knowledge of the genetics and molecular biology of the epithelial tumourigenic component of these cancers, including the identification of cancer stem or tumour-initiating cells. Several key genetic alterations have been identified including the near ubiquitous loss of the CDKN2A/p16INK4A and p53 pathways and telomerase activation, together with frequent inactivation of the NOTCH1 canonical pathway either by somatic genetic alterations or by the presence of human papilloma virus. There is also evidence that OSCCs arise from a ‘field' of altered cells and that malignant conversion takes place pre-dominantly at the microscopic level. However, in the last decade, it has been realised that tumour development and progression are influenced by the cells of the microenvironment with cross-talk between the epithelial (tumour) and mesenchymal components. OSCCs, especially those that have bypassed cellular senescence, produce an array of proteins and metabolites that induce cellular senescence in the normal surrounding cells; indeed, senescence is a common property of cancer-associated fibroblasts (CAFs). Cellular senescence is defined as an irreversible cell cycle arrest and is associated with the release of molecules known as the senescence-associated secretory phenotype that can selectively promote the growth of pre-neoplastic keratinocytes (osteopontin) and cancer invasion (transforming growth factor β, matrix metalloproteinases, interleukin 6 and lactate). In addition, both old and new work has shown that keratinocytes harbouring NOTCH loss-of-function mutations that lead to defective keratinocyte differentiation and loss of squamous epithelial barrier function may act as a tumour-promoting stimulus for initiated cells harbouring RAS pathway mutations by activating a wound response in the tumour mesenchyme. Thus, not all keratinocytes in the tumour tissue may be tumourigenic and may instead act as promoters of tumour growth and progression analogous to the much-studied CAFs which co-evolve with the genetically altered tumourigenic cells. This new data is discussed in relation to attempts to develop novel non-invasive diagnostics and therapeutics for oral cancer.

Prolonged overexpression of Wnt10b induces epidermal keratinocyte transformation through activating EGF pathway

Wnt10b is a signaling protein regulating skin development and homeostasis, and the expression of Wnt10b is restricted to epidermal keratinocytes in embryonic and postnatal skin. Recent studies indicate an elevated expression of Wnt10b in skin tumors. However, how Wnt10b regulates skin tumorigenesis remains largely unknown. Here we report that continuous expression of Wnt10b mediates transformation of epidermal keratinocytes through activating genes involved in EGF/MAPK signaling pathways. We first established a prolonged Wnt10b overexpression system in JB6P- cells to represent the elevated Wnt10b expression level in skin keratinocytes. Through expression assays and observations under phase-contrast microscopy, prolonged expression of Wnt10b activated Wnt/β-catenin pathway and induced morphological changes of cells showing longer protrusions and multilayer growth, indicating early-stage cell transformation. Wnt10b also increased cellular proliferation and migration according to BrdU incorporation and cell mobility assays. Furthermore, multi-doses of AdWnt10b treatment to JB6P- cells induced colony formation, stronger invasive ability in transwell system, and anchorage-independent growth in agar gel. In molecular level, AdWnt10b treatment induced increased transcriptional expressions of Egf, downstream Mapk pathway factors, and MMPs. Administration of Wnt antagonist DKK1 blocked the tumor promotion process induced by Wnt10b. Taken together, these findings clearly demonstrate that Wnt10b promotes epidermal keratinocyte transformation through induced Egf pathway.

DNA-damage-induced type I interferon promotes senescence and inhibits stem cell function

Expression of type I interferons (IFNs) can be induced by DNA-damaging agents, but the mechanisms and significance of this regulation are not completely understood. We found that the transcription factor IRF3, activated in an ATM-IKKα/β-dependent manner, stimulates cell-autonomous IFN-β expression in response to double-stranded DNA breaks. Cells and tissues with accumulating DNA damage produce endogenous IFN-β and stimulate IFN signaling in vitro and in vivo. In turn, IFN acts to amplify DNA-damage responses, activate the p53 pathway, promote senescence, and inhibit stem cell function in response to telomere shortening. Inactivation of the IFN pathway abrogates the development of diverse progeric phenotypes and extends the lifespan of Terc knockout mice. These data identify DNA-damage-response-induced IFN signaling as a critical mechanism that links accumulating DNA damage with senescence and premature aging.

Persistent DNA damage-induced premature senescence alters the functional features of human bone marrow mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) are adult multipotent stem cells located in various tissues, including the bone marrow. In contrast to terminally differentiated somatic cells, adult stem cells must persist and function throughout life to ensure tissue homeostasis and repair. For this reason, they must be equipped with DNA damage responses able to maintain genomic integrity while ensuring their lifelong persistence. Evaluation of hMSC response to genotoxic insults is of great interest considering both their therapeutic potential and their physiological functions. This study aimed to investigate the response of human bone marrow MSCs to the genotoxic agent Actinomycin D (ActD), a well-known anti-tumour drug. We report that hMSCs react by undergoing premature senescence driven by a persistent DNA damage response activation, as hallmarked by inhibition of DNA synthesis, p21 and p16 protein expression, marked Senescent Associated β-galactosidase activity and enlarged γH2AX foci co-localizing with 53BP1 protein. Senescent hMSCs overexpress several senescence-associated secretory phenotype (SASP) genes and promote motility of lung tumour and osteosarcoma cell lines in vitro. Our findings disclose a multifaceted consequence of ActD treatment on hMSCs that on the one hand helps to preserve this stem cell pool and prevents damaged cells from undergoing neoplastic transformation, and on the other hand alters their functional effects on the surrounding tissue microenvironment in a way that might worsen their tumour-promoting behaviour.

Connections of nicotine to cancer

This Opinion article discusses emerging evidence of direct contributions of nicotine to cancer onset and growth. The list of cancers reportedly connected to nicotine is expanding and presently includes small-cell and non-small-cell lung carcinomas, as well as head and neck, gastric, pancreatic, gallbladder, liver, colon, breast, cervical, urinary bladder and kidney cancers. The mutagenic and tumour-promoting activities of nicotine may result from its ability to damage the genome, disrupt cellular metabolic processes, and facilitate growth and spreading of transformed cells. The nicotinic acetylcholine receptors (nAChRs), which are activated by nicotine, can activate several signalling pathways that can have tumorigenic effects, and these receptors might be able to be targeted for cancer therapy or prevention. There is also growing evidence that the unique genetic makeup of an individual, such as polymorphisms in genes encoding nAChR subunits, might influence the susceptibility of that individual to the pathobiological effects of nicotine. The emerging knowledge about the carcinogenic mechanisms of nicotine action should be considered during the evaluation of regulations on nicotine product manufacturing, distribution and marketing.

Noninvasive assessment of the risk of tobacco abuse in oral mucosa using fluorescence spectroscopy: a clinical approach

Tobacco abuse and alcoholism cause cancer, emphysema, and heart disease, which contribute to high death rates, globally. Society pays a significant cost for these habits whose first demonstration in many cases is in the oral cavity. Oral cavity disorders are highly curable if a screening procedure is available to diagnose them in the earliest stages. The aim of the study is to identify the severity of tobacco abuse, in oral cavity, as reflected by the emission from endogenous fluorophores and the chromophore hemoglobin. A group who had no tobacco habits and another with a history of tobacco abuse were included in this study. To compare the results with a pathological condition, a group of leukoplakia patients were also included. Emission from porphyrin and the spectral filtering modulation effect of hemoglobin were collected from different sites. Multivariate analysis strengthened the spectral features with a sensitivity of 60% to 100% and a specificity of 76% to 100% for the discrimination. Total hemoglobin and porphyrin levels of habitués and leukoplakia groups were comparable, indicating the alarming situation about the risk of tobacco abuse. Results prove that fluorescence spectroscopy along with multivariate analysis is an effective noninvasive tool for the early diagnosis of pathological changes due to tobacco abuse.

p38MAPK plays a crucial role in stromal-mediated tumorigenesis

Neoplastic cells rely on the tumor microenvironment (TME) for survival and progression factors. Indeed, senescent and cancer-associated fibroblasts (CAF) express factors that promote tumorigenesis that are collectively referred to as the senescence-associated secretory phenotype (SASP). Despite their importance in tumorigenesis, the mechanisms that control TME-derived factor expression remain poorly understood. Here, we address a key unanswered question: how the SASP is sustained in senescent fibroblasts and CAFs. We find that the mitogen-activated protein kinase p38 (p38MAPK) controls AUF1 occupancy on SASP mRNAs and thus controls their stability. The importance of this regulatory mechanism is underscored by our findings that stromal-specific p38MAPK inhibition abrogates the tumor-promoting activities of CAFs and senescent fibroblasts. Our data suggest that targeting SASP mRNA stability through inhibition of p38MAPK will significantly aid the development of clinical strategies to target the TME.

SIGNIFICANCE

The TME plays a key role in tumorigenesis. We demonstrate that p38MAPK governs a posttranscriptional mechanism that sustains the protumorigenic SASP. Inhibition of p38MAPK abrogates the tumor-promoting activities of CAFs and senescent fibroblasts. Thus, p38MAPK is a TME-specific Achilles' heel that may be exploited as a new therapeutic target.

The senescence arrest program and the cell cycle

All living organisms are subject to progressive loss of function and damage to their tissues, a process known as aging. At the cellular level, the accumulation of damage to DNA, proteins, and organelles induces cellular senescence, a stress-response pathway that likely influences the aging process. Although the senescence arrest program was initially described in vitro, accumulating evidence suggests that this damage response program occurs in a variety of pathologic settings. This review discusses aspects of the senescence program, their interrelationships with damage arrest pathways, the cell cycle, and the impact of senescence in vivo.

Mesenchymal stroma: primary determinant and therapeutic target for epithelial cancer

Multifocal and recurrent epithelial tumors, originating from either dormant or de novo cancer cells, are major causes of morbidity and mortality. The age-dependent increase of cancer incidence has long been assumed to result from the sequential accumulation of cancer-driving or -facilitating mutations with induction of cellular senescence as a protective mechanism. However, recent evidence suggests that the initiation and development of epithelial cancer results from a close interplay with its altered tissue microenvironment, with chronic inflammation, stromal senescence, autophagy, and the activation of cancer-associated fibroblasts (CAFs) playing possible primary roles. We will discuss recent progress in these areas, and highlight how this understanding may be used for devising novel preventive and therapeutic approaches to the epithelial cancer problem.

The impact of radiation therapy on the antitumor immunity: local effects and systemic consequences

The main antitumor efficacy of irradiation relies in its direct cytotoxic effect. Increasing evidence indicates a systemic effect of radiation though, mediated mainly by the immune system. In this review we wish to focus on the radiotherapy induced modifications of the soluble and cellular mediators of the antitumor immune response and summarize some of the mechanisms by which radiation driven local and systemic bystander effects can influence tumor immunogenicity. In different tumor types due to the intrinsic immunogenicity of the tumor cells and the immunological characteristics of the tumor microenvironment, different radiation induced immune modulatory mechanisms are predominant. Radiation most probably can only amplify or augment a pro-immunogenic phenotype and can hardly change by itself a net immune suppressing environment into an immune stimulating one. This immune modulatory potential of radiotherapy could be exploited in tumor treatment by developing combined radiotherapeutic and immunotherapeutic approaches. The last few years showed a dramatic increase in the knowledge of radiation induced out-of field and systemic effects, which foresees a rapid progress in the development and clinical application of these new, combined therapies for cancer cure.

Cigarette smoke condensate promotes pro-tumourigenic stromal-epithelial interactions by suppressing miR-145

BACKGROUND

Exposure to factors released from tobacco during chewing or smoking is recognized as a major risk factor for oral carcinogenesis and influences the phenotype of oral epithelial cells and fibroblasts within the underlying stroma. Micro(mi)RNA can regulate the expression of genes within cells, and previous studies show that tobacco products can alter the miRNA profiles in lung epithelial cells. However, the molecular alterations occurring in oral fibroblasts exposed to tobacco constituents remain to be elucidated.

METHODS

Oral fibroblasts were exposed to cigarette smoke condensate (CSC) and miRNA expression compared to untreated controls using tiling low-density arrays (TLDA). Expression of miRNA-145 was confirmed by quantitative (q)RT-PCR. The effect of CSC on fibroblast cell viability, motility and matrix metalloproteinase (MMP)-2 expression was measured using MTS, a wound scratch assay and qRT-PCR, respectively. Oral cancer cell migration in response to culture supernatants from mock, control or pre-miR-145-transfected CSC-treated fibroblasts was analysed by chemotaxis assay.

RESULTS

TLDA analysis identified widespread changes in the miRNA expression profile of fibroblasts exposed to CSC. Pri-, pre- and mature miRNA-145 were significantly down-regulated in response to CSC, and this was accompanied by up-regulated expression of MMP-2 and increased migration of fibroblasts compared to untreated controls. Re-expression of miR-145 abrogated the ability of fibroblasts to promote oral cancer cell chemotaxis in response to CSC.

CONCLUSION

These findings suggest that tobacco constituents influence the expression of miRNA within oral fibroblasts promoting a phenotype that increases oral cancer migration and sheds new light on the mechanisms underlying oral cancer pathogenesis.

Differential cell-specific cytotoxic responses of oral cavity cells to tobacco preparations

To examine the effects of standardized (reference) tobacco preparations on human oral cavity cells, two oral squamous cell carcinoma cell lines (101A, 101B) and normal human gingival epithelial cells (HGEC) were treated with cigarette smoke total particulate matter (TPM), smokeless tobacco extracted with complete artificial saliva (ST/CAS), or whole-smoke conditioned media (WS-CM). EC-50 values, as determined by sulforhodamine B assays, varied among the cell types and agents. When normalized to nicotine content, cytotoxicity for WS-CM and TPM was higher compared to that observed with ST/CAS. Nicotine alone had no or only minimal cytotoxicity for all cell types in the applied range. Activation of pro-apoptotic caspase-3 was examined in all cell types at their respective EC-50 doses for the three agents. TPM, but not ST/CAS or WS-CM significantly activated caspase-3 in all three cell types. Fluorescence-activated cell sorting (FACS) for expression of the early apoptosis marker Annexin V and for nuclear staining by 7-aminoactinomycin (7-AAD) revealed different extents of apoptosis versus non-apoptotic cell death for the three agents. These data characterize differential responses of normal and malignant oral cells after exposure to TPM, ST/CAS, or WS-CM. They assist in understanding differential effects of combustible versus non-combustible tobacco products, and in identifying novel biomarkers for tobacco smoke exposure and effect in the oral cavity.

Smoking and the skin

Cigarette smoking has been associated with significant morbidity affecting all systems of the body, including the integumentary system. We review the many dermatologic hazards of tobacco use. It is important to distinguish between the effects of tobacco smoke from effects of pure nicotine on the skin. All skin cells express several subtypes of the nicotinic class of acetylcholine receptors, including the α7 receptor. Many chronic dermatoses are affected by smoking either negatively or positively. Elucidation of positive associations with a particular disease can lead to improvement from smoking cessation, whereas inverse correlation may lead to development of a disease-specific treatment with nicotinergic agonists.

Acute effects of cigarette smoke on three-dimensional cultures of normal human oral mucosa

CONTEXT

Human oral mucosa is the combustion chamber of cigarette, but scanty evidence is available about the early smoke effects.

OBJECTIVE

The present work aimed at evaluating from a morphological point of view whole smoke early effects on epithelial intercellular adhesion and keratinocyte terminal differentiation in a three-dimensional model of human oral mucosa.

MATERIALS AND METHODS

Biopsies of keratinized oral mucosa of healthy nonsmoking women (n = 5) were collected. After culturing in a Transwell system, one fragment of each biopsy was exposed to the smoke of one single cigarette; the remnant represented the internal control. The distribution of epithelial differentiation markers (keratin-10, K10, and keratin-14, K14, for suprabasal and basal cells respectively), desmosomes (desmoglein-1, desmoglein-3), tight junctions (occludin), adherens junctions (E-cadherin, β-catenin), and apoptotic cells (p53, caspase 3) were evaluated by immunofluorescence.

RESULTS

Quantitative analysis of K14 immunolabeling revealed an overexpression in the suprabasal layers as early as 3 h after smoke exposure, without impairment of the epithelial junctional apparatus and apoptosis induction.

DISCUSSION AND CONCLUSION

These results suggested that the first significant response to cigarette smoke came from the basal and suprabasal layers of the human oral epithelium. The considered model maintained the three-dimensional arrangement of the human mucosa in the oral cavity and mimicked the inhalation/exhalation cycle during the exposure to cigarette smoke, offering a good possibility to extrapolate the reported observations to humans.

ZO proteins and redox-dependent processes

SIGNIFICANCE

ZO-1, ZO-2, and ZO-3 are scaffold proteins of the tight junction (TJ) that belong to the MAGUK protein family characterized for exhibiting PDZ, SH3, and GuK domains. ZO proteins are present only in multicellular organisms, being the placozoa the first to have them. ZO proteins associate among themselves and with other integral and adaptor proteins of the TJ, of the ZA and of gap junctions, as with numerous signaling proteins and the actin cytoskeleton. ZO proteins are also present at the nucleus of proliferating cells.

RECENT ADVANCES

Oxidative stress disassembles the TJs of endothelial and epithelial cells.

CRITICAL ISSUES

Oxidative stress alters ZO proteins expression and localization, in conditions like hypoxia, bacterial and viral infections, vitamin deficiencies, age-related diseases, diabetes and inflammation, alcohol and tobacco consumption.

FUTURE DIRECTIONS

Molecules present in the signaling pathways triggered by oxidative stress can be targets for therapeutic intervention.

Epithelial-mesenchymal transition induced by senescent fibroblasts

Depending on the cell type and tissue environment, epithelial and mesenchymal cell phenotypes are not static and can be highly dynamic. Epithelial-mesenchymal transitions (EMTs) and reverse EMTs provide flexibility during embryogenesis. While EMTs are a critical normal process during development and wound healing, properties of the EMT have been implicated in human pathology, particularly cancer metastasis. A normal undamaged epithelium does not typically exhibit features of an EMT. However, particularly under the influence of the surrounding microenvironment, cancer cells may reactivate developmental phenotypes out of context in the adult. This reactivation, such as the EMT, can facilitate tumor cell invasion and metastasis, and therefore is a major mechanism of tumor progression. Conversely, cellular senescence, which is associated with aging, is a process by which cells enter a state of permanent cell cycle arrest, thereby constituting a potent tumor suppressive mechanism. However, accumulating evidence shows that senescent cells can have deleterious effects on the tissue microenvironment. The most significant of these effects is the acquisition of a senescence-associated secretory phenotype (SASP) that turns senescent fibroblasts into pro-inflammatory cells having the ability to promote tumor progression, in part by inducing an EMT in nearby epithelial cells. Here, we summarize the potential impacts of SASP factors, particularly interleukins, on tissue microenvironments and their ability to stimulate tumor progression through induction of an EMT.

Whole cigarette smoke promotes human gingival epithelial cell apoptosis and inhibits cell repair processes

BACKGROUND AND OBJECTIVE

Smoking cigarettes increases the risk of developing various types of human diseases, including cancers and periodontitis. As gingival epithelial cells are known to play an active role in innate immunity via the secretion of a wide variety of mediators, and as these cells are the first ones exposed to environmental stimuli such as cigarette smoke, we sought to investigate the effects of whole cigarette smoke on normal human gingival epithelial cells and tissue.

MATERIAL AND METHODS

Human gingival epithelial cells were extracted from healthy nonsmokers and used either as a monolayer or as an engineered human oral mucosa to investigate the effect of whole cigarette smoke on cell growth, apoptosis and wound repair/migration.

RESULTS

Our findings show that when gingival epithelial cells were exposed once to whole cigarette smoke, this resulted in a significant inhibition of cell growth through an apoptotic pathway, as confirmed by an increase of Bax and a decrease of Bcl-xL and caspase-3 activity. Cigarette smoke also inhibited epithelial cell migration. These effects may explain the disorganization of the engineered human oral mucosa tissue when exposed to whole cigarette smoke.

CONCLUSION

Exposure to whole cigarette smoke markedly inhibits epithelial cell growth through an apoptosis/necrosis pathway that involves Bax and Bcl-xL proteins and caspase-3 activity. Cigarette smoke also disrupts epithelial cell migration, which may negatively affect periodontal wound healing.

Effects of whole cigarette smoke on human gingival fibroblast adhesion, growth, and migration

The aim of this study was to investigate the effects of a single exposure to whole cigarette smoke on human gingival fibroblast behavior. Normal oral mucosa fibroblasts were exposed once to whole cigarette smoke for 5, 15, or 30 min, and then were used to analyze cell adhesion, β1-integrin expression, cell growth and viability, cell capacity to contract collagen gel, and cell migration following wound infliction. Our findings showed that when gingival fibroblasts were exposed once to whole cigarette smoke, this resulted in a significant inhibition of cell adhesion, a decrease in the number of β1-integrin-positive cells, increased LDH activity in the target cells, and reduced growth. The smoke-exposed fibroblasts were also not able to contract collagen gel matrix and migrate following insult. Overall results demonstrate that a single exposure to whole cigarette smoke produced significant morphological and functional deregulation in gingival fibroblasts. This may explain the higher predisposition of tobacco users to oral infections and diseases such as cancer.