Age-dependent changes in the distribution of BrdU- and TUNEL-positive cells in the murine gingival tissue

Comparative Analysis of Gene Expression Patterns for Oral Epithelium-Related Functions with Aging

Epithelial cells and functions of the epithelium are critical to the health of the oral cavity. We used a nonhuman primate model to profile the transcriptome of gingival tissues in health across the lifespan and hypothesized that in older animals, epithelial-related transcriptome patterns would reflect epithelial cells that are aggressively responsive to the surrounding environment and less able to modulate and resolve the noxious challenge from the bacteria. Rhesus monkeys (n = 34) with a healthy periodontium were distributed into four groups: ≤3 years (young), 3-7 years (adolescent), 12-16 years (adult), and 18-23 years (aged), and a buccal gingival sample from the premolar/molar region of each animal was obtained. RNA was subjected to a microarray analysis (GeneChip^® Rhesus Macaque Genome Array, Affymetrix), and 336 genes examined that are linked to epithelium and epithelial cell functions categorized into 9 broad functional groups: extracellular matrix and cell structure; extracellular matrix remodeling enzymes; cell adhesion molecules, cytoskeleton regulation; inflammatory response; growth factors; kinases/cell signaling; cell surface receptors; junction associated molecules; autophagy/apoptosis; antimicrobial peptides; and transcription factors. Total of 255 genes displayed a normalized signal >100, and differences across the age groups were observed primarily in extracellular matrix and cell structure, cell adhesion molecules, and cell surface receptor gene categories with elevations in the aged tissues. Keratins 2, 5, 6B, 13, 16, 17 were all significantly increased in healthy-aged tissues versus adults, and keratins 1 and 2 were significantly decreased in young animals. Approximately 15 integrins are highly expressed in the gingival tissues across the age groups with only ITGA8, ITGAM (CD11b), and ITGB2 significantly increased in the aged tissues. Little impact of aging on desmosomal/hemidesmosomal genes was noted. These results suggest that healthy gingival aging has a relatively limited impact on the broader functions of the epithelium and epithelial cells, with some effects on genes for extracellular matrix and cell adhesion molecules (e.g., integrins). Thus, while there is a substantial impact of aging on immune system targets even in healthy gingiva, it appears that the epithelial barrier remains reasonably molecularly intact in this model system.

Aging, inflammation, immunity and periodontal disease

The increased prevalence and severity of periodontal disease have long been associated with aging, such that this oral condition affects the majority of the adult population over 50 years of age. Although the immune system is a critical component for maintaining health, aging can be characterized by quantitative and qualitative modifications of the immune system. This process, termed 'immunosenescence', is a progressive modification of the immune system that leads to greater susceptibility to infections, neoplasia and autoimmunity, presumably reflecting the prolonged antigenic stimulation and/or stress responses that occur across the lifespan. Interestingly, the global reduction in the host capability to respond effectively to these challenges is coupled with a progressive increase in the general proinflammatory status, termed 'inflammaging'. Consistent with the definition of immunosenescence, it has been suggested that the cumulative effect of prolonged exposure of the periodontium to microbial challenge is, at least in part, a contributor to the effects of aging on these tissues. Thus, it has also been hypothesized that alterations in the function of resident immune and nonimmune cells of the periodontium contribute to the expression of inflammaging in periodontal disease. Although the majority of aging research has focused on the adaptive immune response, it is becoming increasingly clear that the innate immune compartment is also highly affected by aging. Thus, the phenomenon of immunosenescence and inflammaging, expressed as age-associated changes within the periodontium, needs to be more fully understood in this era of precision and personalized medicine and dentistry.

The junctional epithelium originates from the odontogenic epithelium of an erupted tooth

The junctional epithelium (JE) is an epithelial component that is directly attached to the tooth surface and has a protective function against periodontal diseases. In this study, we determined the origin of the JE using a bioengineered tooth technique. We transplanted the bioengineered tooth germ into the alveolar bone with an epithelial component that expressed green fluorescence protein. The reduced enamel epithelium from the bioengineered tooth fused with the oral epithelium, and the JE was apparently formed around the bioengineered tooth 50 days after transplantation. Importantly, the JE exhibited green fluorescence for at least 140 days after transplantation, suggesting that the JE was not replaced by oral epithelium. Therefore, our results demonstrated that the origin of the JE was the odontogenic epithelium, and odontogenic epithelium-derived JE was maintained for a relatively long period.

Oxidative stress caused by a low concentration of hydrogen peroxide induces senescence-like changes in mouse gingival fibroblasts

Periodontal tissue deteriorates under persistent oxidative stress induced by inflammatory reactions in the microflora of the oral cavity. This study aimed to evaluate the cellular properties of mouse gingival fibroblasts (MGFs) in the presence of oxidative stress. MGFs from 10-, 30- and 52-week-old mice were used to evaluate the changes in the cellular properties with aging. The study investigated the effects of oxidative stress on the cellular properties of MGFs from 10-week-old mice. The expression of p53, p21 and murine double minute 2 (Mdm2) in the MGFs in response to oxidative stress was also examined. By day 8, the number of MGFs increased in culture. However, the increase was markedly lower in MGFs derived from aged mice. Oxidative stress due to hydrogen peroxide (H2O2)-induced morphological changes characterized by a round shape with enlarged nuclei and expanded cytoplasm. The cell number of MGFs was decreased subsequent to treatment with 50 µM or a higher concentration of H₂O₂. MGFs treated with H₂O₂ at 20 µM showed a similar cell growth curve as the one seen in 52-week-old mice. Phosphorylated p53 protein was increased in MGFs subsequent to treatment with 20 µM H2O2, along with an upregulated transcription of p21 and Mdm2 mRNAs. These results suggest that treatment with a lower concentration of H₂O₂ in MGFs induces cell cycle arrest, resulting in stress-induced premature senescence, possibly correlated with the development of periodontal diseases.

Localization of heat shock protein 27 (hsp27) in the rat gingiva and its changes with tooth eruption

Heat shock protein 27 kDa (Hsp27) functions as a molecular chaperon to prevent apoptosis as well as to contribute to the regulation of cell proliferation and differentiation during development. In the present study, the localization of Hsp27 in the oral epithelium of rats and its expression change during formation of the gingiva with the tooth eruption were examined immunohistochemically to elucidate the roles of Hsp27 in the oral mucosa.

In adult rats, Hsp27-immunoreactivity was localized in the prickle and granular layers but absent in the basal and horny layers of the oral epithelium. On the other hand, in the outer and sulcular epithelia of the free gingival, Hsp27-immunoreactivity was detected in the whole layers, while it was not found in the proliferation zone of the junctional epithelium immunoreactive for Ki67. In immature rats on 10th postnatal day, Hsp27-immunoreactivity was intense in the prickle and granular layers of the oral epithelium, but was not detected in its basal layer. In rats at the eruptive phase on 15th postnatal day, Hsp27-immunoreactivity was detected in sites of the basal layer adjacent to where the dental cusps penetrated through the oral epithelium. Although the immunoreactivity for Ki67 was found in the basal layer of the oral epithelium, it was not localized in the Hsp27-immunopositive sites of tooth-penetration in the basal layer. Just after the tooth-eruption on 20th postnatal day, Hsp27-immunoreactivity was not found in the stratified squamous epithelium at the dentogingival junction, whereas it was intense in a single layer of cuboidal epithelial cells attached to the tooth neck. Ki67-positive cells were scattered in the stratified squamous epithelium at the dentogingival junction, whereas no positive cells were found in the portion of a single layer of cuboidal epithelial cells.

These findings suggest that the outer and sulcular epithelia of the free gingiva have a relatively slower rate of proliferation than other gingival and oral epithelia, and that Hsp27 might inhibit the proliferation of the basal cells. Such specific phenomenon in the free gingiva occurred immediately after the dental cusps were exposed to the oral cavity.

Effects of aging on mouse tongue epithelium focusing on cell proliferation rate and morphological aspects

The aim of this study was to investigate cell proliferation rate and certain morphological features of mouse epithelium as aging progresses. Tongue biopsies were performed on female mice (Mus domesticus domesticus) at 2, 8, 14 and 20 months of age as indicative of adolescence, adulthood, early senescence and senescence, respectively. Histological sections of tongue were stained with hematoxylin-eosin and subjected to silver staining for active nucleolar organizer region counting. Cell proliferation rate and epithelial thickness analysis were carried out. Analysis of variance detected no differences between the groups in terms of numbers of silver-stained dots associated with nucleolar proteins. There was an increase in mean epithelial thickness in adult animals, followed by a gradual reduction until senescence. Mean keratin thickness presented an increase at 8 and 20 months of age. This difference is probably related to puberty, growth or dietary habits. Aging has no influence on oral epithelial proliferation rate in mice. A gradual reduction in epithelial thickness is a feature of aging in mammals. A conspicuous increase in the keratin layer was observed in senescence as an adaptative response to the reduction in epithelial thickness. These results suggest that aging affects the oral epithelium maturation process through a mechanism that is not related to cell proliferation.

Age-dependent differential expression of apoptosis markers in the gingival tissue

OBJECTIVE

The current study was performed to test the hypothesis that periodontal disease produces age-dependent activation of apoptotic markers in the gingival tissues.

METHODS

To address the hypothesis a prospective experimental study was designed and twenty-two patients were enrolled. Out of the twenty-two patients, gingival tissue biopsies samples were obtained from active sites of ten and twelve periodontal-healthy (HS) and periodontal disease (PD, probing depths >5mm patients, respectively. The groups were further divided into 25-50 and <5 years age subgroups.

RESULTS

A significant decrease in the expression of TRADD (Tumour Necrosis Factor Receptor-Associated Death Domain) was observed in 25-50 years of PD group compared to the HS group. Bax (BCL(2)-associated X protein) expression in the PD groups was significantly decreased in PD 25-50 years age group but increased in the >50 years age group compared to respective HS age groups. PD patients of both 25-50 years and >50 years age exhibited a significant increase in the expression of Cytochrome C and Caspase-3 compared to the respective HS groups. The PD patients exhibited a stronger correlation with age in the expression of TRADD and Bax compared to the HS groups. Further analyses revealed that the expression of Caspase-3 correlated with an increase in the age of the healthy patients.

CONCLUSIONS

The data suggested that modulation of apoptotic cascade may contribute to the damage of gingival tissues particularly in PD patients >50 years age.

Morphometric, histomorphometric, and microcomputed tomographic analysis of periodontal inflammatory lesions in a murine model

BACKGROUND

Porphyromonas gingivalis is recognized as one of the major periodontal pathogens in chronic periodontitis, a common infectious disease characterized by inflammation and destruction of periodontal tissues. Several animal models with P. gingivalis have been used in periodontitis studies. Additionally, multiple approaches have also been applied to measuring alveolar bone loss in periodontitis models, including histomorphometry, morphometry, and radiography. The aims of this study were to assess periodontal inflammatory lesions after P. gingivalis-induced periodontitis and use this model to compare three approaches for assessing alveolar bone loss.

METHODS

Twelve-week-old male C57BL/6 mice were divided into two groups: 48 P. gingivalis-infected and 52 untreated control mice. Periodontitis was induced by wrapping P. gingivalis-soaked ligatures around the left maxillary second molar and changing the ligatures every other day. Mice were euthanized on days 0, 3, 7, and 10 after ligature placement, for a total of 12 experimental and 13 control mice per time point. Epithelial downgrowth, inflammation, and osteoclast activity were evaluated; alveolar bone loss was determined by histomorphometry, morphometry, and microcomputed tomography.

RESULTS

The P. gingivalis-infected group showed significantly increased epithelial downgrowth (P <0.05), inflammation (P <0.05), alveolar bone loss (P <0.05), and osteoclast activity (P <0.05) throughout the experimental period compared to the controls. All three methods yielded efficient evaluation of alveolar bone loss.

CONCLUSIONS

Our results show evidence that the P. gingivalis-soaked ligature-induced murine model mounts an adequate inflammatory response and exhibits periodontal tissue breakdown compatible with other models of periodontal disease. In addition, alveolar bone loss can accurately be quantified using any of the three alveolar bone analyses presented in this article.

Age-dependent changes in cell proliferation and cell death in the periodontal tissue and the submandibular gland in mice: a comparison with other tissues and organs

This study investigated the age-dependent changes in the number of BrdU- and TUNEL-positive cells in murine gingival tissue and submandibular gland, and compared the findings with those in other tissues and organs. The cell proliferative activity was decreased after 20 weeks of age in epithelial cells of the gingiva, tongue, buccal mucosa and skin. A decreased cell proliferative activity was also associated with aging in the liver and kidney parenchymal cells. Meanwhile, cell death showed peculiar changes in gingival subepithelial tissue, and mucous and serous acini of the submandibular gland. An increase of TUNEL-positive cells was demonstrated in gingival subepithelial tissue after 20-week-old of age. A significant increase of TUNEL-positive cells was also found in the mucous acinar cells in the 20-week-old mice and in the serous acini after 20 weeks. The fluctuation in the number of TUNEL-positive cells in the subepithelial tissue of the skin, and BrdU- and TUNEL-positive staining ratios in the liver was smaller than that in other tissue and organs throughout life. This study may provide useful information for better understanding the influence of aging on the functional alteration that occurs in the gingival tissue and submandibular gland of the elderly.

Effects of a high-cholesterol diet on cell behavior in rat periodontitis

Studies have shown an association between periodontitis and serum cholesterol levels. We hypothesized that high dietary cholesterol could influence periodontitis as a result of proliferation of the junctional epithelium. Rats were divided into 4 groups. Two groups were fed a regular diet, and 2 groups were fed a high-cholesterol diet. One of each dietary group was treated with periodontitis-inducing agents (lipopolysaccharide and proteases), while the other was treated with pyrogen-free water. Feeding rats with a high-cholesterol diet induced an increase in blood total cholesterol and a decrease in high-density lipoprotein cholesterol. Proliferation of the junctional epithelium with increasing bone resorption was promoted by the consumption of a high-cholesterol diet. High dietary cholesterol further increased the cell-proliferative activity of the junctional epithelium induced by lipopolysaccharide and proteases. These results suggest that high dietary cholesterol can initiate and augment periodontitis in the rat periodontitis model.

Junctional epithelium in rats is characterized by slow cell proliferation

BACKGROUND

The integrity of junctional epithelium (JE) and a firm epithelial adhesion to the tooth surface are maintained by the balance between cell proliferation and cell death. Maintaining the JE structure is essential for the protection of periodontal connective tissues against oral microbes. In this study, the proliferative activity and the expression of caspase 3, a cysteine protease associated with cell death, were studied in rat JE and other epithelial structures during molar tooth development.

METHODS

Fourteen rats aged 10 to 70 days were injected with bromodeoxyuridine (BrdU). Samples of first and second molars were selected for immunohistochemical staining. BrdU incorporation was studied in oral epithelium (OE) covering the erupting tooth, reduced enamel epithelium (REE), and gingival epithelium (GE), sulcular epithelium (SE), and JE. Samples were also subjected to immunohistochemical analysis for proliferating cell nuclear antigen (PCNA) and caspase 3.

RESULTS

The basal cells of the GE were actively proliferating, but in the JE, only a few cells were positive for BrdU or PCNA immunostaining. Some outer REE cells were proliferating during tooth eruption. Caspase 3 expression was in specific areas of REE after completion of amelogenesis.

CONCLUSIONS

Results showed slow proliferative activity in the rat JE. However, specific studies on cellular turnover and cell migration are needed to understand tissue homeostasis in this area.

The effects of different decalcification protocols on TUNEL and general cartilage staining

Apoptosis is characterized by DNA strand breaks with a 3'-OH terminus, which are analyzed by terminal deoxy(d)-UTP nick end labeling (TUNEL). Proteinase K digestion is thought to be an essential step in the TUNEL procedure. The effects of decalcifying reagents on general staining and the TUNEL assay for cartilage sections are largely unknown. The effects of these reagents on retention and integrity of DNA in chondrocytes have not been described until now. We evaluated the effects of various decalcifying solutions, including 10% EDTA, 10% citric acid, 5% trichloroacetic acid, 5% acetic acid and a commercial hydrochloric acid-based reagent, on general cartilage staining and the TUNEL assay for cartilage. The effects of proteinase K on nucleus preservation were also examined. Decalcification with 10% EDTA gave the best result for general cartilage staining. Chondrocyte DNA was retained and intact after using this reagent. Decalcification with 10% EDTA is also the safest method of decalcification if the TUNEL assay is applied to cartilage. Proteinase K digestion may have adverse effects on nucleus preservation in cartilage. Awareness of these effects is important whenever the TUNEL assay is applied.

Initial Apical Migration of Junctional Epithelium in Rats Following Application of Lipopolysaccharide and Proteases

BACKGROUND

Apical migration of junctional epithelium (JE) occurs in association with periodontal pocket formation. The aim of this study was to investigate the gingival changes occurring during apical migration of the JE following application of factors associated with inflammatory periodontal disease pathogenesis.

METHODS

Six-week-old male Wistar rats were divided into six groups: three experimental groups to investigate gingival changes following 2, 4, and 8 weeks topical application of lipopolysaccharide (LPS) and proteases and three control groups using pyrogen-free water. After 2, 4 or 8 weeks, nuclear DNA fragmentation was detected in periodontal ligament (PDL) fibroblasts using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) method, and proliferative activities of the basal cells and fibroblasts were evaluated through expression of proliferating cell nuclear antigen (PCNA). Collagen destruction was examined histologically.

RESULTS

Gingiva treated with LPS and proteases showed an increase in PCNA-positive basal cells but not the fibroblasts. Collagen destruction was observed at 2 weeks; apical migration of the JE and TUNEL-positive fibroblasts was seen at 4 weeks.

CONCLUSIONS

Following application of LPS and proteases to rat gingival sulci, the apical migration of the JE appears to occur simultaneously with the apoptosis of PDL fibroblasts, which in turn follows proliferation of the basal cells and collagen destruction.

Immunohistochemical analysis of lymphocyte subpopulations in cyclosporin A-induced gingival overgrowth

BACKGROUND

Cyclosporin A (CsA) is an immunosuppressive agent that is known to induce gingival overgrowth (GO). Pharmacological, genetic, immunologic, and inflammatory factors seem to be involved in the complex pathogenesis of drug-induced GO. Lymphocyte subpopulations in human gingival connective tissue have been implicated in the pathogenesis of inflammatory periodontal diseases. One purpose of this study was to quantify CD4, CD8-, CD57-, and epithelial membrane antigen (EMA)-positive cells in the gingiva of renal transplant recipients treated with CsA, and compare them to findings in healthy controls. A second aim was to correlate cell numbers with clinical findings.

METHODS

The study included 19 kidney recipients who were taking CsA and had significant GO (CsAGO+), 13 recipients who were taking CsA but showed no GO (CsAGO-), and 14 systemically healthy individuals with gingivitis (C). Sections from gingival biopsies were incubated with monoclonal antibodies for CD4, CD8, EMA, and CD57, and then analyzed using the avidin-biotin complex method. In each specimen, the mononuclear cell types were quantified and their distribution was evaluated in 3 separate tissue zones: S = subepithelial connective tissue beneath the sulcular epithelium; O = subepithelial connective tissue beneath the oral epithelium; and M = middle connective tissue.

RESULTS

There were no significant differences among the groups with respect to the numbers of CD4+ and CD8+ cells in each of the 3 zones (P >0.05). In zone S, the CsAGO+ group had significantly more EMA-positive cells than either the C or CsAGO- groups (P <0.05). There were significant differences among the groups regarding numbers of CD57+ (natural killer) cells in zone M, with the lowest cell numbers in the CsAGO+ patients (P<0.05).

CONCLUSIONS

The results showed that low numbers of natural killer cells are important in the expression of plaque-induced inflammatory changes in CsA-associated GO. It appears that these cells may influence the drug's ability to induce proliferative activity.

An organotypic in vitro model that mimics the dento-epithelial junction

BACKGROUND

The dento-epithelial junction forms the primary periodontal defense structure against oral microbes. The cells of the junctional epithelium (JE) attach both to a basement membrane (BM) facing the connective tissue and to a hard dental tissue by structurally similar but molecularly distinct mechanisms. Here we describe a new organotypic cell culture model for the dento-epithelial junction comprising not only epithelial and mesenchymally derived components, but also a tooth surface equivalent.

METHODS

Rat palatal keratinocytes were seeded on fibroblast-collagen gels. A tooth slice was placed on top of the epithelial cells and the multilayer cultures were grown at the air-liquid interface. Formation of the epithelial structures, BM components, and the epithelial attachment to the tooth surface were studied by immunofluorescence and light and electron microscopy. The findings were compared to the structure of the dento-epithelial junction in vivo.

RESULTS

A well-differentiated stratified epithelium was formed. Under the tooth slice the epithelium remained thin and non-differentiated. Attachment of the epithelial cells to the tooth surface was mediated by hemidesmosomes (HDs) as in vivo. Laminin-5 (Ln-5) was present in the extracellular matrix (ECM) between the tooth and the epithelium as well as in the BM structure between the epithelium and the fibroblast-collagen matrix. Instead, Ln-10/11 was present only at the mesenchymal tissue side as is known to be the case in vivo.

CONCLUSIONS

The organotypic model presented expresses the characteristic structural and molecular features of the dento-epithelial junction and may be applied for studying physiological and pathological processes in the epithelial attachment.

The junctional epithelium around murine teeth differs from gingival epithelium in its basement membrane composition

It is not known whether epithelial differentiation patterns are reflected in the composition of gingival basement membranes (BMs). We have investigated the expression of laminin isoforms and associated BM components in the murine dento-epithelial junction by using immunofluorescence microscopy. Our results show that chains of laminins 5/6/7/10/11 are expressed in the BM of outer gingival epithelium. The external BM between junctional epithelium (JE) and connective tissue differs from gingival BM by lacking laminin-7 and -11 chains. The internal basal lamina (IBL) between JE and tooth contains only laminin-5. Collagen chains alpha1,2(IV) and nidogen-1 are present in other BMs except the IBL. The dento-epithelial junction thus has a unique BM composition, suggesting that epithelial cells are able to secrete two extracellular matrices in a polarized manner. The exclusive expression of the non-self-polymerizing laminin-5 indicates that the IBL is not a BM by definition, but rather a simple extracellular matrix lacking network structure.

Gingival recession-its significance and management

OBJECTIVES

To review the prevalence and current concepts of the mechanisms and aetiology of gingival recession and present the principles of assessment and management of the patient with gingival recession.

DATA AND SOURCES

The literature was searched for review and original research papers relating prevalence, mechanisms, aetiology, assessment, and treatment of gingival recession using Medline and manual tracing of references cited in key papers otherwise not elicited.

STUDY SELECTION

Studies with gingival recession as focus and pertinent to key aspects of review.

RESULTS

Gingival recession is a common condition and its extent and prevalence increase with age. Many factors including trauma and periodontal disease have a role in its aetiology. The patient may develop signs and symptoms including pain from exposed dentine, root caries and aesthetic concerns. Management of gingival recession requires thorough patient assessment, identification of aetiological factors, and recording and monitoring of the extent and severity of the condition. Treatment should be directed at prevention of further progression and the control of symptoms and disease. The patient's aesthetic concerns should be appreciated. Surgical treatment of recession may be indicated to cover exposed root surfaces. Many surgical techniques have been described with varied reported clinical effectiveness.

CONCLUSIONS

Gingival recession should be thoroughly assessed and evaluated in order to offer the most suitable management.

Butyric-acid-induced apoptosis in murine thymocytes and splenic T- and B-cells occurs in the absence of p53

Butyric acid, an extracellular metabolite from periodontopathic bacteria, induces apoptosis in murine thymocytes, splenic T-cells, and human Jurkat T-cells. The present study examines the contributions of apoptosis-related proteins (Bcl-2, Bcl-XL, Bax, and p21WAF1/CIP1) in the regulation of T-cell death induced by butyric acid, using p53 knock-out (p53-/-) and wild-type (p53+/+) mice. The results of a DNA fragmentation assay indicated that thymocytes, splenic T-cells, and B-cells from p53-/- mice were susceptible to butyric-acid-induced apoptosis to a degree similar to those from p53+/+ mice. Moreover, butyric acid significantly induced apoptosis in lymphocytes from both p53+/+ and p53-/- mice in a concentration- and time-dependent fashion. Experiments with fractionated subpopulations of splenic T-cells revealed that DNA fragmentation was equally observed in CD4+ and CD8+ splenic T-cells from both p53+/+ and p53-/- lymphocytes. Activation of caspase-3, caspase-6, and caspase-8, but not of caspase-1, in butyric-acid-induced T-cell apoptosis occurred regardless of the presence of p53. Western blotting analysis of splenic T-cells showed that butyric acid treatment decreased Bcl-2 and Bcl-XL expressions in p53+/+ and p53-/- cells. Splenic T-cells had barely detectable Bax and p21WAF1/CIP1, regardless of whether butyric acid and/or p53 was present. These results suggest that butyric-acid-mediated apoptosis of murine T-cells takes place via a pathway that is independent of p53, and is followed by the p53-regulated proteins Bax and p21WAF1/CIP1, which lower the levels of the apoptosis antagonists Bcl-2 and Bcl-XL in cells.

Effects of various decalcification protocols on detection of DNA strand breaks by terminal dUTP nick end labelling

To analyse DNA strand breaks by terminal deoxy(d)-UTP nick-end labelling (TUNEL) in calcified tissues including bones and teeth, it is important to decalcify the tissues first. However, the effects of decalcifying reagents on the integrity of DNA are largely unknown. In the present study, we evaluated the usefulness of various decalcifying reagents including 10% EDTA (pH 7.4), 5% trichloroacetic acid (TCA), 5% formic acid, 5% HCl, 10% nitric acid, Plank-Rychlo's solution, Morse's solution and K-CX solution in TUNEL staining. Mouse maxilla was selected as the experimental system. Apoptotic cells naturally occurring in the epithelium were analysed. Tissues were assessed by soft X-ray imaging to confirm complete decalcification. The time required for decalcification of the tissue was 7 days with 10% EDTA and 2 days with other decalcifiers. Decalcified tissues were stained with Methyl/Green-Pyronine Y or 4',6-diamidino-2-phenylindole for assessment of DNA integrity. Nuclei of epithelial cells were strongly positive for both dyes after decalcification with 10% EDTA, 5% TCA, Morse's solution and 5% formic acid. The other reagents failed to retain DNA. Our results demonstrated good TUNEL staining of the maxilla treated with 10% EDTA or 5% TCA. Based on the required time for processing and the signal-noise ratio, we recommend 5% TCA as the decalcifying reagent to analyse for DNA strand breaks.