OP0110 A COHORT STUDY ON THE BIDIRECTIONAL RELATIONSHIP BETWEEN PERIODONTITIS AND OSTEOARTHRITIS OVER A 15-YEAR FOLLOW-UP

Background:

Recently, osteoarthritis has been proposed to be driven by complement-mediated inflammatory cascades. That is, in addition to the conventional degenerative model, our knowledge of osteoarthritis pathogenesis has been expanded with an inflammation-dependent theory.

Objectives:

To identify the relationship between osteoarthritis and periodontitis.

Methods:

144,788 periodontitis patients and 144,788 propensity score-matched controls without history of periodontitis were enrolled in this cohort study. A Cox proportional hazard model was used to estimate the risk of osteoarthritis. Survival analysis was utilized to assess the time-dependent effect of periodontitis on osteoarthritis. Age and gender were stratified to identify susceptible subgroups. A symmetrical case-control analysis was designed to determine the relationship between periodontitis and history of osteoarthritis.

Results:

Patients with periodontitis had higher risk of osteoarthritis (HR =1.15, 95% CI =1.12–1.17, P < 0.001) and severe osteoarthritis that led to total knee/hip replacement (HR =1.12, 95% CI =1.03–1.21, P < 0.01) than controls, which was time-dependent (log-rank test P < 0.01). The effect of periodontitis on osteoarthritis was significant in both genders and age subgroups over 30 years old (all P < 0.001). Among them, females (HR=1.27, 95% CI = 1.13–1.42, P < 0.001) and patients aged over 51 (HR= 1.21, 95% CI =1.10-1.33, P < 0.001) with periodontitis were predisposed to severe osteoarthritis that led to total knee/hip replacement. In addition, periodontitis patients were more likely to have a history of osteoarthritis (OR = 1.11, 95% CI = 1.06 - 1.17, P < 0.001).

Conclusion:

These findings suggest a bidirectional relationship between osteoarthritis and periodontitis. Patients with periodontitis presented with a higher risk of osteoarthritis, including severe osteoarthritis that led to total knee/hip replacement. Likewise, periodontitis was more likely to develop following osteoarthritis.

References:

[1]Wang Q, Rozelle AL, Lepus CM, et al. Identification of a central role for complement in osteoarthritis. Nat Med 2011;17:1674-9. Temoin S, Chakaki A, Askari A, et al.

[2]Identification of oral bacterial DNA in synovial fluid of patients with arthritis with native and failed prosthetic joints. J Clin Rheumatol 2012;18:117-21.

Disclosure of Interests:

None declared

OP0088 A COHORT STUDY ON THE BIDIRECTIONAL RELATIONSHIP BETWEEN FIBROMYALGIA AND PERIODONTITIS OVER A 15-YEAR FOLLOW-UP

Background:

Fibromyalgia has been proposed to be driven by chronic inflammation and infections that are associated with early rheumatoid arthritis and inflammatory arthritis. Other than the central sensitization model, our knowledge of fibromyalgia pathogenesis has been expanded with an inflammation-dependent theory, which is stimulated by prolonged spinal cord hyperexcitability.

Objectives:

To determine the relationship between periodontitis and fibromyalgia.

Methods:

In this cohort study, 196,428 periodontitis patients and 196,428 propensity score-matched non-periodontitis controls were enrolled. A Cox proportional hazard model was utilized to estimate the risk of fibromyalgia and survival analysis was adopted to assess the time-dependent effect of periodontitis on fibromyalgia. Subgroup analyses stratified by age, gender, and follow-up years were conducted to identify susceptible populations. A symmetrical cohort was designed to ascertain the relationship between fibromyalgia and the risk of periodontitis.

Results:

Patients with history of periodontitis were more likely to develop fibromyalgia than non-periodontitis controls (HR =1.42, 95% CI =1.39–1.44, P < 0.001), which persisted in the survival analysis (log-rank test P < 0.0001). This effect was significant in both genders and all age subgroups, and was particularly evident in males (HR=1.52, 95% CI = 1.48–1.56, P < 0.001) and younger periodontitis patients (HR= 1.55, 95% CI =1.50-1.60, P < 0.001). Fibromyalgia patients who never had periodontitis presented with higher risk for periodontitis over time (HR = 1.43, 95% CI = 1.40 - 1.45, P < 0.001).

Conclusion:

This is the first longitudinal study that addresses the bidirectional relationship between fibromyalgia and periodontitis, in which periodontitis may serve as a risk factor or early sign of fibromyalgia. Based on the observed relationship between fibromyalgia and periodontitis, regular follow-ups and patient education are recommended for patients with either disease.

Disclosure of Interests:

None declared

Serum Amyloid A Contributes to Chronic Apical Periodontitis via TLR2 and TLR4

In the current concept of bacterial infections, pathogen-associated molecular patterns (PAMPs) derived from pathogens and damage-associated molecular patterns (DAMPs) released from damaged/necrotic host cells are crucial factors in induction of innate immune responses. However, the implication of DAMPs in apical and marginal periodontitis is unknown. Serum amyloid A (SAA) is a DAMP that is involved in the development of various chronic inflammatory diseases, such as rheumatoid arthritis. In the present study, we tested whether SAA is involved in the pathogenesis of periapical lesions, using human periapical surgical specimens and mice deficient in SAA and Toll-like receptors (TLR). SAA1/2 was locally expressed in human periapical lesions at the mRNA and protein levels. The level of SAA protein appeared to be positively associated with the inflammatory status of the lesions. In the development of mouse periapical inflammation, SAA1.1/2.1 was elevated locally and systemically in wild-type (WT) mice. Although SAA1.1/2.1 double-knockout and SAA3 knockout mice had redundant attenuation of the extent of periapical lesions, these animals showed strikingly improved inflammatory cell infiltration versus WT. Recombinant human SAA1 (rhSAA1) directly induced chemotaxis of WT neutrophils in a dose-dependent manner in vitro. In addition, rhSAA1 stimulation significantly prolonged the survival of WT neutrophils as compared with nonstimulated neutrophils. Furthermore, rhSAA1 activated the NF-κB pathway and subsequent IL-1α production in macrophages in a dose-dependent manner. However, TLR2/TLR4 double deficiency substantially diminished these SAA-mediated proinflammatory responses. Taken together, the SAA-TLR axis plays an important role in the chronicity of periapical inflammation via induction of inflammatory cell infiltration and prolonged cell survival. The interactions of PAMPs and DAMPs require further investigation in dental/oral inflammation.

Diet-Induced Obesity and Its Differential Impact on Periodontal Bone Loss

Obesity is associated with abnormal lipid metabolism and impaired bone homeostasis. The aim of our study was to investigate the impact of specific elevated fatty acid (FA) levels on alveolar bone loss in a Porphyromonas gingivalis-induced model of periodontal disease and to analyze underlying cellular mechanisms in bone-resorbing osteoclasts and bone-forming osteoblasts in mice. Four-week-old male C57BL/6 mice were randomly divided in groups and subjected to a palmitic acid (PA)- or oleic acid (OA)-enriched high-fat diet (HFD) (20% of calories from FA) or a normal caloric diet (C group) (10% of calories from FA) for 16 wk. Starting at week 10, mice were infected orally with P. gingivalis (W50) or placebo to induce alveolar bone loss. Animals were sacrificed, and percentage fat, serum inflammation (tumor necrosis factor [TNF]-α), and bone metabolism (osteocalcin [OC], carboxy-terminal collagen crosslinks [CTX], and N-terminal propeptides of type I procollagen [P1NP]) markers were measured. Osteoblasts and osteoclasts were cultured in the presence of elevated PA or OA levels and exposed to P. gingivalis. Animals on FA-enriched diets weighed significantly more compared with animals on a normal caloric diet (P < 0.05). Both obese groups had similar percentages of fat (P = nonsignificant); however, alveolar bone loss was significantly greater in animals that were on the PA-enriched HFD (P < 0.05). TNF-α levels were highest in the PA group (P < 0.001) and increased in all groups in response to P. gingivalis inoculation (P < 0.01), whereas bone remodeling markers OC, CTX, and P1NP were lowest in the PA group (P < 0.001) and highest in the C group. Bacterial challenge decreased bone metabolism markers in all groups (P < 0.01). Further, osteoclasts showed an augmented inflammatory response to P. gingivalis in the presence of hyperlipidemic PA levels as opposed to OA cultures, which responded similarly to controls. These findings indicate that the specific FA profile of diet rather than weight gain and obesity alone modulates bone metabolism and can therefore influence alveolar bone loss.

Subgingival microbial profiles of Sudanese patients with aggressive periodontitis

Background and Objective

Aggressive periodontitis (AgP) is prevalent and shows a rapid course in African individuals. Although a strong focus has been placed on Aggregatibacter actinomycetemcomitans, new methods support the existence of a complex subgingival microflora in AgP. The purpose of the present study was to map the subgingival microbiota as well as explore the presence of A. actinomycetemcomitans and the JP2 clone in a group of Sudanese individuals with AgP, using different analytical methods.

Material and Methods

A study population consisting of 19 patients with AgP was recruited from patients seeking treatment at University of Science and Technology (UST) in Khartoum. Fifteen healthy subjects were included as controls. Plaque samples were analyzed for 272 taxa using human oral microbe identification microarrays and for 26 periodontal taxa using DNA-DNA hybridization checkerboard. Conventional polymerase chain reaction (PCR) was applied for the detection of A. actinomycetemcomitans and the JP2 clone in plaque. Saliva from patients with AgP was analyzed using quantitative PCR (qPCR) for the detection of A. actinomycetemcomitans.

Results

Eubacterium yurii was detected more frequently in patients with AgP than in controls, and E. nodatum was found in patients with AgP only. A. actinomycetemcomitans was found in plaque samples of two (12%) patients by human oral microbe identification microarrays and in five (29%) patients with AgP by conventional PCR, as well as in six (32%) of the AgP saliva samples by qPCR. The JP2 clone was identified in only one patient.

Conclusion

The classical periodontal pathogens were not present in high amounts in AgP in the population studied here. Species of Eubacterium, which are not typically associated with AgP, were often detected in individuals with disease. Using laboratory methods with different sensitivities and detection levels allowed identification of variances in microbial communities. The findings reported in this study provide a basis for the further understanding of AgP.

Computer-assisted measurement of vessel shape from 3T magnetic resonance angiography of mouse brain

Blood vessel morphology (vessel radius, branching pattern, and tortuosity) is altered by a multitude of diseases. Although murine models of human pathology are important to the investigation of many diseases, there are few publications that address quantitative measurements of murine vascular morphology. This report outlines methods of imaging mice in vivo using magnetic resonance angiograms obtained on a clinical 3T unit, of defining mouse vasculature from these images, and of quantifying measures of vessel shape. We provide examples of both healthy and diseased vasculature and illustrate how the approach can be used to assess pathology both visually and quantitatively. The method is amenable to the assessment of many diseases in both human beings and mice.

Gingivitis susceptibility and its relation to periodontitis in men

The objective of this cross-sectional study was to evaluate whether gingivitis susceptibility is associated with periodontitis. We analyzed data of 462 men in the VA Dental Longitudinal Study aged 47 to 92 years who had never smoked or had quit smoking 5+ years previously. Multiple logistic regression models, with tooth-level bleeding on probing at sites with attachment loss<or=2 mm as the dependent variable, were derived with adjustment for plaque, calculus, crown coverage, age, income, education, marital status, body mass index, diabetes, and vitamin C intake, and stratification by age (<65, 65+ years). Periodontitis and mean attachment loss were positively associated with bleeding on probing, with stronger associations among men<65 years old (for periodontitis, OR 2.1; 95% CI 1.5, 3.1) than men 65+ years of age (OR 1.2; 95% CI 0.9, 1.6). Our results suggest that among never and former smokers, gingivitis susceptibility is higher among men with periodontitis compared with that in men without periodontitis.

Subgingival and tongue microbiota during early periodontitis

Periodontal infections have a microbial etiology. Association of species with early disease would be useful in determining which microbes initiate periodontitis. We hypothesized that the microbiota of subgingival and tongue samples would differ between early periodontitis and health. A cross-sectional evaluation of 141 healthy and early periodontitis adults was performed with the use of oligonucleotide probes and PCR. Most species differed in associations with sample sites; most subgingival species were associated with subgingival samples. Few species were detected more frequently in early periodontitis by DNA probes. Porphyromonas gingivalis and Tannerella forsythia (Tannerella forsythensis) were associated with early periodontitis by direct PCR. In conclusion, the microbiota of tongue samples was less sensitive than that of subgingival samples in detecting periodontal species, and there was overlap in species detected in health and early periodontitis. Detection of periodontal pathogens in early periodontitis suggests an etiology similar to that of more advanced disease.

Malignancy-associated vessel tortuosity: a computer-assisted, MR angiographic study of choroid plexus carcinoma in genetically engineered mice

BACKGROUND AND PURPOSE

The ability to assess tumor malignancy and monitor treatment response noninvasively would be of value to both clinicians and animal investigators. This report describes the MR imaging characteristics of a genetically engineered mouse model of choroid plexus carcinoma (CPC) during tumor growth and progression to malignancy. We assess the ability of vessel tortuosity measurements, as calculated from high-resolution MR angiographic (MRA) images, to detect emerging CPC cancers.

METHODS

MR images of 9 healthy mice and of 20 CPC mice with precancerous choroid dysplasia or with cancer over a wide range of sizes were analyzed. Two vessel tortuosity measures and a measure of vessel attenuation (vessel count) were calculated from MRA images. Malignancy assessment was based upon a statistical analysis of vessel tortuosity, by using an equation derived from an earlier study of human brain tumor patients.

RESULTS

Choroid dysplasia was correctly judged nonmalignant. On the basis of vessel count, neoangiogenesis could not be detected until cancers were full-blown and had reached a volume of approximately 80 mm3. Vessel tortuosity measurements, however, correctly identified emerging malignancy in lesions larger than 0.3 mm3.

CONCLUSION

To the best of our knowledge, this report provides the first description of in vivo, MR imaging characteristics of genetically engineered CPC mice during the progression from dysplasia to cancer. Vessel tortuosity measurements offer promise of correctly defining even tiny tumors as malignant.

Moesin: a potential LPS receptor on human monocytes

Bacterial endotoxin (lipopolysaccharide, LPS), a glycolipid found in the outer membrane of Gram-negative bacteria, induces the secretion of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha ), interleukin (IL)-1, and IL-6 by monocytes/macrophages. The secretion of these biologically active compounds leads to multiple pathological conditions, such as septic shock. There is substantial evidence that chronic exposure to LPS in periodontal diseases mediates, at least in part, the tissue destruction associated with the Gram-negative infection. LPS receptor has been shown to be CD14, a 55 kDa protein. LPS-CD14 interactions mediate many monocyte/macrophage functions in the inflammatory response. However, CD14 lacks a cytoplasmic domain, or any known signal transduction sequence motif, suggesting the existence of another cell surface domain capable of transducing signals. More recently, significant work has implicated Toll proteins in LPS-mediated signaling. The purpose of the present work was to investigate, identify, and characterize secondary LPS binding cell surface domain(s) on monocytes/macrophages. Initial experiments with anti-CD14 blocking antibody revealed only partial blocking of the LPS induced TNF-alpha response. The kinetics of these experiments suggested a second, low-affinity receptor. Cross-linking experiments were performed to identify LPS binding sites. Two domains were identified: a 55 kDa protein which was inhibited by anti-CD14 (presumably the CD14 receptor) and a second 78 kDa domain. Partial protein sequencing of the 78 kDa domain using mass spectroscopic analysis ascribed this domain to Moesin (membrane organizing extension spike protein). Preliminary experiments using anti-Moesin monoclonal antibody revealed a dose-dependent blocking of LPS induced TNF-alpha response with a total blocking at 50 microg/ml. Irrelevant isotype controls had no effect. Additional experiments were performed to evaluate the specificity of the anti-Moesin blocking. Separate experiments evaluated anti-Moesin effects on monocyte chemotaxis, IL-1 production in response to IL-1 stimulation, and TNF-alpha secretion in response to Staphylococcus aureus stimulation. Anti-Moesin antibody only blocked LPS-mediated events. Histological analysis of tissue sections harvested from LPS-induced skin lesions exhibited a 3-fold reduction of the polymorphonuclear neutrophil infiltrate in Moesin-deficient mice compared to wild type mice. The data suggest that Moesin functions as an independent LPS receptor on human monocytes.

Clinical and microbial evaluation of a histatin-containing mouthrinse in humans with experimental gingivitis

OBJECTIVE

P-113, a 12 amino acid histatin-based peptide, was evaluated in a mouthrinse formulation for safety, prevention of the development of experimental gingivitis, and for its effects on periodontal flora.

METHOD

159 periodontally healthy subjects abstained from oral hygiene procedures and self-administered either 0.005%, 0.01%, 0.05% P-113 or placebo mouthrinse formulations twice daily over a four week treatment period. During this time, the safety, anti-plaque, and anti-gingivitis effects of P-113 were evaluated.

RESULTS

There was a significant reduction in plaque (p=0.046) and a reduction in gingivitis (p=0.086) for subjects using 0.01% P-113 mouthrinse. Significantly more subjects in the 0.01% and 0.05% treatment groups showed a small increase in plaque index of <0.25 as compared to the placebo group (p<0.05). Similar trends were noted for changes in the % of sites with bleeding on probing in the 0.01% P-113 group. There were no treatment-related adverse events, and there were no adverse shifts in supragingival microflora during the study.

CONCLUSION

These data suggest that P-113 mouthrinse is safe and reduces plaque, gingivitis and gingival bleeding in the human experimental gingivitis model.

Lipopolysaccharides from distinct pathogens induce different classes of immune responses in vivo

The adaptive immune system has evolved distinct responses against different pathogens, but the mechanism(s) by which a particular response is initiated is poorly understood. In this study, we investigated the type of Ag-specific CD4(+) Th and CD8(+) T cell responses elicited in vivo, in response to soluble OVA, coinjected with LPS from two different pathogens. We used Escherichia coli LPS, which signals through Toll-like receptor 4 (TLR4) and LPS from the oral pathogen Porphyromonas gingivalis, which does not appear to require TLR4 for signaling. Coinjections of E. coli LPS + OVA or P. gingivalis LPS + OVA induced similar clonal expansions of OVA-specific CD4(+) and CD8(+) T cells, but strikingly different cytokine profiles. E. coli LPS induced a Th1-like response with abundant IFN-gamma, but little or no IL-4, IL-13, and IL-5. In contrast, P. gingivalis LPS induced Th and T cell responses characterized by significant levels of IL-13, IL-5, and IL-10, but lower levels of IFN-gamma. Consistent with these results, E. coli LPS induced IL-12(p70) in the CD8alpha(+) dendritic cell (DC) subset, while P. gingivalis LPS did not. Both LPS, however, activated the two DC subsets to up-regulate costimulatory molecules and produce IL-6 and TNF-alpha. Interestingly, these LPS appeared to have differences in their ability to signal through TLR4; proliferation of splenocytes and cytokine secretion by splenocytes or DCs from TLR4-deficient C3H/HeJ mice were greatly impaired in response to E. coli LPS, but not P. gingivalis LPS. Therefore, LPS from different bacteria activate DC subsets to produce different cytokines, and induce distinct types of adaptive immunity in vivo.

Nasal biopsies of children exposed to air pollutants

Southwest Metropolitan Mexico City (SWMMC) atmosphere is a complex mixture of air pollutants, including ozone, particulate matter, and aldehydes. Children in SWMMC are exposed chronically and sequentially to numerous toxicants, and they exhibit significant nasal damage. The objective of this study was to assess p53 accumulation by immunohistochemistry in nasal biopsies of SWMMC children. We evaluated 111 biopsies from 107 children (83 exposed SWMMC children and 24 control children residents in a pollutant-compliant Caribbean island). Complete clinical histories and physical examinations, including an ear-nose-throat (ENT) exam were done. There was a significant statistical difference in the upper and lower respiratory symptomatology and ENT findings between control and exposed children (p < 0.001). Control children gave no respiratory symptomatology in the 3 months prior to the study; their biopsies exhibited normal ciliated respiratory epithelium and were p53-negative. SWMMC children complained of epistaxis, nasal obstruction. and crusting. Irregular areas of whitish-gray recessed mucosa over the inferior and middle turbinates were seen in 25% of SWMMC children, and their nasal biopsies displayed basal cell hyperplasia, decreased numbers of ciliated and goblet cells, neutrophilic epithelial infiltrates, squamous metaplasia. and mild dysplasia. Four of 21 SWMMC children with grossly abnormal mucosal changes exhibited strong transmural nuclear p53 staining in their nasal biopsies (p 0.005, odds ratio 26). In the context of lifetime exposures to toxic and potentially carcinogenic air pollutants, p53 nasal induction in children could potentially represent. a) a checkpoint response to toxic exposures, setting up a selective condition for p53 mutation, or b) a p53 mutation has already occurred as a result of such selection. Because the biological significance of p53 nuclear accumulation in the nasal biopsies of these children is not clear at this point, we strongly suggest that children with macroscopic nasal mucosal abnormalities should be closely monitored by the ENT physician. Parents should be advised to decrease the children's number of outdoor exposure hours and encourage a balanced diet with an important component of fresh fruits and vegetables.

Selective inactivation of p53 facilitates mouse epithelial tumor progression without chromosomal instability

We examined the selective pressure for, and the impact of, p53 inactivation during epithelial tumor evolution in a transgenic brain tumor model. In TgT(121) mice, cell-specific inactivation of the pRb pathway in brain choroid plexus epithelium initiates tumorigenesis and induces p53-dependent apoptosis. We previously showed that p53 deficiency accelerates tumor growth due to diminished apoptosis. Here we show that in a p53(+/-) background, slow-growing dysplastic tissue undergoes clonal progression to solid angiogenic tumors in all animals. p53 is inactivated in all progressed tumors, with loss of the wild-type allele occurring in 90% of tumors. Moreover, similar progression occurs in 38% of TgT(121)p53(+/+) mice, also with loss of at least one p53 allele and inactivation of p53. Thus, the selective pressure for p53 inactivation, likely based on its apoptotic function, is high. Yet, in all cases, p53 inactivation correlates with progression beyond apoptosis reduction, from dysplasia to solid vascularized tumors. Hence, p53 suppresses tumor progression in this tissue by multiple mechanisms. Previous studies of fibroblasts and hematopoietic cells show that p53 deficiency can be associated with chromosomal instability, a mechanism that may drive tumor progression. To determine whether genomic gains or losses are present in tumors that progress in the absence of p53, we performed comparative genomic hybridization analysis. Surprisingly, the only detectable chromosomal imbalance was partial or complete loss of chromosome 11, which harbors the p53 gene and is thus the selected event. Flow cytometry confirmed that the majority of tumor cells were diploid. These studies indicate that loss of p53 function is frequent under natural selective pressures and furthermore that p53 loss can facilitate epithelial tumor progression by a mechanism in addition to apoptosis reduction and distinct from chromosomal instability.

Paradoxical inhibition of c-myc-induced carcinogenesis by Bcl-2 in transgenic mice

Here, we investigated changes in apoptosis during tumor progression by analyzing the effect of coexpressing various antiapoptotic genes on the multistage process of c-myc-induced hepatocarcinogenesis in transgenic mice. Whereas continuous c-myc gene overexpression in the liver led to cellular hepatocarcinoma, the coexpression of the bcl-2 gene inhibited the emergence of liver tumors, by inhibiting a pretumoral phase characterized by increased proliferation and apoptosis. This antioncogenic effect was specific to Bcl-2 and was not shared by other antiapoptotic genes such as bcl-xL and a dominant negative form of p53. Thus, we have shown that Bcl-2 can have a tumor suppressor effect in vivo on c-myc-induced hepatocarcinogenesis during the emergence of neoplastic foci.

Critical role for Atm in suppressing V(D)J recombination-driven thymic lymphoma

Chromosome translocations involving T cell receptor (TCR) loci have been found in tumors from Ataxia telangiectasia (AT) patients and in mouse Atm-/- thymoma, suggesting the involvement of V(D)J recombination in these malignancies. By introducing a RAG-1 deficiency into Atm-/- mice in the presence of a TCR transgene, we show that V(D)J recombination is critical for thymoma development in these mice. Therefore, aberrant V(D)J recombination, normally suppressed by Atm, facilitates tumorigenic events leading to cancer. Because V(D)J recombination is dispensable for lymphomagenesis upon p53 deficiency, this study also indicates that Atm and p53 function by distinct mechanisms in suppressing thymoma.

Animal models for Porphyromonas gingivalis-mediated periodontal disease

Porphyromonas gingivalis is one of the principal pathogens in the development of adult periodontitis. Several different animal models have been used to evaluate the complex interactions between P. gingivalis and the host and these have been an important research tool for studying the pathogenesis of P. gingivalis-mediated periodontal diseases.

Key roles for E2F1 in signaling p53-dependent apoptosis and in cell division within developing tumors

Apoptosis induced by the p53 tumor suppressor can attenuate cancer growth in preclinical animal models. Inactivation of the pRb proteins in mouse brain epithelium by the T121 oncogene induces aberrant proliferation and p53-dependent apoptosis. p53 inactivation causes aggressive tumor growth due to an 85% reduction in apoptosis. Here, we show that E2F1 signals p53-dependent apoptosis since E2F1 deficiency causes an 80% apoptosis reduction. E2F1 acts upstream of p53 since transcriptional activation of p53 target genes is also impaired. Yet, E2F1 deficiency does not accelerate tumor growth. Unlike normal cells, tumor cell proliferation is impaired without E2F1, counterbalancing the effect of apoptosis reduction. These studies may explain the apparent paradox that E2F1 can act as both an oncogene and a tumor suppressor in experimental systems.

No requirement for V(D)J recombination in p53-deficient thymic lymphoma

The p53 tumor suppressor is activated in response to a variety of cellular stress signals, although specific in vivo signals that trigger tumor suppression are unknown. In mouse thymocytes, where p53 inactivation leads to tumorigenesis, several observations suggest that V(D)J recombination of T-cell receptor (TCR) loci could provide a DNA damage signal triggering p53-dependent apoptosis and tumor suppression. Inactivation of p53 would allow V(D)J driven mutation of additional cancer genes, facilitating tumorigenesis. Here, we show that mice with a p53 deficiency in thymocytes and unable to carry out V(D)J recombination are not impaired in the development of thymoma. Recombination-activating gene (RAG) deficiencies were introduced into both p53-/- mice and TgTDeltaN transgenic mice, a strain in which 100% of the mice develop thymoma due to thymocyte-specific inactivation of p53 by a simian virus 40 T-antigen variant. V(D)J recombination was dispensable for tumorigenesis since thymomas developed with or without the RAG-1 or RAG-2 gene, although some delay was observed. When V(D)J recombination was suppressed by expression of rearranged TCR transgenes, 100% of the TgTDeltaN mice developed thymoma, surprisingly with reduced latency. Further introduction of a RAG deficiency into these mice had no impact on the timing or frequency of tumorigenesis. Finally, karyotype and chromosome painting analyses showed no evidence for TCR gene translocations in p53-deficient thymomas, although abundant aneuploidy involving frequent duplication of certain chromosomes was present. Thus, contrary to the current hypothesis, these studies indicate that signals other than V(D)J recombination promote p53 tumor suppression in thymocytes and that the mechanism of tumorigenesis is distinct from TCR translocation oncogene activation.

Apoptosis and cancer mechanisms

For nearly two decades, studies in the cancer research field focussed on identifying genes that act as positive and negative regulators of cell growth. Only relatively recently was it recognized that the regulation of cell death (apoptosis) is also an important modulator of tumorigenesis. At least two genes linked to human cancers, BCL2 and TP53, have been shown to regulate apoptosis. The correlation between apoptosis modulating genes and human tumours raises an important question as to how dysregulation of apoptosis contributes to neoplastic transformation and malignant cell growth. Cell culture studies have clearly demonstrated that TP53 can induce and BCL2 can suppress apoptosis in response to various stimuli. Studies of mammalian viruses, which possess mechanisms for both inducing and evading apoptosis, have also extended our understanding of this process. On the basis of such findings, several animal models have been developed which begin to address the role of apoptosis regulation in tumorigenesis. This chapter discusses those animal models, focussing on bcl-2 (and its relatives) and p53.

Expression of the putative proto-oncogene His-1 in normal and neoplastic tissues

The His-1 gene is expressed as a 3-kb spliced and polyadenylated RNA that is believed to function in the absence of an encoded protein. The precise function of the His-1 gene is unknown, but its transcriptional activation in a series of mouse leukemias has implicated the His-1 RNA in leukemogenesis when it is abnormally expressed. To study the oncogenic potential of this gene in more detail, we have examined the normal tissue distribution of His-1 RNA during mouse embryogenesis and in various adult tissues. His-1 expression was detected at low levels in the epithelia of the adult mouse stomach, prostate, seminal vesicle, and the developing choroid plexus by in situ hybridization. All other tissues examined lacked detectable levels of hybridizing RNA, suggesting that normal His-1 gene expression is highly restricted to these epithelial sites. These transcripts were not detectable by Northern blot analysis of normal tissues but were readily identified in five mouse leukemias and in five carcinomas of the choroid plexus. These data indicate that the His-1 gene expression is highly restricted and suggest that inappropriate activation of this gene may contribute to carcinogenesis.

Bax suppresses tumorigenesis and stimulates apoptosis in vivo

The protein p53 is a key tumour-suppressor, as evidenced by its frequent inactivation in human cancers. Animal models have indicated that attenuation of p53-dependent cell death (apoptosis) can contribute to both the initiation and progression of cancer, but the molecular mechanisms are unknown. Although p53-mediated transcriptional activation is one possible explanation, none of the known p53-responsive genes has been shown to function in p53-dependent apoptosis. Here we test the role of the death-promoting gene bax in a transgenic mouse brain tumour, a model in which p53-mediated apoptosis attenuates tumour growth. Inactivation of p53 causes a dramatic acceleration of tumour growth owing to a reduction in apoptosis of over ninety per cent. We show that p53-dependent expression of bax is induced in slow-growing apoptotic tumours. Moreover, tumour growth is accelerated and apoptosis drops by fifty per cent in Bax-deficient mice, indicating that it is required for a full p53-mediated response. To our knowledge this is the first demonstration that Bax acts as a tumour suppressor, and our findings indicate that Bax could be a component of the p53-mediated apoptotic response in this system.

Tissue-specific inactivation of p53 tumor suppression in the mouse

The p53 gene is the most frequent target of structural and functional genetic mutations in human cancer. Thus, considerable effort has been devoted to mapping the functional domains of p53 with regard to their impact on tumorigenesis in vivo. Studies have shown that the carboxy-terminal domain of p53 is sufficient for transformation in vitro. To determine whether a transdominant-negative p53 protein could be used to elicit a tissue-specific p53-null effect in vivo, we tested whether a carboxy-terminal p53 fragment (amino acids 302-390) could abolish p53-dependent apoptosis in an established tumor progression model. We showed previously that loss of p53-dependent apoptosis accelerates brain tumorigenesis in a transgenic mouse model. Here, we show that the same effect can be elicited by expressing a dominant-negative p53 protein tissue specifically in the presence of wild-type p53. Transgenic mice in which pRb function has been disrupted and that coexpress a p53 carboxy-terminal dominant-negative fragment (p53DD) develop aggressive brain tumors mimicking genetic loss of p53 in this model. Inactivation of endogenous p53, which we show to be complexed with p53DD, results in a reduction in apoptosis and acceleration of tumorigenesis. These studies establish a mechanism for tissue-specific knock out of p53 function in vivo.

Targeted in vivo expression of the cyclin-dependent kinase inhibitor p21 halts hepatocyte cell-cycle progression, postnatal liver development and regeneration

The CDK inhibitor p21 (WAF-1/CIP-1/SDI-1) has been implicated in DNA damage-induced p53-mediated G1 arrest, as well as in physiological processes, such as cell differentiation and senescence, that do not involve p53 function. To determine the impact of p21 on normal development and cell-cycle regulation in vivo, we have generated transgenic mice that abundantly express p21 specifically in hepatocytes. During postnatal liver development, when transgenic p-21 protein becomes detectable, hepatocyte proliferation is inhibited dramatically. This disturbance causes a reduction in the overall number of adult hepatocytes, resulting in aberrant tissue organization, runted liver and body growth, and increased mortality. The transgenic p21 protein is associated with most, if not all, of the cyclin D1-CDK4 in liver but not significantly with other cyclin/CDK proteins, indicating the importance of cyclin D1-CDK4 function in normal liver development. The appearance of large polyploid nuclei in some hepatocytes indicates that p21 may also cause arrest during the G2 phase of the cell cycle. Significantly, partial hepatectomy failed to stimulate hepatocytes to proliferate in p21 transgenic animals. These results provide the first in vivo evidence that appropriate p21 levels are critical in normal development and further implicate p21 in the control of multiple cell-cycle phases.

p53-dependent apoptosis suppresses tumor growth and progression in vivo

To determine the contribution of p53 loss to tumor progression, we have induced abnormal proliferation in the brain choroid plexus epithelium of transgenic mice using a SV40 T antigen fragment that perturbs pRB family function but does not affect p53 function. Tumors induced by this mutant develop slowly compared with those induced by wild-type T antigen. Suppressed tumor growth is directly attributable to p53 function, since rapid tumor development occurs when the T antigen fragment is expressed in p53-null mice. In p53-heterozygous mice, stochastic loss of the wild-type p53 allele results in the focal emergence of aggressive tumor nodules characteristic of tumor progression. In each case, aggressive tumor development in the absence of p53 function corresponds to a decrease in the level of apoptosis. These results provide in vivo evidence that p53-dependent apoptosis, occurring in response to oncogenic events, is a critical regulator of tumorigenesis.

Regulation of apoptosis in transgenic mice by simian virus 40 T antigen-mediated inactivation of p53

Several proteins encoded by DNA tumor viruses are thought to disrupt cellular growth control by interacting with key cellular proteins, such as p53 and pRB, that normally function to regulate cell growth. However, the biological consequences of intracellular complexing between the viral oncoproteins and cellular proteins have remained unclear. Such complexes could either facilitate functional inactivation of the cellular proteins, leading to a loss-of-function phenotype, or could activate new functions, leading to a gain-of-function phenotype. Here we demonstrate that the simian virus 40 large tumor (T) antigen produces a loss-of-p53-function phenotype when introduced into the thymocytes of transgenic mice. Like thymocytes from the recently characterized p53-null mice, thymocytes from transgenic mice expressing a T-antigen variant capable of binding to p53 are resistant to irradiation-induced apoptosis. Thymocytes from transgenic mice expressing a mutant T antigen that is unable to complex p53, but retains the ability to complex the pRB and p107 proteins, retain sensitivity to irradiation. We further demonstrate that although irradiation-induced apoptosis is impaired by T antigen, clonal deletion of autoreactive thymocytes via p53-independent apoptosis is not perturbed by T antigen. These results provide convincing evidence that T antigen inactivates p53 in thymocytes in vivo and suggest a mechanism by which T antigen predisposes thymocytes to tumorigenesis in T antigen-transgenic mice.

Induction versus progression of brain tumor development: differential functions for the pRB- and p53-targeting domains of simian virus 40 T antigen

The ability of simian virus 40-encoded large T antigen to disrupt the growth control of a variety of cell types is related to its ability to interfere with certain cellular proteins, such as p53 and the retinoblastoma susceptibility gene product (pRB). We have used wild-type and mutant forms of T antigen in transgenic mice to dissect the roles of pRB, p53, and other cellular proteins in tumorigenesis of different cell types. In this study, using a cell-specific promoter to target expression specifically to brain epithelium (the choroid plexus) and to B and T lymphoid cells, we characterize the tumorigenic capacity of a T-antigen fragment that comprises only the amino-terminal 121 residues. This fragment (dl1137) retains the ability to interact with pRB and p107 but lacks the p53-binding domain. While loss of the p53-binding region results in loss of the capacity to induce lymphoid abnormalities, dl1137 retains the ability to induce choroid plexus tumors that are histologically indistinguishable from those induced by wild-type T antigen. Tumors induced by dl1137 develop much more slowly, however, reaching an end point at around 8 months of age rather than at 1 to 2 months. Analysis of tumor progression indicates that tumor induction by dl1137 does not require secondary genetic or epigenetic events. Rather, the tumor growth rate is significantly slowed, indicating that the T-antigen C-terminal region contributes to tumor progression in this cell type. In contrast, the pRB-binding region appears essential for tumorigenesis as mutation of residue 107, known to disrupt pRB and p107 binding to wild-type T antigen, abolishes the ability of the dl1137 protein to induce growth abnormalities in the brain.

Use of transgenic mice reveals cell-specific transformation by a simian virus 40 T-antigen amino-terminal mutant

We have used the multifunctional transforming protein, simian virus 40 T antigen, as a probe to study the mechanisms of cell growth regulation in the intact organism. T antigen appears to perturb cell growth, at least in part, by stably interacting with specific cellular proteins that function to maintain normal cell growth properties. Experiments in cultured cells indicate that at least three distinct regions of simian virus 40 T antigen have roles in transformation. Two regions correlate with the binding of known cellular proteins, p53, pRB, and p107. A third activity, located near the amino terminus, has been defined genetically but not biochemically. By targeting expression of wild-type and mutant forms of T antigen to distinct cell types in transgenic mice, we have begun to systematically determine which activities play a role in tumorigenesis of each cell type. In this study, we sought to determine the role of the amino-terminal transformation function with such an analysis of the T-antigen mutant dl1135. This protein, which lacks amino acids 17 to 27, retains the p53-, pRB-, and p107-binding activities yet fails to transform cells in culture. To direct expression in transgenic mice, we used the lymphotropic papovavirus transcriptional signals that are specific for B and T lymphocytes and the choroid plexus epithelium of the brain. We show here that although defective in cell culture, dl1135 specifically induced the development of thymic lymphomas in the mouse. Expression of the protein was routinely observed in B- and T-lymphoid cells, although B-cell abnormalities were not observed. Choroid plexus tumors were observed only infrequently; however, dl1135 was not consistently expressed in this tissue. Within a given transgenic line, the penetrance of T-cell tumorigenesis was 100% but appeared to require secondary events, as judged from the clonal nature of the tumors. These experiments suggest that the amino-terminal region of T antigen has a role in the transformation of certain cell types (such as fibroblasts in culture and B lymphocytes) but is dispensable for the transformation of T lymphocytes.

T-antigen mutant activities in vivo: roles of p53 and pRB binding in tumorigenesis of the choroid plexus

To study the mechanism by which SV40 large T antigen transforms cells under physiological conditions, we analysed several mutant forms of T antigen for their ability to induce cell proliferation and tumorigenesis in transgenic mice. These mutant proteins, which differ in their ability to form complexes with the tumor suppressors pRB and p53, were analysed under conditions in which wild-type T antigen induces choroid plexus papillomas as a result of uniform proliferation of the entire choroid plexus epithelium. The results presented here show that binding of T antigen to p53 is not required for induction of choroid plexus tumors. However, tumorigenesis does appear to require the binding of T antigen to pRB/p107. An additional activity, resident in the amino-terminal one-fifth of the protein, may also play a role. These experiments indicate the importance of whole-animal assays in determining the molecular basis of transformation, since each of these mutants possessed similar transformation phenotypes in culture but showed distinct phenotypes in the choroid plexus of the animal.

Correlation of subclinical candidal colonization of the dorsal tongue surface with the Walter Reed staging scheme for patients infected with HIV-1

The correlation between subclinical candidal colonization of the dorsal tongue surface and the Walter Reed staging scheme for patients positive for human immunodeficiency virus (HIV-1) antibody is reported. Of 76 cytologic smears of the dorsal tongue surface, 12 (16.2%) demonstrated subclinical colonization. The mean peripheral helper T-lymphocyte count for patients with subclinical colonization was 304 +/- 226 cells/mm3 and was not significantly different from seropositive patients without colonization (411 +/- 209 cells/mm3). The Walter Reed scheme for assessing progressive immunodysregulation did not significantly correlate with the presence of subclinical colonization. This study suggests a more complex pathogenesis for oral candidiasis in HIV-1-infected patients rather than a direct link to peripheral helper T-lymphocyte depletion below a count of 400 cells/mm3.

Uniform cell-autonomous tumorigenesis of the choroid plexus by papovavirus large T antigens

The simian virus 40 (SV40) large tumor antigen (T antigen) under its natural regulatory elements induces choroid plexus papillomas in transgenic mice. Because these tumors develop focally after several months, it has been suggested that secondary cellular alterations are required to induce a tumor in this tissue. In contrast to SV40, the related lymphotropic papovavirus early region induces rapid nonfocal choroid plexus neoplasia in transgenic mice. Here, using hybrid gene constructs, we showed that T antigen from either virus in in fact sufficient to induce these tumors. Their abilities to induce proliferative abnormalities in other tissues, such as kidney and thymus, were also indistinguishable. Differences in the rate of choroid plexus tumorigenesis reflected differences in the control regions of the two viruses, rather than differences in T antigen per se. Under SV40 regulation, expression was limited to a fraction of the choroid plexus cells prior to the formation of focal tumors. When SV40 T antigen was placed under lymphotropic papovavirus control, in contrast, expression was generally uniform in the choroid plexus and rapid expansion of the tissue ensued. We found a direct relationship between T-antigen expression, morphological transformation, and proliferation of the choroid plexus epithelial cells. Analysis of mosaic transgenic mice indicated further that T antigen exerts its mitogenic effect cell autonomously. These studies form the foundation for elucidating the role of various T-antigen subactivities in tumorigenesis.

Complex formation between the lymphotropic papovavirus large tumor antigen and the tumor suppressor protein p53

The simian B-lymphotropic papovavirus (LPV) encodes a large tumor antigen (T antigen) which is 45% identical to both the simian virus 40 (SV40) and the polyomavirus (PyV) large T antigens. In transgenic mice, the transforming properties of the LPV T antigen are similar to those of the SV40 T antigen. However, little is known about its biochemical activities. Since SV40 T antigen forms a complex with and stabilizes the host cell tumor suppressor protein p53 while the PyV large T antigen does not, we characterized the LPV T antigen for its ability to complex p53. We demonstrate an association between LPV T antigen and p53 in both a tumor-derived cell line and BALB/c 3T3 cells transformed in culture. A third protein of approximately 68 kDa which was found associated with the LPV T antigen-p53 complex in tumor-derived cells appears to be heat shock protein 70 (hsp70). The half-life of p53 in all LPV T-antigen-transformed cells was extended significantly; i.e., it was 3 to 7 h compared with 19 minutes in BALB/c 3T3 cells. The half-life of the LPV T antigen itself was 5 to 9 h depending on the cell line origin. That p53 was stabilized because of association with LPV T antigen and not because of mutation was demonstrated with the p53 conformation-dependent monoclonal antibody PAb246. This antibody distinguishes between wild-type p53 (PAb246+) and mutant, oncogenic p53 (PAb246-). Sequential immunoprecipitation showed all detectable p53 to be of the PAb246+ class in each LPV-transformed cell line, suggesting that the stable p53 was indeed wild type.

NMR detection of creatine kinase expressed in liver of transgenic mice: determination of free ADP levels

To use the equilibrium established by creatine kinase (CK) to determine hepatic free ADP levels, the transcriptional control elements of the transthyretin gene were used to direct expression of the CK B isozyme to the livers of transgenic mice. Activities of CK ranging from 80-250 mumol per min per g (wet weight) were detected in liver extracts from five founder mice. The CK activity was stably transmitted to subsequent generations. Isozyme gels and immunoblots confirmed that the activity detected in extracts was due to the B isozyme of CK. Immunohistology indicated that the protein was expressed uniformly throughout the liver and was localized primarily to the cytoplasm. 31P NMR spectroscopy was used to detect the metabolic product of the CK reaction, phosphocreatine, demonstrating that the enzyme was active in vivo. The phosphocreatine level fell rapidly during anoxia (t1/2 = 1 min), indicating that the CK reaction was integrated into hepatic energy metabolism. The equilibrium established by CK was used to calculate a hepatic free ADP level of 0.059 +/- 0.004 mumol/g (wet weight). In vivo NMR studies of these mice will be valuable for studying the role of free ADP in regulating liver metabolism.

Lymphotropic papovavirus early region is specifically regulated transgenic mice and efficiently induces neoplasia

Transgenic mice have been generated which carry the early region of lymphotropic papovavirus (LPV). Eight of eleven founder animals died before 3 months of age after developing one or both of two distinct proliferative disorders. Of the three surviving animals, two are known to have rearranged or partial copies of the LPV genes. The majority of the founder animals (six) developed debilitating choroid plexus tumors by 26 to 42 days. Although this is the same tumor type induced by the simian virus 40 T-antigen gene, those induced by LPV appeared at a much younger age. The LPV early region was expressed in the brain tumors of these mice, as well as in the thymus and spleen. Expression in the latter two tissues reflects the cell-type specificity of the LPV enhancer demonstrated in cultured cells (i.e., lymphoid cells). Two founder animals (LP41 and LP50) gave rise to lines of mice that routinely develop lymphoproliferative disorders. LP50 and its LPV-positive offspring developed aggressive lymphomas and choroid plexus tumors. The transgenic offspring of LP41 also developed lymphomas. High levels of LPV RNA were expressed in the lymphomas of these mice as well as in the spleens and thymuses. The origin of the lymphomas from B- and T-cell lineages suggests that the LPV early genes are expressed in and can transform both of these cell types in vivo.

Organization of human histone genes

We describe the isolation and initial characterization of seven independent lambda Charon 4A recombinant phages which contain human histone genomic sequences (designated lambda HHG). Restriction maps of these clones and localization of the genes coding for histones H2A, H2B, H3, and H4 are presented. The presence of histone encoding regions in the lambda HHG clones was demonstrated by several independent criteria including hybridization with specific DNA probes, hybrid selection/in vitro translation, and hybridization of lambda HHG DNAs to reserve Southern blots containing cytoplasmic RNAs from G1-, S-, and arabinofuranosylcytosine (cytosine arabinoside)-treated S-phase cells. In addition, the lambda HHG DNAs were shown to protect in vivo labeled H4 mRNAs from S1 nuclease digestion. Based on the analysis of the lambda HHG clones, human histone genes appear to be clustered in the genome. However, gene clusters do not seem to be present in identical tandem repeats. The lambda HHG clones described in this report fall into at least three distinct types of arrangement. One of these arrangements contains two coding regions for each of the histones H3 and H4. The arrangement of histone genes in the human genome, therefore, appears to be different from that in the sea urchin and Drosophila genomes in which each of the five histone-encoding regions (H1, H2A, H2B, H3, and H4) is present only once in each tandemly repeated cluster. At least one clone, lambda HHG 41, contains, in addition to the histone genes, a region that hybridizes with a cytoplasmic RNA approximately 330 nucleotides in length. This RNA is not similar in size to known histone-encoding RNAs and is present in the cytoplasm of HeLa cells predominantly in the G1 phase of the cell cycle.