An ameloblastin C-terminus variant is present in human adipose tissue

Objective

Transcriptional regulatory elements in the ameloblastin (AMBN) promoter indicate that adipogenesis may influence its expression. The objective here was to investigate if AMBN is expressed in adipose tissue, and have a role during differentiation of adipocytes.

Design

AMBN expression was examined in adipose tissue and adipocytes by real-time PCR and ELISA. Distribution of ameloblastin was investigated by immunofluorescence in sections of human subcutaneous adipose tissue. The effect of recombinant proteins resembling AMBN and its processed products on proliferation of primary human pre-adipocytes and murine 3T3-L1 cell lines was measured by [³H]-thymidine incorporation. The effect on adipocyte differentiation was evaluated by the expression profile of the adipogenic markers PPARγ and leptin, and the content of lipids droplets (Oil-Red-O staining).

Results

AMBN was found to be expressed in human adipose tissue, human primary adipocytes, and in 3T3-L1 cells. The C-terminus of the AMBN protein and a 45 bp shorter splice variant was identified in human subcutaneous adipose tissue. The expression of AMBN was found to increase four-fold during differentiation of 3T3-L1 cells. Administration of recombinant AMBN reduced the proliferation, and enhanced the expression of PPARγ and leptin in 3T3-L1 and human pre-adipocytes, respectively.

Conclusions

The AMBN C-terminus variant was identified in adipocytes. This variant may be encoded from a short splice variant. Increased expression of AMBN during adipogenesis and its effect on adipogenic factors suggests that AMBN also has a role in adipocyte development.

Ameloblastin expression during craniofacial bone formation in rats

Based on previous results showing the expression of ameloblastin (Ambn; amelin) in the formation of mesenchymal dental hard tissues, we investigated its presence during bone development. Immunohistochemistry (IHC), in situ hybridization (ISH), and reverse transcription-polymerase chain reaction (RT-PCR) were used to investigate the expression of ameloblastin protein and mRNA during craniofacial development in rats. Tissue samples were collected on embryonic day 18 and from days 2-28 postnatally. IHC revealed the expression of ameloblastin during bone formation at embryonic and early postnatal stages with different patterns of expression in intramembranous and endochondral ossification. In intramembranous ossification, ameloblastin expression was detected in the superficial layer of the condensed vascularized primitive connective tissue and in the cellular layer covering the surface of the newly formed woven bone. In endochondral ossification, ameloblastin was expressed within the extracellular matrix of the cartilage templates and in the perichondrium. Between days 2 and 28 the expression decreased markedly, concordant with the maturation of the bone, and disappeared after completion of bone remodeling. The results obtained by IHC were confirmed by ISH and RT-PCR, showing the expression of ameloblastin mRNA during craniofacial bone formation. This study indicates the expression of the putative dental protein ameloblastin during craniofacial bone development in rats.

Ameloblastin fusion protein enhances pulpal healing and dentin formation in porcine teeth

Ameloblastin (Ambn, also named "amelin" or "sheathlin") is a protein participating in enamel formation and mesenchymal-ectodermal interaction during early dentin formation in developing teeth. Experiments have demonstrated an association between Ambn expression and healing of acute pulp wounds. The purpose of this study was to investigate if local application of recombinant fusion Ambn (rAmbn) could influence reparative dentin formation in pulpotomized teeth. In this randomized, double-blinded study, pulpotomy was performed in 28 lower central incisors in 17 adult miniature pigs. Following the surgical procedure, the exposed pulp tissue was covered either with rAmbn or with calcium hydroxide. After 2, 4, or 8 weeks, the teeth were extracted and examined by histomorphometry and immunohistochemistry using antibodies against porcine ameloblastin, collagen type I, and dentin sialoprotein (DSP). In rAmbn-treated teeth, a substantial amount of newly formed reparative dentin was observed at the application site, completely bridging the pulpal wound. Dentin formation was also observed in calcium hydroxide-treated teeth; however, the amount of reparative dentin was significantly smaller (P < 0.001) than after rAmbn treatment. Immunohistochemistry confirmed that the new hard tissue formed was similar to dentin. This is the first time a direct link between ameloblastin and dentin formation has been made in vivo. The results suggest potential for rAmbn as a biologically active pulp-dressing agent for enhanced pulpal wound healing and reparative dentin formation after pulpotomy procedures.

Periodontal infections and coronary heart disease: role of periodontal bacteria and importance of total pathogen burden in the Coronary Event and Periodontal Disease (CORODONT) study

BACKGROUND

Chronic inflammation from any source is associated with increased cardiovascular risk. Periodontitis is a possible trigger of chronic inflammation. We investigated the possible association between periodontitis and coronary heart disease (CHD), focusing on microbiological aspects.

METHODS

A total of 789 subjects (263 patients with angiographically confirmed, stable CHD and 526 population-based, age- and sex-matched controls without a history of CHD) were included in the Coronary Event and Periodontal Disease (CORODONT) study. Subgingival biofilm samples were analyzed for periodontal pathogens Actinobacillus actinomycetemcomitans, Tannerella forsythensis, Porphyromonas gingivalis, Prevotella intermedia, and Treponema denticola using DNA-DNA hybridization. The need for periodontal treatment in each subject was assessed using the Community Periodontal Index of Treatment Needs (CPITN). The main outcome measures included total periodontal pathogen burden, number of the various periodontal pathogens in the subgingival biofilm, and periodontal treatment needs (according to the CPITN).

RESULTS

In multivariable analyses, we found a statistically significant association between the periodontal pathogen burden (log10 of the sum of all pathogens) (odds ratio [OR], 1.92; 95% confidence interval [CI], 1.34-2.74; P<.001) or the number of A actinomycetemcomitans in periodontal pockets (log10) (OR, 2.70; 95% CI, 1.79-4.07; P<.001) and the presence of CHD. In addition, a statistically significant association between an increase in mean CPITN score by 1 and the presence of CHD (OR, 1.67; 95% CI, 1.08-2.58; P = .02) was observed.

CONCLUSIONS

Our findings suggest an association between periodontitis and presence of CHD. Periodontal pathogen burden, and particularly infection with A actinomycetemcomitans, may be of special importance.

Mice deficient in the chemokine receptor CXCR4 exhibit impaired limb innervation and myogenesis

The chemokine CXCL12/SDF-1 and its receptor CXCR4 regulate the development and the function of the hematopoietic system and control morphogenesis of distinct brain areas. Here, we demonstrate that inactivation of CXCR4 results in a massive loss of spinal cord motoneurons and dorsal root ganglion neurons and, subsequently, in a reduced innervation of the developing mouse fore- and hindlimbs. However, only the death of sensory neurons seems to be a direct consequence of receptor inactivation as suggested by the observations that DRG neurons, but not motoneurons, of wild-type animals express CXCR4 and respond to CXCL12 with an increase in cell survival. In contrast, the increased death of motoneurons in CXCR4-deficient animals seems to result from impaired limb myogenesis and a subsequent loss of muscle-derived neurotrophic support. In summary, our findings unravel a previously unrecognized complex role of CXCL12/CXCR4 in the control of limb neuromuscular development.

GDNF elicits distinct immediate-early gene responses in cultured cortical and mesencephalic neurons

Glial cell line-derived neurotrophic factor (GDNF) has been recognized as a survival-promoting molecule for several neuronal populations in the central nervous system (CNS), including midbrain dopaminergic neurons and cortical neurons. Whereas it is well established that GDNF affects dopaminergic cell survival through a receptor complex composed of the tyrosine kinase, Ret, and the glycosylphosphatidylinositol (GPI)-anchored protein, GFRalpha-1, c-Ret is basically undetectable in cortical neurons. In the present study, we have compared GDNF signaling in cortical and mesencephalic neurons by using GDNF-induced expression of the immediate-early genes, c-fos and mgif, as a readout. We found that stimulation of embryonic day (E)17 cortical cultures for 3 hr with GDNF at concentrations ranging from 10 to 80 ng/ml did not result in detectable c-fos expression. In contrast, c-fos expression occurred in E14 mesencephalic cultures exposed to both low and high GDNF concentrations. Vice versa, cortical neurons responded to high GDNF concentrations (80 ng/ml) with an increase in mRNA encoding mGIF, while a similar mGIF response was absent in mesencephalic cultures. Cleavage of GFRalpha receptor subunits from their GPI anchors by phosphatidylinositol-specific phospholipase C (PIPLC) abolished GDNF-induced c-fos expression in mesencephalic cultures, but did not interfere with the effects of GDNF on cortical mgif expression. Together, these findings point to distinct differences in the GDNF recognition and/or signal transduction machinery of cortical and mesencephalic neurons.

Neurotrophin and GDNF expression increases in rat adrenal glands during experimental colitis

OBJECTIVES

Neurotrophins and GDNF have been recently recognized as important local regulators of inflammatory processes of the gut.

RESULTS

We now demonstrate that experimental TNBS-colitis is associated with the increased expression of neurotrophins and GDNF in the adrenal glands. In histological sections of the adrenals from untreated control animals, faint immunolabeling for BDNF, NT-3 and NGF was detectable in the adrenal cortex, with some additional labeling for NGF over the adrenal medulla, whereas GDNF immunolabeling was confined to the adrenal medulla. Induction of TNBS-colitis markedly increased NGF, BDNF, and NT-3 expression within the adrenal cortex after 8 h. NGF declined to basal levels after 7 days. In case of BDNF and NT-3 basal expression levels were reached after 14 days. GDNF expression was robustly upregulated in the adrenal medulla 8 h after induction of colitis and stayed elevated for up to 14 days.

CONCLUSION

Together these observations suggest that neurotrophins and GDNF might act as local modulators of components of the HPA-axis during peripheral inflammation.

Evidence for a ligand-specific signaling through GFRalpha-1, but not GFRalpha-2, in the absence of Ret

Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) are two homologeous proteins that have been recognized as potent survival factors for distinct neuronal populations. GDNF and NTN act through a two-component receptor system consisting of the ligand-specific binding subunits GDNF family receptor (GFR)alpha-1 and GFRalpha-2 and the common transducing subunit c-Ret. In addition, it has been demonstrated that GDNF can signal through GFRalpha-1 in the absence of c-Ret. In the present study, we sought to determine whether a similar c-Ret-independent signaling applies for GFRalpha-2. In addition, we have characterized the ligand specificity of the c-Ret-independent action of GFRalphas. To establish an assay system for these studies, several neural cell lines were screened for the presence of GDNF and NTN receptor subunits by RT-PCR and immunoblot analysis. c-Ret expression was detectable only in Neuro2A cells, which did not express GFRalpha-1 or GFRalpha-2. The neuronal cell line LS expressed GFRalpha-2, and the glial cell line Mes42 expressed GFRalpha-1, whereas the neuronal cell line B104 expressed both GFRalpha-1 and GFRalpha-2. Stimulation of B104 and Mes42 cells with GDNF, but not with NTN, for 10 min resulted in CREB phosphorylation. In apparent contrast, neither NTN nor GDNF promoted CREB activation in LS and Neuro2A cells. Moreover, exposure of LS cells to NTN or GDNF also failed to activate AKT and ERK. Together these findings provide evidence that, in contrast to GFRalpha-1, GFRalpha-2 fails to signal in the absence of c-Ret. In addition, these observations reveal that c-Ret-independent signaling of GFRalpha-1 is ligand- specific and occurs only with GDNF.

Centrally administered oligodeoxynucleotides in rats: occurrence of non-specific effects

We studied the effects of various intracerebroventricularly administered oligodeoxynucleotides on body temperature, locomotor activity, food intake and water consumption in rats during a 24 h period with a radio-telemetric system. Both complete phosphorothioate oligodeoxynucleotides and end-inverted oligodeoxynucleotides dose-dependently elevated body temperature, suppressed food and fluid intake and inhibited nighttime activity. Apparently these effects do not depend on the nucleotide sequence because antisense and sense arginine vasopressin and oxytocin oligodeoxynucleotides, as well as a missense oligodeoxynucleotide produced comparable changes in the autonomous and behavioral parameters. In control experiments neither contaminants from the chemical synthesis nor endotoxins produced such effects, whereas native DNA from salmon sperm did. Fever and sickness-like behavior in response to missense phosphorothioate oligodeoxynucleotides were accompanied by elevated concentrations of circulating corticosterone and by a marked increase in interleukin 6 mRNA in brain and spleen, indicating that centrally administered oligodeoxynucleotides stimulate the production of pyrogenic inflammatory mediators in both central nervous system and peripheral tissues. Our results indicate that centrally administered oligodeoxynucleotides produce beside their intended sequence-specific effects also transient and sequence-independent effects due to their nucleic acid structure.

Intracerebroventricular administration of missense oligodeoxynucleotide induces interleukin-6 mRNA expression in brain and spleen of rats

After intracerebroventricular (i.c.v.) injection of a missense oligodeoxynucleotide (MS-ODN) solution in rats, transcripts of the proinflammatory cytokine interleukin (IL)-6 were induced in hypothalamus, hippocampus, cortex and spleen and increased levels of circulating IL-6 and corticosterone were detected. Moreover, using a biotelemetric method body temperature of rats injected with ODN or Ringer solution was monitored over a period of 24 h after the injection. The i.c.v. injection of ODN induced a fever response which peaked at 6 h post-injection. These observations demonstrate that central administration of ODNs generates an inflammatory response in the central nervous system (CNS) and in the periphery as well.

Corticosterone controls interleukin-1 beta expression and sickness behavior in the rat

We studied the effect of corticosterone on interleukin (IL)-1 beta synthesis, body temperature, general activity, food consumption and fluid intake in rats treated with bacterial lipopolysaccharide (LPS). Radiotelemetry was used to assess body temperature and locomotor activity in combination with continuous automated recordings of feeding and drinking. This technique was developed as a novel method to identify and measure sickness behavior in rodents. The animals were (a) sham-operated, (b) adrenalectomized or (c) sham-operated and treated with corticosterone (10 mg/kg, subcutaneously). They were then intraperitoneally injected with vehicle or LPS at a dose (100 micrograms/kg) that in sham-operated rats induced fever and anorexia, reduced spontaneous activity and increased IL1-beta mRNA in spleen and adrenals as determined by Northern blot analysis. Adrenalectomized rats produced larger amounts of splenic IL-1 beta mRNA, reduced their general activity much more and developed a mild adipsia as compared with adrenal-intact animals. Administration of corticosterone 1 h before LPS lowered the splenic IL-1 beta mRNA content compared to LPS-treated adrenal-intact rats that did not receive corticosterone and inhibited fever and anorexia, whereas the glucocorticoid did not attenuate the endotoxin-induced suppression of locomotor activity. Our data suggest that during inflammatory conditions body temperature, sickness behavior and the synthesis of IL-1 beta are controlled by corticosterone. Different components of sickness behavior seem to be independently regulated and are under differential control by glucocorticoids.

Soluble interleukin-6 (IL-6) receptor augments central effects of IL-6 in vivo

The pleiotropic cytokine interleukin-6 (IL-6) controls both the peripheral and central components of the acute-phase response. These activities are mediated via the IL-6 membrane receptor, but probably also via agonistic soluble IL-6 receptors (sIL-6Rs). In the present study we conducted dose-response experiments with rats that were intracerebroventricularly i.c.v.) injected with recombinant human IL-6 and sIL-6R and determined body temperature, locomotor activity, food intake, and water consumption using radiotelemetry and continuous recordings of feeding and drinking. IL-6 injected i.c.v. at 1, 10, and 100 ng increased body temperature and decreased locomotor activity and food intake, but it did not affect water consumption. When 10 ng sIL-6R, which lacked detectable biological activity, was injected i.c.v. 1 h before 1 ng IL-6, the central effects of IL-6 were enhanced and prolonged, and this was not due to endotoxin contamination of the recombinant proteins. Our data suggest that IL-6 plays an important role in the regulation of body temperature, general activity, and food intake in sick animals. Moreover, we have shown for the first time that it is possible to potentiate the effects of a mediator in vivo by administration of the corresponding receptor, which is a novel pharmacological tool for increasing receptor capacity.