Molecular and circadian controls of ameloblasts

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90102/1/j.1600-0722.2011.00918.x.pd

BMP2 commitment to the osteogenic lineage involves activation of Runx2 by DLX3 and a homeodomain transcriptional network

Several homeodomain (HD) proteins are critical for skeletal patterning and respond directly to BMP2 as an early step in bone formation. RUNX2, the earliest transcription factor proven essential for commitment to osteoblastogenesis, is also expressed in response to BMP2. However, there is a gap in our knowledge of the regulatory cascade from BMP2 signaling to the onset of osteogenesis. Here we show that BMP2 induces DLX3, a homeodomain protein that activates Runx2 gene transcription. Small interfering RNA knockdown studies in osteoblasts validate that DLX3 is a potent regulator of Runx2. Furthermore in Runx2 null cells, DLX3 forced expression suffices to induce transcription of Runx2, osteocalcin, and alkaline phosphatase genes, thus defining DLX3 as an osteogenic regulator independent of RUNX2. Our studies further show regulation of the Runx2 gene by several homeodomain proteins: MSX2 and CDP/cut repress whereas DLX3 and DLX5 activate endogenous Runx2 expression and promoter activity in non-osseous cells and osteoblasts. These HD proteins exhibit distinct temporal expression profiles during osteoblast differentiation as well as selective association with Runx2 chromatin that is related to Runx2 transcriptional activity and recruitment of RNA polymerase II. Runx2 promoter mutagenesis shows that multiple HD elements control expression of Runx2 in relation to the stages of osteoblast maturation. Our studies establish mechanisms for commitment to the osteogenic lineage directly through BMP2 induction of HD proteins DLX3 and DLX5 that activate Runx2, thus delineating a transcriptional regulatory pathway mediating osteoblast differentiation. We propose that the three homeodomain proteins MSX2, DLX3, and DLX5 provide a key series of molecular switches that regulate expression of Runx2 throughout bone formation. <br/

Aspects cellulaires des processus de minéralisation et de résorption du complexe pulpo-dentinaire dans la dent temporaire

Plusieurs types cellulaires sont impliqués dans les processus de minéralisation et de résorption physiopathologiques observés au niveau du complexe pulpo-dentinaire des dents temporaires. L’intérêt de ce travail est de souligner les particularités fonctionnelles de ces cellules face à ces processus, que ce soit au cours de développement dentaire ou dans le cadre particulier de quelques thérapeutiques ou de certaines pathologies. La compréhension du mécanisme cellulaire de la résorption dentinaire et la découverte des nouvelles cellules souches pulpaires impliquées dans les processus de minéralisation ouvrent la voie à de multiples perspectives dans le cadre de la maîtrise de ces deux processus

Topography of the pulp chamber in the maxillary primary molars of a Tunisian children

Background: Knowledge of the variations in pulp chamber topography is very useful to the dentist while performing endodontic access cavity in primary teeth. Aim: To determine the horizontal crown dimensions and the pulp chamber topography of shedding maxillary primary molars in a sample of Tunisian children. Materials and Methods: Forty two maxillary primary molars (24 first and 18 second molars) were used. Teeth were ultrasonically cleaned before taking morphometric measurements of the buccolingual and mesiodistal sizes. Statistical student test was used comparing the mean sizes. Results: All the crown measurements were higher in the second molar. While the buccolingual dimension of the pulp chamber was higher in the second molar, the mesiodistal sizes were equivalent among the teeth. The thickest walls were in the buccal side of the first molar and in the mesial side of the second one. The ratio of several measurements indicate that the pulp cavity is more vestibularly and distally located in the second molar. Conclusion: Mesiodistal dimension of the pulp cavity is not proportional to that of the dental crown. Endodontic access cavity have to be shifted to the distal and vestibular sides from the first to the second upper molar

Aeromonas hydrophila disturbs water and electrolyte transport in Mugil cephalus L. intestine

Fish diseases create a menace to aquaculture farms. They provoke disastrous economic losses and sanitary risks for the consumer. The present study aims to investigate the effect of the bacteria,Aeromonas hydrophila on water and electrolyte (Na+, K+, Cl-, HCO3-) flux of Mugil cephalus (L, 1758) intestine. Anterior, middle and distal gut segments of M. cephalus (L) intestine were used in an in vitromodel; Everted Gut Sac (EGS). The sacs were exposed to bacteria suspension (108 cells/ ml) at 25°C for 2 h. Our results showed a significant reduction of water absorption at the anterior and the midintestine (P< 0.05), and a significant increase of K+ secretion only at the anterior intestine (P < 0.01). However, HCO3-secretion increase was significant at the anterior and the mid intestine (P < 0.05).Paradoxically, an increased absorption of Na+, and Cl- was recorded at the mid (P < 0.01) and at the distal gut segments (P < 0.05). Histological studies were assessed by light microscopy. EGS exposedto Ringer solution (12%, pH 8.5) revealed the presence of intact intestinal tract. However, infected EGS showed intestinal damages characterized by epithelium lesions, detachment of degenerateenterocytes with voluminous and spherical shape, disappearance of enterocyte brush border and lesions at cellular junction. It can be concluded that A. hydrophila resulted in a disturbance ofhydroelectrolytic flux and alterations of M. cephalus intestinal tract. The most serious damage was noted at the anterior segment

Mandibular bone alterations of ovariectomized rats under vitamin D insufficiency

Experimental osteoporosis was studied in mandible bone by means of ovariectomy and vitamin D insufficiency. METHODS: 42 female Wistar rats were divided into the following four groups: (1) ovariectomized rats maintained in 12h day-night light conditions (ov-l), (2) ovariectomized rats maintained in 24h dark light conditions (ov-ob), (3) sham-operated rats maintained in 12h day-night light conditions (ch-l) and (4) sham-operated rats maintained in 24 h dark conditions (ch-ob). 12 weeks later the animals were sacrificed, the mandibles were excised, cleaned and weighed, the right side of the mandibles were histologically examined and the left side of the mandibles were prepared for mineral phase analysis by X-ray diffraction. Immunohistochemical analysis was performed to detect apoptotic cells by anti-PARP p85 antibody. RESULTS: In group 2, the weight of mandibles significantly decreased. Chondroid areas were observed in ovariectomized groups and polarized light observation validated the collagen distribution disturbance in these groups (groups 1 and 2). Apoptotic osteoblasts were localized in groups 1, 2 and 4. They were numerous in group 2. The mineral phase analysis did not find differences between the groups. CONCLUSION: This study validates a new model of osteoporotic animal associating estrogens deficiency and vitamin D insufficiency where matrix synthesis and osteoblast biology are altered, but not biomineralization

Attenuation of endoplasmic reticulum stress and mitochondrial injury in kidney with ischemic postconditioning application and trimetazidine treatment.

International audienceUNLABELLED: ABSTRACT: BACKGROUND: Endoplasmic reticulum (ER) and mitochondria have been implicated in the pathology of renal ischemia/reperfusion (I/R). In the present study, we investigated whether the use of ischemic postconditioning (IPostC) and trimetazidine (TMZ) separately or combined could reduce ER stress and mitochondria damage after renal ischemia. METHODS: Kidneys of Wistar rats were subjected to 60-min of warm ischemia followed by 120-min of reperfusion (I/R group, n = 6), or to 6 cycles of ischemia/reperfusion (10-s each cycle) just after 60-min of warm ischemia (IPostC group, n = 6), or to i.p. injection of TMZ (3 mg/kg) 30-min before ischemia (TMZ group, n = 6), or to the combination of both treatments (IPostC+TMZ group, n = 6). The results of these experimental groups were compared to those of a sham-operated group in which rat renal pedicles were only dissected. Sodium reabsorption rate, creatinine clearance lactate deshydrogenase (LDH) activity in plasma, and concentration of malonedialdehyde (MDA) in tissue were determined. In addition, Western blot analysis was performed to identify the amounts of cytochrome c, c-JunNH2-terminal kinase (JNK), voltage-dependent anion channel (VDAC), glycogen synthase kinase 3-beta (GSK3-β), and ER stress parameters. RESULTS: IPostC or/and TMZ significantly decreased cytolysis, oxidative stress and improved renal function in comparison to I/R group. IPostC but not TMZ significantly attenuated ER stress parameters versus I/R group. Indeed, it down-regulated the glucose-regulated protein 78 (GRP78), the activating transcription factor 4 (ATF4), the RNA activated protein kinase (PKR)-like ER kinas (PERK), the X box binding protein-1 (XBP-1) and the caspase12 protein levels. TMZ treatment significantly augmented GSK3-β phosphorylation and reduced levels of cytochrome c and VDAC phosphorylation in comparison to IPostC application. The combination of both treatments gave a synergetic effect. It significantly improved the survival rate, attenuated cytolysis, oxidative stress and improved renal function. CONCLUSION: This study revealed that IPostC protects kidney from I/R injury by suppressing ER stress while the beneficial effects of TMZ are mediated by mitochondria protection. The combination of both treatments ameliorated functional recovery

Molecular Consequences of a Frameshifted DLX3 Mutant Leading to Tricho-Dento-Osseous Syndrome*

The homeodomain protein Distal-less-3 (Dlx3) plays a crucial role during embryonic development. This transcription factor is known to be essential for placental formation and to be involved in skin and skeletal organogenesis. In humans, a frameshift mutation in the coding sequence of the DLX3 gene results in an ectodermal dysplasia called Tricho-Dento-Osseous syndrome (TDO). The main features of this autosomal dominant disorder are defects in hair, teeth, and bone. To investigate the functional alterations caused by the mutated DLX3TDO isoform ex vivo, we used tetracycline-inducible osteoblastic and keratinocyte cell lines and calvarial derived osteoblasts in which the expression of DLX3WT and/or DLX3TDO could be regulated and monitored. Immunocytochemical analysis revealed that both DLX3WT and DLX3TDO recombinant proteins are targeted to the nucleus. However, as demonstrated by electrophoresis mobility shift assay, DLX3TDO is not able to bind to the canonical Dlx3 binding site. Furthermore, we demonstrate that the frameshifted C-terminal domain in DLX3TDO is accountable for the loss of DNA binding activity because the C-terminal domain in DLX3WT is not required for DNA binding activity. Although DLX3TDO alone cannot bind to a Dlx3 responsive element, when DLX3WT and DLX3TDO are co-expressed they form a complex that can bind DNA. Concomitant with the inability to bind DNA, DLX3TDO has a defective transcriptional activity. Moreover, the transcriptional activity of DLX3WT is significantly reduced in the presence of the mutated isoform, indicating that DLX3TDO has a dominant negative effect on DLX3WT transcriptional activity

Mineral features of connective dental hard tissues in hypoplastic amelogenesis imperfecta.

OBJECTIVE: To explore the mineral features of dentin and cementum in hypoplastic Amelogenesis imperfecta AI teeth. MATERIALS AND METHODS: Forty-four (44) teeth cleaned and free of caries were used: 20 control and 24 affected by hypoplastic amelogenesis imperfecta. Thirty-two teeth were studied by pQCT, cut in sections, and analyzed under microradiography, polarized light microscopy, and confocal Raman spectroscopy. Eight teeth were observed under scanning electron microscope. Four teeth were used for an X-ray diffraction. The mineral density data were analyzed statistically with the Mann-Whitney U test, using GraphPad InStat software. RESULTS: Both coronal dentin and radicular dentin were less mineralized in AI teeth when compared to control (respectively 6.2% and 6.8%; p < .001). Root dentinal walls were thin and irregular, while the cellular cementum layers were thick, reaching sometimes the cervical region of the tooth. Regular dentinal tubules and sclerotic dentin areas were noticed. Partially tubular or cellular dysplastic dentin and hyper-, normo-, or hypomineralized areas were noticed in the inter-radicular areas of hypoplastic AI teeth. The main mineral component was carbonate hydroxyapatite as explored by Raman spectroscopy and X-ray diffraction. CONCLUSIONS: Dentin and cementum in hypoplastic AI teeth are (i) hypomineralized, (ii) constituted of carbonate hydroxyapatite, and (iii) of non-homogenous structure