Downregulation of KCNMB4 expression and changes in BK channel subtype in hippocampal granule neurons following seizure activity.

A major challenge is to understand maladaptive changes in ion channels that sets neurons on a course towards epilepsy development. Voltage- and calcium-activated K+ (BK) channels contribute to early spike timing in neurons, and studies indicate that the BK channel plays a pathological role in increasing excitability early after a seizure. Here, we have investigated changes in BK channels and their accessory ß4 subunit (KCNMB4) in dentate gyrus (DG) granule neurons of the hippocampus, key neurons that regulate excitability of the hippocampus circuit. Two days after pilocarpine-induced seizures, we found that the predominant effect is a downregulation of the ß4 accessory subunit mRNA. Consistent with reduced expression, single channel recording and pharmacology indicate a switch in the subtype of channels expressed; from iberiotoxin-resistant, type II BK channels (BK α/ß4) that have higher channel open probability and slow gating, to iberiotoxin-sensitive type I channels (BK α alone) with low open probability and faster gating. The switch to a majority of type I channel expression following seizure activity is correlated with a loss of BK channel function on spike threshold while maintaining the channel's contribution to increased early spike frequency. Using heterozygous ß4 knockout mice, we find reduced expression is sufficient to increase seizure sensitivity. We conclude that seizure-induced downregulation of KCNMB4 is an activity dependent mechanism that increases the excitability of DG neurons. These novel findings indicate that BK channel subtypes are not only defined by cell-specific expression, but can also be plastic depending on the recent history of neuronal excitability.

Immortalized mouse dental papilla mesenchymal cells preserve odontoblastic phenotype and respond to bone morphogenetic protein 2.

Odontogenesis is the result of the reciprocal interactions between epithelial-mesenchymal cells leading to terminally differentiated odontoblasts. This process from dental papilla mesenchymal cells to odontoblasts is regulated by a complex signaling pathway. When isolated from the developing tooth germs, odontoblasts quickly lose their potential to maintain the odontoblast-specific phenotype. Therefore, generation of an odontoblast-like cell line would be a good surrogate model for studying the dental mesenchymal cell differentiation into odontoblasts and the molecular events of dentin formation. In this study, immortalized dental papilla mesenchymal cell lines were generated from the first mouse mandibular molars at postnatal day 3 using pSV40. These transformed cells were characterized by RT-PCR, immunohistochemistry, Western blot, and analyzed for alkaline phosphatase activity and mineralization nodule formation. One of these immortalized cell lines, iMDP-3, displayed a high proliferation rate, but retained the genotypic and phenotypic characteristics similar to primary cells as determined by expression of tooth-specific markers and demonstrated the ability to differentiate and form mineralized nodules. Furthermore, iMDP-3 cells had high transfection efficiency as well as were inducible and responded to BMP2 stimulation. We conclude that the establishment of the stable murine dental papilla mesenchymal cell line might be used for studying the mechanisms of dental cell differentiation and dentin formation.

Binding of amelogenin to MMP-9 and their co-expression in developing mouse teeth.

Amelogenin is the most abundant matrix protein in enamel. Proper amelogenin processing by proteinases is necessary for its biological functions during amelogenesis. Matrix metalloproteinase 9 (MMP-9) is responsible for the turnover of matrix components. The relationship between MMP-9 and amelogenin during tooth development remains unknown. We tested the hypothesis that MMP-9 binds to amelogenin and they are co-expressed in ameloblasts during amelogenesis. We evaluated the distribution of both proteins in the mouse teeth using immunohistochemistry and confocal microscopy. At postnatal day 2, the spatial distribution of amelogenin and MMP-9 was co-localized in preameloblasts, secretory ameloblasts, enamel matrix and odontoblasts. At the late stages of mouse tooth development, expression patterns of amelogenin and MMP-9 were similar to that seen in postnatal day 2. Their co-expression was further confirmed by RT-PCR, Western blot and enzymatic zymography analyses in enamel organ epithelial and odontoblast-like cells. Immunoprecipitation assay revealed that MMP-9 binds to amelogenin. The MMP-9 cleavage sites in amelogenin proteins across species were found using bio-informative software program. Analyses of these data suggest that MMP-9 may be involved in controlling amelogenin processing and enamel formation.

Expression and processing of small integrin-binding ligand N-linked glycoproteins in mouse odontoblastic cells.

OBJECTIVE: Small integrin-binding ligand N-linked glycoproteins (SIBLINGs) are expressed in dentin and believed to control dentinogenesis. Five members of SIBLING family include bone sialoprotein (BSP), osteopontin (OPN), matrix extracellular phosphoglycoprotein (MEPE), dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP). These genes are clustered on chromosome 4q in humans and share similar biological features. DSPP and DMP1 are processed into given structural/functional fragments in rat and porcine. It still remains unclear whether these evidences occur in mouse and other SIBLING members are also processed into given fragments from their parent precursors. The aim of this study was to identify expression and processing of the five proteins in two mouse odontoblastic cell lines. DESIGN: Two mouse odontoblastic cells were used to study expression and processing of the five SIBLING proteins by immunohistochemistry and Western blot analyses. RESULTS: Immunohistochemistry study showed that all of the five SIBLING members were expressed within the cytoplasm and cellular processes in the mouse odontoblastic cell lines. Expression levels of DMP1 and DSPP were higher in differentiated mouse odontoblasts than undifferentiated mouse odontoblasts. Immunolabelling signal of DSP and MEPE was also detected within the nucleus in the two cell lines. Western blot assay indicated that all five members were processed into at least two fragments in these cells. CONCLUSIONS: These results suggest that different processed products and expression levels of the SIBLING proteins may play distinct biological functions in tooth development and mineralisation.

Bone morphogenetic protein 2 mediates dentin sialophosphoprotein expression and odontoblast differentiation via NF-Y signaling.

Dentin sialophosphoprotein (DSPP), an important odontoblast differentiation marker, is necessary for tooth development and mineralization. Bone morphogenetic protein 2 (BMP2) plays a vital role in odontoblast function via diverse signal transduction systems. We hypothesize that BMP2 regulates DSPP gene transcription and thus odontoblast differentiation. Here we report that expression of BMP2 and DSPP is detected during mouse odontogenesis by in situ hybridization assay, and BMP2 up-regulates DSPP mRNA and protein expression as well as DSPP-luciferase promoter activity in mouse preodontoblasts. By sequentially deleting fragments of the mouse DSPP promoter, we show that a BMP2-response element is located between nucleotides -97 and -72. By using antibody and oligonucleotide competition assays in electrophoretic mobility shift analysis and chromatin immunoprecipitation experiments, we show that the heterotrimeric transcription factor Y (NF-Y) complex physically interacts with the inverted CCAAT box within the BMP2-response element. BMP2 induces NF-Y accumulation into the nucleus increasing its recruitment to the mouse DSPP promoter in vivo. Furthermore, forced overexpression of NF-Y enhances promoter activity and increases endogenous DSPP protein levels. In contrast, mutations in the NF-Y-binding motif reduce BMP2-induced DSPP transcription. Moreover, inhibiting BMP2 signaling by Noggin, a BMP2 antagonist, results in significant inhibition of DSPP gene expression in preodontoblasts. Taken together, these results indicate that BMP2 mediates DSPP gene expression and odontoblast differentiation via NF-Y signaling during tooth development.

Arachidonic acid and prostaglandin E2 influence human osteoblast (MG63) response to titanium surface roughness.

Prior studies have shown that implant surface roughness affects osteoblast proliferation, differentiation, matrix synthesis, and local factor production. Further, cell response is modulated by systemic factors, such as 1,25(OH)2D3 and estrogen as well as mechanical forces. Based on the fact that peri-implant bone healing occurs in a site containing elevated amounts of prostaglandin E2 (PGE2), the hypothesis of the current study is that PGE2 and arachidonic acid (AA), the substrate used by cyclooxygenase to form PGE2, influence osteoblast response to implant surface roughness. To test this hypothesis, 4 different types of commercially pure titanium (cpTi) disks with surfaces of varying roughness (smooth Ti, R(a) 0.30 microm; smooth and acid etched Ti [SAE Ti], R(a) 0.40 microm; rough Ti, R(a) 4.3 microm; rough and acid etched Ti [RAE Ti], R(a) 4.15 (microm) were prepared. MG63 osteoblasts were seeded onto the surfaces, cultured to confluence, and then treated for the last 24 hours of culture with AA (0, 0.1, 1, and 10 nM), PGE2 (0, 1, 10, 25, and 100 nM), or the general cyclooxygenase inhibitor indomethacin (0 or 100 nM). At harvest, the effect of treatment on cell proliferation was assessed by measuring cell number and [3H]-thymidine incorporation, and the effect on cell differentiation was determined by measuring alkaline phosphatase (ALP) specific activity. The effect of AA and PGE2 on cell number was somewhat variable but showed a general decrease on plastic and smooth surfaces and an increase on rough surfaces. In contrast, [3H]-thymidine incorporation was uniformly decreased with treatment on all surfaces. ALP demonstrated the most prominent effect of treatment. On smooth surfaces, AA and PGE2 dose-dependently increased ALP, while on rough surfaces, treatment dose-dependently decreased enzyme specific activity. Indomethacin treatment had either no effect or a slightly inhibitory effect on [3H]-thymidine incorporation on all surfaces. In contrast, indomethacin inhibited ALP on smooth surfaces and stimulated ALP on rough. Taken together, the results indicate that both AA and PGE2 influence osteoblast response by promoting osteoblast differentiation on smooth surfaces, while inhibiting it on rough surfaces. Because implants with rough surfaces are acknowledged to be superior to those with smooth surfaces, these results suggest that use of nonsterioidal anti-inflammatory drugs to block PGE2 production and reduce inflammation may be beneficial in the postoperative period after implant placement. They also indicate that manipulation of the AA metabolic pathway may offer a new therapeutic approach for modulating bone healing after implant placement. Because peri-implant healing takes place in a complex cellular environment quite different from the one used in the present study, additional work will be necessary to substantiate these possibilities.

Nitric oxide donors selectively reduce the expression of matrix metalloproteinases-8 and -9 by human diabetic skin fibroblasts.

BACKGROUND: Chronic, nonhealing skin wounds are a common ailment in uncontrolled diabetes and are associated with significant morbidity. The nonhealing diabetic foot wound displays pathologically elevated matrix metalloproteinase (MMP) activity. In contrast, the concentration of nitric oxide (NO) is significantly reduced in these chronic ulcers. Addition of NO to diabetic wounds improves wound healing, but the mechanism for this effect is poorly understood. MATERIALS AND METHODS: Diabetic and nondiabetic human skin fibroblasts were cultured to confluence and then treated with 0, 1, 10, and 100 nm concentrations of three NO donors (NOR-3, SNAP, and SNOG) with varying half-lives for 1, 3, and 7 days. At harvest, the cultures were analyzed for their production of NO and the effect of NO donor treatment on cell proliferation (cell number) and MMP expression (MMP-1, -2, -8, -9, and -13). RESULTS: The NO donor with the shortest half-life (NOR-3) produced a rise in NO on day 1 in both normal and diabetic fibroblasts at the highest concentration used; there was a corresponding decrease in both MMP-8 and MMP-9 expression in the diabetic fibroblasts and a decrease in only MMP-9 expression in the normal fibroblasts. After longer times in culture or at lower concentrations, NOR-3 was without effect on NO production or MMP expression. Further, NOR-3 had no effect on cell proliferation. In contrast to NOR-3, NO donors with longer half-lives (SNAP and SNOG) significantly (P < 0.05) increased NO production by both normal and diabetic fibroblasts during the entire course of the experiment and even after a media change lacking additional NO donor at day 3. SNAP and SNOG dose-dependently reduced MMP-8 and -9 mRNA expression in both normal and diabetic fibroblasts through day 7. The expression of MMP-1, -2, and -13 was not significantly affected by any of the NO donor treatments. CONCLUSIONS: These experiments show distinct deficits in NO production and elevations in MMP-8 and -9 expression in diabetic human skin fibroblasts compared to normal. In addition, treating these cultures with NO donor compounds with half-lives greater than 5 h selectively raised NO production by the cells, increased cell proliferation, and decreased MMP-8 and -9 expression in a dose-dependent manner. There was no effect of the NO donor compounds on MMP-1, -2, or -13 expression. One possible mechanism to account for NO's beneficial effect on wound healing may involve stimulation of cell proliferation and down-regulation of MMP expression.

Differential regulation of dentin sialophosphoprotein expression by Runx2 during odontoblast cytodifferentiation.

Dentin sialophosphoprotein (DSPP) consists of dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). The spatial-temporal expression of DSPP is largely restricted during differentiational stages of dental cells. DSPP plays a vital role in tooth development. It is known that an osteoblast-specific transcription factor, Runx2, is essential for osteoblast differentiation. However, effects of Runx2 on DSPP transcription remain unknown. Here, we studied different roles of Runx2 in controlling DSPP expression in mouse preodontoblast (MD10-F2) and odontoblast (MO6-G3) cells. Two Runx2 isoforms were expressed in preodontoblast and odontoblast cells, and in situ hybridization assay showed that DSPP expression increased, whereas Runx2 was down-regulated during odontoblast differentiation and maturation. Three potential Runx2 sites are present in promoters of mouse and rat DSPP genes. Runx2 binds to these sites as demonstrated by electrophoretic mobility shift assay and supershift experiments. Mutations of Runx2 sites in mouse DSPP promoter resulted in a decline of promoter activity in MD10-F2 cells compared with an increase of its activity in MO6-G3 cells. Multiple Runx2 sites were more active than a single site in regulating the DSPP promoter. Furthermore, forced overexpression of Runx2 isoforms induced increases of endogenous DSPP protein levels in MD10-F2 cells but reduced its expression in MO6-G3 cells consistent with the DSPP promoter analysis. Thus, our results suggest that differential positive and negative regulation of DSPP by Runx2 is dependent on use of cytodifferentiation of dental ectomesenchymal-derived cells that may contribute to the spatial-temporal expression of DSPP during tooth development.

Altered gene expression in human cleidocranial dysplasia dental pulp cells.

Cleidocranial dysplasia (CCD) is an autosomal dominant disorder characterised by defects of bone and tooth development. The dental manifestations in CCD patients include supernumerary teeth, delayed tooth eruption, tooth hypoplasia and absence of cellular cementum formation. This disorder is associated with mutations in the osteoblast-specific transcription factor Runx2. To identify morphological and molecular alterations associated with CCD dental tissues, human primary dental pulp cell cultures were established from age- and sex-matched CCD and normal patients. Dental pulp cells were compared for general morphology, proliferation rates, and gene expression profiles using cDNA microarray technology. CCD pulp cells were about four-fold larger than normal cells, however the normal pulp proliferation rates were two- and three-fold greater at time points tested than the CCD cells. Of the 226 genes analysed by blot microarray, 18.6% displayed significant differences at least two-fold in expression levels. This includes 25 genes (11.1%) that were up-regulated, while 17 (7.5%) that were down-regulated in the CCD cells as compared to the normal cells. Expression of selected genes was further verified by quantitative real-time polymerase chain reaction (qRT-PCR). Comparison between the CDD and normal cells revealed that gene expression of cytokines and growth factors, such as leukemia inhibitory factor (LIF), interleukin-6 (IL-6) and transforming growth factor beta receptor II (TGF-betaRII) and vascular endothelial growth factor B (VEGFB) were higher while bone morphogenetic protein 2 (BMP2) was lower in the CCD cells. Furthermore, potential Runx2 binding sites were found in all putative target gene promoters. This study suggests that in addition to bone and tooth cell differentiation, Runx2 may be involved in controlling cell growth during tooth development.

Regulation of the Cell Type-specific dentin sialophosphoprotein gene expression in mouse odontoblasts by a novel transcription repressor and an activator CCAAT-binding factor.

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) with a highly restricted expression pattern in tooth and bone. Mutations of the DSPP gene are associated with dentin genetic diseases. Regulation of tissue-specific DSPP expression has not been described. To define the molecular basis of this cell-specific expression, we characterized the promoter responsible for the cell-specific expression of the DSPP gene in odontoblasts. Within this region, DNase I footprinting and electrophoretic mobility shift assays delineated one element that contains an inverted CCAAT-binding factor site and a protein-DNA binding site using nuclear extracts from odontoblasts. A series of competitive electrophoretic mobility shift assay analyses showed that the protein-DNA binding core sequence, ACCCCCA, is a novel site sufficient for protein binding. These two protein-DNA binding sequences are conserved at the same proximal position in the mouse, rat, and human DSPP gene promoters and are ubiquitously present in the promoters of other tooth/bone genes. Mutations of the CCAAT-binding factor binding site resulted in a 5-fold decrease in promoter activity, whereas abolishment of the novel protein-DNA binding site increased promoter activity by about 4.6-fold. In contrast to DSPP, expression levels of the novel protein were significantly reduced during odontoblastic differentiation and dentin mineralization. The novel protein was shown to have a molecular mass of 72 kDa. This study shows that expression of the cell type-specific DSPP gene is mediated by the combination of inhibitory and activating mechanisms.