Immunolocalization of CD44 and the ezrin-radixin-moesin (ERM) family in the stratum intermedium and papillary layer of the mouse enamel organ

Loss of BMP2 and BMP4 Signaling in the Dental Epithelium Causes Defective Enamel Maturation and Aberrant Development of Ameloblasts

BMP signaling is crucial for differentiation of secretory ameloblasts, the cells that secrete enamel matrix. However, whether BMP signaling is required for differentiation of maturation-stage ameloblasts (MA), which are instrumental for enamel maturation into hard tissue, is hitherto unknown. To address this, we used an in vivo genetic approach which revealed that combined deactivation of the Bmp2 and Bmp4 genes in the murine dental epithelium causes development of dysmorphic and dysfunctional MA. These fail to exhibit a ruffled apical plasma membrane and to reabsorb enamel matrix proteins, leading to enamel defects mimicking hypomaturation amelogenesis imperfecta. Furthermore, subsets of mutant MA underwent pathological single or collective cell migration away from the ameloblast layer, forming cysts and/or exuberant tumor-like and gland-like structures. Massive apoptosis in the adjacent stratum intermedium and the abnormal cell-cell contacts and cell-matrix adhesion of MA may contribute to this aberrant behavior. The mutant MA also exhibited severely diminished tissue non-specific alkaline phosphatase activity, revealing that this enzyme’s activity in MA crucially depends on BMP2 and BMP4 inputs. Our findings show that combined BMP2 and BMP4 signaling is crucial for survival of the stratum intermedium and for proper development and function of MA to ensure normal enamel maturation.

Balance Between Tooth Size and Tooth Number Is Controlled by Hyaluronan

While the function of proteins and genes has been widely studied during vertebrate development, relatively little work has addressed the role of carbohydrates. Hyaluronan (HA), also known as hyaluronic acid, is an abundant carbohydrate in embryonic tissues and is the main structural component of the extracellular matrix of epithelial and mesenchymal cells. HA is able to absorb large quantities of water and can signal by binding to cell-surface receptors. During organ development and regeneration, HA has been shown to regulate cell proliferation, cell shape, and migration. Here, we have investigated the function of HA during molar tooth development in mice, in which, similar to humans, new molars sequentially bud off from a pre-existing molar. Using an ex vivo approach, we found that inhibiting HA synthesis in culture leads to a significant increase in proliferation and subsequent size of the developing molar, while the formation of sequential molars was inhibited. By cell shape analysis, we observed that inhibition of HA synthesis caused an elongation and reorientation of the major cell axes, indicating that disruption to cellular orientation and shape may underlie the observed phenotype. Lineage tracing demonstrated the retention of cells in the developing first molar (M1) at the expense of the generation of a second molar (M2). Our results highlight a novel role for HA in controlling proliferation, cell orientation, and migration in the developing tooth, impacting cellular decisions regarding tooth size and number.

Single-Cell RNA-Sequencing From Mouse Incisor Reveals Dental Epithelial Cell-Type Specific Genes

Dental epithelial stem cells give rise to four types of dental epithelial cells: inner enamel epithelium (IEE), outer enamel epithelium (OEE), stratum intermedium (SI), and stellate reticulum (SR). IEE cells further differentiate into enamel-forming ameloblasts, which play distinct roles, and are essential for enamel formation. These are conventionally classified by their shape, although their transcriptome and biological roles are yet to be fully understood. Here, we aimed to use single-cell RNA sequencing to clarify the heterogeneity of dental epithelial cell types. Unbiased clustering of 6,260 single cells from incisors of postnatal day 7 mice classified them into two clusters of ameloblast, IEE/OEE, SI/SR, and two mesenchymal populations. Secretory-stage ameloblasts expressed Amel and Enam were divided into Dspp + and Ambn + ameloblasts. Pseudo-time analysis indicated Dspp + ameloblasts differentiate into Ambn + ameloblasts. Further, Dspp and Ambn could be stage-specific markers of ameloblasts. Gene ontology analysis of each cluster indicated potent roles of cell types: OEE in the regulation of tooth size and SR in the transport of nutrients. Subsequently, we identified novel dental epithelial cell marker genes, namely Pttg1, Atf3, Cldn10, and Krt15. The results not only provided a resource of transcriptome data in dental cells but also contributed to the molecular analyses of enamel formation.

Hyaluronan and hyaluronan synthases expression and localization in embryonic mouse molars

Hyaluronan (HA) and hyaluronan synthases (HASs) have been shown to play critical roles in embryogenesis and organ development. However, there have not been any studies examining HA and HAS expression and localization during tooth development. The present study was designed to investigate the expression of HA and three isoforms of HASs (HAS1, 2, 3) in embryonic mouse molars. The first mandibular embryonic mouse molars were examined by immunohistochemistry at E11.5, E13.5, E14.5, E16.5, and E18.5. PCR and western blot analyses were performed on RNA and proteins samples from E13.5 to E18.5 tooth germs. At the initial stage (E11.5), HA and HASs were expressed in the dental epithelium but not the underlying dental mesenchyme. HA immunostaining gradually increased in the enamel organ from the bud stage (E13.5) to the late bell stage (E18.5), and HA and HASs were highly expressed in the stellate reticulum and stratum intermedium. HA immunostaining was also enhanced in the dental mesenchyme and its derived tissues, but it was not expressed in the ameloblast and odontoblast regions. The three HAS isoforms had distinct expression patterns, and they were expressed in the dental mesenchyme and odontoblast at various levels. Furthermore, HAS1 and HAS2 expression decreased, while HAS3 expression increased from E13.5 to E18.5. These results suggested that HA synthesized by different HASs is involved in embryonic mouse molar morphogenesis and cytodifferentiation.

Protective effects of ezrin on cold storage preservation injury in the pig kidney proximal tubular epithelial cell line (LLC-PK1)

BACKGROUND

Renal damage caused by cold preservation and warm reperfusion has been well documented and involves tissue edema, cell swelling, ATP depletion, calcium toxicity, and oxidative stress. However, more common proximal mechanisms have not been identified, which may limit the development of effective clinical treatment strategies. Previous work indicates that many cytoskeletal structures are affected by cold preservation and reperfusion, including membrane-rich ezrin-associated complexes. The aim of this study was to investigate whether the sublamellar cytoskeletal protein ezrin is causally involved in cold preservation injury in renal tubule epithelial cells.

METHODS

We created a stably transfected cell line (LLC-EZ) using the pig kidney proximal tubular epithelial cell line (LLC-PK1), which constitutively overexpresses wild-type ezrin. These cells were cold stored in University of Wisconsin Solution and reperfused in vitro to model renal tubule preservation injury, which was assessed by biochemical, metabolic, functional, and structural endpoints.

RESULTS

Overexpression of ezrin increased cell viability (lactate dehydrogenase release), mitochondrial activity (ATP synthesis, dehydrogenase activity, and inner mitochondrial membrane potential), and protected the structure of cell membrane microvilli and mitochondria after cold storage preservation injury. Reperfusion-induced apoptosis was also significantly reduced in LLC-EZ cells overexpressing ezrin.

CONCLUSIONS

Enhanced ezrin expression protects tubule epithelial cells from cold storage preservation injury, possibly by membrane or mitochondrial mechanisms.

Immunocytochemical and biochemical detection of EMMPRIN in the rat tooth germ: differentiation-dependent co-expression with MMPs and co-localization with caveolin-1 in membrane rafts of dental epithelial cells

In tooth development matrix metalloproteinases (MMPs) are under the control of several regulatory mechanisms including the upregulation of expression by inducers and downregulation by inhibitors. The aim of the present study was to monitor the occurrence and distribution pattern of the extracellular matrix metalloproteinase inducer (EMMPRIN), the metalloproteinases MMP-2 and MT1-MMP and caveolin-1 during the cap and bell stage of rat molar tooth germs by means of immunocytochemistry. Strong EMMPRIN immunoreactivity was detected on the cell membranes of ameloblasts and cells of the stratum intermedium in the bell stage of the enamel organ. Differentiating odontoblasts exhibited intense EMMPRIN immunoreactivity, especially at their distal ends. Caveolin-1 immunoreactivity was evident in cells of the internal enamel epithelium and in ameloblasts. Double immunofluorescence studies revealed a focal co-localization between caveolin-1 and EMMPRIN in ameloblastic cells. Finally, western blotting experiments demonstrated the expression of EMMPRIN and caveolin-1 in dental epithelial cells (HAT-7 cells). A substantial part of EMMPRIN was detected in the detergent-insoluble caveolin-1-containing low-density raft membrane fraction of HAT-7 cells suggesting a partial localization within lipid rafts. The differentiation-dependent co-expression of MMPs with EMMPRIN in the enamel organ and in odontoblasts indicates that EMMPRIN takes part in the induction of proteolytic enzymes in the rat tooth germ. The localization of EMMPRIN in membrane rafts provides a basis for further investigations on the role of caveolin-1 in EMMPRIN-mediated signal transduction cascades in ameloblasts.

Ezrin Immunoreactivity Reveals Specific Astrocyte Activation in Cerebral HIV

The actin-binding protein ezrin is associated with cellular shape changes, motility, tumor invasion, and lymphocyte activation. We have earlier shown that ezrin immunoreactivity (IR) is faintly present in normal astrocytes but increased in malignant human astrogliomas. We studied the role of ezrin in astrocyte activation, applying immunostaining on serial paraffin sections from human autopsied brain tissues (51 cases). Cerebral HIV infection was chosen as a model displaying consistent exemplary astrocyte activation. Semiquantitative ezrin-IR was compared with the common glial markers GFAP, ferritin, and HLA-DR in relation to clinical and morphologic criteria of HIV encephalopathy. In all cases with HIV infection, GFAP-, HLA-DR-, and ferritin-IR were elevated in comparison to normal brain tissues. In contrast, high ezrin-IR in HIV infection strictly correlated with additional HIV encephalopathy. HIV encephalopathy with particularly high ezrin-IR was correlated with neuronal apoptosis (TUNEL). Combined ezrin-IR and GFAP-IR thus reveals 2 distinct states of astrocytic activation. Normal ezrin-IR, when paralleled by upregulated GFAP, reflects astroglial activation not associated with neuronal apoptosis. High ezrin-IR indicates specific astrocyte stressors related to cellular damage within the central nervous system. Ezrin-IR might also provide a diagnostic tool for the classification of HIV encephalopathy.

Characteristic distribution of immunoreaction for estrogen receptor alpha in rat ameloblasts

Estrogen has a diverse function, including cell proliferation and differentiation via estrogen receptors (ER), which have been reported to be the case in various tissues in addition to female reproductive organs. A recent immunocytochemical study has reported the expression of ERalpha, a subtype of ER, in rat odontoblasts, suggesting an involvement of estrogen in the differentiation of tooth-forming cells. However, there is no information on the ERalpha immunoexpression in ameloblasts. The present study was therefore undertaken to examine the localization of ERalpha immunoreaction in rat ameloblasts during amelogenesis. A computer-assisted quantitative analysis under a confocal laser scanning microscope was employed to demonstrate the stage-specific localization pattern of ERalpha immunoreaction. Immunohistochemistry of the rat enamel organ revealed ERalpha expression as nuclear localization in ameloblasts, stratum intermedium, stellate reticulum, and papillary layer, in addition to mature and immature odontoblasts. The ratio of immunopositive nuclei to total nuclei (immunopositive ratio) in ameloblasts was high at the apical loop region and gradually declined at the presecretory stage to zero at the secretory stage with statistically significant difference. The ERalpha immunolabeling pattern exhibited a periodic change at the maturation stage proper with constant higher labeling in ruffle-ended ameloblasts than in smooth-ended ameloblasts. The positive ratio was then followed by a statistically significant increase in immunolabeling thereafter. This stage-specific immunolabeling pattern during amelogenesis suggests a possible role of ERalpha in ameloblast proliferation and differentiation.

The expression pattern of hyaluronan synthase during human tooth development

In previous studies, hyaluronan (HA) and its major cell surface receptor CD44 have been suggested to play an important role during tooth development. HA synthases (HASs) are the enzymes that polymerize hyaluronan. Data on the expression pattern of HASs during tooth development is lacking and the aim of the present study was to investigate the localisation of HAS by immunohistochemistry in human tooth germs from different developmental stages. The distribution pattern of HAS in the various tissues of the "bell stage" tooth primordia corresponded to that of hyaluronan in most locations: positive HAS immunoreactivity was observed in the dental lamina cells, inner- and outer-enamel epithelium. On the stellate reticulum cells, moderate HAS signal was observed, similar to the layers of the oral epithelium, where faint HAS immunoreactivity was detected. At the early phase of dental hard tissues mineralization, strong HAS immunoreactivity was detected in the odontoblasts and their processes, as well as in the secretory ameloblasts and their apical processes and also, the pulpal mesenchymal cells. The HAS signals observed in odontoblasts and ameloblasts gradually decreased with age. Our results demonstrate that hyaluronan synthesised locally by different dental cells and these results provide additional indirect support to the suggestion that HA may contribute both to the regulation of tooth morphogenesis and dental hard tissue formation.

Cell-cell and cell-matrix interactions during initial enamel organ histomorphogenesis in the mouse

Relationships between cell-cell/cell-matrix interactions and enamel organ histomorphogenesis were examined by immunostaining and electron microscopy. During the cap-bell transition in the mouse molar, laminin-5 (LN5) disappeared from the basement membrane (BM) associated with the inner dental epithelium (IDE), and nondividing IDE cells from the enamel knot (EK) underwent a tooth-specific segregation in as many subpopulations as cusps develop. In the incisor, the basement membrane (BM) in contact with EK cells showed strong staining for LN5 and integrin alpha 6 beta 4. LN5 seems to provide stable adhesion, while its proteolytic processing might facilitate cell segregation. In both teeth, immunostaining for antigens associated with desmosomes or adherens junctions was similar for EK cells and neighboring IDE cells. Outside the EK, IDE cell-BM interactions changed locally during the initial molar cusp delimitation and on the labial part of the incisor cervical loop. Conversely, cell-cell junctions stabilized the anterior part of the incisor during completion of morphogenesis. Time and space regulation of cell-matrix and cell-cell interactions might thus play complementary roles in allowing plasticity during tooth morphogenesis and stabilization at later stages of epithelial histogenesis.

The distribution pattern of the hyaluronan receptor CD44 during human tooth development

The aim was to investigate the expression pattern of the major cell-surface hyaluronan receptor CD44, as there are no existing data on its presence or absence in human dental structures at different developmental stages. Immunohistochemical localization of CD44 was studied using a monoclonal antibody, H3, that specifically recognizes an epitope in the common backbone of all CD44 isoforms. The dental lamina displayed a strong CD44 signal; the external enamel epithelium was negative. In the coronal region of the tooth germ the presecretory ameloblasts showed an intense reaction whereas the less differentiated inner enamel epithelial cells showed no signal at the cervical loop where they meet the external enamel epithelium. In the stellate reticulum a moderate reaction was detected. The secretory ameloblasts and the stratum intermedium showed a strong cell-surface CD44 signal. A strong signal was also observed on the odontoblasts and their processes. In the pulp, close to the odontoblastic layer, weak labelling was seen in the walls of capillary vessels. The distribution of CD44 in the human tooth germ corresponds to that of hyaluronan in most locations, suggesting that during tooth development this transmembrane protein plays an important part in hyaluronan-mediated events.