BMP4 signaling mediates Zeb family in developing mouse tooth

Regulation of osteoclast differentiation and inflammatory signaling by TCF8 in periodontitis

OBJECTIVES

The aim of this study was to explore the potential role of zinc-finger homeodomain transcription factor (TCF8) in osteoclastogenesis and inflammation during periodontitis.

MATERIALS AND METHODS

Rats with periodontitis were induced via Porphyromonas gingivalis-lipopolysaccharide (Pg-LPS) injection. The recombinant lentivirus delivering short hairpin RNA (shRNA) against TCF8 was used to downregulate TCF8 in vivo. Alveolar bone loss in rats was determined by micro-computed tomography (Micro-CT). Typical pathological changes, periodontal tissue inflammation, and osteoclastogenesis were evaluated via histological analyses. The RAW264.7-derived osteoclasts were induced by RANKL stimulation. TCF8 downregulation in vitro was achieved by lentivirus infection. The osteoclast differentiation and inflammatory signaling in RANKL-induced cells were measured via immunofluorescence methods and molecular biology approaches.

RESULTS

Porphyromonas gingivalis-lipopolysaccharide induced rats exhibited overexpressed TCF8 in their periodontal tissues, while TCF8 knockdown attenuated the bone loss, tissue inflammation, and osteoclastogenesis in LPS-induced rats. Besides, TCF8 silencing inhibited RANKL-induced osteoclast differentiation in RAW264.7 cells, as evidenced by the reduced numbers of TRAP-positive osteoclasts, less formation of F-actin rings, and downregulated expressions of osteoclast-specific markers. It also exerted an inhibitory effect on the NF-κB signaling in RANKL-induced cells via blocking NF-κB p65 phosphorylation and nuclear translocation.

CONCLUSIONS

TCF8 silencing inhibited alveolar bone loss, osteoclast differentiation, and inflammation in periodontitis.

ZEB2, the Mowat-Wilson Syndrome Transcription Factor: Confirmations, Novel Functions, and Continuing Surprises

After its publication in 1999 as a DNA-binding and SMAD-binding transcription factor (TF) that co-determines cell fate in amphibian embryos, ZEB2 was from 2003 studied by embryologists mainly by documenting the consequences of conditional, cell-type specific Zeb2 knockout (cKO) in mice. In between, it was further identified as causal gene causing Mowat-Wilson Syndrome (MOWS) and novel regulator of epithelial-mesenchymal transition (EMT). ZEB2's functions and action mechanisms in mouse embryos were first addressed in its main sites of expression, with focus on those that helped to explain neurodevelopmental and neural crest defects seen in MOWS patients. By doing so, ZEB2 was identified in the forebrain as the first TF that determined timing of neuro-/gliogenesis, and thereby also the extent of different layers of the cortex, in a cell non-autonomous fashion, i.e., by its cell-intrinsic control within neurons of neuron-to-progenitor paracrine signaling. Transcriptomics-based phenotyping of Zeb2 mutant mouse cells have identified large sets of intact-ZEB2 dependent genes, and the cKO approaches also moved to post-natal brain development and diverse other systems in adult mice, including hematopoiesis and various cell types of the immune system. These new studies start to highlight the important adult roles of ZEB2 in cell-cell communication, including after challenge, e.g., in the infarcted heart and fibrotic liver. Such studies may further evolve towards those documenting the roles of ZEB2 in cell-based repair of injured tissue and organs, downstream of actions of diverse growth factors, which recapitulate developmental signaling principles in the injured sites. Evident questions are about ZEB2's direct target genes, its various partners, and ZEB2 as a candidate modifier gene, e.g., in other (neuro)developmental disorders, but also the accurate transcriptional and epigenetic regulation of its mRNA expression sites and levels. Other questions start to address ZEB2's function as a niche-controlling regulatory TF of also other cell types, in part by its modulation of growth factor responses (e.g., TGFβ/BMP, Wnt, Notch). Furthermore, growing numbers of mapped missense as well as protein non-coding mutations in MOWS patients are becoming available and inspire the design of new animal model and pluripotent stem cell-based systems. This review attempts to summarize in detail, albeit without discussing ZEB2's role in cancer, hematopoiesis, and its emerging roles in the immune system, how intense ZEB2 research has arrived at this exciting intersection.

Epigenetic modification cooperates with Zeb1 transcription factor to regulate Bmp4 to promote chicken PGCs formation

BMP4 is the critical gene of primordial germ cell formation in mammal, however, the mechanism of PGCs formation in chicken still unknown. In this research, we compared the evolution relationship of different species. Although the protein sequence is highly conservative between mouse, human and chicken, promotors vary among avian and mammal species. Therefore, it is easily to predict that there would be different regulation mechanism of Bmp4 expression in chicken. Here, we elucidate the function of chicken Bmp4 during PGCs formation. In vivo, Bmp4 can promote PGCs development and migration, and increase the expression of key genes (Cvh, c-kit, cxcr4, etc.). Whereas, the expression of these genes will decrease after knocking out Bmp4. After over-expression and knockout Bmp4 in vitro, we found that overexpression of Bmp4 could promote the formation of embryoid bodies (EB) and up-regulate the key genes of PGCs formation and migration, while knockout Bmp4 could inhibit the formation of embryoid bodies and decrease the expression of related genes. Flow and indirect immunofluorescence also indicated the same result. These all results proved that chicken Bmp4 could also promote the formation of PGCs. Furthermore, dual-luciferase activity detection showed that the promotor activity of Bmp4 was positively regulated by transcription factor Zeb1. Overexpression of Zeb1 can also increase the mRNA and protein expression of Bmp4. At the same time, DNA methylation inhibited Bmp4 transcription and histone methylation was able to promote its transcription. In conclusion, this study established that chicken Bmp4 can promote the formation of chicken PGCs. This gene is regulated by DNA, histone methylation and transcription factor Zeb1. These results lay a theoretical foundation for exploring the function and molecular mechanism of Bmp4 in the process of PGCs formation.

Zeb1 Promotes Odontoblast Differentiation in a Stage-Dependent Manner

A comprehensive study of odontoblastic differentiation is essential to understand the process of tooth development and to achieve the ability of tooth regeneration in the future. Zinc finger E-box-binding homeobox 1 (Zeb1) is a transcription factor expressed in various neural crest-derived tissues, including the mesenchyme of the tooth germ. However, its role in odontoblastic differentiation remains unknown. In this study, we found the expression of Zeb1 gradually increased during odontoblast differentiation in vivo, as well as during induced differentiation of cultured primary murine dental papilla cells (mDPCs) in vitro. In addition, the differentiation of mDPCs was repressed in Zeb1-silenced cells. We used RNA sequencing (RNA-seq) to identify the transcriptome-wide targets of Zeb1 and used assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) to explore the direct targets of Zeb1 in both the early stage (embryonic day 16.5; E16.5) and the late stage (postnatal day 0; PN0) of tooth development. We identified the motifs of transcription factors enriched in Zeb1-dependent accessible chromatin regions and observed that only in the early stage of mDPCs could Zeb1 significantly change the accessibility of chromatin regions. In vivo and in vitro experiments confirmed that silencing of Zeb1 at E16.5 inhibited dentinogenesis. Analysis of RNA-seq and ATAC-seq resulted in the identification of Runx2, a gene directly regulated by Zeb1 during early odontoblast differentiation. Zeb1 enhances the expression of Runx2 by binding to its cis-elements, and ZEB1 interacts with RUNX2. In the late stage of tooth development, we found that ZEB1 could directly bind to and increase the enhancer activity of an element upstream of Dspp and promote dentinogenesis. In this study, for the first time, we revealed that ZEB1 promoted odontoblast differentiation in the early stage by altering chromatin accessibility of cis-elements near genes such as Runx2, while in the late stage, it directly enhanced Dspp transcription, thereby performing a dual role.

Functional Diversification of SRSF Protein Kinase to Control Ubiquitin-Dependent Neurodevelopmental Signaling

Conserved protein kinases with core cellular functions have been frequently redeployed during metazoan evolution to regulate specialized developmental processes. The Ser/Arg (SR)-rich splicing factor (SRSF) protein kinase (SRPK), which is implicated in splicing regulation, is one such conserved eukaryotic kinase. Surprisingly, we show that SRPK has acquired the capacity to control a neurodevelopmental ubiquitin signaling pathway. In mammalian embryonic stem cells and cultured neurons, SRPK phosphorylates Ser-Arg motifs in RNF12/RLIM, a key developmental E3 ubiquitin ligase that is mutated in an intellectual disability syndrome. Processive phosphorylation by SRPK stimulates RNF12-dependent ubiquitylation of nuclear transcription factor substrates, thereby acting to restrain a neural gene expression program that is aberrantly expressed in intellectual disability. SRPK family genes are also mutated in intellectual disability disorders, and patient-derived SRPK point mutations impair RNF12 phosphorylation. Our data reveal unappreciated functional diversification of SRPK to regulate ubiquitin signaling that ensures correct regulation of neurodevelopmental gene expression.

Bone Cell Activity in Clinical Prostate Cancer Bone Metastasis and Its Inverse Relation to Tumor Cell Androgen Receptor Activity

Advanced prostate cancer frequently metastasizes to bone and induces a mixed osteoblastic/osteolytic bone response. Standard treatment for metastatic prostate cancer is androgen-deprivation therapy (ADT) that also affects bone biology. Treatment options for patients relapsing after ADT are limited, particularly in cases where castration-resistance does not depend on androgen receptor (AR) activity. Patients with non-AR driven metastases may, however, benefit from therapies targeting the tumor microenvironment. Therefore, the current study specifically investigated bone cell activity in clinical bone metastases in relation to tumor cell AR activity, in order to gain novel insight into biological heterogeneities of possible importance for patient stratification into bone-targeting therapies. Metastasis tissue obtained from treatment-naïve (n = 11) and castration-resistant (n = 28) patients was characterized using whole-genome expression analysis followed by multivariate modeling, functional enrichment analysis, and histological evaluation. Bone cell activity was analyzed by measuring expression levels of predefined marker genes representing osteoclasts (ACP5, CTSK, MMP9), osteoblasts (ALPL, BGLAP, RUNX2) and osteocytes (SOST). Principal component analysis indicated a positive correlation between osteoblast and osteoclast activity and a high variability in bone cell activity between different metastases. Immunohistochemistry verified a positive correlation between runt-related transcription factor 2 (RUNX2) positive osteoblasts and tartrate-resistant acid phosphatase (TRAP, encoded by ACP5) positive osteoclasts lining the metastatic bone surface. No difference in bone cell activity was seen between treatment-naïve and castration-resistant patients. Importantly, bone cell activity was inversely correlated to tumor cell AR activity (measured as AR, FOXA1, HOXB13, KLK2, KLK3, NKX3-1, STEAP2, and TMPRSS2 expression) and to patient serum prostate-specific antigen (PSA) levels. Functional enrichment analysis indicated high bone morphogenetic protein (BMP) signaling in metastases with high bone cell activity and low tumor cell AR activity. This was confirmed by BMP4 immunoreactivity in tumor cells of metastases with ongoing bone formation, as determined by histological evaluation of van Gieson-stained sections. In conclusion, the inverse relation observed between bone cell activity and tumor cell AR activity in prostate cancer bone metastasis may be of importance for patient response to AR and/or bone targeting therapies, but needs to be evaluated in clinical settings in relation to serum markers for bone remodeling, radiography and patient response to therapy. The importance of BMP signaling in the development of sclerotic metastasis lesions deserves further exploration.

BMP7 and EREG Contribute to the Inductive Potential of Dental Mesenchyme

Odontogenesis is accomplished by reciprocal signaling between the epithelial and mesenchymal compartments. It is generally accepted that the inductive mesenchyme is capable of inducing the odontogenic commitment of both dental and non-dental epithelial cells. However, the duration of this signal in the developing dental mesenchyme and whether adult dental pulp tissue maintains its inductive capability remain unclear. This study investigated the contribution of growth factors to regulating the inductive potential of the dental mesenchyme. Human oral epithelial cells (OEs) were co-cultured with either human dental mesenchymal/papilla cells (FDPCs) or human dental pulp cells (ADPCs) under 2-dimensional or 3-dimensional conditions. Odontogenic-associated genes and proteins were detected by qPCR and immunofluorescence, respectively, and significant differences were observed between the two co-culture systems. The BMP7 and EREG expression levels in FDPCs were significantly higher than in ADPCs, as indicated by human growth factor PCR arrays and immunofluorescence analyses. OEs co-cultured with ADPCs supplemented with BMP7 and EREG expressed ameloblastic differentiation genes. Our study suggests that BMP7 and EREG expression in late bell-stage human dental papilla contributes to the inductive potential of dental mesenchyme. Furthermore, adult dental pulp cells supplemented with these two growth factors re-established the inductive potential of postnatal dental pulp tissue.

Upregulation of gingival tissue miR-200b in obese periodontitis subjects

Increased local immune and inflammatory responses in obese individuals with periodontitis may explain the aggressive clinical presentation and altered treatment response when compared to that of normal weight subjects. Our goal was to identify any differences in microRNA (miRNA) expression profiles of gingival tissue in periodontitis when obesity is present, which may suggest novel molecular pathways that this miRNA network may affect. Total RNA was extracted from gingival tissue biopsies collected from normal weight and obese individuals with periodontitis; miRNA expression profiling was performed with Affymetrix GeneChip miRNA 3.0 arrays; and results were validated with quantitative reverse transcription polymerase chain reaction (qRT-PCR). In silico identification of previously confirmed miRNA gene targets was conducted through miRTarBase and miRWalk databases, and pathway enrichment analysis identified enriched miRNA gene sets. Expression of selected genes in the same biopsy samples was tested with qRT-PCR. The gingival tissue miRNA profile of obese patients, compared to that of normal weight patients, showed 13 upregulated and 22 downregulated miRNAs, among which miR-200b was validated by qRT-PCR to be significantly increased in obesity. Functional analysis of 51 experimentally validated miR-200b gene targets identified enrichment of genes involved in cell motility, differentiation, DNA binding, response to stimulus, and vasculature development pathways not previously identified in the obesity-specific disease profile. Furthermore, the expression of the miR-200b gene targets ZEB1/2, GATA2, and KDR was confirmed by qRT-PCR as being lower in obese patients with periodontitis versus normal weight patients, suggesting a role of miR-200b in regulation of a set of gene targets and biological pathways relevant to wound healing and angiogenesis. Functional studies to explore the role of miR-200b in the above processes may offer new insights on putative therapeutic targets for this group of patients.

Comparison of gene expression between mandibular and iliac bone-derived cells

OBJECTIVES

The purpose of this study is to investigate the differences in gene expression between the human mandibular and iliac bone-derived cells (BCs) for better understanding of the site-specific characteristics of bones.

METHODS

Primary cells were obtained from mandibular and iliac bones from six healthy, elderly donors. To investigate site-specific differences, gene expression profile of mandibular and iliac BC from the same donors were compared via cDNA microarray analysis.

RESULTS

A comparison of the gene expression profiles revealed that 82 genes were significantly upregulated and 66 genes were downregulated with 1.5 fold or greater in mandibular versus iliac BCs. The most significantly differentially regulated genes were associated with skeletal system development or morphogenesis (SIX1, MSX1, MSX2, HAND2, PRRX1, OSR2, HOX gene family, PITX2). Especially, upregulated genes in mandibular BC were related with tooth morphogenesis, originated from the ectomesenchyme. Microarray analysis revealed that Msx1 was 2.03-fold and Msx2 was 1.99-fold upregulated in mandibular versus iliac BCs (both p < 0.01). Furthermore, in mandibular BCs, all members of the HOX gene family that were analyzed were downregulated (p < 0.01) and osteopontin was also downregulated by 2.84-fold (p < 0.01).

CONCLUSIONS

Site-specific differences between jaw and long bones can be explained by the differences in gene expression patterns. Our results suggest that bone cell-derived cells maintain the genetic characteristics of their embryological origin.

CLINICAL RELEVANCE

This study revealed fundamental differences in gene expression between the mandibular and iliac bone in humans. These differences could be important for understanding jaw bone-specific development of bisphosphonate-related osteonecrosis of the jaw.

An atypical canonical bone morphogenetic protein (BMP) signaling pathway regulates Msh homeobox 1 (Msx1) expression during odontogenesis

Bone morphogenetic protein (BMP) signaling plays an essential role in early tooth development, evidenced by disruption of BMP signaling leading to an early arrested tooth development. Despite being a central mediator of BMP canonical signaling pathway, inactivation of Smad4 in dental mesenchyme does not result in early developmental defects. In the current study, we investigated the mechanism of receptor-activated Smads (R-Smads) and Smad4 in the regulation of the odontogenic gene Msx1 expression in the dental mesenchyme. We showed that the canonical BMP signaling is not operating in the early developing tooth, as assessed by failed activation of the BRE-Gal transgenic allele and the absence of phospho-(p)Smad1/5/8-Smad4 complexes. The absence of pSmad1/5/8-Smad4 complex appeared to be the consequence of saturation of Smad4 by pSmad2/3 in the dental mesenchyme as knockdown of Smad2/3 or overexpression of Smad4 led to the formation of pSmad1/5/8-Smad4 complexes and activation of canonical BMP signaling in dental mesenchymal cells. We showed that Smad1/5 but not Smad4 are required for BMP-induced expression of Msx1 in dental mesenchymal cells. We further presented evidence that in the absence of Smad4, BMPs are still able to induce pSmad1/5/8 nuclear translocation and their binding to the Msx1 promoter directly in dental mesenchymal cells. Our results demonstrate the functional operation of an atypical canonical BMP signaling (Smad4-independent and Smad1/5/8-dependent) pathway in the dental mesenchyme during early odontogenesis, which may have general implication in the development of other organs.

Signaling pathways bridging fate determination of neural crest cells to glial lineages in the developing peripheral nervous system

Fate determination of neural crest cells is an essential step for the development of different crest cell derivatives. Peripheral glia development is marked by the choice of the neural crest cells to differentiate along glial lineages. The molecular mechanism underlying fate acquisition is poorly understood. However, recent advances have identified different transcription factors and genes required for the complex instructive signaling process that comprise both local environmental and cell intrinsic cues. Among others, at least the roles of Sox10, Notch, and neuregulin 1 have been documented in both in vivo and in vitro models. Cooperative interactions of such factors appear to be necessary for the switch from multipotent neural crest cells to glial lineage precursors in the peripheral nervous system. This review summarizes recent advances in the understanding of fate determination of neural crest cells into different glia subtypes, together with the potential implications in regenerative medicine.

The Histochemistry and Cell Biology compendium: a review of 2012

The year 2012 was another exciting year for Histochemistry and Cell Biology. Innovations in immunohistochemical techniques and microscopy-based imaging have provided the means for advances in the field of cell biology. Over 130 manuscripts were published in the journal during 2012, representing methodological advancements, pathobiology of disease, and cell and tissue biology. This annual review of the manuscripts published in the previous year in Histochemistry and Cell Biology serves as an abbreviated reference for the readership to quickly peruse and discern trends in the field over the past year. The review has been broadly divided into multiple sections encompassing topics such as method advancements, subcellular components, extracellular matrix, and organ systems. We hope that the creation of this subdivision will serve to guide the reader to a specific topic of interest, while simultaneously providing a concise and easily accessible encapsulation of other topics in the broad area of Histochemistry and Cell Biology.