TIEG1/KLF10 modulates Runx2 expression and activity in osteoblasts

The kruppel-like factor (KLF) family, diseases, and physiological events

The Kruppel-Like Factor family of regulatory proteins, which has 18 members, is transcription factors. This family contains zinc finger proteins, regulates the activation and suppression of transcription, and binds to DNA, RNA, and proteins. Klfs related to the immune system are Klf1, Klf2, Klf3, Klf4, Klf6, and Klf14. Klfs related to adipose tissue development and/or glucose metabolism are Klf3, Klf7, Klf9, Klf10, Klf11, Klf14, Klf15, and Klf16. Klfs related to cancer are Klf3, Klf4, Klf5, Klf6, Klf7, Klf8, Klf9, Klf10, Klf11, Klf12, Klf13, Klf14, Klf16, and Klf17. Klfs related to the cardiovascular system are Klf4, Klf5, Klf10, Klf13, Klf14, and Klf15. Klfs related to the nervous system are Klf4, Klf7, Klf8, and Klf9. Klfs are associated with diseases such as carcinogenesis, oxidative stress, diabetes, liver fibrosis, thalassemia, and the metabolic syndrome. The aim of this review is to provide information about the relationship of Klfs with some diseases and physiological events and to guide future studies.

Exploration of key factors in Gingival Crevicular fluids from patients undergoing Periodontally Accelerated Osteogenic Orthodontics (PAOO) using proteome analysis

BACKGROUND

The aims of this study are to explore protein changes in gingival crevicular fluid at different time points after PAOO by proteomics method and to select significant bone metabolization-related biomarkers.

METHODS

This study included 10 adult patients experiencing PAOO. After orthodontic alignment and leveling, the maxillary anterior teeth were treated with PAOO, which is classified as the experimental area. The traditional orthodontic treatment was performed in the mandibular dentition as the control. Gingival crevicular fluid samples were collected at the following time points: the day before the PAOO (T1) and at 1 week, 2 weeks, 1 month, 2 months and 6 months after PAOO (T2, T3, T4, T5 and T6, respectively). The label-free quantitative proteomic assay was used to evaluate the gingival crevicular fluid in PAOO and control areas at time point T1, T2, and T4. Bioinformatics analysis was carried out to categorize proteins based on biological processes, cellular component and molecular function, which is in compliance with gene ontology (GO) standards. The changes of proteins were confirmed by ELISA.

RESULTS

A total of 134 proteins were selected by keywords (Osteoblast markers, Osteoclast markers, Osteoclastogenesis regulating genes and inflammatory marker). 33 of them were statistically different between groups, and 12 were related to bone metabolism. 5 proteins selected by label-free quantitative proteomics were KLF10, SYT7, APOA1, FBN1 and NOTCH1. KLF10 decreased after PAOO, hitting a trough at T4, and then leveled off. SYT7 increased after PAOO, reaching a peak at T3, and then stabilized until T6. APOA1 ascended to a peak at T4 after PAOO, and then remained stable until T6. The FBN1 rose after PAOO, reaching a peak at T4, and then went down slowly. NOTCH1 ascended rapidly in the first two weeks after PAOO and continued its slow growth trend.

CONCLUSION

In this study, protein changes in gingival crevicular fluid were detected by proteomics method, and significant bone metabolization-related proteins were selected. It is speculated that APOA1, FBN1, NOTCH1, SYT7 and KLF10 played key roles in regulating bone metabolic balance and in reversible osteopenia after PAOO, which might be involved in the accelerated tooth movement.

TRIAL REGISTRATION

This study was registered in the Chinese Clinical Trial Registry (Clinical trial registration number: ChiCTR-ONRC-13,004,129) (26/04/2013).

G-protein coupled receptor 5C (GPRC5C) is required for osteoblast differentiation and responds to EZH2 inhibition and multiple osteogenic signals

Osteoblast differentiation is epigenetically suppressed by the H3K27 methyltransferase EZH2, and induced by the morphogen BMP2 and transcription factor RUNX2. These factors also regulate distinct G protein coupled receptors (GPRCs; e.g., PTH1R, GPR30/GPER1). Because GPRCs transduce many physiological stimuli, we examined whether BMP2 or EZH2 inhibition (i.e., GSK126) regulates other GPRC genes in osteoblasts. RNA-seq screening of >400 mouse GPRC-related genes showed that many GPRCs are downregulated during osteogenic differentiation. The orphan receptor GPRC5C, along with a small subset of other GPRCs, is induced by BMP2 or GSK126 during Vitamin C dependent osteoblast differentiation, but not by all-trans retinoic acid. ChIP-seq analysis revealed that GSK126 reduces H3K27me3 levels at the GPRC5C gene locus in differentiating MC3T3-E1 osteoblasts, consistent with enhanced GPRC5C mRNA expression. Loss of function analyses revealed that shRNA-mediated depletion of GPRC5C decreases expression of bone markers (e.g., BGLAP and IBSP) and mineral deposition in response to BMP2 or GSK126. GPRC5C mRNA was found to be reduced in the osteopenic bones of KLF10 null mice which have compromised BMP2 signaling. GPRC5C mRNA is induced by the bone-anabolic activity of 17β-estradiol in trabecular but not cortical bone following ovariectomy. Collectively, these findings suggest that GPRC5C protein is a key node in a pro-osteogenic axis that is normally suppressed by EZH2-mediated H3K27me3 marks and induced during osteoblast differentiation by GSK126, BMP2, and/or 17β-estradiol. Because GPRC5C protein is an understudied orphan receptor required for osteoblast differentiation, identification of ligands that induce GPRC5C signaling may support therapeutic strategies to mitigate bone-related disorders.

Krüppel-like Factor 10 as a Prognostic and Predictive Biomarker of Radiotherapy in Pancreatic Adenocarcinoma

The prognosis of pancreatic adenocarcinoma (PDAC) remains poor, with a 5-year survival rate of 12%. Although radiotherapy is effective for the locoregional control of PDAC, it does not have survival benefits compared with systemic chemotherapy. Most patients with localized PDAC develop distant metastasis shortly after diagnosis. Upfront chemotherapy has been suggested so that patients with localized PDAC with early distant metastasis do not have to undergo radical local therapy. Several potential tissue markers have been identified for selecting patients who may benefit from local radiotherapy, thereby prolonging their survival. This review summarizes these biomarkers including SMAD4, which is significantly associated with PDAC failure patterns and survival. In particular, Krüppel-like factor 10 (KLF10) is an early response transcription factor of transforming growth factor (TGF)-β. Unlike TGF-β in advanced cancers, KLF10 loss in two-thirds of patients with PDAC was associated with rapid distant metastasis and radioresistance; thus, KLF10 can serve as a predictive and therapeutic marker for PDAC. For patients with resectable PDAC, a combination of KLF10 and SMAD4 expression in tumor tissues may help select those who may benefit the most from additional radiotherapy. Future trials should consider upfront systemic therapy or include molecular biomarker-enriched patients without early distant metastasis.

Kruppel-like Factors in Skeletal Physiology and Pathologies

Kruppel-like factors (KLFs) belong to a large group of zinc finger-containing transcription factors with amino acid sequences resembling the Drosophila gap gene Krüppel. Since the first report of molecular cloning of the KLF family gene, the number of KLFs has increased rapidly. Currently, 17 murine and human KLFs are known to play crucial roles in the regulation of transcription, cell proliferation, cellular differentiation, stem cell maintenance, and tissue and organ pathogenesis. Recent evidence has shown that many KLF family molecules affect skeletal cells and regulate their differentiation and function. This review summarizes the current understanding of the unique roles of each KLF in skeletal cells during normal development and skeletal pathologies.

Krüppel-like factors in bone biology

The krüppel-like factor (KLF) family is a group of zinc finger transcription factors and contributes to different cellular processes such as differentiation, proliferation, migration, and apoptosis. While different studies show the roles of this family in skeletal development-specifically in chondrocyte and osteocyte development and bone homeostasis-there are few reviews summarizing their importance. To fill this gap, this review discusses current knowledge on different functions of the KLF family during skeletal development, including their roles in stem cell maintenance and differentiation, cell apoptosis, and cell cycle. To understand the importance of the KLF family, we also review genotype-phenotype correlations in different animal models. We also discuss how KLF proteins function through different signaling pathways and display their paramount importance in skeletal development. To highlight their roles in cartilage- or bone-related cells, we also use single-cell RNA sequencing publicly available data on mouse hindlimb. We also challenge our knowledge of how the KLF family is epigenetically regulated-e.g., using DNA methylation, histone modifications, and noncoding RNAs-during chondrocyte and osteocyte development.

MiR-133a delivery to osteoblasts ameliorates mechanical unloading-triggered osteopenia progression in vitro and in vivo

Mechanical unloading-induced bone loss is a clinical challenge, and deep understanding for this disease is necessary for developing novel and effective therapies. MicroRNAs (miRNAs) are small non-coding RNAs, and involved in bone remodeling. In the study, we attempted to explore the potential of miR-133a in regulating osteoblast activation and its anti-osteopenia function both in vitro and in vivo. Our in vitro studies at first showed that miR-133a could significantly promote the expression of osteocalcin (OCN), Collagen I, alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2) and osterix (Osx), promoting the activation and mineralization of osteoblasts. Then, hindlimb unloading (HU)-challenged mice were established with or without intravenous injection of agomir-miR-133a using an osteoblast-targeting delivery system. We found that miR-133a in osteoblasts significantly alleviated the bone loss, microstructural, and biomechanical property in mice with mechanical unloading, contributing to osteopenia alleviation. Furthermore, both in vitro and in vivo experiments showed that miR-133a could restrain osteoclastogenesis via tartrate-resistant acid phosphatase (TRAP) staining. In conclusion, our results suggested that miR-133a may be a promising factor in mediating the occurrence and progression of osteopenia caused by mechanical unloading, and thus targeting miR-133a could be considered as an effective therapeutic strategy for the suppression of pathological osteopenia.

Topological Analysis of Regulatory Networks Reveals Functionally Key Genes and miRNAs Involved in the Differentiation of Mesenchymal Stem Cells

Background

The details of molecular mechanisms underlying the differentiation of Mesenchymal Stem Cells (MSCs) into specific lineages are not well understood.

Objectives

We aimed to construct the interactome network and topology analysis of bone marrow mesenchymal stem cell of CAGE data. Applying the enrichment results, we wanted to introduce the common genes and hub-microRNA and hub-genes of these giant network.

Materials and Methods

In this study, we constructed gene regulatory networks for each non-mesenchymal cell lineage according to their gene expression profiles obtained from FANTOM5 database. The putative interactions of TF-gene and protein-protein were determined using TRED, STRING, HPRD and GeneMANIA servers. In parallel, a regulatory network including corresponding miRNAs and total differentially expressed genes (DEGs) was constructed for each cell lineage.

Results

The results indicated that analysis of networks' topology can significantly distinguish the hub regulatory genes and miRNAs involved in the differentiation of MSCs. The functional annotation of identified hub genes and miRNAs revealed that several signal transduction pathways i.e. AKT, WNT and TGFβ and cell proliferation related pathways play a pivotal role in the regulation of MSCs differentiation. We also classified cell lineages into two groups based on their predicted miRNA profiles.

Conclusions

In conclusion, we found a number of hub genes and miRNAs which seem to have key regulatory functions during differentiation of MSCs. Our results also introduce a number of new regulatory genes and miRNAs which can be considered as the new candidates for genetic manipulation of MSCs in vitro.

KLF10 is a modulatory factor of chondrocyte hypertrophy in developing skeleton

To define the functional role of Krüppel-like factor (KLF) 10 as a modulator of chondrocyte hypertrophy in developing skeleton, the developmental features in the long bone of KLF10 knockout (KO) mice were investigated and the mesenchymal stem cells (MSCs) from KLF10 KO mice were characterized regarding chondrogenesis and osteogenesis. Delayed long bone growth and delayed formation of primary ossification center were observed in an early embryonic stage in KLF10 KO mouse along with very low Indian hedgehog expression in epiphyseal plate. While the chondrogenic potential of mouse MSCs from KLF10 KO mice appeared normal or slight decreased, hypertrophy and osteogenesis were extensively suppressed. These findings suggest that KLF10 is a mediator of chondrocyte hypertrophy in developing skeleton, and that suppression of KLF10 may be employed as a new strategy for preventing hypertrophy in cartilage regeneration using MSCs.

Novel role of Tieg1 in muscle metabolism and mitochondrial oxidative capacities

AIM

Tieg1 is involved in multiple signalling pathways, human diseases, and is highly expressed in muscle where its functions are poorly understood.

METHODS

We have utilized Tieg1 knockout (KO) mice to identify novel and important roles for this transcription factor in regulating muscle ultrastructure, metabolism and mitochondrial functions in the soleus and extensor digitorum longus (EDL) muscles. RNA sequencing, immunoblotting, transmission electron microscopy, MRI, NMR, histochemical and mitochondrial function assays were performed.

RESULTS

Loss of Tieg1 expression resulted in altered sarcomere organization and a significant decrease in mitochondrial number. Histochemical analyses demonstrated an absence of succinate dehydrogenase staining and a decrease in cytochrome c oxidase (COX) enzyme activity in KO soleus with similar, but diminished, effects in the EDL. Decreased complex I, COX and citrate synthase (CS) activities were detected in the soleus muscle of KO mice indicating altered mitochondrial function. Complex I activity was also diminished in KO EDL. Significant decreases in CS and respiratory chain complex activities were identified in KO soleus. ¹ H-NMR spectra revealed no significant metabolic difference between wild-type and KO muscles. However, ³¹ P spectra revealed a significant decrease in phosphocreatine and ATPγ. Altered expression of 279 genes, many of which play roles in mitochondrial and muscle function, were identified in KO soleus muscle. Ultimately, all of these changes resulted in an exercise intolerance phenotype in Tieg1 KO mice.

CONCLUSION

Our findings have implicated novel roles for Tieg1 in muscle including regulation of gene expression, metabolic activity and organization of tissue ultrastructure. This muscle phenotype resembles diseases associated with exercise intolerance and myopathies of unknown consequence.

Sclerostin antibody treatment rescues the osteopenic bone phenotype of TGFβ inducible early gene-1 knockout female mice

Deletion of TGFβ inducible early gene-1 (TIEG) in mice results in an osteopenic phenotype that exists only in female animals. Molecular analyses on female TIEG knockout (KO) mouse bones identified increased expression of sclerostin, an effect that was confirmed at the protein level in serum. Sclerostin antibody (Scl-Ab) therapy has been shown to elicit bone beneficial effects in multiple animal model systems and human clinical trials. For these reasons, we hypothesized that Scl-Ab therapy would reverse the low bone mass phenotype of female TIEG KO mice. In this study, wildtype (WT) and TIEG KO female mice were randomized to either vehicle control (Veh, n = 12/group) or Scl-Ab therapy (10 mg/kg, 1×/wk, s.c.; n = 12/group) and treated for 6 weeks. Following treatment, bone imaging analyses revealed that Scl-Ab therapy significantly increased cancellous and cortical bone in the femur of both WT and TIEG KO mice. Similar effects also occurred in the vertebra of both WT and TIEG KO animals. Additionally, histomorphometric analyses revealed that Scl-Ab therapy resulted in increased osteoblast perimeter/bone perimeter in both WT and TIEG KO animals, with a concomitant increase in P1NP, a serum marker of bone formation. In contrast, osteoclast perimeter/bone perimeter and CTX-1 serum levels were unaffected by Scl-Ab therapy, irrespective of mouse genotype. Overall, our findings demonstrate that Scl-Ab therapy elicits potent bone-forming effects in both WT and TIEG KO mice and effectively increases bone mass in female TIEG KO mice.

Osteoporosis genome-wide association study variant c.3781 C>A is regulated by a novel anti-osteogenic factor miR-345-5p

Upstream transcription factor family member 3 (USF3) c.3781C>A (rs1026364) in the 3'-untranslated region (3'-UTR) has been firmly associated with bone mineral density (BMD) in genome-wide association study (GWAS). However, the molecular mechanism by which it influences BMD and osteoporosis is unknown. Bioinformatics analyses suggested that the risk c.3781A allele creates a target site for hsa-miR-345-5p binding. Luciferase assay validated that the c.3781A allele displayed significantly lower luciferase activities than the c.3781C allele in the human osteoblast cell line hFOB1.19, osteosarcoma cell lines U-2OS and Saos-2, and embryonic kidney cell line 293T. Furthermore, hsa-miR-345-5p regulated USF3 expression on both messenger RNA and protein levels in hFOB1.19 and U937 cells with heterozygous A/C genotype. Transfection of hsa-miR-345-5p antagomiR in heterozygous hFOB1.19 cells significantly increased the expression of osteogenic marker genes RUNX2, OSTERIX, COL1A1, ALP, OPN, OCN, and alkaline phosphatase activity and matrix mineralization level. Importantly, we found that hsa-miR-345-5p also inhibits osteoblast maturation in cell lines U-2OS with hsa-miR-345-5p nonbinding C/C genotype by targeting RUNX3 and SMAD1. Our findings uncovered a novel pathogenetic mechanism of osteoporosis by GWAS variant c.3781C>A-mediated disruption of hsa-miR-345-5p binding at the 3'-UTR of USF3 and the functional role of hsa-miR-345-5p in osteogenic differentiation.

miR-892b Inhibits Hypertrophy by Targeting KLF10 in the Chondrogenesis of Mesenchymal Stem Cells

We investigated the functional role of miR-892b as a novel inhibitor of chondrocyte hypertrophy during TGF-β-mediated chondrogenesis of human mesenchymal stem cells (hMSCs). The expression of miR-892b during TGF-β-mediated chondrogenesis of hMSCs and the effects of miR-892b overexpression on chondrogenic and hypertrophic marker genes in the chondrogenesis of hMSCs were investigated. Targets of miR-892b were identified and verified by overexpression of synthetic miRNA mimics and luciferase assays. Cross-talk between Kruppel-like factor 10 (KLF10) and Indian hedgehog (Ihh) was investigated using KLF10 knockdown (KD). miR-892b enhanced chondrogenic makers and suppressed hypertrophy in hMSC chondrogenesis, mimicking parathyroid hormone-related peptide (PTHrP). KLF10, a transcription factor and miR-892b target, directly regulated Ihh promoter activity. Like miR-892b, KLF10 KD enhanced hMSC chondrogenesis and inhibited hypertrophy. Our findings suggest a key role of miR-892b in targeting the KLF10-Ihh axis as a regulator of hypertrophy in TGF-β-mediated chondrogenesis of hMSCs and provide a novel strategy for preventing hypertrophy in chondrogenesis from MSCs.

Triamcinolone Acetonide affects TGF-β signaling regulation of fibrosis in idiopathic carpal tunnel syndrome

Background

Fibroblast behavior and cell-matrix interactions of cells from normal and idiopathic carpal tunnel syndrome (CTS) subsynovial connective tissue (SSCT) with and without Triamcinolone Acetonide (TA) were compared in this study. A cell-seeded gel contraction model was applied to investigate the effect of steroid treatment on SSCT fibroblast gene expression and function.

Methods

SSCT cells were obtained from CTS patients and fresh cadavers. Cells were isolated by mechanical and collagenase digestion. Collagen gels (1 mg/ml) were prepared with SSCT cells (1 × 10⁶/mL). A sterile Petri dish with a cloning ring in the center was prepared. The area between the ring and outer dish was filled with cell-seeded collagen solution and gelled for 1 h. The gel was released from the outer way of the petri dish to allow gel contraction. Cell seeded gels were treated with 10 M triamcinolone acetonide (TA) or vehicle (DMSO) in modified MEM. Every 4 h for 3 days the contracting gels were photographed and areas calculated. Duplicate contraction tests were performed with each specimen, and the averages were used in the analyses, which were conducted using two-factor analysis of variance in a generalized linear model framework utilizing generalized estimating equations (GEE) to account for the correlation between samples. The contraction rate was determined by the area change over time, and the decay time constant was calculated. A customized mechanical test system was used to determine gel stiffness and tensile strength. Gene expression was assessed using Human Fibrosis and Cell Motility PCR arrays.

Results

TA-treated gels had a significantly higher contraction rate, tensile strength and stiffness than the untreated gels. Proteinases involved in remodeling had increased expression in TA-treated gels of the patient group. Pro-fibrotic genes and ECM regulators, such as TGF-β, collagens and integrins, were down-regulated by TA, indicating that TA may work in part by decreasing fibrotic gene expression.

Conclusions

This study showed that TA affects cell-matrix interaction and suppresses fibrotic gene expression in the SSCT cells of CTS patients.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2260-y) contains supplementary material, which is available to authorized users.

Krüppel-like factor 10 (KLF10) is transactivated by the transcription factor C/EBPβ and involved in early 3T3-L1 preadipocyte differentiation

Adipose tissue stores energy and plays an important role in energy homeostasis. CCAAT/enhancer-binding protein β (C/EBPβ) is an important early transcription factor for 3T3-L1 preadipocyte differentiation, facilitating mitotic clonal expansion (MCE) and transactivating C/EBPα and peroxisome proliferator-activated receptor-γ (PPARγ) to promote adipogenesis. C/EBPβ is induced early, but the expression of antimitotic C/EBPα and PPARγ is not induced until ∼48 h. The delayed expression of C/EBPα and PPARγ is thought to ensure MCE progression, but the molecular mechanism for this delay remains elusive. Here, we show that the zinc-finger transcription factor Krüppel-like factor 10 (KLF10) is induced after adipogenic induction and that its expression positively correlates with that of C/EBPβ but inversely correlates with expression of C/EBPα and PPARγ. C/EBPβ bound to the KLF10 promoter and transactivated its expression during MCE. KLF10 overexpression in 3T3-L1 preadipocyte repressed adipogenesis and decreased C/EBPα and PPARγ expression, whereas siRNA-mediated down-regulation of KLF10 enhanced adipogenesis and increased C/EBPα and PPARγ expression. Luciferase assays revealed an inhibitory effect of KLF10 on C/EBPα promoter activity. Using promoter deletion and mutation analysis, we identified a KLF10-binding site within the proximal promoter region of C/EBPα. Furthermore, KLF10 interacted with and recruited histone deacetylase 1 (HDAC1) to the C/EBPα promoter, decreasing acetylated histone H4 on the C/EBPα promoter and inactivating C/EBPα transcription. Because C/EBPα can transactivate PPARγ, our results suggest a mechanism by which expression of C/EBPα and PPARγ is delayed via KLF10 expression and shed light on the negative feedback loop for C/EBPβ-regulated adipogenesis in 3T3-L1 preadipocyte.

Expression of the ectodomain-releasing protease ADAM17 is directly regulated by the osteosarcoma and bone-related transcription factor RUNX2

Osteoblast differentiation is controlled by transcription factor RUNX2 which temporally activates or represses several bone-related genes, including those encoding extracellular matrix proteins or factors that control cell-cell, and cell-matrix interactions. Cell-cell communication in the many skeletal pericellular micro-niches is critical for bone development and involves paracrine secretion of growth factors and morphogens. This paracrine signaling is in part regulated by "A Disintegrin And Metalloproteinase" (ADAM) proteins. These cell membrane-associated metalloproteinases support proteolytic release ("shedding") of protein ectodomains residing at the cell surface. We analyzed microarray and RNA-sequencing data for Adam genes and show that Adam17, Adam10, and Adam9 are stimulated during BMP2 mediated induction of osteogenic differentiation and are robustly expressed in human osteoblastic cells. ADAM17, which was initially identified as a tumor necrosis factor alpha (TNFα) converting enzyme also called (TACE), regulates TNFα-signaling pathway, which inhibits osteoblast differentiation. We demonstrate that Adam17 expression is suppressed by RUNX2 during osteoblast differentiation through the proximal Adam17 promoter region (-0.4 kb) containing two functional RUNX2 binding motifs. Adam17 downregulation during osteoblast differentiation is paralleled by increased RUNX2 expression, cytoplasmic-nuclear translocation and enhanced binding to the Adam17 proximal promoter. Forced expression of Adam17 reduces Runx2 and Alpl expression, indicating that Adam17 may negatively modulate osteoblast differentiation. These findings suggest a novel regulatory mechanism involving a reciprocal Runx2-Adam17 negative feedback loop to regulate progression through osteoblast differentiation. Our results suggest that RUNX2 may control paracrine signaling through regulation of ectodomain shedding at the cell surface of osteoblasts by directly suppressing Adam17 expression.

KLF10 as a Tumor Suppressor Gene and Its TGF-β Signaling

Krüppel-like factor 10 (KLF10), originally named TGF-β (Transforming growth factor beta) inducible early gene 1 (TIEG1), is a DNA-binding transcriptional regulator containing a triple C2H2 zinc finger domain. By binding to Sp1 (specificity protein 1) sites on the DNA and interactions with other regulatory transcription factors, KLF10 encourages and suppresses the expression of multiple genes in many cell types. Many studies have investigated its signaling cascade, but other than the TGF-β/Smad signaling pathway, these are still not clear. KLF10 plays a role in proliferation, differentiation as well as apoptosis, just like other members of the SP (specificity proteins)/KLF (Krüppel-like Factors). Recently, several studies reported that KLF10 KO (Knock out) is associated with defects in cell and organs such as osteopenia, abnormal tendon or cardiac hypertrophy. Since KLF10 was first discovered, several studies have defined its role in cancer as a tumor suppressor. KLF10 demonstrate anti-proliferative effects and induce apoptosis in various carcinoma cells including pancreatic cancer, leukemia, and osteoporosis. Collectively, these data indicate that KLF10 plays a significant role in various biological processes and diseases, but its role in cancer is still unclear. Therefore, this review was conducted to describe and discuss the role and function of KLF10 in diseases, including cancer, with a special emphasis on its signaling with TGF-β.

GATA4 Directly Regulates Runx2 Expression and Osteoblast Differentiation

GATA4 is a zinc‐finger transcription factor that is a pioneer factor in various tissues and regulates tissue‐specific gene regulation. In vivo deletion of Gata4 using Cre‐recombinase under the control of the Col1a1 2.3 kb promoter showed significantly reduced values for trabecular bone properties by microCT analysis of femur and tibia of 14‐week‐old male and female mice, suggesting GATA4 is necessary for maintaining normal adult bone phenotype. Quantitative PCR analysis revealed higher expression of Gata4 in trabecular bone compared with cortical bone, suggesting a role for GATA4 in maintaining normal trabecular bone mass. In vivo and in vitro, reduction of Gata4 correlates with reduced Runx2 gene expression, along with reduced osteoblast mineralization. To determine if Runx2 is a direct target of GATA4, chromatin immunoprecipitation (ChIP) was performed, and it demonstrated that GATA4 is recruited to the two Runx2 promoters and an enhancer region. Furthermore, when Gata4 is knocked down, the chromatin at the Runx2 region is not open, as detected by DNase assays and ChIP with antibodies to the open chromatin marks H3K4me2 (histone 3 lysine 4 dimethylation) and H3K27ac (histone 3 lysine 27 acetylation) and the closed chromatin mark H3K27me2 (histone 3 lysine 27 trimethylation). Together, the data suggest that GATA4 binds near the Runx2 promoter and enhancer and helps maintain open chromatin to regulate Runx2 expression leading to bone mineralization. © 2017 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

MIF Plays a Key Role in Regulating Tissue-Specific Chondro-Osteogenic Differentiation Fate of Human Cartilage Endplate Stem Cells under Hypoxia

Degenerative cartilage endplate (CEP) shows decreased chondrification and increased ossification. Cartilage endplate stem cells (CESCs), with the capacity for chondro-osteogenic differentiation, are responsible for CEP restoration. CEP is avascular and hypoxic, while the physiological hypoxia is disrupted in the degenerated CEP. Hypoxia promoted chondrogenesis but inhibited osteogenesis in CESCs. This tissue-specific differentiation fate of CESCs in response to hypoxia was physiologically significant with regard to CEP maintaining chondrification and refusing ossification. MIF, a downstream target of HIF1A, is involved in cartilage and bone metabolisms, although little is known about its regulatory role in differentiation. In CESCs, MIF was identified as a key point through which HIF1A regulated the chondro-osteogenic differentiation. Unexpectedly, unlike the traditionally recognized mode, increased nuclear-expressed MIF under hypoxia was identified to act as a transcriptional regulator by interacting with the promoter of SOX9 and RUNX2. This mode of HIF1A/MIF function may represent a target for CEP degeneration therapy.

•

The hypoxic microenvironment is disrupted in degenerative CEP

•

Hypoxia promotes chondrogenesis but inhibits osteogenesis in CESCs

•

Hypoxia regulates chondro-osteogenesis through HIF1A/MIF pathway

•

MIF acts as a transcriptional regulator under hypoxia

TIEG and estrogen modulate SOST expression in the murine skeleton

TIEG knockout (KO) mice exhibit a female-specific osteopenic phenotype and altered expression of TIEG in humans is associated with osteoporosis. Gene expression profiling studies identified sclerostin as one of the most highly up-regulated transcripts in the long bones of TIEG KO mice relative to WT littermates suggesting that TIEG may regulate SOST expression. TIEG was shown to substantially suppress SOST promoter activity and the regulatory elements through which TIEG functions were identified using promoter deletion and chromatin immunoprecipitation assays. Knockdown of TIEG in IDG-SW3 osteocyte cells using shRNA and CRISPR-Cas9 technology resulted in increased SOST expression and delayed mineralization, mimicking the results obtained from TIEG KO mouse bones. Given that TIEG is an estrogen regulated gene, and as changes in the hormonal milieu affect SOST expression, we performed ovariectomy (OVX) and estrogen replacement therapy (ERT) studies in WT and TIEG KO mice followed by miRNA and mRNA sequencing of cortical and trabecular compartments of femurs. SOST expression levels were considerably higher in cortical bone compared to trabecular bone. In cortical bone, SOST expression was increased following OVX only in WT mice and was suppressed following ERT in both genotypes. In contrast, SOST expression in trabecular bone was decreased following OVX and significantly increased following ERT. Interestingly, a number of miRNAs that are predicted to target sclerostin exhibited inverse expression levels in response to OVX and ERT. These data implicate important roles for TIEG and estrogen-regulated miRNAs in modulating SOST expression in bone.

TIEG1 modulates β-catenin sub-cellular localization and enhances Wnt signaling in bone

We have previously demonstrated that TGFβ Inducible Early Gene-1 (TIEG1), also known as KLF10, plays important roles in mediating skeletal development and homeostasis in mice. TIEG1 has also been identified in clinical studies as one of a handful of genes whose altered expression levels or allelic variations are associated with decreased bone mass and osteoporosis in humans. Here, we provide evidence for the first time that TIEG1 is involved in regulating the canonical Wnt signaling pathway in bone through multiple mechanisms of action. Decreased Wnt signaling in the absence of TIEG1 expression is shown to be in part due to impaired β-catenin nuclear localization resulting from alterations in the activity of AKT and GSK-3β. We also provide evidence that TIEG1 interacts with, and serves as a transcriptional co-activator for, Lef1 and β-catenin. Changes in Wnt signaling in the setting of altered TIEG1 expression and/or activity may in part explain the observed osteopenic phenotype of TIEG1 KO mice as well as the known links between TIEG1 expression levels/allelic variations and patients with osteoporosis.

SIRT1 is a positive regulator of the master osteoblast transcription factor, RUNX2

Activation of SIRT1 has previously been shown to protect mice against osteoporosis through yet ill-defined mechanisms. In this study, we outline a role for SIRT1 as a positive regulator of the master osteoblast transcription factor, RUNX2. We find that ex vivo deletion of sirt1 leads to decreased expression of runx2 downstream targets, but not runx2 itself, along with reduced osteoblast differentiation. Reciprocally, treatment with a SIRT1 agonist promotes osteoblast differentiation, as well as the expression of runx2 downstream targets, in a SIRT1-dependent manner. Biochemical and luciferase reporter assays demonstrate that SIRT1 interacts with and promotes the transactivation potential of RUNX2. Intriguingly, mice treated with the SIRT1 agonist, resveratrol, show similar increases in the expression of RUNX2 targets in their calvaria (bone tissue), validating SIRT1 as a physiologically relevant regulator of RUNX2.

Impact of TIEG1 on the structural properties of fast- and slow-twitch skeletal muscle

INTRODUCTION

Transforming growth factor-beta (TGF-β)-inducible early gene-1 (TIEG1) is a transcription factor that is highly expressed in skeletal muscle. The purpose of this study was to characterize the structural properties of both fast-twitch (EDL) and slow-twitch (soleus) muscles in the hindlimb of TIEG1-deficient (TIEG1^-/- ) mice.

METHODS

Ten slow and 10 fast muscles were analyzed from TIEG1^-/- and wild-type (WT) mice using MRI texture (MRI-TA) and histological analyses.

RESULTS

MRI-TA could discriminate between WT slow and fast muscles. Deletion of the TIEG1 gene led to changes in the texture profile within both muscle types. Specifically, muscle isolated from TIEG1^-/- mice displayed hypertrophy, hyperplasia, and a modification of fiber area distribution.

CONCLUSIONS

We demonstrated that TIEG1 plays an important role in the structural properties of skeletal muscle. This study further implicates important roles for TIEG1 in the development of skeletal muscle and suggests that defects in TIEG1 expression and/or function may be associated with muscle disease. Muscle Nerve 55: 410-416, 2017.

TIEG1 enhances Osterix expression and mediates its induction by TGFβ and BMP2 in osteoblasts

Deletion of TIEG1/KLF10 in mice results in an osteopenic skeletal phenotype with significant decreases in both bone mineral density and content throughout the skeleton. Calvarial osteoblasts isolated from TIEG1 knockout (KO) mice display numerous changes in gene expression and exhibit significant delays in their mineralization rates relative to wild-type (WT) controls. Here, we demonstrate that loss of TIEG1 expression in osteoblasts results in decreased levels of Osterix mRNA. Suppression of TIEG1 expression in WT osteoblasts leads to decreased Osterix expression while restoration of TIEG1 expression in TIEG1 KO osteoblasts results in increased levels of Osterix. Transient transfection and chromatin immunoprecipitation assays reveal that TIEG1 directly binds to and activates the Osterix promoter and demonstrate that the zinc finger-containing DNA binding domain of TIEG1 is necessary for this regulation. Furthermore, we reveal that TIEG1 expression is essential for the induction of Osterix expression by important bone-related cytokines such as TGFβ and BMP2 in osteoblast cells. Taken together, these data implicate an important role for TIEG1 in regulating the expression of Osterix, a master regulator of osteoblast differentiation and bone formation, and suggest that decreased expression of Osterix, as well as impaired TGFβ and BMP2 signaling, contribute to the observed osteopenic bone phenotype of TIEG1 KO mice.

Klf10 regulates odontoblast differentiation and mineralization via promoting expression of dentin matrix protein 1 and dentin sialophosphoprotein genes

Klf10, a member of the Krüppel-like family of transcription factors, is critical for osteoblast differentiation, bone formation and mineralization. However, whether Klf10 is involved in odontoblastic differentiation and tooth development has not been determined. In this study, we investigate the expression patterns of Klf10 during murine tooth development in vivo and its role in odontoblastic differentiation in vitro. Klf10 protein was expressed in the enamel organ and the underlying mesenchyme, ameloblasts and odontoblasts at early and later stages of murine molar formation. Furthermore, the expression of Klf10, Dmp1, Dspp and Runx2 was significantly elevated during the process of mouse dental papilla mesenchymal differentiation and mineralization. The overexpression of Klf10 induced dental papilla mesenchymal cell differentiation and mineralization as detected by alkaline phosphatase staining and alizarin red S assay. Klf10 additionally up-regulated the expression of odontoblastic differentiation marker genes Dmp1, Dspp and Runx2 in mouse dental papilla mesenchymal cells. The molecular mechanism of Klf10 in controlling Dmp1 and Dspp expression is thus to activate their regulatory regions in a dosage-dependent manner. Our results suggest that Klf10 is involved in tooth development and promotes odontoblastic differentiation via the up-regulation of Dmp1 and Dspp transcription.

Sex steroid actions in male bone

Sex steroids are chief regulators of gender differences in the skeleton, and male gender is one of the strongest protective factors against osteoporotic fractures. This advantage in bone strength relies mainly on greater cortical bone expansion during pubertal peak bone mass acquisition and superior skeletal maintenance during aging. During both these phases, estrogens acting via estrogen receptor-α in osteoblast lineage cells are crucial for male cortical and trabecular bone, as evident from conditional genetic mouse models, epidemiological studies, rare genetic conditions, genome-wide meta-analyses, and recent interventional trials. Genetic mouse models have also demonstrated a direct role for androgens independent of aromatization on trabecular bone via the androgen receptor in osteoblasts and osteocytes, although the target cell for their key effects on periosteal bone formation remains elusive. Low serum estradiol predicts incident fractures, but the highest risk occurs in men with additionally low T and high SHBG. Still, the possible clinical utility of serum sex steroids for fracture prediction is unknown. It is likely that sex steroid actions on male bone metabolism rely also on extraskeletal mechanisms and cross talk with other signaling pathways. We propose that estrogens influence fracture risk in aging men via direct effects on bone, whereas androgens exert an additional antifracture effect mainly via extraskeletal parameters such as muscle mass and propensity to fall. Given the demographic trends of increased longevity and consequent rise of osteoporosis, an increased understanding of how sex steroids influence male bone health remains a high research priority.

TGF-β signaling regulates fibrotic expression and activity in carpal tunnel syndrome

Fibrosis of the subsynovial connective tissue (SSCT) is a predominant feature of carpal tunnel syndrome (CTS). While the nature of CTS has been extensively studied, little is known about the etiology of this disease. We investigated SSCT tissue from patients with CTS and control subjects using fibrosis arrays and cell culture analysis. Twofold changes in fibrotic gene expression were found in multiple genes from patient SSCT using fibrosis arrays. This data was confirmed via qRT-PCR on a subset of genes; collagen I (Col1), collagen III (Col3), connective tissue growth factor (CTGF), transforming growth factor β (TGF-β), and SMAD3 (P < 0.05) which significantly corroborate the fold changes found in the fibrosis arrays. To further explore the nature of SSCT fibrosis, cells were isolated from patient and control tissue. Col1, Col3, TGF-β, and SMAD3 were highly expressed in patient SSCT fibroblasts as compared to control (P < 0.05). Further, fibrotic genes expression was decreased by inhibiting TGF-β receptor I (TβRI) activity (P < 0.05). TGF-β second messenger SMAD activity was significantly activated in SSCT fibroblasts from patients and this activation was abrogated by inhibiting TβRI signaling (P < 0.05). These findings suggest that blocking TGF-β signaling may be an important therapeutic approach to treating the underlying fibrosis of SSCT in CTS patients.

Microarray meta-analysis identifies evolutionarily conserved BMP signaling targets in developing long bones

In vertebrates, BMP signaling has been demonstrated to be sufficient for bone formation in several tissue contexts. This suggests that genes necessary for bone formation are expressed in a BMP signaling dependent manner. However, till date no gene has been reported to be expressed in a BMP signaling dependent manner in bone. Our aim was to identify such genes. On searching the literature we found that several microarray experiments have been conducted where the transcriptome of osteogenic cells in absence and presence of BMP signaling activation have been compared. However, till date, there is no evidence to suggest that any of the genes found to be upregulated in presence of BMP signaling in these microarray analyses is indeed a target of BMP signaling in bone. We wanted to utilize this publicly available information to identify candidate BMP signaling target genes in vivo. We performed a meta-analysis of six such comparable microarray datasets. This analysis and subsequent experiments led to the identification of five targets of BMP signaling in bone that are conserved both in mouse and chick. Of these Lox, Klf10 and Gpr97 are likely to be direct transcriptional targets of BMP signaling pathway. Dpysl3, is a novel BMP signaling target identified in our study. Our data demonstrate that Dpysl3 is important for osteogenic differentiation of mesenchymal cells and is involved in cell secretion. We have demonstrated that the expression of Dpysl3 is co-operatively regulated by BMP signaling and Runx2. Based on our experimental data, in silico analysis of the putative promoter-enhancer regions of Bmp target genes and existing literature, we hypothesize that BMP signaling collaborates with multiple signaling pathways to regulate the expression of a unique set of genes involved in endochondral ossification.

TGFβ inducible early gene-1 plays an important role in mediating estrogen signaling in the skeleton

TGFβ Inducible Early Gene-1 (TIEG1) knockout (KO) mice display a sex-specific osteopenic phenotype characterized by low bone mineral density, bone mineral content, and overall loss of bone strength in female mice. We, therefore, speculated that loss of TIEG1 expression would impair the actions of estrogen on bone in female mice. To test this hypothesis, we employed an ovariectomy (OVX) and estrogen replacement model system to comprehensively analyze the role of TIEG1 in mediating estrogen signaling in bone at the tissue, cell, and biochemical level. Dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and micro-CT analyses revealed that loss of TIEG1 expression diminished the effects of estrogen throughout the skeleton and within multiple bone compartments. Estrogen exposure also led to reductions in bone formation rates and mineralizing perimeter in wild-type mice with little to no effects on these parameters in TIEG1 KO mice. Osteoclast perimeter per bone perimeter and resorptive activity as determined by serum levels of CTX-1 were differentially regulated after estrogen treatment in TIEG1 KO mice compared with wild-type littermates. No significant differences were detected in serum levels of P1NP between wild-type and TIEG1 KO mice. Taken together, these data implicate an important role for TIEG1 in mediating estrogen signaling throughout the mouse skeleton and suggest that defects in this pathway are likely to contribute to the sex-specific osteopenic phenotype observed in female TIEG1 KO mice.

Proteomic analysis of synovial fluid: insight into the pathogenesis of knee osteoarthritis

PURPOSE

We conducted a proteomic analysis of synovial fluid (SF) to identify differentially expressed proteins and analyse their correlation with osteoarthritis (OA) severity. Our primary purpose was to gain insight into the pathogenesis of OA.

METHODS

SF samples were acquired from 12 knee OA patients and 12 non-OA controls (ten had a meniscus injury, two had a discoid meniscus and all exhibited intact articular cartilage) and sequentially subjected to two-dimensional electrophoresis (2-DE). The radiographic grading of knee OA was performed using the Kellgren-Lawrence criteria. Differentially expressed proteins were identified by matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS). Proteins of interest identified from SF were detected using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 31 protein spots showed significant differences (p < 0.05) between the sample groups; 25 of the 31 spots (80.6 %) were identified as proteins of interest. Among them 20 corresponded to up-regulation and five to down-regulation in OA samples. HLA-DR was one of the proteins up-regulated, which was confirmed by ELISA.

CONCLUSIONS

These observations have implications in delineating the protein expression underlying the pathogenesis of OA and facilitate further elucidation of molecular mechanisms involved in disease progression. Substantial alterations of the protein profile in SF may be associated with OA severity.

Runx2 protein represses Axin2 expression in osteoblasts and is required for craniosynostosis in Axin2-deficient mice

Runx2 and Axin2 regulate craniofacial development and skeletal maintenance. Runx2 is essential for calvarial bone development, as Runx2 haploinsufficiency causes cleidocranial dysplasia. In contrast, Axin2-deficient mice develop craniosynostosis because of high β-catenin activity. Axin2 levels are elevated in Runx2(-/-) calvarial cells, and Runx2 represses transcription of Axin2 mRNA, suggesting a direct relationship between these factors in vivo. Here we demonstrate that Runx2 binds several regions of the Axin2 promoter and that Runx2-mediated repression of Axin2 transcription depends on Hdac3. To determine whether Runx2 contributes to the etiology of Axin2 deficiency-induced craniosynostosis, we generated Axin2(-/-):Runx2(+/-) mice. These double mutant mice had longer skulls than Axin2(-/-) mice, indicating that Runx2 haploinsufficiency rescued the craniosynostosis phenotype of Axin2(-/-) mice. Together, these studies identify a key mechanistic pathway for regulating intramembranous bone development within the skull that involves Runx2- and Hdac3-mediated suppression of Axin2 to prevent the untimely closure of the calvarial sutures.