Knockdown of NFIC Promotes Bovine Myoblast Proliferation through the CENPF/CDK1 Axis

As cellular transcription factors and DNA replicators, nuclear factor I (NFI) family members play an important role in mammalian development. However, there is still a lack of research on the muscle regeneration of NFI family members in cattle. In this study, the analysis of NFI family factors was conducted on their characterization, phylogenetics, and functional domains. We found that NFI family members were relatively conserved among different species, but there was heterogeneity in amino acid sequences, DNA coding sequences, and functional domain among members. Furthermore, among NFI family factors, we observed that NFIC exhibited highly expression in bovine muscle tissues, particularly influencing the expression of proliferation marker genes in myoblasts. To investigate the influence of NFIC on myoblast proliferation, we knocked down NFIC (si-NFIC) and found that the proliferation of myoblasts was significantly promoted. In terms of regulation mechanism, we identified that si-NFIC could counteract the inhibitory effect of the cell cycle inhibitor RO-3306. Interestingly, CENPF, as the downstream target gene of NFIC, could affect the expression of CDK1, CCNB1, and actively regulate the cell cycle pathway and cell proliferation. In addition, when CENPF was knocked down, the phosphorylation of p53 and the expression of Bax were increased, but the expression of Bcl2 was inhibited. Our findings mainly highlight the mechanism by which NFIC acts on the CENPF/CDK1 axis to regulate the proliferation of bovine myoblasts.

NFIB-MLL1 complex is required for the stemness and Dlx5-dependent osteogenic differentiation of C3H10T1/2 mesenchymal stem cells

Despite significant progress in our understanding of the molecular mechanism of mesenchymal stem cell (MSC) differentiation, less is known about the factors maintaining the stemness and plasticity of MSCs. Here, we show that the NFIB-MLL1 complex plays key roles in osteogenic differentiation and stemness of C3H10T1/2 MSCs. We find that depletion of either NFIB or MLL1 results in a severely hampered osteogenic potential and failed activation of key osteogenic transcription factors, such as Dlx5, Runx2, and Osx, following osteogenic stimuli. In addition, the NFIB-MLL1 complex binds directly to the promoter of Dlx5, and exogenous expression of Myc-Dlx5, but not the activation of either the BMP- or the Wnt-signaling pathway, is sufficient to restore the osteogenic potential of cells depleted of NFIB or MLL1. Moreover, chromatin immunoprecipitation (ChIP) and ChIP-sequencing analysis showed that the NFIB-MLL1 complex mediates the deposition of trimethylated histone H3K4 at both Dlx5 and Cebpa, key regulator genes that function at the early stages of osteogenic and adipogenic differentiation, respectively, in uncommitted C3H10T1/2 MSCs. Surprisingly, the depletion of either NFIB or MLL1 leads to decreased trimethylated histone H3K4 and results in elevated trimethylated histone H3K9 at those developmental genes. Furthermore, gene expression profiling and ChIP-sequencing analysis revealed lineage-specific changes in chromatin landscape and gene expression in response to osteogenic stimuli. Taken together, these data provide evidence for the hitherto unknown role of the NFIB-MLL1 complex in the maintenance and lineage-specific differentiation of C3H10T1/2 MSCs and support the epigenetic regulatory mechanism underlying the stemness and plasticity of MSCs.

NFIC regulates ribosomal biology and ER stress in pancreatic acinar cells and restrains PDAC initiation

Pancreatic acinar cells rely on PTF1 and other transcription factors to deploy their transcriptional program. We identify NFIC as a NR5A2 interactor and regulator of acinar differentiation. NFIC binding sites are enriched in NR5A2 ChIP-Sequencing peaks. Nfic knockout mice have a smaller, histologically normal, pancreas with reduced acinar gene expression. NFIC binds and regulates the promoters of acinar genes and those involved in RNA/protein metabolism, and Nfic knockout pancreata show defective ribosomal RNA maturation. NFIC dampens the endoplasmic reticulum stress program through binding to gene promoters and is required for resolution of Tunicamycin-mediated stress. NFIC is down-regulated during caerulein pancreatitis and is required for recovery after damage. Normal human pancreata with low levels of NFIC transcripts display reduced expression of genes down-regulated in Nfic knockout mice. NFIC expression is down-regulated in mouse and human pancreatic ductal adenocarcinoma. Consistently, Nfic knockout mice develop a higher number of mutant Kras-driven pre-neoplastic lesions.

The role of wnt signaling in diabetes-induced osteoporosis

Osteoporosis, a chronic complication of diabetes mellitus, is characterized by a reduction in bone mass, destruction of bone microarchitecture, decreased bone strength, and increased bone fragility. Because of its insidious onset, osteoporosis renders patients highly susceptible to pathological fractures, leading to increased disability and mortality rates. However, the specific pathogenesis of osteoporosis induced by chronic hyperglycemia has not yet been fully elucidated. But it is currently known that the disruption of Wnt signaling triggered by chronic hyperglycemia is involved in the pathogenesis of diabetic osteoporosis. There are two main types of Wnt signaling pathways, the canonical Wnt signaling pathway (β-catenin-dependent) and the non-canonical Wnt signaling pathway (non-β-catenin-dependent), both of which play an important role in regulating the balance between bone formation and bone resorption. Therefore, this review systematically describes the effects of abnormal Wnt pathway signaling on bone homeostasis under hyperglycemia, hoping to reveal the relationship between Wnt signaling and diabetic osteoporosis to further improve understanding of this disease.

NFIC1 inhibits the migration and invasion of MDA-MB-231 cells through S100A2-mediated inactivation of MEK/ERK pathway

NFIC is a potent transcriptional factor involved in many physiological and pathological processes, including tumorigenesis. However, the role of NFIC1, the longest isoform of NFIC, in the progression of triple negative breast cancer (TNBC) remains elusive. Our study demonstrates that overexpression of NFIC1 inhibits the migration and invasion of TNBC MDA-MB-231 cells. NFIC1 regulates the expression of S100A2, and knockdown of S100A2 reverses the inhibitive effects of NFIC1 on the migration and invasion of MDA-MB-231 cells. Furthermore, knockdown of S100A2 activates the MEK/ERK signaling transduction pathway that is inhibited by NFIC1 overexperssion. Treatment with MEK/ERK pathway inhibitor, U0126, abolishes the effects of S100A2 knockdown. In addition, overexpression of NFIC1 in MDA-MB-231 cells increases the expression of epithelial markers and decreases the expression of mesenchymal markers, and these effects could also be reversed by knockdown of S100A2. Collectively, these results demonstrate that NFIC1 inhibits the Epithelial-mesenchymal transition (EMT) of MDA-MB-231 cells by regulating S100A2 expression, which suppress the activation of MEK/ERK pathway. Therefore, our study confirms the role of NFIC1 as a tumor repressor in TNBC, and reveals the molecular mechanism through which NFIC1 inhibits the migration and invasion of MDA-MB-231 cells.

TBX3 regulates the transcription of VEGFA to promote osteoblasts proliferation and microvascular regeneration

Objective

Osteochondral decellularization can promote local vascular regeneration, but the exact mechanism is unknown. The aim of this study is to study osteogenic microvascular regeneration in single cells.

Methods

The scRNA-seq dataset of human periosteal-derived cells (hPDCs) were analyzed by pySCENIC. To examine the role of TBX3 in osteogenesis and vascularization, cell transfection, qRT-PCR, western blot, and CCK-8 cell proliferation assays were performed.

Results

TCF7L2, TBX3, FLI1, NFKB2, and EZH2 were found to be transcription factors (TFs) most closely associated with corresponding cells. The regulatory network of these TFs was then visualized. Our study knocked down the expression of TBX3 in human osteoblast cell lines. In the TBX3 knockdown group, we observed decreased expression of VEGFA, VEGFB, and VEGFC. Moreover, Western blot analysis showed that downregulating TBX3 resulted in a reduction of VEGFA expression. And TBX3 stimulated osteoblast proliferation in CCK-8 assays.

Conclusion

TBX3 regulates VEGFA expression and promotes osteoblast proliferation in skeletal microvasculature formation. The findings provide a theoretical basis for investigating the role of TBX3 in promoting local vascular regeneration.

Oncostatin M receptor regulates osteoblast differentiation via extracellular signal-regulated kinase/autophagy signaling

Background

Oncostatin M receptor (OSMR), as one of the receptors for oncostatin M (OSM), has previously been shown to mediate the stimulatory role of OSM in osteoclastogenesis and bone resorption. However, it remains to be clarified whether and how OSMR affects the differentiation of osteoblasts.

Methods

The expression level of OSMR during osteoblast and adipocyte differentiation was examined. The role of OSMR in the differentiation was investigated using in vitro gain-of-function and loss-of-function experiments. The mechanisms by which OSMR regulates bone cell differentiation were explored. Finally, in vivo function of OSMR in cell fate determination and bone homeostasis was studied after transplantation of OSMR-silenced bone marrow stromal cells (BMSCs) to the marrow of ovariectomized mice.

Results

OSMR was regulated during osteogenic and adipogenic differentiation of marrow stromal progenitor cells and increased in the metaphysis of ovariectomized mice. OSMR suppressed osteogenic differentiation and stimulated adipogenic differentiation of progenitor cells. Mechanistic investigations showed that OSMR inhibited extracellular signal-regulated kinase (ERK) and autophagy signaling. The downregulation of autophagy, which was mediated by ERK inhibition, suppressed osteogenic differentiation of progenitor cells. Additionally, inactivation of ERK/autophagy signaling attenuated the stimulation of osteogenic differentiation induced by Osmr siRNA. Furthermore, transplantation of BMSCs in which OSMR was silenced to the marrow of mice promoted osteoblast differentiation, attenuated fat accumulation and osteoclast differentiation, and thereby relieved the osteopenic phenotype in the ovariectomized mice.

Conclusions

Our study has for the first time established the direct role of OSMR in regulating osteogenic differentiation of marrow stromal progenitor cells through ERK-mediated autophagy signaling. OSMR thus contributes to bone homeostasis through dual regulation of osteoblasts and osteoclasts. It also suggests that OSMR may be a potential target for the treatment of metabolic disorders such as osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02958-1.

A Quartet Network Analysis Identifying Mechanically Responsive Long Noncoding RNAs in Bone Remodeling

Mechanical force, being so ubiquitous that it is often taken for granted and overlooked, is now gaining the spotlight for reams of evidence corroborating their crucial roles in the living body. The bone, particularly, experiences manifold extraneous force like strain and compression, as well as intrinsic cues like fluid shear stress and physical properties of the microenvironment. Though sparkled in diversified background, long noncoding RNAs (lncRNAs) concerning the mechanotransduction process that bone undergoes are not yet detailed in a systematic way. Our principal goal in this research is to highlight the potential lncRNA-focused mechanical signaling systems which may be adapted by bone-related cells for biophysical environment response. Based on credible lists of force-sensitive mRNAs and miRNAs, we constructed a force-responsive competing endogenous RNA network for lncRNA identification. To elucidate the underlying mechanism, we then illustrated the possible crosstalk between lncRNAs and mRNAs as well as transcriptional factors and mapped lncRNAs to known signaling pathways involved in bone remodeling and mechanotransduction. Last, we developed combinative analysis between predicted and established lncRNAs, constructing a pathway–lncRNA network which suggests interactive relationships and new roles of known factors such as H19. In conclusion, our work provided a systematic quartet network analysis, uncovered candidate force-related lncRNAs, and highlighted both the upstream and downstream processes that are possibly involved. A new mode of bioinformatic analysis integrating sequencing data, literature retrieval, and computational algorithm was also introduced. Hopefully, our work would provide a moment of clarity against the multiplicity and complexity of the lncRNA world confronting mechanical input.

N-myc downstream regulated gene 1 suppresses osteoblast differentiation through inactivating Wnt/β-catenin signaling

Background

N-myc downstream regulated gene 1 (NDRG1) plays a role in a variety of biological processes including differentiation of osteoclasts. However, it is not known if and how NDRG1 regulates osteogenic differentiation of marrow stromal progenitor cells.

Methods

Gene expression profiling analysis was performed to study the expression level of Ndrg1 during osteogenic and adipogenic differentiation. Gain-of-function and/or loss-of function experiments were carried out to study the role of NDRG1 in the proliferation and differentiation of marrow stromal progenitor cells and the mechanism underlying the function was investigated. Finally, in vivo transfection of Ndrg1 siRNA was done and its effect on osteogenic and adipogenic differentiation in mice was explored.

Results

Gene expression profiling analysis revealed that NDRG1 level was regulated during osteogenic and adipogenic differentiation of progenitor cells. The functional experiments demonstrated that NDRG1 negatively regulated the cell growth, and reciprocally modulated the osteogenic and adipogenic commitment of marrow stromal progenitor cells, driving the cells to differentiate toward adipocytes at the expense of osteoblast differentiation. Moreover, NDRG1 interacted with low-density lipoprotein receptor-related protein 6 (LRP6) in the stromal progenitor cells and inactivated the canonical Wnt/β-catenin signaling cascade. Furthermore, the impaired differentiation of progenitor cells induced by Ndrg1 siRNA could be attenuated when β-catenin was simultaneously silenced. Finally, in vivo transfection of Ndrg1 siRNA to the marrow of mice prevented the inactivation of canonical Wnt signaling in the BMSCs of ovariectomized mice, and ameliorated the reduction of osteoblasts on the trabeculae and increase of fat accumulation in the marrow observed in the ovariectomized mice.

Conclusion

This study has provided evidences that NDRG1 plays a role in reciprocally modulating osteogenic and adipogenic commitment of marrow stromal progenitor cells through inactivating canonical Wnt signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02714-5.

High mobility group AT-hook 2 regulates osteoblast differentiation and facial bone development

The mutation and deletion of high mobility group AT-hook 2 (Hmga2) gene exhibit skeletal malformation, but almost nothing is known about the mechanism. This study examined morphological anomaly of facial bone in Hmga2-/- mice and osteoblast differentiation of pre-osteoblast MC3T3-E1 cells with Hmga2 gene knockout (A2KO). Hmga2-/- mice showed the size reduction of anterior frontal part of facial bones. Hmga2 protein and mRNA were expressed in mesenchymal cells at ossification area of nasal bone. A2KO cells differentiation into osteoblasts after reaching the proliferation plateau was strongly suppressed by alizarin red and alkaline phosphatase staining analyses. Expression of osteoblast-related genes, especially Osterix, was down-regulated in A2KO cells. These results demonstrate a close association of Hmga2 with osteoblast differentiation of mesenchymal cells and bone growth. Although future studies are needed, the present study suggests an involvement of Hmga2 in osteoblast-genesis and bone growth.

CircNFIC Balances Inflammation and Apoptosis by Sponging miR-30e-3p and Regulating DENND1B Expression

Disordered inflammation and apoptosis are closely related to diseases, and inflammation can also promote cell apoptosis, where growing evidence has shown that circular RNAs (circRNAs) play important roles. Lipopolysaccharide (LPS) is the main component of the cytoderm of gram-negative bacterium, which can cause inflammatory responses in macrophages. We constructed an inflammatory model by exposing chicken macrophage cell lines (also known as HD11) to LPS for in vitro experiments. In this study, we validated a novel circRNA-circNFIC-which was dramatically up-regulated in tissues infected by coccidia and cells exposed to LPS. Besides, circNFIC could significantly promote the expression levels of pro-inflammation factors, including (IL-1β, TNFα, and IFNγ) and pro-apoptosis maker genes (caspase 3 and caspase 8) in HD11 exposed to LPS or not. In terms of mechanism, circNFIC exerted notable effects on DENND1B to regulate cell inflammation and apoptosis by sponging miR-30e-3p. The molecular functions played by miR-30e-3p and DENND1B have been explored, respectively. In addition, the effects of circNFIC knockdown suppressing the expression of pro-inflammatory and pro-apoptosis functions could be reversed by a miR-30e-3p inhibitor. On the whole, circNFIC promoted cell inflammation and apoptosis via the miR-30e-3p/DENND1B axis.

Transcriptomic profiling and functional prediction reveal aberrant expression of circular RNAs during osteogenic differentiation in human umbilical cord mesenchymal stromal cells

Circular RNAs (circRNAs) are crucial elements of non-coding RNA, that regulate various biological processes. To date, expression patterns and functional roles of circRNAs during osteogenic differentiation of human umbilical cord mesenchymal stromal cells (hUCMSCs) remain unknown. In this study, we analyzed RNA-sequence data to reveal expression profiles of circRNAs during osteogenesis of hUCMSCs, then elucidated the underlying mechanisms of action. We identified a total of 5457 circRNAs in hUCMSCs, of which 34 and 33 were upregulated and downregulated, respectively. We applied Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses to determine functions and related pathways of differentially expressed circRNAs. Moreover, we applied bioinformatics tools to construct competing endogenous RNA networks, comprising 10 circRNAs, 46 micro RNAs and 413 mRNAs. Furthermore, we predicted protein-coding potential of the upregulated circRNAs then constructed a co-expression network comprising the top 5 upregulated circRNAs and 75 RNA-binding proteins. Next, we validated 6 differentially-expressed circRNAs and found that overexpressing circ-CTTN could promote osteogenesis of hUCMSCs. Overall, our findings indicate that clusters of circRNAs are aberrantly expressed in hUCMSCs during osteogenic differentiation, hence lay a foundation for future research into promoting hUCMSCs osteogenic differentiation and bone regeneration.

High-mobility group AT-Hook 1 mediates the role of nuclear factor I/X in osteogenic differentiation through activating canonical Wnt signaling

It was previously reported that the loss of the transcription factor nuclear factor I/X (NFIX) gene in mice impaired endochondral ossification and mineralization in bone. However, the cellular and molecular basis for the defect remains unexplored. In this study, we investigated if and how NFIX regulates osteoblast differentiation. Nfix mRNA was induced during osteogenic and adipogenic differentiation of progenitor cells. Loss-of-function and gain-of-function studies revealed that NFIX induced osteoblast differentiation and impaired adipocyte formation from progenitor cells. RNA-seq and promoter analysis revealed that NFIX transcriptionally stimulated the expression of high-mobility group AT-Hook 1 (HMGA1). We then demonstrated that HMGA1 stimulated osteogenic differentiation of progenitor cells at the expense of adipogenic differentiation. The effect of Nfix siRNA on the differentiation of progenitor cells could be attenuated when HMGA1 was simultaneously overexpressed. Further investigations revealed the stimulatory effect of NFIX and HMGA1 on canonical wingless-type MMTV integration site family (Wnt) signaling. HMGA1 transcriptionally activates the expression of low-density lipoprotein receptor-related protein 5. Finally, in vivo transfection of Nfix siRNA to the marrow of mice reduced osteoblasts and increased fat accumulation in the marrow, and inactivated HMGA1/β-catenin signaling in bone marrow mesenchymal stem cells. This study suggests that HMGA1 plays a role in osteoblast commitment and mediates the function of NFIX through transcriptionally activating canonical Wnt signaling.

Downregulation of miR-184 facilitates osseous differentiation in periodontal ligament stem cells by modulating nuclear factor I-C

Background/purpose

PDLSCs (periodontal ligament stem cells), derived from dental tissues, are candidate cells for regeneration of dental tissues. MiRNAs could regulate osteogenic differentiation and the transformation into osteoblasts. This study was conducted to figure out how miR-184 regulates osteoblastic differentiation in PDLSCs.

Materials and methods

PDLSCs were isolated from premolars, and the osteoblastic differentiation was validated via Alizarin red staining and determination of ALP (alkaline phosphatase) activity. Expression of osteogenic specific genes were evaluated by western blot, and the expression pattern of miR-184 was determined by qRT-PCR. Target gene of miR-184 was then verified by dual luciferase reporter assay.

Results

Osteogenic-induced PDLSCs were successfully established with increased mineral deposition, ALP activity and protein expression of RUNX2 (runt-related transcription factor 2), osterix and BSP (bone sialoprotein). MiR-184 was reduced during osteoblastic differentiation of PDLSCs, and over-expression of miR-184 suppressed osteoblastic differentiation, as evidenced by reduction in mineral deposition, ALP activity and protein expression of RUNX2, osterix and BSP. MiR-184 could target NFI-C (nuclear factor I-C), and inhibit NFI-C expression in PDLSCs. NFI-C was enhanced during osteoblastic differentiation of PDLSCs, suggesting negative correlation with miR-184. Forced NFI-C expression promoted osteoblastic differentiation, and counteracted with the suppressive effects of miR-184 on osteoblastic differentiation.

Conclusion

Downregulation of miR-184 facilitates osteoblastic differentiation in PDLSCs by modulating NFI-C, providing novel therapeutic strategy for regeneration of dental tissues.

TRAF4 acts as a fate checkpoint to regulate the adipogenic differentiation of MSCs by activating PKM2

BACKGROUND

Mesenchymal stem cells (MSCs) selectively differentiate into adipocytes or osteoblasts, and several molecules control the fate determination of MSCs. Understanding these key checkpoints greatly contributes to the ability to induce specific MSC differentiation for clinical applications. In this study, we aimed to explore whether TNF receptor-associated factor 4 (TRAF4) affects MSC adipogenic differentiation, which we previously reported that could positively regulated the osteogenic differentiation.

METHODS

Western blotting and Real-time Polymerase Chain Reaction were used to detected the expression pattern of TRAF4 during adipogenic differentiation. Lentivirus was constructed to regulate TRAF4 expression, and oil red O staining and Western blotting were used to assess its role in adipogenesis, which was confirmed in vivo by implanting an MSC-matrigel mixture into nude mice. Western blotting was used to detect the activated signaling pathways, and a specific inhibitor and agonist were used to clear the roles of the key signaling pathways. Additionaly, Co-Immunoprecipitation was conducted to find that Pyruvate kinase isozyme type M2 (PKM2) interacts with TRAF4, and to further explore their binding and functional domains. Finally, an RNA-binding protein immunoprecipitation assay and Western blotting were used to detect whether N6-methyladenosine mediates the decreased TRAF4 expression during adipogenic differentiation.

FINDINGS

The results demonstrated that TRAF4 negatively regulates MSC adipogenesis in vitro and in vivo. Mechanistically, we revealed that TRAF4 binds to PKM2 to activate the kinase activity of PKM2, which subsequently activates β-catenin signaling and then inhibits adipogenesis. Furthermore, TRAF4 downregulation during adipogenesis is regulated by ALKBH5-mediated N6-methyladenosine RNA demethylation.

INTERPRETATION

TRAF4 negatively regulates the adipogenesis of MSCs by activating PKM2 kinase activity, which may act as a checkpoint to fine-tune the balance of adipo-osteogenic differentiation, and suggests that TRAF4 may be a novel target of MSCs in clinical use and may also illuminate the underlying mechanisms of bone metabolic diseases.

FUNDING

This study was supported by the National Natural Science Foundation of China (81871750 and 81971518) and the Science and Technology Project of Guangdong Province (2019B02023600 and 2017A020215070).

A novel Sprouty4-ERK1/2-Wnt/β-catenin regulatory loop in marrow stromal progenitor cells controls osteogenic and adipogenic differentiation

BACKGROUND

Sprouty (SPRY) proteins play critical roles in controlling cell proliferation, differentiation, and survival by inhibiting receptor tyrosine kinase (RTK)-mediated extracellular signal-regulated kinase (ERK) signaling. Recent studies have demonstrated that SPRY4 negatively regulates angiogenesis and tumor growth. However, whether SPRY4 regulates osteogenic and/or adipogenic differentiation of mesenchymal stem cells remains to be explored.

RESULTS

In this study, we investigated the expression pattern of Spry4 and found that its expression was regulated during the differentiation of mouse marrow stromal progenitor cells and increased in the metaphysis of ovariectomized mice. In vitro loss-of-function and gain-of-function studies demonstrated that SPRY4 inhibited osteogenic differentiation and stimulated adipogenic differentiation of progenitor cells. In vivo experiments showed that silencing of Spry4 in the marrow of C57BL/6 mice blocked fat accumulation and promoted osteoblast differentiation in ovariectomized mice. Mechanistic investigations revealed the inhibitory effect of SPRY4 on canonical wingless-type MMTV integration site (Wnt) signaling and ERK pathway. ERK1/2 was shown to interact with low-density lipoprotein receptor-related protein 6 (LRP6) and activate the canonical Wnt signaling pathway. Inactivation of Wnt signaling attenuated the inhibition of adipogenic differentiation and stimulation of osteogenic differentiation by Spry4 small interfering RNA (siRNA). Finally, promoter study revealed that β-catenin transcriptionally inhibited the expression of Spry4.

CONCLUSIONS

Our study for the first time suggests that a novel SPRY4-ERK1/2-Wnt/β-catenin regulatory loop exists in marrow stromal progenitor cells and plays a key role in cell fate determination. It also highlights the potential of SPRY4 as a novel therapeutic target for the treatment of metabolic bone disorders such as osteoporosis.

AFF4 enhances odontogenic differentiation of human dental pulp cells

AFF4 is a component of super elongation complex (SECs) and functions as a scaffold protein to bridge the transcription elongation factors. It is associated with leukemia, HIV transcription, and head neck cancer. However, its role in odontogenic differentiation of dental pulp cells (DPCs) is unclear. Here, we show the expression of AFF4 is increased during odontogenesis. Depletion of AFF4 in human DPCs leads to a decrease of alkaline phosphatase (ALP) activity, calcium mineralization and odontogenic-related genes expression. On the contrary, Lentivirus-mediated overexpression of AFF4 induces the odontogenic potential of DPCs. Mechanistically, we found AFF4 regulates the transcription of NFIC, a key factor for tooth root formation. Overexpression of NFIC successfully rescues the restricted differentiation of AFF4-depleted cells. Our data demonstrate that AFF4 serves as a previously unknown regulator of odontogenesis.

Osteoporosis- and obesity-risk interrelationships: an epigenetic analysis of GWAS-derived SNPs at the developmental gene TBX15

A major challenge in translating findings from genome-wide association studies (GWAS) to biological mechanisms is pinpointing functional variants because only a very small percentage of variants associated with a given trait actually impact the trait. We used an extensive epigenetics, transcriptomics, and genetics analysis of the TBX15/WARS2 neighbourhood to prioritize this region's best-candidate causal variants for the genetic risk of osteoporosis (estimated bone density, eBMD) and obesity (waist-hip ratio or waist circumference adjusted for body mass index). TBX15 encodes a transcription factor that is important in bone development and adipose biology. Manual curation of 692 GWAS-derived variants gave eight strong candidates for causal SNPs that modulate TBX15 transcription in subcutaneous adipose tissue (SAT) or osteoblasts, which highly and specifically express this gene. None of these SNPs were prioritized by Bayesian fine-mapping. The eight regulatory causal SNPs were in enhancer or promoter chromatin seen preferentially in SAT or osteoblasts at TBX15 intron-1 or upstream. They overlap strongly predicted, allele-specific transcription factor binding sites. Our analysis suggests that these SNPs act independently of two missense SNPs in TBX15. Remarkably, five of the regulatory SNPs were associated with eBMD and obesity and had the same trait-increasing allele for both. We found that WARS2 obesity-related SNPs can be ascribed to high linkage disequilibrium with TBX15 intron-1 SNPs. Our findings from GWAS index, proxy, and imputed SNPs suggest that a few SNPs, including three in a 0.7-kb cluster, act as causal regulatory variants to fine-tune TBX15 expression and, thereby, affect both obesity and osteoporosis risk.

RNA-binding protein PUM2 regulates mesenchymal stem cell fate via repression of JAK2 and RUNX2 mRNAs

The differentiation of mesenchymal stem cells (MSCs) into unwanted lineages can generate potential problems in clinical trials. Thus, understanding the molecular mechanisms, involved in this process, would help prevent unexpected complications. Regulation of gene expression, at the posttranscriptional level, is a new approach in cell therapies. PUMILIO is a conserved posttranscriptional regulator. However, the underlying mechanisms of PUMILIO, in vertebrate stem cells, remain elusive. Here, we show that depletion of PUMILIO2 (PUM2) blocks MSC adipogenesis and enhances osteogenesis. We also demonstrate that PUM2 works as a negative regulator on the 3'-untranslated regions of JAK2 and RUNX2 via direct binding. CRISPR/Cas9-mediated gene silencing of Pum2 inhibited lipid accumulation and induced excessive bone formation in zebrafish larvae. Our findings reveal novel roles of PUM2 in MSCs and provide potential therapeutic targets for related diseases.

The rate of fluid shear stress is a potent regulator for the differentiation of mesenchymal stem cells

We have previously demonstrated that the rate of fluid shear stress (ΔSS) can manipulate the fate of mesenchymal stem cells (MSCs) to osteogenic or chondrogenic cells. However, whether ΔSS is comparable to other two means of induction medium and substrate stiffness that have been proven to be potent in differentiation control is unknown. In this study, we subjected MSCs to 1-7 days of osteogenic or chondrogenic chemical induction, or 1-4 days of 37 or 86 kPa of substrate stiffness induction, followed by 20 min of Fast ΔSS (0-0') or Slow ΔSS (0-2'), which is a laminar FSS that linearly increased from 0 to 10 dyn/cm ² in 0 (Fast) or 2 min (Slow) and maintained at 10 dyn/cm ² for a total of 20 min. We found that 20 min of ΔSS could compete with 5 days' chemical and 2 days' substrate stiffness inductions. Our study confirmed that ΔSS is a powerful tool to control the differentiation of MSCs, which stressed the possible application in MSCs linage specification.

Wnt signaling pathway in osteoporosis: Epigenetic regulation, interaction with other signaling pathways, and therapeutic promises

Wnt is a major signaling pathway involved in multifaceted roles of various biological processes. Bones are dynamic tissues which are able to remodel and maintain the tissue homeostasis. Wnt signaling cascade leads to the promotion of bone formation and suppression of bone resorption, leading to a balance in bone remodeling. Recent evidence has reinforced the inevitable role of Wnt signaling in osteoporosis. The complex genetic and epigenetic regulations of Wnt signaling factors and their interaction with other master signaling pathways such as TGF-β, BMP, PI3K/AKT, and Hedgehog outline their importance in diagnosis and treatment of osteoporosis. In this review, we highlighted the recent advances in function of Wnt signaling-related epigenetic regulation, different signaling pathways interacting with Wnt, and their roles in osteoporosis. Finally, we discussed novel promises in molecular targeted therapy of osteoporosis.

NFIC promotes the vitality and osteogenic differentiation of rat dental follicle cells

Nuclear factor I-C (NFIC) plays critical roles in the regulation of tooth development by influencing the biological behaviors of stem cells in the dental germ. This study aimed to investigate the effect of NFIC on the vitality and osteogenic/cementogenic differentiation of rat dental follicle cells (DFCs). DFCs were isolated from dental follicles in the first molars of neonatal rats. DFCs expressed mesenchymal stromal cell markers CD29, CD44 and CD90 and had capabilities for self-renewal and multipotent differentiation. Overexpression of NFIC promoted the proliferation of DFCs without markedly influencing the apoptosis of DFCs. Moreover, NFIC increased alkaline phosphatase (ALP) activity in DFCs and upregulated the mRNA levels of osteogenic-related markers, namely, collagen type I (Col I), Runt-related transcription factor 2 (Runx2) and ALP, as well as β-catenin. In contrast, silencing NFIC by siRNA increased the apoptosis of DFCs and downregulated the expression of osteogenic-related markers. In conclusion, these results suggested that upregulation of NFIC may promote the proliferation and osteogenic/cementogenic differentiation of DFCs.

Update on the impact of type 2 diabetes mellitus on bone metabolism and material properties

The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide, especially as a result of our aging society, high caloric intake and sedentary lifestyle. Besides the well-known complications of T2DM on the cardiovascular system, the eyes, kidneys and nerves, bone strength is also impaired in diabetic patients. Patients with T2DM have a 40-70% increased risk for fractures, despite having a normal to increased bone mineral density, suggesting that other factors besides bone quantity must account for increased bone fragility. This review summarizes the current knowledge on the complex effects of T2DM on bone including effects on bone cells, bone material properties and other endocrine systems that subsequently affect bone, discusses the effects of T2DM medications on bone and concludes with a model identifying factors that may contribute to poor bone quality and increased bone fragility in T2DM.

A Novel Regulatory Circuit "C/EBPα/miR-20a-5p/TOB2" Regulates Adipogenesis and Lipogenesis

Recent studies have identified growing importance of microRNAs as key regulators of adipocyte differentiation. We have previously reported that miR-20a-5p is able to induce adipogenesis of established adipogenic cell lines and bone marrow derived mesenchymal stem cells (BMSCs). However, the molecular mechanisms by which miR-20a-5p controls adipogenesis and by which miR-20a-5p expression is regulated need to be further explored. In the current study we found that miR-20a-5p expression was induced during adipocyte differentiation from preadipocyte 3T3-L1 and was increased in epididymal white adipose tissue from either ob/ob mice or high fat diet-induced obese mice. Functional studies identified miR-20a-5p as a positive regulator of adipocyte differentiation and lipogenesis in 3T3-L1 by using either synthetic mimics to supplement miR-20a-5p, or using synthetic inhibitor or sponge lentivirus to inactivate endogenous miR-20a-5p. Luciferase activity assay revealed that TOB2 is a novel target of miR-20a-5p and functional experiment demonstrated its negative regulatory role in adipocyte differentiation. Moreover, Tob2 overexpression significantly attenuated adipocyte formation induced by miR-20a-5p supplementation. In-depth investigation of mechanisms that govern miR-20a-5p expression clarified that C/EBPα transcriptionally activated miR-20a-5p expression via binding to the promoter of miR-20a-5p. Taken together, we conclude that a novel C/EBPα/miR-20a-5p/TOB2 circuit exists and regulates adipogenesis and lipogenesis.

Long noncoding RNA Plnc1 controls adipocyte differentiation by regulating peroxisome proliferator-activated receptor γ

Detailed understanding of molecular mechanisms controlling adipogenesis is of great importance to identify new targets for treating obesity. Emerging evidence suggests that long noncoding RNAs (lncRNAs) may play a pivotal role in adipogenesis. Here, we have identified a novel lncRNA, Plnc1, which is transcribed from a position ∼25,000 bp upstream of the peroxisome proliferator-activated receptor γ2 ( PPAR-γ2) gene. Plnc1 is abundantly expressed in adipose tissue, and obese mice have higher Plnc1 expression in adipose tissue than nonobese mice. Plnc1 was induced in established adipogenic lines ST2, 3T3-L1, and C3H10T1/2 as well as in bone marrow stromal cells (BMSCs) after adipogenic treatment. Plnc1 knockdown blocked differentiation of ST2 cells and BMSCs into mature adipocytes, along with the reduction of PPAR-γ, CCAAT/enhancer binding protein-α, and adipocyte protein 2. Conversely, overexpression of Plnc1 promoted ST2 cells and BMSCs to fully differentiate. Mechanism studies revealed that Plnc1 could reduce the methylation level of CpG region in the PPAR-γ2 promoter and enhance the transcriptional activity of the promoter and thereby increase PPAR-γ2 transcription. Our study suggests that Plnc1 promotes adipogenic differentiation through controlling the key adipogenic transcription factor PPAR-γ and highlights the potential of Plnc1 as a target for new therapies to control metabolic disorders like obesity.-Zhu, E., Zhang, J., Li, Y., Yuan, H., Zhou, J., Wang, B. Long noncoding RNA Plnc1 controls adipocyte differentiation by regulating peroxisome proliferator-activated receptor γ.

Multiple Functional Variants at 13q14 Risk Locus for Osteoporosis Regulate RANKL Expression Through Long-Range Super-Enhancer

RANKL is a key regulator involved in bone metabolism, and a drug target for osteoporosis. The clinical diagnosis and assessment of osteoporosis are mainly based on bone mineral density (BMD). Previous powerful genomewide association studies (GWASs) have identified multiple intergenic single-nucleotide polymorphisms (SNPs) located over 100 kb upstream of RANKL and 65 kb downstream of AKAP11 at 13q14.11 for osteoporosis. Whether these SNPs exert their roles on osteoporosis through RANKL is unknown. In this study, we conducted integrative analyses combining expression quantitative trait locus (eQTL), genomic chromatin interaction (high-throughput chromosome conformation capture [Hi-C]), epigenetic annotation, and a series of functional assays. The eQTL analysis identified six potential functional SNPs (rs9533090, rs9594738, r8001611, rs9533094, rs9533095, and rs9594759) exclusively correlated with RANKL gene expression (p < 0.001) at 13q14.11. Co-localization analyses suggested that eQTL signal for RANKL and BMD-GWAS signal shared the same causal variants. Hi-C analysis and functional annotation further validated that the first five osteoporosis SNPs are located in a super-enhancer region to regulate the expression of RANKL via long-range chromosomal interaction. Particularly, dual-luciferase assay showed that the region harboring rs9533090 in the super-enhancer has the strongest enhancer activity, and rs9533090 is an allele-specific regulatory SNP. Furthermore, deletion of the region harboring rs9533090 using CRISPR/Cas9 genome editing significantly reduced RANKL expression in both mRNA level and protein level. Finally, we found that the rs9533090-C robustly recruits transcription factor NFIC, which efficiently elevates the enhancer activity and increases the RANKL expression. In summary, we provided a feasible method to identify regulatory noncoding SNPs to distally regulate their target gene underlying the pathogenesis of osteoporosis by using bioinformatics data analyses and experimental validation. Our findings would be a potential and promising therapeutic target for precision medicine in osteoporosis. © 2018 American Society for Bone and Mineral Research.

Comprehensive review and annotation of susceptibility SNPs associated with obesity-related traits

We aimed to summarize the results of genetic association studies for obesity and provide a comprehensive annotation of all susceptibility single nucleotide polymorphisms (SNPs). A total of 72 studies were summarized, resulting in 90,361 susceptibility SNPs (738 index SNPs and 89,623 linkage disequilibrium SNPs). Over 90% of the susceptibility SNPs are located in non-coding regions, and it is challenging to understand their functional significance. Therefore, we annotated these SNPs by using various functional databases. We identified 24,623 functional SNPs, including 4 nonsense SNPs, 479 missense SNPs, 399 untranslated region SNPs which might affect microRNA binding, 262 promoter and 5,492 enhancer SNPs which might affect transcription factor binding, 7 splicing sites, 76 SNPs which might affect gene methylation levels, 1,839 SNPs under natural selection and 17,351 SNPs which might modify histone binding. Expression quantitative trait loci analyses for functional SNPs identified 98 target genes, including 69 protein coding genes, 27 long non-coding RNAs and 3 processed transcripts. The percentage of protein coding genes that could be correlated with obesity-related pathways directly or through gene-gene interaction is 75.36 (52/69). Our results may serve as an encyclopaedia of obesity susceptibility SNPs and offer guide for functional experiments.

miR-20a-5p promotes adipogenic differentiation of murine bone marrow stromal cells via targeting Kruppel-like factor 3

miR-20a-5p has recently been identified to induce adipogenesis of established adipogenic cell lines in our previous study. However, its role and molecular mechanisms in the regulation of adipocyte lineage commitment of bone marrow-derived stromal cells (BMSCs) still need to be explored. In this report, we demonstrated the expression of miR-20a-5p was promoted gradually during adipogenic differentiation in BMSCs. We also confirmed that miR-20a-5p has a positive function in the adipogenic differentiation of BMSCs by gain-of-function study with overexpression lentivirus or synthetic mimics of miR-20a-5p, and loss-of-function study with sponge lentivirus or synthetic inhibitor of miR-20a-5p. Dual luciferase reporter assay, GFP repression assay and Western blotting suggested Kruppel-like factor 3 (Klf3) was a direct target of miR-20a-5p. Furthermore, siRNA-mediated silencing of Klf3 recapitulated the potentiation of adipogenesis induced by miR-20a-5p overexpression, whereas enhanced expression of Klf3 attenuated the effect of miR-20a-5p. As Klf3 was reported to play an inhibitory role in adipogenesis at the initial stage of differentiation, the findings we present here indicate that miR-20a-5p promotes adipocyte differentiation from BMSCs by targeting and negatively regulating Klf3 in the early phase during the procedure of adipogenesis.

NFIA co-localizes with PPARγ and transcriptionally controls the brown fat gene program

Brown fat dissipates energy as heat and protects against obesity. Here, we identified nuclear factor I-A (NFIA) as a transcriptional regulator of brown fat by a genome-wide open chromatin analysis of murine brown and white fat followed by motif analysis of brown-fat-specific open chromatin regions. NFIA and the master transcriptional regulator of adipogenesis, PPARγ, co-localize at the brown-fat-specific enhancers. Moreover, the binding of NFIA precedes and facilitates the binding of PPARγ, leading to increased chromatin accessibility and active transcription. Introduction of NFIA into myoblasts results in brown adipocyte differentiation. Conversely, the brown fat of NFIA-knockout mice displays impaired expression of the brown-fat-specific genes and reciprocal elevation of muscle genes. Finally, expression of NFIA and the brown-fat-specific genes is positively correlated in human brown fat. These results indicate that NFIA activates the cell-type-specific enhancers and facilitates the binding of PPARγ to control the brown fat gene program.

The role of nuclear factor I-C in tooth and bone development

Nuclear factor I-C (NFI-C) plays a pivotal role in various cellular processes such as odontoblast and osteoblast differentiation. Nfic-deficient mice showed abnormal tooth and bone formation. The transplantation of Nfic-expressing mouse bone marrow stromal cells rescued the impaired bone formation in Nfic^-/- mice. Studies suggest that NFI-C regulate osteogenesis and dentinogenesis in concert with several factors including transforming growth factor-β1, Krüppel-like factor 4, and β-catenin. This review will focus on the function of NFI-C during tooth and bone formation and on the relevant pathways that involve NFI-C.