Inhibition of Notch1 signaling by Runx2 during osteoblast differentiation

RING finger E3 ligase, RNF138 inhibits osteoblast differentiation by negatively regulating Runx2 protein turnover

A few ubiquitin ligases have been shown to target Runx2, the key osteogenic transcription factor and thereby regulate bone formation. The regulation of Runx2 expression and function are controlled both at the transcriptional and posttranslational levels. Really interesting new gene (RING) finger ubiquitin ligases of which RNF138 is a member are important players in the ubiquitin-proteasome system, contributing to the regulation of protein turnover and cellular processes. Here, we demonstrated that RNF138 negatively correlated with Runx2 protein levels in osteopenic ovariectomized rats which implied its role in bone loss. Accordingly, RNF138 overexpression potently inhibited osteoblast differentiation of mesenchyme-like C3H10T1/2 as well primary rat calvarial osteoblast (RCO) cells in vitro, whereas overexpression of catalytically inactive mutant RNF138Δ18-58 (lacks RING finger domain) had mild to no effect. Contrarily, RNF138 depletion copiously enhanced endogenous Runx2 levels and augmented osteogenic differentiation of C3H10T1/2 as well as RCOs. Mechanistically, RNF138 physically associates within multiple regions of Runx2 and ubiquitinates it leading to its reduced protein stability in a proteasome-dependent manner. Moreover, catalytically active RNF138 destabilized Runx2 which resulted in inhibition of its transactivation potential and physiological function of promoting osteoblast differentiation leading to bone loss. These findings underscore the functional involvement of RNF138 in bone formation which is primarily achieved through its modulation of Runx2 by stimulating ubiquitin-mediated proteasomal degradation. Thus, our findings indicate that RNF138 could be a promising novel target for therapeutic intervention in postmenopausal osteoporosis.

The expression of Runx2 in the pathogenesis of periodontitis

OBJECTIVE

Runt-related transcription factor 2 (Runx2) plays an important role in bone metabolism; however, the relationship between Runx2 and periodontitis remains unclear. We investigated Runx2 expression in the gingiva of patients to explore its role in periodontitis.

METHODS

Gingival samples of patients were collected, including healthy samples (control group) and periodontitis samples (P group). Periodontitis samples were divided into three groups based on the periodontitis stage. Samples with stage I and grade B periodontitis were in the P1 group, stage II and grade B in the P2 group, and stage III or IV and grade B in the P3 group. Immunohistochemistry and western blotting were performed to detect Runx2 levels. The probing (PD) and clinical attachment loss (CAL) were recorded.

RESULTS

Runx2 expression levels in the P and P3 groups were higher than those in the control group. In addition, Runx2 expression was positively correlated with CAL and PD (r1 = 0.435, r2 = 0.396).

CONCLUSION

The high expression level of Runx2 in the gingiva of patients with periodontitis may be correlated with the pathogenesis of periodontitis.

Upregulated LncRNA H19 Sponges MiR-106a-5p and Contributes to Aldosterone-Induced Vascular Calcification via Activating the Runx2-Dependent Pathway

BACKGROUND

Excess aldosterone is implicated in vascular calcification (VC), but the mechanism by which aldosterone-MR (mineralocorticoid receptor) complex promotes VC is unclear. Emerging evidence indicates that long-noncoding RNA H19 (H19) plays a critical role in VC. We examined whether aldosterone-induced osteogenic differentiation of vascular smooth muscle cells (VSMCs) through H19 epigenetic modification of Runx2 (runt-related transcription factor-2) in a MR-dependent manner.

METHODS

We induced in vivo rat model of chronic kidney disease using a high adenine and phosphate diet to explore the relationship among aldosterone, MR, H19, and VC. We also cultured human aortic VSMCs to explore the roles of H19 in aldosterone-MR complex-induced osteogenic differentiation and calcification of VSMCs.

RESULTS

H19 and Runx2 were significantly increased in aldosterone-induced VSMC osteogenic differentiation and VC, both in vitro and in vivo, which were significantly blocked by the MR antagonist spironolactone. Mechanistically, our findings reveal that the aldosterone-activated MR bound to H19 promoter and increased its transcriptional activity, as determined by chromatin immunoprecipitation, electrophoretic mobility shift assay, and luciferase reporter assay. Silencing H19 increased microRNA-106a-5p (miR-106a-5p) expression, which subsequently inhibited aldosterone-induced Runx2 expression at the posttranscriptional level. Importantly, we observed a direct interaction between H19 and miR-106a-5p, and downregulation of miR-106a-5p efficiently reversed the suppression of Runx2 induced by H19 silencing.

CONCLUSIONS

Our study clarifies a novel mechanism by which upregulation of H19 contributes to aldosterone-MR complex-promoted Runx2-dependent VSMC osteogenic differentiation and VC through sponging miR-106a-5p. These findings highlight a potential therapeutic target for aldosterone-induced VC.

Novel Adipokines and Their Role in Bone Metabolism: A Narrative Review

The growing burden of obesity and osteoporosis is a major public health concern. Emerging evidence of the role of adipokines on bone metabolism has led to the discovery of novel adipokines over the last decade. Obesity is recognized as a state of adipose tissue inflammation that adversely affects bone health. Adipokines secreted from white adipose tissue (WAT) and bone marrow adipose tissue (BMAT) exerts endocrine and paracrine effects on the survival and function of osteoblasts and osteoclasts. An increase in marrow fat is implicated in osteoporosis and, hence, it is crucial to understand the complex interplay between adipocytes and bone. The objective of this review is to summarize recent advances in our understanding of the role of different adipokines on bone metabolism.

METHODS

This is a comprehensive review of the literature available in PubMED and Cochrane databases, with an emphasis on the last five years using the keywords.

RESULTS

Leptin has shown some positive effects on bone metabolism; in contrast, both adiponectin and chemerin have consistently shown a negative association with BMD. No significant association was found between resistin and BMD. Novel adipokines such as visfatin, LCN-2, Nesfatin-1, RBP-4, apelin, and vaspin have shown bone-protective and osteoanabolic properties that could be translated into therapeutic targets.

CONCLUSION

New evidence suggests the potential role of novel adipokines as biomarkers to predict osteoporosis risk, and as therapeutic targets for the treatment of osteoporosis.

Circ_CUX1/miR-130b-5p/p300 axis for parathyroid hormone-stimulation of Runx2 activity in rat osteoblasts: A combined bioinformatic and experimental approach

Parathyroid hormone (PTH) regulates the expression of bone remodeling genes by enhancing the activity of Runx2 in osteoblasts. p300, a histone acetyltransferase, acetylated Runx2 to activate the expression of its target genes. PTH stimulated the expression of p300 in rat osteoblastic cells. Increasing studies suggested the potential of non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and circular RNAs (circRNAs), in regulating gene expression under both physiological and pathological conditions. In this study, we hypothesized that PTH regulates Runx2 activity via ncRNAs-mediated p300 expression in rat osteoblastic cells. Bioinformatics and experimental approaches identified PTH-upregulation of miR-130b-5p and circ_CUX1 that putatively target p300 and miR-130b-5p, respectively. An antisense-mediated knockdown of circ_CUX1 was performed to determine the sponging activity of circ_CUX1. Knockdown of circ_CUX1 promoted miR-130b-5p activity and reduced p300 expression, resulting in decreased Runx2 acetylation in rat osteoblastic cells. Further, bioinformatics analysis identified the possible signaling pathways that regulate Runx2 activity and osteoblast differentiation via circ_CUX1/miR-130b-5p/p300 axis. The predicted circ_CUX1/miR-130b-5p/p300 axis might pave the way for better diagnostic and therapeutic approaches for bone-related diseases.

The role of Notch signaling pathway in metabolic bone diseases

Metabolic bone diseases is the third most common endocrine diseases after diabetes and thyroid diseases. More than 500 million people worldwide suffer from metabolic bone diseases. The generation and development of bone metabolic diseases is a complex process regulated by multiple signaling pathways, among which the Notch signaling pathway is one of the most important pathways. The Notch signaling pathway regulates the differentiation and function of osteoblasts and osteoclasts, and affects the process of cartilage formation, bone formation and bone resorption. Genetic mutations in upstream and downstream of Notch signaling genes can lead to a series of metabolic bone diseases, such as Alagille syndrome, Adams-Oliver syndrome and spondylocostal dysostosis. In this review, we analyzed the mechanisms of Notch ligands, Notch receptors and signaling molecules in the process of signal transduction, and summarized the progress on the pathogenesis and clinical manifestations of bone metabolic diseases caused by Notch gene mutation. We hope to draw attention to the role of the Notch signaling pathway in metabolic bone diseases and provide new ideas and approaches for the diagnosis and treatment of metabolic bone diseases.

Ginsenoside Rg1 interferes with the progression of diabetic osteoporosis by promoting type H angiogenesis modulating vasculogenic and osteogenic coupling

Ginsenoside Rg1 (Rg1) has been demonstrated to have antidiabetic and antiosteoporotic activities. The aim of this study was to investigate the protective effect of Rg1 against diabetic osteoporosis and the underlying mechanism. In vitro, we found that Rg1 increased the number of osteoprogenitors and alleviated high glucose (HG) induced apoptosis of osteoprogenitors by MTT assays and flow cytometry. qRT‒PCR and western blot analysis suggested that Rg1 can also promote the secretion of vascular endothelial growth factor (VEGF) by osteoprogenitors and promote the coupling of osteogenesis and angiogenesis. Rg1 can also promote the proliferation of human umbilical vein endothelial cells (HUVECs) cultured in high glucose, enhance the angiogenic ability of endothelial cells, and activate the Notch pathway to promote endothelial cells to secrete the osteogenesis-related factor Noggin to regulate osteogenesis, providing further feedback coupling of angiogenesis and osteogenesis. Therefore, we speculated that Rg1 may have similar effects on type H vessels. We used the Goto-Kakizaki (GK) rat model to perform immunofluorescence staining analysis on two markers of type H vessels, Endomucin (Emcn) and CD31, and the osteoblast-specific transcription factor Osterix, and found that Rg1 stimulates type H angiogenesis and bone formation. In vivo experiments also demonstrated that Rg1 promotes VEGF secretion, activates the Noggin/Notch pathway, increases the level of coupling between type H vessels and osteogenesis, and improves the bone structure of GK rats. All of these data reveal that Rg1 is a promising candidate drug for treating diabetic osteoporosis as a potentially bioactive molecule that promotes angiogenesis and osteointegration coupling.

Epigenetic Upregulation of H19 and AMPK Inhibition Concurrently Contribute to S-Adenosylhomocysteine Hydrolase Deficiency-Promoted Atherosclerotic Calcification

BACKGROUND

S-adenosylhomocysteine (SAH) is a risk factor of cardiovascular disease; inhibition of SAH hydrolase (SAHH) results in SAH accumulation and induces endothelial dysfunction and atherosclerosis. However, the effect and mechanism of SAHH in atherosclerotic calcification is still unclear. We aimed to explore the role and mechanism of SAHH in atherosclerotic calcification.

METHODS

The relationship between SAHH and atherosclerotic calcification was investigated in patients with coronary atherosclerotic calcification. Different in vivo genetic models were used to examine the effect of SAHH deficiency on atherosclerotic calcification. Human aortic and murine vascular smooth muscle cells (VSMCs) were cultured to explore the underlying mechanism of SAHH on osteoblastic differentiation of VSMCs.

RESULTS

The expression and activity of SAHH were decreased in calcified human coronary arteries and inversely associated with coronary atherosclerotic calcification severity, whereas plasma SAH and total homocysteine levels were positively associated with coronary atherosclerotic calcification severity. Heterozygote knockout of SAHH promoted atherosclerotic calcification. Specifically, VSMC-deficient but not endothelial cell-deficient or macrophage-deficient SAHH promoted atherosclerotic calcification. Mechanistically, SAHH deficiency accumulated SAH levels and induced H19-mediated Runx2 (runt-related transcription factor 2)-dependent osteoblastic differentiation of VSMCs by inhibiting DNMT3b (DNA methyltransferase 3 beta) and leading to hypomethylation of the H19 promoter. On the other hand, SAHH deficiency resulted in lower intracellular levels of adenosine and reduced AMPK (AMP-activated protein kinase) activation. Adenosine supplementation activated AMPK and abolished SAHH deficiency-induced expression of H19 and Runx2 and osteoblastic differentiation of VSMCs. Finally, AMPK activation by adenosine inhibited H19 expression by inducing Sirt1-mediated histone H3 hypoacetylation and DNMT3b-mediated hypermethylation of the H19 promoter in SAHH deficiency VSMCs.

CONCLUSIONS

We have confirmed a novel correlation between SAHH deficiency and atherosclerotic calcification and clarified a new mechanism that epigenetic upregulation of H19 and AMPK inhibition concurrently contribute to SAHH deficiency-promoted Runx2-dependent atherosclerotic calcification.

Signaling network regulating osteogenesis in mesenchymal stem cells

Osteogenesis is an important developmental event that results in bone formation. Bone forming cells or osteoblasts develop from mesenchymal stem cells (MSCs) through a highly controlled process regulated by several signaling pathways. The osteogenic lineage commitment of MSCs is controlled by cell-cell interactions, paracrine factors, mechanical signals, hormones, and cytokines present in their niche, which activate a plethora of signaling molecules belonging to bone morphogenetic proteins, Wnt, Hedgehog, and Notch signaling. These signaling pathways individually as well as in coordination with other signaling molecules, regulate the osteogenic lineage commitment of MSCs by activating several osteo-lineage specific transcription factors. Here, we discuss the key signaling pathways that regulate osteogenic differentiation of MSCs and the cross-talk between them during osteogenic differentiation. We also discuss how these signaling pathways can be modified for therapy for bone repair and regeneration.

Microfibrillar-associated protein 5 regulates osteogenic differentiation by modulating the Wnt/β-catenin and AMPK signaling pathways

Background

Dysfunctional osteogenesis of bone marrow mesenchymal stem cells (BMSCs) plays an important role in osteoporosis occurrence and development. However, the molecular mechanisms of osteogenic differentiation remain unclear. This study explored whether microfibrillar-associated protein 5 (MFAP5) regulated BMSCs osteogenic differentiation.

Methods

We used shRNA or cDNA to knock down or overexpress MFAP5 in C3H10 and MC3T3-E1 cells. AR-S- and ALP-staining were performed to quantify cellular osteogenic differentiation. The mRNA levels of the classical osteogenic differentiation biomarkers Runx2, Col1α1, and OCN were quantified by qRT-PCR. Finally, we employed Western blotting to measure the levels of Wnt/β-catenin and AMPK signaling proteins.

Results

At days 0, 3, 7, and 14 after osteogenic induction, AR-S- and ALP-staining was lighter in MFAP5 knockdown compared to control cells, as were the levels of Runx2, Col1α1 and OCN. During osteogenesis, the levels of β-catenin, p-GSK-3β, AMPK, and p-AMPK were upregulated, while that of GSK-3β was downregulated, indicating that Wnt/β-catenin and AMPK signaling were activated. The relevant molecules were expressed at lower levels in the knockdown than control group; the opposite was seen for overexpressing cell lines.

Conclusions

MFAP5 regulates osteogenesis via Wnt/β‑catenin- and AMPK-signaling; MFAP5 may serve as a therapeutic target in patients with osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00413-0.

Enhanced Osteogenesis of Dental Pulp Stem Cells In Vitro Induced by Chitosan-PEG-Incorporated Calcium Phosphate Cement

The use of bone graft materials is required for the treatment of bone defects damaged beyond the critical defect; therefore, injectable calcium phosphate cement (CPC) is actively used after surgery. The application of various polymers to improve injectability, mechanical strength, and biological function of injection-type CPC is encouraged. We previously developed a chitosan–PEG conjugate (CS/PEG) by a sulfur (VI) fluoride exchange reaction, and the resulting chitosan derivative showed high solubility at a neutral pH. We have demonstrated the CPC incorporated with a poly (ethylene glycol) (PEG)-grafted chitosan (CS/PEG) and developed CS/PEG CPC. The characterization of CS/PEG CPC was conducted using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The initial properties of CS/PEG CPCs, such as the pH, porosity, mechanical strength, zeta potential, and in vitro biocompatibility using the WST-1 assay, were also investigated. Moreover, osteocompatibility of CS/PEG CPCs was carried out via Alizarin Red S staining, immunocytochemistry, and Western blot analysis. CS/PEG CPC has enhanced mechanical strength compared to CPC, and the cohesion test also demonstrated in vivo stability. Furthermore, we determined whether CS/PEG CPC is a suitable candidate for promoting the osteogenic ability of Dental Pulp Stem Cells (DPSC). The elution of CS/PEG CPC entraps more calcium ion than CPC, as confirmed through the zeta potential test. Accordingly, the ion trapping effect of CS/PEG is considered to have played a role in promoting osteogenic differentiation of DPSCs. The results strongly suggested that CS/PEG could be used as suitable additives for improving osteogenic induction of bone substitute materials.

Long noncoding RNA HCG18 inhibits the differentiation of human bone marrow-derived mesenchymal stem cells in osteoporosis by targeting miR-30a-5p/NOTCH1 axis

Background

Recent studies have demonstrated that long non-coding RNAs (LncRNAs) can influence bone cell differentiation and formation. However, it is unclear whether lncRNA HCG18 is involved in osteoporosis (OP). This study was conducted to investigate the regulation of HCG18 in osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs).

Methods

BMSCs were isolated and cultured from mouse pathological models and osteoporosis patients. RT-qPCR was performed to detect the expression of HCG18 and miR-30a-5p in BMSCs. The interaction between HCG18 and miR-30a-5p was analyzed by dual luciferase assay and RNA pulldown assay. The interaction between miR-30a-5p and NOTCH1 3′-UTR was analyzed by dual luciferase assay. RT-qPCR and Western blotting were used to detect the expression of osteogenic genes Runx2, OCN and OPN. Hindlimb-unloaded (HU) mice model was established, and HCG18 was knocked down on bone-formation surfaces by using lentivirus mediated shRNA transfection.

Results

The expression of HCG18 was increased in BMSCs of OP patients, while the expression of miR-30a-5p was decreased. The expression of HCG18 and miR-30a-5p was negatively correlated in BMSCs. During the differentiation from BMSCs to osteoblasts, the expression of HCG18 was significantly downregulated, and the expression of miR-30a-5p was significantly upregulated. Overexpression of HCG18 was able to reverse the osteogenic-induced upregulation of miR-30a-5p expression, and knockdown of HCG18 further promoted the expression of miR-30a-5p. In addition, miR-30a-5p partially abolished the effect of HCG18 on osteogenic differentiation of BMSCs. NOTCH1 was a target protein of miR-30a-5p, and upregulation of NOTCH1 reversed the effect of miR-30a-5p on osteogenic differentiation of BMSCs. Furthermore, this study found that lentivirus mediated HCG18 knockdown on the bone-formation surfaces of hindlimb-unloaded (HU) mice partially alleviated unloading-induced bone loss

Conclusions

HCG18 inhibited osteogenic differentiation of BMSCs induced by OP via the miR-30a-5p/NOTCH1 axis. HCG18 can be identified as a regulator of osteogenic differentiation of BMSCs.

Akt1-Mediated Phosphorylation of RBP-Jk Controls Notch1 Signaling

The Notch1 signaling pathway plays a crucial role in determining cell fate, including cell growth and differentiation. In this study, we demonstrated that the antagonistic action of RTK (receptor tyrosine kinase) signaling pathway on the Notch1 signaling pathway is mediated via Ras-PI3K-Akt1. The PI3K-Akt1 signaling pathway was shown to inhibit Notch1 signaling via phosphorylation of RBP-Jk. We observed not only reduced association between Notch1 and RBP-Jk, but also suppression of the Notch1 transcriptional activity. Our results demonstrated that Akt1 functions as a natural inhibitor of the Notch1 signaling pathway via phosphorylation of RBP-Jk.

miR-487b-3p impairs osteoblastogenesis by targeting Notch-regulated ankyrin-repeat protein (Nrarp)

miRNAs have appeared as critical controllers of gene expression at post-transcriptional level either by degrading RNA transcripts or repressing translation. It is evident from the ever-growing scientific literature that miRNAs play a significant role in osteoblast commitment and differentiation. Here, we report that overexpression of miR-487b-3p leads to inhibition of osteoblastic differentiation. Using in silico approaches, Nrarp was found to be the direct target of miR-487b-3p, which was further validated by luciferase 3' UTR reporter assay. Nrarp inhibits Notch-1 signaling and promotes Wnt signaling by stabilization of LEF-1. Role of miR-487b-3p in regulating canonical Wnt and Notch signaling was determined by western blotting. Protein levels of Nrarp, RUNX-2, Lef1 and β catenin were reduced in osteoblasts cells transfected with miR-487b-3p, whereas protein levels of Notch1, Hes1 and P-β catenin were upregulated when osteoblast cells were transfected with miR-487b-3p. These outcomes were reversed after treating cells with anti-miR-487b-3p. Further silencing of miR-487b-3p in neonatal Balb/c mice attenuated all the inhibitory actions of miR-487b-3p on osteoblast differentiation. Importantly, in vivo action of anti-miR-487b-3p to ovariectomized osteopenic BALB/c mice steered to significant enhancement in trabecular bone microarchitecture. Furthermore, the bio-mechanical properties of isolated femurs were enhanced in anti-miR-487b-3p-treated mice. Overall, miR-487b-3p negatively regulates osteogenesis by suppressing Nrarp expression, which in turn, suppresses Runx-2 and Wnt signaling, both of which play a pivotal action in osteoblast differentiation.

RUNX family: Oncogenes or tumor suppressors (Review)

Runt-related transcription factor (RUNX) proteins belong to a transcription factors family known as master regulators of important embryonic developmental programs. In the last decade, the whole family has been implicated in the regulation of different oncogenic processes and signaling pathways associated with cancer. Furthermore, a suppressor tumor function has been also reported, suggesting the RUNX family serves key role in all different types of cancer. In this review, the known biological characteristics, specific regulatory abilities and experimental evidence of RUNX proteins will be analyzed to demonstrate their oncogenic potential and tumor suppressor abilities during oncogenic processes, suggesting their importance as biomarkers of cancer. Additionally, the importance of continuing with the molecular studies of RUNX proteins' and its dual functions in cancer will be underlined in order to apply it in the future development of specific diagnostic methods and therapies against different types of cancer.

Activation of Notch1 signaling by HTLV-1 Tax promotes proliferation of adult T-cell leukemia cells

Human T-cell leukemia virus 1 (HTLV-1), an oncogenic retrovirus, and Notch1 signaling, implicated in tumor formation and progression, are both associated with the development of adult T-cell leukemia (ATL). Here we explored the possibility of a mechanistic link between the two. We observed that the expression of Notch intracellular domain (NICD) was elevated in HTLV-1 infected cell lines. Knocking down of Notch1 in ATL cells repressed cellular proliferation and tumor formation both in vitro and in vivo. As a mechanism for these actions, we found that Tax activated Notch1 signaling by prolonging the half-life of NICD. We then showed that Tax, NICD, and RBP-jκ formed a ternary complex, that Tax enhanced the association of NICD with RBP-jκ, and that Tax, NICD, and RBP-jκ were bound to RBP-jκ-responsive elements. Hence, our results suggest that HTLV-1 promotes cellular proliferation and tumor formation of ATL cells by modulating Notch signaling via a posttranslational mechanism that involves interactions between Tax, NICD, and RBP-jκ.

The regulatory roles of Notch in osteocyte differentiation via the crosstalk with canonical Wnt pathways during the transition of osteoblasts to osteocytes

Osteocytes comprise more than 90% of the cells in bone and are differentiated from osteoblasts via an unknown mechanism. Recently, it was shown that Notch signaling plays an important role in osteocyte functions. To gain insights into the mechanisms underlying the functions of Notch in regulating the transition of osteoblasts to osteocytes, we performed a luciferase assay by cloning the proximal E11 and dentin matrix acidic phosphoprotein 1 (DMP1) promotor regions into pGluc-Basic 2 vectors, which were subsequently transfected into the IDG-SW3 (osteocytes), MC3T3 (osteoblasts) and 293T (non-osteoblastic cells) cell lines. Two approaches were used to activate Notch signaling in vitro. One was a Notch1 extracellular antibody-coated cell culture plate, and the other was transfection of a Hairy/Enhancer of Split 1 (Hes1) overexpression vector. The interaction between the Notch and Wnt signaling pathways was probed by assessing the expression of a series of phosphorylated proteins involved in the cascade of both signaling pathways. Our data suggested that Notch signaling regulates E11 expression through Hes1 activity, while Hes1 solely did not initiate the expression of DMP1. The regulatory function of E11 by Hes1 was not observed in the 293T cell line, indicating a cell context-dependent manner of the Notch signaling pathway. Additionally, we found that Notch inhibited Wnt signaling at the late differentiation stage of osteocytes by both directly repressing phosphorylated Akt and preventing the nuclear aggregation of β-catenin. These findings provide profound understandings of Notch's regulatory function in osteocyte differentiation.

Notch signaling negatively regulates BMP9-induced osteogenic differentiation of mesenchymal progenitor cells by inhibiting JunB expression

Although interaction between BMP and Notch signaling has been demonstrated to be crucial for osteogenic differentiation of mesenchymal stem cells (MSCs), the precise molecular mechanism remains unknown. Here, we show that Notch intracellular domain (NICD) overexpression inhibits BMP9-induced C3H10T1/2 cell osteogenesis in vivo and in vitro. Our results show that activated Notch signaling results in down-regulation of Runx2 and early osteogenesis differentiation factors, without affecting p-Smad1/5/8 expression, and that blocking Notch signaling with DAPT (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) significantly increases p-Smad1/5/8 expression. Interestingly, Notch signaling also regulates the cell cycle by increasing PCNA (proliferation cell nuclear antigen) and CyclinD1 expression. Furthermore, similar results were obtained by ectopic bone formation and histological analyses, indicating that Notch signaling activation significantly inhibits BMP9-induced MSC osteogenic, cartilage and adipogenic differentiation. Moreover, we are the first to show that Notch regulates by suppressing JunB synthesis and that the negative effect of Notch is partially reversed by treatment with the JunB activator TPA (12-O-tetradeca-noylphorbol-13-acetate). Our findings demonstrate that Notch signaling significantly enhances cell proliferation but inhibits MSC osteogenic differentiation induced by BMP9 via JunB protein suppression rather than by BMP/Smad signaling regulation.

Pathophysiology of Aortic Stenosis and Mitral Regurgitation

The global impact of the spectrum of valve diseases is a crucial, fast-growing, and underrecognized health problem. The most prevalent valve diseases, requiring surgical intervention, are represented by calcific and degenerative processes occurring in heart valves, in particular, aortic and mitral valve. Due to the increasing elderly population, these pathologies will gain weight in the global health burden. The two most common valve diseases are aortic valve stenosis (AVS) and mitral valve regurgitation (MR). AVS is the most commonly encountered valve disease nowadays and affects almost 5% of elderly population. In particular, AVS poses a great challenge due to the multiple comorbidities and frailty of this patient subset. MR is also a common valve pathology and has an estimated prevalence of 3% in the general population, affecting more than 176 million people worldwide. This review will focus on pathophysiological changes in both these valve diseases, starting from the description of the anatomical aspects of normal valve, highlighting all the main cellular and molecular features involved in the pathological progression and cardiac consequences. This review also evaluates the main approaches in clinical management of these valve diseases, taking into account of the main published clinical guidelines. © 2017 American Physiological Society. Compr Physiol 7:799-818, 2017.

Gene expression profile in human induced pluripotent stem cells: Chondrogenic differentiation in vitro, part B

The development of human induced pluripotent stem cells (hiPSCs) is considered a turning point in tissue engineering. However, more data are required to improve understanding of key aspects of the cell differentiation process, including how specific chondrogenic processes affect the gene expression profile of chondrocyte‑like cells and the relative value of cell differentiation markers. The main aims of the present study were as follows: To determine the gene expression profile of chondrogenic‑like cells derived from hiPSCs cultured in mediums conditioned with HC‑402‑05a cells or supplemented with transforming growth factor β3 (TGF‑β3), and to assess the relative utility of the most commonly‑used chondrogenic markers as indicators of cell differentiation. These issues are relevant with regard to the use of human fibroblasts in the reprogramming process to obtain hiPSCs. Human fibroblasts are derived from mesoderm and thus share a wide range of properties with chondrocytes, which originate from the mesenchyme. The hiPSCs were obtained from human primary dermal fibroblasts during a reprogramming process. Two methods, both involving embryoid bodies (EB), were used to obtain chondrocytes from the hiPSCs: EBs formed in the presence of a chondrogenic medium with TGF‑β3 (10 ng/ml) and EBs formed in a medium conditioned with growth factors from HC‑402‑05a cells. Based on reverse transcription-quantitative polymerase chain reaction analysis, the results demonstrated that hiPSCs are capable of effective chondrogenic differentiation, with the cells obtained in the HC‑402‑05a medium presenting with morphological features and markers characteristic of mature human chondrocytes. In contrast, cells differentiated in the presence of TGF‑β3 presented with certain undesirable hypertrophic characteristics. Several genes, most notably runt‑related transcription factor 2, transforming growth factor β2 and transforming growth factor β3, were good markers of advanced and late hiPSC chondrogenic differentiation, whereas transforming growth factor β3I, II, III receptors and bone morphogenetic protein-2, bone morphogenetic protein-4 and growth differentiation factor 5 were less valuable. These findings provide valuable data on the use of stem cells in cartilage tissue regeneration.

Up-regulation of microRNA let-7c by quercetin inhibits pancreatic cancer progression by activation of Numbl

Pancreatic Ductal Adenocarcinoma (PDA) is a highly malignant tumor with poor prognosis. MicroRNAs (miRs) may offer novel therapeutic approaches to treatment. The polyphenol quercetin, present in many fruits and vegetables, possesses anti-carcinogenic properties. To unravel the effect of quercetin to miR signaling we performed miR profiling in PDA cells before and after quercetin treatment, followed by biostatistical analysis. miR let-7c was among the top up-regulated candidates after quercetin treatment, as measured by qRT-PCR and confirmed in two established and one primary PDA cell lines. By computational analysis we identified the Notch-inhibitor Numbl as let-7c target gene. This was strengthened by luciferase assays, where lipofected let-7c mimics induced a Numbl 3-UTR wild type construct, but not the mutated counterpart. Let-7c induced Numbl mRNA and protein expression but inhibited Notch just like quercetin. It also inhibited colony formation, wound healing, and protein expression of progression markers. In vivo xenotransplantation of PDA cells and subsequent intravenous injection of let-7c resulted in a significant decrease in tumor mass without obvious toxic effects in the fertilized chick egg model. The delivery rate of the miR mimics to the tumor mass was 80%, whereas minor amounts were present in host tissue. By immunohistochemistry we demonstrated that let-7c inhibited Notch and progression markers but up-regulated Numbl. These findings show that quercetin-induced let-7c decreases tumor growth by posttranscriptional activation of Numbl and indirect inhibition of Notch.

BMP9 a possible alternative drug for the recently withdrawn BMP7? New perspectives for (re-)implementation by personalized medicine

Promotion of rhBMP2 and rhBMP7 for the routine use to support fracture healing has been hampered by high costs, safety concerns and reasonable failure rates, imposing restrictions in its clinical use. Since there is little debate regarding its treatment potential, there is rising need for a better understanding of the mode of action of these BMPs to overcome its drawbacks and promote more efficacious treatment strategies for bone regeneration. Recently, BMP9, owing to its improved osteogenic potential, is gaining attention as a promising therapeutic alternative. Our study aimed at identifying specific gene expression patterns which may predict and explain individual responses to rhBMP7 and rhBMP9 treatments. Therefore, we investigated the effect of rhBMP7 and rhBMP9 on primary human osteoblasts from 110 donors and corresponding THP-1-derived osteoclasts. This was further compared with each other and our reported data on rhBMP2 response. Based on the individual donor response, we found three donor groups profiting from rhBMP treatment either directly via stimulation of osteoblast function or viability and/or indirectly via inhibition of osteoclasts. The response on rhBMP7 treatment correlated with expression levels of the genes BAMBI, SOST, Noggin, Smad4 and RANKL, while the response of rhBMP9 correlated to the expression levels of Alk6, Endoglin, Smurf1, Smurf2, SOST and RANKL in these donors. Noteworthy, rhBMP9 treatment showed significantly increased osteogenic activity (AP activity and Smad nuclear translocation) when compared to the two clinically used rhBMPs. Based on patient's respective expression profiles, clinical application of rhBMP9 either solely or in combination with rhBMP2 and/or rhBMP7 can become a promising new approach to fit the patient's needs to promote fracture healing.

Tumor Suppressor HIPK2 Regulates Malignant Growth via Phosphorylation of Notch1

The receptor Notch1 plays an important role in malignant progression of many cancers, but its regulation is not fully understood. In this study, we report that the kinase HIPK2 is responsible for facilitating the Fbw7-dependent proteasomal degradation of Notch1 by phosphorylating its intracellular domain (Notch1-IC) within the Cdc4 phosphodegron motif. Notch1-IC expression was higher in cancer cells than normal cells. Under genotoxic stress, Notch1-IC was phosphorylated constitutively by HIPK2 and was maintained at a low level through proteasomal degradation. HIPK2 phosphorylated the residue T2512 in Notch1-IC. Somatic mutations near this residue rendered Notch1-IC resistant to degradation, as induced either by HIPK2 overexpression or adriamycin treatment. In revealing an important mechanism of Notch1 stability, the results of this study could offer a therapeutic strategy to block Notch1-dependent progression in many types of cancer. Cancer Res; 76(16); 4728-40. ©2016 AACR.

Cells and extracellular matrix interplay in cardiac valve disease: because age matters

Cardiovascular aging is a physiological process affecting all components of the heart. Despite the interest and experimental effort lavished on aging of cardiac cells, increasing evidence is pointing at the pivotal role of extracellular matrix (ECM) in cardiac aging. Structural and molecular changes in ECM composition during aging are at the root of significant functional modifications at the level of cardiac valve apparatus. Indeed, calcification or myxomatous degeneration of cardiac valves and their functional impairment can all be explained in light of age-related ECM alterations and the reciprocal interplay between altered ECM and cellular elements populating the leaflet, namely valvular interstitial cells and valvular endothelial cells, is additionally affecting valve function with striking reflexes on the clinical scenario. The initial experimental findings on this argument are underlining the need for a more comprehensive understanding on the biological mechanisms underlying ECM aging and remodeling as potentially constituting a pharmacological therapeutic target or a basis to improve existing prosthetic devices and treatment options. Given the lack of systematic knowledge on this topic, this review will focus on the ECM changes that occur during aging and on their clinical translational relevance and implications in the bedside scenario.

Skp2 inhibits osteogenesis by promoting ubiquitin-proteasome degradation of Runx2

Osteogenic transcription factor Runx2 is essential for osteoblast differentiation. The activity of Runx2 is tightly regulated at transcriptional as well as post-translational level. However, regulation of Runx2 stability by ubiquitin mediated proteasomal degradation by E3 ubiquitin ligases is little-known. Here, for the first time we demonstrate that Skp2, an SCF family E3 ubiquitin ligase negatively targets Runx2 by promoting its polyubiquitination and proteasome dependent degradation. Co-immunoprecipitation studies revealed that Skp2 physically interacts with Runx2 both in a heterologous as well as physiologically relevant system. Functional consequences of Runx2-Skp2 physical interaction were then assessed by promoter reporter assay. We show that Skp2-mediated downregulation of Runx2 led to reduced Runx2 transactivation and osteoblast differentiation. On the contrary, inhibition of Skp2 restored Runx2 levels and promoted osteoblast differentiation. We further show that Skp2 and Runx2 proteins are co-expressed and show inverse relation in vivo such as in lactating, ovariectomized and estrogen-treated ovariectomized animals. Together, these data demonstrate that Skp2 targets Runx2 for ubiquitin mediated degradation and hence negatively regulate osteogenesis. Therefore, the present study provides a plausible therapeutic target for osteoporosis or cleidocranial dysplasia caused by the heterozygous mutation of Runx2 gene.

The soluble form of BMPRIB is a novel therapeutic candidate for treating bone related disorders

Bone morphogenetic proteins (BMPs) are multi-functional growth factors that belong to the TGF-beta superfamily. Recently, several soluble BMP receptors, such as ActRIIA-Fc, ActRIIB-Fc, and ALK1-Fc, are undergoing clinical trials. Both BMPRIA and BMPRIB are type I BMP receptors, and while BMPRIA-Fc has been reported to have bone-increasing properties, there have been no investigations concerning the biological functions of BMPRIB-Fc. Therefore, comparing the effects of BMPRIA-Fc and BMPRIB-Fc in vivo should be helpful in revealing the differences in biological function between BMPRIA and BMPRIB, and would also aid in the evaluation of BMPRIB-Fc as a therapeutic agent. Here, we produced Tg chimeras in which BMPRIA-Fc and BMPRIB-Fc proteins circulated at high concentrations (36.8–121.4 μg/mL). Both Tg chimeras showed a significant increase of bone volume and strength. Using histological analysis, adenoma of the glandular stomach was observed only in BMPRIA-Fc chimeras suggesting the tumorigenic activity of this protein. Administration of recombinant BMPRIB-Fc protein to normal mice also increased bone volumes. Finally, treatment with BMPRIB-Fc decreased the area of osteolytic regions in a mouse model of breast cancer metastasis. In conclusion, our data suggest that BMPRIB-Fc can be used for the treatment of bone-related disorders with a lower risk than BMPRIA-Fc.

E3 Ubiquitin Ligase Fbw7 Negatively Regulates Osteoblast Differentiation by Targeting Runx2 for Degradation

Runx2, a master regulator of osteoblast differentiation, is tightly regulated at both transcriptional and post-translational levels. Post-translational modifications such as phosphorylation and ubiquitination have differential effects on Runx2 functions. Here, we show that the reduced expression and functions of Runx2 upon its phosphorylation by GSK3β are mediated by its ubiquitin-mediated degradation through E3 ubiquitin ligase Fbw7α. Fbw7α through its WD domain interacts with Runx2 both in a heterologous (HEK293T cells) system as well as in osteoblasts. GSK3β was also present in the same complex as determined by co-immunoprecipitation. Furthermore, overexpression of either Fbw7α or GSK3β was sufficient to down-regulate endogenous Runx2 expression and function; however, both failed to inhibit endogenous Runx2 when either of them was depleted in osteoblasts. Fbw7α-mediated inhibition of Runx2 expression also led to reduced Runx2 transactivation and osteoblast differentiation. In contrast, inhibition of Fbw7α restored Runx2 levels and promoted osteoblast differentiation. We also observed reciprocal expression levels of Runx2 and Fbw7α in models of bone loss such as lactating (physiological bone loss condition) and ovariectomized (induction of surgical menopause) animals that show reduced Runx2 and enhanced Fbw7α, whereas this was reversed in the estrogen-treated ovariectomized animals. In addition, methylprednisolone (a synthetic glucocorticoid) treatment to neonatal rats showed a temporal decrease in Runx2 with a reciprocal increase in Fbw7 in their calvarium. Taken together, these data demonstrate that Fbw7α negatively regulates osteogenesis by targeting Runx2 for ubiquitin-mediated degradation in a GSK3β-dependent manner and thus provides a plausible explanation for GSK3β-mediated bone loss as described before.

Acute Lymphoblastic Leukemia Cells Inhibit the Differentiation of Bone Mesenchymal Stem Cells into Osteoblasts In Vitro by Activating Notch Signaling

The disruption of normal hematopoiesis has been observed in leukemia, but the mechanism is unclear. Osteoblasts originate from bone mesenchymal stem cells (BMSCs) and can maintain normal hematopoiesis. To investigate how leukemic cells inhibit the osteogenic differentiation of BMSCs and the role of Notch signaling in this process, we cocultured BMSCs with acute lymphoblastic leukemia (ALL) cells in osteogenic induction medium. The expression levels of Notch1, Hes1, and the osteogenic markers Runx2, Osteopontin (OPN), and Osteocalcin (OCN) were assessed by real-time RT-PCR and western blotting on day 3. Alkaline phosphatase (ALP) activity was analyzed using an ALP kit, and mineralization deposits were detected by Alizarin red S staining on day 14. And then we treated BMSCs with Jagged1 and anti-Jagged1 neutralizing Ab. The expression of Notch1, Hes1, and the abovementioned osteogenic differentiation markers was measured. Inhibition of the expression of Runx2, OPN, and OCN and reduction of ALP activity and mineralization deposits were observed in BMSCs cocultured with ALL cells, while Notch signal inhibiting rescued these effects. All these results indicated that ALL cells could inhibit the osteogenic differentiation of BMSCs by activating Notch signaling, resulting in a decreased number of osteoblastic cells, which may impair normal hematopoiesis.

Impact of electromagnetic fields on stem cells: common mechanisms at the crossroad between adult neurogenesis and osteogenesis

In the recent years adult neural and mesenchymal stem cells have been intensively investigated as effective resources for repair therapies. In vivo and in vitro studies have provided insights on the molecular mechanisms underlying the neurogenic and osteogenic processes in adulthood. This knowledge appears fundamental for the development of targeted strategies to manipulate stem cells. Here we review recent literature dealing with the effects of electromagnetic fields on stem cell biology that lends support to their use as a promising tool to positively influence the different steps of neurogenic and osteogenic processes. We will focus on recent studies revealing that extremely-low frequency electromagnetic fields enhance adult hippocampal neurogenesis by inducing epigenetic modifications on the regulatory sequences of genes responsible for neural stem cell proliferation and neuronal differentiation. In light of the emerging critical role played by chromatin modifications in maintaining the stemness as well as in regulating stem cell differentiation, we will also attempt to exploit epigenetic changes that can represent common targets for electromagnetic field effects on neurogenic and osteogenic processes.

In vitro models of aortic valve calcification: solidifying a system

Calcific aortic valve disease (CAVD) affects 25% of people over 65, and the late-stage stenotic state can only be treated with total valve replacement, requiring 85,000 surgeries annually in the US alone (University of Maryland Medical Center, 2013, http://umm.edu/programs/services/heart-center-programs/cardiothoracic-surgery/valve-surgery/facts). As CAVD is an age-related disease, many of the affected patients are unable to undergo the open-chest surgery that is its only current cure. This challenge motivates the elucidation of the mechanisms involved in calcification, with the eventual goal of alternative preventative and therapeutic strategies. There is no sufficient animal model of CAVD, so we turn to potential in vitro models. In general, in vitro models have the advantages of shortened experiment time and better control over multiple variables compared to in vivo models. As with all models, the hypothesis being tested dictates the most important characteristics of the in vivo physiology to recapitulate. Here, we collate the relevant pieces of designing and evaluating aortic valve calcification so that investigators can more effectively draw significant conclusions from their results.

Control of hair cell development by molecular pathways involving Atoh1, Hes1 and Hes5

Atoh1, Hes1 and Hes5 are crucial for normal inner ear hair cell development. They regulate the expression of each other in a complex network, while they also interact with many other genes and pathways, such as Notch, FGF, SHH, WNT, BMP and RA. This paper summarized molecular pathways that involve Atoh1, Hes1, and Hes5. Some of the pathways and gene regulation mechanisms discussed here were studied in other tissues, yet they might inspire studies in inner ear hair cell development. Thereby, we presented a complex regulatory network involving these three genes, which might be crucial for proliferation and differentiation of inner ear hair cells.

Runx2 is a novel regulator of mammary epithelial cell fate in development and breast cancer

Regulators of differentiated cell fate can offer targets for managing cancer development and progression. Here, we identify Runx2 as a new regulator of epithelial cell fate in mammary gland development and breast cancer. Runx2 is expressed in the epithelium of pregnant mice in a strict temporally and hormonally regulated manner. During pregnancy, Runx2 genetic deletion impaired alveolar differentiation in a manner that disrupted alveolar progenitor cell populations. Conversely, exogenous transgenic expression of Runx2 in mammary epithelial cells blocked milk production, suggesting that the decrease in endogenous Runx2 observed late in pregnancy is necessary for full differentiation. In addition, overexpression of Runx2 drove epithelial-to-mesenchymal transition-like changes in normal mammary epithelial cells, whereas Runx2 deletion in basal breast cancer cells inhibited cellular phenotypes associated with tumorigenesis. Notably, loss of Runx2 expression increased tumor latency and enhanced overall survival in a mouse model of breast cancer, with Runx2-deficient tumors exhibiting reduced cell proliferation. Together, our results establish a previously unreported function for Runx2 in breast cancer that may offer a novel generalized route for therapeutic interventions. Cancer Res; 74(18); 5277-86. ©2014 AACR.

Cux2 acts as a critical regulator for neurogenesis in the olfactory epithelium of vertebrates

Signaling pathways and transcription factors are crucial regulators of vertebrate neurogenesis, exerting their function in a spatial and temporal manner. Despite recent advances in our understanding of the molecular regulation of embryonic neurogenesis, little is known regarding how different signaling pathways interact to tightly regulate this process during the development of neuroepithelia. To address this, we have investigated the events lying upstream and downstream of a key neurogenic factor, the Cut-like homeodomain transcription factor-2 (Cux2), during embryonic neurogenesis in chick and mouse. By using the olfactory epithelium as a model for neurogenesis we have analyzed mouse embryos deficient in Cux2, as well as chick embryos exposed to Cux2 silencing (si) RNA or a Cux2 over-expression construct. We provide evidence that enhanced BMP activity increases Cux2 expression and suppresses olfactory neurogenesis in the chick olfactory epithelium. In addition, our results show that up-regulation of Cux2, either BMP-induced or ectopically over-expressed, reduce Delta1 expression and suppress proliferation. Interestingly, the loss of Cux2 activity, using mutant mice or siRNA in chick, also diminishes neurogenesis, Notch activity and cell proliferation in the olfactory epithelium. Our results suggest that controlled low levels of Cux2 activity are necessary for proper Notch signaling, maintenance of the proliferative pool and ongoing neurogenesis in the olfactory epithelium. Thus, we demonstrate a novel conserved mechanism in vertebrates in which levels of Cux2 activity play an important role for ongoing neurogenesis in the olfactory epithelium.

Effect of radiation on the Notch signaling pathway in osteoblasts

Notch signaling has been shown to be important in osteoblast differentiation. Therapeutic radiation has been shown to alter the skeletal system, yet little information is available on the changes in Notch signaling in irradiated osteoblasts. The purpose of this study was to analyze the effect of radiation therapy with 2 and 4 Gy on Notch signaling in osteoblasts. In order to assess the radiation damage on osteoblast differentiation, total RNA and protein were collected three days after exposure to radiation. The effects of radiation on Notch signaling at the early and terminal stages of osteoblastic MC3T3-E1 cell differentiation was analyzed by qRT-PCR and western blot analysis. Our study applied a previously established method to induce MC3T3-E1 cell differentiation into osteoblasts and osteoblast precursors. Our results showed that the expression of Notch receptors (Notch1-4), ligands (Jagged1, Jagged2 and Delta1), target of Notch signaling (Hes1) and markers (ALP, M-CSF, RANKL and OPG) were altered following 2 and 4 Gy of irradiation. The present research did not indicate a strong relationship between Notch1 regulation and suppression of osteoblast differentiation. We found Hes1 may play a role in the radiation effect on osteoblast differentiation. Our results indicate that radiated osteoblast precursors and osteoblasts promoted osteoclast differentiation and proliferation.

Calcific aortic valve stenosis: methods, models, and mechanisms

Calcific aortic valve stenosis (CAVS) is a major health problem facing aging societies. The identification of osteoblast-like and osteoclast-like cells in human tissue has led to a major paradigm shift in the field. CAVS was thought to be a passive, degenerative process, whereas now the progression of calcification in CAVS is considered to be actively regulated. Mechanistic studies examining the contributions of true ectopic osteogenesis, nonosseous calcification, and ectopic osteoblast-like cells (that appear to function differently from skeletal osteoblasts) to valvular dysfunction have been facilitated by the development of mouse models of CAVS. Recent studies also suggest that valvular fibrosis, as well as calcification, may play an important role in restricting cusp movement, and CAVS may be more appropriately viewed as a fibrocalcific disease. High-resolution echocardiography and magnetic resonance imaging have emerged as useful tools for testing the efficacy of pharmacological and genetic interventions in vivo. Key studies in humans and animals are reviewed that have shaped current paradigms in the field of CAVS, and suggest promising future areas for research.