USP24-dependent stabilization of Runx2 recruits a p300/NCOA3 complex to transactivate ADAMTS genes and promote degeneration of intervertebral disc in chronic inflammation mice

BACKGROUND

Intervertebral disc degeneration (IDD) naturally occurs during the aging process. Its occurrence is closely related to chronic inflammation; however, the causal relationship between them is controversial. This study aimed to investigate if inflammation would promote IDD incidence and explore the underlying mechanism.

METHODS

A chronic inflammation mouse model was established by intraperitoneal injection of lipopolysaccharide (LPS). Enzyme-linked immunosorbent assay was performed to determine proinflammatory cytokines in serum. Histological staining was used to evaluate the degeneration of IVDs. Immunoblots and RT-qPCR analyses were performed to measure protein and mRNA expression levels. Immunoprecipitation, mass spectrometry, and co-immunoprecipitation assays were used to determine the assembly of protein complex.

RESULTS

We found that an inflammatory microenvironment activated p38 kinase, which phosphorylated the Runx2 transcription factor at the Ser28 site. The phosphorylated Runx2 (pRunx2) then recruited a deubiquitinase, ubiquitin-specific peptidase 24 (USP24), which stabilized pRunx2 and protected it from ubiquitin-dependent proteasomal degradation. The stabilized pRunx2 recruited histone acetyltransferase p300 and nuclear receptor coactivator 3 (NCOA3) to assemble a complex. This NCOA3-p300-pRunx2 complex then transactivated the expression of 13 ADAMTS (a disintegrin and metalloproteinase with thrombospondin motif) genes, thereby promoting the degradation of extracellular matrix (ECM) in intervertebral discs (IVDs) and causing IDD. Administration of either a p38 inhibitor (doramapimod), a NCOA3 inhibitor (bufalin), or a p300 inhibitor (EML425) significantly decreased the expression of the 13 ADAMTS genes and slowed the degeneration of IVDs.

CONCLUSION

In summary, our results demonstrate that USP24 protects pRunx2 from proteasomal degradation under chronic inflammation conditions, enabling pRunx2 to transactivate ADAMTS genes and degrade ECM. Our findings provide direct evidence that chronic inflammation triggers IDD and offer a therapeutic strategy for retarding IDD in patients with chronic inflammation.

Runx2 activates hepatic stellate cells to promote liver fibrosis via transcriptionally regulating Itgav expression

BACKGROUNDS AND AIMS

As a central event during liver fibrosis, hepatic stellate cells (HSC) have been thought to be a potential therapeutic target for liver fibrosis. Previous studies have shown that runt-related transcription factor 2 (Runx2) is associated with the development of non-alcoholic fatty liver disease, while its specific role in HSC activation and hepatic fibrosis remains elusive.

APPROACH AND RESULTS

In this study, we found that Runx2 expression was significantly upregulated in human liver fibrosis with different aetiologies. Runx2 expression was also gradually elevated in mouse liver during fibrosis, and Runx2 was mainly expressed in the activated HSC. Knockdown of Runx2 in HSC markedly alleviated CCl₄ -induced, 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced or methionine-choline deficient (MCD)-induced liver fibrosis, while hepatic overexpression of Runx2 via HBAAV-Runx2 or VA-Lip-Runx2 injection exacerbated CCl₄ -induced liver fibrosis. In vitro analysis demonstrated that Runx2 promoted HSC activation and proliferation, whereas Runx2 knockdown in HSC suppressed these effects. RNA-seq and Runx2 ChIP-seq analysis demonstrated that Runx2 could promote integrin alpha-V (Itgav) expression by binding to its promoter. Blockade of Itgav attenuated Runx2-induced HSC activation and liver fibrosis. Additionally, we found that cytokines (TGF-β1, PDGF, EGF) promote the expression and nuclear translocation of Runx2 through protein kinase A (PKA) in HSC.

CONCLUSIONS

Runx2 is critical for HSC activation via transcriptionally regulating Itgav expression during liver fibrosis, and may be a promising therapeutic target for liver fibrosis.

Complement Cross Talks With H-K-ATPase to Upregulate Runx2 in Human Aortic Valve Interstitial Cells

INTRODUCTION

Calcific aortic valve disease (CAVD) is a slowly progressive fibro-calcific valve leaflet disorder. The underlying pathophysiology is complex and not yet well understood. Complement is known to play a role in the pathogenesis of CAVD by upregulating Runx2 to induce profibrogenic change in human aortic valve interstitial cells (AVICs). Furthermore, H-K-ATPase has independently been shown to induce tissue calcification. Therefore, we hypothesized that complement cross talks with H-K-ATPase to upregulate Runx2 in human AVICs.

MATERIALS AND METHODS

Human AVICs were isolated from normal and calcified aortic valves. Cells were treated with a variation of complement, H-K-ATPase, or ERK1/2 inhibitors. H-K-ATPase and its association with complement in AVICs were investigated by reverse transcriptase-polymerase chain reaction, immunofluorescence, and Western blot.

RESULTS

Calcified human AVICs expressed significantly higher H-K-ATPase level than normal human AVICs. Presence of complement C3 with H-K-ATPase is found in AVICs after complement treatment. Complement induced both H-K-ATPase and Runx2 expression in AVICs, which was associated with increased phosphorylation of ERK1/2 and its downstream molecule p-70 S6. Pharmacological inhibition of either H-K-ATPase or Erk1/2 abolished complement-induced Runx2 expression.

CONCLUSIONS

These findings indicate that complement cross talks with H-K-ATPase to upregulate Runx2 in human AVICs by activation of ERK1/2 signaling pathways. The study revealed the potential role of H-K-ATPase in the pathogenesis of CAVD and therapeutically targeting either complement system or H-K-ATPase may limit the development of CAVD.

Reciprocal Effect of Environmental Stimuli to Regulate the Adipogenesis and Osteogenesis Fate Decision in Bone Marrow-Derived Mesenchymal Stem Cells (BM-MSCs)

Mesenchymal stem cells derived from bone marrow (BM-MSCs) can differentiate into adipocytes and osteoblasts. Various external stimuli, including environmental contaminants, heavy metals, dietary, and physical factors, are shown to influence the fate decision of BM-MSCs toward adipogenesis or osteogenesis. The balance of osteogenesis and adipogenesis is critical for the maintenance of bone homeostasis, and the interruption of BM-MSCs lineage commitment is associated with human health issues, such as fracture, osteoporosis, osteopenia, and osteonecrosis. This review focuses on how external stimuli shift the fate of BM-MSCs towards adipogenesis or osteogenesis. Future studies are needed to understand the impact of these external stimuli on bone health and elucidate the underlying mechanisms of BM-MSCs differentiation. This knowledge will inform efforts to prevent bone-related diseases and develop therapeutic approaches to treat bone disorders associated with various pathological conditions.

Plum-Derived Exosome-like Nanovesicles Induce Differentiation of Osteoblasts and Reduction of Osteoclast Activation

Osteoblasts and osteoclasts play crucial roles in bone formation and bone resorption. We found that plum-derived exosome-like nanovesicles (PENVs) suppressed osteoclast activation and modulated osteoblast differentiation. PENVs increased the proliferation, differentiation, and mineralization of osteoblastic MC3T3-E1 cells and osteoblasts from mouse bone marrow cultures. Notably, PENVs elevated the expression of osteoblastic transcription factors and osteoblast differentiation marker proteins in MC3T3-E1 cells. Higher levels of phosphorylated BMP-2, p38, JNK, and smad1 proteins were detected in PENV-treated MC3T3-E1 cells. Additionally, the number of TRAP-positive cells was significantly decreased in PENV-treated osteoclasts isolated from osteoblasts from mouse bone marrow cultures. Importantly, osteoclastogenesis of marker proteins such as PPAR-gamma, NFATc1, and c-Fos were suppressed by treatment with PENVs (50 μg/mL). Taken together, these results demonstrate that PENVs can be used as therapeutic targets for treating bone-related diseases by improving osteoblast differentiation and inhibiting osteoclast activation for the first time.

Inhibition of GSK-3β Enhances Osteoblast Differentiation of Human Mesenchymal Stem Cells through Wnt Signalling Overexpressing Runx2

Small-molecule-inhibitor-based bone differentiation has been recently exploited as a novel approach to regulating osteogenesis-related signaling pathways. In this study, we identified 1-Azakenpaullone, a highly selective inhibitor of glycogen synthase kinase-3β (GSK-3β), as a powerful inducer of osteoblastic differentiation and mineralization of human mesenchymal stem cells (MSCs). GSK-3β is a serine-threonine protein kinase that plays a major role in different disease development. GSK-3β is a key regulator of Runx2 activity in osteoblastic formation. We evaluated alkaline phosphatase activity and staining assays to assess osteoblast differentiation and Alizarin Red staining to assess the mineralization of cultured human MSCs. Gene expression profiling was assessed using an Agilent microarray platform, and bioinformatics were performed using Ingenuity Pathway Analysis software. Human MSCs treated with 1-Azakenpaullone showed higher ALP activity, increased in vitro mineralized matrix formation, and the upregulation of osteoblast-specific marker gene expression. Global gene expression profiling of 1-Azakenpaullone-treated human MSCs identified 1750 upregulated and 2171 downregulated mRNA transcripts compared to control cells. It also suggested possible changes in various signaling pathways, including Wnt, TGFβ, and Hedgehog. Further bioinformatics analysis employing Ingenuity Pathway Analysis recognized significant enrichment in the 1-Azakenpaullone-treated cells of genetic networks involved in CAMP, PI3K (Complex), P38 MAPK, and HIF1A signaling and functional categories associated with connective tissue development. Our results suggest that 1-Azakenpaullone significantly induced the osteoblastic differentiation and mineralization of human MSCs mediated by the activation of Wnt signaling and the nuclear accumulation of β-catenin, leading to the upregulation of Runx2, a key transcription factor that ultimately promotes the expression of osteoblast-specific genes. Thus, 1-Azakenpaullone could be used as an osteo-promotor factor in bone tissue engineering.

Runx2 overexpression promotes bone repair of osteonecrosis of the femoral head (ONFH)

BACKGROUND

Runt-related transcription factor-2 (Runx2) has been considered an inducer to improve bone repair ability of mesenchymal stem cells (MSCs).

METHODS AND RESULTS

Twenty-four rabbits were used to establish Osteonecrosis of the femoral head (ONFH) and randomly devided into four groups: Adenovirus Runx2 (Ad-Runx2) group, Runx2-siRNA group, MSCs group and Model group. At 1 week after model establishment, the Ad-Runx2 group was treated with 5 × 107 MSCs transfected through Ad-Runx2, the Runx2-siRNA group was treated with 5 × 107 MSCs transfected through Runx2-siRNA, the MSCs group was injected with 5 × 107 untreated MSCs, and the Model group was treated with saline. The injection was administered at 1 week and 3 weeks after model establishment. The expression of bone morphogenetic protein 2 (BMP-2), Runx2 and Osterix from the femoral head was detected at 3 and 6 weeks after MSCs being injected, and Masson Trichrome Staining, Gross Morphology, X-ray and CT images observation were used to evaluate the repair effect of ONFH. The data revealed that the expression of BMP-2, Runx2 and Osterix in the Runx2-siRNA group was reduced at 3 weeks compared with the MSCs group, and then the expression further reduced at 6 weeks, but was still higher than the Model group besides Osterix; The expression of these three genes in the Ad-Runx2 group was higher than in the MSCs group. Masson Trichrome Staining, Gross Morphology and X-ray and CT images observation revealed that necrotic femoral head of the MSCs group was more regular and smooth than the Runx2-siRNA group, which has a collapsed and irregular femoral head. In the Ad-Runx2 group, necrotic femoral head was basically completely repaired and covered by rich cartilage and bone tissue.

CONCLUSIONS

Overexpression of Runx2 can improve osteoblastic phenotype maintenance of MSCs and promote necrotic bone repair of ONFH.

The role of MACF1 on acute myeloid leukemia cell proliferation is involved in Runx2-targeted PI3K/Akt signaling

Acute myeloid leukemia (AML) is a type of hematologic diseases, which is related to abnormal genes. The aberrant microtubule actin cross-linking factor 1 (MACF1) is associated with progression of multiple tumors by initiating cell proliferation. Nevertheless, the function and action mechanism of MACF1 in AML cell proliferation remain mostly unknown. Our study aimed to explore the influence of MACF1 on AML cell proliferation by CCK-8 and EdU staining assays. Moreover, we aimed to explore the effect of MACF1 on downstream Runx2 and the PI3K/Akt signaling. MACF1 expression in AML patients was predicted by bioinformatics analysis. Cells were transfected with si-con, si-MACF1 or Runx2 using Lipofectamine 2000. Upregulated MACF1 was found in AML patients and predicted worse overall survival. MACF1 expression was upregulated in AML cells compared with that in hematopoietic stem and progenitor cells. MACF1 silencing reduced AML cell proliferation. Runx2 level was increased in AML cells, and decreased by silencing MACF1. Runx2 upregulation rescued MACF1 silencing-mediated inhibition of proliferation. MACF1 downregulation inhibited activation of the PI3K/Akt pathway by decreasing Runx2. Activation of the PI3K/Akt pathway abrogated the suppressive role of MACF1 downregulation in AML cell proliferation. In conclusion, MACF1 knockdown decreased AML cell proliferation by reducing Runx2 and inactivating the PI3K/Akt signaling.

Inhibition of miR-101-3p prevents human aortic valve interstitial cell calcification through regulation of CDH11/SOX9 expression

BACKGROUND

Calcific aortic valve disease (CAVD) is the second leading cause of adult heart diseases. The purpose of this study is to investigate whether miR-101-3p plays a role in the human aortic valve interstitial cells (HAVICs) calcification and the underlying mechanisms.

METHODS

Small RNA deep sequencing and qPCR analysis were used to determine changes in microRNA expression in calcified human aortic valves.

RESULTS

The data showed that miR-101-3p levels were increased in the calcified human aortic valves. Using cultured primary HAVICs, we demonstrated that the miR-101-3p mimic promoted calcification and upregulated the osteogenesis pathway, while anti-miR-101-3p inhibited osteogenic differentiation and prevented calcification in HAVICs treated with the osteogenic conditioned medium. Mechanistically, miR-101-3p directly targeted cadherin-11 (CDH11) and Sry-related high-mobility-group box 9 (SOX9), key factors in the regulation of chondrogenesis and osteogenesis. Both CDH11 and SOX9 expressions were downregulated in the calcified human HAVICs. Inhibition of miR-101-3p restored expression of CDH11, SOX9 and ASPN and prevented osteogenesis in HAVICs under the calcific condition.

CONCLUSION

miR-101-3p plays an important role in HAVIC calcification through regulation of CDH11/SOX9 expression. The finding is important as it reveals that miR-1013p may be a potential therapeutic target for calcific aortic valve disease.

Crosstalk between protein kinase C α and transforming growth factor β signaling mediated by Runx2 in intestinal epithelial cells

Tight coordination of growth regulatory signaling is required for intestinal epithelial homeostasis. Protein kinase C α (PKCα) and transforming growth factor β (TGFβ) are negative regulators of proliferation with tumor suppressor properties in the intestine. Here, we identify novel crosstalk between PKCα and TGFβ signaling. RNA-Seq analysis of nontransformed intestinal crypt-like cells and colorectal cancer cells identified TGFβ receptor 1 (TGFβR1) as a target of PKCα signaling. RT-PCR and immunoblot analysis confirmed that PKCα positively regulates TGFβR1 mRNA and protein expression in these cells. Effects on TGFβR1 were dependent on Ras-extracellular signal-regulated kinase 1/2 (ERK) signaling. Nascent RNA and promoter-reporter analysis indicated that PKCα induces TGFβR1 transcription, and Runx2 was identified as an essential mediator of the effect. PKCα promoted ERK-mediated activating phosphorylation of Runx2, which preceded transcriptional activation of the TGFβR1 gene and induction of Runx2 expression. Thus, we have identified a novel PKCα→ERK→Runx2→TGFβR1 signaling axis. In further support of a link between PKCα and TGFβ signaling, PKCα knockdown reduced the ability of TGFβ to induce SMAD2 phosphorylation and cell cycle arrest, and inhibition of TGFβR1 decreased PKCα-induced upregulation of p21^Cip1 and p27^Kip1 in intestinal cells. The physiological relevance of these findings is also supported by The Cancer Genome Atlas data showing correlation between PKCα, Runx2, and TGFβR1 mRNA expression in human colorectal cancer. PKCα also regulated TGFβR1 in endometrial cancer cells, and PKCα, Runx2, and TGFβR1 expression correlates in uterine tumors, indicating that crosstalk between PKCα and TGFβ signaling may be a common mechanism in diverse epithelial tissues.

Emerging RUNX2-Mediated Gene Regulatory Mechanisms Consisting of Multi-Layered Regulatory Networks in Skeletal Development

Skeletal development is tightly coordinated by chondrocytes and osteoblasts, which are derived from skeletal progenitors, and distinct cell-type gene regulatory programs underlie the specification and differentiation of cells. Runt-related transcription factor 2 (Runx2) is essential to chondrocyte hypertrophy and osteoblast differentiation. Genetic studies have revealed the biological functions of Runx2 and its involvement in skeletal genetic diseases. Meanwhile, molecular biology has provided a framework for our understanding of RUNX2-mediated transactivation at a limited number of cis-regulatory elements. Furthermore, studies using next-generation sequencing (NGS) have provided information on RUNX2-mediated gene regulation at the genome level and novel insights into the multiple layers of gene regulatory mechanisms, including the modes of action of RUNX2, chromatin accessibility, the concept of pioneer factors and phase separation, and three-dimensional chromatin organization. In this review, I summarize the emerging RUNX2-mediated regulatory mechanism from a multi-layer perspective and discuss future perspectives for applications in the treatment of skeletal diseases.

Glucose-stimulated PGC-1α couples with CBP and Runx2 to mediate intervertebral disc degeneration through transactivation of ADAMTS4/5 in diet-induced obesity mice

Emerging evidence suggests that type 2 diabetes mellitus (T2DM) is associated with the pathogenesis of intervertebral disc degeneration (IDD). However, it is still unclear how T2DM contributes to IDD. Herein, we observed the accumulation of blood glucose and degenerative lumbar discs in mice fed a high-fat diet. Detection of differentially expressed genes in degenerative lumbar discs revealed that ADAMTS4 (A Disintegrin and Metalloproteinase with Thrombospondin motifs) and ADAMTS5 genes were significantly increased. In vitro analyses demonstrated that Runt-Related Transcription Factor 2 (Runx2) recruited both PPARgamma Coactivator 1alpha (PGC-1α) and CREB-Binding Protein (CBP) to transactivate the expression of ADAMTS4/5. Glucose stimulation could dose-dependently induce the accumulation of PGC-1α and promoted the binding of the CBP-PGC-1α-Runx2 complex to the promoters of ADAMTS4/5. Depletion of CBP-PGC-1α-Runx2 complex members and treatment with either PGC-1α inhibitor SR-18292 or CBP inhibitor EML425 in vitro could dramatically inhibit the glucose-induced expression of ADAMTS4/5. Administration of SR-18292 and EML425 in diabetic mice could prevent the degeneration of lumbar discs. Collectively, our results revealed a molecular mechanism by which the hyperglycemia-dependent CBP-PGC-1α-Runx2 complex was required for the transactivation of ADAMTS4/5. The blockage of this complex in diabetic mice may help prevent IDD.

MicroRNA-145 and microRNA-486 are potential serum biomarkers for vascular calcification

INTRODUCTION

MicroRNAs (miRs) regulate vascular calcification (VC), their quantification may contribute to suspect the presence of VC.

MATERIAL AND METHODS

The study was performed in 4 phases. 1) miRs sequencing of rat calcified and non-calcified aortas. 2) miRs with the highest rate of change, plus miR-145 (the most abundant miR in vascular smooth muscle cells (VSMCs), were validated in aortas and serum from rats with and without VC. 3) The selected miRs were analyzed in epigastric arteries from kidney donors and recipients, and serum samples from general population. 4) VSMCs were exposed to different phosphorus concentrations and miR-145 and miR-486 were overexpressed to investigate their role in VC.

RESULTS

miR-145, miR-122-5p, miR-486 and miR-598-3p decreased in the rat calcified aortas, but only miR-145 and miR-486, were detected in serum. In human epigastric arteries, miR-145 and miR-486 were lower in kidney transplant recipients compared to donors. Both miRs inversely correlated with arterial calcium content and with VC (Kauppila index). In the general population, the severe VC was associated with the lowest serum levels of both miRs. The ROC curve showed that serum miR-145 was a good biomarker of VC. In VSMCs exposed to high phosphorus, calcium content, osteogenic markers (Runx2 and Osterix) increased, and the contractile marker (α-actin), miR-145 and miR-486 decreased. Overexpression of miR-145, and in lesser extent miR-486, prevented the increase in calcium content induced by high phosphorus, the osteogenic differentiation, and the loss of the contractile phenotype.

CONCLUSION

miR-145 and miR-486 regulate the osteogenic differentiation of VSMCs, their quantification in serum could serve as markers of VC.

KAP1 modulates osteogenic differentiation via the ERK/Runx2 cascade in vascular smooth muscle cells

BACKGROUND

Osteoblast phenotypic transition in vascular smooth muscle cells (VSMCs) has been unveiled as a common cause of vascular calcification (VC). Krüppel-Associated Box (KRAB)-Associated Protein 1(KAP1) is a transcriptional corepressor that modulates various intracellular pathological processes from gene expression to DNA repair to signal transduction. However, the function and mechanism of KAP1 on the osteoblastic differentiation of VSMCs have not been evaluated yet.

METHODS AND RESULTS

We demonstrate that the expression of KAP1 in VSMCs is significantly enhanced in vivo and in vitro calcification models. Downregulating the expression of KAP1 suppresses the osteoblast phenotypic transition of VSMCs, which is indicated by a decrease in the expression of osteoblast marker collagenase type I (COL I) and an increase in the expression of VSMC marker α-smooth muscle actin (α-SMA). Conversely, exogenous overexpression of KAP1 could promote osteoblast phenotypic transition of VSMCs. Moreover, KAP1 upregulated the expression of RUNX family transcription factor 2 (Runx2), an inducer of osteoblast that positively regulates many osteoblast-related genes, such as COL I. Evaluation of the potential mechanism demonstrated that KAP1 promoted osteoblast phenotypic transition of VSMCs by activating the extracellular regulated protein kinases (ERK) signaling pathway, which could activate Runx2. In support of this finding, KAP1-induced cell osteoblast phenotypic transition is abolished by treatment with PD0325901, a specific ERK inhibitor.

CONCLUSIONS

The present study suggested that KAP1 participated in the osteoblast differentiation of VSMCs via the ERK/Runx2 cascade and served as a potential diagnostics and therapeutics target for vascular calcification.

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.

Basal and inducible Osterix expression reflect equine mesenchymal progenitor cell osteogenic capacity

Introduction

Mesenchymal stem cells are characterized by their capacities for extensive proliferation through multiple passages and, classically, tri-lineage differentiation along osteogenic, chondrogenic and adipogenic lineages. This study was carried out to compare osteogenesis in equine bone marrow-, synovium- and adipose-derived cells, and to determine whether osteogenic capacity is reflected in the basal expression of the critical osteogenic transcription factors Runx2 and Osterix.

Methods

Bone marrow, synovium and adipose tissue was collected from six healthy 2-year-old horses. Cells were isolated from these sources and expanded through two passages. Basal expression of Runx2 and Osterix was assessed in undifferentiated third passage cells, along with their response to osteogenic culture conditions.

Results

Bone marrow-derived cells had significantly higher basal expression of Osterix, but not Runx2. In osteogenic medium, bone-marrow cells rapidly developed dense, multicellular aggregates that stained strongly for mineral and alkaline phosphatase activity. Synovial and adipose cell cultures showed far less matrix mineralization. Bone marrow cells significantly up-regulated alkaline phosphatase mRNA expression and enzymatic activity at 7 and 14 days. Alkaline phosphatase expression and activity were increased in adipose cultures after 14 days, although these values were less than in bone marrow cultures. There was no change in alkaline phosphatase in synovial cultures. In osteogenic medium, bone marrow cultures increased both Runx2 and Osterix mRNA expression significantly at 7 and 14 days. Expression of both transcription factors did not change in synovial or adipose cultures.

Discussion

These results demonstrate that basal Osterix expression differs significantly in progenitor cells derived from different tissue sources and reflects the osteogenic potential of the cell populations.

LncRNA TEX41 regulates autophagy by increasing Runx2 expression in lung adenocarcinoma bone metastasis

OBJECTIVE

To investigate the mechanism underlying the role of TEX41 in lung adenocarcinoma (LUAD) bone metastasis (BM).

METHODS

We analyzed the biological functions and molecular mechanisms of TEX41 using bioinformatics. TEX41 and Runx2 expressions were measured in clinical tissue samples and cell lines by quantitative PCR. The effects of TEX41 on LUAD cell proliferation, migration, invasion and metastasis as well as its mechanism of action were investigated. Fluorescence in-situ hybridization (FISH) was performed to determine TEX41 and Runx2 colocalization. Subcutaneous tumor growth and BM were evaluated in nude mice by X-ray and hematoxylin and eosin (HE) staining.

RESULTS

TEX41 was dramatically increased in LUAD BM tissue, indicating a poorer prognosis in patients with LUAD and BM. TEX41 knockdown suppressed the migration and metastasis of LUAD cells, whereas TEX41 overexpression promoted these processes. Data from X-ray and HE staining showed that TEX41 supported the BM in LUAD. TEX41 overexpression induced autophagy in LUAD cells, as demonstrated by changes in autophagy markers. Results of FISH showed that TEX41 and Runx2 colocalized in the nucleus, and Runx2 expression was regulated by TEX41. The effects of TEX41 on LUAD cell migration, invasion, metastasis and autophagy were counteracted by Runx2 inhibition. Moreover, the role of TEX41 in the metastasis was partially dependent on autophagy, and phosphoinositide 3-kinase (PI3K)-AKT might be the major signaling pathway involved in TEX41-regulated autophagy.

CONCLUSION

TEX41 promotes autophagy in LUAD cells by upregulating Runx2 to mediate LUAD migration, invasion and BM.

Positive Effects of UV-Photofunctionalization of Titanium Oxide Surfaces on the Survival and Differentiation of Osteogenic Precursor Cells-An In Vitro Study

INTRODUCTION

The UVC-irradiation ("UV-photofunctionalization") of titanium dental implants has proved to be capable of removing carbon contamination and restoring the ability of titanium surfaces to attract cells involved in the process of osteointegration, thus significantly enhancing the biocompatibility of implants and favoring the post-operative healing process. To what extent the effect of UVC irradiation is dependent on the type or the topography of titanium used, is still not sufficiently established.

OBJECTIVE

The present study was aimed at analyzing the effects of UV-photofunctionalization on the TiO₂ topography, as well as on the gene expression patterns and the biological activity of osteogenic cells, i.e., osteogenic precursors cultured in vitro in the presence of different titanium specimens.

METHODOLOGY

The analysis of the surface roughness was performed by atomic force microscopy (AFM) on machined surface grade 2, and sand-blasted/acid-etched surface grades 2 and 4 titanium specimens. The expression of the genes related with the process of healing and osteogenesis was studied in the MC3T3-E1 pre-osteoblastic murine cells, as well as in MSC murine stem cells, before and after exposure to differently treated TiO₂ surfaces.

RESULTS

The AFM determinations showed that the surface topographies of titanium after the sand-blasting and acid-etching procedures, look very similar, independently of the grade of titanium. The UVC-irradiation of the TiO₂ surface was found to induce an increase in the cell survival, attachment and proliferation, which was positively correlated with an increased expression of the osteogenesis-related genes Runx2 and alkaline phosphatase (ALP).

CONCLUSION

Overall, our findings expand and further support the current view that UV-photofunctionalization can indeed restore biocompatibility and osteointegration of TiO₂ implants, and suggest that this at least in part occurs through a stimulation of the osteogenic differentiation of the precursor cells.

Diminished arachidonate 5-lipoxygenase perturbs phase separation and transcriptional response of Runx2 to reverse pathological ventricular remodeling

BACKGROUND

Arachidonate 5-lipoxygenase (Alox5) belongs to a class of nonheme iron-containing dioxygenases involved in the catalysis of leukotriene biosynthesis. However, the effects of Alox5 itself on pathological cardiac remodeling and heart failure remain elusive.

METHODS

The role of Alox5 in pathological cardiac remodeling was investigated by Alox5 genetic depletion, AAV9-mediated overexpression in cardiomyocytes, and a bone marrow (BM) transplantation approach. Neonatal rat cardiomyocytes were used to explore the effects of Alox5 in vitro. Molecular and signaling pathways were revealed by CUT &Tag, IP-MS, RNA sequencing and bioinformatic analyses.

FINDINGS

Untargeted metabolomics showed that serum 5-HETE (a primary product of Alox5) levels were little changed in patients with cardiac hypertrophy, while Alox5 expression was significantly upregulated in murine hypertensive cardiac samples and human cardiac samples of hypertrophy, which prompted us to test whether high Alox5 levels under hypertensive stimuli were directly associated with pathologic myocardium in an enzymatic activity-independent manner. Herein, we revealed that Alox5 deficiency significantly ameliorated transverse aortic constriction (TAC)-induced hypertrophy. Cardiomyocyte-specific Alox5 depletion attenuated hypertensive ventricular remodeling. Conversely, cardiac-specifical Alox5 overexpression showed a pro-hypertrophic cardiac phenotype. Ablation of Alox5 in bone marrow-derived cells did not affect pathological cardiac remodeling and heart failure. Mechanically, Runx2 was identified as a target of Alox5. In this regard, Alox5 PEST domain could directly bind to Runx2 PTS domain, promoting nuclear localization of Runx2 in an enzymatic activity-independent manner, simultaneously contributed to liquid-liquid phase separation (LLPS) of Runx2 at specific domain in the nucleus and increased transcription of EGFR in cardiomyocytes. Runx2 depletion alleviated hypertrophy in Ang II-pretreated Alox5-overexpressing cardiomyocytes.

INTERPRETATION

Overall, our study demonstrated that targeting Alox5 exerted a protective effect against cardiac remodeling and heart failure under hypertensive stimuli by disturbing LLPS of Runx2 and substantial reduction of EGFR transcription activation in cardiomyocytes. Our findings suggest that negative modulation of Alox5-Runx2 may provide a therapeutic approach against pathological cardiac remodeling and heart failure.

FUNDING

National Natural Science Foundation of China.

Metformin protects against vascular calcification through the selective degradation of Runx2 by the p62 autophagy receptor

Vascular calcification is associated with aging, type 2 diabetes, and atherosclerosis, and increases the risk of cardiovascular morbidity and mortality. It is an active, highly regulated process that resembles physiological bone formation. It has previously been established that pharmacological doses of metformin alleviate arterial calcification through adenosine monophosphate-activated protein kinase (AMPK)-activated autophagy, however the specific pathway remains elusive. In the present study we hypothesized that metformin protects against arterial calcification through the direct autophagic degradation of runt-related transcription factor 2 (Runx2). Calcification was blunted in vascular smooth muscle cells (VSMCs) by metformin in a dose-dependent manner (0.5-1.5 mM) compared to control cells (p < 0.01). VSMCs cultured under high-phosphate (Pi) conditions in the presence of metformin (1 mM) showed a significant increase in LC3 puncta following bafilomycin-A1 (Baf-A; 5 nM) treatment compared to control cells (p < 0.001). Furthermore, reduced expression of Runx2 was observed in the nuclei of metformin-treated calcifying VSMCs (p < 0.0001). Evaluation of the functional role of autophagy through Atg3 knockdown in VSMCs showed aggravated Pi-induced calcification (p < 0.0001), failure to induce autophagy (punctate LC3) (p < 0.001) and increased nuclear Runx2 expression (p < 0.0001) in VSMCs cultured under high Pi conditions in the presence of metformin (1 mM). Mechanistic studies employing three-way coimmunoprecipitation with Runx2, p62, and LC3 revealed that p62 binds to both LC3 and Runx2 upon metformin treatment in VSMCs. Furthermore, immunoblotting with LC3 revealed that Runx2 specifically binds with p62 and LC3-II in metformin-treated calcified VSMCs. Lastly, we investigated the importance of the autophagy pathway in vascular calcification in a clinical setting. Ex vivo clinical analyses of calcified diabetic lower limb artery tissues highlighted a negative association between Runx2 and LC3 in the vascular calcification process. These studies suggest that exploitation of metformin and its analogues may represent a novel therapeutic strategy for clinical intervention through the induction of AMPK/Autophagy Related 3 (Atg3)-dependent autophagy and the subsequent p62-mediated autophagic degradation of Runx2.

Runx2 regulates chromatin accessibility to direct the osteoblast program at neonatal stages

The transcriptional regulator Runx2 (runt-related transcription factor 2) has essential but distinct roles in osteoblasts and chondrocytes in skeletal development. However, Runx2-mediated regulatory mechanisms underlying the distinctive programming of osteoblasts and chondrocytes are not well understood. Here, we perform an integrative analysis to investigate Runx2-DNA binding and chromatin accessibility ex vivo using neonatal osteoblasts and chondrocytes. We find that Runx2 engages with cell-type-distinct chromatin-accessible regions, potentially interacting with different combinations of transcriptional regulators, forming cell-type-specific hotspots, and potentiating chromatin accessibility. Genetic analysis and direct cellular reprogramming studies suggest that Runx2 is essential for establishment of chromatin accessibility in osteoblasts. Functional enhancer studies identify an Sp7 distal enhancer driven by Runx2-dependent binding and osteoblast-specific chromatin accessibility, contributing to normal osteoblast differentiation. Our findings provide a framework for understanding the regulatory landscape encompassing Runx2-mediated and cell-type-distinct enhancer networks that underlie the specification of osteoblasts.

Hojo et al. investigate the gene-regulatory landscape underlying specification of skeletal cell types in neonatal mice. Runx2, an osteoblast determinant, engages with cell-type-distinct chromatin-accessible regions and is essential for establishment of chromatin accessibility in osteoblasts. The study provides insights into enhancer networks in skeletal development.

The Role of Runx2 in Microtubule Acetylation in Bone Metastatic Breast Cancer Cells

Bone metastasis of breast cancer results in severe bone loss, fractures, and death. Crosstalk between breast cancer cells and bone resident cells promotes osteoclast activity and the release of growth factors from the bone matrix resulting in aggressive tumor growth and bone loss. We and others have shown that Runt-related transcription factor-2 (Runx2) promotes metastatic tumor growth-associated bone loss. Breast cancer cells also induce autophagy to survive metabolic stress at the metastatic site. Recently, we reported a Runx2-dependent increase in autophagy. In this study, to examine the underlying mechanisms of metastasis and tumor resistance to stress, we used a bone metastatic isogenic variant of breast cancer MDA-MB-231 cells isolated from a xenograft tumor mouse model of metastasis. Our results with immunofluorescence and biochemical approaches revealed that Runx2 promotes microtubule (MT) stability to facilitate autophagy. Stable MTs are critical for autophagosome trafficking and display increased acetylation at Lysine 40 of α-tubulin. Runx2 silencing decreases acetylated α-tubulin levels. The expression levels of HDAC6 and αTAT1, which serve to regulate the acetylation of α-tubulin, were not altered with Runx2 silencing. We found that HDAC6 interaction with α-tubulin is inhibited by Runt-related factor-2 (Runx2). We show that the expression of wild-type Runx2 can restore the acetylated polymer of MTs in Runx2 knockdown cells, while the C-terminal deletion mutant fails to rescue the polymer of MTs. Importantly, cellular stress, such as glucose starvation also increases the acetylation of α-tubulin. We found that the loss of Runx2 increases the sensitivity of breast cancer cells to MT-targeting agents. Overall, our results indicate a novel regulatory mechanism of microtubule acetylation and suggest that Runx2 and acetylated microtubules may serve as therapeutic targets for bone metastatic tumors.

Overexpression of transcription factor FoxA2 in the developing skeleton causes an enlargement of the cartilage hypertrophic zone, but it does not trigger ectopic differentiation in immature chondrocytes

We previously found that FoxA factors are necessary for chondrocyte differentiation. To investigate whether FoxA factors alone are sufficient to drive chondrocyte hypertrophy, we build a FoxA2 transgenic mouse in which FoxA2 cDNA is driven by a reiterated Tetracycline Response Element (TRE) and a minimal CMV promoter. This transgenic line was crossed with a col2CRE;Rosa26^rtTA/+ mouse line to generate col2CRE;Rosa26^rtTA/+;TgFoxA2^+/- mice for inducible expression of FoxA2 in cartilage using doxycycline treatment. Ectopic expression of FoxA2 in the developing skeleton reveals skeletal defects and shorter skeletal elements in E17.5 mice. The chondro-osseous border was frequently mis-shaped in mutant mice, with small islands of col.10+ hypertrophic cells extending in the metaphyseal bone. Even though overexpression of FoxA2 causes an accumulation of hypertrophic chondrocytes, it did not trigger ectopic hypertrophy in the immature chondrocytes. This suggests that FoxA2 may need transcriptional co-factors (such as Runx2), whose expression is restricted to the hypertrophic zone, and absent in the immature chondrocytes. To investigate a potential FoxA2/Runx2 interaction in immature chondrocytes versus hypertrophic cells, we separated these two subpopulations by FACS to obtain CD24⁺CD200⁺ hypertrophic chondrocytes and CD24⁺CD200^- immature chondrocytes and we ectopically expressed FoxA2 alone or in combination with Runx2 via lentiviral gene delivery. In CD24⁺CD200⁺ hypertrophic chondrocytes, FoxA2 enhanced the expression of chondrocyte hypertrophic markers collagen 10, MMP13, and alkaline phosphatase. In contrast, in the CD24⁺CD200^- immature chondrocytes, neither FoxA2 nor Runx2 overexpression could induce ectopic expression of hypertrophic markers MMP13, alkaline phosphatase, or PTH/PTHrP receptor. Overall these findings mirror our in vivo data, and suggest that induction of chondrocyte hypertrophy by FoxA2 may require other factors in addition to Runx2 (i.e., Hif2α, MEF2C, or perhaps unknown factors), whose expression/activity is rate-limiting in immature chondrocytes.

Identification and characterization of TGF-β1-responsive Runx2 acetylation sites for matrix Metalloproteinase-13 expression in osteoblastic cells

In skeletal tissues, transforming growth factor-beta 1 (TGF-β1) serves a number of activities. For example, in osteoblastic cells, TGF-β1 stimulates the expression of matrix metalloproteinase-13 (MMP-13, a bone remodeling gene), which requires the bone transcription factor Runx2. Although TGF-β1 is known to stimulate Runx2 acetylation, the sites involved in MMP-13 gene activation remain unknown. Mass spectrometry analysis revealed that Runx2 was acetylated at one site (K134) and three sites (K24, K134, and K169) following control and TGF-β1-treatment, respectively, in osteoblastic cells. In addition, we mutated the lysine residues in the Runx2 construct into arginine and transfected the construct into mouse mesenchymal stem cells (C3H10T1/2). Wild-type Runx2 expression and acetylation were significantly increased by TGF-β1-treatment, whereas this effect was decreased in the presence of the Runx2 double mutant construct (K24 + K169) in C3H10T1/2 cells. TGF-β1 enhanced MMP-13 promoter activity in cells transfected with the wild-type Runx2 construct, but this effect was considerably reduced in cells transfected with the Runx2 double mutant construct (K24 + K169), according to a luciferase reporter test. Hence, the stability of Runx2 may be mediated by TGF-β1-induced acetylation at K24 and K169 and is required for MMP-13 expression in osteoblastic cells. These findings add to our knowledge of TGF-β1, Runx2, and MMP-13's physiological roles in bone metabolism.

Species-specific sensitivity to TGFβ signaling and changes to the Mmp13 promoter underlie avian jaw development and evolution

Precise developmental control of jaw length is critical for survival, but underlying molecular mechanisms remain poorly understood. The jaw skeleton arises from neural crest mesenchyme (NCM), and we previously demonstrated that these progenitor cells express more bone-resorbing enzymes including Matrix metalloproteinase 13 (Mmp13) when they generate shorter jaws in quail embryos versus longer jaws in duck. Moreover, if we inhibit bone resorption or Mmp13, we can increase jaw length. In the current study, we uncover mechanisms establishing species-specific levels of Mmp13 and bone resorption. Quail show greater activation of and sensitivity to transforming growth factor beta (TGFβ) signaling than duck; where intracellular mediators like SMADs and targets like Runt-related transcription factor 2 (Runx2), which bind Mmp13, become elevated. Inhibiting TGFβ signaling decreases bone resorption, and overexpressing Mmp13 in NCM shortens the duck lower jaw. To elucidate the basis for this differential regulation, we examine the Mmp13 promoter. We discover a SMAD-binding element and single nucleotide polymorphisms (SNPs) near a RUNX2-binding element that distinguish quail from duck. Altering the SMAD site and switching the SNPs abolish TGFβ sensitivity in the quail Mmp13 promoter but make the duck promoter responsive. Thus, differential regulation of TGFβ signaling and Mmp13 promoter structure underlie avian jaw development and evolution.