Inducible expression of Runx2 results in multiorgan abnormalities in mice

Enhanced osteogenic differentiation of human mesenchymal stem cells by direct delivery of Cbfβ protein

Core binding factor β (Cbfβ) is a non-DNA binding cofactor of Runx2 that potentiates DNA binding. Previously, it has been reported that Cbfβ plays an essential role in osteogenic differentiation and skeletal development by inhibition adipogenesis. Here, we delivered the recombinant Cbfβ protein into human mesenchymal stem cells (MSCs) and triggered osteogenic lineage commitment. The efficient delivery of Cbfβ was achieved by fusing 30Kc19 protein, which is a cell-penetrating protein derived from the silkworm. After the production of the recombinant Cbfβ-30Kc19 protein in the Escherichia coli expression system, and confirmation of its intracellular delivery, MSCs were treated with the Cbfβ-30Kc19 once or twice up to 300 µg/ml. By investigating the upregulation of osteoblast-specific genes and phenotypical changes, such as calcium mineralization, we demonstrated that Cbfβ-30Kc19 efficiently induced osteogenic differentiation in MSCs. At the same time, Cbfβ-30Kc19 suppressed adipocyte formation and downregulated the expression of adipocyte-specific genes. Our results demonstrate that the intracellularly delivered Cbfβ-30Kc19 enhances osteogenesis in MSCs, whereas it suppresses adipogenesis by altering the transcriptional regulatory network involved in osteoblast-adipocyte lineage commitment. Cbfβ-30Kc19 holds great potential for the treatment of bone-related diseases, such as osteoporosis, by allowing transcriptional regulation in MSCs, and overcoming the limitations of current therapies.

Cell-specific elevation of Runx2 promotes hepatic infiltration of macrophages by upregulating MCP-1 in high-fat diet-induced mice NAFLD

OBJECTIVE

We have demonstrated runt-related transcription factor 2 (Runx2) plays important role in atherosclerosis. It has been indicated that atherosclerosis shares the similar histopathology with nonalcoholic steatohepatitis (NASH), a progressive stage of nonalcoholic fatty liver disease (NAFLD), on macrophages infiltration. However, the function of Runx2 in NAFLD is completely unknown. Here, we investigated the underlying mechanism of Runx2 triggering macrophages infiltration in the development of NAFLD.

METHODS

Mice were fed with high-fat diet (HFD) for a long time. Histopathologic features, macrophages infiltration, expression of monocyte chemotactic protein 1 (MCP-1), and Runx2 were, respectively, analyzed in vivo. Lentivirus or short interfering RNA were transfected in murine hepatic stellate cells (HSCs) and the transwell assay was performed to verify the contribution of Runx2 for macrophages migration in vitro.

RESULTS

Long-term treatment with HFD induced the progression of NAFLD, and NASH was initiated from 8 months on diet. HFD increased the expression of F4/80 upon HFD feeding, indicated HFD promotes hepatic infiltration of macrophages in NAFLD. In addition, HFD upregulated the expression of MCP-1 and Runx2 during NAFLD development. Unexpectedly, Runx2 upregulation is cell-type depended in NAFLD, and only abundantly elevated in activated HSCs. Furthermore, we found that Runx2 could increase or decrease the expression of MCP-1 in HSCs, and regulate macrophages migration by influencing MCP-1 production in vitro.

CONCLUSIONS

Our results give evidence that the upregulation of Runx2 specific in activated HSCs promotes hepatic infiltration of macrophages by increasing MCP-1 expression in NAFLD, which reveals a novel mechanism and provides a cell-specific therapeutic target for NAFLD.

Distal-less homeobox 3, a negative regulator of myogenesis, is downregulated by microRNA-133

Distal-less homeobox 3 (Dlx3), a member of the Dlx family of homeobox proteins, is a transcriptional activator of runt-related transcription factor 2 (Runx2) during osteogenic differentiation. It has been demonstrated that forced expression of Runx2 induces an osteogenic program and ectopic calcification in muscles. Therefore, it would be reasonable to predict that Dlx3 also affects myogenic differentiation. The relationship between Dlx3 and myogenesis, however, remains poorly understood. Therefore, in this study, the role and regulation of Dlx3 during myogenic differentiation were investigated. Expression level of Dlx3 was downregulated in human mesenchymal stem cells (MSCs), mouse MSCs, and C2C12 cells cultured in myogenic medium. Dlx3 level was inversely correlated with myogenic differentiation 1 and the muscle-specific microRNA, microRNA-133 (miR-133). The expression level of Runx2 was closely regulated by Dlx3 even under myogenic conditions. Overexpression of Dlx3 markedly downregulated expression levels of myogenic transcription factors and myotube formation in C2C12 cells, whereas Dlx3 knockdown enhanced myogenic differentiation. The Dlx3 3'-untranslated region (3'-UTR) has two potential binding sites for miR-133. Luciferase reporter assays demonstrated that Dlx3 is a direct target of miR-133a and miR-133b, and that the two target sites are redundantly active. Taken together, these results suggest that Dlx3 is a negative regulator of myogenic differentiation and that miR-133a and miR-133b enhance myogenic differentiation, partly through inhibition of Dlx3 expression via direct targeting of the Dlx3 3'-UTR.

A three-generation family with metaphyseal dysplasia, maxillary hypoplasia and brachydactyly (MDMHB) due to intragenic RUNX2 duplication

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly (MDMHB) is an autosomal-dominant skeletal dysplasia characterised by metaphyseal flaring of the long bones, enlargement of the medial halves of the clavicles, maxillary hypoplasia, brachydactyly, dental anomalies and mild osteoporosis. To date, only one large French Canadian family and a Finnish woman have been reported with the condition. In both, intragenic duplication encompassing exons 3-5 of the RUNX2 gene was identified. We describe a new, three-generation family with clinical features of MDMHB and an intragenic tandem duplication of RUNX2 exons 3-6. Dental problems were the primary presenting feature in all four affected individuals. We compare the features in our family to those previously reported in MDMHB, review the natural history of this condition and highlight the importance of considering an underlying skeletal dysplasia in patients presenting with significant dental problems and other suggestive features, including disproportionate short stature and/or digital anomalies.

Osteogenic Programming of Human Mesenchymal Stem Cells with Highly Efficient Intracellular Delivery of RUNX2

Mesenchymal stem cells (MSCs) are being exploited in regenerative medicine due to their tri-lineage differentiation and immunomodulation activity. Currently, there are two major challenges when directing the differentiation of MSCs for therapeutic applications. First, chemical and growth factor strategies to direct osteogenesis in vivo lack specificity for targeted delivery with desired effects. Second, MSC differentiation by gene therapy is difficult as transfection with existing approaches is clinically impractical (viral transfection) or have low efficacy (lipid-mediated transfection). These challenges can be avoided by directly delivering nonvirally derived recombinant protein transcription factors with the glycosaminoglycan-binding enhanced transduction (GET) delivery system (P21 and 8R peptides). We used the osteogenic master regulator, RUNX2 as a programming factor due to its stage-specific role in osteochondral differentiation pathways. Herein, we engineered GET-fusion proteins and compared sequential osteogenic changes in MSCs, induced by exposure to GET fusion proteins or conventional stimulation methods (dexamethasone and Bone morphogenetic protein 2). By assessing loss of stem cell-surface markers, upregulation of osteogenic genes and matrix mineralization, we demonstrate that GET-RUNX2 efficiently transduces MSCs and triggers osteogenesis by enhancing target gene expression directly. The high transduction efficiency of GET system holds great promise for stem cell therapies by allowing reproducible transcriptional control in stem cells, potentially bypassing problems observed with high-concentration growth-factor or pleiotropic steroid therapies. Stem Cells Translational Medicine 2017;6:2146-2159.

Mitotic Inheritance of mRNA Facilitates Translational Activation of the Osteogenic-Lineage Commitment Factor Runx2 in Progeny of Osteoblastic Cells

Epigenetic mechanisms mediate the acquisition of specialized cellular phenotypes during tissue development, maintenance and repair. When phenotype-committed cells transit through mitosis, chromosomal condensation counteracts epigenetic activation of gene expression. Subsequent post-mitotic re-activation of transcription depends on epigenetic DNA and histone modifications, as well as other architecturally bound proteins that "bookmark" the genome. Osteogenic lineage commitment, differentiation and progenitor proliferation require the bone-related runt-related transcription factor Runx2. Here, we characterized a non-genomic mRNA mediated mechanism by which osteoblast precursors retain their phenotype during self-renewal. We show that osteoblasts produce maximal levels of Runx2 mRNA, but not protein, prior to mitotic cell division. Runx2 mRNA partitions symmetrically between daughter cells in a non-chromosomal tubulin-containing compartment. Subsequently, transcription-independent de novo synthesis of Runx2 protein in early G1 phase results in increased functional interactions of Runx2 with a representative osteoblast-specific target gene (osteocalcin/BGLAP2) in chromatin. Somatic transmission of Runx2 mRNAs in osteoblasts and osteosarcoma cells represents a versatile mechanism for translational rather than transcriptional induction of this principal gene regulator to maintain osteoblast phenotype identity after mitosis.

The role of microRNAs in bone remodeling

Bone remodeling is balanced by bone formation and bone resorption as well as by alterations in the quantities and functions of seed cells, leading to either the maintenance or deterioration of bone status. The existing evidence indicates that microRNAs (miRNAs), known as a family of short non-coding RNAs, are the key post-transcriptional repressors of gene expression, and growing numbers of novel miRNAs have been verified to play vital roles in the regulation of osteogenesis, osteoclastogenesis, and adipogenesis, revealing how they interact with signaling molecules to control these processes. This review summarizes the current knowledge of the roles of miRNAs in regulating bone remodeling as well as novel applications for miRNAs in biomaterials for therapeutic purposes.

Estrogens antagonize RUNX2-mediated osteoblast-driven osteoclastogenesis through regulating RANKL membrane association

In addition to its thoroughly investigated role in bone formation, the osteoblast master transcription factor RUNX2 also promotes osteoclastogenesis and bone resorption. Here we demonstrate that 17β-estradiol (E2), strongly inhibits RUNX2-mediated osteoblast-driven osteoclastogenesis in co-cultures. Towards deciphering the underlying mechanism, we induced premature expression of RUNX2 in primary murine pre-osteoblasts, which resulted in robust differentiation of co-cultured splenocytes into mature osteoclasts. This was attributable to RUNX2-mediated increase in RANKL secretion, determined by ELISA, as well as to RUNX2-mediated increase in RANKL association with the osteoblast membrane, demonstrated using confocal fluorescence microscopy. The increased association with the osteoblast membrane was recapitulated by transiently expressed GFP-RANKL. E2 abolished the RUNX2-mediated increase in membrane-associated RANKL and GFP-RANKL, as well as the concomitant osteoclastogenesis. RUNX2-mediated RANKL cellular redistribution was attributable in part to a decrease in Opg expression, but E2 did not influence Opg expression either in the presence or absence of RUNX2. Diminution of RUNX2-mediated osteoclastogenesis by E2 occurred regardless of whether the pre-osteoclasts were derived from wild type or estrogen receptor alpha (ERα)-knockout mice, suggesting that activated ERα inhibited osteoblast-driven osteoclastogenesis by acting in osteoblasts, possibly targeting RUNX2. Indeed, microarray analysis demonstrated global attenuation of the RUNX2 response by E2, including abrogation of Pstpip2 expression, which likely plays a critical role in membrane trafficking. Finally, the selective ER modulators (SERMs) tamoxifen and raloxifene mimicked E2 in abrogating the stimulatory effect of osteoblastic RUNX2 on osteoclast differentiation in the co-culture assay. Thus, E2 antagonizes RUNX2-mediated RANKL trafficking and subsequent osteoclastogenesis. Targeting RUNX2 and/or downstream mechanisms that regulate RANKL trafficking may lead to the development of improved SERMs and possibly non-hormonal therapeutic approaches to high turnover bone disease.

MicroRNAs regulate bone metabolism

Osteoporosis is caused by an unbalance between bone formation and bone resorption. Bone homeostasis is regulated by intricate mechanisms. Recently, a novel class of regulatory factors termed microRNAs (miRNAs) has been found to play a crucial role in cell cycle control, apoptosis and other cellular processes including metabolism and differentiation. Published data have shown that some miRNAs regulate bone homeostasis, including bone formation, resorption, remodeling, repair and bone-related disease, by regulating the expression of certain cytokines and transcription factors. This review highlights the current knowledge of miRNAs and their involvement in the regulation of bone formation, bone resorption and the pathways regulating the progression of osteoporosis.

A tetracycline expression system in combination with Sox9 for cartilage tissue engineering

Cartilage tissue engineering using controllable transcriptional therapy together with synthetic biopolymer scaffolds shows higher potential for overcoming chondrocyte degradation and constructing artificial cartilages both in vivo and in vitro. Here, the potential regulating tetracycline expression (Tet-on) system was used to express Sox9 both in vivo and in vitro. Chondrocyte degradation was measured in vitro and overcome by Soxf9 expression. Experiments confirmed the feasibility of the combined use of Sox9 and Tet-on system in cartilage tissue engineering. Engineered poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) scaffolds were seeded with recombinant chondrocytes which were transfected with Tet-induced Sox9 expression; the scaffolds were implanted under the skin of 8-week-old rats. The experimental group was injected with Dox in the abdomen, while the control group was injected with normal saline. After 4 or 8 days of implantation in vivo, the newly formed pieces of articular chondrocytes were taken out and measured. Dox injection in vivo showed positive effect on recombinant chondrocytes, in which Sox9 expression was up-regulated by an inducible system with specific matrix proteins. The results demonstrate this controllable transcriptional therapy is a potential approach for tissue engineering.

The RUNX family in breast cancer: relationships with estrogen signaling

The three RUNX family members are lineage specific master regulators, which also have important, context-dependent roles in carcinogenesis as either tumor suppressors or oncogenes. Here we review evidence for such roles in breast cancer (BCa). RUNX1, the predominant RUNX family member in breast epithelial cells, has a tumor suppressor role reflected by many somatic mutations found in primary tumor biopsies. The classical tumor suppressor gene RUNX3 does not consist of such a mutation hot spot, but it too seems to inhibit BCa; it is often inactivated in human BCa tumors and its haploinsufficiency in mice leads to spontaneous BCa development. The tumor suppressor activities of RUNX1 and RUNX3 are mediated in part by antagonism of estrogen signaling, a feature recently attributed to RUNX2 as well. Paradoxically, however RUNX2, a master osteoblast regulator, has been implicated in various aspects of metastasis in general and bone metastasis in particular. Reciprocating the anti-estrogenic tumor suppressor activity of RUNX proteins, inhibition of RUNX2 by estrogens may help explain their context-dependent anti-metastatic roles. Such roles are reserved to non-osseous metastasis, because ERα is associated with increased, not decreased skeletal dissemination of BCa cells. Finally, based on diverse expression patterns in BCa subtypes, the successful use of future RUNX-based therapies will most likely require careful patient selection.

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly is caused by a duplication in RUNX2

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly (MDMHB) is an autosomal-dominant bone dysplasia characterized by metaphyseal flaring of long bones, enlargement of the medial halves of the clavicles, maxillary hypoplasia, variable brachydactyly, and dystrophic teeth. We performed genome-wide SNP genotyping in five affected and four unaffected members of an extended family with MDMHB. Analysis for copy-number variations revealed that a 105 kb duplication within RUNX2 segregated with the MDMHB phenotype in a region with maximum linkage. Real-time PCR for copy-number variation in genomic DNA in eight samples, as well as sequence analysis of fibroblast cDNA from one subject with MDMHB confirmed that affected family members were heterozygous for the presence of an intragenic duplication encompassing exons 3 to 5 of RUNX2. These three exons code for the Q/A domain and the functionally essential DNA-binding runt domain of RUNX2. Transfection studies with murine Runx2 cDNA showed that cellular levels of mutated RUNX2 were markedly higher than those of wild-type RUNX2, suggesting that the RUNX2 duplication found in individuals with MDMHB leads to a gain of function. Until now, only loss-of-function mutations have been detected in RUNX2; the present report associates an apparent gain-of-function alteration of RUNX2 function with a distinct rare disease.

Detection of RUNX2 gene expression in cumulus cells in women undergoing controlled ovarian stimulation

BACKGROUND

RUNX2 is a transcription factor, whose expression has been recently identified in the mouse ovary. Regulation of RUNX2 expression and its function in the human ovary have not been determined yet. The aim of the present study is the investigation of the possible correlation between RUNX2 gene expression in cumulus cells and controlled ovarian stimulation and pregnancy outcomes after ART treatment.

METHODS

A total of 41 patients undergoing ICSI treatment for male factor infertility were enrolled into a specific ART program, during which cumulus cells were collected. The expression of RUNX2 gene in cumulus cells was examined by real-time PCR.

RESULTS

Concerning RUNX2 gene expression, 12 out of 41 women were detected with RUNX2 expression, with ratios ranging from 0.84 to 1.00, while 28 out of 41 women had no expression (ratio = 0). Only 1 woman presented a weak RUNX2 gene expression (ratio = 0.52). From 8 women that proceeded to pregnancy, 7 of them did not express RUNX2 gene in cumulus cells, while one was the woman with weak gene expression that also achieved pregnancy. The group of women without RUNX2 expression presented higher number of follicles (p = 0.013), higher number of retrieved oocytes (p = 0.016), higher basal LH serum levels (p = 0.016) and higher peak estradiol levels (p = 0.013), while the number of fertilized oocytes differed marginally between the two groups (p = 0.089). Moreover, RUNX2 expression was negatively associated with LH levels (OR = 0.22, p = 0.021) and E2 levels (OR = 0.25, p = 0.026).

CONCLUSIONS

Consequently, based on the preliminary findings of the present pilot study a potential inhibitory mechanism of RUNX2 gene is observed in the ovary when high mRNA levels are detected, suggesting that RUNX2 could possibly be used as a candidate genetic marker in the monitoring of the outcome of an ART treatment.

Regulators of skeletal development: a cluster analysis of 206 bone tumors reveals diagnostically useful markers

The molecules Indian hedgehog (IHH), SP7 (also known as osterix), sex-determining region Y-box 9 (SOX9), runt-related transcription factor 2 (RUNX2) and TWIST1 regulate the normal differentiation of osteo- and chondrogenic cells from precursors during skeletal development and remodeling. The aberrant function of the same molecules has been implicated in the pathogenesis of bone tumors. Preliminary studies suggest that antibodies against these molecules have practical, diagnostic or prognostic utility in tumors. However, a comprehensive analysis of the expression of these molecules in a large, diverse set of bone tumors has yet to be reported. The goals of this study were to compare the immunohistochemical profiles of IHH, SP7, SOX9, RUNX2 and TWIST1 among bone tumors and to determine the optimum panel for diagnostic utility. Tissue microarrays prepared from 206 undecalcified tumors (71 osteosarcomas, 26 osteoblastomas/osteoid osteomas, 50 giant cell tumors, 5 chondromyxoid fibromas and 54 chondroblastomas) were stained with antibodies to IHH, SP7, SOX9, RUNX2 and TWIST1. The stains were scored for intensity (0-3+) and distribution. The results were analyzed by cluster analysis. Optimum antibody panels for diagnostic sensitivity and specificity were calculated. Analysis revealed six main clusters that corresponded well to tumor types and suggested a close relationship between the stromal cells of giant cell tumor and the osteoblasts of osteosarcoma. The expression profile of chondromyxoid fibroma and chondroblastoma also suggested related differentiation. The distribution of osteoblastomas and osteoid osteomas was more heterogeneous. RUNX2, SOX9 and TWIST1 represented the most sensitive and specific immunohistochemical panel to distinguish among these diagnoses with the limitation that no result could discriminate between chondroblastoma and chondromyxoid fibroma. IHH and SP7 did not yield additional utility.

MicroRNA control of bone formation and homeostasis

MicroRNAs (miRNAs) repress cellular protein levels to provide a sophisticated parameter of gene regulation that coordinates a broad spectrum of biological processes. Bone organogenesis is a complex process involving the differentiation and crosstalk of multiple cell types for formation and remodeling of the skeleton. Inhibition of mRNA translation by miRNAs has emerged as an important regulator of developmental osteogenic signaling pathways, osteoblast growth and differentiation, osteoclast-mediated bone resorption activity and bone homeostasis in the adult skeleton. miRNAs control multiple layers of gene regulation for bone development and postnatal functions, from the initial response of stem/progenitor cells to the structural and metabolic activity of the mature tissue. This Review brings into focus an emerging concept of bone-regulating miRNAs, the evidence for which has been gathered largely from in vivo mouse models and in vitro studies in human and mouse skeletal cell populations. Characterization of miRNAs that operate through tissue-specific transcription factors in osteoblast and osteoclast lineage cells, as well as intricate feedforward and reverse loops, has provided novel insights into the supervision of signaling pathways and regulatory networks controlling normal bone formation and turnover. The current knowledge of miRNAs characteristic of human pathologic disorders of the skeleton is presented with a future goal towards translational studies.