Runx1/AML1/Cbfa2 mediates onset of mesenchymal cell differentiation toward chondrogenesis

Regulation of Skeletal Development and Maintenance by Runx2 and Sp7

Runx2 (runt related transcription factor 2) and Sp7 (Sp7 transcription factor 7) are crucial transcription factors for bone development. The cotranscription factor Cbfb (core binding factor beta), which enhances the DNA-binding capacity of Runx2 and stabilizes the Runx2 protein, is necessary for bone development. Runx2 is essential for chondrocyte maturation, and Sp7 is partly involved. Runx2 induces the commitment of multipotent mesenchymal cells to osteoblast lineage cells and enhances the proliferation of osteoprogenitors. Reciprocal regulation between Runx2 and the Hedgehog, fibroblast growth factor (Fgf), Wnt, and parathyroid hormone-like hormone (Pthlh) signaling pathways and Dlx5 (distal-less homeobox 5) plays an important role in these processes. The induction of Fgfr2 (Fgf receptor 2) and Fgfr3 expression by Runx2 is important for the proliferation of osteoblast lineage cells. Runx2 induces Sp7 expression, and Runx2+ osteoprogenitors become Runx2+Sp7+ preosteoblasts. Sp7 induces the differentiation of preosteoblasts into osteoblasts without enhancing their proliferation. In osteoblasts, Runx2 is required for bone formation by inducing the expression of major bone matrix protein genes, including Col1a1 (collagen type I alpha 1), Col1a2, Spp1 (secreted phosphoprotein 1), Ibsp (integrin binding sialoprotein), and Bglap (bone gamma carboxyglutamate protein)/Bglap2. Bglap/Bglap2 (osteocalcin) regulates the alignment of apatite crystals parallel to collagen fibrils but does not function as a hormone that regulates glucose metabolism, testosterone synthesis, and muscle mass. Sp7 is also involved in Co1a1 expression and regulates osteoblast/osteocyte process formation, which is necessary for the survival of osteocytes and the prevention of cortical porosity. SP7 mutations cause osteogenesis imperfecta in rare cases. Runx2 is an important pathogenic factor, while Runx1, Runx3, and Cbfb are protective factors in osteoarthritis development.

Endogenous Tissue Engineering for Chondral and Osteochondral Regeneration: Strategies and Mechanisms

Increasing attention has been paid to the development of effective strategies for articular cartilage (AC) and osteochondral (OC) regeneration due to their limited self-reparative capacities and the shortage of timely and appropriate clinical treatments. Traditional cell-dependent tissue engineering faces various challenges such as restricted cell sources, phenotypic alterations, and immune rejection. In contrast, endogenous tissue engineering represents a promising alternative, leveraging acellular biomaterials to guide endogenous cells to the injury site and stimulate their intrinsic regenerative potential. This review provides a comprehensive overview of recent advancements in endogenous tissue engineering strategies for AC and OC regeneration, with a focus on the tissue engineering triad comprising endogenous stem/progenitor cells (ESPCs), scaffolds, and biomolecules. Multiple types of ESPCs present within the AC and OC microenvironment, including bone marrow-derived mesenchymal stem cells (BMSCs), adipose-derived mesenchymal stem cells (AD-MSCs), synovial membrane-derived mesenchymal stem cells (SM-MSCs), and AC-derived stem/progenitor cells (CSPCs), exhibit the ability to migrate toward injury sites and demonstrate pro-regenerative properties. The fabrication and characteristics of scaffolds in various formats including hydrogels, porous sponges, electrospun fibers, particles, films, multilayer scaffolds, bioceramics, and bioglass, highlighting their suitability for AC and OC repair, are systemically summarized. Furthermore, the review emphasizes the pivotal role of biomolecules in facilitating ESPCs migration, adhesion, chondrogenesis, osteogenesis, as well as regulating inflammation, aging, and hypertrophy-critical processes for endogenous AC and OC regeneration. Insights into the applications of endogenous tissue engineering strategies for in vivo AC and OC regeneration are provided along with a discussion on future perspectives to enhance regenerative outcomes.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Alginate Improves the Chondrogenic Capacity of 3D PCL Scaffolds In Vitro: A Histological Approach

Polycaprolactone (PCL) scaffolds have demonstrated an effectiveness in articular cartilage regeneration due to their biomechanical properties. On the other hand, alginate hydrogels generate a 3D environment with great chondrogenic potential. Our aim is to generate a mixed PCL/alginate scaffold that combines the chondrogenic properties of the two biomaterials. Porous PCL scaffolds were manufactured using a modified salt-leaching method and embedded in a culture medium or alginate in the presence or absence of chondrocytes. The chondrogenic capacity was studied in vitro. Type II collagen and aggrecan were measured by immunofluorescence, cell morphology by F-actin fluorescence staining and gene expression of COL1A1, COL2A1, ACAN, COL10A1, VEGF, RUNX1 and SOX6 by reverse transcription polymerase chain reaction (RT-PCR). The biocompatibility of the scaffolds was determined in vivo using athymic nude mice and assessed by histopathological and morphometric analysis. Alginate improved the chondrogenic potential of PCL in vitro by increasing the expression of type II collagen and aggrecan, as well as other markers related to chondrogenesis. All scaffolds showed good biocompatibility in the in vivo model. The presence of cells in the scaffolds induced an increase in vascularization of the PCL/alginate scaffolds. The results presented here reinforce the benefits of the combined use of PCL and alginate for the regeneration of articular cartilage.

[Latest Findings on the Role of RUNX1 in Bone Development and Disorders]

Runt-related transcription factor (RUNX1) is a transcription factor closely involved in hematopoiesis. RUNX1 gene mutation plays an essential pathogenic role in the initiation and development of hematological tumors, especially in acute myeloid leukemia. Recent studies have shown that RUNX1 is also involved in the regulation of bone development and the pathological progression of bone-related diseases. RUNX1 promotes the differentiation of mesenchymal stem cells into chondrocytes and osteoblasts and modulates the maturation and extracellular matrix formation of chondrocytes. The expression of RUNX1 in mesenchymal stem cells, chondrocytes, and osteoblasts is of great significance for maintaining normal bone development and the mass and quality of bones. RUNX1 also inhibits the differentiation and bone resorptive activities of osteoclasts, which may be influenced by sexual dimorphism. In addition, RUNX1 deficiency contributes to the pathogenesis of osteoarthritis, delayed fracture healing, and osteoporosis, which was revealed by the RUNX1 conditional knockout modeling in mice. However, the roles of RUNX1 in regulating the hypertrophic differentiation of chondrocytes, the sexual dimorphism of activities of osteoclasts, as well as bone loss in diabetes mellitus, senescence, infection, chronic inflammation, etc, are still not fully understood. This review provides a systematic summary of the research progress concerning RUNX1 in the field of bone biology, offering new ideas for using RUNX1 as a potential target for bone related diseases, especially osteoarthritis, delayed fracture healing, and osteoporosis.

Kartogenin-loaded polyvinyl alcohol/nano-hydroxyapatite composite hydrogel promotes tendon-bone healing in rabbits after anterior cruciate ligament reconstruction

Accumulating evidence supports the role of cartilage tissue engineering in cartilage defect repair, but the biological function has yet to be fully explained. In this work, kartogenin (KGN), an emerging chondroinductive nonprotein small molecule, was incorporated into a composite hydrogel of polyvinyl alcohol/nano-hydroxyapatite (PVA/n-HA) to fabricate an appropriate microenvironment for tendon-bone healing after anterior cruciate ligament (ACL) reconstruction. KGN/PVA/n-HA composite hydrogel scaffolds were prepared by in situ synthesis and physical adsorption, followed by characterization under a scanning electron microscope. The scaffolds were transplanted into healthy New Zealand White (NZW) rabbits. It was confirmed that KGN/PVA/n-HA scaffolds were successfully prepared and exhibited good supporting properties and excellent biocompatibility. Unilateral ACL reconstruction was constructed with tendon autograft in NZW rabbits, and the morphology and diameter of collagen fiber were analyzed. The scaffolds were shown to promote ACL growth and collagen fiber formation. Furthermore, microcomputerized tomography analysis and bone formation histology were performed to detect new bone formation. KGN/PVA/n-HA scaffolds effectively alleviated cartilage damage and prevented the occurrence of osteoarthritis. Meanwhile, ligament-bone healing and bone formation were observed in the presence of KGN/PVA/n-HA scaffolds. In conclusion, these results suggest that the KGN/PVA/n-HA scaffolds can facilitate tendon-bone healing after ACL reconstruction and might be considered novel hydrogel biomaterials in cartilage tissue engineering.

A Novel RUNX1 Genetic Variant Identified in a Young Male with Severe Osteoporosis

This case describes a young man with an unusual cause of severe osteoporosis and markedly deranged bone microarchitecture resulting in multiple fractures. A potentially pathogenic germline variant in the runt-related transcription factor 1 (RUNX1) gene was discovered by a focused 51-gene myeloid malignancy panel during investigation for his unexplained normochromic normocytic anemia. Further bone-specific genetic testing and a pedigree analysis were declined by the patient. Recent experimental evidence demonstrates that RUNX1 plays a key role in the regulation of osteogenesis and bone homeostasis during skeletal development, mediated by the bone morphogenic protein and Wnt signaling pathways. Therefore, rarer causes of osteoporosis, including those affecting bone formation, should be considered in young patients with multiple unexpected minimal trauma fractures. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Cbfβ Is a Novel Modulator against Osteoarthritis by Maintaining Articular Cartilage Homeostasis through TGF-β Signaling

TGF-β signaling is a vital regulator for maintaining articular cartilage homeostasis. Runx transcription factors, downstream targets of TGF-β signaling, have been studied in the context of osteoarthritis (OA). Although Runx partner core binding factor β (Cbfβ) is known to play a pivotal role in chondrocyte and osteoblast differentiation, the role of Cbfβ in maintaining articular cartilage integrity remains obscure. This study investigated Cbfβ as a novel anabolic modulator of TGF-β signaling and determined its role in articular cartilage homeostasis. Cbfβ significantly decreased in aged mouse articular cartilage and human OA cartilage. Articular chondrocyte-specific Cbfb-deficient mice (Cbfb△ac/△ac) exhibited early cartilage degeneration at 20 weeks of age and developed OA at 12 months. Cbfb△ac/△ac mice showed enhanced OA progression under the surgically induced OA model in mice. Mechanistically, forced expression of Cbfβ rescued Type II collagen (Col2α1) and Runx1 expression in Cbfβ-deficient chondrocytes. TGF-β1-mediated Col2α1 expression failed despite the p-Smad3 activation under TGF-β1 treatment in Cbfβ-deficient chondrocytes. Cbfβ protected Runx1 from proteasomal degradation through Cbfβ/Runx1 complex formation. These results indicate that Cbfβ is a novel anabolic regulator for cartilage homeostasis, suggesting that Cbfβ could protect OA development by maintaining the integrity of the TGF-β signaling pathway in articular cartilage.

Multiparity and Aging Impact Chondrogenic and Osteogenic Potential at Symphyseal Enthesis: New Insights into Interpubic Joint Remodeling

Pregnancy and childbirth cause adaptations to the birth canal to allow for delivery and fast recovery. To accommodate delivery through the birth canal, the pubic symphysis undergoes changes that lead to the interpubic ligament (IpL) and enthesis formation in primiparous mice. However, successive deliveries influence joint recovery. We aimed to understand tissue morphology and chondrogenic and osteogenic potential at symphyseal enthesis during pregnancy and postpartum in primiparous and multiparous senescent female mice. Morphological and molecular differences were found at the symphyseal enthesis among the study groups. Despite the apparent incapacity to restore cartilage in multiparous senescent animals, the symphyseal enthesis cells are active. However, these cells have reduced expression of chondrogenic and osteogenic markers and are immersed in densely packed collagen fibers contiguous to the persistent IpL. These findings may indicate alterations of key molecules in the progenitor cell population maintenance of the chondrocytic and osteogenic lineages at the symphyseal enthesis in multiparous senescent animals, possibly compromising the mouse joint histoarchitecture recovery. This sheds light on the distention of the birth canal and the pelvic floor that may play a role in pubic symphysis diastasis (PSD) and pelvic organ prolapse (POP), both in orthopedic and urogynecological practice in women.

The roles of Runx1 in skeletal development and osteoarthritis: A concise review

Runt-related transcription factor-1 (Runx1) is well known for its functions in hematopoiesis and leukemia but recent research has focused on its role in skeletal development and osteoarthritis (OA). Deficiency of the Runx1 gene is fatal in early embryonic development, and specific knockout of Runx1 in cell lineages of cartilage and bone leads to delayed cartilage formation and impaired bone calcification. Runx1 can regulate genes including collagen type II (Col2a1) and X (Col10a1), SRY-box transcription factor 9 (Sox9), aggrecan (Acan) and matrix metalloproteinase 13 (MMP-13), and the up-regulation of Runx1 improves the homeostasis of the whole joint, even in the pathological state. Moreover, Runx1 is activated as a response to mechanical compression, but impaired in the joint with the pathological progress associated with osteoarthritis. Therefore, interpretation about the role of Runx1 could enlarge our understanding of key marker genes in the skeletal development and an increased understanding of Runx1 could be helpful to identify treatments for osteoarthritis. This review provides the most up-to-date advances in the roles and bio-mechanisms of Runx1 in healthy joints and osteoarthritis from all currently published articles and gives novel insights in therapeutic approaches to OA based on Runx1.

TATTOO-seq delineates spatial and cell type-specific regulatory programs in the developing limb

The coordinated differentiation of progenitor cells into specialized cell types and their spatial organization into distinct domains is central to embryogenesis. Here, we developed and applied an unbiased spatially resolved single-cell transcriptomics method to identify the genetic programs underlying the emergence of specialized cell types during mouse limb development and their spatial integration. We identify multiple transcription factors whose expression patterns are predominantly associated with cell type specification or spatial position, suggesting two parallel yet highly interconnected regulatory systems. We demonstrate that the embryonic limb undergoes a complex multiscale reorganization upon perturbation of one of its spatial organizing centers, including the loss of specific cell populations, alterations of preexisting cell states' molecular identities, and changes in their relative spatial distribution. Our study shows how multidimensional single-cell, spatially resolved molecular atlases can allow the deconvolution of spatial identity and cell fate and reveal the interconnected genetic networks that regulate organogenesis and its reorganization upon genetic alterations.

Functional Testing of Bone Morphogenetic Protein (BMP) Pathway Variants Identified on Whole-Exome Sequencing in a Patient with Delayed-Onset Fibrodysplasia Ossificans Progressiva (FOP) Using ACVR1R206H -Specific Human Cellular and Zebrafish Models

Bone morphogenetic protein (BMP) signaling is critical in skeletal development. Overactivation can trigger heterotopic ossification (HO) as in fibrodysplasia ossificans progressiva (FOP), a rare, progressive disease of massive HO formation. A small subset of FOP patients harboring the causative ACVR1^R206H mutation show strikingly mild or delayed-onset HO, suggesting that genetic variants in the BMP pathway could act as disease modifiers. Whole-exome sequencing of one such patient identified BMPR1A^R443C and ACVR2A^V173I as candidate modifiers. Molecular modeling predicted significant structural perturbations. Neither variant decreased BMP signaling in ACVR1^R206H HEK 293T cells at baseline or after stimulation with BMP4 or activin A (AA), ligands that activate ACVR1^R206H signaling. Overexpression of BMPR1A^R443C in a Tg(ACVR1-R206Ha) embryonic zebrafish model, in which overactive BMP signaling yields ventralized embryos, did not alter ventralization severity, while ACVR2A^V173I exacerbated ventralization. Co-expression of both variants did not affect dorsoventral patterning. In contrast, BMPR1A knockdown in ACVR1^R206H HEK cells decreased ligand-stimulated BMP signaling but did not affect dorsoventral patterning in Tg(ACVR1-R206Ha) zebrafish. ACVR2A knockdown decreased only AA-stimulated signaling in ACVR1^R206H HEK cells and had no effect in Tg(ACVR1-R206Ha) zebrafish. Co-knockdown in ACVR1^R206H HEK cells decreased basal and ligand-stimulated signaling, and co-knockdown/knockout (bmpr1aa/ab; acvr2aa/ab) decreased Tg(ACVR1-R206Ha) zebrafish ventralization phenotypes. Our functional studies showed that knockdown of wild-type BMPR1A and ACVR2A could attenuate ACVR1^R206H signaling, particularly in response to AA, and that ACVR2A^V173I unexpectedly increased ACVR1^R206H -mediated signaling in zebrafish. These studies describe a useful strategy and platform for functionally interrogating potential genes and genetic variants that may impact the BMP signaling pathway. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Runx1 is a key regulator of articular cartilage homeostasis by orchestrating YAP, TGFβ, and Wnt signaling in articular cartilage formation and osteoarthritis

Runt-related transcription factor 1 (Runx1) plays a key role in cartilage formation, but its function in articular cartilage formation is unclear. We generated non-inducible and inducible Runx1-deficient mice (Runx1f/fCol2α1-Cre and Runx1f/fCol2α1-CreER mice) and found that chondrocyte-specific Runx1-deficient mice developed a spontaneous osteoarthritis (OA)-like phenotype and showed exacerbated articular cartilage destruction under OA, characterized by articular cartilage degradation and cartilage ossification, with decreased Col2α1 expression and increased Mmp13 and Adamts5 expression. RNA-sequencing analysis of hip articular cartilage from the Runx1f/fCol2α1-Cre mice compared to that from wild-type mice and subsequent validation analyses demonstrated that Runx1 is a central regulator in multiple signaling pathways, converging signals of the Hippo/Yap, TGFβ/Smad, and Wnt/β-catenin pathways into a complex network to regulate the expression of downstream genes, thereby controlling a series of osteoarthritic pathological processes. RNA-sequencing analysis of mutant knee joints showed that Runx1's role in signaling pathways in articular cartilage is different from that in whole knee joints, indicating that Runx1 regulation is tissue-specific. Histopathologic analysis confirmed that Runx1 deficiency decreased the levels of YAP and p-Smad2/3 and increased the levels of active β-catenin. Overexpression of Runx1 dramatically increased YAP expression in chondrocytes. Adeno-associated virus-mediated Runx1 overexpression in the knee joints of osteoarthritic mice showed the protective effect of Runx1 on articular cartilage damaged in OA. Our results notably showed that Runx1 is a central regulator of articular cartilage homeostasis by orchestrating the YAP, TGFβ, and Wnt signaling pathways in the formation of articular cartilage and OA, and targeting Runx1 and its downstream genes may facilitate the design of novel therapeutic approaches for OA.

Sexually Dimorphic Increases in Bone Mass Following Tissue-specific Overexpression of Runx1 in Osteoclast Precursors

Many metabolic bone diseases arise as a result excessive osteoclastic bone resorption, which has motivated efforts to identify new molecular targets that can inhibit the formation or activity of these bone-resorbing cells. Mounting evidence indicates that the transcription factor Runx1 acts as a transcriptional repressor of osteoclast formation. Prior studies using a conditional knockout approach suggested that Runx1 in osteoclast precursors acts as an inhibitor of osteoclastogenesis; however, the effects of upregulation of Runx1 on osteoclast formation remain unknown. In this study, we investigated the skeletal effects of conditional overexpression of Runx1 in preosteoclasts by crossing novel Runx1 gain-of-function mice (Rosa26-LSL-Runx1) with LysM-Cre transgenic mice. We observed a sex-dependent effect whereby overexpression of Runx1 in female mice increased trabecular bone microarchitectural indices and improved torsion biomechanical properties. These effects were likely mediated by delayed osteoclastogenesis and decreased bone resorption. Transcriptomics analyses during osteoclastogenesis revealed a distinct transcriptomic profile in the Runx1-overexpressing cells, with enrichment of genes related to redox signaling, apoptosis, osteoclast differentiation, and bone remodeling. These data further confirm the antiosteoclastogenic activities of Runx1 and provide new insight into the molecular targets that may mediate these effects.

Upregulation of Runt related transcription factor 1 (RUNX1) contributes to tendon-bone healing after anterior cruciate ligament reconstruction using bone mesenchymal stem cells

Background

Anterior cruciate ligament (ACL) injury could lead to functional impairment along with disabilities. ACL reconstruction often fails owing to the regeneration failure of tendon–bone interface. Herein, we aimed to investigate the effects of Runt related transcription factor 1 (RUNX1) on tendon–bone healing after ACL reconstruction using bone mesenchymal stem cells (BMSCs).

Methods

BMSCs were isolated from the marrow cavity of rat femur, followed by the modification of RUNX1 with lentiviral system. Then, an ACL reconstruction model of rats was established with autografts.

Results

Results of flow cytometry exhibited positive-antigen CD44 and CD90, as well as negative-antigen CD34 and CD45 of the BMSCs. Then, we found that RUNX1-upregulated BMSCs elevated the decreased biomechanical strength of the tendon grafts after ACL reconstruction. Moreover, based on the histological observation, upregulation of RUNX1 was linked with better recovery around the bone tunnel, a tighter tendon–bone interface, and more collagen fibers compared to the group of BMSCs infected with LV-NC. Next, RUNX1-upregulated BMSCs promoted osteogenesis after ACL reconstruction, as evidenced by the mitigation of severe loss and erosion of the cartilage and bone in the tibial and femur area, as well as the increased number of osteoblasts identified by the upregulation of alkaline phosphatase, osteocalcin, and osteopontin in the tendon–bone interface.

Conclusion

Elevated expression of RUNX1 contributed to tendon–bone healing after ACL reconstruction using BMSCs.

Effects of Separate and Combined Exposure of Cadmium and Lead on the Endochondral Ossification in Bufo gargarizans

Cadmium (Cd) and lead (Pb) are ubiquitous in aquatic environments and most studies have examined the potential effects of Cd or Pb alone on aquatic organisms. In the present study, chronic effects of Cd and Pb, alone and in combination, on Bufo gargarizans were investigated by exposing embryos to these contaminants throughout metamorphosis. Significant reductions in body mass and snout-to-vent length were observed in B. gargarizans at Gosner stage 42 (Gs 42) and Gs 46 exposed to a Cd/Pb mixture. Single and combined exposure with Cd and Pb induced histological alterations of the thyroid gland characterized by reduced colloid area and thickness of epithelial cells. There was a significant decrease in the maximum jump distance of froglets exposed to Cd alone and the Cd/Pb mixture, and the jumping capacity showed a positive correlation with hind limb length and tibia/fibula. Moreover, single metals and their mixture induced reduction of endochondral bone formation in B. gargarizans. Transcriptomic and real-time quantitative polymerase chain reaction results showed that genes involved in skeletal ossification (TRα, TRβ, Dio2, Dio3, MMP9, MMP13, Runx1, Runx2, and Runx3) were transcriptionally dysregulated by Cd and Pb exposure alone or in combination. Our results suggested that despite the low concentration tested, the Cd/Pb mixture induced more severe impacts on B. gargarizans. In addition, the Cd/Pb mixture might reduce chances of survival for B. gargarizans froglets by decreasing size at metamorphosis, impaired skeletal ossification, and reduction in jumping ability, which might result from dysregulation of genes involved in thyroid hormone action and endochondral ossification. The findings obtained could add a new dimension to understanding of the mechanisms underpinning skeletal ossification response to heavy metals in amphibians. Environ Toxicol Chem 2022;41:1228-1245. © 2022 SETAC.

Preparation and characterization of a novel drug-loaded Bi-layer scaffold for cartilage regeneration

The incidence of articular cartilage defects is increasing year by year. In order to repair the cartilage tissue at the defect, scaffolds with nanofiber structure and biocompatibility have become a research hotspot. In this study, we designed and fabricated a bi-layer scaffold prepared from an upper layer of drug-dispersed gelatin methacrylate (GELMA) hydrogel and a lower layer of a drug-encapsulated coaxial fiber scaffold prepared from silk fiber (SF) and polylactic acid (PLA). These bi-layer scaffolds have porosity (91.26 ± 3.94%) sufficient to support material exchange and pore size suitable for cell culture and infiltration, as well as mechanical properties (2.65 ± 0.31 MPa) that meet the requirements of cartilage tissue engineering. The coaxial fiber structure exhibited excellent drug release properties, maintaining drug release for 14 days in PBS. In vitro experiments indicated that the scaffolds were not toxic to cells and were amenable to chondrocyte migration. Notably, the growth of cells in a bi-layer scaffold presented two states. In the hydrogel layer, cells grow through interconnected pores and take on a connective tissue-like shape. In the coaxial fiber layer, cells grow on the surface of the coaxial fiber mats and appeared tablet-like. This is similar to the structure of the functional partitions of natural cartilage tissue. Together, the bi-layer scaffold can play a positive role in cartilage regeneration, which could be a potential therapeutic choice to solve the current problems of clinical cartilage repair.

Potential of Using Infrapatellar–Fat–Pad–Derived Mesenchymal Stem Cells for Therapy in Degenerative Arthritis: Chondrogenesis, Exosomes, and Transcription Regulation

Infrapatellar fat pad–derived mesenchymal stem cells (IPFP-MSCs) are a type of adipose-derived stem cell (ADSC). They potentially contribute to cartilage regeneration and modulation of the immune microenvironment in patients with osteoarthritis (OA). The ability of IPFP-MSCs to increase chondrogenic capacity has been reported to be greater, less age dependent, and less affected by inflammatory changes than that of other MSCs. Transcription-regulatory factors strictly regulate the cartilage differentiation of MSCs. However, few studies have explored the effect of transcriptional factors on IPFP-MSC-based neocartilage formation, cartilage engineering, and tissue functionality during and after chondrogenesis. Instead of intact MSCs, MSC-derived extracellular vesicles could be used for the treatment of OA. Furthermore, exosomes are increasingly being considered the principal therapeutic agent in MSC secretions that is responsible for the regenerative and immunomodulatory functions of MSCs in cartilage repair. The present study provides an overview of advancements in enhancement strategies for IPFP-MSC chondrogenic differentiation, including the effects of transcriptional factors, the modulation of released exosomes, delivery mechanisms for MSCs, and ethical and regulatory points concerning the development of MSC products. This review will contribute to the understanding of the IPFP-MSC chondrogenic differentiation process and enable the improvement of IPFP-MSC-based cartilage tissue engineering.

Cre/LoxP Genetic Recombination Sustains Cartilage Anabolic Factor Expression in Hyaluronan Encapsulated MSCs Alleviates Intervertebral Disc Degeneration

(1) Background: Inexplicable low back and neck pain frequently results from spinal disc degeneration with an imbalanced intervertebral disc (IVD) cell homeostasis. We hypothesize that introducing MSC expressing a sustained cartilage-anabolic factor in the IVD may stimulate the mucoid materials secreted from the IVD cells, promote the MSC’s chondrogenesis and maintain the hydration content providing mechanical strength to decelerate the disc degeneration progression; (2) Methods: This study expressed a cartilage-anabolic factor runx1 by a baculoviral vector (BV) transduced MSCs through a Cre/LoxP gene editing and recombination system for sustained recombinant runx1 transcription factor production. The Cre/LoxP BV modified MSCs were encapsulated by hyaluronan hydrogel, due to its’ vital composition in ECM of a healthy disc and transplanted to a punctured coccygeal disc in rats through micro-injection, followed by X-ray radiography and histological analysis at the 4- and 12-weeks post-transplantation; (3) Results: Data reveals the Cre/LoxP BV system-mediated long-termed runx1 gene expression, possessing good biosafety characteristics in the in vitro cell transduction and in vivo MSCs transplantation, and maintained superior hydration content in the disc than that of mock transduced MSCs; (4) Conclusions: This proof-of-concept study fulfills the need of implanting therapeutic cells accompanied with microinjection in the disc, such as a discography and paves a road to manufacture composite hyaluronan, such as peptide modified hyaluronan as an MSC carrier for IVD regeneration in the future study.

Runx1 Messenger RNA Delivered by Polyplex Nanomicelles Alleviate Spinal Disc Hydration Loss in a Rat Disc Degeneration Model

Vertebral disc degenerative disease (DDD) affects millions of people worldwide and is a critical factor leading to low back and neck pain and consequent disability. Currently, no strategy has addressed curing DDD from fundamental aspects, because the pathological mechanism leading to DDD is still controversial. One possible mechanism points to the homeostatic status of extracellular matrix (ECM) anabolism, and catabolism in the disc may play a vital role in the disease's progression. If the damaged disc receives an abundant amount of cartilage, anabolic factors may stimulate the residual cells in the damaged disc to secrete the ECM and mitigate the degeneration process. To examine this hypothesis, a cartilage anabolic factor, Runx1, was expressed by mRNA through a sophisticated polyamine-based PEG-polyplex nanomicelle delivery system in the damaged disc in a rat model. The mRNA medicine and polyamine carrier have favorable safety characteristics and biocompatibility for regenerative medicine. The endocytosis of mRNA-loaded polyplex nanomicelles in vitro, mRNA delivery efficacy, hydration content, disc shrinkage, and ECM in the disc in vivo were also examined. The data revealed that the mRNA-loaded polyplex nanomicelle was promptly engulfed by cellular late endosome, then spread into the cytosol homogeneously at a rate of less than 20 min post-administration of the mRNA medicine. The mRNA expression persisted for at least 6-days post-injection in vivo. Furthermore, the Runx1 mRNA delivered by polyplex nanomicelles increased hydration content by ≈43% in the punctured disc at 4-weeks post-injection (wpi) compared with naked Runx1 mRNA administration. Meanwhile, the disc space and ECM production were also significantly ameliorated in the polyplex nanomicelle group. This study demonstrated that anabolic factor administration by polyplex nanomicelle-protected mRNA medicine, such as Runx1, plays a key role in alleviating the progress of DDD, which is an imbalance scenario of disc metabolism. This platform could be further developed as a promising strategy applied to regenerative medicine.

Altered microRNAs in C3H10T1/2 cells induced by p.E95K mutant IHH signaling

Background

Indian Hedgehog (IHH), an important cell signaling protein, plays a key regulatory role in development of cartilage and chondrogenesis. Earlier studies have shown that heterozygous missense mutations in IHH gene may cause brachydactyly type A1 (BDA1), an autosomal dominant inheritance disease characterized by apparent shortness or absence of the middle phalanges of all digits. MicroRNAs (miRNAs) have been found to be significant post-transcriptional regulators of gene expression and significantly influence the process of bone-development. Therefore, it is possible that miRNAs are involved in the mechanism underlying the development of BDA1. However, the relationship between miRNAs and the pathogenesis of BDA1 remains unclear.

Methods

In this study, we used microarray-based miRNA profiling to investigate the role of miRNAs in BDA1 by characterization of differentially expressed miRNAs in C3H10T1/2 cell line induced by wild type (WT) and p.E95K mutant (MT) IHH signaling.

Results

Our results identified 6 differentially expressed miRNAs between WT and control (CT) group and 5 differentially expressed miRNAs between MT and CT groups. In particular, miR-135a-1-3p was found to be a significantly differentially expressed miRNA between WT and CT group. Results of dual-luciferase reporter gene experiment successfully discovered Hoxd10 was one of the target gene of miR-135a-1-3p. Additionally, our pathway analysis revealed that the targets of these miRNAs of interest were highly involved with Runx1/2, Notch and collagen-related pathways.

Conclusions

Taken together, our findings provided important clue for future study of the process of miRNA-regulation in IHH signaling and novel insights into the regulatory role of miRNA in pathogenesis of BDA1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-021-00207-8.

Runx1 protects against the pathological progression of osteoarthritis

Runt-related transcription factor-1 (Runx1) is required for chondrocyte-to-osteoblast lineage commitment by enhancing both chondrogenesis and osteogenesis during vertebrate development. However, the potential role of Runx1 in joint diseases is not well known. In the current study, we aimed to explore the role of Runx1 in osteoarthritis induced by anterior cruciate ligament transaction (ACLT) surgery. We showed that chondrocyte-specific Runx1 knockout (Runx1f/fCol2a1-Cre) aggravated cartilage destruction by accelerating the loss of proteoglycan and collagen II in early osteoarthritis. Moreover, we observed thinning and ossification of the growth plate, a decrease in chondrocyte proliferative capacity and the loss of bone matrix around the growth plate in late osteoarthritis. We overexpressed Runx1 by adeno-associated virus (AAV) in articular cartilage and identified its protective effect by slowing the destruction of osteoarthritis in cartilage in early osteoarthritis and alleviating the pathological progression of growth plate cartilage in late osteoarthritis. ChIP-seq analysis identified new targets that interacted with Runx1 in cartilage pathology, and we confirmed the direct interactions of these factors with Runx1 by ChIP-qPCR. This study helps us to understand the function of Runx1 in osteoarthritis and provides new clues for targeted osteoarthritis therapy.

FoxO3a cooperates with RUNX1 to promote chondrogenesis and terminal hypertrophic of the chondrogenic progenitor cells

FoxO transcription factors (FoxOs) have recently been shown to protect against chondrocyte dysfunction and modulate cartilage homeostasis in osteoarthritis. The mechanism underlying of FoxOs regulate chondrocyte differentiation remains unknown. Runt related transcription factor 1 (RUNX1) mediated both chondrocyte and osteoblast differentiation. Our data showed that FoxO3a and RUNX1 are co-expressed in ATDC5 cells and undifferentiated mesenchyme cells and have similar high levels in chondrocytes undergoing transition from proliferation to hypertrophy. Overexpression of FoxO3a in ATDC5 cells or mouse mesenchymal cells resulted in a potent induction of the chondrocyte differentiation markers. Knockdown FoxO3a or RUNX1 potently inhibits the expressions of chondrocyte differentiation markers, including Sox9, Aggrecan, Col2, and hypertrophic chondrocyte markers including RUNX2, ColX, MMP13 and ADAMTs-5 in ATDC5 cells. Co-immunoprecipitation showed that FoxO3a binds the transcriptional regulator RUNX1. Immunohistochemistry showed that FoxO3a and RUNX1 are highly co-expressed in the proliferative chondrocytes of the growth plates in the hind limbs of newborn mice. Collectively, we revealed that FoxO3a cooperated with RUNX1 promoted chondrocyte differentiation through enhancing both early chondrogenesis and terminal hypertrophic of the chondrogenic progenitor cells, indicating FoxO3a interacting with RUNX1 may be a therapeutic target for the treatment of osteoarthritis and other bone diseases.

Alginate-Agarose Hydrogels Improve the In Vitro Differentiation of Human Dental Pulp Stem Cells in Chondrocytes. A Histological Study

Matrix-assisted autologous chondrocyte implantation (MACI) has shown promising results for cartilage repair, combining cultured chondrocytes and hydrogels, including alginate. The ability of chondrocytes for MACI is limited by different factors including donor site morbidity, dedifferentiation, limited lifespan or poor proliferation in vitro. Mesenchymal stem cells could represent an alternative for cartilage regeneration. In this study, we propose a MACI scaffold consisting of a mixed alginate-agarose hydrogel in combination with human dental pulp stem cells (hDPSCs), suitable for cartilage regeneration. Scaffolds were characterized according to their rheological properties, and their histomorphometric and molecular biology results. Agarose significantly improved the biomechanical behavior of the alginate scaffolds. Large scaffolds were manufactured, and a homogeneous distribution of cells was observed within them. Although primary chondrocytes showed a greater capacity for chondrogenic differentiation, hDPSCs cultured in the scaffolds formed large aggregates of cells, acquired a rounded morphology and expressed high amounts of type II collagen and aggrecan. Cells cultured in the scaffolds expressed not only chondral matrix-related genes, but also remodeling proteins and chondrocyte differentiation factors. The degree of differentiation of cells was proportional to the number and size of the cell aggregates that were formed in the hydrogels.

Long Non-coding RNA 332443 Inhibits Preadipocyte Differentiation by Targeting Runx1 and p38-MAPK and ERK1/2-MAPK Signaling Pathways

Long non-coding RNAs (lncRNAs) have emerged as integral regulators of pathophysiological processes, but their specific roles and mechanisms in adipose tissue development remain largely unknown. Here, through microarray analysis, co-expression, and tissue specific analysis of adipocyte tissues after fasting for 72 h, we found that Lnc-FR332443 expression was dramatically decreased, as well as the expression of Runx1. The UCSC database and Ensembl database indicated that Lnc-FR332443 is the antisense lncRNA of Runx1. Lnc-FR332443 and Runx1 are highly enriched in adipose tissue and downregulated during adipogenic differentiation. Adipose tissue-specific knockdown of Lnc-FR332443 increased fat mass in vivo, and specific knockdown of Lnc-FR332443 in 3T3-L1 preadipocytes promoted adipogenic differentiation. In this process, Runx1 expression was decreased when Lnc-FR332443 was downregulated in adipocytes or 3T3-L1 preadipocytes, and vice versa, when Lnc-FR332443 was upregulated, the expression of Runx1 was increased. However, overexpression of Runx1 decreased the expression of the adipocyte cell marker genes PPARγ, C/EBPα and FABP4 significantly, while not affected the expression of Lnc-FR332443. Mechanistically, Lnc-FR332443 positively regulates Runx1 expression in mouse adipocytes and suppresses adipocyte differentiation by attenuating the phosphorylation of MAPK-p38 and MAPK-ERK1/2 expression. Thus, this study indicated that Lnc-FR332443 inhibits adipogenesis and which might be a drug target for the prevention and treatment of obesity.

Chitosan/polycaprolactone multilayer hydrogel: A sustained Kartogenin delivery model for cartilage regeneration

Cartilage regeneration using biomaterial-guided delivery systems presents improved therapeutic efficacy of the biomolecules while minimizing side effects. Here, our hypothesis was to design a multilayer scaffold of chitosan (CS) hydrogel and polycaprolactone (PCL) mat to enhance the mechanical properties, integrity and stability of CS, especially for subsequent in vivo transplantation. After conjugation of the Kartogenin (KGN) into this structure, its gradual release can promote chondrogenesis of mesenchymal stem cells (MSCs). Initially, a thin electrospun PCL layer was sandwiched between two CS hydrogels. Subsequently, KGN was superficially immobilized onto the CS matrix. The successful conjugation was confirmed by scanning electron microscopy (SEM) and infrared spectroscopy. These novel KGN-conjugated scaffolds possessed lower swelling and higher compressive modulus and showed gradual release of KGN in longer retention times. Immunofluorescent and histological staining represented more cells located in lacunae as well as more Coll2 and Sox9 positive cells on KGN-conjugated scaffolds. Gene expression analysis also revealed that SOX9, COLL2 and ACAN expression levels were higher in the presence of KGN, while COLLX expression was down-regulated, indicating a hypertrophy phenomenon with synergistic effect of TGF-β. This multilayer structure not only facilitates the effective treatment, but also provides a proper mechanical structure for cartilage engineering.

ChondroGELesis: Hydrogels to harness the chondrogenic potential of stem cells

The extracellular matrix is a highly complex microenvironment, whose various components converge to regulate cell fate. Hydrogels, as water-swollen polymer networks composed by synthetic or natural materials, are ideal candidates to create biologically active substrates that mimic these matrices and target cell behaviour for a desired tissue engineering application. Indeed, the ability to tune their mechanical, structural, and biochemical properties provides a framework to recapitulate native tissues. This review explores how hydrogels have been engineered to harness the chondrogenic response of stem cells for the repair of damaged cartilage tissue. The signalling processes involved in hydrogel-driven chondrogenesis are also discussed, identifying critical pathways that should be taken into account during hydrogel design.

Runx1 is a central regulator of osteogenesis for bone homeostasis by orchestrating BMP and WNT signaling pathways

Runx1 is highly expressed in osteoblasts, however, its function in osteogenesis is unclear. We generated mesenchymal progenitor-specific (Runx1f/fTwist2-Cre) and osteoblast-specific (Runx1f/fCol1α1-Cre) conditional knockout (Runx1 CKO) mice. The mutant CKO mice with normal skeletal development displayed a severe osteoporosis phenotype at postnatal and adult stages. Runx1 CKO resulted in decreased osteogenesis and increased adipogenesis. RNA-sequencing analysis, Western blot, and qPCR validation of Runx1 CKO samples showed that Runx1 regulates BMP signaling pathway and Wnt/β-catenin signaling pathway. ChIP assay revealed direct binding of Runx1 to the promoter regions of Bmp7, Alk3, and Atf4, and promoter mapping demonstrated that Runx1 upregulates their promoter activity through the binding regions. Bmp7 overexpression rescued Alk3, Runx2, and Atf4 expression in Runx1-deficient BMSCs. Runx2 expression was decreased while Runx1 was not changed in Alk3 deficient osteoblasts. Atf4 overexpression in Runx1-deficient BMSCs did not rescue expression of Runx1, Bmp7, and Alk3. Smad1/5/8 activity was vitally reduced in Runx1 CKO cells, indicating Runx1 positively regulates the Bmp7/Alk3/Smad1/5/8/Runx2/ATF4 signaling pathway. Notably, Runx1 overexpression in Runx2-/- osteoblasts rescued expression of Atf4, OCN, and ALP to compensate Runx2 function. Runx1 CKO mice at various osteoblast differentiation stages reduced Wnt signaling and caused high expression of C/ebpα and Pparγ and largely increased adipogenesis. Co-culture of Runx1-deficient and wild-type cells demonstrated that Runx1 regulates osteoblast-adipocyte lineage commitment both cell-autonomously and non-autonomously. Notably, Runx1 overexpression rescued bone loss in OVX-induced osteoporosis. This study focused on the role of Runx1 in different cell populations with regards to BMP and Wnt signaling pathways and in the interacting network underlying bone homeostasis as well as adipogenesis, and has provided new insight and advancement of knowledge in skeletal development. Collectively, Runx1 maintains adult bone homeostasis from bone loss though up-regulating Bmp7/Alk3/Smad1/5/8/Runx2/ATF4 and WNT/β-Catenin signaling pathways, and targeting Runx1 potentially leads to novel therapeutics for osteoporosis.

Over-expression of MEG3 promotes differentiation of bone marrow mesenchymal stem cells into chondrocytes by regulating miR-129-5p/RUNX1 axis

This study explored the role of MEG3 in the cartilage differentiation of bone marrow mesenchymal stem cells (BMSCs). We investigated the effects of over-expression and knockdown of MEG3 on cell viability, cell differentiation, and the expressions of MEG3, miR-129-5p, COL2, chondrocyte differentiation-related genes (sry-type high-mobility-group box 9 (SOX9), SOX5, Aggrecan, silent information regulator 1 (SIRT1), and Cartilage oligomeric matrix protein (COMP)). The targeting relationship between MEG3 and miR-129-5p and the target gene of miR-129-5p was confirmed through Starbase, TargetScan and luciferase experiments. Finally, a series of rescue experiments were conducted to study the regulatory effects of MEG3 and miR-129-5p. BMSCs were identified as CD29⁺ and CD44⁺ positive, and their differentiation was time-dependent. As BMSCs differentiated, MEG3 expression was up-regulated, but miR-129-5p was down-regulated. Over-expressed MEG3 promoted the viability and differentiation of BMSCs, up-regulated the expressions of COL2 and chondrocyte differentiation-related genes, and inhibited miR-129-5p. Runt-related transcription factor 1 (RUNX1) was negatively regulated as a target gene of miR-129-5p. Results of rescue experiments showed that the inhibitory effect of miR-129-5p mimic on BMSCs could be partially reversed by MEG3. Over-expression of MEG3 regulated the miR-129-5p/RUNX1 axis to promote the differentiation of BMSCs into chondrocytes. This study provides a reliable basis for the application of lncRNA in articular cartilage injury.

Runx1 up-regulates chondrocyte to osteoblast lineage commitment and promotes bone formation by enhancing both chondrogenesis and osteogenesis

One of the fundamental questions in bone biology is where osteoblasts originate and how osteoblast differentiation is regulated. The mechanism underlying which factors regulate chondrocyte to osteoblast lineage commitment remains unknown. Our data showed that Runt-related transcription factor 1 (Runx1) is expressed at different stages of both chondrocyte and osteoblast differentiation. Runx1 chondrocyte-specific knockout (Runx1f/fCol2α1-cre) mice exhibited impaired cartilage formation, decreased bone density, and an osteoporotic phenotype. The expressions of chondrocyte differentiation regulation genes, including Sox9, Ihh, CyclinD1, PTH1R, and hypertrophic chondrocyte marker genes including Col2α1, Runx2, MMP13, Col10α1 in the growth plate were significantly decreased in Runx1f/fCol2α1-cre mice chondrocytes. Importantly, the expression of osteoblast differentiation regulation genes including Osx, Runx2, ATF4, and osteoblast marker genes including osteocalcin (OCN) and osteopontin (OPN) were significantly decreased in the osteoblasts of Runx1f/fCol2α1-cre mice. Notably, our data showed that osteoblast differentiation regulation genes and marker genes are also expressed in chondrocytes and the expressions of these marker genes were significantly decreased in the chondrocytes of Runx1f/fCol2α1-cre mice. Our data showed that chromatin immunoprecipitation (ChIP) and promoter mapping analysis revealed that Runx1 directly binds to the Indian hedgehog homolog (Ihh) promoter to regulate its expression, indicating that Runx1 directly regulates the transcriptional expression of chondrocyte genes. Collectively, we revealed that Runx1 signals chondrocyte to osteoblast lineage commitment and promotes endochondral bone formation through enhancing both chondrogenesis and osteogenesis genes expressions, indicating Runx1 may be a therapeutic target to enhance endochondral bone formation and prevent osteoporosis fractures.

Runt-related transcription factor 1 is required for murine osteoblast differentiation and bone formation

Despite years of research investigating osteoblast differentiation, the mechanisms by which transcription factors regulate osteoblast maturation, bone formation, and bone homeostasis is still unclear. It has been reported that runt-related transcription factor 1 (Runx1) is expressed in osteoblast progenitors, pre-osteoblasts, and mature osteoblasts; yet, surprisingly, the exact function of RUNX1 in osteoblast maturation and bone formation remains unknown. Here, we generated and characterized a pre-osteoblast and differentiating chondrocyte-specific Runx1 conditional knockout mouse model to study RUNX1's function in bone formation. Runx1 ablation in osteoblast precursors and differentiating chondrocytes via osterix-Cre (Osx-Cre) resulted in an osteoporotic phenotype and decreased bone density in the long bones and skulls of Runx1f/fOsx-Cre mice compared with Runx1f/f and Osx-Cre mice. RUNX1 deficiency reduced the expression of SRY-box transcription factor 9 (SOX9), Indian hedgehog signaling molecule (IHH), Patched (PTC), and cyclin D1 in the growth plate, and also reduced the expression of osteocalcin (OCN), OSX, activating transcription factor 4 (ATF4), and RUNX2 in osteoblasts. ChIP assays and promoter activity mapping revealed that RUNX1 directly associates with the Runx2 gene promoter and up-regulates Runx2 expression. Furthermore, the ChIP data also showed that RUNX1 associates with the Ocn promoter. In conclusion, RUNX1 up-regulates the expression of Runx2 and multiple bone-specific genes, and plays an indispensable role in bone formation and homeostasis in both trabecular and cortical bone. We propose that stimulating Runx1 activity may be useful in therapeutic approaches for managing some bone diseases such as osteoporosis.

Network Analysis Identifies Gene Regulatory Network Indicating the Role of RUNX1 in Human Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD) is a multifactorial physiological process which is often associated with lower back pain. Previous studies have identified some molecular markers associated with disc degeneration, which despite their significant contributions, have provided limited insight into the etiology of IDD. In this study, we utilized a network medicine approach to uncover potential molecular mediators of IDD. Our systematic analyses of IDD associated with 284 genes included functional annotation clustering, interaction networks, network cluster analysis and Transcription factors (TFs)-target gene network analysis. The functional enrichment and protein–protein interaction network analysis highlighted the role of inflammatory genes and cytokine/chemokine signaling in IDD. Moreover, sub-network analysis identified significant clusters possessing organized networks of 24 cytokine and chemokine genes, which may be considered as key modulators for IDD. The expression of these genes was validated in independent microarray datasets. In addition, the regulatory network analysis identified the role of multiple transcription factors, with RUNX1 being a master regulator in the pathogenesis of IDD. Our analyses highlighted the role of cytokine genes and interacting pathways in IDD and further improved our understanding of the genetic mechanisms underlying IDD.

hsa_circ_0026827 Promotes Osteoblast Differentiation of Human Dental Pulp Stem Cells Through the Beclin1 and RUNX1 Signaling Pathways by Sponging miR-188-3p

Previous studies have found that circular RNA (circRNA) hsa_circ_0026827 plays a role during osteoblast differentiation, but the mechanism is unclear. The aim of this study was to illuminate the role of hsa_circ_0026827 in human dental pulp stem cells (DPSCs) during osteoblast differentiation. The results show that hsa_circ_0026827 expression significantly increased during osteoblast differentiation, while knockdown of hsa_circ_0026827 suppressed DPSC-derived osteoblast differentiation. microRNA (miRNA) expression profile analysis showed that downregulation of hsa_circ_0026827 promoted miR-188-3p expression. miR-188-3p downregulation restored osteogenic differentiation of DPSCs after hsa_circ_0026827 was silenced. Luciferase reporter assays verified that miR-188-3p was the target of hsa_circ_0026827 and also demonstrated that Beclin1 and RUNX1 were miR-188-3p downstream targets. miR-188-3p overexpression suppressed DPSC osteogenic differentiation by targeting Beclin-1-mediated autophagy and runt-related transcription factor 1 (RUNX1). In vivo studies using a heterotopic bone model also found that hsa_circ_0026827 overexpression plays an important role in promoting heterotopic bone formation. In conclusion, our research indicates that hsa_circ_0026827 promotes osteoblast differentiation of DPSCs via Beclin1 and the RUNX1 signaling pathways by sponging miR-188-3p, which suggests novel therapeutics for osteoporosis treatment.

Injectable double-crosslinked hydrogels with kartogenin-conjugated polyurethane nano-particles and transforming growth factor β3 for in-situ cartilage regeneration

Articular cartilage has a limited ability for self-repair after injury. Implantation of scaffolds functionalized with bioactive molecules that could induce the migration and chondrogenesis of endogenous mesenchymal stem cells (MSCs) provides a convenient alternative for in-situ cartilage regeneration. In this study, we found the synergistic effects of kartogenin (KGN) and transforming growth factor β3 (TGF-β3) on chondrogenesis of MSCs in vitro, indicating that KGN and TGF-β3 are a good match for cartilage regeneration. Furthermore, we confirmed that KGN promoted the chondrogenesis of MSCs through attenuating the degradation of Runx1, which physically interacted with p-Smad3 in nuclei of MSCs. Meanwhile, we designed an injectable double-crosslinked hydrogel with superior mechanical property and longer support for cartilage regeneration by modifying sodium alginate and gelatin. When loaded with KGN conjugated polyurethane nanoparticles (PN-KGN) and TGF-β3, this hydrogel showed biological functions by the release of KGN and TGF-β3, which promoted the MSC migration and cartilage regeneration in one system. In conclusion, the cell-free hydrogel, along with PN-KGN and TGF-β3, provides a promising strategy for cartilage repair by attracting endogenous MSCs and inducing chondrogenesis of recruited cells in a single-step procedure.

Enhancement of chondrogenic differentiation supplemented by a novel small compound for chondrocyte-based tissue engineering

Purpose

Chondrocyte -based tissue engineering has been a promising option for the treatment of cartilage lesions. In previous literature, TD198946 has been shown to promote chondrogenic differentiation which could prove useful in cartilage regeneration therapies. Our study aimed to investigate the effects of TD198946 in generating engineered cartilage using dedifferentiated chondrocyte-seeded collagen scaffolds treated with TD198946.

Methods

Articular chondrocytes were isolated from mini pig knees and expanded in 2-dimensional cell culture and subsequently used in the experiments. 3-D pellets were then cultured for two weeks. Cells were also cultured in a type I collagen scaffolds for four weeks. Specimens were cultured with TD198946, BMP-2, or both in combination. Outcomes were determined by gene expression levels of RUNX1, SOX9, ACAN, COL1A1, COL2A1 and COL10A1, the glycosaminoglycan content, and characteristics of histology and immunohistochemistry. Furthermore, the maturity of the engineered cartilage cultured for two weeks was evaluated through subcutaneous implantation in nude mice for four weeks.

Results

Addition of TD198946 demonstrated the upregulation of gene expression level except for ACAN, type II collagen and glycosaminoglycan synthesis in both pellet and 3D scaffold cultures. TD198946 and BMP-2 combination cultures showed higher chondrogenic differentiation than TD198946 or BMP-2 alone. The engineered cartilage maintained its extracellular matrices for four weeks post implantation. In contrast, engineered cartilage treated with either TD198946 or BMP-2 alone was mostly absorbed.

Conclusions

Our results indicate that TD198946 could improve quality of engineered cartilage by redifferentiation of dedifferentiated chondrocytes pre-implantation and promoting collagen and glycosaminoglycan synthesis.

Mesenchymal stem cell-loaded thermosensitive hydroxypropyl chitin hydrogel combined with a three-dimensional-printed poly(ε-caprolactone) /nano-hydroxyapatite scaffold to repair bone defects via osteogenesis, angiogenesis and immunomodulation

Chitin-derived hydrogels are commonly used in bone regeneration because of their high cell compatibility; however, their poor mechanical properties and little knowledge of the interaction between the materials and host cells have limited their practical application. Methods: To evaluate osteoinductivity and enhance the mechanical properties of a newly synthesized thermosensitive hydroxypropyl chitin hydrogel (HPCH), a mesenchymal stem cell (MSC)-encapsulated HPCH was infused into a three-dimensional-printed poly (ε-caprolactone) (PCL)/ nano-hydroxyapatite (nHA) scaffold to form a hybrid scaffold. The mechanical properties and cell compatibility of the scaffold were tested. The interaction between macrophages and scaffold for angiogenesis and osteogenesis were explored in vitro and in vivo. Results: The hybrid scaffold showed improved mechanical properties and high cell viability. When MSCs were encapsulated in HPCH, osteo-differentiation was promoted properly via endochondral ossification. The co-culture experiments showed that the hybrid scaffold facilitated growth factor secretion from macrophages, thus promoting vascularization and osteoinduction. The Transwell culture proved that MSCs modulated the inflammatory response of HPCH. Additionally, subcutaneous implantation of MSC-encapsulated HPCH confirmed M2 activation. In situ evaluation of calvarial defects confirmed that the repair was optimal in the MSC-loaded HPCH + PCL/nHA group. Conclusions: PCL/nHA + HPCH hybrid scaffolds effectively promoted vascularization and osteoinduction via osteogenesis promotion and immunomodulation, which suggests promising applications for bone regeneration.

Kartogenin enhances the therapeutic effect of bone marrow mesenchymal stem cells derived exosomes in cartilage repair

The effectiveness of mesenchymal stem cells (MSC) in the treatment of cartilage diseases has been demonstrated to be attributed to the paracrine mechanisms, especially the mediation of exosomes. But the exosomes derived from unsynchronized MSCs may be nonhomogeneous and the therapeutic effect varies between samples. Aim: To produce homogeneous and more effective exosomes for the regeneration of cartilage. Materials & methods: In this study we produced specific exosomes from bone marrow MSCs (BMSC) through kartogenin (KGN) preconditioning and investigated their performance in either in vitro or in vivo experiments. Results & conclusion: The exosomes derived from KGN-preconditioned BMSCs (KGN-BMSC-Exos) performed more effectively than the exosomes derived from BMSCs (BMSC-Exos). KGN preconditioning endowed BMSC-Exos with stronger chondral matrix formation and less degradation.

RUNX transcription factors: orchestrators of development

RUNX transcription factors orchestrate many different aspects of biology, including basic cellular and developmental processes, stem cell biology and tumorigenesis. In this Primer, we introduce the molecular hallmarks of the three mammalian RUNX genes, RUNX1, RUNX2 and RUNX3, and discuss the regulation of their activities and their mechanisms of action. We then review their crucial roles in the specification and maintenance of a wide array of tissues during embryonic development and adult homeostasis.

Runx1 contributes to articular cartilage maintenance by enhancement of cartilage matrix production and suppression of hypertrophic differentiation

Osteoarthritis (OA) results from an imbalance of the dynamic equilibrium between the breakdown and repair of joint tissues. Previously, we reported that Runx1 enhanced chondrogenic differentiation through transcriptional induction of COL2A1, and suppressed hypertrophic differentiation. Here, we investigated the involvement of Runx1 in OA development as well as its potential underlying molecular mechanism. When we analysed OA development in Col2a1-Cre;Runx1^fl/fl and Runx1^fl/fl mice by surgically inducing joint instability, Cartilage degradation and osteophyte formation of Col2a1-Cre;Runx1^fl/fl joints was accelerated compared with joints in Runx1^fl/fl animals 8 weeks after surgery. To investigate chondrocyte regulation by Runx1, we analysed interactions with co-factors and downstream molecules. Runx1 enhanced cartilage matrix production in cooperation with Sox5, Sox6, and Sox9, and co-immunoprecipitation assays showed protein–protein binding between Runx1 and each Sox protein. Knockdown of Runx1 increased expression of a hypertrophic marker, Co10a1, in mouse articular cartilage and primary chondrocytes. This expression was accompanied by decreased expression of Bapx1, a potent suppressor of hypertrophic differentiation. Notably, Runx1-induced suppression of hypertrophic differentiation was diminished by siRNA silencing of Bapx1, whereas chondrogenic markers were unaltered. Thus, Runx1 contributes to articular cartilage maintenance by enhancing matrix production in cooperation with Sox proteins, and suppressing hypertrophic differentiation at least partly via Bapx1 induction.

Treatment of Intervertebral Disk Disease by the Administration of mRNA Encoding a Cartilage-Anabolic Transcription Factor

Intervertebral disk (IVD) degeneration is often associated with severity of lower back pain. IVD core is an avascular, highly hydrated tissue composed of type II collagen, glycosaminoglycans, and proteoglycans. The disk degeneration is not only a destruction of IVD structure but also is related to a disorder of the turnover of the disk matrix, leading the jelly-like IVD core to be replaced by fibrous components. Here we present a disease-modifying strategy for IVD degenerative diseases by direct regulation of the cells in the IVD using mRNA medicine, to alter the misbalanced homeostasis during disk degeneration. When mRNA encoding a cartilage-anabolic transcription factor, runt-related transcription factor-1, was administered to a rat model of coccygeal disk degeneration using a polyplex nanomicelle composed of polyethylene glycol-polyamino acid block copolymers and mRNA, the disk height was maintained to a significantly higher extent (≈81%) compared to saline control (69%), with prevention of fibrosis in the disk tissue. In addition, the use of nanomicelles effectively prevented inflammation, which was observed by injection of naked mRNA into the disk. This proof-of-concept study revealed that mRNA medicine has a potential for treating IVD degenerative diseases by introducing a cartilage-anabolic factor into the host cells, proposing a new therapeutic strategy using mRNA medicine.

Identification of Novel Loci Associated With Hip Shape: A Meta-Analysis of Genomewide Association Studies

We aimed to report the first genomewide association study (GWAS) meta-analysis of dual-energy X-ray absorptiometry (DXA)-derived hip shape, which is thought to be related to the risk of both hip osteoarthritis and hip fracture. Ten hip shape modes (HSMs) were derived by statistical shape modeling using SHAPE software, from hip DXA scans in the Avon Longitudinal Study of Parents and Children (ALSPAC; adult females), TwinsUK (mixed sex), Framingham Osteoporosis Study (FOS; mixed), Osteoporotic Fractures in Men study (MrOS), and Study of Osteoporotic Fractures (SOF; females) (total N = 15,934). Associations were adjusted for age, sex, and ancestry. Five genomewide significant (p < 5 × 10-9 , adjusted for 10 independent outcomes) single-nucleotide polymorphisms (SNPs) were associated with HSM1, and three SNPs with HSM2. One SNP, in high linkage disequilibrium with rs2158915 associated with HSM1, was associated with HSM5 at genomewide significance. In a look-up of previous GWASs, three of the identified SNPs were associated with hip osteoarthritis, one with hip fracture, and five with height. Seven SNPs were within 200 kb of genes involved in endochondral bone formation, namely SOX9, PTHrP, RUNX1, NKX3-2, FGFR4, DICER1, and HHIP. The SNP adjacent to DICER1 also showed osteoblast cis-regulatory activity of GSC, in which mutations have previously been reported to cause hip dysplasia. For three of the lead SNPs, SNPs in high LD (r2  > 0.5) were identified, which intersected with open chromatin sites as detected by ATAC-seq performed on embryonic mouse proximal femora. In conclusion, we identified eight SNPs independently associated with hip shape, most of which were associated with height and/or mapped close to endochondral bone formation genes, consistent with a contribution of processes involved in limb growth to hip shape and pathological sequelae. These findings raise the possibility that genetic studies of hip shape might help in understanding potential pathways involved in hip osteoarthritis and hip fracture. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

ACVR1R206H FOP mutation alters mechanosensing and tissue stiffness during heterotopic ossification

An activating bone morphogenetic proteins (BMP) type I receptor ACVR1 (ACVR1^R206H) mutation enhances BMP pathway signaling and causes the rare genetic disorder of heterotopic (extraskeletal) bone formation fibrodysplasia ossificans progressiva. Heterotopic ossification frequently occurs following injury as cells aberrantly differentiate during tissue repair. Biomechanical signals from the tissue microenvironment and cellular responses to these physical cues, such as stiffness and rigidity, are important determinants of cell differentiation and are modulated by BMP signaling. We used an Acvr1^R206H/+ mouse model of injury-induced heterotopic ossification to examine the fibroproliferative tissue preceding heterotopic bone and identified pathologic stiffening at this stage of repair. In response to microenvironment stiffness, in vitro assays showed that Acvr1^R206H/+ cells inappropriately sense their environment, responding to soft substrates with a spread morphology similar to wild-type cells on stiff substrates and to cells undergoing osteoblastogenesis. Increased activation of RhoA and its downstream effectors demonstrated increased mechanosignaling. Nuclear localization of the pro-osteoblastic factor RUNX2 on soft and stiff substrates suggests a predisposition to this cell fate. Our data support that increased BMP signaling in Acvr1^R206H/+ cells alters the tissue microenvironment and results in misinterpretation of the tissue microenvironment through altered sensitivity to mechanical stimuli that lowers the threshold for commitment to chondro/osteogenic lineages.

Runx1 regulates osteogenic differentiation of BMSCs by inhibiting adipogenesis through Wnt/β-catenin pathway

OBJECTIVE

Bone marrow stem cells (BMSCs) can commit to both adipocyte and osteoblast lineages. However, the mechanism underlying how transcription factors regulate this process remains elusive. Our aims were to determine the role of runt-related transcription factor 1 (Runx1) in BMSCs lineage determination and the underlying mechanisms.

STUDY DESIGN

BMSCs from mouse femur bone marrow were harvested and cultured in osteogenic medium. Runx1 was knocked down in BMSCs using lentivirus. Alkaline phosphatase (ALP), Von Kossa and Oil Red O staining were performed on the Runx1-transduced BMSCs and control cells to see the differences of osteogenic and adipogenic differentiation in these groups. Real-time quantitative PCR and Western blot were performed to analyse the expression levels of osteogenic and adipogenic factors regulated by Runx1 at gene and protein levels.

RESULTS

In BMSCs with Runx1 knockdown, the expression levels of osteogenic-related genes decreased significantly while the adipogenic genes C/EBPα, PPARγ and Fabp4 increased by 12-fold, 10-fold, and 30-fold, respectively, compared with the control cells. ALP activity and Von kossa staining were greatly decreased in Runx1-transfected cells while the Oil Red O staining was comparable to that in the control groups. Canonical Wnt signaling was investigated in the Runx1-deficient BMSCs, and a 50% decrease in the expression of active β-catenin in these cells was found. Lef1 and Tcf1, which are regulated by β-catenin were also decreased in Runx1-deficient cells compared with the levels in controls. Moreover, although there was no difference in the expression of Wnt3a among the three groups of cells, the expression of Wnt10b decreased by 80% in Runx1-deficient BMSCs compared with the levels in the other two groups.

CONCLUSIONS

Our results show Runx1 promotes the capacity of osteogenesis in BMSCs while inhibits their adipogenesis through canonical Wnt/β-catenin pathway, which provides new insights into osteoblast development.

Maternal undernutrition during early pregnancy inhibits postnatal growth of the tibia in the female offspring of rats by alteration of chondrogenesis

Epidemiological research has suggested that birth weights are correlated with adult leg lengths. However, the relationship between prenatal undernutrition (UN) and postnatal leg growth remains controversial. We investigated the effects of UN during early pregnancy on postnatal hindlimb growth and determined whether early embryonic malnutrition affects the functions of postnatal chondrocytes in rats. Undernourished Wistar dams were fed 40% of the daily intake of rats in the control groups from gestational days 5.5-11.5, and femurs, tibias, and trunks or spinal columns were morphologically measured at birth and at 16 weeks of age in control and undernourished offspring of both sexes. We evaluated cell proliferation and differentiation of cultured chondrocytes derived from neonatal tibias of female offspring and determined chondrocyte-related gene expression levels in neonatal epiphysis and embryonic limb buds. Tibial lengths of undernourished female, but not male, offspring were longer at birth and shorter at 16 weeks of age (p < .05) compared with those of control rats. In chondrocyte culture studies, stimulating effects of IGF-1 on cell proliferation (p < .01) were significantly decreased and levels of type II collagen were lower in female undernourished offspring (p < .05). These phenomena were accompanied by decreased expression levels of Col2a1 and Igf1r and increased expression levels of Fgfr3 (p < .05), which might be attributable to the decreased expression of specificity protein 1 (p < .05), a key transactivator of Col2a1 and Igf1r. In conclusion, UN stress during early pregnancy reduces postnatal tibial growth in female offspring by altering the function of chondrocytes, likely reflecting altered expression of gene transactivators.

Anti-inflammatory and anti-osteoarthritis effects of tectorigenin

Osteoarthritis (OA) is a common and dynamic disease of the joints, including the articular cartilage, underlying bones and synovium. In particular, OA is considered as the degeneration of the cartilage. Tectorigenin (Tec) is known to affect many biological processes; however, its effects on articular chondrocytes remain unclear. This study aimed to assess the effects of Tec on articular cartilage. In vitro, Tec inhibited the expression levels of type X collagen, cyclooxigenase-2, matrix metalloproteinase (MMP)-3 and MMP-13, but enhanced the expression of Runx1, type II collagen and aggrecan in the presence of IL-1β. Meanwhile, Tec inhibited apoptosis through the Bax/Bcl-2/caspase-3 pathway, upregulating p-Bad, downregulating the Bax/Bcl-2 ratio, and activating caspase-3 compared with IL-1β treatment only. Moreover, this process was partially regulated by NF-κB P65. In vivo, the chondroprotective effects of Tec were assessed by establishing a model of surgically induced OA. Tec-treated joints exhibited fewer osteoarthritic changes than saline-treated joints. Meanwhile, 1.5 μg/kg Tec treatment produced a greater protective effect than 0.75 μg/kg Tec. The Osteoarthritis Research Society International (OARSI) scoring system, employed to assess histopathological grading of the models, as well immunohistochemistry for Aggrecan Neoepitope and MMP-3, further confirmed the results. In conclusion, this study showed that Tec plays a chondroprotective role in the OA process by preventing articular cartilage degeneration and chondrocyte apoptosis via the NF-κB P65 pathway.

Summary: Tectorigenin exerts anti-inflammatory and anti-osteoarthritis effects by inhibiting apoptosis in chondrocytes via the NF-κB P65 pathway.

RUNX1 Plays an Important Role in Mediating BMP9-Induced Osteogenic Differentiation of Mesenchymal Stem Cells Line C3H10T1/2, Murine Multi-Lineage Cells Lines C2C12 and MEFs

As one of the least studied bone morphogenetic proteins (BMPs), BMP9 is highly capable of promoting osteogenic differentiation. However, the underlying mechanism involved remains largely unknown. Recent studies have demonstrated that RUNX1 (runt-related transcription factor 1) is essential in osteoblast/chondrocyte maturation. In this study, we investigated the function of RUNX1 in BMP9-induced osteogenic of murine mesenchymal stem cell line (C3H10T1/2) and murine multi-lineage cell lines (C2C12 and MEFs). Our data showed that BMP9 promoted the endogenous expression of RUNX1 in C3H10T1/2, C2C12 and MEFs. Moreover, RUNX1 was probably a direct target of BMP9/Smad signaling. BMP9-induced osteogenic differentiation was enhanced by overexpression of RUNX1, whereas inhibited by knockdown RUNX1 in C3H10T1/2, C2C12 and MEFs. Further mechanism studies demonstrated that RUNX1 might affect BMP9-induced phosphorylation of Smad1/5/8, but not the phosphorylation of p38 and ERK1/2.Our results suggest that RUNX1 may be an essential modulator in BMP9- induced osteogenic differentiation of MSCs (Mesenchymal stem cells).

Regeneration of fat cells from myofibroblasts during wound healing

Although regeneration through the reprogramming of one cell lineage to another occurs in fish and amphibians, it has not been observed in mammals. We discovered in the mouse that during wound healing, adipocytes regenerate from myofibroblasts, a cell type thought to be differentiated and nonadipogenic. Myofibroblast reprogramming required neogenic hair follicles, which triggered bone morphogenetic protein (BMP) signaling and then activation of adipocyte transcription factors expressed during development. Overexpression of the BMP antagonist Noggin in hair follicles or deletion of the BMP receptor in myofibroblasts prevented adipocyte formation. Adipocytes formed from human keloid fibroblasts either when treated with BMP or when placed with human hair follicles in vitro. Thus, we identify the myofibroblast as a plastic cell type that may be manipulated to treat scars in humans.

IGF1 regulates RUNX1 expression via IRS1/2: Implications for antler chondrocyte differentiation

Although IGF1 is important for the proliferation and differentiation of chondrocytes, its underlying molecular mechanism is still unknown. Here we addressed the physiologic function of IGF1 in antler cartilage and explored the interplay of IGF1, IRS1/2 and RUNX1 in chondrocyte differentiation. The results showed that IGF1 was highly expressed in antler chondrocytes. Exogenous rIGF1 could increase the proliferation of chondrocytes and cell proportion in the S phase, whereas IGF1R inhibitor PQ401 abrogated the induction by rIGF1. Simultaneously, IGF1 could stimulate the expression of IHH which was a well-known marker for prehypertrophic chondrocytes. Further analysis evidenced that IGF1 regulated the expression of IRS1/2 whose silencing resulted in a rise of IHH mRNA levels, but the regulation was impeded by PQ401. Knockdown of IRS1 or IRS2 with specific siRNA could greatly enhance rIGF1-induced chondrocyte differentiation and reduce the expression of RUNX1. Extraneous rRUNX1 might rescue the effects of IRS1 or IRS2 siRNA on the differentiation. In antler chondrocytes, IGF1 played a role in modulating the expression of RUNX1 through IGF1R. Moreover, attenuation of RUNX1 expression advanced the differentiation elicited by rIGF1, while administration of rRUNX1 to chondrocytes treated with IGF1 siRNA or PQ401 reduced their differentiation. Additionally, siRNA-mediated downregulation of IRS1 or IRS2 in the chondrocytes impaired the interaction between IGF1 and RUNX1. Collectively, IGF1 could promote the proliferation and differentiation of antler chondrocytes. Furthermore, IRS1/2 might act downstream of IGF1 to regulate chondrocyte differentiation through targeting RUNX1.

Roles of RUNX in Hypoxia-Induced Responses and Angiogenesis

During the past two decades, Runt domain transcription factors (RUNX1, 2, and 3) have been investigated in regard to their function, structural elements, genetic variants, and roles in normal development and pathological conditions. The Runt family proteins are evolutionarily conserved from Drosophila to mammals, emphasizing their physiological importance. A hypoxic microenvironment caused by insufficient blood supply is frequently observed in developing organs, growing tumors, and tissues that become ischemic due to impairment or blockage of blood vessels. During embryonic development and tumor growth, hypoxia triggers a stress response that overcomes low-oxygen conditions by increasing erythropoiesis and angiogenesis and triggering metabolic changes. This review briefly introduces hypoxic conditions and cellular responses, as well as angiogenesis and its related signaling pathways, and then describes our current knowledge on the functions and molecular mechanisms of Runx family proteins in hypoxic responses, especially in angiogenesis.