Nuclear factor of activated T cells 1 and 2 are required for vertebral homeostasis

Electroactive membranes enhance in-situ alveolar ridge preservation via spatiotemporal electrical modulation of cell motility

Post-extraction alveolar bone resorption invariably compromises implant placement and aesthetic restoration outcomes. Current non-resorbable membranes exhibit limited efficacy in alveolar ridge preservation (ARP) due to insufficient cell recruitment and osteoinductive capabilities. Herein, we introduce a multifunctional electroactive membrane (PPy-BTO/P(VDF-TrFE), PB/PT) designed to spatiotemporally regulate cell migration and osteogenesis, harmonizing with the socket healing process. Initially, the membrane's endogenous-level surface potential recruits stem cells from the socket. Subsequently, adherent cell-migration-triggered forces generate on-demand piezopotential, stimulating intracellular calcium ion fluctuations and activating the Ca2+/calcineurin/NFAT1 signaling pathway via Cav3.2 channels. This enhances cell motility and osteogenic differentiation predominantly in the coronal socket region, counteracting the natural healing trajectory. The membrane's self-powered energy supply, proportional to cell migration velocity and manifested as nanoparticle deformation, mitigates ridge shrinkage, both independently and in conjunction with bone grafts. This energy-autonomous membrane, based on the spatiotemporal modulation of cell motility, presents a novel approach for in-situ ARP treatment and the development of 4D bionic scaffolds.

Coupling of Intracellular Calcium Homeostasis and Formation and Secretion of Matrix Vesicles: Their Role in the Mechanism of Biomineralization

The human bone is a dynamic, highly vascularized tissue composed of 60-70% minerals, which include mainly calcium phosphate (CaP) in the form of hydroxyapatite (HA) crystals, 30% organic matrix composed of type I collagen fibers, and less than 5% water and lipids. The crystals are formed inside the matrix vesicles (MVs) and are then released in the organic collagen-based fibrous matrix. Extracellular matrix (ECM) formation and mineralization processes, named osteogenesis, are associated with human mesenchymal stem cells (hMSCs) undergoing differentiation into osteoblasts (osteoblastogenesis). Osteogenesis is regulated by multiple intracellular signaling and genetic pathways and by environmental factors. Calcium flow is finely regulated and plays a key role in both osteoblastogenesis and osteogenesis. The formation and accumulation of CaP, the biogenesis of MVs, their secretion, and the deposition of HA crystals to fill the organic bone matrix are the fundamental events in the biomineralization process. In this paper, I will describe and discuss the recent findings and hypothesis on the molecular mechanism regulating this process.

Janus Membrane with Intrafibrillarly Strontium-Apatite-Mineralized Collagen for Guided Bone Regeneration

Commercial collagen membranes face difficulty in guided bone regeneration (GBR) due to the absence of hierarchical structural design, effective interface management, and diverse bioactivity. Herein, a Janus membrane called SrJM is developed that consists of a porous collagen face to enhance osteogenic function and a dense face to maintain barrier function. Specifically, biomimetic intrafibrillar mineralization of collagen with strontium apatite is realized by liquid precursors of amorphous strontium phosphate. Polycaprolactone methacryloyl is further integrated on one side of the collagen as a dense face, which endows SrJM with mechanical support and a prolonged lifespan. In vitro experiments demonstrate that the dense face of SrJM acts as a strong barrier against fibroblasts, while the porous face significantly promotes cell adhesion and osteogenic differentiation through activation of calcium-sensitive receptor/integrin/Wnt signaling pathways. Meanwhile, SrJM effectively enhances osteogenesis and angiogenesis by recruiting stem cells and modulating osteoimmune response, thus creating an ideal microenvironment for bone regeneration. In vivo studies verify that the bone defect region guided by SrJM is completely repaired by newly formed vascularized bone. Overall, the outstanding performance of SrJM supports its ongoing development as a multifunctional GBR membrane, and this study provides a versatile strategy of fabricating collagen-based biomaterials for hard tissue regeneration.

The circular RNA circHelz enhances cardiac fibrosis by facilitating the nuclear translocation of YAP1

Cardiac fibrosis is a common pathological change in the development of heart disease. Circular RNA (circRNA) has been shown to be related to the occurrence and development of various cardiovascular diseases. This study aimed to evaluate the effects and potential mechanisms of circHelz in cardiac fibrosis. Knockdown of circHelz alleviated cardiac fibrosis and myocardial fibroblast activation induced by myocardial infarction (MI) or angiotensin II (AngII) in vivo and transforming growth factor-β (TGF-β) in vitro. Overexpression of circHelz exacerbated cell proliferation and differentiation. Mechanistically, nuclear factor of activated T cells, cytoplasmic 2 (NFATc2) was found to act as a transcriptional activator to upregulate the expression of circHelz. The increased circHelz was demonstrated to bind to Yes-associated protein (YAP) and facilitate its localization in the nucleus to promote cell proliferation and growth. Moreover, silencing YAP1 reversed the detrimental effects caused by circHelz in vitro, as indicated by the observed decreases in cell viability, fibrotic marker expression levels, proliferation and migration. Collectively, the protective effect of circHelz knockdown against cardiac fibrosis injury is accomplished by inhibiting the nuclear translocation of YAP1. Thus, circHelz may be a novel target for the prevention and treatment of cardiovascular disease.

Role of nuclear factor of activated T cells in chondrogenesis osteogenesis and osteochondroma formation

PURPOSE

Nuclear factor of activated T cells (NFATc) are transcription factors that play a function in the immune response and in osteoclast differentiation. In the present work, we define the function of NFATc2 in chondrogenic and osteogenic cells.

METHODS

Nfatc2^loxP/loxP and Nfatc1^loxP/loxP;Nfatc2^loxP/loxP conditional mice were crossed with Prx1-Cre transgenics to inactivate Nfatc2 singly and with Nfatc1. Femurs and vertebrae were examined by microcomputed tomography (µCT) X-Ray images and histology and analyzed for the presence of osteochondromas.

RESULTS

µCT demonstrated that Prx1-Cre;Nfatc2^∆/∆ female mice had transient osteopenia and male mice did not have a cancellous or a cortical bone phenotype when compared to control mice. In contrast, the dual inactivation of Nfatc1 and Nfatc2 in Prx1-expressing cells resulted in cancellous osteopenia and small bones at 1 month of age in both sexes. Nfatc1;Nfatc2 deleted mice exhibited a ~ 50% decrease in bone volume and connectivity. Total bone area, periosteal and endocortical bone perimeters and femoral length were reduced indicating smaller bones. As the mice matured, the shortening of the femoral length persisted, but the osteopenic phenotype resolved and cancellous femoral bone of 4-month-old Nfatc1;Nfatc2 deleted mice was not different from controls although male mice had vertebral osteopenia. In addition, Nfatc1;Nfatc2 deleted mice displayed distortion of the distal metaphysis and, as they matured, the articular presence of mineralized tumors with the appearance of osteochondromas.

CONCLUSION

Our studies reveal that NFATc1 and NFATc2 are necessary for optimal bone homeostasis and the suppression of osteochondroma formation.

Dynamic transcriptome analysis of NFAT family in guided bone regeneration with occlusive periosteum in swine model

OBJECTIVE

To investigate the dynamic expression of NFAT family of periosteum in guided bone regeneration process.

MATERIAL AND METHODS

The swine ribs on one side were used as the trauma group and the contralateral side as the control group. After rib segment was removed, periosteum was sutured to form a closed cavity mimicking guided bone regeneration. The periosteum and regenerated bone tissue were collected at nine time points for gene sequencing and hematoxylin-eosin staining. The expression data of each member were extracted for analysis. Expression correlations among various members were analyzed.

RESULTS

Staining showed the guided bone regeneration was almost completed 1 month after the operation with later stage for bone remodeling. The expression levels of each member in both groups changed greatly, especially within postoperative 1.5 months. The expression of NFATc1 and NFATC2IP in trauma group was significantly correlated with those of control group. The foldchange of each member also had large fluctuations especially within 1.5 months. In the trauma group, NFATc2 and NFATc4 were significantly upregulated, and there was a significant aggregation correlation of NFAT family expression between the various time points within one month, similar to the "pattern-block" phenomenon.

CONCLUSION

This study revealed the dynamic expression of NFAT family in guided bone regeneration, and provided a reference for the specific mechanism. The first 1.5 months is a critical period and should be paid attention to. The significant high-expression of NFATc2 and NFATc4 may role importantly in this process, which needs further research to verify it.

[Metformin and lipopolysaccharide regulate transcription of NFATc2 gene via the transcription factor RUNX2]

OBJECTIVE

To construct a luciferase reporter gene vector carrying human nuclear factor of activated T cells 2 (NFATc2) gene promoter and examine the effects of metformin and lipopolysaccharide (LPS) on the transcriptional activity of NFATc2 gene.

METHODS

The promoter sequence of human NFATc2 gene was acquired from UCSC website for PCR amplification. NFATc2 promoter fragment was inserted into pGL3-basic plasmid double cleaved with Kpn Ⅰ and Hind Ⅲ. The resultant recombinant plasmid pGL3-NFATC2-promoter was co-transfected with the internal reference plasmid pRL-TK in 293F cells, and luciferase activity in the cells was detected. Reporter gene vectors of human NFATc2 gene promoter with different fragment lengths were also constructed and assayed for luciferase activity. The changes in transcription activity of NFATc2 gene were assessed after treatment with different concentrations of metformin and LPS for 24 h. We also examined the effect of mutation in RUNX2-binding site in NFATC2 gene promoter on the regulatory effects of metformin and LPS on NFATc2 transcription.

RESULTS

We successfully constructed pGL3-NFATc2-promoter plasmids carrying different lengths (2170 bp, 2077 bp, 1802 bp, 1651 bp, 1083 bp, 323 bp) of NFATc2 promoter sequences as verified by enzymatic digestion and sequencing. Transfection of 293F cells with the plasmid carrying a 1651 bp NFATc2 promoter (pGL3-1651 bp) resulted in the highest transcriptional activity of NFATc2 gene, and the luciferase activity was approximately 3.3 times that of pGL3-2170 bp (1.843 ± 0.146 vs 0.547 ± 0.085). Moderate (5 mmol/L) and high (10 mmol/L) concentrations of metformin significantly upregulated the transcriptional activity of pGL3-1651 bp by up to 2.5 and 3 folds, respectively. LPS at different doses also upregulated the transcriptional activity of pGL3-1651 bp by at least 1.6 folds. The mutation in the RUNX2 binding site on pGL3-1651 bp obviously reduced metformin- and LPS-induced enhancement of pGL3-1651bp transcription by 1.7 and 2 folds, respectively.

CONCLUSION

pGL3-NFATc2-promoter can be transcribed and activated in 293F cells, and LPS and metformin can activate the transcription of pGL3- NFATc2-promoter in a RUNX2-dependent manner.

The role of Ca2+ /Calcineurin/NFAT signalling pathway in osteoblastogenesis

The bone remodelling process is closely related to bone health. Osteoblasts and osteoclasts participate in the bone remodelling process under the regulation of various factors inside and outside. Excessive activation of osteoclasts or lack of function of osteoblasts will cause occurrence and development of multiple bone‐related diseases. Ca²⁺/Calcineurin/NFAT signalling pathway regulates the growth and development of many types of cells, such as cardiomyocyte differentiation, angiogenesis, chondrogenesis, myogenesis, bone development and regeneration, etc. Some evidences indicate that this signalling pathway plays an extremely important role in bone formation and bone pathophysiologic changes. This review discusses the role of Ca²⁺/Calcineurin/NFAT signalling pathway in the process of osteogenic differentiation, as well as the influence of regulating each component in this signalling pathway on the differentiation and function of osteoblasts, whereby the relationship between Ca²⁺/Calcineurin/NFAT signalling pathway and osteoblastogenesis could be deeper understood.

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

With increasing life expectations, more and more patients suffer from fractures either induced by intensive sports or other bone-related diseases. The balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption is the basis for maintaining bone health. Osterix (Osx) has long been known to be an essential transcription factor for the osteoblast differentiation and bone mineralization. Emerging evidence suggests that Osx not only plays an important role in intramembranous bone formation, but also affects endochondral ossification by participating in the terminal cartilage differentiation. Given its essentiality in skeletal development and bone formation, Osx has become a new research hotspot in recent years. In this review, we focus on the progress of Osx's function and its regulation in osteoblast differentiation and bone mass. And the potential role of Osx in developing new therapeutic strategies for osteolytic diseases was discussed.