PIASxbeta is a key regulator of osterix transcriptional activity and matrix mineralization in osteoblasts

Designer Micro-/Nanocrumpled MXene Multilayer Coatings Accelerate Osteogenesis and Regulate Macrophage Polarization

Effective tissue regeneration and immune responses are essential for the success of biomaterial implantation. Although the interaction between synthetic materials and biological systems is well-recognized, the role of surface topographical cues in regulating the local osteoimmune microenvironment─specifically, their impact on host tissue and immune cells, and their dynamic interactions─remains underexplored. This study addresses this gap by investigating the impact of surface topography on osteogenesis and immunomodulation. We fabricated MXene/hydroxyapatite (HAP)-coated surfaces with controlled 2.5D nano-, submicro-, and microscale topographical patterns using our custom bottom-up patterning method. These engineered surfaces were employed to assess the behavior of osteoblast precursor cells and macrophage polarization. Our results demonstrate that MXene/HAP-coated surfaces with microscale crumpled topography significantly influence osteogenic activity and macrophage polarization: these surfaces notably enhanced osteoblast precursor cell spreading, proliferation, and differentiation and facilitated a shift in macrophages toward an anti-inflammatory, prohealing M2 phenotype. The observed cell responses indicate that the physical cues from the crumpled topographies, combined with the chemical cues from the MXene/HAP coatings, synergistically create a favorable osteoimmune microenvironment. This study presents the first evidence of employing MXene/HAP-multilayer coated surfaces with finely crumpled topography to concurrently facilitate osteogenesis and immunomodulation for improved implant-to-tissue integration. The tunable topographic patterns of these coatings coupled with a facile and scalable fabrication process make them widely applicable for various biomedical purposes. Our results highlight the potential of these multilayer coatings with controlled topography to improve the in vivo performance and fate of implants by modulating the host response at the material interface.

SUMOylation in Skeletal Development, Homeostasis, and Disease

The modification of proteins by small ubiquitin-related modifier (SUMO) molecules, SUMOylation, is a key post-translational modification involved in a variety of biological processes, such as chromosome organization, DNA replication and repair, transcription, nuclear transport, and cell signaling transduction. In recent years, emerging evidence has shown that SUMOylation regulates the development and homeostasis of the skeletal system, with its dysregulation causing skeletal diseases, suggesting that SUMOylation pathways may serve as a promising therapeutic target. In this review, we summarize the current understanding of the molecular mechanisms by which SUMOylation pathways regulate skeletal cells in physiological and disease contexts.

Genetic and serum markers in adult degenerative scoliosis: a literature review

STUDY DESIGN

Literature review.

OBJECTIVE

Adult degenerative scoliosis (ADS) is becoming a more prevalent diagnosis with an increasing elderly population. Our objective is to provide a literature review of genetic and serum markers in ADS.

METHODS

A literature review was conducted in the various databases from their inception to July 2020. Studies that reviewed any genetic or serum markers of ADS whether in detection or progression were selected. Studies that reviewed congenital scoliosis or adolescent idiopathic scoliosis (AIS) were excluded.

RESULTS

A total of 1447 titles were identified of which 14 were included in the final review. Two papers reported on serum markers pertaining to serum cartilage metabolites and pentosidine. Twelve studies reported on genetic markers including gene polymorphisms in estrogen receptors, parathyroid hormone receptors, interleukin 6, cyclooxygenase-2 (COX-2), COL2A1, GPRIN1, TRAIL, GRIN receptor, RIMS, LBX1 as well as copy number variations.

CONCLUSIONS

Serum markers of osteoarthritis and sarcopenia have been found to be significantly elevated in ADS patients as well. Numerous polymorphisms have been found in a variety of genes playing key roles in bone formation and regulation. Further research is needed in validating previous studies as well as identifying other biomarkers for patients at risk for developing ADS.

Micro- and Nanohemispherical 3D Imprints Modulate the Osteogenic Differentiation and Mineralization Tendency of Bone Cells

Surface topography has been reported to play a key role in modulating cell behaviors, yet the mechanism through which it modulates these behaviors is not fully understood, especially in the case of three-dimensional (3D) topographies. In this study, a series of novel hemispherical 3D imprints ranging from the nanoscale to the microscale were prepared on titanium (Ti) surfaces using a customized interfacial lithography method. Mouse embryo osteoblast precursor cells (MC3T3-E1) were selected to investigate the solitary effect of specific hemispherical 3D imprints on cellular behaviors. The results indicated that varied hemispherical 3D imprints can affect the formation of filopodia and the arrangement of the cytoskeleton in different ways. Specifically, they can alter the spreading morphologies of cells and lead to deformation of the nucleus, which eventually affects cell proliferation and osteogenic differentiation. Cells cultured on different hemispherical 3D imprints exhibited promoted proliferation and osteogenic differentiation to different degrees; for example, cells cultured on 90 and 500 nm hemispherical imprints formed abundant filopodia and exhibited the highest alkaline phosphatase activity and osteogenic gene expression, respectively. Four-week tibia implantation also confirmed that 90 nm hemispherical imprints improved the osteogenic ability in vivo compared with an unpatterned Ti substrate. In addition to promoted proliferation, colonization of more cells on the surface of implants and induction of rapid osteogenic differentiation can occur. Our work provides a rational way to balance cell proliferation and differentiation, which can accelerate bone integration of an implant and host tissue.

SIRT7 has a critical role in bone formation by regulating lysine acylation of SP7/Osterix

SP7/Osterix (OSX) is a master regulatory transcription factor that activates a variety of genes during differentiation of osteoblasts. However, the influence of post-translational modifications on the regulation of its transactivation activity is largely unknown. Here, we report that sirtuins, which are NAD(+)-dependent deacylases, regulate lysine deacylation-mediated transactivation of OSX. Germline Sirt7 knockout mice develop severe osteopenia characterized by decreased bone formation and an increase of osteoclasts. Similarly, osteoblast-specific Sirt7 knockout mice showed attenuated bone formation. Interaction of SIRT7 with OSX leads to the activation of transactivation by OSX without altering its protein expression. Deacylation of lysine (K) 368 in the C-terminal region of OSX by SIRT7 promote its N-terminal transactivation activity. In addition, SIRT7-mediated deacylation of K368 also facilitates depropionylation of OSX by SIRT1, thereby increasing OSX transactivation activity. In conclusion, our findings suggest that SIRT7 has a critical role in bone formation by regulating acylation of OSX.

SP7/Osterix is a transcription factor involved in osteoblast differentiation. Here, the authors show that Sirtuin 7 activates Osterix posttranslationally by regulating its lysine acylation, and that mice lacking Sirtuin 7 in osteoblasts show reduced bone formation.

Ginkgolic acid, a sumoylation inhibitor, promotes adipocyte commitment but suppresses adipocyte terminal differentiation of mouse bone marrow stromal cells

Sumoylation is a post-translational modification process having an important influence in mesenchymal stem cell (MSC) differentiation. Thus, sumoylation-modulating chemicals might be used to control MSC differentiation for skeletal tissue engineering. In this work, we studied how the differentiation of mouse bone marrow stromal cells (mBMSCs) is affected by ginkgolic acid (GA), a potent sumoylation inhibitor also reported to inhibit histone acetylation transferase (HAT). Our results show that GA promoted the differentiation of mBMSCs into adipocytes when cultured in osteogenic medium. Moreover, mBMSCs pre-treated with GA showed enhanced pre-adipogenic gene expression and were more efficiently differentiated into adipocytes when subsequently cultured in the adipogenic medium. However, when GA was added at a later stage of adipogenesis, adipocyte maturation was markedly inhibited, with a dramatic down-regulation of multiple lipogenesis genes. Moreover, we found that the effects of garcinol, a HAT inhibitor, differed from those of GA in regulating adipocyte commitment and adipocyte maturation of mBMSCs, implying that the GA function in adipogenesis is likely through its activity as a sumoylation inhibitor, not as a HAT inhibitor. Overall, our studies revealed an unprecedented role of GA in MSC differentiation and provide new mechanistic insights into the use of GA in clinical applications.

Dihydrotestosterone, a robust promoter of osteoblastic proliferation and differentiation: understanding of time-mannered and dose-dependent control of bone forming cells

Objective(s):

The present study was aimed to evaluate the time-mannered and dose-dependent effects of 5α-dihydrotestosterone (5α-DHT) on the proliferation and differentiation of bone forming cells using MC3T3-E1 cells.

Materials and Methods:

Cell proliferation was analyzed using MTS and phase contrast microscopic assays. Osteogenic differentiation was assessed through a series of in vitro experiments including crystal violet staining, alkaline phosphatase (ALP) activity, and Van Gieson (VG) staining. Taken together, the efficiency of bone mineralization was examined by using alizarin red s (ARS) staining, Von Kossa staining, scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analysis.

Results:

The resulting data revealed that 5α-DHT exhibits promising potential particularly at a dose of 0.1 ng/ml, in promoting the growth of MC3T3-E1 cells compared to the control group (CN). Moreover, a significantly higher ALP activity was evident in the experimental group treated with 5α-DHT compared to the CN group at various time intervals. MC3T3-E1 cells treated with 5α-DHT also expressed a remarkably higher collagen deposition and mineralization (calcium and phosphate contents) compared to the CN group at various time intervals.

Conclusion:

Conclusively, we suggest that 5α-DHT exhibits outstanding potential of promoting proliferation and differentiation in osteoblasts which could be the in vitro basis for the efficacy of 5α-DHT in the treatment of androgen-deficient male osteoporosis.

Development of an efficient screening system to identify novel bone metabolism-related genes using the exchangeable gene trap mutagenesis mouse models

Despite numerous genetic studies on bone metabolism, understanding of the specific mechanisms is lacking. We developed an efficient screening system to identify novel genes involved in bone metabolism using mutant mouse strains registered with the Exchangeable Gene Trap Clones (EGTC) database. From 1278 trap clones in the EGTC database, 52 candidate lines were selected in the first screening, determined based on "EST profile", "X-gal", "Related article", and "Novel gene". For the second screening, bone morphometric analysis, biomechanical strength analysis, bone X-gal staining, etc. were performed on candidate lines. Forty-two male trap lines (80.8%) showed abnormalities with either bone morphometric analysis or biomechanical strength analysis. In the screening process, X-gal staining was significantly efficient (P = 0.0057). As examples, Lbr and Nedd4 trap lines selected using the screening system showed significant bone decrease and fragility, suggesting a relationship with osteoblast differentiation. This screening system using EGTC mouse lines is extremely efficient for identifying novel genes involved in bone metabolism. The gene trap lines identified as abnormal using this screening approach are highly likely to trap important genes for bone metabolism. These selected trap mice will be valuable for use as novel bio-resources in bone research.

Eurycoma longifolia as a potential alternative to testosterone for the treatment of osteoporosis: Exploring time-mannered proliferative, differentiative and morphogenic modulation in osteoblasts

ETHNOPHARMACOLOGICAL RELEVANCE

Eurycoma longifolia (EL) has been well-studied traditionally as a chief ingredient of many polyherbal formulations for the management of male osteoporosis. It has also been well-recognised to protect against bone calcium loss in orchidectomised rats.

AIM OF THE STUDY

To evaluate the effects of EL on the time-mannered sequential proliferative, differentiative, and morphogenic modulation in osteoblasts compared with testosterone.

MATERIALS AND METHODS

Cell proliferation was analysed using MTS assay and phase contrast microscopy. Osteogenic differentiation of MC3T3-E1 cells was assessed through a series of characteristic assays which include crystal violet staining, alkaline phosphatase (ALP) activity and Van Gieson staining. Taken together, the bone mineralization of extra cellular matrix (ECM) was estimated using alizarin red s (ARS) staining, von kossa staining, scanning electron microscopic (SEM) and energy dispersive x-ray (EDX) analysis.

RESULTS

The cell proliferation data clearly revealed the efficiency of EL particularly at a dose of 25µg/mL, in improving the growth of MC3T3-E1 cells compared with the untreated cells. Data also showed the prominence of EL in significantly promoting ALP activity throughout the entire duration of treatment compared with the testosterone-treated cells. The osteogenic differentiation potential of EL was further explored by analysing mineralization data which revealed that the calcified nodule formation (calcium deposition) and phosphate deposition was more pronounced in cells treated with 25µg/mL concentration of EL at various time points compared with the untreated and testosterone treated cells. The scanning electron microscopic (SEM) analysis also revealed highest globular masses of mineral deposits (identified as white colour crystals) in the ECM of cultured cells treated with 25µg/mL concentration of EL.

CONCLUSION

Compared to testosterone, greater potential of EL in promoting the proliferation and osteogenic differentiation of MC3T3-E1 cells provides an in vitro basis for the prevention of male osteoporosis. Thus, we anticipate that EL can be considered as an alternative approach to testosterone replacement therapy (TRT) for the treatment of male osteoporosis.

The differently expressed proteins in MSCs of degenerative scoliosis

PURPOSE

Degenerative scoliosis (DS) is an important degenerative lumbar disease causing spinal dysfunction. The true reason or pathogenesis of DS is still unknown. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are the stem/progenitor cells of the osteoblasts. The diseases associated with osteogenesis could be caused by abnormality of the MSCs. The purpose of this study was to find the differential proteins expressed in MSCs of patients with DS.

METHODS

We collected and cultured the MSCs from 12 DS patients and 12 age- and gender-matched patients with lumbar spinal stenosis. Then the MSC samples were analyzed with 2D-DIGE and MALDI-TOF-MS to find the differential proteins which were further validated by Western blot.

RESULTS

We found 115 spots that were differently expressed in the MSC of DS patients with 2D-DIGE, and 44 proteins were identified from samples of DS and control using MALDI-TOF-MS. Of these proteins, PIAS2, NDUFA2, and TRIM 68, which were up-regulated in DS more than 4 times were validated by Western blot.

CONCLUSIONS

The information obtained with this proteomics analysis will be useful in understanding the pathophysiology of DS. Further investigations on the functioning pathway, the specificity and the mechanism of these proteins will be carried out.

Effects of combined mechanical stimulation on the proliferation and differentiation of pre-osteoblasts

We observed how combined mechanical stimuli affect the proliferation and differentiation of pre-osteoblasts. For this research, a bioreactor system was developed that can simultaneously stimulate cells with cyclic strain and ultrasound, each of which is known to effectively stimulate bone tissue regeneration. MC3T3-E1 pre-osteoblasts were chosen for bone tissue engineering due to their osteoblast-like characteristics. 3-D scaffolds were fabricated with polycaprolactone and poly-L-lactic acid using the salt leaching method. The cells were stimulated by the bioreactor with cyclic strain and ultrasound. The bioreactor was set at a frequency of 1.0 Hz and 10 % strain for cyclic strain and 1.0 MHz and 30 mW/cm(2) for ultrasound. Three experimental groups (ultrasound, cyclic strain, and combined stimulation) and a control group were examined. Each group was stimulated for 20 min/day. Mechanical stimuli did not affect MC3T3-E1 cell proliferation significantly up to 10 days when measured with the cell counting kit-8. However, gene expression analysis of collagen type-I, osteocalcin, RUNX2, and osterix revealed that the combined mechanical stimulation accelerated the matrix maturation of MC3T3-E1 cells. These results indicate that the combined mechanical stimulation can enhance the differentiation of pre-osteoblasts more efficiently than simple stimuli, in spite of no effect on cell proliferation.

Essential role of nuclear factor of activated T cells (NFAT)-mediated Wnt signaling in osteoblast differentiation induced by strontium ranelate

The antiosteoporotic treatment strontium ranelate (SrRan) was shown to increase bone mass and strength by dissociating bone resorption and bone formation. To identify the molecular mechanisms of action of SrRan on osteoblasts, we investigated its effects on calcineurin-NFAT (nuclear factor of activated T cells) signaling, an important calcium sensitive pathway controlling bone formation. Using murine MC3T3-E1 and primary murine osteoblasts, we demonstrate that SrRan induces NFATc1 nuclear translocation, as shown by immunocytochemical and Western blot analyses. Molecular analysis showed that SrRan increased NFATc1 transactivation in osteoblasts, an effect that was fully abrogated by the calcineurin inhibitors cyclosporin A or FK506, confirming that SrRan activates NFATc1 signaling in osteoblasts. This has functional implications because calcineurin inhibitors blunted the enhanced osteoblast replication and expression of the osteoblast phenotypic markers Runx2, alkaline phosphatase, and type I collagen induced by SrRan. We further found that SrRan increased the expression of Wnt3a and Wnt5a as well as beta-catenin transcriptional activity in osteoblasts, and these effects were abolished by calcineurin inhibitors. The Wnt inhibitors sFRP1 and DKK1 abolished SrRan-induced osteoblast gene expression. Furthermore, blunting the Wnt5a receptor Ryk or RhoA that acts downstream of Ryk abrogated cell proliferation and osteoblast gene expression induced by SrRan. These results indicate that activation of NFATc1 and downstream canonical and non-canonical Wnt signaling pathways mediate SrRan-induced osteoblastic cell replication and differentiation, which provides novel insights into the mechanisms of action of this antiosteoporotic agent in osteoblastogenesis.

Nuclear factor of activated T cells mediates fluid shear stress- and tensile strain-induced Cox2 in human and murine bone cells

Mechanical loading such as interstitial fluid shear stress and tensile strain stimulates bone cells, which respond by changing bone mass and structure to maintain optimal skeletal architecture. Bone cells also adapt to bone implants and altered mechanical loading. Osseous integration between host bone and implants is a prerequisite for the stability of implants. Fluctuating fluid pressure and interfacial strains occur between bone cells and implants due to mechanical loading during walking and other daily activities. In this study, we examined the signaling mechanism by which mechanical stimulation activates a novel transcription factor in human and mouse bone cells. Nuclear factor of activated T cells (NFAT) is one of the transcription factors that act downstream of the Ca(++)/calcineurin (Ca(++)/Cn) network: a well-known pathway of inflammation. In this study, we hypothesized that NFAT2 is activated in response to mechanical stimulation and mediates Cox2 expression. Fluid shear stress and tensile strain results in nuclear translocation of NFAT in cells of the osteoblastic lineage. A peptide inhibitor of the Cn/NFAT axis was found to block the mechanical stimulation-mediated Cox2 induction. Further, chromatin immunoprecipitation assay shows direct interaction between NFAT2 and the human Cox2 promoter region. Additionally, CnAbeta knockout calvarial bone cells were found to be less sensitive than control bone cells to mechanical stimulation. Our study provides new evidence for a novel role for NFAT in bone mechanotransduction in the context of cytokine gene induction in bone cells.

Msx2 exerts bone anabolism via canonical Wnt signaling

Msx2 is a homeodomain transcription factor first identified in craniofacial bone and human femoral osteoblasts. We hypothesized that Msx2 might activate skeletal Wnt signaling. Therefore, we analyzed the effects of CMV-Msx2 transgene (Msx2Tg) expression on skeletal physiology and composition. Skeletal Msx2 expression was increased 2-3-fold by Msx2Tg, with expanded protein accumulation in marrow, secondary ossification centers, and periosteum. Microcomputed tomography established increased bone volume in Msx2Tg mice, with increased numbers of plate-like trabeculae. Histomorphometry revealed increased bone formation in Msx2Tg mice versus non-Tg siblings, arising from increased osteoblast numbers. While decreasing adipogenesis, Msx2Tg increased osteogenic differentiation via mechanisms inhibited by Dkk1, an antagonist of Wnt receptors LRP5 and LRP6. Bone from Msx2Tg mice elaborated higher levels of Wnt7 canonical agonists, with diminished Dkk1, changes that augment canonical signaling. Analysis of non-Tg and Msx2Tg siblings possessing the TOPGAL reporter confirmed this; Msx2Tg up-regulated skeletal beta-galactosidase expression (p </= 0.01), along with Wnt7a and Wnt7b, and reduced circulating Dkk1. To better understand molecular mechanisms, we studied C3H10T1/2 osteoprogenitor cells. As in bone, Msx2 increased Wnt7 genes and down-regulated Dkk1, while inducing the osteoblast gene alkaline phosphatase. Msx2-directed RNA interference increased Dkk1 expression and promoter activity, while reducing Wnt7a, Wnt7b, and alkaline phosphatase. Moreover, Msx2 inhibited Dkk1 promoter activity and reduced RNA polymerase association with Dkk1 chromatin. RNA interference-mediated knockdown of Wnt7a, Wnt7b, and LRP6 significantly reduced Msx2-induced alkaline phosphatase. Msx2 exerts bone anabolism in part by reducing Dkk1 expression and enhancing Wnt signaling, thus promoting osteogenic differentiation of skeletal progenitors.