p38α MAPK Regulates Lineage Commitment and OPG Synthesis of Bone Marrow Stromal Cells to Prevent Bone Loss under Physiological and Pathological Conditions

Loss of PA28γ exacerbates imbalanced differentiation of bone marrow stromal cells during bone formation and bone healing in mice

Proteasome activator subunit 3 (PA28γ) is a member of the proteasome activator family, which mainly regulates the degradation and stability of proteins. Studies have shown that it plays crucial roles in lipid formation, stemness maintenance, and blood vessel formation. However, few studies have clarified the association between PA28γ and bone diseases. Herein, we identified PA28γ as a previously unknown regulator of bone homeostasis that coordinates bone formation and lipid accumulation. PA28γ-knockout mice presented with the characteristics of low bone mass and accumulation of lipids. Suppressed expression of PA28γ restrained the osteogenic differentiation and enhanced the adipogenic differentiation of bone marrow stromal cells (BMSCs). Overexpression of PA28γ promoted osteogenic differentiation and inhibited adipogenic differentiation of BMSCs. Mechanistically, PA28γ interacted with Wnt5α, and the two interactors appeared to be positively correlated. PA28γ mainly activated the downstream Wnt/β-catenin signaling pathway, which affects BMSCs differentiation homeostasis. Deletion of Wnt5α significantly delayed the promotion of osteogenic differentiation and partially alleviated the inhibitory effect of adipogenic differentiation of BMSCs in the PA28γ-overexpressing group. Furthermore, we demonstrated that PA28γ-knockout mice had an inhibited rate of bone healing in a drill-hole femoral bone defect model in vivo. Therefore, our results confirm the effects of PA28γ on bone formation and bone defect repair, indicating that PA28γ mainly interacts with Wnt5α to activate the Wnt/β-catenin signaling pathway regulating BMSCs differentiation homeostasis. Our results reveal the function of PA28γ in bone diseases and provide a new theoretical basis for expanding the treatment of bone diseases.

The recent progress of endocrine therapy-induced osteoporosis in estrogen-positive breast cancer therapy

Breast cancer is a significant global health concern, and the discovery of endocrine therapy has played a crucial role in the treatment of estrogen-positive breast cancer. However, these therapies are often associated with osteoporosis-related adverse events, which increase the risk of fractures in breast cancer patients and can result in limited mobility and reduced quality of life. Previous studies have shown that osteoporosis is essential side effects of the breast cancer therapy, although the exact mechanisms remain mostly unclear. Current clinical treatments, such as bisphosphonates, cause side effects and may impact the therapeutic response to endocrine drugs. In this review, we explore the likelihood of endocrine therapy-induced osteoporosis in estrogen-positive breast cancer therapy and discuss the involved mechanisms as well as the therapeutic potential of drugs and drug combination strategies.

Libanoridin Isolated from Corydalis heterocarpa Inhibits Adipogenic Differentiation of Bone Marrow-Derived Mesenchymal Stromal Cells

Bone marrow adiposity is a complication in osteoporotic patients. It is a result of the imbalance between adipogenic and osteogenic differentiation of bone marrow cells. Phytochemicals can alleviate osteoporotic complications by hindering bone loss and decreasing bone marrow adiposity. Corydalis heterocarpa is a biennial halophyte with reported bioactivities, and it is a source of different coumarin derivatives. Libanoridin is a coumarin isolated from C. heterocarpa, and the effect of libanoridin on adipogenic differentiation of human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) was evaluated in the present study. Cells were induced to undergo adipogenesis, and their intracellular lipid accumulation and expression of adipogenic markers were observed under libanoridin treatment. Results showed that 10 μM libanoridin-treated adipocytes accumulated 44.94% less lipid compared to untreated adipocytes. In addition, mRNA levels of PPARγ, C/EBPα, and SREBP1c were dose-dependently suppressed with libanoridin treatment, whereas only protein levels of PPARγ were decreased in the presence of libanoridin. Fluorescence staining of adipocytes also revealed that cells treated with 10 μM libanoridin expressed less PPARγ compared to untreated adipocytes. Protein levels of perilipin and leptin, markers of mature adipocytes, were also suppressed in adipocytes treated with 10 μM libanoridin. Analysis of MAPK phosphorylation levels showed that treatment with libanoridin inhibited the activation of p38 and JNK MAPKs observed by decreased levels of phosphorylated p38 and JNK protein. It was suggested that libanoridin inhibited adipogenic differentiation of hBM-MSCs via suppressing MAPK-mediated PPARγ signaling. Future studies revealing the anti-adipogenic effects of libanoridin in vivo and elucidating its action mechanism will pave the way for libanoridin to be utilized as a nutraceutical with anti-osteoporotic properties.

Exploring the Potential Mechanism of Artemisinin and Its Derivatives in the Treatment of Osteoporosis Based on Network Pharmacology and Molecular Docking

Objective

This study is aimed at predicting and contrasting the mechanisms of artemisinin (ARS), dihydroartemisinin (DHA), artesunate (ART), artemether (ARM), and arteether (ARE) in the treatment of osteoporosis (OP) using network pharmacology and molecular docking.

Methods

The targets of ARS, DHA, ART, ARM, and ARE were obtained from the SwissTargetPrediction. The targets related to OP were obtained from the TTD, DrugBank, Genecards, and DisGeNet databases. Then, the anti-OP targets of ARS, DHA, ART, ARM, and ARE were obtained and compared using the Venn diagram. Afterward, the protein-protein interaction (PPI) networks were built using the STRING database, and Cytoscape was used to select hub targets. Moreover, molecular docking validated the binding association between five molecules and hub targets. Finally, GO enrichment and KEGG pathway enrichment were conducted using the DAVID database. The common pathways of five molecules were analysed.

Results

A total of 28, 37, 36, 27, and 33 anti-OP targets of ARS, DHA, ART, ARM, and ARE were acquired. EGFR, EGFR, CASP3, MAPK8, and CASP3 act as the top 1 anti-OP targets of ARS, DHA, ART, ARM, and ARE, respectively. MAPK14 is the common target of five molecules. All five molecules can bind well with these hubs and common targets. Meanwhile, functional annotation showed that MAPK, Serotonergic synapse, AMPK, prolactin, and prolactin signaling pathways are the top 1 anti-OP pathway of ARS, DHA, ART, ARM, and ARE, respectively. IL-17 signaling pathway and prolactin signaling pathway are common anti-OP pathways of five molecules. Besides, GO enrichment showed five biological processes and three molecular functions are common anti-OP mechanisms of five molecules.

Conclusion

ARS, DHA, ART, ARM and ARE can treat OP through multi-targets and multi pathways, respectively. All five molecules can treat OP by targeting MAPK14 and acting on the IL-17 and prolactin signaling pathways.

Moxibustion as adjuvant therapy for preventing bone loss in postmenopausal women: protocol for a randomised controlled trial

INTRODUCTION

Postmenopausal osteoporosis, caused by ageing and oestrogen deficiency, seriously threatens women's physical and mental health. Postmenopausal osteopenia is the transition from healthy bone to osteoporosis, and it may be the key period for preventing bone loss. Moxibustion, a physical therapy of Traditional Chinese Medicine, has potential benefits for osteoporosis treatment and prevention, but it has not been adequately studied. This study aims to explore the clinical effects and safety of moxibustion in delaying bone loss in postmenopausal women.

METHODS AND ANALYSIS

In this parallel-design, randomised, patient-blind and assessor-blind, controlled clinical study, 150 women with osteopenia at low fracture risk will be randomly assigned to a moxibustion treatment (MT) group or a placebo-moxibustion control (PMC) group in a 1:1 ratio. In addition to the fundamental measures (vitamin D3 and calcium) as recommended by the guidelines, participants of the two groups will receive MT or PMC treatment for 42 sessions over 12 months. The primary outcome will be the bone mineral density (BMD) of the lumbar spine at the end of the 12-month treatment, and secondary outcomes will be the BMD of the femoral neck and total hip, T-scores, bone turnover markers, serum calcium levels, serum magnesium levels, serum phosphorus levels, serum parathyroid hormone levels and 25-hydroxyvitamin D levels, intensity of bone pain, quality of life, incidence of osteoporosis and fractures, usage of emergency drugs or surgery, participant self-evaluation of therapeutic effects and the rate of adverse events. All statistical analyses will be performed based on the intention-to-treat and per-protocol principle.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from the Ethics Committee on Biomedical Research, West China Hospital of Sichuan University (permission number: 2021-1243). The results are expected to be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ChiCTR2100053953.

Role of Platelet-Rich Plasma Gel in Promoting Wound Healing Based on Medical Images of Wounds

A wound is the pathological change of soft tissue under normal skin caused by various factors, such as collision, contusion, hot crush, avulsion, corrosive chemicals, operations, excessive wound tension after operations, local pressure that cannot be relieved for a long time, liquid immersion, local infection, and rejection reactions caused by allogeneic substances. The skin itself or its underlying soft tissue loses its integrity and continuity, thus losing its normal physiological function. Medical image analysis is a medical term that refers to the interdisciplinary fields of integrated medical imaging, artificial intelligence, digital image processing and analysis, mathematical modeling, and numerical algorithms. According to the time of wound formation, they can be divided into acute and chronic wounds. The common acute wounds include lacerations caused by trauma, surgical incisions, burns, and donor sites formed after skin graft operations. This article mainly studies the role of platelet-rich plasma gel nanocomposites in promoting wound healing. It is proven that ptt-rich plasma gel can significantly promote tissue repair and regeneration and accelerate wound healing in patients with severe burns. The atomic number of the nanocomposite has a better treatment effect on the nanoparticle approach. In this paper, chitosan nanocomposite membrane, nanocomposite algorithm, and the calculation method of enthalpy of formation of high alloy nanomaterials were used to study the role of ptt-rich plasma gel combined chitosan nanocomposite membrane loaded bone marrow stromal cells in promoting wound healing, and its effects were applied to the repair of special site burns, special burns, and different age burns. Good wound repair benefits from the correct treatment of the wound, which directly affects the stability and development of the internal environment. The difference in healing time between the two groups was statistically significant, and the recovery time of the PRP group was 0.001 less than that of the control group. The results showed that the wound healing time of the PRP group was significantly shorter than that of the control group (P < 0.05); after treatment, the content of VEGF in the wound tissue of the two groups increased, especially in the PRP group; the effective rate of the PRP group was 75.0%, which was higher than 68.8% of the control group. It can play an important role in the regulation of expression and the pathophysiological process of wound healing.

Small extracellular vesicle-mediated miR-320e transmission promotes osteogenesis in OPLL by targeting TAK1

Ossification of the posterior longitudinal ligament (OPLL) is an emerging spinal disease caused by heterotopic ossification of the posterior longitudinal ligament. The pathological mechanism is poorly understood, which hinders the development of nonsurgical treatments. Here, we set out to explore the function and mechanism of small extracellular vesicles (sEVs) in OPLL. Global miRNA sequencings are performed on sEVs derived from ligament cells of normal and OPLL patients, and we have showed that miR-320e is abundantly expressed in OPLL-derived sEVs compare to other sEVs. Treatment with either sEVs or miR-320e significantly promote the osteoblastic differentiation of normal longitudinal ligament cells and mesenchymal stem cells and inhibit the osteoclastic differentiation of monocytes. Through a mechanistic study, we find that TAK1 is a downstream target of miR-320e, and we further validate these findings in vivo using OPLL model mice. Together, our data demonstrate that OPLL ligament cells secrete ossification-promoting sEVs that contribute to the development of ossification through the miR-320e/TAK1 axis.

The pathological mechanisms that lead to Ossification of the posterior longitudinal ligament (OPLL) are unclear. Here, the authors show that OPLL ligament cells produce small extracellular vesicles that induce ossification via miR-320e/TAK1 signaling in mice and human posterior longitudinal ligament cells.

Hydroxyapatite Use in Spine Surgery—Molecular and Clinical Aspect

Hydroxyapatite possesses desirable properties as a scaffold in tissue engineering: it is biocompatible at a site of implantation, and it is degradable to non-toxic products. Moreover, its porosity enables infiltration of cells, nutrients and waste products. The outcome of hydroxyapatite implantation highly depends on the extent of the host immune response. Authors emphasise major roles of the chemical, morphological and physical properties of the surface of biomaterial used. A number of techniques have been applied to transform the theoretical osteoconductive features of HAp into spinal fusion systems—from integration of HAp with autograft to synthetic intervertebral implants. The most popular uses of HAp in spine surgery include implants (ACDF), bone grafts in posterolateral lumbar fusion and transpedicular screws coating. In the past, autologous bone graft has been used as an intervertebral cage in ACDF. Due to the morbidity related to autograft harvesting from the iliac bone, a synthetic cage with osteoconductive material such as hydroxyapatite seems to be a good alternative. Regarding posterolateral lumbar fusion, it requires the graft to induce new bone growth and reinforce fusion between the vertebrae. Hydroxyapatite formulations have shown good results in that field. Moreover, the HAp coating has proven to be an efficient method of increasing screw fixation strength. It can decrease the risk of complications such as screw loosening after pedicle screw fixation in osteoporotic patients. The purpose of this literature review is to describe in vivo reaction to HAp implants and to summarise its current application in spine surgery.

Impact of Myeloid p38α/MAPK on Orthodontic Tooth Movement

Objectives: Myeloid p38α/MAPK regulate and coordinate osteoclastogenesis. The present study was conducted to investigate the role of myeloid p38α/MAPK during orthodontic tooth movement. Methods: Orthodontic tooth movement was performed in wildtype and p38α^Δmyel mice lacking p38α/MAPK expression in myeloid cells. First, bone parameter as well as osteoblast and osteoclast number were determined in tibiae. RNA was isolated from the untreated and orthodontically treated maxillary jaw side and expression of genes involved in inflammation and bone remodelling were analysed. Finally, periodontal bone loss, alveolar bone density and extent of orthodontic tooth movement were assessed. Results: Bone density was increased in p38α^Δmyel mice compared to wildtype mice in tibiae (p = 0.043) and alveolar bone (p = 0.003). This was accompanied by a reduced osteoclast number in tibiae (p = 0.005) and TRAP5b in serum (p = 0.015). Accordingly, expression of osteoclast-specific genes was reduced in p38α^Δmyel mice. Extent of tooth movement was reduced in p38α^Δmyel mice (p = 0.024). This may be due to the higher bone density of the p38αΔmyel mice. Conclusions: Myeloid p38α/MAPK thus appears to play a regulatory role during orthodontic tooth movement by regulating osteoclastogenesis.

The ATF3-OPG Axis Contributes to Bone Formation by Regulating the Differentiation of Osteoclasts, Osteoblasts, and Adipocytes

Activating transcription factor 3 (ATF3) has been identified as a negative regulator of osteoblast differentiation in in vitro study. However, it was not associated with osteoblast differentiation in in vivo study. To provide an understanding of the discrepancy between the in vivo and in vitro findings regarding the function of ATF3 in osteoblasts, we investigated the unidentified roles of ATF3 in osteoblast biology. ATF3 enhanced osteoprotegerin (OPG) production, not only in osteoblast precursor cells, but also during osteoblast differentiation and osteoblastic adipocyte differentiation. In addition, ATF3 increased nodule formation in immature osteoblasts and decreased osteoblast-dependent osteoclast formation, as well as the transdifferentiation of osteoblasts to adipocytes. However, all these effects were reversed by the OPG neutralizing antibody. Taken together, these results suggest that ATF3 contributes to bone homeostasis by regulating the differentiation of various cell types in the bone microenvironment, including osteoblasts, osteoclasts, and adipocytes via inducing OPG production.

The therapeutic potential of mesenchymal stem cells in treating osteoporosis

Osteoporosis (OP), a common systemic metabolic bone disease, is characterized by low bone mass, increasing bone fragility and a high risk of fracture. At present, the clinical treatment of OP mainly involves anti-bone resorption drugs and anabolic agents for bone, but their long-term use can cause serious side effects. The development of stem cell therapy and regenerative medicine has provided a new approach to the clinical treatment of various diseases, even with a hope for cure. Recently, the therapeutic advantages of the therapy have been shown for a variety of orthopedic diseases. However, these stem cell-based researches are currently limited to animal models; the uncertainty regarding the post-transplantation fate of stem cells and their safety in recipients has largely restricted the development of human clinical trials. Nevertheless, the feasibility of mesenchymal stem cells to treat osteoporotic mice has drawn a growing amount of intriguing attention from clinicians to its potential of applying the stem cell-based therapy as a new therapeutic approach to OP in the future clinic. In the current review, therefore, we explored the potential use of mesenchymal stem cells in human OP treatment.

Astragalus Polysaccharide Injection Ameliorates the Apoptosis of Chondrocytes in the Ovariectomized Osteoporosis Mouse Model via Modulating Protein Kinase B/Glycogen Synthase Kinase 3 Beta Signal Transduction

The Akt/GSK3 signal pathway exerts an impact on the apoptosis of chondrocytes. We planned to elucidate the role and mechanism of Akt/GSK3 signal transduction in ovariectomized osteoporosis. 50 female mice in SPF-graded and healthy condition were processed to establish the ovariectomized osteoporosis model, while 12 of the healthy mice were set as blank controls. The successfully established ovariectomized osteoporosis models were divided into model group (12 mice) and Astragalus group (12 mice). The following measurements were conducted: the bone mineral density in the left humerus, serum estrogen level and Cx43 protein level in osteoblasts, proportion of apoptotic cells, as well as the protein and mRNA levels of Akt and GSK3β in murine bone tissues via Western blotting and RT-PCR detection, respectively. The bone mineral density of mice in Astragalus group was the highest (0.174±0.04) g/cm2. The positive rate of Cx43 protein expression, apoptosis rate, as well as the protein and mRNA levels of Akt in osteocytes were significantly decreased (P < 0.05), but still significantly higher than model group. Estrogen level in Astragalus group was (87.52 ±8.69) pmol/L. The positive rate of Cx43 expression, apoptosis rate, as well as the protein and mRNA levels of GSK3β in osteocytes were decreased in comparison to model group (P < 0.05). Astragalus polysaccharide injection could ameliorate the apoptosis of chondrocytes and downregulate Cx43 protein via modulating Akt/GSK3β signal transduction, thereby exerting a therapeutic effect on ovariectomized osteoporosis.

Acute Inflammatory Response in Osteoporotic Fracture Healing Augmented with Mechanical Stimulation is Regulated In Vivo through the p38-MAPK Pathway

Low-magnitude high-frequency vibration (LMHFV) has previously been reported to modulate the acute inflammatory response of ovariectomy-induced osteoporotic fracture healing. However, the underlying mechanisms are not clear. In the present study, we investigated the effect of LMHFV on the inflammatory response and the role of the p38 MAPK mechanical signaling pathway in macrophages during the healing process. A closed femoral fracture SD rat model was used. In vivo results showed that LMHFV enhanced activation of the p38 MAPK pathway at the fracture site. The acute inflammatory response, expression of inflammatory cytokines, and callus formation were suppressed in vivo by p38 MAPK inhibition. However, LMHFV did not show direct in vitro enhancement effects on the polarization of RAW264.7 macrophage from the M1 to M2 phenotype, but instead promoted macrophage enlargement and transformation to dendritic monocytes. The present study demonstrated that p38 MAPK modulated the enhancement effects of mechanical stimulation in vivo only. LMHFV may not have exerted its enhancement effects directly on macrophage, but the exact mechanism may have taken a different pathway that requires further investigation in the various subsets of immune cells.

Systems pharmacology dissection of action mechanisms for herbs in osteoporosis treatment

Objective

Osteoporosis has become the biggest cause of non-fatal health issue. Currently, the limitations of traditional anti-osteoporosis drugs such as long-term ill-effects and drug resistance, have raised concerns toward complementary and alternative therapies, particularly herbal medicines and their natural active compounds. Thus, this study aimed to provide an integrative analysis of active chemicals, drug targets and interacting pathways of the herbs for osteoporosis treatment.

Methods

Here, we introduced a systematic pharmacology model, combining the absorption, distribution, metabolism, and excretion (ADME) screening model, drug targeting and network pharmacology, to probe into the therapeutic mechanisms of herbs in osteoporosis.

Results

We obtained 86 natural compounds with favorable pharmacokinetic profiles and their 58 targets from seven osteoporosis-related herbs. Network analysis revealed that they probably synergistically work through multiple mechanisms, such as suppressing inflammatory response, maintaining bone metabolism or improving organism immunity, to benefit patients with osteoporosis. Furthermore, experimental results showed that all the five compounds (calycosin, asperosaponin VI, hederagenin, betulinic acid and luteolin) enhanced osteoblast proliferation and differentiation in vitro, which corroborated the validity of this system pharmacology approach. Notably, gentisin and aureusidin among the identified compounds were first predicted to be associated with osteoporosis.

Conclusion

Herbs and their natural compounds, being characterized as the classical combination therapies, might be engaged in multiple mechanisms to coordinately improve the osteoporosis symptoms. This work may contribute to offer novel strategies and clues for the therapy and drug discovery of osteoporosis and other complex diseases.

Exploring the Relationship of Bone Turnover Markers and Bone Mineral Density in Community-Dwelling Postmenopausal Women

Aims

To explore the relationships of procollagen type 1 N-terminal propeptide (P1NP) and β cross-linked C-telopeptide of type 1 collagen (β-CTX) with bone mineral density (BMD) in postmenopausal women.

Methods

All postmenopausal women were selected from a community-based case-control study. The anteroposterior L1-L4 and left proximal femur BMD were measured. P1NP and β-CTX were also collected and tested. The main correlation analysis was applied to explore the relationships of BMD, P1NP, and β-CTX.

Results

The total 1055 postmenopausal women were enrolled. The BMD at all sites kept a decrease continually with age (P < 0.01). In addition, the level of β-CTX increased significantly from 45 to 50 years old and remained at a high level in the later stage, while the level of P1NP changed little or even decreased with age. Logistic regression model showed that β-CTX has better ability to predict BMD than P1NP, as demonstrated by an area under the curve (AUC) of 0.63.

Conclusion

P1NP and β-CTX are important markers to monitor bone metabolism. This trial is registered with ChiCTR-SOC-17013090. The date of registration is Oct. 23, 2017.

Circadian transcription factor Dbp promotes rat calvarial osteoprogenitors osteogenic differentiation through Kiss1/GnRH/E2 signaling pathway loop

To determine the mechanism by which D-site-binding protein (Dbp) regulates rat calvarial osteoprogenitors (OPCs) osteogenic differentiation. α-Smooth muscle actin (α-SMA) + rat calvarial OPCs were extracted and purified using immunomagnetic beads. Cells were transduced with Dbp-lentivirus and divided into Dbp knockdown, Dbp overexpression and vehicle groups. After osteogenic induction for 21 days, Alizarin red staining and alkaline phosphatase (ALP) activity were examined. Expression levels of Runx2, Ocn, Osterix, Bmp4, Kiss1, and GnRH were determined using a quantitative real-time polymerase chain reaction. The observed changes in Kisspeptin, GnRH, ERα, and Runx2 were further validated via Western blot analysis. Furthermore, E2 and GnRH secretion levels were detected via an enzyme-linked immunosorbent assay (ELISA). Chromatin immunoprecipitation (ChIP) and luciferase assay were used to assess the effects of Dbp on the Kiss1 gene promoter. The coexpression of Dbp and Kisspeptin or GnRH was also evaluated via immunofluorescence. Following osteogenic induction, Dbp overexpression significantly increased calcium nodule formation and ALP activity, as well as Runx2, Ocn, Osterix, Bmp4, Kiss1, and GnRH messenger RNA expression, while Dbp knockdown presented the opposite results. Western blot analysis and ELISA results showed that Dbp significantly promotes Runx2, E2/ERα, Kisspeptin, and GnRH expression. These findings were confirmed by the ChIP assay, which indicated that the estrogen receptor promotes Kisspeptin expression after binding to the Kiss1 gene promoter, which is regulated by Dbp. Immunofluorescence assay showed that Dbp coexpression with Kisspeptin or GnRH varied depending on Dbp expression levels. Collectively, the circadian transcription factor Dbp promotes α-SMA + rat calvarial OPCs osteoblastic differentiation through Kiss1/GnRH/E2 signaling pathway loop.

Knockdown of LAP2α inhibits osteogenic differentiation of human adipose-derived stem cells by activating NF-κB

BACKGROUND

Lamina-associated polypeptide 2α (LAP2α) is a nucleoplasmic protein that has been involved in the regulation of the cell cycle, gene transcription, and adult stem cell function. LAP2α down-regulation is linked to age-related osteoporosis and bone deformities; however, the underlying mechanisms remain obscure. The present study aimed to elucidate the function of LAP2α in the osteogenic differentiation of human adipose-derived stem cells (hASCs), which are attractive sources for bone tissue engineering.

METHODS

The expression of LAP2α during the osteogenic differentiation of hASCs was detected firstly. A loss of function investigation was then carried out to characterize the function of LAP2α in osteogenic differentiation of hASCs both in vitro and in vivo. Moreover, RNA-sequences, western blotting, and confocal analyses were performed to clarify the molecular mechanism of LAP2α-regulated osteogenesis.

RESULTS

We found that LAP2α expression was upregulated upon osteogenic induction. Both in vitro and in vivo experiments indicated that LAP2α knockdown resulted in impaired osteogenic differentiation of hASCs. Mechanistically, we revealed that LAP2α deficiency activated nuclear factor kappa B (NF-κB) signaling by controlling the cytoplasmic-nuclear translocation of p65.

CONCLUSIONS

Collectively, our findings revealed that LAP2α functions as an essential regulator for osteogenesis of hASCs by modulating NF-κB signaling, thus providing novel insights for mesenchymal stem cell-mediated bone tissue engineering.

The relationship between bone marrow adipose tissue and bone metabolism in postmenopausal osteoporosis

Postmenopausal osteoporosis (PMOP) is a prevalent skeletal disorder associated with menopause-related estrogen withdrawal. PMOP is characterized by low bone mass, deterioration of the skeletal microarchitecture, and subsequent increased susceptibility to fragility fractures, thus contributing to disability and mortality. Accumulating evidence indicates that abnormal expansion of marrow adipose tissue (MAT) plays a crucial role in the onset and progression of PMOP, in part because both bone marrow adipocytes and osteoblasts share a common ancestor lineage. The cohabitation of MAT adipocytes, mesenchymal stromal cells, hematopoietic cells, osteoblasts and osteoclasts in the bone marrow creates a microenvironment that permits adipocytes to act directly on other cell types in the marrow. Furthermore, MAT, which is recognized as an endocrine organ, regulates bone remodeling through the secretion of adipokines and cytokines. Although an enhanced MAT volume is linked to low bone mass and fractures in PMOP, the detailed interactions between MAT and bone metabolism remain largely unknown. In this review, we examine the possible mechanisms of MAT expansion under estrogen withdrawal and further summarize emerging findings regarding the pathological roles of MAT in bone remodeling. We also discuss the current therapies targeting MAT in osteoporosis. A comprehensive understanding of the relationship between MAT expansion and bone metabolism in estrogen deficiency conditions will provide new insights into potential therapeutic targets for PMOP.

RelA promotes proliferation but inhibits osteogenic and chondrogenic differentiation of mesenchymal stem cells

NF-κB is known to be implicated in skeletal development and related diseases. Previous studies have shown that RelA, a key subunit of NF-κB, is involved in osteoblast and chondrocyte survival and differentiation. Yet, the physiological roles of RelA in mesenchymal stem cells (MSCs), which give rise to both chondrocytes and osteoblasts, are still poorly understood. Here, we generated Prrx1-Cre;RelA^f/f mice to delete RelA in Prrx1⁺ bone marrow MSCs and found that RelA deletion led to decreased MSC proliferation and altered differentiation, with increased osteogenic and chondrogenic differentiation but decreased adipogenic differentiation. Bone size and mass were not significantly changed in the mutant mice, although they developed moderate osteoarthritis-like phenotypes. Thus, our studies reveal important but discordant functions of RelA in MSC proliferation and differentiation, and provide an explanation why MSC-specific RelA knockout mice only develop minor skeletal phenotypes.

Corylin, a flavonoid derived from Psoralea Fructus, induces osteoblastic differentiation via estrogen and Wnt/β-catenin signaling pathways

Corylin is a naturally occurring flavonoid isolated from the fruit of Psoralea corylifolia L. (Fabaceae), which is a Chinese medicinal herb in treating osteoporosis. Although a variety of pharmacological activities of corylin have been reported, its osteogenic action and the underlying mechanism in bone development remain unclear. In the present study, the involvement of bone-specific genes in corylininduced differentiated osteoblasts was analyzed by RT-PCR, promoter-reporter assay, and Western blotting. In cultured osteoblasts, corylin-induced cell differentiation and mineralization, as well as increased the expressions of vital biological markers for osteogenesis, such as Runx2, Osterix, Col1, and ALP. Corylin was proposed to have dual pathways in triggering the osteoblastic differentiation. First, the osteogenic function of corylin acted through the activation of Wnt/β-catenin signaling. The nuclear translocation of β-catenin of cultured osteoblasts, as determined by flow cytometry and confocal microscopy, was triggered by applied corylin, and which was blocked by DKK-1, an inhibitor of Wnt/β-catenin signaling. Second, the application of corylin-induced estrogenic response in a dose-dependent manner, and which was blocked by ICI 182 780, an antagonist of estrogen receptor. Furthermore, the activation of Runx2 promoter by corylin was abolished by both DKK-1 and ICI 182,780, indicating that the corylin exhibited its osteogenic effect via estrogen and Wnt/β-catenin signaling pathways. In addition, corylin regulated the metabolic profiles, as well as the membrane potential of mitochondria, in cultured osteoblasts. Corylin also stimulated the osteogenesis in bone micromass derived from mesenchymal progenitor cells. This study demonstrated the osteogenic activities of corylin in osteoblasts and micromass, suggesting that corylin has the potential to be developed as a novel pro-osteogenic agent in targeting for the treatment of osteoblast-mediated osteoporosis.

The noncanonical BMP signaling pathway plays an important role in club cell regeneration

The bronchiole is a major site for the development of several life-threatening disorders, including chronic obstructive pulmonary disease and lung adenocarcinomas. The bronchiolar epithelium is composed of club cells and ciliated epithelial cells, with club cells serving as progenitor cells. Presently, the identity of the cells involved in regeneration of bronchiolar epithelium and the underlying mechanisms remain incompletely understood. Here, we show that Prrx1, a homeobox transcription factor, can mark club cells in adult mice during homeostasis and regeneration. We further show that the noncanonical signaling pathway of BMPs, BMPR1A-Tak1-p38MAPK, plays a critical role in club cell regeneration. Ablation of Bmpr1a, Tak1, or Mapk14 (encoding p38α) in Prrx1⁺ club cells caused minimal effect on bronchiolar epithelium homeostasis, yet it resulted in severe defects in club cell regeneration and bronchiole repair in adult mice. We further show that this pathway supports proliferation and expansion of the regenerating club cells. Our findings thus identify a marker for club cells and reveal a critical role for the BMP noncanonical pathway in club cell regeneration.

Vaspin protects mouse mesenchymal stem cells from oxidative stress-induced apoptosis through the MAPK/p38 pathway

The aim of the work was to study the influence of vaspin on oxidative stress-induced apoptosis of mouse mesenchymal stem cells (MSCs). MSCs originated from bone marrow of C57BL/6 mouse were treated with vaspin and/or H₂O₂ in a dose-dependent manner. Cellular viability detected by CCK-8 and cell apoptosis studied by flow cytometry and TUNEL assay were observed in these cells. The protein expressions of PI3K, p-PI3K, Akt, p-Akt, T-ERK1/2, p-ERK1/2, p38, p-p38, JNK, and p-JNK were tested by Western blot. Vaspin had no significant effect on cellular viability, but significantly reduced H₂O₂-induced apoptosis. Western blot assay showed that pretreatment with vaspin promoted the activation of p-p38. Inhibition of p38 by SB203580 suppressed the protective effect of vaspin on oxidative stress-induced apoptosis. Vaspin inhibits oxidative stress-induced apoptosis of MSCs via the activation of MAPK/p38 signaling pathway. These findings indicate that vaspin is prone to osteoporosis protection.

Effect of risperidone on proliferation and apoptosis of MC3T3-E1 cells

This aim of this study was to assess the molecular mechanism of osteoporosis in schizophrenia patients with risperidone use. Here, we investigated the effects of risperidone on cellular proliferation and apoptosis of a preosteoblast cell line, MC3T3-E1. Cell viability and apoptotic rate of MC3T3-E1 were detected by cell counting kit-8 and flow cytometry at a serial dose of risperidone and at different time points, respectively. Bone transformation relevant gene serum osteocalcin (BGP), collagen 1, tumor necrosis factor-α (TNF-α), osteoprotegerin (OPG), and receptor activator of nuclear factor-κB ligand (RANKL) mRNA levels were determined by real-time PCR (qPCR). Their protein expression patterns were evaluated using western blot. The results revealed that risperidone dramatically inhibited MC3T3-E1 cell proliferation in a dose-dependent manner. It also significantly induced MC3T3-E1 cell apoptosis. TNF-α gene and protein levels were greatly enhanced after risperidone treatment. In contrast, BGP, collagen 1, OPG, and RANKL gene and protein levels were markedly downregulated. Our study indicated that risperidone suppressed MC3T3-E1 cell proliferation and induced apoptosis. It also regulated BGP gene and protein expression.

Tsc1 ablation in Prx1 and Osterix lineages causes renal cystogenesis in mouse

Tuberous Sclerosis Complex (TSC) is caused by mutations in TSC1 or TSC2, which encode negative regulators of the mTOR signaling pathway. The renal abnormalities associated with TSC include angiomyolipoma, cysts, and renal cell carcinoma. Here we report that specific ablation of Tsc1 using the mesenchymal stem cell-osteoblast lineage markers induced cystogenesis in mice. Using Rosa-tdTomato mice, we found that Prx1- or Dermo1-labeled cells were present in the nephron including glomerulus but they were not stained by markers for podocytes, mesangial cells, endothelial cells, or proximal or loop of Henle tubular cells, while Osx is known to label tubular cells. Tsc1 deficiency in Prx1 lineage cells caused development of mild cysts that were positive only for Tamm-Horsfall protein (THP), a loop of Henle marker, while Tsc1 deficiency in Osx lineage cells caused development of cysts that were positive for Villin, a proximal tubular cell marker. On the other hand, Tsc1 deficiency in the Dermo1 lineage did not produce detectable phenotypical changes in the kidney. Cyst formation in Prx1-Cre; Tsc1^f/f and Osx-Cre; Tsc1^f/f mice were associated with increase in both proliferative and apoptotic cells in the affected tissue and were largely suppressed by rapamycin. These results suggest that Prx1 and Osx lineages cells may contribute to renal cystogenesis in TSC patients.

Phloretin Promotes Adipogenesis via Mitogen-Activated Protein Kinase Pathways in Mouse Marrow Stromal ST2 Cells

Phloretin, a glucose transporter (GLUT) inhibitor, has pleiotropic effects. The present study examined the effects of phloretin on the commitment of marrow stromal cells to adipocytes, using the mouse marrow stromal cell line ST2. Oil red O staining showed that treatment with phloretin 10–100 µM promoted lipid accumulation. Real-time PCR showed that phloretin significantly increased the expression of adipogenic markers, including PPARγ, C/EBPα, fatty acid synthase, fatty acid-binding protein 4, and adiponectin. Western blotting showed that phloretin inhibited ERK1/2 and JNK but activated p38 MAPK. Treatment with a MAPK/ERK kinase inhibitor and a JNK inhibitor enhanced adipogenesis, similar to phloretin. In contrast, a p38 MAPK inhibitor suppressed phloretin-induced adipogenesis. Although phloretin phosphorylated AMP-activated protein kinase (AMPK), co-incubation with an AMPK inhibitor did not block phloretin-induced adipogenesis. The 2-deoxyglucose colorimetric assay showed that phloretin and siRNA silencing of GLUT1 decreased glucose uptake. However, unlike phloretin treatment, GLUT1 silencing inhibited adipogenesis. In addition, phloretin enhanced adipogenesis in GLUT1 knocked-down cells. Taken together, phloretin induced adipogenesis of marrow stromal cells by inhibiting ERK1/2 and JNK and by activating p38 MAPK. The adipogenic effects of phloretin were independent of glucose uptake inhibition. Phloretin may affect energy metabolism by influencing adipogenesis and adiponectin expression.

BMPRIA is required for osteogenic differentiation and RANKL expression in adult bone marrow mesenchymal stromal cells

Bone morphogenetic proteins (BMPs) activate the canonical Smad1/5/8 and non-canonical Tak1-MAPK pathways via BMP receptors I and II to regulate skeletal development and bone remodeling. Specific ablation of Bmpr1a in immature osteoblasts, osteoblasts, or osteocytes results in an increase in cancellous bone mass, yet opposite results have been reported regarding the underlying mechanisms. Moreover, the role for BMPRIA-mediated signaling in bone marrow mesenchymal stromal cells (BM-MSCs) has not been explored. Here, we specifically ablated Bmpr1a in BM-MSCs in adult mice to study the function of BMPR1A in bone remodeling and found that the mutant mice showed an increase in cancellous and cortical bone mass, which was accompanied by a decrease in bone formation rate and a greater decrease in bone resorption. Decreased bone formation was associated with a defect in BM-MSC osteogenic differentiation whereas decreased bone resorption was associated with a decrease in RANKL production and osteoclastogenesis. However, ablation of Tak1, a critical non-canonical signaling molecule downstream of BMP receptors, in BM-MSCs at adult stage did not affect bone remodeling. These results suggest that BMP signaling through BMPRIA controls BM-MSC osteogenic differentiation/bone formation and RANKL expression/osteoclastogenesis in adult mice independent of Tak1 signaling.

Estrogen regulates stemness and senescence of bone marrow stromal cells to prevent osteoporosis via ERβ-SATB2 pathway

Decline of pluripotency in bone marrow stromal cells (BMSCs) associated with estrogen deficiency leads to a bone formation defect in osteoporosis. Special AT-rich sequence binding protein 2 (SATB2) is crucial for maintaining stemness and osteogenic differentiation of BMSCs. However, whether SATB2 is involved in estrogen-deficiency associated-osteoporosis is largely unknown. In this study, we found that estrogen mediated pluripotency and senescence of BMSCs, primarily through estrogen receptor beta (ERβ). BMSCs from the OVX rats displayed increased senescence and weaker SATB2 expression, stemness, and osteogenic differentiation, while estrogen could rescue these phenotypes. Inhibition of ERβ or ERα confirmed that SATB2 was associated with ERβ in estrogen-mediated pluripotency and senescence of BMSCs. Furthermore, estrogen mediated the upregulation of SATB2 through the induction of ERβ binding to estrogen response elements (ERE) located at -488 of the SATB2 gene. SATB2 overexpression alleviated senescence and enhanced stemness and osteogenic differentiation of OVX-BMSCs. SATB2-modified BMSCs transplantation could prevent trabecular bone loss in an ovariectomized rat model. Collectively, our study revealed the role of SATB2 in stemness, senescence, and osteogenesis of OVX-BMSCs. These results indicate that estrogen prevents osteoporosis by promoting stemness and osteogenesis, and inhibiting senescence of BMSCs through an ERβ-SATB2 pathway. Therefore, SATB2 is a novel anti-osteoporosis target gene.

Soluble Factors on Stage to Direct Mesenchymal Stem Cells Fate

Mesenchymal stem cells (MSCs) are multipotent stromal cells that are identified by in vitro plastic adherence, colony-forming capacity, expression of a panel of surface molecules, and ability to differentiate at least toward osteogenic, adipogenic, and chondrogenic lineages. They also produce trophic factors with immunomodulatory, proangiogenic, and antiapoptotic functions influencing the behavior of neighboring cells. On the other hand, a reciprocal regulation takes place; in fact, MSCs can be isolated from several tissues, and depending on the original microenvironment and the range of stimuli received from there, they can display differences in their essential characteristics. Here, we focus mainly on the bone tissue and how soluble factors, such as growth factors, cytokines, and hormones, present in this microenvironment can orchestrate bone marrow-derived MSCs fate. We also briefly describe the alteration of MSCs behavior in pathological settings such as hematological cancer, bone metastasis, and bone marrow failure syndromes. Overall, the possibility to modulate MSCs plasticity makes them an attractive tool for diverse applications of tissue regeneration in cell therapy. Therefore, the comprehensive understanding of the microenvironment characteristics and components better suited to obtain a specific MSCs response can be extremely useful for clinical use.

Bone Size and Quality Regulation: Concerted Actions of mTOR in Mesenchymal Stromal Cells and Osteoclasts

The bone size and quality, acquired during adolescent growth under the influence of anabolic hormones, growth factors, and nutrients, determine the height and bone stability and forecast osteoporosis risks in late life. Yet bone size and quality control mechanisms remain enigmatic. To study the roles of mammalian target of rapamycin (mTOR) signaling, sensor of growth factors and nutrients, in bone size and quality regulation, we ablated Tsc1, a suppressor of mTOR, in mesenchymal stromal cells (MSCs), monocytes, or their progenies osteoblasts and osteoclasts. mTOR activation in MSCs, but much less in osteoblasts, increased bone width and mass due to MSC hyperproliferation, but decreased bone length and mineral contents due to defective MSC differentiation. mTOR activation promotes bone mineral accretion by inhibiting osteoclast differentiation and activity directly or via coupling with MSCs. Tuberous sclerosis complex patient studies confirmed these findings. Thus, mTOR regulates bone size via MSCs and bone quality by suppressing catabolic activities of osteoclasts.

p38α MAPK regulates proliferation and differentiation of osteoclast progenitors and bone remodeling in an aging-dependent manner

Bone mass is determined by the balance between bone formation, carried out by mesenchymal stem cell-derived osteoblasts, and bone resorption, carried out by monocyte-derived osteoclasts. Here we investigated the potential roles of p38 MAPKs, which are activated by growth factors and cytokines including RANKL and BMPs, in osteoclastogenesis and bone resorption by ablating p38α MAPK in LysM+monocytes. p38α deficiency promoted monocyte proliferation but regulated monocyte osteoclastic differentiation in a cell-density dependent manner, with proliferating p38α^−/− cultures showing increased differentiation. While young mutant mice showed minor increase in bone mass, 6-month-old mutant mice developed osteoporosis, associated with an increase in osteoclastogenesis and bone resorption and an increase in the pool of monocytes. Moreover, monocyte-specific p38α ablation resulted in a decrease in bone formation and the number of bone marrow mesenchymal stem/stromal cells, likely due to decreased expression of PDGF-AA and BMP2. The expression of PDGF-AA and BMP2 was positively regulated by the p38 MAPK-Creb axis in osteoclasts, with the promoters of PDGF-AA and BMP2 having Creb binding sites. These findings uncovered the molecular mechanisms by which p38α MAPK regulates osteoclastogenesis and coordinates osteoclastogenesis and osteoblastogenesis.

Knockdown of SLC41A1 magnesium transporter promotes mineralization and attenuates magnesium inhibition during osteogenesis of mesenchymal stromal cells

BACKGROUND

Magnesium is essential for numerous physiological functions. Magnesium exists mostly in bone and the amount is dynamically regulated by skeletal remodeling. Accelerating bone mass loss occurs when magnesium intake is insufficient; whereas high magnesium could lead to mineralization defects. However, the underlying magnesium regulatory mechanisms remain elusive. In the present study, we investigated the effects of high extracellular magnesium concentration on osteogenic differentiation of mesenchymal stromal/stem cells (MSCs) and the role of magnesium transporter SLC41A1 in the mineralization process.

METHODS

Murine MSCs derived from the bone marrow of BALB/c mouse or commercially purchased human MSCs were treated with osteogenic induction medium containing 5.8 mM magnesium chloride and the osteogenic differentiation efficiency was compared with that of MSCs in normal differentiation medium containing 0.8 mM magnesium chloride by cell morphology, gene expression profile of osteogenic markers, and Alizarin Red staining. Slc41a1 gene knockdown in MSCs was performed by siRNA transfection using Lipofectamine RNAiMAX, and the differentiation efficiency of siRNA-treated MSCs was also assessed.

RESULTS

High concentration of extracellular magnesium ion inhibited mineralization during osteogenic differentiation of MSCs. Early osteogenic marker genes including osterix, alkaline phosphatase, and type I collagen were significantly downregulated in MSCs under high concentration of magnesium, whereas late marker genes such as osteopontin, osteocalcin, and bone morphogenetic protein 2 were upregulated with statistical significance compared with those in normal differentiation medium containing 0.8 mM magnesium. siRNA treatment targeting SLC41A1 magnesium transporter, a member of the solute carrier family with a predominant Mg2+ efflux system, accelerated the mineralization process and ameliorated the inhibition of mineralization caused by high concentration of magnesium. High concentration of magnesium significantly upregulated Dkk1 gene expression and the upregulation was attenuated after the Slc41a1 gene was knocked down. Immunofluorescent staining showed that Slc41a1 gene knockdown promoted the translocation of phosphorylated β-catenin into nuclei. In addition, secreted MGP protein was elevated after Slc41a1 was knocked down.

CONCLUSIONS

High concentration of extracellular magnesium modulates gene expression of MSCs during osteogenic differentiation and inhibits the mineralization process. Additionally, we identified magnesium transporter SLC41A1 that regulates the interaction of magnesium and MSCs during osteogenic differentiation. Wnt signaling is suggested to be involved in SLC41A1-mediated regulation. Tissue-specific SLC41A1 could be a potential treatment for bone mass loss; in addition, caution should be taken regarding the role of magnesium in osteoporosis and the design of magnesium alloys for implantation.