Transplantation of osteoporotic bone marrow stromal cells rejuvenated by the overexpression of SATB2 prevents alveolar bone loss in ovariectomized rats. Exp Gerontol. 2016;84:71-79. [PMID: 27599698 DOI: 10.1016/j.exger.2016.09.001]

Autophagy Regulates Age-Related Jawbone Loss via LepR+ Stromal Cells

Bone aging and decreased autophagic activity are related but poorly explored in the jawbone. This study aimed to characterize the aging jawbones and jawbone-derived stromal cells (JBSCs) and determine the role of autophagy in jawbone mass decline. We observed that the jawbones of older individuals and mice exhibited similar age-related bone loss. Furthermore, leptin receptor (LepR)-lineage cells served as the primary source for in vitro cultured and expanded JBSCs, referred to as LepR-Cre+/JBSCs. RNA-sequencing data from the jawbones and LepR-Cre+/JBSCs showed the upregulated expression of the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway during aging. Through single-cell transcriptomics, we identified a decrease in the proportion of osteogenic lineage cells and the activation of the PI3K/AKT pathway in LepR-lineage cells in aging bone tissues. Reduced basal autophagic activity, diminished autophagic flux, and decreased osteogenesis occurred in the jawbones and LepR-Cre+/JBSCs from older mice (O-mice; O-JBSCs). Pharmacologic and constitutive autophagy activation alleviated the impaired osteogenesis in O-JBSCs. In addition, the suppression of mTOR-induced autophagy improved the aging phenotype of O-JBSCs. The activation of autophagy in LepR-Cre+/JBSCs using chemical autophagic activators reduced the alveolar bone resorption in O-mice. Therefore, our study demonstrated that ATG molecules and pathways are crucial in jawbone aging, providing novel approaches to understanding age-related jawbone loss.

Autophagy regulates age-related delayed jawbone regeneration and decreased osteoblast osteogenesis by degrading FABP3

The regenerative ability of limb bones after injury decreases during aging, but whether a similar phenomenon occurs in jawbones and whether autophagy plays a role in this process remain unclear. Through retrospective analysis of clinical data and studies on a mouse model of jawbone defects, we confirmed the presence of delayed or impaired bone regeneration in the jawbones of old individuals and mice. Subsequently, osteoblasts (OBs) derived from mouse jawbones were isolated, showing reduced osteogenesis in senescent osteoblasts (S-OBs). We observed a reduction in autophagy within both aged jawbones and S-OBs. Additionally, pharmacological inhibition of autophagy in normal OBs (N-OBs) led to cell aging and decreased osteogenesis, while autophagic activation reversed the aging phenotype of S-OBs. The activator rapamycin (RAPA) increased the autophagy level and bone regeneration in aged jawbones. Finally, we found that fatty acid-binding protein 3 (FABP3) was degraded by autolysosomes through its interaction with sequestosome 1 (P62/SQSTM1). Autophagy inhibition within senescent jawbones and S-OBs led to the excessive accumulation of FABP3, and FABP3 knockdown partially rescued the decreased osteogenesis in S-OBs and alleviated age-related compromised jawbone regeneration. In summary, we confirmed that autophagy inhibition plays an important role in delaying bone regeneration in aging jawbones. Autophagic activation or FABP3 knockdown can partially rescue the osteogenesis of S-OBs and the regeneration of aging jawbones, providing insight into jawbone aging.

Mesoporous bioactive glass scaffolds for the delivery of bone marrow stem cell-derived osteoinductive extracellular vesicles lncRNA promote senescent bone defect repair by targeting the miR-1843a-5p/Mob3a/YAP axis

Bone repair in elderly patients poses a huge challenge due to the age-related progressive decline in regenerative abilities attributed to the senescence of bone marrow stem cells (BMSCs). Bioactive scaffolds have been applied in bone regeneration due to their various biological functions. In this study, we aimed to fabricate functionalized bioactive scaffolds through loading osteoinductive extracellular vesicles (OI-EVs) based on mesoporous bioactive glass (MBG) scaffolds (1010 particles/scaffold) and to investigate its effects on osteogenesis and senescence of BMSCs. The results suggested that OI-EVs upregulate the proliferative and osteogenic capacities of senescent BMSCs. More importantly, The results showed that loading OI-EVs into MBG scaffolds achieved better bone regeneration. Furthermore, OI-EVs and BMSCs RNAs bioinformatics analysis indicated that OI-EVs play roles through transporting pivotal lncRNA acting as a "sponge" to compete with Mob3a for miR-1843a-5p to promote YAP dephosphorylation and nuclear translocation, ultimately resulting in elevated proliferation and osteogenic differentiation and reduced senescence-related phenotypes. Collectively, these results suggested that the OI-EVs lncRNA ceRNA regulatory networks might be the key point for senescent osteogenesis. More importantly, the study indicated the feasibility of loading OI-EVs into scaffolds and provided novel insights into biomaterial design for facilitating bone regeneration in the treatment of senescent bone defects. STATEMENT OF SIGNIFICANCE: Constructing OI-EVs/MBG delivering system and verification of its bone regeneration enhancement in senescent defect repair. Aging bone repair poses a huge challenge due to the age-related progressive degenerative decline in regenerative abilities attributed to the senescence of BMSCs. OI-EVs/MBG delivering system were expected as promising treatment for senescent bone repair, which could provide an effective strategy for bone regeneration in elderly patients. Clarification of potential OI-EVs lncRNA ceRNA regulatory mechanism in senescent bone regeneration OI-EVs play important roles through transferring lncRNA-ENSRNOG00000056625 sponging miR-1843a-5p that targeted Mob3a to activate YAP translocation into nucleus, ultimately alleviate senescence, promote proliferation and osteogenic differentiation in O-BMSCs, which provides theoretical basis for EVs-mediated therapy in future clinical works.

Mesenchymal stem cells and dental implant osseointegration during aging: from mechanisms to therapy

Dental implants are widely used to replace missing teeth, providing patients with unparalleled levels of effectiveness, convenience, and affordability. The biological basis for the clinical success of dental implants is osseointegration. Bone aging is a high-risk factor for the reduced osseointegration and survival rates of dental implants. In aged individuals, mesenchymal stem cells (MSCs) in the bone marrow show imbalanced differentiation with a reduction in osteogenesis and an increase in adipogenesis. This leads to impaired osseointegration and implant failure. This review focuses on the molecular mechanisms underlying the dysfunctional differentiation of aged MSCs, which primarily include autophagy, transcription factors, extracellular vesicle secretion, signaling pathways, epigenetic modifications, microRNAs, and oxidative stress. Furthermore, this review addresses the pathological changes in MSCs that affect osseointegration and discusses potential therapeutic interventions to enhance osseointegration by manipulating the mechanisms underlying MSC aging.

SATB2-associated syndrome: characterization of skeletal features and of bone fragility in a prospective cohort of 19 patients

Background

Individuals with pathogenic variants in SATB2 display intellectual disability, speech and behavioral disorders, dental abnormalities and often features of Pierre Robin sequence. SATB2 encodes a transcription factor thought to play a role in bone remodeling. The primary aim of our study was to systematically review the skeletal manifestations of SATB2-associated syndrome. For this purpose, we performed a non-interventional, multicenter cohort study, from 2017 to 2018. We included 19 patients, 9 females and 10 males ranging in age from 2 to 19 years-old. The following data were collected prospectively for each patient: clinical data, bone markers and calcium and phosphate metabolism parameters, skeletal X-rays and bone mineral density.

Results

Digitiform impressions were present in 8/14 patients (57%). Vertebral compression fractures affected 6/17 patients (35%). Skeletal demineralization (16/17, 94%) and cortical thinning of vertebrae (15/17) were the most frequent radiological features at the spine. Long bones were generally demineralized (18/19). The distal phalanges were short, thick and abnormally shaped. C-telopeptide (CTX) and Alkaline phosphatase levels were in the upper normal values and osteocalcin and serum procollagen type 1 amino-terminal propeptide (P1NP) were both increased. Vitamin D insufficiency was frequent (66.7%).

Conclusion

We conclude that SATB2 pathogenic variants are responsible for skeletal demineralization and osteoporosis. We found increased levels of bone formation markers, supporting the key role of SATB2 in osteoblast differentiation. These results support the need for bone evaluation in children and adult patients with SATB2-associated syndrome (SAS).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02229-5.

Transplantation of bone marrow mesenchymal stem cells and fibrin glue into extraction socket in maxilla promoted bone regeneration in osteoporosis rat

AIMS

Bone defect repair in osteoporosis remains a tremendous challenge for clinicians due to increased bone metabolism resulted from estrogen deficiency. This study aims to investigate the effect of bone marrow mesenchymal stem cells (BMSCs) combined with fibrin glue (FG) in the extraction socket healing process of osteoporosis rats, as well as estimate the role of estrogen receptors (ERs) played in BMSCs differentiation in vitro and in the alveolar bone reconstruction process in vivo.

MAIN METHODS

Forty rats were randomly divided into four groups, under general anesthesia, three groups underwent bilateral ovariectomy(OVX) and one group with the sham operation. Three months later, the osteogenic ability of BMSCs, isolated from healthy and osteoporosis rats, respectively, was tested. The ERα and ERβ mRNA expression in BMSCs was also evaluated by RT-PCR analysis. In vivo experiment, Micro-CT detection, histological and immunofluorescent analysis, tissue PCR was conducted up to 2, 4 and 6 weeks after transplantation of BMSCs/FG to assess the newly formed bone in the extraction socket.

KEY FINDINGS

The BMSCs from osteoporosis rats displayed weaker osteogenic potential and lower ERs expression compared with the BMSCs from healthy rats. Newly formed bone tissue filled the socket defect in BMSCs/FG treated VOX rats after six weeks, which was comparable to the sham group, while reduced ERs expression was found in the regenerated bone of the OVX group.

SIGNIFICANCE

The BMSCs seeded within FG might provide an alternative therapeutic method for repairing the extraction socket defect in osteoporosis condition.

Evaluation of the Efficacy of Stem Cell Therapy in Ovariectomized Osteoporotic Rats Based on Micro-CT and Dual-Energy X-Ray Absorptiometry: A Systematic Review and Meta-Analysis

Objective

Osteoporosis is an abnormal bone metabolism disease characterized by microstructural degeneration of bone tissue and reduction in bone mass, resulting in increased brittleness of bone tissue and susceptibility to fracture. Due to the tissue regenerative potential of stem cell transplantation, it is now used in the treatment of various disease models such as osteoporosis. The purpose of this work is to carry out a systematic review and meta-analysis of the efficacy of stem cell therapy in ovariectomized (OVX) osteoporotic rats.

Methods

PubMed, Cochrane Library, ScienceDirect, Embase, CNKI, and Wanfang Databases were used to search for articles that met the inclusion criteria. Two researchers independently screened the articles that met the inclusion criteria. RevMan 5.3 and STATA 16.0 were used for data analysis. This meta-analysis was registered at INPLASY with reference number ID: INPLASY202150017.

Results

Thirteen eligible studies were selected, including 405 rats. The sources of stem cells are divided into four main categories: bone marrow mesenchymal stem cells (BMSCs), adipose-derived stem cells (ADSCs), amniotic membrane mesenchymal stem cells (AM-MSCs), and human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs). Compared with the OVX group, both stem cell transplantation groups had higher bone mineral density (BMD) (BMSCs: SMD = 2.01, 95% CI: [1.38, 2.63], P < 0.001, I² = 76.6%; ADSCs: SMD = 2.24, 95% CI: [0.79, 3.69], P = 0.003, I² = 86.7%) and bone volume/total volume (BV/TV) (hUCB-MSCs: SMD = 1.71, 95% CI: [0.97, 2.44], P < 0.001, I² = 0%; ADSCs: SMD = 2.16, 95% CI: [0.27, 4.04], P = 0.025, I² = 82.6%). In the BMSC treatment groups, the trabecular numbers (Tb.N) (SMD = 4.28, 95% CI: [0.91, 7.64], P = 0.013, I² = 94.9%) were significantly higher, whereas the results for trabecular thickness (Tb.Th) (SMD = 2.7, 95% CI: [-0.34, 5.73], P = 0.081, I² = 95.4%) and trabecular spacing (Tb.Sp) (SMD = −3.08, 95% CI: [-6.55, 0.38], P = 0.081, I² = 96.3%) were not statistically significant compared to those of the OVX group. The stem cell transplantation group had a low BMD, BV/TV, and Tb.N compared to the sham operation group.

Conclusion

Stem cell therapy may increase bone strength, bone volume, and the number of trabeculae in OVX osteoporotic rats. The results of this meta-analysis showed the potential therapeutic effect of stem cell transplantation in OVX osteoporotic rats, bringing new therapeutic ideas and directions to the clinical treatment of osteoporosis. Due to the limited number and quality of studies related to some outcomes, more high-quality RCTs are still needed in the future to complement the existing findings.

Peptide 11R‑VIVIT promotes fracture healing in osteoporotic rats

Osteoporotic fracture healing is a complex clinical issue. The present study was conducted to investigate the repair properties of 11R‑VIVIT on osteoporotic fractures and to examine the potential effects of 11R‑VIVIT on osteoporotic bone marrow‑derived mesenchymal stem cells (BMSCs), A rat model of osteoporotic femoral fracture was established, and the effects of the daily local injection of 11R‑VIVIT or saline on fracture repairing were evaluated by micro‑CT scans and H&E staining. Moreover, BMSCs from osteoporotic rats were treated with 11R‑VIVIT, and the osteogenic and adipogenic differentiation of BMSCs was evaluated. The results revealed that 11R‑VIVIT promoted bone formation and increased fracture healing. In addition, 11R‑VIVIT promoted the differentiation of osteoporotic BMSCs into osteoblasts rather than adipocytes. Furthermore, mechanistic analysis revealed that 11R‑VIVIT promoted autophagy by blocking the protein kinase B (AKT)/nuclear factor of activated T‑cells (NFATc1) signaling pathway. Consistently, the activation and inhibition of autophagy using rapamycin and LY294002 confirmed the regulatory effects of 11R‑VIVIT on autophagy. On the whole, the findings of the present study demonstrate that 11R‑VIVIT promotes fracture healing in osteoporotic rats and enhances the osteogenic differentiation of osteoporotic BMSCs by dysregulating the AKT/NFATc1 signaling pathway.

A CREB1-miR-181a-5p loop regulates the pathophysiologic features of bone marrow stromal cells in fibrous dysplasia of bone

BACKGROUND

Fibrous dysplasia (FD) is a bone marrow stromal cell (BMSC) disease caused by activating mutations of guanine nucleotide-binding protein alpha-stimulating activity polypeptide (GNAS) and is characterized by increased proliferative activity and disrupted osteogenesis of BMSCs. However, the molecular mechanisms regulating the pathophysiologic features of BMSCs in FD remain unknown. This study aimed to identify and verify the roles of the CREB1-miR-181a-5p regulatory loop in FD pathophysiology.

METHODS

MicroRNA (miRNA) sequencing analysis was used to identify the possible miRNAs implicated in FD. The proliferation, apoptosis, and osteogenic differentiation of BMSCs, as well as the osteoclast-induced phenotype, were measured and compared after exogenous miR-181a-5p transfection into FD BMSCs or miR-181a-5p inhibitor transfection into normal BMSCs. Chromatin immunoprecipitation and luciferase reporter assays were performed to verify the interactions between CREB1 and miR-181a-5p and their effects on the FD pathological phenotype.

RESULTS

Compared to normal BMSCs, FD BMSCs showed decreased miR-181a-5p levels and exhibited increased proliferative activity, decreased apoptotic capacity, and impaired osteogenesis. FD BMSCs also showed a stronger osteoclast activation effect. miR-181a-5p overexpression reversed the pathophysiologic features of FD BMSCs, whereas miR-181a-5p suppression induced an FD-like phenotype in normal BMSCs. Mechanistically, miR-181a-5p was the downstream target of CREB1, and CREB1 was posttranscriptionally regulated by miR-181a-5p.

CONCLUSIONS

Our study identifies that the interaction loop between CREB1 and miR-181a-5p plays a crucial role in regulating the pathophysiologic features of FD BMSCs. MiR-181a-5p may be a potential therapeutic target for the treatment of FD.

Knockdown of hsa_circ_0001275 reverses dexamethasone-induced osteoblast growth inhibition via mediation of miR-377/CDKN1B axis

BACKGROUND

Osteoporosis affects the quality of life among middle-aged and elderly individuals. In addition, dysfunction of osteoblasts can lead to the progression of osteoporosis. Circular (circ)RNAs are involved in various types of diseases, including osteoporosis. Moreover, it has been reported that hsa_circ_0001275 expression is upregulated in osteoporosis. However, the effects of hsa_circ_0001275 on the growth of osteoblasts remain unclear.

METHODS

In the present study, the gene and protein expression levels in hFOB1.19 cells were detected via reverse transcription-quantitative (RT-qPCR) and western blot analyses, respectively. In addition, alkaline phosphatase (ALP) activity and calcium nodules were examined by ALP and alizarin red staining, respectively. Cell proliferation was measured using the Cell Counting Kit-8 assay. Cell apoptosis and cell cycle were analyzed by flow cytometry. Furthermore, dual luciferase reporter and RNA pull-down assay were used to confirm the association among hsa_circ_0001275, microRNA (miR)-377 and CDKN1B.

RESULTS

DEX-induced hFOB1.19 cell growth inhibition was significantly reversed by silencing hsa_circ_0001275. Moreover, DEX significantly increased ALP activity and calcium nodules in hFOB1.19 cells, while this effect was significantly reversed in the presence of hsa_circ_0001275 small interfering RNA. In addition, miR-377 was sponged by hsa_circ_0001275 and CDKN1B was directly targeted by miR-377 in hFOB1.19 cells. Furthermore, the therapeutic effect of hsa_circ_0001275 knockdown on osteoporosis was notably reversed by miR-377 antagomir.

CONCLUSION

The data demonstrated that knockdown of hsa_circ_0001275 reversed DEX-induced osteoblast growth inhibition via activation of the miR-377/CDKN1B axis. Therefore, this study might shed new lights on the treatment of osteoporosis.

SATB2: A versatile transcriptional regulator of craniofacial and skeleton development, neurogenesis and tumorigenesis, and its applications in regenerative medicine

SATB2 (special AT-rich sequence-binding protein 2) is a member of the special AT-rich binding protein family. As a transcription regulator, SATB2 mainly integrates higher-order chromatin organization. SATB2 expression appears to be tissue- and stage-specific, and is governed by several cellular signaling molecules and mediators. Expressed in branchial arches and osteoblast-lineage cells, SATB2 plays a significant role in craniofacial pattern and skeleton development. In addition to regulating osteogenic differentiation, SATB2 also displays versatile functions in neural development and cancer progression. As an osteoinductive factor, SATB2 holds great promise in improving bone regeneration toward bone defect repair. In this review, we have summarized our current understanding of the physiological and pathological functions of SATB2 in craniofacial and skeleton development, neurogenesis, tumorigenesis and regenerative medicine.

Metformin promotes the osseointegration of titanium implants under osteoporotic conditions by regulating BMSCs autophagy, and osteogenic differentiation

Osteoporosis is a common bone disorder with adverse effects on oral osseointegration, and the effects of metformin on bone metabolism have received increasing attention. The aim of the present study was to test the hypothesis that metformin promoted osteogenesis of bone mesenchymal stem cells (BMSCs) and osseointegration of titanium implants. BMSCs were treated with metformin to assess autophagic capacity, reactive oxygen species (ROS) production, anti-aging ability, and osteogenic differentiation. To determine its potential application in peri-implant of the maxilla, metformin was injected around the implant each day, immediately after the implant was embedded into the tooth socket. The results showed that metformin increased the autophagic capacity and decreased ROS production of osteoporotic BMSCs under hypoxia and serum deprivation (H/SD) culturing conditions. Metformin treatment significantly enhanced stemness properties and mineralized nodule formation, and increased the expression of osteogenic markers, including runt related transcription factor 2 (Runx2), osteocalcin (OCN), and alkaline phosphatase (ALP). Moreover, metformin substantially accelerated the formation of new bone, ameliorated the bone microarchitecture and promoted osseointegration of the dental implant. Collectively, metformin induces an osteogenic effect around the implant. Considering the widespread use of metformin, the results of the present study might promote a novel understanding of the positive effects of local metformin delivery on alveolar ridge defect, and have potential clinical application for the acceleration of osseointegration.

Age-dependent role of SIRT6 in jawbone via regulating senescence and autophagy of bone marrow stromal cells

Age-related jawbone loss directly impact the function of oral cavity resulted from tooth loss, implant failure, and jaw fracture. Numerous evidences show that age-related senescence of bone marrow stromal cells (BMSCs) play a critical role in bone loss, but little attention has been paid to jawbone. Here, we delineated the critical role of sirtuin family protein 6 (SIRT6) in senescence, autophagy, and osteogenesis of BMSCs from jawbones. Radiography analysis showed less jawbone quality in elderly than young people. We also showed that SIRT6 expression decreased in bone tissue and BMSCs from the elderly by immunochemical staining. BMSCs from the elderly exhibited decreased osteogenic differentiation and inclined senescence which these phenotypes could be simulated by SIRT6 knockdown. Furthermore, accompanied with the inhibition of SIRT6, the autophagy level and ostogenesis of BMSCs was also decreased. However, using rapamycin, an autophagy activator, could rescue these adverse effects of BMSCs caused by SIRT6 inhibition. Mechanistically, SIRT6 regulated the autophagy and osteogenesis of BMSCs by activating AKT-mTOR pathway, at least in part. Finally, a decreased jawbone quality was shown in SIRT6 haploinsufficiency mice by Wnt1 specific tissue knockdown (Wnt1-Cre;SIRT6^fl/+) model. Taken together, our data revealed that SIRT6 adjusted senescence and osteogenesis of BMSCs via altering autophagy level, and associated with age-related bone loss. SIRT6 could be as a promising therapeutic target for age-related osteoporosis of jawbone.

Role of p53 deficiency in socket healing after tooth extractions

p53 is known to advance the cell arrest and cell senescence in human tumors. In this study, we displayed that osteogenic ability of p53-knockout (p53^-/-) mice was significantly increased in the tooth extraction socket compared with wild-type (WT) counterparts. Bone marrow mesenchymal stem cells (BM-MSCs) from mandibular were collected and exhibited with elevated proliferation potential and colony-forming units compared with the control, as well as stronger mineral deposits and osteogenic markers. Besides, the bone mass and bone parameter in p53^-/- mice were markedly enhanced compared with the counterpart after extractions by micro-CT. Masson's trichrome staining and immunohistochemistry also revealed that new bone filling and osterix/osteocalcin (Osx/OCN)-immunopositive staining in p53^-/- mice were remarkably increased at each time point. Furthermore, consistent with the enhanced osteogenic markers, the angiogenic marker of blood vessels (alpha smooth muscle actin, α-SMA) was significantly elevated in p53^-/- mice in contrast to WT mice. Importantly, we found that the osteoclast numbers exhibited an increased trend in p53^-/- mice compared with WT mice during socket healing. Collectively, our result suggest that p53 deficiency could promote the osteogenesis and angiogenesis in the tooth extraction socket and might lend possibility for p53-based therapeutic approaches in acceleration of extraction bone healing.

Bone mesenchymal stem cell therapy for ovariectomized osteoporotic rats: a systematic review and meta-analysis

Background

Previous studies have found that bone mesenchymal stem cells (BMSCs) were capable of self-replication, multi-differentiation, and regeneration. The aim of this study was to carry out a systematic review and meta-analysis of the efficacy of BMSC therapy for ovariectomized rats.

Methods

The PubMed, Embase, Web of Science, China National Knowledge Infrastructure, VIP, and Chinese Sinomed databases were searched systematically from their initiation date to October 5, 2018. Two researchers independently screened the literatures, which used the bone mineral density (BMD), total bone volume by total tissue volume (BV/TV) (%), and trabecular thickness/spacing (Tb/Sp) as the outcome measures.

Results

Five eligible studies were selected. In the BMSC treatment groups, the BMD values and normalized BV/TV values remarkably increased. In addition, in the BMSCs plus other treatment groups, the BMD and Tb/Sp values significantly increased.

Conclusion

This study showed that BMSCs could accelerate callus maturity, ossification and restore mechanical properties of bones in osteoporotic fractures.

Effect of aging on behaviour of mesenchymal stem cells

Organs whose source is the mesoderm lineage contain a subpopulation of stem cells that are able to differentiate among mesodermal derivatives (chondrocytes, osteocytes, adipocytes). This subpopulation of adult stem cells, called "mesenchymal stem cells" or "mesenchymal stromal cells (MSCs)", contributes directly to the homeostatic maintenance of their organs; hence, their senescence could be very deleterious for human bodily functions. MSCs are easily isolated and amenable their expansion in vitro because of the research demanding to test them in many diverse clinical indications. All of these works are shown by the rapidly expanding literature that includes many in vivo animal models. We do not have an in-depth understanding of mechanisms that induce cellular senescence, and to further clarify the consequences of the senescence process in MSCs, some hints may be derived from the study of cellular behaviour in vivo and in vitro, autophagy, mitochondrial stress and exosomal activity. In this particular work, we decided to review these biological features in the literature on MSC senescence over the last three years.

Tanshinone prevents alveolar bone loss in ovariectomized osteoporosis rats by up-regulating phosphoglycerate dehydrogenase

Osteoporosis is manifested by reduced bone mass. Tanshinone has been shown to affect osteoclast differentiation, but its role in osteoporosis remains less clear. This study aimed to investigate the effects and molecular mechanisms of tanshinone on osteoporosis. Osteoporosis was induced by bilateral ovariectomy (OVX) in adult female rats treated with or without tanshinone. Trabecular bone structure was assessed by micro-computed tomography (micro-CT). Bone marrow stromal cells (BMSCs) were isolated for analysis of stemness and senescence. mRNA levels of age related genes were examined and the role of the gene that was upregulated by tanshinone treatment was suppressed to determine its involvement in tanshinone mediated effects. Finally, the mechanism underlying tanshinone induced gene upregulation was explored. We found that tanshinone treatment restored alveolar bone structure in OVX rats as well as the stemness and senescence status of BMSCs isolated from OVX rats. Tanshinone upregulated Phgdh mRNA levels and inhibition of phosphoglycerate dehydrogenase Phgdh, the protein encoded by the Phgdh gene, abolished the effects of tanshinone on BMSC stemness and senescence. Finally, we found that OVX lead to hypermethylation of the promoter region of Phgdh which was suppressed by tanshinone treatment. Our study shows that tanshinone potently suppress OVX induced osteoporosis and BMSC senescence through upregulation of PHGDH.

Connexin 43 hemichannels protect bone loss during estrogen deficiency

Estrogen deficiency in postmenopausal women is a major cause of bone loss, resulting in osteopenia, osteoporosis, and a high risk for bone fracture. Connexin 43 (Cx43) hemichannels (HCs) in osteocytes play an important role in osteocyte viability, bone formation, and remodeling. We showed here that estrogen deficiency reduced Cx43 expression and HC function. To determine if functional HCs protect osteocytes and bone loss during estrogen deficiency, we adopted an ovariectomy model in wild-type (WT) and two transgenic Cx43 mice: R76W (dominant-negative mutant inhibiting only gap junction channels) and Cx43 Δ130–136 (dominant-negative mutant compromising both gap junction channels and HCs). The bone mineral density (BMD), bone structure, and histomorphometric changes of cortical and trabecular bones after ovariectomy were investigated. Our results showed that the Δ130–136 transgenic cohort had greatly decreased vertebral trabecular bone mass compared to WT and R76W mice, associated with a significant increase in the number of apoptotic osteocyte and empty lacunae. Moreover, osteoclast surfaces in trabecular and cortical bones were increased after ovariectomy in the R76W and WT mice, respectively, but not in ∆130–136 mice. These data demonstrate that impairment of Cx43 HCs in osteocytes accelerates vertebral trabecular bone loss and increase in osteocyte apoptosis, and further suggest that Cx43 HCs in osteocytes protect trabecular bone against catabolic effects due to estrogen deficiency.

Channels that form between cells and their extracellular environment help protect bone tissue from the damage wrought by low estrogen levels, a major cause of bone loss in post-menopausal women. Jean Jiang from the UT Health San Antonio and colleagues showed that depleting the estrogen hormone in mouse bone cells reduced levels of connexin 43 and impaired the protein’s ability to forms pores known as ‘hemichannels’. The researchers surgically removed the ovaries of various mouse strains to induce estrogen deficiencies. They found that transgenic mice without working hemichannels had reduced bone mass compared to normal mice or mice that could make hemichannels but lacked the ability for those channels to come together to form complete passageways. The findings highlight the importance of connexin 43 hemichannels in protecting bone tissue against osteoporosis.

Zoledronic acid promotes TLR-4-mediated M1 macrophage polarization in bisphosphonate-related osteonecrosis of the jaw

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a detrimental side effect of the long-term administration of bisphosphonates. Although macrophages were reported to be an important mediator of BRONJ, the detailed potential mechanism of BRONJ remains unclear. Here, we reported an elevated TLR-4 expression in macrophages under action of zoledronic acid (ZA), resulting in enhanced M1 macrophage polarization and decreased M2 macrophage polarization both in vitro and in vivo. After inhibiting the TLR-4 signaling pathway, the activation of the TLR-4/NF-κB signaling pathway and the induction of NF-κB nuclear translocation and production of proinflammatory cytokines by ZA were suppressed in macrophages, thereby inhibiting M1 macrophage polarization. By utilizing the TLR-4^-/- mice, development of BRONJ was markedly ameliorated, and M1 macrophages were significantly attenuated in the extraction socket tissues in the TLR-4^-/- mice. Importantly, the systemic administration of the TLR-4 inhibitor TAK-242 improved the wound healing of the extraction socket and decreased the incidence rate of BRONJ. Taken together, our findings suggest that TLR-4-mediated macrophage polarization participates in the pathogenesis of BRONJ in mice, and TLR-4 may be a potential target for the prevention and therapeutic treatment of BRONJ.-Zhu, W., Xu, R., Du, J., Fu, Y., Li, S., Zhang, P., Liu, L., Jiang, H. Zoledronic acid promotes TLR-4-mediated M1 macrophage polarization in bisphosphonate-related osteonecrosis of the jaw.

HDAC8, A Potential Therapeutic Target, Regulates Proliferation and Differentiation of Bone Marrow Stromal Cells in Fibrous Dysplasia

Fibrous dysplasia (FD) is a disease of postnatal skeletal stem cells caused by activating mutations of guanine nucleotide-binding protein alpha-stimulating activity polypeptide (GNAS). FD is characterized by high proliferation and osteogenesis disorder of bone marrow stromal cells (BMSCs), resulting in bone pain, deformities, and fractures. The cAMP-CREB pathway, which is activated by GNAS mutations, is known to be closely associated with the occurrence of FD. However, so far there is no available targeted therapeutic strategy for FD, as a critical issue that remains largely unknown is how this pathway is involved in FD. Our previous study revealed that histone deacetylase 8 (HDAC8) inhibited the osteogenic differentiation of BMSCs via epigenetic regulation. Here, compared with normal BMSCs, FD BMSCs exhibited significantly high proliferation and weak osteogenic capacity in response to HDAC8 upregulation and tumor protein 53 (TP53) downregulation. Moreover, inhibition of cAMP reduced HDAC8 expression, increased TP53 expression and resulted in the improvement of FD phenotype. Importantly, HDAC8 inhibition prevented cAMP-induced cell phenotype and promoted osteogenesis in nude mice that were implanted with FD BMSCs. Mechanistically, HDAC8 was identified as a transcriptional target gene of CREB1 and its transcription was directly activated by CREB1 in FD BMSCs. In summary, our study reveals that HDAC8 associates with FD phenotype and demonstrates the mechanisms regulated by cAMP-CREB1-HDAC8 pathway. These results provide insights into the molecular regulation of FD pathogenesis, and offer novel clues that small molecule inhibitors targeting HDAC8 are promising clinical treatment for FD. Stem Cells Translational Medicine 2019;8:148&14.

MicroRNA-31a-5p from aging BMSCs links bone formation and resorption in the aged bone marrow microenvironment

The alteration of age‐related molecules in the bone marrow microenvironment is one of the driving forces in osteoporosis. These molecules inhibit bone formation and promote bone resorption by regulating osteoblastic and osteoclastic activity, contributing to age‐related bone loss. Here, we observed that the level of microRNA‐31a‐5p (miR‐31a‐5p) was significantly increased in bone marrow stromal cells (BMSCs) from aged rats, and these BMSCs demonstrated increased adipogenesis and aging phenotypes as well as decreased osteogenesis and stemness. We used the gain‐of‐function and knockdown approach to delineate the roles of miR‐31a‐5p in osteogenic differentiation by assessing the decrease of special AT‐rich sequence‐binding protein 2 (SATB2) levels and the aging of BMSCs by regulating the decline of E2F2 and recruiting senescence‐associated heterochromatin foci (SAHF). Notably, expression of miR‐31a‐5p, which promotes osteoclastogenesis and bone resorption, was markedly higher in BMSCs‐derived exosomes from aged rats compared to those from young rats, and suppression of exosomal miR‐31a‐5p inhibited the differentiation and function of osteoclasts, as shown by elevated RhoA activity. Moreover, using antagomiR‐31a‐5p, we observed that, in the bone marrow microenvironment, inhibition of miR‐31a‐5p prevented bone loss and decreased the osteoclastic activity of aged rats. Collectively, our results reveal that miR‐31a‐5p acts as a key modulator in the age‐related bone marrow microenvironment by influencing osteoblastic and osteoclastic differentiation and that it may be a potential therapeutic target for age‐related osteoporosis.