Hypoxia reduces the osteogenic differentiation of peripheral blood mesenchymal stem cells by upregulating Notch-1 expression

Low-dose radiation-induced SUMOylation of NICD1 negatively regulates osteogenic differentiation in BMSCs

Various biological effects of ionizing radiation, especially continuous exposure to low-dose radiation (LDR), have attracted considerable attention. Impaired bone structure caused by LDR has been reported, but little is known about the mechanism involved in the disruption of bone metabolism. In this study, given that LDR was found to (at a cumulative dose of 0.10 Gy) disturb the serum Mg2+ level and Notch1 signal in the mouse femur tissues, the effects of LDR on osteogenesis and the underlying molecular mechanisms were investigated based on an in vitro culture system for bone marrow stromal cells (BMSCs). Our data showed that cumulative LDR suppressed the osteogenic potential in BMSCs as a result of upregulation of Notch1 signaling. Further analyses indicated that the upregulation of NICD1 (Notch1 intracellular domain), the key intracellular domain for Notch1 signaling, under LDR was a consequence of enhanced protein stabilization caused by SUMOylation (small ubiquitin-like modification). Specifically, the downregulation of SENP1 (sentrin/SUMO-specific protease 1) expression induced by LDR enhanced the SUMOylation of NICD1, causing the accumulation of Notch1 signaling, which eventually inhibited the osteogenic potential of BMSCs. In conclusion, this work expounded on the mechanisms underlying the impacts of LDR on bone metabolism and shed light on the research on bone regeneration under radiation.

Research progress in the pathogenesis of hormone-induced femoral head necrosis based on microvessels: a systematic review

Hormonal necrosis of the femoral head is caused by long-term use of glucocorticoids and other causes of abnormal bone metabolism, lipid metabolism imbalance and blood microcirculation disorders in the femoral head, resulting in bone trabecular fracture, bone tissue necrosis collapse, and hip dysfunction. It is the most common type of non-traumatic necrosis of the femoral head, and its pathogenesis is complex, while impaired blood circulation is considered to be the key to its occurrence. There are a large number of microvessels in the femoral head, among which H-type vessels play a decisive role in the "angiogenesis and osteogenesis coupling", and thus have an important impact on the occurrence and development of femoral head necrosis. Glucocorticoids can cause blood flow injury of the femoral head mainly through coagulation dysfunction, endothelial dysfunction and impaired angiogenesis. Glucocorticoids may inhibit the formation of H-type vessels by reducing the expression of HIF-1α, PDGF-BB, VGEF and other factors, thus causing damage to the "angiogenesis-osteogenesis coupling" and reducing the ability of necrosis reconstruction and repair of the femoral head. Leads to the occurrence of hormonal femoral head necrosis. Therefore, this paper reviewed the progress in the study of the mechanism of hormone-induced femoral head necrosis based on microvascular blood flow at home and abroad, hoping to provide new ideas for the study of the mechanism of femoral head necrosis and provide references for clinical treatment of femoral head necrosis.

ICA/SDF-1α/PBMSCs loaded onto alginate and gelatin cross-linked scaffolds promote damaged cartilage repair

A three-dimensional alginate-coated scaffold (GAIS) was constructed in the present study to showcase the multidifferentiation potential of peripheral blood mesenchymal stem cells (PBMSCs) and to investigate the role and mechanism by which Icariin (ICA)/stromal cell-derived factor (SDF-1α)/PBMSCs promote damaged articular repair. In addition, the ability of ICA, in combination with SDF-1α, to promote the migration and proliferation of stem cells was validated through the utilization of CCK-8 and migration experiments. The combination of ICA and SDF-1α inhibited the differentiation of PBMSCs into cartilage, as demonstrated by in vivo experiments and histological staining. Both PCR and western blot experiments showed that GAIS could upregulate the expression of particular genes in chondrocytes. In comparison to scaffolds devoid of alginate (G0), PBMSCs seeded into GAIS scaffolds exhibited a greater rate of proliferation, and the conditioned medium derived from scaffolds containing SDF-1α enhanced the capacity for cell migration. Moreover, after a 12-week treatment period, GAIS, when successfully transplanted into osteochondral defects of mice, was found to promote cartilage regeneration and repair. The findings, therefore, demonstrate that GAIS enhanced the in vitro capabilities of PBMSCs, including proliferation, migration, homing and chondrogenic differentiation. In addition, ICA and SDF-1α effectively collaborated to support cartilage formation in vivo. Thus, the ICA/SDF-1α/PBMSC-loaded biodegradable alginate-gelatin scaffolds showcase considerable potential for use in cartilage repair.

3D-Printed Magnesium Peroxide-Incorporated Scaffolds with Sustained Oxygen Release and Enhanced Photothermal Performance for Osteosarcoma Multimodal Treatments

The hypoxic microenvironment in osteosarcoma inevitably compromises the antitumor effect and local bone defect repair, suggesting an urgent need for sustained oxygenation in the tumor. The currently reported oxygen-releasing materials have short oxygen-releasing cycles, harmful products, and limited antitumor effects simply by improving hypoxia. Therefore, the PCL/nHA/MgO2/PDA-integrated oxygen-releasing scaffold with a good photothermal therapy effect was innovatively constructed in this work to achieve tumor cell killing and bone regeneration functions simultaneously. The material distributes MgO2 powder evenly on the scaffold material through 3D printing technology and achieves the effect of continuous oxygen release (more than 3 weeks) through its slow reaction with water. The in vitro and in vivo results also indicate that the scaffold has good biocompatibility and sustained-release oxygen properties, which can effectively induce the proliferation and osteogenic differentiation of bone mesenchymal stem cells, achieving excellent bone defect repair. At the same time, in vitro cell experiments and subcutaneous tumorigenesis experiments also confirmed that local oxygen supply can promote osteosarcoma cell apoptosis, inhibit proliferation, and reduce the expression of heat shock protein 60, thereby enhancing the photothermal therapy effect of polydopamine and efficiently eliminating osteosarcoma. Taken together, this integrated functional scaffold provides a unique and efficient approach for antitumor and tumor-based bone defect repair for osteosarcoma treatment.

Stimulating factors for regulation of osteogenic and chondrogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs), distributed in many tissues in the human body, are multipotent cells capable of differentiating in specific directions. It is usually considered that the differentiation process of MSCs depends on specialized external stimulating factors, including cell signaling pathways, cytokines, and other physical stimuli. Recent findings have revealed other underrated roles in the differentiation process of MSCs, such as material morphology and exosomes. Although relevant achievements have substantially advanced the applicability of MSCs, some of these regulatory mechanisms still need to be better understood. Moreover, limitations such as long-term survival in vivo hinder the clinical application of MSCs therapy. This review article summarizes current knowledge regarding the differentiation patterns of MSCs under specific stimulating factors.

The Role of HIF-1α in Bone Regeneration: A New Direction and Challenge in Bone Tissue Engineering

The process of repairing significant bone defects requires the recruitment of a considerable number of cells for osteogenesis-related activities, which implies the consumption of a substantial amount of oxygen and nutrients. Therefore, the limited supply of nutrients and oxygen at the defect site is a vital constraint that affects the regenerative effect, which is closely related to the degree of a well-established vascular network. Hypoxia-inducible factor (HIF-1α), which is an essential transcription factor activated in hypoxic environments, plays a vital role in vascular network construction. HIF-1α, which plays a central role in regulating cartilage and bone formation, induces vascular invasion and differentiation of osteoprogenitor cells to promote and maintain extracellular matrix production by mediating the adaptive response of cells to changes in oxygen levels. However, the application of HIF-1α in bone tissue engineering is still controversial. As such, clarifying the function of HIF-1α in regulating the bone regeneration process is one of the urgent issues that need to be addressed. This review provides insight into the mechanisms of HIF-1α action in bone regeneration and related recent advances. It also describes current strategies for applying hypoxia induction and hypoxia mimicry in bone tissue engineering, providing theoretical support for the use of HIF-1α in establishing a novel and feasible bone repair strategy in clinical settings.

Insight into the effect of biomaterials on osteogenic differentiation of mesenchymal stem cells: A review from a mitochondrial perspective

Bone damage may be triggered by a variety of factors, and the damaged area often requires a bone graft. Bone tissue engineering can serve as an alternative strategy for repairing large bone defects. Mesenchymal stem cells (MSCs), the progenitor cells of connective tissue, have become an important tool for tissue engineering due to their ability to differentiate into a variety of cell types. The precise regulation of the growth and differentiation of the stem cells used for bone regeneration significantly affects the efficiency of this type of tissue engineering. During the process of osteogenic induction, the dynamics and function of localized mitochondria are altered. These changes may also alter the microenvironment of the therapeutic stem cells and result in mitochondria transfer. Mitochondrial regulation not only affects the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell. To date, bone tissue engineering research has mainly focused on the influence of biomaterials on phenotype and nuclear genotype, with few studies investigating the role of mitochondria. In this review, we provide a comprehensive summary of researches into the role of mitochondria in MSCs differentiation and critical analysis regarding smart biomaterials that are able to "programme" mitochondria modulation was proposed. STATEMENT OF SIGNIFICANCE: : • This review proposed the precise regulation of the growth and differentiation of the stem cells used to seed bone regeneration. • This review addressed the dynamics and function of localized mitochondria during the process of osteogenic induction and the effect of mitochondria on the microenvironment of stem cells. • This review summarized biomaterials which affect the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell through the regulation of mitochondria.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

β-Catenin promotes long-term survival and angiogenesis of peripheral blood mesenchymal stem cells via the Oct4 signaling pathway

Stem cell therapy has been extensively studied to improve heart function following myocardial infarction; however, its therapeutic potency is limited by low rates of engraftment, survival, and differentiation. Here, we aimed to determine the roles of the β-catenin/Oct4 signaling axis in the regulation of long-term survival and angiogenesis of peripheral blood mesenchymal stem cells (PBMSCs). These cells were obtained from rat abdominal aortic blood. We showed that β-catenin promotes the self-renewal, antiapoptotic effects, and long-term survival of PBMSCs by activating the Oct4 pathway through upregulation of the expression of the antiapoptotic factors Bcl2 and survivin and the proangiogenic cytokine bFGF and suppression of the levels of the proapoptotic factors Bax and cleaved caspase-3. β-Catenin overexpression increased Oct4 expression. β-Catenin knockdown suppressed Oct4 expression in PBMSCs. However, β-catenin levels were not affected by Oct4 overexpression or knockdown. Chromatin immunoprecipitation assays proved that β-catenin directly regulates Oct4 transcription in PBMSCs. In vivo, PBMSCs overexpressing β-catenin showed high survival in infarcted hearts and resulted in better myocardial repair. Further functional analysis identified Oct4 as the direct upstream regulator of Ang1, bFGF, HGF, VEGF, Bcl2, and survivin, which cooperatively drive antiapoptosis and angiogenesis of engrafted PBMSCs. These findings revealed the regulation of β-catenin in PBMSCs by the Oct4-mediated antiapoptotic/proangiogenic signaling axis and provide a breakthrough point for improving the long-term survival and therapeutic effects of PBMSCs.

Boosting expression of a specific gene has allowed researchers to generate stem cells with increased capacity for tissue repair after a heart attack. Several studies have shown that treatment with a population of circulating cells known as ‘peripheral blood mesenchymal stem cells’ (PBMSCs) can regenerate cardiac tissue. These cells generally have a short lifespan when used therapeutically, but researchers led by Shaoheng Zhang at Jinan University in Guangzhou China have increased long-term survival and performance by boosting expression of the gene encoding β-catenin, a protein that promotes cell survival and proliferation. PBMSCs expressing increased levels of β-catenin preserved heart function in a rat model of heart attack, stimulating blood vessel growth and improving animal survival. This study also reveals proteins regulated by β-catenin, which could potentially be exploited for finer control of PBMSC function.

How the mechanical microenvironment of stem cell growth affects their differentiation: a review

Stem cell differentiation is of great interest in medical research; however, specifically and effectively regulating stem cell differentiation is still a challenge. In addition to chemical factors, physical signals are an important component of the stem cell ecotone. The mechanical microenvironment of stem cells has a huge role in stem cell differentiation. Herein, we describe the knowledge accumulated to date on the mechanical environment in which stem cells exist, which consists of various factors, including the extracellular matrix and topology, substrate stiffness, shear stress, hydrostatic pressure, tension, and microgravity. We then detail the currently known signalling pathways that stem cells use to perceive the mechanical environment, including those involving nuclear factor-kB, the nicotinic acetylcholine receptor, the piezoelectric mechanosensitive ion channel, and hypoxia-inducible factor 1α. Using this information in clinical settings to treat diseases is the goal of this research, and we describe the progress that has been made. In this review, we examined the effects of mechanical factors in the stem cell growth microenvironment on stem cell differentiation, how mechanical signals are transmitted to and function within the cell, and the influence of mechanical factors on the use of stem cells in clinical applications.

Osteostatin improves the Osteogenic differentiation of mesenchymal stem cells and enhances angiogenesis through HIF-1α under hypoxia conditions in vitro

BACKGROUND

Hypoxia conditions induced by bone defects would prolong the duration of bone regeneration. The effect of osteostatin (OST) on the osteogenic differentiation of mesenchymal stem cells (MSCs) and angiogenesis under hypoxia conditions remain unexplored.

METHODS

SPF mice were obtained, and MSCs were isolated from bone marrow. MSCs were treated with 1% oxygen for hypoxia induction, and 200 nM of OST was used to treat cells under nomorxia or hypoxia conditions. Cell proliferation was evaluated using CCK8 assay, and trypan blue staining was implemented for determining cell death ratio. Alkaline phosphatase activity and alizarin redS staining was conducted to histologically evaluated osteogenic differentiation. Flow cytometry was used for the detection of CD31^hiEmcn^hi cells (Type H ECs), whose migration was detected by Transwell assay and angiogenesis was measured by tube formation assay. Protein level was measured by western blotting and mRNA level was monitored via RT-qPCR.

RESULTS

The MSC proliferation was enhanced by OST under hypoxia conditions. The osteogenic differentiation of MSCs was decreased under hypoxia conditions, and treatment of OST significantly reversed its inhibitory effect. The hypoxia treated culture medium of MSCs promoted the proliferation, migration, and angiogenesis of type H ECs, while the effects were further strengthened by OST addition. HIF-1α was found to be upregulated in hypoxia treated MSCs, whereas silencing of HIF-1α had reversed effects on the angiogenic capacity of Type H ECs.

CONCLUSION

OST improved the proliferation and osteogenic differentiation of MSCs and further promoted angiogenesis of type H ECs through upregulating HIF-1α expression.

Recent Advances in Enhancement Strategies for Osteogenic Differentiation of Mesenchymal Stem Cells in Bone Tissue Engineering

Although bone is an organ that displays potential for self-healing after damage, bone regeneration does not occur properly in some cases, and it is still a challenge to treat large bone defects. The development of bone tissue engineering provides a new approach to the treatment of bone defects. Among various cell types, mesenchymal stem cells (MSCs) represent one of the most promising seed cells in bone tissue engineering due to their functions of osteogenic differentiation, immunomodulation, and secretion of cytokines. Regulation of osteogenic differentiation of MSCs has become an area of extensive research over the past few years. This review provides an overview of recent research progress on enhancement strategies for MSC osteogenesis, including improvement in methods of cell origin selection, culture conditions, biophysical stimulation, crosstalk with macrophages and endothelial cells, and scaffolds. This is favorable for further understanding MSC osteogenesis and the development of MSC-based bone tissue engineering.

The Proliferation and Stemness of Peripheral Blood-Derived Mesenchymal Stromal Cells Were Enhanced by Hypoxia

This study aimed to address the dilemma of low peripheral blood-derived mesenchymal stromal cell (PBMSC) activity and reduced phenotype in bone or cartilage tissue engineering. Rat PBMSCs (rPBMSCs) were obtained by density gradient centrifugation, and stromal cell characteristics were confirmed by flow cytometry (FCM) and multi-differentiation potential induction experiments. Cell growth curve, viability experiments, and clone formation experiments were performed by [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) and cell counting, and the cell cycle was confirmed by cell FCM. The proliferation signal pathway and stemness-related proteins were detected by molecular methods including Western blot and real-time polymerase chain reaction. CD73, CD90, and CD105 were highly expressed, and CD14, CD19, CD34, CD45, and HLA-DR were barely expressed in rPBMSCs. rPBMSCs possessed the potential to differentiate into chondrocytes, adipocytes, and osteoblasts under their respective induction conditions. Cell growth curve and viability experiments were performed under hypoxic conditions: 19% O₂, 5% O₂, and 1% O₂. Specifically, 5% O₂ accelerated the proliferation and expression of the stemness of PBMSCs. Cycle experiments proved that hypoxia promoted the cell transition from the G1 phase to the S phase. Molecular experiments confirmed that 5% O₂ hypoxia significantly elevated the expressions of hypoxia-inducible factor 1α and β-catenin and simultaneously the expressions of cycle-related genes including CyclinE/CDK2 and stemness-related genes including Nanog and SOX2. The appropriate concentration of hypoxia (i.e., 5% O₂) enhanced the proliferation and stemness of rPBMSCs and increased the multidirectional differentiation potential of stromal cells. The proposed culture method could improve the viability and maintain the phenotype of rPBMSCs in cartilage or bone tissue engineering.

Bone defect reconstruction via endochondral ossification: A developmental engineering strategy

Traditional bone tissue engineering (BTE) strategies induce direct bone-like matrix formation by mimicking the embryological process of intramembranous ossification. However, the clinical translation of these clinical strategies for bone repair is hampered by limited vascularization and poor bone regeneration after implantation in vivo. An alternative strategy for overcoming these drawbacks is engineering cartilaginous constructs by recapitulating the embryonic processes of endochondral ossification (ECO); these constructs have shown a unique ability to survive under hypoxic conditions as well as induce neovascularization and ossification. Such developmentally engineered constructs can act as transient biomimetic templates to facilitate bone regeneration in critical-sized defects. This review introduces the concept and mechanism of developmental BTE, explores the routes of endochondral bone graft engineering, highlights the current state of the art in large bone defect reconstruction via ECO-based strategies, and offers perspectives on the challenges and future directions of translating current knowledge from the bench to the bedside.

3D printed polycaprolactone/beta-tricalcium phosphate/magnesium peroxide oxygen releasing scaffold enhances osteogenesis and implanted BMSCs survival in repairing the large bone defect

Ischemia and hypoxia in the bone defect area remain an intractable problem when treating large bone defects. Thus, oxygen-releasing biomaterials have been widely researched in recent years. Magnesium peroxide (MgO2) can release oxygen (O2), and magnesium ions (Mg2+), simultaneously, which is seen to have significant potential in bone substitutes. In this study, we used 3D printing technology to fabricate a MgO2-contained composite scaffold, which was composed of polycaprolactone (PCL), beta-tricalcium phosphate (β-TCP) and magnesium peroxide (MgO2). Physical properties and O2/Mg2+ releasing behavior of the scaffold were studied. Then, we evaluated the effects of the scaffold on cell survival, proliferation, migration, adhesion and osteogenic differentiation by the co-culture of bone marrow mesenchymal stem cells (BMSCs) and scaffold under normoxia and hypoxia in vitro. Finally, the osteogenic properties of the scaffold in vivo were evaluated via the rat femoral condylar bone defect model. The PCL/β-TCP/MgO2 scaffold showed good mechanical properties and sustained O2 and Mg2+ release for about three weeks. Meanwhile, the scaffold showed appreciable promotion on the survival, proliferation, migration and osteogenic differentiation of BMSCs under hypoxia compared with control groups. The results of imaging studies and histological analysis showed that implantation of PCL/β-TCP/MgO2 scaffold could promote seed cell survival and significantly increased new bone formation. In sum, the PCL/β-TCP/MgO2 scaffold is promising with great potential for treating large bone defects.

The mechanisms of cellular crosstalk between mesenchymal stem cells and natural killer cells: Therapeutic implications

Mesenchymal stem cells (MSCs) are mesenchymal precursors of various origins, with well-known immunomodulatory effects. Natural killer (NK) cells, the major cells of the innate immune system, are critical for the antitumor and antiviral defenses; however, in certain cases, they may be the main culprits in the pathogenesis of some NK-related conditions such as autoimmunities and hematological malignancies. On the other hand, these cells seem to be the major responders in beneficial phenomena like graft versus leukemia. Substantial data suggest that MSCs can variably affect NK cells and can be affected by these cells. Accordingly, acquiring a profound understanding of the crosstalk between MSCs and NK cells and the involved mechanisms seems to be a necessity to develop therapeutic approaches based on such interactions. Therefore, in this study, we made a thorough review of the existing literature on the interactions between MSCs and NK cells with a focus on the underlying mechanisms. The current knowledge herein suggests that MSCs possess a great potential to be used as tools for therapeutic targeting of NK cells in disease context and that preconditioning of MSCs, as well as their genetic manipulation before administration, may provide a wider variety of options in terms of eliciting more specific and desirable therapeutic outcomes. Nevertheless, our knowledge regarding the effects of MSCs on NK cells is still in its infancy, and further studies with well-defined conditions are warranted herein.

Hypoxia alleviates dexamethasone-induced inhibition of angiogenesis in cocultures of HUVECs and rBMSCs via HIF-1α

BACKGROUND AND AIM

Inadequate vascularization is a challenge in bone tissue engineering because internal cells are prone to necrosis due to a lack of nutrient supply. Rat bone marrow-derived mesenchymal stem cells (rBMSCs) and human umbilical vein endothelial cells (HUVECs) were cocultured to construct prevascularized bone tissue in osteogenic induction medium (OIM) in vitro. The angiogenic capacity of HUVECs was limited in the coculture system. In this study, the effects of the components in the medium on HUVEC angiogenesis were analyzed.

METHODS

The coculture system was established in OIM. Alizarin red staining and alkaline phosphatase staining were used to assess the osteogenic ability of MSCs. A Matrigel tube assay was used to assess the angiogenic ability of HUVECs in vitro. The proliferation of HUVECs was evaluated by cell counting and CCK-8 assays, and migration was evaluated by the streaked plate assay. The expression levels of angiogenesis-associated genes and proteins in HUVECs were measured by qRT-PCR and Western blotting, respectively.

RESULTS

Dexamethasone in the OIM suppressed the proliferation and migration of HUVECs, inhibiting the formation of capillary-like structures. Our research showed that dexamethasone stimulated HUVECs to secrete tissue inhibitor of metalloproteinase (TIMP-3), which competed with vascular endothelial growth factor (VEGF-A) to bind to vascular endothelial growth factor receptor 2 (VEGFR2, KDR). This effect was related to inhibiting the phosphorylation of ERK and AKT, which are two downstream targets of KDR. However, under hypoxia, the enhanced expression of hypoxia-inducible factor-1α (HIF-1α) decreased the expression of TIMP-3 and promoted the phosphorylation of KDR, improving HUVEC angiogenesis in the coculture system.

CONCLUSION

Coculture of hypoxia-preconditioned HUVECs and MSCs showed robust angiogenesis and osteogenesis in OIM, which has important implications for prevascularization in bone tissue engineering in the future.

The Blood Circulating Rare Cell Population. What is it and What is it Good For?

Blood contains a diverse cell population of low concentration hematopoietic as well as non-hematopoietic cells. The majority of such rare cells may be bone marrow-derived progenitor and stem cells. This paucity of circulating rare cells, in particular in the peripheral circulation, has led many to believe that bone marrow as well as other organ-related cell egress into the circulation is a response to pathological conditions. Little is known about this, though an increasing body of literature can be found suggesting commonness of certain rare cell types in the peripheral blood under physiological conditions. Thus, the isolation and detection of circulating rare cells appears to be merely a technological problem. Knowledge about rare cell types that may circulate the blood stream will help to advance the field of cell-based liquid biopsy by supporting inter-platform comparability, making use of biological correct cutoffs and “mining” new biomarkers and combinations thereof in clinical diagnosis and therapy. Therefore, this review intends to lay ground for a comprehensive analysis of the peripheral blood rare cell population given the necessity to target a broader range of cell types for improved biomarker performance in cell-based liquid biopsy.

Fibroblast growth factor 2-induced human amniotic mesenchymal stem cells combined with autologous platelet rich plasma augmented tendon-to-bone healing

Objective

The purpose of this study was to explore the effect of fibroblast growth factor 2 (FGF-2) on collagenous fibre formation and the osteogenic differentiation of human amniotic mesenchymal stem cells (hAMSCs) in vitro, as well as the effect of FGF-2–induced hAMSCs combined with autologous platelet-rich plasma (PRP) on tendon-to-bone healing in vivo.

Methods

In vitro, hAMSCs were induced by various concentrations of FGF-2 (0, 10, 20, and 40 ​ng/ml) for 14 days, and the outcomes of ligamentous differentiation and osteogenic differentiation were detected by quantitative real-time reverse transcription PCR, Western blot, immunofluorescence, and picrosirius red staining. In addition, a lentivirus carrying the FGF-2 gene was used to transfect hAMSCs, and transfection efficiency was detected by quantitative real time reverse transcription PCR (qRT-PCR) and Western blot. In vivo, the effect of hAMSCs transfected with the FGF-2 gene combined with autologous PRP on tendon-to-bone healing was detected via histological examination, as well as biomechanical analysis and radiographic analysis.

Results

In vitro, different concentrations of FGF-2 (10, 20, and 40 ​ng/ml) all promoted the ligamentous differentiation and osteogenic differentiation of hAMSCs, and the low concentration of FGF-2 (10 ​ng/ml) had a good effect on differentiation. In addition, the lentivirus carrying the FGF-2 gene was successfully transfected into hAMSCs with an optimal multiplicity of infection (MOI) (50), and autologous PRP was prepared successfully. In vivo, the hAMSCs transfected with the FGF-2 gene combined with autologous PRP had a better effect on tendon-to-bone healing than the other groups (p ​< ​0.05), as evidenced by histological examination, biomechanical analysis, and radiographic analysis.

Conclusion

hAMSCs transfected with the FGF-2 gene combined with autologous PRP could augment tendon-to-bone healing in a rabbit extra-articular model.

The translational potential of this article

hAMSCs transfected with the FGF-2 gene combined with autologous PRP may be a good clinical treatment for tendon-to-bone healing, especially for acute sports-related tendon–ligament injuries.

FGF-2-Induced Human Amniotic Mesenchymal Stem Cells Seeded on a Human Acellular Amniotic Membrane Scaffold Accelerated Tendon-to-Bone Healing in a Rabbit Extra-Articular Model

Background

FGF-2 (basic fibroblast growth factor) has a positive effect on the proliferation and differentiation of many kinds of MSCs. Therefore, it represents an ideal molecule to facilitate tendon-to-bone healing. Nonetheless, no studies have investigated the application of FGF-2-induced human amniotic mesenchymal stem cells (hAMSCs) to accelerate tendon-to-bone healing in vivo.

Objective

The purpose of this study was to explore the effect of FGF-2 on chondrogenic differentiation of hAMSCs in vitro and the effect of FGF-2-induced hAMSCs combined with a human acellular amniotic membrane (HAAM) scaffold on tendon-to-bone healing in vivo.

Methods

In vitro, hAMSCs were transfected with a lentivirus carrying the FGF-2 gene, and the potential for chondrogenic differentiation of hAMSCs induced by the FGF-2 gene was assessed using immunofluorescence and toluidine blue (TB) staining. HAAM scaffold was prepared, and hematoxylin and eosin (HE) staining and scanning electron microscopy (SEM) were used to observe the microstructure of the HAAM scaffold. hAMSCs transfected with and without FGF-2 were seeded on the HAAM scaffold at a density of 3 × 10⁵ cells/well. Immunofluorescence staining of vimentin and phalloidin staining were used to confirm cell adherence and growth on the HAAM scaffold. In vivo, the rabbit extra-articular tendon-to-bone healing model was created using the right hind limb of 40 New Zealand White rabbits. Grafts mimicking tendon-to-bone interface (TBI) injury were created and subjected to treatment with the HAAM scaffold loaded with FGF-2-induced hAMSCs, HAAM scaffold loaded with hAMSCs only, HAAM scaffold, and no special treatment. Macroscopic observation, imageological analysis, histological assessment, and biomechanical analysis were conducted to evaluate tendon-to-bone healing after 3 months.

Results

In vitro, cartilage-specific marker staining was positive for the FGF-2 overexpression group. The HAAM scaffold displayed a netted structure and mass extracellular matrix structure. hAMSCs or hAMSCs transfected with FGF-2 survived on the HAAM scaffold and grew well. In vivo, the group treated with HAAM scaffold loaded with FGF-2-induced hAMSCs had the narrowest bone tunnel after three months as compared with other groups. In addition, macroscopic and histological scores were higher for this group than for the other groups, along with the best mechanical strength.

Conclusion

hAMSCs transfected with FGF-2 combined with the HAAM scaffold could accelerate tendon-to-bone healing in a rabbit extra-articular model.