Stem cell-mediated osteogenesis: therapeutic potential for bone tissue engineering

Metabolic and Transcriptional Changes across Osteogenic Differentiation of Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) are multipotent post-natal stem cells with applications in tissue engineering and regenerative medicine. MSCs can differentiate into osteoblasts, chondrocytes, or adipocytes, with functional differences in cells during osteogenesis accompanied by metabolic changes. The temporal dynamics of these metabolic shifts have not yet been fully characterized and are suspected to be important for therapeutic applications such as osteogenesis optimization. Here, our goal was to characterize the metabolic shifts that occur during osteogenesis. We profiled five key extracellular metabolites longitudinally (glucose, lactate, glutamine, glutamate, and ammonia) from MSCs from four donors to classify osteogenic differentiation into three metabolic stages, defined by changes in the uptake and secretion rates of the metabolites in cell culture media. We used a combination of untargeted metabolomic analysis, targeted analysis of ¹³C-glucose labelled intracellular data, and RNA-sequencing data to reconstruct a gene regulatory network and further characterize cellular metabolism. The metabolic stages identified in this proof-of-concept study provide a framework for more detailed investigations aimed at identifying biomarkers of osteogenic differentiation and small molecule interventions to optimize MSC differentiation for clinical applications.

Analyzing Metabolic States of Adipogenic and Osteogenic Differentiation in Human Mesenchymal Stem Cells via Genome Scale Metabolic Model Reconstruction

Since their initial discovery in 1976, mesenchymal stem cells (MSCs) have been gathering interest as a possible tool to further the development and enhancement of various therapeutics within regenerative medicine. However, our current understanding of both metabolic function and existing differences within the varying cell lineages (e.g., cells in either osteogenesis or adipogenesis) is severely lacking making it more difficult to fully realize the therapeutic potential of MSCs. Here, we reconstruct the MSC metabolic network to understand the activity of various metabolic pathways and compare their usage under different conditions and use these models to perform experimental design. We present three new genome-scale metabolic models (GEMs) each representing a different MSC lineage (proliferation, osteogenesis, and adipogenesis) that are biologically feasible and have distinctive cell lineage characteristics that can be used to explore metabolic function and increase our understanding of these phenotypes. We present the most distinctive differences between these lineages when it comes to enriched metabolic subsystems and propose a possible osteogenic enhancer. Taken together, we hope these mechanistic models will aid in the understanding and therapeutic potential of MSCs.

miR-140-3p aggregates osteoporosis by targeting PTEN and activating PTEN/PI3K/AKT signaling pathway

Osteoporosis (OP) is a systemic bone metabolic disorder, which negatively affects the quality of life in the elders and postmenopausal females. Healthy volunteers and postmenopausal females with OP were enrolled in the present study. Bone densitometry (BMD) was detected by dual-energy X-ray absorptiometry (DXA). CD14+PBMCs and C2C12 cells were cultured to induce osteoclast differentiation and osteoblast differentiation, respectively. The interaction between miR‑140-3p and PTEN was predicted and verified by TargetScan 7.2 and dual luciferase reporter assay, respectively. miRNA/RNA level and protein level were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot, respectively. Cell proliferation and apoptosis were detected by 5-ethynyl-2'-deoxyuridine (EdU) staining and flow cytometry, respectively. Cell differentiation of CD14+PBMCs and C2C12 cells were detected by tartrate-resistant acid phosphatase (TRAP) staining and alizarin red staining, respectively. The activity of alkaline phosphatase (ALP) was detected by ALP assay. Differences were observed in age, body mass index (BMI), and BMD between the OP group and the control group. Higher miR‑140-3p level and lower PTEN level were found in PBMCs of OP group compared to control group; there was a negative correlation between them in the serum of OP group. miR-140-3p targeted and downregulated the expression of PTEN. miR-140-3p inhibitor inhibited cell proliferation, differentiation, and promoted cell apoptosis of CD14+PBMCs; while promoted cell proliferation, differentiation and inhibited cell apoptosis of C2C12 cells, by targeting PTEN and inactivating PTEN/PI3K/AKT signaling pathway. These findings suggested a potential therapeutic role of miR-140-3p in the treatment of patients with OP.

Current Status and Future Prospects of Genome-Scale Metabolic Modeling to Optimize the Use of Mesenchymal Stem Cells in Regenerative Medicine

Mesenchymal stem cells are a promising source for externally grown tissue replacements and patient-specific immunomodulatory treatments. This promise has not yet been fulfilled in part due to production scaling issues and the need to maintain the correct phenotype after re-implantation. One aspect of extracorporeal growth that may be manipulated to optimize cell growth and differentiation is metabolism. The metabolism of MSCs changes during and in response to differentiation and immunomodulatory changes. MSC metabolism may be linked to functional differences but how this occurs and influences MSC function remains unclear. Understanding how MSC metabolism relates to cell function is however important as metabolite availability and environmental circumstances in the body may affect the success of implantation. Genome-scale constraint based metabolic modeling can be used as a tool to fill gaps in knowledge of MSC metabolism, acting as a framework to integrate and understand various data types (e.g., genomic, transcriptomic and metabolomic). These approaches have long been used to optimize the growth and productivity of bacterial production systems and are being increasingly used to provide insights into human health research. Production of tissue for implantation using MSCs requires both optimized production of cell mass and the understanding of the patient and phenotype specific metabolic situation. This review considers the current knowledge of MSC metabolism and how it may be optimized along with the current and future uses of genome scale constraint based metabolic modeling to further this aim.

miR-193-3p ameliorates bone resorption in ovariectomized mice by blocking NFATc1 signaling

BACKGROUND

Nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) as a key transcription factor contributes to osteoclast differentiation and bone resorption. However, the post-transcriptional mechanisms of microRNAs (miRNAs) targeted to NFATc1 have not been completely clarified in postmenopausal osteoporosis (PMO). In our study, we aimed to investigate the role of miR-193-3p in ovariectomy (OVX)-induced bone loss by regulating the NFATc1 pathway.

METHODS

Female C57BL/6J mice underwent sham or OVX operation. Injection of Agomir-Control or Agomir-miR-193-3p was performed in OVX mice. Serum, urine and tibia were collected for experimental measurements, including biochemical markers, RT-qPCR and western blotting assays.

RESULTS

We identified NFATc1 as a direct target of miR-193-3p. Up-regulation of NFATc1 and down-regulation of miR-193-3p were found in the tibia of OVX mice. Gain-of-function of miR-193-3p resulted in the reduction of NFATc1 mRNA and protein expression in vivo and in vitro. Furthermore, injection of Agomir-miR-193-3p markedly ameliorated OVX-induced Ca²⁺ dyshomeostasis and bone loss by inhibiting the expression of NFATc1 and its downstream targets of osteoclast-specific genes, Ctsk, TRAP and Car2.

CONCLUSION

Overexpression of miR-193-3p had an osteoprotective effect in OVX mice by suppressing NFATc1 pathways.

Rat sinus mucosa- and periosteum-derived exosomes accelerate osteogenesis

Guided bone regeneration (GBR) is commonly used for alveolar bone augmentation. The paracrine mechanism in the field of bone tissue engineering has been emphasized in recent years and exosomes are considered to have the potential of promoting osteogenesis. We aimed to study the influence of sinus mucosa and periosteum on bone regeneration through paracrine stimulation, especially via exosomes, and compare the differences between them. Here, we report that conditioned medium (CM) from sinus mucosa-derived cells (SMCs) and periosteum-derived cells (PCs) and the isolated exosomes enhanced the proliferation, migration and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs) in vitro. A rat model of femoral bone defects was used to demonstrate that the exosomes derived from SMCs (SMC-Exos) and PCs (PC-Exos) can accelerate bone formation in vivo. Furthermore, we present a preliminary discussion of the possible functional components involved in the effects of SMC-Exos and PC-Exos on bone regeneration. In conclusion, these results demonstrated that the sinus mucosa and periosteum can accelerate osteogenesis through paracrine effects and the exosomes play important roles in this process.

Biomaterial Enhanced Regeneration Design Research for Skin and Load Bearing Applications

Biomaterial enhanced regeneration (BER) falls mostly under the broad heading of Tissue Engineering: the use of materials (synthetic and natural) usually in conjunction with cells (both native and genetically modified as well as stem cells) and/or biological response modifiers (growth factors and cytokines as well as other stimuli, which alter cellular activity). Although the emphasis is on the biomaterial as a scaffold it is also the use of additive bioactivity to enhance the healing and regenerative properties of the scaffold. Enhancing regeneration is both moving more toward regeneration but also speeding up the process. The review covers principles of design for BER as well as strategies to select the best designs. This is first general design principles, followed by types of design options, and then specific strategies for applications in skin and load bearing applications. The last section, surveys current clinical practice (for skin and load bearing applications) including limitations of these approaches. This is followed by future directions with an attempt to prioritize strategies. Although the review is geared toward design optimization, prioritization also includes the commercializability of the devices. This means a device must meet both the clinical performance design constraints as well as the commercializability design constraints.

MicroRNA‑100‑5p inhibits osteoclastogenesis and bone resorption by regulating fibroblast growth factor 21

MicroRNAs (miRNAs/miRs) are post‑transcriptional regulators that serve important roles in osteoclastogenesis and bone metabolism; however, the roles of miRNAs have not been completely clarified. The present study aimed to investigate the effects of miR‑100‑5p on the mechanism of liver‑bone endocrine metabolism. A miRNA microarray analysis was conducted to evaluate the miRNA expression profile during receptor activator of nuclear factor‑κB ligand‑stimulated osteoclastogenesis. Hematoxylin and eosin and tartrate‑resistant acid phosphatase staining were performed to analyze the trabecular bone microstructure and osteoclast differentiation. The mRNA and protein expression levels were assessed by reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. The results revealed that in vitro osteoclast differentiation and in vivo bone resorption were suppressed by miR‑100‑5p overexpression. In vivo, a decrease in miR‑100‑5p and an increase in FGF21 were simultaneously observed in mice following ovariectomy (OVX). Bioinformatics analysis and experimental data confirmed that FGF21 was a direct target of miR‑100‑5p. Conversely, augmentation of miR‑100‑5p using a specific agomir in OVX‑operated mice decreased the levels of FGF21 in the serum and liver, and prevented osteoclastogenesis and bone loss. The present study revealed that FGF21 may be a signal molecule associated with the mechanism of liver‑bone endocrine metabolism and may be targeted by miR‑100‑5p. In addition, miR‑100‑5p may serve an important role in protecting against OVX‑induced osteoporosis.

Mesenchymal Stem Cells and Transforming Growth Factor-β₃ (TGF-β₃) to Enhance the Regenerative Ability of an Albumin Scaffold in Full Thickness Wound Healing

Pressure ulcers are one of the most common forms of skin injury, particularly in the spinal cord injured (SCI). Pressure ulcers are difficult to heal in this population requiring at least six months of bed rest. Surgical treatment (grafting) is the fastest recovery time, but it still requires six weeks of bed rest plus significant additional costs and a high recurrence rate. A significant clinical benefit would be obtained by speeding the healing rate of a non-surgical treatment to close to that of surgical treatment (approximately doubling of healing rate). Current non-surgical treatment is mostly inactive wound coverings. The goal of this project was to look at the feasibility of doubling the healing rate of a full-thickness defect using combinations of three treatments, for the first time, each shown to increase healing rate: application of transforming growth factor-β₃ (TGF-β₃), an albumin based scaffold, and mesenchymal stem cells (MSCs). At one week following surgery, the combined treatment showed the greatest increase in healing rate, particularly for the epithelialization rate. Although the target level of a 100% increase in healing rate over the control was not quite achieved, it is anticipated that the goal would be met with further optimization of the treatment.

A Molecular View of Pathological Microcalcification in Breast Cancer

Breast microcalcification is a potential diagnostic indicator for non-palpable breast cancers. Microcalcification type I (calcium oxalate) is restricted to benign tissue, whereas type II (calcium hydroxyapatite) occurs both in benign as well as in malignant lesions. Microcalcification is a pathological complication of the mammary gland. Over the past few decades, much attention has been paid to exploit this property, which forms the basis for advances in diagnostic procedures and imaging techniques. The mechanism of its formation is still poorly understood. Hence, in this paper, we have attempted to address the molecular mechanism of microcalcification in breast cancer. The central theme of this communication is "how a subpopulation of heterogeneous breast tumor cells attains an osteoblast-like phenotype, and what activities drive the process of pathophysiological microcalcification, especially at the invasive or infiltrating front of breast tumors". The role of bone morphogenetic proteins (BMPs) and tumor associated macrophages (TAMs) along with epithelial to mesenchymal transition (EMT) in manipulating this pathological process has been highlighted. Therefore, this review offers a novel insight into the mechanism underlying the development of microcalcification in breast carcinomas.

Prospect of Stem Cells in Bone Tissue Engineering: A Review

Mesenchymal stem cells (MSCs) have been the subject of many studies in recent years, ranging from basic science that looks into MSCs properties to studies that aim for developing bioengineered tissues and organs. Adult bone marrow-derived mesenchymal stem cells (BM-MSCs) have been the focus of most studies due to the inherent potential of these cells to differentiate into various cell types. Although, the discovery of induced pluripotent stem cells (iPSCs) represents a paradigm shift in our understanding of cellular differentiation. These cells are another attractive stem cell source because of their ability to be reprogramed, allowing the generation of multiple cell types from a single cell. This paper briefly covers various types of stem cell sources that have been used for tissue engineering applications, with a focus on bone regeneration. Then, an overview of some recent studies making use of MSC-seeded 3D scaffold systems for bone tissue engineering has been presented. The emphasis has been placed on the reported scaffold properties that tend to improve MSCs adhesion, proliferation, and osteogenic differentiation outcomes.

Regeneration of rabbit calvarial defects using cells-implanted nano-hydroxyapatite coated silk scaffolds

Background

The aim of this study was to characterize the efficacy of nano-hydroxyapatite-coated silk fibroin constructs as a scaffold for bone tissue engineering and to determine the osteogenic effect of human dental pulp and periodontal ligament derived cells at an early stage of healing in rabbits. 3D silk fibroin constructs were developed and coated using nano-hydroxyapatite crystals. Dental pulp and periodontal ligament cells from extracted human third molars were cultured and seeded onto the silk scaffolds prior to in vivo implantation into 8 male New Zealand White rabbits. Four circular windows 8 mm in diameter were created in the calvarium of each animal. The defects were randomly allocated to the groups; (1) silk scaffold with dental pulp cells (DPSS), (2) silk scaffold with PDL cells (PDLSS), (3) normal saline-soaked silk scaffold (SS), and (4) empty control. The animals were sacrificed 2 (n = 4) or 4 weeks (n = 4) postoperatively. The characteristics of the silk scaffolds before and after cell seeding were analyzed using SEM. Samples were collected for histologic and histomorphometic analysis. ANOVA was used for statistical analysis.

Result

Histologic view of the experimental sites showed well-maintained structure of the silk scaffolds mostly unresorbed at 4 weeks. The SEM observations after cell-seeding revealed attachment of the cells onto silk fibroin with production of extracellular matrix. New bone formation was observed in the 4 week groups occurring from the periphery of the defects and the silk fibers were closely integrated with the new bone. There was no significant difference in the amount of bone formation between the SS group and the DPSS and PDLSS groups.

Conclusion

Within the limitations of this study, silk scaffold is a biocompatible material with potential expediency as an osteoconductive scaffold in bone tissue engineering. However, there was no evidence to suggest that the addition of hDPCs and hPDLCs to the current rabbit calvarial defect model can produce an early effect in augmenting osteogenesis.

Differentiation of immortalized human precartilaginous stem cells into nucleus pulposus-like cells

OBJECTIVE

We aimed to explore the differentiation of immortalized human precartilaginous stem cells (IPSCs) into nucleus pulposus (NP)-like cells induced by transforming growth factor-β1 (TGF-β1) and examine its biological characteristics.

METHODS

The IPSCs were seeded onto chitosan/glycerophosphate (C/GP) scaffolds and induced into NP-like cells by adding TGF-β1 under hypoxic conditions. The growth and differentiation of IPSCs were observed, and the formation of glycosaminoglycans (GAG) in the extracellular matrix of differentiating cells was detected by Alcian Blue staining. The expressions of type II collagen and aggrecan genes in NP-like cells were examined by reverse transcription-polymerase chain reaction (RT-PCR). The expressions of Sox9 and β-catenin were analyzed by Western blotting.

RESULTS

The IPSCs were observed to grow well on the C/GP scaffolds. After 7 days, Alcian Blue staining demonstrated the formation of GAG. The RT-PCR results showed that expression of type II collagen and aggrecan were upregulated compared with control group (P<0.05, P<0.05). Likewise, western blotting results showed that the expression of Sox9 and β-catenin was upregulated compared with control group (P<0.05, P<0.05).

CONCLUSIONS

The findings demonstrate that IPSCs could be differentiated into NP-like cells following induction by TGF-β1.

Biocompatibility and in vivo osteogenic capability of novel bone tissue engineering scaffold A-W-MGC/CS

BACKGROUND

This study aims to investigate the biocompatibility and in vivo osteogenic capability of the novel bone tissue engineering scaffold apatite-wollastonite-magnetic glass ceramic/chitosan (A-W-MGC/CS).

METHODS

Rabbit bone marrow stromal cells (BMSCs) were transfected with adenovirus-human bone morphogenetic protein-2-green fluorescent protein (Ad-hBMP2-GFP). The transfected BMSCs were then inoculated onto the scaffold material A-W-MGC/CS to construct tissue-engineered bone. The attachment and proliferation of BMSCs were observed by scanning electron microscopy (SEM) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) detection, respectively. Rabbit models of bone defects were established and divided into three groups. Experimental group 1 was implanted with prepared tissue-engineered bone. Experimental group 2 was implanted with A-W-MGC/CS without transfected BMSCs. The blank group was injected with transfected BMSCs, without implantation of any scaffold. In the 12th week after surgery, the repair of bone defect was observed by X-ray examination, and histological observations of the area of bone defect were performed.

RESULTS

A-W-MGC/CS resulted in good BMSC attachment and had no obvious effects on cell proliferation. In experimental group 1, good repair of bone defect was observed, and the scaffold material degraded completely. In experimental group 2, new bone was formed, but its quality was poor. In the blank group, there was mainly filling of fibrous connective tissues with no observable bone defect repair.

CONCLUSION

A-W-MGC/CS possesses good biocompatibility and in vivo osteogenic capability for bone defect repair.

Enhanced healing of rat calvarial defects with MSCs loaded on BMP-2 releasing chitosan/alginate/hydroxyapatite scaffolds

In this study, we designed a chitosan/alginate/hydroxyapatite scaffold as a carrier for recombinant BMP-2 (CAH/B2), and evaluated the release kinetics of BMP-2. We evaluated the effect of the CAH/B2 scaffold on the viability and differentiation of bone marrow mesenchymal stem cells (MSCs) by scanning electron microscopy, MTS, ALP assay, alizarin-red staining and qRT-PCR. Moreover, MSCs were seeded on scaffolds and used in a 8 mm rat calvarial defect model. New bone formation was assessed by radiology, hematoxylin and eosin staining 12 weeks postoperatively. We found the release kinetics of BMP-2 from the CAH/B2 scaffold were delayed compared with those from collagen gel, which is widely used for BMP-2 delivery. The BMP-2 released from the scaffold increased MSC differentiation and did not show any cytotoxicity. MSCs exhibited greater ALP activity as well as stronger calcium mineral deposition, and the bone-related markers Col1α, osteopontin, and osteocalcin were upregulated. Analysis of in vivo bone formation showed that the CAH/B2 scaffold induced more bone formation than other groups. This study demonstrates that CAH/B2 scaffolds might be useful for delivering osteogenic BMP-2 protein and present a promising bone regeneration strategy.

Interaction between immobilized polyelectrolyte complex nanoparticles and human mesenchymal stromal cells

BACKGROUND

Implant loosening or deficient osseointegration is a major problem in patients with systemic bone diseases (eg, osteoporosis). For this reason, the stimulation of the regional cell population by local and sustained drug delivery at the bone/implant interface to induce the formation of a mechanical stable bone is promising. The purpose of this study was to investigate the interaction of polymer-based nanoparticles with human bone marrow-derived cells, considering nanoparticles' composition and surface net charge.

MATERIALS AND METHODS

Polyelectrolyte complex nanoparticles (PECNPs) composed of the polycations poly(ethyleneimine) (PEI), poly(L-lysine) (PLL), or (N,N-diethylamino)ethyldextran (DEAE) in combination with the polyanions dextran sulfate (DS) or cellulose sulfate (CS) were prepared. PECNPs' physicochemical properties (size, net charge) were characterized by dynamic light scattering and particle charge detector measurements. Biocompatibility was investigated using human mesenchymal stromal cells (hMSCs) cultured on immobilized PECNP films (5-50 nmol·cm(-2)) by analysis for metabolic activity of hMSCs in dependence of PECNP surface concentration by MTS (3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium, inner salt) assay, as well as cell morphology (phase contrast microscopy).

RESULTS

PECNPs ranging between ~50 nm and 150 nm were prepared. By varying the ratio of polycations and polyanions, PECNPs with a slightly positive (PEC(+)NP) or negative (PEC(-)NP) net charge were obtained. The PECNP composition significantly affected cell morphology and metabolic activity, whereas the net charge had a negligible influence. Therefore, we classified PECNPs into "variant systems" featuring a significant dose dependency of metabolic activity (DEAE/CS, PEI/DS) and "invariant systems" lacking such a dependency (DEAE/DS, PEI/CS). Immunofluorescence imaging of fluorescein isothiocyanate isomer I (FITC)-labeled PECNPs suggested internalization into hMSCs remaining stable for 8 days.

CONCLUSION

Our study demonstrated that PECNP composition affects hMSC behavior. In particular, the PEI/CS system showed biocompatibility in a wide concentration range, representing a suitable system for local drug delivery from PECNP-functionalized bone substitute materials.