Adipose-derived adult stromal cells heal critical-size mouse calvarial defects

Elevated Expression of Dkk-1 by Glucocorticoid Treatment Impairs Bone Regenerative Capacity of Adipose Tissue-Derived Mesenchymal Stem Cells

Glucocorticoids are steroid hormones used as anti-inflammatory treatments. However, this strong immunomodulation causes undesirable side effects that impair bones, such as osteoporosis. Glucocorticoid therapy is a major risk factor for developing steroid-induced osteonecrosis of the femur head (ONFH). Since ONFH is incurable, therapy with mesenchymal stem cells (MSCs) that can differentiate into osteoblasts are a first-line choice. Bone marrow-derived MSCs (BM-MSCs) are often used as a source of stem cell therapy for ONFH, but their proliferative activity is impaired after steroid treatment. Adipose tissue-derived MSCs (AT-MSCs) may be an attractive alternative source; however, it is unknown whether AT-MSCs from steroid-induced ONFH (sAT-MSCs) have the same differentiation ability as BM-MSCs or normal AT-MSCs (nAT-MSCs). In this study, we demonstrate that nAT-MSCs chronically exposed to glucocorticoids show lower alkaline phosphatase activity leading to reduced osteogenic differentiation ability. This impaired osteogenesis is mediated by high expression of Dickkopf1 (Dkk-1) that inhibits wnt/β-catenin signaling. Increased Dkk-1 also causes impaired osteogenesis along with reductions in bone regenerative capacity in sAT-MSCs. Of note, plasma Dkk-1 levels are elevated in steroid-induced ONFH patients. Collectively, our findings suggest that glucocorticoid-induced expression of Dkk-1 could be a key factor in modulating the differentiation ability of MSCs used for ONFH and other stem cell therapies.

Bone regeneration strategies: Engineered scaffolds, bioactive molecules and stem cells current stage and future perspectives

Bone fractures are the most common traumatic injuries in humans. The repair of bone fractures is a regenerative process that recapitulates many of the biological events of embryonic skeletal development. Most of the time it leads to successful healing and the recovery of the damaged bone. Unfortunately, about 5-10% of fractures will lead to delayed healing or non-union, more so in the case of co-morbidities such as diabetes. In this article, we review the different strategies to heal bone defects using synthetic bone graft substitutes, biologically active substances and stem cells. The majority of currently available reviews focus on strategies that are still at the early stages of development and use mostly in vitro experiments with cell lines or stem cells. Here, we focus on what is already implemented in the clinics, what is currently in clinical trials, and what has been tested in animal models. Treatment approaches can be classified in three major categories: i) synthetic bone graft substitutes (BGS) whose architecture and surface can be optimized; ii) BGS combined with bioactive molecules such as growth factors, peptides or small molecules targeting bone precursor cells, bone formation and metabolism; iii) cell-based strategies with progenitor cells combined or not with active molecules that can be injected or seeded on BGS for improved delivery. We review the major types of adult stromal cells (bone marrow, adipose and periosteum derived) that have been used and compare their properties. Finally, we discuss the remaining challenges that need to be addressed to significantly improve the healing of bone defects.

Improved osteogenic differentiation of human dental pulp stem cells in a layer-by-layer-modified gelatin scaffold

Dental pulp stem cell is a new type of mesenchymal stem cell that has a potential for tissue regeneration. Gelatin sponges are often used for hemostasis in dental surgery. In this study, we aimed to evaluate the dental pulp stem cells' proliferation and osteogenic differentiation in different layer-by-layer-modified gelatin sponge scaffolds including the G, G + P (gelatin sponge+ poly-l-lysine modification), G + M (gelatin sponge + mineralization modification), and G + M + P (gelatin sponge + mineralization modification + poly-l-lysine modification) groups in vitro and assessed them in vivo. The results showed that dental pulp stem cells had a great potential for osteogenic differentiation. In vitro, the G + M + P group not only enhanced the adhesion and proliferation of dental pulp stem cells but also facilitated their osteogenic differentiation. However, alkaline phosphatase activity was prohibited after modification. In vivo, both dental pulp stem cells and cells from nude mice grew well on the scaffold, and G + M and G + M + P groups could promote the mineralization deposit formation and the expression of osteocalcin in osteogenic differentiation of dental pulp stem cells. In conclusion, the combination of dental pulp stem cells and G + M + P scaffold has a great potential for bone tissue engineering.

Mesenchymal Stem Cell Therapy for Bone Regeneration

Mesenchymal stem cells (MSCs) have been used in clinic for approximately 20 years. During this period, various new populations of MSCs have been found or manipulated. However, their characters and relative strength for bone regeneration have not been well known. For a comprehensive understanding of MSCs, we reviewed the literature on the multipotent cells ranging from the definition to the current research progress for bone regeneration. Based on our literature review, bone marrow MSCs have been most widely studied and utilized in clinical settings. Among other populations of MSCs, adipose-derived MSCs and perivascular MSCs might be potential candidates for bone regeneration, whose efficacy and safety still require further investigation.

Aspirin promotes osteogenic differentiation of human dental pulp stem cells

Human dental pulp stem cells (hDPSCs) possess self‑renewal and osteogenic differentiation properties, and have been used for orofacial bone regeneration and periodontal treatment. Aspirin has been demonstrated to enhance the regeneration of bone marrow mesenchymal stem cells (MSCs); however, the impact of aspirin on the osteogenic differentiation of hDPSCs remains unknown. In the present study, hDPSCs were characterized by flow cytometry, while their clonogenic potential and multipotency were assessed using alizarin red, Oil red O and alcian blue staining. The effect of aspirin on hDPSC viability was assessed using Cell Counting Kit‑8 assay. Osteogenic capacity was examined by alkaline phosphatase activity, alizarin red staining, reverse transcription‑polymerase chain reaction and western blotting. Furthermore, in vivo cranial defects were established in Sprague‑Dawley rats to evaluate the effect of aspirin on hDPSC‑based bone regeneration. Anorganic bovine bone was used as a bone replacement material and as the carrier for hDPSCs. New bone formation was observed through radiographic and histological analysis. The study demonstrated that hDPSCs expressed MSC markers and possessed multipotency in vitro. Aspirin was non‑toxic to hDPSCs at a concentration of ≤100 µg/ml and enhanced the osteogenesis of hDPSCs in vitro. Aspirin significantly increased hDPSC‑based bone formation in the rat cranial defect model at 8 or 12 weeks post‑implantation (P<0.05). The data suggested that aspirin promotes the osteogenic potential of hDPSCs in vitro and in vivo. Overall, the present study indicated that aspirin improves the bone regeneration capacity of hDPSCs.

Stimulation of calvarial bone healing with human bone marrow stromal cells versus inhibition with adipose-tissue stromal cells on nanostructured β-TCP-collagen

Bioactive functional scaffolds are essential for support of cell-based strategies to improve bone regeneration. Adipose-tissue-derived-stromal cells (ASC) are more accessible multipotent cells with faster proliferation than bone-marrow-derived-stromal-cells (BMSC) having potential to replace BMSC for therapeutic stimulation of bone-defect healing. Their osteogenic potential is, however, lower compared to BMSC, a deficit that may be overcome in growth factor-rich orthotopic bone defects with enhanced bone-conductive scaffolds. Objective of this study was to compare the therapeutic potency of human ASC and BMSC for bone regeneration on a novel nanoparticulate β-TCP/collagen-carrier (β-TNC). Cytotoxicity of β-TCP nanoparticles and multilineage differentiation of cells were characterized in vitro. Cell-seeded β-TNC versus cell-free controls were implanted into 4 mm calvarial bone-defects in immunodeficient mice and bone healing was quantified by µCT at 4 and 8 weeks. Tissue-quality and cell-origin were assessed by histology. β-TNC was non-toxic, radiolucent and biocompatible, lent excellent support for human cell persistence and allowed formation of human bone tissue by BMSC but not ASC. Opposite to BMSC, ASC-grafting significantly inhibited calvarial bone healing compared to controls. Bone formation progressed significantly from 4 to 8 weeks only in BMSC and controls yielding 5.6-fold more mineralized tissue in BMSC versus ASC-treated defects. Conclusively, β-TNC was simple to generate, biocompatible, osteoconductive, and stimulated osteogenicity of BMSC to enhance calvarial defect healing while ASC had negative effects. Thus, an orthotopic environment and β-TNC could not compensate for cell-autonomous deficits of ASC which should systematically be considered when choosing the right cell source for tissue engineering-based stimulation of bone regeneration.

STATEMENT OF SIGNIFICANCE

Bone-marrow-derived-stromal cells (BMSC) implanted on bone replacement materials can support bone defect healing and adipose-tissue-derived-stromal cells (ASC) being more accessible and better proliferating are considered as alternate source. This first standardized comparison of the bone regeneration potency of human ASC and BMSC was performed on a novel nanoparticular β-TCP-enriched collagen-carrier (β-TNC) designed to overcome the known inferior osteogenicity of ASC. β-TNC was non-toxic, biocompatible and osteoconductive supporting human bone formation and defect-closure by BMSC but not ASC. Long-term cell-persistence and the distinct secretome of ASC appear as main reasons why ASC inhibited bone healing opposite to BMSC. Overall, ASC-grafting is at considerable risk of producing negative effects on bone-healing while no such risks are known for BMSC.

Revisiting the Advances in Isolation, Characterization and Secretome of Adipose-Derived Stromal/Stem Cells

Adipose-derived stromal/stem cells (ASCs) seems to be a promising regenerative therapeutic agent due to the minimally invasive approach of their harvest and multi-lineage differentiation potential. The harvested adipose tissues are further digested to extract stromal vascular fraction (SVF), which is cultured, and the anchorage-dependent cells are isolated in order to characterize their stemness, surface markers, and multi-differentiation potential. The differentiation potential of ASCs is directed through manipulating culture medium composition with an introduction of growth factors to obtain the desired cell type. ASCs have been widely studied for its regenerative therapeutic solution to neurologic, skin, wound, muscle, bone, and other disorders. These therapeutic outcomes of ASCs are achieved possibly via autocrine and paracrine effects of their secretome comprising of cytokines, extracellular proteins and RNAs. Therefore, secretome-derivatives might offer huge advantages over cells through their synthesis and storage for long-term use. When considering the therapeutic significance and future prospects of ASCs, this review summarizes the recent developments made in harvesting, isolation, and characterization. Furthermore, this article also provides a deeper insight into secretome of ASCs mediating regenerative efficacy.

Applications of stem cells in orthodontics and dentofacial orthopedics: Current trends and future perspectives

A simple overview of daily orthodontic practice involves use of brackets, wires and elastomeric modules. However, investigating the underlying effect of orthodontic forces shows various molecular and cellular changes. Also, orthodontics is in close relation with dentofacial orthopedics which involves bone regeneration. In this review current and future applications of stem cells (SCs) in orthodontics and dentofacial orthopedics have been discussed. For craniofacial anomalies, SCs have been applied to regenerate hard tissue (such as treatment of alveolar cleft) and soft tissue (such as treatment of hemifacial macrosomia). Several attempts have been done to reconstruct impaired temporomandibular joint. Also, SCs with or without bone scaffolds and growth factors have been used to regenerate bone following distraction osteogenesis of mandibular bone or maxillary expansion. Current evidence shows that SCs also have potential to be used to regenerate infrabony alveolar defects and move the teeth into regenerated areas. Future application of SCs in orthodontics could involve accelerating tooth movement, regenerating resorbed roots and expanding tooth movement limitations. However, evidence supporting these roles is weak and further studies are required to evaluate the possibility of these ideas.

Cell viability assessed in a reproducible model of human osteoblasts derived from human adipose-derived stem cells

Human adipose tissue-derived stem cells (hASCs) have been subjected to extensive investigation because of their self-renewal properties and potential to restore damaged tissues. In the literature, there are several protocols for differentiating hASCs into osteoblasts, but there is no report on the control of cell viability during this process. In this study, we used osteoblasts derived from hASCs of patients undergoing abdominoplasty. The cells were observed at the beginning and end of bone matrix formation, and the expression of proteins involved in this process, including alkaline phosphatase and osteocalcin, was assessed. RANKL, Osterix, Runx2, Collagen3A1, Osteopontin and BSP expression levels were analyzed using real-time PCR, in addition to a quantitative assessment of protein levels of the markers CD45, CD105, STRO-1, and Nanog, using immunofluorescence. Rhodamine (Rho123), cytochrome-c, caspase-3, P-27, cyclin D1, and autophagy cell markers were analyzed by flow cytometry to demonstrate potential cellular activity and the absence of apoptotic and tumor cell processes before and after cell differentiation. The formation of bone matrix, along with calcium nodules, was observed after 16 days of osteoinduction. The gene expression levels of RANKL, Osterix, Runx2, Collagen3A1, Osteopontin, BSP and alkaline phosphatase activity were also elevated after 16 days of osteoinduction, whereas the level of osteocalcin was higher after 21 days of osteoinduction. Our data also showed that the cells had a high mitochondrial membrane potential and a low expression of apoptotic and tumor markers, both before and after differentiation. Cells were viable after the different phases of differentiation. This proposed methodology, using markers to evaluate cell viability, is therefore successful in assessing different phases of stem cell isolation and differentiation.

Gene Therapy for Bone Repair Using Human Cells: Superior Osteogenic Potential of Bone Morphogenetic Protein 2-Transduced Mesenchymal Stem Cells Derived from Adipose Tissue Compared to Bone Marrow

Ex vivo regional gene therapy strategies using animal mesenchymal stem cells genetically modified to overexpress osteoinductive growth factors have been successfully used in a variety of animal models to induce both heterotopic and orthotopic bone formation. However, in order to adapt regional gene therapy for clinical applications, it is essential to assess the osteogenic capacity of transduced human cells and choose the cell type that demonstrates the best clinical potential. Bone-marrow stem cells (BMSC) and adipose-derived stem cells (ASC) were selected in this study for in vitro evaluation, before and after transduction with a lentiviral two-step transcriptional amplification system (TSTA) overexpressing bone morphogenetic protein 2 (BMP-2; LV-TSTA-BMP-2) or green fluorescent protein (GFP; LV-TSTA-GFP). Cell growth, transduction efficiency, BMP-2 production, and osteogenic capacity were assessed. The study demonstrated that BMSC were characterized by a slower cell growth compared to ASC. Fluorescence-activated cell sorting analysis of GFP-transduced cells confirmed successful transduction with the vector and revealed an overall higher but not statistically significant transduction efficiency in ASC versus BMSC (90.2 ± 4.06% vs. 80.4 ± 8.51%, respectively; p = 0.146). Enzyme-linked immunosorbent assay confirmed abundant BMP-2 production by both cell types transduced with LV-TSTA-BMP-2, with BMP-2 production being significantly higher in ASC versus BMSC (239.5 ± 116.55 ng vs. 70.86 ± 24.7 ng; p = 0.001). Quantitative analysis of extracellular deposition of calcium (Alizarin red) and alkaline phosphatase activity showed that BMP-2-transduced cells had a higher osteogenic differentiation capacity compared to non-transduced cells. When comparing the two cell types, ASC/LV-TSTA-BMP-2 demonstrated a significantly higher mineralization potential compared to BMSC/LV-TSTA-BMP-2 7 days post transduction (p = 0.014). In conclusion, this study demonstrates that transduction with LV-TSTA-BMP-2 can significantly enhance the osteogenic potential of both human BMSC and ASC. BMP-2-treated ASC exhibited higher BMP-2 production and greater osteogenic differentiation capacity compared to BMP-2-treated BMSC. These results, along with the fact that liposuction is an easy procedure with lower donor-site morbidity compared to BM aspiration, indicate that adipose tissue might be a preferable source of MSCs to develop a regional gene therapy approach to treat difficult bone-repair scenarios.

The Role of Skeletal Stem Cells in the Reconstruction of Bone Defects

Craniofacial surgery, since its inauguration, has been the culmination of collaborative efforts to solve complex congenital, dysplastic, oncological, and traumatic cranial bone defects. Now, 50 years on from the first craniofacial meeting, the collaborative efforts between surgeons, scientists, and bioengineers are further advancing craniofacial surgery with new discoveries in tissue regeneration. Recent advances in regenerative medicine and stem cell biology have transformed the authors' understanding of bone healing, the role of stem cells governing bone healing, and the effects of the niche environment and extracellular matrix on stem cell fate. This review aims at summarizing the advances within each of these fields.

MAPK signaling has stage-dependent osteogenic effects on human adipose-derived stem cells in vitro

OVERVIEW

The use of pro-osteogenic growth factors, such as BMP2, in human adipose-derived stem cell (ASC) osteogenesis is well described. Because these growth factors work via signal transduction pathways, such as the mitogen-activated protein kinase (MAPK) cascade, a study of the relationship between MAPK signaling and ASC osteogenesis was conducted.

MATERIALS AND METHODS

ERK, JNK, and p38MAPK activation were measured in ASCs osteo-induced using either dexamethasone or vitamin D3 and correlated with mineralization. Activation and mineralization were also measured without dexamethasone or using the glucocorticoid, cortisone. The expression of the MAPK phosphatase, MKP1, and its relationship to mineralization was also assessed. The effect of decreasing MAPK activation on mineralization through the use of exogenous inhibitors was examined along with siRNA-knockdown and adenoviral overexpression of ERK1/2. Finally, the effect of ERK1/2 overexpression on ASCs induced on PLGA scaffolds was assessed.

RESULTS

ASC mineralization in dexamethasone or vitamin D3-induced ASCs correlated with both increased ERK1/2 and JNK1/2 activation. ASCs induced without dexamethasone also mineralized, with JNK1/2 signaling possibly mediating this event. No link between cortisone induction and MAPK signaling could be ascertained. ASCs treated with ERK, JNK, or p38MAPK inhibitors showed decreased osteogenic gene expression and diminished mineralization. Mineralization levels were also affected by viruses designed to inhibit or augment ERK1/2 expression and activity. Finally, ASC mineralization appeared to be a balance between the MAPK kinase activity and MKP1.

CONCLUSIONS

It is likely that MAPK signaling plays a significant role in ASC osteogenesis, affecting differentiation in kinase- and stage-specific manners.

Cartilage Tissue Engineering Via Icariin and Adipose-derived Stem Cells in Fibrin Scaffold

Background:

Nowadays, cartilage tissue engineering is the best candidate for regeneration of cartilage defects. This study evaluates the function of herbal extracts icariin (ICA), the major pharmacological constituent of herba Epimedium, compared with transforming growth factor β3 (TGFβ3) to prove its potential effect for cartilage tissue engineering.

Materials and Methods:

ICA, TGFβ3, and TGFβ3 + ICA were added fibrin-cell constructions derived from adipose tissue stem cells. After 14 days, cell viability analyzed by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H- tetrazolium bromide assay and the expression of cartilage genes was evaluated with real-time polymerase chain reaction (RT-PCR).

Results:

The results showed ICA, TGFβ3, and TGFβ3 + ICA increased the rate of proliferation and viability of cells; but there were no significant differences between them (P > 0.05). Furthermore, quantitative RT-PCR analysis demonstrated that cooperation of ICA with TGFβ3 showed a better effect in expression of cartilaginous specific genes and increased Sox9, type II collagen, and aggrecan expression significantly. Furthermore, the results of the expression of type I and X collagens revealed that TGFβ3 increased the expression of them (P < 0.01); However, treatment with ICA + TGFβ3 down regulated the expression of these genes significantly.

Conclusion:

The results indicated ICA could be a potential factor for chondrogenesis and in cooperation with TGFβ3 could reduce its hypertrophic effects and it is a promising factor for cartilage tissue engineering.

Micro-Nanostructures of Cellulose-Collagen for Critical Sized Bone Defect Healing

Bone tissue engineering strategies utilize biodegradable polymeric matrices alone or in combination with cells and factors to provide mechanical support to bone, while promoting cell proliferation, differentiation, and tissue ingrowth. The performance of mechanically competent, micro-nanostructured polymeric matrices, in combination with bone marrow stromal cells (BMSCs), is evaluated in a critical sized bone defect. Cellulose acetate (CA) is used to fabricate a porous microstructured matrix. Type I collagen is then allowed to self-assemble on these microstructures to create a natural polymer-based, micro-nanostructured matrix (CAc). Poly (lactic-co-glycolic acid) matrices with identical microstructures serve as controls. Significantly higher number of implanted host cells are distributed in the natural polymer based micro-nanostructures with greater bone density and more uniform cell distribution. Additionally, a twofold increase in collagen content is observed with natural polymer based scaffolds. This study establishes the benefits of natural polymer derived micro-nanostructures in combination with donor derived BMSCs to repair and regenerate critical sized bone defects. Natural polymer based materials with mechanically competent micro-nanostructures may serve as an alternative material platform for bone regeneration.

Bone regeneration by human dental pulp stem cells using a helioxanthin derivative and cell-sheet technology

BACKGROUND

Human dental pulp stem cells (DPSCs), which have the ability to differentiate into multiple lineages, were recently identified. DPSCs can be collected readily from extracted teeth and are now considered to be a type of mesenchymal stem cell with higher clonogenic and proliferative potential than bone marrow stem cells (BMSCs). Meanwhile, the treatment of severe bone defects, such as fractures, cancers, and congenital abnormalities, remains a great challenge, and novel bone regenerative techniques are highly anticipated. Several studies have previously shown that 4-(4-methoxyphenyl)pyrido[40,30:4,5]thieno[2,3-b]pyridine-2-carboxamide (TH), a helioxanthin derivative, induces osteogenic differentiation of preosteoblastic and mesenchymal cells. However, the osteogenic differentiation activities of TH have only been confirmed in some mouse cell lines. Therefore, in this study, toward the clinical use of TH in humans, we analyzed the effect of TH on the osteogenic differentiation of DPSCs, and the in-vivo osteogenesis ability of TH-induced DPSCs, taking advantage of the simple transplantation system using cell-sheet technology.

METHODS

DPSCs were obtained from dental pulp of the wisdom teeth of five healthy patients (18-22 years old) and cultured in regular medium and osteogenic medium with or without TH. To evaluate osteogenesis of TH-induced DPSCs in vivo, we transplanted DPSC sheets into mouse calvaria defects.

RESULTS

We demonstrated that osteogenic conditions with TH induce the osteogenic differentiation of DPSCs more efficiently than those without TH and those with bone morphogenetic protein-2. However, regular medium with TH did not induce the osteogenic differentiation of DPSCs. TH induced osteogenesis in both DPSCs and BMSCs, although the gene expression pattern in DPSCs differed from that in BMSCs up to 14 days after induction with TH. Furthermore, we succeeded in bone regeneration in vivo using DPSC sheets with TH treatment, without using any scaffolds or growth factors.

CONCLUSIONS

Our results demonstrate that TH-induced DPSCs are a useful cell source for bone regenerative medicine, and the transplantation of DPSC sheets treated with TH is a convenient scaffold-free method of bone healing.

Craniofacial Tissue Engineering

The craniofacial complex is composed of fundamental components such as blood vessels and nerves, and also a variety of specialized tissues such as craniofacial bones, cartilages, muscles, ligaments, and the highly specialized and unique organs, the teeth. Together, these structures provide many functions including speech, mastication, and aesthetics of the craniofacial complex. Craniofacial defects not only influence the structure and function of the jaws and face, but may also result in deleterious psychosocial issues, emphasizing the need for rapid and effective, precise, and aesthetic reconstruction of craniofacial tissues. In a broad sense, craniofacial tissue reconstructions share many of the same issues as noncraniofacial tissue reconstructions. Therefore, many concepts and therapies for general tissue engineering can and have been used for craniofacial tissue regeneration. Still, repair of craniofacial defects presents unique challenges, mainly because of their complex and unique 3D geometry.

Proposal of a Novel Natural Biomaterial, the Scleral Ossicle, for the Development of Vascularized Bone Tissue In Vitro

Recovering of significant skeletal defects could be partially abortive due to the perturbations that affect the regenerative process when defects reach a critical size, thus resulting in a non-healed bone. The current standard treatments include allografting, autografting, and other bone implant techniques. However, although they are commonly used in orthopedic surgery, these treatments have some limitations concerning their costs and their side effects such as potential infections or malunions. On this account, the need for suitable constructs to fill the gap in wide fractures is still urgent. As an innovative solution, scleral ossicles (SOs) can be put forward as natural scaffolds for bone repair. SOs are peculiar bony plates forming a ring at the scleral-corneal border of the eyeball of lower vertebrates. In the preliminary phases of the study, these ossicles were structurally and functionally characterized. The morphological characterization was performed by SEM analysis, MicroCT analysis and optical profilometry. Then, UV sterilization was carried out to obtain a clean support, without neither contaminations nor modifications of the bone architecture. Subsequently, the SO biocompatibility was tested in culture with different cell lines, focusing the attention to the differentiation capability of endothelial and osteoblastic cells on the SO surface. The results obtained by the above mentioned analysis strongly suggest that SOs can be used as bio-scaffolds for functionalization processes, useful in regenerative medicine.

Osteointegration of Porous Poly-ε-Caprolactone-Coated and Previtalised Magnesium Implants in Critically Sized Calvarial Bone Defects in the Mouse Model

Metallic biomaterials are widely used in maxillofacial surgery. While titanium is presumed to be the gold standard, magnesium-based implants are a current topic of interest and investigation due to their biocompatible, osteoconductive and degradable properties. This study investigates the effects of poly-ε-caprolactone-coated and previtalised magnesium implants on osteointegration within murine calvarial bone defects: After setting a 3 mm × 3 mm defect into the calvaria of 40 BALB/c mice the animals were treated with poly-ε-caprolactone-coated porous magnesium implants (without previtalisation or previtalised with either osteoblasts or adipose derived mesenchymal stem cells), porous Ti6Al4V implants or without any implant. To evaluate bone formation and implant degradation, micro-computertomographic scans were performed at day 0, 28, 56 and 84 after surgery. Additionally, histological thin sections were prepared and evaluated histomorphometrically. The outcomes revealed no significant differences within the differently treated groups regarding bone formation and the amount of osteoid. While the implant degradation resulted in implant shifting, both implant geometry and previtalisation appeared to have positive effects on vascularisation. Although adjustments in degradation behaviour and implant fixation are indicated, this study still considers magnesium as a promising alternative to titanium-based implants in maxillofacial surgery in future.

Low-dose strontium stimulates osteogenesis but high-dose doses cause apoptosis in human adipose-derived stem cells via regulation of the ERK1/2 signaling pathway

Background

Strontium is a widely used anti-osteoporotic agent due to its dual effects on inhibiting bone resorption and stimulating bone formation. Thus, we studied the dose response of strontium on osteo-inductive efficiency in human adipose-derived stem cells (hASCs).

Method

Qualitative alkaline phosphatase (ALP) staining, quantitative ALP activity, Alizarin Red staining, real-time polymerase chain reaction and Western blot were used to investigate the in vitro effects of a range of strontium concentrations on hASC osteogenesis and associated signaling pathways.

Results

In vitro work revealed that strontium (25–500 μM) promoted osteogenic differentiation of hASCs according to ALP activity, extracellular calcium deposition, and expression of osteogenic genes such as runt-related transcription factor 2, ALP, collagen-1, and osteocalcin. However, osteogenic differentiation of hASCs was significantly inhibited with higher doses of strontium (1000–3000 μM). These latter doses of strontium promoted apoptosis, and phosphorylation of ERK1/2 signaling was increased and accompanied by the downregulation of Bcl-2 and increased phosphorylation of BAX. The inhibition of ERK1/2 decreased apoptosis in hASCs.

Conclusion

Lower concentrations of strontium facilitate osteogenic differentiation of hASCs up to a point; higher doses cause apoptosis of hASCs, with activation of the ERK1/2 signaling pathway contributing to this process.

Tissue-engineered autologous grafts for facial bone reconstruction

Facial deformities require precise reconstruction of the appearance and function of the original tissue. The current standard of care-the use of bone harvested from another region in the body-has major limitations, including pain and comorbidities associated with surgery. We have engineered one of the most geometrically complex facial bones by using autologous stromal/stem cells, native bovine bone matrix, and a perfusion bioreactor for the growth and transport of living grafts, without bone morphogenetic proteins. The ramus-condyle unit, the most eminent load-bearing bone in the skull, was reconstructed using an image-guided personalized approach in skeletally mature Yucatán minipigs (human-scale preclinical model). We used clinically approved decellularized bovine trabecular bone as a scaffolding material and crafted it into an anatomically correct shape using image-guided micromilling to fit the defect. Autologous adipose-derived stromal/stem cells were seeded into the scaffold and cultured in perfusion for 3 weeks in a specialized bioreactor to form immature bone tissue. Six months after implantation, the engineered grafts maintained their anatomical structure, integrated with native tissues, and generated greater volume of new bone and greater vascular infiltration than either nonseeded anatomical scaffolds or untreated defects. This translational study demonstrates feasibility of facial bone reconstruction using autologous, anatomically shaped, living grafts formed in vitro, and presents a platform for personalized bone tissue engineering.

Inferior In Vivo Osteogenesis and Superior Angiogenesis of Human Adipose‐Derived Stem Cells Compared with Bone Marrow‐Derived Stem Cells Cultured in Xeno‐Free Conditions

The possibility of using adipose tissue-derived stromal cells (ATSC) as alternatives to bone marrow-derived stromal cells (BMSC) for bone repair has garnered interest due to the accessibility, high cell yield, and rapid in vitro expansion of ATSC. For clinical relevance, their bone forming potential in comparison to BMSC must be proven. Distinct differences between ATSC and BMSC have been observed in vitro and comparison of osteogenic potential in vivo is not clear to date. The aim of the current study was to compare the osteogenesis of human xenofree-expanded ATSC and BMSC in vitro and in an ectopic nude mouse model of bone formation. Human MSC were implanted with biphasic calcium phosphate biomaterials in subcutis pockets for 8 weeks. Implant groups were: BMSC, ATSC, BMSC and ATSC mixed together in different ratios, as well as MSC primed with either osteogenic supplements (250 μM ascorbic acid, 10 mM β-glycerolphosphate, and 10 nM dexamethasone) or 50 ng/ml recombinant bone morphogenetic protein 4 prior to implantation. In vitro results show osteogenic gene expression and differentiation potentials of ATSC. Despite this, ATSC failed to form ectopic bone in vivo, in stark contrast to BMSC, although osteogenic priming did impart minor osteogenesis to ATSC. Neovascularization was enhanced by ATSC compared with BMSC; however, less ATSC engrafted into the implant compared with BMSC. Therefore, in the content of bone regeneration, the advantages of ATSC over BMSC including enhanced angiogenesis, may be negated by their lack of osteogenesis and prerequisite for osteogenic differentiation prior to transplantation. Stem Cells Translational Medicine 2017;6:2160-2172.

Human Adipose-Derived Stromal Cell Isolation Methods and Use in Osteogenic and Adipogenic In Vivo Applications

Adipose tissue represents an abundant and easily accessible source of multipotent cells, which may serve as excellent building blocks for tissue engineering. This article presents a newly described protocol for isolating adipose-derived stromal cells (ASCs) from human lipoaspirate, compared to the standard protocol for harvesting ASCs established in 2001. Human ASC isolation is performed using two methods, and resultant cells are compared through cell yield, cell viability, cell proliferation and regenerative potential. The osteogenic and adipogenic potential of ASCs isolated using both protocols are assessed in vitro and gene expression analysis is performed. The focus of this series of protocols is the regenerative potential of both cell populations in vivo. As such, the two in vivo animal models described are fat graft retention (soft tissue reconstruction) and calvarial defect healing (bone regeneration). The techniques described comprise fat grafting with cell assisted lipotransfer, and calvarial defect creation healed with cell-seeded scaffolds. © 2017 by John Wiley & Sons, Inc.

Loss of mechanosensitive sclerostin may accelerate cranial bone growth and regeneration

OBJECTIVE

Cranial defects can result from trauma, infection, congenital malformations, and iatrogenic causes and represent a surgical challenge. The current standard of care is cranioplasty, with either autologous or allogeneic material. In either case, the intrinsic vascularity of the surrounding tissues allows for bone healing. The objective of this study was to determine if mechanotransductive gene manipulation would yield non-weight-bearing bone regeneration in a critical size calvarial defect in mice.

METHODS

A mouse model of Sost deletion in Sost knockout (KO) mice was created in which the osteocytes do not express sclerostin. A critical size calvarial defect (4 mm in diameter) was surgically created in the parietal bone in 8-week-old wild-type (n = 8) and Sost KO (n = 8) male mice. The defects were left undisturbed (no implant or scaffold) to simulate a traumatic calvariectomy model. Eight weeks later, the animals were examined at necropsy by planimetry, histological analysis of new bone growth, and micro-CT scanning of bone thickness.

RESULTS

Defects created in wild-type mice did not fill with bone over the study period of 2 months. Genetic downregulation of sclerostin yielded animals that were able to regenerate 40% of the initial critical size defect area 8 weeks after surgery. A thin layer of bone covered a significant portion of the original defect in all Sost KO animals. A statistically significant increase in bone volume (p < 0.05) was measured in Sost KO mice using radiodensitometric analysis. Immunohistochemical analysis also confirmed that this bone regeneration occurred through the Wnt pathway and originated from the edge of the defect; BMP signaling did not appear to be affected by sclerostin.

CONCLUSIONS

Mechanical loading is an important mechanism of bone formation in the cranial skeleton and is poorly understood. This is partially due to the fact that it is difficult to load bone in the craniomaxillofacial skeleton. This study suggests that modulation of the Wnt pathway, as is able to be done with monoclonal antibodies, is a potentially efficacious method for bone regeneration that requires further study.

Adipose stem cells for bone tissue repair

Adipose-derived stem/stromal cells (ASCs), together with adipocytes, vascular endothelial cells, and vascular smooth muscle cells, are contained in fat tissue. ASCs, like the human bone marrow stromal/stem cells (BMSCs), can differentiate into several lineages (adipose cells, fibroblast, chondrocytes, osteoblasts, neuronal cells, endothelial cells, myocytes, and cardiomyocytes). They have also been shown to be immunoprivileged, and genetically stable in long-term cultures. Nevertheless, unlike the BMSCs, ASCs can be easily harvested in large amounts with minimal invasive procedures. The combination of these properties suggests that these cells may be a useful tool in tissue engineering and regenerative medicine.

Osteogenesis of Crouzon-Mutated Cells in an Experimental Model

Crouzon syndrome is an autosomal-dominant congenital disease due to a mutation in the fibroblast growth factor receptor 2 protein. The purpose of this study is to evaluate wound-healing potential of Crouzon osteoblasts and adipose-derived stem cells (ADSCs) in a murine model. Parietal skull defects were created in Crouzon and mature wild-type (WT) CD-1 mice. One group of WT and Crouzon mice were left untreated. Another group was transplanted with both WT and Crouzon adipose-derived stem cells. Additional groups compared the use of a fibrin glue scaffold and periosteum removal. Skulls were harvested from each group and evaluated histologically at 8-week and/or 16-week periods. Mean areas of defect were quantified and compared via ANOVA F-test. The average area of defect after 8 and 16 weeks in untreated Crouzon mice was 15.37 ± 1.08 cm and 16.69 ± 1.51 cm, respectively. The average area of the defect in untreated WT mice after 8 and 16 weeks averaged 14.17 ± 1.88 cm and 14.96 ± 2.26 cm, respectively. WT mice with autologous ADSCs yielded an average area of 15.35 ± 1.34 cm after 16 weeks while Crouzon mice with WT ADSCs healed to an average size of 12.98 ± 1.89 cm. Crouzon ADSCs transplanted into WT mice yielded an average area of 15.47 ± 1.29 cm while autologous Crouzon ADSCs yielded an area of 14.22 ± 3.32 cm. ANOVA F-test yielded P = .415. The fibroblast growth factor receptor 2 mutation in Crouzon syndrome does not promote reossification of critical-sized defects in mature WT and Crouzon mice. Furthermore, Crouzon ADSCs do not possess osteogenic advantage over WT ADSCs.

Adipose Tissue as a Strategic Source of Mesenchymal Stem Cells in Bone Regeneration: A Topical Review on the Most Promising Craniomaxillofacial Applications

Bone regeneration in craniomaxillofacial surgery represents an issue that involves both surgical and aesthetic aspects. The most recent studies on bone tissue engineering involving adipose-derived stromal/stem cells (ASCs) have clearly demonstrated that such cells can play a crucial role in the treatment of craniomaxillofacial defects, given their strong commitment towards the osteogenic phenotype. A deeper knowledge of the molecular mechanisms underlying ASCs is crucial for a correct understanding of the potentialities of ASCs-based therapies in the most complex maxillofacial applications. In this topical review, we analyzed the molecular mechanisms of ASCs related to their support toward angiogenesis and osteogenesis, during bone regeneration. Moreover, we analyzed both case reports and clinical trials reporting the most promising clinical applications of ASCs in the treatment of craniomaxillofacial defects. Our study aimed to report the main molecular and clinical features shown by ASCs, used as a therapeutic support in bone engineering, as compared to the use of conventional autologous and allogeneic bone grafts.

* Calvarial Defects: Cell-Based Reconstructive Strategies in the Murine Model

Calvarial defects pose a continued clinical dilemma for reconstruction. Advancements within the fields of stem cell biology and tissue engineering have enabled researchers to develop reconstructive strategies using animal models. We review the utility of various animal models and focus on the mouse, which has aided investigators in understanding cranial development and calvarial bone healing. The murine model has also been used to study regenerative approaches to critical-sized calvarial defects, and we discuss the application of stem cells such as bone marrow-derived mesenchymal stromal cells, adipose-derived stromal cells, muscle-derived stem cells, and pluripotent stem cells to address deficient bone in this animal. Finally, we highlight strategies to manipulate stem cells using various growth factors and inhibitors and ultimately how these factors may prove crucial in future advancements within calvarial reconstruction using native skeletal stem cells.

Cryopreserved Adipose Tissue-Derived Stromal/Stem Cells: Potential for Applications in Clinic and Therapy

Adipose-Derived Stromal/Stem Cells (ASC) have considerable potential for regenerative medicine due to their abilities to proliferate, differentiate into multiple cell lineages, high cell yield, relative ease of acquisition, and almost no ethical concerns since they are derived from adult tissue. Storage of ASC by cryopreservation has been well described that maintains high cell yield and viability, stable immunophenotype, and robust differentiation potential post-thaw. This ability is crucial for banking research and for clinical therapeutic purposes that avoid the morbidity related to repetitive liposuction tissue harvests. ASC secrete various biomolecules such as cytokines which are reported to have immunomodulatory properties and therapeutic potential to reverse symptoms of multiple degenerative diseases/disorders. Nevertheless, safety regarding the use of these cells clinically is still under investigation. This chapter focuses on the different aspects of cryopreserved ASC and the methods to evaluate their functionality for future clinical use.

Sandwich-type PLLA-nanosheets loaded with BMP-2 induce bone regeneration in critical-sized mouse calvarial defects

To overcome serious clinical problems caused by large bone defects, various approaches to bone regeneration have been researched, including tissue engineering, biomaterials, stem cells and drug screening. Previously, we developed a free-standing biodegradable polymer nanosheet composed of poly(L-lactic acid) (PLLA) using a simple fabrication process consisting of spin-coating and peeling techniques. Here, we loaded recombinant human bone morphogenetic protein-2 (rhBMP-2) between two 60-nm-thick PLLA nanosheets, and investigated these sandwich-type nanosheets in bone regeneration applications. The PLLA nanosheets displayed constant and sustained release of the loaded rhBMP-2 for over 2months in vitro. Moreover, we implanted the sandwich-type nanosheets with or without rhBMP-2 into critical-sized defects in mouse calvariae. Bone regeneration was evident 4weeks after implantation, and the size and robustness of the regenerated bone had increased by 8weeks after implantation in mice implanted with the rhBMP-2-loaded nanosheets, whereas no significant bone formation occurred over a period of 20weeks in mice implanted with blank nanosheets. The PLLA nanosheets loaded with rhBMP-2 may be useful in bone regenerative medicine; furthermore, the sandwich-type PLLA nanosheet structure may potentially be applied as a potent prolonged sustained-release carrier of other molecules or drugs.

STATEMENTS OF SIGNIFICANCE

Here we describe sandwich-type poly(L-lactic acid) (PLLA) nanosheets loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) as a novel method for bone regeneration. Biodegradable 60-nm-thick PLLA nanosheets display strong adhesion without any adhesive agent. The sandwich-type PLLA nanosheets displayed constant and sustained release of the loaded rhBMP-2 for over 2months in vitro. The nanosheets with rhBMP-2 markedly enhanced bone regeneration when they were implanted into critical-sized defects in mouse calvariae. In addition to their application for bone regeneration, PLLA nanosheets may be useful for various purposes in combination with various drugs or molecules, because they displays excellent capacity as a sustained-release carrier.

CXCL12 overexpression promotes the angiogenesis potential of periodontal ligament stem cells

Periodontal ligament stem cells (PDLSCs) are a major source of mesenchymal stem cells (MSCs) in adults and are effective for tissue engineering, like promoting angiogenesis and bone regeneration. CXCL12 has been reported to be involved in the recruitment and engraftment of MSCs in wound sites. However, whether CXCL12 potentiates the angiogenesis of PDLSCs is not clear. In this experiment, we transduced PDLSCs with CXCL12, and evaluated the angiogenesis potential of CXCL12-modified PDLSCs through in vitro and in vivo studies. The results showed that CXCL12 overexpression significantly stimulated the gene and protein expressions of bFGF, VEGF, SCF and PLGF in PDLSCs; CXCL12 gene modified PDLSCs formed longer capillary‐like structure; Moreover, in vivo transplanted PDLSCs transduced with CXCL12 could significantly promote bone tissue repair and angiogenesis in a rat critical-sized calvarial bone defect model. Taken together, our study confirmed that CXCL12 can enhance the angiogenesis potential of PDLSCs, which are crucial in the repair and regeneration of bone tissue.

Improved Bone Regeneration With Multiporous PLGA Scaffold and BMP-2-Transduced Human Adipose-Derived Stem Cells by Cell-Permeable Peptide

OBJECTIVE

Currently, much work has focused on the engineering of bone using adipose-derived stem cells (ADSCs), which differentiate into osteogenic cells. This study was conducted to assess the bone-regenerating capacity of ADSCs with genetic modification.

MATERIALS AND METHODS

ADSCs were cultured and transduced with recombinant adenovirus-expressing bone morphogenetic protein-2 (rAd/BMP-2). Two 5-mm full-thickness bone defects were created on the parietal bones of 24 rats. The defects were left empty (n = 12), restored with a scaffold alone (n = 12), transplanted with ADSCs in osteogenic media (n = 12), or transplanted with rAd/BMP-2-transduced ADSCs (n = 12). Six defects from each group were assessed by histologic observation, histomorphometric analysis, and microcomputed tomography (micro-CT) imaging at 4 and 8 weeks after transplantation.

RESULTS

Increased new bone formation was observed in the rAd/BMP-2-transduced ADSC groups, compared with the other groups. On micro-CT, significant differences were noted in bone volume-to-tissue volume ratios between rAd/BMP-2-transduced ADSCs group and the other groups at both time points (P < 0.05).

CONCLUSION

The result demonstrates that transferring BMP-2 promotes the osteogenic differentiation of ADSCs and enhances bone regeneration. Under limitation of this study, genetic modification of ADSCs with BMP-2 could be adopted in clinical application.

Adipose-derived stem cells: Comparison between two methods of isolation for clinical applications

Background

Adipose-derived stem cells are recognized as being an effective mesenchymal stem cell population with enormous potential in different fields of regenerative medicine and stem cell therapy. Although there is unanimous agreement on the harvesting procedure for adipose tissue, there are various protocols for adipose-derived stem cell isolation. The aim of this study was compare two methods of adipose-derived stem cells (ASCs) isolation, one based on a mechanical + enzymatic (ME) procedure and the other one exclusively mechanical (MC), in order to determine which one was superior to the other in accordance with current European and US legislation.

Methods

We reported step by step the two different methods ASCs isolation by comparing them. The ME procedure included the use of a centrifuge, an incubator and collagenase digestion solution (Collagenase NB 6 GMP Grade 17458; Serva GmbH, Heidelberg, Germany). The MC procedure was performed by vibrating shaker and centrifuge, both placed in a laminar airflow bench.

Results

With the ME procedure, a mean of 9.06 × 10⁵ ASCs (range, 8.4 to 9.72 × 10⁵; SD ± 6.6 × 10⁵) was collected, corresponding to 25.9% of the total number of harvested cells. With the MC procedure, a mean of 5 × 10⁵ ASCs (range: 4.0 to 6.0 × 10⁵; SD, ±1 × 10⁵) was collected, corresponding to 5% of the total number of harvested cells.

Conclusion

Based on data collected, from the same amount of lipoaspirate the ME procedure allowed to isolate a greater number of ASCs (25,9%) compared to the MC one (5%).

•

Adipose-derived stem cells (ASCs) are effective mesenchymal stem cell population with enormous potential.

•

In this study we compared two methods of adipose-derived stem cells (ASCs) isolation.

•

Gathered data showed a greater amount of isolated ASCs by the ME procedure as compared to the MC one.

A Versatile Protocol for Studying Calvarial Bone Defect Healing in a Mouse Model

Animal models are vital tools for the preclinical development and testing of therapies aimed at providing solutions for several musculoskeletal disorders. For bone tissue engineering strategies addressing nonunion conditions, rodent models are particularly useful for studying bone healing in a controlled environment. The mouse calvarial defect model permits evaluation of drug, growth factor, or cell transplantation efficacy, together with offering the benefit of utilizing genetic models to study intramembranous bone formation within defect sites. In this study, we describe a detailed methodology for creating calvarial defects in mouse and present our results on bone morphogenetic protein-2-loaded fibrin scaffolds, thus advocating the utility of this functional orthotopic mouse model for the evaluation of therapeutic interventions (such as growth factors or cells) intended for successful bone regeneration therapies.

Keratin/chitosan UV-crosslinked composites promote the osteogenic differentiation of human adipose derived stem cells

Keratin has intrinsic biocompatibility and contains several peptide-binding motifs that support the attachment of a wide variety of cell types. We have previously shown that keratin extracted from human hair can promote cell adhesion and proliferation of 3T3 fibroblasts, MG63 osteoblasts, and human adipose stem cells (hASCs). Despite its bioactivity advantages, keratin possesses fragile mechanical properties that introduce challenges for tissue engineering. To remedy this, we examined the results of combining keratin with chitosan, a combination facilitated via induction of an azide functional group, which acted as a photocrosslinker, to improve mechanical strength. Analysis of the keratin/chitosan composite showed that films of this material demonstrated good adhesion and promoted the proliferation of human adipose stem cells. Most importantly, this biomaterial was shown to promote the osteogenic differentiation of hASCs, in terms of up-regulations in type I collagen, runt-related transcription factor 2, and alkaline phosphatase gene expression. We further demonstrated that lyophilizing the keratin/chitosan forms highly interconnected and porous scaffolds that might provide an ideal environment for tissue culture. We believe that keratin/chitosan composite biomaterials can be used in bioactive surface modification, and the crosslinkable properties can produce natural polymer 3D scaffolds for the application of tissue engineering research.

Mechanoresponsiveness of human adipose stem cells on nanocomposite and micro-hybrid composite

Resin-based composites are used for bone repair applications and comprise resin matrix and different sized filler particles. Nanometer-sized filler particles improve composite's mechanical properties compared with micrometer-sized filler particles, but whether differences exist in the biological response to these composites is unknown. Natural bone comprises a nanocomposite structure, and nanoscale interactions with extracellular matrix components influence stem cell differentiation. Therefore we hypothesized that nanometer-sized filler particles in resin-based composites enhance osteogenic differentiation of stem cells showing a more bone cell-like response to mechanical loading compared with micrometer-sized filler particles. Pulsating fluid flow (PFF; 5 Hz, mean shear stress: 0.7 Pa; 1 h) rapidly, within 5 min, increased nitric oxide production in human adipose stem cells (hASCs) on nanocomposite, but not on micro-hybrid composite. PFF increased RUNX2 expression in hASCs on micro-hybrid composite, but not on nanocomposite after 2 h post-incubation. PFF did not affect mean cell orientation and shape index of hASCs on both composites. In conclusion, the PFF-increased nitric oxide production in hASCs on nanocomposite, and increased osteogenic differentiation of hASCs on micro-hybrid composite suggest different responses to mechanical loading of hASCs on composite with nanometer-sized and micrometer-sized filler particles. This might have important implications for bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2986-2994, 2017.

The biological and clinical basis for the use of adipose-derived stem cells in the field of wound healing

Worldwide, hard-to-heal lower limb wounds are estimated to affect 1.5–3% of the adult population with a treatment-related annual cost of $10 billion. Thus, chronic skin ulcers of the lower limb are a matter of economic and public concern. Over the years, multiple medical and surgical approaches have been proposed but they are still inadequate, and no effective therapy yet exists. Regenerative medicine and stem cell-based therapies hold great promise for wound healing. Recently, many plastic surgeons have studied the potential clinical application of adipose-derived stem cells (ASCs), which are a readily available adult stem cell population that can undergo multilineage differentiation and secrete growth factors that can enhance wound-healing processes by promoting angiogenesis, and hence increase local blood supply. ASCs have been widely studied in vitro and in vivo in animal models. However, there are few randomized clinical trials on humans, and these are still ongoing or recruiting patients. Moreover, there is no consensus on a common isolation protocol that is clinically feasible and which would ensure reproducible results. The authors aim to provide readers with an overview of the biological properties of ASCs as well as their clinical application, to help better understanding of present and future strategies for the treatment of hard-to-heal wounds by means of stem cell-based therapies.

•

Worldwide, hard-to-heal wounds are a matter of economic and public concern.

•

The emerging fields of regenerative medicine and stem cell-based therapies hold great promise for wound healing.

•

ASCs can potentially give the support necessary for recovery of hard-to-heal wounds.

•

ASCs can be easily harvested from adipose tissue by means of standard wet liposuction technique.

•

ASCs have been widely studied in vitro and in vivo to demonstrate their potential and safety.

A Novel Method of Human Adipose-Derived Stem Cell Isolation with Resultant Increased Cell Yield

BACKGROUND

The authors have developed a novel protocol for isolating adipose-derived stem cells from human lipoaspirate. In this study, they compare their new method to a previously published standard protocol.

METHODS

Human adipose-derived stem cell isolation was performed using two methods to compare cell yield, cell viability, cell proliferation, and regenerative potential. The new and conventional isolation methods differ in two key areas: the collagenase digestion buffer constituents and the use of an orbital shaker. The osteogenic and adipogenic potential of adipose-derived stem cells isolated using both protocols was assessed in vitro, and gene expression analysis was performed. To assess the ability of the isolated cells to generate bone in vivo, the authors created critical-size calvarial defects in mice, which were treated with adipose-derived stem cells loaded onto hydroxyapatite-coated poly(lactic-co-glycolic acid) scaffolds. To test the ability of the isolated cells to enhance adipogenesis, the cells were added to lipoaspirate and placed beneath the scalp of immunocompromised mice. Fat graft volume retention was subsequently assessed by serial computed tomographic volumetric scanning.

RESULTS

The new method resulted in a 10-fold increased yield of adipose-derived stem cells compared with the conventional method. Cells harvested using the new method demonstrated significantly increased cell viability and proliferation in vitro (p < 0.05). New method cells also demonstrated significantly enhanced osteogenic and adipogenic differentiation capacity in vitro (p < 0.05) in comparison with the conventional method cells. Both cell groups demonstrated equivalent osteogenic and adipogenic regenerative potential in mice.

CONCLUSIONS

The authors have developed a protocol that maximizes the yield of adipose-derived stem cells derived from lipoaspirate. The new method cells have increased osteogenic and adipogenic potential in vitro and are not inferior to conventional method cells in terms of their ability to generate bone and fat in vivo.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Surface micromorphology of cross-linked tetrafunctional polylactide scaffolds inducing vessel growth and bone formation

In the presented study, we have developed a synthetic strategy allowing a gradual variation of a polylactide arms' length, which later influences the micromorphology of the scaffold surface, formed by a two-photon polymerization technique. It has been demonstrated that the highest number of cells is present on the scaffolds with the roughest surface made of the polylactide with longer arms (PLA760), and osteogenic differentiation of mesenchymal stem cells is most pronounced on such scaffolds. According to the results of biological testing, the PLA760 scaffolds were implanted into a created cranial defect in a mouse for an in vivo assessment of the bone tissue formation. The in vivo experiments have shown that, by week 10, deposition of calcium phosphate particles occurs in the scaffold at the defect site, as well as, the formation of a new bone and ingrowth of blood vessels from the surrounding tissues. These results demonstrate that the cross-linked microstructured tetrafunctional polylactide scaffolds are promising microstructures for bone regeneration in tissue engineering.

Induction of osteoblastic differentiation of neural crest-derived stem cells from hair follicles

The neural crest (NC) arises near the neural tube during embryo development. NC cells migrate throughout the embryo and have potential to differentiate into multiple cell types, such as peripheral nerves, glial, cardiac smooth muscle, endocrine, and pigment cells, and craniofacial bone. In the present study, we induced osteoblast-like cells using whisker follicles obtained from the NC of mice. Hair follicle cells derived from the NC labeled with enhanced green fluorescent protein (EGFP) were collected from protein zero-Cre/floxed-EGFP double transgenic mice and cultured, then treated and cultured in stem cell growth medium. After growth for 14 days, results of flow cytometry analysis showed that 95% of the EGFP-positive (EGFP+) hair follicle cells derived from the NC had proliferated and 76.2% of those expressed mesenchymal stem cells markers, such as platelet-derived growth factor α and stem cell antigen-1, and also showed constitutive expression of Runx2 mRNA. Cells stimulated with bone morphogenetic protein-2 expressed osteocalcin, osterix, and alkaline phosphatase mRNA, resulting in production of mineralized matrices, which were detected by von Kossa and alizarin red staining. Moreover, EGFP+ hair follicle cells consistently expressed macrophage colony-stimulating factor and osteoprotegerin (OPG). Addition of 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] (10-8 M) to the cultures suppressed OPG expression and induced RANKL production in the cells. Furthermore, multinucleated osteoclasts appeared within 6 days after starting co-cultures of bone marrow cells with EGFP+ cells in the presence of 1,25(OH)2D3 and PGE2. These results suggest that NC-derived hair follicle cells possess a capacity for osteoblastic differentiation and may be useful for developing new bone regenerative medicine therapies.

Postnatal Calvarial Skeletal Stem Cells Expressing PRX1 Reside Exclusively in the Calvarial Sutures and Are Required for Bone Regeneration

Post-natal skeletal stem cells expressing PRX1 (pnPRX1+) have been identified in the calvaria and in the axial skeleton. Here we characterize the location and functional capacity of the calvarial pnPRX1⁺ cells. We found that pnPRX1⁺ reside exclusively in the calvarial suture niche and decrease in number with age. They are distinct from preosteoblasts and osteoblasts of the sutures, respond to WNT signaling in vitro and in vivo by differentiating into osteoblasts, and, upon heterotopic transplantation, are able to regenerate bone. Diphtheria toxin A (DTA)-mediated lineage ablation of pnPRX1⁺ cells and suturectomy perturb regeneration of calvarial bone defects and confirm that pnPRX1⁺ cells of the sutures are required for bone regeneration. Orthotopic transplantation of sutures with traceable pnPRX1⁺ cells into wild-type animals shows that pnPRX1⁺ cells of the suture contribute to calvarial bone defect regeneration. DTA-mediated lineage ablation of pnPRX1⁺ does not, however, interfere with calvarial development.

•

The suture is the exclusive niche of the calvarial PRX1-expressing cells

•

Postnatal PRX1-expressing cells of the calvaria are required for bone regeneration

•

Postnatal Prx1-expressing cells of the calvaria are dispensable for development

Opposite Effects of Mechanical Action of Fluid Flow on Proangiogenic Factor Secretion From Human Adipose-Derived Stem Cells With and Without Oxidative Stress

Mechanical forces, hypoxia, and oxidative stress contribute to skin renewal, perfusion, and wound healing, but how are they regulating subcutaneous adipose-derived stem cells (ASCs) in the inflammatory microenvironment associated to skin repair and disorders is unknown. In this study, ASCs were isolated from lipoaspirate samples from plastic surgery patients, primary cultured and their differentiation and secretion of a panel of cytokines with pronounced effects on skin repair and angiogenesis were studied under mechanical stimulation by intermittent fluid flow, 1% hypoxia and oxidative stress by glutathione (GSH) depletion with buthionine sulfoximine (BSO) treatment. Mechanical action of fluid flow did not alter mesenchymal phenotype of CD90⁺ /CD29⁺ /CD44⁺ /CD34^- /CD106^- /CD45^- ASCs; however, it remarkably induced ASC secretion of human umbilical vein endothelial cell (HUVEC) migration-stimulating factors. Multiplex Luminex assay further confirmed an increased secretion of VEGF, G-CSF, HGF, Leptin, IL-8, PDGF-BB, Angiopoietin-2, and Follistatin from mechanically-stimulated ASCs via cyclooxygenase-2. Consistent with this mechanism, GSH depletion and hypoxia also increased ASC secretion of VEGF, IL-8, leptin, Angiopoitein-2, and PDGF-BB. However, mechanical action of fluid flow abrogated VEGF and HUVEC migration-stimulating activity from GSH-depleted and hypoxic ASCs. Conversely, GSH depletion and hypoxia abrogated VEGF and HUVEC migration-stimulating activity from mechano-stimulated ASCs. Although mechanical action of fluid flow, hypoxia, and GSH-depletion had independent proangiogenic-stimulating activity on ASCs, mechanical stimulation had opposite effects on proangiogenic factor secretion from ASCs with and without oxidative stress. These data uncover the role of hypoxia and endogenous redox balance during the proangiogenic response of ASCs and other mesenchymal-derived cell types to mechanical action of interstitial fluid flow. J. Cell. Physiol. 232: 2158-2167, 2017. © 2016 Wiley Periodicals, Inc.

Generation and characterization of two immortalized human osteoblastic cell lines useful for epigenetic studies

Different model systems using osteoblastic cell lines have been developed to help understand the process of bone formation. Here, we report the establishment of two human osteoblastic cell lines obtained from primary cultures upon transduction of immortalizing genes. The resulting cell lines had no major differences to their parental lines in their gene expression profiles. Similar to primary osteoblastic cells, osteocalcin transcription increased following 1,25-dihydroxyvitamin D₃ treatment and the immortalized cells formed a mineralized matrix, as detected by Alizarin Red staining. Moreover, these human cell lines responded by upregulating ALPL gene expression after treatment with the demethylating agent 5-aza-2'-deoxycytidine (AzadC), as shown before for primary osteoblasts. We further demonstrate that these cell lines can differentiate in vivo, using a hydroxyapatite/tricalcium phosphate composite as a scaffold, to produce bone matrix. More importantly, we show that these cells respond to demethylating treatment, as shown by the increase in SOST mRNA levels, the gene encoding sclerostin, upon treatment of the recipient mice with AzadC. This also confirms, in vivo, the role of DNA methylation in the regulation of SOST expression previously shown in vitro. Altogether our results show that these immortalized cell lines constitute a particularly useful model system to obtain further insight into bone homeostasis, and particularly into the epigenetic mechanisms regulating sclerostin production.

A Comprehensive In Vitro Comparison of Preparation Techniques for Fat Grafting

BACKGROUND

Lipomodeling is a technique that uses the patient's own fat for tissue regeneration and augmentation. The extent of regenerative effect is reported to be determined by the numbers of adipose-derived stem cells and the viability of cells in processed adipose tissue which, together with other factors, influence the degree of graft retention. This study addresses whether differences exist in properties of fat graft obtained by three commonly used techniques.

METHODS

Adipose tissue harvested from the hypogastric regions of 14 patients was processed by decantation, centrifugation, and membrane-based tissue filtration. The morphology of each preparation was assessed by electron microscopy and overall cell viability was assessed by live/dead assay. The number of adipose-derived stem cells was determined and their stem cell character was assessed by the presence of cell surface molecules (i.e., CD105, CD90, CD31, and CD45) and by their capacity to differentiate into adipogenic and osteogenic lineages.

RESULTS

First, morphologies of processed fat samples obtained by individual procedures differed, but no preparation caused obvious damage to cellular or acellular components. Second, although the highest numbers of adipose-derived stem cells were contained in the upper fraction of centrifuged lipoaspirates, the difference between preparations was marginal. Third, the maximal concentration of adipose fraction (removal of watery component) of lipoaspirate was achieved by membrane-based tissue filtration. Finally, no significant differences in overall viability were detected.

CONCLUSIONS

Properties of processed lipoaspirate were influenced by the preparation procedure. However, the differences were not dramatic; both centrifugation and membrane-based filtration are methods of choice whose selection depends on other criteria (e.g., practicality) for individual surgical settings.

Potentiating bioactivity of BMP-2 by polyelectrolyte complexation with sulfonated polyrotaxanes to induce rapid bone regeneration in a mouse calvarial defect

Bone reconstruction is a challenging issue in the regeneration of surgically removed bone and disease-related bone defects. Although bone morphogenetic protein-2 (BMP-2) has received considerable attention as a bone regeneration inducer, a high dose of BMP-2 is typically required due to its short life-time under in vivo conditions. We have proposed a method to enhance the osteogenetic differentiation ability of BMP-2 in vitro that is based on supramolecular polyelectrolyte complexation with sulfonated polyrotaxanes (PRXs) consisting of sulfopropyl ether (SPE)-modified α-cyclodextrins threaded along a poly(ethylene glycol) chain capped with terminal bulky stopper molecules. In this study, we evaluated the in vivo bone regeneration ability of the SPE-PRX/BMP-2 complexes in a mouse calvarial defect model in comparison to free BMP-2 and heparin/BMP-2 complexes. The regenerated bone area was determined by X-ray computed microtomography, and the mice implanted with sulfonated PRX/BMP-2 complexes exhibited rapid and significant bone regeneration compared to those implanted with free BMP-2 and heparin/BMP-2 complexes. We concluded that the sulfonated PRX/BMP-2 complexes are a promising candidate for clinical bone regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1355-1363, 2017.