Effect of Incomplete Cryoablation and Matrix Metalloproteinase Inhibition on Intratumoral CD8+ T-Cell Infiltration in Murine Hepatocellular Carcinoma

Background Image-guided tumor ablation is the first-line therapy for early-stage hepatocellular carcinoma (HCC), with ongoing investigations into its combination with immunotherapies. Matrix metalloproteinase (MMP) inhibition demonstrates immunomodulatory potential and reduces HCC tumor growth when combined with ablative treatment. Purpose To evaluate the effect of incomplete cryoablation with or without MMP inhibition on the local immune response in residual tumors in a murine HCC model. Materials and Methods Sixty 8- to 10-week-old female BALB/c mice underwent HCC induction with use of orthotopic implantation of syngeneic Tib-75 cells. After 7 days, mice with a single lesion were randomized into treatment groups: (a) no treatment, (b) MMP inhibitor, (c) incomplete cryoablation, and (d) incomplete cryoablation and MMP inhibitor. Macrophage and T-cell subsets were assessed in tissue samples with use of immunohistochemistry and immunofluorescence (cell averages calculated using five 1-μm2 fields of view [FOVs]). C-X-C motif chemokine receptor type 3 (CXCR3)- and interferon γ (IFNγ)-positive T cells were assessed using flow cytometry. Groups were compared using unpaired Student t tests, one-way analysis of variance with Tukey correction, and the Kruskal-Wallis test with Dunn correction. Results Mice treated with incomplete cryoablation (n = 6) showed greater infiltration of CD206+ tumor-associated macrophages (mean, 1.52 cells per FOV vs 0.64 cells per FOV; P = .03) and MMP9-expressing cells (mean, 0.89 cells per FOV vs 0.11 cells per FOV; P = .03) compared with untreated controls (n = 6). Incomplete cryoablation with MMP inhibition (n = 6) versus without (n = 6) led to greater CD8+ T-cell (mean, 15.8% vs 8.29%; P = .04), CXCR3+CD8+ T-cell (mean, 11.64% vs 8.47%; P = .004), and IFNγ+CD8+ T-cell infiltration (mean, 11.58% vs 5.18%; P = .02). Conclusion In a mouse model of HCC, incomplete cryoablation and systemic MMP inhibition showed increased cytotoxic CD8+ T-cell infiltration into the residual tumor compared with either treatment alone. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Gemmete in this issue.

Rationale and design of the Nephrotic Syndrome Study Network (NEPTUNE) Match in glomerular diseases: designing the right trial for the right patient, today

Glomerular diseases are classified using a descriptive taxonomy that is not reflective of the heterogeneous underlying molecular drivers. This limits not only diagnostic and therapeutic patient management, but also impacts clinical trials evaluating targeted interventions. The Nephrotic Syndrome Study Network (NEPTUNE) is poised to address these challenges. The study has enrolled >850 pediatric and adult patients with proteinuric glomerular diseases who have contributed to deep clinical, histologic, genetic, and molecular profiles linked to long-term outcomes. The NEPTUNE Knowledge Network, comprising combined, multiscalar data sets, captures each participant's molecular disease processes at the time of kidney biopsy. In this editorial, we describe the design and implementation of NEPTUNE Match, which bridges a basic science discovery pipeline with targeted clinical trials. Noninvasive biomarkers have been developed for real-time pathway analyses. A Molecular Nephrology Board reviews the pathway maps together with clinical, laboratory, and histopathologic data assembled for each patient to compile a Match report that estimates the fit between the specific molecular disease pathway(s) identified in an individual patient and proposed clinical trials. The NEPTUNE Match report is communicated using established protocols to the patient and the attending nephrologist for use in their selection of available clinical trials. NEPTUNE Match represents the first application of precision medicine in nephrology with the aim of developing targeted therapies and providing the right medication for each patient with primary glomerular disease.

Evidence that pyrophosphate acts as an extracellular signalling molecule to exert direct functional effects in primary cultures of osteoblasts and osteoclasts

Extracellular pyrophosphate (PPi) is well known for its fundamental role as a physiochemical mineralisation inhibitor. However, information about its direct actions on bone cells remains limited. This study shows that PPi decreased osteoclast formation and resorptive activity by ≤50 %. These inhibitory actions were associated with reduced expression of genes involved in osteoclastogenesis (Tnfrsf11a, Dcstamp) and bone resorption (Ctsk, Car2, Acp5). In osteoblasts, PPi present for the entire (0-21 days) or latter stages of culture (7-21/14-21 days) decreased bone mineralisation by ≤95 %. However, PPi present for the differentiation phase only (0-7/0-14 days) increased bone formation (≤70 %). Prolonged treatment with PPi resulted in earlier matrix deposition and increased soluble collagen levels (≤2.3-fold). Expression of osteoblast (RUNX2, Bglap) and early osteocyte (E11, Dmp1) genes along with mineralisation inhibitors (Spp1, Mgp) was increased by PPi (≤3-fold). PPi levels are regulated by tissue non-specific alkaline phosphatase (TNAP) and ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1). PPi reduced NPP1 expression in both cell types whereas TNAP expression (≤2.5-fold) and activity (≤35 %) were increased in osteoblasts. Breakdown of extracellular ATP by NPP1 represents a key source of PPi. ATP release from osteoclasts and osteoblasts was decreased ≤60 % by PPi and by a selective TNAP inhibitor (CAS496014-12-2). Pertussis toxin, which prevents Gαi subunit activation, was used to investigate whether G-protein coupled receptor (GPCR) signalling mediates the effects of PPi. The actions of PPi on bone mineralisation, collagen production, ATP release, gene/protein expression and osteoclast formation were abolished or attenuated by pertussis toxin. Together these findings show that PPi, modulates differentiation, function and gene expression in osteoblasts and osteoclasts. The ability of PPi to alter ATP release and NPP1/TNAP expression and activity indicates that cells can detect PPi levels and respond accordingly. Our data also raise the possibility that some actions of PPi on bone cells could be mediated by a Gαi-linked GPCR.

Identifying Fibroblast Growth Factor Receptor 3 as a Mediator of Periosteal Osteochondral Differentiation through the Construction of microRNA-Based Interaction Networks

Human periosteum-derived progenitor cells (hPDCs) have the ability to differentiate towards both the chondrogenic and osteogenic lineages. This coordinated and complex osteochondrogenic differentiation process permits endochondral ossification and is essential in bone development and repair. We have previously shown that humanised cultures of hPDCs enhance their osteochondrogenic potentials in vitro and in vivo; however, the underlying mechanisms are largely unknown. This study aimed to identify novel regulators of hPDC osteochondrogenic differentiation through the construction of miRNA-mRNA regulatory networks derived from hPDCs cultured in human serum or foetal bovine serum as an alternative in silico strategy to serum characterisation. Sixteen differentially expressed miRNAs (DEMis) were identified in the humanised culture. In silico analysis of the DEMis with TargetScan allowed for the identification of 1503 potential miRNA target genes. Upon comparison with a paired RNAseq dataset, a 4.5% overlap was observed (122 genes). A protein-protein interaction network created with STRING interestingly identified FGFR3 as a key network node, which was further predicted using multiple pathway analyses. Functional analysis revealed that hPDCs with the activating mutation FGFR3N540K displayed increased expressions of chondrogenic gene markers when cultured under chondrogenic conditions in vitro and displayed enhanced endochondral bone formation in vivo. A further histological analysis uncovered known downstream mediators involved in FGFR3 signalling and endochondral ossification to be upregulated in hPDC FGFR3N540K-seeded implants. This combinational approach of miRNA-mRNA-protein network analysis with in vitro and in vivo characterisation has permitted the identification of FGFR3 as a novel mediator of hPDC biology. Furthermore, this miRNA-based workflow may also allow for the identification of drug targets, which may be of relevance in instances of delayed fracture repair.

A Machine Learning-Based Image Segmentation Method to Quantify In Vitro Osteoclast Culture Endpoints

Quantification of in vitro osteoclast cultures (e.g. cell number) often relies on manual counting methods. These approaches are labour intensive, time consuming and result in substantial inter- and intra-user variability. This study aimed to develop and validate an automated workflow to robustly quantify in vitro osteoclast cultures. Using ilastik, a machine learning-based image analysis software, images of tartrate resistant acid phosphatase-stained mouse osteoclasts cultured on dentine discs were used to train the ilastik-based algorithm. Assessment of algorithm training showed that osteoclast numbers strongly correlated between manual- and automatically quantified values (r = 0.87). Osteoclasts were consistently faithfully segmented by the model when visually compared to the original reflective light images. The ability of this method to detect changes in osteoclast number in response to different treatments was validated using zoledronate, ticagrelor, and co-culture with MCF7 breast cancer cells. Manual and automated counting methods detected a 70% reduction (p < 0.05) in osteoclast number, when cultured with 10 nM zoledronate and a dose-dependent decrease with 1-10 μM ticagrelor (p < 0.05). Co-culture with MCF7 cells increased osteoclast number by ≥ 50% irrespective of quantification method. Overall, an automated image segmentation and analysis workflow, which consistently and sensitively identified in vitro osteoclasts, was developed. Advantages of this workflow are (1) significantly reduction in user variability of endpoint measurements (93%) and analysis time (80%); (2) detection of osteoclasts cultured on different substrates from different species; and (3) easy to use and freely available to use along with tutorial resources.

Novel insights on the effect of sclerostin on bone and other organs

As a key regulator of bone homeostasis, sclerostin has garnered a lot of interest over the last two decades. Although sclerostin is primarily expressed by osteocytes and is well known for its role in bone formation and remodelling, it is also expressed by a number of other cells and potentially plays a role in other organs. Herein, we aim to bring together recent sclerostin research and discuss the effect of sclerostin on bone, cartilage, muscle, liver, kidney and the cardiovascular and immune systems. Particular focus is placed on its role in diseases, such as osteoporosis and myeloma bone disease, and the novel development of sclerostin as a therapeutic target. Anti-sclerostin antibodies have recently been approved for the treatment of osteoporosis. However, a cardiovascular signal was observed, prompting extensive research into the role of sclerostin in vascular and bone tissue crosstalk. The study of sclerostin expression in chronic kidney disease was followed by the investigation of its role in liver-lipid-bone interactions, and the recent discovery of sclerostin as a myokine prompted new research into sclerostin within the bone-muscle relationship. Potentially, the effects of sclerostin reach beyond that of bone alone. We further summarise recent developments in the use of sclerostin as a potential therapeutic for osteoarthritis, osteosarcoma and sclerosteosis. Overall, these new treatments and discoveries illustrate progress within the field, however, also highlight remaining gaps in our knowledge.

The Prrx1eGFP Mouse Labels the Periosteum During Development and a Subpopulation of Osteogenic Periosteal Cells in the Adult

The identity of the cells that form the periosteum during development is controversial with current dogma suggesting these are derived from a Sox9-positive progenitor. Herein, we characterize a newly created Prrx1eGFP reporter transgenic mouse line during limb formation and postnatally. Interestingly, in the embryo Prrx1eGFP-labeled cells become restricted around the Sox9-positive cartilage anlage without themselves becoming Sox9-positive. In the adult, the Prrx1eGFP transgene live labels a subpopulation of cells within the periosteum that are enriched at specific sites, and this population is diminished in aged mice. The green fluorescent protein (GFP)-labeled subpopulation can be isolated using fluorescence-activated cell sorting (FACS) and represents approximately 8% of all isolated periosteal cells. The GFP-labeled subpopulation is significantly more osteogenic than unlabeled, GFP-negative periosteal cells. In addition, the osteogenic and chondrogenic capacity of periosteal cells in vitro can be extended with the addition of fibroblast growth factor (FGF) to the expansion media. We provide evidence to suggest that osteoblasts contributing to cortical bone formation in the embryo originate from Prrx1eGFP-positive cells within the perichondrium, which possibly piggyback on invading vascular cells and secrete new bone matrix. In summary, the Prrx1eGFP mouse is a powerful tool to visualize and isolate periosteal cells and to quantify their properties in the embryo and adult. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Reprogramming bone progenitor identity and potency through control of collagen density and oxygen tension

The biophysical microenvironment of the cell is being increasingly used to control cell signaling and to direct cell function. Herein, engineered 3D tuneable biomimetic scaffolds are used to control the cell microenvironment of Adipose-derived Mesenchymal Stromal Cells (AMSC), which exhibit a collagen density-specific profile for early and late stage bone cell lineage status. Cell potency was enhanced when AMSCs were cultured within low collagen density environments in hypoxic conditions. A transitional culture containing varied collagen densities in hypoxic conditions directed differential cell fate responses. The early skeletal progenitor identity (PDPN⁺CD146⁻CD73⁺CD164⁺) was rescued in the cells which migrated into low collagen density gels, with cells continuously exposed to the high collagen density gels displaying a transitioned bone-cartilage-stromal phenotype (PDPN⁺CD146⁺CD73⁻CD164^-). This study uncovers the significant contributions of the physical and physiological cell environment and highlights a chemically independent methodology for reprogramming and isolating skeletal progenitor cells from an adipose-derived cell population.

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Fabrication of a 3D transitional culture to control adipose-derived MSC (AMSC) fate

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AMSC potency is enhanced in low collagen density gels under hypoxic conditions

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Early skeletal progenitor identity of AMSCs is enriched in a low collagen density gel

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Bone-cartilage-stromal identity of AMSCs is enriched in a high collagen density gel

Mindfulness-Based Stress Reduction May Improve Stress, Disease Activity and Inflammatory Cytokine Levels in Autoimmune Hepatitis Patients

Background & Aims

Psychological and life stressors may impact autoimmune hepatitis (AIH) disease activity and increase relapse risk. Mindfulness-based stress reduction (MBSR) is a validated course that reduces stress reactivity, and improves stress and emotion regulation. This single-arm exploratory pilot study of adult patients with AIH aimed to define the impact of an 8-week MBSR program on quality of life, disease activity, and cytokine mediators.

Methods

The perceived stress survey-10 (PSS) and the brief self-control scale (BSCS) measured subjective distress and self-control. Serum alanine aminotransferase (ALT) and cytokine levels were measured, and immunosuppressant doses recorded.

Results

Seventeen patients completed the MBSR program. Post-MBSR, 71% (n = 12) showed PSS score improvement at 8 weeks vs. baseline (median 15 vs. 21, p = 0.02). At 12 months, PSS improvement persisted vs. baseline (median 15 vs. 21, p = 0.02). Post-MBSR, 71% (n = 12) showed BSCS score improvement at 8 weeks vs. baseline (median 4.1 vs. 3.8, p = 0.03). At 12 months, the median BSCS score remained significant (3.9 vs. 3.8, p = 0.03). After the 8-week MBSR, the 35% of patients with ALT >34 U/L had a median ALT reduction (44.5 vs. 71.5 U/L, p = 0.06), whereas the 71% of patients on prednisone had significant dose reductions (5.75 vs. 10 mg, p = 0.02) which persisted at 12 months vs. baseline (3.75 vs. 10 mg, p = 0.02) without a compensatory increase in steroid-sparing dosing. Significant improvement was noted in peripheral blood cytokine levels (IL-6, IL-8, IL-10, IL-17, IL-23, and sCD74/MIF ratio) from baseline to 8 weeks.

Conclusions

MBSR significantly improved perceived stress and self-control scores while decreasing ALT levels, steroid requirements, and inflammatory cytokine levels in this pilot study in adult AIH. Stress modification may impact quality of life and disease activity, and should be further evaluated as an intervention in AIH.

Clinical Trials registration

This study is registered at ClinicalTrials.gov (NCT02950077).

Lay summary

Autoimmune hepatitis can reduce quality of life and mental health, while stress may impact autoimmune hepatitis itself. We piloted mindfulness-based stress reduction as a strategy to reduce stress in adult patients with autoimmune hepatitis and found that the intervention reduced perceived stress and may have also impacted the disease by improving inflammation and medication needs. Stress reduction should be further studied to improve quality of life and possibly to impact disease activity in autoimmune hepatitis.

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Autoimmune hepatitis (AIH) reduces quality of life and mental health; psychological stress may also impact AIH activity.

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Mindfulness-based stress reduction (MBSR) is a strategy to reduce stress and improve quality of life.

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A pilot study of MBSR in adult patients with AIH evaluated its effect on stress, disease activity, and cytokines.

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MBSR reduced perceived stress, which persisted after the study; ALT, medication doses, and cytokines also improved.

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Stress reduction should be further studied in AIH to improve quality of life and possibly to impact disease activity.

Human pluripotent stem cell-derived cartilaginous organoids promote scaffold-free healing of critical size long bone defects

Background

Bones have a remarkable capacity to heal upon fracture. Yet, in large defects or compromised conditions healing processes become impaired, resulting in delayed or non-union. Current therapeutic approaches often utilize autologous or allogeneic bone grafts for bone augmentation. However, limited availability of these tissues and lack of predictive biological response result in limitations for clinical demands. Tissue engineering using viable cell-based implants is a strategic approach to address these unmet medical needs.

Methods

Herein, the in vitro and in vivo cartilage and bone tissue formation potencies of human pluripotent stem cells were investigated. The induced pluripotent stem cells were specified towards the mesodermal lineage and differentiated towards chondrocytes, which subsequently self-assembled into cartilaginous organoids. The tissue formation capacity of these organoids was then challenged in an ectopic and orthotopic bone formation model.

Results

The derived chondrocytes expressed similar levels of collagen type II as primary human articular chondrocytes and produced stable cartilage when implanted ectopically in vivo. Upon targeted promotion towards hypertrophy and priming with a proinflammatory mediator, the organoids mediated successful bridging of critical size long bone defects in immunocompromised mice.

Conclusions

These results highlight the promise of induced pluripotent stem cell technology for the creation of functional cartilage tissue intermediates that can be explored for novel bone healing strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02580-7.

Dual neutralisation of IL-17F and IL-17A with bimekizumab blocks inflammation-driven osteogenic differentiation of human periosteal cells

OBJECTIVES

Interleukin (IL)-17 signalling has been shown to be a key regulator of disease in ankylosing spondylitis (AS) with several IL-17 blockers currently clinically approved. Despite this, the role of IL-17 in bone pathology is poorly understood. This study aimed to investigate IL-17 signalling in the context of pathological bone formation.

METHODS

A biomimetic human periosteum-derived cell (hPDC) model of osteogenic differentiation was used in combination with recombinant IL-17 cytokines, T-cell supernatants or serum from patients with AS. IL-17A, IL-17F and bimekizumab monoclonal antibodies were used to block IL-17 cytokine action.

RESULTS

Recombinant IL-17A and IL-17F are pro-osteogenic with respect to hPDC differentiation. T helper 17 or γδ-T cell supernatants also potently stimulated in vitro bone formation, which was blocked deeper by dual inhibition of IL-17A and IL-17F than by neutralisation of IL-17A or IL-17F individually. Osteogenic blockade may be due to an increase in expression of the Wnt antagonist DKK1. Interestingly, osteocommitment was also induced by serum obtained from patients with AS, which was also abrogated by dual neutralisation of IL-17A and IL-17F.

CONCLUSIONS

These data show for the first time that IL-17A and IL-17F enhance in vitro osteogenic differentiation and bone formation from hPDCs, inhibition of which may offer an attractive therapeutic strategy to prevent pathological bone formation.

Role of Biliary Organoids in Cholestasis Research and Regenerative Medicine

Translational studies in human cholestatic diseases have for years been hindered by various challenges, including the rarity of the disorders, the difficulty in obtaining biliary tissue from across the spectrum of the disease stage, and the difficulty culturing and maintaining primary cholangiocytes. Organoid technology is increasingly being viewed as a technological breakthrough in translational medicine as it allows the culture and biobanking of self-organizing cells from various sources that facilitate the study of pathophysiology and therapeutics, including from individual patients in a personalized approach. This review describes current research using biliary organoids for the study of human cholestatic diseases and the emerging applications of organoids to regenerative medicine directed at the biliary tree. Challenges and possible solutions to the current hurdles in this emerging field, particularly the need for standardization of terminology and clarity on source materials and techniques, are also discussed.

Mapping human serum-induced gene networks as a basis for the creation of biomimetic periosteum for bone repair

BACKGROUND

The periosteum is a highly vascularized, collagen-rich tissue that plays a crucial role in directing bone repair. This is orchestrated primarily by its resident progenitor cell population. Indeed, preservation of periosteum integrity is critical for bone healing. Cells extracted from the periosteum retain their osteochondrogenic properties and as such are a promising basis for tissue engineering strategies for the repair of bone defects. However, the culture expansion conditions and the way in which the cells are reintroduced to the defect site are critical aspects of successful translation. Indeed, expansion in human serum and implantation on biomimetic materials has previously been shown to improve in vivo bone formation.

AIM

This study aimed to develop a protocol to allow for the expansion of human periosteum derived cells (hPDCs) in a biomimetic periosteal-like environment.

METHODS

The expansion conditions were defined through the investigation of the bioactive cues involved in augmenting hPDC proliferative and multipotency characteristics, based on transcriptomic analysis of cells cultured in human serum.

RESULTS

Master regulators of transcriptional networks were identified, and an optimized periosteum-derived growth factor cocktail (PD-GFC; containing β-estradiol, FGF2, TNFα, TGFβ, IGF-1 and PDGF-BB) was generated. Expansion of hPDCs in PD-GFC resulted in serum mimicry with regard to the cell morphology, proliferative capacity and chondrogenic differentiation. When incorporated into a three-dimensional collagen type 1 matrix and cultured in PD-GFC, the hPDCs migrated to the surface that represented the matrix topography of the periosteum cambium layer. Furthermore, gene expression analysis revealed a down-regulated WNT and TGFβ signature and an up-regulation of CREB, which may indicate the hPDCs are recreating their progenitor cell signature.

CONCLUSION

This study highlights the first stage in the development of a biomimetic periosteum, which may have applications in bone repair.

From skeletal development to the creation of pluripotent stem cell-derived bone-forming progenitors

Bone has many functions. It is responsible for protecting the underlying soft organs, it allows locomotion, houses the bone marrow and stores minerals such as calcium and phosphate. Upon damage, bone tissue can efficiently repair itself. However, healing is hampered if the defect exceeds a critical size and/or is in compromised conditions. The isolation or generation of bone-forming progenitors has applicability to skeletal repair and may be used in tissue engineering approaches. Traditionally, bone engineering uses osteochondrogenic stem cells, which are combined with scaffold materials and growth factors. Despite promising preclinical data, limited translation towards the clinic has been observed to date. There may be several reasons for this including the lack of robust cell populations with favourable proliferative and differentiation capacities. However, perhaps the most pertinent reason is the failure to produce an implant that can replicate the developmental programme that is observed during skeletal repair. Pluripotent stem cells (PSCs) can potentially offer a solution for bone tissue engineering by providing unlimited cell sources at various stages of differentiation. In this review, we summarize key embryonic signalling pathways in bone formation coupled with PSC differentiation strategies for the derivation of bone-forming progenitors.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Novel actions of sclerostin on bone

The discovery that two rare autosomal recessive high bone mass conditions were caused by the loss of sclerostin expression prompted studies into its role in bone homeostasis. In this article, we aim to bring together the wealth of information relating to sclerostin in bone though discussion of rare human disorders in which sclerostin is reduced or absent, sclerostin manipulation via genetic approaches and treatment with antibodies that neutralise sclerostin in animal models and in human. Together, these findings demonstrate the importance of sclerostin as a regulator of bone homeostasis and provide valuable insights into its biological mechanism of action. We summarise the current state of knowledge in the field, including the current understanding of the direct effects of sclerostin on the canonical WNT signalling pathway and the actions of sclerostin as an inhibitor of bone formation. We review the effects of sclerostin, and its inhibition, on bone at the cellular and tissue level and discuss new findings that suggest that sclerostin may also regulate adipose tissue. Finally, we highlight areas in which future research is expected to yield additional insights into the biology of sclerostin.

Anabolic Strategies to Augment Bone Fracture Healing

PURPOSE OF REVIEW

The development of therapeutics that target anabolic pathways involved in skeletogenesis is of great importance with regard to disease resulting in bone loss, or in cases of impaired bone repair. This review aims to summarize recent developments in this area.

RECENT FINDINGS

A greater understanding of how drugs that modulate signaling pathways involved in skeletogenesis exert their efficacy, and the molecular mechanisms resulting in bone formation has led to novel pharmacological bone repair strategies. Furthermore, crosstalk between pathways and molecules has suggested signaling synergies that may be exploited for enhanced tissue formation. The sequential pharmacological stimulation of the molecular cascades resulting in tissue repair is a promising strategy for the treatment of bone fractures. It is proposed that a therapeutic strategy which mimics the natural cascade of events observed during fracture repair may be achieved through temporal targeting of tissue repair pathways.

Decellularized Cartilage Directs Chondrogenic Differentiation: Creation of a Fracture Callus Mimetic

Complications that arise from impaired fracture healing have considerable socioeconomic implications. Current research in the field of bone tissue engineering predominantly aims to mimic the mature bone tissue microenvironment. This approach, however, may produce implants that are intrinsically unresponsive to the cues present during the initiation of fracture repair. As such, this study describes the development of decellularized xenogeneic hyaline cartilage matrix in an attempt to mimic the initial reparative phase of fracture repair. Three approaches based on vacuum-assisted osmotic shock (Vac-OS), Triton X-100 (Vac-STx), and sodium dodecyl sulfate (Vac-SDS) were investigated. The Vac-OS methodology reduced DNA content below 50 ng/mg of tissue, while retaining 85% of the sulfate glycosaminoglycan content, and as such was selected as the optimal methodology for decellularization. The resultant Vac-OS scaffolds (decellularized extracellular matrix [dcECM]) were also devoid of the immunogenic alpha-Gal epitope. Furthermore, minimal disruption to the structural integrity of the dcECM was demonstrated using differential scanning calorimetry and fluorescence lifetime imaging microscopy. The biological integrity of the dcECM was confirmed by its ability to drive the chondrogenic commitment and differentiation of human chondrocytes and periosteum-derived cells, respectively. Furthermore, histological examination of dcECM constructs implanted in immunocompetent mice revealed a predominantly M2 macrophage-driven regenerative response both at 2 and 8 weeks postimplantation. These findings contrasted with the implanted native costal cartilage that elicited a predominantly M1 macrophage-mediated inflammatory response. This study highlights the capacity of dcECM from the Vac-OS methodology to direct the key biological processes of endochondral ossification, thus potentially recapitulating the callus phase of fracture repair.

Advancing osteochondral tissue engineering: bone morphogenetic protein, transforming growth factor, and fibroblast growth factor signaling drive ordered differentiation of periosteal cells resulting in stable cartilage and bone formation in vivo

Background

Chondrogenic mesenchymal stem cells (MSCs) have not yet been used to address the clinical demands of large osteochondral joint surface defects. In this study, self-assembling tissue intermediates (TIs) derived from human periosteum-derived stem/progenitor cells (hPDCs) were generated and validated for stable cartilage formation in vivo using two different animal models.

Methods

hPDCs were aggregated and cultured in the presence of a novel growth factor (GF) cocktail comprising of transforming growth factor (TGF)-β1, bone morphogenetic protein (BMP)2, growth differentiation factor (GDF)5, BMP6, and fibroblast growth factor (FGF)2. Quantitative polymerase chain reaction (PCR) and immunohistochemistry were used to study in vitro differentiation. Aggregates were then implanted ectopically in nude mice and orthotopically in critical-size osteochondral defects in nude rats and evaluated by microcomputed tomography (µCT) and immunohistochemistry.

Results

Gene expression analysis after 28 days of in vitro culture revealed the expression of early and late chondrogenic markers and a significant upregulation of NOGGIN as compared to human articular chondrocytes (hACs). Histological examination revealed a bilayered structure comprising of chondrocytes at different stages of maturity. Ectopically, TIs generated both bone and mineralized cartilage at 8 weeks after implantation. Osteochondral defects treated with TIs displayed glycosaminoglycan (GAG) production, type-II collagen, and lubricin expression. Immunostaining for human nuclei protein suggested that hPDCs contributed to both subchondral bone and articular cartilage repair.

Conclusion

Our data indicate that in vitro derived osteochondral-like tissues can be generated from hPDCs, which are capable of producing bone and cartilage ectopically and behave orthotopically as osteochondral units.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0787-3) contains supplementary material, which is available to authorized users.

Folic Acid Exposure Rescues Spina Bifida Aperta Phenotypes in Human Induced Pluripotent Stem Cell Model

Neural tube defects (NTDs) are severe congenital abnormalities, caused by failed closure of neural tube during early embryonic development. Periconceptional folic acid (FA) supplementation greatly reduces the risk of NTDs. However, the molecular mechanisms behind NTDs and the preventive role of FA remain unclear. Here, we use human induced pluripotent stem cells (iPSCs) derived from fetuses with spina bifida aperta (SBA) to study the pathophysiology of NTDs and explore the effects of FA exposure. We report that FA exposure in SBA model is necessary for the proper formation and maturation of neural tube structures and robust differentiation of mesodermal derivatives. Additionally, we show that the folate antagonist methotrexate dramatically affects the formation of neural tube structures and FA partially reverts this aberrant phenotype. In conclusion, we present a novel model for human NTDs and provide evidence that it is a powerful tool to investigate the molecular mechanisms underlying NTDs, test drugs for therapeutic approaches.

Combinatorial Analysis of Growth Factors Reveals the Contribution of Bone Morphogenetic Proteins to Chondrogenic Differentiation of Human Periosteal Cells

Successful application of cell-based strategies in cartilage and bone tissue engineering has been hampered by the lack of robust protocols to efficiently differentiate mesenchymal stem cells into the chondrogenic lineage. The development of chemically defined culture media supplemented with growth factors (GFs) has been proposed as a way to overcome this limitation. In this work, we applied a fractional design of experiment (DoE) strategy to screen the effect of multiple GFs (BMP2, BMP6, GDF5, TGF-β1, and FGF2) on chondrogenic differentiation of human periosteum-derived mesenchymal stem cells (hPDCs) in vitro. In a micromass culture (μMass) system, BMP2 had a positive effect on glycosaminoglycan deposition at day 7 (p < 0.001), which in combination with BMP6 synergistically enhanced cartilage-like tissue formation that displayed in vitro mineralization capacity at day 14 (p < 0.001). Gene expression of μMasses cultured for 7 days with a medium formulation supplemented with 100 ng/mL of BMP2 and BMP6 and a low concentration of GDF5, TGF-β1, and FGF2 showed increased expression of Sox9 (1.7-fold) and the matrix molecules aggrecan (7-fold increase) and COL2A1 (40-fold increase) compared to nonstimulated control μMasses. The DoE analysis indicated that in GF combinations, BMP2 was the strongest effector for chondrogenic differentiation of hPDCs. When transplanted ectopically in nude mice, the in vitro-differentiated μMasses showed maintenance of the cartilaginous phenotype after 4 weeks in vivo. This study indicates the power of using the DoE approach for the creation of new medium formulations for skeletal tissue engineering approaches.

Early warning of footpad dermatitis and hockburn in broiler chicken flocks using optical flow, bodyweight and water consumption

Footpad dermatitis and hockburn are serious welfare and economic issues for the production of broiler (meat) chickens. The authors here describe the use of an inexpensive camera system that monitors the movements of broiler flocks throughout their lives and suggest that it is possible to predict, even in young birds, the cross-sectional prevalence at slaughter of footpad dermatitis and hockburn before external signs are visible. The skew and kurtosis calculated from the authors' camera-based optical flow system had considerably more power to predict these outcomes in the 50 flocks reported here than water consumption, bodyweight or mortality and therefore have the potential to inform improved flock management through giving farmers early warning of welfare issues. Further trials are underway to establish the generality of the results.

Biomimetic strategies for fracture repair: Engineering the cell microenvironment for directed tissue formation

Complications resulting from impaired fracture healing have major clinical implications on fracture management strategies. Novel concepts taken from developmental biology have driven research strategies towards the elaboration of regenerative approaches that can truly harness the complex cellular events involved in tissue formation and repair. Advances in polymer technology and a better understanding of naturally derived scaffolds have given rise to novel biomaterials with an increasing ability to recapitulate native tissue environments. This coupled with advances in the understanding of stem cell biology and technology has opened new avenues for regenerative strategies with true clinical translatability. These advances have provided the impetus to develop alternative approaches to enhance the fracture repair process. We provide an update on these advances, with a focus on the development of novel biomimetic approaches for bone regeneration and their translational potential.

Early BMP, Wnt and Ca(2+)/PKC pathway activation predicts the bone forming capacity of periosteal cells in combination with calcium phosphates

The development of osteoinductive calcium phosphate- (CaP) based biomaterials has, and continues to be, a major focus in the field of bone tissue engineering. However, limited insight into the spatiotemporal activation of signalling pathways has hampered the optimisation of in vivo bone formation and subsequent clinical translation. To gain further knowledge regarding the early molecular events governing bone tissue formation, we combined human periosteum derived progenitor cells with three types of clinically used CaP-scaffolds, to obtain constructs with a distinct range of bone forming capacity in vivo. Protein phosphorylation together with gene expression for key ligands and target genes were investigated 24 hours after cell seeding in vitro, and 3 and 12 days post ectopic implantation in nude mice. A computational modelling approach was used to deduce critical factors for bone formation 8 weeks post implantation. The combined Ca(2+)-mediated activation of BMP-, Wnt- and PKC signalling pathways 3 days post implantation were able to discriminate the bone forming from the non-bone forming constructs. Subsequently, a mathematical model able to predict in vivo bone formation with 96% accuracy was developed. This study illustrates the importance of defining and understanding CaP-activated signalling pathways that are required and sufficient for in vivo bone formation. Furthermore, we demonstrate the reliability of mathematical modelling as a tool to analyse and deduce key factors within an empirical data set and highlight its relevance to the translation of regenerative medicine strategies.

Uncovering the periosteum for skeletal regeneration: the stem cell that lies beneath

The cartilage- and bone-forming properties of the periosteum have long since been recognized. As one of the major sources of skeletal progenitor cells, the periosteum plays a crucial role not only in bone development and growth, but also during bone fracture healing. Aided by the continuous expansion of tools and techniques, we are now starting to acquire more insight into the specific role and regulation of periosteal cells. From a therapeutic point of view, the periosteum has attracted much attention as a cell source for bone tissue engineering purposes. This interest derives not only from the physiological role of the periosteum during bone repair, but is also supported by the unique properties and marked bone-forming potential of expanded periosteum-derived cells. We provide an overview of the current knowledge of periosteal cell biology, focusing on the cellular composition and molecular regulation of this remarkable tissue, as well as the application of periosteum-derived cells in regenerative medicine approaches. This article is part of a Special Issue entitled "Stem Cells and Bone".

Sox9 reprogrammed dermal fibroblasts undergo hypertrophic differentiation in vitro and trigger endochondral ossification in vivo

Strategies for bone regeneration are undergoing a paradigm shift, moving away from the replication of end-stage bone tissue and instead aiming to recapture the initial events of fracture repair. Although this is known to resemble endochondral bone formation, chondrogenic cell types with favorable proliferative and hypertrophic differentiation properties are lacking. Recent advances in cellular reprogramming have allowed the creation of alternative cell populations with specific properties through the forced expression of transcription factors. Herein, we investigated the in vitro hypertrophic differentiation and in vivo tissue formation capacity of induced chondrogenic cells (iChon cells) obtained through direct reprogramming. In vitro hypertrophic differentiation was detected in iChon cells that contained a doxycycline-inducible expression system for Klf4, cMyc, and Sox9. Furthermore, endochondral bone formation was detected after implantation in nude mice. The bone tissue was derived entirely from host origin, whereas cartilage tissue contained cells from both host and donor. The results obtained highlight the promise of cellular reprogramming for the creation of functional skeletal cells that can be used for novel bone healing strategies.

Humanized culture of periosteal progenitors in allogeneic serum enhances osteogenic differentiation and in vivo bone formation

The translation of stem cell-based regenerative solutions from the laboratory to the clinic is often hindered by the culture conditions used to expand cell populations. Although fetal bovine serum (FBS) is widely used, regulatory bodies and safety concerns encourage alternative, xeno-free culturing practices. In an attempt to apply this approach to a bone-forming combination product of human periosteal progenitors (human periosteum derived cells) on a clinically used calcium phosphate carrier, FBS was substituted for human allogeneic serum (hAS) during cell expansion. It was found that cell proliferation was increased in hAS along with an apparent commitment to the osteogenic lineage, indicated by enhanced Runx2 expression, as well as alkaline phosphatase activity and matrix mineralization. Following analysis of signaling pathways, it was found that interferon-mediated signaling was downregulated, whereas JAK-STAT signaling was upregulated. STAT3 phosphorylation was enhanced in hAS-cultured human periosteum derived cells, inhibition of which ablated the proliferative effect of hAS. Furthermore, following in vivo implantation of hAS-cultured cells on NuOss scaffolds, enhanced bone formation was observed compared with FBS (71% increase, p < .001). Interestingly, the de novo-formed bone appeared to have a higher ratio of immature regions to mature regions, indicating that after 8 weeks implantation, tissue-formation processes were continuing. Integration of the implant with the environment appeared to be altered, with a decrease in calcium phosphate grain size and surface area, indicative of accelerated resorption. This study highlights the advantages of using humanized culture conditions for the expansion of human periosteal progenitors intended for bone regeneration.

Insulin-like growth factor-I enhances proliferation and differentiation of human mesenchymal stromal cells in vitro

Human mesenchymal stromal cells (hMSCs) offer great potential for bone tissue engineering applications, but their in vivo performance remains limited. Preconditioning of these cells with small molecules to improve their differentiation before implantation, or incorporation of growth factors are possible solutions. Insulin-like growth factor-1 (IGF-1) is one of the most abundant growth factors in bone, involved in growth, development, and metabolism, but its effects on hMSCs are still subject of debate. Here we examined the effects of IGF-1 on proliferation and differentiation of hMSCs in vitro and we found that serum abolished the effects of IGF-1. Only in the absence of serum, IGF-1 increased proliferation, alkaline phosphatase expression, and osteogenic gene expression of hMSCs. Furthermore, we examined synergistic effects of bone morphogenetic protein-2 (BMP-2) and IGF-1 and, although IGF-1 enhanced BMP-2-induced mineralization, IGF-1 only slightly affected in vivo bone formation.

Mapping calcium phosphate activated gene networks as a strategy for targeted osteoinduction of human progenitors

Although calcium phosphate-containing biomaterials are promising scaffolds for bone regenerative strategies, the osteoinductive capacity of such materials is poorly understood. In this study, we investigated whether endogenous mechanisms of in vivo calcium phosphate-driven, ectopic bone formation could be identified and used to induce enhanced differentiation in vitro of the same progenitor population. To accomplish this, human periosteum derived cells (hPDCs) were seeded on hydroxyapatite/collagen scaffolds (calcium phosphate rich matrix or CPRM), or on decalcified scaffolds (calcium phosphate depleted matrix or CPDM), followed by subcutaneous implantation in nude mice to trigger ectopic bone formation. In this system, osteoblast differentiation occurred in CPRM scaffolds, but not in CPDM scaffolds. Gene expression was assessed by human full-genome microarray at 20 h after seeding, and 2, 8 and 18 days after implantation. In both matrices, implantation of the cell constructs triggered a similar gene expression cascade, however, gene expression dynamics progressed faster in CPRM scaffolds than in CPDM scaffolds. The difference in gene expression dynamics was associated with differential activation of hub genes and molecular signaling pathways related to calcium signaling (CREB), inflammation (TNFα, NFkB, and IL6) and bone development (TGFβ, β-catenin, BMP, EGF, and ERK signaling). Starting from this set of pathways, a growth factor cocktail was developed that robustly enhanced osteogenesis in vitro and in vivo. Taken together, our data demonstrate that through the identification and subsequent stimulation of genes, proteins and signaling pathways associated with calcium phosphate mediated osteoinduction, a focused approach to develop targeted differentiation protocols in adult progenitor cells can be achieved.

Engineering vascularized bone: osteogenic and proangiogenic potential of murine periosteal cells

One of the key challenges in bone tissue engineering is the timely formation of blood vessels that promote the survival of the implanted cells in the construct. Fracture healing largely depends on the presence of an intact periosteum but it is still unknown whether periosteum-derived cells (PDC) are critical for bone repair only by promoting bone formation or also by inducing neovascularization. We first established a protocol to specifically isolate murine PDC (mPDC) from long bones of adult mice. Mesenchymal stem cells were abundantly present in this cell population as more than 50% of the mPDC expressed mesenchymal markers (CD73, CD90, CD105, and stem cell antigen-1) and the cells exhibited trilineage differentiation potential (chondrogenic, osteogenic, and adipogenic). When transplanted on a collagen-calcium phosphate scaffold in vivo, mPDC attracted numerous blood vessels and formed mature bone which comprises a hematopoiesis-supportive stroma. We explored the proangiogenic properties of mPDC using in vitro culture systems and showed that mPDC promote the survival and proliferation of endothelial cells through the production of vascular endothelial growth factor. Coimplantation with endothelial cells demonstrated that mPDC can enhance vasculogenesis by adapting a pericyte-like phenotype, in addition to their ability to stimulate blood vessel ingrowth from the host. In conclusion, these findings demonstrate that periosteal cells contribute to fracture repair, not only through their strong osteogenic potential but also through their proangiogenic features and thus provide an ideal cell source for bone regeneration therapies.

18F-FDG labeling of mesenchymal stem cells and multipotent adult progenitor cells for PET imaging: effects on ultrastructure and differentiation capacity

Because of their extended differentiation capacity, stem cells have gained great interest in the field of regenerative medicine. For the development of therapeutic strategies, more knowledge on the in vivo fate of these cells has to be acquired. Therefore, stem cells can be labeled with radioactive tracer molecules such as (18)F-FDG, a positron-emitting glucose analog that is taken up and metabolically trapped by the cells. The aim of this study was to optimize the radioactive labeling of mesenchymal stem cells (MSCs) and multipotent adult progenitor cells (MAPCs) in vitro with (18)F-FDG and to investigate the potential radiotoxic effects of this labeling procedure with a range of techniques, including transmission electron microscopy (TEM).

METHODS

Mouse MSCs and rat MAPCs were used for (18)F-FDG uptake kinetics and tracer retention studies. Cell metabolic activity, proliferation, differentiation and ultrastructural changes after labeling were evaluated using an Alamar Blue reagent, doubling time calculations and quantitative TEM, respectively. Additionally, mice were injected with MSCs and MAPCs prelabeled with (18)F-FDG, and stem cell biodistribution was investigated using small-animal PET.

RESULTS

The optimal incubation period for (18)F-FDG uptake was 60 min. Significant early tracer washout was observed, with approximately 30%-40% of the tracer being retained inside the cells 3 h after labeling. Cell viability, proliferation, and differentiation capacity were not severely affected by (18)F-FDG labeling. No major changes at the ultrastructural level, considering mitochondrial length, lysosome size, the number of lysosomes, the number of vacuoles, and the average rough endoplasmic reticulum width, were observed with TEM. Small-animal PET experiments with radiolabeled MAPCs and MSCs injected intravenously in mice showed a predominant accumulation in the lungs and a substantial elution of (18)F-FDG from the cells.

CONCLUSION

MSCs and MAPCs can be successfully labeled with (18)F-FDG for molecular imaging purposes. The main cellular properties are not rigorously affected. TEM confirmed that the cells' ultrastructural properties are not influenced by (18)F-FDG labeling. Small-animal PET studies confirmed the intracellular location of the tracer and the possibility of imaging injected prelabeled stem cell types in vivo. Therefore, direct labeling of MSCs and MAPCs with (18)F-FDG is a suitable technique to noninvasively assess cell delivery and early retention with PET.

Fluorescent oxygen sensitive microbead incorporation for measuring oxygen tension in cell aggregates

Molecular oxygen is a main regulator of various cell functions. Imaging methods designed as screening tools for fast, in situ, 3D and non-interfering measurement of oxygen tension in the cellular microenvironment would serve great purpose in identifying and monitoring this vital and pivotal signalling molecule. We describe the use of dual luminophore oxygen sensitive microbeads to measure absolute oxygen concentrations in cellular aggregates. Stable microbead integration, a prerequisite for their practical application, was ensured by a site-specific delivery method that is based on the interactions between streptavidin and biotin. The spatial stability introduced by this method allowed for long term measurements of oxygen tension without interfering with the cell aggregation process. By making multiple calibration experiments we further demonstrated the potential of these sensors to measure local oxygen tension in optically dense cellular environments.

Critical illness-related bone loss is associated with osteoclastic and angiogenic abnormalities

Critically ill patients are at increased risk of fractures during rehabilitation, and can experience impaired healing of traumatic and surgical bone fractures. In addition, markers of bone resorption are markedly increased in critically ill patients, while markers of bone formation are decreased. In the current study, we have directly investigated the effect of critical illness on bone metabolism and repair. In a human in vitro model of critical illness, Fluorescence-activated cell sorting (FACS) analysis revealed an increase in circulating CD14+/CD11b+ osteoclast precursors in critically ill patient peripheral blood compared to healthy controls. In addition, the formation of osteoclasts was increased in patient peripheral blood mononuclear cell (PBMC) cultures compared to healthy controls, both in the presence and absence of osteoclastogenic factors receptor activator of NF-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Culturing PBMCs with 10% critically ill patient serum further increased osteoclast formation and activity in patient PBMCs only, and neutralization studies revealed that immunoglobulin G (IgG) antibody signaling through the immunoreceptor Fc receptor common γ chain III (FcRγIII) played an important role. When analyzing bone formation, no differences in osteogenic differentiation were observed using human periosteal-derived cells (hPDCs) treated with patient serum in vitro, but a decrease in the expression of vascular endothelial growth factor receptor 1 (VEGF-R1) suggested impaired vascularization. This was confirmed using serum-treated hPDCs implanted onto calcium phosphate scaffolds in a murine in vivo model of bone formation, where decreased vascularization and increased osteoclast activity led to a decrease in bone formation in scaffolds with patient serum-treated hPDCs. Together, these findings may help to define novel therapeutic targets to prevent bone loss and optimize fracture healing in critically ill patients.

Relating the chondrocyte gene network to growth plate morphology: from genes to phenotype

During endochondral ossification, chondrocyte growth and differentiation is controlled by many local signalling pathways. Due to crosstalks and feedback mechanisms, these interwoven pathways display a network like structure. In this study, a large-scale literature based logical model of the growth plate network was developed. The network is able to capture the different states (resting, proliferating and hypertrophic) that chondrocytes go through as they progress within the growth plate. In a first corroboration step, the effect of mutations in various signalling pathways of the growth plate network was investigated.

A semi-autonomous model of endochondral ossification for developmental tissue engineering

Bone tissue engineering is currently undergoing a paradigm shift regarding the concepts used to develop cell-based therapies for skeletal repair. In place of the "trial and error" approach, researchers aim at developing cellular concepts that mirror developmental and postnatal processes. Herein, we describe a model for in vivo endochondral remodeling of an in vitro derived cartilaginous intermediate and its applicability to bone engineering. In vitro differentiation of the continuous cell line, ATDC5, in pellet culture was enhanced in a medium containing ascorbic acid, insulin-transferrin-selenium, dexamethasone, and transforming growth factor β1, when compared with other tested preparations. This differentiation was characterized by the elevated expression of Collagen type II and X along with glycosaminoglycan (GAG) accumulation and the onset of hypertrophy. On combination with NuOss™, a clinically used bone void filler, and implantation in nude mice, the differentiated pellets further matured into GAG rich cartilaginous intermediates after 4 weeks. This was subsequently partially remodeled into osteocalcin-positive bone tissue after 8 weeks without further external manipulation, indicating the semi-autonomous nature of this implant. Mineralized tissue along with active osteoclast resorption and neo-angiogenesis was apparent throughout the implant. The bone volume was approximately eightfold higher (10.70%±0.99%) when using a cartilaginous intermediate (based on differentiated cell pellets) than when observed with cell-seeded scaffolds (1.19%±0.24% and 1.48%±0.35%), in both a differentiated and an undifferentiated state. This study highlights the potential of endochondral strategies for bone tissue engineering and allows the identification of the key cellular parameters for this process.

Ectopic bone formation by 3D porous calcium phosphate-Ti6Al4V hybrids produced by perfusion electrodeposition

Successful clinical repair of non-healing skeletal defects requires the use of bone substitutes with robust bone inductivity and excellent biomechanical stability. Thus, three-dimensionally functionalised porous calcium phosphate-Ti6Al4V (CaP-Ti) hybrids were produced by perfusion electrodeposition, and the in vitro and in vivo biological performances were evaluated using human periosteum derived cells (hPDCs). By applying various current densities at the optimised deposition conditions, CaP coatings with sub-micrometer to nano-scale porous crystalline structures and different ion dissolution kinetics were deposited on the porous Ti6Al4V scaffolds. These distinctive physicochemical properties caused a significant impact on in vitro proliferation, osteogenic differentiation, and matrix mineralisation of hPDCs. This includes a potential role of hPDCs in mediating osteoclastogenesis for the resorption of CaP coatings, as indicated by a significant down-regulation of osteoprotegerin (OPG) gene expression and by the histological observation of abundant multi-nucleated giant cells near to the coatings. By subcutaneous implantation, the produced hybrids induced ectopic bone formation, which was highly dependent on the physicochemical properties of the CaP coating (including the Ca(2+) dissolution kinetics and coating surface topography), in a cell density-dependent manner. This study provided further insight on stem cell-CaP biomaterial interactions, and the feasibility to produced bone reparative units that are predictively osteoinductive in vivo by perfusion electrodeposition technology.

Validation of a PicoGreen-based DNA quantification integrated in an RNA extraction method for two-dimensional and three-dimensional cell cultures

DNA measurement and RNA extraction are two frequently used methods for cell characterization. In the conventional protocols, they require similar, but separate samples and in most cases, different pretreatments. The few combined protocols that exist still include time-consuming steps. Hence, to establish an efficient combined RNA extraction and DNA measurement protocol for two-dimensional (2D) and three-dimensional (3D) cell cultures, a PicoGreen-based DNA measurement was integrated in an existing RNA extraction protocol. It was validated by analysis of the influence of different lysis buffers, RLT, RA1, or Trizol, used for RNA extraction on the measured DNA concentration. The DNA cell yield was evaluated both in cell suspensions (2D) and on 3D cell-seeded scaffolds. Results showed that the different RNA lysis buffers caused a concentration-dependent perturbation of the PicoGreen signal. The measured DNA concentrations in 2D and 3D using RLT and RA1 buffer were comparable, also to the positive control. We, therefore, concluded that RNA extraction protocols using RA1 or RLT buffer allow the integration of a DNA quantification step without the buffer influencing the results. Hence, the combined DNA measurement and RNA extraction offer an alternative for DNA measurement techniques that is time and sample saving, for both 2D cell cultures and specific 3D constructs.

Langerhans cells facilitate epithelial DNA damage and squamous cell carcinoma

Polyaromatic hydrocarbons (PAHs) are prevalent, potent carcinogens, and 7,12-dimethylbenz[a]anthracene (DMBA) is a model PAH widely used to study tumorigenesis. Mice lacking Langerhans cells (LCs), a signatory epidermal dendritic cell (DC), are protected from cutaneous chemical carcinogenesis, independent of T cell immunity. Investigation of the underlying mechanism revealed that LC-deficient skin was relatively resistant to DMBA-induced DNA damage. LCs efficiently metabolized DMBA to DMBA-trans-3,4-diol, an intermediate proximal to oncogenic Hras mutation, and DMBA-treated LC-deficient skin contained significantly fewer Hras mutations. Moreover, DMBA-trans-3,4-diol application bypassed tumor resistance in LC-deficient mice. Additionally, the genotoxic impact of DMBA on human keratinocytes was significantly increased by prior incubation with human-derived LC. Thus, tissue-associated DC can enhance chemical carcinogenesis via PAH metabolism, highlighting the complex relation between immune cells and carcinogenesis.

Differentiation potential of human postnatal mesenchymal stem cells, mesoangioblasts, and multipotent adult progenitor cells reflected in their transcriptome and partially influenced by the culture conditions

Several adherent postnatal stem cells have been described with different phenotypic and functional properties. As many of these cells are being considered for clinical therapies, it is of great importance that the identity and potency of these products is validated. We compared the phenotype and functional characteristics of human mesenchymal stem cells (hMSCs), human mesoangioblasts (hMab), and human multipotent adult progenitor cells (hMAPCs) using uniform standardized methods. Human MAPCs could be expanded significantly longer in culture. Differences in cell surface marker expression were found among the three cell populations with CD140b being a distinctive marker among the three cell types. Differentiation capacity towards adipocytes, osteoblasts, chondrocytes, and smooth muscle cells in vitro, using established protocols, was similar among the three cell types. However, only hMab differentiated to skeletal myocytes, while only hMAPCs differentiated to endothelium in vitro and in vivo. A comparative transcriptome analysis confirmed that the three cell populations are distinct and revealed gene signatures that correlated with their specific functional properties. Furthermore, we assessed whether the phenotypic, functional, and transcriptome features were mediated by the culture conditions. Human MSCs and hMab cultured under MAPC conditions became capable of generating endothelial-like cells, whereas hMab lost some of their ability to generate myotubes. By contrast, hMAPCs cultured under MSC conditions lost their endothelial differentiation capacity, whereas this was retained when cultured under Mab conditions, however, myogenic capacity was not gained under Mab conditions. These studies demonstrate that hMSCs, hMab, and hMAPCs have different properties that are partially mediated by the culture conditions.

Does tranexamic acid stabilised fibrin support the osteogenic differentiation of human periosteum derived cells?

Fibrin sealants have long been used as carrier for osteogenic cells in bone regeneration. However, it has not been demonstrated whether fibrin's role is limited to delivering cells to the bone defect or whether fibrin enhances osteogenesis. This study investigated fibrin's influence on the behaviour of human periosteum-derived cells (hPDCs) when cultured in vitro under osteogenic conditions in two-dimensional (fibrin substrate) and three-dimensional (fibrin carrier) environments. Tranexamic acid (TEA) was used to reduce fibrin degradation after investigating its effect on hPDCs in monolayer culture on plastic.TEA did not affect proliferation nor calcium deposition of hPDCs under these conditions. Expression profiles of specific osteogenic markers were also maintained within the presence of TEA, apart from reduced alkaline phosphatase (ALP) expression (day 14). Compared to plastic, proliferation was upregulated on 2D fibrin substrates with a 220% higher DNA content by day 21. Gene expression was also altered, with significantly (p<0.05) decreased Runx2 (day 7) and ALP (day 14) expression and increased collagen I expression (day 14 and 21). In contrast to plastic, mineralisation was absent on fibrin substrates. Inside fibrin carriers, hPDCs were uniformly distributed. Moderate cell growth and reduced osteogenic marker expression was observed inside fibrin carriers. After 2 weeks, increased cell death was present in the carrier's centre. In conclusion, fibrin negatively influences osteogenic differentiation, compared to culture plastic, but enhanced proliferation (at least in 2D cultures) for hPDCs cultured in osteogenic conditions. TEA maintained the integrity of fibrin-based constructs, with minor effects on the osteogenic differentiation of hPDCs.

The combined bone forming capacity of human periosteal derived cells and calcium phosphates

Current knowledge suggests that the periosteum, a fibrous tissue which covers the surface of all bones, contains a population of progenitor cells which mediate the repair of bone defects. In an effort to optimise the utilisation of this source of cells for bone engineering, herein we describe the rational selection of calcium phosphate (CaP) containing materials, based on biomaterial properties, and evaluation of their combined bone forming capacity. Five different commercially available orthopaedic 3D matrices composed of CaP particles in an open collagen network (NuOss™, CopiOs™, Bio-Oss(®), Collagraft™ and Vitoss(®)) were evaluated in vitro and in vivo with human periosteal derived cells (hPDCs). It was found that the cell-material combinations behaved quite differently in vivo, despite apparent in vitro similarities in gene expression profiles. Bone formation was highest within the NuOss™/hPDC implant at 13.03%, which also contained the highest incidence of bone marrow formation. The bone formed in this implant was chimeric with approximately 65% originating from implanted cells. Upon analysis of human specific gene expression, although it was found that predominantly osteogenic differentiation was observed within NuOss™/hPDC implants, a lesser induction of chondrogenic genes was also observed. The formation of a cartilage intermediate was confirmed by histology. Additionally the NuOss™/hPDC implant integrated into the mouse environment with apparent active scaffold resorption. This study demonstrates the importance of matching a cell support/biological matrix with a cell type and subsequently has outlined parameters which can be used for the rational selection of biomaterials for bone engineering.

Probing the osteoinductive effect of calcium phosphate by using an in vitro biomimetic model

The use of calcium phosphate (CaP)-based carriers in bone engineering is a promising approach to induce in vivo bone formation. However, the exact mechanism of osteoinduction by CaP is not known. Here, by mimicking the in vivo Ca(2+) and P(i)-enriched environment in an in vitro model, we assessed the effects of these ions on human periosteum-derived cells. We observed a significant Ca(2+) and P(i)-induced cell proliferation, which was found to be through the modulation of cell cycle progression, in a dose- and time-dependent manner. In addition, Ca(2+), P(i), and combined Ca-P upregulated osteogenic gene expression in a dose- and time-dependent manner. Encouragingly, both ions administered individually or in combination persistently and dose dependently upregulated bone morphogenetic protein-2 gene expression. This suggested a potential osteoinductive effect through an autonomous activation of the bone morphogenetic protein signaling pathway by released Ca(2+) and P(i), which may serve as an autocrine/paracrine osteoinduction loop that drives the cellularized CaP constructs toward effective bone formation in vivo. In conclusion, through an in vitro biomimetic model, we have partially probed the roles of the released Ca(2+) and P(i) on the osteoinductivity of CaP-based biomaterials.

Engineering embryonic stem-cell aggregation allows an enhanced osteogenic differentiation in vitro

Pluripotent embryonic stem (ES) cells hold great promise for the field of tissue engineering, with numerous studies investigating differentiation into various cell types including cardiomyocytes, chondrocytes, and osteoblasts. Previous studies have detailed osteogenic differentiation via dissociated embryoid body (EB) culture in osteoinductive media comprising of ascorbic acid, beta-glycerophosphate, and dexamethasone. It is hoped that these osteogenic cultures will have clinical application in bone tissue repair and regeneration and pharmacological testing. However, differentiation remains highly inefficient and generates heterogeneous populations. We have previously reported an engineered three-dimensional culture system for controlled ES cell-ES cell interaction via the avidin-biotin binding complex. Here we investigate the effect of such engineering on ES cell differentiation. Engineered EBs exhibit enhanced osteogenic differentiation assessed by cadherin-11, Runx2, and osteopontin expression, alkaline phosphatase activity, and bone nodule formation. Results show that cultures produced from intact EBs aggregated for 3 days generated the greatest levels of osteogenic differentiation when cultured in osteoinductive media. However, when cultured in control media, only engineered samples appeared to exhibit bone nodule formation. In addition, polymerase chain reaction analysis revealed a decrease in endoderm and ectoderm expression within engineered samples. This suggests that engineered ES cell aggregation has increased mesoderm homogeneity, contributing to enhanced osteogenic differentiation.

Controlled embryoid body formation via surface modification and avidin-biotin cross-linking

Cell-cell interaction is an integral part of embryoid body (EB) formation controlling 3D aggregation. Manipulation of embryonic stem (ES) cell interactions could provide control over EB formation. Studies have shown a direct relationship between EB formation and ES cell differentiation. We have previously described a cell surface modification and cross-linking method for influencing cell-cell interaction and formation of multicellular constructs. Here we show further characterisation of this engineered aggregation. We demonstrate that engineering accelerates ES cell aggregation, forming larger, denser and more stable EBs than control samples, with no significant decrease in constituent ES cell viability. However, extended culture >/=5 days reveals significant core necrosis creating a layered EB structure. Accelerated aggregation through engineering circumvents this problem as EB formation time is reduced. We conclude that the proposed engineering method influences initial ES cell-ES cell interactions and EB formation. This methodology could be employed to further our understanding of intrinsic EB properties and their effect on ES cell differentiation.