Generation, Characterization, and Multilineage Potency of Mesenchymal-Like Progenitors Derived from Equine Induced Pluripotent Stem Cells

Footprint-free induced pluripotent stem cells can be successfully differentiated into mesenchymal stromal cells in the feline model

BACKGROUND

Induced pluripotent stem cells (iPSCs) can propagate indefinitely and give rise to every other cell type, rendering them invaluable for disease modelling, drug development research, and usage in regenerative medicine. While feline iPSCs have been described, there are currently no reports on generating genome integration (footprint)-free iPSCs from domestic cats. Therefore, the objective of this study was to generate feline iPSCs from fetal fibroblasts using non-integrative Sendai virus (SeV) vectors carrying human transcription factors. Moreover, these iPSCs were differentiated into mesenchymal stromal cells (MSCs), which can be used as an alternative to tissue-derived MSCs.

METHODS

Feline fetal fibroblasts were transduced with CytoTune-iPS 2.0 Sendai Reprogramming vectors at recommended multiplicity of infections (MOI) and cultured for about 6 days. At 7 days post transduction cells were dissociated, replated on inactivated feeder cells and maintained in iPSC medium for 28 days with daily medium change. Emerging iPSC colonies were mechanically passaged and transferred to fresh feeder cells and further passaged every 6-8 days. Four feline iPSC lines were generated, with two selected for further in-depth characterization. Feline iPSCs were then differentiated into MSCs using a serial plating strategy and an inhibitor of the transforming growth factor-β (TGF-β) type I receptor.

RESULTS

Feline iPSCs exhibited characteristic colony morphology, high nuclear-to-cytoplasmic ratio, positive alkaline phosphatase activity, and expressed feline OCT4, SOX2, and Nanog homeobox (NANOG) stem cell markers. Expression of SeV-derived transgenes decreased during passaging to be eventually lost from the host cells and feline iPSCs could be stably maintained for over 35 passages. Feline iPSCs differentiated into embryoid bodies in vitro and did not form fully differentiated teratomas; instead, they generated in vivo masses containing mesodermal tissue derivatives when injected into immunodeficient mice. Feline iPSC-derived MSCs were plastic adherent, displayed MSC-like morphology, expressed MSC-specific surface markers, and differentiated into cells from the mesodermal lineage in vitro. RNA deep sequencing identified 1,189 differentially expressed genes in feline iPSC-derived MSCs compared to feline iPSCs.

CONCLUSION

We demonstrated the generation of footprint-free iPSCs from domestic cats and their directed differentiation potential towards MSCs. These SeV-derived feline iPSCs and iPSC-derived MSCs will provide valuable models to study feline diseases and explore novel therapeutic strategies and can serve as translational models for human health, leading to increased knowledge on disease pathogenesis and improved therapeutic interventions.

Computer controlled expansion of equine cord blood mesenchymal stromal cells on microcarriers in 3 L vertical-wheel® bioreactors

Mesenchymal stromal cells (MSCs) are an ideal cell source for allogenic cell therapy due to their immunomodulatory and differentiation properties. Equine MSCs (eMSCs) have been found to be a promising treatment for equine joint injuries including meniscal injuries, cartilage degradation, and osteoarthritis. Although the use of eMSCs has shown efficacy in preliminary studies, challenges associated with biomanufacturing remain. To achieve the required cell numbers for clinical application, bioreactor-based processes are required. Initial studies have shown that eMSCs can be cultivated in microcarrier-based, stirred suspension bioreactor culture at the laboratory 0.1 L scale using a Vertical-Wheel® (VW) bioreactor. However, investigations regarding scale up of these processes to the required biomanufacturing scales are required. This study investigated the scale-up of a equine cord blood MSC (eCB-MSC) bioprocess in VW bioreactors at three scales. This included scale-up from the 0.1-0.5 L bioreactor, scale-up from static culture to the 3 L computer-controlled bioreactor, and scale-up into the 3 L computer-controlled bioreactor using a mock clinical trial process. Results from the various scale-up experiments demonstrated similar cell expansion at the various tested scales. The 3 L computer-controlled system resulted in a final cell densities of 1.5 × 105 cells/cm2 on average, achieving 1.5 × 109 harvested cells. Biological testing of the cells showed that cell phenotype and functionality were maintained after scale-up. These findings demonstrate the scalability of an eCB-MSC bioprocess using microcarriers in VW bioreactors to achieve clinically relevant cell numbers, a critical step to translate MSC treatments from research to clinical applications. This study also represents the first known published study expanding any cell type in the 3 L VW bioreactor.

Induced pluripotent stem cells in companion animals: how can we move the field forward?

Following a one medicine approach, the development of regenerative therapies for human patients leads to innovative treatments for animals, while pre-clinical studies on animals provide knowledge to advance human medicine. Among many different biological products under investigation, stem cells are among the most prominent. Mesenchymal stromal cells (MSCs) are extensively investigated, but they present challenges such as senescence and limited differentiation ability. Embryonic stem cells (ESCs) are pluripotent cells with a virtually unlimited capacity for self-renewal and differentiation, but the use of embryos carries ethical concerns. Induced pluripotent stem cells (iPSCs) can overcome all of these limitations, as they closely resemble ESCs but are derived from adult cells by reprogramming in the laboratory using pluripotency-associated transcription factors. iPSCs hold great potential for applications in therapy, disease modeling, drug screening, and even species preservation strategies. However, iPSC technology is less developed in veterinary species compared to human. This review attempts to address the specific challenges associated with generating and applying iPSCs from companion animals. Firstly, we discuss strategies for the preparation of iPSCs in veterinary species and secondly, we address the potential for different applications of iPSCs in companion animals. Our aim is to provide an overview on the state of the art of iPSCs in companion animals, focusing on equine, canine, and feline species, as well as to identify which aspects need further optimization and, where possible, to provide guidance on future advancements. Following a "step-by-step" approach, we cover the generation of iPSCs in companion animals from the selection of somatic cells and the reprogramming strategies, to the expansion and characterization of iPSCs. Subsequently, we revise the current applications of iPSCs in companion animals, identify the main hurdles, and propose future paths to move the field forward. Transferring the knowledge gained from human iPSCs can increase our understanding in the biology of pluripotent cells in animals, but it is critical to further investigate the differences among species to develop specific approaches for animal iPSCs. This is key for significantly advancing iPSC application in veterinary medicine, which at the same time will also allow gaining pre-clinical knowledge transferable to human medicine.

Differences in the intrinsic chondrogenic potential of human mesenchymal stromal cells and iPSC-derived multipotent cells

BACKGROUND

Human multipotent progenitor cells (hiMPCs) created from induced pluripotent stem cells (iPSCs) represent a new cell source for cartilage regeneration. In most studies, bone morphogenetic proteins (BMPs) are needed to enhance transforming growth factor-β (TGFβ)-induced hiMPC chondrogenesis. In contrast, TGFβ alone is sufficient to result in robust chondrogenesis of human primary mesenchymal stromal cells (hMSCs). Currently, the mechanism underlying this difference between hiMPCs and hMSCs has not been fully understood.

METHODS

In this study, we first tested different growth factors alone or in combination in stimulating hiMPC chondrogenesis, with a special focus on chondrocytic hypertrophy. The reparative capacity of hiMPCs-derived cartilage was assessed in an osteochondral defect model created in rats. hMSCs isolated from bone marrow were included in all studies as the control. Lastly, a mechanistic study was conducted to understand why hiMPCs and hMSCs behave differently in responding to TGFβ.

RESULTS

Chondrogenic medium supplemented with TGFβ3 and BMP6 led to robust in vitro cartilage formation from hiMPCs with minimal hypertrophy. Cartilage tissue generated from this new method was resistant to osteogenic transition upon subcutaneous implantation and resulted in a hyaline cartilage-like regeneration in osteochondral defects in rats. Interestingly, TGFβ3 induced phosphorylation of both Smad2/3 and Smad1/5 in hMSCs, but only activated Smad2/3 in hiMPCs. Supplementing BMP6 activated Smad1/5 and significantly enhanced TGFβ's compacity in inducing hiMPC chondrogenesis. The chondro-promoting function of BMP6 was abolished by the treatment of a BMP pathway inhibitor.

CONCLUSIONS

This study describes a robust method to generate chondrocytes from hiMPCs with low hypertrophy for hyaline cartilage repair, as well as elucidates the difference between hMSCs and hiMPCs in response to TGFβ. Our results also indicated the importance of activating both Smad2/3 and Smad1/5 in the initiation of chondrogenesis.

Proteomic analysis of the IPF mesenchymal progenitor cell nuclear proteome identifies abnormalities in key nodal proteins that underlie their fibrogenic phenotype

IPF is a progressive fibrotic lung disease whose pathogenesis remains incompletely understood. We have previously discovered pathologic mesenchymal progenitor cells (MPCs) in the lungs of IPF patients. IPF MPCs display a distinct transcriptome and create sustained interstitial fibrosis in immune deficient mice. However, the precise pathologic alterations responsible for this fibrotic phenotype remain to be uncovered. Quantitative mass spectrometry and interactomics is a powerful tool that can define protein alterations in specific subcellular compartments that can be implemented to understand disease pathogenesis. We employed quantitative mass spectrometry and interactomics to define protein alterations in the nuclear compartment of IPF MPCs compared to control MPCs. We identified increased nuclear levels of PARP1, CDK1, and BACH1. Interactomics implicated PARP1, CDK1, and BACH1 as key hub proteins in the DNA damage/repair, differentiation, and apoptosis signaling pathways respectively. Loss of function and inhibitor studies demonstrated important roles for PARP1 in DNA damage/repair, CDK1 in regulating IPF MPC stemness and self-renewal, and BACH1 in regulating IPF MPC viability. Our quantitative mass spectrometry studies combined with interactomic analysis uncovered key roles for nuclear PARP1, CDK1, and BACH1 in regulating IPF MPC fibrogenicity.

Novel cell sources for bone regeneration

A plethora of both acute and chronic conditions, including traumatic, degenerative, malignant, or congenital disorders, commonly induce bone disorders often associated with severe persisting pain and limited mobility. Over 1 million surgical procedures involving bone excision, bone grafting, and fracture repair are performed each year in the U.S. alone, resulting in immense levels of public health challenges and corresponding financial burdens. Unfortunately, the innate self-healing capacity of bone is often inadequate for larger defects over a critical size. Moreover, as direct transplantation of committed osteoblasts is hindered by deficient cell availability, limited cell spreading, and poor survivability, an urgent need for novel cell sources for bone regeneration is concurrent. Thanks to the development in stem cell biology and cell reprogramming technology, many multipotent and pluripotent cells that manifest promising osteogenic potential are considered the regenerative remedy for bone defects. Considering these cells' investigation is still in its relative infancy, each of them offers their own particular challenges that must be conquered before the large-scale clinical application.

Induced Pluripotent Stem Cells in Dental and Nondental Tissue Regeneration: A Review of an Unexploited Potential

Cell-based therapies currently represent the state of art for tissue regenerative treatment approaches for various diseases and disorders. Induced pluripotent stem cells (iPSCs), reprogrammed from adult somatic cells, using vectors carrying definite transcription factors, have manifested a breakthrough in regenerative medicine, relying on their pluripotent nature and ease of generation in large amounts from various dental and nondental tissues. In addition to their potential applications in regenerative medicine and dentistry, iPSCs can also be used in disease modeling and drug testing for personalized medicine. The current review discusses various techniques for the production of iPSC-derived osteogenic and odontogenic progenitors, the therapeutic applications of iPSCs, and their regenerative potential in vivo and in vitro. Through the present review, we aim to explore the potential applications of iPSCs in dental and nondental tissue regeneration and to highlight different protocols used for the generation of different tissues and cell lines from iPSCs.

Differentiation of equine induced pluripotent stem cells into mesenchymal lineage for therapeutic use

In previous work, we established an equine induced pluripotent stem cell line (E-iPSCs) from equine adipose-derived stem cells (ASCs) using a lentiviral vector encoding four transcription factors: Oct4, Sox2, Klf4, and c-Myc. In the current study, we attempted to differentiate these established E-iPSCs into mesenchymal stem cells (MSCs) by serial passaging using MSC-defined media for stem cell expansion. Differentiation of the MSCs was confirmed by analyzing expression levels of the MSC surface markers CD44 and CD29, and the pluripotency markers Nanog and Oct4. Results indicated that the E-iPSC-derived MSCs (E-iPSC-MSCs) retained the characteristics of MSCs, including the ability to differentiate into chondrogenic, osteogenic, or myogenic lineages. E-iPSC-MSCs were rendered suitable for therapeutic use by inhibiting immune rejection through exposure to transforming growth factor beta 2 (TGF-β2) in culture, which down-regulated the expression of major histocompatibility complex class I (MHC class I) proteins that cause immune rejection if they are incompatible with the MHC antigen of the recipient. We reported 16 cases of E-iPSC-MSC transplantations into injured horses with generally positive effects, such as reduced lameness and fraction lines. Our findings indicate that E-iPSC-MSCs can demonstrate MSC characteristics and be safely and practically used in the treatment of musculoskeletal injuries in horses.

Large Animal Models for the Clinical Application of Human Induced Pluripotent Stem Cells

Induced pluripotent stem cell (iPSC) technology offers a practically infinite and ethically acceptable source to obtain a variety of somatic cells. Coupled with the biotechnologies of cell therapy or tissue engineering, iPSC technology will enormously contribute to human regenerative medicine. Before clinical application, such human iPSC (hiPSC)-based therapies should be assessed using large animal models that more closely match biological or biomechanical properties of human patients. Therefore, it is critical to generate large animal iPSCs, obtain their iPSC-derived somatic cells, and preclinically evaluate their therapeutic efficacy and safety in large animals. During the past decade, the establishment of iPSC lines of a series of large animal species has been documented, and the acquisition and preclinical evaluation of iPSC-derived somatic cells has also been reported. Despite this progress, significant obstacles, such as obtaining or preserving the bona fide pluripotency of large animal iPSCs, have been encountered. Simultaneously, studies of large animal iPSCs have been overlooked in comparison with those of mouse and hiPSCs, and this field deserves more attention and support due to its important preclinical relevance. Herein, this review will focus on the large animal models of pigs, dogs, horses, and sheep/goats, and summarize current progress, challenges, and potential future directions of research on large animal iPSCs.

Induced pluripotent stem cells throughout the animal kingdom: Availability and applications

Up until the mid 2000s, the capacity to generate every cell of an organism was exclusive to embryonic stem cells. In 2006, researchers Takahashi and Yamanaka developed an alternative method of generating embryonic-like stem cells from adult cells, which they coined induced pluripotent stem cells (iPSCs). Such iPSCs possess most of the advantages of embryonic stem cells without the ethical stigma associated with derivation of the latter. The possibility of generating “custom-made” pluripotent cells, ideal for patient-specific disease models, alongside their possible applications in regenerative medicine and reproduction, has drawn a lot of attention to the field with numbers of iPSC studies published growing exponentially. IPSCs have now been generated for a wide variety of species, including but not limited to, mouse, human, primate, wild felines, bovines, equines, birds and rodents, some of which still lack well-established embryonic stem cell lines. The paucity of robust characterization of some of these iPSC lines as well as the residual expression of transgenes involved in the reprogramming process still hampers the use of such cells in species preservation or medical research, underscoring the requirement for further investigations. Here, we provide an extensive overview of iPSC generated from a broad range of animal species including their potential applications and limitations.

The combination of Decitabine and EPZ-6438 effectively facilitate adipogenic differentiation of induced pluripotent stem cell-derived mesenchymal stem cells

As a novel type of mesenchymal stem cell, induced pluripotent stem cell-derived mesenchymal stem cells (iPMSCs) have huge potential for cell therapy. iPMSCs exhibited the typical characteristics of MSCs, whereas the tri-lineage differentiation potential is limited, especially the adipogenic propensity. Here, to reveal the molecular mechanism we carried out the epigenetic comparisons between the iPMSCs and the bone marrow-derived mesenchymal stem cells (BMSCs) and embryonic stem cell-derived mesenchymal stem cells (EMSCs). We found that the iPMSCs was significantly higher than the BMSCs in terms of genome-wide DNA methylation. Meanwhile, the adipogenic gene PPARγ promoter region existed hypermethylation. In addition, compared with EMSCs and BMSCs, iPMSCs had significant differences in the histones epigenetic modification of methylation and acetylation, especially high levels of histone 27 lysine trimethylation (H3K27me3). Furthermore, the epigenetic modifiers Decitabine and EPZ6438 effectively upregulated the gene expression of PPARγ and promoted the adipogenic differentiation of iPMSCs via chromatin remodeling. Taken together, our findings set new metrics to the applications for improving the efficiency and the therapeutic potential of iPMSCs.

Equine Cord Blood Mesenchymal Stromal Cells Have Greater Differentiation and Similar Immunosuppressive Potential to Cord Tissue Mesenchymal Stromal Cells

Mesenchymal stromal cells (MSCs) are the most common cell population studied for therapeutic use in veterinary medicine. MSCs obtained from neonatal sources such as umbilical cord tissue (CT-MSCs) or cord blood (CB-MSCs) are appealing due to the non-invasive nature of procurement and the time allowed for characterization of cells before use. However, it remains unclear as to whether CB- or CT-MSCs have equivalent progenitor and non-progenitor functions. CB-MSCs have been shown to have superior chondrogenic potential to MSCs from other sources, whereas their immunomodulatory capacity does not seem to vary significantly. Using equine CB-MSCs and CT-MSCs from the same donors, we hypothesized that MSCs from both sources would have a similar immunophenotype, that CB-MSCs would be more amenable to differentiation, and that they can equally suppress lymphocyte proliferation. We evaluated cells from both sources for "classic" equine MSC markers CD90, CD105, CD29, and CD44, as well as pericyte markers CD146, NG2, and α-SMA. Contrary to our hypothesis, CB-MSCs showed mid- to high expression of pericyte surface markers CD146 and NG2, whereas expression in CT-MSCs was absent. On trilineage differentiation, CB-MSCs were more osteogenic and chondrogenic based on alkaline phosphatase activity and glycosaminoglycan content, respectively. Finally, using a mononuclear cell (MNC) suppression assay, we determined that both CB-MSCs and CT-MSCs are capable of suppressing stimulated MNC proliferation to a similar degree. We have determined that the choice of MSC tissue source should be made with the intended application in mind. This appears to be particularly relevant if pursuing a progenitor-based treatment strategy.

Osteoblast differentiation of equine induced pluripotent stem cells

Bone fractures occur in horses following traumatic and non-traumatic (bone overloading) events. They can be difficult to treat due to the need for the horse to bear weight on all legs during the healing period. Regenerative medicine to improve fracture union and recovery could significantly improve horse welfare. Equine induced pluripotent stem cells (iPSCs) have previously been derived. Here we show that equine iPSCs cultured for 21 days in osteogenic induction media on an OsteoAssay surface upregulate the expression of osteoblast associated genes and proteins, including COL1A1, SPARC, SPP1, IBSP, RUNX2 and BGALP. We also demonstrate that iPSC-osteoblasts are able to produce a mineralised matrix with both calcium and hydroxyapatite deposition. Alkaline phosphatase activity is also significantly increased during osteoblast differentiation. Although the genetic background of the iPSC donor animal affects the level of differentiation observed after 21 days of differentiation, less variation between lines of iPSCs derived from the same horse was observed. The successful, direct, differentiation of equine iPSCs into osteoblasts may provide a source of cells for future regenerative medicine strategies to improve fracture repair in horses undergoing surgery. iPSC-derived osteoblasts will also provide a potential tool to study equine bone development and disease.

Summary: Horse iPSCs can be turned directly into bone forming cells but the efficiency is affected by the donor horse. Less variability is observed using different iPSC lines derived from the same horse.

Bone marrow mesenchymal stem cells as nuclear donors improve viability and health of cloned horses

Introduction

Cell plasticity is crucial in cloning to allow an efficient nuclear reprogramming and healthy offspring. Hence, cells with high plasticity, such as multipotent mesenchymal stem cells (MSCs), may be a promising alternative for horse cloning. In this study, we evaluated the use of bone marrow-MSCs (BM-MSCs) as nuclear donors in horse cloning, and we compared the in vitro and in vivo embryo development with respect to fibroblasts.

Materials and methods

Zona-free nuclear transfer was performed using BM-MSCs (MSC group, n=3432) or adult fibroblasts (AF group, n=4527). Embryos produced by artificial insemination (AI) recovered by uterine flushing and transferred to recipient mares were used as controls (AI group).

Results

Blastocyst development was higher in the MSC group than in the AF group (18.1% vs 10.9%, respectively; p<0.05). However, pregnancy rates and delivery rates were similar in both cloning groups, although they were lower than in the AI group (pregnancy rates: 17.7% [41/232] for MSC, 12.5% [37/297] for AF and 80.7% [71/88] for AI; delivery rates: 56.8% [21/37], 41.5% [17/41] and 90.1% [64/71], respectively). Remarkably, the gestation length of the AF group was significantly longer than the control (361.7±10.9 vs 333.9±8.7 days), in contrast to the MSC group (340.6±8.89 days). Of the total deliveries, 95.2% (20/21) of the MSC-foals were viable, compared to 52.9% (9/17) of the AF-foals (p<0.05). In addition, the AF-foals had more physiological abnormalities at birth than the MSC-foals; 90.5% (19/21) of the MSC-delivered foals were completely normal and healthy, compared to 35.3% (6/17) in the AF group. The abnormalities included flexural or angular limb deformities, umbilical cord enlargement, placental alterations and signs of syndrome of neonatal maladjustment, which were treated in most cases.

Conclusion

In summary, we obtained 29 viable cloned foals and found that MSCs are suitable donor cells in horse cloning. Even more, these cells could be more efficiently reprogrammed compared to fibroblasts.

Allogeneic Stem Cells Alter Gene Expression and Improve Healing of Distal Limb Wounds in Horses

Distal extremity wounds are a significant clinical problem in horses and humans and may benefit from mesenchymal stem cell (MSC) therapy. This study evaluated the effects of direct wound treatment with allogeneic stem cells, in terms of gross, histologic, and transcriptional features of healing. Three full-thickness cutaneous wounds were created on each distal forelimb in six healthy horses, for a total of six wounds per horse. Umbilical cord-blood derived equine MSCs were applied to each wound 1 day after wound creation, in one of four forms: (a) normoxic- or (b) hypoxic-preconditioned cells injected into wound margins, or (c) normoxic- or (d) hypoxic-preconditioned cells embedded in an autologous fibrin gel and applied topically to the wound bed. Controls were one blank (saline) injected wound and one blank fibrin gel-treated wound per horse. Data were collected weekly for 6 weeks and included wound surface area, thermography, gene expression, and histologic scoring. Results indicated that MSC treatment by either delivery method was safe and improved histologic outcomes and wound area. Hypoxic-preconditioning did not offer an advantage. MSC treatment by injection resulted in statistically significant increases in transforming growth factor beta and cyclooxygenase-2 expression at week 1. Histologically, significantly more MSC-treated wounds were categorized as pro-healing than pro-inflammatory. Wound area was significantly affected by treatment: MSC-injected wounds were consistently smaller than gel-treated or control wounds. In conclusion, MSC therapy shows promise for distal extremity wounds in horses, particularly when applied by direct injection into the wound margin. Stem Cells Translational Medicine 2018;7:98-108.

Inhibitory Effect and Mechanism of Mesenchymal Stem Cells Cultured in 3D System on Hepatoma Cells HepG2

Mesenchymal stem cells (MSCs) exhibit the feature of homing to tumor site and being immunosuppressive, which have broad prospects in tumor therapy. However, MSCs are commonly cultured in a two-dimensional (2D) condition, which would gradually loss some in vivo important properties. In this study, we built a three-dimensional (3D) system with collagen/Matrigel scaffolds to culture MSCs. The results indicated that MSCs in 3D scaffolds showed higher proliferation ability than that of in 2D cells. In vitro, 3D-cultured MSC-conditioned media (CM) significantly inhibited the proliferation of hepatoma cells HepG2 than that of in 2D-cultured MSC-CM and control groups. In vivo, animal transplantation experiment showed that the treatment of 3D-cultured MSC-CM could further significantly delay the tumor initiation and decrease the tumor volume. The microarray, quantitative PCR, and ELISA assay found that MSCs cultured in the 3D system expressed and secreted more amounts of IL-24. RT-PCR and western blot results showed that IL-24 can activate JAK1-STAT3 pathway via IL22R1 and IL20R2, and further inhibit the proliferation of HepG2 cells. Taken together, these results demonstrated that MSCs cultured in the 3D system had an inhibitory effect on the proliferation of HepG2 cells, probably through secreting more IL-24, which activated JAK1-STAT3 signaling and finally inhibited the cell proliferation to delay tumor initiation. This study also provided a simpler and more reliable approach for MSCs to suppress tumor cells, and provided effective experimental data for clinical treatment of tumor and experimental basis.

Induced pluripotent stem cells as a new getaway for bone tissue engineering: A systematic review

OBJECTIVES

Mesenchymal stem cells (MSCs) are frequently used for bone regeneration, however, they are limited in quantity. Moreover, their proliferation and differentiation capabilities reduce during cell culture expansion. Potential application of induced pluripotent stem cells (iPSCs) has been reported as a promising alternative source for bone regeneration. This study aimed to systematically review the available literature on osteogenic potential of iPSCs and to discuss methods applied to enhance their osteogenic potential.

METHODS AND MATERIALS

A thorough search of MEDLINE database was performed from January 2006 to September 2016, limited to English-language articles. All in vitro and in vivo studies on application of iPSCs in bone regeneration were included.

RESULTS

The current review is organized according to the PRISMA statement. Studies were categorized according to three different approaches used for osteo-induction of iPSCs. Data are summarized and reported according to the following variables: types of study, cell sources used for iPSC generation, applied reprogramming methods, applied osteo-induction methods and treatment groups.

CONCLUSION

According to the articles reviewed, osteo-induced iPSCs revealed osteogenic capability equal to or superior than MSCs; cell sources do not significantly affect osteogenic potential of iPSCs; addition of resveratrol to the osteogenic medium (OM) and irradiatiation after osteogenic induction reduce teratoma formation in animal models; transfection with lentiviral bone morphogenetic protein 2 results in higher mineralization compared to osteo-induction in OM; addition of TGF-β, IGF-1 and FGF-β to OM increases osteogenic capability of iPSCs.

Increased activity of TNAP compensates for reduced adenosine production and promotes ectopic calcification in the genetic disease ACDC

ACDC (arterial calcification due to deficiency of CD73) is an autosomal recessive disease resulting from loss-of-function mutations in NT5E, which encodes CD73, a 5'-ectonucleotidase that converts extracellular adenosine monophosphate to adenosine. ACDC patients display progressive calcification of lower extremity arteries, causing limb ischemia. Tissue-nonspecific alkaline phosphatase (TNAP), which converts pyrophosphate (PPi) to inorganic phosphate (Pi), and extracellular purine metabolism play important roles in other inherited forms of vascular calcification. Compared to cells from healthy subjects, induced pluripotent stem cell-derived mesenchymal stromal cells (iMSCs) from ACDC patients displayed accelerated calcification and increased TNAP activity when cultured under conditions that promote osteogenesis. TNAP activity generated adenosine in iMSCs derived from ACDC patients but not in iMSCs from control subjects, which have CD73. In response to osteogenic stimulation, ACDC patient-derived iMSCs had decreased amounts of the TNAP substrate PPi, an inhibitor of extracellular matrix calcification, and exhibited increased activation of AKT, mechanistic target of rapamycin (mTOR), and the 70-kDa ribosomal protein S6 kinase (p70S6K), a pathway that promotes calcification. In vivo, teratomas derived from ACDC patient cells showed extensive calcification and increased TNAP activity. Treating mice bearing these teratomas with an A2b adenosine receptor agonist, the mTOR inhibitor rapamycin, or the bisphosphonate etidronate reduced calcification. These results show that an increase of TNAP activity in ACDC contributes to ectopic calcification by disrupting the extracellular balance of PPi and Pi and identify potential therapeutic targets for ACDC.