Gene-Activated Matrix Comprised of Atelocollagen and Plasmid DNA Encoding BMP4 or Runx2 Promotes Rat Cranial Bone Augmentation

Role and Mechanism of BMP4 in Regenerative Medicine and Tissue Engineering

Bone morphogenetic protein 4 (BMP4) is emerging as a promising cytokine for regenerative medicine and tissue engineering. BMP4 has been shown to promote the regeneration of teeth, periodontal tissue, bone, cartilage, the thymus, hair, neurons, nucleus pulposus, and adipose tissue, as well as the formation of skeletal myotubes and vessels. BMP4 can also contribute to the formation of tissues in the heart, lung, and kidney. However, there are certain deficiencies, including the insufficiency of the mechanism of BMP4 in some fields and an appropriate carrier of BMP4 for clinical use. There has also been a lack of in vivo experiments and orthotopic transplantation studies in some fields. BMP4 has great distance from the clinical application. Therefore, there are many BMP4-related studies waiting to be explored. This review mainly discusses the effects, mechanisms, and applications of BMP4 in regenerative medicine and tissue engineering over the last 10 years in various domains and possible improvements. BMP4 has shown great potential in regenerative medicine and tissue engineering. The research of BMP4 has broad development space and great value.

Gene-Activated Matrix with Self-Assembly Anionic Nano-Device Containing Plasmid DNAs for Rat Cranial Bone Augmentation

We have developed nanoballs, a biocompatible self-assembly nano-vector based on electrostatic interactions that arrange anionic macromolecules to polymeric nanomaterials to create nucleic acid carriers. Nanoballs exhibit low cytotoxicity and high transfection efficiently in vivo. This study investigated whether a gene-activated matrix (GAM) composed of nanoballs containing plasmid (p) DNAs encoding bone morphogenetic protein 4 (pBMP4) could promote bone augmentation with a small amount of DNA compared to that composed of naked pDNAs. We prepared nanoballs (BMP4-nanoballs) constructed with pBMP4 and dendrigraft poly-L-lysine (DGL, a cationic polymer) coated by γ-polyglutamic acid (γ-PGA; an anionic polymer), and determined their biological functions in vitro and in vivo. Next, GAMs were manufactured by mixing nanoballs with 2% atelocollagen and β-tricalcium phosphate (β-TCP) granules and lyophilizing them for bone augmentation. The GAMs were then transplanted to rat cranial bone surfaces under the periosteum. From the initial stage, infiltrated macrophages and mesenchymal progenitor cells took up the nanoballs, and their anti-inflammatory and osteoblastic differentiations were promoted over time. Subsequently, bone augmentation was clearly recognized for up to 8 weeks in transplanted GAMs containing BMP4-nanoballs. Notably, only 1 μg of BMP4-nanoballs induced a sufficient volume of new bone, while 1000 μg of naked pDNAs were required to induce the same level of bone augmentation. These data suggest that applying this anionic vector to the appropriate matrices can facilitate GAM-based bone engineering.

Current Biomaterial-Based Bone Tissue Engineering and Translational Medicine

Bone defects cause significant socio-economic costs worldwide, while the clinical "gold standard" of bone repair, the autologous bone graft, has limitations including limited graft supply, secondary injury, chronic pain and infection. Therefore, to reduce surgical complexity and speed up bone healing, innovative therapies are needed. Bone tissue engineering (BTE), a new cross-disciplinary science arisen in the 21st century, creates artificial environments specially constructed to facilitate bone regeneration and growth. By combining stem cells, scaffolds and growth factors, BTE fabricates biological substitutes to restore the functions of injured bone. Although BTE has made many valuable achievements, there remain some unsolved challenges. In this review, the latest research and application of stem cells, scaffolds, and growth factors in BTE are summarized with the aim of providing references for the clinical application of BTE.

Gene-activated matrix harboring a miR20a-expressing plasmid promotes rat cranial bone augmentation

Gene-activated matrix (GAM) has a potential usefulness in bone engineering as an alternate strategy for the lasting release of osteogenic proteins but efficient methods to generate non-viral GAM remain to be established. In this study, we investigated whether an atelocollagen-based GAM containing naked-plasmid (p) DNAs encoding microRNA (miR) 20a, which may promote osteogenesis in vivo via multiple pathways associated with the osteogenic differentiation of mesenchymal stem/progenitor cells (MSCs), facilitates rat cranial bone augmentation. First, we confirmed the osteoblastic differentiation functions of generated pDNA encoding miR20a (pmiR20a) in vitro, and its transfection regulated the expression of several of target genes, such as Bambi1 and PPARγ, in rat bone marrow MSCs and induced the increased expression of BMP4. Then, when GAMs fabricated by mixing 100 μl of 2% bovine atelocollagen, 20 mg β-TCP granules and 0.5 mg (3.3 μg/μl) AcGFP plasmid-vectors encoding miR20a were transplanted to rat cranial bone surface, the promoted vertical bone augmentation was clearly recognized up to 8 weeks after transplantation, as were upregulation of VEGFs and BMP4 expressions at the early stages of transplantation. Thus, GAM-based miR delivery may provide an alternative non-viral approach by improving transgene efficacy via a small sequence that can regulate the multiple pathways.

Delivery of transcription factors as modulators of cell differentiation

Fundamental studies performed during the last decades have shown that cell fate is much more plastic than previously considered, and technologies for its manipulation are a keystone for many new tissue regeneration therapies. Transcription factors (TFs) are DNA-binding proteins that control gene expression, and they have critical roles in the control of cell fate and other cellular behavior. TF-based therapies have much medical potential, but their use as drugs depends on the development of suitable delivery technologies that can help them reach their action site inside of the cells. TFs can be used either as proteins or encoded in polynucleotides. When used in protein form, many TFs require to be associated to a cell-penetrating peptide or another transduction domain. As polynucleotides, they can be delivered either by viral carriers or by non-viral systems such as polyplexes and lipoplexes. TF-based therapies have extensively shown their potential to solve many tissue-engineering problems, including bone, cartilage and cardiac regeneration. Yet, their use has expanded beyond regenerative medicine to other prominent disease areas such as cancer therapy and immunomodulation. This review summarizes some of the delivery options for effective TF-based therapies and their current main applications.

mRNA-activated matrices encoding transcription factors as primers of cell differentiation in tissue engineering

Gene-activated matrices (GAMs) encoding pivotal transcription factors (TFs) represent a powerful tool to direct stem cell specification for tissue engineering applications. However, current TF-based GAMs activated with pDNA, are challenged by their low transfection efficiency and delayed transgene expression. Here, we report a GAM technology activated with mRNAs encoding TFs SOX9 (cartilage) and MYOD (muscle). We find that these mRNA-GAMs induce a higher and faster TF expression compared to pDNA-GAMs, especially in the case of RNase resistant mRNA sequences. This potent TF expression was translated into a high synthesis of cartilage- and muscle-specific markers, and ultimately, into successful tissue specification in vitro. Additionally, we show that the expression of tissue-specific markers can be further modulated by altering the properties of the mRNA-GAM environment. These results highlight the value of this GAM technology for priming cell lineage specification, a key centerpiece for future tissue engineering devices.

Effects of Tissue Pressure on Transgene Expression Characteristics via Renal Local Administration Routes from Ureter or Renal Artery in the Rat Kidney

We previously developed a renal pressure-mediated transfection method (renal pressure method) as a kidney-specific in vivo gene delivery system. However, additional information on selecting other injection routes and applicable animals remains unclear. In this study, we selected renal arterial and ureteral injections as local administration routes and evaluated the characteristics of gene delivery such as efficacy, safety, and distribution in pressured kidney of rat. Immediately after the naked pDNA injection, via renal artery or ureter, the left kidney of the rat was pressured using a pressure controlling device. Transfection efficiency of the pressured kidney was about 100-fold higher than that of the injection only group in both administration routes. The optimal pressure intensity in the rat kidney was 1.2 N/cm² for renal arterial injection and 0.9 N/cm² for ureteral injection. We found that transgene expression site differs according to administration route: cortical fibroblasts and renal tubule in renal arterial injection and cortical and medullary tubule and medullary collecting duct in ureteral injection. This is the first report to demonstrate that the renal pressure method can also be effective, after renal arterial and ureteral injections, in rat kidney.

Genetically Engineered-MSC Therapies for Non-unions, Delayed Unions and Critical-size Bone Defects

The normal bone regeneration process is a complex and coordinated series of events involving different cell types and molecules. However, this process is impaired in critical-size/large bone defects, with non-unions or delayed unions remaining a major clinical problem. Novel strategies are needed to aid the current therapeutic approaches. Mesenchymal stem/stromal cells (MSCs) are able to promote bone regeneration. Their beneficial effects can be improved by modulating the expression levels of specific genes with the purpose of stimulating MSC proliferation, osteogenic differentiation or their immunomodulatory capacity. In this context, the genetic engineering of MSCs is expected to further enhance their pro-regenerative properties and accelerate bone healing. Herein, we review the most promising molecular candidates (protein-coding and non-coding transcripts) and discuss the different methodologies to engineer and deliver MSCs, mainly focusing on in vivo animal studies. Considering the potential of the MSC secretome for bone repair, this topic has also been addressed. Furthermore, the promising results of clinical studies using MSC for bone regeneration are discussed. Finally, we debate the advantages and limitations of using MSCs, or genetically-engineered MSCs, and their potential as promoters of bone fracture regeneration/repair.

MACF1 Overexpression by Transfecting the 21 kbp Large Plasmid PEGFP-C1A-ACF7 Promotes Osteoblast Differentiation and Bone Formation

Microtubule actin crosslinking factor 1 (MACF1) is a large spectraplakin protein known to have crucial roles in regulating cytoskeletal dynamics, cell migration, growth, and differentiation. However, its role and action mechanism in bone remain unclear. The present study investigated optimal conditions for effective transfection of the large plasmid PEGFP-C1A-ACF7 (∼21 kbp) containing full-length human MACF1 cDNA, as well as the potential role of MACF1 in bone formation. To enhance MACF1 expression, the plasmid was transfected into osteogenic cells by electroporation in vitro and into mouse calvaria with nanoparticles. Then, transfection efficiency, osteogenic marker expression, calvarial thickness, and bone formation were analyzed. Notably, MACF1 overexpression triggered a drastic increase in osteogenic gene expression, alkaline phosphatase activity, and matrix mineralization in vitro. Mouse calvarial thickness, mineral apposition rate, and osteogenic marker protein expression were significantly enhanced by local transfection. In addition, MACF1 overexpression promoted β-catenin expression and signaling. In conclusion, MACF1 overexpression by transfecting the large plasmid containing full-length MACF1 cDNA promotes osteoblast differentiation and bone formation via β-catenin signaling. Current data will provide useful experimental parameters for the transfection of large plasmids and a novel strategy based on promoting bone formation for prevention and therapy of bone disorders.

Recent advances in gene-enhanced bone tissue engineering

The loss of bone tissue represents a critical clinical condition that is frequently faced by surgeons. Substantial progress has been made in the area of bone research, providing insight into the biology of bone under physiological and pathological conditions, as well as tools for the stimulation of bone regeneration. The present review discusses recent advances in the field of gene-enhanced bone tissue engineering. Gene transfer strategies have emerged as highly effective tissue engineering approaches for supporting the repair of the musculoskeletal system. By contrast to treatment with recombinant proteins, genetically engineered cells can release growth factors at the site of injury over extended periods of time. Of particular interest are the expedited technologies that can be applied during a single surgical procedure in a cost-effective manner, allowing translation from bench to bedside. Several promising methods based on the intra-operative genetic manipulation of autologous cells or tissue fragments have been developed in preclinical studies. Moreover, gene therapy for bone regeneration has entered the clinical stage with clinical trials for the repair of alveolar bone. Current trends in gene-enhanced bone engineering are also discussed with respect to the movement of the field towards expedited, translational approaches. It is possible that gene-enhanced bone tissue engineering will become a clinical reality within the next few years.

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

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

Micro and nanotechnologies for bone regeneration: Recent advances and emerging designs

Treatment of critical-size bone defects is a major medical challenge since neither the bone tissue can regenerate nor current regenerative approaches are effective. Emerging progresses in the field of nanotechnology have resulted in the development of new materials, scaffolds and drug delivery strategies to improve or restore the damaged tissues. The current article reviews promising nanomaterials and emerging micro/nano fabrication techniques for targeted delivery of biomolecules for bone tissue regeneration. In addition, recent advances in fabrication of bone graft substitutes with similar properties to normal tissue along with a brief summary of current commercialized bone grafts have been discussed.

Delivering Nucleic-Acid Based Nanomedicines on Biomaterial Scaffolds for Orthopedic Tissue Repair: Challenges, Progress and Future Perspectives

As well as acting to fill defects and allow for cell infiltration and proliferation in regenerative medicine, biomaterial scaffolds can also act as carriers for therapeutics, further enhancing their efficacy. Drug and protein delivery on scaffolds have shown potential, however, supraphysiological quantities of therapeutic are often released at the defect site, causing off-target side effects and cytotoxicity. Gene therapy involves the introduction of foreign genes into a cell in order to exert an effect; either replacing a missing gene or modulating expression of a protein. State of the art gene therapy also encompasses manipulation of the transcriptome by harnessing RNA interference (RNAi) therapy. The delivery of nucleic acid nanomedicines on biomaterial scaffolds - gene-activated scaffolds -has shown potential for use in a variety of tissue engineering applications, but as of yet, have not reached clinical use. The current state of the art in terms of biomaterial scaffolds and delivery vector materials for gene therapy is reviewed, and the limitations of current procedures discussed. Future directions in the clinical translation of gene-activated scaffolds are also considered, with a particular focus on bone and cartilage tissue regeneration.