MicroRNA functionalized microporous titanium oxide surface by lyophilization with enhanced osteogenic activity

Mesenchymal stem cells and dental implant osseointegration during aging: from mechanisms to therapy

Dental implants are widely used to replace missing teeth, providing patients with unparalleled levels of effectiveness, convenience, and affordability. The biological basis for the clinical success of dental implants is osseointegration. Bone aging is a high-risk factor for the reduced osseointegration and survival rates of dental implants. In aged individuals, mesenchymal stem cells (MSCs) in the bone marrow show imbalanced differentiation with a reduction in osteogenesis and an increase in adipogenesis. This leads to impaired osseointegration and implant failure. This review focuses on the molecular mechanisms underlying the dysfunctional differentiation of aged MSCs, which primarily include autophagy, transcription factors, extracellular vesicle secretion, signaling pathways, epigenetic modifications, microRNAs, and oxidative stress. Furthermore, this review addresses the pathological changes in MSCs that affect osseointegration and discusses potential therapeutic interventions to enhance osseointegration by manipulating the mechanisms underlying MSC aging.

MicroRNA-138: an emerging regulator of skeletal development, homeostasis, and disease

Noncoding microRNAs are powerful epigenetic regulators of cellular processes by their ability to target and suppress expression of numerous protein-coding mRNAs. This multitargeting function is a unique and complex feature of microRNAs. It is now well-described that microRNAs play important roles in regulating the development and homeostasis of many cell/tissue types, including those that make up the skeletal system. In this review, we focus on microRNA-138 (miR-138) and its effects on regulating bone and cartilage cell differentiation and function. In addition to its reported role as a tumor suppressor, miR-138 appears to function as an inhibitor of osteoblast differentiation. This review provides additional information on studies that have attempted to alter miR-138 expression in vivo as a means to dampen ectopic calcification or alter bone mass. However, a review of the published literature on miR-138 in cartilage reveals a number of contradictory and inconclusive findings with respect to regulating chondrogenesis and chondrocyte catabolism. This highlights the need for more research in understanding the role of miR-138 in cartilage biology and disease. Interestingly, a number of studies in other systems have reported miR-138-mediated effects in dampening inflammation and pain responses. Future studies will reveal if a multifunctional role of miR-138 involving suppression of ectopic bone, inflammation, and pain will be beneficial in skeletal conditions such as osteoarthritis and heterotopic ossification.

Gene-activated titanium implants for gene delivery to enhance osseointegration

Osseointegration is the direct and intimate contact between mineralized tissue and titanium implant at the bone-implant interface. Early establishment and stable maintenance of osseointegration is the key to long-term implant success. However, in patients with compromised conditions such as osteoporosis and patients beginning early load-bearing activities such as walking, lower osseointegration around titanium implants is often observed, which might result in implant early failure. Gene-activated implants show an exciting prospect of combining gene delivery and biomedical implants to solve the problems of poor osseointegration formation, overcoming the shortcomings of protein therapy, including rapid degradation and overdose adverse effects. The conception of gene-activated titanium implants is based on "gene-activated matrix" (GAM), which means scaffolds using non-viral vectors for in situ gene delivery to achieve a long-term and efficient transfection of target cells. Current preclinical studies in animal models have shown that plasmid DNA (pDNA), microRNA (miRNA), and small interference RNA (siRNA) functionalized titanium implants can enhance osseointegration with safety and efficiency, leading to the expectation of applying this technique in dental and orthopedic clinical scenarios. This review aims to comprehensively summarize fabrication strategies, current applications, and futural outlooks of gene-activated implants, emphasizing nucleic acid targets, non-viral vectors, implant surface modification techniques, nucleic acid/vector complexes loading strategies.

Influence of epigenetics on periodontitis and peri-implantitis pathogenesis

Periodontitis is a disease characterized by tooth-associated microbial biofilms that drive chronic inflammation and destruction of periodontal-supporting tissues. In some individuals, disease progression can lead to tooth loss. A similar condition can occur around dental implants in the form of peri-implantitis. The immune response to bacterial challenges is not only influenced by genetic factors, but also by environmental factors. Epigenetics involves the study of gene function independent of changes to the DNA sequence and its associated proteins, and represents a critical link between genetic and environmental factors. Epigenetic modifications have been shown to contribute to the progression of several diseases, including chronic inflammatory diseases like periodontitis and peri-implantitis. This review aims to present the latest findings on epigenetic influences on periodontitis and to discuss potential mechanisms that may influence peri-implantitis, given the paucity of information currently available.

MicroRNAs as therapeutic targets in breast cancer metastasis

Breast cancer is a complex disease with multiple risk factors involved in its pathogenesis. Among these factors, microRNAs are considered for playing a fundamental role in the development and progression of malignant breast tumors. In recent years, various studies have demonstrated that several microRNAs exhibit increased or decreased expression in metastatic breast cancer, acting as indicators of metastatic potential in body fluids and tissue samples. The identification of these microRNA expression patterns could prove instrumental for the development of novel therapeutic molecules that either mimic or inhibit microRNA action. Additionally, an efficient delivery system mediated by viral vectors, nonviral carriers, or scaffold biomaterials is a prerequisite for implementing microRNA-based therapies; therefore, this review attempts to highlight essential microRNA molecules involved in the metastatic process of breast cancer and discuss recent advances in microRNA-based therapeutic approaches with potential future applications to the treatment sequence of breast cancer.

Bioactive coatings with anti-osteoclast therapeutic agents for bone implants: Enhanced compliance and prolonged implant life

The use of therapeutic agents that inhibit bone resorption is crucial to prolong implant life, delay revision surgery, and reduce the burden on the healthcare system. These therapeutic agents include bisphosphonates, various nucleic acids, statins, proteins, and protein complexes. Their use in systemic treatment has several drawbacks, such as side effects and insufficient efficacy in terms of concentration, which can be eliminated by local treatment. This review focuses on the incorporation of osteoclast inhibitors (antiresorptive agents) into bioactive coatings for bone implants. The ability of bioactive coatings as systems for local delivery of antiresorptive agents to achieve optimal loading of the bioactive coating and its release is described in detail. Various parameters such as the suitable concentrations, release times, and the effects of the antiresorptive agents on nearby cells or bone tissue are discussed. However, further research is needed to support the optimization of the implant, as this will enable subsequent personalized design of the coating in terms of the design and selection of the coating material, the choice of an antiresorptive agent and its amount in the coating. In addition, therapeutic agents that have not yet been incorporated into bioactive coatings but appear promising are also mentioned. From this work, it can be concluded that therapeutic agents contribute to the biocompatibility of the bioactive coating by enhancing its beneficial properties.

Selenomethionine-Modified Polyethylenimine-Based Nanoparticles Loaded with miR-132-3p Inhibitor-Biofunctionalized Titanium Implants for Improved Osteointegration

Titanium and its alloys have been widely used as bone implants, but for reduced treatment span, improvements are urgently needed to achieve faster and better osteointegration. In this study, we found that miR-132-3p inhibited bone-marrow-derived stem cell (BMSC) osteogenic differentiation via targeting BMP2, and that inhibiting miR-132-3p could significantly improve the osteogenic capability of BMSCs. Moreover, we fabricated a biocompatible selenomethionine (SEMET)-modified polyethylene glycol (PEG)/polyethylenimine (PEI) nanoparticle (SeNP) cross-linked with 0.2% gelatin solutions and delivered miR-132-3p inhibitor to biofunctionalize alkali heat-treated titanium implants, resulting in the development of a novel coating for reverse transfection. The biological performances of PEG/PEI/miR-132-3p inhibitor and SeNP/miR-132-3p inhibitor-biofunctionalized titanium were compared. The biological effects, including cell viability, cytotoxicity, adhesion, cellular uptake, and osteogenic capacity of SeNP/miR-132-3p inhibitor-biofunctionalized titanium implants, were then assessed. Results showed that SeNPs presented appropriate morphology, diameter, and positive zeta potential for efficient gene delivery. The transfection efficiency of the SeNP/miR-132-3p inhibitor was comparable to that of the PEG/PEI/miR-132-3p inhibitor, but the former induced less reactive oxygen species (ROS) production and lower apoptosis rates. Confocal laser scanning microscopy (CLSM) demonstrated that SeNP/miR-132-3p inhibitor nanoparticles released from the titanium surfaces and were taken up by adherent BMSCs. In addition, the release profile showed that transfection could obtain a long-lasting silencing effect for more than 2 weeks. The cell viability, cytotoxicity, and cell spreading of SeNP/miRNA-132-3p inhibitor-biofunctionalized titanium were comparable with those of untreated titanium and the SeNP/miRNA-132-3p inhibitor negative control (NC)-biofunctionalized titanium but resulted in higher ALP activity and osteogenic gene expression levels. In vivo animal studies further certified that SeNP/miRNA-132-3p inhibitor nanoparticles from titanium surfaces promoted osteointegration, which was revealed by microcomputed tomography (micro-CT) and histological observations. Taken together, these findings suggested that selenomethionine-modified PEI-based nanoparticles could achieve better biocompatibility. Moreover, titanium implants biofunctionalized by SeNP/miRNA-132-3p inhibitor nanoparticles might have significant clinical potential for more effective osteointegration.

Osteogenic effects of microRNA-335-5p/lipidoid nanoparticles coated on titanium surface

OBJECTIVE

In this study, we aimed to investigate the therapeutic potential of miR-335-5p lipidoid nanocomplexes coated on Titanium (Ti) SLActive surface by lyophilization.

DESIGN

In our model, we coated miR-335-5p/Lipidoid nanoparticles on titanium implant, seeded GFP-labelled mouse bone marrow stromal cells (BMSCs) onto the functionalized Ti implant surface, and analyzed the transfection efficiency, cell adhesion, proliferation, and osteogenic activity of the bone-implant interface.

RESULTS

The Ti SLActive surface displayed a suitable hydrophilicity ability and provided a large surface area for miRNA loading, enabling spatial retention of the miRNAs within the nanopores until cellular delivery. We demonstrated a high transfection efficiency of miR-335-5p lipidoid nanoparticles in BMSCs seeded onto the Ti SLActive surface, even after 14 days. Alkaline phosphatase (ALP) activity and cell vitality were significantly increased in BMSCs transfected with miR-335-5p at 7 and 14 days as opposed to cells transfected with negative controls. When miR-335-5p transfected BMSCs were induced to undergo osteogenic differentiation, we detected increased mRNA expression of osteogenic markers including Alkaline phosphatase (ALP), collagen I (COL1), osteocalcin (OCN) and bone sialoprotein (BSP) at 7 and 14 days as compared with negative controls.

CONCLUSION

MiR-335-5p lipidoid nanoparticles could be used as a new cost-effective methodology to increase the osteogenic capacity of biomedical Ti implants.

MicroRNA in Implant Dentistry: From Basic Science to Clinical Application

Specific microRNA (miRNA) expression profiles have been reported to be predictive of specific clinical outcomes of dental implants and might be used as biomarkers in implant dentistry with diagnostic and prognostic purposes. The aim of the present narrative review was to summarize current knowledge regarding the use of miRNAs in implant dentistry. The authors attempted to identify all available evidence on the topic and critically appraise it in order to lay the foundation for the development of further research oriented towards the clinical application of miRNAs in implant dentistry.

Transcript-Activated Coatings on Titanium Mediate Cellular Osteogenesis for Enhanced Osteointegration

Osteointegration is one of the most important factors for implant success. Several biomolecules have been used as part of drug delivery systems to improve implant integration into the surrounding bone tissue. Chemically modified mRNA (cmRNA) is a new form of therapeutic that has been used to induce bone healing. Combined with biomaterials, cmRNA can be used to develop transcript-activated matrices for local protein production with osteoinductive potential. In this study, we aimed to utilize this technology to create bone morphogenetic protein 2 (BMP2) transcript-activated coatings for titanium (Ti) implants. Therefore, different coating methodologies as well as cmRNA incorporation strategies were evaluated. Three different biocompatible biomaterials were used for the coating of Ti, namely, poly-d,l-lactic acid (PDLLA), fibrin, and fibrinogen. cmRNA-coated Ti disks were assayed for transfection efficiency, cmRNA release, cell viability and proliferation, and osteogenic activity in vitro. We found that cmRNA release was significantly delayed in Ti surfaces previously coated with biomaterials. Consequently, the transfection efficiency was greatly improved. PDLLA coating improved the transfection efficiency in a concentration-dependent manner. Lower PDLLA concentration used for the coating of Ti resulted in higher transfection efficiency. Fibrin and fibrinogen coatings showed even higher transfection efficiencies compared to all PDLLA concentrations. In those disks, not only the expression was up to 24-fold higher but also the peak of maximal expression was delayed from 24 h to 5 days, and the duration of expression was also extended until 7 days post-transfection. For fibrin, higher transfection efficiencies were obtained in the coatings with the lowest thrombin amounts. Accordingly, fibrinogen coatings gave the best results in terms of cmRNA transfection. All biomaterial-coated Ti surfaces showed improved cell viability and proliferation, though this was more noticeable in the fibrinogen-coated disks. The latter was also the only coating to support significant amounts of BMP2 produced by C2C12 cells in vitro. Osteogenesis was confirmed using BMP2 cmRNA fibrinogen-coated Ti disks, and it was dependent of the cmRNA amount present. Alkaline phosphatase (ALP) activity of C2C12 increased when using fibrinogen coatings containing 250 ng of cmRNA or more. Similarly, mineralization was also observed that increased with increasing cmRNA concentration. Overall, our results support fibrinogen as an optimal material to deliver cmRNA from titanium-coated surfaces.

The Role of Epigenetic Functionalization of Implants and Biomaterials in Osseointegration and Bone Regeneration-A Review

The contribution of epigenetic mechanisms as a potential treatment model has been observed in cancer and autoimmune/inflammatory diseases. This review aims to put forward the epigenetic mechanisms as a promising strategy in implant surface functionalization and modification of biomaterials, to promote better osseointegration and bone regeneration, and could be applicable for alveolar bone regeneration and osseointegration in the future. Materials and Methods: Electronic and manual searches of the literature in PubMed, MEDLINE, and EMBASE were conducted, using a specific search strategy limited to publications in the last 5 years to identify preclinical studies in order to address the following focused questions: (i) Which, if any, are the epigenetic mechanisms used to functionalize implant surfaces to achieve better osseointegration? (ii) Which, if any, are the epigenetic mechanisms used to functionalize biomaterials to achieve better tissue regeneration? Findings from several studies have emphasized the role of miRNAs in functionalizing implants surfaces and biomaterials to promote osseointegration and bone regeneration, respectively. However, there are scarce data on the role of DNA methylation and histone modifications for these specific applications, despite being commonly applied in cancer research. Studies over the past few years have demonstrated that biomaterials are immunomodulatory rather than inert materials. In this context, epigenetics can act as next generation of advanced treatment tools for future regenerative techniques. Yet, there is a need to evaluate the efficacy/cost effectiveness of these techniques in comparison to current standards of care.

Chitosan-miRNA functionalized microporous titanium oxide surfaces via a layer-by-layer approach with a sustained release profile for enhanced osteogenic activity

BACKGROUND

The biofunctionalization of titanium implants for high osteogenic ability is a promising approach for the development of advanced implants to promote osseointegration, especially in compromised bone conditions. In this study, polyelectrolyte multilayers (PEMs) were fabricated using the layer-by-layer approach with a chitosan-miRNA (CS-miRNA) complex and sodium hyaluronate (HA) as the positively and negatively charged polyelectrolytes on microarc-oxidized (MAO) Ti surfaces via silane-glutaraldehyde coupling.

METHODS

Dynamic contact angle and scanning electron microscopy measurements were conducted to monitor the layer accumulation. RiboGreen was used to quantify the miRNA loading and release profile in phosphate-buffered saline. The in vitro transfection efficiency and the cytotoxicity were investigated after seeding mesenchymal stem cells (MSCs) on the CS-antimiR-138/HA PEM-functionalized microporous Ti surface. The in vitro osteogenic differentiation of the MSCs and the in vivo osseointegration were also evaluated.

RESULTS

The surface wettability alternately changed during the formation of PEMs. The CS-miRNA nanoparticles were distributed evenly across the MAO surface. The miRNA loading increased with increasing bilayer number. More importantly, a sustained miRNA release was obtained over a timeframe of approximately 2 weeks. In vitro transfection revealed that the CS-antimiR-138 nanoparticles were taken up efficiently by the cells and caused significant knockdown of miR-138 without showing significant cytotoxicity. The CS-antimiR-138/HA PEM surface enhanced the osteogenic differentiation of MSCs in terms of enhanced alkaline phosphatase, collagen production and extracellular matrix mineralization. Substantially enhanced in vivo osseointegration was observed in the rat model.

CONCLUSIONS

The findings demonstrated that the novel CS-antimiR-138/HA PEM-functionalized microporous Ti implant exhibited sustained release of CS-antimiR-138, and notably enhanced the in vitro osteogenic differentiation of MSCs and in vivo osseointegration. This novel miRNA-functionalized Ti implant may be used in the clinical setting to allow for more effective and robust osseointegration.

Microarc oxidation surface of titanium implants promote osteogenic differentiation by activating ERK1/2-miR-1827-Osterix

There has been a constant requirement from the clinic to develop biomedical titanium (Ti) implants with high osteogenic ability. In this study, we clarified a novel mechanism of how MAO (microarc oxidation) coating of Ti implants facilitates osteogenic differentiation of human bone marrow mesenchymal stem cells (hB-MSCs) by activating ERK1/2-miR-1827-Osterix signaling pathway in vitro. MAO surface of titanium implant was more favorable to promote osteogenic differentiation than SLA and AOS coating. Besides, titanium implants regulated hB-MSCs osteogenesis through the p38 MAPK pathway and ERK1/2 might be the most efficient target. Furthermore, MAO coating induced osteogenic differentiation though ERK1/2-miR-1827 pathway. Finally, we verified miR-1827 regulated osteogenic differentiation partially through Osterix. Our study reveals novel insights that MAO surface of titanium implant is a prior choice for biomedical trial and for its use in periprosthetic osteolysis (PIO) treatment in an evidence-based rationale.

Nanoscale delivery systems for microRNAs in cancer therapy

Concomitant with advances in research regarding the role of miRNAs in sustaining carcinogenesis, major concerns about their delivery options for anticancer therapies have been raised. The answer to this problem may come from the world of nanoparticles such as liposomes, exosomes, polymers, dendrimers, mesoporous silica nanoparticles, quantum dots and metal-based nanoparticles which have been proved as versatile and valuable vehicles for many biomolecules including miRNAs. In another train of thoughts, the general scheme of miRNA modulation consists in inhibition of oncomiRNA expression and restoration of tumor suppressor ones. The codelivery of two miRNAs or miRNAs in combination with chemotherapeutics or small molecules was also proposed. The present review presents the latest advancements in miRNA delivery based on nanoparticle-related strategies.

Iduna protects HT22 cells by inhibiting parthanatos: The role of the p53-MDM2 pathway

Traumatic brain injury (TBI) is common and often fatal in current times. The role of poly(adenosine diphosphate-ribose) polymerase (PARP)-induced cell death (parthanatos) in TBI has not been well studied. Our past study showed that oxidative stress-induced cell death includes parthanatos by confirming the occurrence of PARP activation and nuclear translocation of apoptosis-inducing factor (AIF). As oxidative stress plays a key role in pathological progression after TBI, we believe TBI may also be alleviated by the expression of Iduna, which is the only known endogenous regulator of parthanatos. Thus, a transection model in HT-22 cells was established for present study. Downregulation of Iduna aggravated the cell damage caused by mechanical cell injury, whereas upregulation of Iduna reduced mitochondrial dysfunction induced by mechanical cell injury but exerted no effect on apoptosis associated with mitochondrial dysfunction. By contrast, Iduna prevented parthanatos by reducing PARP activation and nuclear translocation of AIF. We also investigated 2 novel p53-MDM2 pathway inhibitors, AMG 232 and Nutlin-3, which substantially reduced the protective effects of Iduna. These findings indicate that Iduna might prevent TBI by specifically inhibiting parthanatos and promoting mitochondrial function, with the p53-MDM2 pathway playing a critical role.

Cytocompatible and Anti-bacterial Adhesion Nanotextured Titanium Oxide Layer on Titanium Surfaces for Dental and Orthopedic Implants

It is widely recognized that surface nanotextures applied on a biomaterial can affect wettability, protein absorption and cellular and/or bacterial adhesion; accordingly, they are nowadays of great interest to promote fast osseointegration and to maintain physiological healing around biomedical implants. In order to be suitable for clinical applications, surface nanotextures must be not only safe and effective, but also, they should be produced through industrial processes scalable to real devices with sustainable processes and costs: this is often a barrier to the market entry. Based on these premises, a chemical surface treatment designed for titanium and its alloys able to produce an oxide layer with a peculiar sponge like nanotexture coupled with high density of hydroxyl group is here presented. The modified Ti-based surfaces previously showed inorganic bioactivity intended as the ability to induce apatite precipitation in simulated body fluid. Physicochemical properties and morphology of the obtained layers have been characterized by means of FESEM, XPS, and Zeta-potential. Biological response to osteoblasts progenitors and bacteria has been tested. The here proposed nanotextured surfaces successfully supported osteoblasts progenitors' adhesion, proliferation and extracellular matrix deposition thus demonstrating good biocompatibility. Moreover, the nanotexture was able to significantly reduce bacteria surface colonization when the orthopedic and the periodontal pathogens Staphylococcus aureus and Aggregatibacter actinomycetemcomitans strains were applied for a short time. Finally, the applicability of the proposed surface treatment to real biomedical devices (a 3D acetabular cup, a dental screw and a micro-sphered laryngeal implant) has been here demonstrated.

Current Progress on MicroRNA-Based Gene Delivery in the Treatment of Osteoporosis and Osteoporotic Fracture

Emerging evidence demonstrates that microRNAs, as important endogenous posttranscriptional regulators, are essential for bone remodeling and regeneration. Undoubtedly, microRNA-based gene therapies show great potential to become novel approaches against bone-related diseases, including osteoporosis and associated fractures. The major obstacles for continued advancement of microRNA-based therapies in clinical application include their poor in vivo stability, nonspecific biodistribution, and unwanted side effects. Appropriate chemical modifications and delivery vectors, which improve the biological performance and potency of microRNA-based drugs, hold the key to translating miRNA technologies into clinical practice. Thus, this review summarizes the current attempts and existing deficiencies of chemical modifications and delivery systems applied in microRNA-based therapies for osteoporosis and osteoporotic fractures to inform further explorations.

Tissue engineering strategies for the induction of angiogenesis using biomaterials

Angiogenesis is touted as a fundamental procedure in the regeneration and restoration of different tissues. The induction of de novo blood vessels seems to be vital to yield a successful cell transplantation rate loaded on various scaffolds. Scaffolds are natural or artificial substances that are considered as one of the means for delivering, aligning, maintaining cell connection in a favor of angiogenesis. In addition to the potential role of distinct scaffold type on vascularization, the application of some strategies such as genetic manipulation, and conjugation of pro-angiogenic factors could intensify angiogenesis potential. In the current review, we focused on the status of numerous scaffolds applicable in the field of vascular biology. Also, different strategies and priming approaches useful for the induction of pro-angiogenic signaling pathways were highlighted.

Titanium Surfaces Functionalized with siMIR31HG Promote Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

Titanium (Ti) implants are widely used in the clinic as bone substitutes and dental implants, but further improvements are needed to obtain high osteogenic ability and consequent osseointegration. Knockdown of long noncoding RNA MIR31HG promotes osteogenic differentiation and bone formation. In this study, we fabricated a Ti surface functionalized with siRNA targeting MIR31HG (siMIR31HG) and accelerated osteogenesis of bone marrow mesenchymal stem cells (BMSCs). Chitosan/siRNA complex was loaded onto the thermal alkali-treated Ti surface to fabricate the siMIR31HG-functionalized Ti surface. The surface morphology, siRNA loading and release efficiency, and transfection efficacy were investigated, and the biological effects, such as cell proliferation, cell morphology, and osteogenic activity, were determined. The results showed that the siMIR31HG-functionalized Ti implant generated an ∼50% knockdown of MIR31HG, with no apparent cytotoxicity, which consequently enhanced osteogenic differentiation of BMSCs, as indicated by the increase of ALP production, extracellular matrix mineralization, osteogenic gene expression, and ectopic bone formation in vivo. The siMIR31HG biofunctionalization can be used to obtain better osseointegration of Ti implant in the clinic.

Caveolae-mediated mesenchymal stem cell labelling by PSS-coated PLGA PFOB nano-contrast agent for MRI

Rationale: Non-invasive tracking of transplanted cells is critical in evaluating delivery, migration and prognosis of cell therapies.

Methods: We formulated a nano-contrast agent consisting of a perfluorooctylbromide (PFOB) core within a shell of poly (lactic-co-glycolic acid) (PLGA) followed by a coat of polystyrene sulfonate (PSS) for ¹⁹F MRI. The nano-contrast agent (PSS-NP) was characterised by DLS and the uptake efficiency of the nano-contrast agent (PSS-NP) was tested using flow cytometry, in vitro MRI and confocal microscopy. In vitro and in vivo assays of labelled cells were tested for their ability to provide an MRI signal while retaining their osteoblastic differentiation capabilities.

Results: PSS-NPs were internalised via caveolae-mediated endocytosis in mesenchymal stromal/stem cells without affecting cell proliferation and differentiation in osteoblasts, both in vitro and in vivo. Furthermore, labelled cells were monitored by ¹⁹F MRI for up to 2 months after transplantation in mice. In particular, PSS-NP-labelled cells can be used to monitor the enhanced immune rejection of grafted human cells in normal BALB/c mice compared to immune-compromised NOD/SCID mice. One week after transplantation, 40% of the ¹⁹F MRI signal was lost in normal mice, whereas only 10% was lost in immune-compromised mice.

Conclusion: Overall, these results show that PSS-NPs can label MSCs effectively, and be employed in vivo as a novel nano-contrast agent for non-invasive cell tracking using clinically relevant ¹⁹F MRI techniques.

Calcium-MicroRNA Complex-Functionalized Nanotubular Implant Surface for Highly Efficient Transfection and Enhanced Osteogenesis of Mesenchymal Stem Cells

Controlling mesenchymal stem cell (MSC) differentiation by RNA interference (RNAi) is a promising approach for next-generation regenerative medicine. However, efficient delivery of RNAi therapeutics is still a limiting factor. In this study, we have developed a simple, biocompatible, and highly effective delivery method of small RNA therapeutics into human MSCs (hMSCs) from an implant surface by calcium ions. First, we demonstrated that simple Ca/siRNA targeting green fluorescent protein (GFP) nanocomplexes were able to efficiently silence GFP in GFP-expressing hMSCs with adequate Ca²⁺ concentration (>5 mM). In addition, a single transfection could obtain a long-lasting silencing effect for more than 2 weeks. All three of the main endocytosis pathways (clathrin- and caveolin-mediated endocytosis and macropinocytosis) were involved in the internalization of the Ca/siRNA complexes by MSCs, and macropinocytosis plays the most dominant role. Furthermore, the Ca/siRNA complexes could be efficiently loaded onto the titanium implant surface when pretreated with anodization to create a nanotube (NT) layer. Because of the hydrophilic property of the NT surface, the Ca/siRNA was quickly loaded (less than 4 h) with high efficiency (nearly 100%), forming an even amorphous coating. The Ca/siRNA-coated NT surface showed an initial burst release of 80% of the siRNA complexes over 2 h, which is adequate to achieve robust gene silencing of attached hMSCs. To demonstrate the therapeutic potential of our Ca/siRNA coating technology, Ca/antimiR-138 complexes were loaded on to the NT surface, which strongly enhanced the osteogenic differentiation of hMSCs. In conclusion, our findings suggest that Ca²⁺ is an effective and biocompatible carrier to deliver small RNA therapeutics into hMSCs, both in solution and from functionalized surfaces, which provides a novel approach to control the MSC differentiation and tissue regeneration.

Mesenchymal stem cell-derived exosomes have altered microRNA profiles and induce osteogenic differentiation depending on the stage of differentiation

Human mesenchymal stem cell (hMSC)-derived exosomes have shown regenerative effects, but their role in osteogenesis and the underlying mechanism are yet to be determined. In this study, we examined the time-course secretion of exosomes by hMSCs during the entire process of osteogenic differentiation. Exosomes derived from hMSCs in various stages of osteogenic differentiation committed homotypic cells to differentiate towards osteogenic lineage, but only exosomes from late stages of osteogenic differentiation induced extracellular matrix mineralisation. Exosomes from expansion and early and late stages of osteogenic differentiation were internalised by a subpopulation of hMSCs. MicroRNA profiling revealed a set of differentially expressed exosomal microRNAs from the late stage of osteogenic differentiation, which were osteogenesis related. Target prediction demonstrated that these microRNAs enriched pathways involved in regulation of osteogenic differentiation and general mechanisms how exosomes exert their functions, such as "Wnt signalling pathway" and "endocytosis". Taken together, the results show that MSCs secrete exosomes with different biological properties depending on differentiation stage of their parent cells. The exosomal cargo transferred from MSCs in the late stage of differentiation induces osteogenic differentiation and mineralisation. Moreover, it is suggested that the regulatory effect on osteogenesis by exosomes is at least partly exerted by exosomal microRNA.

Scaffold-Based microRNA Therapies in Regenerative Medicine and Cancer

microRNA-based therapies are an advantageous strategy with applications in both regenerative medicine (RM) and cancer treatments. microRNAs (miRNAs) are an evolutionary conserved class of small RNA molecules that modulate up to one third of the human nonprotein coding genome. Thus, synthetic miRNA activators and inhibitors hold immense potential to finely balance gene expression and reestablish tissue health. Ongoing industry-sponsored clinical trials inspire a new miRNA therapeutics era, but progress largely relies on the development of safe and efficient delivery systems. The emerging application of biomaterial scaffolds for this purpose offers spatiotemporal control and circumvents biological and mechanical barriers that impede successful miRNA delivery. The nascent research in scaffold-mediated miRNA therapies translates know-how learnt from studies in antitumoral and genetic disorders as well as work on plasmid (p)DNA/siRNA delivery to expand the miRNA therapies arena. In this progress report, the state of the art methods of regulating miRNAs are reviewed. Relevant miRNA delivery vectors and scaffold systems applied to-date for RM and cancer treatment applications are discussed, as well as the challenges involved in their design. Overall, this progress report demonstrates the opportunity that exists for the application of miRNA-activated scaffolds in the future of RM and cancer treatments.

Delivery of antagomiR204-conjugated gold nanoparticles from PLGA sheets and its implication in promoting osseointegration of titanium implant in type 2 diabetes mellitus

Impaired osseointegration of the implant remains the big hurdle for dental implant therapy in diabetic patients. In this study, the authors first identified that miR204 was strikingly highly expressed in the bone mesenchymal stem cells (BMSCs) of diabetic rats. Forced expression of miR204 repressed the osteogenic potential of BMSCs, while inhibition of miR204 significantly increased the osteogenic capacity. Moreover, the miR204 inhibitor was conjugated with gold nanoparticles (AuNP-antagomiR204) and dispersed them in the poly(lactic-co-glycolic acid) (PLGA) solution. The AuNP-antagomiR204 containing PLGA solution was applied for coating the surface of titanium implant. Electron microscope revealed that an ultrathin sheet was formed on the surface of the implant, and the AuNPs were evenly dispersed in the coated PLGA sheet. Cellular experiments revealed that these encapsulated AuNP-antagomiR204 were able to be released from the PLGA sheet and uptaken by adherent BMSCs. In vivo animal study further confirmed that the AuNP-antagomiR204 released from PLGA sheet promoted osseointegration, as revealed by microcomputerized tomography (microCT) reconstruction and histological assay. Taken together, this study established that miR204 misexpression accounted for the deficient osseointegation in diabetes mellitus, while PLGA sheets aided the release of AuNP-antagomiR204, which would be a promising strategy for titanium implant surface functionalization toward better osseointegration.

Silencing tumor necrosis factor-alpha in vitro from small interfering RNA-decorated titanium nanotube array can facilitate osteogenic differentiation of mesenchymal stem cells

Titanium implants are known for their bone bonding ability. However, the osseointegration may be severely disturbed in the inflammation environment. In order to enhance osseointegration of the implant in an inflamed environment, the small interfering RNA (siRNA) targeting tumor necrosis factor alpha (TNF-α) was used to functionalize titanium surface for gene silencing. The chitosan–tripolyphosphate–hyaluronate complexes were used to formulate nanoparticles (NPs) with siRNA, which were adsorbed directly by the anodized titanium surface. The surface characterization was analyzed by scanning electron microscope, atomic force microscopy, as well as contact angle measurement. The fluorescence microscope was used to monitor the degradation of the layer. The coculture system was established with mesenchymal stem cells (MSCs) grown directly on functionalized titanium surface and RAW264.7 cells (preactivated by lipopolysaccharide) grown upside in a transwell chamber. The transfection and knockdown efficiency of TNF-α in RAW264.7 cells were determined by fluorescence microscope, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay. The cytoskeleton and osteogenic differentiation of MSCs were also analyzed. Regular vertical aligned nanotubes (~100 nm diameter and ~300 nm length) were generated after anodization of polished titanium. After loading with NPs, the nanotubes were filled and covered by a layer of amorphous particles. The surface topography changed and wettability decreased after covering with NPs. As expected, a burst degradation of the film was observed, which could provide sufficient NPs in the released supernatant and result in transfection and knockdown effects in RAW264.7 cells. The cytoskeleton arrangement of MSCs was elongated and the osteogenic differentiation was also significantly improved on NPs loading surface. In conclusion, the siRNA decorated titanium implant could simultaneously suppress inflammation and improve osteogenesis, which may be suitable for peri-implant bone formation under inflammatory conditions.

Next generation bone tissue engineering: non-viral miR-133a inhibition using collagen-nanohydroxyapatite scaffolds rapidly enhances osteogenesis

Bone grafts are the second most transplanted materials worldwide at a global cost to healthcare systems valued over $30 billion every year. The influence of microRNAs in the regenerative capacity of stem cells offers vast therapeutic potential towards bone grafting; however their efficient delivery to the target site remains a major challenge. This study describes how the functionalisation of porous collagen-nanohydroxyapatite (nHA) scaffolds with miR-133a inhibiting complexes, delivered using non-viral nHA particles, enhanced human mesenchymal stem cell-mediated osteogenesis through the novel focus on a key activator of osteogenesis, Runx2. This study showed enhanced Runx2 and osteocalcin expression, as well as increased alkaline phosphatase activity and calcium deposition, thus demonstrating a further enhanced therapeutic potential of a biomaterial previously optimised for bone repair applications. The promising features of this platform offer potential for a myriad of applications beyond bone repair and tissue engineering, thus presenting a new paradigm for microRNA-based therapeutics.

Nanosheet-pore topographical titanium substrates: a biophysical regulator of the fate of mesenchymal stem cells

Sub-micrometer nanosheet-pore topographic titanium substrates are fabricated with a distinct effect on the adhesion and osteogenic differentiation of MSCs in vitro.

Regenerative Medicine for Periodontal and Peri-implant Diseases

The balance between bone resorption and bone formation is vital for maintenance and regeneration of alveolar bone and supporting structures around teeth and dental implants. Tissue regeneration in the oral cavity is regulated by multiple cell types, signaling mechanisms, and matrix interactions. A goal for periodontal tissue engineering/regenerative medicine is to restore oral soft and hard tissues through cell, scaffold, and/or signaling approaches to functional and aesthetic oral tissues. Bony defects in the oral cavity can vary significantly, ranging from smaller intrabony lesions resulting from periodontal or peri-implant diseases to large osseous defects that extend through the jaws as a result of trauma, tumor resection, or congenital defects. The disparity in size and location of these alveolar defects is compounded further by patient-specific and environmental factors that contribute to the challenges in periodontal regeneration, peri-implant tissue regeneration, and alveolar ridge reconstruction. Efforts have been made over the last few decades to produce reliable and predictable methods to stimulate bone regeneration in alveolar bone defects. Tissue engineering/regenerative medicine provide new avenues to enhance tissue regeneration by introducing bioactive models or constructing patient-specific substitutes. This review presents an overview of therapies (e.g., protein, gene, and cell based) and biomaterials (e.g., resorbable, nonresorbable, and 3-dimensionally printed) used for alveolar bone engineering around teeth and implants and for implant site development, with emphasis on most recent findings and future directions.

Improving the osteogenesis of rat mesenchymal stem cells by chitosan-based-microRNA nanoparticles

MicroRNAs (miRNAs) play important roles in the osteogenic differentiation of stem cells. However, the application of miRNA in bone regeneration has been limited by its poor stability, low cellular uptake, and undesired immune response. In this study, chitosan (CS)/tripolyphosphate (TPP)/Hyaluronic Acid (HA) nanoparticles (CTH NPs) were prepared to deliver antimiR-138 to bone marrow mesenchymal stem cells (MSCs). The particle size, polydispersity index, and zeta potential of CTH NPs were related to the weight ratio of CS:TPP:HA. At optimum N/P ratio (20:1), the highest encapsulation efficiency was obtained. Both blank CTH NPs and CTH/antmiR-138 NPs exhibited no cytotoxicity to MSCs. A high transfection efficiency (nearly 70%) and significant enhancement of the osteogenesis of MSCs were observed. Above results demonstrated that CTH NPs was a potential candidate as an efficient non-viral miRNA vector to regulate the osteogenic differentiation of MSCs.

Microarc-oxidized titanium surfaces functionalized with microRNA-21-loaded chitosan/hyaluronic acid nanoparticles promote the osteogenic differentiation of human bone marrow mesenchymal stem cells

Dental implants have been widely used for the replacement of missing teeth in the clinic, but further improvements are needed to meet the clinical demands for faster and tighter osseointegration. In this study, we fabricated safe and biocompatible chitosan (CS)/hyaluronic acid (HA) nanoparticles to deliver microRNA-21 (miR-21) and thereby accelerate osteogenesis in human bone marrow mesenchymal stem cells (hBMMSCs). The CS/HA/miR-21 nanoparticles were cross-linked with 0.2% gel solution onto microarc oxidation (MAO)-treated titanium (Ti) surfaces to fabricate the miR-21-functionalized MAO Ti surface, resulting in the development of a novel coating for reverse transfection. To characterize the CS/HA/miR-21 nanoparticles, their particle size, zeta potential, surface morphology, and gel retardation ability were sequentially investigated. Their biological effects, such as cell viability, cytotoxicity, and expression of osteogenic genes by hBMMSCs on the miR-21-functionalized MAO Ti surfaces, were evaluated. Finally, we explored appropriate CS/HA/miR-21 nanoparticles with a CS/HA ratio of 4:1 and N/P ratio 20:1 for transfection, which presented good spherical morphology, an average diameter of 160.4±10.75 nm, and a positive zeta potential. The miR-21-functionalized MAO Ti surfaces demonstrated cell viability, cytotoxicity, and cell spreading comparable to those exhibited by naked MAO Ti surfaces and led to significantly higher expression of osteogenic genes. This novel miR-21-functionalized Ti implant may be used in the clinic to allow more effective and robust osseointegration.

The Diagnostic Efficacy and Biological Effects of microRNA-29b for Colon Cancer

BACKGROUND

Colorectal cancer is one of the most common cancers worldwide in terms of both incidence and mortality. The associations of expressions of tissue and plasma miR-29b were not detected in this study.

METHODS

There are 400 healthy age- and gender-matched controls enrolled in this study in a rate of 1:2. The receiver operating characteristic curve analysis was undertaken using the expression level for miR-29b in the colorectal cancer specimens from patients with cancer and healthy controls to assess the diagnostic accuracy of both tissue and plasma miR-29b levels.

RESULTS

It was found that the expression of plasma miR-29b is associated with the tissue miR-29b. Advanced study showed that aberrant miR-29b expression in both cancer tissues and plasma is associated with the clinicopathological data of patients with colorectal cancer. Tissue miR-29b showed an AUC of 0.883, with a sensitivity of 81.6% and a specificity of 84.9%. However, the AUC for plasma miR-29b was 0.743, with a sensitivity of 61.4% and a specificity of 72.5%. The analyses of the biological effects of miR-29b for colorectal cancer showed that miR-29b could inhibit the cell viability and migration.

CONCLUSION

In summary, our data suggest that both the tissue and the plasma miR-29b levels have some value as a diagnostic tool for colorectal cancer. Advanced biological effects were conducted to detect the potential effect on the cell viability and migration. Future investigations including larger patient populations and patients with early-stage colorectal cancer are needed to confirm the potential diagnostic value of miRNA-29b in colorectal cancer.

The role of microRNAs in bone remodeling

Bone remodeling is balanced by bone formation and bone resorption as well as by alterations in the quantities and functions of seed cells, leading to either the maintenance or deterioration of bone status. The existing evidence indicates that microRNAs (miRNAs), known as a family of short non-coding RNAs, are the key post-transcriptional repressors of gene expression, and growing numbers of novel miRNAs have been verified to play vital roles in the regulation of osteogenesis, osteoclastogenesis, and adipogenesis, revealing how they interact with signaling molecules to control these processes. This review summarizes the current knowledge of the roles of miRNAs in regulating bone remodeling as well as novel applications for miRNAs in biomaterials for therapeutic purposes.

MicroRNA delivery for regenerative medicine

MicroRNA (miRNA) directs post-transcriptional regulation of a network of genes by targeting mRNA. Although relatively recent in development, many miRNAs direct differentiation of various stem cells including induced pluripotent stem cells (iPSCs), a major player in regenerative medicine. An effective and safe delivery of miRNA holds the key to translating miRNA technologies. Both viral and nonviral delivery systems have seen success in miRNA delivery, and each approach possesses advantages and disadvantages. A number of studies have demonstrated success in augmenting osteogenesis, improving cardiogenesis, and reducing fibrosis among many other tissue engineering applications. A scaffold-based approach with the possibility of local and sustained delivery of miRNA is particularly attractive since the physical cues provided by the scaffold may synergize with the biochemical cues induced by miRNA therapy. Herein, we first briefly cover the application of miRNA to direct stem cell fate via replacement and inhibition therapies, followed by the discussion of the promising viral and nonviral delivery systems. Next we present the unique advantages of a scaffold-based delivery in achieving lineage-specific differentiation and tissue development.

Chitosan/siCkip-1 biofunctionalized titanium implant for improved osseointegration in the osteoporotic condition

Biofunctionalization with siRNA targeting the key negative modulators of bone turnover involved in the molecular mechanism of osteoporosis, such as casein kinase-2 interacting protein-1 (Ckip-1), may lead to enhanced Ti osseointegration in the osteoporotic condition. In this study, even siRNA loading was accomplished by the thermal alkali (TA) treatment to make the Ti ultrahydrophilic and negatively charged to facilitate the physical adsorption of the positively charged CS/siR complex, designated as TA-CS/siR. The intracellular uptake of the CS/siR complex and the gene knockdown efficiency were assessed with bone marrow mesenchymal stem cells (MSCs) as well as the green fluorescent protein (GFP) expressing H1299 cells. In vitro osteogenic activity of TA-CS/siCkip-1 targeting Ckip-1 was assessed with MSCs. In vivo osseointegration of TA-CS/siCkip-1 was assessed in the osteoporotic rat model. TA-CS/siR showed excellent siRNA delivery efficiency and gene silencing effect. TA-CS/siCkip-1 significantly improved the in vitro osteogenic differentiation of MSCs in terms of the enhanced alkaline phosphatase and collagen product and extracellular matrix mineralization, and led to dramatically enhanced in vivo osseointegration in the osteoporostic rat model, showing promising clinical potential for the osteoporotic condition application. TA-CS/siR may constitute a general approach for developing the advanced Ti implants targeting specific molecular mechanism.

MicroRNA-26a-modified adipose-derived stem cells incorporated with a porous hydroxyapatite scaffold improve the repair of bone defects

Tissue-engineered bone substitutes are frequently used to repair bone defects. Adipose-derived stem cells (ASCs) are a promising source of cells for repairing bone tissue, however, insufficient osteogenic potency remains the main obstacle for their application. The present study aimed to enhance the osteogenic potency of ASCs by transfection of microRNA (miR)-26a, a novel osteogenic and angiogenic promoting miRNA. An inverted fluorescence microscope was used to observe transfection efficiency, while a scanning electron microscope was used to detect morphological alterations. Cell proliferation was monitored continuously for 7 days using a Cell Counting kit-8 assay. Osteogenic differentiation was determined by reverse transcription quantitative polymerase chain reaction, alkaline phosphatase (ALP) staining, collagen secretion and extracellular matrix (ECM) mineralization. ASCs were incorporated with a porous hydroxyapatite (HA) scaffold to create a novel tissue-engineered bone substitute and inserted into the critical tibia defect of rats. New bone formation was evaluated by hematoxylin and eosin and Masson's trichrome staining. The results demonstrated that miR-26a was successfully delivered into the cytoplasm, while the morphology and proliferation of ASCs were not significantly altered. Osteogenic-associated genes were markedly upregulated and ALP production, collagen secretion and ECM mineralization were all increased following transfection of miR-26a. Histological evaluation demonstrated that the modified cells accompanied with a porous HA scaffold markedly promoted new bone formation within the defective area. In conclusion, miR-26a transfection significantly improved the osteogenic potency of ASCs suggesting that modified ASCs incorporated with a HA scaffold may be used as a potential bone substitute.

Biofunctionalization of titanium implant with chitosan/siRNA complex through loading-controllable and time-saving cathodic electrodeposition

For the first time, siRNA has been cathodically electrodeposited on a titanium surface for efficient target gene silencing.

Engineering and functionalization of biomaterials via surface modification

Recent progress pertaining to the surface treatment of implantable macro-scale biomaterials and using micro- and nano-biomaterials for disease diagnosis and drug/gene delivery is reviewed.

A novel collagen-nanohydroxyapatite microRNA-activated scaffold for tissue engineering applications capable of efficient delivery of both miR-mimics and antagomiRs to human mesenchymal stem cells

Manipulation of gene expression through the use of microRNAs (miRNAs) offers tremendous potential for the field of tissue engineering. However, the lack of sufficient site-specific and bioactive delivery systems has severely hampered the clinical translation of miRNA-based therapies. In this study, we developed a novel non-viral bioactive delivery platform for miRNA mimics and antagomiRs to allow for a vast range of therapeutic applications. By combining nanohydroxyapatite (nHA) particles with reporter miRNAs (nanomiRs) and collagen-nanohydroxyapatite scaffolds, this work introduces the first non-viral, non-lipid platform to date, capable of efficient delivery of mature miRNA molecules to human mesenchymal stem cells (hMSCs), a particularly difficult cell type to transfect effectively, with minimal treatment-associated cytotoxicity. Firstly, miRNAs were successfully delivered to hMSCs in monolayer, with internalisation efficiencies of 17.4 and 39.6% for nanomiR-mimics and nanoantagomiRs respectively, and both nanomiR-mimics and nanoantagomiRs yielded sustained interfering activity of greater than 90% in monolayer over 7 days. When applied to 3D scaffolds, significant RNA interference of 20% for nanomiR-mimics and 88.4% for nanoantagomiRs was achieved with no cytotoxicity issues over a 7 day period. In summary, in-house synthesised non-viral nHA particles efficiently delivered reporter miRNAs both in monolayer and on scaffolds demonstrating the immense potential of this innovative miRNA-activated scaffold system for tissue engineering applications.

Incorporation of osteogenic and angiogenic small interfering RNAs into chitosan sponge for bone tissue engineering

Engineered bone substitutes are being extensively explored in response to growing demand. However, the angiogenesis that occurs during bone formation is often overlooked in scaffold design. In this novel study, we incorporated two small interfering RNAs (siRNAs), ie, small interfering RNA targets casein kinase 2 interaction protein 1 (siCkip-1) and small interfering RNA targets soluble VEGF receptor 1 (siFlt-1), which can promote osteogenesis and angiogenesis, into a chitosan sponge. This scaffold could maintain siRNAs for over 2 weeks in neutral phosphate-buffered saline and degraded rapidly in the presence of lysozyme. The chitosan sponge with siCkip-1 and siFlt-1 in vitro bioactivity was investigated using mesenchymal stem cells. Target genes were significantly suppressed, and osteocalcin, alkaline phosphatase, and vascular endothelial growth factor were significantly upregulated. Alizarin Red staining revealed that mineralization of the extracellular matrix was markedly enhanced by dual transfection. Further analysis by immunofluorescence confirmed that the siRNA-modified scaffold simultaneously improved the expression of osteocalcin and von Willebrand factor. In vivo testing in a skull critical-size defect model showed marked bone regeneration in rats treated with siCkip-1 and siFlt-1. In conclusion, chitosan sponge containing osteogenic and angiogenic siRNAs may be used as a scaffold for bone regeneration. The dual siRNA concept may also be useful in the biofunctionalization of other materials.

Concise review: new frontiers in microRNA-based tissue regeneration

In recent years, the role of miRNAs in post-transcriptional gene regulation has come to the fore with strong evidence to indicate an important role for microRNAs (miRNAs) in the regulation of a wide range of fundamental biological processes. Notably, this includes the regulation of both endogenous tissue repair mechanisms and the growth and differentiation of stem cells (both adult and pluripotent). As a result, manipulation of miRNA signaling holds great promise for regenerative medicine, which aims to harness either endogenous or implanted cells to promote tissue repair. However, to fully realize this potential, it will be necessary to combine advances in our biological understanding with new technologies that allow precise spatiotemporal modulation of specific miRNA candidates. In this review, we highlight the role of miRNAs in tissue regeneration, discuss key challenges in translating this knowledge to the clinic, and outline recent technological advances that aim to address these issues. By combining a comprehensive knowledge of miRNA biology with cutting-edge delivery technologies, it is clear that miRNAs hold significant promise for tissue regenerative therapies in the future.

Non-viral oligonucleotide antimiR-138 delivery to mesenchymal stem cell sheets and the effect on osteogenesis

Cell-sheet technology has already constituted an important part in the regenerative medicine. Nonetheless, oligonucleotide delivery that has been widely performed on isolated stem cells to foster specific function is rarely conducted on the cell sheets. This study is designed with the two-fold aims of verifying the feasibility of non-viral oligonucleotide delivery for the cell sheets and confirming the osteogenesis enhancing effect of antimiR-138 on the cell sheets composed of bone marrow mesenchymal stem cells (BMSCs). The BMSC sheets are fabricated by a vitamin C inducing method, which can be successfully delivered with the oligonucleotides with a high delivery efficiency of nearly 100% by the properly adapted and optimized Lipofactamine2000 based formulation. The antimiR-138 delivery significantly enhances the in vitro osteogenic differentiation of BMSC sheets, indicated by the higher alkaline phosphatase (ALP) production, denser extracellular matrix mineralization and up-regulated osteogenesis related genes including runt-related transcription factor-2 (RUNX2), osterix, ALP, osteocalcin and bone morphogenetic protein-2 at both mRNA and protein levels, compared to controls. Regarding the underlying mechanism, the antimiR-138 delivery down-regulates the endogenous miR-138 levels in the BMSC sheets, consequently activates the extracellular signal regulated kinases 1/2 pathway and enhances the RUNX2 expression. The in vivo results indicate a robust enhancing effect of the antimiR-138 delivery on the bone regeneration ability of BMSC sheets. Massive bone with good vascularization is regenerated by the antimiR-138 delivered BMSC sheets, showing immense clinical significance for bone defect repair/regeneration applications. More importantly, the feasibility of non-viral oligonucleotide delivery system for the cell sheets as verified by our study shall hold a general significance for the cell sheets of various cell type and therapeutic purposes.