Nanohydroxyapatite (nHAp) Doped with Iron Oxide Nanoparticles (IO), miR-21 and miR-124 Under Magnetic Field Conditions Modulates Osteoblast Viability, Reduces Inflammation and Inhibits the Growth of Osteoclast - A Novel Concept for Osteoporosis Treatment: Part 1

A potential function for MicroRNA-124 in normal and pathological bone conditions

Cells produce short single-stranded non-coding RNAs (ncRNAs) called microRNAs (miRNAs), which actively regulate gene expression at the posttranscriptional level. Several miRNAs have been observed to exert significant impacts on bone health and bone-related disorders. One of these, miR-124, is observed in bone microenvironments and is conserved across species. It affects bone cell growth and differentiation by activating different transcription factors and signaling pathways. In-depth functional analyses of miR-124 have revealed several physiological and pathological roles exerted through interactions with other ncRNAs. Deciphering these RNA-mediated signaling networks and pathways is essential for understanding the potential impacts of dysregulated miRNA functions on bone biology. In this review, we aim to provide a comprehensive analysis of miR-124's involvement in bone physiology and pathology. We highlight the importance of miR-124 in controlling transcription factors and signaling pathways that promote bone growth. This review reveals therapeutic implications for the treatment of bone-related diseases.

miR-21 attenuated inflammation targeting MyD88 in human chondrocytes stimulated with Hyaluronan oligosaccharides

Inflammation is the body's response to injuries, which depends on numerous regulatory factors. Among them, miRNAs have gained much attention for their role in regulating inflammatory gene expression at multiple levels. In particular, miR-21 is up-regulated during the inflammatory response and reported to be involved in the resolution of inflammation by down-regulating pro-inflammatory mediators, including MyD88. Herein, we evaluated the regulatory effects of miR-21 on the TLR-4/MyD88 pathway in an in vitro model of 6-mer HA oligosaccharides-induced inflammation in human chondrocytes. The exposition of chondrocytes to 6-mer HA induced the activation of the TLR4/MyD88 pathway, which culminates in NF-kB activation. Changes in miR-21, TLR-4, MyD88, NLRP3 inflammasome, IL-29, Caspase1, MMP-9, iNOS, and COX-2 mRNA expression of 6-mer HA-stimulated chondrocytes were examined by qRT-PCR. Protein amounts of TLR-4, MyD88, NLRP3 inflammasome, p-ERK1/2, p-AKT, IL-29, caspase1, MMP-9, p-NK-kB p65 subunit, and IKB-a have been evaluated by ELISA kits. NO and PGE2 levels have been assayed by colorimetric and ELISA kits, respectively. HA oligosaccharides induced a significant increase in the expression of the above parameters, including NF-kB activity. The use of a miR-21 mimic attenuated MyD88 expression levels and the downstream effectors. On the contrary, treatment with a miR-21 inhibitor induced opposite effects. Interestingly, the use of a MyD88 siRNA confirmed MyD88 as the target of miR-21 action. Our results suggest that miR-21 expression could increase in an attempt to reduce the inflammatory response, targeting MyD88.

Stimuli-Mediated Macrophage Switching, Unraveling the Dynamics at the Nanoplatforms-Macrophage Interface

Macrophages play an essential role in immunotherapy and tissue regeneration owing to their remarkable plasticity and diverse functions. Recent bioengineering developments have focused on using external physical stimuli such as electric and magnetic fields, temperature, and compressive stress, among others, on micro/nanostructures to induce macrophage polarization, thereby increasing their therapeutic potential. However, it is difficult to find a concise review of the interaction between physical stimuli, advanced micro/nanostructures, and macrophage polarization. This review examines the present research on physical stimuli-induced macrophage polarization on micro/nanoplatforms, emphasizing the synergistic role of fabricated structure and stimulation for advanced immunotherapy and tissue regeneration. A concise overview of the research advancements investigating the impact of physical stimuli, including electric fields, magnetic fields, compressive forces, fluid shear stress, photothermal stimuli, and multiple stimulations on the polarization of macrophages within complex engineered structures, is provided. The prospective implications of these strategies in regenerative medicine and immunotherapeutic approaches are highlighted. This review will aid in creating stimuli-responsive platforms for immunomodulation and tissue regeneration.

Osteoporotic osseointegration: therapeutic hallmarks and engineering strategies

Osteoporosis is a systemic skeletal disease caused by an imbalance between bone resorption and formation. Current treatments primarily involve systemic medication and hormone therapy. However, these systemic treatments lack directionality and are often ineffective for locally severe osteoporosis, with the potential for complex adverse reactions. Consequently, treatment strategies using bioactive materials or external interventions have emerged as the most promising approaches. This review proposes twelve microenvironmental treatment targets for osteoporosis-related pathological changes, including local accumulation of inflammatory factors and reactive oxygen species (ROS), imbalance of mitochondrial dynamics, insulin resistance, disruption of bone cell autophagy, imbalance of bone cell apoptosis, changes in neural secretions, aging of bone cells, increased local bone tissue vascular destruction, and decreased regeneration. Additionally, this review examines the current research status of effective or potential biophysical and biochemical stimuli based on these microenvironmental treatment targets and summarizes the advantages and optimal parameters of different bioengineering stimuli to support preclinical and clinical research on osteoporosis treatment and bone regeneration. Finally, the review addresses ongoing challenges and future research prospects.

Bone Targeting Nanoparticles for the Treatment of Osteoporosis

Osteoporosis (OP) affects millions of people worldwide, especially postmenopausal women and the elderly. Although current available anti-OP agents can show promise in slowing down bone resorption, most are not specifically delivered to the hard tissue, causing significant toxicity. A bone-targeted nanodrug delivery system can reduce side effects and precisely deliver drug candidates to the bone. This review focuses on the progress of bone-targeted nanoparticles in OP therapy. We enumerate the existing OP medications, types of bone-targeted nanoparticles and categorize pairs of the most common bone-targeting functional groups. Finally, we summarize the potential use of bone-targeted nanoparticles in OP treatment. Ongoing research into the development of targeted ligands and nanocarriers will continue to expand the possibilities of OP-targeted therapies into clinical application.

Milk-Derived Small Extracellular Vesicles Promote Osteogenic Differentiation and Inhibit Inflammation via microRNA-21

Chronic apical periodontitis (CAP) is a disease with characteristics of inflammation and bone loss. In this study, our objective was to examine the function of small extracellular vesicles (sEVs) obtained from milk in encouraging osteogenic differentiation and inhibiting inflammation by miR-21 in CAP. The expression of miR-21 was detected using qRT-PCR in human CAP samples. The impact of miR-21 on the process of osteogenic differentiation was investigated using CCK-8, qRT-PCR, immunofluorescence staining, and Western blot analysis. The evaluation of RAW 264.7 cell polarization and the assessment of inflammatory factor expression were conducted through qRT-PCR. The influence of sEVs on MC3T3-E1 cells and RAW 264.7 cells was examined, with a particular emphasis on the involvement of miR-21. In human CAP samples, a decrease in miR-21 expression was observed. MiR-21 increased the expression of osteogenesis-related genes and M2 polarization genes while decreasing the expression of M1 polarization genes and inflammatory cytokines. Treatment with milk-derived sEVs also promoted osteogenesis and M2 polarization while inhibiting M1 polarization and inflammation. Conversely, the addition of miR-21 inhibitors resulted in opposite effects. Our results indicated that sEVs derived from milk had a positive effect on bone formation and activation of anti-inflammatory (M2) macrophages and simultaneously reduced inflammation by regulating miR-21 in CAP.

Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvβ3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

Modulating osteoclasts with nanoparticles: A path for osteoporosis management?

Osteoclasts are the cells responsible for the bone resorption process during bone remodeling. In a healthy situation, this process results from an equilibrium between new matrix formation by osteoblast and matrix resorption by osteoclast. Osteoporosis (OP) is a systemic bone disease characterized by a decreased bone mass density and alterations in bone microarchitecture, increasing fracture predisposition. Despite the variety of available therapies for OP management there is a growing gap in its treatment associated to the low patients´ adherence owing to concerns related with long-term efficacy or safety. This makes the development of new and safe treatments necessary. Among the newly developed strategies, the use of synthetic and natural nanoparticles to modulate osteoclasts differentiation, activity, apoptosis or crosstalk with osteoblasts have arisen. Synthetic nanoparticles exert their therapeutic effect either by loading antiresorptive drugs or including molecules for osteoclasts gene regulation. Moreover, this control over osteoclasts can be improved by their targeting to bone extracellular matrix or osteoclast membranes. Furthermore, natural nanoparticles, also known as extracellular vesicles, have been identified to play a key role in bone homeostasis. Consequently, these systems have been widely studied to control osteoblasts and osteoclasts under variable environments. Additionally, the ability to bioengineer extracellular vesicles has allowed to obtain biomimetic systems with desirable characteristics as drug carriers for osteoclasts. The analyzed information reveals the possibility of modulating osteoclasts by different mechanisms through nanoparticles decreasing bone resorption. These findings suggest that controlling osteoclast activity using nanoparticles has the potential to improve osteoporosis management. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

MiR-21-5p regulates the dynamic of mitochondria network and rejuvenates the senile phenotype of bone marrow stromal cells (BMSCs) isolated from osteoporotic SAM/P6 mice

BACKGROUND

Progression of senile osteoporosis is associated with deteriorated regenerative potential of bone marrow-derived mesenchymal stem/stromal cells (BMSCs). According to the recent results, the senescent phenotype of osteoporotic cells strongly correlates with impaired regulation of mitochondria dynamics. Moreover, due to the ageing of population and growing osteoporosis incidence, more efficient methods concerning BMSCs rejuvenation are intensely investigated. Recently, miR-21-5p was reported to play a vital role in bone turnover, but its therapeutic mechanisms in progenitor cells delivered from senile osteoporotic patients remain unclear. Therefore, the goal of this paper was to investigate for the first time the regenerative potential of miR-21-5p in the process of mitochondrial network regulation and stemness restoration using the unique model of BMSCs isolated from senile osteoporotic SAM/P6 mice model.

METHODS

BMSCs were isolated from healthy BALB/c and osteoporotic SAM/P6 mice. We analysed the impact of miR-21-5p on the expression of crucial markers related to cells' viability, mitochondria reconstruction and autophagy progression. Further, we established the expression of markers vital for bone homeostasis, as well as defined the composition of extracellular matrix in osteogenic cultures. The regenerative potential of miR-21 in vivo was also investigated using a critical-size cranial defect model by computed microtomography and SEM-EDX imaging.

RESULTS

MiR-21 upregulation improved cells' viability and drove mitochondria dynamics in osteoporotic BMSCs evidenced by the intensification of fission processes. Simultaneously, miR-21 enhanced the osteogenic differentiation of BMSCs evidenced by increased expression of Runx-2 but downregulated Trap, as well as improved calcification of extracellular matrix. Importantly, the analyses using the critical-size cranial defect model indicated on a greater ratio of newly formed tissue after miR-21 application, as well as upregulated content of calcium and phosphorus within the defect site.

CONCLUSIONS

Our results demonstrate that miR-21-5p regulates the fission and fusion processes of mitochondria and facilitates the stemness restoration of senile osteoporotic BMSCs. At the same time, it enhances the expression of RUNX-2, while reduces TRAP accumulation in the cells with deteriorated phenotype. Therefore, miR-21-5p may bring a novel molecular strategy for senile osteoporosis diagnostics and treatment.

Smart Orthopedic Biomaterials and Implants

Musculoskeletal injuries including bone defects continue to present a significant challenge in orthopedic surgery due to suboptimal healing. Bone reconstruction strategies focused on the use of biological grafts and bone graft substitutes in the form of biomaterials-based 3D structures in fracture repair. Recent advances in biomaterials science and engineering have resulted in the creation of intricate 3D bone-mimicking structures that are mechanically stable, biodegradable, and bioactive to support bone regeneration. Current efforts are focused on improving the biomaterial and implant physicochemical properties to promote interactions with the host tissue and osteogenesis. The "smart" biomaterials and their 3D structures are designed to actively interact with stem/progenitor cells and the extracellular matrix (ECM) to influence the local environment towards osteogenesis and de novo tissue formation. This article will summarize such smart biomaterials and the methodologies to apply either internal or external stimuli to control the tissue healing microenvironment. A particular emphasis is also made on the use of smart biomaterials and strategies to create functional bioactive implants for bone defect repair and regeneration.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

Magnetic Hydroxyapatite Composite Nanoparticles for Augmented Differentiation of MC3T3-E1 Cells for Bone Tissue Engineering

Progressive aging harms bone tissue structure and function and, thus, requires effective therapies focusing on permanent tissue regeneration rather than partial cure, beginning with regenerative medicine. Due to advances in tissue engineering, stimulating osteogenesis with biomimetic nanoparticles to create a regenerative niche has gained attention for its efficacy and cost-effectiveness. In particular, hydroxyapatite (HAP, Ca₁₀(PO₄)₆(OH)₂) has gained significant interest in orthopedic applications as a major inorganic mineral of native bone. Recently, magnetic nanoparticles (MNPs) have also been noted for their multifunctional potential for hyperthermia, MRI contrast agents, drug delivery, and mechanosensitive receptor manipulation to induce cell differentiation, etc. Thus, the present study synthesizes HAP-decorated MNPs (MHAP NPs) via the wet chemical co-precipitation method. Synthesized MHAP NPs were evaluated against the preosteoblast MC3T3-E1 cells towards concentration-dependent cytotoxicity, proliferation, morphology staining, ROS generation, and osteogenic differentiation. The result evidenced that MHAP NPs concentration up to 10 µg/mL was non-toxic even with the time-dependent proliferation studies. As nanoparticle concentration increased, FACS apoptosis assay and ROS data showed a significant rise in apoptosis and ROS generation. The MC3T3-E1 cells cocultured with 5 µg/mL MHAP NPs showed significant osteogenic differentiation potential. Thus, MHAP NPs synthesized with simple wet chemistry could be employed in bone regenerative therapy.

Iron Oxide Nanoparticles Combined with Static Magnetic Fields in Bone Remodeling

Iron oxide nanoparticles (IONPs) are extensively used in bone-related studies as biomaterials due to their unique magnetic properties and good biocompatibility. Through endocytosis, IONPs enter the cell where they promote osteogenic differentiation and inhibit osteoclastogenesis. Static magnetic fields (SMFs) were also found to enhance osteoblast differentiation and hinder osteoclastic differentiation. Once IONPs are exposed to an SMF, they become rapidly magnetized. IONPs and SMFs work together to synergistically enhance the effectiveness of their individual effects on the differentiation and function of osteoblasts and osteoclasts. This article reviewed the individual and combined effects of different types of IONPs and different intensities of SMFs on bone remodeling. We also discussed the mechanism underlying the synergistic effects of IONPs and SMFs on bone remodeling.

MicroRNA-124-3p-enriched small extracellular vesicles as a therapeutic approach for Parkinson's disease

Parkinson's disease is a neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra with no effective cure available. MicroRNA-124 has been regarded as a promising therapeutic entity for Parkinson's disease due to its pro-neurogenic and neuroprotective roles. However, its efficient delivery to the brain remains challenging. Here, we used umbilical cord blood mononuclear cell-derived extracellular vesicles as a biological vehicle to deliver microRNA (miR)-124-3p and evaluate its therapeutic effects in a mouse model of Parkinson's disease. In vitro, miR-124-3p-loaded small extracellular vesicles induced neuronal differentiation in subventricular zone neural stem cell cultures and protected N27 dopaminergic cells against 6-hydroxydopamine-induced toxicity. In vivo, intracerebroventricularly administered small extracellular vesicles were detected in the subventricular zone lining the lateral ventricles and in the striatum and substantia nigra, the brain regions most affected by the disease. Most importantly, although miR-124-3p-loaded small extracellular vesicles did not increase the number of new neurons in the 6-hydroxydopamine-lesioned striatum, the formulation protected dopaminergic neurons in the substantia nigra and striatal fibers, which fully counteracted motor behavior symptoms. Our findings reveal a novel promising therapeutic application of small extracellular vesicles as delivery agents for miR-124-3p in the context of Parkinson's disease.

MicroRNA-loaded biomaterials for osteogenesis

The large incidence of bone defects in clinical practice increases not only the demand for advanced bone transplantation techniques but also the development of bone substitute materials. A variety of emerging bone tissue engineering materials with osteogenic induction ability are promising strategies for the design of bone substitutes. MicroRNAs (miRNAs) are a class of non-coding RNAs that regulate intracellular protein expression by targeting the non-coding region of mRNA3′-UTR to play an important role in osteogenic differentiation. Several miRNA preparations have been used to promote the osteogenic differentiation of stem cells. Therefore, multiple functional bone tissue engineering materials using miRNA as an osteogenic factor have been developed and confirmed to have critical efficacy in promoting bone repair. In this review, osteogenic intracellular signaling pathways mediated by miRNAs are introduced in detail to provide a clear understanding for future clinical treatment. We summarized the biomaterials loaded with exogenous cells engineered by miRNAs and biomaterials directly carrying miRNAs acting on endogenous stem cells and discussed their advantages and disadvantages, providing a feasible method for promoting bone regeneration. Finally, we summarized the current research deficiencies and future research directions of the miRNA-functionalized scaffold. This review provides a summary of a variety of advanced miRNA delivery system design strategies that enhance bone regeneration.

Paradoxical role of reactive oxygen species in bone remodelling: implications in osteoporosis and possible nanotherapeutic interventions

Osteoporosis is a metabolic bone disorder that affects both sexes and is the most common cause of fractures. Osteoporosis therapies primarily inhibit osteoclast activity, and are seldom designed to trigger new bone growth thereby frequently causing severe systemic adverse effects. Physiologically, the intracellular redox state depends on the ratio of pro-oxidants, oxidizing agents (reactive oxygen species, ROS) and antioxidants. ROS is the key contributor to oxidative stress in osteoporosis as changes in redox state are responsible for dynamic bone remodeling and bone regeneration. Imbalances in ROS generation vs. antioxidant systems play a pivotal role in pathogenesis of osteoporosis, stimulating osteoblasts and osteocytes towards osteoclastogenesis. ROS prevents mineralization and osteogenesis, causing increased turnover of bone loss. Alternatively, antioxidants either directly or indirectly, contribute to activation of osteoblasts leading to differentiation and mineralization, thereby reducing osteoclastogenesis. Owing to the unpredictability of immune responsiveness and reported adverse effects, despite promising outcomes from drugs against oxidative stress, treatment in clinics targeting osteoclast has been limited. Nanotechnology-mediated interventions have gained remarkable superiority over other treatment modalities in regenerative medicine. Nanotherapeutic approaches exploit the antioxidant properties of nanoparticles for targeted drug delivery to trigger bone repair, by enhancing their osteogenic and anti-osteoclastogenic potentials to influence the biocompatibility, mechanical properties and osteoinductivity. Therefore, exploiting nanotherapeutics for maintaining the differentiation and proliferation of osteoblasts and osteoclasts is quintessential.

Nur77 Prevents Osteoporosis by Inhibiting the NF-κB Signalling Pathway and Osteoclast Differentiation

Inflammation is a major risk factor for osteoporosis, and reducing inflammatory levels is important for the prevention of osteoporosis. Although nuclear receptor 77 (Nur77) protects against inflammation in a variety of diseases, its role in osteoporosis is unknown. Therefore, the main purpose of this study was to investigate the osteoprotective and anti‐inflammatory effects of Nur77. The microCT and haematoxylin and eosin staining results indicated that knockout of Nur77 accelerated femoral bone loss in mice. The enzyme‐linked immunosorbent assay (ELISA) results showed that knockout of Nur77 increased the serum levels of hsCRP and IL‐6. The expression levels of NF‐κB, IL‐6, TNF‐α and osteoclastogenesis factors (TRAP, NFATC1, Car2, Ctsk) in the femurs of Nur77 knockout mice were increased significantly. Furthermore, in vitro, shNur77 promoted the differentiation of RAW264.7 cells into osteoclasts by activating NF‐κB, which was confirmed by PDTC treatment. Mechanistically, Nur77 inhibited osteoclast differentiation by inducing IκB‐α and suppressing IKK‐β. In RAW264.7 cells, overexpression of Nur77 alleviated inflammation induced by siIκB‐α, while siIKK‐β alleviated inflammation induced by shNur77. Consistent with the in vivo studies, we found that compared with control group, older adults with high serum hsCRP levels were more likely to suffer from osteoporosis (OR = 1.76, p < 0.001). Our data suggest that Nur77 suppresses osteoclast differentiation by inhibiting the NF‐κB signalling pathway, strongly supporting the notion that Nur77 has the potential to prevent and treat osteoporosis.

Applications of Calcium-Based Nanomaterials in Osteoporosis Treatment

With rapidly aging populations worldwide, osteoporosis has become a serious global public health problem. Caused by disordered systemic bone remodeling, osteoporosis manifests as progressive loss of bone mass and microarchitectural deterioration of bone tissue, increasing the risk of fractures and eventually leading to osteoporotic fragility fractures. As fracture risk increases, antiosteoporosis treatments transition from nonpharmacological management to pharmacological intervention, and finally to the treatment of fragility fractures. Calcium-based nanomaterials (CBNMs) have unique advantages in osteoporosis treatment because of several characteristics including similarity to natural bone, excellent biocompatibility, easy preparation and functionalization, low pH-responsive disaggregation, and inherent pro-osteogenic properties. By combining additional ingredients, CBNMs can play multiple roles to construct antiosteoporotic biomaterials with different forms. This review covers recent advances in CBNMs for osteoporosis treatment. For ease of understanding, CBNMs for antiosteoporosis treatment can be classified as locally applied CBNMs, such as implant coatings and filling materials for osteoporotic bone regeneration, and systemically administered CBNMs for antiosteoporosis treatment. Locally applied CBNMs for osteoporotic bone regeneration develop faster than the systemically administered CBNMs, an important consideration given the serious outcomes of fragility fractures. Nevertheless, many innovations in construction strategies and preparation methods have been applied to build systemically administered CBNMs. Furthermore, with increasing interest in delaying osteoporosis progression and avoiding fragility fracture occurrence, research into systemic administration of CBNMs for antiosteoporosis treatment will have more development prospects. Deep understanding of the CBNM preparation process and optimizing CBNM properties will allow for increased application of CBNMs in osteoporosis treatments in the future.

Osteopontin, a bridge links osteoarthritis and osteoporosis

Osteoarthritis (OA) is the most prevalent joint disease characterized by degradation of articular cartilage, inflammation, and changes in periarticular and subchondral bone of joints. Osteoporosis (OP) is another systemic skeletal disease characterized by low bone mass and bone mineral density (BMD) accompanied by microarchitectural deterioration in bone tissue and increased bone fragility and fracture risk. Both OA and OP are mainly affected on the elderly people. Recent studies have shown that osteopontin (OPN) plays a vital role in bone metabolism and homeostasis. OPN involves these biological activities through participating in the proliferation, migration, differentiation, and adhesion of several bone-related cells, including chondrocytes, synoviocytes, osteoclasts, osteoblasts, and marrow mesenchymal stem cells (MSCs). OPN has been demonstrated to be closely related to the occurrence and development of many bone-related diseases, such as OA and OP. This review summarizes the role of OPN in regulating inflammation activity and bone metabolism in OA and OP. Furthermore, some drugs that targeted OPN to treat OA and OP are also summarized in the review. However, the complex mechanism of OPN in regulating OA and OP is not fully elucidated, which drives us to explore the depth effect of OPN on these two bone diseases.

Novel Nanohydroxyapatite (nHAp)-Based Scaffold Doped with Iron Oxide Nanoparticles (IO), Functionalized with Small Non-Coding RNA (miR-21/124) Modulates Expression of Runt-Related Transcriptional Factor 2 and Osteopontin, Promoting Regeneration of Osteoporotic Bone in Bilateral Cranial Defects in a Senescence-Accelerated Mouse Model (SAM/P6). PART 2

Purpose

Healing of osteoporotic defects is challenging and requires innovative approaches to elicit molecular mechanisms promoting osteoblasts-osteoclasts coupling and bone homeostasis.

Methods

Cytocompatibility and biocompatibility of previously characterised nanocomposites, i.e Ca₅(PO₄)₃OH/Fe₃O₄ (later called nHAp/IO) functionalised with microRNAs (nHAp/IO@miR-21/124) was tested. In vitro studies were performed using a direct co-culture system of MC3T3-E1 pre-osteoblast and 4B12 pre-osteoclasts. The analysis included determination of nanocomposite influence on cultures morphology (confocal imaging), viability and metabolic activity (Alamar Blue assay). Pro-osteogenic signals were identified at mRNA, miRNA and protein level with RT-qPCR, Western blotting and immunocytochemistry. Biocompatibility of biomaterials was tested using bilateral cranial defect performed on a senescence-accelerated mouse model, ie SAM/P6 and Balb/c. The effect of biomaterial on the process of bone healing was monitored using microcomputed tomography.

Results

The nanocomposites promoted survival and metabolism of bone cells, as well as enhanced functional differentiation of pre-osteoblasts MC3T3-E1 in co-cultures with pre-osteoclasts. Differentiation of MC3T3-E1 driven by nHAp/IO@miR-21/124 nanocomposite was manifested by improved extracellular matrix differentiation and up-regulation of pro-osteogenic transcripts, ie late osteogenesis markers. The nanocomposite triggered bone healing in a cranial defect model in SAM/P6 mice and was replaced by functional bone in Balb/c mice.

Conclusion

This study demonstrates that the novel nanocomposite nHAp/IO can serve as a platform for therapeutic miRNA delivery. Obtained nanocomposite elicit pro-osteogenic signals, decreasing osteoclasts differentiation, simultaneously improving osteoblasts metabolism and their transition toward pre-osteocytes and bone mineralisation. The proposed scaffold can be an effective interface for in situ regeneration of osteoporotic bone, especially in elderly patients.