TGF beta receptor II interacting protein-1, an intracellular protein has an extracellular role as a modulator of matrix mineralization

ECM-binding properties of extracellular vesicles: advanced delivery strategies for therapeutic applications in bone and joint diseases

Extracellular vesicles (EVs) and the extracellular matrix (ECM) are essential in maintaining bone and joint health by facilitating intercellular communication, regulating tissue processes and providing structural support. EVs with a large surface area carry diverse biomolecules to steer the function of cells in their surroundings. To understand how EVs localize to specific sites, we here review the available knowledge on EV surface biomolecules and their interactions with ECM components that are crucial for regulating bone remodeling, cartilage maintenance, and immune responses, playing roles in both tissue homeostasis and pathological conditions, such as arthritis and osteoporosis. More importantly, using analyses of animal experimental data, we illustrate the effect of ECM-based biomaterials (e.g. hydrogels, decellularized matrices, and ECM-mimetic scaffolds) as carriers for EVs toward effective EV delivery in regenerative and immunomodulatory therapies in bone and joint tissue. These biomaterials enable sustained release and targeted delivery of EVs, promoting bone and cartilage regeneration. The insights of this review can be utilized to advance the development of cutting-edge therapies for skeletal tissue regeneration and disease management.

The impact of exosomes on bone health: A focus on osteoporosis

Osteoporosis is a widespread chronic condition. Although standard treatments are generally effective, they are frequently constrained by side effects and the risk of developing drug resistance. A promising area of research is the investigation of extracellular vesicles (EVs), including exosomes, microvesicles, and apoptotic bodies, which play a crucial role in bone metabolism. Exosomes, in particular, have shown significant potential in both the diagnosis and treatment of osteoporosis. EVs derived from osteoclasts, osteoblasts, mesenchymal stem cells, and other sources can influence bone metabolism, while exosomes from inflammatory and tumor cells may exacerbate bone loss, highlighting their dual role in osteoporosis pathology. This review offers a comprehensive overview of EV biogenesis, composition, and function in osteoporosis, focusing on their diagnostic and therapeutic potential. We examine the roles of various types of EVs and their cargo-proteins, RNAs, and lipids-in bone metabolism. Additionally, we explore the emerging applications of EVs as biomarkers and therapeutic agents, emphasizing the need for further research to address current challenges and enhance EV-based strategies for managing osteoporosis.

Mineral matrix deposition of MC3T3-E1 pre-osteoblastic cells exposed to silicocarnotite and nagelschmidtite bioceramics: In vitro comparison to hydroxyapatite

This work presents the effect of the silicocarnotite (SC) and nagelschmidtite (Nagel) phases on in vitro osteogenesis. The known hydroxyapatite of biological origin (BHAp) was used as a standard of osteoconductive characteristics. The evaluation was carried out in conventional and osteogenic media for comparative purposes to assess the osteogenic ability of the bioceramics. First, the effect of the material on cell viability at 24 h, 7 and 14 days of incubation was evaluated. In addition, cell morphology and attachment on dense bioceramic surfaces were observed by fluorescence microscopy. Specifically, alkaline phosphatase (ALP) activity was evaluated as an osteogenic marker of the early stages of bone cell differentiation. Mineralized extracellular matrix was observed by calcium phosphate deposits and extracellular vesicle formation. Furthermore, cell phenotype determination was confirmed by scanning electron microscope. The results provided relevant information on the cell attachment, proliferation, and osteogenic differentiation processes after 7 and 14 days of incubation. Finally, it was demonstrated that SC and Nagel phases promote cell proliferation and differentiation, while the Nagel phase exhibited a superior osteoconductive behavior and could promote MC3T3-E1 cell differentiation to a higher extent than SC and BHAp, which was reflected in a higher number of deposits in a shorter period for both conventional and osteogenic media.

Caffeine regulates both osteoclast and osteoblast differentiation via the AKT, NF-κB, and MAPK pathways

Background: Although caffeine generally offers benefits to human health, its impact on bone metabolism remains unclear. Aim and Methods: This study aimed to systematically evaluate the long-term effects of caffeine administration on osteoclasts, osteoblasts, and ovariectomy-induced postmenopausal osteoporosis (OP). Results: Our in vitro findings revealed that 3.125 and 12.5 μg/mL caffeine inhibited RANKL-mediated osteoclastogenesis in RAW 264.7 cells through the MAPK and NF-κB pathways, accompanied by the inactivation of nuclear translocation of nuclear factor NFATc1. Similarly, 3.125 and 12.5 μg/mL of caffeine modulated MC3T3-E1 osteogenesis via the AKT, MAPK, and NF-κB pathways. However, 50 μg/mL of caffeine promoted the phosphorylation of IκBα, P65, JNK, P38, and AKT, followed by the activation of NFATc1 and the inactivation of Runx2 and Osterix, ultimately disrupting the balance between osteoblastogenesis and osteoclastogenesis. In vivo studies showed that gavage with 55.44 mg/kg caffeine inhibited osteoclastogenesis, promoted osteogenesis, and ameliorated bone loss in ovariectomized mice. Conclusion: Conversely, long-term intake of high-dose caffeine (110.88 mg/kg) disrupted osteogenesis activity and promoted osteoclastogenesis, thereby disturbing bone homeostasis. Collectively, these findings suggest that a moderate caffeine intake (approximately 400 mg in humans) can regulate bone homeostasis by influencing both osteoclasts and osteoblasts. However, long-term high-dose caffeine consumption (approximately 800 mg in humans) could have detrimental effects on the skeletal system.

Bone-Targeted Exosomes: Strategies and Applications

As the global population ages, bone-related diseases have increasingly become a major social problem threatening human health. Exosomes, as natural cell products, have been used to treat bone-related diseases due to their superior biocompatibility, biological barrier penetration, and therapeutic effects. Moreover, the modified exosomes exhibit strong bone-targeting capabilities that may improve efficacy and avoid systemic side effects, demonstrating promising translational potential. However, a review of bone-targeted exosomes is still lacking. Thus, the recently developed exosomes for bone-targeting applications in this review are focused. The biogenesis and bone-targeting regulatory functions of exosomes, the constructive strategies of modified exosomes to improve bone-targeting, and their therapeutic effects for bone-related diseases are introduced. By summarizing developments and challenges in bone-targeted exosomes, It is striven to shed light on the selection of exosome constructive strategies for different bone diseases and highlight their translational potential for future clinical orthopedics.

Insights into the Structure and Function of TRIP-1, a Newly Identified Member in Calcified Tissues

Eukaryotic initiation factor subunit I (EIF3i), also called as p36 or TRIP-1, is a component of the translation initiation complex and acts as a modulator of TGF-β signaling. We demonstrated earlier that this intracellular protein is not only exported to the extracellular matrix via exosomes but also binds calcium phosphate and promotes hydroxyapatite nucleation. To assess other functional roles of TRIP-1, we first examined their phylogeny and showed that it is highly conserved in eukaryotes. Comparing human EIF3i sequence with that of 63 other eukaryotic species showed that more than 50% of its sequence is conserved, suggesting the preservation of its important functional role (translation initiation) during evolution. TRIP-1 contains WD40 domains and predicting its function based on this structural motif is difficult as it is present in a vast array of proteins with a wide variety of functions. Therefore, bioinformatics analysis was performed to identify putative regulatory functions for TRIP-1 by examining the structural domains and post-translational modifications and establishing an interactive network using known interacting partners such as type I collagen. Insight into the function of TRIP-1 was also determined by examining structurally similar proteins such as Wdr5 and GPSß, which contain a ß-propeller structure which has been implicated in the calcification process. Further, proteomic analysis of matrix vesicles isolated from TRIP-1-overexpressing preosteoblastic MC3T3-E1 cells demonstrated the expression of several key biomineralization-related proteins, thereby confirming its role in the calcification process. Finally, we demonstrated that the proteomic signature in TRIP1-OE MVs facilitated osteogenic differentiation of stem cells. Overall, we demonstrated by bioinformatics that TRIP-1 has a unique structure and proteomic analysis suggested that the unique osteogenic cargo within the matrix vesicles facilitates matrix mineralization.

Extracellular Vesicles in Bone Remodeling and Osteoporosis

Osteoporosis is a systemic disorder characterized by bone mass loss, leading to fractures due to weak and brittle bones. The bone tissue deterioration process is related to an impairment of bone remodeling orchestrated mainly by resident bone cells, including osteoblasts, osteoclasts, osteocytes, and their progenitors. Extracellular vesicles (EVs) are nanoparticles emerging as regulatory molecules and potential biomarkers for bone loss. Although the progress in studies relating to EVs and bone loss has increased in the last years, research on bone cells, animal models, and mainly patients is still limited. Here, we aim to review the recent advances in this field, summarizing the effect of EV components such as proteins and miRNAs in regulating bone remodeling and, consequently, osteoporosis progress and treatment. Also, we discuss the potential application of EVs in clinical practice as a biomarker and bone loss therapy, demonstrating that this rising field still needs to be further explored.

Exosomes: A new option for osteoporosis treatment

Osteoporosis is a systemic bone disease characterized by reduced bone mass and destruction of bone microarchitecture, leading to increased bone fragility and susceptibility to fracture. However, the pathogenesis and molecular mechanisms of this disease remain unclear. Extracellular vesicles, structures originating from the plasma membrane and ranging from 30 nm to 5 µm in diameter, play an important role in intercellular communication in the bone microenvironment. Exosomes are extracellular vesicles that deliver cargo molecules, including endogenous proteins, lipids and nucleic acids. These cargo molecules are encapsulated in a lipid bilayer and internalized by target cells through receptor-ligand interactions or lipid membrane fusion. With the advancement of exosome research, exosome therapy for osteoporosis is fast becoming a research hotspot for researchers. This review aims to discuss the role of exosomes in the pathogenesis of osteoporosis. In addition, emerging diagnostic and therapeutic properties of exosomes are described to highlight the potential role of exosomes in osteoporosis.

Advances of Mesenchymal Stem Cells Released Extracellular Vesicles in Periodontal Bone Remodeling

Extracellular vesicles (EVs) are nanoparticles that include exosomes, microvesicles, and apoptotic bodies; they interact with target cell surface receptors and transport contents, including mRNA, proteins, and enzymes into the cytoplasm of target cells to function. The biological fingerprints of EVs practically mirror those of the parental cells they originated from. In the bone remodeling microenvironment, EVs could act on osteoblasts to regulate the bone formation, promote osteoclast differentiation, and regulate bone resorption. Therefore, there have been many attempts wherein EVs were used to achieve targeted therapy in bone-related diseases. Periodontitis, a common bacterial infectious disease, could cause severe alveolar bone resorption, resulting in tooth loss, whereas research on periodontal bone regeneration is also an urgent question. Therefore, EVs-related studies are important for periodontal bone remodeling. In this review, we summarize the current knowledge of mesenchymal stem cell-EVs involved in periodontal bone remodeling and explore the functional gene expression through a comparative analysis of transcriptomic content.

Liver cancer cells with nuclear MET overexpression release translation regulatory protein-enriched extracellular vesicles exhibit metastasis promoting activity

MET receptor tyrosine kinase is a cell surface receptor that plays important role in embryonic development and tissue regeneration. Aberrant MET activation has been widely reported in different human cancers, making MET an attractive therapeutic target. The presence of truncated MET within the nucleus (nMET) with potential novel functions poses a great challenge to the current therapeutic strategies against MET surface receptor. Previous work has demonstrated the promoting effect of nMET in aggressive properties of hepatocellular carcinoma (HCC) cells by activating TAK1/NF-κB signalling pathway. Herein, we report the role of nMET in modulating tumour microenvironment and tumour metastasis mediated by extracellular vesicles (EVs). EVs released by nMET overexpressing cells enhanced cell motility and provoked metastasis. Proteomic profiling revealed the enrichment of translational regulatory proteins in EVs derived from nMET overexpressing cells. These proteins include eukaryotic initiation factor (EIF), ribosomal protein small subunit (RPS) and ribosomal protein larger subunit (RPL) gene families. Knockdown of EIF3I, RPS3A and RPL10 diminished the promoting effect of EVs in cell migration invasiveness and metastasis. In conclusion, the findings reveal an unrecognized capacity of nMET to augment HCC through the release of EVs with oncogenic effect. Targeting these translation-related proteins may serve as an alternative treatment for patients with nMET overexpression.

Identifying the Efficacy of Extracellular Vesicles in Osteogenic Differentiation: An EV-Lution in Regenerative Medicine

Mesenchymal stromal cells (MSCs) have long been the focus for regenerative medicine and the restoration of damaged or aging cells throughout the body. However, the efficacy of MSCs in cell-based therapy still remains unpredictable and carries with it enumerable risks. It is estimated that only 3-10% of MSCs survive transplantation, and there remains undefined and highly variable heterogeneous biological potency within these administered cell populations. The mode of action points to secreted factors produced by MSCs rather than the reliance on engraftment. Hence harnessing such secreted elements as a replacement for live-cell therapies is attractive. Extracellular vesicles (EVs) are heterogenous lipid bounded structures, secreted by cells. They comprise a complex repertoire of molecules including RNA, proteins and other factors that facilitate cell-to-cell communication. Described as protected signaling centers, EVs can modify the cellular activity of recipient cells and are emerging as a credible alternative to cell-based therapies. EV therapeutics demonstrate beneficial roles for wound healing by preventing apoptosis, moderating immune responses, and stimulating angiogenesis, in addition to promoting cell proliferation and differentiation required for tissue matrix synthesis. Significantly, EVs maintain their signaling function following transplantation, circumventing the issues related to cell-based therapies. However, EV research is still in its infancy in terms of their utility as medicinal agents, with many questions still surrounding mechanistic understanding, optimal sourcing, and isolation of EVs for regenerative medicine. This review will consider the efficacy of using cell-derived EVs compared to traditional cell-based therapies for bone repair and regeneration. We discuss the factors to consider in developing productive lines of inquiry and establishment of standardized protocols so that EVs can be harnessed from optimal secretome production, to deliver reproducible and effective therapies.

Biomineralization of Enamel and Dentin Mediated by Matrix Proteins

Biomineralization of enamel, dentin, and bone involves the deposition of apatite mineral crystals within an organic matrix. Bone and teeth are classic examples of biomaterials with unique biomechanical properties that are crucial to their function. The collagen-based apatite mineralization and the important function of noncollagenous proteins are similar in dentin and bone; however, enamel is formed in a unique amelogenin-containing protein matrix. While the structure and organic composition of enamel are different from those of dentin and bone, the principal molecular mechanisms of protein-protein interactions, protein self-assembly, and control of crystallization events by the organic matrix are common among these apatite-containing tissues. This review briefly summarizes enamel and dentin matrix components and their interactions with other extracellular matrix components and calcium ions in mediating the mineralization process. We highlight the crystallization events that are controlled by the protein matrix and their interactions in the extracellular matrix during enamel and dentin biomineralization. Strategies for peptide-inspired biomimetic growth of tooth enamel and bioinspired mineralization of collagen to stimulate repair of demineralized dentin and bone tissue engineering are also addressed.

Extracellular Vesicles: Potential Mediators of Psychosocial Stress Contribution to Osteoporosis?

Osteoporosis is characterized by low bone mass and damage to the bone tissue’s microarchitecture, leading to increased fracture risk. Several studies have provided evidence for associations between psychosocial stress and osteoporosis through various pathways, including the hypothalamic-pituitary-adrenocortical axis, the sympathetic nervous system, and other endocrine factors. As psychosocial stress provokes oxidative cellular stress with consequences for mitochondrial function and cell signaling (e.g., gene expression, inflammation), it is of interest whether extracellular vesicles (EVs) may be a relevant biomarker in this context or act by transporting substances. EVs are intercellular communicators, transfer substances encapsulated in them, modify the phenotype and function of target cells, mediate cell-cell communication, and, therefore, have critical applications in disease progression and clinical diagnosis and therapy. This review summarizes the characteristics of EVs, their role in stress and osteoporosis, and their benefit as biological markers. We demonstrate that EVs are potential mediators of psychosocial stress and osteoporosis and may be beneficial in innovative research settings.

STIM1 a calcium sensor promotes the assembly of an ECM that contains Extracellular vesicles and factors that modulate mineralization

Osteoblasts and odontoblasts, are non-excitable cells and facilitate mass calcium transport during matrix mineralization. A sophisticated Ca²⁺ sensing mechanism is used to maintain Ca²⁺ homeostasis. STIM1 (Stromal interaction molecule 1) is a calcium sensor protein localized in the ER membrane and maintains calcium homeostasis by initiating the store-operated Ca²⁺ entry (SOCE) process, following store depletion. The role of STIM1 in dentin mineralization is yet to be elucidated. Therefore, transgenic DPSCs were generated in which overexpression or knockdown of STIM1 was achieved to study its function in matrix mineralization. Gene expression analysis and Alizarin Red staining assay demonstrated upregulation of genes involved in odontogenic differentiation and matrix mineralization with increased calcium deposition with STIM1 overexpression. Topology of the ECM examined by Field Emission Scanning Electron Microscopy (FESEM) showed the presence of large amounts of extracellular microvesicles with mineral deposits. Interestingly, silencing STIM1 resulted in fewer vesicles and less mineral deposits in the ECM. Analysis of the dentin-pulp complex of STIM1- deficient mice by micro-CT show reduced dentin thickness, malformed and highly porous alveolar bone, suggesting a cell intrinsic role for STIM1 in dentin mineralization. Confocal microscopy showed that DMP1-mediated depletion of store Ca²⁺ resulted in aggregation or "puncta-formation" of STIM1 at the plasma membrane indicative of a gating arrangement with Orai1 for Ca²⁺ influx. Together, our data provide evidence for an important role for STIM1 in dentin and alveolar bone mineralization by influencing intracellular Ca²⁺ oscillations that could provide signals for a wide array of cellular functions. STATEMENT OF SIGNIFICANCE: Calcium signaling and transport are fundamental to bone and dentin mineralization. Osteoblasts and odontoblasts transport large amounts of Ca²⁺ to the extracellular matrix. These cells maintain calcium homeostasis by spatially distributed calcium pumps and channels at the plasma membrane. STIM1 an ER Ca²⁺ sensor protein is an important component of the store-operated calcium entry (SOCE) process. In this study, we examined the role of STIM1 during the differentiation of dental pulp stem cells into functional odontoblasts and formation of mineralized dentin matrix. Stimulation of these cells with DMP1, a key regulatory protein in matrix mineralization, stimulates STIM1-mediated release of ER Ca²⁺ and SOCE activation. Silencing of STIM1 impairs signaling events, release of exosomes containing matrix proteins and matrix mineralization.

Extracellular vesicles in bone and periodontal regeneration: current and potential therapeutic applications

Oral mesenchymal stem cells (MSCs) and their secretomes are considered important factors in the field of medical tissue engineering and cell free biotherapy due to their ease of access, differentiation potential, and successful therapeutic outcomes. Extracellular vesicles (EVs) and the conditioned medium (CM) from MSCs are gaining more attraction as an alternative to cell-based therapies due to the less ethical issues involved, and their easier acquisition, preservation, long term storage, sterilization, and packaging. Bone and periodontal regenerative ability of EVs and CM have been the focus of some recent studies. In this review, we looked through currently available literature regarding MSCs' EVs or conditioned medium and their general characteristics, function, and regenerative potentials. We will also review the novel applications in regenerating bone and periodontal defects.

eIF3i regulation of protein synthesis, cell proliferation, cell cycle progression, and tumorigenesis

eIF3i, a 36-kDa protein, is a putative subunit of the eIF3 complex important for translation initiation of mRNAs. It is a WD40 domain-containing protein with seven WD40 repeats that forms a β-propeller structure with an important function in pre-initiation complex formation and mRNA translation initiation. In addition to participating in the eIF3 complex formation for global translational control, eIF3i may bind to specific mRNAs and regulate their translation individually. Furthermore, eIF3i has been shown to bind to TGF-β type II receptor and participate in TGF-β signaling. It may also participate in and regulate other signaling pathways including Wnt/β-catenin pathway via translational regulation of COX-2 synthesis. These multiple canonical and noncanonical functions of eIF3i in translational control and in regulating signal transduction pathways may be responsible for its role in cell differentiation, cell cycle regulation, proliferation, and tumorigenesis. In this review, we will critically evaluate recent progresses and assess future prospects in studying eIF3i.

[Review for different sources of exosomes in bone tissue engineering research]

Exosomes are 40-100 nm vesicles that are released into the extracellular environment upon the fusion of multivesicular bodies with the plasma membrane. The biologically cargoes transported by exosomes are diverse. Exosomes are important carriers of signal transmission and interaction between cells. Exosomes are believed to play an important role in tissue repair and bone regeneration. Studies have evaluated that exosomes secreted by cells play an increasingly significant roles in bone tissue engineering and have multiple functions, including regulating immunity, promoting cell proliferation and differentiation, enhancing bone regeneration and angiogenesis. The review analyzes the characteristics and biological properties of different cell-derived exosomes in the bone environment, summarizes their research progress in bone repair, and discusses the challenges and future directions for their application in bone tissue engineering.

The Development of Extracellular Vesicle-Integrated Biomaterials for Bone Regeneration

The clinical need for effective bone regeneration remains in huge demands. Although autologous and allogeneic bone grafts are generally considered "gold standard" treatments for bone defects, these approaches may result in various complications. Furthermore, safety considerations of gene- and cell-based therapies require further clarification and approval from regulatory authorities. Therefore, developing new therapeutic biomaterials that can empower endogenous regenerative properties to accelerate bone repair and regeneration is of great significance. Extracellular vesicles (EVs) comprise a heterogeneous population of naturally derived nanoparticles that play a critical role in mediating cell-cell communication. The vast amount of biological processes that EVs are involved in, such as immune modulation, senescence, and angiogenesis, and the versatility of manner in which they can influence the behavior of recipient cells make EVs an interesting source for both diagnostic and therapeutic applications. Advancement of knowledge in the fields of immunology and cell biology has sparked the exploration of the potential of EVs in the field of regenerative medicine. EVs travel between cells and deliver functional cargoes, such as proteins and RNAs, thereby regulating the recruitment, proliferation, and differentiation of recipient cells. Numerous studies have demonstrated the pivotal role of EVs in tissue regeneration both in vitro and in vivo. In this chapter, we will outline current knowledge surrounding EVs, summarize their functional roles in bone regenerative medicine, and elaborate on potential application and challenges of EV-integrated biomaterials in bone tissue engineering.

The Role of Exosomes in Bone Remodeling: Implications for Bone Physiology and Disease

Bone remodeling represents a physiological phenomenon of continuous bone tissue renewal that requires fine orchestration of multiple cell types, which is critical for the understanding of bone disease but not yet clarified in precise detail. Exosomes, which are cell-secreted nanovesicles drawing increasing attention for their broad biosignaling functions, can shed new light on how multiple heterogeneous cells communicate for the purpose of bone remodeling. In the healthy bone, exosomes transmit signals favoring both bone synthesis and resorption, regulating the differentiation, recruitment, and activity of most cell types involved in bone remodeling and even assuming an active role in extracellular matrix mineralization. Additionally, in the ailing bone, they actively participate in pathogenic processes constituting also potential therapeutic agents and drug vectors. The present review summarizes the current knowledge on bone exosomes and bone remodeling in health and disease.

TRIP-1 in the extracellular matrix promotes nucleation of calcium phosphate polymorphs

In search for bone and dentin extracellular matrix (ECM) proteins, transforming growth factor beta receptor II interacting protein 1 (TRIP-1) was identified as a novel protein synthesized by osteoblasts and odontoblasts and exported to the ECM. TRIP-1 is a WD-40 (WD is Tryptophan-Aspartic acid dipeptide) protein that has been well recognized for its physiological role in the endoplasmic reticulum (ER). In the ER, TRIP-1 functions as an essential subunit of eukaryotic elongation initiation factor 3 and is involved in the protein translational machinery. Recently, we reported that TRIP-1 is localized in the ECM of bone and dentin. In this study, we demonstrate that varying concentrations of TRIP-1 can participate in the nucleation of calcium phosphate polymorphs. Nucleation studies performed with high calcium and phosphate concentration demonstrated that recombinant TRIP-1 could orchestrate the formation of hydroxyapatite crystals. Nucleation experiments performed on demineralized and deproteinized dentin wafer under physiological conditions and subsequent transmission electron microscope analysis of the deposits at the end of 7 and 14 days showed that TRIP-1 promoted the deposition of calcium phosphate mineral aggregates in the gap-overlap region of type I collagen. Taken together, we provide mechanistic insight into the role of this intracellular protein in matrix mineralization.

TRIP-1 Promotes the Assembly of an ECM That Contains Extracellular Vesicles and Factors That Modulate Angiogenesis

Transforming growth factor beta receptor II interacting protein-1 (TRIP-1) was recently localized in the mineralized matrices of bone and dentin. The function of TRIP-1 in the ECM is enigmatic, as it is known to function as an intracellular endoplasmic reticulum protein during protein synthesis. Based on its localization pattern in bones and teeth, we posited that TRIP-1 must function as a regulatory protein with multiple functions during mineralization. In this study, we determined the in vivo function of TRIP-1 by an implantation assay performed using recombinant TRIP-1 and TRIP-1 overexpressing and knocked down cells embedded in a 3D biomimetic scaffold. After 4 weeks, the subcutaneous tissues from TRIP-1 overexpressing cells and scaffolds containing recombinant TRIP-1 showed higher expression levels of several ECM proteins such as fibronectin and collagen I. Picrosirius red and polarized microscopy was used to identify the birefringence of the collagen fibrils in the extracellular matrix (ECM). Interestingly, knockdown of TRIP-1 resulted in lower fibronectin and downregulation of the activation of the ERK MAP kinase. We further demonstrate that TRIP-1 overexpression leads to higher expression of pro-angiogenic marker VEGF and downregulation of anti-angiogenic factors such as pigment epithelium-derived factor and thrombospondin. Field emission scanning electron microscope results demonstrated that TRIP-1 overexpressing cells released large amount of extracellular microvesicles which were localized on the fibrillar matrix in the ECM. Overall, this study demonstrates that TRIP-1 can promote secretion of extracellular vesicles, synthesis of key osteogenic ECM matrix proteins and promote angiogenesis.

Support of bone mineral deposition by regulation of pH

Osteoblasts secrete collagen and isolate bone matrix from extracellular space. In the matrix, alkaline phosphatase generates phosphate that combines with calcium to form mineral, liberating 8 H⁺ per 10 Ca⁺² deposited. However, pH-dependent hydroxyapatite deposition on bone collagen had not been shown. We studied the dependency of hydroxyapatite deposition on type I collagen on pH and phosphate by surface plasmon resonance in 0-5 mM phosphate at pH 6.8-7.4. Mineral deposition saturated at <1 mM Ca²⁺ but was sensitive to phosphate. Mineral deposition was reversible, consistent with amorphous precipitation; stable deposition requiring EDTA removal appeared with time. At pH 6.8, little hydroxyapatite deposited on collagen; mineral accumulation increased 10-fold at pH 7.4. Previously, we showed high expression Na⁺/H⁺ exchanger (NHE) and ClC transporters in osteoblasts. We hypothesized that, in combination, these move protons across osteoblasts to the general extracellular space. We made osteoblast membrane vesicles by nitrogen cavitation and used acridine orange quenching to characterize proton transport. We found H⁺ transport dependent on gradients of chloride or sodium, consistent with apical osteoblast ClC family Cl^-,H⁺ antiporters and basolateral osteoblast NHE family Na⁺/H⁺ exchangers. Little, if any, active H⁺ transport, supported by ATP, occurred. Major transporters include cariporide-sensitive NHE1 in basolateral membranes and ClC3 and ClC5 in apical osteoblast membranes. The mineralization inhibitor levamisole reduced bone formation and expression of alkaline phosphatase, NHE1, and ClC5. We conclude that mineral deposition in bone collagen is pH-dependent, in keeping with H⁺ removal by Cl^-,H⁺ antiporters and Na⁺/H⁺-exchangers. Periodic orientation hydroxyapatite is organized on type I collagen-coiled coils.

Lung epithelial-specific TRIP-1 overexpression maintains epithelial integrity during hyperoxia exposure

The onset and degree of injury occurring in animals that develop hyperoxic acute lung injury (HALI) is dependent on age at exposure, suggesting that developmentally regulated pathways/factors must underlie initiation of the epithelial injury and subsequent repair. Type II TGFβ receptor interacting protein-1 (TRIP-1) is a negative regulator of TGFβ signaling, which we have previously shown is a developmentally regulated protein with modulatory effects on epithelial-fibroblastic signaling. The aim of this study was to assess if type II alveolar epithelial cells overexpressing TRIP-1 are protected against hyperoxia-induced epithelial injury, and in turn HALI. Rat lung epithelial cells (RLE) overexpressing TRIP-1 or LacZ were exposed to 85% oxygen for 4 days. A surfactant protein C (SPC)-driven TRIP-1 overexpression mouse (TRIP-1AECTg+ ) was generated and exposed to hyperoxia (>95% for 4 days) at 4 weeks of age to assess the effects TRIP-1 overexpression has on HALI. RLE overexpressing TRIP-1 resisted hyperoxia-induced apoptosis. Mice overexpressing TRIP-1 in their lung type II alveolar epithelial cells (TRIP-1AECTg+ ) showed normal lung development, increased phospho-AKT level and E-cadherin, along with resistance to HALI, as evidence by less TGFβ activation, apoptosis, alveolar macrophage influx, KC expression. Taken together, these findings point to existence of a TRIP-1 mediated molecular pathway affording protection against epithelial/acute lung injury.

Exosomes in Extracellular Matrix Bone Biology

PURPOSE OF REVIEW

Exosomes are membrane vesicles that are released by most cell types into the extracellular environment. The purpose of this article is to discuss the main morphological features and contents of bone-derived exosomes, as well as their major isolation and physical characterization techniques. Furthermore, we present various scenarios and discuss potential clinical applications of bone-derived exosomes in bone repair and regeneration.

RECENT FINDINGS

Exosomes were believed to be nanosized vesicles derived from the multivesicular body. Reports now suggest that nanovesicles could bud directly from the plasma membrane. However, the exosome cargo is cell-type specific and is derived from the parent cell. In the bone matrix, several intracellular proteins lacking a signal peptide are transported to the ECM by exosomes. Besides proteins, several mRNA, miRNA, and lipids are exported to the ECM by bone cells and bone marrow stromal cells. Recent evidence suggests that several of the functional components in the cargo could regulate processes of bone formation, inhibit osteoclast activity, and promote fracture repair. Exosomes are powerful cellular molecular machines produced without human intervention and packaged with physiological cargo that could be utilized for molecular therapy in several skeletal disorders such as osteoporosis, osteogenesis imperfecta, and fracture healing. Although much work has been done, there is a lot of information that is still unknown, as exosomes contain a multitude of molecules whose identity and function have yet to be identified.