Matrix vesicles: Are they anchored exosomes?

Toward understanding the cellular control of vertebrate mineralization: The potential role of mitochondria

This review examines the possible role of mitochondria in maintaining calcium and phosphate ion homeostasis and participating in the mineralization of bone, cartilage and other vertebrate hard tissues. The paper builds on the known structural features of mitochondria and the documented observations in these tissues that the organelles contain calcium phosphate granules. Such deposits in mitochondria putatively form to buffer excessively high cytosolic calcium ion concentrations and prevent metabolic deficits and even cell death. While mitochondria protect cytosolic enzyme systems through this buffering capacity, the accumulation of calcium ions by mitochondria promotes the activity of enzymes of the tricarboxylic acid (TCA/Krebs) cycle, increases oxidative phosphorylation and ATP synthesis, and leads to changes in intramitochondrial pH. These pH alterations influence ion solubility and possibly the transitions and composition in the mineral phase structure of the granules. Based on these considerations, mitochondria are proposed to support the mineralization process by providing a mobile store of calcium and phosphate ions, in smaller cluster or larger granule form, while maintaining critical cellular activities. The rise in the mitochondrial calcium level also increases the generation of citrate and other TCA cycle intermediates that contribute to cell function and the development of extracellular mineral. This paper suggests that another key role of the mitochondrion, along with the effects just noted, is to supply phosphate ions, derived from the breakdown of ATP, to endolysosomes and autophagic vesicles originating in the endoplasmic reticulum and Golgi and at the plasma membrane. These many separate but interdependent mitochondrial functions emphasize the critical importance of this organelle in the cellular control of vertebrate mineralization.

Light-induced Extracellular Vesicle Adsorption

The role of extracellular vesicles (EVs) in human health and disease has garnered considerable attention over the past two decades. However, while several types of EVs are known to interact dynamically with the extracellular matrix and there is great potential value in producing high-fidelity EV micropatterns, there are currently no label-free, high-resolution, and tunable platform technologies with this capability. We introduce Light-induced Extracellular Vesicle Adsorption (LEVA) as a powerful solution to rapidly advance the study of matrix- and surface-bound EVs and other particles. The versatility of LEVA is demonstrated using commercial GFP-EV standards, EVs from glioblastoma bioreactors, and E. coli outer membrane vesicles (OMVs), with the resulting patterns used for single EV characterization, single cell migration on migrasome-mimetic trails, and OMV-mediated neutrophil swarming. LEVA will enable rapid advancements in the study of matrix- and surface-bound EVs and other particles, and should encourage researchers from many disciplines to create novel diagnostic, biomimetic, immunoengineering, and therapeutic screening assays.

Integrated transcriptomic and metabolomic analyses reveal potential regulatory pathways regulating bone metabolism pre- and postsexual maturity in hens

At the onset of sexual maturity, the increasing circulating estrogen stimulates the formation of medullary bone, which provides available calcium for eggshell formation. The bone loss of laying hens is caused by the continuous dynamic changes of structure bone leading to bone fragility and susceptibility. The degree of medullary bone mineralization in sexual maturity is positively correlated with bone quality in the late laying stage. This study aimed to explore the molecular regulation mechanism of bone metabolism pre- and postsexual maturity in hens based on the joint analysis of transcriptome and metabolome. A total of 50 Hy-line Sonia pullets with comparable body weight at 13 wk were selected. Eight pullets were killed at 15 wk (juvenile hens, JH) and 19 wk (laying hens, LH), and LHs were killed within 3 h after oviposition. Differentially expressed genes and metabolites in tibia were analyzed based on transcriptome and metabolome, and then combined to construct the relevant metabolisms and hub genes. In the LH hens, plasma levels of estrogen and tartrate-resistant acid phosphatase were significantly elevated by 1.7 and 1.3 times. In addition, the midpoint diameter, bone mineral density and bone mineral content of the tibia and femur were higher at 19 wk of age. A total of 580 differentially expressed genes were found between the JH and LH group in the tibia, including 280 up-regulated, and 300 down-regulated genes in the LH group. Gene set enrichment analysis (GSEA) showed that the intracellular biosynthesis and secretion of matrix vesicles were significantly enrichment in the LH hens. A total of 21 differential metabolites were identified between JH and LH group. Estradiol valerate positively correlated with L-theanine, tryptophan betaine, dopamine, and perindopril. Joint analysis showed that the top 20 hub genes were enriched in cholesterol biosynthesis and phospholipid metabolism, which played a key regulatory role in bone metabolism during pre- and postsexual maturity. These results provide a theoretical foundation for maintaining efficient egg production and reducing bone health problems in laying hens.

Aged breast matrix bound vesicles promote breast cancer invasiveness

Aging is one of the inherent risk factors for breast cancer. Although the influence of age-related cellular alterations on breast cancer development has been extensively explored, little is known about the alterations in the aging breast tissue microenvironment, specifically the extracellular matrix (ECM). Here, for the first time in literature, we have identified tissue resident matrix bound vesicles (MBVs) within the healthy mouse breast ECM, investigated and compared their characteristics in young and aged healthy breast tissues, and studied the effects of these MBVs on normal (KTB21) and cancerous (MDA-MB-231) human mammary epithelial cells with respect to the tissue age that they are extracted from. Using vesicle labeling technology, we were able to visualize cellular uptake of the MBVs directly from the native decellularized tissue sections, showing that these MBVs have regulatory roles in the tissue microenvironment. We mimicked the ECM by embedding the MBVs in collagen gels, and showed that MBVs could be taken up by the cells. The miRNA and cytokine profiling showed that MBVs shifted towards a more tumorigenic and invasive phenotype with age, as evidenced by the more pronounced presence of cancer-associated cytokines, and higher expression levels of oncomiRs miR-10b, miR-30e, and miR-210 in MBVs isolated from aged mice. When treated with MBVs or these upregulated factors, KTB21 and MDA-MB-231 cells showed significantly higher motility and invasion compared to untreated controls. Treatment of cells with a cocktail of miRNAs (miR-10b, miR-30e, and miR-210) or with the agonist of adiponectin (AdipoRon), which both were enriched in the aged MBVs, recapitulated the effect of aged MBVs on cells. This study shows for the first time that the MBVs have a regulatory role in the tissue microenvironment and that the MBV contents change towards cancer-promoting upon aging. Studying the effects of MBVs and their cargos on cellular behavior could lead to a better understanding of the critical roles of MBVs played in breast cancer progression and metastasis.

Do Media Extracellular Vesicles and Extracellular Vesicles Bound to the Extracellular Matrix Represent Distinct Types of Vesicles?

Mineralization-competent cells, including hypertrophic chondrocytes, mature osteoblasts, and osteogenic-differentiated smooth muscle cells secrete media extracellular vesicles (media vesicles) and extracellular vesicles bound to the extracellular matrix (matrix vesicles). Media vesicles are purified directly from the extracellular medium. On the other hand, matrix vesicles are purified after discarding the extracellular medium and subjecting the cells embedded in the extracellular matrix or bone or cartilage tissues to an enzymatic treatment. Several pieces of experimental evidence indicated that matrix vesicles and media vesicles isolated from the same types of mineralizing cells have distinct lipid and protein composition as well as functions. These findings support the view that matrix vesicles and media vesicles released by mineralizing cells have different functions in mineralized tissues due to their location, which is anchored to the extracellular matrix versus free-floating.

Extracellular vesicles on the move: Traversing the complex matrix of tissues

Extracellular vesicles are small particles involved in intercellular signaling. They are produced by virtually all cell types, transport biological molecules, and are released into the extracellular space. Studies on extracellular vesicles have become more numerous in recent years, leading to promising research on their potential impact on health and disease. Despite significant progress in understanding the bioactivity of extracellular vesicles, most in vitro and in vivo studies overlook their transport through the extracellular matrix in tissues. The interaction or free diffusion of extracellular vesicles in their environment can provide valuable insights into their efficacy and function. Therefore, understanding the factors that influence the transport of extracellular vesicles in the extracellular matrix is essential for the development of new therapeutic approaches that involve the use of these extracellular vesicles. This review discusses the importance of the interaction between extracellular vesicles and the extracellular matrix and the different factors that influence their diffusion. In addition, we evaluate their role in tissue homeostasis, pathophysiology, and potential clinical applications. Understanding the complex interaction between extracellular vesicles and the extracellular matrix is critical in order to develop effective strategies to target specific cells and tissues in a wide range of clinical applications.

Annexin A5 derived from matrix vesicles protects against osteoporotic bone loss via mineralization

Matrix vesicles (MVs) have shown strong effects in diseases such as vascular ectopic calcification and pathological calcified osteoarthritis and in wound repair of the skeletal system due to their membranous vesicle characteristics and abundant calcium and phosphorus content. However, the role of MVs in the progression of osteoporosis is poorly understood. Here, we report that annexin A5, an important component of the matrix vesicle membrane, plays a vital role in bone matrix homeostasis in the deterioration of osteoporosis. We first identified annexin A5 from adherent MVs but not dissociative MVs of osteoblasts and found that it could be sharply decreased in the bone matrix during the occurrence of osteoporosis based on ovariectomized mice. We then confirmed its potential in mediating the mineralization of the precursor osteoblast lineage via its initial binding with collagen type I to achieve MV adhesion and the subsequent activation of cellular autophagy. Finally, we proved its protective role in resisting bone loss by applying it to osteoporotic mice. Taken together, these data revealed the importance of annexin A5, originating from adherent MVs of osteoblasts, in bone matrix remodeling of osteoporosis and provided a new strategy for the treatment and intervention of bone loss.

Vascular calcification: from the perspective of crosstalk

Vascular calcification (VC) is highly correlated with cardiovascular disease morbidity and mortality, but anti-VC treatment remains an area to be tackled due to the ill-defined molecular mechanisms. Regardless of the type of VC, it does not depend on a single cell but involves multi-cells/organs to form a complex cellular communication network through the vascular microenvironment to participate in the occurrence and development of VC. Therefore, focusing only on the direct effect of pathological factors on vascular smooth muscle cells (VSMCs) tends to overlook the combined effect of other cells and VSMCs, including VSMCs-VSMCs, ECs-VMSCs, Macrophages-VSMCs, etc. Extracellular vesicles (EVs) are a collective term for tiny vesicles with a membrane structure that are actively secreted by cells, and almost all cells secrete EVs. EVs docked on the surface of receptor cells can directly mediate signal transduction or transfer their contents into the cell to elicit a functional response from the receptor cells. They have been proven to participate in the VC process and have also shown attractive therapeutic prospects. Based on the advantages of EVs and the ability to be detected in body fluids, they may become a novel therapeutic agent, drug delivery vehicle, diagnostic and prognostic biomarker, and potential therapeutic target in the future. This review focuses on the new insight into VC molecular mechanisms from the perspective of crosstalk, summarizes how multi-cells/organs interactions communicate via EVs to regulate VC and the emerging potential of EVs as therapeutic methods in VC. We also summarize preclinical experiments on crosstalk-based and the current state of clinical studies on VC-related measures.

Osteoblast-Derived Matrix Vesicles Exhibit Exosomal Traits and a Unique Subset of microRNA: Their Caveolae-Dependent Endocytosis Results in Reduced Osteogenic Differentiation

Matrix vesicles (MVs) are nano-sized extracellular vesicles that are anchored in the extracellular matrix (ECM). In addition to playing a role in biomineralization, osteoblast-derived MVs were recently suggested to have regulatory duties. The aims of this study were to establish the characteristics of osteoblast-derived MVs in the context of extracellular vesicles like exosomes, assess their role in modulating osteoblast differentiation, and examine their mechanism of uptake. MVs were isolated from the ECM of MG63 human osteoblast-like cell cultures and characterized via enzyme activity, transmission electron microscopy, nanoparticle tracking analysis, Western blot, and small RNA sequencing. Osteoblasts were treated with MVs from two different culture conditions (growth media [GM]; osteogenic media [OM]) to evaluate their effects on the differentiation and production of inflammatory markers and on macrophage polarization. MV endocytosis was assessed using a lipophilic, fluorescent dye and confocal microscopy with the role of caveolae determined using methyl-β-cyclodextrin. MVs exhibited a four-fold enrichment in alkaline phosphatase specific activity compared to plasma membranes; were 50-150 nm in diameter; possessed exosomal markers CD63, CD81, and CD9 and endosomal markers ALIX, TSG101, and HSP70; and were selectively enriched in microRNA linked to an anti-osteogenic effect and to M2 macrophage polarization. Treatment with GM or OM MVs decreased osteoblast differentiation. Osteoblasts endocytosed MVs using a mechanism that involves caveolae. These results support the hypothesis that osteoblasts produce MVs that participate in the regulation of osteogenesis.

Low Magnesium Concentration Enforces Bone Calcium Deposition Irrespective of 1,25-Dihydroxyvitamin D3 Concentration

Efficient coordination between Mg²⁺ and vitamin D maintains adequate Ca²⁺ levels during lactation. This study explored the possible interaction between Mg²⁺ (0.3, 0.8, and 3 mM) and 1,25-dihydroxyvitamin D₃ (1,25D; 0.05 and 5 nM) during osteogenesis using bovine mesenchymal stem cells. After 21 days, differentiated osteocytes were subjected to OsteoImage analysis, alkaline phosphatase (ALP) activity measurements, and immunocytochemistry of NT5E, ENG (endoglin), SP7 (osterix), SPP1 (osteopontin), and the BGLAP gene product osteocalcin. The mRNA expression of NT5E, THY1, ENG, SP7, BGLAP, CYP24A1, VDR, SLC41A1, SLC41A2, SLC41A3, TRPM6, TRPM7, and NIPA1 was also assessed. Reducing the Mg²⁺ concentration in the medium increased the accumulation of mineral hydroxyapatite and ALP activity. There was no change in the immunocytochemical localization of stem cell markers. Expression of CYP24A1 was higher in all groups receiving 5 nM 1,25D. There were tendencies for higher mRNA abundance of THY1, BGLAP, and NIPA1 in cells receiving 0.3 mM Mg²⁺ and 5 nM 1,25D. In conclusion, low levels of Mg²⁺ greatly enhanced the deposition of bone hydroxyapatite matrix. The effect of Mg²⁺ was not modulated by 1,25D, although the expression of certain genes (including BGLAP) tended to be increased by the combination of low Mg²⁺ and high 1,25D concentrations.

Extracellular vesicles: From bone development to regenerative orthopedics

Regenerative medicine aims to promote the replacement of tissues lost to damage or disease. While positive outcomes have been observed experimentally, challenges remain in their clinical translation. This has led to growing interest in applying extracellular vesicles (EVs) to augment or even replace existing approaches. Through the engineering of culture environments or direct/indirect manipulation of EVs themselves, multiple avenues have emerged to modulate EV production, targeting, and therapeutic potency. Drives to modulate release using material systems or functionalize implants for improved osseointegration have also led to outcomes that could have real-world impact. The purpose of this review is to highlight advantages in applying EVs for the treatment of skeletal defects, outlining the current state of the art in the field and emphasizing avenues for further investigation. Notably, the review identifies inconsistencies in EV nomenclature and outstanding challenges in defining a reproducible therapeutic dose. Challenges also remain in the scalable manufacture of a therapeutically potent and pure EV product, with a need to address scalable cell sources and optimal culture environments. Addressing these issues will be critical if we are to develop regenerative EV therapies that meet the demands of regulators and can be translated from bench to bedside.

Aged Breast Matrix Bound Vesicles Promote Breast Cancer Invasiveness

Aging is one of the inherent risk factors for breast cancer. Although the influence of age-related cellular alterations on breast cancer development has been extensively explored, little is known about the alterations in the aging breast tissue microenvironment, specifically the extracellular matrix (ECM). Here, for the first time in literature, we have identified tissue resident matrix bound vesicles (MBVs) within the healthy mouse breast ECM, investigated and compared their characteristics in young and aged healthy breast tissues, and studied the effects of these MBVs on normal (KTB21) and cancerous (MDA-MB-231) human mammary epithelial cells with respect to the tissue age that they are extracted from. Using vesicle labeling technology, we were able to visualize cellular uptake of the MBVs directly from the native decellularized tissue sections, showing that these MBVs have regulatory roles in the tissue microenvironment. We mimicked the ECM by embedding the MBVs in collagen gels, and showed that MBVs could be taken up by the cells. The miRNA and cytokine profiling showed that MBVs shifted towards a more tumorigenic and invasive phenotype with age, as evidenced by the more pronounced presence of cancer-associated cytokines, and higher expression levels of oncomiRs miR-10b, miR-30e, and miR-210 in MBVs isolated from aged mice. When treated with MBVs or these upregulated factors, KTB21 and MDA-MB-231 cells showed significantly higher motility and invasion compared to untreated controls. Treatment of cells with a cocktail of miRNAs (miR-10b, miR-30e, and miR-210) or with the agonist of adiponectin (AdipoRon), which both were enriched in the aged MBVs, recapitulated the effect of aged MBVs on cells. This study shows for the first time that the MBVs have a regulatory role in the tissue microenvironment and that the MBV contents change towards cancer-promoting upon aging. Studying the effects of MBVs and their cargos on cellular behavior could lead to a better understanding of the critical roles of MBVs played in breast cancer progression and metastasis.

Epidermal growth factor receptor inhibition prevents vascular calcifying extracellular vesicle biogenesis

Chronic kidney disease (CKD) increases the risk of cardiovascular disease, including vascular calcification, leading to higher mortality. The release of calcifying extracellular vesicles (EVs) by vascular smooth muscle cells (VSMCs) promotes ectopic mineralization of vessel walls. Caveolin-1 (CAV1), a structural protein in the plasma membrane, plays a major role in calcifying EV biogenesis in VSMCs. Epidermal growth factor receptor (EGFR) colocalizes with and influences the intracellular trafficking of CAV1. Using a diet-induced mouse model of CKD followed by a high-phosphate diet to promote vascular calcification, we assessed the potential of EGFR inhibition to prevent vascular calcification. Furthermore, we computationally analyzed 7,651 individuals in the Multi-Ethnic Study of Atherosclerosis (MESA) and Framingham cohorts to assess potential correlations between coronary artery calcium and single-nucleotide polymorphisms (SNPs) associated with elevated serum levels of EGFR. Mice with CKD developed widespread vascular calcification, associated with increased serum levels of EGFR. In both the CKD mice and human VSMC culture, EGFR inhibition significantly reduced vascular calcification by mitigating the release of CAV1-positive calcifying EVs. EGFR inhibition also increased bone mineral density in CKD mice. Individuals in the MESA and Framingham cohorts with SNPs associated with increased serum EGFR exhibit elevated coronary artery calcium. Given that EGFR inhibitors exhibit clinical safety and efficacy in other pathologies, the current data suggest that EGFR may represent an ideal target to prevent pathological vascular calcification in CKD.NEW & NOTEWORTHY Here, we investigate the potential of epidermal growth factor receptor (EGFR) inhibition to prevent vascular calcification, a leading indicator of and contributor to cardiovascular morbidity and mortality. EGFR interacts and affects the trafficking of the plasma membrane scaffolding protein caveolin-1. Previous studies reported a key role for caveolin-1 in the development of specialized extracellular vesicles that mediate vascular calcification; however, no role of EGFR has been reported. We demonstrated that EGFR inhibition modulates caveolin-1 trafficking and hinders calcifying extracellular vesicle formation, which prevents vascular calcification. Given that EGFR inhibitors are clinically approved for other indications, this may represent a novel therapeutic strategy for vascular calcification.

Spatiotemporal Analysis of Osteoblast Morphology and Wnt Signal‐Induced Osteoblast Reactivation during Bone Modeling in Vitro

Bone nodule formation by differentiating osteoblasts is considered an in vitro model that mimics bone modeling. However, the details of osteoblast behavior and matrix production during bone nodule formation are poorly understood. Here, we present a spatiotemporal analysis system for evaluating osteoblast morphology and matrix production during bone modeling in vitro via two-photon microscopy. Using this system, a change in osteoblast morphology from cuboidal to flat was observed during the formation of mineralized nodules, and this change was quantified. Areas with high bone formation were densely populated with cuboidal osteoblasts, which were characterized by blebs, protruding structures on their cell membranes. Cuboidal osteoblasts with blebs were highly mobile, and osteoblast blebs exhibited a polar distribution. Furthermore, mimicking romosozumab treatment, when differentiated flattened osteoblasts were stimulated with BIO, a GSK3β inhibitor, they were reactivated to acquire a cuboidal morphology with blebs on their membranes and produced more matrix than nonstimulated cells. Our analysis system is a powerful tool for evaluating the cell morphology and function of osteoblasts during bone modeling. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Vascular Calcification: In Vitro Models under the Magnifying Glass

Vascular calcification is a systemic disease contributing to cardiovascular morbidity and mortality. The pathophysiology of vascular calcification involves calcium salt deposition by vascular smooth muscle cells that exhibit an osteoblast-like phenotype. Multiple conditions drive the phenotypic switch and calcium deposition in the vascular wall; however, the exact molecular mechanisms and the connection between vascular smooth muscle cells and other cell types are not fully elucidated. In this hazy landscape, effective treatment options are lacking. Due to the pathophysiological complexity, several research models are available to evaluate different aspects of the calcification process. This review gives an overview of the in vitro cell models used so far to study the molecular processes underlying vascular calcification. In addition, relevant natural and synthetic compounds that exerted anticalcifying properties in in vitro systems are discussed.

Gingival epithelial cell-derived microvesicles activate mineralization in gingival fibroblasts

Soft tissue calcification occurs in many parts of the body, including the gingival tissue. Epithelial cell-derived MVs can control many functions in fibroblasts but their role in regulating mineralization has not been explored. We hypothesized that microvesicles (MVs) derived from gingival epithelial cells could regulate calcification of gingival fibroblast cultures in osteogenic environment. Human gingival fibroblasts (HGFs) were cultured in osteogenic differentiation medium with or without human gingival epithelial cell-derived MV stimulation. Mineralization of the cultures, localization of the MVs and mineral deposits in the HGF cultures were assessed. Gene expression changes associated with MV exposure were analyzed using gene expression profiling and real-time qPCR. Within a week of exposure, epithelial MVs stimulated robust mineralization of HGF cultures that was further enhanced by four weeks. The MVs taken up by the HGF's did not calcify themselves but induced intracellular accumulation of minerals. HGF gene expression profiling after short exposure to MVs demonstrated relative dominance of inflammation-related genes that showed increases in gene expression. In later cultures, OSX, BSP and MMPs were significantly upregulated by the MVs. These results suggest for the first time that epithelial cells maybe associated with the ectopic mineralization process often observed in the soft tissues.

Skeletal and extraskeletal disorders of biomineralization

The physiological process of biomineralization is complex and deviation from it leads to a variety of diseases. Progress in the past 10 years has enhanced understanding of the genetic, molecular and cellular pathophysiology underlying these disorders; sometimes, this knowledge has both facilitated restoration of health and clarified the very nature of biomineralization as it occurs in humans. In this Review, we consider the principal regulators of mineralization and crystallization, and how dysregulation of these processes can lead to human disease. The knowledge acquired to date and gaps still to be filled are highlighted. The disorders of mineralization discussed comprise a broad spectrum of conditions that encompass bone disorders associated with alterations of mineral quantity and quality, as well as disorders of extraskeletal mineralization (hyperphosphataemic familial tumoural calcinosis). Included are disorders of alkaline phosphatase (hypophosphatasia) and phosphate homeostasis (X-linked hypophosphataemic rickets, fluorosis, rickets and osteomalacia). Furthermore, crystallopathies are covered as well as arterial and renal calcification. This Review discusses the current knowledge of biomineralization derived from basic and clinical research and points to future studies that will lead to new therapeutic approaches for biomineralization disorders.

Matrix Vesicle-Mediated Mineralization and Potential Applications

Hard tissues, including the bones and teeth, are a fundamental part of the body, and their formation and homeostasis are critically regulated by matrix vesicle-mediated mineralization. Matrix vesicles have been studied for 50 y since they were first observed using electron microscopy. However, research progress has been hampered by various technical barriers. Recently, there have been great advancements in our understanding of the intracellular biosynthesis of matrix vesicles. Mitochondria and lysosomes are now considered key players in matrix vesicle formation. The involvement of mitophagy, mitochondrial-derived vesicles, and mitochondria-lysosome interaction have been suggested as potential detailed mechanisms of the intracellular pathway of matrix vesicles. Their main secretion pathway may be exocytosis, in addition to the traditionally understood mechanism of budding from the outer plasma membrane. This basic knowledge of matrix vesicles should be strengthened by novel nano-level microscopic technologies, together with basic cell biologies, such as autophagy and interorganelle interactions. In the field of tissue regeneration, extracellular vesicles such as exosomes are gaining interest as promising tools in cell-free bone and periodontal regenerative therapy. Matrix vesicles, which are recognized as a special type of extracellular vesicles, could be another potential alternative. In this review, we outline the recent significant progress in the process of matrix vesicle-mediated mineralization and the potential clinical applications of matrix vesicles for tissue regeneration.

The Protective Effects of Osteocyte-Derived Extracellular Vesicles Against Alzheimer's Disease Diminished with Aging

Both Alzheimer's disease (AD) and osteoporosis (OP) are common age-associated degenerative diseases and are strongly correlated with clinical epidemiology. However, there is a lack of clear pathological relationship between the brain and bone in the current understanding. Here, it is found that young osteocyte, the most abundant cells in bone, secretes extracellular vesicles (OCY^Young -EVs) to ameliorate cognitive impairment and the pathogenesis of AD in APP/PS1 mice and model cells. These benefits of OCY^Young -EVs are diminished in aged osteocyte-derived EVs (OCY^Aged -EVs). Based on the self-constructed OCY-EVs tracer transgenic mouse models and the in vivo fluorescent imaging system, OCY-EVs have been observed to be transported to the brain under physiological and pathological conditions. In the hippocampal administration of Aβ40 induced young AD model mice, the intramedullary injection of Rab27a-shRNA adenovirus inhibits OCY^Young -EVs secretion from bone and aggravates cognitive impairment. Proteomic quantitative analysis reveals that OCY^Young -EVs, compared to OCY^Aged -EVs, enrich multiple protective factors of AD pathway. The study uncovers the role of OCY-EV as a regulator of brain health, suggesting a novel mechanism in bone-brain communication.

The Role of Matrix-Bound Extracellular Vesicles in the Regulation of Endochondral Bone Formation

Matrix vesicles are key players in the development of the growth plate during endochondral bone formation. They are involved in the turnover of the extracellular matrix and its mineralization, as well as being a vehicle for chondrocyte communication and regulation. These extracellular organelles are released by the cells and are anchored to the matrix via integrin binding to collagen. The exact function and makeup of the vesicles are dependent on the zone of the growth plate in which they are produced. Early studies defined their role as sites of initial calcium phosphate deposition based on the presence of crystals on the inner leaflet of the membrane and subsequent identification of enzymes, ion transporters, and phospholipid complexes involved in mineral formation. More recent studies have shown that they contain small RNAs, including microRNAs, that are distinct from the parent cell, raising the hypothesis that they are a distinct subset of exosomes. Matrix vesicles are produced under complex regulatory pathways, which include the action of steroid hormones. Once in the matrix, their maturation is mediated by the action of secreted hormones. How they convey information to cells, either through autocrine or paracrine actions, is now being elucidated.

Aged bone matrix-derived extracellular vesicles as a messenger for calcification paradox

Adipocyte differentiation of bone marrow mesenchymal stem/stromal cells (BMSCs) instead of osteoblast formation contributes to age- and menopause-related marrow adiposity and osteoporosis. Vascular calcification often occurs with osteoporosis, a contradictory association called “calcification paradox”. Here we show that extracellular vesicles derived from aged bone matrix (AB-EVs) during bone resorption favor BMSC adipogenesis rather than osteogenesis and augment calcification of vascular smooth muscle cells. Intravenous or intramedullary injection of AB-EVs promotes bone-fat imbalance and exacerbates Vitamin D3 (VD3)-induced vascular calcification in young or old mice. Alendronate (ALE), a bone resorption inhibitor, down-regulates AB-EVs release and attenuates aging- and ovariectomy-induced bone-fat imbalance. In the VD3-treated aged mice, ALE suppresses the ovariectomy-induced aggravation of vascular calcification. MiR-483-5p and miR-2861 are enriched in AB-EVs and essential for the AB-EVs-induced bone-fat imbalance and exacerbation of vascular calcification. Our study uncovers the role of AB-EVs as a messenger for calcification paradox by transferring miR-483-5p and miR-2861.

This study uncovers the role of extracellular vesicles from bone matrix as a messenger in the development of osteoporosis and vascular calcification (calcification paradox) during skeletal aging and menopause by transferring miR-483-5p and miR-2861.

Exosome-derived noncoding RNAs: Function, mechanism, and application in tumor angiogenesis

Exosomes are extracellular vesicles released by various cell types that perform various biological functions, mainly mediating communication between different cells, especially those active in cancer. Noncoding RNAs (ncRNAs), of which there are many types, were recently identified as enriched and stable in the exocrine region and play various roles in the occurrence and progression of cancer. Abnormal angiogenesis has been confirmed to be related to human cancer. An increasing number of studies have shown that exosome-derived ncRNAs play an important role in tumor angiogenesis. In this review, we briefly outline the characteristics of exosomes, ncRNAs, and tumor angiogenesis. Then, the mechanism of the impact of exosome-derived ncRNAs on tumor angiogenesis is analyzed from various angles. In addition, we focus on the regulatory role of exosome-derived ncRNAs in angiogenesis in different types of cancer. Furthermore, we emphasize the potential role of exosome-derived ncRNAs as biomarkers in cancer diagnosis and prognosis and therapeutic targets in the treatment of tumors.

Exosomes in the Pathogenesis, Progression, and Treatment of Osteoarthritis

Osteoarthritis (OA) is a prevalent and debilitating age-related joint disease characterized by articular cartilage degeneration, synovial membrane inflammation, osteophyte formation, as well as subchondral bone sclerosis. OA drugs at present are mainly palliative and do not halt or reverse disease progression. Currently, no disease-modifying OA drugs (DMOADs) are available and total joint arthroplasty remains a last resort. Therefore, there is an urgent need for the development of efficacious treatments for OA management. Among all novel pharmaco-therapeutical options, exosome-based therapeutic strategies are highly promising. Exosome cargoes, which include proteins, lipids, cytokines, and various RNA subtypes, are potentially capable of regulating intercellular communications and gene expression in target cells and tissues involved in OA development. With extensive research in recent years, exosomes in OA studies are no longer limited to classic, mesenchymal stem cell (MSC)-derived vesicles. New origins, structures, and functions of exosomes are constantly being discovered and investigated. This review systematically summarizes the non-classic origins, biosynthesis, and extraction of exosomes, describes modification and delivery techniques, explores their role in OA pathogenesis and progression, and discusses their therapeutic potential and hurdles to overcome in OA treatment.

A protease-mediated switch regulates the growth of magnetosome organelles in Magnetospirillum magneticum

Biomineralization, the process by which elaborate three-dimensional structures are built out of organic and inorganic molecules, is central to health and survival of many organisms. In some magnetotactic bacteria, the growth of magnetosome membranes is closely correlated to the progression of mineral formation. However, the molecular mechanisms of such regulation are not clear. We show that the serine protease MamE links magnetosome membrane growth to the controlled production of magnetite nanoparticles through the processing of mineral-associated MamD protein. Our results indicate that membrane growth directly controls mineral growth and shed light on how an organelle’s size can determine its physiological output. Manipulation of the MamE pathway may also open the door for control of nanoparticle size in future biotechnological applications.

Magnetosomes are lipid-bound organelles that direct the biomineralization of magnetic nanoparticles in magnetotactic bacteria. Magnetosome membranes are not uniform in size and can grow in a biomineralization-dependent manner. However, the underlying mechanisms of magnetosome membrane growth regulation remain unclear. Using cryoelectron tomography, we systematically examined mutants with defects at various stages of magnetosome formation to identify factors involved in controlling membrane growth. We found that a conserved serine protease, MamE, plays a key role in magnetosome membrane growth regulation. When the protease activity of MamE is disrupted, magnetosome membrane growth is restricted, which, in turn, limits the size of the magnetite particles. Consistent with this finding, the upstream regulators of MamE protease activity, MamO and MamM, are also required for magnetosome membrane growth. We then used a combination of candidate and comparative proteomics approaches to identify Mms6 and MamD as two MamE substrates. Mms6 does not appear to participate in magnetosome membrane growth. However, in the absence of MamD, magnetosome membranes grow to a larger size than the wild type. Furthermore, when the cleavage of MamD by MamE protease is blocked, magnetosome membrane growth and biomineralization are severely inhibited, phenocopying the MamE protease-inactive mutant. We therefore propose that the growth of magnetosome membranes is controlled by a protease-mediated switch through processing of MamD. Overall, our work shows that, like many eukaryotic systems, bacteria control the growth and size of biominerals by manipulating the physical properties of intracellular organelles.

Matrix Vesicles as a Therapeutic Target for Vascular Calcification

Vascular calcification (VC) is linked to an increased risk of heart disease, stroke, and atherosclerotic plaque rupture. It is a cell-active process regulated by vascular cells rather than pure passive calcium (Ca) deposition. In recent years, extracellular vesicles (EVs) have attracted extensive attention because of their essential role in the process of VC. Matrix vesicles (MVs), one type of EVs, are especially critical in extracellular matrix mineralization and the early stages of the development of VC. Vascular smooth muscle cells (VSMCs) have the potential to undergo phenotypic transformation and to serve as a nucleation site for hydroxyapatite crystals upon extracellular stimulation. However, it is not clear what underlying mechanism that MVs drive the VSMCs phenotype switching and to result in calcification. This article aims to review the detailed role of MVs in the progression of VC and compare the difference with other major drivers of calcification, including aging, uremia, mechanical stress, oxidative stress, and inflammation. We will also bring attention to the novel findings in the isolation and characterization of MVs, and the therapeutic application of MVs in VC.

Osteon-mimetic 3D nanofibrous scaffold enhances stem cell proliferation and osteogenic differentiation for bone regeneration

The scaffold microstructure is important for bone tissue engineering. Failure to synergistically imitate the hierarchical microstructure of the components of bone, such as an osteon with concentric multilayers assembled by nanofibers, hinders the performance for guiding bone regeneration. Here, a 2D bilayer nanofibrous membrane (BLM) containing poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL) composite membranes in similar compositions (PCL15 and PCL20), but possessing different degrees of shrinkage, was fabricated via sequential electrospinning. Upon incubation in phosphate buffered saline (PBS) (37 °C), the 2D BLM spontaneously deformed into a 3D shape induced by PCL crystallization within the PLGA matrix, and the PCL15 and PCL20 layer formed a concave and convex surface, respectively. The 3D structure contained curved multilayers with an average diameter of 776 ± 169 μm, and on the concave and convex surface the nanofiber diameters were 792 ± 225 and 881 ± 259 nm, respectively. The initial 2D structure facilitated the even distribution of seeded cells. Adipose-derived stem cells from rats (rADSCs) proliferated faster on a concave surface than on a convex surface. For the 3D BLM, the osteogenic differentiation of rADSCs was significantly higher than that on 2D surfaces, even without osteogenic supplements, which resulted from the stretched cell morphology on the curved sublayer leading to increased expression of lamin-A. After being implanted into cranial defects in Sprague Dawley (SD) rats, 3D BLM significantly accelerated bone formation. In summary, 3D BLM with an osteon-like structure provides a potential strategy to repair bone defects.

Cancer extracellular vesicles, tumoroid models, and tumor microenvironment

Cancer extracellular vesicles (EVs), or exosomes, promote tumor progression through enhancing tumor growth, initiating epithelial-to-mesenchymal transition, remodeling the tumor microenvironment, and preparing metastatic niches. Three-dimensionally (3D) cultured tumoroids / spheroids aim to reproduce some aspects of tumor behavior in vitro and show increased cancer stem cell properties. These properties are transferred to their EVs that promote tumor growth. Moreover, recent tumoroid models can be furnished with aspects of the tumor microenvironment, such as vasculature, hypoxia, and extracellular matrix. This review summarizes tumor tissue culture and engineering platforms compatible with EV research. For example, the combination experiments of 3D-tumoroids and EVs have revealed multifunctional proteins loaded in EVs, such as metalloproteinases and heat shock proteins. EVs or exosomes are able to transfer their cargo molecules to recipient cells, whose fates are often largely altered. In addition, the review summarizes approaches to EV labeling technology using fluorescence and luciferase, useful for studies on EV-mediated intercellular communication, biodistribution, and metastatic niche formation.

Enzymatic Approach in Calcium Phosphate Biomineralization: A Contribution to Reconcile the Physicochemical with the Physiological View

Biomineralization is the process by which organisms produce hard inorganic matter from soft tissues with outstanding control of mineral deposition in time and space. For this purpose, organisms deploy a sophisticated "toolkit" that has resulted in significant evolutionary innovations, for which calcium phosphate (CaP) is the biomineral selected for the skeleton of vertebrates. While CaP mineral formation in aqueous media can be investigated by studying thermodynamics and kinetics of phase transitions in supersaturated solutions, biogenic mineralization requires coping with the inherent complexity of biological systems. This mainly includes compartmentalization and homeostatic processes used by organisms to regulate key physiological factors, including temperature, pH and ion concentration. A detailed analysis of the literature shows the emergence of two main views describing the mechanism of CaP biomineralization. The first one, more dedicated to the study of in vivo systems and supported by researchers in physiology, often involves matrix vesicles (MVs). The second one, more investigated by the physicochemistry community, involves collagen intrafibrillar mineralization particularly through in vitro acellular models. Herein, we show that there is an obvious need in the biological systems to control both where and when the mineral forms through an in-depth survey of the mechanism of CaP mineralization. This necessity could gather both communities of physiologists and physicochemists under a common interest for an enzymatic approach to better describe CaP biomineralization. Both homogeneous and heterogeneous enzymatic catalyses are conceivable for these systems, and a few preliminary promising results on CaP mineralization for both types of enzymatic catalysis are reported in this work. Through them, we aim to describe the relevance of our point of view and the likely findings that could be obtained when adding an enzymatic approach to the already rich and creative research field dealing with CaP mineralization. This complementary approach could lead to a better understanding of the biomineralization mechanism and inspire the biomimetic design of new materials.

Inhibition of Sphingosine-1-Phosphate Receptor 2 by JTE013 Promoted Osteogenesis by Increasing Vesicle Trafficking, Wnt/Ca2+, and BMP/Smad Signaling

Sphingosine-1-phosphate receptor 2 (S1PR2) is a G protein-coupled receptor that regulates various immune responses. Herein, we determine the effects of a S1PR2 antagonist (JTE013) or a S1PR2 shRNA on osteogenesis by culturing murine bone marrow stromal cells (BMSCs) in osteogenic media with JTE013, dimethylsulfoxide (DMSO), a S1PR2 shRNA, or a control shRNA. Treatment with JTE013 or the S1PR2 shRNA increased alkaline phosphatase and alizarin red s staining, and enhanced alkaline phosphatase, RUNX2, osteocalcin, and osterix mRNA levels in BMSCs compared with the controls. Protein analysis revealed that a high dose of JTE013 (4 or 8 μM) increased vesicle trafficking-associated proteins (F-actin, clathrin, Early Endosome Antigen 1 (EEA1), and syntaxin 6) and Wnt/Ca2+ signaling. On the other hand, a low dose of JTE013 (1 to 2 μM) increased BMP/Smad signaling. In contrast, the S1PR2 shRNA reduced vesicle trafficking-associated proteins and attenuated Wnts and BMP/Smad signaling, but enhanced p-CaMKII compared with the control, suggesting that the S1PR2 shRNA influenced osteogenesis via different signaling pathways. Moreover, inhibiting protein trafficking by brefeldin A in BMSCs suppressed Wnts and BMPRs expressions. These data supported that enhanced osteogenesis in JTE013-treated BMSCs is associated with increased vesicle trafficking, which promotes the synthesis and transport of osteogenic protein and matrix vesicles and enhances matrix mineralization.

Two-faced Janus: The dual role of macrophages in atherosclerotic calcification

Calcification is an independent predictor of atherosclerosis-related cardiovascular events. Microcalcification is linked to inflamed, unstable lesions, in comparison to the fibrotic stable plaque phenotype generally associated with advanced calcification. This paradox relates to recognition that calcification presents in a wide spectrum of manifestations that differentially impact plaque’s fate. Macrophages, the main inflammatory cells in atherosclerotic plaque, have a multifaceted role in disease progression. They crucially control the mineralization process, from microcalcification to the osteoid metaplasia of bone-like tissue. It is a bilateral interaction that weighs heavily on the overall plaque fate but remains rather unexplored. This review highlights current knowledge about macrophage phenotypic changes in relation to and interaction with the calcifying environment. On the one hand, macrophage-led inflammation kickstarts microcalcification through a multitude of interlinked mechanisms, which in turn stimulates phenotypic changes in vascular cell types to drive microcalcification. Macrophages may also modulate the expression/activity of calcification inhibitors and inducers, or eliminate hydroxyapatite nucleation points. Contrarily, direct exposure of macrophages to an early calcifying milieu impacts macrophage phenotype, with repercussions for plaque progression and/or stability. Macrophages surrounding macrocalcification deposits show a more reparative phenotype, modulating extracellular matrix, and expressing osteoclast genes. This phenotypic shift favours gradual displacement of the pro-inflammatory hubs; the lipid necrotic core, by macrocalcification. Parallels to bone metabolism may explain many of these changes to macrophage phenotype, with advanced calcification able to show homeostatic osteoid metaplasia. As the targeted treatment of vascular calcification developing in atherosclerosis is thus far severely lacking, it is crucial to better understand its mechanisms of development.

Cell Interplay in Osteoarthritis

Osteoarthritis (OA) is a common chronic disease and a significant health concern that needs to be urgently solved. OA affects the cartilage and entire joint tissues, including the subchondral bone, synovium, and infrapatellar fat pads. The physiological and pathological changes in these tissues affect the occurrence and development of OA. Understanding complex crosstalk among different joint tissues and their roles in OA initiation and progression is critical in elucidating the pathogenic mechanism of OA. In this review, we begin with an overview of the role of chondrocytes, synovial cells (synovial fibroblasts and macrophages), mast cells, osteoblasts, osteoclasts, various stem cells, and engineered cells (induced pluripotent stem cells) in OA pathogenesis. Then, we discuss the various mechanisms by which these cells communicate, including paracrine signaling, local microenvironment, co-culture, extracellular vesicles (exosomes), and cell tissue engineering. We particularly focus on the therapeutic potential and clinical applications of stem cell-derived extracellular vesicles, which serve as modulators of cell-to-cell communication, in the field of regenerative medicine, such as cartilage repair. Finally, the challenges and limitations related to exosome-based treatment for OA are discussed. This article provides a comprehensive summary of key cells that might be targets of future therapies for OA.

Extracellular vesicles and the extracellular matrix: a new paradigm or old news?

Extracellular vesicles (EV) are implicated in a variety of functions affecting the extracellular matrix (ECM), including matrix degradation, cross-linking of matrix proteins and matrix calcification. These processes are important in many physiological contexts such as angiogenesis and wound healing, and dysregulation of ECM homeostasis contributes to a wide range of diseases including fibrosis, cancer and arthritis. Most studies of EV have focussed on their roles in cell:cell communication, but EV can exist as integral components of the ECM. By far the most well-characterised ECM-resident EV are matrix vesicles (MV) in bone, but the broader role of EV in the ECM is not well understood. This review will explore what is known of the roles of EV in the ECM and will also highlight the similarities and differences between MV and other EV.

Exosomes: Emerging modulators of signal transduction in colorectal cancer from molecular understanding to clinical application

Exosomes are small cell derived membrane nano-vesicles that carry various components including lipids, proteins and nucleic acids. There is accumulating evidence that exosomes have a role in tumorigenesis, tumor invasiveness and metastasis. Furthermore, oncogene mutation may influence exosome release from tumor cells. Exosomes may induce colorectal cancer by altering signaling cascades such as the Wnt/β-catenin and KRAS pathways that are involved in cell proliferation, apoptosis, dissemination, angiogenesis, and drug resistance. The aim of this review was to overview recent findings evaluating the association between tumor cells-derived exosomes and their content in modulating signaling pathways in colorectal cancer.

Osteoblast Differentiation and Signaling: Established Concepts and Emerging Topics

Osteoblasts, the cells that build up our skeleton, are remarkably versatile and important cells that need tight regulation in all the phases of their differentiation to guarantee proper skeletal development and homeostasis. Although we know many of the key pathways involved in osteoblast differentiation and signaling, it is becoming clearer and clearer that this is just the tip of the iceberg, and we are constantly discovering novel concepts in osteoblast physiology. In this review, we discuss well-established pathways of osteoblastic differentiation, i.e., the classical ones committing mesenchymal stromal cells to osteoblast, and then osteocytes as well as recently emerged players. In particular, we discuss micro (mi)RNAs, long non-coding (lnc)RNAs, circular (circ)RNAs, and extracellular vesicles, focusing on the mechanisms through which osteoblasts are regulated by these factors, and conversely, how they use extracellular vesicles to communicate with the surrounding microenvironment.

Extracellular Vesicles: An Emerging Mechanism Governing the Secretion and Biological Roles of Tenascin-C

ECM composition and architecture are tightly regulated for tissue homeostasis. Different disorders have been associated to alterations in the levels of proteins such as collagens, fibronectin (FN) or tenascin-C (TnC). TnC emerges as a key regulator of multiple inflammatory processes, both during physiological tissue repair as well as pathological conditions ranging from tumor progression to cardiovascular disease. Importantly, our current understanding as to how TnC and other non-collagen ECM components are secreted has remained elusive. Extracellular vesicles (EVs) are small membrane-bound particles released to the extracellular space by most cell types, playing a key role in cell-cell communication. A broad range of cellular components can be transported by EVs (e.g. nucleic acids, lipids, signalling molecules and proteins). These cargoes can be transferred to target cells, potentially modulating their function. Recently, several extracellular matrix (ECM) proteins have been characterized as bona fide EV cargoes, exosomal secretion being particularly critical for TnC. EV-dependent ECM secretion might underpin diseases where ECM integrity is altered, establishing novel concepts in the field such as ECM nucleation over long distances, and highlighting novel opportunities for diagnostics and therapeutic intervention. Here, we review recent findings and standing questions on the molecular mechanisms governing EV–dependent ECM secretion and its potential relevance for disease, with a focus on TnC.

A narrative review of exosomes in vascular calcification

Vascular calcification (VC) is the abnormal deposition of calcium, phosphorus, and other minerals in the vessel wall and can be commonly observed in diabetes, chronic kidney disease, and chronic inflammatory disease. It is closely associated with mortality from cardiovascular events. Traditionally, calcification is considered as a degenerative disease associated with the aging process, while increasing evidence has shown that the occurrence and development of calcification is an active biological process, which is highly regulated by multiple factors. The molecular mechanisms of VC have not yet been fully elucidated. Exosomes, as important transporters of substance transport and intercellular communication, have been shown to participate in VC. The regulation of VC by exosomes involves a number of complex biological processes, which occur through a variety of interaction mechanisms. However, the specific role and mechanism of exosomes in the process of VC are still not fully understood and require further study. This review will briefly describe the roles of exosomes in the process of VC including in the promotion of extracellular mineral deposits, induction of phenotypic conversion of vascular smooth muscle cells (VSMCs), transport of microRNA between cells, and regulation on autophagy and oxidative stress, with the aim of providing novel ideas for the clinical diagnosis and treatment of VC.

Matrix Vesicles: Role in Bone Mineralization and Potential Use as Therapeutics

Bone is a complex organ maintained by three main cell types: osteoblasts, osteoclasts, and osteocytes. During bone formation, osteoblasts deposit a mineralized organic matrix. Evidence shows that bone cells release extracellular vesicles (EVs): nano-sized bilayer vesicles, which are involved in intercellular communication by delivering their cargoes through protein–ligand interactions or fusion to the plasma membrane of the recipient cell. Osteoblasts shed a subset of EVs known as matrix vesicles (MtVs), which contain phosphatases, calcium, and inorganic phosphate. These vesicles are believed to have a major role in matrix mineralization, and they feature bone-targeting and osteo-inductive properties. Understanding their contribution in bone formation and mineralization could help to target bone pathologies or bone regeneration using novel approaches such as stimulating MtV secretion in vivo, or the administration of in vitro or biomimetically produced MtVs. This review attempts to discuss the role of MtVs in biomineralization and their potential application for bone pathologies and bone regeneration.

Emerging role of exosomes in arterial and renal calcification

Exosomes are small, cell-derived vesicles of 30-100 nm that participate in cell-to-cell communication. They are released by many cells, such as dendritic cells (DC), lymphocytes, platelets, epithelial cells, endothelial cells (EC), and are found in most body fluids, including blood, saliva, urine, and breast milk. The exosomes released from cells within the cardiovascular system may contain either inhibitors of calcification in normal physiological conditions or promoters in the pathological environment [atherosclerosis (AS), and Chronic Kidney Disease (CKD)]. The exosomes of the vascular smooth muscle cells (VSMCs) are novel players in vascular repair processes and calcification. Several studies have shown that the cytoplasmic contents of exosomes are rich in a variety of proteins, nucleic acids, and lipids. Currently, exosomal micro RNAs and proteins are increasingly being recognized as biomarkers for the diagnosis of several diseases, including those of kidney and liver, as well as different types of cancer. In this review, we summarize recent advances in the role of exosomes in vascular calcification and their potential applications as diagnostic markers as well as a brief overview of the role of stem cell-derived exosomes in cardiovascular diseases.

From organic and inorganic phosphates to valvular and vascular calcifications

Calcification of the arterial wall and valves is an important part of the pathophysiological process of peripheral and coronary atherosclerosis, aortic stenosis, ageing, diabetes, and chronic kidney disease. This review aims to better understand how extracellular phosphates and their ability to be retained as calcium phosphates on the extracellular matrix initiate the mineralization process of arteries and valves. In this context, the physiological process of bone mineralization remains a human model for pathological soft tissue mineralization. Soluble (ionized) calcium precipitation occurs on extracellular phosphates; either with inorganic or on exposed organic phosphates. Organic phosphates are classified as either structural (phospholipids, nucleic acids) or energetic (corresponding to phosphoryl transfer activities). Extracellular phosphates promote a phenotypic shift in vascular smooth muscle and valvular interstitial cells towards an osteoblast gene expression pattern, which provokes the active phase of mineralization. A line of defense systems protects arterial and valvular tissue calcifications. Given the major roles of phosphate in soft tissue calcification, phosphate mimetics, and/or prevention of phosphate dissipation represent novel potential therapeutic approaches for arterial and valvular calcification.

A Review of the Functions of Matrix Vesicles in Periodontal Tissues

Periodontal tissues consist of cementum, periodontal ligaments, and alveolar bone, which provide indispensable support for physiological activities involving mastication, swallowing, and pronunciation. The formation of periodontal tissues requires a complex process, during which a close relationship with biomineralization is noticeable. Alveolar bone and cementum are physically hard, both of which are generated from biomineralization and possess the exact mechanical properties resembling other hard tissues. However, when periodontitis, congenital abnormalities, periapical diseases, and other pathological conditions affect the organism, the most common symptom, alveolar bone defect, is always unavoidable, which results in difficulties for current clinical treatment. Thus, exploring effective therapies to improve the prognosis is important. Matrix vesicles (MVs), a special subtype of extracellular vesicles related to histogenesis, are widely produced by the stem cells of developing hard tissues. With the assistance of the enzymes and transporters contained within them, MVs can construct the extracellular matrix and an adequate microenvironment, thus promoting biomineralization and periodontal development. Presently, MVs can be effectively extracted and delivered by scaffolds and generate hard tissues in vitro and in vivo, which are expected to be translated into therapies for alveolar bone defects. In this review, we generalize recent research progress on MV morphology, molecular composition, biological mechanism, and, in particular, the biological functions in periodontal development. In addition to the above unique roles of MVs, we further describe the available MV-related biotechnologies and achievements that make them promising for coping with existing problems and improving the treatment of alveolar bone defects.

Multiple Pathways for Pathological Calcification in the Human Body

Biomineralization of skeletal components (e.g., bone and teeth) is generally accepted to occur under strict cellular regulation, leading to mineral-organic composites with hierarchical structures and properties optimized for their designated function. Such cellular regulation includes promoting mineralization at desired sites as well as inhibiting mineralization in soft tissues and other undesirable locations. In contrast, pathological mineralization, with potentially harmful health effects, can occur as a result of tissue or metabolic abnormalities, disease, or implantation of certain biomaterials. This progress report defines mineralization pathway components and identifies the commonalities (and differences) between physiological (e.g., bone remodeling) and pathological calcification formation pathways, based, in part, upon the extent of cellular control within the system. These concepts are discussed in representative examples of calcium phosphate-based pathological mineralization in cancer (breast, thyroid, ovarian, and meningioma) and in cardiovascular disease. In-depth mechanistic understanding of pathological mineralization requires utilizing state-of-the-art materials science imaging and characterization techniques, focusing not only on the final deposits, but also on the earlier stages of crystal nucleation, growth, and aggregation. Such mechanistic understanding will further enable the use of pathological calcifications in diagnosis and prognosis, as well as possibly provide insights into preventative treatments for detrimental mineralization in disease.

Exosome-Derived Noncoding RNAs as a Promising Treatment of Bone Regeneration

The reconstruction of large bone defects remains a crucial challenge in orthopedic surgery. The current treatments including autologous and allogenic bone grafting and bioactive materials have their respective drawbacks. While mesenchymal stem cell (MSC) therapy may address these limitations, growing researches have demonstrated that the effectiveness of MSC therapy depends on paracrine factors, particularly exosomes. This aroused great focus on the exosome-based cell-free therapy in the treatment of bone defects. Exosomes can transfer various cargoes, and noncoding RNAs are the most widely studied cargo through which exosomes exert their ability of osteoinduction. Here, we review the research status of the exosome-derived noncoding RNAs in bone regeneration, the potential application of exosomes, and the existing challenges.

Extracellular Matrix in Calcific Aortic Valve Disease: Architecture, Dynamic and Perspectives

Calcific Aortic Valve Disease (CAVD) is the most common valvular heart disease in developed countries and in the ageing population. It is strongly correlated to median age, affecting up to 13% of the population over the age of 65. Pathophysiological analysis indicates CAVD as a result of an active and degenerative disease, starting with sclerosis and chronic inflammation and then leaflet calcification, which ultimately can account for aortic stenosis. Although CAVD has been firstly recognized as a passive event mostly resulting from a degenerative aging process, much evidences suggests that calcification arises from different active processes, involving both aortic valve-resident cells (valve endothelial cells, valve interstitial cells, mesenchymal stem cells, innate immunity cells) and circulating cells (circulating mesenchymal cells, immunity cells). Moreover, a role for the cell-derived "matrix vesicles" and extracellular matrix (ECM) components has also been recognized. The aim of this work is to review the cellular and molecular alterations occurring in aortic valve during CAVD pathogenesis, focusing on the role of ECM in the natural course of the disease.

Mechanisms of RANKL delivery to the osteoclast precursor cell surface

RANKL is biosynthesized as a single-pass transmembrane protein, and soluble molecular species are produced by enzymatic cleavage at the cell surface. Recent studies have revealed that the transmembrane form of RANKL is a major contributor to the induction of mature osteoclasts under physiological conditions in vivo. In osteoblasts and osteocytes, most newly synthesized RANKL forms a protein complex with OPG and is selectively sorted to lysosomes. Only the small proportion of newly synthesized RANKL that does not form a complex with OPG is transported to the cell surface. Then, the transmembrane RANKL is delivered to the surface of osteoclast precursors to stimulate RANK, and induces the activation of a downstream signaling pathway. The ability of osteocytes to support the formation of mature osteoclasts appears to depend upon the amount of RANKL molecules present on their cell surfaces. However, the way in which osteocytes, which are embedded in the bone matrix, deliver transmembrane RANKL to the cell surfaces of osteoclast precursors, which are localized in the bone marrow cavity, remains to be elucidated. Further studies are needed to clarify the mechanisms underlying this process.

Phylogeny and chemistry of biological mineral transport

Three physiologically mineralizing tissues - teeth, cartilage and bone - have critical common elements and important evolutionary relationships. Phylogenetically the most ancient densely mineralized tissue is teeth. In jawless fishes without skeletons, tooth formation included epithelial transport of phosphates, a process echoed later in bone physiology. Cartilage and mineralized cartilage are skeletal elements separate from bone, but with metabolic features common to bone. Cartilage mineralization is coordinated with high expression of tissue nonspecific alkaline phosphatase and PHOSPHO1 to harvest available phosphate esters and support mineralization of collagen secreted locally. Mineralization in true bone results from stochastic nucleation of hydroxyapatite crystals within the cross-linked collagen fibrils. Mineral accumulation in dense collagen is, at least in major part, mediated by amorphous aggregates - often called Posner clusters - of calcium and phosphate that are small enough to diffuse into collagen fibrils. Mineral accumulation in membrane vesicles is widely suggested, but does not correlate with a definitive stage of mineralization. Conversely mineral deposition at non-physiologic sites where calcium and phosphate are adequate has been shown to be regulated in large part by pyrophosphate. All of these elements are present in vertebrate bone metabolism. A key biological element of bone formation is an epithelial-like cellular organization which allows control of phosphate, calcium and pH during mineralization.

Role of matrix vesicles and crystal ghosts in bio-mineralization

Matrix vesicles (MVs) are extracellular membrane-bound vesicles of about ~ 50-200 nm in diameter that play a role in the bio-mineralization process of hard tissue formation. The present review is based on the empirical phenomenon of primary mineralization process via matrix vesicle-mediated mechanism with special reference to crystal ghosts as well as the mechanism on the organic-inorganic relationship between matrix vesicles and crystal ghosts, and the transformation that these structures undergo during bio-mineralization.

PBPK Modeling of Slightly Soluble Silver Nanomaterials and Regulatory Acceptance

International efforts to promote predictive toxicology incorporate some form of modeling based on the regularities, insights, and hypotheses gained from analyzing laboratory studies compiled in databases. While there has been a broad commentary on definitions, metadata, and test methodologies, all necessary to establishing data repositories, there has been less on translating the resulting insights into computational models. The recent use of a computational model to support a recommended exposure limit for nanoparticulate silver is an opportunity to examine physiologically based toxicokinetics in terms of data availability, model verification and validation, and regulatory acceptance. The resulting suggestions align with findings from the EU-US Roadmap Nanoinformatics 2030 and the 2018 acceptance of a computational model by the European Food Safety Authority.