Extracellular DNA: A Missing Link in the Pathogenesis of Ectopic Mineralization

Bacteria-mediated resistance of neutrophil extracellular traps to enzymatic degradation drives the formation of dental calculi

Dental calculi can cause gingival bleeding and periodontitis, yet the mechanism underlying the formation of such mineral build-ups, and in particular the role of the local microenvironment, are unclear. Here we show that the formation of dental calculi involves bacteria in local mature biofilms converting the DNA in neutrophil extracellular traps (NETs) from being degradable by the enzyme DNase I to being degradation resistant, promoting the nucleation and growth of apatite. DNase I inhibited NET-induced mineralization in vitro and ex vivo, yet plasma DNases were ineffective at inhibiting ectopic mineralization in the oral cavity in rodents. The topical application of the DNA-intercalating agent chloroquine in rodents fed with a dental calculogenic diet reverted NET DNA to its degradable form, inhibiting the formation of calculi. Our findings may motivate therapeutic strategies for the reduction of the prevalence of the deposition of bacteria-driven calculi in the oral cavity.

Calcified apoptotic vesicles from PROCR+ fibroblasts initiate heterotopic ossification

Heterotopic ossification (HO) comprises the abnormal formation of ectopic bone in extraskeletal soft tissue. The factors that initiate HO remain elusive. Herein, we found that calcified apoptotic vesicles (apoVs) led to increased calcification and stiffness of tendon extracellular matrix (ECM), which initiated M2 macrophage polarization and HO progression. Specifically, single-cell transcriptome analyses of different stages of HO revealed that calcified apoVs were primarily secreted by a PROCR+ fibroblast population. In addition, calcified apoVs enriched calcium by annexin channels, absorbed to collagen I via electrostatic interaction, and aggregated to produce calcifying nodules in the ECM, leading to tendon calcification and stiffening. More importantly, apoV-releasing inhibition or macrophage deletion both successfully reversed HO development. Thus, we are the first to identify calcified apoVs from PROCR+ fibroblasts as the initiating factor of HO, and might serve as the therapeutic target for inhibiting pathological calcification.

Macrophage-Derived Extracellular DNA Initiates Heterotopic Ossification

Heterotopic ossification (HO) severely affects people's lives; however, its pathological mechanism remains poorly understood. Although extracellular DNA (ecDNA) has been shown to play important roles in pathological calcification, its effects in HO development and progression remain unknown. The in vivo rat Achilles tendon injury model and in vitro collagen I calcification model were used to evaluate the effects of ecDNA in the ectopic calcifications and the main cell types involved in those pathological process. Histology, immunofluorescent staining, reverse transcriptase-polymerase chain reaction analysis and micro-computed tomography were used to identify the distribution of macrophage-derived ecDNA and elucidate their roles in HO. The results showed that the amount of ecDNA and ectopic calcification increased significantly and exhibited a strong correlation in the injured tendons of HO model compared with those of the controls, which was accompanied by a significantly increased number of M2 macrophages in the injured tendon. During in vitro co-culture experiments, M2 macrophages calcified the reconstituted type I collagen and ectopic bone collected from the injured tendons of HO rats, while those effects were inhibited by deoxyribonuclease. More importantly, deoxyribonuclease reversed the pathological calcification in the injured rat tendon HO model. The present study showed that ecDNA from M2 macrophages initiates pathological calcification in HO, and the elimination of ecDNA might be developed into a clinical strategy to prevent ectopic mineralization diseases. The use of deoxyribonuclease for the targeted degradation of ecDNA at affected tissue sites provides a potential solution to treat diseases associated with ectopic mineralization.

Untapped Potential of Deep Eutectic Solvents for the Synthesis of Bioinspired Inorganic-Organic Materials

Since the discovery of deep eutectic solvents (DESs) in 2003, significant progress has been made in the field, specifically advancing aspects of their preparation and physicochemical characterization. Their low-cost and unique tailored properties are reasons for their growing importance as a sustainable medium for the resource-efficient processing and synthesis of advanced materials. In this paper, the significance of these designer solvents and their beneficial features, in particular with respect to biomimetic materials chemistry, is discussed. Finally, this article explores the unrealized potential and advantageous aspects of DESs, focusing on the development of biomineralization-inspired hybrid materials. It is anticipated that this article can stimulate new concepts and advances providing a reference for breaking down the multidisciplinary borders in the field of bioinspired materials chemistry, especially at the nexus of computation and experiment, and to develop a rigorous materials-by-design paradigm.

Effect of Extracellular Ribonucleic Acids on Neurovascularization in Osteoarthritis

Osteoarthritis is a degenerative disease characterized by abnormal neurovascularization at the osteochondral junctions, the regulatory mechanisms of which remain poorly understood. In the present study, a murine osteoarthritic model with augmented neurovascularization at the osteochondral junction is used to examine this under-evaluated facet of degenerative joint dysfunction. Increased extracellular RNA (exRNA) content is identified in neurovascularized osteoarthritic joints. It is found that the amount of exRNA is positively correlated with the extent of neurovascularization and the expression of vascular endothelial growth factor (VEGF). In vitro binding assay and molecular docking demonstrate that synthetic RNAs bind to VEGF via electrostatic interactions. The RNA-VEGF complex promotes the migration and function of endothelial progenitor cells and trigeminal ganglion cells. The use of VEGF and VEGFR2 inhibitors significantly inhibits the amplification of the RNA-VEGF complex. Disruption of the RNA-VEGF complex by RNase and polyethyleneimine reduces its in vitro activities, as well as prevents excessive neurovascularization and osteochondral deterioration in vivo. The results of the present study suggest that exRNAs may be potential targets for regulating nerve and blood vessel ingrowth under physiological and pathological joint conditions.

A seminal perspective on the role of chondroitin sulfate in biomineralization

Chondroitin sulfate (CS) is an important extracellular matrix component of mineralized tissues. It participates in biomineralization, osteoblast differentiation and promotes bone tissue repair in vitro. However, the mechanism in which CS functions is unclear. Accordingly, an in-depth investigation of how CS participates in mineralization was conducted in the present study. Chondroitin sulfate was found to directly induce intrafibrillar mineralization of the collagen matrix. The mineralization outcome was dependent on whether CS remained free in the extracellular matrix or bound to core proteins; mineralization only occurred when CS existed in a free state. The efficacy of mineralization appeared to increase with ascending CS concentration. This discovery spurred the authors to identify the cause of heterotopic ossification in the Achilles tendon. Chondroitin sulfate appeared to be a therapeutic target for the management of diseases associated with heterotopic calcification. A broader perspective was presented on the applications of CS in tissue engineering.

Matrix is everywhere: extracellular DNA is a link between biofilm and mineralization in Bacillus cereus planktonic lifestyle

To date, the mechanisms of biomineralization induced by bacterial cells in the context of biofilm formation remain the subject of intensive studies. In this study, we analyzed the influence of the medium components on the induction of CaCO₃ precipitation by the Bacillus cereus cells and composition of the extracellular matrix (ECM) formed in the submerged culture. While the accumulation of extracellular polysaccharides and amyloids appeared to be independent of the presence of calcium and urea during the growth, the accumulation of extracellular DNA (eDNA), as well as precipitation of calcium carbonate, required the presence of both ingredients in the medium. Removal of eDNA, which was sensitive to treatment by DNase, did not affect other matrix components but resulted in disruption of cell network formation and a sixfold decrease in the precipitate yield. An experiment with a cell-free system confirmed the acceleration of mineral formation after the addition of exogenous salmon sperm DNA. The observed pathway for the formation of CaCO₃ minerals in B. cereus planktonic culture included a production of exopolysaccharides and negatively charged eDNA lattice promoting local Ca²⁺ supersaturation, which, together with an increase in the concentration of carbonate ions due to pH rise, resulted in the formation of an insoluble precipitate of calcium carbonate. Precipitation of amorphous CaCO₃ on eDNA matrix was followed by crystal formation via the ACC-vaterite-calcite/aragonite pathway and further formation of larger mineral aggregates in complex with extracellular polymeric substances. Taken together, our data showed that DNA in extracellular matrix is an essential factor for triggering the biomineralization in B. cereus planktonic culture.

Robust and Scalable In Vitro Surface Mineralization of Inert Polymers with a Rationally Designed Molecular Bridge

The artificial integration of inorganic materials onto polymers to create the analogues of natural biocomposites is an attractive field in materials science. However, due to significant diversity in the interfacial properties of two kinds of materials, advanced synthesis methods are quite complicated and the resultant materials are always vulnerable to external environments, which limits their application scenarios and makes them unsuitable for scalable production. Herein, we report a simple and universal approach to achieve robust and scalable surface mineralization of polymers using a rationally designed triple functional molecular bridge of fluorosilane, 3-[(perfluorohexyl sulfonyl) amino] propyltriethoxy silane (PFSS). In a two-step solution deposition, the fluoroalkyl and siloxane of the PFSS take charge of its adhesion and immobilization onto polymers by hydrophobic interaction and wrapping-like chemical cross-linking, and then the assembly and growth of inorganic nanoclusters for integration are achieved by strong chemical coordination of PFSS sulfonamide. The versatile mineralization of inorganic oxides (e.g., TiO₂, SiO₂, and Fe₂O₃) onto chemically inert polymer surfaces was realized very well. The resultant mineralized materials exhibit robust and multiple functionalities for hostile applications, such as hydrophilic membranes for removing oils in strong acidic and alkaline wastewaters, fabrics with advanced anti-bacteria for healthy wearing, and plates with strong mechanical performance for better use. Experimental results and theoretical calculations confirmed the homogenous distribution of the PFSS onto polymers via cross-linking for robust coordination with inorganic oxides. These results demonstrate a skillful enlightenment in the design of high-performance mineralized polymer materials used as membranes, fabrics, and medical devices.

Extrafibrillarly Demineralized Dentin Matrix for Bone Regeneration

Dentin is a natural extracellular matrix, but its availability in bone grafting and tissue engineering applications is underestimated due to a lack of proper treatment. In this study, the concept of extrafibrillar demineralization is introduced into the construction of dentin-derived biomaterials for bone regeneration for the first time. Calcium chelating agents with large molecular weights are used to selectively remove the extrafibrillar apatite minerals without disturbing the intrafibrillar minerals within dentin collagen, resulting in the formation of an extrafibrillarly demineralized dentin matrix (EDM). EDM with distinctive nanotopography and bone-like mechanical properties is found to significantly promote cell adhesion, migration, and osteogenic differentiation in vitro while enhancing in vivo bone healing of rat calvarial defects. The outstanding osteogenic performance of EDM is further confirmed to be related to the activation of the focal adhesion-cytoskeleton-nucleus mechanotransduction axis. Overall, this study shows that extrafibrillar demineralization of dentin has great potential to produce hierarchical collagen-based scaffolds for bone regeneration, and this facile top-down fabrication method brings about new ideas for the biomedical application of naturally derived bioactive materials.

Role of Phosphorus-Containing Molecules on the Formation of Nano-Sized Calcium Phosphate for Bone Therapy

Calcium phosphate (CaP) is the principal inorganic constituent of bone and teeth in vertebrates and has various applications in biomedical areas. Among various types of CaPs, amorphous calcium phosphate (ACP) is considered to have superior bioactivity and biodegradability. With regard to the instability of ACP, the phosphorus-containing molecules are usually adopted to solve this issue, but the specific roles of the molecules in the formation of nano-sized CaP have not been clearly clarified yet. Herein, alendronate, cyclophosphamide, zoledronate, and foscarnet are selected as the model molecules, and theoretical calculations were performed to elucidate the interaction between calcium ions and different model molecules. Subsequently, CaPs were prepared with the addition of the phosphorus-containing molecules. It is found that cyclophosphamide has limited influence on the generation of CaPs due to their weak interaction. During the co-precipitation process of Ca2+ and PO43-, the competitive relation among alendronate, zoledronate, and foscarnet plays critical roles in the produced inorganic-organic complex. Moreover, the biocompatibility of CaPs was also systematically evaluated. The DFT calculation provides a convincing strategy for predicting the structure of CaPs with various additives. This work is promising for designing CaP-based multifunctional drug delivery systems and tissue engineering materials.