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.

Disrupted de novo pyrimidine biosynthesis impairs adult hippocampal neurogenesis and cognition in pyridoxine-dependent epilepsy.

Despite seizure control by early high-dose pyridoxine (vitamin B6) treatment, at least 75% of pyridoxine-dependent epilepsy (PDE) patients with ALDH7A1 mutation still suffer from intellectual disability. It points to a need for additional therapeutic interventions for PDE beyond pyridoxine treatment, which provokes us to investigate the mechanisms underlying the impairment of brain hemostasis by ALDH7A1 deficiency. In this study, we show that ALDH7A1-deficient mice with seizure control exhibit altered adult hippocampal neurogenesis and impaired cognitive functions. Mechanistically, ALDH7A1 deficiency leads to the accumulation of toxic lysine catabolism intermediates, α-aminoadipic-δ-semialdehyde and its cyclic form, δ-1-piperideine-6-carboxylate, which in turn impair de novo pyrimidine biosynthesis and inhibit NSC proliferation and differentiation. Notably, supplementation of pyrimidines rescues abnormal neurogenesis and cognitive impairment in ALDH7A1-deficient adult mice. Therefore, our findings not only define the important role of ALDH7A1 in the regulation of adult hippocampal neurogenesis but also provide a potential therapeutic intervention to ameliorate the defective mental capacities in PDE patients with seizure control.

Interorgan communication in neurogenic heterotopic ossification: the role of brain-derived extracellular vesicles.

Brain-derived extracellular vesicles participate in interorgan communication after traumatic brain injury by transporting pathogens to initiate secondary injury. Inflammasome-related proteins encapsulated in brain-derived extracellular vesicles can cross the blood‒brain barrier to reach distal tissues. These proteins initiate inflammatory dysfunction, such as neurogenic heterotopic ossification. This recurrent condition is highly debilitating to patients because of its relatively unknown pathogenesis and the lack of effective prophylactic intervention strategies. Accordingly, a rat model of neurogenic heterotopic ossification induced by combined traumatic brain injury and achillotenotomy was developed to address these two issues. Histological examination of the injured tendon revealed the coexistence of ectopic calcification and fibroblast pyroptosis. The relationships among brain-derived extracellular vesicles, fibroblast pyroptosis and ectopic calcification were further investigated in vitro and in vivo. Intravenous injection of the pyroptosis inhibitor Ac-YVAD-cmk reversed the development of neurogenic heterotopic ossification in vivo. The present work highlights the role of brain-derived extracellular vesicles in the pathogenesis of neurogenic heterotopic ossification and offers a potential strategy for preventing neurogenic heterotopic ossification after traumatic brain injury. Brain-derived extracellular vesicles (BEVs) are released after traumatic brain injury. These BEVs contain pathogens and participate in interorgan communication to initiate secondary injury in distal tissues. After achillotenotomy, the phagocytosis of BEVs by fibroblasts induces pyroptosis, which is a highly inflammatory form of lytic programmed cell death, in the injured tendon. Fibroblast pyroptosis leads to an increase in calcium and phosphorus concentrations and creates a microenvironment that promotes osteogenesis. Intravenous injection of the pyroptosis inhibitor Ac-YVAD-cmk suppressed fibroblast pyroptosis and effectively prevented the onset of heterotopic ossification after neuronal injury. The use of a pyroptosis inhibitor represents a potential strategy for the treatment of neurogenic heterotopic ossification.

Lysosomal destabilization: A missing link between pathological calcification and osteoarthritis.

Calcification of cartilage by hydroxyapatite is a hallmark of osteoarthritis and its deposition strongly correlates with the severity of osteoarthritis. However, no effective strategies are available to date on the prevention of hydroxyapatite deposition within the osteoarthritic cartilage and its role in the pathogenesis of this degenerative condition is still controversial. Therefore, the present work aims at uncovering the pathogenic mechanism of intra-cartilaginous hydroxyapatite in osteoarthritis and developing feasible strategies to counter its detrimental effects. With the use of in vitro and in vivo models of osteoarthritis, hydroxyapatite crystallites deposited in the cartilage are found to be phagocytized by resident chondrocytes and processed by the lysosomes of those cells. This results in lysosomal membrane permeabilization (LMP) and release of cathepsin B (CTSB) into the cytosol. The cytosolic CTSB, in turn, activates NOD-like receptor protein-3 (NLRP3) inflammasomes and subsequently instigates chondrocyte pyroptosis. Inhibition of LMP and CTSB in vivo are effective in managing the progression of osteoarthritis. The present work provides a conceptual therapeutic solution for the prevention of osteoarthritis via alleviation of lysosomal destabilization.

Upregulated Mitochondrial Dynamics Is Responsible for the Procatabolic Changes of Chondrocyte Induced by α2-Adrenergic Signal Activation.

OBJECTIVE: Activation of sympathetic tone is important for cartilage degradation in osteoarthritis (OA). Recent studies reported that sympathetic signals can affect the mitochondrial function of target cells. It is unknown whether this effect exits in chondrocytes and affects chondrocyte catabolism. The contribution of mitochondrial dynamics in the activation of α2-adrenergic signal-mediated chondrocyte catabolism was investigated in this study. DESIGN: Primary chondrocytes were stimulated with norepinephrine (NE) alone, or pretreated with an α2-adrenergic receptor (Adra2) antagonist (yohimbine) and followed by stimulation with NE. Changes in chondrocyte metabolism and their mitochondrial dynamics were investigated. RESULTS: We demonstrated that NE stimulation induced increased gene and protein expressions of matrix metalloproteinase-3 and decreased level of aggrecan by chondrocytes. This was accompanied by upregulated mitochondriogenesis and the number of mitochondria, when compared with the vehicle-treated controls. Mitochondrial fusion and fission, and mitophagy also increased significantly in response to NE stimulation. Inhibition of Adra2 attenuated chondrocyte catabolism and mitochondrial dynamics induced by NE. CONCLUSIONS: The present findings indicate that upregulation of mitochondrial dynamics through mitochondriogenesis, fusion, fission, and mitophagy is responsible for activation of α2-adrenergic signal-mediated chondrocyte catabolism. The hypothesis that "α2-adrenergic signal activation promotes cartilage degeneration in temporomandibular joint osteoarthritis (TMJ-OA) by upregulating mitochondrial dynamics in chondrocytes" is validated. This represents a new regulatory mechanism in the chondrocytes of TMJ-OA that inhibits abnormal activation of mitochondrial fusion and fission is a potential regulator for improving mitochondrial function and inhibiting chondrocyte injury and contrives a potentially innovative therapeutic direction for the prevention of TMJ-OA.

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.

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.

Fibrotic Matrix Induces Mesenchymal Transformation of Epithelial Cells in Oral Submucous Fibrosis.

Oral submucous fibrosis (OSF) is a potentially malignant disorder of the oral mucosa; however, whether and how the fibrotic matrix of OSF is involved in the malignant transformation of epithelial cells remains unknown. Herein, oral mucosa tissue from patients with OSF, OSF rat models, and their controls were used to observe the extracellular matrix changes and epithelial-mesenchymal transformation (EMT) in fibrotic lesions. Compared with controls, oral mucous tissues from patients with OSF showed an increased number of myofibroblasts, a decreased number of blood vessels, and increased type I and type III collagen levels. In addition, the oral mucous tissues from humans and OSF rats showed increased stiffness, accompanied by increased EMT activities of epithelial cells. The EMT activities of stiff construct-cultured epithelial cells were increased significantly by exogenous piezo-type mechanosensitive ion channel component 1 (Piezo1) activation, and decreased by yes-associated protein (YAP) inhibition. During ex vivo implantation, oral mucosal epithelial cells of the stiff group showed increased EMT activities and increased levels of Piezo1 and YAP compared with those in the sham and soft groups. These results indicate that increased stiffness of the fibrotic matrix in OSF led to increased proliferation and EMT of mucosal epithelial cells, in which the Piezo1-YAP signal transduction is important.

Bioactive semaphorin 3A promotes sequential formation of sensory nerve and type H vessels during in situ osteogenesis.

Introduction: Sensory nerves and vessels are critical for skeletal development and regeneration, but crosstalk between neurovascular network and mineralization are not clear. The aim of this study was to explore neurovascular changes and identify bioactive regulators during in situ osteogenesis. Method: In situ osteogenesis model was performed in male rats following Achilles tenotomy. At 3, 6 and 9 weeks after surgery, mineralization, blood vessels, sensory innervation, and bioactive regulators expression were evaluated via micro-computed tomography, immunofluorescent staining, histology and reverse transcriptase-polymerase chain reaction analyses. Result: In the process of in situ osteogenesis, the mineral density increased with time, and the locations of minerals, nerves and blood vessels were highly correlated at each time point. The highest density of sensory nerve was observed in the experimental group at the 3rd week, and then gradually decreased with time, but still higher than that in the sham control group. Among many regulatory factors, semaphorin 3A (Sema3A) was highly expressed in experimental model and its expression was temporally sequential and spatially correlated sensory nerve. Conclusion: The present study showes that during in situ osteogenesis, innervation and angiogenesis are highly correlated, and Sema3A is associated with the position and expression of the sensory nerve.

A biomaterial-based therapy using a sodium hyaluronate/bioglass composite hydrogel for the treatment of oral submucous fibrosis.

Oral submucous fibrosis (OSF) is a chronic, inflammatory and potentially malignant oral disorder. Its pathophysiology is extremely complex, including excessive collagen deposition, massive inflammatory infiltration, and capillary atrophy. However, the existing clinical treatment methods do not fully take into account all the pathophysiological processes of OSF, so they are generally low effective and have many side effects. In the present study, we developed an injectable sodium hyaluronate/45S5 bioglass composite hydrogel (BG/HA), which significantly relieved mucosal pallor and restricted mouth opening in OSF rats without any obvious side effects. The core mechanism of BG/HA in the treatment of OSF is the release of biologically active silicate ions, which inhibit collagen deposition and inflammation, and promote angiogenesis and epithelial regeneration. Most interestingly, silicate ions can overall regulate the physiological environment of OSF by down-regulating α-smooth muscle actin (α-SMA) and CD68 and up-regulating CD31 expression, as well as regulating the expression of pro-fibrotic factors [transforming growth factor-ß1 (TGF-ß1), interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α) and tissue inhibitors of metalloproteinase-1 (TIMP-1)] and anti-fibrotic factors [interleukin-1ß (IL-1ß)] in macrophage. In conclusion, our study shows that BG/HA has great potential in the clinical treatment of OSF, which provides an important theoretical basis for the subsequent development of new anti-fibrotic clinical preparations. STATEMENT OF SIGNIFICANCE: : Oral submucous fibrosis (OSF) is a chronic, inflammatory and potentially malignant mucosal disease with significant impact on the quality of patients' life. However, the existing clinical treatments have limited efficacy and many side effects. There is an urgent need for development of specific drugs for OSF treatment. In the present study, bioglass (BG) composited with sodium hyaluronate solution (HA) was used to treat OSF in an arecoline-induced rat model. BG/HA can significantly inhibit collagen deposition, regulate inflammatory response, promote angiogenesis and repair damaged mucosal epithelial cells, and thereby mitigate the development of fibrosis in vivo.

Autophagic LC3+ calcified extracellular vesicles initiate cartilage calcification in osteoarthritis.

Pathological cartilage calcification plays an important role in osteoarthritis progression but in which the origin of calcified extracellular vesicles (EVs) and their effects remain unknown. Here, we demonstrate that pathological cartilage calcification occurs in the early stage of the osteoarthritis in which the calcified EVs are closely involved. Autophagosomes carrying the minerals are released in EVs, and calcification is induced by those autophagy-regulated calcified EVs. Autophagy-derived microtubule-associated proteins 1A/1B light chain 3B (LC3)-positive EVs are the major population of calcified EVs that initiate pathological calcification. Release of LC3-positive calcified EVs is caused by blockage of the autophagy flux resulted from histone deacetylase 6 (HDAC6)-mediated microtubule destabilization. Inhibition of HDAC6 activity blocks the release of the LC3-positive calcified EVs by chondrocytes and effectively reverses the pathological calcification and degradation of cartilage. The present work discovers that calcified EVs derived from autophagosomes initiate pathological cartilage calcification in osteoarthritis, with potential therapeutic targeting implication.

Interaction of Neurovascular Signals in the Degraded Condylar Cartilage.

Introduction: Degradation of the condylar cartilage during temporomandibular joint osteoarthritis (TMJ-OA) results in the infiltration of nerves, blood vessels and inflammatory cells from the subchondral bone into the cartilage. The interaction among innervation, angiogenesis and inflammation in the condylar cartilage of TMJ-OA remains largely unknown. Method: In the present study, microarray-based transcriptome analysis was used to detect, and quantitative real-time polymerase chain reaction was used to validate transcriptome changes in the condylar cartilage from a well-established rat TMJ-OA model. Gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG) pathway and protein-protein interaction (PPI) analyses were conducted. Result: There were 1817 differentially expressed genes (DEGs, fold change ≥2, p < 0.05) between TMJ-OA and control cartilages, with 553 up-regulated and 1,264 down-regulated genes. Among those genes, representative DEGs with known/suspected roles in innervation, angiogenesis and inflammation were further validated by enriched GO terms and KEGG pathways. The DEGs related to innervation were predominately enriched in the GO terms of neurogenesis, generation of neurons, and KEGG pathways of cholinergic synapse and neurotrophin signaling. Genes related to angiogenesis were enriched in GO terms of vasculature and blood vessel development, and KEGG pathways of hypoxia-inducible factor 1 (HIF-1) pathway and calcium signaling pathway. For inflammation, the DEGs were enriched in the GO terms of immune system process and immune response, and KEGG pathways of Toll-like receptor and transforming growth factor ß (TGFß) signaling. Analysis with PPI indicated that the aforementioned DEGs were highly-interacted. Several hub genes such as v-akt murine thymoma viral oncogene homolog 1 (Akt1), glycogen synthase kinase 3ß (Gsk3b), fibroblast growth factor 2 (Fgf2) and nerve growth factor receptor (Ngfr) were validated. Conclusion: The present study demonstrated, for the first time, that intimate interactions exist among innervation, angiogenesis and inflammation in the condylar cartilage of TMJ-OA.

Polyphosphate-crosslinked collagen scaffolds for hemostasis and alveolar bone regeneration after tooth extraction.

Post-extraction bleeding and alveolar bone resorption are the two frequently encountered complications after tooth extraction that result in poor healing and rehabilitation difficulties. The present study covalently bonded polyphosphate onto a collagen scaffold (P-CS) by crosslinking. The P-CS demonstrated improved hemostatic property in a healthy rat model and an anticoagulant-treated rat model. This improvement is attributed to the increase in hydrophilicity, increased thrombin generation, platelet activation and stimulation of the intrinsic coagulation pathway. In addition, the P-CS promoted the in-situ bone regeneration and alveolar ridge preservation in a rat alveolar bone defect model. The promotion is attributed to enhanced osteogenic differentiation of bone marrow stromal cells. Osteogenesis was improved by both polyphosphate and blood clots. Taken together, P-CS possesses favorable hemostasis and alveolar ridge preservation capability. It may be used as an effective treatment option for post-extraction bleeding and alveolar bone loss. Statement of significance: Collagen scaffold is commonly used for the treatment of post-extraction bleeding and alveolar bone loss after tooth extraction. However, its application is hampered by insufficient hemostatic and osteoinductive property. Crosslinking polyphosphate with collagen produces a modified collagen scaffold that possesses improved hemostatic performance and augmented bone regeneration potential.

Smart, Biomimetic Periosteum Created from the Cerium(III, IV) Oxide-Mineralized Eggshell Membrane.

The periosteum orchestrates the microenvironment of bone regeneration, including facilitating local neuro-vascularization and regulating immune responses. To mimic the role of natural periosteum for bone repair enhancement, we adopted the principle of biomimetic mineralization to delicately inlay amorphous cerium oxide within eggshell membranes (ESMs) for the first time. Cerium from cerium oxide possesses unique ability to switch its oxidation state from cerium III to cerium IV and vice versa, which provides itself promising potential for biomedical applications. ESMs are mineralized with cerium(III, IV) oxide and examined for their biocompatibility. Apart from serving as physical barriers, periosteum-like cerium(III, IV) oxide-mineralized ESMs are biocompatible and can actively regulate immune responses and facilitate local neuro-vascularization along with early-stage bone regeneration in a murine cranial defect model. During the healing process, cerium-inlayed biomimetic periosteum can boost early osteoclastic differentiation of macrophage lineage cells, which may be the dominant mediator of the local repair microenvironment. The present work provides novel insights into expanding the definition and function of a biomimetic periosteum to boost early-stage bone repair and optimize long-term repair with robust neuro-vascularization. This new treatment strategy which employs multifunctional bone-and-periosteum-mimicking systems creates a highly concerted microenvironment to expedite bone regeneration.

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

Although deoxyribonucleic acid (DNA) is the genetic coding for the very essence of life, these macromolecules or components thereof are not necessarily lost after a cell dies. There appears to be a link between extracellular DNA and biomineralization. Here the authors demonstrate that extracellular DNA functions as an initiator of collagen intrafibrillar mineralization. This is confirmed with in vitro and in vivo biological mineralization models. Because of their polyanionic property, extracellular DNA molecules are capable of stabilizing supersaturated calcium phosphate solution and mineralizing 2D and 3D collagen matrices completely as early as 24 h. The effectiveness of extracellular DNA in biomineralization of collagen is attributed to the relatively stable formation of amorphous liquid droplets triggered by attraction of DNA to the collagen fibrils via hydrogen bonding. These findings suggest that extracellular DNA is biomimetically significant for fabricating inorganic-organic hybrid materials for tissue engineering. DNA-induced collagen intrafibrillar mineralization provides a clue to the pathogenesis of ectopic mineralization in different body tissues. The use of DNase for targeting extracellular DNA at destined tissue sites provides a potential solution for treatment of diseases associated with ectopic mineralization.

Matrix stiffening by self-mineralizable guided bone regeneration.

Collagen membranes produced in vitro with different degrees of intrafibrillar mineralization are potentially useful for guided bone regeneration (GBR). However, highly-mineralized collagen membranes are brittle and difficult for clinical manipulation. The present study aimed at developing an intrafibrillar self-mineralization strategy for GBR membrane by covalently conjugating high-molecular weight polyacrylic acid (HPAA) on Bio-Gide® membranes (BG). The properties of the self-mineralizable membranes (HBG) and their potential to induce bone regeneration were investigated. The HBG underwent the progressive intrafibrillar mineralization as well as the increase in stiffness after immersed in supersaturated calcium phosphate solution, osteogenic medium, or after being implanted into a murine calvarial bone defect. The HBG promoted in-situ bone regeneration via stimulating osteogenic differentiation of mesenchymal stromal cells (MSCs). Hippo signaling was inhibited when MSCs were cultured on the self-mineralized HBG, and in HBG-promoted MSC osteogenesis during in-situ bone regeneration. This resulted in translocation of the transcription co-activators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) into the nucleus to induce transcription of genes promoting osteogenic differentiation of MSCs. Taken together, these findings indicated that HBG possessed the ability to self-mineralize in situ via intrafibrillar mineralization. The increase in stiffness of the extracellular matrix expedited in-situ bone regeneration by inactivating the Hippo-YAP/TAZ signaling cascade. STATEMENT OF SIGNIFICANCE: Guided bone regeneration (GBR) membranes made of naturally derived collagen have been widely used in the bone defect restoration. However, application of collagen GBR membranes run into the bottleneck with the challenges like insufficient stress strength, relatively poor dimensional stability and unsatisfactory osteoinductivity. This study develops a modified GBR membrane that can undergo progressive self-mineralization and matrix stiffening in situ. Increase in extracellular matrix stiffness provides the mechanical cues required for MSCs differentiation and expedites in-situ bone regeneration by inactivating the Hippo-YAP/TAZ signaling cascade.

Geochemical and Geological Characteristics of the Upper Ordovician-Lower Silurian Shales in the Upper Yangtze Basin, South China: Implication for the Shale Gas Exploration.

Shale gas exploration in the Upper Yangtze Basin has been conducted for over ten years. The successful drillings in the region suggest that well-planned geological survey and reservoir evaluation are indispensable for the success of these drillings. In this study, the shale gas potential of Late Ordovician to Early Silurian mudstones/shales of the Wufeng-Longmaxi formations in the Upper Yangtze Basin was evaluated. First, all of the available geochemical and petrological data from Late Ordovician to Early Silurian mudstones/shales in the region were compiled. Distributional patterns of total organic carbon (TOC) values, thickness, thermal maturity, and burial depth of organic-rich mudstones/shales from the targeted formations were then analyzed. Our results show that TOC values range from 1.20 to 5.12%; R o values range from 1.92 to 2.86%; porosity varies from 0.77 to 9.2%; permeability varies from 0.015 to 1.99 md; the composition of quartz group of mineral component ranges from 18 to 85%, 59% in average; and clay mineral component ranges from 7 to 56%, 31% in average. Finally, based on these comprehensive analysis, three areas with great potential, that is, Luzhou-Xishui, western Chongqing, and Wulong-Shizhu, were selected as targets for further shale gas exploration and exploitation.

Pathological calcification in osteoarthritis: an outcome or a disease initiator?

In the progression of osteoarthritis, pathological calcification in the affected joint is an important feature. The role of these crystallites in the pathogenesis and progression of osteoarthritis is controversial; it remains unclear whether they act as a disease initiator or are present as a result of joint damage. Recent studies reported that the molecular mechanisms regulating physiological calcification of skeletal tissues are similar to those regulating pathological or ectopic calcification of soft tissues. Pathological calcification takes place when the equilibrium is disrupted. Calcium phosphate crystallites are identified in most affected joints and the presence of these crystallites is closely correlated with the extent of joint destruction. These observations suggest that pathological calcification is most likely to be a disease initiator instead of an outcome of osteoarthritis progression. Inhibiting pathological crystallite deposition within joint tissues therefore represents a potential therapeutic target in the management of osteoarthritis.

Conditional deletion of Adrb2 in mesenchymal stem cells attenuates osteoarthritis-like defects in temporomandibular joint.

ß2-adrenergic signal transduction in mesenchymal stem cells (MSCs) induces subchondral bone loss in osteoarthritis (OA) of temporomandibular joints (TMJs). However, whether conditional deletion of ß2-adrenergic receptor (Adrb2) in nestin+ MSCs can alleviate TMJ-OA development remains unknown. In this study, nestin-Cre mice were crossed with Adrb2 flox mice to generate mice lacking Adrb2 expression specifically in the nestin+ MSCs (Adrb2-/-), and TMJ-OA development in such mice was investigated. Adrb2 flox mice (Adrb2+/+) and Adrb2-/- mice were subjected to unilateral anterior crossbite (UAC), while mice in the control group were subjected to sham operation. Adrb2+/+ and Adrb2-/- mice in the control group showed no distinguishable phenotypic changes in body weight and length, mandibular condylar size, and other histomorphological parameters of the condylar subchondral bone. A significant increase in subchondral bone loss and cartilage degradation was observed in Adrb2+/+ UAC mice; the former was characterized by decreased bone mineral density, bone volume fraction, and trabecular plate thickness, and increased trabecular separation, osteoclast number and osteoclast surface, and pro-osteoclastic factor expression; the latter was characterized by decreased cartilage thickness, chondrocyte density, proteoglycan area, and collagen II and aggrecan expression, but increased matrix metalloproteinase and alkaline phosphatase expression and percentage area of calcified cartilage. Adrb2 deletion in nestin+ MSCs largely attenuated UAC-induced increase in condylar subchondral bone loss, cartilage degradation, and aberrant calcification at the osteochondral interface. Thus, Adrb2-expressing MSCs in the condylar subchondral bone play an important role in TMJ-OA progression and may serve as novel therapeutic targets for TMJ-OA.