Plasminogen/plasmin modulates bone metabolism by regulating the osteoblast and osteoclast function

The emerging role of tranexamic acid and its principal target, plasminogen, in skeletal health

The worldwide burden of skeletal diseases such as osteoporosis, degenerative joint disease and impaired fracture healing is steadily increasing. Tranexamic acid (TXA), a plasminogen inhibitor and anti-fibrinolytic agent, is used to reduce bleeding with high effectiveness and safety in major surgical procedures. With its widespread clinical application, the effects of TXA beyond anti-fibrinolysis have been noticed and prompted renewed interest in its use. Some clinical trials have characterized the effects of TXA on reducing postoperative infection rates and regulating immune responses in patients undergoing surgery. Also, several animal studies suggest potential therapeutic effects of TXA on skeletal diseases such as osteoporosis and fracture healing. Although a direct effect of TXA on the differentiation and function of bone cells in vitro was shown, few mechanisms of action have been reported. Here, we summarize recent findings of the effects of TXA on skeletal diseases and discuss the underlying plasminogen-dependent and -independent mechanisms related to bone metabolism and the immune response. We furthermore discuss potential novel indications for TXA application as a treatment strategy for skeletal diseases.

Osteogenic Differentiation of Human Gingival Fibroblasts Inhibits Osteoclast Formation

Gingival fibroblasts (GFs) can differentiate into osteoblast-like cells and induce osteoclast precursors to differentiate into osteoclasts. As it is unclear whether these two processes influence each other, we investigated how osteogenic differentiation of GFs affects their osteoclast-inducing capacity. To establish step-wise mineralization, GFs were cultured in four groups for 3 weeks, without or with osteogenic medium for the final 1, 2, or all 3 weeks. The mineralization was assessed by ALP activity, calcium concentration, scanning electron microscopy (SEM), Alizarin Red staining, and quantitative PCR (qPCR). To induce osteoclast differentiation, these cultures were then co-cultured for a further 3 weeks with peripheral blood mononuclear cells (PBMCs) containing osteoclast precursors. Osteoclast formation was assessed at different timepoints with qPCR, enzyme-linked immunosorbent assay (ELISA), TRAcP activity, and staining. ALP activity and calcium concentration increased significantly over time. As confirmed with the Alizarin Red staining, SEM images showed that the mineralization process occurred over time. Osteoclast numbers decreased in the GF cultures that had undergone osteogenesis. TNF-α secretion, a costimulatory molecule for osteoclast differentiation, was highest in the control group. GFs can differentiate into osteoblast-like cells and their degree of differentiation reduces their osteoclast-inducing capacity, indicating that, with appropriate stimulation, GFs could be used in regenerative periodontal treatments.

The Roles of Fibrinolytic Factors in Bone Destruction Caused by Inflammation

Chronic inflammatory diseases, such as rheumatoid arthritis, spondyloarthritis, systemic lupus erythematosus, Crohn's disease, periodontitis, and carcinoma metastasis frequently result in bone destruction. Pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and IL-17 are known to influence bone loss by promoting the differentiation and activation of osteoclasts. Fibrinolytic factors, such as plasminogen (Plg), plasmin, urokinase-type plasminogen activator (uPA), its receptor (uPAR), tissue-type plasminogen activator (tPA), α2-antiplasmin (α2AP), and plasminogen activator inhibitor-1 (PAI-1) are expressed in osteoclasts and osteoblasts and are considered essential in maintaining bone homeostasis by regulating the functions of both osteoclasts and osteoblasts. Additionally, fibrinolytic factors are associated with the regulation of inflammation and the immune system. This review explores the roles of fibrinolytic factors in bone destruction caused by inflammation.

Maintaining the balance: the critical role of plasmin activity in orthopedic surgery injury response

The musculoskeletal system plays vital roles in the body, facilitating movement, protecting vital structures, and regulating hematopoiesis and mineral metabolism. Injuries to this system are common and can cause chronic pain, loss of range of motion, and disability. The acute phase response (APR) is a complex process necessary for surviving and repairing injured musculoskeletal tissue. To conceptualize the APR, it is useful to divide it into 2 distinct phases, survival and repair. During the survival-APR, a "damage matrix" primarily composed of fibrin, via thrombin activity, is produced to contain the zone of injury. Once containment is achieved, the APR transitions to the repair phase, where reparative inflammatory cells use plasmin to systematically remove the damage matrix and replace it with new permanent matrices produced by differentiated mesenchymal stem cells. The timing of thrombin and plasmin activation during their respective APR phases is crucial for appropriate regulation of the damage matrix. This review focuses on evidence indicating that inappropriate exuberant activation of plasmin during the survival-APR can result in an overactive APR, leading to an "immunocoagulopathy" that may cause "immunothrombosis" and death. Conversely, preclinical data suggest that too little plasmin activity during the repair-APR may contribute to failed tissue repair, such as a fracture nonunion, and chronic inflammatory degenerative diseases like osteoporosis. Future clinical studies are required to affirm these findings. Therefore, the temporal-spatial functions of plasmin in response to musculoskeletal injury and its pharmacologic manipulation are intriguing new targets for improving orthopedic care.

The uPA/uPAR System Orchestrates the Inflammatory Response, Vascular Homeostasis, and Immune System in Fibrosis Progression

Fibrotic diseases, such as systemic sclerosis (SSc), idiopathic pulmonary fibrosis, renal fibrosis and liver cirrhosis are characterized by tissue overgrowth due to excessive extracellular matrix (ECM) deposition. Fibrosis progression is caused by ECM overproduction and the inhibition of ECM degradation due to several events, including inflammation, vascular endothelial dysfunction, and immune abnormalities. Recently, it has been reported that urokinase plasminogen activator (uPA) and its receptor (uPAR), known to be fibrinolytic factors, orchestrate the inflammatory response, vascular homeostasis, and immune homeostasis system. The uPA/uPAR system may show promise as a potential therapeutic target for fibrotic diseases. This review considers the role of the uPA/uPAR system in the progression of fibrotic diseases.

Fibrinolysis Regulation: A Promising Approach to Promote Osteogenesis

Soon after bone fracture, the initiation of the coagulation cascade results in the formation of a blood clot, which acts as a natural material to facilitate cell migration and osteogenic differentiation at the fracture site. The existence of hematoma is important in early stage of bone healing, but the persistence of hematoma is considered harmful for bone regeneration. Fibrinolysis is recently regarded as a period of critical transition in angiogenic-osteogenic coupling, it thereby is vital for the complete healing of the bone. Moreover, the enhanced fibrinolysis is proposed to boost bone regeneration through promoting the formation of blood vessels, and fibrinolysis system as well as the products of fibrinolysis also play crucial roles in the bone healing process. Therefore, the purpose of this review is to elucidate the fibrinolysis-derived effects on osteogenesis and summarize the potential approaches-improving bone healing by regulating fibrinolysis, with the purpose to further understand the integral roles of fibrinolysis in bone regeneration and to provide theoretical knowledge for potential fibrinolysis-related osteogenesis strategies. Impact statement Fibrinolysis emerging as a new and viable therapeutic intervention to be contained within osteogenesis strategies, however to now, there have been no review articles which collates the information between fibrinolysis and osteogenesis. This review, therefore, focusses on the effects that fibrinolysis exerts on bone healing, with a purpose to provide theoretical reference to develop new strategies to modulate fibrinolysis to accelerate fibrinolysis thus enhancing bone healing.

A Novel Enolase-1 Antibody Targets Multiple Interacting Players in the Tumor Microenvironment of Advanced Prostate Cancer

Prostate cancer is one of the most common causes of cancer death in men worldwide, and the treatment options are limited for patients with advanced stages of prostate cancer. Upon oncogenic or inflammatory stimulation, tumor cells or immune cells express cell surface enolase-1 (ENO1) as plasminogen receptor to facilitate their migration via plasmin activation. Little is known about the roles of ENO1 in prostate cancer, especially in the tumor microenvironment (TME). We hypothesized that targeting surface ENO1 with specific mAbs would exert multifactorial therapeutic potentials against prostate cancer. In vivo, we showed ENO1 mAb (HuL227) reduced the growth of subcutaneous PC-3 xenograft, monocytes recruitment, and intratumoral angiogenesis. In a PC-3 intratibial implantation model, HuL227 reduced tumor growth and osteoclast activation in the bone. To investigate the antitumor mechanism of ENO1 mAb, we found that blocking surface ENO1 significantly reduced VEGF-A-induced tube formation of endothelial cells in vitro. Furthermore, HuL227 inhibited inflammation-enhanced osteoclasts activity and the secretion of invasion-related cytokines CCL2 and TGFβ from osteoclasts. In addition, inflammation-induced migration and chemotaxis of androgen-independent prostate cancer cells were dose-dependently inhibited by HuL227. In summary, we showed that, ENO1 mAb targets multiple TME niches involved in prostate cancer progression and bone metastasis via a plasmin-related mechanism, which may provide a novel immunotherapy approach for men with advanced prostate cancer.

Platelets and osteoblasts: secretome connections

Megakaryocyte hyperplasia associated with myeloproliferative neoplasms commonly leads to abnormal bone tissue deposition in the bone marrow, known as osteosclerosis. In this study, we aimed to synthesize the known proteomics literature describing factors released by megakaryocytes and platelets and to examine if any of the secreted factors have a known ability to stimulate the bone-forming cells, osteoblasts. Using a systematic search of Medline, we identified 77 articles reporting on factors secreted by platelets and megakaryocytes. After a full-text screening and analysis of the studies, we selected seven papers that reported proteomics data for factors secreted by platelets from healthy individuals. From 60 proteins reported in at least two studies, we focused on 23 that contained a putative signal peptide, which we searched for a potential osteoblast-stimulatory function. From nine proteins with a positive effect on osteoblast formation and function, two extracellular matrix (ECM) proteins, secreted protein acidic and rich in cysteine (SPARC) and tissue inhibitor of metalloproteinase-1 (TIMP1), and three cellular proteins with known extracellular function, the 70-kDa heat shock protein (HSP70), thymosin-β4 (TB4), and super dismutase (SOD), were identified as hypothetical candidate molecules to be examined as potential mediators in mouse models of osteomyelofibrosis. Thus, careful analysis of prior literature can be beneficial in assisting the planning of future experimental studies.

α2-Antiplasmin as a Potential Therapeutic Target for Systemic Sclerosis

Systemic sclerosis is a connective tissue disease of unknown origin that is characterized by immune system abnormalities, vascular damage, and extensive fibrosis of the skin and visceral organs. α2-antiplasmin is known to be the main plasmin inhibitor and has various functions such as cell differentiation and cytokine production, as well as the regulation of the maintenance of the immune system, endothelial homeostasis, and extracellular matrix metabolism. The expression of α2-antiplasmin is elevated in dermal fibroblasts from systemic sclerosis patients, and the blockade of α2-antiplasmin suppresses fibrosis progression and vascular dysfunction in systemic sclerosis model mice. α2-antiplasmin may have promise as a potential therapeutic target for systemic sclerosis. This review considers the role of α2-antiplasmin in the progression of systemic sclerosis.

Alpha2-antiplasmin deficiency affects depression and anxiety-like behavior and apoptosis induced by stress in mice

OBJECTIVES

Depression is a psychiatric disorder that affects about 10% of the world's population and is accompanied by anxiety. Depression and anxiety are often caused by various stresses. However, the etiology of depression and anxiety remains unknown. It has been reported that alpha2-antiplasmin (α2AP) not only inhibits plasmin but also has various functions such as cytokine production and cell growth. This study aimed to determine the roles of α2AP on the stress-induced depression and anxiety.

METHODS

We investigated the mild repeated restraint stress-induced depressive and anxiety-like behavior in the α2AP^+/+ and α2AP^-/- mice using the social interaction test (SIT), sucrose preference test (SPT), and elevated plus maze (EPM).

RESULTS

The stresses such as the mild repeated restraint stress suppressed α2AP expression in the hippocampus of mice, and the treatment of fluoxetine (selective serotonin reuptake inhibitor [SSRI]) recovered the stress-caused α2AP suppression. We also showed that α2AP deficiency promoted the mild restraint stress-stimulated depression-like behavior such as social withdrawal and apathy and apoptosis in mice. In contrast, α2AP deficiency attenuated the mild restraint stress induced the anxiety-like behavior in mice.

CONCLUSIONS

α2AP affects the pathogenesis of depression and anxiety induced by stress.

Plasminogen Regulates Fracture Repair by Promoting the Functions of Periosteal Mesenchymal Progenitors

Defective or insufficient bone repair and regeneration are common in patients as a result of major trauma or severe disease. Cell therapy with periosteal mesenchymal progenitors, which can be limited in severe injury, serves as a promising approach; however, its efficacy is limited due to a repair-hostile ischemic tissue microenvironment after traumatic fracture. Here we report that plasminogen (Plg), a factor that is upregulated in these environments, is critical for fracture healing. Plg knockout mice had impaired trabecular and cortical bone structure and exhibited delayed and incomplete fracture healing. Interestingly, Plg deficiency greatly reduced the thickness of expanded periosteum, suggesting a role of Plg in periosteal mesenchymal progenitor-mediated bone repair. In culture, Plg increased cell proliferation and migration in periosteal mesenchymal progenitors and inhibited cell death under ischemic conditions. Mechanistically, we revealed that Plg cleaved and activated Cyr61 to regulate periosteal progenitor function. Thus, our study uncovers a cellular mechanism underlying fracture healing, by which Plg activates Cyr61 to promote periosteal progenitor proliferation, survival, and migration and improves bone repair after fracture. Targeting Plg may offer a rational and effective therapeutic opportunity for improving fracture healing. © 2021 American Society for Bone and Mineral Research (ASBMR).

α2-antiplasmin positively regulates endothelial-to-mesenchymal transition and fibrosis progression in diabetic nephropathy

BACKGROUND

Diabetic nephropathy (DN), is microvascular complication of diabetes causes to kidney dysfunction and renal fibrosis. It is known that hyperglycemia and advanced glycation end products (AGEs) produced by hyperglycemic condition induce myofibroblast differentiation and endothelial-to-mesenchymal transition (EndoMT), and exacerbate fibrosis in DN. Recently, we demonstrated that α2-antiplasmin (α2AP) is associated with inflammatory response and fibrosis progression.

METHODS

We investigated the role of α2AP on fibrosis progression in DN using a streptozotocin-induced DN mouse model.

RESULTS

α2AP deficiency attenuated EndoMT and fibrosis progression in DN model mice. We also showed that the high glucose condition/AGEs induced α2AP production in fibroblasts (FBs), and the reduction of receptor for AGEs (RAGE) by siRNA attenuated the AGEs-induced α2AP production in FBs. Furthermore, the bloackade of α2AP by the neutralizing antibody attenuated the high glucose condition-induced pro-fibrotic changes in FBs. On the other hand, the hyperglycemic condition/AGEs induced EndoMT in vascular endothelial cells (ECs), the FBs/ECs co-culture promoted the high glucose condition-induced EndoMT compared to ECs mono-culture. Furthermore, α2AP promoted the AGEs-induced EndoMT, and the blockade of α2AP attenuated the FBs/ECs co-culture-promoted EndoMT under the high glucose condition.

CONCLUSIONS

The high glucose conditions induced α2AP production, and α2AP is associated with EndoMT and fibrosis progression in DN. These findings provide a basis for clinical strategies to improve DN.

Knockdown of SERPINB2 enhances the osteogenic differentiation of human bone marrow mesenchymal stem cells via activation of the Wnt/β-catenin signalling pathway

Background

Globally, bone fractures are the most common musculoskeletal trauma, and approximately 8–10% of cases that fall into the categories of delayed or non-union healing. To date, there are no efficient pharmacological agents to accelerate the healing of bone fractures. Thus, it is necessary to find new strategies that accelerate bone healing and reduce the incidence of non-union or delayed fracture healing. Previous studies have revealed that the plasminogen activation system has been demonstrated to play an important role in bone metabolism. However, the function of SERPINB2 in the osteogenesis of hBMSCs remains unclear. Therefore, in this study, we investigated the effects and mechanism of SERPINB2 on osteogenic differentiation.

Methods

We investigated the osteogenesis effects of hBMSCs by both exogenous SerpinB2 protein and SERPINB2 gene silencing in vitro. Cell proliferation assay was used to assess the effect of exogenous SerpinB2 or SERPINB2 silencing on proliferation of hBMSCs. qPCR and Western blotting analysis detected the expression of target genes and proteins respectively. ALP staining was used to evaluated ALP activity and Alizarin Red staining (ARS) was used to evaluate mineral deposition. In vivo, a murie tibial fracture model was established, histological evaluation and radiographic analysis was used to confirm the therapeutic effects of SERPINB2 silencing in fracture healing. Statistical significance between two groups was determined by Student’s t test, one-way ANOVA or Bonferroni’s post-hoc test according to the distribution of the tested population.

Results

The addition of exogenous SerpinB2 protein inhibted osteoblast differentiation of hBMSCs in vitro, while SERPINB2 gene silencing significant promote osteoblast differentiation of hBMSCs in vitro. And silenced SERPINB2 gene also increased mineral deposits. Moreover, β-catenin levels were up-regulated by SERPINB2 gene depletion. And the enhancement of osteogenic differentiation induced by SERPINB2 silencing was almost inhibited by specific Wnt/β-catenin signaling pathway inhibitor. In a murine tibial fracture model, local injection of SERPINB2 siRNA improved bone fracture healing.

Conclusions

Taken together, these findings indicate that SERPINB2 silencing promoted osteogenic differentiation of BMSCs via the Wnt/β-catenin signaling pathway, and silenced SERPINB2 in vivo effectively promotes fracture healing, suggesting that SERPINB2 may be a novel target for bone fracture healing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02581-6.

Identification of differentially expressed proteins between fused and open sutures in sagittal nonsyndromic craniosynostosis during suture development by quantitative proteomic analysis

PURPOSE

Nonsyndromic craniosynostosis (NCS), the premature fusion of cranial sutures, results in an abnormal skull shape and is associated with a significant morbidity. Proteomics is a promising tool for disease characterization and biomarker discovery; we aimed to identify biologically relevant differentially expressed proteins for NCS.

EXPERIMENTAL DESIGN

Label-based quantitative proteomic profiling using TMT was performed on protein extracted from mesenchymal stem cells, osteoblasts and bone tissue of five open and five fused sutures of sagittal NCS (sNCS) and analyzed using quantitative LC-MS/MS based bottom-up proteomics. Differential protein abundance between open and fused sutures was determined to identify biologically relevant proteins of interest. Proteins were validated in an independent sample set by western blot and immunohistochemistry.

RESULTS

We observed 838 differentially expressed proteins between open and fused sutures of sNCS. Decorin, lumican, and asporin were significantly downregulated while COL4A1 and TGFβ1|1 were upregulated in fused compared to open sutures.

CONCLUSIONS AND CLINICAL RELEVANCE

The majority of significantly differentially expressed proteins between open and fused sutures were observed in the proteomes of osteoblasts suggesting that protein changes contributing to premature sagittal suture fusion occur predominantly at the osteoblast level. Our findings suggest a possible ineffective ECM deposition at the osteoblast cell stage.

Transcriptomics-based analysis of the mechanism by which Wang-Bi capsule alleviates joint destruction in rats with collagen-induced arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease accompanied with joint destruction that often leads to disability. Wang-Bi capsule (WB), a traditional Chinese medicine-based herbs formula, has exhibited inhibition effect on joint destruction of collagen-induced arthritis (CIA) animal model in our previous study. But its molecular mechanisms are still obscure.

METHODS

CIA rats were treated intragastrical with WB for eight weeks, and the effect of joints protection were evaluated by hematoxylin and eosin (H&E) staining, safranin O fast green staining, tartrate-resistant acid phosphatase (TRAP) staining and micro‑CT scanning analysis. The transcriptomic of tarsal joints were used to investigate how WB alleviated joint destruction.

RESULTS

The histological examination of ankle joints showed WB alleviated both cartilage damage and bone destruction of CIA rats. This protective effect on joints were further evidenced by micro-CT analysis. The transcriptomic analysis showed that WB prominently changed 12 KEGG signaling pathways ("calcium signaling pathway", "cAMP signaling pathway", "cell adhesion molecules", "chemokine signaling pathway", "complement and coagulation cascades", "MAPK signaling pathway", "NF-kappa B signaling pathway", "osteoclast differentiation", "PI3K-Akt signaling pathway", "focal adhesion", "Gap junction" and "Rap1 signaling pathway") associated with bone or cartilage. Several genes (including Il6, Tnfsf11, Ffar2, Plg, Tnfrsf11b, Fgf4, Fpr1, Siglec1, Vegfd, Cldn1, Cxcl13, Chad, Arrb2, Fgf9, Egfr) regulating bone resorption, bone formation and cartilage development were identified by further analysis. Meanwhile, these differentially expressed genes were validated by real-time quantitative PCR.

CONCLUSIONS

Overall, the protective effect of WB treatment on joint were confirmed in CIA rats, and its basic molecular mechanisms may be associated with regulating some genes (including Il6, Tnfsf11, Ffar2 and Plg etc.) involved in bone resorption, bone formation and cartilage development.

Trps1 transcription factor represses phosphate-induced expression of SerpinB2 in osteogenic cells

Serine protease inhibitor SerpinB2 is one of the most upregulated proteins following cellular stress. This multifunctional serpin has been attributed a number of pleiotropic activities, including roles in cell survival, proliferation, differentiation, immunity and extracellular matrix (ECM) remodeling. Studies of cancer cells demonstrated that expression of SerpinB2 is directly repressed by the Trps1 transcription factor, which is a regulator of skeletal and dental tissues mineralization. In our previous studies, we identified SerpinB2 as one of the novel genes highly upregulated by phosphate (P_i) at the initiation of the mineralization process, however SerpinB2 has never been implicated in formation nor homeostasis of mineralized tissues. The aim of this study was to establish, if SerpinB2 is involved in function of cells producing mineralized ECM and to determine the interplay between P_i signaling and Trps1 in the regulation of SerpinB2 expression specifically in cells producing mineralized ECM. Analyses of the SerpinB2 expression pattern in mouse skeletal and dental tissues detected high SerpinB2 protein levels specifically in cells producing mineralized ECM. qRT-PCR and Western blot analyses demonstrated that SerpinB2 expression is activated by elevated P_i specifically in osteogenic cells. However, the P_i-induced SerpinB2 expression was diminished by overexpression of Trps1. Decreased SerpinB2 levels were also detected in osteoblasts and odontoblasts of 2.3Col1a1-Trps1 transgenic mice. Chromatin immunoprecipitation assay (ChIP) revealed that the occupancy of Trps1 on regulatory elements in the SerpinB2 gene changes in response to P_i. In vitro functional assessment of the consequences of SerpinB2 deficiency in cells producing mineralized ECM detected impaired mineralization in SerpinB2-deficient cells in comparison with controls. In conclusion, high and specific expression of SerpinB2 in cells producing mineralized ECM, the impaired mineralization of SerpinB2-deficient cells and regulation of SerpinB2 expression by two molecules regulating formation of mineralized tissues suggest involvement of SerpinB2 in physiological mineralization.

Roles of fibrinolytic factors in the alterations in bone marrow hematopoietic stem/progenitor cells during bone repair

In bone tissues, metabolic turnover through bone resorption by osteoclasts and bone formation by osteoblasts, termed bone remodeling, is strictly controlled and maintains homeostasis. Fibrinolytic factors are expressed in osteoclasts and osteoblasts, and are involved in bone remodeling through bone resorption and formation. The repair/regeneration process after bone injury is divided into the acute inflammatory, repair, and remodeling stages. Osteoblasts, osteoclasts, chondrocytes, and macrophages involved in the bone repair process originate from hematopoietic stem/progenitor cells (HSPCs) and mesenchymal stem cells (MSCs) in the bone marrow. Therefore, stem cells in the bone marrow may be strongly influenced by bone injury. The urokinase-type PA (u-PA)/plasminogen (Plg) system functions in macrophage accumulation/phagocytosis through chemokines in the acute inflammatory stage, and Plg increases blood vessel-related growth factor expression, being involved in vascularization in mice. Plasminogen activator inhivitor-1 (PAI-1) causes bone loss and delayed bone repair through the inhibition of osteoblast differentiation in a drug-induced diabetes model in mice. Plg is considered to induce transforming growth factor-β (TGF-β) production in macrophages in the bone repair process, TGF-β release from the extracellular matrix through the activation of matrix metalloproteinase-9 (MMP-9), and stromal cell-derived factor-1 (SDF-1) expression in endosteal preosteoblasts, leading to the induction of bone marrow HSPCs in mice. Based on the above, establishment of a fibrinolytic factor-targeting method efficiently promoting bone repair/regeneration and fracture healing, and development of a new osteoporosis treatment method and diagnostic marker are awaited.

Novel LRAP-binding partner revealing the plasminogen activation system as a regulator of cementoblast differentiation and mineral nodule formation in vitro

Amelogenin isoforms, including full-length amelogenin (AMEL) and leucine-rich amelogenin peptide (LRAP), are major components of the enamel matrix, and are considered as signaling molecules in epithelial-mesenchymal interactions regulating tooth development and periodontal regeneration. Nevertheless, the molecular mechanisms involved are still poorly understood. The aim of the present study was to identify novel binding partners for amelogenin isoforms in the cementoblast (OCCM-30), using an affinity purification assay (GST pull-down) followed by mass spectrometry and immunoblotting. Protein-protein interaction analysis for AMEL and LRAP evidenced the plasminogen activation system (PAS) as a potential player regulating OCCM-30 response to amelogenin isoforms. For functional assays, PAS was either activated (plasmin) or inhibited (ε-aminocaproic acid [aminocaproic]) in OCCM-30 cells and the cell morphology, mineral nodule formation, and gene expression were assessed. PAS inhibition (EACA 100 mM) dramatically decreased mineral nodule formation and expression of OCCM-30 differentiation markers, including osteocalcin (Bglap), bone sialoprotein (Ibsp), osteopontin (Spp1), tissue-nonspecific alkaline phosphatase (Alpl) and collagen type I (Col1a1), and had no effect on runt-related transcription factor 2 (Runx2) and Osterix (Osx) mRNA levels. PAS activation (plasmin 5 µg/µl) significantly increased Col1a1 and decreased Bglap mRNA levels (p < .05). Together, our findings shed new light on the potential role of plasminogen signaling pathway in the control of the amelogenin isoform-mediated response in cementoblasts and provide new insights into the development of targeted therapies.

Osteoprotegerin (OPG) Promotes Recruitment of Endothelial Progenitor Cells (EPCs) via CXCR4 Signaling Pathway to Improve Bone Defect Repair

Background

The aim of this study was to investigate the effect of using osteoprotegerin (OPG) to treat bone defects mediated by endothelial progenitor cell (EPC) recruitment and migration through the CXCR4 signaling pathway.

Material/Methods

The EPCs extracted from human peripheral blood were cultured in vitro and the expression of CXCR4 and its downstream p-AKT was monitored by the Western blot analysis after OPG treatment. Using the scratch wound healing test and Transwell assay, we assessed the variables influencing the effect of OPG on EPCs after pre-treatment with CXCR4 blocker (AMD3100) and PI3K blocker (Ly294002). After 4 weeks, the bone defect repair condition was estimated via micro-CT and staining with HE and Masson trichrome. Then, immunofluorescence staining was performed to assess angiogenesis in bone defects, while the expression of EPC marker and vascular endothelial growth factor receptor 2 (VEGFR2) was detected by immunohistochemical staining.

Results

The EPCs treated with OPG had increased levels of CXCR4 and p-AKT. Moreover, the difference in EPC levels among groups in the scratch wound healing experiment and migration experiment indicated that the OPG treatment promoted cell migration and AMD3100 and LY294002 inhibited the function of OPG. In addition, OPG promoted angiogenesis and repair of bone defect in rats, and these effects were abolished by AMD3100 and LY294002 administration.

Conclusions

OPG enhanced the proliferation and migration of EPCs through the CXCR4 pathway and promoted angiogenesis and bone formation at bone defect sites.

Rhoifolin ameliorates titanium particle-stimulated osteolysis and attenuates osteoclastogenesis via RANKL-induced NF-κB and MAPK pathways

Prosthesis loosening is a highly troublesome clinical problem following total joint arthroplasty. Wear-particle-induced osteoclastogenesis has been shown to be the primary cause of periprosthetic osteolysis that eventually leads to aseptic prosthesis loosening. Therefore, inhibiting osteoclastogenesis is a promising strategy to control periprosthetic osteolysis. The possible mechanism of action of rhoifolin on osteoclastogenesis and titanium particle-induced calvarial osteolysis was examined in this study. The in vitro study showed that rhoifolin could strongly suppress the receptor activators of nuclear factor-κB (NF-κB) ligand-stimulated osteoclastogenesis, hydroxyapatite resorption, F-actin formation, and the gene expression of osteoclast-related genes. Western blot analysis illustrated that rhoifolin could attenuate the NF-κB and mitogen-activated protein kinase pathways, and the expression of transcriptional factors nuclear factor of activated T cells 1 (NFATc1) and c-Fos. Further studies indicated that rhoifolin inhibited p65 translocation to the nucleus and the activity of NFATc1 and NF-κB rhoifolin could decrease the number of tartrate-resistant acid phosphate-positive osteoclasts and titanium particle-induced C57 mouse calvarial bone loss in vivo. In conclusion, our results suggest that rhoifolin can ameliorate the osteoclasts-stimulated osteolysis, and may be a potential agent for the treatment of prosthesis loosening.

Structural studies of plasmin inhibition

Plasminogen (Plg) is the zymogen form of the serine protease plasmin (Plm), and it plays a crucial role in fibrinolysis as well as wound healing, immunity, tissue remodeling and inflammation. Binding to the targets via the lysine-binding sites allows for Plg activation by plasminogen activators (PAs) present on the same target. Cellular uptake of fibrin degradation products leads to apoptosis, which represents one of the pathways for cross-talk between fibrinolysis and tissue remodeling. Therapeutic manipulation of Plm activity plays a vital role in the treatments of a range of diseases, whereas Plm inhibitors are used in trauma and surgeries as antifibrinolytic agents. Plm inhibitors are also used in conditions such as angioedema, menorrhagia and melasma. Here, we review the rationale for the further development of new Plm inhibitors, with a particular focus on the structural studies of the active site inhibitors of Plm. We compare the binding mode of different classes of inhibitors and comment on how it relates to their efficacy, as well as possible future developments.

The Role of Fibrinolytic Regulators in Vascular Dysfunction of Systemic Sclerosis

Systemic sclerosis (SSc) is a connective tissue disease of autoimmune origin characterized by vascular dysfunction and extensive fibrosis of the skin and visceral organs. Vascular dysfunction is caused by endothelial cell (EC) apoptosis, defective angiogenesis, defective vasculogenesis, endothelial-to-mesenchymal transition (EndoMT), and coagulation abnormalities, and exacerbates the disease. Fibrinolytic regulators, such as plasminogen (Plg), plasmin, α2-antiplasmin (α2AP), tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) and its receptor (uPAR), plasminogen activator inhibitor 1 (PAI-1), and angiostatin, are considered to play an important role in the maintenance of endothelial homeostasis, and are associated with the endothelial dysfunction of SSc. This review considers the roles of fibrinolytic factors in vascular dysfunction of SSc.

Jatrorrhizine Hydrochloride Suppresses RANKL-Induced Osteoclastogenesis and Protects against Wear Particle-Induced Osteolysis

Wear particle-induced aseptic prosthetic loosening is a major complication associated with total joint arthroplasty (TJA). A growing body of evidence suggests that receptor activator of nuclear factor κ-B ligand (RANKL)-stimulated osteoclastogenesis and bone resorption are responsible for peri-implant loosening. Thus, agents which attenuate excessive osteoclast differentiation and function have been considered to offer therapeutic potential for prolonging the life of TJA implants. Jatrorrhizine hydrochloride (JH), a major protoberberine alkaloid isolated from the traditional Chinese herb Coptis chinensis, has been reported to have antimicrobial, antitumor, and antihypercholesterolemic and neuroprotective activities. However, its effects on osteoclast biology remain unknown. Here, we found that JH inhibited RANKL-induced osteoclast formation and bone resorption in vitro and exerted protection against titanium (Ti) particle-induced osteolysis in vivo. Biochemical analysis demonstrated that JH suppressed RANKL-induced activation of MAPKs (p38 and ERK) which down-regulated the production of NFATc1 and NFATc1-regulated osteoclastic marker genes, such as TRAP, CTR and CTSK. Collectively, our findings suggest that JH may be a promising anti-osteoclastogenesis agent for treating periprosthetic osteolysis or other osteoclast-related osteolytic diseases.

Effects of interleukin-7/interleukin-7 receptor on RANKL-mediated osteoclast differentiation and ovariectomy-induced bone loss by regulating c-Fos/c-Jun pathway

To explore the effects of IL-7/IL-7R on the RANKL-mediated osteoclast differentiation in vitro and OVX-induced bone loss in vivo. BMMs and RAW264.7 were transfected with IL-7, IL-7R siRNA, c-Fos siRNA, and c-jun siRNA and later stimulated by RANKL. TRAP and toluidine blue staining were used to observe osteoclast formation and bone resorption, respectively. HE and TRAP staining were used to detect trabecular bone microstructure and osteoclasts of mice, respectively. qRT-PCR and Western blot analysis were used to examine expression. IL-7 unregulated the expression of CTSK, NFATc1, MMP9, and the phosphorylation of p38 and Akt by activating the c-Fos/c-Jun pathway, which increased osteoclast numbers and bone resorption in RANKL-stimulated macrophages. While IL-7R siRNA and c-Fos siRNA decreased the expression, as well as and the phosphorylation of p38 and Akt.IL-7 decreased the BMD and OPG expression in OVX-induced mice and increased the TRAP positive cells, the mRNA expression of c-fos, c-jun, and RANKL, which was contradictory to IL-7R siRNA, and c-Fos siRNA. Furthermore, IL-7R siRNA and c-Fos siRNA caused thicker trabeculae, increased trabecular number, and decreased osteolysis in OVX mice. IL-7/IL-7R can promote RANKL-mediated osteoclast formation and bone resorption by activating the c-Fos/c-Jun pathway, as well as inducing bone loss in OVX mice.

The roles of cellular and molecular components of a hematoma at early stage of bone healing

Bone healing is a complex repair process that commences with the formation of a blood clot at the injured bone, termed hematoma. It has evidenced that a lack of a stable hematoma causes delayed bone healing or non-union. The hematoma at the injured bone constitutes the early healing microenvironment. It appears to dictate healing pathways that ends in a regenerative bone. However, the hematoma is often clinically removed from the damaged site. Conversely, blood-derived products have been used in bone tissue engineering for treating critical sized defects, including fibrin gels and platelet-rich plasma. A second generation of platelet concentrate that is based on leukocyte and fibrin content has also been developed and introduced in market. Conflicting effect of these products in bone repair are reported. We propose that the bone healing response becomes dysregulated if the blood response and subsequent formation and properties of a hematoma are altered. This review focuses on the central structural, cellular, and molecular components of a fracture hematoma, with a major emphasis on their roles in regulating bone healing mechanism, and their interactions with mesenchymal stem cells. New angles towards a better understanding of these factors and relevant mechanisms involved at the beginning of bone healing may help to clarify limited or adverse effects of blood-derived products on bone repair. We emphasize that the recreation of an early hematoma niche with critical compositions might emerge as a viable therapeutic strategy for enhanced skeletal tissue engineering.

α2-antiplasmin modulates bone formation by negatively regulating osteoblast differentiation and function

α2-antiplasmin (α2AP) is known to be a physiological inhibitor of plasmin. Previously, we showed that α2AP displays various functions, such as promotion of extracellular matrix production, cell growth, and cell differentiation that are not promoted by its function as a plasmin inhibitor. We herein investigated the role of α2AP in bone formation by examining calcein incorporation after its injection in α2AP-deficient mice. We found that α2AP deficiency enhanced the bone formation rate in mice. We also found that the osteocalcin expression and alkaline phosphatase activity were elevated in the femur and serum of the α2AP-deficient mice. Intriguingly, α2AP deficiency promoted osteoblast (OB) differentiation of primary calvarial OBs. In contrast, α2AP attenuated OB differentiation of mouse osteoblastic the MC3T3-E1 cells. Furthermore, α2AP attenuated Wnt-3a-induced β-catenin expression and low‑density lipoprotein receptor-related protein 6 activation in the MC3T3-E1 cells. These results suggest that α2AP negatively affects OB differentiation and function by inhibiting the Wnt/β-catenin pathway. These findings provide a basis for clinical strategies to improve various bone disorders.

uPA-derived peptide, Å6 is involved in the suppression of lipopolysaccaride-promoted inflammatory osteoclastogenesis and the resultant bone loss

Introduction

Chronic inflammatory diseases such as rheumatoid arthritis and periodontitis frequently cause bone destruction. Inflammation‐induced bone loss results from the increase of bone‐resorbing osteoclasts. Recently, we demonstrated that urokinase type plasminogen activator (uPA) suppressed lipopolysaccaride (LPS)‐inflammatory osteoclastogenesis through the adenosine monophosphate‐activated protein kinase (AMPK) pathway, whereas its receptor (uPAR) promoted that through the Akt pathway.

Methods

We investigated the effects of uPA‐derived peptide (Å6) in the LPS‐induced inflammatory osteoclastogenesis and bone destruction.

Results

We found that Å6 attenuated inflammatory osteoclastogenesis and bone loss induced by LPS in mice. We also showed that Å6 attenuated the LPS‐promoted inflammatory osteoclastogenesis by inactivation of NF‐κB in RAW264.7 mouse monocyte/macrophage lineage cells. Furthermore, we showed that Å6 attenuated the Akt phosphorylation, and promoted the AMPK phosphorylation.

Conclusion

Å6 is involved in the suppression of LPS‐promoted inflammatory osteoclastgensis and bone destruction by regulating the AMPK and Akt pathways. These findings provide a basis for clinical strategies to improve the bone loss caused by inflammatory diseases.

Plasminogen deficiency is associated with improved glucose tolerance, and lower DPP-4 activity

Plasminogen (Plg), which is the inactive form of plasmin, deficiency enhanced insulin secretion, and was associated with improved oral glucose tolerance in mice. Additionally, Plg deficiency was associated with lower dipeptidyl peptidase-4 (DPP-4) activity, and enhanced glucagons-like peptide-1 (GLP-1) expression. Plg may regulate the DPP-4 activity and the glucose metabolism.

The blocking of uPAR suppresses lipopolysaccharide-induced inflammatory osteoclastogenesis and the resultant bone loss through attenuation of integrin β3/Akt pathway

Introduction

Chronic inflammatory diseases, such as rheumatoid arthritis and periodontitis, cause the bone destruction by promotion of the differentiation of monocyte/macrophage lineage cells into mature osteoclasts (OCs) with active bone‐resorbing character. However, the detailed mechanisms underlying this disorder remain unclear. We herein investigated the role of urokinase plasminogen activator receptor (uPAR) in the bone destruction caused by chronic inflammation.

Methods

We investigated that the effect of uPAR on inflammatory OC formation induced by lipopolysaccharide (LPS) in inflammatory diseases.

Results

We found that the LPS more weakly induced OC formation and the resultant bone loss in uPAR‐deficient mice than in wild‐type mice. Additionally, we demonstrated that uPAR significantly potentiated LPS‐induced OC formation of RAW264.7 mouse monocyte/macrophage linage cells in integrin β3/Akt‐dependent manner. Moreover, we showed that the blocking of uPAR function by the administration of anti‐uPAR neutralizing antibody significantly attenuated the LPS‐induced OC formation and the resultant bone loss in mice.

Conclusions

These results strongly suggest that uPAR negatively regulates the LPS‐induced inflammatory OC formation and the resultant bone loss mediated through the integrin β3/Akt pathway. Our findings partly clarify the molecular mechanisms underlying bone destruction caused by chronic inflammatory diseases, and would benefit research on identifying antibody therapy for the treatment of these diseases.

Structural properties of fracture haematoma: current status and future clinical implications

Blood clots (haematomas) that form immediately following a bone fracture have been shown to be vital for the subsequent healing process. During the clotting process, a number of factors can influence the fibrin clot structure, such as fibrin polymerization, growth factor binding, cellular infiltration (including platelet retraction), protein concentrations and cytokines. The modulation of the fibrin clot structure within the fracture site has important clinical implications and could result in the development of multifunctional scaffolds that mimic the natural structure of a haematoma. Artificial haematoma structures such as these can be created from the patient's own blood and can therefore act as an ideal bone defect filling material for potential clinical application to accelerate bone regeneration. Copyright © 2016 John Wiley & Sons, Ltd.

Correlations Between Abnormal Glucose Metabolism and Bone Mineral Density or Bone Metabolism

Background

The aim of this meta-analysis was to explore the correlations of abnormal glucose metabolism (AGM) with bone mineral density (BMD) and bone metabolism.

Material/Methods

Relevant studies were identified using computerized and manual search strategies. The included studies were in strict accordance with inclusion and exclusion criteria. Statistical analyses were conducted with the Comprehensive Meta-analysis 2.0 (Biostat Inc., Englewood, NJ, USA).

Results

Our present meta-analysis initially searched 844 studies, and 7 studies were eventually incorporated in the present meta-analysis. These 7 cohort studies included 1123 subjects altogether (560 patients with AGM and 563 healthy controls). The results showed that bone mass index (BMI), insulin, and insulin resistance (IR) of patients with AGM were significantly higher than that of the population with normal glucose metabolism (BMI: SMD=1.658, 95% CI=0.663~2.654, P=0.001; insulin: SMD=0.544, 95% CI=0.030~1.058, P=0.038; IR: SMD=8.767, 95% CI=4.178~13.356, P<0.001). However, the results also indicated there was no obvious difference in osteocalcin (OC) and BMD in patients with AGM and the population with normal glucose metabolism (OC: SMD=0.293, 95% CI=−0.023~0.609, P=0.069; BMD: SMD=0.805, 95% CI=−0. 212~1.821, P=0.121).

Conclusions

Our meta-analysis results suggest that AGM might lead to increased BMI, insulin, and IR, while it has no significant correlation with BMD or bone metabolism.

uPA Attenuated LPS-induced Inflammatory Osteoclastogenesis through the Plasmin/PAR-1/Ca(2+)/CaMKK/AMPK Axis

Chronic inflammatory diseases, such as rheumatoid arthritis and periodontitis-caused bone destruction, results from an increase of bone-resorbing osteoclasts (OCs) induced by inflammation. However, the detailed mechanisms underlying this disorder remain unclear. We herein investigated that the effect of urokinase-type plasminogen activator (uPA) on inflammatory osteoclastogenesis induced by lipopolysaccharide (LPS), which is a potent stimulator of bone resorption in inflammatory diseases. We found that the uPA deficiency promoted inflammatory osteoclastogenesis and bone loss induced by LPS. We also showed that LPS induced the expression of uPA, and the uPA treatment attenuated the LPS-induced inflammatory osteoclastogenesis of RAW264.7 mouse monocyte/macrophage lineage cells. Additionally, we showed that the uPA-attenuated inflammatory osteoclastgenesis is associated with the activation of plasmin/protease-activated receptor (PAR)-1 axis by uPA. Moreover, we examined the mechanism underlying the effect of uPA on inflammatory osteoclastogenesis, and found that uPA/plasmin/PAR-1 activated the adenosine monophosphate-activated protein kinase (AMPK) pathway through Ca2+/calmodulin dependent protein kinase kinase (CaMKK) activation, and attenuated inflammatory osteoclastogenesis by inactivation of NF-κB in RAW264.7 cells. These data suggest that uPA attenuated inflammatory osteoclastogenesis through the plasmin/PAR-1/Ca2+/CaMKK/AMPK axis. Our findings may provide a novel therapeutic approach to bone loss caused by inflammatory diseases.

α₂-Antiplasmin is involved in bone loss induced by ovariectomy in mice

The mechanism of postmenopausal osteoporosis is not fully understood. α2-Antiplasmin (α2-AP) is the primary inhibitor of plasmin in the fibrinolytic system, but is known to have activities beyond fibrinolysis. However, its role in bone metabolism and the pathogenesis of osteoporosis remains unknown. In the current study, we therefore examined the effects of α2-AP deficiency on ovariectomy (OVX)-induced bone loss by using wild-type and α2-AP-deficient mice. Quantitative computed tomography analysis revealed that α2-AP deficiency blunted OVX-induced trabecular bone loss in mice. Moreover, α2-AP deficiency significantly blunted serum levels of bone-specific alkaline phosphatase, cross-linked C-telopeptide of type I collagen, and interleukin (IL)-1β elevated by OVX. α2-AP treatment elevated the levels of IL-1β and tumor necrosis factor (TNF)-α mRNA in RAW 264.7 cells, although it suppressed osteoclast formation induced by receptor activator of nuclear factor-κB ligand. α2-AP treatment activated ERK1/2 and p38 MAP kinase pathways in RAW 264.7 cells, and these MAP kinase inhibitors antagonized the levels of IL-1β mRNA elevated by α2-AP. The data demonstrate that α2-AP is linked to bone loss due to OVX, through a mechanism that depends in part on the production of IL-1β and TNF-α in monocytes.

Thrombin receptor deficiency leads to a high bone mass phenotype by decreasing the RANKL/OPG ratio

Thrombin and its receptor (TR) are, respectively, expressed in osteoclasts and osteoblasts. However, their physiological roles on bone metabolism have not been fully elucidated. Here we investigated the bone microarchitecture by micro-computed tomography (μCT) and demonstrated increased trabecular and cortical bone mass in femurs of TR KO mice compared to WT littermates. Trabecular thickness and connectivity were significantly enhanced. The physiological role of TR on both inorganic and organic phases of bone is illustrated by a significant increase in BMD and a decrease in urinary deoxypyridinoline (DPD) crosslink concentration in TR KO mice. Moreover, TR KO cortical bone expanded and had a higher polar moment of inertia (J), implying stronger bone. Bone histomorphometry illustrated unaltered osteoblast and osteoclast number and surface in femoral metaphyses, indicating that thrombin/TR regulates osteoblasts and osteoclasts at functional levels. Serum analysis showed a decrease in RANKL and an increase in osteoprotegerin (OPG) levels and reflected a reduced RANKL/OPG ratio in the TR KO group. In vitro experiments using MC3T3 pre-osteoblasts demonstrated a TR-dependent stimulatory effect of thrombin on the RANKL/OPG ratio. This effect was blocked by TR antagonist and p42/p44-ERK inhibitor. In addition, thrombin also intensified p42/p44-ERK expression and phosphorylation. In conclusion, the thrombin/TR system maintains normal bone remodeling by activating RANKL and limiting OPG synthesis by osteoblasts through the p42/44-ERK signaling pathway. Consequently, TR deficiency inhibits osteoclastogenesis, resulting in a high bone mass phenotype.

Fibrin accumulation secondary to loss of plasmin-mediated fibrinolysis drives inflammatory osteoporosis in mice

OBJECTIVE

Osteoporosis is a skeletal disorder characterized by low bone mass and increased bone fragility associated with aging, menopause, smoking, obesity, or diabetes. Persistent inflammation has been identified as an instigating factor in progressive bone loss. In addition to the role of fibrin in coagulation, inordinate fibrin deposition within a tissue matrix results in increased local inflammation. Given that fibrin accumulation is a hallmark of osteoporosis-related comorbidities, we undertook this study to test the hypothesis that persistent fibrin deposition causes inflammatory osteoporosis.

METHODS

Multiple imaging modalities, bone integrity metrics, and histologic analyses were employed to evaluate skeletal derangements in relation to fibrin deposition, circulating fibrinogen levels, and systemic markers of inflammation in mice that were plasminogen deficient and in plasminogen-deficient mice that were concomitantly either fibrinogen deficient or carrying a mutant form of fibrinogen lacking the αM β2 binding motif.

RESULTS

Mice generated with a genetic deficit in the key fibrinolytic protease, plasmin, uniformly developed severe osteoporosis. Furthermore, the development of osteoporosis was fibrin(ogen) dependent, and the derangements in the bone remodeling unit were mechanistically tied to fibrin(ogen)-mediated activation of osteoclasts via activation of the leukocyte integrin receptor αM β2 on monocytes and secondary stimulation of osteoblasts by RANKL. Notably, the genetic elimination of fibrin(ogen) or the expression of a mutant form of fibrinogen retaining clotting function but lacking the αM β2 binding motif prevented the degenerative skeletal phenotypes, resulting in normal local and systemic cytokine levels.

CONCLUSION

Taken together, these data reveal for the first time that fibrin promotes inflammation-driven systemic osteoporosis, which suggests a novel association between hemostasis, inflammation, and bone biology.

Plasminogen plays a crucial role in bone repair

The further development in research of bone regeneration is necessary to meet the clinical demand for bone reconstruction. Plasminogen is a critical factor of the tissue fibrinolytic system, which mediates tissue repair in the skin and liver. However, the role of the fibrinolytic system in bone regeneration remains unknown. Herein, we investigated bone repair and ectopic bone formation using plasminogen-deficient (Plg⁻/⁻) mice. Bone repair of the femur is delayed in Plg⁻/⁻ mice, unlike that in the wild-type (Plg⁺/⁺) mice. The deposition of cartilage matrix and osteoblast formation were both decreased in Plg⁻/⁻ mice. Vessel formation, macrophage accumulation, and the levels of vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β) were decreased at the site of bone damage in Plg⁻/⁻ mice. Conversely, heterotopic ossification was not significantly different between Plg⁺/⁺ and Plg⁻/⁻ mice. Moreover, angiogenesis, macrophage accumulation, and the levels of VEGF and TGF-β were comparable between Plg⁺/⁺ and Plg⁻/⁻ mice in heterotopic ossification. Our data provide novel evidence that plasminogen is essential for bone repair. The present study indicates that plasminogen contributes to angiogenesis related to macrophage accumulation, TGF-β, and VEGF, thereby leading to the enhancement of bone repair.

Urinary plasmin inhibits TRPV5 in nephrotic-range proteinuria

Urinary proteins that leak through the abnormal glomerulus in nephrotic syndrome may affect tubular transport by interacting with membrane transporters on the luminal side of tubular epithelial cells. Patients with nephrotic syndrome can develop nephrocalcinosis, which animal models suggest may develop from impaired transcellular Ca(2+) reabsorption via TRPV5 in the distal convoluted tubule (DCT). In nephrotic-range proteinuria, filtered plasminogen reaches the luminal side of DCT, where it is cleaved into active plasmin by urokinase. In this study, we found that plasmin purified from the urine of patients with nephrotic-range proteinuria inhibits Ca(2+) uptake in TRPV5-expressing human embryonic kidney 293 cells through the activation of protease-activated receptor-1 (PAR-1). Preincubation with a plasmin inhibitor, a PAR-1 antagonist, or a protein kinase C (PKC) inhibitor abolished the effect of plasmin on TRPV5. In addition, ablation of the PKC phosphorylation site S144 rendered TRPV5 resistant to the action of plasmin. Patch-clamp experiments showed that a decreased TRPV5 pore size and a reduced open probability accompany the plasmin-mediated reduction in Ca(2+) uptake. Furthermore, high-resolution nuclear magnetic resonance spectroscopy demonstrated specific interactions between calmodulin and residues 133-154 of the N-terminus of TRPV5 for both wild-type and phosphorylated (S144pS) peptides. In summary, PAR-1 activation by plasmin induces PKC-mediated phosphorylation of TRPV5, thereby altering calmodulin-TRPV5 binding, resulting in decreased channel activity. These results indicate that urinary plasmin could contribute to the downstream effects of proteinuria on the tubulointerstitium by negatively modulating TRPV5.

Targeting bone remodeling by isoflavone and 3,3'-diindolylmethane in the context of prostate cancer bone metastasis

Prostate cancer (PCa) bone metastases have long been believed to be osteoblastic because of bone remodeling leading to the formation of new bone. However, recent studies have shown increased osteolytic activity in the beginning stages of PCa bone metastases, suggesting that targeting both osteolytic and osteoblastic mediators would likely inhibit bone remodeling and PCa bone metastasis. In this study, we found that PCa cells could stimulate differentiation of osteoclasts and osteoblasts through the up-regulation of RANKL, RUNX2 and osteopontin, promoting bone remodeling. Interestingly, we found that formulated isoflavone and 3,3′-diindolylmethane (BR-DIM) were able to inhibit the differentiation of osteoclasts and osteoblasts through the inhibition of cell signal transduction in RANKL, osteoblastic, and PCa cell signaling. Moreover, we found that isoflavone and BR-DIM down-regulated the expression of miR-92a, which is known to be associated with RANKL signaling, EMT and cancer progression. By pathway and network analysis, we also observed the regulatory effects of isoflavone and BR-DIM on multiple signaling pathways such as AR/PSA, NKX3-1/Akt/p27, MITF, etc. Therefore, isoflavone and BR-DIM with their multi-targeted effects could be useful for the prevention of PCa progression, especially by attenuating bone metastasis mechanisms.

Plasminogen deficiency attenuates postnatal erythropoiesis in male C57BL/6 mice through decreased activity of the LH-testosterone axis

Novel roles for the serine protease plasmin have been implicated recently in physiological and pathological processes. However, whether plasmin is involved in erythropoiesis is not known. In the present study, we studied the consequences of plasminogen deficiency on erythropoiesis in plasminogen-deficient (Plg knockout [KO]) mice. Erythroid differentiation was attenuated in male Plg KO mice and resulted in erythroblastic accumulation within the spleen and bone marrow, with increased apoptosis in the former, erythrocytosis, and splenomegaly, whereas similar erythropoietic defect was less prominent in female Plg KO mice. In addition, erythrocyte lifespan was shorter in both male and female Plg KO mice. Erythropoietin levels were compensatory increased in both male and female Plg KO mice, and resulted in a higher frequency of burst-forming units-erythroid within the spleen and bone marrow. Surprisingly, we found that male Plg KO mice, but not their female counterparts, exhibited normochromic normocytic anemia. The observed sex-linked erythropoietic defect was attributed to decreased serum testosterone levels in Plg KO mice as a consequence of impaired secretion of the pituitary luteinizing hormone (LH) under steady-state condition. Surgical castration causing testosterone deficiency and stimulating LH release attenuated erythroid differentiation and induced anemia in wild-type animals, but did not further decrease the hematocrit levels in Plg KO mice. In addition, complementation of LH using human choriogonadotropin, which increases testosterone production, improved the erythropoietic defect and anemia in Plg KO mice. The present results identify a novel role for plasmin in the hormonal regulation of postnatal erythropoiesis by the LH-testosterone axis.