Thrombomodulin is synthesized by osteoblasts, stimulated by 1,25-(OH)2D3 and activates protein C at their cell membrane

Chondrocyte Thrombomodulin Protects against Osteoarthritis

Osteoarthritis (OA) is a prevalent form of arthritis that affects over 32.5 million adults worldwide, causing significant cartilage damage and disability. Unfortunately, there are currently no effective treatments for OA, highlighting the need for novel therapeutic approaches. Thrombomodulin (TM), a glycoprotein expressed by chondrocytes and other cell types, has an unknown role in OA. Here, we investigated the function of TM in chondrocytes and OA using various methods, including recombinant TM (rTM), transgenic mice lacking the TM lectin-like domain (TM^LeD/LeD), and a microRNA (miRNA) antagomir that increased TM expression. Results showed that chondrocyte-expressed TM and soluble TM [sTM, like recombinant TM domain 1 to 3 (rTMD123)] enhanced cell growth and migration, blocked interleukin-1β (IL-1β)-mediated signaling and protected against knee function and bone integrity loss in an anterior cruciate ligament transection (ACLT)-induced mouse model of OA. Conversely, TM^LeD/LeD mice exhibited accelerated knee function loss, while treatment with rTMD123 protected against cartilage loss even one-week post-surgery. The administration of an miRNA antagomir (miR-up-TM) also increased TM expression and protected against cartilage damage in the OA model. These findings suggested that chondrocyte TM plays a crucial role in counteracting OA, and miR-up-TM may represent a promising therapeutic approach to protect against cartilage-related disorders.

Influence of Vitamin D Status on the Maintenance Dose of Warfarin in Patients Receiving Chronic Warfarin Therapy

INTRODUCTION

Considering the anticoagulant actions of vitamin D, we hypothesize that vitamin D status might affect the required dose of warfarin for maintaining the therapeutic international normalized ratio (INR).

METHODS

In a retrospective single-center cohort study, serum levels of 25-hydroxyvitamin D were assessed for 89 subjects receiving a stable dose of warfarin for 3 months or longer and had a stable INR between 2 and 3.5 for at least three consecutive visits. A warfarin sensitivity index (WSI), defined as the steady-state INR divided by the mean daily warfarin dose, was used for measuring the warfarin dose response. The relation between the serum level of 25-hydroxyvitamin D and WSI value and the difference in the mean WSI value between the subjects with different vitamin D status categories (sufficient, insufficient, and deficient) were assessed.

RESULTS

Twenty-one subjects had vitamin D deficiency, 43 had vitamin D insufficiency, and only 25 had normal levels of 25-hydroxyvitamin D. Based on the multiple linear regression analysis, there was a significant but weakly positive correlation between WSI and 25-hydroxyvitamin D serum levels, as the value of WSI increases by almost 0.0027434 for every unit increase in 25-hydroxyvitamin D serum level (p value = 0.041). Using one-way ANOVA analysis, there was a trend in a significant difference between the groups with different vitamin D status categories regarding the mean WSI value (F = 2.95, p value = 0.057), as subjects with sufficient vitamin D state compared to those with vitamin D deficiency had a higher WSI value.

CONCLUSIONS

Although the study's limitations limit our ability to draw definite conclusions, the present data suggest that in addition to other traditional factors, vitamin D status might also affect warfarin sensitivity and maintenance dose requirement. However, to more clearly explain this link, further studies with high involvement subjects are required.

Thrombomodulin Functional Domains Support Osteoblast Differentiation and Bone Healing in Diabetes in Mice

Thrombomodulin (TM) is a transmembrane glycoprotein that contains five functional domains. Soluble TM (sTM), comprising extracellular domains TMD1 (lectin-like), TMD2 (epidermal growth factor [EGF]-like repeat containing), and TMD3 (serine-threonine rich), can be shed from cells by the intramembrane protease rhomboid-like-2 (RHBDL2). TM is expressed by osteoblasts, yet its role there has not been determined. Herein we aimed to investigate the properties of TM and its domains in osteoblast function and bone repair following injury in diabetes. In response to a scratch injury of cultured osteoblast-like MG63 cells, expression of TM and RHBDL2 was enhanced, with increased release of sTM. Conditioned media from the injured cells promoted osteoblast migration, an effect that was lacking with conditioned media from MG63 cells in which TM was silenced by shRNA. Exogenous recombinant TMD1 had no effect on osteoblast activities or on bone repair in vivo. However, TM domains 2 and 3 (TMD2/3), induced MG63 cell migration, proliferation and mineralization in vitro, and when locally administered in mice, improved in vivo healing of injured calvarium. This beneficial effect of TMD2/3, mediated via fibroblast growth factor receptor (FGFR)/ERK signaling pathways, was also observed in vitro under high glucose conditions where endogenous TM expression was reduced, and in vivo in diabetic mice following tibia fracture or calvarium injury, where the osteoblastic response and healing were otherwise dampened. Taken together, osteoblast TM participates in bone healing, and recombinant TMD2/3 holds promise as a novel therapy for diabetic bone defect healing. © 2020 American Society for Bone and Mineral Research.

Protective Effects of Recombinant Human Soluble Thrombomodulin on Lipopolysaccharide-Induced Acute Kidney Injury

Thrombomodulin (TM) is a single transmembrane, multidomain glycoprotein receptor for thrombin, and is best known for its role as a cofactor in a clinically important natural anticoagulant pathway. In addition to its anticoagulant function, TM has well-defined anti-inflammatory properties. Soluble TM levels increase significantly in the plasma of septic patients; however, the possible involvement of recombinant human soluble TM (rTM) transduction in the pathogenesis of lipopolysaccharide (LPS)-induced nephrotoxicity, including acute kidney injury (AKI), has remained unclear. Mice were injected intraperitoneally with 15 mg/kg LPS. rTM (3 mg/kg) or saline was administered to the animals before the 3 and 24 h LPS-injection. At 24 and 48 h, blood urea nitrogen, the inflammatory cytokines in sera and kidney, and histological findings were assessed. Cell activation and apoptosis signal was assessed by Western blot analysis. In this study using a mouse model of LPS-induced AKI, we found that rTM attenuated renal damage by reducing both cytokine and cell activation and apoptosis signals with the accumulation of CD4+ T-cells, CD11c+ cells, and F4/80+ cells via phospho c-Jun activations and Bax expression. These findings suggest that the mechanism underlying these effects of TM may be mediated by a reduction in inflammatory cytokine production in response to LPS. These molecules might thereby provide a new therapeutic strategy in the context of AKI with sepsis.

Plasminogen/thrombomodulin signaling enhances VEGF expression to promote cutaneous wound healing

Plasminogen (Plg) and thrombomodulin (TM) are glycoproteins well known for fibrinolytic and anticoagulant functions, respectively. Both Plg and TM are essential for wound healing. However, their significance during the reparative process was separately demonstrated in previous studies. Here, we investigate the interaction between Plg and epithelial TM and its effect on wound healing. Characterization of the wound margin revealed that Plg and TM were simultaneously upregulated at the early stage of wound healing and the two molecules were bound together. In vitro, TM silencing or knockout in keratinocytes inhibited Plg activation. Plg treatment enhanced keratinocyte proliferation and migration, and these actions were abolished by TM antibody. Keratinocyte-expressed vascular endothelial growth factor (VEGF), which presented a dose-response relationship with Plg treatment, can be suppressed by TM silencing. Moreover, treatment with VEGF antibody inhibited Plg-enhanced keratinocyte proliferation and wound recovery. In vivo, TM antibody treatment and keratinocyte-specific TM knockout can impede Plg-enhanced wound healing in mice. In high-glucose environments, Plg-enhanced VEGF expression and wound healing were suppressed due at least in part to downregulation of keratinocyte-expressed TM. Taken together, our findings suggest that activation of Plg/TM signaling may hold therapeutic potential for chronic wounds in diabetic or non-diabetic individuals. KEY MESSAGES: Plg binds to TM in cutaneous wound healing. TM facilitates the activation of Plg to Plm in keratinocytes. Epithelial TM regulates Plg-enhanced wound healing through VEGF expression.

The Effect of High-Dose Vitamin D3 on Soluble P-Selectin and hs-CRP Level in Patients With Venous Thromboembolism

High plasma level of P-selectin is associated with the development of venous thromboembolism (VTE). Furthermore, supplementation of vitamin D could decrease thrombotic events. Hence, this study was designed to examine whether the administration of vitamin D can influence the plasma level of P-selectin in patients with VTE. In the randomized controlled trial, 60 patients with confirmed acute deep vein thrombosis and/or pulmonary embolism (PE) were randomized into the intervention (n = 20) and control (n = 40) groups. The intervention arm was given an intramuscular single dose of 300 000 IU vitamin D3. Plasma level of 25-hydroxy vitamin D, P-selectin, and high-sensitive C-reactive protein (hs-CRP) was measured at baseline and 4 weeks after. The plasma level of P-selectin (95% confidence interval = −5.99 to −1.63, P = .022) and hs-CRP ( P = .024) significantly declined in vitamin D-treated group, while only hs-CRP was significantly decreased in the control group ( P = .011). However, the magnitude of these reductions was not statistically significant. This study could not support the potential benefit of the high-dose vitamin D on plasma level of P-selectin and hs-CRP in patients with VTE.

Is There Any Association Between Thrombosis and Tissue Factor Pathway Inhibitor Levels in Patients With Vitamin D Deficiency?

Objective:

The aim of this study was to evaluate the relationship between vitamin D levels and hemostatic factors like tissue factor pathway inhibitor (TFPI).

Methods:

Patients who had 25-hydroxyvitamin D3 (25(OH)D3) levels measured were included. Coagulation and hemostatic parameters were evaluated. Patients were divided into 3 groups based on 25(OH)D3 levels as group 1 (25(OH)D3 < 10 ng/mL, n = 25), group 2 (25(OH)D3 = 10-19.9 ng/mL, n = 22), and group 3 (25(OH)D3 ≥ 20 ng/mL, n = 28).

Results:

A total of 75 patients with a mean age of 39 (range 18-57) years were included in the study. Prothrombin time was longer in group 3 than in group 2 ( P = .043). The TFPI levels were higher in group 3 than in the other groups ( P < .001). There was a strong positive correlation between 25(OH)D3 and TFPI levels ( r = .47, P < .001).

Conclusion:

Further studies are needed for evaluation of the role of TFPI in hemostasis and thrombotic process in patients with vitamin D deficiency.

Recombinant thrombomodulin of different domains for pharmaceutical, biomedical, and cell transplantation applications

Thrombomodulin (TM) is a membrane glycoprotein mainly expressed by vascular endothelial cells and is involved in many physiological and pathological processes, such as coagulation, inflammation, cancer development, and embryogenesis. Human TM consists of 557 amino acids divided into five distinct domains: N-terminal lectin-like domain (designated as TMD1); six epidermal growth factor (EGF)-like domain (TMD2); Ser/Thr-rich domain (TMD3); transmembrane domain (TMD4); and cytoplasmic tail domain (TMD5). The different domains are responsible for different biological functions of TM. In the past decades, various domains of TM have been cloned and expressed for TM structural and functional study. Further, recombinant TMs of different domains show promising antithrombotic and anti-inflammatory activity in both rodents and primates and a recombinant soluble TM has been approved for therapeutic application. This review highlights recombinant TMs of diverse structures and their biological functions, as well as the complex interactions of TM with factors involved in the related biological processes. Particularly, recent advances in exploring recombinant TM of different domains for pharmaceutical, biomedical, and cell transplantation applications are summarized.

Thrombomodulin and the vascular endothelium: insights into functional, regulatory, and therapeutic aspects

Thrombomodulin (TM) is a 557-amino acid protein with a broad cell and tissue distribution consistent with its wide-ranging physiological roles. When expressed on the lumenal surface of vascular endothelial cells in both large vessels and capillaries, its primary function is to mediate endothelial thromboresistance. The complete integral membrane-bound protein form displays five distinct functional domains, although shorter soluble (functional) variants comprising the extracellular domains have also been reported in fluids such as serum and urine. TM-mediated binding of thrombin is known to enhance the specificity of the latter serine protease toward both protein C and thrombin activatable fibrinolysis inhibitor (TAFI), increasing their proteolytic activation rate by almost three orders of magnitude with concomitant anticoagulant, antifibrinolytic, and anti-inflammatory benefits to the vascular wall. Recent years have seen an abundance of research into the cellular mechanisms governing endothelial TM production, processing, and regulation (including flow-mediated mechanoregulation)--from transcriptional and posttranscriptional (miRNA) regulation of TM gene expression, to posttranslational processing and release of the expressed protein--facilitating greater exploitation of its therapeutic potential. The goal of the present paper is to comprehensively review the endothelial/TM system from these regulatory perspectives and draw some fresh conclusions. This paper will conclude with a timely examination of the current status of TM's growing therapeutic appeal, from novel strategies to improve the clinical efficacy of recombinant TM analogs for resolution of vascular disorders such as disseminated intravascular coagulation (DIC), to an examination of the complex pleiotropic relationship between statin treatment and TM expression.

Thrombomodulin and its role in inflammation

The goal is to provide an extensive review of the physiologic role of thrombomodulin (TM) in maintaining vascular homeostasis, with a focus on its anti-inflammatory properties. Data were collected from published research. TM is a transmembrane glycoprotein expressed on the surface of all vascular endothelial cells. Expression of TM is tightly regulated to maintain homeostasis and to ensure a rapid and localized hemostatic and inflammatory response to injury. By virtue of its strategic location, its multidomain structure and complex interactions with thrombin, protein C (PC), thrombin activatable fibrinolysis inhibitor (TAFI), complement components, the Lewis Y antigen, and the cytokine HMGB1, TM exhibits a range of physiologically important anti-inflammatory, anti-coagulant, and anti-fibrinolytic properties. TM is an essential cofactor that impacts on multiple biologic processes. Alterations in expression of TM and its partner proteins may be manifest by inflammatory and thrombotic disorders. Administration of soluble forms of TM holds promise as effective therapies for inflammatory diseases, and infections and malignancies that are complicated by disseminated intravascular coagulation.

Activated protein C stimulates osteoblast proliferation via endothelial protein C receptor

INTRODUCTION

Bone is continually remodeled by the action of osteoblasts, osteocytes, and osteoclasts. Resting osteoblasts are able to proliferate and differentiate into mature osteoblasts when physiologically required, as after tissue injury. Activated protein C (APC) is a serine protease that functions in anticoagulation, anti-inflammation, anti-apoptosis, cell proliferation, and wound repair. In this study, we examined the effect of APC on osteoblast proliferation and differentiation.

MATERIALS AND METHODS

We examined the presence of protein C in human fracture hematoma by immunohistochemical staining. We then evaluated the effect of APC, diisopropyl fluorophosphate-inactivated APC (DIP-APC) or protein C zymogen on normal human osteoblast (NHOst) proliferation using tetrazolium salt assay in the presence or absence of aprotinin, hirudin, protein C, antibody against protein C, endothelial protein C receptor (EPCR) or protease-activated receptor (PAR)-1. Finally, activation of p44/42 MAP kinase was evaluated by Western blot analysis.

RESULTS

Both APC and DIP-APC increased osteoblast proliferation in a dose-dependent manner, while protein C did not. The APC-induced increased proliferation of osteoblast was not affected by aprotinin, hirudin, and anti-protein C antibody which inhibits the protease activity of APC. Treatment with protein C or anti-EPCR antibody which inhibits APC binding to EPCR inhibited APC-mediated osteoblast proliferation, while treatment with anti-PAR-1 antibody did not. APC promoted the phosphorylation of p44/42 MAP kinase within osteoblasts; this effect was inhibited by the anti-EPCR antibody.

CONCLUSIONS

APC stimulates osteoblast proliferation by activating p44/42 MAP kinase through a mechanism that requires EPCR but not PAR-1 or the proteolytic activity of APC. APC generated at fracture sites may contribute to fracture healing by promoting osteoblast proliferation.

Coordinated activation of notch, Wnt, and transforming growth factor-beta signaling pathways in bone morphogenic protein 2-induced osteogenesis. Notch target gene Hey1 inhibits mineralization and Runx2 transcriptional activity

To examine early events in osteoblast differentiation, we analyzed the expression of about 9,400 genes in the murine MC3T3 cell line, whose robust differentiation was documented cytochemically and molecularly. The cells were stimulated for 1 and 3 days with the osteogenic stimulus containing bone morphogenic protein 2. Total RNA was extracted and analyzed by Affymetrix GeneChip oligonucleotide arrays. A regulated expression of 394 known genes and 295 expressed sequence tags was detected. The sensitivity and reliability of detection by microarrays was shown by confirming the expression pattern for 20 genes by radioactive quantitative reverse transcription-PCR. Functional classification of regulated genes was performed, defining the groups of regulated growth factors, receptors, and transcription factors. The most interesting finding was concomitant activation of transforming growth factor-beta, Wnt, and Notch signaling pathways, confirmed by strong up-regulation of their target genes by PCR. The transforming growth factor-beta pathway is activated by stimulated production of the growth factor itself, while the exact mechanism of Wnt and Notch activation remains elusive. We showed that bone morphogenic protein 2 stimulated expression of Hey1, a direct Notch target gene, in mouse MC3T3 and C2C12 cells, in human mesenchymal cells, and in mouse calvaria. Small interfering RNA-mediated inhibition of Hey1 induction led to an increase in osteoblast matrix mineralization, suggesting that Hey1 is a negative regulator of osteoblast maturation. This negative regulation is apparently achieved via interaction with Runx2: Hey1 completely abrogated Runx2 transcriptional activity. These findings identify the Notch-Hey1 pathway as a negative regulator of osteoblast differentiation/maturation, which is a completely novel aspect of osteogenesis and could point to possible new targets for bone anabolic agents.

Thrombomodulin: an overview and potential implications in vascular disorders

Thrombomodulin (TM), a high affinity thrombin receptor present on endothelial cell membrane, plays an important role as a natural anticoagulant. It acts as a cofactor of thrombin-catalyzed activation of protein C, and inhibits the procoagulant functions of thrombin. TM is also located in other cells (keratinocytes, osteoblasts, macrophages,...) where it might be involved in cell differentiation or in inflammation. In the presence of cytokines, activated neutrophils and macrophages, endothelial TM is cleaved enzymatically, releasing soluble fragments which circulate in the blood and are eliminated in urine. Plasma TM level (pTM) can be measured using a two-site enzyme-linked immunosorbent assay (ELISA). pTM level is regarded as a molecular marker reflecting injury of endothelial cells. It is often increased in case of diffuse endothelial damage as in disseminated intravascular coagulation, diabetic microangiopathy, Plasmodium falciparum and rickettsial infections. pTM is also a predictive marker of hypertensive complications in pregnancy. In several systemic inflammatory diseases, pTM levels are correlated to the activity of the disease.

Anticoagulant Effects of 1α,25-Dihydroxyvitamin D3 on Human Myelogenous Leukemia Cells and Monocytes

The hormonally active form of vitamin D is 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], which is a principal regulator of calcium homeostasis. It also affects hormone secretion, cell differentiation, and proliferation by a mode of action that involves stereospecific interaction with an intracellular vitamin D receptor (VDR). We recently found that retinoids, which are vitamin A derivatives, exert anticoagulant effects by upregulating thrombomodulin (TM) and downregulating tissue factor (TF) expression in acute promyelocytic leukemia cells and monoblastic leukemia cells. Both the VDR and retinoid receptors belong to the same family of receptors. A heterodimer consisting of the retinoid X receptor and the VDR binds to vitamin D responsive elements on genes regulated by vitamin D. To determine whether 1,25(OH)2D3 would exhibit anticoagulant effects similar to retinoids, we measured the antigen level, activity, and mRNA level of TM and TF in human leukemic cells, vascular endothelial cells, and monocytes treated with 1,25(OH)2D3. We found that 1,25(OH)2D3 upregulates antigen expression, activity, and mRNA levels of TM and downregulates antigen expression, activity, and mRNA levels of TF in human monocytic leukemia cells, some acute myelogenous leukemia cells, and monocytes, but not in umbilical vein endothelial cells. Transient transfection studies with reporter plasmids in monocytic leukemia cells and mobility gel-shift assay showed interaction with 1,25(OH)2D3 and functional retinoic acid responsive elements present in the 5′-flanking region of the TM gene. However, auxiliary factors or other elements in the TM gene may contribute to VDR specificity and transactivation of the gene in specific target cells. These findings indicate that 1,25(OH)2D3 resembles the retinoids in its control of the transcription of the TM and TF genes in human monocytic cells. Analogs of 1,25(OH)2D3with anticoagulant activity may serve as adjunctive antithrombotic agents in monocytic leukemia and atherosclerotic disease.

Protein C inhibitor is a potent inhibitor of the thrombin-thrombomodulin complex

Protein C inhibitor (PCI), a plasma serine protease inhibitor, inhibits several proteases including the anticoagulant enzyme, activated protein C (APC), and the coagulation enzymes, thrombin and factor Xa. Previous studies have shown that thrombin and APC are inhibited at similar rates by PCI and that heparin accelerates PCI inhibition of both enzymes more than 20-fold. We now demonstrate that the thrombin-binding proteoglycan, rabbit thrombomodulin, accelerates inhibition of thrombin by PCI approximately equal to 140-fold (k2 = 2.4 x 10(6) in the presence of TM compared to 1.7 x 10(4) M-1 S-1 in the absence of TM). Most of this effect is mediated by protein-protein interactions since the active fragment of TM composed of epidermal growth factor-like domains 4-6 (TM 4-6) accelerates inhibition by PCI approximately equal to 59-fold (k2 = 1.0 x 10(6) M-1 S-1). The mechanism by which TM alters reactivity with PCI appears to reside in part in an alteration of the S2 specificity pocket. Replacing Phe353 with Pro at the P2 position in the reactive loop of PCI yields a mutant that inhibits thrombin better in the absence of TM (k2 = 6.3 x 10(5) M-1 S-1), but TM 4-6 enhances inhibition by this mutant approximately equal to 9-fold (k2 = 5.8 x 10(6) M-1 S-1) indicating that TM alleviates the inhibitory effect of the less favored Phe residue. These results indicate that PCI is a potent inhibitor of the protein C anticoagulant pathway at the levels of both zymogen activation and enzyme inhibition.