Membrane-Bound Thrombomodulin Regulates Macrophage Inflammation in Abdominal Aortic Aneurysm.

OBJECTIVE: Thrombomodulin (TM), a glycoprotein constitutively expressed in the endothelium, is well known for its anticoagulant and anti-inflammatory properties. Paradoxically, we recently found that monocytic membrane-bound TM (ie, endogenous TM expression in monocytes) triggers lipopolysaccharide- and gram-negative bacteria-induced inflammatory responses. However, the significance of membrane-bound TM in chronic sterile vascular inflammation and the development of abdominal aortic aneurysm (AAA) remains undetermined. APPROACH AND RESULTS: Implicating a potential role for membrane-bound TM in AAA, we found that TM signals were predominantly localized to macrophages and vascular smooth muscle cells in human aneurysm specimens. Characterization of the CaCl2-induced AAA in mice revealed that during aneurysm development, TM expression was mainly localized in infiltrating macrophages and vascular smooth muscle cells. To investigate the function of membrane-bound TM in vivo, transgenic mice with myeloid- (LysMcre/TM(flox/flox)) and vascular smooth muscle cell-specific (SM22-cre(tg)/TM(flox/flox)) TM ablation and their respective wild-type controls (TM(flox/flox) and SM22-cre(tg)/TM(+/+)) were generated. In the mouse CaCl2-induced AAA model, deficiency of myeloid TM, but not vascular smooth muscle cell TM, inhibited macrophage accumulation, attenuated proinflammatory cytokine and matrix metalloproteinase-9 production, and finally mitigated elastin destruction and aortic dilatation. In vitro TM-deficient monocytes/macrophages, versus TM wild-type counterparts, exhibited attenuation of proinflammatory mediator expression, adhesion to endothelial cells, and generation of reactive oxygen species. Consistently, myeloid TM-deficient hyperlipidemic mice (ApoE(-/-)/LysMcre/TM(flox/flox)) were resistant to AAA formation induced by angiotensin II infusion, along with reduced macrophage infiltration, suppressed matrix metalloproteinase activities, and diminished oxidative stress. CONCLUSIONS: Membrane-bound TM in macrophages plays an essential role in the development of AAA by enhancing proinflammatory mediator elaboration, macrophage recruitment, and oxidative stress.

Tumor endothelial marker 1 is upregulated in heart after cardiac injury and participates in cardiac remodeling.

Tumor endothelial marker 1 (TEM1) is a transmembrane glycoprotein that appears on mesenchymal lineage-derived cells during embryogenesis, but its expression greatly reduces after birth. Re-upregulation of TEM1 is found in tumor angiogenesis, organ fibrosis and wound healing indicating its potential role in tissue remodeling and repair. The expression level and function of TEM1 in adult heart are unknown. In explanted hearts from heart failure (HF) patients received cardiac transplantation, immunofluorescence staining showed TEM1 was expressed in cardiomyocytes (CMs) and cardiac fibroblasts. Bioinformatics analysis showed TEM1 upregulation in mouse heart after coronary ligation. Cardiac TEM1 expression was reconfirmed in mouse HF induced by coronary ligation or doxorubicin injection. TEM1 expression increased in cultured CMs stimulated with mechanical stretch, doxorubicin and hypoxia. Further studies showed recombinant TEM1 (rTEM1) was a functional protein that influenced cell behaviors of CMs. It directly activated Erk and Akt through interaction with PDGF receptor. TEM1lacZ/lacZ mice had less collagen deposition and worse cardiac function than wild type mice. These results indicate that TEM1 expression increases in the heart after cardiac injury and works as a functional protein that participates in cardiac remodeling.

Thrombomodulin is upregulated in cardiomyocytes during cardiac hypertrophy and prevents the progression of contractile dysfunction.

BACKGROUND: Cardiac hypertrophy is a common response to pressure overload and leads to left ventricular (LV) dysfunction. Thrombomodulin (TM), an endothelial anticoagulant protein, was found to have direct effects on cellular proliferation and inflammation. We examined the TM expression in cardiomyocytes during cardiac hypertrophy and investigated its physiological significance. METHODS AND RESULTS: TM expression was evaluated in cardiomyocytes from hearts of mice that underwent transverse aortic constriction (TAC). The effects of recombinant TM protein on cardiomyocytes apoptosis and related signaling pathways were examined. Recombinant TM protein was administered continuously in mice that underwent TAC, and serial LV function was determined. There was significant TM expression in cardiomyocytes during cardiac hypertrophy elicited by TAC in mice. TM treatment decreased doxorubicin-induced apoptosis of cardiomyocytes and increased the Bcl-2/Bax ratio. It also increased cardiomyocytes hypertrophy, expression of atrial natriuretic peptide, and significantly activated the extracellular signal-regulated kinase 1/2 (ERK1/2) and the phosphatidylinositol-3-kinase (PI3-K)/protein kinase B (Akt) signaling pathways in cardiomyocytes. Continuous TM supply after TAC prevented the progression of LV contractile dysfunction in mice. CONCLUSIONS: TM treatment decreased cardiomyocyte apoptosis and maintained LV contractile function in response to pressure overload.

The role of vascular smooth muscle cell membrane-bound thrombomodulin in neointima formation.

BACKGROUND AND AIMS: Thrombomodulin (TM) is an endothelial cell membrane-bound anticoagulant protein expressed in normal arteries. After vascular injury, medial and neointimal smooth muscle cells (SMCs) exhibit large amounts of TM. The purpose of this study was to investigate the physiological significance of vascular SMC-bound TM. METHODS: The morphology, expression of phenotype markers and cell behaviors of cultured aortic SMCs after knockdown of TM were observed. Transgenic mice with SMC-specific TM deletion were generated, and carotid neointima formation was induced by carotid ligation. RESULTS: Cultured human aortic SMCs displayed a synthetic phenotype with a rhomboid-shaped morphology and expressed TM. TM knockdown induced a spindle-shaped change in morphology with an increased expression of contractile phenotype marker and decreased expression of synthetic phenotype marker. TM knockdown not only attenuated the proliferation of SMCs but also reduced tumor necrosis factor-α-induced nuclear factor-κB activation and interlukin-6 production. In a carotid artery ligation model, transgenic mice with SMC-specific TM deletion (SM22-cretg/TMflox/flox) had significantly less cellular proliferation in arterial walls compared with wild type mice (SM22-cretg/TM+/+). The neointima area and neointima/media area ratio were smaller in SM22-cretg/TMflox/flox mice at 4 weeks after ligation. CONCLUSIONS: Our results indicate that vascular SMC-bound TM plays a role in changes of the SMC phenotype. It also influences SMC cell behavior and injury-induced neointima formation.

Recombinant Thrombomodulin Exerts Anti-autophagic Action in Endothelial Cells and Provides Anti-atherosclerosis Effect in Apolipoprotein E Deficient Mice.

Stress-induced alteration in endothelial cells (ECs) integrity precedes the development of atherosclerosis. Previous studies showed that the soluble recombinant thrombomodulin (rTM) not only increases ECs proliferation but also exerts anti-apoptotic activity in ECs. However, the functional significance of soluble rTM on autophagy-related apoptosis in ECs is still undetermined. Implicating a cytoprotective role for rTM in persistent serum starvation (SS)-induced autophagy in cultured ECs, we found that treatment of rTM decreased the expression of SS-induced autophagy-related proteins, ATG5 and LC3, and the formation of autophagosomes through activation of AKT/mTOR pathway. In addition, treatment of rTM decreased SS-induced EC apoptosis, but this effect of rTM could not be recapitulated by co-treatment with a potent autophagy inducer, rapamycin and in ECs with ATG5 knockdown. In human atherosclerosis specimens, expression of autophagy markers, ATG13 and LC3, were more abundant in aortic intimal ECs with severe atherosclerosis than those without atherosclerosis. Moreover, compared to saline treatment group, administration of rTM reduced LC3 and ATG13 expression, intimal EC apoptosis, and atherosclerotic lesion severity in the aorta of apolipoprotein E deficient mice. In conclusion, treatment with rTM suppressed stress-induced autophagy overactivation in ECs, provided ECs protective effects, and decreased atherosclerosis in apolipoprotein E deficient mice.

Tracheoinnominate artery fistula caused by migration of a Kirschner wire.

Iatrogenic injury is an underreported but potentially devastating complication of orthopedic wire migration. We report a 48-year-old man with a tracheoinnominate artery fistula caused by migration of a Kirschner wire that was inserted for fixation of a left clavicle fracture nine years before. Following surgical removal of the wire and repair of both trachea and innominate artery, the patient recovered eventually. Although migration of orthopedic wire to the trachea has been reported twice in previous literature, such a complication involving both the trachea and arch vessel was not previously described. Physicians who care for patients with orthopedic wires in place should be aware of migration with tracheoinnominate artery fistula and other iatrogenic injuries as potentially lethal complications.