Release of leukotriene B4, transforming growth factor-beta1 and microparticles in relation to aortic valve calcification.

BACKGROUND AND AIM OF THE STUDY: Aortic stenosis, the most frequent valvulopathy in the Western world, is characterized by an important extracellular matrix (ECM) remodeling and a process of calcification in the aortic valves. One physiopathological assumption is that transforming growth factor-beta1 (TGF-beta1) acts through ECM remodeling and plays a role in calcification, implicating also microparticles (MPs). Another recent notion is the active involvement of inflammatory mediators in the calcification process of aortic stenosis. METHODS: A total of 105 aortic valves was collected from patients suffering from calcified aortic stenosis with either tricuspid valve (AS) or bicuspid aortic valve (BAV), rheumatic aortic stenosis (RA), endocarditis, or aortic regurgitation (AR). Each valve was incubated for 24 h in culture medium and the supernatants (conditioned media) were used to measure the concentrations of leukotriene B4 (LTB4) and TGF-beta1 and to quantify the number of MPs released. Valvular calcification was evaluated using biphotonic absorptiometry. RESULTS: LTB4 concentrations were significantly higher in media conditioned by AS valves compared to those conditioned by RA and endocarditis valves. In addition, LTB4 concentrations correlated significantly with the calcium content of the aortic valves. In contrast, the concentrations of TGF-beta1 and MPs in the conditioned media did not differ significantly between the various groups of valves, and there was no significant correlation between calcification and either TGF-beta1 or the number of MPs released from the aortic valves. CONCLUSION: Taken together, these results indicate that inflammatory signaling through LTB4 may be more closely linked to calcification and aortic stenosis than signaling through TGF-beta1 and MPs.

The human cytomegalovirus-encoded chemokine receptor US28 induces caspase-dependent apoptosis.

Viral subversion of apoptosis regulation plays an important role in the outcome of host/virus interactions. Although human cytomegalovirus (HCMV) encodes several immediate early (IE) antiapoptotic proteins (IE1, IE2, vMIA and vICA), no proapoptotic HCMV protein has yet been identified. Here we show that US28, a functional IE HCMV-encoded chemokine receptor, which may be involved in both viral dissemination and immune evasion, constitutively induces apoptosis in several cell types. In contrast, none of nine human cellular chemokine receptors, belonging to three different subfamilies, induced any significant level of apoptosis. US28-induced cell death involves caspase 10 and caspase 8 activation, but does not depend on the engagement of cell-surface death receptors of the tumour necrosis factor receptor/CD95 family. US28 cell-death induction is prevented by coexpression of C-FLIP, a protein that inhibits Fas-associated death domain protein (FADD)-mediated activation of caspase 10 and caspase 8, and by coexpression of the HCMV antiapoptotic protein IE1. The use of US28 mutants indicated that the DRY sequence of its third transmenbrane domain, required for constitutive G-protein signalling, and the US28 intracellular terminal domain required for constitutive US28 endocytosis, are each partially required for cell-death induction. Thus, in HCMV-infected cells, US28 may function either as a chemokine receptor, a phospholipase C activator, or a proapoptotic factor, depending on expression levels of HCMV and/or cellular antiapoptotic proteins.

CD95 ligand-dependant endothelial cell death initiates oral mucosa damage in a murine model of acute graft versus host disease.

Oral mucosa lesions are one of the common pathological consequences of acute graft versus host disease (aGVHD), the major complication of allogeneic bone marrow transplantation caused by mature T lymphocytes of donor origin. Oral mucosa damage in aGVHD is characterized by apoptosis induction in the basal keratinocytes, associated with immune effector T-cell infiltration, but its pathogenesis remains unclear because these lesions might result from the patient conditioning therapy that includes radiation and/or chemotherapy. Here, using a murine model of aGVHD that does not involve any conditioning treatment, we show that the earliest detectable oral mucosa lesion is apoptosis of the endothelial cells from chorion capillaries, which precedes basal keratinocyte apoptosis induction. Neither vascular damage nor epithelial-cell death occurred in recipients of allogeneic lymphocytes from CD95 ligand (CD95L)-defective mice. Our findings indicate that oral mucosa lesions in aGVHD are initiated by endothelial-cell death and require CD95L expression by the allogeneic lymphocytes. This early vascular damage may contribute to the induction of further tissue damage in the oral mucosa, through the induction of hypoxia and vascular leakage of immune cells or soluble proapoptotic mediators.