Matrix metalloproteinase 9 is involved in Crohn's disease-associated platelet hyperactivation through the release of soluble CD40 ligand.

BACKGROUND: Patients with Crohn's disease have an increased risk for systemic thromboembolism. Their platelets are hyperactive and possess an elevated endogenous content of CD40 ligand (CD40L), a tumour necrosis factor alpha family protein member. Under basal conditions and after stimulation, these platelets express more CD40L on their surface and release higher amounts of soluble (s)CD40L than control platelets, through a mechanism that might be mediated by matrix metalloproteinases (MMPs).
OBJECTIVE: The aim of this work is to study whether enhanced sCD40L release secondary to changes in the platelet content of MMPs contributes to the higher state of activation of platelets from patients with Crohn's disease.
METHODS: State of activation, CD40L and metalloproteinases content of platelets isolated from patients with Crohn's disease and age- and sex-matched control individuals were analysed, respectively, by flow cytometry, western blot and gelatin zymography.
RESULTS: The hyperactive state of platelets from patients with Crohn's disease might rely on their enhanced release of sCD40L, since its inhibition by a broad-range inhibitor of MMPs (GM6001) reduced fibrinogen binding induced by platelet stimulation. Analysis of the content of MMPs in platelets from patients with Crohn's disease showed an exclusive increase in MMP-9 activity. Moreover, MMP-9 inhibition diminished sCD40L release and fibrinogen binding to activated platelets.
CONCLUSIONS: The results suggest that platelets from patients with Crohn's disease release more sCD40L than controls as a consequence of their higher endogenous content of CD40L and of MMP-9, which is involved in CD40L shedding. The increased levels of released sCD40L might be responsible, at least in part, for the high state of activation of platelets from patients with Crohn's disease.