Significance of Platelet Activation on Arterial Stiffness in Normal and Hypoxic Environments

Abstract

Introduction: Arterial stiffness (AS) is associated with various cardiovascular diseases. Different risk factors such as age, arterial hypertension and tobacco smoking contribute to the progress of arterial stiffening causing disturbance of blood perfusion. Platelets are small anucleate cell fragments from megakaryocytes which derive from the bone marrow. They are known to play a major role in primary hemostasis and inflammatory processes within the vessel. Moreover, they have also proven their impact for multiple cardiovascular and life-threatening ischemic events. Nonetheless, their role in promoting arterial stiffness by interfering with stiffness-related gene and protein expression in resident and infiltrating inflammatory cells of the mostly hypoxic injured vessel wall has not been sufficiently investigated. Methods: Human platelets were isolated from donor blood and activated to obtain activated platelet supernatants (APS). M1 macrophages (Macro), adventitial fibroblasts (Fib) and vascular smooth-muscle cells (VSMC) were thereafter exposed to APS in normal and hypoxic (O2 concentration of 2%) environment. Stiffness-related gene and protein expression was investigated utilizing qRT-PCR and Western Blot, respectively. Results: The aforementioned experiments have shown that M 1 Macro, Fib and VSMC are capable to resist for up to 6 hours (h) in a hypoxic environment. Upon exposure to APS, we observed an up-regulation of Elastin degrading enzymes Matrix-Metalloproteinase (MMP) -2 and -9. This regulation was enhanced in hypoxic conditions. No differences for collagens were observed. Of interest, we found marked up-regulation of the inflammatory cytokine Osteopontin (OPN) in inflammatory macrophages following APS exposure. OPN reveals various cleaving sites for different enzymes producing OPN fragments. Notably, these OPN fragments which are generated from active enzymes also influenced stiffness related gene expression. Conclusion: Our results indicate a platelet-dependent activation of stiffness-related gene and protein expression in vessel wall target cell types, suggesting platelet activation as a potential source of arterial stiffness. Clinical relevance of our findings has yet to be proven. Disclosure: Nothing to disclose