Wound healing is a multicomponent event that involves a network of molecular and cellular crosstalk between cells, including leukocytes, platelets and fibroblasts. Despite increased knowledge over the past decades regarding the regulation of cell and tissue growth, the inter- and intracellular systems that control wound healing are incompletely understood. The platelet is a rich source of growth factors essential to natural tissue repair. In the present thesis, the role of platelets and platelet-derived factors on fibroblast proliferation was evaluated, and related to the generation of reactive oxygen species (ROS) and eicosanoids.
We found that whole platelets, platelet-derived growth factor (PDGF), transforming growth factor-ß (TGF-ß) and sphingosine-1-phosphate (S1P) induce fibroblast proliferation. Exposure of fibroblasts to these stimuli caused an extensive intracellular production of ROS, measured as increase in dichlorofluorescein fluorescence. Both fibroblast growth and the associated ROS production were inhibited by intracellular antioxidants (N-acetyl-L-cysteine (NAC) and pyrrolidinethiocarbamate (PDTC)) and NADPH-oxidase inhibitors (diphenyleneiodonium chloride (DPI) and apocynin). Moreover, platelet-mediated fibroblast proliferation was abrogated in the presence of the sphingosine kinase inhibitor DL-threo-dihydrosphingosine, but only slightly affected by antibodies directed against PDGF and TGF-ß.
The production of the arachidonic acid metabolite 5-hydroxyeicosatetraenoic acid (5-HETE) in fibroblasts, analysed by HPLC, was markedly elevated in the presence of platelets. Furthermore, inhibition of phospholipase A2, by 7,7-dimethyl-5,8-eicosadienoic acid (DMDA), or 5-lipoxygenase, by 5,8,11-eicosatriynoic acid (ETI) or 5,6-dehydro arachidonic acid (5,6-dAA), decreased the platelet-induced fibroblast proliferation and formation of 5-HETE. This indicate a role for transcellular metabolism of arachidonic acid during platelet-fibroblast interaction.
We conclude that the production of ROS and 5-HETE is crucial in the plateletmediated stimulation of fibroblast growth. These findings may represent new targets in the future therapy for a successful wound healing.
Linköping: Linköpings universitet , 2003. , 48 p.
2003-11-28, Elsa Brändströmsalen, Hälsouniversitetet, Linköping, 13:00 (Swedish)