p38 mitogen-activated protein kinase regulates mitochondrial function and microvesicle release in riboflavin- and ultraviolet light-treated apheresis platelet concentrates

BACKGROUND: Biochemical analyses of mechanisms triggered in platelets (PLTs) upon pathogen inactivation (PI) are crucial to further understand the impact of PI on PLT functionality and, subsequently, quality. STUDY DESIGN AND METHODS: PLT concentrates (PCs) were split into four small illumination bags: 1) untreated control, 2) treated with riboflavin and ultraviolet light (RF/UV), and spiked with 3) solvent control dimethyl sulfoxide and 4) p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 before RF/UV treatment. Flow cytometry was used to monitor PLT mitochondrial potential (Delta Psi(m)); generation of intracellular reactive oxygen species (ROS); and release of microvesicles (MVs), mitochondria (MT), and MVs containing MT (MVs/MT). Quantitative polymerase chain reaction (qPCR) was used to quantify extracellular mitochondrial DNA (mtDNA). Translocation of selected mitochondrial proteins was analyzed in subcellular fractions by immunoblot. RESULTS: RF/UV treatment triggered an increased mitochondrial translocation of both Bax and Bid (p< 0.05, Day 7) and cytochrome c release (p< 0.01, Day 7), loss of Delta Psi(m) (p< 0.05, Day 5 and Day 7), and ROS generation (p< 0.01, Day 5 and Day 7) in PCs compared to the untreated control during storage. These PI-triggered changes were inhibited by SB203580 (p< 0.05). The release of MVs, MT, and MVs/MT was increased upon the RF/UV treatment during storage (p< 0.05) and, with the exception of MT, the release was decreased by the inhibitor (p< 0.05). qPCR analysis showed that RF/UV does not trigger mtDNA release during storage. CONCLUSION: These findings further our understanding of mechanisms in PLTs initiated by the RF/UV treatment, demonstrating that this treatment induces p38 MAPK-dependent mitochondrial signaling and MV release in apheresis PCs.