Increased platelet extracellular vesicle release and platelet mitochondrial bioenergetic changes in relapsing Multiple Sclerosis (MS)

Background: Beyond their role in haemostasis, platelets participate in immune system interactions. This role has not been extensively characterised in MS. Studies in MS suggest increased platelet adhesiveness and elevated microparticle release. Mitochondrial membrane potential (Δψm), a key indicator of respiratory chain function has not been previously studied in MS platelets.Objectives: To study platelet Δψm, and the response to respiratory chain inhibition in a well-characterised cohort of relapsing MS patients and healthy controls. Further, to characterise total plasma extracellular vesicle (microparticle and exosome) levels and determine the proportion of particles derived from activated platelets.Methods: 28 control subjects and 82 multiple sclerosis patients were recruited across the three experiments. Platelet Δψm was assessed over one hour on FACSII Canto flow cytometer using the cationic potentiometric probe JC-1 and mitochondrial com-plex-1 inhibition achieved with 10 μM rotenone. Plasma particles, up to 1000 nm in size, were quantified using nanoparticle tracking analysis. Platelet-derived microparticles and proportion of activated particles were measured with CD41 and CD62P antibodies, respectively, by flow cytometry.Results: Total plasma extracellular vesicle number is elevated in MS vs controls (mean 4336 vs 2141 x108 particles/ml plasma respectively, p=0.008). This was observed for exosomes (30-150nm) and microparticles (151-1000nm). Platelet-derived particles (CD41) and CD62P+ve particles are increased in MS vs controls (mean 12285 vs 7583 events/min, p=0.014 and 1183 vs 582, p=0.002, respectively). Basal Δψm is hyperpolarised in MS platelets vs controls (p<0.05). Response to complex-1 inhibition differs, with MS exhibiting rapid depolarisation of Δψm.Conclusions: We hypothesise that platelets, activated in relapsing MS and exhibiting alterations in Δψm are an important component of MS pathophysiology and offer multiple targets for further study and potential therapeutic intervention.