Platelet extracellular vesicles and their mitochondrial content improve the mitochondrial bioenergetics of cellular immune recipients

Mitochondria play a critical role in the production of cell energy and the regulation of cell death. Therefore, mitochondria orchestrate numerous cell effector functions, including fine-tuning the immune system. While mitochondria are mainly found intracellularly, they can escape the confine of the cell during the process of extracellular vesicle release. Platelets patrol blood vessels to ensure vasculature integrity and to support the immune system. In blood, platelets are the primary source of circulating mitochondria. Activated platelets produce extracellular vesicles, including a subset of mitochondria-containing vesicles.

Researchers at the CHU de Québec-Université Laval Research Center characterized mitochondrial functions in platelet-derived extracellular vesicles, and examined whether they could impact the bioenergetics of cellular immune recipients using an extracellular flux analyzer to measure real-time bioenergetics. They validated that extracellular vesicles derived from activated platelets contain the necessary mitochondrial machinery to respirate and generate energy. Moreover, neutrophils and monocytes efficiently captured platelet-derived extracellular vesicles, enhancing their mitochondrial fitness. This process required functional mitochondria from donor platelets, as it was abolished by the inactivation of extracellular mitochondria using mitochondrial poison.

Platelet-derived extracellular vesicles (pEVs) contain functional mitochondria

(A) Schematization of pEV production from mice blood. (B) Gating strategy to analyze the mitochondrial content (DsRed) and CD41 expression of pEVs. Size was evaluated using FSC-PMT parameter. Dot plots are representative of 10 different preparations. All particles showing positivity for DsRed (DsRed+) are considered mitlets. (C) The pie chart represents the mean ± SD of each pEV subpopulation (n = 10). Geometric mean fluorescence (MFI) were calculated for the size (FSC-PMT) and complexity (SSC) of each subpopulation of pEVs. One-way ANOVA with Tukey’s multiple-comparison test was performed (****p ≤ .0001). (D) Voltage-dependent anion channel (VDAC) and actin proteins were assessed by immunoblot analysis in mice pEVs and isolated mitochondria (20 μg of protein per lane). (E) The functionality of mitochondria was determined by measurement of the oxygen consumption rate per μg of pEVs (blue line, n = 3) or isolated mitochondria (red line, n = 3) as described in the methods. Green zones represent when the mitochondria are functional and red zones when mitochondrial complexes are inactivated. (F) ATP was measured after incubation of pEVs (n = 4) and isolated mitochondria (n = 3) for 5 min with or without ATP precursors. Data were normalized by the total amount of pEVs/mitochondrial proteins. Ratio-paired Student’s t-test (**p ≤ .01; ***p ≤ .001).

Together, the data suggest that extracellular mitochondria produced by platelets may support other metabolic functions through transcellular bioenergetics.