Project description:CD14+ monocytes, the predominant population in human blood, are primarily engaged in host defense and pro-inflammatory cytokine responses. Aberrant monocyte activity causes life-threatening cytokine storms, while dysfunctional monocytes lead to 'immunoparalysis.' Understanding the mechanisms controlling monocyte functions is therefore paramount. Here, we reveal platelets' vital role in human monocytes' pro-inflammatory responses. Natural low platelet counts in patients with immune thrombocytopenia (ITP) , platelet depletion in healthy human monocytes, or in vivo platelet depletion in mice, result in monocyte immunoparalysis, characterized by reduced pro-inflammatory gene expression and weakened cytokine responses to immune challenge. Remarkably, supplementation with fresh platelets reverses monocyte immunoparalysis. In mice, thrombocytopenia results in down-regulation of myeloid innate immune genes, and compromised host defense transcriptional programs in monocytes despite normal responses to LPS. Platelets control monocyte cytokines independently of traditional cross-talk pathways, acting as reservoirs of transcription factors like NF?B and MAPK p38. We pinpointed a vesicle-derived NF?B2 transfer to human monocytes by mass spectrometry-based proteomics. Functionally, platelets proportionally restored impaired cytokine secretion in human monocytes lacking MAPK p38a and NF?B p65 and NF?B2. We unveil the intercellular transfer of inflammatory regulators, positioning platelets as central checkpoints in monocyte-mediated inflammation.
Project description:Extracellular vesicles (EV) convey biological messages through their cargoes. Herein we focus on monocyte/platelet aggregates characteristic of several cardiovascular diseases with an analysis of monocyte-derived EV (mEVs) effects on the atherosclerotic plaque. Monocyte preparations were stimulated with TNF-α in presence or absence of prostacyclin and EVs isolated via centrifugation. EV physical characteristics were determined by Nanoparticle Tracking analysis while surface profile was analysed using imaging flow cytometry. Atherosclerotic plaques from 5 patients undergoing endarterectomy were cultured with or without mEVs. Cytokines and proteins released in the culture media were measured by multiplex ELISA and mass spectrometry. Proteomic of mEVs prepared in different incubation settings was also conducted. Monocyte isolation yielded ~80% platelet-monocyte aggregates. TNF-α stimulation produced CD14+ EVs as well as a subset bearing the CD41 marker for platelets (CD14+/CD41+). Prostacyclin addition did not modulate monocyte/platelet aggregates, but impacted on mEV numbers. Addition of TNF-α mEVs on atherosclerotic plaque fragments impacted on general protein release (19 upregulated and 7 downregulated) and elevated cytokine release. mEVs generated by TNF-α and prostacyclin produced minimal changes on plaque reactivity. Proteomic analysis of mEVs revealed a distinctive composition when the cell preparation was activated with TNF-α alone or with prostacyclin. In conclusion, mEVs activate the atherosclerotic plaque. Attenuating platelet activation has an effect on EV composition with downstream modulation of their pro-inflammatory actions. EV heterogeneity reflects the mode of activation of the cell of origin and may differently contribute to the development and progression of atherosclerosis.