Background: Vasculopathy, microvascular endothelial cell dysfunction, platelet activation, and interstitial lung disease (ILD) are hallmarks of systemic sclerosis (SSc). Recently, extramedullary thrombopoiesis, involving the adaptation of megakaryocytes (Mks) to stress conditions, has been described in infectious and inflammatory contexts. Activated Mks and platelets both release extracellular vesicles (EVs) and mitochondria. Little is known about Mks activation in SSc.

Objectives: We investigated whether Mks-derived EVs, detectable in the blood and amenable to analysis in vitro and in vivo, can provide insights into the state of Mk activation in SSc.

Methods: We examined 35 SSc patients and 25 age- and sex-matched healthy donors (HD). EVs were assessed in platelet-free plasma by flow cytometry, and EVs were purified through sequential ultracentrifugation ^[1,2] . In vitro experiments involved evaluating mitochondria transfer to microvascular primary lung endothelial cells, while lung histology was assessed post-EVs transfer in NSG mice, known for their receptiveness to human tissues.

Results: Mks-derived EVs and platelet-derived EVs, containing or lacking mitochondria, accumulated in the plasma of SSc patients (see Table 1). The concentration of both total Mks-EVs and mitochondria-containing Mks-EVs was significantly higher in SSc patients with ILD (see Figure 1). Encapsulation into EVs seemed to enhance the horizontal transfer of mitochondria to nucleated cells. In vivo experiments demonstrated that the injection of SSc-EVs, but not purified mitochondria, rapidly induced lung fibrosis.

Table 1.

*: P<0.05 vs healthy donors; ^# : P<0.05 vs patients with ILD

Conclusion: The accumulation of plasma Mks-derived EVs may serve as an indicator of lung involvement in SSc patients. Further investigations are needed to understand whether extramedullary Mks indeed contribute to the natural history of the disease.

REFERENCES: [1] Manfredi AA; et al. Platelet Phagocytosis via P-selectin Glycoprotein Ligand 1 and Accumulation of Microparticles in Systemic Sclerosis. Arthritis Rheumatol. 2022. 10.1002/art.41926.

[2] Maugeri N; et al. Platelet microparticles sustain autophagy-associated activation of neutrophils in systemic sclerosis. Sci Transl Med. 2018; 10. 10.1126/scitranslmed.aao3089.

Acknowledgements: This project is funded by the European Union - Next Generation EU - NRRP M6C2 - Investment 2.1 Enhancement and strengthening of biomedical research in the NHS.

Disclosure of Interests: None declared.