Deep proteome profiling of mature and reticulated platelets in patients with chronic coronary syndrome using mass cytometry

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by the German Center for Cardiovascular

Research (DZHK grant number Deutsches Zentrum für Herz-

Kreislaufforschung 81 × 3600606 to D.B.).

Abstract:

Background/Introduction

Reticulated platelets (RPs) are prothrombotic RNA-rich platelets suggested to be detrimental in patients with chronic coronary syndrome (CCS) and high on treatment platelet reactivity. In addition, circulating RPs levels are independent predictor for adverse cardiovascular events in CCS patients and other pathological settings. However, RPs biology still need to be investigated.

Purpose

We thought to investigate the RPs proteome on single-cell level at rest and after activation using time-of-flight mass cytometry (CyTOF).

Method

Thrombocytes from peripheral blood of 11 CCS patients were isolated, prepared for CyTOF and stained with a custom-made CyTOF-antibody panel of 20 antibodies targeting important transmembrane proteins (anti-CD9, anti-CD29, anti-CD31, anti-CD36-, anti-CD40, anti-CD41, anti-CD42a, anti-CD42b-, anti-CD47, anti-CD61, anti-CD62P-, anti-CD63, anti-CD69, anti-CD107a, anti-CD154, anti-GPVI, anti-GPIIbIIa complex, anti-Par1, anti-PEAR-1 and the negative control anti-CD3 coupled with different metal isotopes). Two samples were prepared from each patient: one baseline sample (non-stimulated platelets) and one sample stimulated with 10 μM thrombin receptor-activating peptide (TRAP). According to previous experiences and common practice, we detected RPs and mature platelets (MPs) based on their RNA content. We analyzed the results with a custom bioinformatic pipeline comparing RPs to MPs expression. Earth mover’s distance (EMD) was assed as a measure of differential expression.

Results

While our bioinformatic analysis revealed that all transmembrane markers are significantly higher expressed in the larger RPs compared to MPs, not all markers differ to the same extend. Interestingly, the four markers with the highest calculated EMD (values in brackets) are all key regulators of platelet activation and aggregation: the collagen receptor GPVI (34.18), the collagen integrin receptor unit CD29 (ITGB1: 33.17), the adhesion protein CD9 (32.94) and the von Willebrand receptor unit CD42b (GPIbalpha) (30.08) (Figure 1A).

Regarding the activation marker expression upon TRAP stimulation, RPs show higher median signal intensities of all four activation markers compared to MPs (Figure 1B and C). Especially, the markers CD107a (LAMP-1) and CD154 (CD40L) are expressed in MPs only to a very low extend, whereas there is a clear overexpression in RPs.

Conclusion

This dataset provides the first high resolution analysis of RPs proteome at rest and upon activation. The pro-thrombotic profile of RPs explains their hyperactivity and could offer the first biomolecular explanation of the detrimental role of RPs in CCS patients. In addition, this dataset provide high resolution biomolecular information which could be useful to personalize antiplatelet therapy in patients with high RPs levels.

Reticulated platelet mass cytometry reveals unexplored therapeutic targets in patients with chronic coronary syndrome

Background

Reticulated platelets (RPs) are young, hyper-reactive thrombocytes that contain more RNA compared with mature platelets (MPs). The measurement of RPs level in peripheral blood with point-of-care systems is fast, reproducible, and inexpensive. Elevated RPs in peripheral blood predict adverse events in patients with acute and chronic coronary syndrome through unknown mechanisms. Preliminary transcriptome analyses reported an enrichment of pro-thrombotic transcripts. However, proteomic analyses are not available, and the biological features of RPs are largely unknown.

Purpose

We aimed to perform the largest proteomic characterization of RPs using mass cytometry with single-cell resolution in patients with chronic coronary syndrome (CCS) undergoing dual antiplatelet therapy (DAPT).

Methods

Thrombocytes from peripheral blood of CCS patients were isolated, prepared for mass cytometry (CyTOF) and stained with a custom-made CyTOF-panel of 20 antibodies targeting important transmembrane proteins (anti-CD9, anti-CD29, anti-CD31, anti-CD36-, anti-CD40, anti-CD41, anti-CD42a, anti-CD42b-, anti-CD47, anti-CD61, anti-CD62P-, anti-CD63, anti-CD69, anti-CD107a, anti-CD154, anti-GPVI, antiGPIIb/GPIIIa complex, anti-Par1, anti-PEAR-1 and the negative control anti-CD3 coupled with different metal isotopes). Two samples were prepared from each donor: one baseline sample (non-stimulated platelets) and one sample stimulated with 10 μM thrombin receptor-activating peptide (TRAP). According to previous experiences and common practice, we detected RPs and MPs based on their RNA content. We analyzed the results with a custom bioinformatic pipeline.

Results

13 patients with CCS on DAPT were included in this study. Mass cytometry highlighted an expression heterogeneity of relevant transmembrane proteins in thrombocytes of CCS patients (Figure 1A-B colored according to expression level: from blue-low to red-high). CyTOF detected an upregulation of important transmembrane receptors in RPs compared to MPs in quiescent platelets: GPVI (p<0.0001), PAR-1 (p<0.0001), GPIX (p<0.0001), and GPIbα (p<0.0001, Figure 1C). After TRAP-stimulation, RPs expressed higher levels of the activation markers P-Selectin (p=0.0016) and LAMP-3 (CD63, p<0.0001) compared to MPs confirming RPs hyperactivity (Figure 1D).

Conclusion

We here describe the first biological proteomic characterization with single-cell resolution of RPs biology in CCS patients. The upregulation of the activation markers P-Selectin and LAMP-3 as well as of specific transmembrane proteins as the collagen receptor GPVI and the thrombin receptor PAR-1 in patients treated with DAPT (schematic overview in Figure 2) provides the first solid biomolecular explanation of RPs hyper-reactivity and involvement in cardiovascular disease. Moreover, these results offer unexplored therapeutic targets to tailor antiplatelet therapy based on platelet protein expression in patients with elevated RPs

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): German Center for Cardiovascular Research (DZHK) Figure 1. Platelet expressionFigure 2. Schematic overview