Effects of Platelet Agonists and Priming on the Formation of Platelet Populations

Platelets from healthy donors display heterogeneity in responsiveness to agonists. The response thresholds of platelets are controlled by multiple bioactive molecules, acting as negatively or positively priming substances. Higher circulating levels of priming substances adenosine and succinate, as well as the occurrence of hypercoagulability, have been described for patients with ischaemic heart disease. Here, we present an improved methodology of flow cytometric analyses of platelet activation and the characterisation of platelet populations following activation and priming by automated clustering analysis. Platelets were treated with adenosine, succinate, or coagulated plasma before stimulation with CRP-XL, 2-MeSADP, or TRAP6 and labelled for activated integrin alpha (IIb) beta (3) (PAC1), CD62P, TLT1, CD63, and GPIX. The Super-Enhanced Dmax subtraction algorithm and 2% marker (quadrant) setting were applied to identify populations, which were further defined by state-of-the-art clustering techniques (tSNE, FlowSOM). Following activation, five platelet populations were identified: resting, aggregating (PAC1+), secreting (alpha- and dense-granules; CD62P+, TLT1+, CD63+), aggregating plus alpha -granule secreting (PAC1+, CD62P+, TLT1+), and fully active platelet populations. The type of agonist determined the distribution of platelet populations. Adenosine in a dose-dependent way suppressed the fraction of fully activated platelets (TRAP6>2-MeSADP>CRP-XL), whereas succinate and coagulated plasma increased this fraction (CRP-XL>TRAP6>2-MeSADP). Interestingly, a subset of platelets showed a constant response (aggregating, secreting, or aggregating plus alpha -granule secreting), which was hardly affected by the stimulus strength or priming substances.

Automated summary

Platelets from healthy donors exhibit heterogeneity in response to agonists, with activation thresholds controlled by various bioactive molecules. Elevated levels of priming substances like adenosine and succinate have been associated with hypercoagulability in patients with ischaemic heart disease. An improved flow cytometry methodology was employed to analyze platelet populations following activation and priming, revealing distinct responses based on the type of agonist used. The study identified five platelet populations post-activation, each with different characteristics depending on the agonist utilized, highlighting the complex and dynamic nature of platelet activation.