Page 205 - Haematologica May 2022

Letters to the Editor
platelets could be mediated through mitochondrial func- tions unrelated to ATP generation. Reactive oxygen species (ROS) have now been established as important signaling molecules responsible for platelet activation.2,12 Mitochondria are a significant source of ROS in platelets12 and selectively scavenging mitochondrial superoxide with mitoTEMPO prevents platelet aggregation.13 ROS release from mitochondria is dependent on inner mito- chondrial membrane polarization, and uncoupling is known to reduce mitochondrial ROS.14 In concurrence, CCCP but not antimycin or oligomycin brought about a significant drop in mitochondrial ROS in thrombin-stim- ulated platelets (Figure 3D, F). These changes were also reflected in intracellular ROS levels, which were signifi- cantly curbed in the presence of CCCP but remained unaffected by antimycin or oligomycin (Figure 3E, G). Phosphatidylserine exposure by platelets is dependent on cyclophilin D-dependent formation of mitochondrial per- meability transition pores, which is triggered by calcium entry into mitochondria through a mitochondrial calcium uniporter along the electrical gradient across the inner mitochondrial membrane.15 We could find inhibition of thrombin-induced mitochondrial calcium transients in the presence of CCCP but not in the presence of antimycin or oligomycin (Figure 3B; Online Supplementary Figure S3A-D). Hence, it was fairly reasonable to posit that CCCP restrains platelet aggregation and procoagu- lant activity through abrogation of mitochondrial ROS and calcium transients, respectively.
In summary, mitochondrial ATP was found to be dis- pensable for platelet aggregation and procoagulant activ- ity, which are fueled by glycolytic ATP. However, main- tenance of a proton gradient across inner mitochondrial membrane plays a vital role in these processes by sup- porting ROS generation and mitochondrial calcium influx, respectively. We discovered that mitochondrial ATP is critical for sustaining platelet granule secretion, platelet-neutrophil interactions and thrombus growth, especially when inadequately compensated by glycolytic ATP (Online Supplementary Figure S3E). This knowledge should have important implications for the development of anti-thrombotic strategies that selectively target platelet granule release in the treatment of thrombo- inflammatory diseases such as acute myocardial infarc- tion, ischemic stroke, deep vein thrombosis and pul- monary embolism.
Paresh P. Kulkarni,1 Mohammad Ekhlak,1 Vijay K. Sonkar2 and Debabrata Dash1
1Center for Advanced Research on Platelet Signaling and Thrombosis Biology, Department of Biochemistry, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh and 2Department of Molecular and Human Genetics, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, India
Correspondence:
DEBABRATA DASH: ddash.biochem@gmail.com doi:10.3324/haematol.2021.279847
Received: August 19, 2021.
Accepted: December 16, 2021.
Pre-published: December 23, 2021.
Disclosures: this research was supported by a J.C. Bose National Fellowship and grants received by DD from the Indian Council of Medical Research (ICMR) under CAR, Department of Biotechnology (DBT) and Science and Engineering Research Board (SERB), Government of India. DD also acknowledges assistance from the Humboldt Foundation, Germany. ME is a recipient of a CSIR-JRF.
Contributions: DD supervised the entire work; DD and PPK designed the research; PPK, ME and VKS performed experiments and analyzed results; DD and PPK wrote the manuscript.
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