For my research rotation and thesis research, I have been working in Dr. Bluestein’s Biofluids lab. One of the projects that the lab focuses on is testing the response and activity of platelets due to shear stresses. Mechanical heart valves and circulatory support devices are effective tools used for the treatment of end-stage heart failure. However, these devices generate large, non-pathophysiological shear stresses at their location of implantation, and these stresses are experienced by the patient’s platelets for short periods of time1. Dr. Bluestein’s research focuses on how these shear stresses affect platelet activation. To expose platelets to various shear stresses, the lab uses a hemodynamic shearing device, which is a cone-plate-Couette viscometer1. Activation is then measured using a prothrombinase assay, which serves as a biomarker for platelet activation. Previous studies by the lab has shown that exposing platelets to high shear stresses will make them more sensitive to lower shear stresses that they experience later on1. The lab also designed experiments using a syringe-capillary viscometer, or platelet hammer, that was able to expose platelets to repeated constant shear stresses2. These experiments showed that exposing platelets to constant high shear stresses repeatedly led to an increase in both initial platelet activation and the rate of platelet activation over time after the experiments2. All of these experiments have shown how platelets are affected by high shear stresses, which provides insight into how platelets are affected by mechanical circulatory support devices.
For the next stage of the research regarding shear-induced platelet activation, we want to examine platelet activation due to shear stresses as it relates to the age of the patient. In order to do this, we are testing the response and activation of umbilical cord blood platelets and comparing it with that of adult platelets. I am especially interested in this topic because of the potential applications that it has for patients of cardiovascular disease. Platelets taken from the peripheral blood of neonates have shown to be hyporesponsive3. The cause for this hyporeactivity is currently not known or well understood. Elucidation of the mechanism behind neonatal activation can be used to potentially generate therapeutics to assist patients that have mechanical circulatory support devices and are currently taking anticoagulants. In order to better understand neonatal platelet activation, we exposed both cord blood and adult platelets to high shear conditions of 70 dynes/cm2 and then used flow cytometry to test for activity. One antibody that was used was for annexin V, which binds to phosphatidylserine and was used to provide information regarding the platelet membrane. For these experiments, umbilical cord blood platelets are being used as an analog for neonatal platelets. The results of these experiments showed that cord blood platelets that have been exposed to high shear stresses have a significant increase in annexin V binding than shear-treated adult platelets. This is interesting because if the results are correct than they would imply that the membranes of cord blood platelets experience more effects due to high shear stresses than adult platelets. I am currently designing a protocol for a set of experiments that will test these results and provide more information regarding the effects of high shear stresses on adult vs. umbilical cord platelets.
References:
1 Sheriff, J., Bluestein, D., Girdhar, G. & Jesty, J. High-shear stress sensitizes platelets to subsequent low-shear conditions. Annals of biomedical engineering 38, 1442-1450, doi:10.1007/s10439-010-9936-2 (2010).
2 Sheriff, J. et al. Repetitive Hypershear Activates and Sensitizes Platelets in a Dose-Dependent Manner. Artificial organs 40, 586-595, doi:10.1111/aor.12602 (2016).
3 Baker-Groberg, S. M., Lattimore, S., Recht, M., McCarty, O. J. & Haley, K. M. Assessment of neonatal platelet adhesion, activation, and aggregation. Journal of thrombosis and haemostasis : JTH 14, 815-827, doi:10.1111/jth.13270 (2016).
Presenting our research at Stony Brook University’s URECA Symposium in April 2017.