# Regulation of Platelet Reactivity by S1P Signaling

> **NIH NIH R01** · THOMAS JEFFERSON UNIVERSITY · 2021 · $523,101

## Abstract

The preeminent cause of morbidity and mortality in humans is cardiovascular disease (CVD). Race is considered
to be an important determinant of the outcome of CVD since compared to whites, blacks have a twofold higher
incidence of CVD even when other confounding factors are accounted for. Myocardial infarction and stroke result
from formation of occlusive platelet thrombus at the site of atherosclerotic plaque rupture. Recently, Dr. Edelstein
and colleagues have shown that differences in platelet reactivity to protease activated receptor 4-activating
peptide (PAR4-AP) is heritable and is associated with racial disparity. They have identified two probable
candidates, a variant of PAR4 protein (120A-T) and increased expression levels of phosphatidyl choline transfer
protein (PCTP) to be contributing for the observed increase in platelet reactivity to PAR4-AP and ethnic
differences seen. However, how these two independent proteins may regulate platelet reactivity to PAR4-AP is
not well understood. We hypothesize that the hyperresponsive PAR4 variant associates with neutral
sphingomyelinase (n-SMase), a key enzyme involved in synthesis of S1P, a potent bioactive lipid that binds to
its receptor on the platelet surface to potentiate platelet reactivity. Enhanced levels of PCTP provide an increased
amount of sphingomyelin (SM) required for S1P synthesis. Together, they enhanced recruitment of platelets in
the growing thrombus thus influencing the outcome of CVD. To test this hypothesis, we propose the following
three specific aims. Specific Aim 1: To evaluate the role of S1P synthetic pathway in influencing PAR4-induced
signaling in platelets. We will evaluate if thrombin/PAR4-AP will differentially induce n-SMase activity as well as
S1P levels in a PAR4 genotype specific manner. Next, we will determine if association of PAR4 with n-SMase is
genotype specific and whether this association will influence association of PAR4 with Gαq. Furthermore, we
will test if blockade of enzymes of S1P synthetic pathway and S1PR1/2 receptors for S1P on platelets will
attenuate PAR4-AP-induced platelet function in PAR4 genotype dependent manner. We will also determine if
genetic ablation of key enzymes of S1P synthesis using CRISPR/Cas9 technology in MEG-01 cells expressing
PAR4 hyperreactive variant will rescue platelet hyperreactivity. In Specific Aim 2, we will evaluate the regulation
of S1P synthesis in platelets by CIB1. It has been shown that CIB1 bind Sphk1/2 and regulate their activity in
cells. We will first determine if Cib1 regulate thrombin-induced S1P synthesis using Cib1-/- mouse platelets. In
Specific Aim 3, we will assess the role of platelet–derived S1P in regulation of thrombosis and transient ischemic
stroke (tMCAO). We will evaluate if platelet specific deletion of Cib1 or inhibition of S1P signaling in mice
expressing human PAR4 variants will differentially alter in vivo thrombotic and ischemic stroke outcomes. Since
racial disparity in thrombosis ...

## Key facts

- **NIH application ID:** 10183303
- **Project number:** 5R01HL142959-03
- **Recipient organization:** THOMAS JEFFERSON UNIVERSITY
- **Principal Investigator:** ULHAS P NAIK
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $523,101
- **Award type:** 5
- **Project period:** 2019-07-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10183303

## Citation

> US National Institutes of Health, RePORTER application 10183303, Regulation of Platelet Reactivity by S1P Signaling (5R01HL142959-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10183303. Licensed CC0.

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