Potential Genetic Link Between Platelet Activity and Cardiovascular Disease Identified

A new study has identified a potential genetic link between platelet activity and cardiovascular disease, with researchers suggesting that the expression of WD-40 repeat domain 1 (WDR1), which is involved in altering the actin cytoskeleton of platelets, may contribute to the platelet-mediated pathogenesis of cardiovascular disease.

The protein may help to single out individuals at higher or lower risk for cardiovascular disease, study authors say.

In a small group of individuals with cardiovascular disease and age- and sex-matched controls, WDR1 expression measured in mRNA was significantly lower in those with established disease. This suggests WDR1 “suppresses platelet activity and may be an important link between platelet activity and cardiovascular disease,” say researchers.  

“Platelets are unique cells without DNA and a nucleus but we were able to look at the platelet transcriptome, or the platelet RNA,” said senior investigator Jeffrey Berger, MD (NYU Langone Medical Center, New York, NY). “We found that indeed there were big differences in people based on their platelet function. We were able to identify several genes, and the one we describe here is WDR1. It’s not been previously described to affect platelet function, and it’s not been previously described to affect cardiovascular disease.”

As part of their research, which was published online September 8, 2016, in Blood, the group analyzed the platelets from 52 healthy subjects, stratifying donors based on platelet reactivity. They performed a mRNA expression profile based on platelet phenotype in six subjects—three with the hyperreactive phenotype and three with hyporeactive platelets—and identified 17 genes downregulated in hyperreactive platelets.

WDR1 was of interest as it is known to be involved in the development of megakaryocytes—the progenitor of platelets—and platelet development. As part of the initial analysis, they showed WDR1 mRNA expression was significantly downregulated in hyperreactive platelets when compared with the hyporeactive platelets. These findings were confirmed in a validation cohort of 50 subjects.   

Next, the researchers studied the human megakaryoblastic cell line (MEG-01) as an in vitro model of human megakaryocytes and platelets to assess whether the downregulation of WDR1 had any functional effects. Speaking with TCTMD, Berger explained that the WDR1 protein appears to be involved in actin-depolymerization, which affects the remodeling of the platelet cytoskeleton. Knocking down WDR1 in MEG-01 cells, they observed an increase in adhesion and spreading of the megakaryocyte cells in their basal and activated state, increased F-actin content, and increased intracellular calcium concentrations.

Berger noted that F-actin is involved in cell motility and cell adhesion so the presumed mechanism is that by affecting the expression of WDR1, it is causing megakaryocytes and platelets to become “stickier,” or more adherent. When platelets are activated, he noted, one of the first steps is increased adhesion.

“In the laboratory, we found that if you alter the regulation of the gene that is the progenitor of the platelet, the megakaryocyte, you actually significantly alter the function of these cells,” said Berger. “You alter not only the function of the megakaryocytes but the platelets they produce. We showed that by altering this gene, we were able to affect how platelets are working.”

When the researchers overexpressed WDR1, there was a reversal of the WDR1-knockdown phenotype of megakaryocytes and platelet-like particles.

Linking WDR1 With Cardiovascular Disease

For Berger, the “real home-run piece of the study” is data showing the gene is associated with cardiovascular disease. While small, including just 27 patients with established disease and 10 age- and sex-matched controls, the analysis showed the differential expression of WDR1 in the mRNA of megakaryocytes, as well as the WDR1 protein in platelets, does identify individuals at higher or lower risk for cardiovascular disease, he said.

“I think as exciting as the data is, it’s observational and I think while mechanistically it makes sense, our next study is to see whether or not alteration of this gene predicts future events,” he told TCTMD. “We have not looked at that, but it’s one thing we’d like to look at. We actually have an ongoing National Institutes of Health study collecting platelet function and platelet RNA in individuals and following them for long-term cardiovascular events. WDR1 will definitely be one gene we look at very carefully.”

Speaking with TCTMD, Paul Gurbel, MD, and Udaya Tantry, PhD (Inova Heart and Vascular Institute, Falls Church, VA) praised the study, calling it provocative, and highlighted the link between RNA expression and platelet function. “People are becoming more and more interested in looking at gene expression and gene expression profiles that can mark platelet physiology,” said Gurbel. “I think this is a very interesting study, and I think we’re pretty much at the beginning of looking at this work of RNA profiling in patients, but it does need to be vetted in a larger-scale study where it can be linked to outcomes.”

As for the current study, Gurbel said that the initial mRNA expression by platelet phenotype was performed in a very limited number of subjects. In addition, there were only a small number of subjects included in the analysis showing lower WDR1 mRNA and protein levels in subjects with cardiovascular disease. He noted that the measured platelet activity in these 27 individuals was higher than in controls, which wouldn’t be expected if these patients were taking aspirin.

Gurbel and Tantry told TCTMD there has been a lot of study of platelet response in patients treated with antiplatelet therapy, such as clopidogrel and aspirin, and its relationship with cardiovascular events. In ADAPT-DES, for example, high platelet reactivity was linked with higher event rates in high-risk PCI patients, they said.      

Berger said that while platelets have a known role in thrombosis and in the initiation and propagation of cardiovascular disease, it is not known if healthy individuals, those in their 30s or 40s with high levels of platelet activity, are at heightened risk for cardiovascular disease. “That’s an idea that some people think should be the case, but data supporting it is weak,” he said.

Regarding platelet function testing, Berger said he does not believe the medical community is able to completely and accurately measure platelet function just yet. “We have a few point-of-care assays, but they are a bit too simplistic to understand the global platelet function,” he said. “I think you need many different assays that target different processes of platelet activation to really understand platelet function. I think there are a few labs in the country that can do that, but I think it’s only available for research purposes for now.”

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