Differences in the Platelet mRNA Landscape Portend Racial Disparities in Platelet Function and Suggest Novel Therapeutic Targets.

The African American (AA) population displays a 1.6 to 3-fold higher incidence of thrombosis and stroke mortality compared with European Americans (EAs). Current antiplatelet therapies target the ADP-mediated signaling pathway, which displays significant pharmacogenetic variation for platelet reactivity. The focus of this study was to define underlying population differences in platelet function in an effort to identify novel molecular targets for future antiplatelet therapy. We performed deep coverage RNA-Seq to compare gene expression levels in platelets derived from a cohort of healthy volunteers defined by ancestry determination. We identified > 13,000 expressed platelet genes of which 480 were significantly differentially expressed genes (DEGs) between AAs and EAs. DEGs encoding proteins known or predicted to modulate platelet aggregation, morphology, or platelet count were upregulated in AA platelets. Numerous G-protein coupled receptors, ion channels, and pro-inflammatory cytokines not previously associated with platelet function were likewise differentially expressed. Many of the signaling proteins represent potential pharmacologic targets of intervention. Notably, we confirmed the differential expression of cytokines IL32 and PROK2 in an independent cohort by quantitative real-time polymerase chain reaction, and provide functional validation of the opposing actions of these two cytokines on collagen-induced AA platelet aggregation. Using Genotype-Tissue Expression whole blood data, we identified 516 expression quantitative trait locuses with Fst values > 0.25, suggesting that population-differentiated alleles may contribute to differences in gene expression. This study identifies gene expression differences at the population level that may affect platelet function and serve as potential biomarkers to identify cardiovascular disease risk. Additionally, our analysis uncovers candidate novel druggable targets for future antiplatelet therapies.

Why African Americans say "No": A Study of Pharmacogenomic Research Participation.

Objective: To identify reasons for nonparticipation by African Americans in cardiovascular pharmacogenomic research. Design: Prospective, open-ended, qualitative survey. Setting: Research staff approached patients eligible for the Discovery Project of The African American Cardiovascular pharmacogenomics CONsorTium in the inpatient or outpatient setting at four different institutions during September and October 2018. Participants: Potential Discovery Project participants self-identified as African American, aged >18 years, were on one of five cardiovascular drugs of interest, and declined enrollment in the Discovery Project. Main Outcome Measures: Reasons for nonparticipation. Methods: After declining participation in the Discovery Project, patients were asked, "What are your reasons for not participating?" We analyzed their responses using a directed content analytic approach. Ultimately, responses were coded into one of nine categories and analyzed using descriptive statistics. Results: Of the 194 people approached for the Discovery Project during an eight-week period, 82 declined participation and provided information for this study. The most common reason for refusal was concern about the amount of blood drawn (19.5%). The next most common reasons for refusal to participate included concerns about genetic testing (14.6%) and mistrust of research (12.2%). Across study sites, significantly more patients enrolled in the inpatient than outpatient setting (P<.001). Significantly more women and younger individuals declined participation due to concerns about genetic testing and too little compensation (P<.05). Conclusions: Collection of blood samples and concerns about genetic testing are obstacles for the recruitment of African Americans to pharmacogenomics studies. Efforts to overcome these barriers to participation are needed to improve representation of minorities in pharmacogenomic research. Enrolling participants from inpatient populations may be a solution to bolster recruitment efforts.

The ACCOuNT Consortium: A Model for the Discovery, Translation, and Implementation of Precision Medicine in African Americans.

The majority of pharmacogenomic (PGx) studies have been conducted on European ancestry populations, thereby excluding minority populations and impeding the discovery and translation of African American-specific genetic variation into precision medicine. Without accounting for variants found in African Americans, clinical recommendations based solely on genetic biomarkers found in European populations could result in misclassification of drug response in African American patients. To address these challenges, we formed the Transdisciplinary Collaborative Center (TCC), African American Cardiovascular Pharmacogenetic Consortium (ACCOuNT), to discover novel genetic variants in African Americans related to clinically actionable cardiovascular phenotypes and to incorporate African American-specific sequence variations into clinical recommendations at the point of care. The TCC consists of two research projects focused on discovery and translation of genetic findings and four cores that support the projects. In addition, the largest repository of PGx information on African Americans is being established as well as lasting infrastructure that can be utilized to spur continued research in this understudied population.