Genetically Determined Levels of Circulating Cytokines and Risk of Stroke

Abstract

Background: Cytokines and growth factors have been implicated in the initiation and propagation of vascular disease. Observational studies have shown associations of their circulating levels with stroke. Our objective was to explore whether genetically determined circulating levels of cytokines and growth factors are associated with stroke and its etiologic subtypes by conducting a 2-sample Mendelian randomization (MR) study.

Methods: Genetic instruments for 41 cytokines and growth factors were obtained from a genome-wide association study of 8293 healthy adults. Their associations with stroke and stroke subtypes were evaluated in the MEGASTROKE genome-wide association study data set (67 162 cases; 454 450 controls) applying inverse variance-weighted meta-analysis, weighted-median analysis, Mendelian randomization-Egger regression, and multivariable Mendelian randomization. The UK Biobank cohort was used as an independent validation sample (4985 cases; 364 434 controls). Genetic instruments for monocyte chemoattractant protein-1 (MCP-1/CCL2) were further tested for association with etiologically related vascular traits by using publicly available genome-wide association study data.

Results: Genetic predisposition to higher MCP-1 levels was associated with higher risk of any stroke (odds ratio [OR] per 1 SD increase, 1.06; 95% CI, 1.02-1.09; P=0.0009), any ischemic stroke (OR, 1.06; 95% CI, 1.02-1.10; P=0.002), large-artery stroke (OR, 1.19; 95% CI, 1.09-1.30; P=0.0002), and cardioembolic stroke (OR, 1.14; 95% CI, 1.06-1.23; P=0.0004), but not with small-vessel stroke or intracerebral hemorrhage. The results were stable in sensitivity analyses and remained significant after adjustment for cardiovascular risk factors. Analyses in the UK Biobank showed similar associations for available phenotypes (any stroke: OR, 1.08; 95% CI, 0.99-1.17; P=0.09; any ischemic stroke: OR, 1.07; 95% CI, 0.97-1.18; P=0.17). Genetically determined higher MCP-1 levels were further associated with coronary artery disease (OR, 1.04; 95% CI, 1.00-1.08; P=0.04) and myocardial infarction (OR, 1.05; 95% CI, 1.01-1.09; P=0.02), but not with atrial fibrillation. A meta-analysis of observational studies showed higher circulating MCP-1 levels in patients with stroke in comparison with controls.

Conclusions: Genetic predisposition to elevated circulating levels of MCP-1 is associated with higher risk of stroke, in particular with large-artery stroke and cardioembolic stroke. Whether targeting MCP-1 or its receptors can lower stroke incidence requires further study.

Keywords: Mendelian randomization analysis; atherosclerosis; chemokine CCL2; cytokines; human genetics; inflammation; stroke.

Figure 1.. Schematic representation of the study design.

Methods used to test for associations and for violations of the Mendelian randomization assumptions (dashed lines). AF, atrial fibrillation; CAD, coronary artery disease; DBP, diastolic blood pressure; HDL, high-density lipoprotein cholesterol; HTN, hypertension; IVW, inverse-variance weighted; LDL, low-density lipoprotein cholesterol; MI, myocardial infarction; MR: Mendelian randomization; MR-PRESSO: Mendelian Randomization Pleiotropy RESidual Sum and Outlier; SBP, systolic blood pressure; SNP, Single-nucleotide polymorphism; T2D. type 2 diabetes mellitus; TG, triglycerides.

Figure 2.. Mendelian randomization associations of circulating cytokine and growth factor levels with stroke and stroke subtypes.

Shown are the results derived from the fixed-effects inverse-variance weighted (IVW) meta-analysis. * Significant heterogeneity (I2>25% or Cochran Q-derived p <0.05) † Bonferroni-corrected threshold for number of tested cytokines ‡ Bonferroni-corrected threshold for number of cytokines and number of phenotypes

Figure 3.. Mendelian randomization analysis for circulating MCP-1 levels and risk of stroke.

(A) MR-derived associations between genetically determined circulating MCP-1 levels (1-SD increase) and risk of any stroke and stroke subtypes. (B) Associations between genetically determined circulating MCP-1 levels and risk of large artery (left) and cardioembolic (right) stroke based on different MR methods. I² refers to heterogeneity in the Mendelian randomization analysis (inverse-variance weighted method). CI, confidence intervals; IVW, inverse-variance weighted; OR, Odds Ratio; SNP, single nucleotide polymorphism.

Figure 4.. Associations between circulating MCP-1 levels and risk of stroke in Mendelian randomization and in observational studies.

(A) MR-derived associations between genetically determined circulating MCP-1 levels (1-SD increase) and risk of any stroke and any ischemic stroke in MEGASTROKE, in UK Biobank, and a meta-analysis of both samples. (B) Meta-analysis-derived associations between circulating MCP-1 levels (1-SD increase) and risk of ischemic stroke in case-control and cohort studies. k refers to number of included studies. I² in Figure 4A refers to heterogeneity in the Mendelian randomization analysis (inverse-variance weighted method) and in Figure 4B in the random-effects meta-analyses of observational studies. CI, confidence interval; HR, hazard ratio; OR, odds ratio; SMD, standardized mean difference; SNP, single nucleotide polymorphism.

Figure 5.. Mendelian randomization analysis for genetically determined circulating MCP-1 levels and etiologically related vascular outcomes.

MR-derived associations between genetically determined circulating MCP-1 levels (1-SD increase) and risk of coronary artery disease, myocardial infarction, and atrial fibrillation. I² refers to heterogeneity in the Mendelian randomization analysis (inverse-variance weighted method).