Identification of a novel proinsulin-associated SNP and demonstration that proinsulin is unlikely to be a causal factor in subclinical vascular remodelling using Mendelian randomisation.

BACKGROUND AND AIMS: Increased proinsulin relative to insulin levels have been associated with subclinical atherosclerosis (measured by carotid intima-media thickness (cIMT)) and are predictive of future cardiovascular disease (CVD), independently of established risk factors. The mechanisms linking proinsulin to atherosclerosis and CVD are unclear. A genome-wide meta-analysis has identified nine loci associated with circulating proinsulin levels. Using proinsulin-associated SNPs, we set out to use a Mendelian randomisation approach to test the hypothesis that proinsulin plays a causal role in subclinical vascular remodelling. METHODS: We studied the high CVD-risk IMPROVE cohort (n = 3345), which has detailed biochemical phenotyping and repeated, state-of-the-art, high-resolution carotid ultrasound examinations. Genotyping was performed using Illumina Cardio-Metabo and Immuno arrays, which include reported proinsulin-associated loci. Participants with type 2 diabetes (n = 904) were omitted from the analysis. Linear regression was used to identify proinsulin-associated genetic variants. RESULTS: We identified a proinsulin locus on chromosome 15 (rs8029765) and replicated it in data from 20,003 additional individuals. An 11-SNP score, including the previously identified and the chromosome 15 proinsulin-associated loci, was significantly and negatively associated with baseline IMTmean and IMTmax (the primary cIMT phenotypes) but not with progression measures. However, MR-Eggers refuted any significant effect of the proinsulin-associated 11-SNP score, and a non-pleiotropic SNP score of three variants (including rs8029765) demonstrated no effect on baseline or progression cIMT measures. CONCLUSIONS: We identified a novel proinsulin-associated locus and demonstrated that whilst proinsulin levels are associated with cIMT measures, proinsulin per se is unlikely to have a causative effect on cIMT.

Soluble CD93 Is Involved in Metabolic Dysregulation but Does Not Influence Carotid Intima-Media Thickness.

Type 2 diabetes and cardiovascular disease are complex disorders involving metabolic and inflammatory mechanisms. Here we investigated whether sCD93, a group XIV c-type lectin of the endosialin family, plays a role in metabolic dysregulation or carotid intima-media thickness (IMT). Although no association was observed between sCD93 and IMT, sCD93 levels were significantly lower in subjects with type 2 diabetes (n = 901, mean ± SD 156.6 ± 40.0 ng/mL) compared with subjects without diabetes (n = 2,470, 164.1 ± 44.8 ng/mL, P < 0.0001). Genetic variants associated with diabetes risk (DIAGRAM Consortium) did not influence sCD93 levels (individually or combined in a single nucleotide polymorphism score). In a prospective cohort, lower sCD93 levels preceded the development of diabetes. Consistent with this, a cd93-deficient mouse model (in addition to apoe deficiency) demonstrated no difference in atherosclerotic lesion development compared with apoe(-/-) cd93-sufficient littermates. However, cd93-deficient mice showed impaired glucose clearance and insulin sensitivity (compared with littermate controls) after eating a high-fat diet. The expression of cd93 was observed in pancreatic islets, and leaky vessels were apparent in cd93-deficient pancreases. We further demonstrated that stress-induced release of sCD93 is impaired by hyperglycemia. Therefore, we propose CD93 as an important component in glucometabolic regulation.