Center for Neurodevelopmental Disorders & Laboratory of Molecular Psychiatry and Neurogenetics, Department of Medicine, University Campus Bio-Medico, Rome, Italy.
Hematology Transfusion Medicine, University Campus Bio-Medico, Rome, Italy.
Hum Mol Genet. 2019 Apr 1;28(7):1153-1161. doi: 10.1093/hmg/ddy421.
Elevated serotonin (5-HT) blood levels, the first biomarker identified in autism research, has been consistently found in 20-30% of patients with Autism Spectrum Disorder (ASD). Hyperserotonemia is mainly due to greater 5-HT uptake into platelets, mediated by the 5-HT transporter (SERT) located at the platelet plasma membrane. The protein complex involved in platelet SERT trafficking and externalization includes integrin β3, the beta subunit of the platelet membrane adhesive GP IIb/IIIa. Integrin β3 is encoded by the ITGB3 gene, previously identified as a quantitative trait locus (QTL) for 5-HT blood levels in ASD at single nucleotide polymorphism (SNP) rs2317385. The present study aims to identify the functional ITGB3 gene variants contributing to hyperserotonemia. ITGB3 gene sequencing in 20 individuals selected on the basis of rs2317385 genotypes defined four haplotypes encompassing six SNPs located in the ITGB3 gene promoter region, all in linkage disequilibrium with rs2317385. Luciferase assays in two hematopoietic cell lines, K-562 and HEL 92.1.7, demonstrate that ITGB3 gene promoter activity is enhanced by the presence of the C allele at rs55827077 specifically during differentiation into megakaryocytes (P < 0.01), with modulatory effects by flanking SNPs. This same allele is strongly associated with (a) higher 5-HT blood levels in 176 autistic individuals (P < 0.001), (b) greater platelet integrin β3 protein expression (P < 0.05) and (c) enhanced SERT trafficking from the cytosol toward the platelet plasma membrane (P = 4.05 × 10-11). Our results support rs55827077 as the functional ITGB3 gene promoter variant contributing to elevated 5-HT blood levels in ASD and define a mechanistic chain of events linking ITGB3 to hyperserotonemia.
血液中血清素（5-HT）水平升高，这是自闭症研究中首次确定的生物标志物，在 20-30%的自闭症谱系障碍（ASD）患者中一直存在。高血清素血症主要是由于血小板中 5-HT 摄取增加所致，这是由位于血小板质膜上的 5-HT 转运体（SERT）介导的。参与血小板 SERT 运输和外化的蛋白质复合物包括整合素β3，血小板膜黏附 GP IIb/IIIa 的β亚基。整合素β3 由 ITGB3 基因编码，该基因先前在 ASD 中被确定为 5-HT 血液水平的数量性状基因座（QTL），单核苷酸多态性（SNP）rs2317385。本研究旨在确定导致高血清素血症的功能性 ITGB3 基因突变。在基于 rs2317385 基因型选择的 20 名个体中对 ITGB3 基因进行测序，定义了包含位于 ITGB3 基因启动子区域的六个 SNP 的四个单倍型，所有 SNP 均与 rs2317385 连锁不平衡。在两种造血细胞系 K-562 和 HEL 92.1.7 中进行的荧光素酶测定表明，ITGB3 基因启动子活性在向巨核细胞分化时被 rs55827077 的 C 等位基因特异性增强（P<0.01），侧翼 SNP 具有调节作用。同一等位基因与（a）176 名自闭症个体的血液中更高的 5-HT 水平（P<0.001），（b）血小板整合素β3 蛋白表达增加（P<0.05）和（c）细胞溶质中 SERT 向血小板质膜的运输增强（P=4.05×10-11）强烈相关。我们的结果支持 rs55827077 作为功能性 ITGB3 基因启动子变异体，导致 ASD 中 5-HT 血液水平升高，并定义了将 ITGB3 与高血清素血症联系起来的机制链。
