DataSheet_1_Association of circulating inflammatory proteins with type 2 diabetes mellitus and its complications: a bidirectional Mendelian randomization study.docx

BackgroundIncreasing evidence indicates that immune response underlies the pathology of type 2 diabetes (T2D). Nevertheless, the specific inflammatory regulators involved in this pathogenesis remain unclear.
MethodsWe systematically explored circulating inflammatory proteins that are causally associated with T2D via a bidirectional Mendelian randomization (MR) study and further investigated them in prevalent complications of T2D. Genetic instruments for 91 circulating inflammatory proteins were derived from a genome-wide association study (GWAS) that enrolled 14,824 predominantly European participants. Regarding the summary-level GWASs of type 2 diabetes, we adopted the largest meta-analysis of European population (74,124 cases vs. 824,006 controls) and a prospective nested case-cohort study in Europe (9,978 cases vs. 12,348 controls). Summary statistics for five complications of T2D were acquired from the FinnGen R9 repository. The inverse variance-weighted method was applied as the primary method for causal inference. MR-Egger, weighted median and maximum likelihood methods were employed as supplementary analyses. Results from the two T2D studies were combined in a meta-analysis. Sensitivity analyses and phenotype-wide association studies (PheWAS) were performed to detect heterogeneity and potential horizontal pleiotropy in the study.
ResultsGenetic evidence indicated that elevated levels of TGF-α (OR = 1.16, 95% CI = 1.15-1.17) and CX3CL1 (OR = 1.30, 95% CI = 1.04-1.63) promoted the occurrence of T2D, and increased concentrations of FGF-21 (OR = 0.87, 95% CI = 0.81-0.93) and hGDNF (OR = 0.96, 95% CI = 0.95-0.98) mitigated the risk of developing T2D, while type 2 diabetes did not exert a significant influence on said proteins. Elevated levels of TGF-α were associated with an increased risk of ketoacidosis, neurological complications, and ocular complications in patients with T2D, and increased concentrations of FGF-21 were potentially correlated with a diminished risk of T2D with neurological complications. Higher levels of hGDNF were associated with an increased risk of T2D with peripheral vascular complications, while CX3CL1 did not demonstrate a significant association with T2D complications. Sensitivity analyses and PheWAS further ensure the robustness of our findings.
ConclusionThis study determined four circulating inflammatory proteins that affected the occurrence of T2D, providing opportunities for the early prevention and innovative therapy of type 2 diabetes and its complications.

**研究背景**

越来越多的证据表明，免疫应答是2型糖尿病（type 2 diabetes, T2D）病理发生的核心机制之一。然而，该发病过程中涉及的特异性炎症调控因子仍未明确。

**研究方法**

本研究通过双向孟德尔随机化（bidirectional Mendelian randomization, MR）研究系统筛选与2型糖尿病存在因果关联的循环炎症蛋白，并进一步探究其与2型糖尿病常见并发症的关联。91种循环炎症蛋白的遗传工具变量源自一项纳入14824名以欧洲血统为主参与者的全基因组关联研究（genome-wide association study, GWAS）。针对2型糖尿病的汇总级GWAS数据，本研究采用了目前规模最大的欧洲人群荟萃分析（meta-analysis）（74124例病例vs 824006例对照）以及一项欧洲人群的前瞻性嵌套病例队列研究（prospective nested case-cohort study）（9978例病例vs 12348例对照）。2型糖尿病5种并发症的汇总统计数据源自FinnGen R9数据库。本研究以逆方差加权法作为因果推断的主要分析方法，并采用MR-Egger、加权中位数法以及极大似然法作为补充分析手段。将两项2型糖尿病相关研究的结果进行荟萃分析整合。同时开展敏感性分析与表型组全关联研究（phenotype-wide association studies, PheWAS），以检测本研究中的异质性与潜在水平多效性。

**研究结果**

遗传证据显示，循环中转化生长因子-α（TGF-α）（比值比（odds ratio, OR）=1.16，95%置信区间（confidence interval, CI）=1.15~1.17）与CX3CL1（OR=1.30，95%CI=1.04~1.63）水平升高会增加2型糖尿病的发病风险；而成纤维细胞生长因子21（FGF-21）（OR=0.87，95%CI=0.81~0.93）与人类胶质细胞源性神经营养因子（hGDNF）（OR=0.96，95%CI=0.95~0.98）浓度升高则可降低2型糖尿病的发病风险，且2型糖尿病本身对上述蛋白水平无显著影响。进一步分析发现，TGF-α水平升高与2型糖尿病患者发生酮症酸中毒、神经系统并发症及眼部并发症的风险升高相关；FGF-21浓度升高可能与2型糖尿病合并神经系统并发症的风险降低存在关联；hGDNF水平升高则与2型糖尿病合并外周血管并发症的风险升高相关，而CX3CL1与2型糖尿病并发症无显著关联。敏感性分析与PheWAS进一步验证了本研究结果的稳健性。

**研究结论**

本研究明确了4种可影响2型糖尿病发病的循环炎症蛋白，为2型糖尿病及其并发症的早期预防与创新治疗提供了新的潜在靶点与思路。