Identification of immune-inflammation targets for intracranial aneurysms: a multiomics and epigenome-wide study integrating summary-data-based Mendelian randomization, single-cell-type expression analysis, and DNA methylation regulation
Authors: Lin Peng-Wei , Lin Zhen-Rong , Wang Wei-Wei , Guo Ai-Shun , Chen Yu-Xiang 
Published: July 2024

Background:
Dysfunction of the immune system and inflammation plays a vital role in developing intracranial aneurysms (IAs). However, the progress of genetic pathophysiology is complicated and not entirely elaborated. This study aimed to explore the genetic associations of immune-related and inflammation-related genes (IIRGs) with IAs and their subtypes using Mendelian randomization, colocalization test, and integrated multiomics functional analysis.

Methods:
The authors conducted a summary-data-based Mendelian randomization (SMR) analysis using data from several genome-wide association studies of gene expression (31 684 European individuals) and protein quantitative trait loci (35 559 Icelanders), as well as information on IAs and their subtypes from The International Stroke Genetics Consortium (IGSC) for discovery phase and the FinnGen study for replication. This analysis aimed to determine the causal relationship between IIRGs and the risk of IAs and their subtypes. Further functional analyses, including DNA methylation regulation (1980, European individuals), single-cell-type expression analysis, and protein-protein interaction, were conducted to detect the specific cell type with enriched expression and discover potential drug targets.

Results:
After integrating multiomics evidence from expression quantitative trait loci (eQTL) and protein quantitative trait loci (pQTL), the authors found that tier 1: RELT [odds ratio (OR): 0.14, 95% CI: 0.04–0.50], TNFSF12 (OR: 1.24, 95% CI: 1.24–1.43), tier 3:ICAM5 (OR: 0.89, 95% CI: 0.82–0.96), and ERAP2 (OR: 1.07, 95% CI: 1.02–1.12) were associated with the risk of IAs; tier 3: RELT (OR: 0.11, 95% CI: 0.02–0.54), ERAP2 (OR: 1.08, 95% CI: 1.02–1.13), and TNFSF12 (OR: 1.24, 95% CI: 1.05–1.47) were associated with the risk of aneurysmal subarachnoid hemorrhage (aSAH); and tier 1:RELT (OR: 0.04, 95% CI: 0.01–0.30) was associated with the risk of unruptured intracranial aneurysms (uIAs). Further functional analyses showed that RELT was regulated by cg06382664 and cg18850434 and ICAM5 was regulated by cg04295144 in IAs; RELT was regulated by cg06382664, cg08770935, cg16533363, and cg18850434 in aSAH; and RELT was regulated by cg06382664 and cg21810604 in uIAs. In addition, the authors found that H6PD (OR: 1.13, 95% CI: 1.01–1.28), NT5M (OR: 1.91, 95% CI: 1.21–3.01), and NPTXR (OR: 1.13, 95% CI: 1.01–1.26) were associated with IAs; NT5M (OR: 2.13, 95% CI: 1.23–3.66) was associated aSAH; and AP4M1 (OR: 0.06, 95% CI: 0.01–0.42) and STX7 (OR: 3.97, 95% CI: 1.41–11.18) were related to uIAs. STX7 and TNFSF12 were mainly enriched in microglial cells, whereas H6PD, STX7, and TNFSF12 were mainly enriched in astrocytes.

Conclusions:
After integrating multiomics evidence, the authors eventually identified IIRGs: RELT, TNFSF12, ICAM5, and ERAP2 were the novel therapy targets for IAs. These new results confirmed a vital role of immune and inflammation in the etiology of IAs, contributing to enhance our understanding of the immune and inflammatory mechanisms in the pathogenesis of IAs and revealing the complex genetic causality of IAs.