In this MR analysis of 179 lipids with eight stroke phenotypes, we identified 133 causal relationships involving six lipid types (sterol esters, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, sphingomyelin, and triacylglycerol) and eight stroke phenotypes. After multiple testing corrections, causal relationships remained between 10 lipids and five stroke phenotypes. This study is the first to analyze the causal relationships between different lipid molecular structures and stroke using MR. Our aim was to assess the link between specific lipid structures and stroke pathogenesis, providing insights for the study of stroke mechanisms and the development of targeted drugs.
A growing body of research indicates that lipid modulation can effectively intervene in the pathogenesis and outcome of stroke [14,15]. Lipids and lipid mediators are crucial for maintaining the normal structure and function of brain tissues, with dyslipidemia being a significant risk factor for stroke [16]. The Emerging Risk Factors Collaboration found that lipoprotein (Lpa) has a consistent and independent association with stroke [17]. Dai et al. [18] demonstrated that total cholesterol, non-high-density lipoprotein cholesterol, and triglyceride levels may predict ischemic stroke. Furthermore, Qin et al. [19] established a causal relationship between low-density lipoprotein cholesterol, apolipoprotein, and large-artery stroke through MR analysis, suggesting that elevated levels of these proteins may increase the risk of large-artery stroke. Our research primarily focused on three lipid types—sterol esters, phosphatidylinositols, and phosphatidylcholines—and examined their various molecular structures. We found that the levels of sterol ester (27:1/20:4) positively correlated with stroke (any type), ischemic stroke, and large blood vessel stroke. Conversely, phosphatidylinositol (18:1_18:2) levels negatively correlated with large blood vessel stroke. Five distinct molecular structures of phosphatidylcholine were positively associated with intracerebral hemorrhage, while phosphatidylcholine (17:0_20:4) exhibited a negative association with subarachnoid hemorrhage.
Lipids, a hydrophobic and heterogeneous group of molecules, vary in structure from simple short-chain hydrocarbons to complex molecules such as triacylglycerols, phospholipids, and sterols, along with their esters. Different lipid categories exhibit structural variation. The structural diversity of lipids and fatty acids leads to distinct metabolic pathways and functional attributes [20]. Sterol esters, which are produced through the esterification of sterols with fatty acids, play various biological roles in the regulation of cell membranes [21], energy storage [22], signal transduction [23], and hormone synthesis [24]. They serve as storage forms for sterols, with esterification leading to formation of chylomicrons, which is closely related to atherosclerosis [25,26]. Plant sterol esters can reduce cholesterol absorption in the intestine, thereby preventing hypercholesterolemia [27]. However, studies have indicated that plant sterol esters can cause endothelial damage, exacerbate cerebral ischemic diseases in experimental mice, and increase plasma sterol concentrations in humans [28]. Phosphatidylinositol, which comprises inositol kinase and phosphatase, is a vital phospholipid that can lead to the biosynthesis of seven forms and plays a crucial role in membrane dynamics as a signaling lipid. Its abnormal metabolism has been associated with various diseases [29,30]. Andres et al. demonstrated that phosphatidylinositol bisphosphate strongly inhibits proton-activated chloride channels, thereby preventing chloride entry into the cells and reducing acid-induced brain damage [31,32]. Studies on phosphatidylinositol and brain injury often focus on the neuroprotective pathway of phosphoinositide-3-kinase (PI3K)–protein kinase B (Akt) [33,34], while other reports have indicated the anti-apoptotic effects of phosphatidylinositol-4-kinase alpha (PI4KA) in the brain [35]. Clinical studies have shown that the serum level of phosphatidylinositol (3,4,5)-trisphosphate can predict acute ischemic stroke [36], and a significant increase in anti-phosphatidylinositol antibodies has been found in young patients with stroke [37]. Phosphatidylcholines are key components of cell membranes and are crucial for neural transmission as they can convert to molecules such as choline and acetylcholine. They also play roles in the blood–brain barrier and inflammatory responses [38]. Magaquian et al. found that phosphatidylcholine could restore neural stem cell plasticity under inflammatory conditions, thereby improving neuronal damage [39]. Huang et al., using liquid chromatography–mass spectrometry, identified hemolytic phosphatidylcholine as a potential biomarker for stroke recovery [40]. Lipids are important components in stroke prevention, treatment, and recovery, and understanding their roles has the potential to clarify stroke prevention and treatment strategies. Our results align with those of previous epidemiological and clinical research, suggesting that various lipids play significant roles in stroke pathophysiology, but provide stronger evidence of causality.
We are the first to assess the causal relationship between 179 lipid species and multiple stroke phenotypes, covering a broader range of lipids and a larger sample size for each phenotype than previous studies [41]. Although MR mitigates common confounders and reverse causality issues in traditional observational studies by using genetic variation as IVs, some limitations of our study should be acknowledged. First, the effectiveness of the MR analysis depends on the quality of the IVs used, and a P value of 5×10 − 5 was chosen to ensure a sufficient number of SNPs. Second, despite using genetic variants highly correlated with lipids, we cannot completely rule out confounding effects on other biological pathways related to stroke phenotypes. Lastly, the SNP source in this study is mainly of European origin, with some coverage of Asian origin. Considering that the population structure is relatively simple, the applicability of the results to various races is limited to a certain extent. Future studies should include more diverse populations for validation.
In summary, our study extensively analyzed the causal relationships between 179 lipids and eight stroke phenotypes. The findings highlight a strong association between lipid profiles and stroke incidence, underscoring the significance of lipids as potential targets for stroke prevention and treatment. Future research, especially focusing on the biological functions of different structural lipids, is expected to offer new insights into stroke prevention and therapeutic strategies.