Our study employed a comprehensive approach to analyze the causal relationship between hypertension and cardiovascular outcomes while also revealing the potential modulatory effect of intermediate-density lipoprotein (IDL) particle concentration. Through Mendelian randomization, we demonstrated that hypertension significantly increases the risk of four major CVDs, coronary heart disease (CHD), peripheral artery disease (PA), stroke, and deep vein thrombosis (DVT). Furthermore, we found that hypertension could reduce the risk of adverse cardiovascular outcomes by decreasing the IDL concentration, particularly by reducing the risk of CHD and PA. The ranking of mediation percentages from high to low was as follows: CHD (22%), peripheral arterial atherosclerosis (13%), DVT (13%), and stroke (4%). This finding has important implications for understanding the role of IDL particles in hypertension and CVDs.
The modulation of IDL concentration as an intermediate factor between hypertension and cardiovascular outcomes is intriguing. The levels of lipids, which are carriers of lipids in the blood, affect lipid metabolism pathways. The colocalization analysis results indicated that hypertension and CVD were associated with genes related to lipid metabolism pathways, suggesting the possible involvement of lipid metabolism pathways in the relationship between hypertension and CVD. Through differential gene expression and lipid metabolism pathway analysis, we further discovered a close connection between genes that are differentially expressed between hypertension and CVDs, especially those involved in the glycerophospholipid pathway. Triglycerides are the main components of IDL particles and have been considered risk factors for CVDs in some studies. Genes closely associated with CVDs and the glycerophospholipid pathway, such as LYPLA2, MGLL, and PLD2, are likely directly related to the association between CVDs and IDL particles, which is crucial for enhancing our molecular understanding of their mechanisms. These results further emphasize the importance of lipid metabolism pathways in the relationship between hypertension and CVD. Additionally, the results of the PheWas analysis further validated the effects of several genes in the lipid metabolism pathway on hypertension and CVDs. This series of findings not only deepens our understanding of the complex relationship between hypertension and CVDs but also provides important clues for further research on the role of lipid metabolism in the pathogenesis of these diseases.
LYPLA2 is closely associated with lysophospholipids37, and MGLL is an important fatty acid metabolism enzyme that converts monoglycerides into free fatty acids (FFAs) and glycerol. Previous studies have shown that MGLL is associated with tumor signaling pathways38. PLD2 plays a key role in cell membrane lipid remodeling39, and earlier studies have confirmed its association with cardiac metabolic diseases40. In our study, we detected slightly increased expression of LYPLA2, MGLL, and PLD2 in hypertension and PA samples. Considering that MR analysis revealed the potential mediating role of IDL particles in the relationship between hypertension and cardiovascular outcomes, the relationships between LYPLA2, MGLL, PLD2, and hypertension and CVDs deserve further attention. We speculate that the upregulation of LYPLA2, MGLL, and PLD2 in hypertension and PA may be associated with the onset and progression of CVDs, especially those related to lipid metabolism.
Hypertension is a major risk factor for CVDs41,42, while dyslipidemia has also been shown to increase the risk of CVDs such as atherosclerosis and stroke7. Previous studies may have used single methods or focused only on certain aspects, such as using epidemiological surveys or genetic association studies to explore the relationship between hypertension or dyslipidemia and CVDs without integrating the associations between them. This may limit the credibility and interpretability of the results. Björnson et al. demonstrated the association between lipoprotein remnants and CHD12, and our study further narrowed the focus to the IDL concentration, proving the significant association between IDL particles and CVDs. Chen et al. reported associations between adipokines and hypertension and CVDs, but due to the cross-sectional nature of their study, specific causal relationships could not be determined43. Wang et al. identified the predictive value of hypertension for CVDs44, focusing on epidemiological surveys without molecular biology methods to validate their results. In contrast, our study employed a comprehensive approach using multiomics analysis methods, emphasizing the role of the IDL concentration as a mediator and providing a more comprehensive and in-depth understanding of the relationship between hypertension and CVDs and their potential underlying mechanisms, with greater credibility and persuasiveness.
The main advantage of our study is the use of two-step MR, which minimizes the influence of confounding factors. The use of bidirectional MR when including intermediate variables excludes variables associated with hypertension bidirectionally, ensuring that the intermediate variables used are influenced by hypertension in one direction only. To our knowledge, we are also the only study to date to analyze the association between IDL concentration/lipid metabolism, an intermediate variable, and hypertension and other CVDs. The results of the MR analysis were further validated via colocalization analysis. In addition, we used GEO data to further molecularly study the CVDs investigated, revealing the intermediate relationship network between IDL concentration and hypertension and other CVDs. However, our study has several limitations. First, due to the lack of DVT-related expression data in the GEO database, we were unable to further investigate the biological mechanisms underlying DVT. Additionally, due to the lack of data related to CHD, we used CAD instead of CHD for differential gene expression analysis. Second, the samples we used mainly came from European populations, which may limit the applicability of the results of this study to other populations. Finally, to identify as many associations as possible during the differential expression analysis, we set the FC threshold to 1.25, which may have led to the presence of false positives.