Combining Single-Cell RNA Sequencing and Mendelian Randomization to Explore Novel Drug Targets for Parkinson's Disease.

Neuroinflammation is a key pathological factor of PD, and T cells play a central role in neuroinflammatory progression. However, the causal effect of T cell-related genes on the risk of PD is still unclear. We explored single-cell RNA sequencing (scRNA-Seq) datasets of the peripheral blood T cells of PD patients and healthy controls, and screened the differentially expressed genes (DEGs) in the cytotoxic CD4 + T cells relative to the other T cell subsets. Pseudo-time series analysis, cell-cell communication analysis, and metabolic pathway analysis was performed for the cytotoxic CD4 + T cells. The DEGs were also functionally annotated through GO and KEGG pathway enrichment analyses. The MR approach was used to establish causal effects of the DEGs (exposure) on PD risk (outcome), and explore new drug targets for PD. The findings of MR analysis were further validated by Steiger filtering, bidirectional MR, Bayesian colocalization analysis, and phenotype scanning, and the GWAS data from an independent PD case-control cohort was used for external validation of the results. Finally, differences in gene expression between PD patients and healthy controls were further validated in scRNA-Seq and bulk transcriptome sequencing data. We found that increased expression of IL-32, GNLY, MT2A, and ARPC2 was significantly associated with a higher risk of PD. In contrast, the increase in ARRB2 was closely related to a lower risk of PD. IL32, GNLY, MT2A, ARRB2, and ARPC2 are the causal genes and potential drug targets of PD. Cytotoxic CD4 + T cells are likely the key effectors of PD-related neuroinflammation. These findings provide new insights into the pathogenesis and treatment options for PD, and further research and clinical trials based on the five potential drug targets and neuroinflammation are necessary.