Raw_Data.zip

We conducted a comprehensive bidirectional and multivariable Mendelian randomization (MR) study using publicly available genetic data to explore the causal association between cathepsins and IgA nephropathy (IgAN), systematically. Additionally, immunohistochemical (IHC) staining and enzyme-linked immunosorbent assay (ELISA) were employed to evaluate cathepsin expression levels in renal tissues and serum of IgAN patients. We investigated the underlying mechanisms via gene set variation analysis (GSVA), gene set enrichment analysis (GSEA), and immune cell infiltration analysis. Molecular docking and virtual screening were also performed to identify potential drug candidates through drug repositioning.Univariate MR analyses demonstrated a significant link between increased cathepsin S (CTSS) levels and a heightened risk of IgAN. This was evidenced by an odds ratio (OR) of 1.041 (95% CI=1.009–1.073, <i>P</i>=0.012) as estimated using the inverse variance weighting (IVW) method. In multivariable MR analysis, even after adjusting for other cathepsins, elevated CTSS levels continued to show a strong correlation with an increased risk of IgAN (IVW <i>P</i>=0.020, OR=1.037, 95% CI=1.006–1.069). However, reverse MR analyses did not establish a causal relationship between IgAN and various cathepsins. IHC and ELISA findings revealed significant overexpression of CTSS in both renal tissues and serum of IgAN patients compared to controls, and this high expression was unique to IgAN compared with several other primary kidney diseases such as membranous nephropathy, minimal change disease and focal segmental glomerulosclerosis. Investigations into immune cell infiltration, GSEA, and GSVA highlighted the role of CTSS expression in the immune dysregulation observed in IgAN. Molecular docking and virtual screening pinpointed Camostat mesylate, c-Kit-IN-1, and Mocetinostat as the top drug candidates for targeting CTSS.本研究依托公开遗传数据开展了一项全面的双向多变量孟德尔随机化(Mendelian randomization, MR)研究，以系统探究组织蛋白酶(cathepsins)与IgA肾病(IgA nephropathy, IgAN)之间的因果关联。此外，本研究采用免疫组化(immunohistochemical, IHC)染色与酶联免疫吸附试验(enzyme-linked immunosorbent assay, ELISA)，检测IgAN患者肾组织与血清中的组织蛋白酶表达水平。本研究通过基因集变异分析(gene set variation analysis, GSVA)、基因集富集分析(gene set enrichment analysis, GSEA)以及免疫细胞浸润分析，探讨了潜在的疾病调控机制。同时，本研究还开展了分子对接与虚拟筛选，通过药物重定位策略识别潜在的靶向候选药物。单变量MR分析结果显示，组织蛋白酶S(cathepsin S, CTSS)水平升高与IgAN患病风险升高存在显著关联：采用逆方差加权(inverse variance weighting, IVW)法估算得到比值比(odds ratio, OR)为1.041（95%置信区间CI=1.009~1.073，*P*=0.012）。多变量MR分析中，即便校正了其他组织蛋白酶的混杂影响，CTSS水平升高仍与IgAN患病风险升高呈现显著强相关（IVW法*P*=0.020，OR=1.037，95%CI=1.006~1.069）。然而，反向MR分析未证实IgAN与各类组织蛋白酶之间存在因果关联。免疫组化与酶联免疫吸附试验结果表明，与对照组相比，IgAN患者肾组织与血清中的CTSS均呈显著高表达；且相较于膜性肾病、微小病变肾病、局灶节段性肾小球硬化等其他多种原发性肾脏疾病，该高表达特征仅特异性出现于IgAN患者中。免疫细胞浸润分析、GSEA与GSVA结果揭示了CTSS表达在IgAN患者免疫失调过程中的重要作用。分子对接与虚拟筛选最终确定甲磺酸卡莫司他(Camostat mesylate)、c-Kit-IN-1以及Mocetinostat为靶向CTSS的顶级候选药物。