Objectives: IgA nephropathy (IgAN) is the most common primary glomerular disease in China, but its pathogenesis remains unclear. This study aims to explore the regulatory role of the mammalian target of rapamycin (mTOR) signaling pathway in autophagy and mesangial proliferation during renal injury in IgA.
Methods: The activity of mTOR and autophagy was evaluated in kidney samples from IgAN patients and in an IgAN mouse model induced by oral bovine serum albumin and carbon tetrachloride (CCl4) injection. mTOR inhibitors (rapamycin) and activators [bpV(phen)] were administered to the IgAN mouse model to observe the effects of mTOR on autophagy and renal lesions. In human mesangial cells treated with polymeric IgA1 (p-IgA1) and mTOR modulators, the expression and distribution of cell cycle proteins were assessed, along with the effects of mTOR on mesangial cell proliferation and autophagy.
Results: Increased mTOR activity and decreased autophagy were observed in kidney tissues from IgAN patients and the mouse model, as evidenced by elevated phosphorylated mTOR (p-mTOR) levels and reduced LC3 expression. In the IgAN mouse model, rapamycin inhibited mTOR, restored autophagy, reduced mesangial IgA deposition, alleviated mesangial cell proliferation, and decreased proteinuria (all P<0.05). In contrast, bpV(phen) activated mTOR, further suppressed autophagy, exacerbated kidney damage, and increased proteinuria (all P<0.05). In vitro, p-IgA1 induced mesangial cell proliferation and inhibited autophagy, effects that were reversed by rapamycin and aggravated by bpV(phen) (all P<0.05). mTOR regulated mesangial cell proliferation by altering cell cycle distribution, with rapamycin inducing G1 phase arrest and bpV(phen) promoting cell cycle progression. Additionally, cyclinD1 expression in renal cortex was up-regulated in the IgAN mouse model, further increased by bpV(phen), and reduced by rapamycin (all P<0.05).
Conclusions: Inhibition of the mTOR signaling pathway enhances renal autophagy, reduces mesangial cell proliferation, and improves renal injury in IgAN.
目的: IgA肾病(IgA nephropathy，IgAN)是中国最常见的原发性肾小球疾病，但其发病机制还有待进一步阐明。本研究旨在探讨哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin，mTOR)在IgAN肾损伤中对自噬和系膜增生的调控作用。方法: 通过IgAN患者的肾脏样本和口服牛血清白蛋白+皮下注射四氯化碳(carbon tetrachloride，CCl4)诱导的IgAN小鼠模型评估mTOR的活性和自噬作用。在IgAN小鼠模型中，分别给予mTOR抑制剂(雷帕霉素)和激活剂[bpV(phen)]，观察mTOR对自噬和肾脏病变的调控作用。检测经聚合IgA1(polymeric IgA1，p-IgA1)和mTOR调节剂处理的人肾小球系膜细胞周期的分布和细胞周期蛋白质表达，及mTOR对肾脏系膜细胞增殖和自噬的影响。结果: 在IgAN患者和小鼠模型的肾脏组织中，mTOR活性增强和自噬作用减弱，具体表现为磷酸化mTOR(phosphorylated mTOR，p-mTOR)水平升高以及LC3表达减少。在IgAN小鼠模型中，雷帕霉素抑制mTOR后，自噬作用得到恢复，系膜IgA沉积减少，系膜细胞增生减轻，且尿蛋白降低(均P<0.05)。相反，bpV(phen)激活mTOR后，进一步抑制了自噬，加重了肾脏病变，并增加了尿蛋白(均P<0.05)。体外实验表明：p-IgA1可诱导系膜细胞增殖并抑制自噬，这些效应可被雷帕霉素逆转，而bpV(phen)则加剧了这些效应(均P<0.05)。雷帕霉素使细胞停滞在G1期，而bpV(phen)则促进细胞进入细胞周期。此外，在IgAN小鼠模型中，肾皮质中周期蛋白D1表达上调，bpV(phen)处理后进一步上调，而雷帕霉素处理则使其表达下调(均P<0.05)。结论: 抑制mTOR信号通路可增强肾脏自噬，减少系膜细胞增生，从而改善IgAN的肾损伤。.
Keywords: IgA nephropathy; autophagy; mammalian target of rapamycin; mesangial proliferation.