Triptolide protects podocytes via autophagy in immunoglobulin A nephropathy

Triptolide is often used to treat patients with immunoglobulin A nephropathy (IgAN), especially in Asia. However, its detailed mechanism remains unclear. In vitro experiments were conducted with podocytes exposed to aggregated IgA (aIgA)-MSC1097-conditioned media. A total of four groups were compared in this study: A control group (CON); a healthy supernatant group (HEAs); an IgAN supernatant group (IgANs); and a triptolide group (TRI). First, aggregated IgA1 (aIgA1) was generated by heating monomeric IgA1 (mIgA1) from IgAN patients or healthy subjects. Next, the conditioned supernatant of MSC-1097 cells cultured with aIgA1 (100 mg/l) from IgAN patients (IgANs) or healthy subjects (HEAs) or without aIgA1 (CON) were harvested and used to incubate MPC5 cells. MPC5 cells in the TRI group were cultured with triptolide (10 ng/ml) and conditioned media from MSC-1097 cells cultured with aIgA1 from IgAN patients. After 24 h of treatment, MPC5 cells were collected to measure autophagy-related protein levels, including microtubule-associated protein light chain 3 (LC3), p62, cluster of differentiation (CD)63, phosphorylated-protein kinase B (Akt), Akt, p-mammalian target of rapamycin (mTOR), and mTOR, via western blotting, immunofluorescence or both, and to determine apoptosis by flow cytometry. All the results showed no difference between the CON and the HEAs. Compared to the CON and the HEAs, MPC5 cells in the IgANs group showed reduced autophagy, which was presented as decreased levels of LC3-II and CD63, as well as accumulation of p62, and an increased podocyte apoptosis rate. This was partly rescued by the addition of triptolide. Moreover, the p-mTOR/mTOR ratio increased in the IgANs group and decreased in the TRI group. Therefore, these results suggest that triptolide protects podocyte autophagy in IgAN patients.