Inonotus obliquus (Chaga) attenuates folic acid-induced renal interstitial fibrosis by inhibiting epithelial-mesenchymal transition through modulating macrophages and T cells activation and interaction

Renal interstitial fibrosis (RIF), with extracellular matrix (ECM) deposition in the renal interstitium as the pathological feature, is triggered by inflammation and is associated with poor outcomes in chronic kidney disease (CKD). Macrophages and T cells are the main inflammatory effectors in RIF. Inonotus obliquus (Chaga), used as food and medicine, was recently found to protect against CKD in our previous study. However, its effect on RIF remains unclear. In this study, C57BL/6 mice were intraperitoneally injected with folic acid (FA) to induce RIF, followed by intragastric administration of chaga for 14 days. The dose-dependent efficacy of 100, 200, and 300 mg/kg chaga in improving RIF was first verified using histopathology. The results revealed that chaga attenuated RIF, and the protective effect was most significant at a dose of 300 mg/kg. In the subsequent study, dynamic courses of chaga at 300 mg/kg reduced renal tubular damage and decreased collagen deposition area were observed on days 3, 7, and 14. In addition, single-cell RNA sequencing and immunohistochemistry studies demonstrated that chaga inhibited macrophage and T cell aggregation in fibrotic kidneys, and further normalized the communication between macrophages and T cells. The latter was based on our analysis that chaga inhibited FA-induced CD86-CD28 ligand-receptor interactions but restored macrophage histocompatibility complex class 1 and CD8 levels between renal macrophages and T cells. In conclusion, chaga effectively suppressed RIF in FA-induced mice by modulating macrophage and T cell activation and interaction.