Qingshen granules inhibits dendritic cell glycolipid metabolism to alleviate renal fibrosis via PI3K-AKT-mTOR pathway

Abstract

Background: Qingshen exhibits anti-inflammatory and immunoregulation effects to renal damage. Dendritic cells (DCs) play a critical role in regulating the pathologic inflammatory environment in renal fibrosis (RF).

Purpose: To investigate the immune modulation mechanism of qingshen granule (QSG) in RF, particularly focusing on the role of DCs.

Methods/study design: Adenine-induced RF animal models were used to study the pharmacological effects of QSG and the immune cells differentiation and function. Glucose uptake, non-esterified fatty acids secretion, mitochondrial membrane potential (MMP) detection, and qPCR were used to explore the effect of QSG to glucose and lipid metabolism in DCs and T cells. The effect of QSG to PI3K-AKT-mTOR axis and the modulation of mTOR to PD-L1 were explored by co-culture experiments, co-immunoprecipitation and western blot assays. The interaction of DCs/CD8⁺T cells and renal tubular epithelial cells (RTECs) was investigated to demonstrate the direct action and/or the immune-mediated regulation of QSG to RF. The components of QSG in the serum were determined by HPLC. And the effect of active ingredients and formula to DCs and T cells was analyzed by cell experiments in vitro.

Results: QSG reduced nephritic histopathological damage and suppressed the release of proinflammatory cytokines in adenine-induced RF mice. Of note, QSG decreased the levels of CD86, MHC-II, and CCR7 on DCs, while, increased PD-L1 expression on DCs in RF. The results demonstrated that QSG promoted the maturation and inhibited the migration of DCs, and QSG decreased the antigen presenting of DCs to T cells. Additionally, QSG reduced the MMP and glucose/lipid utilization ratio in DCs. QSG also down-regulated the level of targeted metabolic genes included glucose transporter 1 (Glut1), sterol-regulatory element-binding protein 1 (Srebp1), acetyl-CoA carboxylase alpha (Acaca), phosphomevalonate kinase (Pmvk), and up-regulated sirtuin2 (Sirt2) in DCs. In terms of mechanism, QSG inhibited the metabolism-related PI3K-AKT-mTOR pathway, followed by regulating the interaction of mTOR with PD-L1 to enhance the membrane stability of PD-L1. Besides, HPLC analysis identified five active ingredients in QSG. The specific anti-inflammatory and immunosuppressive actions of these ingredients were found to be weaker than QSG as a whole. Finally, inhibiting DC function by QSG disrupted the communication among DCs, T cells, and RTECs. This disruption was associated with low expression of α-smooth muscle actin (α-SMA) and collagen type I (Col-I) in the kidney.

Conclusions: QSG inhibits DC metabolism and function via the PI3K-AKT-mTOR pathway to alleviate RF. The study highlights the importance of the specific composition of the formula in targeting DC-mediated immune regulation.

Keywords: Dendritic cells; Glycolipid metabolism; PI3K-AKT-mTOR pathway; Qingshen granules; Renal fibrosis.