Indoxyl Sulfate Contributes to mTORC1-Induced Renal Fibrosis via The OAT/NADPH Oxidase/ROS Pathway

Abstract

Activation of mTORC1 (mechanistic target of rapamycin complex 1) in renal tissue has been reported in chronic kidney disease (CKD)-induced renal fibrosis. However, the molecular mechanisms responsible for activating mTORC1 in CKD pathology are not well understood. The purpose of this study was to identify the uremic toxin involved in mTORC1-induced renal fibrosis. Among the seven protein-bound uremic toxins, only indoxyl sulfate (IS) caused significant activation of mTORC1 in human kidney 2 cells (HK-2 cells). This IS-induced mTORC1 activation was inhibited in the presence of an organic anion transporter inhibitor, a NADPH oxidase inhibitor, and an antioxidant. IS also induced epithelial–mesenchymal transition of tubular epithelial cells (HK-2 cells), differentiation of fibroblasts into myofibroblasts (NRK-49F cells), and inflammatory response of macrophages (THP-1 cells), which are associated with renal fibrosis, and these effects were inhibited in the presence of rapamycin (mTORC1 inhibitor). In in vivo experiments, IS overload was found to activate mTORC1 in the mouse kidney. The administration of AST-120 or rapamycin targeted to IS or mTORC1 ameliorated renal fibrosis in Adenine-induced CKD mice. The findings reported herein indicate that IS activates mTORC1, which then contributes to renal fibrosis. Therapeutic interventions targeting IS and mTORC1 could be effective against renal fibrosis in CKD.

A combination of 5/6‐nephrectomy and unilateral ureteral obstruction model accelerates progression of remote organ fibrosis in chronic kidney disease

“…IS gets quickly excreted through the urine in healthy renal function; however, it accumulates in the blood 9 and causes renal dysfunction in various organs 39 . IS, when taken up by cells and tissues, promotes tissue fibrosis by increasing oxidative stress 40 and inflammation 41 . Additionally, IS polarizes macrophages into a proinflammatory phenotype (M1 macrophages), 42 which contributes to tissue damage 43 .…”

JBP485, A Dual Inhibitor of Organic Anion Transporters (OATs) and Renal Dehydropeptidase-I (DHP-I), Protects Against Imipenem-Induced Nephrotoxicity

“…HK-2 cells are human-derived proximal tubular epithelial cells and have been commonly used as an in vitro model to evaluate drug nephrotoxicity and the potential mechanisms of renal diseases ( Qiu et al, 2018 ; Bejoy et al, 2022 ). The uremic toxins indoxyl sulphate and p-Cresyl sulphate are taken up into HK-2 cells via OATs and induce cytotoxicity in HK-2 cells, suggesting that OATs are expressed in HK-2 cells and contribute to the cytotoxicity of toxins ( Motojima et al, 2003 ; Miyamoto et al, 2011 ; Nakano et al, 2021 ). In the present study, protein expressions of both OAT1/3 and DHP-I were identified in HK-2 cells, which confirms that HK-2 cells are a suitable model for the investigation of DDIs mediated by OAT1/3 and DHP-I.…”

Mesenchymal stem cell‐derived extracellular vesicles in treatment against renal fibrosis

“…discovered that indoxyl sulphate (IS) contributes to mammalian target of rapamycin complex1 (mTORC1)‐induced RF via the organic anion transporters/nicotinamide adenine dinucleotide phosphate (NADPH) oxidase /ROS pathway. After IS enters cells, mTORC1 is activated by producing ROS associated with NADPH oxidase activation, which leads to EMT of renal tubular epithelial cells, differentiation of fibroblasts to myofibroblasts and inflammatory responses by macrophages 43 …”