Indoxyl Sulfate Promotes Vascular Calcification in Association with Oxidative Stress and Activation of ERK and Wnt/β-Catenin Signaling Pathways

Vascular calcification (VC) is a major complication of chronic kidney disease (CKD) that is strongly associated with cardiovascular mortality. While indoxyl sulfate (IS), a protein-bound uremic toxin, has been implicated in the progression of VC, the underlying molecular mechanisms remain unclear. We investigated the procalcific effects of IS using a two-step nephrectomy-induced CKD mouse model and cultured vascular smooth muscle cells. In vivo, progressive renal impairment was associated with elevated circulating IS levels and enhanced VC. In vitro, IS dose- and time-dependently induced calcium deposition, increased reactive oxygen species (ROS) production, and upregulated osteogenic markers, including runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), and osteocalcin (OCN), whereas N-acetyl-L-cysteine (NAC) partially attenuated IS-induced ROS accumulation and cell injury. Mechanistically, IS exposure activated extracellular signal-regulated kinase (ERK) and Wnt/β-catenin signaling while suppressing nuclear factor erythroid 2-related factor 2 (Nrf2)-related antioxidant responses, as reflected by reductions in the phosphorylated Nrf2 (pNrf2) to total Nrf2 and heme oxygenase-1 (HO-1) expression. Pharmacological inhibition of ERK and Wnt/β-catenin signaling attenuated IS-induced osteogenic responses. These findings indicate that IS promotes VC in association with increased oxidative stress, activation of ERK and Wnt/β-catenin signaling, and impaired Nrf2-related antioxidant defense. These integrated findings provide mechanistic insight into IS-associated VC and highlight oxidative stress-related signaling networks as potential therapeutic targets in CKD.