Transforming growth factor (TGF)-β1 mediates glycosaminoglycan (GAG) chain hyperelongation on secreted proteoglycans and these modifications are associated with increased lipid binding in the vessel wall and the development of atherosclerosis. In vascular smooth muscle cells (VSMCs), TGF-β1 regulated GAG elongation via extracellular signal-regulated kinase (ERK) and p38 as well as Smad2 linker region phosphorylation. In this study, our aim was to identify the TGF-β1 mediated signalling pathway involving reactive oxygen species (ROS) and Smad2 linker region phosphorylation that regulate the mRNA expression of GAG synthesizing enzymes, chondroitin 4-O-sulfotransferase 1 (CHST11) and chondroitin sulfate synthase 1 (CHSY1) which are the rate limiting enzymes involved in GAG chain elongation. Signalling molecules were assessed by western blotting, quantitative real-time PCR was used for analysis of gene expression and intracellular ROS level was measured by a fluorescence based assay. TGF-β1 induced ROS production in VSMCs. Nicotinamide adenine dinucleotide phosphate oxidase (Nox) inhibitors, diphenyleneiodonium (DPI) and apocynin blocked TGF-β1 mediated Smad2 linker region phosphorylation. TGF-β1 treatment increased the mRNA levels of CHST11 and CHSY1. Pharmacological inhibition of Nox blocked TGF-β1 mediated mitogen activated protein kinases (MAPKs) phosphorylation and TGF-β1 stimulated CHST11 and CHSY1 mRNA expression. These findings demonstrated that TGF-β1 mediated expression of CHST11 and CHSY1 can occur via Nox-dependent pathways and Smad2 linker region phosphorylation. KeywordsAtherosclerosis . Nox . Reactive oxygen species . Mitogen activated protein kinases . Glycosaminoglycan Abbreviations CHST11 Chondroitin 4-Ο-sulfotransferase 1 CHSY1 Chondroitin synthase 1 DPI Diphenyleneiodonium ERK Extracellular signal-regulated kinase GAG Glycosaminoglycan JNK C-Jun N-terminal kinase MAPKs Mitogen activated protein kinases. Nox Nicotinamide adenine dinucleotide phosphate oxidase ROS Reactive oxygen species TGFBR1 Transforming growth factor-β receptor type 1 TGF-β1 Transforming growth factor β1 VSMCs Vascular smooth muscle cells * Hossein Babaahmadi-Rezaei

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Individual Smad2 linker region phosphorylation sites determine the expression of proteoglycan and glycosaminoglycan synthesizing genes. Cls (2018),