TGFB1 and chronic kidney disease: Indoxyl sulfate (IS), which is a representative uremic toxin and a metabolite of tryptophan derived from dietary protein, also accumulates in the circulation of CKD patients, and induces glomerulosclerosis9,10, mesangial cell proliferation11 and expression of fibrotic genes such as TGF-β1 and type-I collagen12 in the kidney.