Background <p>Developing regenerative therapies to restore kidney function in patients with progressive renal disease represents a major challenge for modern molecular nephrology. Kidney organoids, three-dimensional kidney-like structures, which can now be generated by the directed differentiation of human pluripotent stem cells, have emerged as a powerful tool to study kidney development, physiology, and mechanisms of renal disease in vitro. Ultimately, kidney organoids may serve as an experimental platform to unravel the pathomechanisms of renal fibrosis and to test regenerative treatment approaches targeting fibrotic kidney diseases. However, the fibrotic phenotype in kidney organoids and its utility as a disease model remain to be fully characterized.</p> Methods <p>Three-dimensional self-organizing kidney organoids containing nephrons and stromal cells were exposed to TGF-β1 cytokine to induce fibrotic remodeling. Organoids were analyzed by RNA sequencing and histology.</p> Results <p>Activation of TGF-β1 signaling in kidney organoids induced hallmarks of human kidney fibrosis, such as tubular atrophy, glomerulosclerosis, and interstitial fibrosis. RNA sequencing highlighted differential regulation of key pathways in kidney fibrosis: epithelial-to-mesenchymal transition, inflammation, metabolism, and JAK/STAT signaling. We identified candidate mediators of kidney fibrosis such as the JAK-STAT downstream target PIM1. Inhibition of PIM1 with the small molecule AZD1208 attenuated fibrosis development in the organoids.</p> Conclusions <p>Kidney organoids are an amenable system for modeling kidney fibrosis and may guide therapeutic discovery.</p>