Abstract

Kidney Organoids for Drug Discovery and Toxicity Screening

Ryuji Morizane, Associate Biologist, Renal Division, Brigham and Women’s Hospital Affiliated Faculty, Harvard Stem Cell Institute

We have developed an efficient, chemically defined protocol for differentiating human embryonic stem (ES) cells and induced pluripotent stem cells (iPSCs) into multipotent nephron progenitor cells (NPCs) that can form nephron-like structures. By recapitulating metanephric kidney development in vitro we generate SIX2+SALL1+WT1+PAX2+ NPCs with 80-90% efficiency within 8-9 days of initiation of differentiation. The NPCs form PAX8+LHX1+ renal vesicles that self-organize into nephron structures. NPCs form kidney organoids containing epithelial nephron-like structures expressing markers of podocytes, proximal tubules, loops of Henle and distal nephrons in an organized, continuous arrangement that resembles the nephron in vivo. The organoids express genes reflecting many transporters seen in adult metanephric-derived kidney as well as important kidney endocrine genes such as the gene responsible for the production of erythropoietin. Stromal cells are also generated with the presence of PDGFRß+ (pericyte), endomucin+ (endothelial cell), or a-SMA+ (myofibroblast) interstitial cells. The entire procedure is performed with completely defined conditions without the need for embryonic spinal cord. This kidney differentiation system can be used to study mechanisms of human kidney development. Organoids can be used to evaluate nephrotoxicity of drugs as we have shown the expression of Kidney Injury Molecule-1 in structures that express markers of proximal tubules after exposure to nephrotoxicants. Glomerular toxins alter the cytoskeletal distribution of the glomerular structures. Epithelial toxins and TGFß can cause increased of stromal cells with characteristics of myofibroblasts. Hence the generated kidney organoids are effective tools to study genetic disorders of the kidney as well as mechanisms of toxicity. Generation of NPCs, when coupled with tissue engineering, may lead the way to generation of functional kidney replacement tissue in the future.