Cellular and Molecular Mechanisms of Kidney Development: From the Embryo to the Kidney Organoid

Abstract

Development of the metanephric kidney is strongly dependent on complex signaling pathways and cell-cell communication between at least four major progenitor cell populations (ureteric bud, nephron, stromal, and endothelial progenitors) in the nephrogenic zone. In recent years, the improvement of human-PSC-derived kidney organoids has opened new avenues of research on kidney development, physiology, and diseases. Moreover, the kidney organoids provide a three-dimensional (3D) in vitro model for the study of cell-cell and cell-matrix interactions in the developing kidney. In vitro re-creation of a higher-order and vascularized kidney with all of its complexity is a challenging issue; however, some progress has been made in the past decade. This review focuses on major signaling pathways and transcription factors that have been identified which coordinate cell fate determination required for kidney development. We discuss how an extensive knowledge of these complex biological mechanisms translated into the dish, thus allowed the establishment of 3D human-PSC-derived kidney organoids.

Keywords: differentiation; kidney development; organoid; renal progenitors; signaling pathways.

FIGURE 1

Major genetic markers involved in kidney development. The cell fate decision of renal cells are coordinately controlled with different genetic markers during nephrogenesis. AIM, anterior intermediate mesoderm; AQP, aquaporin; BMP, bone morphogenetic protein; Brn1, Bruno-like1; CALB1, calbindin; CD, Collecting duct; CM, cap mesenchyme; CSB, comma-shaped body; EMX, empty spiracles homolog; Eya1, eyes absent 1; FGF, fibroblast growth factor; FOXi1, forkhead box protein i1; FRS2α, fibroblast growth factor receptor substrate 2α; GATA, trans-acting T-cell-specific transcription factor; GDNF, glial cell–derived neurotrophic factor; GFRα1, glial cell line derived neurotrophic factor family receptor α1; Jag1, Jagged 1; HOX, homeobox; IM, intermediate mesoderm; Kdr, kinase insert domain protein receptor; LHX1, LIM-class homeodomain 1; LTL, lotus tetragonolobus lectin; MM, metanephric mesenchyme; NPCs, nephron progenitor cells; NPHS1, nephrosis 1; Osr1, odd skipped related 1; PAX, paired box protein; PI3K, phosphoinositide 3-kinases; PIM, posterior intermediate mesoderm; PTA, pre-tubular aggregate; RV, renal vesicle; SIX2, sine oculis-related homeobox 2; SLC2614, solute carrier 2614; SSB, S-shaped body; SYNPO, synaptopodin; TGFβ, transforming growth factor beta; UB, ureteric bud; UMOD, uromodulin; WNT, wingless-type mouse mammary tumor virus integration site; WD, Wolffian duct.

FIGURE 2

Crosstalk between major signaling pathways during nephron progenitor cell (NPC) differentiation. WNT9b, BMP7, and FGF2/9 are secreted by UB cells (green color). Stromal cells secret Decorin, SFRP1, Fat4, and TGFβ2 (orange color). High levels of WNT9b/β-catenin increase expression of the differentiation-specific genes (PAX8, C1qdc2, and WNT4) of nephron progenitor cells (NPCs). Fat4/Hippo signaling amplifies β-catenin activity. On the other hand, WNT signaling can be inhibited by SFRP1 and DKK1 to arrive appropriate number of nephrons in a definitive kidney. The BMP7/SMAD1/5 signaling pathway promotes differentiation of NPCs. Decorin antagonizes BMP7/SMAD signaling in NPCs. BMP7 activates proliferation by the TAK1-JNK-JUN cascade. FOS activation is regulated by FGF9. AP1 (a dimeric transcription factor composed of Jun and FOS) acts as a point of collaboration between the BMP7 and FGF9 signaling pathways. AP-1 activates transcription of a variety of genes (MYC, BCL-2, and p53) related to the cell cycle and anti-apoptotic events; thereby, it regulates survival and proliferation of NPCs. The FGF/RAS-MAPK, FGF/PI3K/AKT signaling pathway promotes survival and proliferation of NPCs. After binding of Notch2 to Notch ligands, NICD is released into the cytoplasm and translocates to the nucleus where the complex decreases self-renewal specific gene expression and primes NPCs for differentiation. TGFβ2 is required for MET-related gene expression during NPCs differentiation. AKT, protein kinase B; ALK, anaplastic lymphoma kinase; AP1, activator protein 1; APC, adenomatous polyposis coli; BMP, bone morphogenetic protein; CK1, casein kinase 1; Csl, CBF1/RBP-J, Su(H), Lag-1, the mammalian, fly, and worm orthologous proteins; DKK1, DKK1, Dickkopf-1; DVL, homologous to drosophila Dishevelled; EC, endothelial cells; ERK, extracellular signal-regulated kinase; Fat4, tumor suppressor homolog 4; FGF, fibroblast growth factor; Frz, Frizzled; GAB1, Grb2-associated binder 1; GSK-3β, glycogen synthase kinase 3β; GRB2, growth factor receptor-bound protein 2; JAK, Janus kinase; JNK, c-Jun N-terminal kinase; LATS1, large tumor suppressor homolog 1; LEF, lymphoid enhancing factor; LRP, low-density lipoprotein receptor-related protein; MAML, mastermind-like; MAPK, mitogen activated protein kinase; MEK, mitogen activated protein kinase; MET, mesenchymal to epithelial transition; MST1/2, Mammalian sterile 20-like kinases; NICD, notch intracellular domain; P, phosphate group; PI3K, phosphatidylinositol 3-kinase; RAS/RAF, Rat sarcoma/rapidly accelerated fibrosarcoma; SFRP1, secreted frizzled-related protein; Smad, Caenorhabditis elegans SMA (“small” worm phenotype) and Drosophila MAD (“Mothers Against Decapentaplegic”); SOS, Son of Sevenless; TAK1, TGF β-activated kinase; TCF, T-cell factor; TEAD, transcription factor family member; TGF-β, transforming growth factor-β; WNT, wingless-type mouse mammary tumor virus integration site; YAP, yes-associated protein.

FIGURE 3

Major signaling pathways in ureteric bud morphogenesis. Branching morphogenesis is tightly regulated by different growth factors such as GDNF, VEGF, and FGFs. GDNF and VEGF are secreted from the MM and FGF7/10 is produced by stromal cells. Binding of these growth factors to their tyrosine kinase receptors activates three major signaling pathways: RAS/MAPK, DAG/PKC/MAPK, and PI3-K/AKT. Thus, they stimulate mitotic proliferation, survival, and migration of UB cells. VEGF-A induces RET activation. Members of the TGF-β super-family, including BMP4 and TGFβ, which are expressed by mesenchymal cells that surround UB, inhibit UB outgrowth in a Smad-dependent manner. AKT, protein kinase B; ALK, anaplastic lymphoma kinase; BMP, bone morphogenetic protein; ERK, extracellular signal-regulated kinase; DAG, diacylglycerol; DVL, homologous to drosophila Dishevelled; EC, endothelial cells; FGF, fibroblast growth factor; FGFR, fibroblast growth factor receptor; FRS2α, fibroblast growth factor receptor substrate 2α; GAB1, Grb2-associated binder 1; GDNF, glial cell-derived neurotrophic factor; GFRα1, glial cell line-derived neurotrophic factor family receptor α1; GRB2, growth factor receptor-bound protein 2; MEK, mitogen activated protein kinase; NRP1, neuropilin 1; P, phosphate group; PI3K, phosphatidylinositol 3-kinase; PKC, protein kinase C; PLC-γ, Phospholipase C-γ; RAS/RAF, Rat sarcoma/rapidly accelerated fibrosarcoma; Smad, Caenorhabditis elegans SMA (“small” worm phenotype) and Drosophila MAD (“Mothers Against Decapentaplegic”); SOS, Son of Sevenless; Smad, Caenorhabditis elegans SMA (“small” worm phenotype) and Drosophila MAD (“Mothers Against Decapentaplegic”); TGF-β, transforming growth factor-β; UB, ureteric bud; VEGF, vascular endothelial growth factor; VEGFR, vascular endothelial growth factor receptor.

FIGURE 4

Molecular control of renal endothelial migration and patterning. VEGF is secreted by UB and NPC cells. Binding of VEGF to its tyrosine kinase receptor (KDR) activates three major signaling pathways: RAS/MAPK, DAG/PKC/MAPK, and PI3-K/AKT. Thus, it stimulates mitotic proliferation, survival, and migration of endothelial cells and promotes vascular network formation. UB cells produce SCF and induce survival, migration, and tube formation of endothelial cells. Expressions of WNT7b and WNT9b in the medullary ureteric epithelium regulate capillary lumen formation through modulation of VE-cadherin localization. AKT, protein kinase B; APC, adenomatous polyposis coli; c-Kit, tyrosine-protein kinase KIT (CD117); CK1, casein kinase 1; DAG, diacylglycerol; EC, endothelial cells; ERK, extracellular signal-regulated kinase; FRS2α, fibroblast growth factor receptor substrate 2; Frz, Frizzled; GAB1, Grb2-associated binder 1; GSK-3β, glycogen synthase kinase 3β; GRB2, growth factor receptor-bound protein 2; KDR, kinase insert domain protein receptor; MAPK, mitogen activated protein kinase; MEK, mitogen activated protein kinase; P, phosphate group; PI3K, phosphatidylinositol 3-kinase; PKC, protein kinase C; PLC-γ, phospholipase C-γ; RAS/RAF, Rat sarcoma/rapidly accelerated fibrosarcoma; SCF, stem cell factor; SOS, Son of Sevenless; VEGF, vascular endothelial growth factor; WNT, wingless-type mouse mammary tumor virus integration site.