Induced pluripotent stem cell-based disease modeling identifies ligand-induced decay of megalin as a cause of Donnai-Barrow syndrome

Abstract

Donnai-Barrow syndrome (DBS) is an autosomal-recessive disorder characterized by multiple pathologies including malformation of forebrain and eyes, as well as resorption defects of the kidney proximal tubule. The underlying cause of DBS are mutations in LRP2, encoding the multifunctional endocytic receptor megalin. Here, we identified a unique missense mutation R3192Q of LRP2 in an affected family that may provide novel insights into the molecular causes of receptor dysfunction in the kidney proximal tubule and other tissues affected in DBS. Using patient-derived induced pluripotent stem cell lines we generated neuroepithelial and kidney cell types as models of the disease. Using these cell models, we documented the inability of megalin R3192Q to properly discharge ligand and ligand-induced receptor decay in lysosomes. Thus, mutant receptors are aberrantly targeted to lysosomes for catabolism, essentially depleting megalin in the presence of ligand in this affected family.

Induced pluripotent stem cells provide mega insights into kidney disease

“…Taking this evidence altogether, Flemming and colleagues 4 propose a model by which mutant megalin could be destroyed within the endolysosomal compartment as a "sacrificial receptor" upon the binding by its cognate ligand SHH, ultimately instigating receptor dysfunction and disease (Figure 1). [1][2][3][4]6,7 The authors' findings extend previous observations showing that mutant LDL receptor fails to properly discharge cholesterol-rich lipoproteins with the endolysosomal system, 8 severely impairing the cellular clearance of lipids, thereby contributing to pathogenesis in familial hypercholesterolemia patients. In line with the latter idea, the previously unknown mutation localizes in an EGFtype repeat, a domain required for endosomal discharge of ligands by megalin.…”

“…In this issue of Kidney International, Flemming and colleagues demonstrate a way of overcoming this hurdle. 4 The researchers took advantage of recent advances in induced pluripotent stem cell (iPSC) technology 5 to create human "disease in a dish" models. Based on the use of patient-derived iPSC lines, the authors deciphered the cascade of molecular events determining the dysfunction of the mutant megalin receptor in a family affected with DBS.…”

“…Mammalian cells use a singlemembrane organelle called an endolysosome for the degradation and recycling of a variety of biological macromolecules, including lipids, carbohydrates, nucleic acids, and proteins. Based on their findings, Flemming et al 4 hypothesized that the loss of megalin induced upon the binding by the ligand GSTÀSHH was due to an abnormal degradation by the endolysosomal system. To verify this hypothesis, they analyzed the subcellular compartmentalizion of megalin in control and patient iPSC-derived neuro-epithelial precursor cells.…”

Endocytic Protein Defects in the Neural Crest Cell Lineage and Its Pathway Are Associated with Congenital Heart Defects

“…LRP2 is expressed in the neuroepithelium and loss of LRP2 in the knockout mouse model results in holoprosencephaly (fusion of the forebrain) [50] and buphthalmia (the overgrowth of the eye globe) [49]. Similar features are noted in patients with Donnai-Barrow/faciooculo-acoustio-renal syndrome, an autosomal recessive disorder caused by LRP2 mutations [55][56][57].…”

GAS1 is required for NOTCH-dependent facilitation of SHH signaling in the ventral forebrain neuroepithelium

“…Next, wild-type and GAS1 KO iPSCs were subjected to differentiation into neural progenitor cells (NPCs) of dorsal or ventral cell identity using established protocols ( Fig. 4 A) ( Chambers et al, 2009 ; Flemming et al, 2020 ). When treated with noggin, dorsomorphin and small molecule SB431542 to block BMP and TGFβ signaling, both wild-type and GAS1 KO iPSCs downregulated the pluripotency marker OCT4 and induced the neuroectodermal marker PAX6 ( Fig.…”