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UBC Theses and Dissertations

Generation, characterization and optimization of mouse models for genetic glomerular disease Refaeli, Ido


Dominant and recessive mutations in podocalyxin (PODXL/Podxl) are associated with human kidney disease. Some PODXL/Podxl mutations manifest as anuria while others are associated with proteinuria. Homozygous loss-of-function mutations in the gene are associated with early-onset congenital nephrotic syndrome. By contrast, PODXL heterozygosity is associated with adult-onset kidney disease and podocalyxin shedding into the urine is a common biomarker of podocyte injury in various nephrotic contexts. It is unknown, however, how different lesions in PODXL/Podxl contribute to these disparate disease pathologies. Here we generated three mutant mouse stains: one that lacks Podxl in all tissues (Podxl-/-), a second that selectively deletes the gene in mature (capillary loop stage) podocytes (Podxl∆ᴾᵒᵈ), and a third that is heterozygous for Podxl in all tissues (Podxl⁺/-). We used histologic and ultrastructural analyses, as well as clinical chemistry assays to evaluate kidney development and function in these strains. In contrast to Podxl-/- mice, which have previously been shown to die 24 hours after birth from anuria and hypertension, we show that Podxl∆ᴾᵒᵈ mice develop an acute congenital nephrotic syndrome characterized by focal segmental glomerulosclerosis and severe proteinuria. Podxl⁺/- mice have a normal lifespan, and fail to develop kidney disease under normal conditions. Intriguingly, although wild-type C57Bl/6J mice are resistant to chemically-induced nephrosis, Podxl⁺/- mice are highly susceptible, as administration of puromycin aminonucleoside induces collapsing FSGS and nephrotic syndrome. The severity of kidney injury in Podxl⁺/- mice in response to puromycin aminonucleoside was optimized through dose-response experiments, and we used this model to evaluate the anti-proteinuric effects of the two calcineurin inhibitors, cyclosporine and voclosporin. Calcineurin inhibition by either voclosporin or cyclosporine did not attenuate proteinuria in Podxl⁺/- mice induced with puromycin aminonucleoside. In conclusion, we find that the developmental timepoint at which Podxl expression is ablated (immature vs. mature podocytes) has a profound impact on the renal disease phenotype due to its critical roles in both the formation and the maintenance of podocyte ultrastructure. In addition, Podxl∆ᴾᵒᵈ and Podxl⁺/- mice offer powerful new tools to evaluate early biomarkers of proteinuric kidney disease, to define the function of genes during kidney injury, and to test new therapies.

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