Podocin Inactivation in Mature Kidneys Causes Focal Segmental Glomerulosclerosis and Nephrotic Syndrome

Abstract

Podocin is a critical component of the glomerular slit diaphragm, and genetic mutations lead to both familial and sporadic forms of steroid-resistant nephrotic syndrome. In mice, constitutive absence of podocin leads to rapidly progressive renal disease characterized by mesangiolysis and/or mesangial sclerosis and nephrotic syndrome. Using established Cre-loxP technology, we inactivated podocin in the adult mouse kidney in a podocyte-specific manner. Progressive loss of podocin in the glomerulus recapitulated albuminuria, hypercholesterolemia, hypertension, and renal failure seen in nephrotic syndrome in humans. Lesions of FSGS appeared after 4 wk, with subsequent development of diffuse glomerulosclerosis and tubulointerstitial damage. Interestingly, conditional inactivation of podocin at birth resulted in a gradient of glomerular lesions, including mesangial proliferation, demonstrating a developmental stage dependence of renal histologic patterns of injury. The development of significant albuminuria in this model occurred only after early and focal foot process effacement had progressed to diffuse involvement, with complete absence of podocin immunolabeling at the slit diaphragm. Finally, we identified novel potential mediators and perturbed molecular pathways, including cellular proliferation, in the course of progression of renal disease leading to glomerulosclerosis, using global gene expression profiling.

Recent advances of animal model of focal segmental glomerulosclerosis

“…Myosin 1e (Myo1e) is one of the two Src homology 3 domain-containing "long-tailed" type I myosins in Actin filament cross-linking protein/Interacts with integrins and strengthens the podocyte-GBM interaction Atypical protein kinase C [68][69][70][71] Tight junctions/Formation of Par complex and interacts with slit diaphragm Rhophilin-1 [80] Rho GTPase activating protein 24 [80] Cytoplasm/Rho GTPase-interacting protein, integrity of glomerular filtration barrier Angiotensin II receptor [55][56][57] Angiotensin-converting enzyme [55][56][57] Membrane/pseudocyst formation at podocyte CD2-associated protein [65][66][67] CD2-associated protein [64] Insertion site of the slit diaphragm/Formation SD complex with podocin and nephrin Laminin subunit beta-2 [81][82][83][84] Laminin subunit beta-2 [81][82][83][84] Podocyte anchoring and differentiation in GBM microRNA 193α [74,75] Cytoplasm/Inhibition of expression of WT-1 Myosin 1e [49,50] Myosin 1e [49,50] Actin binding long-tailed motor protein/Regulation of actin cytoskeleton Nuclear factor of activated T cells [76,77] Transient receptor potential 6 [53,54] Membrane/the activation of calcineurin-NFAT/Wnt signaling via the increased calcium influx Podocin [46] Podocin [58,59] Insertion site of the SD/SD assembly and maintaining the signaling of nephrin Shroom family member 3 …”

“…Utilization of inducible Cre recombinase technology enabled the creation of a mouse model of podocinrelated NS through elective inactivation of podocin in mature mouse kidneys. Postnatal inactivation of podocin in mature kidneys by elective Cre induction led to massive proteinuria, glomerulosclerosis, and death in renal failure within a median of 11 weeks [59]. Nephrin (encoded by the NPHS1 gene) was identified as the cause of disease in congenital NS of the Finnish type [60].…”

Podocyte Purinergic P2X4 Channels Are Mechanotransducers That Mediate Cytoskeletal Disorganization

“…42 Therefore, we next analyzed the involvement of podocin in mechanical P 2 X 4 activation. To this end, podocin knockdown podocytes isolated from Nphs2 flox/flox , Cre +/+ mice 31,43 were used and tested for successful in vitro podocin downregulation according to Western blot analysis (Supplemental Figure 7). Interestingly, mechanically induced currents were completely abolished in podocin knockdown podocytes compared with respective control podocytes (Figure 6, E-G), whereas ATP-induced currents were unchanged (Supplemental Figure 8).…”

A Homozygous Missense Mutation in the Ciliary Gene TTC21B Causes Familial FSGS

“…20 Proteins from glomeruli, tubules, total kidney, or cultured podocytes were extracted in 50 mM Tris-HCl, 150 mM NaCl, 0.5% sodium deoxycholate, 2 mM EDTA, 1% Triton X-100, and 0.1% sodium dodecyl sulfate. Protein dosage was then performed using the BCA protein assay kit (Thermo Scientific).…”