Mutation in NUP155 Causes Activation of Autophagy in Podocytes through Retraining the YAP in the Cytoplasm to Induce Podocyte Loss and Subsequent Nephrotic Syndrome

Background: Hereditary nephrotic syndrome (HNS) is a clinical syndrome characterized by increased permeability of the glomerular filtration barrier. Recently, mutations in a class of genes encoding nucleoporins (NUPs) have been found to cause NS. Methods: First, whole-exome sequencing, and Sanger sequencing were performed in Chinese familial patients with NS. A Drosophila model with Nup154 (the NUP155 ortholog) knockdown (KD) was established. NUP155-Knockdown stably transfected cell lines of human immortalized podocytes were constructed and the rescued experiments were performed by overexpressing the mutants and wild NUP155 in NUP155-KD cells. Co-IP mass spectrometry was used to explore the downstream mechanism of NUP155 mutation causing NS. Results: We identified mutations in the NUP155 gene, coding an inner ring sub-unit of the nuclear pore complex, in Chinese familial patients with NS, manifested as FSGS. The missense variant (c.397G>T) results in p.Asp133Tyr. The other mutation in the splice region (c.4037+2T>C) led to four kinds of alternative splicing transcripts, all encoding premature proteins. The intensity of NUP155 in the patients' kidneys was diffusely decreased compared with the control. Meanwhile, podocyte-specific expression of WT1 and NPHS2 was significantly reduced, showing podocyte loss. In adult Nup154-KD drosophila, the number of nephrocytes is decreased. NUP155-KD podocytes exhibit reduced proliferation and migration abilities and heightened susceptibility to injury. Recovering two mutant proteins cannot rescue these phenotypes. The variants in NUP155 affected the interaction with NUP133 and NUP93, causing disrupted nuclear pore complex (NPC) assembly. Additionally, autophagy activation, an increase in YAP phosphorylation, and a reduction of nuclear YAP localization in NUP155-KD podocytes and proband kidney, suggesting NUP155 is essential for YAP nuclear import and aberrant nuclear localization of YAP leads to increased autophagy. Conclusion: We show that the mutations in NUP155 could cause NS, which led to abnormal NPC, retraining nucleocytoplasmic shuttling of YAP, and activation of autophagy, eventually leading to dysplasia and impaired function of glomerular podocytes.