Tubular cell loss in early inv/nphp2 mutant kidneys represents a possible homeostatic mechanism in cortical tubular formation

Abstract

Inversion of embryonic turning (inv) cystic mice develop multiple renal cysts and are a model for type II nephronophthisis (NPHP2). The defect of planar cell polarity (PCP) by oriented cell division was proposed as the underlying cellular phenotype, while abnormal cell proliferation and apoptosis occur in some polycystic kidney disease models. However, how these cystogenic phenotypes are linked and what is most critical for cystogenesis remain largely unknown. In particular, in early cortical cytogenesis in the inv mutant cystic model, it remains uncertain whether the increased proliferation index results from changes in cell cycle length or cell fate determination. To address tubular cell kinetics, doubling time and total number of tubular cells, as well as amount of genomic DNA (gDNA), were measured in mutant and normal control kidneys. Despite a significantly higher bromodeoxyuridine (BrdU)-proliferation index in the mutant, total tubular cell number and doubling time were unaffected. Unexpectedly, the mutant had tubular cell loss, characterized by a temporal decrease in tubular cells incorporating 5-ethynyl-2´-deoxyuridine (EdU) and significantly increased nuclear debris. Based on current data we established a new multi-population shift model in postnatal renal development, indicating that a few restricted tubular cell populations contribute to cortical tubular formation. As in the inv mutant phenotype, the model simulation revealed a large population of tubular cells with rapid cell cycling and tubular cell loss. The proposed cellular kinetics suggest not only the underlying mechanism of the inv mutant phenotype but also a possible renal homeostatic mechanism for tubule formation.

Identification of renal cyst cells of type I Nephronophthisis by single-nucleus RNA sequencing

“…An imbalance in the regulation of proliferation and apoptosis in renal cyst cells has been recognized as an important factor contributing to cyst formation in ADPKD and NPH( Sugiyama and Yokoyama, 2006 ; Ibrahim, 2007 ; Lee, 2016 ; Shigeta et al, 2018 ). Our snRNA-seq results showed that PCNA , Cyclin D1 and Caspase3 levels were increased in cyst cells compared to all other kidney cells ( Supplementary Figure S2 ).…”

“…Whether Niban1 regulates cyst cell formation through the same pathways as in cancer cells remains to be verified. Previous studies had shown that the protein encoded by NPHP1 had an anti-apoptotic function, that silencing NPHP1 increases susceptibility to apoptosis, leading to significantly higher levels of apoptosis ( Wodarczyk et al, 2010 ; Shigeta et al, 2018 ; Mannella et al, 2019 ). These observations were consistent with the findings of the present study, in which we found that, unlike in ADPKD, apoptosis appears to be more predominant than cell proliferation in NPHP1.…”