The renal inflammatory network of nephronophthisis

SOX9-dependent fibrosis drives renal function in nephronophthisis

Fibrosis is a key feature of a broad spectrum of cystic kidney diseases, especially autosomal recessive kidney disorders such as nephronophthisis (NPHP). However, its contribution to kidney function decline and the underlying molecular mechanism(s) remains unclear. Here, we show that kidney-specific deletion of Fbxw7, the recognition receptor of the SCFFBW7 E3 ubiquitin ligase, results in a juvenile-adult NPHP-like pathology characterized by slow-progressing corticomedullary cysts, tubular degeneration, severe fibrosis, and gradual loss of kidney function. Expression levels of SOX9, a known substrate of FBW7, and WNT4, a potent pro-fibrotic factor and downstream effector of SOX9, were elevated upon loss of FBW7. Heterozygous deletion of Sox9 in compound mutant mice led to the normalization of WNT4 levels, reduced fibrosis, and preservation of kidney function without significant effects on cystic dilatation and tubular degeneration. These data suggest that FBW7-SOX9-WNT4-induced fibrosis drives kidney function decline in NPHP and, possibly, other forms of autosomal recessive kidney disorders.

Granulomatous nephropathy: have you thought about genetics?

We report here the case of a 16-year-old girl with chronic kidney disease, where biopsy revealed tubulointerstitial nephropathy with granulomas. Initial treatments included immunosuppressive therapy unless genetic testing with exome sequencing identified nephronophthisis due to a homozygous deletion of the NPHP1 gene, marking a unique instance of granulomatous nephropathy related to nephronophthisis. With severe kidney damage, her function has not recovered, necessitating peritoneal dialysis and transplantation. This case highlights the need to consider nephronophthisis in inflammatory interstitial and granulomatous nephropathy, especially when it appears severe and early in life. In addition, it underscores the importance of genetic testing for accurate diagnosis and management in pediatric nephropathies.

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

Background: Nephronophthisis (NPH) is the most common genetic cause of end-stage renal disease (ESRD) in childhood, and NPHP1 is the major pathogenic gene. Cyst formation at the corticomedullary junction is a pathological feature of NPH, but the mechanism underlying cystogenesis is not well understood. The isolation and identification of cystic cell subpopulation could help to identify their origins and provide vital clues to the mechanisms underlying cystogenesis in NPH. Methods: Single-nucleus RNA sequencing (snRNA-seq) was performed to produce an atlas of NPHP1 renal cells. Kidney samples were collected from WT (Nphp1 +/+) mice and NPHP1 (Nphp1 del2-20/del2-20) model mice. Results: A comprehensive atlas of the renal cellular landscape in NPHP1 was generated, consisting of 14 basic renal cell types as well as a subpopulation of DCT cells that was overrepresented in NPHP1 kidneys compared to WT kidneys. GO analysis revealed significant downregulation of genes associated with tubular development and kidney morphogenesis in this subpopulation. Furthermore, the reconstruction of differentiation trajectories of individual cells within this subpopulation confirmed that a specific group of cells in NPHP1 mice become arrested at an early stage of differentiation and proliferate to form cysts. We demonstrate that Niban1 is a specific molecular marker of cystic cells in both mice and human NPHP1. Conclusion: In summary, we report a novel subpopulation of DCT cells, marked by Niban1, that are classified as cystic cells in the NPHP1 mice kidney. These results offer fresh insights into the cellular and molecular basis of cystogenesis in NPH.

A2BAR Antagonism Decreases the Glomerular Expression and Secretion of Chemoattractants for Monocytes and the Pro-Fibrotic M2 Macrophages Polarization during Diabetic Nephropathy

Some chemoattractants and leukocytes such as M1 and M2 macrophages are known to be involved in the development of glomerulosclerosis during diabetic nephropathy (DN). In the course of diabetes, an altered and defective cellular metabolism leads to the increase in adenosine levels, and thus to changes in the polarity (M1/M2) of macrophages. MRS1754, a selective antagonist of the A2B adenosine receptor (A2BAR), attenuated glomerulosclerosis and decreased macrophage-myofibroblast transition in DN rats. Therefore, we aimed to investigate the effect of MRS1754 on the glomerular expression/secretion of chemoattractants, the intraglomerular infiltration of leukocytes, and macrophage polarity in DN rats. Kidneys/glomeruli of non-diabetic, DN, and MRS1754-treated DN rats were processed for transcriptomic analysis, immunohistopathology, ELISA, and in vitro macrophage migration assays. The transcriptomic analysis identified an upregulation of transcripts and pathways related to the immune system in the glomeruli of DN rats, which was attenuated using MRS1754. The antagonism of the A2BAR decreased glomerular expression/secretion of chemoattractants (CCL2, CCL3, CCL6, and CCL21), the infiltration of macrophages, and their polarization to M2 in DN rats. The in vitro macrophages migration induced by conditioned-medium of DN glomeruli was significantly decreased using neutralizing antibodies against CCL2, CCL3, and CCL21. We concluded that the pharmacological blockade of the A2BAR decreases the transcriptional expression of genes/pathways related to the immune response, protein expression/secretion of chemoattractants, as well as the infiltration of macrophages and their polarization toward the M2 phenotype in the glomeruli of DN rats, suggesting a new mechanism implicated in the antifibrotic effect of MRS1754.

Repurposing small molecules for Nephronophthisis and related renal ciliopathies

Nephronophthisis is an autosomal recessive tubulo-interstitial nephropathy, belonging to the ciliopathy disorders, characterized by fibrosis and/or cysts. It is the most common genetic cause of renal failure in children and young adults. Clinically and genetically heterogeneous, it is caused by variants in ciliary genes resulting in either an isolated kidney disease or syndromic forms in association with other manifestations of ciliopathy disorders. No curative treatment is currently available. Over the past two decades, advances in understanding disease mechanisms have identified several dysregulated signaling pathways, some shared with other cystic kidney diseases. Notably, molecules previously developed to target these pathways have shown promising beneficial effects in orthologous mouse models. In addition to these knowledge-based repurposing approaches, unbiased "in cellulo" phenotypic screens of "repurposing" libraries identified small molecules able to rescue the ciliogenesis defects observed in nephronophthisis conditions. Those compounds appeared to act on relevant pathways and, when tested, showed beneficial nephronophthisis-associated kidney and/or extra-renal defects in mice. In this review, we have summarized those studies which highlight the drug repurposing strategies in the context of a rare disorders such as nephronophthisis-related ciliopathies, with broad genetic heterogeneity and systemic manifestations but with shared disease mechanisms.