The nephronophthisis protein GLIS2/NPHP7 is required for the DNA damage response in kidney tubular epithelial cells

Abstract

Nephronophthisis (NPH) is an autosomal-recessive cystic kidney disease representing the most frequent genetic cause of end-stage kidney failure in children and adolescents. NPH is caused by genetic variants in >20 NPHP genes. Although nearly all NPHP genes encode ciliary proteins, classifying NPH as a renal ciliopathy, there is evidence for a pathogenic role of a compromised DNA damage response (DDR). Here, we present a novel Nphp7/Glis2-deficient mouse model with an early stop codon using CRISPR/Cas9-mediated genome editing (Glis2Y122X). Homozygous mice displayed dilated kidney tubules progressing to cystic kidney disease with significant fibrosis at a higher age. Interestingly, the kidneys of these animals exhibited an accumulation of DNA damage (DD) early on, even before any functional impairment of the kidneys became apparent. Interactome analysis for GLIS2 revealed an array of DDR-related proteins within the GLIS2 protein complex. Consistent with the in vivo data, the knockdown of Glis2 in kidney epithelial cells led to increased DNA damage. Moreover, supporting the role of GLIS2 in the DDR, we demonstrate that a substantial proportion of GLIS2 is present within the chromatin fraction of cells, which is further increased upon UV-induced DD. Live-cell imaging revealed the rapid recruitment of green fluorescent protein (GFP)-tagged GLIS2 to sites of laser-induced DD, a response diminished in Glis2Y122X and a variant of Glis2 resembling a known patient mutation. Overall, our data provide compelling evidence for the direct involvement of GLIS2 in the DDR, highlighting the loss of genome stability as an important factor contributing to the pathogenesis of renal ciliopathies.