Abstract
BACKGROUND: Nephronophthisis (NPH) is classified under the category of renal ciliopathies and is the most common genetic disease leading to renal failure in children. Early-onset and progressive renal tubulointerstitial fibrosis represents one of the most significant features, culminating in renal insufficiency. However, the molecular mechanism of tubulointerstitial fibrosis remains unclear. Previously, we constructed an NPH mouse model via CRISPR-Cas9. This mouse model demonstrated typical features of tubulointerstitial fibrosis. In this study, we aimed to explore the pathogenesis of tubulointerstitial fibrosis in NPH and identify early intervention targets in both the NPH models and patients. METHODS: In this study, transcriptome changes in mouse kidneys were analyzed through RNA sequencing to explore the molecular mechanisms of renal tubulointerstitial fibrosis in NPH. We found an increased abundance of calpain1 in both the NPH models and patients. Pathway enrichment analysis indicated autophagy-lysosomal pathway was altered in the NPH models. Western blot, immunofluorescence or immunohistochemical staining were used to verify the expression of calpain1. We also detected autophagy activities in NPH models by lysotracker staining and transmission electron microscopy (TEM). Epithelial or mesenchymal-specific markers and Masson's trichrome staining were used to detect the status of tubulointerstitial fibrosis. Furthermore, NPH models were treated with a calpain1 inhibitor to explore the role of calpain1 in autophagy-lysosomal pathway and tubulointerstitial fibrosis. RESULTS: The increased abundance of calpain1 impaired the autophagy-lysosomal pathway and induced tubulointerstitial fibrosis by promoting epithelial-to-mesenchymal transition. On the other hand, calpain1 inhibition could enhance the autophagy-lysosomal pathway and ameliorate the phenotypes of tubulointerstitial fibrosis in NPH models. CONCLUSIONS: Calpain1-mediated autophagy-lysosomal pathway disorder may be an important cause of tubulointerstitial fibrosis in NPH. Calpain1 may have therapeutic implications for renal tubulointerstitial fibrosis.