Investigation of notch pathway activation and its relation to gremlin in autosomal dominant polycystic kidney disease

Abstract Background and Aims Activation of the NOTCH signalling pathway has been described in several progressive kidney diseases. Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a genetic disease caused by PKD1 or PKD2 mutations, which codify for the Polycystin-1 and Polycystin-2 proteins, respectively. ADPKD prevalence is among 1:800 and 1:1000 of live births and is characterized by fluid-filled renal cysts. During this process the production of chemokines, cytokines and growth factors by epithelial cells, interstitial fibroblasts and inflammatory cells, such as macrophages, increases, leading to end-stage renal disease (ESRD). GREMLIN has been proposed GREMLIN as an important mediator of chronic kidney disease in preclinical studies. In addition, urinary levels of GREMLIN may be a biomarker in any renal disease. However, there are no studies on GREMLIN in polycystic kidney disease. Method We have done the studies in an orthologous murine model of polycystic kidney disease (Pkd1cond/cond;Tam-Cre−/+) where we investigated the role of GREMLIN and its related mechanisms (its receptor VEGFR2 and the Notch signalling pathway) in different stages of renal cystic progression. The polycystic phenotype was induced in lactating mice by administering tamoxifen to the mother on postnatal days 10 and 11, causing a deletion in Pkd1 gene. Studies were performed considering different sacrifice points: at 18, 30 and 45 days. Furthermore, in urine and renal tissue from ADPKD patients, we studied the expression of GREMLIM. Results We have been able to see how in Pkd1−/+ mutant mice, grem-1 renal expression (that encoding GREMLIN protein), was increased from 18 days, with a significant increase at 30 days. This increase was associated with progressive cysts expansion and detriment in renal function measured by BUN. These results were confirmed at the protein level by western blot. Immunohistochemistry revealed positive GREMLIM staining since pre-cystic tubuloepithelial cells, which remained elevated in the tubules at later times. Positive GREMLIN expression was observed in biopsy samples of cysts from ADPKD patients as well as GREMLIN protein presence in urine samples. In the polycystic model, GREMLIN induction was correlated with VEGFR2 activation in the same tubular segments. Cyst formation was associated with activation of the NOTCH pathway, characterized by NOTCH1 and NOTCH3 activation. Conclusion Thus, we can suggest that GREMLIN expression may be an important mediator of renal damage progression in ADPKD and this protein would act through the Notch pathway.