Cingulin-like 1 (Cgnl1) Plays a Role in Hypertension and Kidney Disease

Around 30 million people of all ages in the United States are affected by chronic kidney disease (CKD), with hypertension being a major cause of patients progressing to kidney failure. Previous genetic analyses involving the Dahl salt‐sensitive (SS) rat identified multiple genetic loci linked to kidney injury, including a region on chromosome 8. To confirm the genetic association, an S.SHR(8) congenic was developed to transfer the linked chromosome 8 genomic segment from the SHR (resistant to kidney injury) onto the SS genetic background. The S.SHR(8) demonstrated significantly reduced proteinuria and improved renal function compared to SS control. Based on whole genome sequencing and bioinformatics analysis of the chromosome 8 region, cingulin‐like 1 ( Cgnl1 ) was identified as a putative gene linked to kidney injury. Cgnl1 is known to localize to adherens and tight cell‐cell junctions mediating junction assembly via regulating the activity of the small GTPases such as RhoA and Rac1. Protein levels of Cgnl1 (via western blot analysis) were found to correlate with increased kidney injury in the SS rat. We have developed a genetic knockout animal (SS‐ Cgnl1 −/− ) to test the hypothesis that loss of Cgnl1 will result in a significant attenuation of hypertension and kidney injury compared to SS‐WT. A temporal analysis of cardiovascular and renal measurements was conducted on SS‐WT and SS‐ Cgnl1 −/− from 6–15 weeks of age under low or high salt diets (0.3% or 2% NaCl). All statistical analysis was performed using one‐way ANOVA/Tukey multiple correction. On low‐salt, SS‐ Cgnl1 −/− animals (n=6) demonstrated reduced proteinuria compared to SS‐WT animals (n=6) for the entirety of the experiment (e.g., 21.9 ± 0.6 versus 87.6 ± 9.3 mg/24hr at week 15, p=0.03). Similar results were seen with high‐salt; SS‐ Cgnl1 −/− animals (n=6) demonstrated reduction in proteinuria compared to SS‐WT (28.7 ± 2.9 versus 161.4 ± 33.1 mg/24hr at week 15, p<0.0001). While high‐salt fed SS‐WT animals exhibited a significant increase in in mean arterial pressure (MAP) compared to low‐salt SS‐WT (156 ± 5.9 versus 133.9 ± 4.0 mmHg, p=0.0095), MAP for SS‐ Cgnl1 −/− remained unchanged between low and high‐salt groups (119.3 ± 3.2 and 124.8 ± 3.8 mmHg respectively, NS). On both low and high‐salt diets SS‐ Cgnl1 −/− animals demonstrated less kidney hypertrophy and lower heart weight compared to SS‐WT, supporting the proteinuria and blood pressure measurements. For example, high‐salt fed SS‐ Cgnl1 −/− kidney weight to body weight ratio (mg/g) = 9.0 ± 0.26 compared to 10.3 ± 0.45 for the SS‐WT, p=0.03; high‐salt SS‐ Cgnl1 −/− heart weight to body weight ratio (mg/g) = 3.64 ± 0.04 compared to 4.46 ± 0.19 for the SS‐WT, p=0.0003. In addition, kidney pathology measures were all significantly improved in SS‐ Cgnl1 −/− compared to SS‐WT animals, including glomerular injury and tubulointerstitial injury (all p<0.05). In total, the physiological characterization of the SS‐ Cgnl1 −/− suggests that Cgnl1 plays an important role in the onset and progression of kidney disease in the Dahl SS model. Current studies are focusing on investigating the molecular mechanism by which altered expression (RNA sequencing) and/or protein function in Cgnl1 is linked to kidney injury and blood pressure in the Dahl SS model.