Loss of Cingulin‐like 1 in Dahl Salt‐Sensitive Rats Leads to Reduced Renal Injury and Blood Pressure

Abstract

Hypertension is both a cause and effect of chronic kidney disease (CKD) and impacts a significant proportion of patients, with a worldwide prevalence of 10‐15%. Previous genetic studies involving the Dahl salt‐sensitive (SS) rat, a model of hypertensive CKD, identified multiple genetic loci linked to kidney injury, including a region on chromosome (Chr) 8. Subsequently, an S.SHR(8) congenic (i.e. transfer of kidney injury resistant SHR genome onto the SS background) demonstrated significantly reduced proteinuria and improved renal function compared to SS control. To identify the gene/s responsible, genome sequencing and bioinformatics analysis identified cingulin‐like 1 (Cgnl1) as a putative gene linked to kidney injury on Chr. 8. 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. A SS‐Cgnl1−/− knockout (KO) was developed to test the hypothesis that loss of Cgnl1 will result in a significant attenuation of kidney injury compared to SS (WT). Both on low and high‐salt (LS=0.3% or HS=2.0% NaCl), KO animals (n=6) demonstrated reduced proteinuria compared to WT animals (n=6) for the entirety of the experiment (HS; KO= 28.7 ± 2.9 versus WT= 161.4 ± 33.1 mg/24hr at week 15, p<0.0001). To further validate Cgnl1’s effect on blood pressure and kidney injury, a temporal analysis (6‐12 weeks) using telemetry and additional renal measurements were conducted on WT and KO animals. On HS, KO animals (n=6) demonstrated reduced proteinuria compared to WT (n=6) for the entirety of the experiment (52.1 ± 7.2 versus 395.9 ± 29.8 mg/24hr at week 12, p<0.0001). While HS fed WT animals exhibited a significant increase in BP compared to LS WT (MAP=197.0 ± 5.0 versus 142.8 ± 3.5 mmHg, p<0001), KO remained unchanged (MAP= 127.6 ± 2.7 and 133.9 ± 3.7 mmHg respectively, NS). Kidney pathology measures, including glomerular and tubular injury were all significantly improved (all p<0.05) in KO compared to WT. Nephron number was measured with no significant difference between WT and KO in young animals, but HS fed WT demonstrated a significant loss of nephrons compared to KO. Bulk RNAseq of kidneys from WT and KO identified Cgnl1 as top downregulated gene with altered expression of many known genes linked with Cgnl1 compared to WT, along downregulation of genes associated with renal injury, mainly reflective of physiological differences from week12‐15. To better identify genes involved in onset of injury, single nuclei RNAseq was performed at week 4 (before physiological differences) to evaluate impact of Cgnl1 in distinct cell populations initiating injury. Additional work is also currently being done on HEK293‐ Cgnl1 knockout cell lines for more mechanistic study of Cgnl1 and pathways. In total, the molecular work, along with the physiological characterization of the SS‐Cgnl1−/−, is expected to provide insight into the role of Cgnl1 in the onset and progression of hypertensive kidney disease and identify new therapeutic targets.