Striking Differences in Urinary Uromodulin, Salt‐sensitive Hypertension and Proteinuria in Dahl SS vs. SS.BN1 Consomic Rats

Abstract

Uromodulin (UMOD) is a protein made exclusively by epithelial cells of the thick ascending limb. Numerous clinical studies have demonstrated that rare missense mutations in UMOD result in autosomal dominant tubulointerstitial kidney diseases manifest by tubulointerstitial fibrosis, tubular cysts and a rapid progression to renal failure. In addition, several genome wide association studies reported that common single nucleotide polymorphisms in the UMOD gene are associated with a 20% and 15% increased risk of chronic kidney disease (CKD) and hypertension, respectively, in the general population. Interestingly, Dahl salt‐sensitive (SS) rats exhibit many of the same pathologies observed in these clinical populations; however, whether UMOD is altered in Dahl SS rats has not been examined.The goal of this study was to assess the qualitative and quantitative aspects of urinary UMOD via western blotting and the extent of SS hypertension and proteinuria in Dahl SS vs. a consomic rat strain in which chromosome 1 of the salt‐resistant Brown‐Norway (BN) rat, harboring the UMOD gene, has been introgressed into the Dahl SS background (SS.BN1). We hypothesized that differences in urinary UMOD would be apparent in SS vs. SS.BN1 rats maintained on a low salt‐diet and that the extent of SS hypertension and proteinuria would be attenuated in SS.BN1 vs SS rats. Western blot of urinary UMOD (mouse monoclonal, sc‐271022) was performed in 16 week old SS (n=5), SS.BN1 (n=7) and BN (n=6) rats maintained on a 0.4% NaCl diet since birth. BP (radiotelemetry) and proteinuria were assessed during 0.4% NaCl feeding and during three weeks of 4.0% NaCl feeding in a different group of 8–10 week old SS (n=5) and SS.BN1 (n=8) rats.For western blotting, loading of urine was normalized to urinary creatinine content and the density of the most abundant occurring 85 kDa band in SS and SS.BN1 samples was normalized to the average density observed in BN rats. The 85 kDa UMOD band was 4.5 fold higher (p<0.01) in SS.BN1 vs. SS rats with similar levels observed between SS.BN1 and BN rats. Interestingly, a unique ~45 kDa UMOD band was only observed in SS rats, suggestive of structural alterations in UMOD. During 0.4% NaCl feeding, substantially higher levels of systolic BP (161±1 vs. 141±2 mmHg, P<0.001) and proteinuria (153±15 vs. 30±5 mg/day) were observed in SS vs. SS.BN1 rats, respectively. Administration of a 4% NaCl diet for three weeks exacerbated these differences in BP (183±3 vs. 149±1 mmHg, P<0.001) and proteinuria (218±24 vs. 68±15 mg/day, P<0.001) in SS vs. SS.BN1 rats, respectively.In summary, these data demonstrate striking qualitative and quantitative differences in urinary UMOD between SS and SS.BN1 rats. The pattern of urinary UMOD expression in SS rats is consistent with that observed in some patient populations of UMOD associated kidney disease. Finally, the evidence that SS.BN1 rats, harboring the UMOD gene from BN rats, exhibit significant protection against SS hypertension and proteinuria is consistent with the notion that an alteration in UMOD structure or function may, in part, be responsible for such pathologies in SS rats.Support or Funding InformationEast Tennessee State University, American Society of Nephrology, American Heart Association, American Physiological SocietyThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.