Uromodulin (UMOD) is a protein made exclusively in the thick ascending limb. Clinical studies have demonstrated that rare missense mutations in UMOD result in autosomal dominant tubulointerstitial kidney diseases manifest by tubulointerstitial fibrosis (TIF), 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 an increased risk of chronic kidney disease (CKD) and hypertension. Interestingly, Dahl salt-sensitive (SS) rats exhibit many of the same pathologies observed in these clinical populations with alterations in UMOD. The goal of this study was to assess the qualitative and quantitative aspects of 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 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 was performed in 16 week old SS (n=5), SS.BN1 (n=7) and BN (n=6) rats maintained on a low salt (LS) diet. BP (radiotelemetry) and proteinuria were assessed during LS feeding and during three weeks of high salt (HS) feeding in a different group of 8-10 week old SS (n=9) and SS.BN1 (n=8) rats. For western blotting, urine was normalized based on the protein concentration, and the density of the 85 kDa UMOD band in SS and SS.BN1 samples were normalized to the average density observed in BN rats. The UMOD band was 4.5 fold higher (p In summary, these data demonstrate striking qualitative and quantitative differences in UMOD between SS and SS.BN1 rats. The pattern of 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 function may, in part, be responsible for such pathologies in SS rats.

Chronic kidney disease (CKD) is defined as glomerular filtration rate (GFR) less than 60 mL/min/1.73 m2 for 3 months and is characterized by progressive loss of renal function. The second leading cause of CKD is hypertension. More than half of CKD patients also suffer from hypertension. Arteries and arterioles adjust to the fluctuations in the systematic blood pressure through a mechanism called autoregulation. In the kidneys, autoregulation protects the delicate glomeruli capillaries from high blood pressure and occurs through myogenic constriction (MC). MC refers to contraction of arterioles in response to an increase in the blood pressure. Chronically hypertensive individuals and animal models have an enhanced MC, leading to minimal renal injury despite their elevated blood pressure. Experimental and clinical evidence point to a role for the MC in the pathogenesis of the CKD, however, the mechanism through which preglomerular arterial MC contributes to CKD has not been fully elucidated. This thesis showed that augmented MC in chronically hypertensive animal models was due to increased thromboxane A2 prostaglandin that was not released from the endothelium (Chapter 2). Nevertheless, inhibiting MC while also reducing the blood pressure prevented salt-induced renal injury even though the blood pressure was still not normalized compared to the normotensive controls (Chapter 3). The resulting improvement in renal structure and function could be attributed to the reduction in the blood pressure, albumin, and uromodulin (UMOD) excretion (Chapter 3). UMOD is a kidney-specific glycoprotein that, based on a genome-wide association study have the strongest association to CKD (Chapter 3). Comparing two CKD hypertensive animal models further revealed that CKD progression was independent of the blood pressure and strongly associated with UMOD excretion levels (Chapter 4). Collectively, the data discussed in this thesis demonstrates potential therapeutic targets in CKD hypertensive animal models. / Dissertation / Doctor of Philosophy (PhD)

This thesis provides an appraisal of the structure of clustering of metabolic phenotypes and evaluates the pathophysiological mechanisms underlying the relationship between urinary uric acid and albumin excretion. Two population-based studies were involved. In the first part, we used data obtained in a large representative cross-sectional survey in the Czech Republic (Czech post-MONICA study). We showed that the urinary albumin/creatinine ratio (uACR) was an independent factor for an increase in serum uric acid (SUA) levels in adults without manifest metabolic syndrome (MetS), but with 1-2 MetS component(s). Furthermore, SUA levels increased by the synergistic interaction of uACR with visceral adiposity and blood pressure, which may suggest obesity-related hypertension with altered renal hemodynamics as the primary mechanism. In the second part, we analyzed data captured in a representative population sample of French Canadians (CARTaGENE study) with more detailed urine biochemical analyses available. This study yielded two novel observations. First, we showed that the rs13129697 major T allele, which has been associated with increased SUA levels in our analysis as well as in prior publications, was associated with a paradoxical decrease in uACR. The reason for this discrepant finding is the...