Urinary Uromodulin, Dietary Sodium Intake and Ambulatory Blood Pressure in Patients With Chronic Kidney Disease

In chronic kidney disease (CKD), hypertension is characterized by the phenomenon of sodium-sensitivity, i.e., the disproportionate increase in blood pressure (BP) due to an increase in dietary sodium consumption to maintain homeostasis through urinary sodium excretion. Impaired renal circulation, blunt suppression of renin-angiotensin-aldosterone system, sympathetic nervous system overactivity, paradoxically reduced levels of atrial natriuretic peptide and hyperinsulinemia represent the main pathophysiologic mechanisms. Accumulated evidence has suggested that uromodulin plays a central role in the development of sodium-sensitive hypertension. Uromodulin is a kidney-specific glycoprotein which is exclusively produced by the epithelial cells lining the thick ascending limb and early distal convoluted tubule. It is currently recognized as a multifaceted player in kidney physiology and disease, with discrete roles for intracellular, urinary, interstitial and serum uromodulin. Among these, urinary uromodulin modulates renal sodium handling through regulating tubular transporters that reabsorb sodium and are targeted by diuretics, i.e., the loop diuretic-sensitive Na+-K+-2Cl- cotransporter type 2 (NKCC2) and the thiazide-sensitive Na+/Cl- cotransporter (NCC). Given these roles, the contribution of uromodulin to sodium-sensitive hypertension has been proposed. In preclinical models, uromodulin deficiency causes decreased BP that is resistant to dietary salt, while uromodulin overexpression causes hypertension due to increased tubular sodium reabsorption that is responsive to furosemide. Genetic human studies have identified robust associations of specific UMOD gene variants with sodium sensitivity and incident hypertension risk, while comprehensive Mendelian randomization studies have affirmed these associations by highlighting the causal relationship between UMOD variants, urinary uromodulin levels and hypertension. Furthermore, clinical studies in both healthy individual