Mechanistic interactions of uromodulin with the thick ascending limb: perspectives in physiology and hypertension

A salty symphony: unraveling the tale of uromodulin and sodium sensitivity

Uromodulin is a kidney-specific glycoprotein which is uniquely synthesized by the epithelial cells lining the thick ascending limb and early distal convoluted tubule. Among multiple roles in complex physiological and pathological processes, uromodulin mediates renal sodium handling through modulating tubular sodium transporters that reabsorb sodium and therefore is putatively linked to hypertension through generating sodium sensitivity of blood pressure. This review aims to present an updated overview of the role of uromodulin in sodium renal handling and summarize the existing evidence originating from preclinical, genetic, and clinical studies that support a relationship between uromodulin and sodium-sensitive hypertension.

Association of serum uromodulin with diabetic kidney disease: a systematic review and meta-analysis

BACKGROUND

Several studies have investigated the association between the changes of serum uromodulin and diabetic kidney disease (DKD). However, the results are still controversial. Therefore, this meta-analysis was conducted to provide a comprehensive evaluation of the association between serum uromodulin levels and DKD.

METHODS

PubMed, Cochrane library, Web of Science, and Scopus were systemically searched following the PRISMA protocol to identify the studies that reported the relationship between serum uromodulin level and DKD. To investigate the association between uromodulin and DKD, a standardized mean difference (SMD) with a 95% confidence interval (CI) was used. When significant heterogeneity was detected (I2 > 50%), sensitivity and subgroup analyses were performed to determine the source of heterogeneity. The quality assessment was determined using the Newcastle-Ottawa scale (NOS), and the publications bias were determined by the funnel plot and Egger's test.

RESULTS

In total, 6 studies with 1774 patients were included in the final analysis. The random effect model was used. The pooled results showed that the serum uromodulin levels were significantly decreased in patients with DKD (SMD: -0.31; 95% CI: -0.48 to -0.13) (I2 = 45%). Upon applying the sensitivity analysis, it showed (SMD: -0.38; 95% CI: -0.49 to -0.27) (I2 = 3%). Subgroup analysis showed that uromodulin level was significantly decreased in DKD regardless of the region of study, in America (SMD: -0.34; 95% CI: -0.51 to -0.17; p < 0.0001), Europe (SMD: -0.54; 95% CI: -1.06 to -0.02; p = 0.04), and Asia (SMD: -0.63; 95% CI: -1.15 to -0.11; p = 0.02), with stronger predictive value in America and Asia than in Europe. Additionally, uromodulin levels were significantly decreased in both type 1 (SMD: -0.34; 95% CI: -0.51 to -0.17; p < 0.0001) and type 2 diabetes (SMD: -0.58; 95% CI: -0.95 to -0.22; p = 0.002).

CONCLUSION

This meta-analysis showed a significant association between low levels of serum uromodulin and DKD. So, it could have a predictive role for DKD. However, its performance varied across subgroup analyses restricted by race and clinical settings. Moreover, further studies are required with a focus on the cut-off value for predicting diagnostic accuracy.

Multiple urinary peptides are associated with hypertension: a link to molecular pathophysiology

OBJECTIVES

Hypertension is a common condition worldwide; however, its underlying mechanisms remain largely unknown. This study aimed to identify urinary peptides associated with hypertension to further explore the relevant molecular pathophysiology.

METHODS

Peptidome data from 2876 individuals without end-organ damage were retrieved from the Human Urinary Proteome Database, belonging to general population (discovery) or type 2 diabetic (validation) cohorts. Participants were divided based on systolic blood pressure (SBP) and diastolic BP (DBP) into hypertensive (SBP ≥140 mmHg and/or DBP ≥90 mmHg) and normotensive (SBP <120 mmHg and DBP <80 mmHg, without antihypertensive treatment) groups. Differences in peptide abundance between the two groups were confirmed using an external cohort ( n  = 420) of participants without end-organ damage, matched for age, BMI, eGFR, sex, and the presence of diabetes. Furthermore, the association of the peptides with BP as a continuous variable was investigated. The findings were compared with peptide biomarkers of chronic diseases and bioinformatic analyses were conducted to highlight the underlying molecular mechanisms.

RESULTS

Between hypertensive and normotensive individuals, 96 (mostly COL1A1 and COL3A1) peptides were found to be significantly different in both the discovery (adjusted) and validation (nominal significance) cohorts, with consistent regulation. Of these, 83 were consistently regulated in the matched cohort. A weak, yet significant, association between their abundance and standardized BP was also observed.

CONCLUSION

Hypertension is associated with an altered urinary peptide profile with evident differential regulation of collagen-derived peptides. Peptides related to vascular calcification and sodium regulation were also affected. Whether these modifications reflect the pathophysiology of hypertension and/or early subclinical organ damage requires further investigation.

The role of uromodulin in cardiovascular disease: a review

Uromodulin, also referred to as Tamm Horsfall protein (THP), is a renal protein exclusively synthesized by the kidneys and represents the predominant urinary protein under normal physiological conditions. It assumes a pivotal role within the renal system, contributing not only to ion transport and immune modulation but also serving as a critical factor in the prevention of urinary tract infections and kidney stone formation. Emerging evidence indicates that uromodulin may serve as a potential biomarker extending beyond renal function. Recent clinical investigations and Mendelian randomization studies have unveiled a discernible association between urinary regulatory protein levels and cardiovascular events and mortality. This review primarily delineates the intricate relationship between uromodulin and cardiovascular disease, elucidates its predictive utility as a novel biomarker for cardiovascular events, and delves into its involvement in various physiological and pathophysiological facets of the cardiovascular system, incorporating recent advancements in corresponding genetics.

Exosomal UMOD gene expression and urinary uromodulin level as early noninvasive diagnostic biomarkers for diabetic nephropathy in type 2 diabetic patients

Background

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Exosomes are promising biomarkers for disease diagnosis and uromodulin is a kidney-specific protein. So, this study was designed to investigate the change in the gene expression of urinary exosomal uromodulin mRNA and urinary uromodulin level and determine the diagnostic potential of these noninvasive biomarkers in the early stage of diabetic nephropathy in type 2 diabetic patients.

Method

This study included 100 participants; urinary exosomes were isolated using polyethylene glycol (PEG). Gene expression of exosomal uromodulin mRNA was determined by quantitative real-time polymerase chain reaction (q-RT-PCR). The urinary uromodulin levels were determined by an enzyme-linked immunosorbent assay (ELISA).

Result

In this study, the gene expression of exosomal uromodulin (UMOD) mRNA and the level of urinary uromodulin showed a significant increase in all diabetic groups with and without nephropathy compared to the control group. The exosomal UMOD mRNA showed a significant positive correlation with urinary uromodulin in all groups. Multiple logistic regression showed that urinary uromodulin was an independent determinant for DN. A diagnostic model of two indicators, exosomal UMOD mRNA and urinary uromodulin, can significantly predict DN. The area under the curve is 0.095, with a 95% confidence interval of 0.98-1, and 0.81, with a 95% confidence interval of 0.69-0.92, for the exosomal UMOD mRNA and urinary uromodulin, respectively.

Conclusion

Urinary exosomal mRNA of UMOD and urinary uromodulin levels are progressively elevated in an early stage of DN, even before the microalbuminuria stage, so they could be used as early predictors for DN.

Uromodulin biology

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, uromodulin modulates renal sodium handling through the regulation of tubular sodium transporters that reabsorb sodium and are targeted by diuretics, such as 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. However, recent studies in humans suggest a more complex interaction between dietary sodium intake, uromodulin and blood pressure. This review presents an updated overview of the uromodulin's biology and its various roles, and focuses on the interaction between uromodulin and sodium-sensitive hypertension.

Pregnancy-associated changes in urinary uromodulin excretion in chronic hypertension

BACKGROUND

Pregnancy involves major adaptations in renal haemodynamics, tubular, and endocrine functions. Hypertensive disorders of pregnancy are a leading cause of maternal mortality and morbidity. Uromodulin is a nephron-derived protein that is associated with hypertension and kidney diseases. Here we study the role of urinary uromodulin excretion in hypertensive pregnancy.

METHODS

Urinary uromodulin was measured by ELISA in 146 pregnant women with treated chronic hypertension (n = 118) and controls (n = 28). We studied non-pregnant and pregnant Wistar Kyoto and Stroke Prone Spontaneously Hypertensive rats (n = 8/strain), among which a group of pregnant Stroke-Prone Spontaneously Hypertensive rats was treated with either nifedipine (n = 7) or propranolol (n = 8).

RESULTS

In pregnant women, diagnosis of chronic hypertension, increased maternal body mass index, Black maternal ethnicity and elevated systolic blood pressure at the first antenatal visit were significantly associated with a lower urinary uromodulin-to-creatinine ratio. In rodents, pre-pregnancy urinary uromodulin excretion was twofold lower in Stroke-Prone Spontaneously Hypertensive rats than in Wistar Kyoto rats. During pregnancy, the urinary uromodulin excretion rate gradually decreased in Wistar Kyoto rats (a twofold decrease), whereas a 1.5-fold increase was observed in Stroke-Prone Spontaneously Hypertensive rats compared to pre-pregnancy levels. Changes in uromodulin were attributed by kidney injury in pregnant rats. Neither antihypertensive changed urinary uromodulin excretion rate in pregnant Stroke-Prone Spontaneously Hypertensive rats.

CONCLUSIONS

In summary, we demonstrate pregnancy-associated differences in urinary uromodulin: creatinine ratio and uromodulin excretion rate between chronic hypertensive and normotensive pregnancies. Further research is needed to fully understand uromodulin physiology in human pregnancy and establish uromodulin's potential as a biomarker for renal adaptation and renal function in pregnancy.

Salt Sensitivity of Blood Pressure in Black People: The Need to Sort Out Ancestry Versus Epigenetic Versus Social Determinants of Its Causation

Race is a social construct, but self-identified Black people are known to have higher prevalence and worse outcomes of hypertension than White people. This may be partly due to the disproportionate incidence of salt sensitivity of blood pressure in Black people, a cardiovascular risk factor that is independent of blood pressure and has no proven therapy. We review the multiple physiological systems involved in regulation of blood pressure, discuss what, if anything is known about the differences between Black and White people in these systems and how they affect salt sensitivity of blood pressure. The contributions of genetics, epigenetics, environment, and social determinants of health are briefly touched on, with the hope of stimulating further work in the field.

The Versatile Role of Uromodulin in Renal Homeostasis and Its Relevance in Chronic Kidney Disease

Uromodulin, also known as the Tamm-Horsfall protein, is predominantly expressed in epithelial cells of the kidney. It is secreted mainly in the urine, although small amounts are also found in serum. Uromodulin plays an important role in maintaining renal homeostasis, particularly in salt/water transport mechanisms and is associated with salt-sensitive hypertension. It also regulates urinary tract infections, kidney stones, and the immune response in the kidneys or extrarenal organs. Uromodulin has been shown to be associated with the renal function, age, nephron volume, and metabolic abnormalities and has been proposed as a novel biomarker for the tubular function or injury. These findings suggest that uromodulin is a key molecule underlying the mechanisms or therapeutic approaches of chronic kidney disease, particularly nephrosclerosis and diabetic nephropathy, which are causes of end-stage renal disease. This review focuses on the current understanding of the role of uromodulin from a biological, physiological, and pathological standpoint.

Serum Uromodulin in Children and Adolescents with Type 1 Diabetes Mellitus and Controls: Its Potential Role in Kidney Health

INTRODUCTION

Uromodulin is a kidney-specific tubular protein, and its assessment in serum (sUMOD) reveals the potential as a novel marker for function and the integrity of renal parenchymal cells and does not directly depend on the glomerular filtration rate. Early diabetic nephropathy parallels glomerular hyperfiltration, often leading to diagnostic misinterpretation. Moreover, traditional kidney function markers are not able to diagnose structural lesions. Recent data show that sUMOD is linked to glucose intolerance in adults. Thus, we launched to assess the hypothesis that sUMOD is also associated with kidney function, biometric data, and quality of metabolic control in children/adolescents with type 1 diabetes.

PATIENTS AND METHODS

Patients with type 1 diabetes (n=135) and healthy controls (n=69) were recruited to participate in the trial. Clinical, biometrical data, sUMOD, and other laboratory parameters were assessed.

RESULTS

The mean concentrations of sUMOD in diabetic patients and controls were comparable (201.19±103.22 vs. 198.32±84.27 ng/mL, p=0.832). However, in contrast to healthy controls, sUMOD levels in patients with diabetes were associated with serum-creatinine (r=-0.368, p<0.0001), age (r=-0.350, p<0.0001), height (r=-0.379, p<0.0001), body weight (r=-0.394, p<0.0001), Body mass index (r=-0.292, p=0.001), daily insulin dosage (r=-0.300, p<0.0001), HbA1c (%) (r=-0.190, p=0.027), standardized HbA1c/IFCC (mmol/mol) (r=-0.189, p=0.028), and systolic (r=-0.299, p<0.0001) and diastolic (r=-0.235, p=0.006) arterial blood pressure.

CONCLUSIONS

Our study shows that children/adolescents with type 1 diabetes disclose similar sUMOD concentrations as healthy controls. Serum UMOD appears to indicate higher risks for kidney tissue remodeling and possibly subsequent cardiovascular alterations. However, further studies are mandatory to settle these findings.

Role of Uromodulin in Salt-Sensitive Hypertension

The exclusive expression of uromodulin in the kidneys has made it an intriguing protein in kidney and cardiovascular research. Genome-wide association studies discovered variants of uromodulin that are associated with chronic kidney diseases and hypertension. Urinary and circulating uromodulin levels reflect kidney and cardiovascular health as well as overall mortality. More recently, Mendelian randomization studies have shown that genetically driven levels of uromodulin have a causal and adverse effect on kidney function. On a mechanistic level, salt sensitivity is an important factor in the pathophysiology of hypertension, and uromodulin is involved in salt reabsorption via the NKCC2 (Na+-K+-2Cl- cotransporter) on epithelial cells of the ascending limb of loop of Henle. In this review, we provide an overview of the multifaceted physiology and pathophysiology of uromodulin including recent advances in its genetics; cellular trafficking; and mechanistic and clinical studies undertaken to understand the complex relationship between uromodulin, blood pressure, and kidney function. We focus on tubular sodium reabsorption as one of the best understood and pathophysiologically and clinically most important roles of uromodulin, which can lead to therapeutic interventions.