Binding of human neutrophils to cell-surface anchored Tamm-Horsfall glycoprotein in tubulointerstitial nephritis

Tamm-Horsfall Protein Regulates Mononuclear Phagocytes in the Kidney

Tamm-Horsfall protein (THP), also known as uromodulin, is a kidney-specific protein produced by cells of the thick ascending limb of the loop of Henle. Although predominantly secreted apically into the urine, where it becomes highly polymerized, THP is also released basolaterally, toward the interstitium and circulation, to inhibit tubular inflammatory signaling. Whether, through this latter route, THP can also regulate the function of renal interstitial mononuclear phagocytes (MPCs) remains unclear, however. Here, we show that THP is primarily in a monomeric form in human serum. Compared with wild-type mice, THP^-/- mice had markedly fewer MPCs in the kidney. A nonpolymerizing, truncated form of THP stimulated the proliferation of human macrophage cells in culture and partially restored the number of kidney MPCs when administered to THP^-/- mice. Furthermore, resident renal MPCs had impaired phagocytic activity in the absence of THP. After ischemia-reperfusion injury, THP^-/- mice, compared with wild-type mice, exhibited aggravated injury and an impaired transition of renal macrophages toward an M2 healing phenotype. However, treatment of THP^-/- mice with truncated THP after ischemia-reperfusion injury mitigated the worsening of AKI. Taken together, our data suggest that interstitial THP positively regulates mononuclear phagocyte number, plasticity, and phagocytic activity. In addition to the effect of THP on the epithelium and granulopoiesis, this new immunomodulatory role could explain the protection conferred by THP during AKI.

Interaction of uromodulin and complement factor H enhances C3b inactivation

Recent studies suggest that uromodulin plays an important role in chronic kidney diseases. It can interact with several complement components, various cytokines and immune system cells. Complement factor H (CFH), as a regulator of the complement alternative pathway, is also associated with various renal diseases. Thus, we have been suggested that uromodulin regulates complement activation by interacting with CFH during tubulointerstitial injury. We detected co‐localization of uromodulin and CFH in the renal tubules by using immunofluorescence. Next, we confirmed the binding of uromodulin with CFH in vitro and found that the affinity constant (K_D) of uromodulin binding to CFH was 4.07 × 10⁻⁶M based on surface plasmon resonance results. The binding sites on CFH were defined as the short consensus repeat (SCR) units SCR1–4, SCR7 and SCR19–20. The uromodulin‐CFH interaction enhanced the cofactor activity of CFH for factor I‐mediated cleavage of C3b to iC3b. These results indicate that uromodulin plays a role via binding and enhancing the function of CFH.

Urinary uromodulin, kidney function, and cardiovascular disease in elderly adults

Urinary uromodulin (uUMOD) is the most common secreted tubular protein in healthy adults. However, the relationship between uUMOD and clinical outcomes is still unclear. Here we measured uUMOD in 192 participants of the Cardiovascular Health Study with over a 30% decline in estimated glomerular filtration rate (eGFR) over 9 years, 54 with incident end-stage renal disease (ESRD), and in a random subcohort of 958 participants. The association of uUMOD with eGFR decline was evaluated using logistic regression and with incident ESRD, cardiovascular disease, heart failure, and mortality using Cox proportional regression. Mean age was 78 years and median uUMOD was 25.8 μg/ml. In a case-control study evaluating eGFR decline (192 cases and 231 controls), each 1-s.d. higher uUMOD was associated with a 23% lower odds of eGFR decline (odds ratio 0.77 (95% CI 0.62-0.96)) and a 10% lower risk of mortality (hazard ratio 0.90 (95% CI 0.83-0.98)) after adjusting for demographics, eGFR, albumin/creatinine ratio, and other risk factors. There was no risk association of uUMOD with ESRD, cardiovascular disease, or heart failure after multivariable adjustment. Thus, low uUMOD levels may identify persons at risk of progressive kidney disease and mortality above and beyond established markers of kidney disease, namely eGFR and the albumin/creatinine ratio. Future studies need to confirm these results and evaluate whether uUMOD is a marker of tubular health and/or whether it plays a causal role in preserving kidney function.

Uromodulin in kidney injury: an instigator, bystander, or protector?

Uromodulin, also known as Tamm-Horsfall protein, is a glycoprotein expressed exclusively by renal tubular cells lining the thick ascending limb of the loop of Henle. Although the physiologic functions of this protein remain elusive, significant progress has been made during the last decade that highlights the importance of uromodulin in the pathophysiology of various diseases, such as medullary cystic kidney disease, urinary tract infections, and nephrolithiasis. Meanwhile, there is renewed interest in the role of uromodulin in kidney injury, both acute and chronic. In this article, we review the existing evidence that supports a role for uromodulin in acute kidney injury, chronic kidney disease, and renal inflammation. Contrary to the conventional view of uromodulin as an instigator in kidney injury, new data from uromodulin knockout mice show a protective role for this protein in acute kidney injury, possibly through downregulating interstitial inflammation. In chronic kidney disease, uromodulin excretion, when adjusted for kidney function, is increased; the significance of this is unclear. Although it has been suggested that uromodulin exacerbates progressive kidney injury, we propose that the elevation in uromodulin secretion is instead reactive to injury and reflects an increase of uromodulin in the renal parenchyma, where it slows the injury process.

A transgenic mouse model for uromodulin-associated kidney diseases shows specific tubulo-interstitial damage, urinary concentrating defect and renal failure

Uromodulin-associated kidney diseases (UAKD) are autosomal-dominant disorders characterized by alteration of urinary concentrating ability, tubulo-interstitial fibrosis, hyperuricaemia and renal cysts at the cortico-medullary junction. UAKD are caused by mutations in UMOD, the gene encoding uromodulin. Although uromodulin is the most abundant protein secreted in urine, its physiological role remains elusive. Several in vitro studies demonstrated that mutations in uromodulin lead to endoplasmic reticulum (ER) retention of mutant protein, but their relevance in vivo has not been studied. We here report on the generation and characterization of the first transgenic mouse model for UAKD. Transgenic mice that express the C147W mutant uromodulin (Tg(Umod)(C147W)), corresponding to the well-established patient mutation C148W, were compared with expression-matched transgenic mice expressing the wild-type protein (Tg(Umod)(wt)). Tg(Umod)(C147W) mice recapitulate most of the UAKD features, with urinary concentrating defect of renal origin and progressive renal injury, i.e. tubulo-interstitial fibrosis with inflammatory cell infiltration, tubule dilation and specific damage of the thick ascending limb of Henle's loop, leading to mild renal failure. As observed in patients, Tg(Umod)(C147W) mice show a marked reduction of urinary uromodulin excretion. Mutant uromodulin trafficking to the plasma membrane is indeed impaired as it is retained in the ER of expressing cells leading to ER hyperplasia. The Tg(Umod)(C147W) mice represent a unique model that recapitulates most of the features associated with UAKD. Our data clearly demonstrate a gain-of-toxic function of uromodulin mutations providing insights into the pathogenetic mechanism of the disease. These findings may also be relevant for other tubulo-interstitial or ER-storage disorders.

Evidence for a role of uromodulin in chronic kidney disease progression

BACKGROUND

Uromodulin (also known as Tamm-Horsfall protein) is the most abundant urinary protein in healthy individuals and exhibits diverse functions including prevention of ascending urinary tract infections by binding type I-fimbriated Escherichia coli. Although uromodulin is targeted to the apical membrane of thick ascending limb (TAL) cells and secreted into the lumen, detectable levels are also found in venous blood. Uromodulin has been shown to interact with and activate specific components of the immune system, and thus, may act as a signalling molecule for renal tubular damage.

METHODS

In order to investigate the potential involvement of uromodulin in chronic kidney disease (CKD), we quantified uromodulin in paired urine and serum from 14 healthy volunteers and 77 CKD patients. Clinical parameters such as estimated GFR (eGFR), proteinuria and urinary N-acetyl-beta-D-glucosaminidase (NAG) were measured. Mean infiltration and atrophy score were assessed in patient biopsies. Additionally, tumour necrosis factor-alpha, interleukin-6 (IL-6), IL-8 and IL-1 beta were measured in serum samples.

RESULTS

eGFR correlated positively with urinary uromodulin and negatively with serum uromodulin. Patients with abnormally low urinary uromodulin showed a broader range of serum uromodulin. Patients with both very low urinary and serum uromodulin had the highest tubular atrophy scores. There was a positive correlation of serum uromodulin with all cytokines measured. Additionally, in in vitro experiments, uromodulin caused a dose-dependent increase in pro-inflammatory cytokine release from whole blood.

CONCLUSIONS

Our data suggest that TAL damage, or damage distal to the TAL, results in an elevated interstitial uromodulin, which stimulates an inflammatory response. Persistent chronic TAL damage reduces TAL cell numbers and attenuates urinary and serum uromodulin concentrations. The combined analysis of serum and urinary uromodulin provides new insights into the role of uromodulin in CKD and suggest that uromodulin may be an active player in CKD progression.

Membrane Targeting and Secretion of Mutant Uromodulin in Familial Juvenile Hyperuricemic Nephropathy

Familial juvenile hyperuricemic nephropathy (FJHN) is an autosomal dominant genetic disorder that is characterized by hyperuricemia, gout, and tubulointerstitial nephritis. FJHN is caused by mutations in the UMOD gene, which encodes for uromodulin, the most abundant urinary protein. Herein is demonstrated that patients with FJHN and renal insufficiency exhibit a profound reduction in urinary uromodulin together with either elevated or decreased plasma uromodulin. One young patient with FJHN, however, had normal serum creatinine and normal urinary uromodulin with elevated plasma uromodulin. These observations suggest that there are different urinary and plasma uromodulin profiles in early and late disease and that there may be an altered direction of uromodulin secretion in the course of FJHN as a result of improper intracellular sorting of the mutated protein in the thick ascending limb. With the use of immunohistochemistry and a quantitative immunoassay, targeting and secretion of wild-type and mutant (C77Y and N128S) uromodulin were investigated in the polarized renal epithelial cell line LLC-PK1. In transfected cells, uromodulin mutants were targeted properly to the apical membrane but were secreted less efficiently to the apical compartment than wild-type protein. The expression of mutant uromodulin had no effect on caspase 3 activity. These results indicate that the mutations studied do not impair glycosyl-phosphatidylinositol-mediated apical targeting of the protein but do affect apical secretion. Because the mutant proteins are secreted as efficiently as wild type to the basolateral compartment, the possibility arises that interactions with the immune system at the site of secretion are a contributing factor to the development of tubulointerstitial nephritis in FJHN.

Tamm-Horsfall protein: a multilayered defence molecule against urinary tract infection

Urinary tract infection (UTI) is the most common nonepidemic bacterial infection in humans, representing a constant danger for the host. Both innate and adaptive components of the immune system as well as stromal cells including bladder epithelium are involved in the prevention and clearance of UTI. However, the particular properties of the urogenital tract, which does not comprise typical physical barriers like a mucus or ciliated epithelium, necessitate soluble mediators with potent immunomodulatory capabilities. One candidate molecule capable of both mediating direct antimicrobial activity and alerting immune cells is the evolutionary conserved Tamm-Horsfall protein (THP). Tamm-Horsfall protein is exclusively produced by the kidney in the distal loop of Henle; however, its definite physiological function remains elusive. Mounting evidence indicates that beyond a mere direct antimicrobial activity, THP exerts potent immunoregulatory activity. Furthermore, the genetic ablation of the THP gene leads to severe infection and lethal pyelonephritis in an experimental model of UTI. Recent data are provided demonstrating that THP links the innate immune response with specific THP-directed cell-mediated immunity. In light of these novel findings we discuss the particular role of THP as a specialized defence molecule. We propose an integrated model of protective mechanisms against UTI where THP acts by two principle nonmutually exclusive mechanisms involving the capture of potentially dangerous microbes and the ability of this peculiar glycoprotein to induce robust protective immune responses against uropathogenic bacteria.

Tamm-Horsfall glycoprotein links innate immune cell activation with adaptive immunity via a Toll-like receptor-4-dependent mechanism

Tamm-Horsfall glycoprotein (THP) is expressed exclusively in the kidney and constitutes the most abundant protein in mammalian urine. A critical role for THP in antibacterial host defense and inflammatory disorders of the urogenital tract has been suggested. We demonstrate that THP activates myeloid DCs via Toll-like receptor-4 (TLR4) to acquire a fully mature DC phenotype. THP triggers typical TLR signaling, culminating in activation of NF-kappaB. Bone marrow-derived macrophages from TLR4- and MyD88-deficient mice were nonresponsive to THP in contrast to those from TLR2- and TLR9-deficient mice. In vivo THP-driven TNF-alpha production was evident in WT but not in Tlr4-/- mice. Importantly, generation of THP-specific Abs consistently detectable in urinary tract inflammation was completely blunted in Tlr4-/- mice. These data show that THP is a regulatory factor of innate and adaptive immunity and therefore could have significant impact on host immunity in the urinary tract.

Familial juvenile hyperuricemic nephropathy: Detection of mutations in the uromodulin gene in five Japanese families

BACKGROUND

Familial juvenile hyperuricemic nephropathy (FJHN) is an autosomal-dominant disease characterized by hyperuricemia of underexcretion type, gout, and chronic renal failure. We previously reported linkage on chromosome 16p12 in a large Japanese family designated as family 1 in the present study. Recent reports on the discovery of mutations of the uromodulin (UMOD) gene in families with FJHN encouraged us to screen UMOD mutations in Japanese families with FJHN, including family 1.

METHODS

Six unrelated Japanese families with FJHN were examined for mutations of the UMOD gene by direct sequencing. To confirm the results of the mutation screening, parametric linkage analyses were performed using markers in 16p12 region and around other candidate genes of FJHN.

RESULTS

Five separate heterozygous mutations (Cys52Trp, Cys135Ser, Cys195Phe, Trp202Ser, and Pro236Leu) were found in five families, including family 1. All mutations were co-segregated with the disease phenotype in all families, except for family 1, in which an individual in the youngest generation was found as a phenocopy by the genetic testing. Revised multipoint linkage analysis showed that the UMOD gene was located in the interval showing logarithm of odds (LOD) score above 6.0. One family carrying no mutation in the UMOD gene showed no linkage to the medullary cystic kidney disease type 1 (MCKD1) locus, the genes of hepatocyte nuclear factor-1beta (HNF-1beta), or urate transporters URAT1 and hUAT.

CONCLUSION

Our results gave an evidence for the mutation of the UMOD gene in the majority of Japanese families with FJHN. Genetic heterogeneity of FJHN was also confirmed. Genetic testing is necessary for definite diagnosis in some cases especially in the young generation.

Tamm-Horsfall glycoprotein: biology and clinical relevance

Tamm-Horsfall glycoprotein (THP) is the most abundant urinary protein in mammals. Urinary excretion occurs by proteolytic cleavage of the large ectodomain of the glycosyl phosphatidylinositol-anchored counterpart exposed at the luminal cell surface of the thick ascending limb of Henle's loop. We describe the physical-chemical structure of human THP and its biosynthesis and interaction with other proteins and leukocytes. The clinical relevance of THP reported here includes: (1) involvement in the pathogenesis of cast nephropathy, urolithiasis, and tubulointerstitial nephritis; (2) abnormalities in urinary excretion in renal diseases; and (3) the recent finding that familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease 2 arise from mutations of the THP gene. We critically examine the literature on the physiological role and mechanism(s) that promote urinary excretion of THP. Some lines of research deal with the in vitro immunoregulatory activity of THP, termed uromodulin when isolated from urine of pregnant women. However, an immunoregulatory function in vivo has not yet been established. In the most recent literature, there is renewed interest in the capacity of urinary THP to compete efficiently with urothelial cell receptors, such as uroplakins, in adhering to type 1 fimbriated Escherichia coli. This property supports the notion that abundant THP excretion in urine is promoted in the host by selective pressure to obtain an efficient defense against urinary tract infections caused by uropathogenic bacteria.

Salt-precipitation method does not isolate to homogeneity Tamm-Horsfall glycoprotein from urine of proteinuric patients and pregnant women

OBJECTIVE

Assessment of the degree of purification of Tamm-Horsfall glycoprotein from anomalous urine.

DESIGN AND METHODS

Two methods have been compared: the method of Tamm & Horsfall (T&H method) consisting in the precipitation of THP by the addition to urine of NaCl up to 0.58 mol/L and the filtration of urine through a diatomaceous earth filter (DEF method) in which THP is selectively trapped because of its gelation/aggregation tendency. The purity of THP preparations has been evaluated by SDS-PAGE analysis and Western blotting developed with anti immunoglobulin G (IgG) antibodies and antichorionic gonadotropin antibodies.

RESULTS

All THPs isolated by T&H method from proteinuric patients were contaminated by IgG and one of the five preparations from pregnant women even by chorionic gonadotropin. A smaller or no contamination was found in THPs isolated by DEF method.

CONCLUSIONS

Although albumin is the most abundant protein in the anomalous urine, it never appears in THP preparations. The consistent contamination with IgG of THP prepared by salt precipitation-method might be related to the formation of a stable complex between the two proteins.

Polarized expression of Tamm-Horsfall protein by renal tubular epithelial cells activates human granulocytes

In renal bacterial infections granulocytes are of major importance in the primary immune defense against invading pathogens. However, the mechanisms of granulocytic activation in renal interstitial invasion have not been clarified. Renal tubular epithelial cell mechanisms inducing granulocytic activation and bacterial killing may include tubular cell expression of Tamm-Horsfall protein (THP), a urinary protein that is known to enhance cytokine expression in monocytes. We studied the role of THP in granulocytic activation. A strong binding of THP to human granulocytes was demonstrated by fluorescence-activated cell sorter analysis. Urinary THP and supernatants of THP-expressing cultured tubular epithelial cells (MDCK) enhanced interleukin-8 (IL-8) expression by human granulocytes. Renal tubular cells growing polarized on polycarbonate membranes were used to study apical versus basal THP expression. By electron microscopy THP immunoreactivity was exclusively found on the apical surfaces of tubular cells and was absent on the basolateral cell membrane. In the apical cell culture compartment we found significantly more stimulatory activity for granulocytic IL-8 expression. CD62L, a selectin less expressed in activated granulocytes, was decreased in granulocytes incubated with urinary THP and in supernatants of THP-producing renal tubular cells but not in supernatants from THP-negative cells. Again, the effect on CD62L expression was found only in apical culture media and was absent in the basal compartment. In summary our data give evidence that renal tubular cell THP expression may be relevant in kidney diseases since THP is a potent activator of human granulocytes. The regulation of apical versus basal THP expression and release in vivo may be crucial in the induction of the inflammatory response, e.g., in bacterial renal diseases.

Mechanism of release of urinary Tamm-Horsfall glycoprotein from the kidney GPI-anchored counterpart

Human Tamm-Horsfall glycoprotein (THP) is synthesised in the thick ascending limb of Henle and convoluted distal tubules, inserted into luminal cell-surface by the glycosyl-phosphatidylinositol (GPI)-anchor and excreted in urine at a rate of 50-100 mg per day. Up to date there is no indication on the way in which THP is excreted into the urinary fluid. In this study, we examined by Western blotting THP from human kidney in comparison to urinary THP. As expected for a GPI-anchored protein, THP was recovered from the kidney lysate in a Triton X-100 insoluble form, which moved in a sucrose gradient to a zone of low density. The apparent molecular weight of kidney THP appeared greater than that of urinary THP, but no difference in the electrophoretic mobility was observed when the former was subjected to GPI-specific phospholipase-C treatment, strongly suggesting that a proteolytic cleavage at the juxtamembrane-ectodomain of kidney THP is responsible for the urinary excretion.