A mucoprotein derived from human urine which reacts with influenza, mumps, and Newcastle disease viruses

Tamm-Horsfall protein in humane urine: sex-dependent differences in the excretion and N-glycosylation pattern

Tamm-Horsfall protein (THP) is a highly N-glycosylated protein from epithelial cells of the ascending limb of Henle loop. It is secreted into the urine as part of the innate immune response against uropathogenic pathogens. As women are more likely to suffer from urinary tract infections, biomedical studies were conducted to investigate sex-differences in THP excretion, as well as differences in the THP N-glycosylation pattern. A total of 238 volunteers (92 men, 146 women, 69 with hormonal contraceptives) participated in this study, providing urine samples. Women showed a clear tendency to have higher THP concentration and excretion rates than men (p < 0.16). Regular intake of hormonal contraceptives had no significant influence on urinary THP concentration compared to no regular intake. The individual N-glycosylation pattern of THP in urine samples from randomly selected individuals (10 female, 10 male) was investigated after enzymatic release and MS analysis of the oligosaccharides. Female subjects tended to have an increased proportion of oligomannose type N-glycans and non-fucosylated glycans, whereas men had an increased proportion of fucosylated complex-type glycans. The higher level of oligomannose-type glycans in THP from women might be explained by a self-defence mechanism to overcome the higher infections pressure by the female anatomical properties.

Characterization of site-specific N-glycosylation signatures of isolated uromodulin from human urine

Uromodulin (Umod, Tamm-Horsfall protein) is the most abundant urinary N-glycoprotein produced exclusively by the kidney. It can form filaments to antagonize the adhesion of uropathogens. However, the site-specific N-glycosylation signatures of Umod in healthy individuals and patients with IgA nephropathy (IgAN) remain poorly understood due to the lack of suitable isolation and analytical methods. In this study, we first presented a simple and fast method based on diatomaceous earth adsorption to isolate Umod. These isolated glycoproteins were digested by trypsin and/or Glu-C. Intact N-glycopeptides with or without HILIC enrichment were analyzed using our developed EThcD-sceHCD-MS/MS. Based on the optimized workflow, we identified a total of 780 unique intact N-glycopeptides (7 N-glycosites and 152 N-glycan compositions) from healthy individuals. As anticipated, these glycosites exhibited glycoform heterogeneity. Almost all N-glycosites were modified completely by the complex type, except for one N-glycosite (N275), which was nearly entirely occupied by the high-mannose type for mediating Umod's antiadhesive activity. Then, we compared the N-glycosylation of Umod between healthy controls (n = 9) and IgAN patients (n = 9). The N-glycosylation of Umod in IgAN patients will drastically decrease and be lost. Finally, we profiled the most comprehensive site-specific N-glycosylation map of Umod and revealed its alterations in IgAN patients. Our method provides a high-throughput workflow for characterizing the N-glycosylation of Umod, which can aid in understanding its roles in physiology and pathology, as well as serving as a potential diagnostic tool for evolution of renal tubular function.

Unveiling the Hidden Power of Uromodulin: A Promising Potential Biomarker for Kidney Diseases

Uromodulin, also known as Tamm-Horsfall protein, represents the predominant urinary protein in healthy individuals. Over the years, studies have revealed compelling associations between urinary and serum concentrations of uromodulin and various parameters, encompassing kidney function, graft survival, cardiovascular disease, glucose metabolism, and overall mortality. Consequently, there has been a growing interest in uromodulin as a novel and effective biomarker with potential applications in diverse clinical settings. Reduced urinary uromodulin levels have been linked to an elevated risk of acute kidney injury (AKI) following cardiac surgery. In the context of chronic kidney disease (CKD) of different etiologies, urinary uromodulin levels tend to decrease significantly and are strongly correlated with variations in estimated glomerular filtration rate. The presence of uromodulin in the serum, attributable to basolateral epithelial cell leakage in the thick ascending limb, has been observed. This serum uromodulin level is closely associated with kidney function and histological severity, suggesting its potential as a biomarker capable of reflecting disease severity across a spectrum of kidney disorders. The UMOD gene has emerged as a prominent locus linked to kidney function parameters and CKD risk within the general population. Extensive research in multiple disciplines has underscored the biological significance of the top UMOD gene variants, which have also been associated with hypertension and kidney stones, thus highlighting the diverse and significant impact of uromodulin on kidney-related conditions. UMOD gene mutations are implicated in uromodulin-associated kidney disease, while polymorphisms in the UMOD gene show a significant association with CKD. In conclusion, uromodulin holds great promise as an informative biomarker, providing valuable insights into kidney function and disease progression in various clinical scenarios. The identification of UMOD gene variants further strengthens its relevance as a potential target for better understanding kidney-related pathologies and devising novel therapeutic strategies. Future investigations into the roles of uromodulin and regulatory mechanisms are likely to yield even more profound implications for kidney disease diagnosis, risk assessment, and management.

Uromodulin: more than a marker for chronic kidney disease progression

PURPOSE OF REVIEW

Uromodulin, a protein that is highly conserved across several species through evolution, functions to maintain homeostasis and prevent disease development and progression. Historically, the role of uromodulin has been thought to be limited to the kidney and genitourinary tract. This review highlights developments indicating a broader role of uromodulin in human health.

RECENT FINDINGS

Although initially discovered in the urine and found to have immunomodulatory properties, recent findings indicate that serum uromodulin (sUMOD) is distinct from urine uromodulin (uUMOD) in its structure, function, and regulation. uUMOD binds pathogenic bacteria in the urine preventing infection and is also upregulated in kidneys undergoing repair after injury. Uromodulin knockout mice exhibit higher mortality in the setting of sepsis which is also associated with upregulation of sUMOD. sUMOD lowers calcification risk but this may be influenced by presence of kidney disease.

SUMMARY

Uromodulin is an evolutionarily conserved protein produced exclusively in the kidney tubule cells with evolving roles being reported both in the kidney and systemically. Further research should be focused at harnessing its use as a potential therapeutic.

Systemic Effects of Tamm-Horsfall Protein in Kidney Disease

Tamm-Horsfall protein (THP) is produced exclusively by the kidney, where it is released into both the urine and the circulation. Although the primary form of circulating THP is nonpolymerizing, urinary THP exists as a mix of polymerizing and nonpolymerizing forms. Urinary THP has been shown to play roles in such disparate processes as prevention of urinary tract infections and kidney stone formation, along with the regulation of multiple ion channels within the kidney. The generation of THP knockout mouse models has allowed the investigation of these phenomena and shown a prospective role for circulating THP in ischemia-reperfusion acute kidney injury as well as sepsis. Recent studies have suggested that THP is protective in ischemic injury owing to its inhibition of oxidative stress via the calcium channel transient receptor potential cation channel, subfamily M, member 2 t(TRPM2), and protection in sepsis is at least partially due to THP's promotion of macrophage function.

The kidney releases a nonpolymerizing form of uromodulin in the urine and circulation that retains the external hydrophobic patch domain

Uromodulin [Tamm-Horsfall protein (THP)] is a glycoprotein uniquely produced in the kidney. It is released by cells of the thick ascending limbs apically in the urine and basolaterally in the renal interstitium and systemic circulation. Processing of mature urinary THP, which polymerizes into supramolecular filaments, requires cleavage of an external hydrophobic patch (EHP) at the COOH-terminus. However, THP in the circulation is not polymerized, and it remains unclear if nonaggregated forms of THP exist natively in the urine. We propose that an alternative processing path, which retains the EHP domain, can lead to a nonpolymerizing form of THP. We generated an antibody that specifically recognizes THP with retained EHP (THP + EHP) and established its presence in the urine in a nonpolymerized native state. Proteomic characterization of urinary THP + EHP revealed its COOH-terminus ending at F617. In the human kidney, THP + EHP was detected in thick ascending limb cells and less strongly in the renal parenchyma. Using immunoprecipitation followed by proteomic sequencing and immunoblot analysis, we then demonstrated that serum THP has also retained EHP. In a small cohort of patients at risk for acute kidney injury, admission urinary THP + EHP was significantly lower in patients who subsequently developed acute kidney injury during hospitalization. Our findings uncover novel insights into uromodulin biology by establishing the presence of an alternative path for cellular processing, which could explain the release of nonpolymerizing THP in the circulation. Larger studies are needed to establish the utility of urinary THP + EHP as a sensitive biomarker of kidney health and susceptibility to injury.NEW & NOTEWORTHY In this work, we discovered and characterized a novel form of uromodulin that does not polymerize because it retains an external hydrophobic patch at the COOH-terminus. These findings establish an alternative form of cellular processing of this protein and elucidate new aspects of its biology. We also provide evidence suggesting that measuring urinary nonpolymerizing uromodulin could be a promising assay to assess the risk of acute kidney injury.

Using human urinary extracellular vesicles to study physiological and pathophysiological states and regulation of the sodium chloride cotransporter

The thiazide-sensitive sodium chloride cotransporter (NCC), expressed in the renal distal convoluted tubule, plays a major role in Na⁺, Cl^- and K⁺ homeostasis and blood pressure as exemplified by the symptoms of patients with non-functional NCC and Gitelman syndrome. NCC activity is modulated by a variety of hormones, but is also influenced by the extracellular K⁺ concentration. The putative "renal-K⁺ switch" mechanism is a relatively cohesive model that links dietary K⁺ intake to NCC activity, and may offer new targets for blood pressure control. However, a remaining hurdle for full acceptance of this model is the lack of human data to confirm molecular findings from animal models. Extracellular vesicles (EVs) have attracted attention from the scientific community due to their potential roles in intercellular communication, disease pathogenesis, drug delivery and as possible reservoirs of biomarkers. Urinary EVs (uEVs) are an excellent sample source for the study of physiology and pathology of renal, urothelial and prostate tissues, but the diverse origins of uEVs and their dynamic molecular composition present both methodological and data interpretation challenges. This review provides a brief overview of the state-of-the-art, challenges and knowledge gaps in current uEV-based analyses, with a focus on the application of uEVs to study the "renal-K⁺ switch" and NCC regulation. We also provide recommendations regarding biospecimen handling, processing and reporting requirements to improve experimental reproducibility and interoperability towards the realisation of the potential of uEV-derived biomarkers in hypertension and clinical practice.

Application of tandem fast protein liquid chromatography to purify intact native monomeric/aggregated Tamm-Horsfall protein from human urine and systematic comparisons with diatomaceous earth adsorption and salt precipitation: yield, purity and time-consumption

Tamm-Horsfall protein (THP) is a high-abundance urinary protein. Although its functions have been studied for years, several aspects of these remain unclear. To achieve more knowledge on THP functions, an effective isolation/purification method providing a high yield and high purity is required. This is the first report that applied tandem fast protein liquid chromatography (FPLC) (by combining Mono Q anion-exchange with Superdex 200 size-exclusion columns in a tandem manner) to isolate intact THP from human urine. Its efficiency was then systematically compared with that of two conventional methods, diatomaceous earth (DE) adsorption and salt precipitation. The first ever systematic comparisons among the three methods revealed that, while Mono Q-Superdex 200 tandem FPLC offered the lowest %yield and was most time-consuming, it provided substantially high %purity and could selectively purify the monomeric and aggregated forms of urinary THP. On the other hand, DE adsorption provided the highest %yield and %purity, whereas salt precipitation offered the lowest %purity. In summary, the tandem FPLC system is most useful for selective purification of the monomeric and aggregated forms of urinary THP for further functional study, whereas DE adsorption remains the method of choice for general purification of THP from human urine.

Uromodulin Isolation and Its N-Glycosylation Analysis by NanoLC-MS/MS

The glycoprotein uromodulin (UMOD) is the most abundant protein in urine, and N-glycans are critical for many biological functions of UMOD. Comprehensive glycan profiling of UMOD provides valuable information to understand the exact mechanisms of glycan-regulated functions. To perform comprehensive glycosylation analysis of UMOD from urine samples with limited volumes, we developed a streamlined workflow that included UMOD isolation from 5 mL of urine from 6 healthy adult donors (3 males and 3 females) and a glycosylation analysis using a highly sensitive and reproducible nanoLC-MS/MS based glycomics approach. In total, 212 N-glycan compositions were identified from the purified UMOD, and 17% were high-mannose glycans, 2% were afucosylated/asialylated, 3% were neutral fucosylated, 28% were sialylated (with no fucose), 46% were fucosylated and sialylated, and 4% were sulfated. We found that isolation of UMOD resulted in a significant decrease in the relative quantity of high-mannose and sulfated glycans with a significant increase of neutral fucosylated glycans in the UMOD-depleted urine relative to the undepleted urine, but depletion had little impact on the sialylated glycans. To our knowledge, this is the first study to perform comprehensive N-glycan profiling of UMOD using nanoLC-MS/MS. This analytical workflow would be very beneficial for studies with limited sample size, such as pediatric studies, and can be applied to larger patient cohorts not only for UMOD interrogation but also for global glycan analysis.

Circulating uromodulin inhibits systemic oxidative stress by inactivating the TRPM2 channel

High serum concentrations of kidney-derived protein uromodulin [Tamm-Horsfall protein (THP)] have recently been shown to be independently associated with low mortality in both older adults and cardiac patients, but the underlying mechanism remains unclear. Here, we show that THP inhibits the generation of reactive oxygen species (ROS) both in the kidney and systemically. Consistent with this experimental data, the concentration of circulating THP in patients with surgery-induced acute kidney injury (AKI) correlated with systemic oxidative damage. THP in the serum dropped after AKI and was associated with an increase in systemic ROS. The increase in oxidant injury correlated with postsurgical mortality and need for dialysis. Mechanistically, THP inhibited the activation of the transient receptor potential cation channel, subfamily M, member 2 (TRPM2) channel. Furthermore, inhibition of TRPM2 in vivo in a mouse model mitigated the systemic increase in ROS during AKI and THP deficiency. Our results suggest that THP is a key regulator of systemic oxidative stress by suppressing TRPM2 activity, and our findings might help explain how circulating THP deficiency is linked with poor outcomes and increased mortality.

The Use of Genomics to Drive Kidney Disease Drug Discovery and Development

As opposed to diseases such as cancer, autoimmune disease, and diabetes, identifying drugs to treat CKD has proven significantly more challenging. Over the past 2 decades, new potential therapeutic targets have been identified as genetically altered proteins involved in rare monogenetic kidney diseases. Other possible target genes have been implicated through common genetic polymorphisms associated with CKD in the general population. Significant challenges remain before translating these genetic insights into clinical therapies for CKD. This paper will discuss how genetic variants may be leveraged to develop drugs and will especially focus on those genes associated with CKD to exemplify the value and challenges in including genetic information in the drug development pipeline.

The Development of a Smart Health Awareness Message Framework Based on the Use of Social Media: Quantitative Study

Background

Social media has recently provided a remarkable means of delivering health information broadly and in a cost-effective way. Despite its benefits, some difficulties are encountered in attempting to influence the public to change their behavior in response to social media health messages.

Objective

This study aimed to explore the factors that affect individuals’ acceptance of using social media as a tool for receiving health awareness messages and adapting such content accordingly by developing a smart health awareness message framework.

Methods

A quantitative method was adapted to validate the hypotheses and proposed framework through the development of a survey based on the technology acceptance model with the extension of other constructs. The survey was distributed on the web to 701 participants from different countries via Qualtrics software; it generated 391 completed questionnaires, and the response rate was 55.8% (391/701).

Results

Of the 391 respondents, 121 (30.9%) used social media platforms often during the week, and 27 participants (6.9%) did not use social media. In addition, 24.0% (94/391) of the respondents used these platforms to seek health information. On the basis of the results, perceived usefulness (β=.37; P<.001), gain-framed message (β=.04; P<.001), and loss-framed message (β=.08; P<.001) were seen to positively and significantly influence people’s intention to use social media as a means to spread information about health promotion. The proposed smart health awareness message framework identifies 64.2% of the variance in intention to use, 55.4% of the variance of perceived usefulness, and 26.2% of the variance of perceived ease of use.

Conclusions

This study sheds light on the factors that are associated with people’s intention to use and adopt social media in the health promotion domain. The findings reveal that the intention of using social media for health awareness purposes is positively impacted by the perception of usefulness of social media and the design of health messages. Future research might seek to explore other factors that relate to people’s behavior. This point of view will assist health organizations in developing their health messages more effectively and to be patient friendly.

Serum uromodulin is associated with the severity of clinicopathological findings in ANCA-associated glomerulonephritis

Background

Uromodulin (UMOD), also known as Tamm-Horsfall protein, is a kidney-specific protein expressed by epithelial cells lining the thick ascending limb of the loop of Henle. In the current study, we aimed to clarify the clinical significance of UMOD in ANCA-associated glomerulonephritis (AAG).

Materials and methods

Sixty-one biopsy-proven AAG patients were included in this study. UMOD was measured using ELISA. The relationships between serum UMOD (sUMOD) levels and various clinicopathological findings were evaluated.

Results

AAG was classified into four categories (focal, crescentic, mixed, and sclerotic). In addition, tubulointerstitial lesions were classified as mild, moderate, and severe. The levels of sUMOD and urinary UMOD (uUMOD) were correlated with each other. A negative correlation between sUMOD levels and serum Cr levels, and positive correlation between sUMOD levels and eGFR were found. Patients in the high sUMOD group were associated with low serum Cr levels, focal classification, and mild tubulointerstitial injury compared to the low sUMOD group. Comparing the characteristics among histopathological classes, patients in the focal class had the best renal function and the highest levels of uUMOD/Cr and sUMOD. The focal class had significantly better renal survival compared with the severe histopathological classes (crescentic, mixed, and sclerotic). In univariate logistic regression analyses, prognostic factors for severe histopathological classes were low uUMOD/Cr, high serum Cr, and low sUMOD. Multivariate analyses revealed that low sUMOD predicted severe histopathological classes independent of serum Cr. The mean levels of sUMOD were significantly different between the focal class and severe histopathological classes, with a sensitivity of 70.6% and specificity of 90.0% (cut-off 143 ng/ml, AUC 0.80) by ROC curves.

Conclusion

Low sUMOD levels were associated with severe clinicopathological findings and might be considered as a risk factor for end stage renal disease in AAG.

Markers of kidney tubule function and risk of cardiovascular disease events and mortality in the SPRINT trial

AIMS

Biomarkers of kidney tubule injury, inflammation and fibrosis have been studied extensively and established as risk markers of adverse kidney and cardiovascular disease (CVD) outcomes. However, associations of markers of kidney tubular function with adverse clinical events have not been well studied, especially in persons with chronic kidney disease (CKD).

METHODS AND RESULTS

Using a sample of 2377 persons with CKD at the baseline Systolic Blood Pressure Intervention Trial (SPRINT) visit, we evaluated the association of three urine tubular function markers, alpha-1 microglobulin (α1m), beta-2 microglobulin (β2m), and uromodulin, with a composite CVD endpoint (myocardial infarction, acute coronary syndrome, stroke, acute decompensated heart failure, or death from cardiovascular causes) and mortality using Cox proportional hazards regression, adjusted for baseline estimated glomerular filtration rate (eGFR), albuminuria, and CVD risk factors. In unadjusted analysis, over a median follow-up of 3.8 years, α1m and β2m had positive associations with composite CVD events and mortality, whereas uromodulin had an inverse association with risk for both outcomes. In multivariable analysis including eGFR and albuminuria, a two-fold higher baseline concentration of α1m was associated with higher risk of CVD [hazard ratio (HR) 1.25; 95% confidence interval (CI): 1.10-1.45] and mortality (HR 1.25; 95% CI: 1.10-1.46), whereas β2m had no association with either outcome. A two-fold higher uromodulin concentration was associated with lower CVD risk (HR 0.79; 95% CI: 0.68-0.90) but not mortality (HR 0.86; 95% CI: 0.73-1.01) after adjusting for similar confounders.

CONCLUSION

Among non-diabetic persons with CKD, biomarkers of tubular function are associated with CVD events and mortality independent of glomerular function and albuminuria.

Urinary Uromodulin Levels and UMOD Variants in Black South Africans with Hypertension-Attributed Chronic Kidney Disease

Uromodulin, the most abundant protein in urine, is synthesized in the thick ascending loop of Henle and distal convoluted tubules. Patients with chronic kidney disease (CKD) have reduced urinary uromodulin levels secondary to tubular damage. Genome wide association studies identified significant single nucleotide polymorphism (SNP) associations with CKD at the uromodulin (UMOD) locus. We examined the association of urinary uromodulin concentrations with CKD and with SNP rs1333226 in the UMOD gene. The study included 71 black South Africans with hypertension-attributed CKD with an eGFR ≤ 60ml/min/1.73m², 52 first-degree relatives, and 58 unrelated controls. Urinary uromodulin concentration was measured using Luminex® multiplex kits. After DNA extraction from blood using the Maxwell® automated platform, genotyping of rs13333226 was performed using real-time PCR using TaqMan® genotyping assays. Urinary uromodulin levels were significantly lower in CKD cases compared to both controls and first-degree relatives and correlated negatively with age, serum uric acid, serum creatinine, and systolic BP and positively with CKD-EPI eGFR. For each 1-standard deviation increase in uromodulin level, the multivariable-adjusted odds ratio for CKD was 0.6 (95% CI [0.48 to 0.81]; p <0.01). There were no significant differences in the minor allele frequency between CKD cases and controls (p = 0.59) nor between first-degree relatives and controls (p = 0.98). There were no significant associations between genotype at rs13333226 and urine uromodulin levels (p = 0.43). Higher levels of urinary uromodulin are associated with lower odds of hypertension-attributed CKD. We did not detect associations of genotype at rs13333226 with urinary uromodulin levels in our sample population. Larger sample size studies from ethnically disparate populations are essential to further categorize this association.

Genomic approaches in the search for molecular biomarkers in chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is recognised as a global public health problem, more prevalent in older persons and associated with multiple co-morbidities. Diabetes mellitus and hypertension are common aetiologies for CKD, but IgA glomerulonephritis, membranous glomerulonephritis, lupus nephritis and autosomal dominant polycystic kidney disease are also common causes of CKD.

MAIN BODY

Conventional biomarkers for CKD involving the use of estimated glomerular filtration rate (eGFR) derived from four variables (serum creatinine, age, gender and ethnicity) are recommended by clinical guidelines for the evaluation, classification, and stratification of CKD. However, these clinical biomarkers present some limitations, especially for early stages of CKD, elderly individuals, extreme body mass index values (serum creatinine), or are influenced by inflammation, steroid treatment and thyroid dysfunction (serum cystatin C). There is therefore a need to identify additional non-invasive biomarkers that are useful in clinical practice to help improve CKD diagnosis, inform prognosis and guide therapeutic management.

CONCLUSION

CKD is a multifactorial disease with associated genetic and environmental risk factors. Hence, many studies have employed genetic, epigenetic and transcriptomic approaches to identify biomarkers for kidney disease. In this review, we have summarised the most important studies in humans investigating genomic biomarkers for CKD in the last decade. Several genes, including UMOD, SHROOM3 and ELMO1 have been strongly associated with renal diseases, and some of their traits, such as eGFR and serum creatinine. The role of epigenetic and transcriptomic biomarkers in CKD and related diseases is still unclear. The combination of multiple biomarkers into classifiers, including genomic, and/or epigenomic, may give a more complete picture of kidney diseases.

Preoperative levels of urinary uromodulin predict acute kidney injury after pediatric cardiopulmonary bypass surgery

BACKGROUND

Acute kidney injury (AKI) is a common complication of cardiopulmonary bypass surgery (CPB) in children. Several promising postoperative AKI biomarkers have been identified, but no preoperative biomarkers are available. We evaluated the association of urinary uromodulin (uUMOD) with postoperative AKI.

METHODS

One hundred and one children undergoing CPB were enrolled. Urine was collected prior to CPB, and AKI was defined as ≧50% increase in serum creatinine from preoperative baseline within 48 h of surgery.

RESULTS

Forty-seven patients (47%) developed AKI, and 92% of participants in the lowest quartile of preoperative uUMOD concentrations developed AKI compared with 8% in the highest quartile. Patients with preoperative uUMOD levels in the lowest quartile had 132.3× increased risk of postoperative AKI versus the highest quartile. Raw uUMOD levels were significantly lower in patients with AKI vs. no AKI. Significance was unchanged after correcting uUMOD levels for urinary creatinine. Receiver operating characteristic analysis showed preoperative uUMOD strongly predicted postoperative AKI, with area under the curve (AUC) 0.90. Stepwise logistic regression analysis revealed a model combining uUMOD, and bypass time predicted AKI at p<0.001. Neither Risk Adjustment for Congenital Heart Surgery 1 (RACHS) score nor age improved the model's ability to predict AKI. Independent analysis demonstrated that while bypass time was associated with AKI, the predictive ability of bypass time (AUC 0.77) was less than that of preoperative uUMOD levels (AUC 0.9).

CONCLUSIONS

Children with lowest preoperative levels of uUMOD have greatly increased risk of AKI post-CPB. If uUMOD were used to risk-stratify patients undergoing CPB, clinical measures could be taken to minimize AKI development.

Tamm-Horsfall Protein is a Potent Immunomodulatory Molecule and a Disease Biomarker in the Urinary System

Tamm–Horsfall protein (THP), or uromodulin (UMOD), is an 80–90-kDa phosphatidylinositol-anchored glycoprotein produced exclusively by the renal tubular cells in the thick ascending limb of the loop of Henle. Physiologically, THP is implicated in renal countercurrent gradient formation, sodium homeostasis, blood pressure regulation, and a defense molecule against infections in the urinary system. Investigations have also revealed that THP is an effective binding ligand for serum albumin, immunoglobulin G light chains, complement components C1 and C1q, interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, and interferon-γ through its carbohydrate side chains for maintaining circulatory and renal immune homeostasis. Thus, THP can be regarded as part of the innate immune system. UMOD mutations play crucial roles in congenital urolithiasis, hereditary hyperuricemia/gout, and medullary cystic kidney diseases. Recent investigations have focused on the immunomodulatory effects of THP on immune cells and on THP as a disease biomarker of acute and chronic kidney diseases. Our studies have suggested that normal urinary THP, through its epidermal growth factor (EGF)-like domains, binds to the surface-expressed EGF-like receptors, cathepsin G, or lactoferrin to enhance polymorphonuclear leukocyte phagocytosis, proinflammatory cytokine production by monocytes/macrophages, and lymphocyte proliferation by activating the Rho family and mitogen-activated protein kinase signaling pathways. Furthermore, our data support both an intact protein core structure and carbohydrate side chains are important for the different protein-binding capacities of THP. Prospectively, parts of the whole THP molecule may be used for anti-TNF-α therapy in inflammatory diseases, autoantibody-depleting therapy in autoimmune disorders, and immune intensification in immunocompromised hosts.

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.

Uromodulin p.Cys147Trp mutation drives kidney disease by activating ER stress and apoptosis

Uromodulin-associated kidney disease (UAKD) is caused by mutations in the uromodulin (UMOD) gene that result in a misfolded form of UMOD protein, which is normally secreted by nephrons. In UAKD patients, mutant UMOD is poorly secreted and accumulates in the ER of distal kidney epithelium, but its role in disease progression is largely unknown. Here, we modeled UMOD accumulation in mice by expressing the murine equivalent of the human UMOD p.Cys148Trp point mutation (UmodC147W/+ mice). Like affected humans, these UmodC147W/+ mice developed spontaneous and progressive kidney disease with organ failure over 24 weeks. Analysis of diseased kidneys and purified UMOD-producing cells revealed early activation of the PKR-like ER kinase/activating transcription factor 4 (PERK/ATF4) ER stress pathway, innate immune mediators, and increased apoptotic signaling, including caspase-3 activation. Unexpectedly, we also detected autophagy deficiency. Human cells expressing UMOD p.Cys147Trp recapitulated the findings in UmodC147W/+ mice, and autophagy activation with mTOR inhibitors stimulated the intracellular removal of aggregated mutant UMOD. Human cells producing mutant UMOD were susceptible to TNF-α- and TRAIL-mediated apoptosis due to increased expression of the ER stress mediator tribbles-3. Blocking TNF-α in vivo with the soluble recombinant fusion protein TNFR:Fc slowed disease progression in UmodC147W/+ mice by reducing active caspase-3, thereby preventing tubule cell death and loss of epithelial function. These findings reveal a targetable mechanism for disease processes involved in UAKD.

From juvenile hyperuricaemia to dysfunctional uromodulin: an ongoing metamorphosis

Familial juvenile hyperuricaemic nephropathy (FJHN) is a diagnosis that is easily missed. It has taken a long time to clarify the pathophysiology and prevalence of this disease entity which has been shown to be genetically identical to medullary cystic kidney disease (MCKD) type II. The initial suspicion that uric acid was the noxious agent has been replaced by the recognition that a mutant uromodulin (UMOD) is the real culprit-although the exact mechanisms of pathogenicity remain uncertain. The mutation has been traced to the UMOD gene in chromosome 16. The disease is characterised by the classic triad of autosomal dominant inheritance, progressive renal failure beginning in the third to fifth decade of life and gout. Phenotypically similar but genotypically distinct entities have been described over the last 10 years, making a clinical diagnosis difficult. These include mutations in the renin, hepatocyte nuclear factor 1-β and mucin 1 genes. UMOD-associated kidney disease has been proposed as a logical diagnostic label to replace FJHN, but given all these other mutations, an over-arching diagnostic term of 'autosomal dominant tubulointerstitial kidney disease' (ADTKD) has been recently adopted. Allopurinol has been suggested as a therapeutic agent, but unfortunately this was based on non-randomised uncontrolled trials with small patient numbers.

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.

Effects of urine composition on epithelial Na+ channel-targeted protease activity

We examined human urinary proteolytic activity toward the Epithelial Sodium Channel (ENaC). We focused on two sites in each of alpha and gamma ENaC that are targets of endogenous and exogenous proteases. We examined the effects of ionic strength, pH and urinary H⁺-buffers, metabolic intermediates, redox molecules, and large urinary proteins. Monoatomic cations caused the largest effect, with sodium inhibiting activity in the 15–515 mEq range. Multivalent cations zinc and copper inhibited urinary proteolytic activity at concentrations below 100 μmol/L. Similar to sodium, urea caused a 30% inhibition in the 0–500 mmol/L range. This was not observed with acetone and ethanol. Modulating urinary redox status modified activity with H₂O₂ stimulated and ascorbate inhibited activity. Minimal effects (<10%) were observed with caffeine, glucose, several TCA cycle intermediates, salicylic acid, inorganic phosphate, albumin, creatinine, and Tamm–Horsfall protein. The cumulative activity of ENaC-cleaving proteases was highest at neutral pH, however, alpha and gamma proteases exhibited an inverse dependence with alpha stimulated at acidic and gamma stimulated at alkaline pH. These data indicate that ENaC-targeting urinary proteolytic activity is sensitive to sodium, urea and pH and changes in these components can modify channel cleavage and activation status, and likely downstream sodium absorption unrelated to changes in protein or channel density.

Isolation of urinary extracellular vesicles from Tamm- Horsfall protein-depleted urine and their application in the development of a lectin-exosome-binding assay

Urine is a readily available source of relatively large quantities of extracellular vesicles (EVs). However, the isolation of urinary EVs (uEVs) is complicated by the presence of Tamm-Horsfall protein (THP), which polymerizes and co-precipitates as a contaminant. This may make glycan analysis of uEVs difficult since THP is heavily glycosylated. To facilitate glycosylation analysis and address the need for elimination of non-uEV glycans, we present a modification of the uEV isolation procedure and use the isolated uEVs in the development of a lectin-exosome binding assay. Salt precipitation was employed to remove THP under conditions originally described for its separation from urine, followed by differential centrifugation. The quality of the isolated uEVs was examined by electron microscopy, SDS-PAGE, and immunoblotting. The uEVs were subsequently immobilized on solid phase and probed with labeled plant lectins using the lectin-exosome binding assay. Our results indicate that the isolated uEVs had preserved structural integrity and reacted with labeled plant lectins in a selective, carbohydrate-dependent manner. The basic lectin binding pattern of uEVs obtained by our method can be used as a reference for assessing the composition of their surface glycans in different physiological and pathological conditions.

The role of glycans in immune evasion: the human fetoembryonic defence system hypothesis revisited

Emerging data suggest that mechanisms to evade the human immune system may be shared by the conceptus, tumour cells, persistent pathogens and viruses. It is therefore timely to revisit the human fetoembryonic defense system (Hu-FEDS) hypothesis that was proposed in two papers in the 1990s. The initial paper suggested that glycoconjugates expressed in the human reproductive system inhibited immune responses directed against gametes and the developing human by employing their carbohydrate sequences as functional groups. These glycoconjugates were proposed to block specific binding interactions and interact with lectins linked to signal transduction pathways that modulated immune cell functions. The second article suggested that aggressive tumour cells and persistent pathogens (HIV, H. pylori, schistosomes) either mimicked or acquired the same carbohydrate functional groups employed in this system to evade immune responses. This subterfuge enabled these pathogens and tumour cells to couple their survival to the human reproductive imperative. The Hu-FEDS model has been repeatedly tested since its inception. Data relevant to this model have also been obtained in other studies. Herein, the Hu-FEDS hypothesis is revisited in the context of these more recent findings. Far more supportive evidence for this model now exists than when it was first proposed, and many of the original predictions have been validated. This type of subterfuge by pathogens and tumour cells likely applies to all sexually reproducing metazoans that must protect their gametes from immune responses. Intervention in these pathological states will likely remain problematic until this system of immune evasion is fully understood and appreciated.

Surface glycosylation profiles of urine extracellular vesicles

Urinary extracellular vesicles (uEVs) are released by cells throughout the nephron and contain biomolecules from their cells of origin. Although uEV-associated proteins and RNA have been studied in detail, little information exists regarding uEV glycosylation characteristics. Surface glycosylation profiling by flow cytometry and lectin microarray was applied to uEVs enriched from urine of healthy adults by ultracentrifugation and centrifugal filtration. The carbohydrate specificity of lectin microarray profiles was confirmed by competitive sugar inhibition and carbohydrate-specific enzyme hydrolysis. Glycosylation profiles of uEVs and purified Tamm Horsfall protein were compared. In both flow cytometry and lectin microarray assays, uEVs demonstrated surface binding, at low to moderate intensities, of a broad range of lectins whether prepared by ultracentrifugation or centrifugal filtration. In general, ultracentrifugation-prepared uEVs demonstrated higher lectin binding intensities than centrifugal filtration-prepared uEVs consistent with lesser amounts of co-purified non-vesicular proteins. The surface glycosylation profiles of uEVs showed little inter-individual variation and were distinct from those of Tamm Horsfall protein, which bound a limited number of lectins. In a pilot study, lectin microarray was used to compare uEVs from individuals with autosomal dominant polycystic kidney disease to those of age-matched controls. The lectin microarray profiles of polycystic kidney disease and healthy uEVs showed differences in binding intensity of 6/43 lectins. Our results reveal a complex surface glycosylation profile of uEVs that is accessible to lectin-based analysis following multiple uEV enrichment techniques, is distinct from co-purified Tamm Horsfall protein and may demonstrate disease-specific modifications.

Protein-Protein Interactions: Gene Acronym Redundancies and Current Limitations Precluding Automated Data Integration

Understanding protein interaction networks and their dynamic changes is a major challenge in modern biology. Currently, several experimental and in silico approaches allow the screening of protein interactors in a large-scale manner. Therefore, the bulk of information on protein interactions deposited in databases and peer-reviewed published literature is constantly growing. Multiple databases interfaced from user-friendly web tools recently emerged to facilitate the task of protein interaction data retrieval and data integration. Nevertheless, as we evidence in this report, despite the current efforts towards data integration, the quality of the information on protein interactions retrieved by in silico approaches is frequently incomplete and may even list false interactions. Here we point to some obstacles precluding confident data integration, with special emphasis on protein interactions, which include gene acronym redundancies and protein synonyms. Three human proteins (choline kinase, PPIase and uromodulin) and three different web-based data search engines focused on protein interaction data retrieval (PSICQUIC, DASMI and BIPS) were used to explain the potential occurrence of undesired errors that should be considered by researchers in the field. We demonstrate that, despite the recent initiatives towards data standardization, manual curation of protein interaction networks based on literature searches are still required to remove potential false positives. A three-step workflow consisting of: (i) data retrieval from multiple databases, (ii) peer-reviewed literature searches, and (iii) data curation and integration, is proposed as the best strategy to gather updated information on protein interactions. Finally, this strategy was applied to compile bona fide information on human DREAM protein interactome, which constitutes liable training datasets that can be used to improve computational predictions.

Biochemical and physical characterisation of urinary nanovesicles following CHAPS treatment

Urinary exosomes represent a precious source of potential biomarkers for disease biology. Currently, the methods for vesicle isolation are severely restricted by the tendency of vesicle entrapment, e.g. by the abundant Tamm-Horsfall protein (THP) polymers. Treatment by reducing agents such as dithiothreitol (DTT) releases entrapped vesicles, thus increasing the final yield. However, this harsh treatment can cause remodelling of all those proteins which feature extra-vesicular domains stabilized by internal disulfide bridges and have detrimental effects on their biological activity. In order to optimize exosomal yield, we explore two vesicle treatment protocols - dithiothreitol (DTT) and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic (CHAPS) - applied to the differential centrifugation protocol for exosomal vesicle isolation. The results show that CHAPS treatment does not affect vesicle morphology or exosomal marker distribution, thus eliminating most of THP interference. Moreover, the recovery and preservation of catalytic activity of two trans-membrane proteases, dipeptidyl peptidase IV and nephrilysin, was examined and found to be clearly superior after CHAPS treatment compared to DTT. Finally, proteomic profiling by mass spectrometry (MS) revealed that 76.2% of proteins recovered by CHAPS are common to those seen for DTT treatment, which illustrates underlining similarities between the two approaches. In conclusion, we provide a major improvement to currently-utilized urinary vesicle isolation strategies to allow recovery of urinary vesicles without the deleterious interference of abundant urinary proteins, while preserving typical protein folding and, consequently, the precious biological activity of urinary proteins which serve as valuable biomarkers.

Detection of mutant uromodulin in transgenic mouse harboring a mutant human UMOD gene

Uromodulin is the most abundant protein secreted in urine, and the mutated form of the uromodulin gene is associated with uromodulin-associated kidney disease (UAKD). Although uromodulin accumulates in the kidney of UAKD patients, it is unclear whether this is the wildtype or mutant form. In this study, we established a liquid chromatography (LC)-mass spectrometry/mass spectrometry (MS/MS)-based method for the detection of uromodulin mutants, using the C148W mutant as a target molecule. Membrane and cytosolic fractions of kidney samples from transgenic (Tg) mice expressing the C148W uromodulin mutant were shown to contain human uromodulin by western blotting, and mutant uromodulin with the C148W mutant sequence was observed by proteomic and selected reaction monitoring analyses. Our LC-MS/MS-based method is therefore useful for detection of mutant uromodulin that is undetectable by western blotting alone.

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.

Human urine proteomics: building a list of human urine cancer biomarkers

In the last decade, several reports have focused on the identification and characterization of proteins present in urine. In an effort to build a list of proteins of interest as biomarkers, we reviewed the largest urine proteomes and built two updated lists of proteins of interest (available as supplementary tables). The first table includes a consensus list of 443 proteins found in urine by independent laboratories and reported on the top three largest urine proteomes currently published. This consensus list of proteins could serve as biomarkers to diagnose, monitor and manage a number of diseases. Here, we focus on a reduced list of 35 proteins with potential interest as cancer biomarkers in urine following two criteria: first, proteins previously detected in urine using bottom-up proteomic experiments, and second, those suggested as cancer protein biomarkers in human plasma. In an effort to standardize the information presented and its use in future studies, here we include the updated International Protein Index (v. 3.80) and primary Swiss-Prot accession numbers, official gene symbols and recommended full names. The main variables that influence urine proteomic experiments are also discussed.

STUDIES OF TWO KINDS OF VIRUS PARTICLES WHICH COMPRISE INFLUENZA A2 VIRUS STRAINS : I. CHARACTERIZATION OF STABLE HOMOGENEOUS SUBSTRAINS IN REACTIONS WITH SPECIFIC ANTIBODY, MUCOPROTEIN INHIBITORS, AND ERYTHROCYTES

Two kinds of virus particles have been found in varying proportions in influenza A2 strains isolated during the 1957 pandemic. Pure populations of the different particles were obtained, and these substrains were genetically stable on serial passage in the chick embryo. The two virus particles differ markedly in several biological properties though they are antigenically similar. One kind of particle, designated "+," is relatively sensitive to specific antibody, is highly sensitive to inhibition by serum inhibitors and urinary mucoprotein, fails to elute or elutes very slowly from human erythrocytes, and is capable of agglutinating erythrocytes treated extensively with V. cholerae filtrate. The other particle, designated "-," is relatively insensitive to antibodies and urinary mucoprotein, completely insensitive to serum inhibitors, elutes rapidly from erythrocytes, and can agglutinate erythrocytes treated extensively with V. cholerae filtrate. Both "+" and "-" particles destroy virus receptors on urinary mucoprotein. The relative proportions of these two particles determine the characteristics of parent strains in reactions with specific antibody, mucoprotein inhibitors, and erythrocytes. The "+" and "-" particles with several easily identifiable markers are well suited for genetic studies.

Tamm-Horsfall protein and urinary exosome isolation

Urinary exosomes have been proposed as starting material for discovery of protein biomarkers of kidney disease. Current protocols for their isolation use a two-step differential centrifugation process. Due to their low density, exosomes are expected to remain in the low-speed (17,000 x g) supernatant and to sediment only when the sample is spun at high speed (200,000 x g). Analysis using western blot and electron microscopy found that urinary exosomes are also present in the low-speed pellet entrapped by polymeric Tamm-Horsfall protein, thus diminishing the procedure's reproducibility. Here we show that addition of dithiothreitol to the low-speed pellet disrupted the polymeric network, presumably by reduction of disulfide bonds linking the monomers. This modification shifted the exosomal proteins from the low- to the high-speed pellet. Also, by shifting the Tamm-Horsfall protein to the high-speed pellet, the use of dithiothreitol makes it feasible to use Tamm-Horsfall protein to normalize excretion rates of exosomal proteins in spot urines. We tested this by western blot, and found that there was a high degree of correlation between exosomal proteins and Tamm-Horsfall protein in the high-speed pellet. Since the yield of exosomes by differential centrifugation can be increased by chemical reduction, Tamm-Horsfall protein may be a suitable normalizing variable for urinary exosome studies when quantitative urine collections are not practical.

Waging war against uropathogenic Escherichia coli: winning back the urinary tract

Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is a substantial economic and societal burden-a formidable public health issue. Symptomatic UTI causes significant discomfort in infected patients, results in lost productivity, predisposes individuals to more serious infections, and usually necessitates antibiotic therapy. There is no licensed vaccine available for prevention of UTI in humans in the United States, likely due to the challenge of targeting a relatively heterogeneous group of pathogenic strains in a unique physiological niche. Despite significant advances in the understanding of UPEC biology, mechanistic details regarding the host response to UTI and full comprehension of genetic loci that influence susceptibility require additional work. Currently, there is an appreciation for the role of classic innate immune responses-from pattern receptor recognition to recruitment of phagocytic cells-that occur during UPEC-mediated UTI. There is, however, a clear disconnect regarding how factors involved in the innate immune response to UPEC stimulate acquired immunity that facilitates enhanced clearance upon reinfection. Unraveling the molecular details of this process is vital in the development of a successful vaccine for prevention of human UTI. Here, we survey the current understanding of host responses to UPEC-mediated UTI with an eye on molecular and cellular factors whose activity may be harnessed by a vaccine that stimulates lasting and sterilizing immunity.

Microfiltration isolation of human urinary exosomes for characterization by MS

PURPOSE

The purpose of this study was to address the hypothesis that small vesicular urinary particles known as exosomes could be selectively microfiltered using low protein-binding size exclusion filters, thereby simplifying their use in clinical biomarker discovery studies.

EXPERIMENTAL DESIGN

We characterized a microfiltration approach using a low protein binding, hydrophilized polyvinylidene difluoride membrane to easily and efficiently isolate urinary exosomes from fresh, room temperature or 4°C urine, with a simultaneous depletion of abundant urinary proteins. Using LC-MS, immunoblot analysis, and electron microscopy methods, we demonstrate this method to isolate intact exosomes and thereby enrich for a low abundant urinary proteome.

RESULTS

In comparison to other standard methods of exosome isolation including ultracentrifugation and nanofiltration, we demonstrate equivalent enrichment of the exosome proteome with reduced co-purification of abundant urinary proteins.

CONCLUSION AND CLINICAL RELEVANCE

In conclusion, we demonstrate a microfiltration isolation method that preserves the exosome structure, reduces contamination from higher abundant urinary proteins, and can be easily implemented into mass spectrometry analysis for biomarker discovery efforts or incorporation into routine clinical laboratory applications to yield higher sample throughput.

Autoimmune Responses to Tamm-Horsfall Protein in the Pathogenesis of Chronic Pyelonephritis

Although the role of bacterial infection as the major determinant in the development of acute pyelonephritis has been well documented for years, the nature of the renal scarring typical of chronic "atrophic" pyelonephritis has been a matter of controversy for at least three decades. In the past, recurrent bacterial infection of the kidney was thought to be responsible for the pathologic entity of "chronic pyelonephritis." However, more recent studies suggest that recurrent bacteriuria, in the absence of some form of obstructive uropathy, rarely produces chronic pyelonephritis. The close association between vesicoureteral reflex and chronic pyelonephritis has also been firmly established and has been observed to occur frequently in the absence of urinary tract infection. However, the mechanism by which vesicoureteral reflux injures the kidney has not been firmly established. A number of observations have suggested that some normal component of urine, particularly Tamm-Horsfall protein, might serve as an antigenic determinant involved in the immunopathogenesis of renal scarring in vesicoureteral reflux. The present studies were designed to investigate the immunopathogenic role of Tamm-Horsfall protein in a rabbit model of tubulointerstitial nephritis, and in a swine model of reflux nephropathy. The immune responses to Tamm-Horsfall protein in patients with recurrent nephrolithiasis were also examined, as were the antigenic similarities between Tamm-Horsfall protein and protein-containing components of uropathic bacteria. The results of these studies indicate that autoimmune responses to Tamm-Horsfall protein may occur after exposure to Tamm-Horsfall protein by intravenous challenge in rabbits, and by urinary reflux in pigs, as well as in recurrent nephrolithiasis in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered glycosylation of Tamm-Horsfall glycoprotein derived from renal allograft recipients leads to changes in its biological function

BACKGROUND

Human urinary Tamm-Horsfall glycoprotein (THP) is a pleotropic protein that binds different cytokines and stimulates various immunocompetent cells. It is unclear whether these important functions of THP are altered in renal transplant patients.

METHODS

We purified THPs from normal individuals (N-THP) and renal transplant patients receiving potent immunosuppressants (R-THP). The carbohydrate (CHO) compositions of THPs were probed by lectin-blotting and lectin-binding ELISA. The functions of THP were assessed by immune cell-stimulation as well as C1q, IL-1beta, IL-8 and TNF-alpha-binding assays. The roles of CHO moieties in THPs were analyzed using CHO-degrading enzyme digestion.

RESULTS

Compared to that of N-THP, the binding capacity of R-THP to Maackia amurensis, Galanthus nivalis and Datura stamonium decreased, indicating that R-THP contained lesser amount of Siaalpha(2,3)Gal/GalNAc, mannose residues, and beta(1,4)GlcNAc, but not GlcNAc/branched mannose. The binding capacity of R-THP to complement C1q and tumor necrosis factor (TNF)-alpha was also decreased. The stimulating effect of R-THP on mononuclear cell (MNC) proliferation and polymorphonuclear neutrophil (PMN) phagocytosis was less potent than that of N-THP. We found that the defective MNC-stimulation by R-THP was due to impaired NF-kappaB p52 nuclear translocation. The cell-stimulating effects of N- and R-THP could be abolished by digesting them with CHO-degrading enzymes, beta-galactosidase and neuraminidase. Interestingly, a potent apoptosis-inducing effect of R-THP on MNC and PMN was noted.

CONCLUSIONS

R-THP is not only modified in glycosylation but bears an apoptosis-inducing capacity on MNC and PMN, leading to an impaired immune function in renal transplant patients.

Factors affecting struvite (MgNH4PO4.6H2O) crystallization in feline urine

Factors affecting struvite, a magnesium-ammonium-phosphate complex (MgNH(4)PO(4).6H(2)O), in feline urine were evaluated. Incubation of just "urine mineral (UM)" solution, in which mineral concentrations are compatible with those in feline urine, for 4 h at 37 degrees C did not induce the formation of crystals. Similarly, incubation of urine alone did not produce crystals. However, struvite crystals were formed by the addition of urine to UM solution. Mg, NH(3) and P were all required for urine-induced struvite crystallization. The lower molecular weight (LMW) fraction of urine was essential for struvite crystal formation, and the higher molecular weight (HMW) fraction enhanced formation of LMW-induced struvite crystals. The effects of urine proteins further fractionated by column chromatography were examined. A protein at >250 kDa and cauxin, a major urine protein recently identified as a regulator of felinine production, potentiated struvite crystal formation induced by the LMW fraction. In contrast, Tamm-Horsfall glycoprotein, a urine protein thought to promote struvite crystallization, did not have this activity. The present study reveals a novel mechanism of feline struvite crystallization.