Structural basis of human uromodulin filament networks in uropathogen capture

Uromodulin (UMOD), the most abundant protein in human urine, is essential for kidney function and urinary tract health. UMOD forms filaments that bind to uropathogenic bacteria, facilitating their aggregation and clearance from the urinary tract. Here, we present the cryo-electron microscopy (cryo-EM) structure of the bacteria-binding D10C domain of UMOD and reveal its binding to the filament core. The details of D10C-core binding explain the formation of distinct filament lattice architectures adopted by UMOD. The D10C-core binding interface gives rise to diverse filament lattice structures, ranging from open and expansive to compact and dense conformations, or a combination of both. We hypothesize that other molecules present in urine may act as cross-linking agents, further stabilizing this binding interface and facilitating the connection of individual filaments into larger networks capable of effectively trapping bacteria. Structural mapping of kidney disease-related mutations points toward the abolition of disulfide bonds and promotion of mutant UMOD aggregation.

Uromodulin and Risk of Upper Urinary Tract Infections: A Mendelian Randomization Study

RATIONALE & OBJECTIVE

Observational studies suggest that uromodulin, produced by the kidneys, is associated with a reduced risk of upper urinary tract infections (UTIs), but inferences are limited by potential confounding factors. This study sought to explore further the validity of this association using Mendelian randomization (MR).

STUDY DESIGN

Two-sample MR study.

SETTING & PARTICIPANTS

The study included 29,315 and 13,956 participants from 18 cohorts of mainly European ancestry with measured urinary and serum uromodulin levels, respectively, and 3,873 and 512,608 participants from the UK Biobank, the Trøndelag Health Study, or the Michigan Genomic Initiative with and without upper UTIs.

EXPOSURES

We identified uncorrelated (r2 < 0.01) single nucleotide variations that were strongly associated (P < 5 × 10-6) with urinary and serum uromodulin levels from the aforementioned two genome-wide association studies. Both studies accounted for kidney function.

OUTCOMES

Genetic associations for the risk of upper UTIs extracted from the aforementioned independent genome-wide association study.

ANALYTICAL APPROACH

Inverse variance-weighted and sensitivity analyses were performed. The strength of each genetic instrument was estimated using the F statistic.

RESULTS

A 1-standard deviation increase in genetically predicted urinary uromodulin level was associated with an odds ratio (OR) for upper UTIs of 0.80 (95% CI, 0.67-0.95; P = 0.01). A 1-standard deviation increase in serum uromodulin was not statistically associated with elevated odds of upper UTIs, OR = 0.95 (95% CI, 0.89-1.01; P = 0.12). These findings were consistent across the sensitivity analyses.

LIMITATIONS

Analyses could be performed on only participants of predominantly European ancestry, potentially decreasing the generalizability of our findings.

CONCLUSIONS

This two-sample MR study found that increased levels of genetically predicted urinary uromodulin were associated with a reduced risk of upper UTIs. These findings support the hypothesis that uromodulin may have a protective role against upper UTIs.

PLAIN-LANGUAGE SUMMARY

Traditional studies have suggested that uromodulin, a protein produced by the kidneys, may reduce the risk of urinary tract infections (UTIs). The certainty of these findings is limited by the potential influence of unmeasured confounding factors. Therefore, we decided to address this concern by using genetic data to perform a two-sample Mendelian randomization analysis, a technique known to limit the influence of such factors. Our findings support the hypothesis that uromodulin in urine may have a protective role against upper UTIs. The findings were consistent across sensitivity and sex-specific analyses. Further research into the implications of these findings for the treatment of UTIs as well as the possible utility of urinary uromodulin as a diagnostic marker is warranted.

Cecropin A-Derived Peptide for the Treatment of Osteomyelitis by Inhibiting the Growth of Multidrug-Resistant Bacteria and Eliminating Inflammation

Osteomyelitis poses substantial therapeutic challenges due to the prevalence of multidrug-resistant bacterial infections and associated inflammation. Current treatment regimens often rely on a combination of corticosteroids and antibiotics, which can lead to complications and impede effective bacterial clearance. In this study, we present CADP-10, a Cecropin A-derived peptide, designed to target methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Escherichia coli (MRE), while simultaneously addressing inflammatory responses. CADP-10 self-assembles into nanobacterial net (NBacN) that selectively identify and bind to bacterial endotoxins (LPS and LTA), disrupting membrane integrity and depolarizing membrane potential, which culminates in bacterial death. Importantly, these NBacN are bound to LPS and LTA from dead bacteria, preventing their engagement with TLR receptors and effectively blocking downstream inflammatory pathways. Our assessments of CADP-10 demonstrate good biosafety in both in vitro and in vivo models. Notably, in a rabbit osteomyelitis model, CADP-10 eliminated MRSA-induced bone infections, mitigated inflammation, and promoted bone tissue regeneration. This research highlights the potential of CADP-10 as a multifunctional antimicrobial agent for the management of infectious inflammatory diseases.

The Identification of Biomarkers and Therapeutic Targets for Diabetic Kidney Disease by Integrating the Proteome with the Genome

Background: The blood proteome is a major source of biomarkers and therapeutic targets. We conducted a proteome-wide Mendelian randomization (MR) study to identify cardiometabolic protein markers for diabetic kidney disease (DKD). Methods: We measured all 369 proteins in the Olink Explore 384 Cardiometabolic and Cardiometabolic panel of 500 patients with type 2 diabetes from 11 communities in Shanghai. Protein quantitative trait loci (pQTLs) were derived by coupling genomic and proteomic data. Cis-pQTLs identified for proteins were used as instrumental variables in MR analyses of DKD risk, and the outcome data were obtained from 8401 Japanese individuals with type 2 diabetes (2809 cases and 5592 controls). Replication MR analysis was performed in the UK Biobank Pharma Proteomics Project (UKB-PPP). Colocalization analysis and the Heidi test were used to examine whether the identified proteins and DKD shared causal variants. Results: Among the 369 proteins, we identified 66 independent cis-pQTLs for 64 proteins. MR analysis suggested that two cardiometabolic proteins (UMOD and SIRPA) may play a causal role in increasing DKD risk, with UMOD showing replication in UKB-PPP. Bayesian colocalization further supported the causal effects of these proteins. Additional analyses indicated that UMOD is highly expressed in renal macrophages. Further downstream analyses suggested that UMOD could be a potential novel target and that SIRPA could be a potential repurposing target for DKD; however, further validation is needed. Conclusions: By integrating proteomic and genetic data from patients with type 2 diabetes, we identified two protein biomarkers potentially associated with DKD risk. These findings provide insights into DKD pathophysiology and therapeutic target development, but further replication and functional studies are needed to confirm these associations.

Complex carbohydrates catabolism capacity of bladder microbiota inhabiting healthy and overactive female bladders

Overactive bladder syndrome (OAB) is a poorly understood symptom complex that affects 40% of females over the age of 40, with clinical features including urinary urgency and incontinence. In addition to inflammation, oxidative stress, nerve damage and reduced blood flow, alterations in the urinary microbiome (urobiome), specifically in bladder bacterial diversity, have been reported to be associated with OAB. Bladder bacteria are members of the urobiome along with viruses, archaea, fungi, and protozoans. The urobiome metabolism, particularly in relationship to host complex sugars (glycans), has been investigated recently in terms of glycosaminoglycan (GAG) utilization. Nevertheless, other urinary free oligosaccharides (FOS) have not yet been explored in both OAB and urobiome contexts. Similarly, a comprehensive search of microbial genes involved in host glycan metabolism in the bladder of adult females with or without OAB has not yet been reported. In this study, we investigated urinary FOS by mass spectrometry in women without OAB (asymptomatic controls), with OAB without incontinence (dry OAB), or with OAB with incontinence (wet OAB or urgency urinary incontinence, UUI). We also questioned the ability of commensal bladder bacteria to digest these FOS and other glycans, using bioinformatic tools to query publicly available bladder genomes isolated from affected and unaffected adult females to identify genes that encode polysaccharide lyases (PL) and glycoside hydrolases (GH). Our results show that FOS are present in a similar level in affected and unaffected controls with a few exceptions: ten FOS were found to differ between the OAB dry groups and either the control (four) or UUI (six) groups. Our results indicate that bladder microbiota from adult females both with and without OAB have the genetic capacity to digest host glycans and dietary sugars with subtle differences. Bladder bacteria isolated from females with OAB possess more GH/PL genes for host mucins, whereas bladder bacteria from controls possess more GH/PL genes for GAG digestion. In the control group, specifically, the genus Streptococcus possessed genes for the PL8 and GH88 enzymes, known to be involved in host GAG digestion. These novel bioinformatic data can enable future biochemical exploration of the urobiome's metabolism toward specific host glycans, such as GAGs, mucins O-glycans and N-glycans.

Rapid and accurate testing for urinary tract infection: new clothes for the emperor

SUMMARYUrinary tract infection (UTI) is among the most common infections in clinical practice. In some cases, if left untreated, it can lead to pyelonephritis and urosepsis. In other cases, UTI resolves without treatment. Clinical diagnosis is typically based on patient symptoms and/or urinalysis, including urine dipsticks. The standard urine culture method is sometimes employed to identify the suspected urinary pathogen (uropathogen) and/or guide antimicrobial choice, but results are rarely available before 24 h. The standard urine culture method also misses fastidious, anaerobic, and slow-growing uropathogens and rarely reports polymicrobial infections. The unexplained combination of negative urine cultures with persistent urinary tract symptoms is distressing to both patients and clinicians. Given the broad appreciation of the advantages provided by rapid testing (e.g., for COVID-19 or influenza A), a rapid, accurate diagnostic test is needed to deliver timely treatment to patients seeking care for UTI that optimizes antibiotic stewardship. Herein, we discuss progress being made toward an accessible, timely (i.e., within hours), accurate assay with results that are clinically useful for the treating clinician within the timeframe of the infection (i.e., the growth rate of the pathogen(s)). New and emerging uropathogens often overlooked by current diagnostic techniques are also reviewed.

Bacterial adhesion strategies and countermeasures in urinary tract infection

Urinary tract infections (UTIs) are compounded by antimicrobial resistance, which increases the risk of UTI recurrence and antibiotic treatment failure. This also intensifies the burden of disease upon healthcare systems worldwide, and of morbidity and mortality. Uropathogen adhesion is a critical step in the pathogenic process, as has been mainly shown for Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Streptococcus agalactiae, Proteus, Enterococcus and Staphylococcus species. Although many bacterial adhesion molecules from these uropathogens have been described, our understanding of their contributions to UTIs is limited. Here we explore knowledge gaps in the UTI field, as we discuss the broader repertoire of uropathogen adhesins, including their role beyond initial attachment and the counter-responses of the host immune system. Finally, we describe the development of therapeutic approaches that target uropathogenic adhesion strategies and provide potential alternatives to antibiotics.

A comprehensive view of N-glycosylation as clinical biomarker in prostate cancer

Alterations in the prostate cancer (PCa) N-glycome have gained attention as a potential biomarker. This comprehensive review explores the diversity of N-glycosylation patterns observed in PCa-related cell lines, tissue, serum and urine, focusing on prostate-specific antigen (PSA) and the total pool of glycoproteins. Within the context of PCa, altered N-glycosylation patterns are a mechanism of immune escape and a disruption in normal glycoprotein distribution and trafficking. Glycoproteins with PCa-induced N-glycosylation patterns tend to accumulate in prostate tissue and the bloodstream, thereby diminishing N-glycan proportions in urine. Based on literary observations, aberrations in N-glycan branching are probably a characteristic of metabolic reprogramming and (chronic) inflammation. Changes in (core) fucosylation, specific N-glycosylation structures (such as N,N'-diacetyllactosamine) and high-mannose glycans otherwise are more likely indicators of cancer development and progression. Further investigation into these PCa-specific alterations holds promise in the discovery of new diagnostic, prognostic and response prediction biomarkers in PCa.

Tamm-Horsfall protein augments neutrophil NETosis during urinary tract infection

Urinary neutrophils are a hallmark of urinary tract infection (UTI), yet the mechanisms governing their activation, function, and efficacy in controlling infection remain incompletely understood. Tamm-Horsfall glycoprotein (THP), the most abundant protein in urine, uses terminal sialic acids to bind an inhibitory receptor and dampen neutrophil inflammatory responses. We hypothesized that neutrophil modulation is an integral part of THP-mediated host protection. In a UTI model, THP-deficient mice showed elevated urinary tract bacterial burdens, increased neutrophil recruitment, and more severe tissue histopathological changes compared with WT mice. Furthermore, THP-deficient mice displayed impaired urinary NETosis during UTI. To investigate the effect of THP on NETosis, we coupled in vitro fluorescence-based NET assays, proteomic analyses, and standard and imaging flow cytometry with peripheral human neutrophils. We found that THP increases proteins involved in respiratory chain, neutrophil granules, and chromatin remodeling pathways; enhances NETosis in an ROS-dependent manner; and drives NET-associated morphologic features including nuclear decondensation. These effects were observed only in the presence of a NETosis stimulus and could not be solely replicated with equivalent levels of sialic acid alone. We conclude that THP is a critical regulator of NETosis in the urinary tract, playing a key role in host defense against UTI.

Advances in uromodulin biology and potential clinical applications

Uromodulin (also known as Tamm-Horsfall protein) is a kidney-specific glycoprotein secreted bidirectionally into urine and into the circulation, and it is the most abundant protein in normal urine. Although the discovery of uromodulin predates modern medicine, its significance in health and disease has been rather enigmatic. Research studies have gradually revealed that uromodulin exists in multiple forms and has important roles in urinary and systemic homeostasis. Most uromodulin in urine is polymerized into highly organized filaments, whereas non-polymeric uromodulin is detected both in urine and in the circulation, and can have distinct roles. The interactions of uromodulin with the immune system, which were initially reported to be a key role of this protein, are now better understood. Moreover, the discovery that uromodulin is associated with a spectrum of kidney diseases, including acute kidney injury, chronic kidney disease and autosomal-dominant tubulointerstitial kidney disease, has further accelerated investigations into the role of this protein. These discoveries have prompted new questions and ushered in a new era in uromodulin research. Here, we delineate the latest discoveries in uromodulin biology and its emerging roles in modulating kidney and systemic diseases, and consider future directions, including its potential clinical applications.

UMOD Genotype and Determinants of Urinary Uromodulin in African Populations

Introduction

Single-nucleotide polymorphisms (SNPs) in the UMOD -PDILT genetic locus are associated with chronic kidney disease (CKD) in European populations, through their effect on urinary uromodulin (uUMOD) levels. The genetic and nongenetic factors associated with uUMOD in African populations remain unknown.

Methods

Clinical parameters, 3 selected UMOD-PDILT SNPs and uUMOD levels were obtained in 1202 young Black and White adults from the African-PREDICT study and 1943 middle aged Black adults from the PURE-NWP-SA study, 2 cross-sectional, observational studies.

Results

Absolute uUMOD and uUMOD/creatinine levels were lower in Black participants compared to White participants. The prime CKD-risk allele at rs12917707 was more prevalent in Black individuals, with strikingly more risk allele homozygotes compared to White individuals. Haplotype analysis of the UMOD-PDILT locus predicted more recombination events and linkage disequilibrium (LD) fragmentation in Black individuals. Multivariate testing and sensitivity analysis showed that higher uUMOD/creatinine associated specifically with risk alleles at rs12917707 and rs12446492 in White participants and with higher serum renin and lower urine albumin-to-creatinine ratio in Black participants, with a significant interaction of ethnicity on the relationship between all 3 SNPs and uUMOD/creatinine. The multiple regression model explained a greater percentage of the variance of uUMOD/creatinine in White adults compared to Black adults (23% vs. 8%).

Conclusion

We evidenced ethnic differences in clinical and genetic determinants of uUMOD levels, in particular an interaction of ethnicity on the relationship between CKD-risk SNPs and uUMOD. These differences should be considered when analyzing the role of uromodulin in kidney function, interpreting genome-wide association studies (GWAS), and precision medicine recommendations.

Bacterial-host adhesion dominated by collagen subtypes remodelled by osmotic pressure

Environmental osmolarity plays a crucial role in regulating the functions and behaviors of both host cells and pathogens. However, it remains unclear whether and how environmental osmotic stimuli modulate bacterial‒host interfacial adhesion. Using single-cell force spectroscopy, we revealed that the interfacial adhesion force depended nonlinearly on the osmotic prestimulation of host cells but not bacteria. Quantitatively, the adhesion force increased dramatically from 25.98 nN under isotonic conditions to 112.45 or 93.10 nN after the host cells were treated with the hypotonic or hypertonic solution. There was a strong correlation between the adhesion force and the number of host cells harboring adherent/internalized bacteria. We further revealed that enhanced overexpression levels of collagen XV and II were responsible for the increases in interfacial adhesion under hypotonic and hypertonic conditions, respectively. This work provides new opportunities for developing host-directed antibacterial strategies related to interfacial adhesion from a mechanobiological perspective.

Uromodulin and the study of urinary extracellular vesicles

Urinary extracellular vesicles (uEVs) are a promising substrate for discovering new biomarkers. In order to investigate the origin of uEVs and the cargo they carry, some types of downstream analysis of uEVs may require concentration and enrichment as well as removal of contaminating substances. Co-isolation of the abundant urinary protein uromodulin with uEVs can be a problem, and may interfere with some techniques, in particular with proteomic analysis tools. Methods of separating out uromodulin and its removal have also not been standardized. This review highlights aspects of uromodulin structure that makes it recalcitrant to separation from uEVs, summarizes frequently used techniques for uEV enrichment and how they affect uromodulin separation, and specific methods for uromodulin removal during preparation of uEVs. The necessity of uromodulin removal for various study endpoints is also examined.

Chronic kidney disease and risk of bloodstream infections and sepsis: a 17-year follow-up of the population-based Trøndelag Health Study in Norway

PURPOSE

Bloodstream infections (BSI) and sepsis are important causes of hospitalization, loss of health, and death globally. Targetable risk factors need to be identified to improve prevention and treatment. In this study, we aimed to evaluate the association of chronic kidney disease (CKD) and risk of and mortality from BSI and sepsis in the general population during a 22-year period.

METHODS

We conducted a prospective cohort study among participants in the population-based Norwegian HUNT Study, where 68,438 participated. The median follow-up time was 17.4 years. The exposures were estimated glomerular filtration rate (eGFR) and albumin-creatinine ratio (ACR) in urine. The outcomes were hazard ratios (HR) of hospital admission or death due to BSI or sepsis. The associations were adjusted for age, sex, diabetes, obesity, systolic blood pressure, smoking status, and cardiovascular disease.

RESULTS

Participants with eGFR < 30 ml/min/1.732 had HR 3.35 for BSI (95% confidence intervals (CI) 2.12-5.3) and HR 2.94 for sepsis (95% CI 1.82-4.8) compared to normal eGFR (≥ 90 ml/min/1.732). HRs of death from BSI and sepsis were 4.2 (95% CI 1.71-10.4) and 4.1 (95% CI 1.88-8.9), respectively. Participants with severely increased albuminuria (ACR > 30 mg/mmol) had HR 3.60 for BSI (95% CI 2.30-5.6) and 3.14 for sepsis (95% CI 1.94-5.1) compared to normal albumin excretion (ACR < 3 mg/mmol). HRs of death were 2.67 (95% CI 0.82-8.7) and 2.16 (95% CI 0.78-6.0), respectively.

CONCLUSION

In this large population-based cohort study, CKD was clearly associated with an increased risk of BSI and sepsis and related death.

A zebrafish gene with sequence similarities to human uromodulin and GP2 displays extensive evolutionary diversification among teleost and confers resistance to bacterial infection

In the process of investigating synaptic changes happening to mutants lacking postsynaptic receptors in the neuromuscular junction, we focused on a hitherto uncharacterized zebrafish gene zgc153932 whose expression was increased in the RNAseq and droplet digital PCR (ddPCR) analysis of a paralyzed mutant sofa potato. The zgc153932 gene which we named omcin5 (omc5) showed amino acid sequence similarity to human uromodulin and GP2, which are expressed in epithelial cells of the kidney and the gut respectively and bind to bacteria pili. omc5 had 14 paralogues in a ∼400 KB region on the chromosome 12 of the zebrafish genome. These genes, named omcin1 through 15, constitute a gene cluster which presumably arose from recent gene duplications in the zebrafish lineage. An antibody raised against the epitope common to 6-9 genes in the omcin family revealed expression in the cloaca of 1 day post fertilization (dpf) embryos which broadened to the urinary and digestive tracts by 5 dpf. Expression of omc5 was increased by exposure of embryos to Escherichia coli (E. coli). Survival of omc5 mutant embryos was shortened in the presence of E. coli, or when they were not maintained in germ-free conditions. Adults omc5 mutants also exhibited susceptibility to infection. Other teleost species which had omcin-like genes in their genomes showed a range of gene duplication, resulting in clusters of 1 to >15 omcin-like genes. We hereby identified a new gene family specific to teleost that include a microbial induced gene which confers resistance to bacterial infection.

Neutrophil extracellular traps protect the kidney from ascending infection and are required for a positive leukocyte dipstick test

Lower urinary tract infection (UTI) is common but only rarely complicated by pyelonephritis. However, the mechanisms preventing extension to the kidney are unclear. Here, we identified neutrophil extracellular traps (NETs) in healthy human urine that provide an antibacterial defense strategy within the urinary tract. In both in vivo murine models of UTI where uropathogenic E. coli are inoculated into the bladder and ex vivo human urine models, NETs interacted with uromodulin to form large webs that entrapped the bacteria. Peptidyl arginine deiminase 4 (PADI4) inhibition in mice blocked NETosis and resulted in progression of cystitis into pyelonephritis, suggesting that NETosis of urinary neutrophils acts to prevent bacterial ascent into the kidney. Analysis of UK Biobank data revealed that genetic variants in PADI4 that associated with increased risk of rheumatoid arthritis in multiple genome-wide association studies were consistently associated with reduced susceptibility to UTI. Last, we showed that urine dipstick testing for leukocyte esterase was negative in the presence of intact blood neutrophils but became positive when neutrophils were stimulated to NET, and this could be prevented by selective PADI4 inhibition, demonstrating that this test does not detect absolute neutrophil count, as has long been assumed, but specifically detects neutrophils that have undergone NETosis. These findings highlight the role of NETosis in preventing ascending infections in the urinary tract and improve our understanding of one of the most common clinical tests in medicine.

Host control of the microbiome: Mechanisms, evolution, and disease

Many species, including humans, host communities of symbiotic microbes. There is a vast literature on the ways these microbiomes affect hosts, but here we argue for an increased focus on how hosts affect their microbiomes. Hosts exert control over their symbionts through diverse mechanisms, including immunity, barrier function, physiological homeostasis, and transit. These mechanisms enable hosts to shape the ecology and evolution of microbiomes and generate natural selection for microbial traits that benefit the host. Our microbiomes result from a perpetual tension between host control and symbiont evolution, and we can leverage the host's evolved abilities to regulate the microbiota to prevent and treat disease. The study of host control will be central to our ability to both understand and manipulate microbiotas for better health.

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.

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.

A hierarchical structure in the N-glycosylation process governs the N-glycosylation output: prolonged cultivation induces glycoenzymes expression variations that are reflected in the cellular N-glycome but not in the protein and site-specific glycoprofile of CHO cells

N-glycosylation is a central component in the modification of secretory proteins. One characteristic of this process is a heterogeneous output. The heterogeneity is the result of both structural constraints of the glycoprotein as well as the composition of the cellular glycosylation machinery. Empirical data addressing correlations between glycosylation output and glycosylation machinery composition are seldom due to the low abundance of glycoenzymes. We assessed how differences in the glycoenzyme expression affected the N-glycosylation output at a cellular as well as at a protein-specific level. Our results showed that cellular N-glycome changes could be correlated with the variation of glycoenzyme expression, whereas at the protein level differential responses to glycoenzymes alterations were observed. We therefore identified a hierarchical structure in the N-glycosylation process: the enzyme levels in this complex pathway determine its capacity (reflected in the N-glycome), while protein-specific parameters determine the glycosite-specificity. What emerges is a highly variable and adaptable protein modification system that represents a hallmark of eukaryotic cells.

IGFBP1 stabilizes Umod expression through m6A modification to inhibit the occurrence and development of cystitis by blocking NF-κB and ERK signaling pathways

Cystitis is a common disease closely associated with urinary tract infections, and the specific mechanisms underlying its occurrence and development remain largely unknown. In this study, we discovered that IGFBP1 suppresses the occurrence and development of cystitis by stabilizing the expression of Umod through m6A modification, inhibiting the NF-κB and ERK signaling pathways. Initially, we obtained a bladder cystitis-related transcriptome dataset from the GEO database and identified the characteristic genes Umod and IGFBP1. Further exploration revealed that IGFBP1 in primary cells of cystitis can stabilize the expression of Umod through m6A modification. Overexpression of both IGFBP1 and Umod significantly inhibited cell apoptosis and the NF-κB and ERK signaling pathways, ultimately suppressing the production of pro-inflammatory factors. Finally, using a rat model of cystitis, we demonstrated that overexpression of IGFBP1 stabilizes the expression of Umod, inhibits the NF-κB and ERK signaling pathways, reduces the production of pro-inflammatory factors, and thus prevents the occurrence and development of cystitis. Our study elucidates the crucial role of IGFBP1 and Umod in cystitis and reveals the molecular mechanisms that inhibit the occurrence and development of cystitis. This research holds promise for offering new insights into the treatment of cystitis in the future.

The assembly platform FimD is required to obtain the most stable quaternary structure of type 1 pili

Type 1 pili are important virulence factors of uropathogenic Escherichia coli that mediate bacterial attachment to epithelial cells in the urinary tract. The pilus rod is comprised of thousands of copies of the main structural subunit FimA and is assembled in vivo by the assembly platform FimD. Although type 1 pilus rods can self-assemble from FimA in vitro, this reaction is slower and produces structures with lower kinetic stability against denaturants compared to in vivo-assembled rods. Our study reveals that FimD-catalysed in vitro-assembled type 1 pilus rods attain a similar stability as pilus rods assembled in vivo. Employing structural, biophysical and biochemical analyses, we show that in vitro assembly reactions lacking FimD produce pilus rods with structural defects, reducing their stability against dissociation. Overall, our results indicate that FimD is not only required for the catalysis of pilus assembly, but also to control the assembly of the most stable quaternary structure.

From Rare Disorders of Kidney Tubules to Acute Renal Injury: Progress and Prospective

Background

Acute kidney injury (AKI) is a severe condition marked by rapid renal function deterioration and elevated mortality, with traditional biomarkers lacking sensitivity and specificity. Rare tubulointerstitial diseases encompass a spectrum of disorders, primarily including monogenic diseases, immune-related conditions, and drug-induced tubulointerstitial diseases. The clinical manifestations vary from electrolyte and acid-base imbalances to kidney function insufficiency, which is associated with AKI in up to 20% of cases. Evidence indicated that rare tubulointerstitial diseases might provide new conceptual insights and perspectives for novel biomarkers and potential therapeutic strategies for AKI.

Summary

Autosomal dominant tubulointerstitial kidney disease (ADTKD) and Fanconi syndrome (FS) are rare tubulointerstitial diseases. In ADTKD, UMOD and REN are closely related to AKI by affecting oxidative stress and tubuloglomerular feedback, which provide potential new biomarkers for AKI. Both rare tubulointerstitial diseases and AKI share etiologies and treatment responses. From the mechanism standpoint, rare tubulointerstitial diseases and AKI involve tubular transporter injury, initially manifesting as tubular dysfunction in tubulointerstitial disorder and progressing to AKI because of the programmed cell death with apoptosis, pyroptosis, or necroptosis of proximal tubule cells. Additionally, mitochondrial dysfunction has been identified as a common mechanism in both tubulointerstitial diseases and AKI induced by drugs, pSS, or monoclonal diseases. In the end, both AKI and FS patients and animal models responded well to the therapy of the primary diseases.

Key Messages

In this review, we describe an overview of ADTKD and FS to identify their associations with AKI. Mitochondrial dysfunction contributes to rare tubulointerstitial diseases and AKI, which might provide a potential therapeutic target.

The impact of glycosylation on the structure, function, and interactions of CD14

CD14 is an innate immune receptor that senses pathogen-associated molecular patterns, such as lipopolysaccharide, to activate the innate immune response. Although CD14 is known to be glycosylated, detailed understanding about the structural and functional significance of this modification is still missing. Herein, an NMR and MS-based study, assisted by MD simulations, has provided a 3D-structural model of glycosylated CD14. Our results reveal the existence of a key N-glycosylation site at Asn282 that exclusively contains unprocessed oligomannnose N-glycans that perfectly fit the concave cavity of the bent-solenoid shaped protein. This site is not accessible to glycosidases and is fundamental for protein folding and secretion. A second N-site at Asn151 displays mostly complex N-glycans, with the typical terminal epitopes of the host cell-line expression system (i.e. βGal, α2,3 and α2,6 sialylated βGal, here), but also particularities, such as the lack of core fucosylation. The glycan at this site points outside the protein surface, resulting in N-glycoforms fully exposed and available for interactions with lectins. In fact, NMR experiments show that galectin-4, proposed as a binder of CD14 on monocytes to induce their differentiation into macrophages-like cells, interacts in vitro with CD14 through the recognition of the terminal glycoepitopes on Asn151. This work provides key information about CD14 glycosylation, which helps to better understand its functional roles and significance. Although protein glycosylation is known to be dynamic and influenced by many factors, some of the features found herein (presence of unprocessed N-glycans and lack of core Fuc) are likely to be protein specific.

Bioinspired Nanozymes as Nanodecoys for Urinary Tract Infection Treatment

Urinary tract infections (UTIs), common bacterial infections in communities and medical facilities, are mainly mediated by FimH. The glycan sites of the uromodulin protein play a crucial role in protecting against UTIs by interacting with FimH. A bioinspired approach using glycan-FimH interactions may effectively reduce bacteria through an antiadhesive mechanism, thereby curbing bacterial resistance. However, typical antiadhesive therapy alone fails to address the excessive reactive oxygen species and inflammatory response during UTIs. To bridge this gap, antioxidant nanozymes with antiadhesive ability were developed as nanodecoys to counter bacteria and inflammation. Specifically, ultrasmall dextran-coated ceria (DEC) was engineered to address UTIs, with dextran blocking FimH adhesion and ceria exhibiting anti-inflammatory properties. DECs, metabolizable by the kidneys, reduced bacterial content in the urinary tract, mitigating inflammation and tissue damage. In murine models, DECs successfully treated acute UTIs, repeated infections, and catheter-related UTIs. This dual approach not only highlights the potential of nanozymes for UTIs but also suggests applicability to other FimH-induced infections in the lungs and bowels, marking a significant advancement in nanozyme-based clinical approaches.

Natural Extracts for Antibacterial Applications

Bacteria-induced epidemics and infectious diseases are seriously threatening the health of people around the world. In addition, antibiotic therapy has been inducing increasingly more serious bacterial resistance, which makes it urgent to develop new treatment strategies to combat bacteria, including multidrug-resistant bacteria. Natural extracts displaying antibacterial activity and good biocompatibility have attracted much attention due to greater concerns about the safety of synthetic chemicals and emerging drug resistance. These antibacterial components can be isolated and utilized as antimicrobials, as well as transformed, combined, or wrapped with other substances by using modern assistive technologies to fight bacteria synergistically. This review summarizes recent advances in natural extracts from three kinds of sources-plants, animals, and microorganisms-for antibacterial applications. This work discusses the corresponding antibacterial mechanisms and the future development of natural extracts in antibacterial fields.

Unveiling the pathogenesis and therapeutic approaches for diabetic nephropathy: insights from panvascular diseases

Diabetic nephropathy (DN) represents a significant microvascular complication in diabetes, entailing intricate molecular pathways and mechanisms associated with cardiorenal vascular diseases. Prolonged hyperglycemia induces renal endothelial dysfunction and damage via metabolic abnormalities, inflammation, and oxidative stress, thereby compromising hemodynamics. Concurrently, fibrotic and sclerotic alterations exacerbate glomerular and tubular injuries. At a macro level, reciprocal communication between the renal microvasculature and systemic circulation establishes a pernicious cycle propelling disease progression. The current management approach emphasizes rigorous control of glycemic levels and blood pressure, with renin-angiotensin system blockade conferring renoprotection. Novel antidiabetic agents exhibit renoprotective effects, potentially mediated through endothelial modulation. Nonetheless, emerging therapies present novel avenues for enhancing patient outcomes and alleviating the disease burden. A precision-based approach, coupled with a comprehensive strategy addressing global vascular risk, will be pivotal in mitigating the cardiorenal burden associated with diabetes.

Identification and characterization of intact glycopeptides in human urine

Glycoproteins in urine have the potential to provide a rich class of informative molecules for studying human health and disease. Despite this promise, the urine glycoproteome has been largely uncharacterized. Here, we present the analysis of glycoproteins in human urine using LC-MS/MS-based intact glycopeptide analysis, providing both the identification of protein glycosites and characterization of the glycan composition at specific glycosites. Gene enrichment analysis reveals differences in biological processes, cellular components, and molecular functions in the urine glycoproteome versus the urine proteome, as well as differences based on the major glycan class observed on proteins. Meta-heterogeneity of glycosylation is examined on proteins to determine the variation in glycosylation across multiple sites of a given protein with specific examples of individual sites differing from the glycosylation trends in the overall protein. Taken together, this dataset represents a potentially valuable resource as a baseline characterization of glycoproteins in human urine for future urine glycoproteomics studies.

Tamm-Horsfall protein augments neutrophil NETosis during urinary tract infection

Urinary neutrophils are a hallmark of urinary tract infection (UTI), yet the mechanisms governing their activation, function, and efficacy in controlling infection remain incompletely understood. Tamm-Horsfall glycoprotein (THP), the most abundant protein in urine, uses terminal sialic acids to bind an inhibitory receptor and dampen neutrophil inflammatory responses. We hypothesized that neutrophil modulation is an integral part of THP-mediated host protection. In a UTI model, THP-deficient mice showed elevated urinary tract bacterial burdens, increased neutrophil recruitment, and more severe tissue histopathological changes compared to WT mice. Furthermore, THP-deficient mice displayed impaired urinary NETosis during UTI. To investigate the impact of THP on NETosis, we coupled in vitro fluorescence-based NET assays, proteomic analyses, and standard and imaging flow cytometry with peripheral human neutrophils. We found that THP increases proteins involved in respiratory chain, neutrophil granules, and chromatin remodeling pathways, enhances NETosis in an ROS-dependent manner, and drives NET-associated morphologic features including nuclear decondensation. These effects were observed only in the presence of a NETosis stimulus and could not be solely replicated with equivalent levels of sialic acid alone. We conclude that THP is a critical regulator of NETosis in the urinary tract, playing a key role in host defense against UTI.

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.

Allelic effects on uromodulin aggregates drive autosomal dominant tubulointerstitial kidney disease

Missense mutations in the uromodulin (UMOD) gene cause autosomal dominant tubulointerstitial kidney disease (ADTKD), one of the most common monogenic kidney diseases. The unknown impact of the allelic and gene dosage effects and fate of mutant uromodulin leaves open the gap between postulated gain-of-function mutations, end-organ damage and disease progression in ADTKD. Based on two prevalent missense UMOD mutations with divergent disease progression, we generated UmodC171Y and UmodR186S knock-in mice that showed strong allelic and gene dosage effects on uromodulin aggregates and activation of ER stress and unfolded protein and immune responses, leading to variable kidney damage. Deletion of the wild-type Umod allele in heterozygous UmodR186S mice increased the formation of uromodulin aggregates and ER stress. Studies in kidney tubular cells confirmed differences in uromodulin aggregates, with activation of mutation-specific quality control and clearance mechanisms. Enhancement of autophagy by starvation and mTORC1 inhibition decreased uromodulin aggregates. These studies substantiate the role of toxic aggregates as driving progression of ADTKD-UMOD, relevant for therapeutic strategies to improve clearance of mutant uromodulin.

Self-assembly of glycoprotein nanostructured filaments for modulating extracellular networks at long range

The intriguing capability of branched glycoprotein filaments to change their hierarchical organization, mediated by external biophysical stimuli, continues to expand understanding of self-assembling strategies that can dynamically rearrange networks at long range. Previous research has explored the corresponding biological, physiological and genetic mechanisms, focusing on protein assemblies within a limited range of nanometric units. Using direct microscopy bio-imaging, we have determined the morpho-structural changes of self-assembled filament networks of the zona pellucida, revealing controlled levels of structured organizations to join distinct evolved stages of the oocyte (Immature, Mature, and Fertilized). This natural soft network reorganizes its corresponding hierarchical network to generate symmetric, asymmetric, and ultimately a state with the lowest asymmetry of the outer surface roughness, and internal pores reversibly changed from elliptical to circular configurations at the corresponding stages. These elusive morpho-structural changes are regulated by the nanostructured polymorphisms of the branched filaments by self-extension/-contraction/-bending processes, modulated by determinate theoretical angles among repetitive filament units. Controlling the nanoscale self-assembling properties by delivering a minimum number of activation bio-signals may be triggered by these specific nanostructured polymorphic organizations. Finally, this research aims to guide this soft biomaterial into a desired state to protect oocytes, eggs, and embryos during development, to favour/prevent the fertilization/polyspermy processes and eventually to impact interactions with bacteria/virus at multiscale levels.

Gut microbiota and neonatal acute kidney injury biomarkers

One of the most frequent issues in newborns is acute kidney injury (AKI), which can lengthen their hospital stay or potentially raise their chance of dying. The gut-kidney axis establishes a bidirectional interplay between gut microbiota and kidney illness, particularly AKI, and demonstrates the importance of gut microbiota to host health. Since the ability to predict neonatal AKI using blood creatinine and urine output as evaluation parameters is somewhat constrained, a number of interesting biomarkers have been developed. There are few in-depth studies on the relationships between these neonatal AKI indicators and gut microbiota. In order to gain fresh insights into the gut-kidney axis of neonatal AKI, this review is based on the gut-kidney axis and describes relationships between gut microbiota and neonatal AKI biomarkers.

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.

Uropathogen and host responses in pyelonephritis

Urinary tract infections (UTIs) are among the most common bacterial infections seen in clinical practice. The ascent of UTI-causing pathogens to the kidneys results in pyelonephritis, which can trigger kidney injury, scarring and ultimately impair kidney function. Despite sizable efforts to understand how infections develop or are cleared in the bladder, our appreciation of the mechanisms by which infections develop, progress or are eradicated in the kidney is limited. The identification of virulence factors that are produced by uropathogenic Escherichia coli to promote pyelonephritis have begun to fill this knowledge gap, as have insights into the mechanisms by which kidney tubular epithelial cells oppose uropathogenic E. coli infection to prevent or eradicate UTIs. Emerging data also illustrate how specific cellular immune responses eradicate infection whereas other immune cell populations promote kidney injury. Insights into the mechanisms by which uropathogenic E. coli circumvent host immune defences or antibiotic therapy to cause pyelonephritis is paramount to the development of new prevention and treatment strategies to mitigate pyelonephritis and its associated complications.

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.

Identification of a Non-Invasive Urinary Exosomal Biomarker for Diabetic Nephropathy Using Data-Independent Acquisition Proteomics

Diabetic nephropathy (DN), as the one of most common complications of diabetes, is generally diagnosed based on a longstanding duration, albuminuria, and decreased kidney function. Some patients with the comorbidities of diabetes and other primary renal diseases have similar clinical features to DN, which is defined as non-diabetic renal disease (NDRD). It is necessary to distinguish between DN and NDRD, considering they differ in their pathological characteristics, treatment regimes, and prognosis. Renal biopsy provides a gold standard; however, it is difficult for this to be conducted in all patients. Therefore, it is necessary to discover non-invasive biomarkers that can distinguish between DN and NDRD. In this research, the urinary exosomes were isolated from the midstream morning urine based on ultracentrifugation combined with 0.22 μm membrane filtration. Data-independent acquisition-based quantitative proteomics were used to define the proteome profile of urinary exosomes from DN (n = 12) and NDRD (n = 15) patients diagnosed with renal biopsy and Type 2 diabetes mellitus (T2DM) patients without renal damage (n = 9), as well as healthy people (n = 12). In each sample, 3372 ± 722.1 proteins were identified on average. We isolated 371 urinary exosome proteins that were significantly and differentially expressed between DN and NDRD patients, and bioinformatic analysis revealed them to be mainly enriched in the immune and metabolic pathways. The use of least absolute shrinkage and selection operator (LASSO) logistic regression further identified phytanoyl-CoA dioxygenase domain containing 1 (PHYHD1) as the differential diagnostic biomarker, the efficacy of which was verified with another cohort including eight DN patients, five NDRD patients, seven T2DM patients, and nine healthy people. Additionally, a concentration above 1.203 μg/L was established for DN based on the ELISA method. Furthermore, of the 19 significantly different expressed urinary exosome proteins selected by using the protein-protein interaction network and LASSO logistic regression, 13 of them were significantly related to clinical indicators that could reflect the level of renal function and hyperglycemic management.

Water Loading and Uromodulin Secretion in Healthy Individuals and Idiopathic Calcium Stone Formers

BACKGROUND

Uromodulin is a protein made only by the kidney and released in urine, circulating in polymerizing and nonpolymerizing forms. This protein's multiple functions include inhibition of stone formation in the urine. The physiological determinants of uromodulin production are incompletely understood.

METHODS

We investigated changes in uromodulin levels and key factors governing its production and release in urine and serum. We performed an experiment to determine whether water loading, a common intervention to prevent stone formation, will alter the rate of uromodulin production. During a 2-day period, 17 stone forming participants and 14 control participants were subjected to water loading (day 1) and normal fluid intake (day 2). Uromodulin levels were measured on timed hourly collections in urine and plasma during the period of the study.

RESULTS

Water loading increased urinary uromodulin secretion (33±4 versus 10±4 μ g/min at baseline, P < 0.0001) in stone formers and control participants. Despite high urine volumes, most participants maintained relatively stable urinary uromodulin concentrations. Native Western blots for polymerizing and nonpolymerizing uromodulin suggest that polymerizing uromodulin was the predominant form at higher urinary flow volumes. Urine flow rates and sodium excretion were significant correlates of urinary uromodulin production. Water loading did not affect serum uromodulin levels, which were also not associated with urinary uromodulin.

CONCLUSIONS

Water loading increases the secretion of polymerizing urinary uromodulin. This increased secretion reduces the variability of urinary uromodulin concentrations despite high urine volumes. Serum uromodulin levels were not affected by this treatment.

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.

Vesicoureteral Reflux and Innate Immune System: Physiology, Physiopathology, and Clinical Aspects

Vesicoureteral reflux represents one of the most concerning topics in pediatric nephrology due to its frequency, clinical expression with the potential to evolve into chronic kidney disease, and last but not least, its socio-economic implications. The presence of vesicoureteral reflux, the occurrence of urinary tract infections, and the development of reflux nephropathy, hypertension, chronic kidney disease, and finally, end-stage renal disease represent a progressive spectrum of a single physiopathological condition. For the proper management of these patients with the best clinical outcomes, and in an attempt to prevent the spread of uropathogens' resistance to antibacterial therapy, we must better understand the physiopathology of urinary tract infections in patients with vesicoureteral reflux, and at the same time, we should acknowledge the implication and response of the innate immune system in this progressive pathological condition. The present paper focuses on theoretical aspects regarding the physiopathology of vesicoureteral reflux and the interconditionality between urinary tract infections and the innate immune system. In addition, we detailed aspects regarding cytokines, interleukins, antimicrobial peptides, and proteins involved in the innate immune response as well as their implications in the physiopathology of reflux nephropathy. New directions of study should focus on using these innate immune system effectors as diagnostic and therapeutic tools in renal pathology.

Structural insights into a cooperative switch between one and two FimH bacterial adhesins binding pauci- and high-mannose type N-glycan receptors

The FimH type-1 fimbrial adhesin allows pathogenic Escherichia coli to adhere to glycoproteins in the epithelial linings of human bladder and intestinal tract, by using multiple fimbriae simultaneously. Pauci- and high-mannose type N-glycans are natural FimH receptors on those glycoproteins. Oligomannose-3 and -5 bind with the highest affinity to FimH by using the same Manα1,3Man branch. Oligomannose-6 is generated from oligomannose-5 in the next step of the biogenesis of high-mannose N-glycans, by the transfer of a mannose in α1,2-linkage onto this branch. Using serial crystallography and by measuring the kinetics of binding, we demonstrate that shielding the high-affinity epitope drives the binding of multiple FimH molecules. First, we profiled FimH glycan binding on a microarray containing paucimannosidic N-glycans and in a FimH LEctPROFILE® assay. To make the transition to oligomannose-6, we measured the kinetics of FimH binding using paucimannosidic N-glycans, glycoproteins and all four α-dimannosides conjugated to bovine serum albumin. Equimolar mixed interfaces of the dimannosides present in oligomannose-6 and molecular dynamics simulations suggest a positive cooperativity in the bivalent binding of Manα1,3Manα1 and Manα1,6Manα1 dimannosides. The binding of core α1,6-fucosylated oligomannose-3 in the co-crystals of FimH is monovalent, but interestingly the GlcNAc1 - Fuc moiety retains highly flexibility. In co-crystals with oligomannose-6, two FimH bacterial adhesins bind the Manα1,3Manα1 and Manα1,6Manα1 endings of the second trimannose core (A-4'-B). This cooperative switch towards bivalent binding appears sustainable beyond a molar excess of oligomannose-6. Our findings provide important novel structural insights for the design of multivalent FimH antagonists that bind with positive cooperativity.

Connecting single-nucleotide polymorphisms, glycosylation status, and interactions of plasma serine protease inhibitors

Understanding the combined impacts of genetic variances and post-translational modifications requires new approaches. Here, we delineate proteoforms of plasma serine protease inhibitors and relate specific proteoforms to their interactions in complexes through the use of native mass spectrometry (MS). First, we dissect the proteoform repertoire of an acute-phase plasma protein, serine protease inhibitor A1 (SERPINA1), resolving four SERPINA1 variants (M1V, M1A, M2, and M3) with common single-nucleotide polymorphisms (SNPs). Investigating the glycosylation status of these variants and their ability to form complexes with a serine protease, elastase, we find that fucosylation stabilizes the interaction of the SERPINA1 M1V variant through its core fucosylation on Asn271. In contrast, antennary fucosylation on Asn271 destabilizes SERPINA1-elastase interactions. We unveil the same opposing effects of core and antennary fucosylation on SERPINA3 interactions with chymotrypsin. Together, our native MS results highlight the modulating effects of fucosylation with different linkages on glycoprotein interactions.

In Silico Prediction of Hub Genes Involved in Diabetic Kidney and COVID-19 Related Disease by Differential Gene Expression and Interactome Analysis

Diabetic kidney disease (DKD) is a frequently chronic kidney pathology derived from diabetes comorbidity. This condition has irreversible damage and its risk factor increases with SARS-CoV-2 infection. The prognostic outcome for diabetic patients with COVID-19 is dismal, even with intensive medical treatment. However, there is still scarce information on critical genes involved in the pathophysiological impact of COVID-19 on DKD. Herein, we characterize differential expression gene (DEG) profiles and determine hub genes undergoing transcriptional reprogramming in both disease conditions. Out of 995 DEGs, we identified 42 shared with COVID-19 pathways. Enrichment analysis elucidated that they are significantly induced with implications for immune and inflammatory responses. By performing a protein-protein interaction (PPI) network and applying topological methods, we determine the following five hub genes: STAT1, IRF7, ISG15, MX1 and OAS1. Then, by network deconvolution, we determine their co-expressed gene modules. Moreover, we validate the conservancy of their upregulation using the Coronascape database (DB). Finally, tissue-specific regulation of the five predictive hub genes indicates that OAS1 and MX1 expression levels are lower in healthy kidney tissue. Altogether, our results suggest that these genes could play an essential role in developing severe outcomes of COVID-19 in DKD patients.

Evolving Concepts in Uromodulin Biology, Physiology, and Its Role in Disease: a Tale of Two Forms

Uromodulin (or Tamm-Horsfall protein) is a glycoprotein uniquely produced in the kidney by tubular cells of the thick ascending limb of the loop of Henle and early distal tubules. This protein exhibits bidirectional secretion in the urine and in the renal interstitium and circulation. The role of this protein in maintaining renal and systemic homeostasis is becoming increasingly appreciated. Furthermore, perturbations of its functions may play a role in various diseases affecting the kidney and distant organs. In this review, we will discuss important advances in understanding its biology, highlighting the recent discoveries of its secretion and differential precursor processing that generates 2 forms: (1) a highly polymerizing form that is apically excreted in the urine and generates filaments and (2) a nonpolymerizing form that retains a polymerization inhibitory pro-peptide and is released basolaterally in the kidney interstitium and circulation, but can also be found in the urine. We will also discuss factors regulating its production and release, taking into account its intricate physiology, and propose best practices to report its levels. We also discuss breaking advances in its role in hypertension, acute kidney injury and progression to chronic disease, immunomodulation and regulating renal and systemic oxidative stress. We anticipate that this work will be a great resource for researchers and clinicians. This review will highlight the importance of defining what regulates the 2 forms of uromodulin, so that modulation of uromodulin levels and function could become a novel tool in our therapeutic armamentarium against kidney disease.

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.

Autosomal dominant tubulointerstitial kidney disease: A review

The clinical characteristics of autosomal dominant tubulointerstitial kidney disease (ADTKD) include bland urinary sediment, slowly progressive chronic kidney disease (CKD) with many patients reaching end stage renal disease (ESRD) between age 20 and 70 years, and autosomal dominant inheritance. Due to advances in genetic diagnosis, ADTKD is becoming increasingly recognized as a cause of CKD. Pathogenic variants in UMOD, MUC1, and REN are the most common causes of ADTKD. ADTKD-UMOD is also associated with hyperuricemia and gout. ADTKD-REN often presents in childhood with mild hypotension, CKD, hyperkalemia, acidosis, and anemia. ADTKD-MUC1 patients present only with CKD. This review describes the pathophysiology, genetics, clinical manifestation, and diagnosis for ADTKD, with an emphasis on genetic testing and genetic counseling suggestions for patients.