Urine soluble urokinase-type plasminogen activator receptor levels correlate with proteinuria in Puumala hantavirus infection

Expression Profile of Human Renal Mesangial Cells Is Altered by Infection with Pathogenic Puumala Orthohantavirus

Acute kidney injury (AKI) with proteinuria is a hallmark of infections with Eurasian orthohantaviruses. Different kidney cells are identified as target cells of hantaviruses. Mesangial cells may play a central role in the pathogenesis of AKI by regulation of inflammatory mediators and signaling cascades. Therefore, we examined the characteristics of hantavirus infection on human renal mesangial cells (HRMCs). Receptor expression and infection with pathogenic Puumala virus (PUUV) and low-pathogenic Tula virus (TULV) were explored. To analyze changes in protein expression in infected mesangial cells, we performed a proteome profiler assay analyzing 38 markers of kidney damage. We compared the proteome profile of in vitro-infected HRMCs with the profile detected in urine samples of 11 patients with acute hantavirus infection. We observed effective productive infection of HRMCs with pathogenic PUUV, but only poor abortive infection for low-pathogenic TULV. PUUV infection resulted in the deregulation of proteases, adhesion proteins, and cytokines associated with renal damage. The urinary proteome profile of hantavirus patients demonstrated also massive changes, which in part correspond to the alterations observed in the in vitro infection of HRMCs. The direct infection of mesangial cells may induce a local environment of signal mediators that contributes to AKI in hantavirus infection.

Severity Biomarkers in Puumala Hantavirus Infection

Annually, over 10,000 cases of hemorrhagic fever with renal syndrome (HFRS) are diagnosed in Europe. Puumala hantavirus (PUUV) causes most of the European HFRS cases. PUUV causes usually a relatively mild disease, which is rarely fatal. However, the severity of the infection varies greatly, and factors affecting the severity are mostly unrevealed. Host genes are known to have an effect. The typical clinical features in PUUV infection include acute kidney injury, thrombocytopenia, and increased vascular permeability. The primary target of hantavirus is the endothelium of the vessels of different organs. Although PUUV does not cause direct cytopathology of the endothelial cells, remarkable changes in both the barrier function of the endothelium and the function of the infected endothelial cells occur. Host immune or inflammatory mechanisms are probably important in the development of the capillary leakage. Several immunoinflammatory biomarkers have been studied in the context of assessing the severity of HFRS caused by PUUV. Most of them are not used in clinical practice, but the increasing knowledge about the biomarkers has elucidated the pathogenesis of PUUV infection.

Flash-Like Albuminuria in Acute Kidney Injury Caused by Puumala Hantavirus Infection

Transient proteinuria and acute kidney injury (AKI) are characteristics of Puumala virus (PUUV) infection. Albuminuria peaks around the fifth day and associates with AKI severity. To evaluate albuminuria disappearance rate, we quantified albumin excretion at different time points after the fever onset. The study included 141 consecutive patients hospitalized due to acute PUUV infection in Tampere University Hospital, Finland. Timed overnight albumin excretion (cU-Alb) was measured during the acute phase in 133 patients, once or twice during the convalescent phase within three months in 94 patients, and at six months in 36 patients. During hospitalization, 30% of the patients had moderately increased albuminuria (cU-Alb 20-200 μg/min), while 57% presented with severely increased albuminuria (cU-Alb >200 μg/min). Median cU-Alb was 311 μg/min (range 2.2-6460) ≤7 days after fever onset, 235 μg/min (range 6.8-5479) at 8-13 days and 2.8 μg/min (range 0.5-18.2) at 14-20 days. After that, only one of the measurements showed albuminuria (35.4 μg/min at day 44). At six months, the median cU-Alb was 2.0 μg/min (range 0.6-14.5). Albuminuria makes a flash-like appearance in PUUV infection and returns rapidly to normal levels within 2-3 weeks after fever onset. In the case of AKI, this is a unique phenomenon.

High plasma resistin associates with severe acute kidney injury in Puumala hantavirus infection

Background

Puumala hantavirus (PUUV) infected patients typically suffer from acute kidney injury (AKI). Adipokines have inflammation modulating functions in acute diseases including AKI. We examined plasma levels of three adipokines (resistin, leptin, and adiponectin) in acute PUUV infection and their associations with disease severity.

Methods

This study included 79 patients hospitalized due to acute PUUV infection. Plasma resistin, leptin, adiponectin, as well as IL-6 and CRP, were measured at the acute phase, recovery phase and one year after hospitalization.

Results

Plasma resistin levels were significantly higher in the acute phase compared to the recovery phase and one year after (median resistin 28 pg/mL (11–107) vs. 17 pg/mL (7–36) vs. 14 pg/mL (7–31), p<0.001). Maximum resistin concentration correlated with maximum plasma creatinine levels (r = 0.63; p<0.001). The higher the amount of albuminuria in the urine dipstick test (0–1+, 2+ or 3+) at admission, the higher the median of maximum resistin (24.7 pg/mL, 25.4 pg/mL and 39.6 pg/mL, respectively, p = 0.002). High resistin was also an independent risk factor for severe AKI (creatinine ≥353.6μmol/L) (OR 1.08, 95% CI 1.02–1.14). Neither plasma leptin nor adiponectin level had any correlation with creatinine concentration or the amount of albuminuria.

Conclusions

Plasma resistin independently associates with the severity of AKI in acute PUUV infection. The association of resistin with the amount of albuminuria suggests that the level of plasma resistin is not only influenced by renal clearance but could have some role in the pathogenesis of AKI during PUUV infection.

Proteinuria and the Clinical Course of Dobrava-Belgrade Hantavirus Infection

Purpose

Human infection with Dobrava-Belgrade virus (DOBV) in Northern Germany causes a mild form of hantavirus disease predominantly characterized by acute kidney injury due to interstitial nephritis. We evaluated the largest number of DOBV-infected patients so far regarding clinical course, proteinuria, and prognostic markers.

Patients and Methods

Patients with DOBV-associated hantavirus disease admitted to the Renal Division of the University of Lübeck (Germany) between 1997 and 2012 were included in this study. Symptoms, clinical course, laboratory parameters, and urinary protein analysis were investigated at admission (baseline, t₀), 3–5 days (t_3–5), 10–17 days (t_10–17), and after 1 year of follow-up (t₃₆₅).

Results

Of the 34 patients (male/female ratio: 23/11; age: 41 ± 14 years) included in the study, 4 underwent hemodialysis (HD). Glomerular filtration rate was 17 ± 14 mL/min at t₀ and increased to 27 ± 26 mL/min (t_3–5), 57 ± 20 mL/min (t_10–17), and 84 ± 16 mL/min (t₃₆₅). Albuminuria and tubular proteinuria (α₁- and β₂-microglobulin) decreased during follow-up; the urinary α₁-microglobulin concentration in patients who required HD was significantly higher than that in patients not requiring HD (t₀: 186 ± 51 vs. 45 ± 26 mg/g creatinine; t_3–5: 87 ± 14 vs. 32 ± 16 mg/g creatinine; t_10–17: 63 ± 18 vs. 28 ± 12 mg/g creatinine; p < 0.001).

Conclusions

DOBV infection of inpatients in Northern Germany is associated with severe kidney injury that recovers within a few weeks and normalizes within 1 year. Tubular proteinuria is associated with the severity of kidney injury and the necessity of renal replacement therapy in these DOBV-infected patients.

A tripartite complex of suPAR, APOL1 risk variants and αvβ3 integrin on podocytes mediates chronic kidney disease

Soluble urokinase plasminogen activator receptor (suPAR) independently predicts chronic kidney disease (CKD) incidence and progression. Apolipoprotein L1 (APOL1) gene variants G1 and G2, but not the reference allele (G0), are associated with an increased risk of CKD in individuals of recent African ancestry. Here we show in two large, unrelated cohorts that decline in kidney function associated with APOL1 risk variants was dependent on plasma suPAR levels: APOL1-related risk was attenuated in patients with lower suPAR, and strengthened in those with higher suPAR levels. Mechanistically, surface plasmon resonance studies identified high-affinity interactions between suPAR, APOL1 and α_vβ₃ integrin, whereby APOL1 protein variants G1 and G2 exhibited higher affinity for suPAR-activated avb3 integrin than APOL1 G0. APOL1 G1 or G2 augments α_vβ₃ integrin activation and causes proteinuria in mice in a suPAR-dependent manner. The synergy of circulating factor suPAR and APOL1 G1 or G2 on α_vβ₃ integrin activation is a mechanism for CKD.

Kidney disease in Puumala hantavirus infection

Acute kidney injury (AKI) remains a predominant clinical expression of nephropathia epidemica (NE). Its pathogenesis is not yet fully understood. Here, we describe the tissue injury comprehensively and present new data aimed to characterize the injury and explain its pathophysiology. When compared to tubulointerstitial nephritis of a wide variety of other aetiologies, a high degree of proteinuria is a distinguished trait of NE, a finding that is also helpful in the clinical suspicion of the disease. Recently, novel biomarkers for the prediction of severe AKI, including neutrophil gelatinase-associated lipocalin (NGAL), have been identified and ultrastructural tissue changes have been more accurately described. A role for soluble urokinase-type plasminogen activator (suPAR) in the pathogenesis of NE has been suggested, and data on gene polymorphisms, in relation to the severity of AKI have been presented. Smoking is a risk factor for NE and smoking is also associated with aggravated AKI in NE. Although no specific treatment is in sight, recent case reports concerning therapy directed against vascular permeability and vasodilation are of interest. In fact, future work trying to explain the pathophysiology of AKI might need concentrated efforts towards the mechanisms of increased vascular permeability and vasodilatation, which irrespective of organ manifestation, are two major determinants of NE.

What Do We Know about How Hantaviruses Interact with Their Different Hosts?

Hantaviruses, like other members of the Bunyaviridae family, are emerging viruses that are able to cause hemorrhagic fevers. Occasional transmission to humans is due to inhalation of contaminated aerosolized excreta from infected rodents. Hantaviruses are asymptomatic in their rodent or insectivore natural hosts with which they have co-evolved for millions of years. In contrast, hantaviruses cause different pathologies in humans with varying mortality rates, depending on the hantavirus species and its geographic origin. Cases of hemorrhagic fever with renal syndrome (HFRS) have been reported in Europe and Asia, while hantavirus cardiopulmonary syndromes (HCPS) are observed in the Americas. In some cases, diseases caused by Old World hantaviruses exhibit HCPS-like symptoms. Although the etiologic agents of HFRS were identified in the early 1980s, the way hantaviruses interact with their different hosts still remains elusive. What are the entry receptors? How do hantaviruses propagate in the organism and how do they cope with the immune system? This review summarizes recent data documenting interactions established by pathogenic and nonpathogenic hantaviruses with their natural or human hosts that could highlight their different outcomes.

Full-length soluble urokinase plasminogen activator receptor down-modulates nephrin expression in podocytes

Increased plasma level of soluble urokinase-type plasminogen activator receptor (suPAR) was associated recently with focal segmental glomerulosclerosis (FSGS). In addition, different clinical studies observed increased concentration of suPAR in various glomerular diseases and in other human pathologies with nephrotic syndromes such as HIV and Hantavirus infection, diabetes and cardiovascular disorders. Here, we show that suPAR induces nephrin down-modulation in human podocytes. This phenomenon is mediated only by full-length suPAR, is time-and dose-dependent and is associated with the suppression of Wilms’ tumor 1 (WT-1) transcription factor expression. Moreover, an antagonist of αvβ3 integrin RGDfv blocked suPAR-induced suppression of nephrin. These in vitro data were confirmed in an in vivo uPAR knock out Plaur^−/− mice model by demonstrating that the infusion of suPAR inhibits expression of nephrin and WT-1 in podocytes and induces proteinuria. This study unveiled that interaction of full-length suPAR with αvβ3 integrin expressed on podocytes results in down-modulation of nephrin that may affect kidney functionality in different human pathologies characterized by increased concentration of suPAR.

Community Acquired Severe Acute Kidney Injury Caused by Hantavirus-Induced Hemorrhagic Fever with Renal Syndrome Has a Favorable Outcome

BACKGROUND

Puumala hantavirus (PUUV) induces an acute tubulointerstitial nephritis and acute kidney injury (AKI). Our aim was to evaluate the prognosis of severe AKI associated with PUUV infection.

METHODS

We examined 556 patients who were treated at Tampere University Hospital during 1982-2013 for acute, serologically confirmed PUUV infection. Plasma creatinine was measured during hospitalization, convalescence, and 1, 2, and 5 years after the acute infection.

RESULTS

Plasma creatinine concentration was elevated (>100 μmol/l) in 459 (83%) patients, while altogether 189 patients (34%) had severe AKI defined as Kidney Disease: Improving Global Outcomes (KDIGO) stage 3, that is, plasma creatinine ≥353.6 μmol/l (4.0 mg/dl) or need of dialysis. There were no fatal cases during the hospitalization or the following 3 months. Fatality rate during the years following PUUV infection did not differ between patients who had suffered from severe AKI versus those without severe AKI. Post-hospitalization plasma creatinine values were available for 188 (34%) patients. One month after the acute infection, patients with prior severe AKI had higher median plasma creatinine concentration (82 µmol/l, range 54-184) than patients without severe AKI (74 µmol/l, range 55-109, p = 0.005). After 1 year, no significant difference existed in median plasma creatinine concentrations between patients with (71 µmol/l, range 36-123) and without prior severe AKI (72 µmol/l, range 34-116, p = 0.711). After 5 years all but 1 patient had normal creatinine levels.

CONCLUSIONS

In contrast to the worldwide well-accepted KDIGO criteria, severe AKI associated with PUUV infection is not associated with excess fatality but has a very good prognosis, both in the short and long terms.

The fundamental role of endothelial cells in hantavirus pathogenesis

Hantavirus, a genus of rodent- and insectivore-borne viruses in the family Bunyaviridae, is a group of emerging zoonotic pathogens. Hantaviruses cause hemorrhagic fever with renal syndrome and hantavirus cardiopulmonary syndrome in man, often with severe consequences. Vascular leakage is evident in severe hantavirus infections, and increased permeability contributes to the pathogenesis. This review summarizes the current knowledge on hantavirus interactions with hematopoietic and endothelial cells, and their effects on the increased vascular permeability.

Circulating suPAR levels are affected by glomerular filtration rate and proteinuria in primary and secondary glomerulonephritis

BACKGROUND

Circulating levels of soluble urokinase-like plasminogen activator receptor (suPAR) have been associated with proteinuria and renal function in focal segmental glomerulosclerosis (FSGS). This study aimed to evaluate if circulating suPAR levels are independently associated with proteinuria in patients with non-FSGS glomerulonephritis.

METHODS

This is a cross-sectional analysis of suPAR levels on 42 patients with primary non-FSGS glomerulonephritis (group GN) and 140 patients with secondary glomerulonephritis within an autoimmune disease (group AID).

RESULTS

suPAR serum levels were significantly higher in AID patients (4,733 ± 3,073 pg/ml) than in healthy controls (1,908 ± 1,685 pg/ml; p < 0.001), whereas GN patients displayed intermediate levels (3,670 ± 2,435 pg/ml; p = 0.021). Multivariate analysis for elevated serum suPAR (>3,000 pg/ml) showed an independent association with estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m(2) [odds ratio (OR) = 4.19, 95% confidence interval (CI): 1.67-10.54, p = 0.002], proteinuria >0.5 g/day (OR = 2.97; 95% CI: 1.32-6.70; p = 0.009) and presence of secondary vs. primary GN (OR = 2.87, 95% CI: 1.25-6.23; p = 0.013). A general linear model confirmed that suPAR levels were significantly affected by proteinuria >0.50 g/day (coefficient +1,477 pg/ml), eGFR (-38 pg/ml per 1 ml/min/1.73 m(2) increase) and presence of secondary vs. primary GN (+1,368 pg/ml).

CONCLUSIONS

This study shows that elevated serum suPAR levels are associated with reduced eGFR and presence of proteinuria in both primary and secondary GN, suggesting that circulating suPAR may represent a common biomarker of renal involvement in a wide spectrum of GN.