Proteomic Analysis of Urinary Extracellular Vesicles Reveals a Role for the Complement System in Medullary Sponge Kidney Disease.

Medullary sponge kidney (MSK) disease is a rare and neglected kidney condition often associated with nephrocalcinosis/nephrolithiasis and cystic anomalies in the precalyceal ducts. Little is known about the pathogenesis of this disease, so we addressed the knowledge gap using a proteomics approach. The protein content of microvesicles/exosomes isolated from urine of 15 MSK and 15 idiopathic calcium nephrolithiasis (ICN) patients was investigated by mass spectrometry, followed by weighted gene coexpression network analysis, support vector machine (SVM) learning, and partial least squares discriminant analysis (PLS-DA) to select the most discriminative proteins. Proteomic data were verified by ELISA. We identified 2998 proteins in total, 1764 (58.9%) of which were present in both vesicle types in both diseases. Among the MSK samples, only 65 (2.2%) and 137 (4.6%) proteins were exclusively found in the microvesicles and exosomes, respectively. Similarly, among the ICN samples, only 75 (2.5%) and 94 (3.1%) proteins were exclusively found in the microvesicles and exosomes, respectively. SVM learning and PLS-DA revealed a core panel of 20 proteins that distinguished extracellular vesicles representing each clinical condition with an accuracy of 100%. Among them, three exosome proteins involved in the lectin complement pathway maximized the discrimination between MSK and ICN: Ficolin 1, Mannan-binding lectin serine protease 2, and Complement component 4-binding protein ß. ELISA confirmed the proteomic results. Our data show that the complement pathway is involved in the MSK, revealing a new range of potential therapeutic targets and early diagnostic biomarkers.

Proteomic Analysis of Urinary Microvesicles and Exosomes in Medullary Sponge Kidney Disease and Autosomal Dominant Polycystic Kidney Disease.

BACKGROUND AND OBJECTIVES: Microvesicles and exosomes are involved in the pathogenesis of autosomal dominant polycystic kidney disease. However, it is unclear whether they also contribute to medullary sponge kidney, a sporadic kidney malformation featuring cysts, nephrocalcinosis, and recurrent kidney stones. We addressed this knowledge gap by comparative proteomic analysis. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: The protein content of microvesicles and exosomes isolated from the urine of 15 patients with medullary sponge kidney and 15 patients with autosomal dominant polycystic kidney disease was determined by mass spectrometry followed by weighted gene coexpression network analysis, support vector machine learning, and partial least squares discriminant analysis to compare the profiles and select the most discriminative proteins. The proteomic data were verified by ELISA. RESULTS: A total of 2950 proteins were isolated from microvesicles and exosomes, including 1579 (54%) identified in all samples but only 178 (6%) and 88 (3%) specific for medullary sponge kidney microvesicles and exosomes, and 183 (6%) and 98 (3%) specific for autosomal dominant polycystic kidney disease microvesicles and exosomes, respectively. The weighted gene coexpression network analysis revealed ten modules comprising proteins with similar expression profiles. Support vector machine learning and partial least squares discriminant analysis identified 34 proteins that were highly discriminative between the diseases. Among these, CD133 was upregulated in exosomes from autosomal dominant polycystic kidney disease and validated by ELISA. CONCLUSIONS: Our data indicate a different proteomic profile of urinary microvesicles and exosomes in patients with medullary sponge kidney compared with patients with autosomal dominant polycystic kidney disease. The urine proteomic profile of patients with autosomal dominant polycystic kidney disease was enriched of proteins involved in cell proliferation and matrix remodeling. Instead, proteins identified in patients with medullary sponge kidney were associated with parenchymal calcium deposition/nephrolithiasis and systemic metabolic derangements associated with stones formation and bone mineralization defects. PODCAST: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_04_24_CJASNPodcast_19_06_.mp3.

Urinary proteome in inherited nephrolithiasis.

In the last decades, proteomics has been largely applied to the Nephrology field, with the double aim to (1) elucidate the biological processes underlying renal diseases; (2) identify disease-specific biomarkers, predictor factors of therapeutic efficacy and prognostic factors of disease progression. Kidney stone disease, and in particular, inherited nephrolithiasis (INL) are not an exception. Given the multifactorial origin of these disorders, the combination of genomics and proteomics studies may complement each other, with the final objective to give a global and comprehensive mechanistic view. In this review, we summarize the results of recent proteomic studies which have expanded our knowledge about INL, focusing the attention on monogenic forms of nephrolithiasis (cystinuria, Dent's disease, Bartter syndrome, distal renal tubular acidosis and primary hyperoxaluria), on polygenic hypercalciuria and on medullary sponge kidney disease.

Proteomic-based research strategy identified laminin subunit alpha 2 as a potential urinary-specific biomarker for the medullary sponge kidney disease.

Medullary sponge kidney (MSK) disease, a rare kidney malformation featuring recurrent renal stones and nephrocalcinosis, continues to be diagnosed using expensive and time-consuming clinical/instrumental tests (mainly urography). Currently, no molecular diagnostic biomarkers are available. To identify such we employed a proteomic-based research strategy utilizing urine from 22 patients with MSK and 22 patients affected by idiopathic calcium nephrolithiasis (ICN) as controls. Notably, two patients with ICN presented cysts. In the discovery phase, the urine of 11 MSK and 10 controls, were randomly selected, processed, and analyzed by mass spectrometry. Subsequently, several statistical algorithms were undertaken to select the most discriminative proteins between the two study groups. ELISA, performed on the entire patients' cohort, was used to validate the proteomic results. After an initial statistical analysis, 249 and 396 proteins were identified exclusive for ICN and MSK, respectively. A Volcano plot and ROC analysis, performed to restrict the number of MSK-associated proteins, indicated that 328 and 44 proteins, respectively, were specific for MSK. Interestingly, 119 proteins were found to differentiate patients with cysts (all patients with MSK and the two ICN with renal cysts) from ICN without cysts. Eventually, 16 proteins were found to be common to three statistical methods with laminin subunit alpha 2 (LAMA-2) reaching the higher rank by a Support Vector Machine, a binary classification/prediction scheme. ELISA for LAMA-2 validated proteomic results. Thus, using high-throughput technology, our study identified a candidate MSK biomarker possibly employable in future for the early diagnosis of this disease.

Long-term treatment with potassium citrate and renal stones in medullary sponge kidney.

BACKGROUND AND OBJECTIVES: Medullary sponge kidney (MSK) is a renal malformation typically associated with nephrocalcinosis and recurrent calcium stones. Incomplete distal renal tubular acidosis, hypocitraturia, and hypercalciuria are common. For stone prevention, patients with MSK generally receive the standard "stone clinic" recommendations and often receive potassium citrate (KC). However, the effect on stone recurrence of citrate treatment in these patients has never been studied. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: The issue was retrospectively analyzed on an outpatient basis in 97 patients with a radiologic diagnosis of MSK: 65 had at least one stone risk factor (SRF; hypercalciuria, hypocitraturia, hyperuricosuria, hyperoxaluria) and received KC [29 +/- 8 (SD) mEq/d]; 10 patients with SRF and 22 without received only general stone clinic suggestions. Follow-up was 78 +/- 13, 72 +/- 15, and 83 +/- 14 months, respectively. The 24-hour urinary excretion of calcium, oxalate, uric acid, citrate, and morning urine pH were investigated at baseline and at the end of follow-up. RESULTS: Parallel to a significant rise in urinary citrate and decreased urinary calcium (all P < 0.001), KC led to a dramatic reduction in the stone event rate (from 0.58 to 0.10 stones/yr per patient). The existence of a group of patients with MSK, those without SRF, with a very low stone rate and no SRF was recognized. CONCLUSIONS: Treatment with KC is effective in preventing renal stones in the typical patient with MSK. It seems that two clinical phenotypes among patients showing typical MSK features during radiologic study exist.

Rabson-Mendenhall syndrome: medullary sponge kidney, a new component.

Rabson-Mendenhall syndrome is a rare genetic disorder characterized by severe insulin resistance, extreme hyperinsulinemia, postprandial hyperglycemia, growth retardation, and dysmorphisms. Enlargement of the kidneys and nephrocalcinosis have been described previously. We report a 10-year-old boy who presented with gross hematuria, unilateral hydronephrosis, and the initial diagnosis of bilateral extensive medullary nephrocalcinosis. Medullary sponge kidney (MSK) was included in the differential diagnosis given the ultrasound findings. Further evaluation by intravenous pyelogram confirmed the suspected bilateral MSK. Given the patient's history of hydronephrosis due to an obstructing renal stone and MSK, urine calcium excretion was assessed and found to be markedly increased at 9.5 mg/kg per day. To our knowledge, this is the first report of Rabson-Mendenhall syndrome and an association with MSK. We recommend evaluation for nephrocalcinosis, MSK, and hypercalciuria in all children diagnosed with Rabson-Mendenhall syndrome.

[Cacchi and Ricci's disease. Radiology, epidemiology and biology]. / Maladie de Cacchi et Ricci. Remarques radiologiques, épidémiologiques et biologiques.

OBJECTIVES: Medullary sponge kidney corresponds to the precaliceal dilatation of renal tubules. The purpose of this article is to draw attention to some of the radiological, epidemiological and laboratory features of this disease. MATERIAL AND METHOD: 500 cases of radiopaque renal stones, corresponding to 310 men and 190 women, were reviewed. One or several urographies, early urographic films, and blood calcium phosphate and 24-hour urinary calcium phosphate and oxalate assessments were available for all subjects. We have added to this series an identical study on 100 cases of stones in North African subjects. RESULTS: From a radiographic point of view, this study shows the value of early urography films, performed between the 2nd and 4th minutes after intravenous injection of iodinated contrast agent, which visualize abnormal opacification of the renal pyramids, before or at the same time as that of the bases of the calices. A radiological sign, not reported in the medical literature, is a clear border between abnormal opacification of the papillae and that of the calices, observed in one or several papillocaliceal zones, which facilitates the diagnosis of medullary sponge kidney. In this series of 500 cases of renal stones, the radiological diagnosis of medullary sponge kidney was established in 103 cases: 20.6%. The distribution varies according to sex, 54 out of 310 (12.59%) in men, 53 out of 190 (27.89%) in women; difference p < 0.001. We found only 3 cases of medullary sponge kidney in the series of 100 cases of radiopaque stones in North African subjects. In terms of laboratory parameters, 24-hour urine tests showed hypercalciuria in 61 out of 103 cases (59.22%), or hyperoxaluria in 66 out of 103 cases (64.08%), while 41 out of 103 cases (39.81%) presented both disorders. Urinary calcium oxalate assessments were normal in 20 out of 103 cases (19.42%). Hyperparathyroidism was never detected in combination with medullary sponge kidney. CONCLUSION: This study shows the value of early urography films for the diagnosis of medullary sponge kidney and demonstrates a useful diagnostic radiological sign: a clear border between abnormal urographic opacification of the papillae and calices. It shows the much higher frequency of medullary sponge kidney in patients with radiopaque stones, with a higher rate in women than in men, and a low frequency in North African subjects, that needs to be confirmed. This study also emphasizes the frequency of hypercalciuria and especially hyperoxaluria, and even the combination of these two disorders in medullary sponge kidney.

Urinary acidification and urinary excretion of calcium and citrate in women with bilateral medullary sponge kidney.

Urinary acidification ability, acid-base status and urinary excretion of calcium and citrate were evaluated in 10 women with bilateral medullary sponge kidney (MSK) and in 10 healthy women. Patients with MSK had higher fasting urine pH compared to normal controls (p < 0.01). Four patients had incomplete renal tubular acidiosis (iRTA), 3 had hypercalciuria, and 5 patients had hypocitraturia. The 24-hour urinary excretion of calcium was increased in the females with MSK (5.23 +/- 0.78 mmol) compared to the healthy females (3.49 +/- 0.29 mmol) (p < 0.02), and increased in MSK patients with iRTA (7.32 +/- 1.45 mmol) compared to patients with normal urinary acidification (3.83 +/- 0.12 mmol) (p < 0.01). The patients with iRTA had reduced levels of plasma standard bicarbonate (20.5 +/- 1.0) after fasting compared to patients with normal urinary acidification (23.8 +/- 0.8) and healthy women (22.7 +/- 0.6) (p < 0.01), and reduced levels of 24-hour urinary excretion of citrate (0.93 +/- 0.25 mmol) compared to patients with normal urinary acidification (3.58 +/- 0.51) and healthy women (2.78 +/- 0.49) (p < 0.005). A positive correlation was found between the degree of acidosis during ammonium chloride loading and urinary excretion of calcium (r = 0.71, p = 0.02), and a negative correlation between the degree of acidosis during ammonium chloride loading and urinary citrate excretion (r = 0.87, p = 0.001). The results suggest that defective urinary acidification might play an important role in the mechanism of hypercalciuria and hypocitraturia in patients with medullary sponge kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal tubular handling of potassium in patients with medullary sponge kidney. A model of renal papillectomy in humans.

Renal tubular function, with special emphasis on potassium excretion, was studied in three patients with medullary sponge kidney (MSK). Urinary acidification and concentration abilities were impaired, while glomerular filtration rates remained normal. After short-term intravenous (IV) potassium chloride loading, maximal excretion of potassium was lower in the patients with MSK than in the normal controls. The kaliuretic response to IV sodium sulfate and acetazolamide infusion was maintained. The capacity of the kidney to sustain potassium balance under conditions of either long-term potassium loading or depletion was preserved. We have concluded that the medullary and papillary segments of the human collecting duct, have an important role in the handling of short-term potassium loading. The integrity of these segments, however, is not essential for adaptation to prolonged potassium surfeit or dietary depletion.

Unilateral and segmental medullary sponge kidney: renal function and calcium excretion.

The renal acidification defect and renal hypercalciuria have been reported in patients with pan-renal and bilateral medullary sponge kidney. However, little is known about patients with unilateral or segmentally affected medullary sponge kidney. We report 2 cases of partially affected medullary sponge kidney with normal acidification ability and normal urinary calcium excretion, although the ability to concentrate urine was diminished. These findings suggest that in patients with partially affected medullary sponge kidney nephrolithiasis is not the consequence of renal hypercalciuria induced by systemic acidosis but is owing to the urinary stasis caused by cystic dilatation of the terminal collecting duct.

Medullary sponge kidney and renal acidification defect.

Medullary sponge kidney ( MSK ) is one of the entities which comprises a subclass of renal cystic disorders. While the clinical signs, symptoms, and radiological findings have been well documented in the past, the literature concerning renal function in these patients is relatively sparse. Thus, the purpose of the present studies was to examine the renal function in 11 patients with MSK and compare them to seven healthy volunteers and ten control patients with bilateral renal stones. Patients with MSK had normal GFR, RPF, and capacity to dilute urine; however, their urine concentrating ability was diminished. Urine pH in MSK patients was higher than in control patients with NH4Cl administration, while titratable acid excretion was lower than normal. Steady-state plasma bicarbonate concentration was lower in MSK patients than in controls but arterial pH was within normal limits. These studies suggest that MSK patients have defects in urinary acidification and concentration mechanism which may, in part, be the result of functional abnormality of the terminal collecting ducts.

Change of urinary excretion of electrolytes after acid, base and furosemide application in sponge kidney.

Sponge kidney is rare clinical and pathological entity, incidentally found in 0.4--1% of all excretory urographies. In the advanced stage of the disease, distal tubules are affected and renal-tubular acidosis, change of urinary laminar flow and Ca2+ wasting syndrome result in frequent formation of Ca-oxalate stones. Alkali therapy is investigated on the excretion of Na+, K+ and Ca2+ and compared to furosemide administration.