Spontaneous calcification process in primary renal cells from a medullary sponge kidney patient harbouring a GDNF mutation

Exploring the relationship of supernumerary recurrent renal calculi formation and tick-borne infections: a case report

A 51-year-old male with a history of Cacchi-Ricci disease and long-standing infection with various species of Borrelia, Babesia, and Bartonella presented with recurrent symptoms of right-sided flank pain. Numerous renal calculi were identified on imaging. The etiology of the calculi had not been previously elucidated. Symptoms intermittently date back to 2002 when uric acid stones were identified. Subsequent calculi analysis revealed calcium oxalate stones. Despite the commonality of nephrolithiasis in patients with Cacchi-Ricci disease, the extreme number of calculi and recurrent presentation of symptoms persisted despite a plethora of medical evaluations, dietary changes, and hereditary testing. This case raises questions of etiology including possible immune deficiency and whether his uncommon microbial history contributes to recurrent stone formation.

OLMALINC/OCT4/BMP2 axis enhances osteogenic-like phenotype of renal interstitial fibroblasts to participate in Randall's plaque formation

BACKGROUND

Randall's plaques (RP) are identified as anchored sites for kidney calcium oxalate stones, but the mechanism remains unclear. Given the importance of osteogenic-like cells in RP formation and OCT4 in reprogramming differentiated cells to osteoblasts, the current study explored the potential role of OCT4 in RP formation.

METHODS

OCT4 and biomineralization were evaluated in RP, and immunofluorescence co-staining was performed to identify these cells with alteration of OCT4 and osteogenic markers. Based on the analysis of tissue, we further investigated the mechanism of OCT4 in regulating osteogenic-like differentiation of primary human renal interstitial fibroblasts (hRIFs) in vitro and vivo.

RESULTS

We identified the upregulated OCT4 in RP, with a positive correlation to osteogenic markers. Interestingly, fibroblast marker Vimentin was partially co-localized with upregulated OCT4 and osteogenic markers in RP. Further investigations revealed that OCT4 significantly enhanced the osteogenic-like phenotype of hRIFs in vitro and in vivo. Mechanically, OCT4 directly bound to BMP2 promoter and facilitated its CpG island demethylation to transcriptionally promote BMP2 expression. Furthermore, combination of RIP and RNA profiling uncovered that lncRNA OLMALINC physically interacted with OCT4 to promote its stabilization via disrupting the ubiquitination. Additionally, OLMALINC was upregulated in fibroblasts in RP visualized by FISH, and a positive correlation was revealed between OLMALINC and OCT4 in RP.

CONCLUSIONS

The upregulation of OCT4 in hRIFs was a pathological feature of RP formation, and OLMALINC/OCT4/BMP2 axis facilitated hRIFs to acquire osteogenic-like phenotype under osteogenic conditions, through which the pathway might participate in RP formation. Our findings opened up a new avenue to better understand RP formation in which osteogenic-like process was partially triggered by lncRNAs and pluripotency maintenance related genes.

Randall's plaque and calcium oxalate stone formation: role for immunity and inflammation

Idiopathic calcium oxalate (CaOx) stones often develop attached to Randall's plaque present on kidney papillary surfaces. Similar to the plaques formed during vascular calcification, Randall's plaques consist of calcium phosphate crystals mixed with an organic matrix that is rich in proteins, such as inter-α-trypsin inhibitor, as well as lipids, and includes membrane-bound vesicles or exosomes, collagen fibres and other components of the extracellular matrix. Kidney tissue surrounding Randall's plaques is associated with the presence of classically activated, pro-inflammatory macrophages (also termed M1) and downregulation of alternatively activated, anti-inflammatory macrophages (also termed M2). In animal models, crystal deposition in the kidneys has been associated with the production of reactive oxygen species, inflammasome activation and increased expression of molecules implicated in the inflammatory cascade, including osteopontin, matrix Gla protein and fetuin A (also known as α2-HS-glycoprotein). Many of these molecules, including osteopontin and matrix Gla protein, are well known inhibitors of vascular calcification. We propose that conditions of urine supersaturation promote kidney damage by inducing the production of reactive oxygen species and oxidative stress, and that the ensuing inflammatory immune response promotes Randall's plaque initiation and calcium stone formation.

Osteogenic Differentiation of Renal Interstitial Fibroblasts Promoted by lncRNA MALAT1 May Partially Contribute to Randall's Plaque Formation

Background

The current belief is that Randall's plaques (RP) constitute a nidus for the formation of idiopathic calcium oxalate stones, but the upstream events in RP formation remain unclear. The present study aimed to investigate whether RP formation shares similarities with biomineralization and to illustrate the potential role played by the lncRNA MALAT1 in osteogenic differentiation of human renal interstitial fibroblasts (hRIFs).

Materials and Methods

Biomineralization and MALAT1 expression were assessed in RP, and hRIFs were isolated and induced under osteogenic conditions for further experiments. The transcription initiation and termination sites in MALAT1 were identified by 5' and 3' RACE. RNA immunoprecipitation assays and luciferase assays were used to validate the interactions among MALAT1, Runx2 and miRNAs.

Results

Upregulated expression of osteogenic markers and MALAT1 was observed in RP and hRIFs induced with osteogenic medium. Biomineralization in RP and calcium phosphate (CaP) deposits in induced hRIFs were further verified by electron microscopy. Furthermore, overexpression of MALAT1 promoted the osteogenic phenotype of hRIFs, while treatment with a miR-320a-5p mimic and knockdown of Runx2 significantly suppressed the osteogenic phenotype. Further analysis showed that MALAT1 functioned as a competing endogenous RNA to sponge miR-320a-5p, leading to upregulation of Runx2 and thus promoting osteogenic differentiation of hRIFs.

Conclusion

Ectopic calcification and MALAT1 partially contributed to the formation of RP, in which MALAT1 might promote Runx2 expression to regulate osteogenic differentiation of hRIFs by sponging miRNA-320a-5p. The current study sheds new light on the lncRNA-directed mechanism of RP formation via a process driven by osteogenic-like cells.

Variable Expressivity of HNF1B Nephropathy, From Renal Cysts and Diabetes to Medullary Sponge Kidney Through Tubulo-interstitial Kidney Disease

Introduction

In humans, heterozygous mutations of hepatocyte nuclear factor 1beta (HNF1B) are responsible for a dominant inherited disease with both renal and extrarenal phenotypes. HNF1B nephropathy is the umbrella term that includes the various kidney phenotypes of the disease, ranging from congenital anomalies of the kidney and urinary tract (CAKUT), to tubular transport abnormalities, to chronic tubulointerstitial and cystic renal disease.

Methods

We describe 7 families containing 13 patients with ascertained HNF1B nephropathy. All patients underwent genetic testing and clinical, laboratory, and instrumental assessment, including renal imaging and evaluation of extrarenal HNF1B manifestations.

Results

Significant inter- and intrafamilial variability of HNF1B nephropathy has been observed. In our cohort, HNF1B pathogenic variants presented with renal cysts and diabetes syndrome (RCAD); renal cystic phenotype mimicking autosomal dominant polycystic kidney disease (ADPKD); autosomal dominant tubulointerstitial kidney disease (ADTKD) with or without hyperuricemia and gout; CAKUT; and nephrogenic diabetes insipidus (NDI). Of note, for the first time, we describe the occurrence of medullary sponge kidney (MSK) in a family harboring the HNF1B whole-gene deletion at chromosome 17q12. Genotype characterization led to the identification of an additional 6 novel HNF1B pathogenic variants, 3 frameshift, 2 missense, and 1 nonsense.

Conclusion

HNF1B nephropathy may present with a highly variable renal phenotype in adult patients. We expand the HNF1B renal clinical picture to include MSK as a potential new finding. Finally, we expand the allelic repertoire of the disease by adding novel HNF1B pathogenic variants.

Suppression of osteogenic-like differentiation in human renal interstitial fibroblasts by miRNA-410-3p through MSX2

Background

The aim of this stay was to determine the effect of calcium ions in promoting osteogenic-like differentiation in human renal interstitial fibroblasts (hRIFs). The role of miRNA-410-3p in upregulating Msh homeobox 2 (MSX2) level in hRIFs was also investigated.

Methods

Quantitative polymerase chain reaction (qPCR) analysis was used to assess the expression levels of miRNA-410-3p in Randall’s plaque (RP) and normal renal papillary (nRP) tissues. Furthermore, the expression levels of osteogenesis-related protein in the RP and nRP tissues were assessed with qPCR and immunohistochemistry (IHC). hRIFs were cultured from isolated human kidney papilla before treatment with calcium chloride or osteogenic medium, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was performed at 1, 5, 9, and 14 days post-treatment. Alizarin red staining was used to estimate the deposits of calcium aggregates. After the overexpression or knockdown of miRNA-410-3p, we evaluated the changes in the osteogenic-like differentiation and osteogenesis-related protein by alizarin red staining and qPCR, respectively. A binding relationship between miRNA-410-3p and MSX2 was established through a dual-luciferase reporter gene assay. Rescue experiments demonstrated that miRNA-410-3p regulated the osteogenic-like differentiation by targeting MSX2.

Results

miRNA-410-3p levels were lower in RP tissue than in control nRP tissues. qPCR and IHC showed that the level of runt-related transcription factor 2 (Runx2), osteocalcin (OCN), and osteopontin (OPN) were higher in RP tissues. The calcium deposition of hRIFs showed a time-dependent trend when treated with osteogenic medium or calcium chloride. The overexpression of miRNA-410-3p downregulated the levels of osteogenesis-related expression and attenuated mineralization. The knockdown of miRNA-410-3p yielded the opposite trend. Dual-luciferase reporter gene assay and rescue experiments indicated that miRNA-410-3p could target MSX2, while the overexpression of MSX2 reversed the effects of miRNA-410-3p on osteogenic-like differentiation.

Conclusions

The current findings suggest that calcium ions could promote the osteogenic-like differentiation of hRIFs and miRNA-410-3p regulates hRIFs osteogenic-like differentiation by inhibiting MSX2.

Long non-coding RNA H19 promotes osteogenic differentiation of renal interstitial fibroblasts through Wnt-β-catenin pathway

Randall's plaque (RP) serves as a nidus on which idiopathic calcium oxalate stones form. Renal interstitial mineralization may be the cause underlying RP, and recent studies demonstrated the similarities between the interstitial mineralization and ectopic calcification. The present study aimed to investigate whether human renal interstitial fibroblasts (hRIFs) could form calcification under osteogenic conditions, and whether long non-coding RNA H19 participated in regulating osteogenic differentiation of hRIFs through Wnt-β-catenin pathway. HRIFs were isolated and induced for osteogenic differentiation under osteogenic conditions. Runx2, OCN, alkaline phosphatase (ALP) activity, and the mineralized nodule formation were used to assess the osteogenic phenotype. Molecule expressions were determined by qRT-PCR, immunofluorescence staining, and western blot. The mineralized nodules were assessed by Alizarin red staining. Compared to the normal renal papillary tissue, Runx2, OCN, and H19 were significantly upregulated in RP. After hRIFs were induced with osteogenic medium, osteogenic markers (Runx2, OCN and ALP), β-catenin and H19 were significantly upregulated, and the mineralized nodules are formed. Additionally, overexpression of H19 promoted the osteogenic phenotype of hRIFs and increased the expression of β-catenin, whereas knock-down of H19 or XAV939 (inhibitor of Wnt-β-catenin signaling pathway) significantly repressed the osteogenic phenotype of hRIFs and decreased the β-catenin. Moreover, XAV939 was shown to abolish the osteogenic differentiation of hRIFs promoted by H19. The study demonstrated that ectopic calcification partly participated in the formation of RP, and H19 promoted osteogenic differentiation of hRIFs by activating Wnt-β-catenin pathway, which shed new light on the molecular mechanism of the RP formation.

The role of the gasotransmitter hydrogen sulfide in pathological calcification

Calcification is the deposition of minerals, mainly hydroxyapatite, inside the cell or in the extracellular matrix. Physiological calcification is central for many aspects of development including skeletal and tooth growth; conversely, pathological mineralization occurs in soft tissues and is significantly associated with malfunction and impairment of the tissue where it is located. Various mechanisms have been proposed to explain calcification. However, this research area lacks a more integrative, systemic, and global perspective that could explain both physiological and pathological processes. In this review, we propose such an integrated explanation. Hydrogen sulfide (H₂ S) is a newly recognized multifunctional gasotransmitters and tis actions have been studied in different physiological and pathological contexts, but little is known about its potential role on calcification. Interestingly, we found that H₂ S promotes calcification under physiological conditions and has an inhibitory effect on pathological processes. This makes H₂ S a potential therapy for diseases related to pathological calcification. LINKED ARTICLES: This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Nephrocalcinosis in adolescent girl with medullary sponge kidney and mild hemihypertrophy: A case report

RATIONALE

Medullary sponge kidney (MSK) is a rare congenital abnormality characterized by cystic dilatation of the medullary collecting tubules. The disorder is likely to be complicated by nephrocalcinosis, urolithiasis, tubular dysfunctions, and urinary tract infections. In addition, it may be rarely associated with extrarenal anomalies.

PATIENT CONCERN

We present a case of 17-year old girl who was referred for metabolic evaluation of bilateral nephrocalcinosis. Physical examination showed signs of mild, left-sided hemihypertrophy involving the lower limb, buttock, trunk, face, and tongue. The imaging studies of kidneys including intravenous urography and contrast computed tomography showed numerous medullary calcification and a typical picture of MSK-"paint brush"/"bouquet of flowers" appearance of the dilated tubules within the renal medulla. Laboratory evaluation revealed sterile pyuria, hypercalciuria, and hypocitraturia.

INTERVENTION

The patient was subsequently treated with potassium citrate, hydrochlorothiazide, low sodium and low oxalate diet accompanied by high fluid intake.

OUTCOMES

After a 1-year therapy the normalization of calciuria and citraturia occurred and no progression of nephrocalcinosis was observed.

LESSONS

We conclude that MSK should always be considered as a cause of nephrocalcinosis. Since the final diagnosis requires specific imaging techniques, the concomitant extrarenal abnormalities such as hemihypertrophy may facilitate diagnostic decisions.

Human proximal tubular cells can form calcium phosphate deposits in osteogenic culture: role of cell death and osteoblast-like transdifferentiation

Nephrocalcinosis is a clinicopathological entity characterized by microscopic calcium crystals in the renal parenchyma, within the tubular lumen or in the interstitium. Crystal binding to tubular cells may be the cause underlying nephrocalcinosis and nephrolithiasis. Pathological circumstances, such as acute cortical necrosis, may induce healthy cells to acquire a crystal-binding phenotype. The present study aimed to investigate whether human renal proximal tubular cells (HK-2 cells) can form calcium phosphate deposits under osteogenic conditions, and whether apoptosis and/or osteogenic-like processes are involved in cell calcification. HK-2 cells were cultured in standard or osteogenic medium for 1, 5, and 15 days. Von Kossa staining and ESEM were used to analyze crystal deposition. Apoptosis was investigated, analyzing caspase activation by in-cell Western assay, membrane translocation of phosphotidylserine by annexin V-FITC/propidium iodide staining, and DNA fragmentation by TUNEL assay. qRT/PCR, immunolabeling and cytochemistry were performed to assess osteogenic activation (Runx2, Osteonectin, Osteopontin and ALP), and early genes of apoptosis (BAX, Bcl-2). HK-2 cell mineralization was successfully induced on adding osteogenic medium. Calcium phosphate deposition increased in a time-dependent manner, and calcified cell aggregates exhibited characteristic signs of apoptosis. At 15 days, calcifying HK-2 cells revealed osteogenic markers, such as Runx2, ALP, osteonectin and osteopontin. Monitoring the processes at 1, 5, and 15 days showed apoptosis starting already after 5 days of osteogenic induction, when the first small calcium phosphate crystals began to appear on areas where cell aggregates were in apoptotic conditions. The cell death process proved caspase-dependent. The importance of apoptosis was reinforced by the time-dependent increase in BAX expression, starting from day 1. These findings strongly support the hypothesis that apoptosis triggered HK-2 calcification even before any calcium phosphate crystal deposition or acquisition of an osteogenic phenotype.

Randall's plaque in stone formers originates in ascending thin limbs

Randall's plaque, an attachment site over which calcium oxalate stones form, begins in the basement membranes of thin limbs of the loop of Henle. The mechanism of its formation is unknown. Possibly, enhanced delivery of calcium out of the proximal tubule, found in many stone formers, increases reabsorption of calcium from the thick ascending limb into the interstitium around descending vasa recta, which convey that calcium into the deep medulla, and raises supersaturations near thin limbs ("vas washdown"). According to this hypothesis, plaque should form preferentially on ascending thin limbs, which do not reabsorb water. We stained serial sections of papillary biopsies from stone-forming patients for aquaporin 1 (which is found in the descending thin limb) and the kidney-specific chloride channel ClC-Ka (which is found in the ascending thin limb). Plaque (which is detected using Yasue stain) colocalized with ClC-Ka, but not with aquaporin 1 (χ² = 464, P < 0.001). We conclude that plaque forms preferentially in the basement membranes of ascending thin limbs, fulfilling a critical prediction of the vas washdown theory of plaque pathogenesis. The clinical implication is that treatments such as a low-sodium diet or thiazide diuretics that raise proximal tubule calcium reabsorption may reduce formation of plaque as well as calcium kidney stones.

Caspase-independent programmed cell death triggers Ca2PO4 deposition in an in vitro model of nephrocalcinosis

Nephrocalcinosis involves the deposition of microscopic crystals in the tubular lumen or interstitium. While the clinical, biochemical, and genetic aspects of the diseases causing nephrocalcinosis have been elucidated, little is known about the cellular events in this calcification process. We previously reported a phenomenon involving the spontaneous formation of Ca2PO4 nodules in primary papillary renal cells from a patient with medullary nephrocalcinosis harboring a rare glial cell-derived neurotrophic factor (GDNF) gene variant. We also demonstrated that cultivating GDNF-silenced human kidney-2 (HK-2) cells in osteogenic conditions for 15 days triggered Ca2PO4 deposits. Given the reportedly close relationship between cell death and pathological calcification, aim of the present study was to investigate whether apoptosis is involved in the calcification of GDNF-silenced HK-2 cells under osteogenic conditions. Silenced and control cells were cultured in standard and osteogenic medium for 1, 5, and 15 days, and any Ca2PO4 deposition was identified by means of von Kossa staining and environmental SEM (ESEM) analyses. Based on the results of annexin V and propidium iodide (PI) analysis, and terminal deoxynucleotidyl transferase dUTP-biotin nick end labeling (TUNEL) assay, the silenced cells in the osteogenic medium showed a significant increase in the percentage of cells in the late phase of apoptosis and an increased Ca2PO4 deposition at 15 days. The results of quantitative real-time PCR (qRT-PCR) of BAX and BCL2, and in-cell Western analysis of caspases indicated that the cell death process was independent of caspase-3, -6, -7, and -9 activation, however. Using this model, we provide evidence of caspase-independent cell death triggering the calcification process in GDNF-silenced HK-2 cells.

Efficacy of Multi-Detector Computed Tomography for the Diagnosis of Medullary Sponge Kidney

Objective

To expand the diagnostic armamentarium for medullary sponge kidney (MSK), we evaluate the use of high-resolution multidetector computed tomography (MDCT) for MSK diagnosis and compare to the standard intravenous urography (IVU). Despite a significant prevalence amongst stone formers, diagnosis of this well described condition has declined. IVU, the gold standard in MSK diagnosis, has largely been replaced by CT, which has previously been shown unable to demonstrate signs of MSK.

Methods and Materials

Patients with known history of MSK based on IVU underwent limited MDCT urogram. Control group patients, without MSK, also had MDCT urograms performed for other clinically indicated conditions. Studies were scored by board-certified radiologists on a 0-2 scale based on the likelihood of MSK. IVU studies, when available, were similarly graded.

Results

MDCT was diagnostic of MSK in 9 out of the 10 patients with known history of MSK. No false positives were present in our series. The one case of MSK not detected on MDCT was graded as a "1" on its respective IVU. Sensitivity and specificity were 90 and 100%, respectively, when compared with IVU.

Conclusion

Concordance with IVU findings, despite a small reduction in sensitivity, indicates MDCT to be a suitable, and more readily available replacement for IVU in the diagnosis of MSK.

Recent advances in managing and understanding nephrolithiasis/nephrocalcinosis

Urinary stone disease is a very common disease whose prevalence is still increasing. Stone formation is frequently associated with other diseases of affluence such as hypertension, osteoporosis, cardiovascular disease, metabolic syndrome, and insulin resistance. The increasing concentration of lithogenic solutes along the different segments of the nephron involves supersaturation conditions leading to the formation, growth, and aggregation of crystals. Crystalline aggregates can grow free in the tubular lumen or coated on the wall of the renal tubule. Plugs of crystalline material have been highlighted in the tubular lumen in some patients, but crystalline growth starting from plaques of calcium phosphate within the renal papillae has been demonstrated in others. Urinary supersaturation is the result of a complex interaction between predisposing genetic features and environmental factors. Dietary intake is certainly the most important environmental risk factor. In particular, an insufficient intake of dietary calcium (<600 mg/day) can increase the intestinal absorption of oxalate and the risk of calcium oxalate stone formation. Other possible risk factors that have been identified include excessive intake of salt and proteins. The potential role of dietary acid load seems to play an important role in causing a state of subclinical chronic acidosis; therefore, the intake of vegetables is encouraged in stone-forming patients. Consumption of sugar-sweetened soda and punch is associated with a higher risk of stone formation, whereas consumption of coffee, tea, beer, wine, and orange juice is associated with a lower risk. A high fluid intake is widely recognized as the cornerstone of prevention of all forms of stones. The effectiveness of protein and salt restriction has been evaluated in some studies that still do not allow definitive conclusions to be made. Calcium stone formation can be prevented by the use of different drugs with different mechanisms of action (thiazide diuretics, allopurinol, and potassium citrate), but there is no ideal drug that is both risk free and well tolerated.

Medullary sponge kidney: A treatment conundrum

Medullary sponge kidney (MSK) is a congenital kidney malformation that is characterized by dilatation of the collecting tubules in the medullary pyramids. Cyst-like areas then form which predispose to nephrocalcinosis, stone formation and recurrent urinary tract infection (UTI). There is an association with defective distal renal tubular acidification and concentration abnormalities such as hypocitraturia. MSK is generally believed to be a sporadic disorder, but an autosomal dominant inheritance is also reported. More recently genetic mutations have been recognised as a possible contributor to the aetiology of the condition. In this article we summarize the available English language literature on the subject of MSK, including its pathogenesis, diagnosis, prognosis and treatment.

Kidney stones

Kidney stones are mineral deposits in the renal calyces and pelvis that are found free or attached to the renal papillae. They contain crystalline and organic components and are formed when the urine becomes supersaturated with respect to a mineral. Calcium oxalate is the main constituent of most stones, many of which form on a foundation of calcium phosphate called Randall's plaques, which are present on the renal papillary surface. Stone formation is highly prevalent, with rates of up to 14.8% and increasing, and a recurrence rate of up to 50% within the first 5 years of the initial stone episode. Obesity, diabetes, hypertension and metabolic syndrome are considered risk factors for stone formation, which, in turn, can lead to hypertension, chronic kidney disease and end-stage renal disease. Management of symptomatic kidney stones has evolved from open surgical lithotomy to minimally invasive endourological treatments leading to a reduction in patient morbidity, improved stone-free rates and better quality of life. Prevention of recurrence requires behavioural and nutritional interventions, as well as pharmacological treatments that are specific for the type of stone. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more-effective drugs.