Aprt/Opn double knockout mice: osteopontin is a modifier of kidney stone disease severity

Atorvastatin Decreases Renal Calcium Oxalate Stone Deposits by Enhancing Renal Osteopontin Expression in Hyperoxaluric Stone-Forming Rats Fed a High-Fat Diet

Calcium oxalate (CaOx) is the major constituent of kidney stones. Growing evidence shows a close connection between hyperlipidemia, cardiovascular disease (CVD), and the formation of kidney stones. Owing to their antioxidant properties, statins control hyperlipidemia and may ameliorate CaOx stone formation. The present study was designed to investigate the suppressive effects of statins on CaOx urolithiasis and their potential mechanism. We used rats fed a high-fat diet (HFD) to achieve hyperlipidemia (HL) and hydroxyproline (HP) water to establish a hyperoxaluric CaOx nephrolithiasis model; the animals were administered statins (A) for 28 days. The rats were divided into eight groups treated or not with A, i.e., Control, HP, HL, HL + HP. HL aggravated urinary calcium crystallization compared to the control. Due to increased expression of renal osteopontin (OPN), a key anti-lithic protein, and reduced free radical production, the calcium crystals in the urinary bladder increased as renal calcium deposition decreased. The levels of the ion activity product of CaOx (AP(CaOx)) decreased after statins administration, and AP(Calcium phosphate) (CaP) increased, which suggested the dominant calcium crystal composition changed from CaOx to CaP after statin administration. In conclusion, atorvastatin decreases renal CaOx stone deposits by restoring OPN expression in hyperoxaluric rats fed a HFD.

A Rare Genetic Mutation in a Stone Former

A 30-year-old woman with history of passage of stones since childhood presented with oliguria and pedal edema for 10 days. She had hypertension with a creatinine of 4.1 mg/dL. Evaluation showed presence of bilateral multiple renal calculi with features of chronicity of kidney disease. Metabolic work-up for nephrolithiasis turned out to be negative and eventually renal biopsy revealed features of chronic interstitial nephritis with greenish brown refractile crystals in the tubular lumen and interstitium. The possibility of dihydroxy adenine crystalline nephropathy was considered. Spectrophotometry of RBC lysates revealed decreased activity of Adenine phosphoribosyl-transferase enzyme. Gene amplification by PCR and sequential analysis identified a missense mutation in exon 3 region of APRT gene in the patient and her family members. This case report highlights the need to contemplate the diagnosis of DHA crystalline nephropathy in young patients with nephrolithiasis and the identification of a rare genetic mutation, which is being reported for the first time in India.

Crosstalk between Renal and Vascular Calcium Signaling: The Link between Nephrolithiasis and Vascular Calcification

Calcium (Ca²⁺) is an important mediator of multicellular homeostasis and is involved in several diseases. The interplay among the kidney, bone, intestine, and parathyroid gland in Ca²⁺ homeostasis is strictly modulated by numerous hormones and signaling pathways. The calcium-sensing receptor (CaSR) is a G protein–coupled receptor, that is expressed in calcitropic tissues such as the parathyroid gland and the kidney, plays a pivotal role in Ca²⁺ regulation. CaSR is important for renal Ca²⁺, as a mutation in this receptor leads to hypercalciuria and calcium nephrolithiasis. In addition, CaSR is also widely expressed in the vascular system, including vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) and participates in the process of vascular calcification. Aberrant Ca²⁺ sensing by the kidney and VSMCs, owing to altered CaSR expression or function, is associated with the formation of nephrolithiasis and vascular calcification. Based on emerging epidemiological evidence, patients with nephrolithiasis have a higher risk of vascular calcification, but the exact mechanism linking the two conditions is unclear. However, a dysregulation in Ca²⁺ homeostasis and dysfunction in CaSR might be the connection between the two. This review summarizes renal calcium handling and calcium signaling in the vascular system, with a special focus on the link between nephrolithiasis and vascular calcification.

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.

Animal Models for Studying Stone Disease

Animals have stone disease too. There are several animal models for the research of human stone disease. Rodents are the most frequently used for stone research, although they are not prone to forming crystals in the kidneys. Ethylene glycol (EG), sodium oxalate and l-hydroxyproline are common lithogenic agents. Dogs and pigs were also reported as a study animal for stone disease. However, the breeding costs and body size are too high. The most-used genetic study animal for stone disease was the mouse, but it was high-cost. Calcium oxalate (CaOx) crystals can also be light microscopically observed in the Malphigian tubules of Drosophila melanogaster, induced by adding EG to the food. Genetic studies of flies can be done by cross-breeding, and this has a lower cost than using mice. The fly model also has several advantages, including minimal breeding equipment, the fact that it is easier to reach larger numbers in a short time with flies, that crystals can be observed under microscopy, and that they allow genetic study. We suggest the fly will be an ideal animal model for stone research in the future.

Osteopontin in Bone Metabolism and Bone Diseases

Osteopontin (OPN), a secreted phosphoprotein, is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family of cell matrix proteins and participates in many biological activities. Studies have shown that OPN plays a role in bone metabolism and homeostasis. OPN not only is an important factor in neuron-mediated and endocrine-regulated bone mass, but also is involved in biological activities such as proliferation, migration, and adhesion of several bone-related cells, including bone marrow mesenchymal stem cells, hematopoietic stem cells, osteoclasts, and osteoblasts. OPN has been demonstrated to be closely related to the occurrence and development of many bone-related diseases, such as osteoporosis, rheumatoid arthritis, and osteosarcoma. As expected, the functions of OPN in the bone have become a research hotspot. In this article, we try to decipher the mechanism of OPN-regulated bone metabolism and bone diseases.

Metabolic syndrome and nephrolithiasis

Problem

This review focuses on the association between the metabolic syndrome (MS) and nephrolithiasis.

Findings

Associations between nephrolithiasis and systemic diseases are recognized, including atherosclerosis, cardiovascular (CV) disease, hypertension (HNT), diabetes mellitus (DM)—composite risk factors grouped as the MS. Kidney stones incidence is increasing in this particularly high risk group. Those with stones are prone to the disease and those with the systemic disease are at risk for stone formation, with the highest incidence in persons with multiple traits of the MS. Pathophysiologic explanations for the increased stone risk related to MS are likely complex and dynamic.

Conclusions

Kidney stones disproportionately affect persons with some or all traits of MS. One unifying theory may be of a common systemic malfunction of inflammation and tissue damage as an underlying mechanism, but it is unlikely to be the only mechanistic explanation. Further research is needed to investigate this and other hypotheses that go beyond population based and urine physiochemical studies in order to elucidate the mechanisms behind the individual disease states themselves.

2,8-Dihydroxyadenine urolithiasis: a not so rare inborn error of purine metabolism

Adenine phosphoribosyltransferase (APRT) deficiency is a rare inherited metabolic disorder that leads to the formation and hyperexcretion of 2,8-dihydroxyadenine (DHA) into urine. The low solubility of DHA results in precipitation and formation of urinary crystals and kidney stones. The disease can be present as recurrent urolithiasis or nephropathy secondary to crystal precipitation into renal parenchyma (DHA nephropathy). The diagnostic tools available, including stone analysis, crystalluria, and APRT activity in red blood cells, make the diagnosis easy to confirm when APRT deficiency is suspected. However, the lack of recognition of this metabolic disorder frequently resulted in a delay in diagnosis and treatment with grave consequences. The early recognition and treatment of APRT deficiency are of crucial importance to prevent irreversible loss of renal function. This review summarizes the genetic and metabolic mechanisms underlying DHA stones formation and chronic kidney disease, along with the issues of diagnosis and management of APRT deficiency. Moreover, we report the mutations in the APRT gene responsible for APRT deficiency in 51 French patients (43 families) including 22 pediatric cases (18 families) among the 64 patients identified in the biochemistry laboratories of Necker Hospital, Paris (1978-2013).

Adenine phosphoribosyltransferase deficiency: Leave no stone unturned

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disease leading to generation of large amounts of 2,8-dihydroxyadenine (DHA). DHA is excreted in urine, where it precipitates into crystals due to its low solubility. DHA crystals can aggregate into stones or cause injury to the renal parenchyma (DHA nephropathy). Recurrent urolithiasis and DHA nephropathy are the two clinical manifestations of APRT deficiency. Diagnosis of APRT deficiency can be made during childhood as well as adulthood. Diagnosis mainly relies on the recognition of DHA in stones or urine crystals. Measurement of APRT activity and genetic testing are useful for confirmation of diagnosis, for family screening and should be considered in difficult cases of urolithiasis or crystalline nephropathy. Allopurinol therapy is the cornerstone of treatment and is highly effective in preventing recurrence of stones and kidney disease. High fluid intake and dietary modifications are also recommended. Early diagnosis and treatment are of paramount importance to prevent renal damage. Unfortunately, diagnosis of APRT deficiency is often overlooked and irreversible renal failure still occurs in a substantial proportion of patients. Clinicians must be alert to the possibility of APRT deficiency and consider the appropriate diagnostic tests in certain cases. This review discusses the genetic and biochemical mechanisms of APRT deficiency, and the issues of diagnosis and management.

Inhibitory effect of ethanol extract of Ocimum sanctum on osteopontin mediated metastasis of NCI-H460 non-small cell lung cancer cells

Background

Osteopontin (OPN) is one of important molecular targets in cancer progression, metastasis as a calcium-binding, extracellular-matrix-associated protein of the small integrin-binding ligand and, N-linked glycoprotein. In the present study, anti-metastatic mechanism of ethanol extracts of Ocimum sanctum (EEOS) was elucidated on OPN enhanced metastasis in NCI-H460 non- small cell lung cancer cells.

Methods

Cell viability was measured by MTT assay. Adhesion and invasion assays were carried out to see that EEOS inhibited cell adhesion and invasion in OPN treated and non-treated NCI-H 460 cells. RT-PCR was used to determine the mRNA levels of uPA, uPAR, and EGFR.

Results

EEOS significantly inhibited cell adhesion and invasion in OPN treated and non treated NCI-H460 cells, though EEOS did not show any toxicity up to 200 μg/ml. EEOS effectively attenuated the expression of OPN and CD44 and also OPN activated the expression of CD44 in NCI-H460 cells. In addition, EEOS effectively suppressed the expression of phosphatidylinositide 3-kinases (PI3K) and cyclooxygenase 2 (COX-2) and the phosphorylation of Akt at protein level in OPN treated NCI-H460 cells. Also, EEOS significantly attenuated the expression of urokinase plasminogen activator (uPA), its receptor (uPAR) and epidermal growth factor receptor (EGFR) at mRNA level and reduced vascular endothelial growth factor (VEGF) production and MMP-9 activity in OPN treated NCI-H460 cells. Furthermore, PI3K/Akt inhibitor LY294002 enhanced anti-metastatic potential of EEOS to attenuate the expression of uPA and MMP-9 in OPN treated NCI-H 460 cells.

Conclusion

Overall, our findings suggest that anti-metastatic mechanism of EEOS is mediated by inhibition of PI3K/Akt in OPN treated NCI-H460 non-small cell lung cancer cells.

Adenine phosphoribosyltransferase deficiency

Complete adenine phosphoribosyltransferase (APRT) deficiency is a rare inherited metabolic disorder that leads to the formation and hyperexcretion of 2,8-dihydroxyadenine (DHA) into urine. The low solubility of DHA results in precipitation of this compound and the formation of urinary crystals and stones. The disease can present as recurrent urolithiasis or nephropathy secondary to crystal precipitation into renal parenchyma (DHA nephropathy). The diagnostic tools available-including stone analysis, crystalluria, and APRT activity measurement-make the diagnosis easy to confirm when APRT deficiency is suspected. However, the disease can present at any age, and the variability of symptoms can present a diagnostic challenge to many physicians. The early recognition and treatment of APRT deficiency are of crucial importance for preventing irreversible loss of renal function, which still occurs in a non-negligible proportion of cases. This review summarizes the genetic and metabolic mechanisms underlying stone formation and renal disease, along with the diagnosis and management of APRT deficiency.

Adenine phosphoribosyltransferase deficiency in children

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder characterized by 2,8-dihydroxyadenine (2,8-DHA) crystalluria that can cause nephrolithiasis and chronic kidney disease. The aim of our study was to assess the clinical presentation, diagnosis, and outcome of APRT deficiency in a large pediatric cohort. All pediatric cases of APRT deficiency confirmed at the same French reference laboratories between 1978 and 2010 were retrospectively reviewed. Twenty-one patients from 18 families were identified. The median age at diagnosis was 3 years. Diagnosis was made after one or more episodes of nephrolithiasis (17 patients), after urinary tract infection (1 patient), and by family screening (3 patients). The diagnosis was based on stone analysis and microscopic examination of urine and/or enzymatic determination of APRT on red blood cells. All children had null APRT enzyme activity in erythrocytes. APRT gene sequencing was performed on 18 patients, revealing six homozygous and 12 compound heterozygous mutations. At diagnosis, half of the patients had decreased kidney function, and two children presented with acute renal failure. Allopurinol treatment was given to all patients at a median dose of 9 mg/kg/day. After a median follow-up of 5 years, all patients showed stabilization or improvement of kidney function, normal growth and development, and six patients had recurrence of nephrolithiasis. Based on these results, we conclude that an excellent outcome can be achieved in children with APRT deficiency who receive the proper treatment.

Role of osteopontin in early phase of renal crystal formation: immunohistochemical and microstructural comparisons with osteopontin knock-out mice

Osteopontin (OPN) is an important matrix protein of renal calcium stone. However, the function of OPN in the early phase of renal crystal formation is not well defined. In this study, we examined OPN expression in the early phase of renal crystal formation with ultra-microstructural observations and immuno-TEM (transmission electron microscopy) in control and OPN knock-out (OPN-KO) mice. Glyoxylate (100 mg/kg) was intra-abdominally administered to male wild-type mice (C57BL/6, 8 weeks of age) and OPN-KO mice (C57BL/6, 8 weeks of age). Kidney was collected before and 6, 12, and 24 h after administration. We examined the relation between renal crystal formation and microstructural OPN location using TEM and immunohistochemical staining of OPN as well as western blotting and quantitative RT-PCR for OPN. OPN protein expression gradually increased in the renal cortex-medulla junction after glyoxylate administration, and OPN mRNA was increased until 12 h, but decreased at 24 h. In ultra-microstructural observation, OPN began to appear on the luminal side of renal distal tubular cells at 6 h and was gradually detected in the tubular lumen at 12 h. OPN was present in the crystal nuclei and collapsed mitochondria in the tubular lumen. In the OPN-KO mice, collapsed mitochondria were present, but no crystal nuclei formation were detected at 24 h. Based on the results this study proposed that the appearance of organelles, such as mitochondria and microvilli, in the tubular lumen after cell injury may be the starting point of crystal nucleus formation due to the aggregation ability of OPN.

From cell to man: evaluation of osteopontin as a possible biomarker of uranium exposure

BACKGROUND

Ore workers are conventionally monitored for exposure by measuring the uranium in their urine, but specific biomarkers of kidney damage still remain to be discovered. A recent toxicogenomics study allowed us to focus on osteopontin (OSTP) normally excreted in human urine and linked to mineral metabolism.

OBJECTIVES

We examined the association between osteopontin and uranium exposure both in vitro, in a human kidney cell model, and in the urine of exposed individuals.

METHODS

OSTP was measured in supernatants of uranium-exposed HK2 cells to establish a dose-response curve and a time course experiment. Its role was studied through a gene extinction experiment. Uranium and OSTP were then monitored in the urine of exposed nuclear fuel industry workers and a chronically exposed population. These levels were compared with those found in a non-exposed population.

RESULTS

The study of HK2 cells indicated that OSTP secretion decreased after uranium exposure in a concentration and time dependent manner, but its suppression does not affect cell sensitivity to uranium. In spite of wide inter-individual variability, this parameter decreases also in human urine when urinary uranium exceeds 30 μg/L after an acute exposure, a value considered to be critical for kidney damage.

CONCLUSION

This study reports how toxicogenomics can highlight putative toxicity biomarkers in an easy to access biological fluid. The decrease of urinary osteopontin in response to uranium exposure suggests kidney damage and would thus be complementary to current markers.

Phenotype and genotype characterization of adenine phosphoribosyltransferase deficiency

Adenine phosphoribosyltransferase (APRT) deficiency is a rare autosomal recessive disorder causing 2,8-dihydroxyadenine stones and renal failure secondary to intratubular crystalline precipitation. Little is known regarding the clinical presentation of APRT deficiency, especially in the white population. We retrospectively reviewed all 53 cases of APRT deficiency (from 43 families) identified at a single institution between 1978 and 2009. The median age at diagnosis was 36.3 years (range 0.5 to 78.0 years). In many patients, a several-year delay separated the onset of symptoms and diagnosis. Of the 40 patients from 33 families with full clinical data available, 14 (35%) had decreased renal function at diagnosis. Diagnosis occurred in six (15%) patients after reaching ESRD, with five diagnoses made at the time of disease recurrence in a renal allograft. Eight (20%) patients reached ESRD during a median follow-up of 74 months. Thirty-one families underwent APRT sequencing, which identified 54 (87%) mutant alleles on the 62 chromosomes analyzed. We identified 18 distinct mutations. A single T insertion in a splice donor site in intron 4 (IVS4 + 2insT), which produces a truncated protein, accounted for 40.3% of the mutations. We detected the IVS4 + 2insT mutation in two (0.98%) of 204 chromosomes of healthy newborns. This report, which is the largest published series of APRT deficiency to date, highlights the underdiagnosis and potential severity of this disease. Early diagnosis is crucial for initiation of effective treatment with allopurinol and for prevention of renal complications.

NF-kappaB activation in renal tubular epithelial cells by oxalate stimulation

OBJECTIVES

The transcription factor nuclear factor-kappaB (NF-kappaB) is involved in inflammatory and immune responses through the induction of various cytokines and growth factors. Recently, the coordinated action of NF-kappaB and activator protein-1 was reported in osteopontin (OPN) expression. In the present study, we demonstrated that oxalate induces OPN expression by activating NF-kappaB in renal tubular cells. Furthermore, we investigated the inhibitory effect of N-acetyl-L-cysteine (NAC) on NF-kappaB activation in the human renal tubular cell line.

METHODS

All of the experiments were carried out using human kidney-2 cells, which are human proximal tubular epithelial cells immortalized by transduction with the human papillomavirus 16E6/E7 gene. The time-dependent extraction of total protein was performed after the uptake of 0.5 mM oxalate by the cells. The NF-kappaB activation and OPN expression were examined by western blotting and immunocytochemistry.

RESULTS

As a result of oxalate stimulation, the amount of p65 subunit in the nucleus increased significantly (P < 0.05), and NAC significantly inhibited the translocation of p65 into the nucleus (P < 0.05).

CONCLUSION

These observations indicate that NAC can be used as a drug to prevent stone formation.

Role of interstitial apatite plaque in the pathogenesis of the common calcium oxalate stone

By using intraoperative papillary biopsy material from kidneys of idiopathic calcium oxalate, intestinal bypass for obesity, brushite, cystine, and distal renal tubular acidosis stone formers during percutaneous nephrolithotomy, we have determined that idiopathic calcium oxalate stone formers appear to be the special case, although the most commonly encountered one, in which stones form external to the kidney and by processes that do not involve the epithelial compartments. It is in this one group of patients that we find not only abundant interstitial plaque, but also strong evidence that the plaque is essential to stone formation. The initial site of plaque formation is always in the papillary tip, and must be in the basement membrane of the thin loop of Henle. With time, plaque spreads throughout the papilla tip to the urothelium, which under conditions we do not understand is denuded and thereby exposes the apatite deposits to the urine. It is on this exposed apatite that a stone forms as an overgrowth, first of amorphous apatite and then layers of calcium oxalate. This process generates an attached stone fixed to the side of a papilla, allowing the ever-changing urine to dictate stone growth and composition.

The temporal expression of osteopontin (SPP-1) in the rodent model of alcoholic steatohepatitis: a potential biomarker

Previous studies from our laboratory have shown that osteopontin (OPN) mediates neutrophil infiltration into the liver in a rodent model of alcoholic steatohepatitis (ASH). The objective of this study was to investigate the temporal and spatial pattern of hepatic OPN mRNA and protein expression during the progression of alcoholic liver disease. OPN mRNA and protein expression were evaluated using real time PCR, in situ hybridization, Western blot and immunohistochemistry respectively. ASH was induced in male Sprague-Dawley rats by feeding EtOH-containing Lieber-DeCarli diet for 6 weeks, followed by a single injection of lipopolysaccharide (LPS, 10 mg/kg, ip). Rats were sacrificed 2-, 12-and 24-hour post LPS injection. A progressive induction of OPN mRNA was observed that preceded hepatic neutrophil infiltration and the increase in OPN mRNA correlated with increases in OPN protein expression. OPN mRNA was localized primarily to the biliary epithelium. The data indicates that OPN is transcribed and translated within the biliary epithelium. These findings suggest a potential role of OPN as an early biomarker in predicting inflammatory liver diseases such as ASH.