The role of claudin-2 in kidney function and dysfunction

Claudin-2 is a tight junction protein expressed in leaky epithelia where it forms paracellular pores permeable to cations and water. The paracellular pore formed by claudin-2 is important in energy-efficient cation and water transport in the proximal tubules of the kidneys. Mounting evidence now suggests that claudin-2 may modulate cellular processes often altered in disease, including cellular proliferation. Also, dysregulation of claudin-2 expression has been linked to various diseases, including kidney stone disease and renal cell carcinoma. However, the mechanisms linking altered claudin-2 expression and function to disease are poorly understood and require further investigation. The aim of this review is to discuss the current understanding of the role of claudin-2 in kidney function and dysfunction. We provide a general overview of the claudins and their organization in the tight junction, the expression, and function of claudin-2 in the kidney, and the evolving evidence for its role in kidney disease.

Early renal structural changes and potential biomarkers in diabetic nephropathy

Diabetic nephropathy is one of the most serious microvascular complications of diabetes mellitus, with increasing prevalence and mortality. Currently, renal function is assessed clinically using albumin excretion rate and glomerular filtration rate. But before the appearance of micro-albumin, the glomerular structure has been severely damaged. Glomerular filtration rate based on serum creatinine is a certain underestimate of renal status. Early diagnosis of diabetic nephropathy has an important role in improving kidney function and delaying disease progression with drugs. There is an urgent need for biomarkers that can characterize the structural changes associated with the kidney. In this review, we focus on the early glomerular and tubular structural alterations, with a detailed description of the glomerular injury markers SMAD1 and Podocalyxin, and the tubular injury markers NGAL, Netrin-1, and L-FABP in the context of diabetic nephropathy. We have summarized the currently studied protein markers and performed bioprocess analysis. Also, a brief review of proteomic and scRNA-seq method in the search of diabetic nephropathy.

Disease Modeling with Kidney Organoids

Kidney diseases often lack optimal treatments, causing millions of deaths each year. Thus, developing appropriate model systems to study human kidney disease is of utmost importance. Some of the most promising human kidney models are organoids or small organ-resembling tissue collectives, derived from human-induced pluripotent stem cells (hiPSCs). However, they are more akin to a first-trimester fetal kidney than an adult kidney. Therefore, new strategies are needed to advance their maturity. They have great potential for disease modeling and eventually auxiliary therapy if they can reach the maturity of an adult kidney. In this review, we will discuss the current state of kidney organoids in terms of their similarity to the human kidney and use as a disease modeling system thus far. We will then discuss potential pathways to advance the maturity of kidney organoids to match an adult kidney for more accurate human disease modeling.

A plant reovirus hijacks the DNAJB12-Hsc70 chaperone complex to promote viral spread in its planthopper vector

Many viruses usurp the functions of endoplasmic reticulum (ER) for virus-encoded membrane proteins proper functional folding or assembly to promote virus spread. Southern rice black-streaked dwarf virus (SRBSDV), a plant reovirus, exploits virus-containing tubules composed of nonstructural membrane protein P7-1 to spread in its planthopper vector Sogatella furcifera. Here, we report that two factors of the ER-associated degradation (ERAD) machinery, the ER chaperone DNAJB12 and its cytosolic co-chaperone Hsc70, are activated by SRBSDV to facilitate ER-to-cytosol export of P7-1 tubules in S. furcifera. Both P7-1 of SRBSDV and Hsc70 directly bind to the J-domain of DNAJB12. DNAJB12 overexpression induces ER retention of P7-1, but Hsc70 overexpression promotes the transport of P7-1 from the ER to the cytosol to initiate tubule assembly. Thus, P7-1 is initially retained in the ER by interaction with DNAJB12 and then delivered to Hsc70. Furthermore, the inhibitors of the ATPase activity of Hsc70 reduce P7-1 tubule assembly, suggesting that the proper folding and assembly of P7-1 tubules is dependent on the ATPase activity of Hsc70. The DNAJB12-Hsc70 chaperone complex is recruited to P7-1 tubules in virus-infected midgut epithelial cells in S. furcifera. The knockdown of DNAJB12 or Hsc70 strongly inhibits P7-1 tubule assembly in vivo, finally suppressing effective viral spread in S. furcifera. Taken together, our results indicate that the DNAJB12-Hsc70 chaperone complex in the ERAD machinery facilitates the ER-to-cytosol transport of P7-1 for proper assembly of tubules, enabling viral spread in insect vectors in a manner dependent on ATPase activity of Hsc70.

Effectiveness of Different Methods in Removing Dentin Caries of Primary Teeth: Micro-CT and SEM Evaluation

OBJECTIVES

With the recent improvements in technology, the expectation of minimal invasion and maximal comfort in caries removal techniques is increasing. This study aims to examine the effectiveness of six caries removal methods in primary teeth.

STUDY DESIGN

Sixty primary molars (10 teeth in each groups) were used. The groups were: Group I (Tungsten Carbide Bur), Group II (Sono abrasion), Group III (Air abrasion), Group IV (Carisolv), Group V (Er:YAG Laser), Group VI (ART). In micro-CT scanning, mineral density at the cavity floor was examined before and after caries removal. After caries removal, the patency of the dentinal tubules was examined in two teeth from each group on SEM images. Statistical analyses were performed using Kruskal-Wallis, Wilcoxon tests.

RESULTS

For six different caries removal methods, tooth mineral (inorganic, total) densities at cavity floors were compared among the groups after the procedures, and no statistically significant difference was found (p>0.05). On the SEM images, it was seen that the dentinal tubules were exposed and no smear layer was formed in the Carisolv group. Significant rough surfaces were exposed in the laser group.

CONCLUSION

It was observed that alternative caries removal methods are at least as effective as the traditional method in primary teeth for clinical applications.

Metabolic and Lipidomic Assessment of Kidney Cells Exposed to Nephrotoxic Vancomycin Dosages

Vancomycin is a glycopeptide antibiotic used against multi-drug resistant gram-positive bacteria such as Staphylococcus aureus (MRSA). Although invaluable against resistant bacteria, vancomycin harbors adverse drug reactions including cytopenia, ototoxicity, as well as nephrotoxicity. Since nephrotoxicity is a rarely occurring side effect, its mechanism is incompletely understood. Only recently, the actual clinically relevant concentration the in kidneys of patients receiving vancomycin was investigated and were found to exceed plasma concentrations by far. We applied these clinically relevant vancomycin concentrations to murine and canine renal epithelial cell lines and assessed metabolic and lipidomic alterations by untargeted and targeted gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry analyses. Despite marked differences in the lipidome, both cell lines increased anabolic glucose reactions, resulting in higher sorbitol and lactate levels. To the best of our knowledge, this is the first endometabolic profiling of kidney cells exposed to clinically relevant vancomycin concentrations. The presented study will provide a valuable dataset to nephrotoxicity researchers and might add to unveiling the nephrotoxic mechanism of vancomycin.

In Vivo Renal Tubule pH in Stone-Forming Human Kidneys

Introduction: There is evidence that patients with a history of ileostomies, who produce acidic urine and form uric acid or calcium oxalate stones, may plug some collecting ducts with calcium phosphate (CaP) and urate crystals. This is a paradoxical finding as such minerals should not form at an acid pH. One possible explanation is the presence of acidification defects due to focal damage to inner medullary collecting duct and Bellini duct (BD) cells. We sought to further investigate this hypothesis through direct measurement of ductal pH in dilated BDs in patients with ileostomies undergoing percutaneous nephrolithotomy (PCNL) for stone removal. Methods: After obtaining institutional review board approval, we used a fiber-optic pH microsensor with a 140-μm-diameter tip to measure intraluminal pH from the bladder, saline irrigant, and dilated BDs of patients undergoing PCNL. Results: Measurements were taken from three patients meeting inclusion criteria. Measured pH of bladder urine ranged from 4.97 to 5.58 and pH of saline irrigant used during surgery ranged from 5.17 to 5.75. BD measurements were achieved in 11 different BDs. Mean intraductal BD pH was more than 1 unit higher than bulk urine (6.43 ± 0.22 vs 5.31 ± 0.22, p < 0.01). Conclusions: This is the first evidence for focal acidification defects within injured/dilated BDs of human kidneys producing highly acidic bulk phase urine. These results may help explain the paradoxical finding of CaP and urate plugs in dilated ducts of patients with stone-forming diseases characterized by highly acidic urine.

Co-cultures of renal progenitors and endothelial cells on kidney decellularized matrices replicate the renal tubular environment in vitro

AIM

Herein we propose creating a bilayer tubular kidney in-vitro model. It is hypothesized that membranes composed of decellularized porcine kidney extracellular matrix are valid substitutes of the tubular basement membrane by mimicking the physiological relevance of the in vivo environment and disease phenotypes.

METHODS

Extracellular matrix was obtained from decellularized porcine kidneys. After processing by lyophilization and milling, it was dissolved in an organic solvent and blended with poly(caprolactone). Porous membranes were obtained by electrospinning and seeded with human primary renal progenitor cells to evaluate phenotypic alterations. To create a bilayer model of the in vivo tubule, the same cells were differentiated into epithelial tubular cells and co-cultured with endothelial cells in opposite sites.

RESULTS

Our results demonstrate increasing metabolic activity, proliferation and total protein content of renal progenitors over time. We confirmed the expression of several genes encoding epithelial transport proteins and we could also detect tubular-specific proteins by immunofluorescence stainings. Functional and transport assays were performed trough the bilayer by quantifying both human serum albumin uptake and inulin leakage. Furthermore, we validated the chemical modulation of nephrotoxicity on this epithelium-endothelium model by cisplatin exposure.

CONCLUSION

The use of decellularized matrices in combination with primary renal cells was shown to be a valuable tool for modelling renal function and disease in vitro. We successfully validated our hypothesis by replicating the physiological conditions of an in vitro tubular bilayer model. The developed system may contribute significantly for the future investigation of advanced therapies for kidney diseases.

microRNA in Extracellular Vesicles Released by Damaged Podocytes Promote Apoptosis of Renal Tubular Epithelial Cells

Tubular injury and fibrosis are associated with progressive kidney dysfunction in advanced glomerular disease. Glomerulotubular crosstalk is thought to contribute to tubular injury. microRNAs (miRNAs) in extracellular vesicles (EVs) can modulate distant cells. We hypothesized that miRNAs in EVs derived from injured podocytes lead to tubular epithelial cell damage. As proof of this concept, tubular epithelial (HK2) cells were cultured with exosomes from puromycin-treated or healthy human podocytes, and damage was assessed. Sequencing analysis revealed the miRNA repertoire of podocyte EVs. RNA sequencing identified 63 upregulated miRNAs in EVs from puromycin-treated podocytes. Among them, five miRNAs (miR-149, -424, -542, -582, and -874) were selected as candidates for inducing tubular apoptosis according to a literature-based search. To validate the effect of the miRNAs, HK2 cells were treated with miRNA mimics. EVs from injured podocytes induced apoptosis and p38 phosphorylation of HK2 cells. The miRNA-424 and 149 mimics led to apoptosis of HK2 cells. These results show that miRNAs in EVs from injured podocytes lead to damage to tubular epithelial cells, which may contribute to the development of tubular injury in glomerular disease.

From a Movement-Deficient Grapevine Fanleaf Virus to the Identification of a New Viral Determinant of Nematode Transmission

Grapevine fanleaf virus (GFLV) and arabis mosaic virus (ArMV) are nepoviruses responsible for grapevine degeneration. They are specifically transmitted from grapevine to grapevine by two distinct ectoparasitic dagger nematodes of the genus Xiphinema. GFLV and ArMV move from cell to cell as virions through tubules formed into plasmodesmata by the self-assembly of the viral movement protein. Five surface-exposed regions in the coat protein called R1 to R5, which differ between the two viruses, were previously defined and exchanged to test their involvement in virus transmission, leading to the identification of region R2 as a transmission determinant. Region R4 (amino acids 258 to 264) could not be tested in transmission due to its requirement for plant systemic infection. Here, we present a fine-tuning mutagenesis of the GFLV coat protein in and around region R4 that restored the virus movement and allowed its evaluation in transmission. We show that residues T258, M260, D261, and R301 play a crucial role in virus transmission, thus representing a new viral determinant of nematode transmission.

Impact of Diabetic Stress Conditions on Renal Cell Metabolome

Diabetic kidney disease is a major complication in diabetes mellitus, and the most common reason for end-stage renal disease. Patients suffering from diabetes mellitus encounter glomerular damage by basement membrane thickening, and develop albuminuria. Subsequently, albuminuria can deteriorate the tubular function and impair the renal outcome. The impact of diabetic stress conditions on the metabolome was investigated by untargeted gas chromatography–mass spectrometry (GC-MS) analyses. The results were validated by qPCR analyses. In total, four cell lines were tested, representing the glomerulus, proximal nephron tubule, and collecting duct. Both murine and human cell lines were used. In podocytes, proximal tubular and collecting duct cells, high glucose concentrations led to global metabolic alterations in amino acid metabolism and the polyol pathway. Albumin overload led to the further activation of the latter pathway in human proximal tubular cells. In the proximal tubular cells, aldo-keto reductase was concordantly increased by glucose, and partially increased by albumin overload. Here, the combinatorial impact of two stressful agents in diabetes on the metabolome of kidney cells was investigated, revealing effects of glucose and albumin on polyol metabolism in human proximal tubular cells. This study shows the importance of including highly concentrated albumin in in vitro studies for mimicking diabetic kidney disease.

A Nonstructural Protein Responsible for Viral Spread of a Novel Insect Reovirus Provides a Safe Channel for Biparental Virus Transmission to Progeny

The Asian citrus psyllid, Diaphorina citri Kuwayama, is an important pest in the worldwide citrus industry. It is the vector of “Candidatus Liberibacter asiaticus,” the bacterial pathogen of Huanglongbing, which is currently considered the most destructive disease of citrus worldwide. DcRV was previously identified based on metagenomics surveys for virus discovery. Here, we found that this novel and persistent insect reovirus took advantage of a virus-encoded nonstructural protein, P10, for efficient vertical transmission from parents to progeny. P10 assembled into a virion-packaging tubular structure and was associated with oocytes of female D. citri and sperm of males. Consistent with this, knockdown of P10 for either male or female D. citri insects inhibited DcRV transmission to offspring. This tubular strategy for viral spread and biparental transmission might serve as a target for controlling viral vertical transmission and population expansion.

Diaphorina citri reovirus (DcRV) was previously identified based on metagenomics surveys for virus discovery. Here, we demonstrated that DcRV induces persistent infection in its psyllid host, Diaphorina citri. DcRV was efficiently vertically passed to offspring in a biparental manner. Transmission electron microscopic and immunological analyses showed that the DcRV-encoded nonstructural protein P10 assembled into a virion-packaging tubular structure which is associated with the spread of DcRV throughout the bodies of D. citri insects. P10 tubules containing virions were associated with oocytes of female and sperm of male D. citri insects, suggesting a role in the highly efficient biparental transmission of DcRV. Knocking down P10 by RNA interference for males reduced the percentage of DcRV-infected progeny and for females reduced the viral accumulation in progeny. These results, for the first time, show that a nonstructural protein of a novel insect reovirus provides a safe and pivotal channel for virus spread and biparental transmission to progeny.

IMPORTANCE The Asian citrus psyllid, Diaphorina citri Kuwayama, is an important pest in the worldwide citrus industry. It is the vector of “Candidatus Liberibacter asiaticus,” the bacterial pathogen of Huanglongbing, which is currently considered the most destructive disease of citrus worldwide. DcRV was previously identified based on metagenomics surveys for virus discovery. Here, we found that this novel and persistent insect reovirus took advantage of a virus-encoded nonstructural protein, P10, for efficient vertical transmission from parents to progeny. P10 assembled into a virion-packaging tubular structure and was associated with oocytes of female D. citri and sperm of males. Consistent with this, knockdown of P10 for either male or female D. citri insects inhibited DcRV transmission to offspring. This tubular strategy for viral spread and biparental transmission might serve as a target for controlling viral vertical transmission and population expansion.

[Relevance of urinary specific protein assay in the diagnosis of kidney diseases]

The analysis of urinary protein composition is an important step in the evaluation and monitoring of kidney diseases. Among the various approaches, the determination of urinary-specific proteins makes it possible to non-invasively detect a preferentially tubular or glomerular injury, to orientate towards a pathological process, to guide the indication of a kidney biopsy, and to follow the evolution of the disease and the effectiveness of a therapy. No study systematically evaluated the performance of urinary-specific proteins for the diagnosis of a renal disease. We conducted this retrospective study to perform an exhaustive analysis of the correlations that may exist between histologically proven kidney disease and the corresponding specific urinary protein composition it in order to evaluate the diagnostic value of each of its components. Urinary concentrations of total protein, albumin, transferrin, alpha1microglobulin, beta2microglobulin, retinol binding protein, and immunoglobulin G were analyzed in more than 500 patients who underwent renal biopsy and concomitant urine specific protein analysis. Our analysis shows that these markers have a limited positive predictive value in this cohort of complex and unselected kidney diseases. In particular, low molecular weight proteins, and especially alpha1microglobulin, are frequently associated with glomerular diseases. We identified transferrin as an independent predictor of minimal changes disese and renal amyloidosis, and beta2microglobulin as an independent predictor of acute tubulointerstitial nephropathy and myelomatous tubulopathy. Finally, we defined the thresholds at which these parameters had excellent negative predictive values.

Inherited and acquired disorders of magnesium homeostasis

PURPOSE OF REVIEW

Magnesium (Mg) imbalances are frequently overlooked. Hypermagnesemia usually occurs in preeclamptic women after Mg therapy or in end-stage renal disease patients, whereas hypomagnesemia is more common with a prevalence of up to 15% in the general population. Increasing evidence points toward a role for mild-to-moderate chronic hypomagnesemia in the pathogenesis of hypertension, type 2 diabetes mellitus, and metabolic syndrome.

RECENT FINDINGS

The kidneys are the major regulator of total body Mg homeostasis. Over the last decade, the identification of the responsible genes in rare genetic disorders has enhanced our understanding of how the kidney handles Mg. The different genetic disorders and medications contributing to abnormal Mg homeostasis are reviewed.

SUMMARY

As dysfunctional Mg homeostasis contributes to the development of many common human disorders, serum Mg deserves closer monitoring. Hypomagnesemic patients may be asymptomatic or may have mild symptoms. In severe hypomagnesemia, patients may present with neurological symptoms such as seizures, spasms, or cramps. Renal symptoms include nephrocalcinosis and impaired renal function. Most conditions affect tubular Mg reabsorption by disturbing the lumen-positive potential in the thick ascending limb or the negative membrane potential in the distal convoluted tubule.

Identification of Ourmiavirus 30K movement protein amino acid residues involved in symptomatology, viral movement, subcellular localization and tubule formation

Several plant viruses encode movement proteins (MPs) classified in the 30K superfamily. Despite a great functional diversity, alignment analysis of MP sequences belonging to the 30K superfamily revealed the presence of a central core region, including amino acids potentially critical for MP structure and functionality. We performed alanine-scanning mutagenesis of the Ourmia melon virus (OuMV) MP, and studied the effects of amino acid substitutions on MP properties and virus infection. We identified five OuMV mutants that were impaired in systemic infection in Nicotiana benthamiana and Arabidopsis thaliana, and two mutants showing necrosis and pronounced mosaic symptoms, respectively, in N. benthamiana. Green fluorescent protein fusion constructs (GFP:MP) of movement-defective MP alleles failed to localize in distinct foci at the cell wall, whereas a GFP fusion with wild-type MP (GFP:MPwt) mainly co-localized with plasmodesmata and accumulated at the periphery of epidermal cells. The movement-defective mutants also failed to produce tubular protrusions in protoplasts isolated from infected leaves, suggesting a link between tubule formation and the ability of OuMV to move. In addition to providing data to support the importance of specific amino acids for OuMV MP functionality, we predict that these conserved residues might be critical for the correct folding and/or function of the MP of other viral species in the 30K superfamily.

Calcium-permeable ion channels in the kidney

Calcium ions (Ca(2+)) are crucial for a variety of cellular functions. The extracellular and intracellular Ca(2+) concentrations are thus tightly regulated to maintain Ca(2+) homeostasis. The kidney, one of the major organs of the excretory system, regulates Ca(2+) homeostasis by filtration and reabsorption. Approximately 60% of the Ca(2+) in plasma is filtered, and 99% of that is reabsorbed by the kidney tubules. Ca(2+) is also a critical signaling molecule in kidney development, in all kidney cellular functions, and in the emergence of kidney diseases. Recently, studies using genetic and molecular biological approaches have identified several Ca(2+)-permeable ion channel families as important regulators of Ca(2+) homeostasis in kidney. These ion channel families include transient receptor potential channels (TRP), voltage-gated calcium channels, and others. In this review, we provide a brief and systematic summary of the expression, function, and pathological contribution for each of these Ca(2+)-permeable ion channels. Moreover, we discuss their potential as future therapeutic targets.

Human Anti-Oxidation Protein A1M--A Potential Kidney Protection Agent in Peptide Receptor Radionuclide Therapy

Peptide receptor radionuclide therapy (PRRT) has been in clinical use for 15 years to treat metastatic neuroendocrine tumors. PRRT is limited by reabsorption and retention of the administered radiolabeled somatostatin analogues in the proximal tubule. Consequently, it is essential to develop and employ methods to protect the kidneys during PRRT. Today, infusion of positively charged amino acids is the standard method of kidney protection. Other methods, such as administration of amifostine, are still under evaluation and show promising results. α₁-microglobulin (A1M) is a reductase and radical scavenging protein ubiquitously present in plasma and extravascular tissue. Human A1M has antioxidation properties and has been shown to prevent radiation-induced in vitro cell damage and protect non-irradiated surrounding cells. It has recently been shown in mice that exogenously infused A1M and the somatostatin analogue octreotide are co-localized in proximal tubules of the kidney after intravenous infusion. In this review we describe the current situation of kidney protection during PRRT, discuss the necessity and implications of more precise dosimetry and present A1M as a new, potential candidate for renal protection during PRRT and related targeted radionuclide therapies.

Urine Collagen Fragments and CKD Progression-The Cardiovascular Health Study

Tubulointerstitial fibrosis is common with ageing and strongly prognostic for ESRD but is poorly captured by eGFR or urine albumin to creatinine ratio (ACR). Higher urine levels of procollagen type III N-terminal propeptide (PIIINP) mark the severity of tubulointerstitial fibrosis in biopsy studies, but the association of urine PIIINP with CKD progression is unknown. Among community-living persons aged ≥65 years, we measured PIIINP in spot urine specimens from the 1996 to 1997 Cardiovascular Health Study visit among individuals with CKD progression (30% decline in eGFR over 9 years, n=192) or incident ESRD (n=54) during follow-up, and in 958 randomly selected participants. We evaluated associations of urine PIIINP with CKD progression and incident ESRD. Associations of urine PIIINP with cardiovascular disease, heart failure, and death were evaluated as secondary end points. At baseline, mean age (±SD) was 78±5 years, mean eGFR was 63±18 ml/min per 1.73 m(2), and median urine PIIINP was 2.6 (interquartile range, 1.4-4.2) μg/L. In a case-control study (192 participants, 231 controls), each doubling of urine PIIINP associated with 22% higher odds of CKD progression (adjusted odds ratio, 1.22; 95% confidence interval, 1.00 to 1.49). Higher urine PIIINP level was also associated with incident ESRD, but results were not significant in fully adjusted models. In a prospective study among the 958 randomly selected participants, higher urine PIIINP was significantly associated with death, but not with incident cardiovascular disease or heart failure. These data suggest higher urine PIIINP levels associate with CKD progression independently of eGFR and ACR in older individuals.

mTOR activates the VPS34-UVRAG complex to regulate autolysosomal tubulation and cell survival

Lysosomes are essential organelles that function to degrade and recycle unwanted, damaged and toxic biological components. Lysosomes also act as signalling platforms in activating the nutrient-sensing kinase mTOR. mTOR regulates cellular growth, but it also helps to maintain lysosome identity by initiating lysosomal tubulation through a process termed autophagosome-lysosome reformation (ALR). Here we identify a lysosomal pool of phosphatidylinositol 3-phosphate that, when depleted by specific inhibition of the class III phosphoinositide 3-kinase VPS34, results in prolonged lysosomal tubulation. This tubulation requires mTOR activity, and we identified two direct mTOR phosphorylation sites on UVRAG (S550 and S571) that activate VPS34. Loss of these phosphorylation sites reduced VPS34 lipid kinase activity and resulted in an increase in number and length of lysosomal tubules. In cells in which phosphorylation at these UVRAG sites is disrupted, the result of impaired lysosomal tubulation alongside ALR activation is massive cell death. Our data imply that ALR is critical for cell survival under nutrient stress and that VPS34 is an essential regulatory element in this process.

Biodistribution and pharmacokinetics of recombinant α1-microglobulin and its potential use in radioprotection of kidneys

Peptide-receptor radionuclide therapy (PRRT) is a systemically administrated molecular targeted radiation therapy for treatment of neuroendocrine tumors. Fifteen years of clinical use show that renal toxicity, due to glomerular filtration of the peptides followed by local generation of highly reactive free radicals, is the main side-effect that limits the maximum activity that can be administrated for efficient therapy. α1-microglobulin (A1M) is an endogenous radical scavenger shown to prevent radiation-induced in vitro cell damage and protect non-irradiated surrounding cells. An important feature of A1M is that, following distribution to the blood, it is equilibrated to the extravascular compartments and filtrated in the kidneys. Aiming at developing renal protection against toxic side-effects of PRRT, we have characterized the pharmacokinetics and biodistribution of intravenously (i.v.) injected (125)I- and non-labelled recombinant human A1M and the (111)In- and fluorescence-labelled somatostatin analogue octreotide. Both molecules were predominantly localized to the kidneys, displaying a prevailing distribution in the cortex. A maximum of 76% of the injected A1M and 46% of the injected octreotide were present per gram kidney tissue at 10 to 20 minutes, respectively, after i.v. injection. Immunohistochemistry and fluorescence microscopy revealed a dominating co-existence of the two substances in proximal tubules, with a cellular co-localization in the epithelial cells. Importantly, analysis of kidney extracts displayed an intact, full-length A1M at least up to 60 minutes post-injection (p.i.). In summary, the results show a highly similar pharmacokinetics and biodistribution of A1M and octreotide, thus enabling the use of A1M to protect the kidneys tissue during PRRT.

Pil1 cytoplasmic rods contain bundles of crosslinked tubules

Cytoskeletal polymers are organized into a wide variety of higher-order structures in cells. The yeast BAR domain protein Pil1 self-assembles into tubules in vitro, and forms linear polymers at cortical eisosomes in cells. In the fission yeast S. pombe, over-expressed Pil1 forms thick rods that detach from the plasma membrane. In this study, we used thin-section electron microscopy to determine the ultrastructure of these cytoplasmic Pil1 rods. We found that cytoplasmic rods contained crosslinked Pil1 tubules that displayed regular, hexagonal spacing. These bundles were stained by filipin, a sterol-binding fluorescent dye, suggesting that they contained lipids. Cytoplasmic Pil1 rods were present but less abundant in sle1Δ and fhn1Δ mutant cells. We also found that endogenous Pil1 formed thick rods under saturated growth conditions. Taken together, our findings suggest the presence of cellular mechanisms that assemble Pil1 tubules into higher-order structures.

Exploring the origin and limitations of kidney regeneration

Epidemiological findings indicate that acute kidney injury (AKI) increases the risk for chronic kidney disease (CKD), although the molecular mechanism remains unclear. Genetic fate mapping demonstrated that nephrons, functional units in the kidney, are repaired by surviving nephrons after AKI. However, the cell population that repairs damaged nephrons and their repair capacity limitations remain controversial. To answer these questions, we generated a new transgenic mouse strain in which mature proximal tubules, the segment predominantly damaged during AKI, could be genetically labelled at desired time points. Using this strain, massive proliferation of mature proximal tubules is observed during repair, with no dilution of the genetic label after the repair process, demonstrating that proximal tubules are repaired mainly by their own proliferation. Furthermore, acute tubular injury caused significant shortening of proximal tubules associated with interstitial fibrosis, suggesting that proximal tubules have a limited capacity to repair. Understanding the mechanism of this limitation might clarify the mechanism of the AKI-to-CKD continuum.

Analysis of the Retromer complex-WASH complex interaction illuminates new avenues to explore in Parkinson disease

The retromer complex mediates endosomal protein sorting by concentrating membrane proteins (cargo) into nascent tubules formed through the action of sorting nexin (SNX) proteins. The WASH complex is recruited to endosomes by binding to the VPS35 subunit of retromer and facilitates cargo protein sorting by promoting formation of endosomally-localized F-actin. The VPS35 protein is mutated in Parkinson disease (PD) and a recent report has revealed that the PD-causing mutation impairs the association of retromer with the WASH complex leading to perturbed endosomal protein sorting. Another important player in endosomal protein sorting is the DNAJC13/RME-8 protein, which associates with SNX1 and has also recently been linked to PD. An additional recent report has now shown that RME-8 also interacts with the WASH complex thus establishing retromer and WASH complex-mediated endosomal protein sorting as a key pathway linked to the pathology of PD and providing new avenues to explore in the search for insights into the disease mechanism.

Crystallographic texture and elemental composition mapped in bovine root dentin at the 200 nm level

The relationship between the mineralization of peritubular dentin (PTD) and intertubular dentin (ITD) is not well understood. Tubules are quite small, diameter ∼2 µm, and this makes the near-tubule region of dentin difficult to study. Here, advanced characterization techniques are applied in a novel way to examine what organic or nanostructural signatures may indicate the end of ITD or the beginning of PTD mineralization. X-ray fluorescence intensity (Ca, P, and Zn) and X-ray diffraction patterns from carbonated apatite (cAp) were mapped around dentintubules at resolutions ten times smaller than the feature size (200 nm pixels), representing a 36% increase in resolution over earlier work. In the near tubule volumes of near-pulp, root dentin, Zn intensity was higher than in ITD remote from the tubules. This increase in Zn(2+), as determined by X-ray absorption near edge structure analysis, may indicate the presence of metalloenzymes or transcription factors important to ITD or PTD mineralization. The profiles of the cAp 00.2 X-ray diffraction rings were fitted with a pseudo-Voigt function, and the spatial and azimuthal distribution of these rings' integrated intensities indicated that the cAp platelets were arranged with their c-axes aligned tangential to the edge of the tubule lumen. This texture was continuous throughout the dentin indicating a lack of structural difference between in the Zn rich near-tubular region and the remote ITD.

Probing endoplasmic reticulum dynamics using fluorescence imaging and photobleaching techniques

This unit describes approaches and tools for studying the dynamics and organization of endoplasmic reticulum (ER) membranes and proteins in living cells using fluorescence microscopy. The ER plays a key role in secretory protein biogenesis, calcium regulation, and lipid synthesis. However, study of these processes has often been restricted to biochemical assays that average millions of lysed cells or imaging of static fixed cells. With new fluorescent protein (FP) reporter tools, sensitive commercial microscopes, and photobleaching techniques, investigators can interrogate the behaviors of ER proteins, membranes, and stress pathways in single live cells. Solutions are described for imaging challenges relevant to the ER, including the mobility of ER membranes, a range of ER structures, and the influence of post-translational modifications on FP reporters. Considerations for performing photobleaching assays for ER proteins are discussed. Finally, reporters and drugs for studying misfolded secretory protein stress and the unfolded protein response are described.

Differential regulation of the bumetanide-sensitive cotransporter (NKCC2) by ovarian hormones

The Na-K-2Cl cotransporter (NKCC2) regulates sodium transport along the thick ascending limb of Henle's loop and is important in control of sodium balance, renal concentrating ability and renin release. To determine if there are sex differences in NKCC2 abundance and/or distribution, and to evaluate the contribution of ovarian hormones to any such differences, we performed semiquantitative immunoblotting and immunoperoxidase immunohistochemistry for NKCC2 in the kidney of Sprague Dawley male, female and ovariectomized (OVX) rats with and without 17-beta estradiol or progesterone supplementation. Intact females demonstrated greater NKCC2 protein in homogenates of whole kidney (334+/-29%), cortex (219+/-20%) and outer medulla (133+/-9%) compared to males. Ovarian hormone supplementation to OVX rats regulated NKCC2 in the outer medulla only, with NKCC2 protein abundance decreasing slightly in response to progesterone but increasing in response to 17-beta estradiol. Immunohistochemistry demonstrated prominent NKCC2 labeling in the apical membrane of thick ascending limb cells. Kidney section NKCC2 labeling confirmed regionalized regulation of NKCC2 by ovarian hormones. Localized regulation of NKCC2 by ovarian hormones may have importance in controlling sodium and water balance over the lifetime of women as the milieu of sex hormones varies.

Chiral molecular self-assembly of phospholipid tubules: a circular dichroism study

We report on spectroscopic studies of the chiral structure in phospholipid tubules formed in mixtures of alcohol and water. Synthetic phospholipids containing diacetylenic moieties in the acyl chains self-assemble into hollow, cylindrical tubules in appropriate conditions. Circular dichroism provides a direct measure of chirality of the molecular structure. We find that the CD spectra of tubules formed in mixtures of alcohol and water depends strongly on the alcohol used and the lipid concentration. The relative spectral intensity of different circular dichroism bands correlates with the number of bilayers observed using microscopy. The results provide experimental evidence that tubule formation is based on chiral packing of the lipid molecules and that interbilayer interactions are important to the tubule structure.