Complete remission of nephrotic syndrome in a young woman with anti-LRP2 nephropathy after immunosuppressive therapy.

BACKGROUND: Anti-low density lipoprotein receptor-related protein 2 (LRP2) nephropathy/anti-brush border antibody (ABBA) disease is a disorder characterized by acute tubulointerstitial injury associated with circulating antibodies to kidney proximal tubular brush border protein LRP2/megalin. Patients are typically elderly and present with acute kidney injury and subnephrotic proteinuria. They progress to end-stage renal disease with poor response to immunosuppressive therapies. CASE PRESENTATION: We report a case of a 29-year-old Chinese woman, who presented with nephrotic syndrome with normal kidney function. Kidney biopsy showed no obvious tubular injury or interstitial inflammation. Positive immunoglobulin G (IgG) staining was revealed along the brush border of proximal tubular cells. Anti-LRP2 antibody was identified in serum, consistent with a diagnosis of anti-LRP2 nephropathy. The patient achieved complete remission after receiving prednisone and cyclophosphamide. CONCLUSIONS: Anti-LRP2 nephropathy can also present as nephrotic syndrome in young patients and complete remission from nephrotic syndrome may be achieved after immunosuppressive therapy.

Lactoferrin-induced myeloid-derived suppressor cell therapy attenuates pathologic inflammatory conditions in newborn mice.

Inflammation plays a critical role in the development of severe neonatal morbidities. Myeloid-derived suppressor cells (MDSCs) were recently implicated in the regulation of immune responses in newborns. Here, we report that the presence of MDSCs and their functional activity in infants are closely associated with the maturity of newborns and the presence of lactoferrin (LF) in serum. Low amounts of MDSCs at birth predicted the development of severe pathology in preterm infants - necrotizing enterocolitis (NEC). In vitro treatment of newborn neutrophils and monocytes with LF converted these cells to MDSCs via the LRP2 receptor and activation of the NF-κB transcription factor. Decrease in the expression of LRP2 was responsible for the loss of sensitivity of adult myeloid cells to LF. LF-induced MDSCs (LF-MDSCs) were effective in the treatment of newborn mice with NEC, acting by blocking inflammation, resulting in increased survival. LF-MDSCs were more effective than treatment with LF protein alone. In addition to affecting NEC, LF-MDSCs demonstrated potent ability to control ovalbumin-induced (OVA-induced) lung inflammation, dextran sulfate sodium-induced (DSS-induced) colitis, and concanavalin A-induced (ConA-induced) hepatitis. These results suggest that cell therapy with LF-MDSCs may provide potent therapeutic benefits in infants with various pathological conditions associated with dysregulated inflammation.

Anti-LRP2 Nephropathy With Abundant IgG4-Positive Plasma Cells: A Case Report.

In older adults, the most common kidney biopsy diagnoses include pauci-immune crescentic glomerulonephritis, membranous nephropathy, and focal segmental glomerulosclerosis. Recently, investigators described a small series of older patients (aged 66-80 years) with acute kidney injury and a kidney biopsy demonstrating tubular basement membrane (TBM) immune deposits of polytypic immunoglobulin G (IgG) and C3, acute tubular injury, and tubulointerstitial inflammation. They identified a circulating antibody against kidney tubular low-density lipoprotein (LDL) receptor-related protein 2 (LRP2; also known as megalin) in patients' sera and colocalization of LRP2 with IgG in TBM deposits. We present a rare case of anti-LRP2 nephropathy/anti-brush border antibody disease and describe the novel feature of abundant IgG4-positive interstitial plasma cells. Along with the combination of TBM deposits, tubulointerstitial nephritis (TIN), and segmental glomerular subepithelial immune deposits seen in both entities, this newly described feature adds to the morphologic overlap with IgG4-related TIN. Identification of large TBM deposits using light microscopy and IgG staining of apical aspects of proximal tubules using immunofluorescence microscopy can point to the correct diagnosis of anti-LRP2 nephropathy and prompt confirmatory studies. Particularly in older patients with immune complex-mediated TIN who lack clinical, laboratory, radiographic, and/or characteristic histologic features of IgG4-TIN or other autoimmune, infectious, or drug-related injury, a diagnosis of anti-LRP2 nephropathy should be considered.

Plasmonic gold nanoparticles as multifaceted probe for tissue imaging.

The localized surface plasmon resonance property of gold nanoparticles enables their application as a versatile and sensitive imaging probe, with intense colour, enhanced fluorescence and strong MS ion intensity for biological tissue imaging.

Immunohistochemical localization of megalin and cubilin in the human inner ear.

Megalin and cubilin are endocytic receptors expressed in many absorptive polarized epithelia. These receptors have been implicated in the transport of gentamicin in the inner ear as possible contributors to ototoxic damage. Megalin and cubilin have been characterized in detail in the mouse and rat inner ear, but not in the human inner ear. In this study, megalin and cubilin were localized by immunohistochemistry using affinity-purified antibodies in formalin fixed frozen cryostat and celloidin embedded sections of the human inner ear. In the cochlea megalin and cubilin were localized in marginal cells of the stria vascularis, epithelial cells of the spiral prominence and the Reissner's membrane. In the macula utricle and cristae ampullaris, megalin and cubilin were localized in transitional and dark cells, but not in vestibular hair cells and supporting cells. In the endolymphatic duct megalin and cubilin were localized in the epithelial cells. The localization of megalin and cubilin in the human inner ear is consistent with previous reports in the inner ear of animal models and suggest that these receptors may play an important role in the inner ear endocytic transport, and maybe potential targets for prevention of ototoxic damage or the delivery of medications.

LDL Receptor-Related Protein 2 (Megalin) as a Target Antigen in Human Kidney Anti-Brush Border Antibody Disease.

Primary renal tubulointerstitial disease resulting from proximal tubule antigen-specific antibodies and immune complex formation has not been well characterized in humans. We report a cohort of patients with a distinct, underappreciated kidney disease characterized by kidney antibrush border antibodies and renal failure (ABBA disease). We identified ten patients with ABBA disease who had a combination of proximal tubule damage, IgG-positive immune deposits in the tubular basement membrane, and circulating antibodies reactive with normal human kidney proximal tubular brush border. All but one of the patients also had segmental glomerular deposits on renal biopsy specimen. Patients with ABBA disease were elderly and presented with AKI and subnephrotic proteinuria. Serum from all patients but not controls recognized a high molecular weight protein in renal tubular protein extracts that we identified as LDL receptor-related protein 2 (LRP2), also known as megalin, by immunoprecipitation and mass spectrometry. Immunostaining revealed that LRP2 specifically colocalized with IgG in the tubular immune deposits on the ABBA biopsy specimen but not the control specimen analyzed. Finally, ABBA serum samples but not control samples showed reactivity against recombinantly expressed N-terminal LRP2 fragments on Western blots and immunoprecipitated the recombinantly expressed N-terminal region of LRP2. This case series details the clinicopathologic findings of patients with ABBA disease and shows that the antigenic target of these autoantibodies is LRP2. Future studies are needed to determine the disease prevalence, stimulus for ABBA, and optimal treatment.

Megalin/Cubulin-Lysosome-mediated Albumin Reabsorption Is Involved in the Tubular Cell Activation of NLRP3 Inflammasome and Tubulointerstitial Inflammation.

Albuminuria contributes to the development and progression of chronic kidney disease by inducing tubulointerstitial inflammation (TI) and fibrosis. However, the exact mechanisms of TI in response to albuminuria are unresolved. We previously demonstrated that NLRP3 and inflammasomes mediate albumin-induced lesions in tubular cells. Here, we further investigated the role of endocytic receptors and lysosome rupture in NLRP3 inflammasome activation. A murine proteinuric nephropathy model was induced by albumin overload as described previously. The priming and activation signals for inflammasome complex formation were evoked simultaneously by albumin excess in tubular epithelial cells. The former signal was dependent on a albumin-triggered NF-κB pathway activation. This process is mediated by the endocytic receptor, megalin and cubilin. However, the silencing of megalin or cubilin inhibited the albumin-induced NLRP3 signal. Notably, subsequent lysosome rupture and the corresponding release of lysosomal hydrolases, especially cathepsin B, were observed in tubular epithelial cells exposed to albumin. Cathepsin B release and distribution are essential for NLRP3 signal activation, and inhibitors of cathepsin B suppressed the NLRP3 signal in tubular epithelial cells. Taken together, our findings suggest that megalin/cubilin and lysosome rupture are involved in albumin-triggered tubular injury and TI. This study provides novel insights into albuminuria-induced TI and implicates the active control of albuminuria as a critical strategy to halt the progression of chronic kidney disease.

Renal LRP2 expression in man and chicken is estrogen-responsive.

In mammals, low-density lipoprotein receptor-related protein-2 (LRP2) is an endocytic receptor that binds multiple ligands and is essential for a wide range of physiological processes. To gain new insights into the biology of this complex protein, we have initiated the molecular characterization of the LRP2 homolog from an oviparous species, the chicken (Gallus gallus). The galline LRP2 cDNA encodes a membrane protein of 4658 residues. Overall, the galline and human proteins are 73% identical, indicating that the avian gene has been well conserved over 300 million years. Unexpectedly, LRP2 transcript and protein levels in the kidney of females and estrogen-treated roosters were significantly higher than those in untreated males. The estrogen-responsiveness of avian LRP2 may be related to the dramatic differences in lipoprotein metabolism between mature roosters and laying hens. Newly identified potential estrogen-responsive elements (ERE) in the human and galline LRP2 gene, and additional Sp1 sites present in the promoter of the chicken gene, are compatible with both direct estrogen induction via the classical ligand-induced ERE pathway and the indirect transcription factor crosstalk pathway engaging the Sp1 sites. In agreement with this assumption, estrogen induction of LRP2 was observed not only in primary cultured chicken kidney cells, but also human kidney cell lines. These findings point to novel regulatory features of the LRP2 gene resulting in sex-specific receptor expression.

Megalin mediates the influence of sonic hedgehog on oligodendrocyte precursor cell migration and proliferation during development.

Oligodendrocyte precursor cells (OPCs) of the optic nerve are generated in the preoptic area, from where they migrate to colonize it entirely. Sonic hedgehog (Shh) induces the proliferation of these cells as well as influencing their migration, acting through its canonical receptor (Ptc-1). However, the multiligand receptor megalin (or LRP-2) is also involved in Shh-induced OPC proliferation and migration, and thus, we have evaluated the relevance of this interaction. During the stages at which Shh influences OPC development, we found megalin to be selectively expressed by optic nerve astrocytes, whereas Ptc-1 and Gli1 were found in OPCs. Indeed, this pattern of expression paralleled the rostral-caudal expression of the three Shh-related molecules during the time course of plp-dm20(+) -OPC colonization. The blockage of megalin partially abolished OPC chemoattraction and fully impaired Shh-induced proliferation. Using in vitro co-cultures of dissociated optic nerve cells, we demonstrated that Shh was internalized by astrocytes via megalin, and sufficient Shh was subsequently released to produce the biological effects on OPCs observed in the nerve. Together, these data indicate that at least part of the influence of Shh on OPCs is mediated by megalin during optic nerve development, and that astrocytes expressing megalin transiently capture Shh to present it to OPCs and/or to control the gradient of this molecule during development.

Expression of the megalin C-terminal fragment by macrophages during liver fibrogenesis in mice.

The low-density-lipoprotein receptor megalin (LRP2, gp330) is strongly expressed in the kidney, where it is responsible for the resorption of metabolites from primary urine. One of the main ligands is the complex of retinol and retinol binding protein. Megalin has been hypothesized to be part of the retinol storage system in liver. Considering the role of hepatic stellate cells in retinol storage and fibrogenesis we investigated mouse strains that developed different degrees of fibrosis after challenge with CCl(4). Immunoblotting revealed the invariable expression of the megalin C-terminal fragment independent of liver damage in all strains. However, only a specific cell population in centrilobular areas of fibrotic livers from DBA/2J mice, which were most susceptible for CCl(4)-induced fibrogenesis in our study, was stained using megalin-specific antibodies. Double immunostaining indicated that a subset of hepatic macrophages might represent the megalin-expressing cells in fibrotic liver. Fluorescence activated cell sorting based isolation of hepatic macrophages and megalin specific expression analysis demonstrated the transcription of the whole megalin gene in liver macrophages. We argue that megalin might exhibit a proinflammatory effect by the uptake of retinoids in recruited monocytes, which thereby differentiate to liver macrophages and potentiate fibrogenesis by the release of proinflammatory mediators. Otherwise, megalin might be activated in macrophages during advanced fibrogenesis and act as a negative regulator of proinflammatory genes.

Antigen identification in membranous nephropathy moves toward targeted monitoring and new therapy.

Membranous nephropathy, a disease characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane, is the most common cause of idiopathic nephrotic syndrome in Caucasian adults. In the rat model described by Heymann in 1959, the target antigen of antibodies is megalin, a multiligand receptor expressed in the rat glomerulus but absent from the human glomerulus. In the past few years, two major antigens have been identified in human membranous nephropathy. The first is neutral endopeptidase, the alloantigen involved in neonatal cases of membranous nephropathy that occur in newborns from neutral endopeptidase-deficient mothers. The second is the type-M phospholipase A2 receptor (PLA(2)R), the first autoantigen identified in idiopathic membranous nephropathy in the adult. Megalin, neutral endopeptidase, and PLA(2)R are all expressed on the podocyte surface where they serve as targets for circulating antibodies, which lead to in situ immune complex formation, complement activation, and proteinuria. The recent discovery of neutral endopeptidase and PLA(2)R provides new tools for monitoring human disease activity and should be of value in designing new antigen-driven therapeutic strategies.

A megalin polymorphism associated with promoter activity and Alzheimer's disease risk.

Elevated cerebral levels of amyloid beta-protein (Abeta) occur in Alzheimer's disease (AD), yet only a few patients show evidence of increased Abeta production. This observation suggests that many, perhaps most, cases of AD are caused by faulty clearance of Abeta. Megalin, which plays an important role in mediating Abeta clearance, is an attractive candidate gene for genetic association with AD. To investigate this hypothesis, we analyzed the megalin gene in a population of 2,183 subjects. Genetic analysis indicated that the rs3755166 (G/A) polymorphism located in the megalin promoter associated with risk for AD, dependently of apolipoprotein E genotype. The rs3755166 AA genotype frequency was significantly greater in AD patients than in control subjects. Furthermore, the luciferase reporter assay indicated that the rs3755166 A variant has 20% less transcriptional activity than the rs3755166 G variant. This study provides strong evidence that this megalin polymorphism confers a greater risk for AD, and supports a biological role for megalin in the neurodegenerative processes involved in AD.

Autoimmune responses against renal tissue proteins in long-term surviving allograft recipients.

Major histocompatibility complex antigens (MHC) are classical targets of recipient responses to allotransplants. However, the role of an immune response directed against autologous graft tissue determinants is poorly defined. In this study, we investigated (i) whether autologous kidney tissue extract can induce an immune response to autologous kidney proteins in normal rats, and (ii) if a similar autologous response develops in the long-term surviving LEW.1A recipients of an MHC-mismatched LEW.1W kidney (RT1(u) to RT1(a)). LEW.1A rats immunized with allo- or syngeneic soluble kidney extracts developed a T-cell response to self antigens as shown by the frequency of specific IFN-gamma-producing T cells from LEW.1A rats in the presence of extracts (ELISPOT). In contrast, they responded only marginally to dominant RT1(u) determinants. The ELISPOT against fractions of soluble autologous kidney extracts separated by an FPLC gel-filtration system indicated a preferential response to megalin, a high molecular weight protein that has been shown to be involved in experimental Heymann nephritis. In a model of long-term kidney allograft survival by anti-CD28 administration, recipients also developed humoral but not cellular responses to megalin. Our data suggest that autoimmune processes develop in long-term surviving kidney allograft recipients.

[Extra-membranous glomerulonephritis: from the experimental model to the human pathology of new-born and adult]. / Glomérulonéphrites extramembraneuses: du modèle expérimental à la pathologie humaine du nouveau-né et de l'adulte.

Membranous nephropathy (MN) is one of the most common glomerulopathies. Current treatments are entirely empirical, and concept-driven therapies are dramatically lacking. In the rat experimental model established by Heymann in 1959, the target antigen is expressed at the surface of podocytes where immune complexes are formed, inducing complement activation results in heavy proteinuria. However, megalin is not detected on human podocytes and in immune deposits in patients with MN. We recently identified neutral endopeptidase (NEP), a podocyte antigen that can digest biologically active peptides, as the target antigen of antibodies deposited in the subepithelial space of glomeruli in a subset of patients with antenatal MN. The mothers became immunized because they are deficient in NEP due to truncating mutations in the gene. MN could be transferred to the rabbit by injection of mothers' Ig. We discuss new pathophysiological aspects of the disease with special emphasis on allo-immunization, novel potential antigenic targets, and therapeutic prospects.

Target antigens and nephritogenic antibodies in membranous nephropathy: of rats and men.

Membranous nephropathy, a disease characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane, is the most common cause of idiopathic nephrotic syndrome in white adults. In the rat model of Heymann nephritis, the target antigen of antibodies is megalin, a multiligand receptor expressed at the podocyte cell surface. This review summarizes key findings provided by this experimental model and by our discovery of neutral endopeptidase being the alloantigen involved in neonatal cases of membranous nephropathy. We discuss the role of alloimmunization as a new mechanism of renal disease and the approach that we use to identify new podocyte antigens. We also summarize current knowledge on the mechanism of proteinuria, with special emphasis on the role of complement. In conclusion, substantial progresses have been made in understanding molecular mechanisms of membranous nephropathy, which should lead to novel therapeutic approaches.

Metallothionein-IIA promotes neurite growth via the megalin receptor.

Metallothionein (MT)-I/II has been shown to be neuroprotective and neuroregenerative in a model of rat cortical brain injury. Here we examine expression patterns of MT-I/II and its putative receptor megalin in rat retina. At neonatal stages, MT-I/II was present in retinal ganglion cells (RGCs) but not glial or amacrine cells; megalin was present throughout the retina. Whilst MT-I/II was absent from adult RGC in normal animals and after optic nerve transection, the constitutive megalin expression in RGCs was lost following optic nerve transection. In vitro MT-IIA treatment stimulated neuritic growth: more RGCs grew neurites longer than 25 microm (P < 0.05) in dissociated retinal cultures and neurite extension increased in retinal explants (P < 0.05). MT-IIA treatment of mixed retinal cultures increased megalin expression in RGCs, and pre-treating cells with anti-megalin antibodies prevented MT-IIA-stimulated neurite extension. Our results indicate that MT-IIA stimulates neurite outgrowth in RGCs and may do so via the megalin receptor; we propose that neurite extension is triggered via signal transduction pathways activated by the NPxY motifs of megalin's cytoplasmic tail.

Immunocytochemistry of renal membrane proteins on epoxy sections.

Immunocytochemistry performed on paraffin or cryosections is often hampered by poor morphology. Epoxy sections, in contrast, generally retain well-preserved tissue architecture. Immunocytochemistry, however, on epoxy-embedded sections is difficult due in part to the plastic itself and to the fixation conditions. Here, we present a technique for visualization of membrane proteins by immunocytochemistry on epoxy sections of kidneys fixed with glutaraldehyde without or with osmium post-fixation. Semithin sections were obtained from Epon 812-embedded mouse and rat kidney blocks. Before immunoperoxidase or immunofluorescence labeling, the sections were etched with the epoxy solvent, methanolic potassium hydroxide, followed by antigen retrieval using microwave heating. The sections were then treated with the primary antibody followed by secondary antibodies as usual. The distribution and expression patterns of a variety of membrane proteins, such as aquaporin (AQP)-1, AQP-2, and megalin, were identical to those observed by traditional immunocytochemical procedures on paraffin or cryosections. The advantages of our novel method include not only enhanced morphological quality but also the feasibility for investigators to visualize antigens of interest using archival specimens in Epon blocks.