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• W2967578945 abstract "The polymeric Ig receptor (PIgR) constitutes an important part of the immune system by mediating transcytosis of dimeric IgA into mucosal fluids. Although well studied in organs such as the intestine, the regulation and localization of PIgR in human kidney are incompletely characterized. Herein, using immunohistochemistry, we show that in healthy human kidneys, PIgR is expressed by the progenitor-like tubular scattered cells of the proximal tubules and by parietal epithelial cells of glomeruli. We further show that proximal tubular expression of PIgR becomes widespread during kidney disease, correlating to elevated levels of urinary secretory IgA. Urinary secretory IgA levels also correlated to the degree of tubular fibrosis, plasma creatinine, and urea levels. In addition, primary tubular cells were cultured to study the function and regulation of PIgR in vitro. Cellular PIgR expression was induced by conditioned medium from activated human leukocytes, as well as by inflammatory cytokines, whereas transforming growth factor-β1 caused decreased expression. Furthermore, interferon-γ increased the transcytosis of dimeric IgA in cultured tubular cells. Finally, a correlation study of mRNA data from the Genotype-Tissue Expression portal indicated that PIGR mRNA expression in kidney correlates to the expression of TNFSF13, a cytokine involved in plasma cell class switching to IgA. These results indicate that PIgR induction is an integral part of the injury phenotype of renal tubular cells. The polymeric Ig receptor (PIgR) constitutes an important part of the immune system by mediating transcytosis of dimeric IgA into mucosal fluids. Although well studied in organs such as the intestine, the regulation and localization of PIgR in human kidney are incompletely characterized. Herein, using immunohistochemistry, we show that in healthy human kidneys, PIgR is expressed by the progenitor-like tubular scattered cells of the proximal tubules and by parietal epithelial cells of glomeruli. We further show that proximal tubular expression of PIgR becomes widespread during kidney disease, correlating to elevated levels of urinary secretory IgA. Urinary secretory IgA levels also correlated to the degree of tubular fibrosis, plasma creatinine, and urea levels. In addition, primary tubular cells were cultured to study the function and regulation of PIgR in vitro. Cellular PIgR expression was induced by conditioned medium from activated human leukocytes, as well as by inflammatory cytokines, whereas transforming growth factor-β1 caused decreased expression. Furthermore, interferon-γ increased the transcytosis of dimeric IgA in cultured tubular cells. Finally, a correlation study of mRNA data from the Genotype-Tissue Expression portal indicated that PIGR mRNA expression in kidney correlates to the expression of TNFSF13, a cytokine involved in plasma cell class switching to IgA. These results indicate that PIgR induction is an integral part of the injury phenotype of renal tubular cells. The mucosal linings of the gastrointestinal and respiratory tracts are continuously bathed with secreted IgA. Secreted IgA is also an important component of breast milk and is found at low levels in urine. This mucosal immunity provides a barrier against external pathogens.1Fagarasan S. Honjo T. Intestinal IgA synthesis: regulation of front-line body defences.Nat Rev Immunol. 2003; 3: 63-72Crossref PubMed Scopus (399) Google Scholar IgA is carried across the mucosal epithelium by the polymeric Ig receptor (PIgR), localized in the basolateral plasma membranes of the epithelial cells. Plasma cells in the underlying lamina propria produce dimeric IgA (dIgA) by joining the Fc regions of two IgA molecules with a protein called joining chain (JC). The JC is recognized by PIgR that mediates transcellular transport of IgA to the apical compartment, where dIgA is cleaved off from PIgR, leaving a piece of PIgR called secretory component (SC) covalently attached to the secreted dIgA (Figure 1). The resulting molecule is called secretory IgA (sIgA). Human urine also contains sIgA2Bienenstock J. Tomasi Jr., T.B. Secretory gamma-A in normal urine.J Clin Invest. 1968; 47: 1162-1171Crossref PubMed Scopus (71) Google Scholar; and as early as in 1969, Tourville et al3Tourville D.R. Adler R.H. Bienenstock J. Tomasi Jr., T.B. The human secretory immunoglobulin system: immunohistological localization of gamma A, secretory “piece,” and lactoferrin in normal human tissues.J Exp Med. 1969; 129: 411-429Crossref PubMed Scopus (228) Google Scholar reported PIgR/SC localization to unspecified kidney tubules of some, but not all, human kidneys. Another early study also reported that some tubules were positive for PIgR/SC, but neither of these studies provided conclusive histology or regulatory data.4Dobrin R.S. Knudson F.E. Michael A.F. The secretory immune system and renal disease.Clin Exp Immunol. 1975; 21: 318-328PubMed Google Scholar The cellular basis for kidney regeneration after injury is still under debate. The classic view of randomly surviving cells undergoing epithelial-to-mesenchymal transition has been challenged by the concept of a renal progenitor cell population mediating repair.5Humphreys B.D. Valerius M.T. Kobayashi A. Mugford J.W. Soeung S. Duffield J.S. McMahon A.P. Bonventre J.V. Intrinsic epithelial cells repair the kidney after injury.Cell Stem Cell. 2008; 2: 284-291Abstract Full Text Full Text PDF PubMed Scopus (678) Google Scholar, 6Lindgren D. Bostrom A.K. Nilsson K. Hansson J. Sjolund J. Moller C. Jirstrom K. Nilsson E. Landberg G. Axelson H. Johansson M.E. Isolation and characterization of progenitor-like cells from human renal proximal tubules.Am J Pathol. 2011; 178: 828-837Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar, 7Sagrinati C. Netti G.S. Mazzinghi B. Lazzeri E. Liotta F. Frosali F. Ronconi E. Meini C. Gacci M. Squecco R. Carini M. Gesualdo L. Francini F. Maggi E. Annunziato F. Lasagni L. Serio M. Romagnani S. Romagnani P. Isolation and characterization of multipotent progenitor cells from the Bowman's capsule of adult human kidneys.J Am Soc Nephrol. 2006; 17: 2443-2456Crossref PubMed Scopus (570) Google Scholar, 8Smeets B. Boor P. Dijkman H. Sharma S.V. Jirak P. Mooren F. Berger K. Bornemann J. Gelman I.H. Floege J. van der Vlag J. Wetzels J.F. Moeller M.J. Proximal tubular cells contain a phenotypically distinct, scattered cell population involved in tubular regeneration.J Pathol. 2013; 229: 645-659Crossref PubMed Scopus (161) Google Scholar, 9Vogetseder A. Palan T. Bacic D. Kaissling B. Le Hir M. Proximal tubular epithelial cells are generated by division of differentiated cells in the healthy kidney.Am J Physiol Cell Physiol. 2007; 292: C807-C813Crossref PubMed Scopus (87) Google Scholar Regardless, a population of tubular cells with bearing on injury and regeneration has been identified scattered throughout the proximal tubules [tubular scattered cells (TSCs)], and these increase in number after injury.6Lindgren D. Bostrom A.K. Nilsson K. Hansson J. Sjolund J. Moller C. Jirstrom K. Nilsson E. Landberg G. Axelson H. Johansson M.E. Isolation and characterization of progenitor-like cells from human renal proximal tubules.Am J Pathol. 2011; 178: 828-837Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar, 8Smeets B. Boor P. Dijkman H. Sharma S.V. Jirak P. Mooren F. Berger K. Bornemann J. Gelman I.H. Floege J. van der Vlag J. Wetzels J.F. Moeller M.J. Proximal tubular cells contain a phenotypically distinct, scattered cell population involved in tubular regeneration.J Pathol. 2013; 229: 645-659Crossref PubMed Scopus (161) Google Scholar Herein, we show that PIgR is expressed by the TSCs in healthy proximal tubules. PIgR expression becomes widespread in injured kidneys, and urinary sIgA levels increase in patients displaying a broad set of kidney diseases. Furthermore, we show that PIgR expression is induced in cultured primary human tubular cells by inflammatory cytokines or conditioned medium from human leukocytes. We also show in vitro that cultured tubular cells perform transcytosis of IgA and that this process is stimulated by interferon-γ (IFN-γ). These results indicate that PIgR expression is part of the tubular response to injury, providing an explanation for the increased sIgA levels found in urine from injured kidneys. Histologic material, plasma, and urine samples were obtained after informed consent from healthy individuals and patients. Ethical permit (number 413-09) was approved by the ethical committee at University of Gothenburg (Gothenburg, Sweden). Clinical data are summarized in Table 1. Tissue was also obtained from kidneys removed by nephrectomy after patient informed consent and with ethical permission from the Regional Ethics Committee at Lund University (Lund, Sweden; LU680-08 and LU289-07). Leukocytes from healthy blood donors were isolated from leukocyte concentrates, and permission for this was obtained from the Regional Ethics Committee at Lund University (LU949-17). The participating individuals provided a written informed consent before the study.Table 1Summary of Patient DataNo.DiseaseAge, yearsSexPlasma albumin, g/LPlasma creatinine, μmol/LPlasma urea, mmol/LRelative urinary sIgARelative plasma sIgAPIgR-positive tubular cells, %Tissue fibrosis, %Blood pressure1DN35Female3617016.514.153.03025120/902DN58Male3720713.614.069.34560138/903DN33Male33784.42.520.0515132/734DN67Female2416415.325.647.92515140/805DN67Male402259.48.836.65050125/706DN29Male3211513.01.120.92020135/807DN70Male2824314.527.919.86060150/728MN49Male24764.211.658.4155125/659MN58Male18933.512.629.8105155/7210MN48Female16523.713.424.8155100/6011MN72Male301619.77.425.23030110/7012MN71Female25685.532.573.3NANA124/8913MN61Male3311511.610.756.72020145/8014MN73Male241267.931.717.9NANA144/7015IgAN43Female321047.917.942.65030151/10116IgAN53Male401407.69.113.22525156/9617IgAN53Male331187.67.234.43020140/8018IgAN26Male371337.92.816.42520146/8919IgAN43Male2432511.821.713.47060130/8020IgAN42Female321047.912.950.0NANA114/7221IgAN41Female35925.71.726.855110/7022IgAN67Male3718111.96.831.62030138/8223CN77Female2611211.718.310.27020125/6024CN56Male3611710.63.318.06015138/7525CN69Male2413611.06.241.03025141/6526CN65Male3618815.23.619.46055150/9527MCD19Female12864.24.52.71515140/8028MCD29Female12773.81.351.5155130/6529MCD25Male26764.20.515.555120/6530MCD28Female12773.81.365.6NANA126/7931MCD20Male23635.81.617.355105/5532MCD44Female12713.84.552.3105112/7733MCD33Female20504.68.047.055120/7034MCD30Male1910611.20.653.81020140/80CN, crescentic glomerulonephritis; DN, diabetic nephropathy; IgAN, IgA nephropathy; MCD, minimal change disease; MN, membranous nephropathy; NA, tissue not available; PIgR, polymeric Ig receptor; sIgA, secretory IgA. Open table in a new tab CN, crescentic glomerulonephritis; DN, diabetic nephropathy; IgAN, IgA nephropathy; MCD, minimal change disease; MN, membranous nephropathy; NA, tissue not available; PIgR, polymeric Ig receptor; sIgA, secretory IgA. Immunohistochemical analysis was performed on sections (4 μm thick) of formalin-fixed, paraffin-embedded kidney tissue. Deparaffinization and epitope retrieval were performed in a PT Link module (Dako, Stockholm, Sweden), and staining was done using Autostainer Plus equipment (Dako), according to the manufacturer's protocols. The following antibodies were used: anti-secretory component of PIgR (sc-20656; dilution 1:200; Santa Cruz Biotechnology, Dallas, TX), anti-vimentin (M0725; dilution 1:1000; Dako), anti-IgJ (sc-133177; dilution 1:50; Santa Cruz Biotechnology), and anti–plasma cell marker (M7077; dilution 1:50; Dako). Grading the extent of PIgR expression in the proximal tubules and degree of tissue fibrosis was performed by a subspecialized kidney pathologist (M.E.J.). The evaluated tissue sections were from the same patients who were included in the present study (Table 1). The extent of fibrosis was evaluated by assessment of the percentage of trichrome blue areas in diseased kidney compared with control material. Trichrome staining was performed using the Dako ArtisanLink system and Masson's Trichrome staining kit AR173 (both from Dako), according to the manufacturer's protocols. For colocalization studies, immunofluorescence was performed on formalin-fixed, paraffin-embedded material from four healthy individuals and three patients with diabetic nephropathy. After deparaffinization, antigen retrieval was performed in DIVA decloaker (Histolab, Gothenburg, Sweden). The antibodies used were mouse anti-vimentin (ab8978; dilution 1:200; Abcam, Cambridge, UK), rabbit anti-secretory component of PIgR (sc-20656; dilution 1:200; Santa Cruz Biotechnology). Secondary anti-mouse and anti-rabbit antibodies conjugated to Alexa Fluor 488 or Alexa Fluor 594, from Thermo Fisher Scientific (Waltham, MA), were used. Sections were mounted with mounting medium containing DAPI (Vector Laboratories, Burlingame, CA). For assessment of IgA and IgG distribution in atrophic tubules, unfixed cryosections were produced, according to standard protocol, and stained with fluorescein isothiocyanate–labeled antisera against IgA or IgG (Dako). Secretory IgA in plasma and urine was analyzed by sandwich enzyme-linked immunosorbent assay in 96-well microplates (Greiner bio-one, Courtaboeuf Cedex, France). Wells were coated with mouse anti-SC antibody (I-6635; Sigma-Aldrich, St. Louis, MO) and blocked with phosphate-buffered saline with Tween-20 containing 1% (w/v) bovine serum albumin. Urine and blood samples were added to the coated wells in triplicates. Secretory IgA was detected using a rabbit anti-human IgA antibody (A0262; Dako), followed by anti-rabbit horseradish peroxidase–linked antibody (NA934V; GE Healthcare, Little Chalfont, UK). O-phenylenediamine was added as a substrate, and plates were incubated for 30 minutes in darkness at room temperature. The reaction was stopped by addition of 3 mol/L sulfuric acid, and absorbance was measured at 492 nm on a FLUOstar Omega plate reader (BMG Labtech, Värmdö, Sweden). For standard curve preparation, purified human secretory IgA (55905; MP Biomedicals, Santa Ana, CA) was used. Urine sIgA levels were normalized to urine creatinine levels. Tubular cell cultures were prepared according to previously published protocols.10Krawczyk K.M. Hansson J. Nilsson H. Krawczyk K.K. Swärd K. Johansson M.E. Injury induced expression of caveolar proteins in human kidney tubules: role of megakaryoblastic leukemia 1.BMC Nephrol. 2017; 18: 320Crossref PubMed Scopus (3) Google Scholar In short, cortical kidney tissue was minced and dissociated in a collagenase type I and DNase I type II solution. Single cells were seeded and cultured in Dulbecco's modified Eagle's medium low glucose with 10% fetal bovine serum and 1% penicillin-streptomycin (Thermo Fisher Scientific) at 37°C and 5% CO2. Cultured cells were treated with recombinant IFN-γ (285-IF; R&D Systems, Minneapolis, MN) at 12.5 ng/mL, transforming growth factor-β1 (240-B; R&D Systems) at 10 ng/mL, IL-1β (201-LB; R&D Systems) at 25 ng/mL, or tumor necrosis factor-α (TNF-α; 8902SF; Cell Signaling, Danvers, MA) at 10 ng/mL. Peripheral blood mononuclear cells were isolated from leukocyte depletion filters from healthy donors, according to a previous publication.11Krawczyk K.M. Nilsson H. Allaoui R. Lindgren D. Arvidsson M. Leandersson K. Johansson M.E. Papillary renal cell carcinoma-derived chemerin, IL-8, and CXCL16 promote monocyte recruitment and differentiation into foam-cell macrophages.Lab Invest. 2017; 97: 1296-1305Crossref PubMed Scopus (24) Google Scholar Conditioned medium from peripheral blood mononuclear cells was collected after 24 hours of culture in Dulbecco's modified Eagle's medium low glucose with 10% heat-inactivated human serum (Sigma-Aldrich) and 1% penicillin-streptomycin solution. To obtain conditioned medium from activated immune cells, 100 ng/mL of lipopolysaccharides from Escherichia coli (Sigma-Aldrich) was added to the culture medium. The mRNA levels of PIGR were measured by real-time quantitative PCR. RNA was isolated from cultured cells using the RNeasy mini kit (Qiagen, Hilden, Germany). cDNA was generated using the RevertAid RT kit (Thermo Fisher Scientific). Real-time quantitative PCRs were prepared in triplicates and performed on a Stratagene Mx3005P (Agilent Technologies, Santa Clara, CA). Results were normalized using two housekeeping genes: HMBS, 5′-GGCAATGCGGCTGCAA-3′ (forward primer) and 5′-GGGTACCCACGCGAATCAC-3′ (reverse primer); and RPL13A, 5′-CCTGGAGGAGAAGAGGAAAGAGA-3′ (forward primer) and 5′-TTGAGGACCTCTGTGTATTTGTCAA-3′ (reverse primer). Primer sequences for PIGR were as follows: 5′-GCCCGAGCTGGTTTATGAAG-3′ (forward) and 5′-AGCCGTGACATTCCCTGGTA-3′ (reverse). Cultured cells were harvested and lysed in radioimmunoprecipitation assay buffer supplemented with complete protease inhibitor cocktail (Sigma-Aldrich). Western blot analysis was performed according to the manufacturer's protocol using precast gels, polyvinylidene difluoride membranes, and Trans-blot Turbo transfer from Bio-Rad Laboratories (Hercules, CA). Antibodies used were anti–β-actin (dilution 1:5000; Sigma-Aldrich) and anti-PIgR/SC (dilution 1:1000; Santa Cruz Biotechnology). Secondary horseradish peroxidase–conjugated anti-mouse and anti-rabbit antibodies (GE Healthcare) were used, and protein bands were visualized with Western blot ECL (AH Diagnostics, Solna, Sweden) and a ChemiDoc camera (Bio-Rad Laboratories). For IgA transport study, tubular cells were seeded on 0.4-μm pore membrane inserts placed in 6-well plates (Corning, Corning, NY) and cultured until confluency. Purified human IgA (P80-102; Bethyl Laboratories, Montgomery, TX) was added to the lower compartment. After 18 hours, medium from both compartments was collected and analyzed for secretory IgA content using sandwich enzyme-linked immunosorbent assay, as described above. For PIgR induction, cells were treated with 12.5 ng/mL IFN-γ for 48 hours before the transport study. RNA-sequencing data from the Genotype-Tissue Expression (GTEx) project (http://www.gtexportal.org)12Consortium G.T. The Genotype-Tissue Expression (GTEx) project.Nat Genet. 2013; 45: 580-585Crossref PubMed Scopus (4307) Google Scholar were downloaded in August 2016. After normalization according to the trimmed mean of M-values method,13Robinson M.D. Oshlack A. A scaling normalization method for differential expression analysis of RNA-seq data.Genome Biol. 2010; 11: R25Crossref PubMed Scopus (4091) Google Scholar correlation analyses were made using the Pearson method. Correlation between PIGR and all other transcripts (56,202) was analyzed in the eight tissue types with highest PIGR levels (n = 57, salivary gland; n = 196, transverse colon; n = 88, terminal ileum; n = 32, kidney; n = 320, lung; n = 193, stomach; n = 119, liver; n = 214, mammary tissue). The sum of correlation coefficients across tissues for all individual RNAs [Rsum (versus PIGR)] was calculated. This sum was sorted in descending order, and the extremes were plotted. Correlations that seemed biologically meaningful [tumor necrosis factor ligand superfamily member 13 (TNFSF13), TNFRSF11A, and STAT1] were next tested using the Spearman method (GraphPad Prism software version 8; GraphPad Software, San Diego, CA) in kidney (n = 32; ie, the smallest data set). GraphPad Prism software was used for statistical analyses. Pairwise comparisons were made using a paired, two-tailed t-test. For multiple comparisons, one-way analysis of variance was used, followed by Dunnett's correction for multiple comparisons. Correlations were calculated using Pearson's method. To determine the presence and localization of PIgR in human kidney, healthy kidney tissue was analyzed by immunohistochemistry. Healthy glomeruli and proximal tubules are visualized by hematoxylin and eosin staining in Figure 2A. Scattered PIgR positivity was detected in the proximal tubules and in the parietal epithelial cells of Bowman capsule (Figure 2B). This staining pattern is similar to what has been previously observed for TSC markers, such as vimentin and CD133.6Lindgren D. Bostrom A.K. Nilsson K. Hansson J. Sjolund J. Moller C. Jirstrom K. Nilsson E. Landberg G. Axelson H. Johansson M.E. Isolation and characterization of progenitor-like cells from human renal proximal tubules.Am J Pathol. 2011; 178: 828-837Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar Vimentin is expressed by kidney stromal cells, endothelial cells, and parietal epithelial cells, but apart from the presence in the TSCs, it is not normally expressed in proximal tubules (Figure 2C). Figure 2D demonstrates the morphology of kidney tissue affected by diabetic nephropathy, with flattened proximal tubular cells and visible interstitial fibrosis. The expression of TSC markers becomes extensive following injury in proximal tubules.6Lindgren D. Bostrom A.K. Nilsson K. Hansson J. Sjolund J. Moller C. Jirstrom K. Nilsson E. Landberg G. Axelson H. Johansson M.E. Isolation and characterization of progenitor-like cells from human renal proximal tubules.Am J Pathol. 2011; 178: 828-837Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar, 8Smeets B. Boor P. Dijkman H. Sharma S.V. Jirak P. Mooren F. Berger K. Bornemann J. Gelman I.H. Floege J. van der Vlag J. Wetzels J.F. Moeller M.J. Proximal tubular cells contain a phenotypically distinct, scattered cell population involved in tubular regeneration.J Pathol. 2013; 229: 645-659Crossref PubMed Scopus (161) Google Scholar Similarly, widespread PIgR expression was found in the proximal tubules of the diseased kidney (Figure 2E). Thus, PIgR shows an overlapping expression pattern in the healthy and diseased kidney with the TSC marker vimentin (Figure 2, C and F). Having established a similar expression pattern of vimentin and PIgR in human healthy and diseased kidney, a potential coexpression of these two markers was studied. Immunofluorescence costaining of vimentin and PIgR shows overlapping staining patterns both in TSCs and in parietal epithelial cells of healthy kidneys (Figure 3, A–D ). A slightly higher number of tubular cells were positive for vimentin, but approximately 80% of the tubular cells that were positive for vimentin also expressed PIgR. Expression of both markers was more widespread in diseased kidney (Figure 3, E–H), and here the degree of colocalization was even higher. PIgR expression was further analyzed in kidney tissue from a pyelonephritis patient displaying heavy injury with blood present in the lumen of proximal tubules (Figure 3I). The injured proximal tubules show widespread apical PIgR staining (Figure 3J). We could also demonstrate the presence of JC in the lumen of these proximal tubules (Figure 3K), indicating the presence of dIgA. Of note, the infiltrating plasma cells found in the interstitium of these kidneys (Figure 3L) were not JC positive (Figure 3K), which might indicate that the dIgA was not produced locally. Finally, immunofluorescence staining for IgA showed positivity in proteinaceous deposits found in the lumen of chronically injured proximal tubules (Figure 3M). In contrast, these deposits were negative for IgG (Figure 3N) that is present in large amounts in blood but is not transported by PIgR. This pattern is seen in chronically injured kidney tissue, where fibrosis is increased, regardless of underlying disease. These results indicate that active PIgR-mediated IgA transport occurs in injured proximal tubules and further support a functional role of increased PIgR expression during chronic kidney injury. To get a more complete understanding of the extent of PIgR expression in different forms of kidney disease, histologic samples from a cohort of 34 patients experiencing various kidney conditions were analyzed (patient data presented in Table 1). PIgR expression and tissue fibrosis, as determined by Masson's trichrome staining, were quantified for all patients from whom tissue was available. Examples of immunohistochemical staining of PIgR from the different conditions are shown in Figure 4. Interestingly, proximal tubule PIgR expression seems to increase with the severity of the disease. A significant positive correlation was found between the percentage of PIgR-positive tubular cells and the extent of tissue fibrosis across all conditions. Tubular PIgR expression was also significantly correlated to plasma creatinine and urea levels, which are classic analytes used to assess kidney injury (Table 2).Table 2Summary of CorrelationsVariableFibrosis, %PIgR, %U-sIgAP-sIgAP-creaP-ureaFibrosis, %10.76****0.44**−0.030.90****0.68****PIgR, %10.54**−0.200.72****0.62***U-sIgA10.140.53**0.44*P-sIgA1−0.070.12P-crea10.70****P-urea1Correlations, as determined by Pearson method, between analyzed patient data, PIgR expression, and extent of kidney fibrosis in samples from the 30 patients in whom tissue was available, as presented in Table 1.*P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001.P-crea, plasma creatinine levels; PIgR, polymeric Ig receptor; P-sIgA, plasma secretory IgA levels; P-urea, plasma urea levels; U-sIgA, urine secretory IgA levels. Open table in a new tab Correlations, as determined by Pearson method, between analyzed patient data, PIgR expression, and extent of kidney fibrosis in samples from the 30 patients in whom tissue was available, as presented in Table 1. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001. P-crea, plasma creatinine levels; PIgR, polymeric Ig receptor; P-sIgA, plasma secretory IgA levels; P-urea, plasma urea levels; U-sIgA, urine secretory IgA levels. To determine whether the observed induction of PIgR expression in injured kidneys would translate into increased urine levels of sIgA, sIgA levels were measured in urine and plasma from the same patient cohort as above. Urinary sIgA levels were increased for all diseases, with the highest average level detected for membranous nephropathy (Figure 5A and Table 1). The only exception was minimal change disease; but more important, this disease is defined by the absence of fibrosis and other histopathologic changes. Not surprisingly, sIgA levels in urine were similar to control values in this category. Interestingly, urinary sIgA levels correlated significantly to PIgR expression and fibrosis, as well as to plasma creatinine and urea levels (Table 2). This pattern is consistent with the pathology and extent of tubular PIgR expression in the different diseases. A wide range of sIgA levels was observed within patient samples, probably explained by the different degree of structural changes in the kidney caused by age and the severity of the disease. Plasma sIgA levels were elevated compared with healthy controls throughout all of the diseases, including minimal change disease, in which no change in urine sIgA was seen, strongly arguing that increased levels in urine were not simply a reflection of increased levels in plasma (Figure 5B). However, no significant correlations between plasma sIgA levels and PIgR expression or degree of renal injury were found (Table 2). These results indicate that the amount of sIgA detected in urine is more dependent on PIgR expression level and transport activity in the kidney, rather than on the amount of sIgA present in the blood. Interestingly, a significant correlation between urinary sIgA levels and increased plasma levels of creatinine and urea, established markers of impaired kidney function, was also observed (Table 2). Immune cell infiltrates are commonly seen in injured kidneys. To investigate a potential role of factors secreted from these immune cells in the induction of tubular PIgR expression, primary tubular cells were isolated from human kidney cortex. Both mRNA (Figure 6A) and protein (Figure 6C) levels of PIgR were significantly higher after culture of tubular cells in conditioned medium from human peripheral blood mononuclear cells activated with lipopolysaccharide compared with control medium. A significant increase in PIGR expression at both the mRNA and protein levels was also seen when cells were stimulated with IFN-γ (Figure 6, B and C), IL-1β (Figure 6, D and G), and TNF-α (Figure 6, E and G), three cytokines known to be involved in the inflammatory response to injury. Contrarily, treatment with the anti-inflammatory cytokine transforming growth factor-β1 resulted in a significant decrease in PIGR mRNA and protein levels (Figure 6, F and H). These results suggest that inflammatory cytokines, secreted by leukocytes recruited to the injured kidney, induce the expression of PIgR in proximal tubular epithelial cells. To confirm that proximal tubule epithelial cells of the kidney are capable of PIgR-mediated transcytosis of IgA, an in vitro transport assay was performed. A confluent layer of human tubular cells was cultured on permeable membranes in 6-well plates. Isolated human IgA was added to the lower compartment; and after 24 hours, the presence of transported IgA in the medium, determined as the amount of IgA linked to a secretory component, was analyzed using a sandwich enzyme-linked immunosorbent assay. Indeed, secretory IgA was found in the upper compartment and, furthermore, when cells were pretreated with IFN-γ to increase PIgR expression, a significant increase in transported sIgA levels was seen (Figure 6I). These results confirm that PIgR, expressed by cultured tubular cells, is functional and capable of performing transcytosis of IgA by taking up dIgA and transporting it across the cell; at the same time, it turns dIgA into sIgA by addition of the secretory component. Finally, to get a more comprehensive understanding of PIGR expression, a cross-organ correlation analysis using data from the GTEx portal from eight different tissue" @default.
• W2967578945 created "2019-08-22" @default.
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• W2967578945 date "2019-10-01" @default.
• W2967578945 modified "2023-10-01" @default.
• W2967578945 title "Localization and Regulation of Polymeric Ig Receptor in Healthy and Diseased Human Kidney" @default.
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