Baker Grade IV Capsular Contracture Is Correlated with an Increased Amount of Silicone Material: An Intrapatient Study.

BACKGROUND: Breast implant surgery is one of the most frequently performed procedures by plastic surgeons worldwide. However, the relationship between silicone leakage and the most common complication, capsular contracture, is far from understood. This study aimed to compare Baker grade I with Baker grade IV capsules regarding their silicone content in an intradonor setting, using two previously validated imaging techniques. METHODS: Twenty-two donor-matched capsules from 11 patients experiencing unilateral complaints were included after bilateral explantation surgery. All capsules were examined using both stimulated Raman scattering (SRS) imaging and staining with modified oil red O (MORO). Evaluation was done visually for qualitative and semiquantitative assessment and automated for quantitative analysis. RESULTS: Using both SRS and MORO techniques, silicone was found in more Baker grade IV capsules (eight of 11 and 11 of 11, respectively) than in Baker grade I capsules (three of 11 and five of 11, respectively). Baker grade IV capsules also showed significantly more silicone content compared with the Baker grade I capsules. This was true for semiquantitative assessment for both SRS and MORO techniques ( P = 0.019 and P = 0.006, respectively), whereas quantitative analysis proved to be significant for MORO alone ( P = 0.026 versus P = 0.248 for SRS, respectively). CONCLUSIONS: In this study, a significant correlation between capsule silicone content and capsular contracture is shown. An extensive and continued foreign body response to silicone particles is likely to be responsible. Considering the widespread use of silicone breast implants, these results affect many women worldwide and warrant a more focused research effort. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

Kidney Disease Associated With Mono-allelic COL4A3 and COL4A4 Variants: A Case Series of 17 Families.

Rationale & Objective: Mono-allelic variants in COL4A3 and COL4A4 (COL4A3/COL4A4) have been identified in a spectrum of glomerular basement membrane nephropathies, including thin basement membrane nephropathy and autosomal dominant Alport syndrome. With the increasing use of next generation sequencing, mono-allelic COL4A3/COL4A4 variants are detected more frequently, but phenotypic heterogeneity impedes counseling. We aimed to investigate the phenotypic spectrum, kidney biopsy results, and segregation patterns of patients with mono-allelic COL4A3/COL4A4 variants identified by whole exome sequencing. Study Design: Case series. Setting & Participants: We evaluated clinical and pathologic characteristics of 17 Dutch index patients with mono-allelic variants in COL4A3/COL4A4 detected by diagnostic whole exome sequencing and 25 affected family members with variants confirmed by Sanger sequencing. Results: Eight different mono-allelic COL4A3/COL4A4 variants were identified across members of 11 families, comprising 7 glycine substituted missense variants and 1 frameshift variant. All index patients had microscopic hematuria at clinical presentation (median age 43 years) and 14 had (micro)albuminuria/proteinuria. All family members showed co-segregation of the variant with at least hematuria. At end of follow-up of all 42 individuals (median age 54 years), 16/42 patients had kidney function impairment, of whom 6 had kidney failure. Reports of kidney biopsies of 14 patients described thin basement membrane nephropathy, focal segmental glomerulosclerosis, minimal change lesions, and Alport syndrome. Electron microscopy images of 7 patients showed a significantly thinner glomerular basement membrane compared with images of patients with idiopathic focal segmental glomerulosclerosis and other hereditary glomerular diseases. No genotype-phenotype correlations could be established. Limitations: Retrospective design, ascertainment bias toward severe kidney phenotypes, and familial hematuria. Conclusions: This study confirms the wide phenotypic spectrum associated with mono-allelic COL4A3/COL4A4 variants, extending from isolated microscopic hematuria to kidney failure with high intra- and interfamilial variability.

Case Report: Evidence of Migratory Silicone Particles Arising From Cohesive Silicone Breast Implants.

Background: Silicone implants have been used since the 1960s for aesthetic purposes and breast reconstructions. During this period, many women have reported up to 40 similar symptoms, including fatigue, the emergence of autoimmune diseases, Raynaud Phenomenon, arthritis, arthralgias, and hair loss, among others. However, most of the time, these symptoms are neglected by doctors across different specialties and are most often considered a psychosomatic disease. Since 2017, many women suffering from the same complaints have formed social media groups to report their histories and subsequently describe the disease as Breast Implant Illness (BII). The phenomenon of gel bleed and silicone toxicity is known and accepted in literature, but silicone migration into the extracapsular space is still poorly demonstrated, due to the difficulty of monitoring its particles and access to patient data. Methods: This work demonstrated the presence of silicone through pathological examination in post-explant breast capsules and in the synovial tissue of the right wrist, detected with special Modified Oil Red O (MORO) staining in a patient with a history of BII. The pathological results were compared to the breast MRI imaging files. Results: The MRI images show the permeability change of the implant shell diagnosed as a water-droplet signal. It was also possible to diagnose the gel bleeding as the silicone-induced granuloma of breast implant capsule (SIGBIC) in both implants. Silicone gel bleed and migration of silicone were detected with MORO staining in and outside the capsule and in the synovial tissue of the right wrist. Conclusion: In this case study, we showed that silicone migration is possible via cohesive silicone gel breast implant leakage. The accumulation of silicone in the synovial tissue of the right wrist suggests local silicone toxicity and defects.

Motile Cilia on Kidney Proximal Tubular Epithelial Cells Are Associated With Tubular Injury and Interstitial Fibrosis.

It is well established that mammalian kidney epithelial cells contain a single non-motile primary cilium (9 + 0 pattern). However, we noted the presence of multiple motile cilia with a central microtubular pair (9 + 2 pattern) in kidney biopsies of 11 patients with various kidney diseases, using transmission electron microscopy. Immunofluorescence staining revealed the expression of the motile cilia-specific markers Radial Spoke Head Protein 4 homolog A, Forkhead-box-protein J1 and Regulatory factor X3. Multiciliated cells were exclusively observed in proximal tubuli and a relative frequent observation in human kidney tissue: in 16.7% of biopsies with tubular injury and atrophy (3 of 18 tissues), in 17.6% of biopsies from patients with membranous nephropathy (3 of 17 tissues) and in 10% of the human kidney tissues derived from the unaffected pole after tumour nephrectomy (3 of 30 tissues). However, these particular tissues showed marked tubular injury and fibrosis. Further analysis showed a significant relation between the presence of multiciliated cells and an increased expression of alpha-smooth-muscle-actin (p-value < 0.01) and presence of Kidney-injury-molecule-1 (p-value < 0.01). Interestingly, multiciliated cells co-showed staining for the scattered tubular cell markers annexin A2, annexin A3, vimentin and phosphofructokinase platelet but not with cell senescence associated markers, like (p16) and degradation of lamin B. In conclusion, multiciliated proximal tubular cells with motile cilia were frequently observed in kidney biopsies and associated with tubular injury and interstitial fibrosis. These data suggest that proximal tubular cells are able to transdifferentiate into multiciliated cells.

Kidney tubule iron loading in experimental focal segmental glomerulosclerosis.

Kidney iron deposition may play a role in the progression of tubulointerstitial injury during chronic kidney disease. Here, we studied the molecular mechanisms of kidney iron loading in experimental focal segmental glomerulosclerosis (FSGS) and investigated the effect of iron-reducing interventions on disease progression. Thy-1.1 mice were injected with anti-Thy-1.1 monoclonal antibody (mAb) to induce proteinuria. Urine, blood and tissue were collected at day (D)1, D5, D8, D15 and D22 after mAb injection. Thy-1.1 mice were subjected to captopril (CA), iron-deficient (ID) diet or iron chelation (deferoxamine; DFO). MAb injection resulted in significant albuminuria at all time points (p < 0.01). Kidney iron loading, predominantly in distal tubules, increased in time, along with urinary kidney injury molecule-1 and 24p3 concentration, as well as kidney mRNA expression of Interleukin-6 (Il-6) and Heme oxygenase-1 (Ho-1). Treatment with CA, ID diet or DFO significantly reduced kidney iron deposition at D8 and D22 (p < 0.001) and fibrosis at D22 (p < 0.05), but not kidney Il-6. ID treatment increased kidney Ho-1 (p < 0.001). In conclusion, kidney iron accumulation coincides with progression of tubulointerstitial injury in this model of FSGS. Reduction of iron loading halts disease progression. However, targeted approaches to prevent excessive kidney iron loading are warranted to maintain the delicate systemic and cellular iron balance.

Assessment of Silicone Particle Migration Among Women Undergoing Removal or Revision of Silicone Breast Implants in the Netherlands.

Importance: Silicone breast implants have been on the market for breast augmentation or breast reconstruction for approximately 60 years but may lead to medical complications, also called breast implant illness. Objective: To evaluate the existence of silicone gel bleed and migration over a long time period, including the period in which the newer cohesive silicone gel breast implants were used. Design, Setting, and Participants: In this single-center case series, capsule tissue and lymph node samples were collected from women who underwent removal or revision of silicone breast implants from January 1, 1986, to August 18, 2020, and data were extracted from the pathological reports and revision of the histology if data were missing. All tissues were examined using standard light microscopy, some extended with modified oil red O staining and energy-dispersive radiographic spectroscopy. A total of 365 women had capsular tissue removed, including 15 patients who also had lymph nodes removed, and 24 women had only lymph nodes removed. Data were analyzed from January to May 2021. Exposures: Silicone breast implants. Main Outcomes and Measures: The main outcome was presence or absence of silicones inside or outside the capsule. One-way analysis of variance was used to determine significance between groups. Results: Among a total of 389 women with silicone breast implants (mean [SD] age, 50.5 [11.2] years), 384 women (98.8%) had silicone particles present in the tissues, indicating silicone gel bleed. In 337 women (86.6%), silicone particles were observed outside the capsule (ie, in tissues surrounding the capsule and/or lymph nodes), indicating silicone migration. In 47 women (12.1%), silicone particles were only present within the capsule. In 5 women (1.2%), no silicone particles were detected in the tissues. Patients were divided into 2 groups, with 46 women who received cohesive silicone gel breast implants and 343 women who received either an older or a newer type of breast implant. There were no differences in silicone gel bleed or migration between groups (silicone detected outside or inside capsule: 44 women [95.7%] vs 340 women [99.1%]; P = .19). Conclusions and Relevance: In this case series including women with noncohesive or cohesive silicone gel breast implants, silicone leakage occurred in 98.8% of women, indicating silicone gel bleed, and in 86.6% of women, migration of silicone particles outside the capsule was detected.

Interleukin-6 is essential for glomerular immunoglobulin A deposition and the development of renal pathology in Cd37-deficient mice.

Immunoglobulin A (IgA) nephropathy (IgAN), the most common glomerulonephritis worldwide, is characterized by IgA depositions in the kidney. Deficiency of CD37, a leukocyte-specific tetraspanin, leads to spontaneous development of renal pathology resembling IgAN. However, the underlying molecular mechanism has not been resolved. Here we found that CD37 expression on B cells of patients with IgAN was significantly decreased compared to B cells of healthy donors. Circulating interleukin (IL)-6 levels, but not tumor necrosis factor-α or IL-10, were elevated in Cd37-/- mice compared to wild-type mice after lipopolysaccharide treatment. Cd37-/- mice displayed increased glomerular neutrophil influx, immune complex deposition, and worse renal function. To evaluate the role of IL-6 in the pathogenesis of accelerated renal pathology in Cd37-/-mice, we generated Cd37xIl6 double-knockout mice. These double-knockout and Il6-/- mice displayed no glomerular IgA deposition and were protected from exacerbated renal failure following lipopolysaccharide treatment. Moreover, kidneys of Cd37-/- mice showed more mesangial proliferation, endothelial cell activation, podocyte activation, and segmental podocyte foot process effacement compared to the double-knockout mice, emphasizing that IL-6 mediates renal pathology in Cd37-/- mice. Thus, our study indicates that CD37 may protect against IgA nephropathy by inhibition of the IL-6 pathway.

CD44 is required for the pathogenesis of experimental crescentic glomerulonephritis and collapsing focal segmental glomerulosclerosis.

A key feature of glomerular diseases such as crescentic glomerulonephritis and focal segmental glomerulosclerosis is the activation, migration and proliferation of parietal epithelial cells. CD44-positive activated parietal epithelial cells have been identified in proliferative cellular lesions in glomerular disease. However, it remains unknown whether CD44-positive parietal epithelial cells contribute to the pathogenesis of scarring glomerular diseases. Here, we evaluated this in experimental crescentic glomerulonephritis and the transgenic anti-Thy1.1 model for collapsing focal segmental glomerulosclerosis in CD44-deficient (cd44-/-) and wild type mice. For both models albuminuria was significantly lower in cd44-/- compared to wild type mice. The number of glomerular Ki67-positive proliferating cells was significantly reduced in cd44-/- compared to wild type mice, which was associated with a reduced number of glomerular lesions in crescentic glomerulonephritis. In collapsing focal segmental glomerulosclerosis, the extracapillary proliferative cellular lesions were smaller in cd44-/- mice, but the number of glomerular lesions was not different compared to wild type mice. For crescentic glomerulonephritis the influx of granulocytes and macrophages into the glomerulus was similar. In vitro, the growth of CD44-deficient murine parietal epithelial cells was reduced compared to wild type parietal epithelial cells, and human parietal epithelial cell migration could be inhibited using antibodies directed against CD44. Thus, CD44-positive proliferating glomerular cells, most likely parietal epithelial cells, are essential in the pathogenesis of scarring glomerular disease.

Cathepsin L is crucial for the development of early experimental diabetic nephropathy.

Proteinuria is one of the first clinical signs of diabetic nephropathy and an independent predictor for the progression to renal failure. Cathepsin L, a lysosomal cysteine protease, can be involved in the development of proteinuria by degradation of proteins that are important for normal podocyte architecture, such as the CD2-associated protein, synaptopodin, and dynamin. Cathepsin L also activates heparanase, a heparan sulfate endoglycosidase previously shown to be crucial for the development of diabetic nephropathy. Here, we evaluated the exact mode of action of cathepsin L in the development of proteinuria in streptozotocin-induced diabetes. Cathepsin L-deficient mice, in contrast to their wild-type littermates, failed to develop albuminuria, mesangial matrix expansion, tubulointerstitial fibrosis, and renal macrophage influx and showed a normal renal function. In wild-type mice the early development of albuminuria correlated with the activation of heparanase and loss of heparan sulfate expression, whereas loss of synaptopodin expression and podocyte damage occurred at a later stage. Thus, cathepsin L is causally involved in the pathogenesis of experimental diabetic nephropathy. Most likely, cathepsin L-dependent heparanase activation is crucial for the development of albuminuria and renal damage.

Distribution and Function of PACAP and Its Receptors in the Healthy and Nephrotic Kidney.

BACKGROUND/AIMS: Plasma deficiency of pituitary adenylate cyclase-activating polypeptide (PACAP) was recently demonstrated in children with nephrotic syndrome (NS). Previous studies have reported an important protective effect of PACAP on kidney proximal tubules. The aim of this study was to explore the expression of PACAP and its receptors PAC1, VPAC1 and VPAC2 in the healthy and nephrotic kidney and to determine if PACAP has an effect on renal proximal tubular cells exposed to albumin. METHODS: Expression of PACAP and its receptors was studied using kidney tissue from healthy and nephrotic children, and in 3 human renal cell lines (glomerular microvascular endothelial cells, podocytes and proximal tubular epithelial HK-2 cells). The functionality of the VPAC1 receptor was tested in HK-2 cells, measuring cyclic adenosine monophosphate levels after PACAP exposure. The influence of PACAP on cell viability and transforming growth factor-ß1 (TGF-ß1) expression was measured in HK-2 cells exposed to albumin, mimicking proteinuria related damage. RESULTS: VPAC1 expression was detected in the tubular proximal epithelial cells and in the glomerular podocytes of renal tissue from healthy and nephrotic children. Increased staining for PACAP was found in the proximal tubules of renal sections from children with NS compared to healthy renal sections. Expression and functionality of VPAC1 were demonstrated in HK-2 cells. Finally, PACAP did not alter cell viability or TGF-ß1 expression of HK-2 cells exposed to albumin. CONCLUSION: VPAC1 is the predominant receptor in the human kidney. The enhanced presence of PACAP in proximal tubular epithelial cells in nephrotic kidneys points to the reabsorption of filtered PACAP. On short term, PACAP has no in vitro effect on cell viability and TGF-ß1 expression of proximal tubular epithelial cells exposed to high concentrations of albumin.

Heparanase Is Essential for the Development of Acute Experimental Glomerulonephritis.

Heparanase, a heparan sulfate (HS)--specific endoglucuronidase, mediates the onset of proteinuria and renal damage during experimental diabetic nephropathy. Glomerular heparanase expression is increased in most proteinuric diseases. Herein, we evaluated the role of heparanase in two models of experimental glomerulonephritis, being anti-glomerular basement membrane and lipopolysaccharide-induced glomerulonephritis, in wild-type and heparanase-deficient mice. Induction of experimental glomerulonephritis led to an increased heparanase expression in wild-type mice, which was associated with a decreased glomerular expression of a highly sulfated HS domain, and albuminuria. Albuminuria was reduced in the heparanase-deficient mice in both models of experimental glomerulonephritis, which was accompanied by a better renal function and less renal damage. Notably, glomerular HS expression was preserved in the heparanase-deficient mice. Glomerular leukocyte and macrophage influx was reduced in the heparanase-deficient mice, which was accompanied by a reduced expression of both types 1 and 2 helper T-cell cytokines. In vitro, tumor necrosis factor-α and lipopolysaccharide directly induced heparanase expression and increased transendothelial albumin passage. Our study shows that heparanase contributes to proteinuria and renal damage in experimental glomerulonephritis by decreasing glomerular HS expression, enhancing renal leukocyte and macrophage influx, and affecting the local cytokine milieu.

Circulating Apoptotic Microparticles in Systemic Lupus Erythematosus Patients Drive the Activation of Dendritic Cell Subsets and Prime Neutrophils for NETosis.

OBJECTIVE: Circulating chromatin-containing apoptotic material and/or neutrophil extracellular traps (NETs) have been proposed to be an important driving force for the antichromatin autoimmune response in patients with systemic lupus erythematosus (SLE). The aim of this study was to determine the exact nature of microparticles in the circulation of SLE patients and to assess the effects of the microparticles on the immune system. METHODS: We analyzed microparticles isolated from the plasma of patients with SLE, rheumatoid arthritis (RA), and systemic sclerosis (SSc), as well as from healthy subjects. The effects of the microparticles on blood-derived dendritic cells (DCs) and neutrophils were assessed by flow cytometry, enzyme-linked immunosorbent assay, and immunofluorescence microscopy. RESULTS: In SLE patients, we identified microparticles that were highly positive for annexin V and apoptosis-modified chromatin that were not present in healthy subjects or in RA or SSc patients. These microparticles were mostly CD31+/CD45- (endothelial), partly CD45+/CD66b+ (granulocyte), and negative for B and T cell markers. Microparticles isolated from the plasma of SLE patients increased the expression of the costimulatory surface molecules CD40, CD80, CD83, and CD86 and the production of proinflammatory cytokines interleukin-6, tumor necrosis factor, and interferon-α by blood-derived plasmacytoid DCs (PDCs) and myeloid DCs (MDCs). SLE microparticles also primed blood-derived neutrophils for NETosis. Microparticles from healthy subjects and from RA or SSc patients exhibited no significant effects on MDCs, PDCs, and NETosis. CONCLUSION: Circulating microparticles in SLE patients include a population of apoptotic cell-derived microparticles that has proinflammatory effects on PDCs and MDCs and enhances NETosis. These results underline the important role of apoptotic microparticles in driving the autoimmune response in SLE patients.

Enhanced activation of dendritic cells by autologous apoptotic microvesicles in MRL/lpr mice.

INTRODUCTION: Systemic lupus erythematosus is associated with a persistent circulation of modified autoantigen-containing apoptotic debris that might be capable of breaking tolerance. We aimed to evaluate apoptotic microvesicles obtained from lupus or control mice for the presence of apoptosis-associated chromatin modifications and for their capacity to stimulate dendritic cells (DC) from lupus and control mice. METHOD: Apoptotic microvesicles were in vitro generated from splenocytes, and ex vivo isolated from plasma of both MRL/lpr lupus mice and normal BALB/c mice. Microvesicles were analyzed using flow cytometry. Bone marrow-derived (BM)-DC cultured from MRL/lpr or BALB/c mice were incubated with microvesicles and CD40 expression and cytokine production were determined as measure of activation. RESULTS: Microvesicles derived from apoptotic splenocytes or plasma of MRL/lpr mice contained more modified chromatin compared to microvesicles of BALB/c mice, and showed enhanced activation of DC, either from MRL/lpr or BALB/c mice, and consecutively an enhanced DC-mediated activation of splenocytes. The content of apoptosis-modified chromatin in microvesicles of apoptotic splenocytes correlated with their potency to induce interleukin-6 (IL-6) production by DC. Microvesicle-activated MRL/lpr DC showed a significant higher production of IL-6 and tumor growth factor-ß (TGF-ß) compared to BALB/c DC, and were more potent in the activation of splenocytes. CONCLUSION: Apoptotic microvesicles from MRL/lpr mice are more potent activators of DC, and DC from MRL/lpr mice appear relatively more sensitive to activation by apoptotic microvesicles. Our findings indicate that aberrations at the level of apoptotic microvesicles and possibly DC contribute to the autoimmune response against chromatin in MRL/lpr mice.

Endo-lysosomal dysfunction in human proximal tubular epithelial cells deficient for lysosomal cystine transporter cystinosin.

Nephropathic cystinosis is a lysosomal storage disorder caused by mutations in the CTNS gene encoding cystine transporter cystinosin that results in accumulation of amino acid cystine in the lysosomes throughout the body and especially affects kidneys. Early manifestations of the disease include renal Fanconi syndrome, a generalized proximal tubular dysfunction. Current therapy of cystinosis is based on cystine-lowering drug cysteamine that postpones the disease progression but offers no cure for the Fanconi syndrome. We studied the mechanisms of impaired reabsorption in human proximal tubular epithelial cells (PTEC) deficient for cystinosin and investigated the endo-lysosomal compartments of cystinosin-deficient PTEC by means of light and electron microscopy. We demonstrate that cystinosin-deficient cells had abnormal shape and distribution of the endo-lysosomal compartments and impaired endocytosis, with decreased surface expression of multiligand receptors and delayed lysosomal cargo processing. Treatment with cysteamine improved surface expression and lysosomal cargo processing but did not lead to a complete restoration and had no effect on the abnormal morphology of endo-lysosomal compartments. The obtained results improve our understanding of the mechanism of proximal tubular dysfunction in cystinosis and indicate that impaired protein reabsorption can, at least partially, be explained by abnormal trafficking of endosomal vesicles.

Hyperuricemia influences tryptophan metabolism via inhibition of multidrug resistance protein 4 (MRP4) and breast cancer resistance protein (BCRP).

Hyperuricemia is related to a variety of pathologies, including chronic kidney disease (CKD). However, the pathophysiological mechanisms underlying disease development are not yet fully elucidated. Here, we studied the effect of hyperuricemia on tryptophan metabolism and the potential role herein of two important uric acid efflux transporters, multidrug resistance protein 4 (MRP4) and breast cancer resistance protein (BCRP). Hyperuricemia was induced in mice by treatment with the uricase inhibitor oxonic acid, confirmed by the presence of urate crystals in the urine of treated animals. A transport assay, using membrane vesicles of cells overexpressing the transporters, revealed that uric acid inhibited substrate-specific transport by BCRP at clinically relevant concentrations (calculated IC50 value: 365±13µM), as was previously reported for MRP4. Moreover, we identified kynurenic acid as a novel substrate for MRP4 and BCRP. This finding was corroborated by increased plasma levels of kynurenic acid observed in Mrp4(-/-) (107±19nM; P=0.145) and Bcrp(-/-) mice (133±10nM; P=0.0007) compared to wild type animals (71±11nM). Hyperuricemia was associated with >1.5 fold increase in plasma kynurenine levels in all strains. Moreover, hyperuricemia led to elevated plasma kynurenic acid levels (128±13nM, P=0.005) in wild type mice but did not further increase kynurenic acid levels in knockout mice. Based on our results, we postulate that elevated uric acid levels hamper MRP4 and BCRP functioning, thereby promoting the retention of other potentially toxic substrates, including kynurenic acid, which could contribute to the development of CKD.

Proximal tubular cells contain a phenotypically distinct, scattered cell population involved in tubular regeneration.

Regeneration of injured tubular cells occurs after acute tubular necrosis primarily from intrinsic renal cells. This may occur from a pre-existing intratubular stem/progenitor cell population or from any surviving proximal tubular cell. In this study, we characterize a CD24-, CD133-, and vimentin-positive subpopulation of cells scattered throughout the proximal tubule in normal human kidney. Compared to adjacent 'normal' proximal tubular cells, these CD24-positive cells contained less cytoplasm, fewer mitochondria, and no brush border. In addition, 49 marker proteins are described that are expressed within the proximal tubules in a similar scattered pattern. For eight of these markers, we confirmed co-localization with CD24. In human biopsies of patients with acute tubular necrosis (ATN), the number of CD24-positive tubular cells was increased. In both normal human kidneys and the ATN biopsies, around 85% of proliferating cells were CD24-positive - indicating that this cell population participates in tubular regeneration. In healthy rat kidneys, the novel cell subpopulation was absent. However, upon unilateral ureteral obstruction (UUO), the novel cell population was detected in significant amounts in the injured kidney. In summary, in human renal biopsies, the CD24-positive cells represent tubular cells with a deviant phenotype, characterized by a distinct morphology and marker expression. After acute tubular injury, these cells become more numerous. In healthy rat kidneys, these cells are not detectable, whereas after UUO, they appeared de novo - arguing against the notion that these cells represent a pre-existing progenitor cell population. Our data indicate rather that these cells represent transiently dedifferentiated tubular cells involved in regeneration.

Secondary, somatic mutations might promote cyst formation in patients with autosomal dominant polycystic liver disease.

BACKGROUND & AIMS: Heterozygous germline mutations in PRKCSH cause autosomal dominant polycystic liver disease (PCLD), but it is not clear how they lead to cyst formation. We investigated whether mutations in cyst epithelial cells and corresponding loss of the PRKCSH gene product (hepatocystin) contributed to cyst development. METHODS: Liver cyst material was collected through laparoscopic cyst fenestration from 8 patients with PCLD who had a heterozygous germline mutation in PRKCSH. Tissue sections from 71 cysts (2-14 per patient) were obtained for hepatocystin staining and mutation analysis. Cyst epithelium was acquired using laser microdissection; DNA was isolated and analyzed for loss of heterozygosity (LOH) and somatic mutations using restriction analysis and sequencing. Common single nucleotide polymorphisms (SNPs) in a 70-kilobase region surrounding the germline mutation were used to determine variations in the genomic region with LOH. RESULTS: The wild-type allele of PRKCSH was lost (LOH) in 76% of cysts (54/71). Hepatocystin was not detected in cyst epithelia with LOH, whereas heterozygous cysts still expressed hepatocystin. The variation observed in the LOH region analysis indicates that cysts develop independently. We also detected somatic mutations in PRKCSH in 17% (2/12) of the cysts without LOH. Trans-heterozygous mutations in SEC63 were not observed. CONCLUSIONS: Among patients with PCLD who have a heterozygous germline mutation in PRKCSH, we found secondary, somatic mutations (second hits) in more than 76% of the liver cyst epithelia. PCLD is recessive at the cellular level, and loss of functional PRKCSH is an important step in cystogenesis.

The tetraspanin CD37 protects against glomerular IgA deposition and renal pathology.

The tetraspanin protein CD37 is a leukocyte-specific transmembrane protein that is highly expressed on B cells. CD37-deficient (CD37(-/-)) mice exhibit a 15-fold increased level of immunoglobulin A (IgA) in serum and elevated numbers of IgA+ plasma cells in lymphoid organs. Here, we report that CD37(-/-) mice spontaneously develop renal pathology with characteristics of human IgA nephropathy. In young naïve CD37(-/-) mice, mild IgA deposition in glomeruli was observed. However, CD37(-/-) mice developed high titers of IgA immune complexes in serum during aging, which was associated with increased glomerular IgA deposition. Severe mesangial proliferation, fibrosis, and hyalinosis were apparent in aged CD37(-/-) mice, whereas albuminuria was mild. To further evaluate the role of CD37 in glomerular disease, we induced anti-glomerular basement membrane (GBM) nephritis in mice. CD37(-/-) mice developed higher IgA serum levels and glomerular deposits of anti-GBM IgA compared with wild-type mice. Importantly, glomerular macrophage and neutrophil influx was significantly higher in CD37(-/-) mice during both the heterologous and autologous phase of anti-GBM nephritis. Taken together, tetraspanin CD37 controls the formation of IgA-containing immune complexes and glomerular IgA deposition, which induces influx of inflammatory myeloid cells. Therefore, CD37 may protect against the development of IgA nephropathy.

Renal progenitor cells contribute to hyperplastic lesions of podocytopathies and crescentic glomerulonephritis.

Glomerular injury can involve excessive proliferation of glomerular epithelial cells, resulting in crescent formation and obliteration of Bowman's space. The origin of these hyperplastic epithelial cells in different glomerular disorders is controversial. Renal progenitors localized to the inner surface of Bowman's capsule can regenerate podocytes, but whether dysregulated proliferation of these progenitors contributes to crescent formation is unknown. In this study, we used confocal microscopy, laser capture microdissection, and real-time quantitative reverse transcriptase-PCR to demonstrate that hypercellular lesions of different podocytopathies and crescentic glomerulonephritis consist of three distinct populations: CD133(+)CD24(+)podocalyxin (PDX)(-)nestin(-) renal progenitors, CD133(+)CD24(+)PDX(+)nestin(+) transitional cells, and CD133(-)CD24(-)PDX(+)nestin(+) differentiated podocytes. In addition, TGF-beta induced CD133(+)CD24(+) progenitors to produce extracellular matrix, and these were the only cells to express the proliferation marker Ki67. Taken together, these results suggest that glomerular hyperplastic lesions derive from the proliferation of renal progenitors at different stages of their differentiation toward mature podocytes, providing an explanation for the pathogenesis of hyperplastic lesions in podocytopathies and crescentic glomerulonephritis.

Ultrastructural proof of polyomavirus in Merkel cell carcinoma tumour cells and its absence in small cell carcinoma of the lung.

BACKGROUND: A new virus called the Merkel Cell Polyomavirus (MCPyV) has recently been found in Merkel Cell Carcinoma (MCC). MCC is a rare aggressive small cell neuroendocrine carcinoma primarily derived from the skin, morphologically indistinguishable from small cell lung carcinoma (SCLC). So far the actual presence of the virus in MCC tumour cells on a morphological level has not been demonstrated, and the presence of MCPyV in other small cell neuroendocrine carcinomas has not been studied yet. METHODOLOGY/PRINCIPAL FINDINGS: We investigated MCC tissue samples from five patients and SCLCs from ten patients for the presence of MCPyV-DNA by PCR and sequencing. Electron microscopy was used to search ultrastructurally for morphological presence of the virus in MCPyV-DNA positive samples. MCPyV was detected in two out of five primary MCCs. In one MCC patient MCPyV-DNA was detected in the primary tumour as well as in the metastasis, strongly suggesting integration of MCPyV in the cellular DNA of the tumour in this patient. In the primary MCC of another patient viral particles in tumour cell nuclei and cytoplasm were identified by electron microscopy, indicating active viral replication in the tumour cells. In none of the SCLCs MCPyV-DNA was detected. CONCLUSIONS/SIGNIFICANCE: Our results strongly suggest that MCPyV is an oncogenic polyomavirus in humans, and is potentially causally related to the development of MCC but not to the morphological similar SCLC.