Author Correction: Glomerulocapillary miRNA response to HLA-class I antibody in vitro and in vivo.

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Recommendations for mRNA analysis of micro-dissected glomerular tufts from paraffin-embedded human kidney biopsy samples.

BACKGROUND: Glomeruli are excellent pre-determined natural structures for laser micro-dissection. Compartment-specific glomerular gene expression analysis of formalin-fixed paraffin-embedded renal biopsies could improve research applications. The major challenge for such studies is to obtain good-quality RNA from small amounts of starting material, as applicable for the analysis of glomerular compartments. In this work, we provide data and recommendations for an optimized workflow of glomerular mRNA analysis. RESULTS: With a proper resolution of the camera and screen provided by the next generation of micro-dissection systems, we are able to separate parietal epithelial cells from glomerular tufts. Selected compartment-specific transcripts (WT1 and GLEPP1 for glomerular tuft as well as PAX2 for parietal epithelial cells) seem to be reliable discriminators for these micro-dissected glomerular substructures. Using the phenol-chloroform extraction and hemalaun-stained sections (2 µm), high amounts of Bowman's capsule transections (> 300) reveal sufficient RNA concentrations (> 300 ng mRNA) for further analysis. For comparison, in unstained sections from a number of 60 glomerular transections upwards, a minimum amount of 157 ng mRNA with a reasonable mRNA purity [A260/A280 ratio of 1.5 (1.4/1.7) median (25th/75th percentiles)] was reversely transcribed into cDNA. Comparing the effect of input RNA (20, 60, 150 and 300 micro-dissected glomerular transections), transcript expression of POLR2A significantly correlated when 60 and 150 laser micro-dissected glomerular transections were used for analysis. There was a lower inter-assay coefficient of variability for ADAMTS13, when at least 60 glomerular transections were used. According to the algorithms of geNormPlus and NormFinder, PGK1 and PPIA are more stable glomerular reference transcripts compared to GUSB, GAPDH, POLR2A, RPLPO, TBP, B2M, ACTB, 18SrRNA and HMBS. CONCLUSIONS: Our approach implements compartment-specific glomerular mRNA expression analysis into research applications, even regarding glomerular substructures like parietal epithelial cells. We recommend using of at least 60 micro-dissected unstained glomerular or 300 hemalaun-stained Bowman's capsule transections to obtain sufficient input mRNA for reproducible results. Hereby, the range of RNA concentrations in 60 micro-dissected glomeruli is low and appropriate normalization of Cq values using our suggested reference transcripts (PGK1 and PPIA) allows compensation with respect to different amounts of RNA purity and quantity.

Glomerulocapillary miRNA response to HLA-class I antibody in vitro and in vivo.

Changes in miRNA expression glomerular of capillaries during antibody-mediated rejection (ABMR) are poorly understood and could contribute to the deleterious inflammation and fibrosis of ABMR via suppression of target genes. A better understanding could lead to novel diagnostic tools and reveal novel therapeutic targets. We explored deregulated miRNAs in an glomeruloendothelial in vitro model of ABMR due to class I human leukocyte antigen (HLA) with and without complement activation. We studied a set of 16 promising candidate miRNAs in microdissected glomeruli a confirmation set of 20 human transplant biopsies (DSA+) compared to 10 matched controls without evidence for ABMR. Twelve out of these 16 glomerulocapillary miRNAs could successfully be confirmed as dysregulated in vivo with 10 upregulated (let-7c-5p, miR-28-3p, miR-30d-5p, miR-99b-5p, miR-125a-5p, miR-195-5p, miR-374b-3p, miR-484, miR-501-3p, miR-520e) and 2 downregulated (miR29b-3p, miR-885-5p) in DSA+ vs. CONTROLS: A random forest analysis based on glomerular miRNAs identified 18/20 DSA+ and 8/10 controls correctly. This glomerulocapillary miRNA signature associated with HLA class I-DSA could improve our understanding of ABMR and be useful for diagnostic or therapeutic purposes.

Comparison of different normalization strategies for the analysis of glomerular microRNAs in IgA nephropathy.

Small nucleolar RNAs (snoRNAs) have been used for normalization in glomerular microRNA (miRNA) quantification without confirmation of validity. Our aim was to identify glomerular reference miRNAs in IgA nephropathy. We compared miRNAs in human paraffin-embedded renal biopsies from patients with cellular-crescentic IgA-GN (n = 5; crescentic IgA-GN) and non-crescentic IgA-GN (n = 5; IgA-GN) to mild interstitial nephritis without glomerular abnormalities (controls, n = 5). Laser-microdissected glomeruli were used for expression profiling of 762 miRNAs by low-density TaqMan arrays (cards A and B). The comparison of different normalization methods (GeNormPlus, NormFinder, global mean and snoRNAs) in crescentic IgA-GN, IgA-GN and controls yielded similar results. However, levels of significance and the range of relative expression differed. In median, two normalization methods demonstrated similar results. GeNormPlus and NormFinder gave different top ranked reference miRNAs. Stability ranking for snoRNAs varied between cards A and B. In conclusion, we suggest the geometric mean of the most stable reference miRNAs found in GeNormPlus (miR-26b-5p), NormFinder (miR-28-5p) and snoRNAs (RNU44) as reference. It should be considered that significant differences could be missed using one particular normalization method. As a starting point for glomerular miRNA studies in IgA nephropathy we provide a library of miRNAs.

Immune Complex-Type Deposits in the Fischer-344 to Lewis Rat Model of Renal Transplantation and a Subset of Human Transplant Glomerulopathy.

BACKGROUND: Antibody-mediated rejection is a leading cause for renal transplant loss. Rodent models are useful to dissect pathomechanisms and to develop treatment strategies. Although used for decades as a model, glomerular histopathological findings of Fischer-344 kidneys transplanted into Lewis rats have never been comprehensively described. METHODS: Kidneys from Fischer-344 rats were transplanted into Lewis rats as life-sustaining allografts without immunosuppression. Lewis isografts and normal Fischer-344 kidneys served as controls. Grafts were harvested at 9 days, 6 and 26 weeks. Histopathological examination included light microscopy, immunohistochemistry, and morphometry. Findings were compared with 51 human biopsies with transplant glomerulopathy. RESULTS: Most glomerular findings in rat allografts resembled human acute and chronic antibody-mediated rejection with glomerulitis, microthrombosis, microaneurysms, glomerular hypertrophy, podocyte loss, glomerular basement membrane splitting, and secondary focal and segmental glomerulosclerosis. In line with previous reports on nonendothelial antigens, glomerular immunoglobulin and C4d deposition was mostly nonendothelial. Only in 26-week allografts, we found mesangial and subendothelial immune complex-type electron-dense deposits. Similar deposits were found in 8 of 51 human biopsies with transplant glomerulopathy after rigorous exclusion of immune complexes of other cause, particularly recurrent glomerulonephritis and hepatitis C. CONCLUSIONS: Thus, our model closely reflects the glomerular changes of acute antibody-mediated rejection in humans and of a special subset of human transplant glomerulopathy. The significance of alloimmune immune complex-type deposits in human transplants deserves further investigation.

Histopathological and clinical findings in renal transplants with Banff type II and III acute cellular rejection without tubulointerstitial infiltrates.

According to the Banff guidelines for renal transplants, pure endothelialitis without any tubulointerstitial infiltrates (with the Banff components v ≥ 1, i0, t0) has to be called acute cellular rejection (ACR). The pathophysiology of this rare lesion abbreviated as v_only is currently unclear, as well as its clinical, serological, and prognostic implications. Therefore, we conducted this retrospective comparative study. We compared all 23 biopsies with v_only from Hannover Medical School between 2003 and 2010 with 23 matched biopsies with the Banff components v ≥ 1, i ≥ 1, and t ≥ 1 (v_plus) and 23 biopsies with v0, i0, and t0 (v0i0t0). Serological (available in 10, 11, and 14 patients, respectively), histological, and clinical data were compared. Of all biopsies, 0.4 % had findings of v_only. v_only, v_plus, and v0i0t0 only showed minimal differences in the Banff components apart from the cohort-defining components. Endothelialitis in v_only more frequently involved the arcuate arteries than the smaller preglomerular vessels compared to v_plus and vice versa. Combining histopathological data and serological data, v_only more frequently showed criteria for acute humoral rejection than v0i0t0 (albeit not persistent after the Bonferroni-Holm correction in pairwise comparisons), while there was no difference between v_only and v_plus. No difference could be demonstrated regarding clinical presentation at biopsy or outcome. Our results show minimal differences regarding clinical presentation, outcome, and histological features between v_only and v_plus. Patients with v_only should be thoroughly investigated for evidence of acute humoral rejection.

Glomerular mRNA expression of prothrombotic and antithrombotic factors in renal transplants with thrombotic microangiopathy.

BACKGROUND: Thrombotic microangiopathy (TMA) in renal transplants (rTx-TMA) is a serious complication and is usually either recurrent TMA (RecTMA) due to humoral rejection (HR-TMA) or due to calcineurin inhibitor toxicity (CNI-TMA). Although the triggers are known, our knowledge about the thrombogenic transcriptome changes in the microvessels is rudimentary. METHODS: We examined the expression of several prothrombotic and antithrombotic genes in 25 biopsies with rTx-TMA (6 RecTMA, 9 HR-TMA, and 10 CNI-TMA) and 8 controls. RNA from microdissected glomeruli of paraffin-embedded tissue was isolated and mRNA transcripts were quantified with real-time polymerase chain reaction after preamplification. Results were correlated with clinicopathologic parameters. RESULTS: Glomerular mRNA expression of KLF2, KLF4, and tPA was lower and that of PAI-1 was higher in rTx-TMA than in the controls. Glomerular mRNA expression of KLF2 and KLF4 correlated with that of tPA and inversely with that of PAI-1 in rTx-TMA. The mRNA expression of complement regulators CD46 and CD59 were higher in rTx-TMA than in the controls. Only in HR-TMA were glomerular ADAMTS13 and CD55 down-regulated. CONCLUSIONS: The glomerular capillary bed seems to contribute to all subtypes of rTx-TMA by down-regulation of the endothelial transcription factors KLF2 and KLF4, indicating dedifferentiation with subsequent up-regulation of PAI-1 and down-regulation of tPA, resulting in inhibition of local fibrinolysis. Decreased glomerular expression of ADAMTS13 and CD55 could be an additional pathway toward microthrombosis exclusively in HR-TMA.

Comprehensive analysis of glomerular mRNA expression of pro- and antithrombotic genes in atypical haemolytic-uremic syndrome (aHUS).

Atypical haemolytic-uremic syndrome (aHUS) is, in most cases, due to hereditary or acquired defects in complement regulation and a life-threatening disease. Despite the rapidly grown knowledge about the primary defects in aHUS, the pathogenesis that links complement dysregulation with microthrombus formation in aHUS is still unknown. Thus, we examined the glomerular microvascular expression of pro- and antithrombotic genes. Glomeruli were microdissected from 12 archival paraffin-embedded biopsies with aHUS and from seven control biopsies. Glomerular mRNA expression was quantified by single real-time PCR reactions after preamplification. In addition immunostains were performed for plasminogen activator inhibitor 1 (PAI-1) and for tissue plasminogen activator (tPA). Results were compared between cases and controls and with clinical data. Glomeruli in aHUS had increased mRNA expression of antifibrinolytic, prothrombotic PAI-1, antithrombotic thrombomodulin (THBD) and CD73 and decreased expression of profibrinolytic, antithrombotic tPA compared to controls. Impaired fibrinolysis due to increased microvascular expression of the antifibrinolytic PAI-1 in combination with the decreased expression of the profibrinolytic tPA seems to be a final common pathway in renal thrombotic microangiopathy that is also effective in aHUS. The concomitant induction of antithrombotic transcripts likely indicates counterregulatory efforts, demonstrating that the capillary bed is not a passive victim of complement attack. Future research should investigate if and how complement activation could induce the reported shift in the expression of PAI-1 and tPA.