No abstract

The inhibitor of apoptosis protein survivin is a bifunctional molecule that regulates cellular division and survival. We have previously shown that survivin protein can be found at high concentrations in the adult kidney, particularly in the proximal tubules. Here, survivin is localized primarily at the apical membrane, a pattern that may indicate absorption of the protein. Several proteins in primary urine are internalized by megalin, an endocytosis receptor, which is in principle found in the same localization as survivin. Immunolabeling for survivin in different species confirmed survivin signal localizing to the apical membrane of the proximal tubule. Immunoelectron microscopy also showed apical localization of survivin in human kidneys. Furthermore, in polarized human primary tubular cells endogenous as well as external recombinant survivin is stored in the apical region of the cells. Costaining of survivin and megalin by immunohistochemistry and immunoelectron microscopy confirmed colocalization. Finally, by surface plasmon resonance we were able to demonstrate that survivin binds megalin and cubilin and that megalin knockout mice lose survivin through the urine. Survivin accumulates at the apical membrane of the renal tubule by reuptake, which is achieved by the endocytic receptor megalin, collaborating with cubilin. For this to occur, survivin will have to circulate in the blood and be filtered into the primary urine. It is not known at this stage what the functional role of tubular survivin is. However, a small number of experimental and clinical reports implicate that renal survivin is important for functional integrity of the kidney.

We present the case of a 73-year-old man who developed an acute, severe febrile illness with multiorgan dysfunction, featuring renal failure, nephrotic-range proteinuria, microhematuria, and a skin rash. Numerous erythrocyte casts were found on urine microscopy. Typically, the finding of urinary erythrocyte casts indicates the presence of an underlying glomerular inflammatory disease. However, on renal biopsy, only amyloid light-chain (AL) amyloidosis and tubular injury were the predominant findings with no signs of glomerular or vascular inflammation. Photomicrographs of urinary sediment as well as renal biopsy histopathology of the presented case are shown. The unusual combination of findings, is then discussed in light of the existing literature on renal amyloidosis as well as erythrocyte casts in conditions other than glomerulonephritis.

Background and Aims In approximately 10% of adults with chronic kidney disease, a hereditary cause can be identified. Important representatives are Alport syndrome and inherited podocytopathies, which often show the histological picture of focal segmental glomerulosclerosis (FSGS). FSGS is a histological finding of various etiologies (primary, hereditary, secondary). Especially in suspected glomerular kidney disease, kidney biopsy is the diagnostic gold standard. The aim of this study was to evaluate a cohort of individuals with genetically confirmed inherited nephropathy and previous kidney biopsy to determine whether the histological examination can provide a clue to the underlying inherited kidney disease. Biopsies were further investigated by proteomics via liquid-chromatography-mass spectrometry (LC-MS) to potentially elucidate the underlying protein defect. Method The cohort for this retrospective study consisted of 23 individuals with a genetically confirmed inherited nephropathy and a previously performed kidney biopsy. A systematic pathological secondary review of the 23 biopsies was carried out (genetic diagnosis unknown at secondary review). The findings of the biopsies were compared with the molecular genetic results. 9 proband and 9 control biopsies were additionally evaluated through LC-MS. Laser capture microdissection was used to extract glomeruli from the tissue samples, which were then further analyzed on alterations in protein expression secondary to the respective disease-causing variants. Results In the cohort, disease-causing variants were identified in the following genes: COL4A3 (n = 3), COL4A5 (n = 4), WT1 (n = 3), UMOD (n = 3), and each n = 1 for the genes INF2, DAAM2, MUC1, COQ8B, NPHP4, TRIM8, CD2AP, NPHS2, CLCN5, and PAX2. The biopsies showed predominantly segmental glomerulosclerosis and parenchymal scarring, as well as podocyte damage. Four individuals with the histological diagnosis of Alport syndrome were genetically confirmed as having X-chromosomal (n = 2; including one female carrier) and autosomal-recessive (n = 2) Alport syndrome. Proteomics showed heterogeneous results. Proband samples carried variants in COL4A3 (n = 3), COL4A5 (n = 3), ADCK4, NPHP4, and WT1 (the last three each n = 1). COL4A3 was detected in 6/9 of control samples and in 0/9 of proband samples; COL4A5 was detected in 5/9 of control samples and in 0/9 of proband samples. ADCK4, NPHP4, and WT1 could not be detected in this analysis, neither in control, nor in proband samples. Conclusion In this study, molecular genetic diagnostics allowed a more precise disease assignment and thus provided information on therapy, prognosis, recurrence in the transplant, possible extrarenal phenotypes, and inheritance. Histological findings can indicate an inherited disease and help to trigger genetic testing (e.g., Alport syndrome). However, genetic diagnostics can also classify cases for which there are no typical morphological criteria described or if severe scarring impairs morphological diagnosis. Numerous cases of a respective monogenic disease would have to be analyzed in order to establish common histopathological criteria, if present. This is a challenge due to the rapid discovery of new disease-associated genes and the rarity of the respective diseases. LC-MS-based proteomics from kidney biopsy samples showed to be of limited value in further characterizing changes associated with specific variants. Unlike the genome, which is consistent due to the stability of DNA, the proteome is influenced by various effects: Different stages of fibrosis depending on the time of biopsy and other factors like coexistent disease lead to varying protein intensities even in two separate samples that present identical genetic variants. The detected protein intensity patterns could not be sufficiently correlated with the genetic findings. Despite the detection of certain proteins of interest like type IV collagens, their intensity variation due to advanced tissue damage did not allow reliable conclusions on the underlying cause. Alternatively, molecular methods such as MALDI imaging could further visualize these changes.