Histogenesis of the acquired cystic kidney disease: an immunohistochemical study

Continuous genetic monitoring of transient mesenchymal gene activities in distal tubule and collecting duct epithelial cells during renal fibrosis

Epithelial cells (ECs) have been proposed to contribute to myofibroblasts or fibroblasts through epithelial-mesenchymal transition (EMT) during renal fibrosis. However, since EMT may occur dynamically, transiently, and reversibly during kidney fibrosis, conventional lineage tracing based on Cre-loxP recombination in renal ECs could hardly capture the transient EMT activity, yielding inconsistent results. Moreover, previous EMT research has primarily focused on renal proximal tubule ECs, with few reports of distal tubules and collecting ducts. Here, we generated dual recombinases-mediated genetic lineage tracing systems for continuous monitoring of transient mesenchymal gene expression in E-cadherin+ and EpCAM+ ECs of distal tubules and collecting ducts during renal fibrosis. Activation of key EMT-inducing transcription factor (EMT-TF) Zeb1 and mesenchymal markers αSMA, vimentin, and N-cadherin, were investigated following unilateral ureteral obstruction (UUO). Our data revealed that E-cadherin+ and EpCAM+ ECs did not transdifferentiate into myofibroblasts, nor transiently expressed these mesenchymal genes during renal fibrosis. In contrast, in vitro a large amount of cultured renal ECs upregulated mesenchymal genes in response to TGF-β, a major inducer of EMT.

Urologic Diseases Germane to the Medical Renal Biopsy: Review of a Large Diagnostic Experience in the Context of the Renal Architecture and Its Environs

The kidney is one of the most complicated organs in development and is susceptible to more types of diseases than other organs. The disease spectrum includes developmental and cystic diseases, involvement by systemic diseases, iatrogenic complications, ascending infections and urinary tract obstruction, and neoplastic diseases. The diagnosis of kidney disease is unique involving 2 subspecialties, urologic pathology and renal pathology. Both renal and urologic pathologists employ the renal biopsy as a diagnostic modality. However, urologic pathologists commonly have a generous specimen in the form of a nephrectomy or partial nephrectomy while a renal pathologist requires ancillary modalities of immunofluorescence and electron microscopy. The 2 subspecialties differ in the disease spectrum they diagnose. This separation is not absolute as diseases of one subspecialty not infrequently appear in the diagnostic materials of the other. The presence of medical renal diseases in a nephrectomy specimen is well described and recommendations for reporting these findings have been formalized. However, urologic diseases appearing in a medical renal biopsy have received less attention. This review attempts to fill that gap by first reviewing the perirenal anatomy to illustrate why inadvertent biopsy of adjacent organs occurs and determine its incidence in renal biopsies followed by a discussion of gross anatomic features relevant to the microscopic domain of the medical renal biopsy. Unsuspected neoplasms and renal cysts and cystic kidney diseases will then be discussed as they create a diagnostic challenge for the renal pathologist who often has limited training and experience in these diseases.

Snail1-induced partial epithelial-to-mesenchymal transition drives renal fibrosis in mice and can be targeted to reverse established disease

Progressive kidney fibrosis contributes greatly to end-stage renal failure, and no specific treatment is available to preserve organ function. During renal fibrosis, myofibroblasts accumulate in the interstitium of the kidney, leading to massive deposition of extracellular matrix and organ dysfunction. The origin of myofibroblasts is manifold, but the contribution of an epithelial-to-mesenchymal transition (EMT) undergone by renal epithelial cells during kidney fibrosis is still debated. We show that the reactivation of Snai1 (encoding snail family zinc finger 1, known as Snail1) in mouse renal epithelial cells is required for the development of fibrosis in the kidney. Damage-mediated Snail1 reactivation induces a partial EMT in tubular epithelial cells that, without directly contributing to the myofibroblast population, relays signals to the interstitium to promote myofibroblast differentiation and fibrogenesis and to sustain inflammation. We also show that Snail1-induced fibrosis can be reversed in vivo and that obstructive nephropathy can be therapeutically ameliorated in mice by targeting Snail1 expression. These results reconcile conflicting data on the role of the EMT in renal fibrosis and provide avenues for the design of novel anti-fibrotic therapies.

Cystic gene dosage influences kidney lesions after nephron reduction

Cystic kidney disease is characterized by the progressive development of multiple fluid-filled cysts. Cysts can be acquired, or they may appear during development or in postnatal life due to specific gene defects and lead to renal failure. The most frequent form of this disease is the inherited polycystic kidney disease (PKD). Experimental models of PKD showed that an increase of cellular proliferation and apoptosis as well as defects in apico-basal and planar cell polarity or cilia play a critical role in cyst development. However, little is known about the mechanisms and the mediators involved in acquired cystic kidney diseases (ACKD). In this study, we used the nephron reduction as a model to study the mechanisms underlying cyst development in ACKD. We found that tubular dilations after nephron reduction recapitulated most of the morphological features of ACKD. The development of tubular dilations was associated with a dramatic increase of cell proliferation. In contrast, the apico-basal polarity and cilia did not seem to be affected. Interestingly, polycystin 1 and fibrocystin were markedly increased and polycystin 2 was decreased in cells lining the dilated tubules, whereas the expression of several other cystic genes did not change. More importantly, Pkd1 haploinsufficiency accelerated the development of tubular dilations after nephron reduction, a phenotype that was associated to a further increase of cell proliferation. These data were relevant to humans ACKD, as cystic genes expression and the rate of cell proliferation were also increased. In conclusion, our study suggests that the nephron reduction can be considered a suitable model to study ACKD and that dosage of genes involved in PKD is also important in ACKD.

Novel role of sorting nexin 5 in renal D(1) dopamine receptor trafficking and function: implications for hypertension

The D1 dopamine receptor (D1R) is widely expressed in the kidney and plays a crucial role in blood pressure regulation. Although much is known about D1R desensitization, especially through G-protein-coupled receptor kinase 4 (GRK4), comparatively little is known about other aspects of D1R trafficking and the proteins involved in the process. We now report the discovery of a dynamic interaction between sorting nexin 5 (SNX5), a component of the mammalian retromer, and D1R in human renal epithelial cells. We show that internalization of agonist-activated D1R is regulated by both SNX5 and GRK4, and that SNX5 is critical to the recycling of the receptor to the plasma membrane. SNX5 depletion increases agonist-activated D1R phosphorylation (>50% at basal condition), prevents D1R internalization and cAMP response, and delays receptor recycling compared to mock siRNA-transfected controls. Moreover, renal restricted subcapsular infusion of Snx5-specific siRNA (vs. mock siRNA) decreases sodium excretion (Δ=-0.2±0.005 mEq/mg creatinine) and further elevates the systolic blood pressure (Δ=48±5 mm Hg) in spontaneously hypertensive rats, indicating that SNX5 depletion impairs renal D1R function. These studies demonstrate an essential role for SNX5 in regulating D1R function, which may have important diagnostic, prognostic, and therapeutic implications in the management of essential hypertension.

The non-neoplastic kidney in tumor nephrectomy specimens: what can it show and what is important?

Surgical nephrectomy is a procedure that has been performed for nearly 100 years. In the presence of a normal contralateral kidney, such as in a renal transplant donor or child with Wilms tumor, it is a benign procedure without deleterious consequences on the remaining kidney. However, many adults and some children postnephrectomy will develop chronic kidney disease. The non-neoplastic kidney in tumor resections may harbor a large number of developmental and acquired diseases predictive of this outcome or that convey other medically significant information. Examination of the non-neoplastic kidney is a fertile opportunity to identify these unsuspected conditions that may ultimately dictate the subsequent clinical course and influence the medical care provided. This review discusses the consequences of unilateral and partial nephrectomy, and illustrates many conditions that may be encountered in the non-neoplastic cortex with a discussion of their clinical implications.

Glomerulocystic kidney: one hundred-year perspective

CONTEXT

Glomerular cysts, defined as Bowman space dilatation greater than 2 to 3 times normal size, are found in disorders of diverse etiology and with a spectrum of clinical manifestations. The term glomerulocystic kidney (GCK) refers to a kidney with greater than 5% cystic glomeruli. Although usually a disease of the young, GCK also occurs in adults.

OBJECTIVE

To assess the recent molecular genetics of GCK, review our files, revisit the literature, and perform in silico experiments.

DATA SOURCES

We retrieved 20 cases from our files and identified more than 230 cases published in the literature under several designations.

CONCLUSIONS

Although GCK is at least in part a variant of autosomal dominant or recessive polycystic kidney disease (PKD), linkage analysis has excluded PKD-associated gene mutations in many cases of GCK. A subtype of familial GCK, presenting with cystic kidneys, hyperuricemia, and isosthenuria is due to uromodullin mutations. In addition, the familial hypoplastic variant of GCK that is associated with diabetes is caused by mutations in TCF2, the gene encoding hepatocyte nuclear factor-1beta. The term GCK disease (GCKD) should be reserved for the latter molecularly recognized/inherited subtypes of GCK (not to include PKD). Review of our cases, the literature, and our in silico analysis of the overlapping genetic entities integrates established molecular-genetic functions into a proposed model of glomerulocystogenesis; a classification scheme emerged that (1) emphasizes the clinical significance of glomerular cysts, (2) provides a pertinent differential diagnosis, and (3) suggests screening for probable mutations.