Puromycin Aminonucleoside Nephrosis Model Research Articles

CRISPR/Cas9 Deletion of a Portion of Exon 2 in the Trpc6 Gene Produces a Hypomorphic Variant that Confers Protection in the Chronic Puromycin Aminonucleoside Nephrosis Model in Sprague‐Dawley Rats

Mutations in TRPC6 channels give rise to rare familial forms of focal and segmental glomerulosclerosis (FSGS). Here we examined the role of TRPC6 channels in the chronic puromycin aminonucleoside (PAN) model of acquired FSGS in Sprague‐Dawley rats, using protocols approved by the University of Houston IACUC. In our disease model, animals received two i.p. injections of PAN at 30 day intervals, a protocol that has long been known to induce albuminuria and FSGS lesions in this species. To test our central hypothesis, we used CRISPR/Cas9 methods to delete a 239‐bp fragment in Exon 2 of Trpc6, which resulted in a frame shift that we expected to introduce numerous premature stop codons downstream of the deletion. However as a result of a recently described process known as exon skipping, short Trpc6 transcripts missing Exon 2 were detected by RT‐PCR in Trpc6del/del rats, albeit at considerably lower levels in renal cortex compared to the normal full‐length transcripts seen in Trpc6wt/wt controls. The Exon 2 deletion encodes a portion of an ankyrin‐repeat domain in the N‐terminal of the channel subunit. The function of that domain in the channel protein is not known. Using two different antibodies directed at different motifs downstream of the deletion, we detected very low levels of TRPC6 protein in immunoblots of the renal cortex of Trpc6del/del rats, whereas signal was robust in Trpc6wt/wt controls with both antibodies. In addition, we did not observe ATP‐activated cationic currents mediated by TRPC6 in whole‐cell recordings from glomerular cells resembling podocytes cultured from Trpc6del/del rats, but these currents were readily seen in Trpc6wt/wt controls. Kidney disease in chronic PAN nephrosis (measured 60 days after the first PAN injection) was markedly decreased in Trpc6del/del rats compared to Trpc6wt/wt littermates. This conclusion is based on reduced 24‐hr albumin excretion, reduced serum cholesterol and triglycerides, and improved blood urea nitrogen in Trpc6del/del rats. Trpc6del/del rats also had reduced glomerulosclerosis, less severe tubulointerstitial disease based on biochemical and histological measures, and reduced foot process effacement and glomerular basement thickening in transmission EM compared to Trpc6wt/wt rats. Protection in Trpc6del/del rats was robust but not complete. Thus, most of the quantifiable parameters of disease severity were reduced by about 50% in Trpc6del/del rats compared to wild‐type littermates. We did not discern any difference between renal function or glomerular structure in saline‐treated Trpc6del/del and Trpc6wt/wt rats. We also observed that glomerular TRPC3 abundance in renal cortex was increased in Trpc6del/del rats, although TRPC3 abundance did not increase further in chronic PAN nephrosis. None of the manipulations in this study affected the abundance of TRPC5 channels in renal cortex. These results support TRPC6 family channels as therapeutic targets for acquired forms of FSGS.Support or Funding InformationSupported by NIH grant RO1‐DK104708This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Semi-automated quantitative image analysis of podocyte desmin immunoreactivity as a sensitive marker for acute glomerular damage in the rat puromycin aminonucleoside nephrosis (PAN) model

Glomerular visceral epithelial cells or podocytes are crucial for glomerular function and podocyte damage has been shown to be inevitably involved in glomerulopathies. Podocytes react to injury in a stereotypic manner. Accompanying morphologic changes is altered expression of intermediate filaments. Desmin is strongly upregulated in injured podocytes. Here we show, that semi-automated quantitative image analysis of desmin immunoreactivity in glomerula is a valid and sensitive marker for acute podocyte and thus glomerular damage in the puromycin aminonucleoside nephrosis (PAN) model in the rat with the potential of an efficacy marker in animal disease models as well as a toxicity marker for podocyte injury. Additionally, a panel of acknowledged urinary kidney biomarkers was evaluated for utility in the PAN model.

Active vitamin D and its analogue, 22-oxacalcitriol, ameliorate puromycin aminonucleoside-induced nephrosis in rats

Recent studies have demonstrated that podocyte injury, which results in proteinuria, leads to tubulointerstitial fibrosis. Although some studies have revealed that vitamin D administration protects renal structure and function in mesangial cell proliferative and/or excessive matrix productive models, the effects of vitamin D on podocyte injury have remained uncertain. In this study, we examined whether administration of active vitamin D (calcitriol) or its analogue, 22-oxacalcitriol (maxacalcitol), is preventative in podocyte injury using the puromycin aminonucleoside nephrosis model with neither mesangial proliferation nor matrix accumulation. Before the onset of proteinuria, renal 1alpha-hydroxylase and 24-hydroxylase were markedly down-regulated and up-regulated, respectively, leading to impaired vitamin D activation. Thereafter, serum 25-hydroxyvitamin D decreased along with the increased excretion of vitamin D-binding protein in urine. After confirming that podocytes express vitamin D receptor and all retinoid X receptors (RXRs) except RXR-alpha, we found that daily administration of calcitriol or its analogue 22-oxacalcitriol ameliorated the nephrotic state by protecting podocytes, as shown by the reduced staining of desmin (podocyte injury marker) and the upregulation of nephrin and podocin. These data suggest that the impairment of the vitamin D system plays a role in increasing proteinuria in podocyte injury. We demonstrated the breakdown of the vitamin D activation system in podocyte injury, and established a preventative role for vitamin D in podocyte injury.

A Study of VEGF and Its Receptors in Two Rat Models of Proteinuria

Background: The high level of expression of vascular endothelial growth factor (VEGF) in normal podocyte foot processes suggests that VEGF has an important role in maintaining normal glomerular function. While altered VEGF expression occurs in many glomerular diseases, a direct role for VEGF in the pathogenesis of proteinuria has not been demonstrated. Methods: Expression of VEGF and its receptors (VEGFR-1 and VEGFR-2) was examined in passive Heymann nephritis (PHN) and puromycin aminonucleoside nephrosis (PAN), by immunohistochemistry, in situ hybridization, Northern and Western blotting. Inhibition of VEGF in the PAN model was performed by administration of a blocking antibody. Results: In both models, glomeruli showed upregulation of VEGF and VEGF receptors compared to control animals. VEGF mRNA was increased most significantly (5-fold) at day 5 after induction of PHN, prior to the onset of proteinuria, with persistent upregulation (3-fold) at day 21. Increased VEGF mRNA was also seen in PAN, but it was less marked. In situ hybridization and immunohistochemistry localized VEGF predominantly to podocytes. Increased expression of VEGFR-1 and VEGFR-2 protein was seen in glomerular endothelial cells of PHN and PAN rats by immunohistochemistry, as was VEGFR-2 mRNA by in situ hybridization. Upregulation of VEGFR-1 by endothelial cells was more striking in the PAN model than PHN. Administration of a blocking antibody to rats with PAN did not affect proteinuria, creatinine clearance or sodium excretion. Conclusion: The expression of VEGF and its receptors is significantly increased in the PHN and PAN rat models of proteinuria suggesting a role for VEGF in the disease process. VEGF may have an important role in promoting glomerular repair in a variety of glomerular diseases.

Retinoids as a potential treatment for experimental puromycin-induced nephrosis.

1 Puromycin aminonucleoside (PAN)-induced nephrosis is a model of human minimal change disease. In rats, PAN induces nephrotic-range proteinuria, renal epithelial cell (podocyte) damage, infiltration of mononuclear leukocytes, and apoptosis of several renal cell types. 2 Retinoic acid (RA) modulates a wide range of biological processes, such as inflammation and apoptosis. Since renal damage by PAN is characterized by inflammatory infiltration and epithelial cell death, the effect of treatment with all-trans RA (tRA) was examined in the PAN nephrosis model and in the cultured differentiated podocyte. 3 Treatment with tRA 4 days after PAN injection did not inhibit the proteinuria peak but reversed it significantly. However, treatment with tRA both before and 2 days after the injection of PAN protected the glomerular epithelial cells, diminishing the cellular edema and diffuseness of the foot process effacement. Preservation of the podocyte architecture correlated with the inhibition of proteinuria. The anti-inflammatory effect of tRA was evidenced by the inhibition of PAN-induced interstitial mononuclear cell infiltration and the decreased renal expression of two molecules involved in monocyte infiltration: fibronectin and monocyte chemoattractant protein-1. TUNEL assays showed that tRA inhibited the PAN-induced apoptosis of cultured differentiated mouse podocytes. 4 We conclude that tRA treatment may prevent proteinuria by protecting the podocytes from injury and diminishing the interstitial mononuclear infiltrate in the model of PAN nephrosis. Retinoids are a potential new treatment for kidney diseases characterized by proteinuria and mononuclear cell infiltration.

Puromycin aminonucleoside suppresses integrin expression in cultured glomerular epithelial cells.

Puromycin aminonucleoside (PAN)-induced nephrosis is a well-described model of human idiopathic nephrotic syndrome, but the mechanism of PAN's effect is not completely understood. Because PAN injection into rats results in retraction of glomerular epithelial cell foot processes and glomerular epithelial cell detachment, it was hypothesized that PAN might alter the contacts between these cells and the glomerular basement membrane. The major integrin expressed by glomerular epithelial cells is alpha3beta1, which mediates attachment of these cells to extracellular matrix proteins including type IV collagen. T-SV 40 immortalized human glomerular epithelial cells were used to study PAN's effects on alpha3beta1 expression, as well as that of podocalyxin and the slit diaphragm component ZO-1. Glomerular epithelial cells were seeded into plastic flasks and allowed to attach and proliferate for 48 h. The cells were then incubated for another 48 h in media containing 0, 0.5, or 5.0 microg/ml PAN. PAN exposure resulted in dose-dependent decreases in alpha3 and beta1 expression, both at the protein level and at the mRNA level. This was accompanied by a significant decrease in the adhesion of glomerular epithelial cells to type IV collagen. PAN did not affect ZO-1 protein expression. Treatment with PAN increased the expression of podocalyxin at the protein and mRNA levels. Reduced glomerular epithelial cell expression of alpha3beta1 integrins and impaired adhesion to type IV collagen may contribute to the glomerular epithelial cell detachment from glomerular basement membrane seen in the PAN nephrosis model.

Inhibition of heparin-binding epidermal growth factor-like growth factor increases albuminuria in puromycin aminonucleoside nephrosis

Our previous work in the acute puromycin aminonucleoside nephrosis (PAN) model has demonstrated up-regulation of heparin-binding epidermal growth factor-like growth factor (HB-EGF) mRNA and protein within glomerular epithelial cells (GECs) prior to the onset of proteinuria. To determine whether increased HB-EGF expression in the acute PAN model contributes to the pathogenesis of proteinuria, a monoclonal antibody (DE10) was produced against recombinant human HB-EGF. The specificity of DE10 for human HB-EGF was confirmed by enzyme-linked immunosorbent assay, immunohistochemical staining, and flow cytometry of transfected cells expressing human and rat HB-EGF, and inhibition of cell proliferation. DE10 also reacted with cells transfected with rat HB-EGF cDNA. Administration of 0.5 mg affinity-purified DE10 to normal rats did not cause significant albuminuria compared with controls. Five days after the induction of the acute PAN model, albuminuria was significantly greater in animals treated with 0.5 mg DE10 than a control mAb (162.6 +/- 32.4 vs. 64.8 +/- 10.2 mg/day, respectively, P < 0.01). Rats treated with DE10 had an earlier onset of severe albuminuria, but no increase in maximal albuminuria at later time points. Electron microscopy showed marked podocyte effacement in both DE10-treated and control animals, but no obvious difference between groups. However, adhesion of the human GEC line 56/10 A1 to laminin and fibronectin, but not to collagens I or IV, was reduced by DE10. This study suggests that HB-EGF contributes to the integrity of the glomerular filtration barrier, particularly when the podocyte has been injured. Following podocyte injury, adhesion to laminin in the glomerular basement membrane by HB-EGF may be important in reducing albuminuria.