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Characteristics of Podocyte Injury in Malignant Hypertensive Nephropathy of Rats (MSHRSP/Kpo Strain)

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Characteristics of Podocyte Injury in Malignant Hypertensive Nephropathy of Rats (MSHRSP/Kpo Strain) Biomedical Research (Tokyo) 36 (5) 313-321, 2015 Characteristics of podocyte injury in malignant hypertensive nephropathy of rats (MSHRSP/Kpo strain) 1, 3 2 3 Takashi KATO , Nobuyuki MIZUGUCHI , and Akihiko ITO 1 Department of Pharmacology, Faculty of Medicine, Kinki University, Osaka, Japan; 2 Life Science Research Institute, Kinki University, Osaka, Japan; and 3 Department of Pathology, Faculty of Medicine, Kinki University, Osaka, Japan (Received 2 July 2015; and accepted 6 August 2015) ABSTRACT Proteinuria is not only a hallmark of renal complication in malignant hypertension, but is also a major deteriorating factor for the progression to end-stage renal disease. Podocyte injury plays a crucial role in the renal damage associated with hypertensive nephropathy, but the underlying mechanism remains unclear. Malignant stroke-prone spontaneously hypertensive rats (MSHRSP/ Kpo) represent an original and useful model of human malignant hypertension. In this study, we disclosed the glomerular injuries in the MSHRSP/Kpo. MSHRSP/Kpo exhibited elevated blood pressure at 6 weeks along with renal dysfunction and proteinuria. Histological analysis of the MSHRSP/Kpo glomeruli revealed a severe atrophy, but no change was found in the podocyte number. The expression levels of podocyte-specific proteins, nephrin, podocin, and synaptopodin were decreased in the MSHRSP/Kpo glomeruli, though another podocyte-specific protein, CD2AP, in the MSHRSP/Kpo glomeruli exhibited a similar extent of staining as in normotensive WKY/ Kpo rats. Furthermore, desmin was not markedly detected in the WKY/Kpo glomeruli, but was strongly positive in MSHRSP/Kpo. By electron microscopy, well-formed foot processes (FP) were replaced by effacement in MSHRSP/Kpo. An original malignant hypertension strain MSHRSP/ Kpo exhibits podocyte injuries associated with the decrease of some podocyte-specific proteins and the upregulation of desmin, along with FP effacement and proteinuria. Malignant hypertension is critical for various kinds rosis, and tubular cell atrophy (26). A number of of vascular event and subsequent organ damage, factors including a defective renal autoregulatory re- such as stroke, cardiac hypertrophy, nephrosis, and sponse to hypertension, renal susceptibility genes, atherosclerosis. Among these, hypertensive nephro- and environmental factors such as salt, smoking, sclerosis from long-standing uncontrolled hyperten- and lead exposure have been suggested to contribute sion is a major cause of chronic kidney disease and to the development of hypertensive nephrosclerosis accounts for significant mortality (3). The histologi- (17). In particular, proteinuria is not only a hallmark cal lesions of hypertensive nephrosclerosis are well of renal complication in hypertension, but is also a recognized and characterized by hyalinization and major deteriorating factor for the progression to end- sclerosis of interlobular and afferent arterioles, to- stage renal diseases (23, 24). gether with tubulointerstitial fibrosis, glomeruloscle- Glomerular epithelial cells, podocytes, which are located on the outside of the glomerulus and cover the capillary wall, play an important role in the glo- Address correspondence to: Dr. Takashi Kato Department of Pharmacology, Faculty of Medicine, Kinki merular filtration of the kidney. The podocytes do University, 377-2 Ohno-higashi, Osakasayama, Osaka not proliferate after birth under normal conditions 589-8511, Japan and are terminally differentiated to maintain an in- Tel: +81-72-366-0221, Fax: +81-72-367-1820 tricate and polarized cellular organization consisting E-mail: [email protected] of a cell body, major processes, and foot process 314 T. Kato et al. (FP). Dysfunction of the podocyte, such as FP ef- sections were used. For synaptopodin, desmin, facement, is associated with the development of pro- CD2AP, and nestin staining, 10% formalin-fixed teinuria and nephrotic syndrome (25). Furthermore, sections were used, as reported previously (11, 12). podocyte injury likely plays a crucial role in the re- Antigen retrieval was performed by using 1 mM nal damage associated with proteinuria and hyper- EDTA at pH 8.0 in microwave for 20 min for these tensive nephrosclerosis (2). Despite the progress staining except PECAM-1 staining. Immunostaining made by many studies in understanding renal dam- assays were performed as described previously (13). age induced by malignant hypertension, the underly- WT-1-positive and total cells in the glomerulus were ing mechanism of podocyte injury remains unclear. counted as described previously (11). Stroke-prone spontaneously hypertensive rats (SHRSP/Kpo) represent a useful model of human Electron microscopy. Deeply anesthetized animals essential hypertension (12, 19). In addition to the tu- were transcardially perfused with PBS followed by bular lesions, we previously reported the thickened ice-cold 1% glutaraldehyde (GA)/1% paraformalde- capillary walls in the SHRSP/Kpo glomeruli (12). hyde (PFA) in PBS. For transmission electron mi- However, we could not find the distinct injuries in croscopy (TEM) analysis, the extracted kidneys the SHRSP/Kpo podocytes. We found that some were fixed in the same solution at 4°C overnight. rats of the SHRSP/Kpo exhibited blood pressure of Tissue specimens were post-fixed in osmium tetrox- 230 mmHg at 10 weeks, continued to inbreed them ide (OsO4) for 2 h at 4°C, dehydrated through an and recently established malignant SHRSP/Kpo ethanol gradient, and embedded in Epon. Ultrathin (MSHRSP/Kpo). In the present study, we therefore sections (90 nm) were cut with an ultra-microtome, disclosed the glomerular injuries, especially in podo- stained with 4% uranyl acetate and 1% lead citrate cytes of MSHRSP/Kpo strain. (Pb), and then examined by TEM (HT7700; Hitachi, Tokyo, Japan). For scanning electron microscopy (SEM) analysis, the specimens were fixed in 2.5% MATERIALS AND METHODS GA overnight at 4°C. After washing with 0.1 M phos- Animal experiment. We maintained MSHRSP/Kpo phate buffer, the specimens were post-fixed in OsO4 and WKY/Kpo (control) rats and measured the for 1 h at 4°C. The specimens were subsequently blood pressure as described previously (12). All ani- dehydrated in a graded series of ethanol and t-butyl mal experiments were carried out according to the alcohol, and then freeze-dried. The dried specimens Guideline for Experimental Animal Care issued by were finally mounted on stubs, coated with gold pal- the Prime Minister’s Office of Japan and approved by ladium, and examined by SEM (SU3500, Hitachi). the Committee on Animal Experimentation of Kinki University School of Medicine. SDS-PAGE analysis Statistical analysis. Student’s t-test was used to de- of urine was performed as described previously (10, termine statistical significance. 11). The concentrations of urinary albumin, blood urea nitrogen (BUN) and serum creatinine were ex- RESULTS amined as described previously (10, 12). Characterization of malignant SHRSP/Kpo Histological analysis. Right kidneys removed at We first examined the blood pressure of MSHRSP/ each autopsy were fixed in either cold 10%-buffered Kpo compared with that of normotensive WKY/Kpo formalin or 70% ethanol for 24 h, and were submit- rats. SHR/Kpo and SHRSP/Kpo strains had almost ted to a routine process for paraffin embedding. The the same level as the WKY/Kpo at 6 weeks of age renal sections were stained with periodic acid Schiff (12). However, MSHRSP/Kpo exhibited an increase (PAS). To detect podocyte proteins, anti-nephrin IgG of blood pressure at 6 weeks (Fig. 1A). MSHRSP/ (sc-19000; Santa Cruz Biotechnology (SCB), Dallas, Kpo further reached to 280 mmHg at 12 weeks TX, USA), anti-podocin IgG (sc-22298, SCB), anti- (Fig. 1A). We next investigated the urinary and se- WT-1 IgG (sc-7385, SCB), anti-synaptopodin IgG rum biochemical parameters in the MSHRSP/Kpo. (65194; Progene, Heidelberg, Germany), anti-CD2AP MSHRSP/Kpo exhibited proteinuria at 15 weeks by IgG (sc-9137, SCB), anti-nestin IgG (556309; BD SDS-PAGE analysis (Fig. 1B). Moreover, BUN and Bioscience, San Jose, CA, USA), anti-desmin IgG serum creatinine levels at 15-week-age MSHRSP/ (M0760; DAKO, Glostrup, Denmark), and anti- Kpo were 3.0- and 1.6-fold higher than in the age- PECAM-1 IgG (555025, BD Bioscience) were used. matched WKY/Kpo, respectively (Fig. 1C and 1D). For nephrin and podocin staining, 70% ethanol-fixed Podocyte in hypertensive rat model 315 Fig. 1 Blood pressure, urinary parameters, and ultrastructures of the glomeruli in MSHRSP/Kpo and WKY/Kpo. (A) Blood pressure of MSHRSP/Kpo and WKY/Kpo at 6 and 12 weeks of age. (B) SDS-PAGE shows albuminuria in MSHRSP/Kpo at 15 weeks. M: protein marker, Arrow head: major urinary protein. (C) BUN and (D) serum creatinine in MSHRSP/Kpo at 6, 10, and 15 weeks of age are compared with those of WKY/Kpo. Values are expressed as the mean ± SD. n = 5 per group, * P < 0.05, ** P < 0.01, *** P < 0.001. Histological analysis of glomerulus Expression of podocyte-specific proteins in MSHRSP/ To evaluate glomerular lesions in MSHRSP/Kpo, we Kpo glomerulus performed histological examinations after PAS stain- Since we could not find any changes in the number ing. As shown in Fig. 2A, the WKY/Kpo glomeruli of podocytes, we focused on podocyte morphology. were normal, but we found a severe glomerular atro- Podocytes form FPs, highly dynamic cellular exten- phy in the MSHRSP/Kpo (Fig. 2B). The number of sions that are connected by a slit diaphragm (SD). glomerular cells was slightly decreased in MSHRSP/ Nephrin is a transmembrane protein of the immuno- Kpo [WKY/Kpo: 61.05 ± 3.23, (20W, n = 5) vs globulin family of cell-adhesion molecules, which is MSHRSP/Kpo: 55.56 ± 5.80, (19W, n = 3)]. Since localized to the SD and constitutes the filtration bar- Wilm’s Tumor-1 (WT-1) was shown to be localized rier of the kidney (16). In the WKY/Kpo glomeruli, in the nucleus of podocytes (11), we counted the nephrin was strongly detected along the extra-capil- WT-1-positive cells in the glomerulus (Fig.
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