Yukinari Masuda

Vascular Endothelial Growth Factor Enhances Glomerular Capillary Repair and Accelerates Resolution of Experimentally Induced Glomerulonephritis

Vascular endothelial growth factor (VEGF) regulates angiogenesis through endothelial cell proliferation and plays an important role in capillary repair in damaged glomeruli. We tested the hypothesis that VEGF might be beneficial in rats with severe glomerular injury in glomerulonephritis (GN) based on its angiogenic and vascular remodeling properties. Acute GN with severe glomerular destruction was induced in rats by injection of anti-Thy-1.1 antibody (day 0) and Habu-snake venom (day 1). Rats were intraperitoneally injected with recombinant human VEGF(165) (10 microg/100 g body wt/day) or vehicle from day 2 to day 9, and monitored changes in glomerular capillaries, development of glomerular inflammation, and progression to glomerular sclerosis after acute glomerular destruction in both groups. Rats that received anti-Thy-1.1 antibody and Habu-snake venom showed severe mesangiolysis and marked destruction of capillary network on day 2. VEGF was expressed on glomerular epithelial cells, proliferating mesangial cells, and some infiltrating leukocytes, and VEGF(165) protein levels increased in damaged glomeruli during day 5 to day 7. Normal, damaged, and regenerating glomerular endothelial cells expressed VEGF receptor flk-1. However, endothelial cell proliferation and capillary repair was rare in vehicle-treated rats with severe glomerular damage, which progressed to global sclerosis and chronic renal failure by week 8. In contrast, in the VEGF-treated group, VEGF(165) significantly enhanced endothelial cell proliferation and capillary repair in glomeruli by day 9 (proliferating endothelial cells: VEGF(165), 4.3 +/- 1.1; control, 2.2 +/- 0.9 cells on day 7, P < 0.001; and glomerular capillaries: VEGF(165), 24.6 +/- 4.8; control, 16.9 +/- 3.4 capillaries on day 7, P < 0.01). Thereafter, damaged glomeruli gradually recovered after development of capillary network by week 8, and significant improvement of renal function was evident in the VEGF-treated group during week 8 (creatinine: VEGF(165), 0.3 +/- 0.1; control, 2.6 +/- 0.9 mg/dl, P < 0.001; proteinuria: VEGF(165), 54 +/- 15; control, 318 +/- 60 mg/day, P < 0.001). We conclude that the beneficial effect of VEGF(165) in severe glomerular injury in GN emphasizes the importance of capillary repair in the resolution of GN, and may allow the design of new therapeutic strategies against severe GN.

Abnormalities in elastic fibers and other connective-tissue components of floppy mitral valve

Histologic, immunohistochemical, and ultrastructural studies were performed on 12 floppy mitral valves, 4 mitral valves showing focal myxomatous changes without prolapse, and 3 normal mitral valves. All floppy mitral valves were thickened by deposits of proteoglycans and also showed diverse structural abnormalities in collagen and elastic fibers. From these observations we conclude that (1) the structure of all major components of connective tissue in floppy mitral valves is abnormal; (2) alterations in collagen and accumulations of proteoglycans are nonspecific changes that may be caused by the abnormal mechanical forces to which floppy mitral valves are subjected because of their excessively large surface area; (3) the presence of excessive amounts of proteoglycans may interfere with the normal assembly of collagen and elastic fibers; (4) abnormalities of elastic fibers resemble those in other conditions characterized by structural dilatation or tissue expansion; and (5) alterations in elastin could result from defective formation, increased degradation, or both.

Peritubular Capillary Regression during the Progression of Experimental Obstructive Nephropathy

Injury to the renal microvasculature may be a major factor contributing to the progression of renal disease. Although severe disruption of peritubular capillaries (PTC) could lead to marked tubulointerstitial scarring, elucidation of that process remains incomplete. This study investigated the morphologic changes in PTC and their likely regulation by vascular endothelial growth factor (VEGF) during the progression of tubulointerstitial injuries. Unilateral ureteral obstruction was induced in Wistar rats by ligation of the left ureter, and the kidneys were then collected at selected times. PTC lumina and the expression of VEGF and its receptor Flk-1 were immunohistochemically detected. Morphologic changes in PTC endothelial cells were examined by using Ki67 staining, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling, and electron-microscopic studies. In the first week of the disease period, immunohistochemical labeling of tubular VEGF intensified, with accompanying deformation and dilation of adjacent thrombomodulin (TM)-positive PTC lumina; an angiogenic response of endothelial cells was demonstrated with Ki67 and TM double-staining. During the subsequent 2 wk, tubular VEGF labeling decreased until it was virtually absent, an effect confirmed by Western blotting. Concomitantly, labeling of the VEGF receptor Flk-1 in PTC endothelial cells decreased and PTC lumina began to regress, demonstrating endothelial cell apoptosis (as detected in terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling and electron-microscopic studies). By the end of week 4, the numbers of TM-positive PTC lumina were significantly decreased in areas of marked tubulointerstitial scarring. These results suggest that PTC regression, involving an early, unsustained, angiogenic response followed by progressive endothelial cell apoptosis, could be a potential factor contributing to tubulointerstitial scarring in this unilateral ureteral obstruction model.

Apoptosis in Glomerular Endothelial Cells during the Development of Glomerulosclerosis in the Remnant-Kidney Model

Capillary obsolescence with subsequent glomerulosclerosis is a common finding in most progressive glomerular diseases. In this study we investigated apoptosis, focusing on glomerular endothelial cells during the development of glomerulosclerosis in five-sixths nephrectomized rats for 6 months. Apoptosis was recognized by light and electron microscopy. Biochemical labeling of apoptosis was morphologically confirmed by in situ end labeling of fragmented DNA using terminal deoxynucleotidyltransferase. Glomerular endothelial cells were identified by electron microscope and immunostaining for thrombomodulin which is known to be an endothelial cell surface glycoprotein. Glomerular hypercellularity occurred by month 2, peaking by month 3, and an extracellular matrix accumulation was evident by month 3. Subsequently, most of the glomeruli progressed to diffuse sclerosis by months 4–6. During the progression of the disease, the glomerular endothelial cells decreased in number and finally could not be detected in the sclerotic lesion, and apoptotic cells apparently increased in number in the lesion. Significant apoptosis was present from month 3, thereafter it gradually increased to peak by month 6. Double immunostaining for apoptosis and thrombomodulin demonstrated that apoptosis occurred in the glomerular endothelial cells as well as in mesangial cells and infiltrating cells. The number of glomerular endothelial cells with apoptosis increased with the development of glomerulosclerosis, and maximum expression was observed by month 6. We conclude that the depletion of glomerular endothelial cells is associated with apoptosis in the remnant-kidney model, and apoptosis in glomerular endothelial cells may contribute to the development of glomerulosclerosis.

Vascular Endothelial Growth Factor165 Resolves Glomerular Inflammation and Accelerates Glomerular Capillary Repair in Rat Anti–Glomerular Basement Membrane Glomerulonephritis

Vascular endothelial growth factor (VEGF) is essential for maintenance of the glomerular capillary network. The present study investigated the effects of VEGF in rats with progressive crescentic glomerulonephritis (GN). Necrotizing and crescentic GN was induced in rats by injection of anti-rat glomerular basement membrane (GBM) antibody. The alterations of glomerular capillaries and glomerular VEGF expression were assessed. In addition, the effects of continuous VEGF165 administration (10 microg/100 g per d) on glomerular capillaries, glomerular inflammation, and the course of crescentic GN were examined. The appropriate timing of VEGF administration in progressive GN also was evaluated. In anti-GBM GN, necrotizing and crescentic glomerular lesions occurred by day 7, and newly formed necrotizing lesions reoccurred by week 3. Expression of VEGF was markedly reduced in necrotizing and crescentic lesions. Capillary repair was impaired after capillary destruction in necrotizing and crescentic glomeruli, which rapidly progressed to sclerotic glomeruli with chronic renal failure. In contrast, in the rats that received VEGF165 administration from day 7, the necrotizing and crescentic lesions recovered and renal function significantly improved in week 4. This was evident by proliferating endothelial cells and glomerular capillary repair. In addition, VEGF administration decreased intercellular adhesion molecule-1 and monocyte chemoattractant protein-1 expression in glomeruli (particularly on endothelial cells), reduced glomerular infiltrating CD8-postive and ED-1-positive cells, and inhibited the newly formed necrotizing lesions. VEGF administration was apparently effective against both the inflammatory and necrotizing glomerular lesions. These results suggest that VEGF administration resolves glomerular inflammation and accelerates glomerular recovery in the progressive necrotizing and crescentic GN. The therapeutic application of VEGF may be clinically useful for severe GN accompanied by extensive glomerular inflammation and endothelial injury.

EXPERIMENTAL MESANGIOPROLIFERATIVE GLOMERULONEPHRITIS IN RATS INDUCED BY INTRAVENOUS ADMINISTRATION OF ANTI-THYMOCYTE SERUM

Focal glomerulonephritis was induced in rats, by a single intravenous injection of anti‐Thy‐1.1 antibody (ATS). One hour after the administration, the glomeruli of affected rats developed necrotic changes of the mesangial cells while after two hours, mesangiolytic changes appeared. From six days onwards, focal segmental mesangial proliferation which persisted until 30 days, occurred. This is thought to be the first report of experimental nephritis induced by pure anti‐mesangial antibody.

Inhibition of matrix metalloproteinases reduces ischemia-reperfusion acute kidney injury.

Matrix metalloproteinases (MMPs) are endopeptidases that degrade extracellular matrix and involved in ischemic organ injuries. The present study was designed to determine the role of MMP-2 in the development of ischemic acute kidney injury (AKI). AKI was induced in MMP-2 wild-type (MMP-2+/+) mice by 30, 60, 90, and 120 min renal ischemia and reperfusion. Renal histology, expression and activity of MMP-2 and MMP-9, and renal function were examined during the development of AKI. AKI was also induced in MMP-2-deficient (MMP-2−/−) mice and MMP-2+/+ mice treated with inhibitor of MMPs (minocycline and synthetic peptide MMP inhibitor). In MMP-2+/+ mice, MMP-2 and MMP-9 activities increased significantly at 2 to 24 h, peaked at 6 h, after reperfusion. Immunohistochemical analysis identified MMP-2 in the interstitium around tubules and peritubular capillaries in the outer medulla. Acute tubular injury (ATI), including apoptosis and necrosis, was evident in the outer medulla at 24 h, along with renal dysfunction. As ischemia period increases, MMP-2 and MMP-9 activities at 6 h and severity of AKI at 24 h increased depending on the duration of ischemia between 30 and 120 min. However, the kidneys of MMP-2−/− mice showed minimal ATI; serum creatinine 24 h after reperfusion was significantly low in these mice. Inhibitors of MMPs reduced ATI and improved renal dysfunction at 24 h. We conclude that MMPs, especially MMP-2 have a pathogenic role in ischemia-reperfusion AKI, and that inhibitors of MMPs can protect against ischemic AKI.

Recovery of Damaged Glomerular Capillary Network with Endothelial Cell Apoptosis in Experimental Proliferative Glomerulonephritis

Capillary repair can occur in damaged glomeruli in recovery models of glomerulonephritis (GN). In order to clarify whether capillary repair is an essential component in glomerular recovery from GN, we have examined the development of the capillary repair after inflammatory injury in both the repairing glomeruli and the segmental sclerotic scar lesions in Thy-1 GN. Mesangiolytic glomerular damage was induced in rats with anti-Thy-1.1 antibody administration. Diffuse mesangiolysis and segmental microaneurysmal ballooning developed in damaged glomeruli by day 3, with reduction of endothelial cellularity. Thereafter, histological proliferative GN developed between day 5 and week 3. Endothelial cell proliferation began on day 1 and peaked on day 5, and the number of glomerular endothelial cells increased and exceeded the level of control values on day 7. Angiogenic glomerular capillary repair occurred through the process of not only capillary regeneration from remaining endothelial cells in capillary aneurysmal lesions but also new capillary growth derived from the glomerular vascular poles by day 7. The number of glomerular capillary lumina also increased to the level of controls by week 3. Susbsequently, mesangial proliferative GN resolved, and most of the glomeruli recovered to their normal structure with the reconstruction of the capillary network by weeks 4–6. In the glomerular capillary repair, significant apoptosis of glomerular endothelial cells was present during the period of mild endothelial cell hypercellularity between day 7 and day 10 (0.06 ± 0.02 apoptotic endothelial cells/glomerular cross section vs. 0.00 ± 0.00 in controls, mean ± SEM; p < 0.05. In Thy-1 GN, most of the damaged glomeruli recovered with angiogenic capillary repair. However, segmental sclerotic scar lesions remained in 10–30% of the glomeruli with an incomplete repair of glomerular capillaries. Therefore, it is concluded that following the destruction of the glomerular capillary network in GN, angiogenic capillary repair plays an essential role in the recovery of damaged glomeruli, and incomplete capillary repair leads to sclerotic scar lesions in damaged glomeruli. Glomerular capillary repair occurs through the process of capillary regeneration from remaining endothelial cells as well as new glomerular capillary growth from the glomerular vascular poles. In glomerular capillary repair, apoptosis is necessary in regulating the number of intrinsic endothelial cells.

Histogenesis of unique elastinophilic fibers of elastofibroma: Ultrastructural and immunohistochemical studies

Electron microscopy and both light and electron microscopic immunohistochemical tests for elastin were employed to study the morphogenesis of the unique elastinophilic fibers of an elastofibroma removed from the subscapular region of a 62-year-old woman. Ultrastructurally, as shown by tannic acid stain, elastinophilic fibers of the elastofibroma consisted of central cores and outer zones. The latter were composed of various sizes of vaguely demarcated, irregularly shaped amorphous components and compactly and randomly arranged large amounts of microfibrils. The electron microscopic immunohistochemical results showed that the small-sized amorphous components and microfibrils in the outer zones of the elastinophilic fibers were stained evenly and of granular texture, but the vaguely outlined large amorphous components were not stained. These findings were interpreted as indicating that the amorphous components of the outer zones of elastinophilic fibers were less compact and allowed the penetration of antielastin antibody. The unique elastinophilic fibers of elastofibromas appear not to be formed by the degeneration of the fibers but by abnormal elastogenesis, including an abnormal arrangement of microfibrils.

Complement-Mediated Killing of Mesangial Cells in Experimental Glomerulonephritis: Cell Death by a Combination of Apoptosis and Necrosis

Immune system mediated, particularly antibody- and complement-mediated, glomerular injury triggers glomerulonephritis (GN). To characterize complement-mediated cytotoxicity in GN, we assessed the process of mesangial cell death induced by C5b-9 attack in Thy-1 GN. Cell injury was recognized morphologically, and nuclear DNA breaks were confirmed by the DNA nick end labeling (TUNEL) method as well as DNA gel electrophoresis. Thy-1 GN was induced in rats with anti-Thy-1.1 antibody injection. Mouse IgG (administered antibody) and rat C3 were detected in all glomeruli within 5 min after antibody injection. Damaged mesangial cells with condensed as well as TUNEL-positive nuclei could be observed at 20 min and became prominent at 40–60 min. Ultrastructurally, damaged mesangial cells contained condensed apoptotic nuclei from 40 to 60 min, whereas the cytoplasm showed necrotic degeneration. This was followed by progressive lysis of both nuclei and cytoplasm. The DNA ‘ladder’ pattern was observed by gel electrophoresis of extracted DNA between 40 and 60 min and correlated with the increased number of TUNEL-positive damaged mesangial cells. To examine the role of complement in this form of cell death, complement depletion was induced in rats by cobra venom factor. Complement-depleted rats showed no rat C3 deposition, rare TUNEL-positive mesangial cells, rare ultrastructural degenerated mesangial cells with apoptotic nuclei and necrotic cytoplasm, and no DNA ‘ladder’ pattern on gel electrophoresis at 40 min, although prominent mouse IgG was seen in glomeruli. To analyze milder forms of complement injury, a low dose of the antibody was administered to rats with a normal complement level. A few TUNEL-positive mesangial cells were detected in the glomeruli which contained apoptotic nuclei and necrotic cytoplasm. Our results indicate that an apoptotic death mechanism accompanies cell necrosis in complement-mediated mesangial cell destruction in GN and that this unusual form of cell death may represent a combination of apoptosis-necrosis within the same cell. Complement injury activates a ‘death program’ which in turn leads to irreversible damage of mesangial cells and which may contribute to initiation and development of GN.