Fig 1.
The areas of glomerular capillaries and glomerular ECM in computer-assessed morphometric analysis.
The area of glomerular tuft (dotted line in A and D), the area and number of glomerular capillaries (green areas in B and E), and the area of glomerular ECM (green areas in C and F) in each glomerulus were assessed by computer-assisted image analyzer. In the nearly normal glomeruli in light microscopic findings (A-C), large glomerular capillary area was noted with minimal ECM accumulation. In contrast, the area of glomerular capillaries decreased with narrowing glomerular capillaries and the accumulation of glomerular ECM in glomerulus in the development of glomerular sclerosis (D-F).
Table 1.
Clinical characteristics at the time of biopsy in MN cases with or without FSGS lesion.
Fig 2.
FSGS lesion in idiopathic membranous nephropathy(MN) (A, C: PAM stain, x600; B, D: CD34 stain, x600).
The biopsy samples from 26 MN-FSGS(+) cases included 534 glomeruli except for 55 global sclerotic glomeruli. In 534 glomeruli, 44 glomeruli (8.2%) had FSGS lesion, consisted of not otherwise specified (NOS) lesion type (31 glomeruli, 70.5%) and perihilar (PH) lesion type (13 glomeruli, 29.5%). In glomeruli with NOS type of FSGS lesion (arrow in A), FSGS lesion was noted in areas other than perihilar region, with hyalinosis and adherence lesion between tuft and Bowman’s capsule. In FSGS lesion (arrow in B), loss of CD34+ capillaries was evident with mesangial ECM accumulation. In glomeruli with PH type of FSGS lesion (arrow in C), perihilar sclerosis with hyalinosis was noted with loss of CD34+ glomerular capillaries (arrow in D) and mesangial ECM accumulation.
Fig 3.
Several glomerular capillary alterations in cases of idiopathic membranous nephropathy without FSGS lesion (CD34 stain, x600).
In the glomeruli with minimal glomerular abnormalities by light microscopy (A), nearly normal glomerular capillary network was identified without ECM accumulation. During the development of capillary narrowing in small glomerular area (B), segmental glomerular area (C), and global glomerular area (D and E), ECM accumulated in mesangium and capillary walls in glomeruli. In global sclerotic glomeruli (F), marked and complete loss of glomerular capillaries was noted with massive accumulation of ECM in glomeruli.
Fig 4.
The activation of mesangial cells, infiltration of inflammatory cells in glomeruli, and the expression of vascular endothelial growth factor (VEGF) on podocytes in idiopathic membranous nephropathy (MN) (A: αSMA, B: MPO, C: CD3, D: CD68, E-F: VEGF, x600).
In MN, the αSMA-positive activation of mesangial cells (arrow in A) was noted with mesangial ECM accumulation. In glomeruli, although infiltration of MPO-positive neutrophils (B) and CD3-positive T cells (C) was hardly observable, CD68-positive macrophages (arrow in D) frequently infiltrated the glomeruli. Similar degree of expression of VEGF (arrow) was evident on podocytes in both MN cases with (E) and without (F) FSGS lesion.
Fig 5.
The injury of the glomerular endothelial cells and podocytes in idiopathic membranous nephropathy (MN).
(A) In MN-FSGS(+) cases, an increase in the number of endothelial cells, swelling of the nuclei and cytoplasm, loss of fenestra, and widening of the subendothelial space were noted, suggesting the development of glomerular endothelial cell injury. (B) Narrowing of the capillary lumen was seen with foot process effacement of podocytes, widening of subendothelial space, and mesangial interposition, suggesting the presence of podocyte injury and the findings of reaction of glomerular endothelial cell injury. (C) Infiltration of monocytes and macrophages was noted in glomerular capillary lumens and subendothelial spaces with swelling of the nuclei and cytoplasm and loss of fenestra in glomerular endothelial cells, suggesting the glomerular endothelial cell injury and macrophage infiltration. (D) In MN-FSGS(−) cases, segmental glomerular endothelial cell damage was detected with infiltration of monocyte and macrophages, thickening of glomerular capillary walls, and loss of foot processes of podocytes, suggesting that, although the severity was mild, injuries of glomerular endothelial cells and podocytes were developed in glomeruli even in MN-FSGS(−) cases.
Fig 6.
The relationship between the areas of glomerular capillaries and glomerular ECM in glomerular cross section in idiopathic membranous nephropathy (MN) by computer-assessed morphometric analysis.
(A) The areas (μm2) of glomerular capillaries (X-axis) and ECM (Y-axis) were measured in MN-FSGS(+) cases (blue rhombus), MN-FSGS(−) cases (red square), and minor glomerular abnormalities in control (yellow x). In MN cases with or without FSGS lesion, increase of glomerular capillary area and/or glomerular ECM area was evident, suggesting the development of glomerular hypertrophy. In MN-FSGS(−) cases, the area of capillaries was positively correlated with the area of ECM in glomeruli. In contrast, there was no correlation between the areas of capillaries and ECM in glomeruli in MN-FSGS(+), suggesting the development of decrease of glomerular capillary area with increase of ECM area in enlarged glomeruli. (B) To avoid the effects of the variation in the size of glomeruli, the areas of glomerular capillaries and ECM in glomeruli were adjusted by using the area of glomerular capillaries / the area of glomerular tuft, and the area of glomerular ECM / the area of glomerular tuft. Regardless of the presence or absence of FSGS lesion, the areas of glomerular capillaries and ECM were negatively correlated, indicating that the narrowing and decrease of glomerular capillaries was associated with the accumulation of ECM. (C, D) We examined the areas of glomerular capillaries and ECM in glomeruli in each stage of MN (stage I to IV) in cases without FSGS lesion (C, FSGS −) and with FSGS lesion (D, FSGS +). The horizontal boundary is set at the average of glomerular capillary area of all glomeruli in control and MN cases with and without FSGS lesion. The longitudinal boundary is set at the average of glomerular ECM area of all glomeruli in control and MN cases with and without FSGS lesion. In accordance with the setting the boundary for the average of the areas of glomerular capillaries and glomerular ECM, all glomeruli were divided into 4 categories; a: large capillary area with minimal accumulation of ECM, b: large capillary area with marked accumulation of ECM, c: decrease of glomerular capillary area with minimal accumulation of ECM, and d: decrease of glomerular capillary area with marked accumulation of ECM. (n = number) is the number of cases of MN with and without FSGS lesion in each category. In MN-FSGS(−) cases (C), many cases, especially stage I and stage II, were present in category a (36/86: 41.9%). In contrast, the most common category in MN-FSGS(+) cases (D), was d (57/95: 60.0%), and many cases of stage III (18/24: 75.0%) and IV (11/17:64.7%) fell into this category. These findings indicate that the decrease of glomerular capillaries with increase of glomerular ECM area was more prominent in MN-FSGS(+) than those in MN-FSGS(−) cases.
Fig 7.
Box and Whisker plot of the glomerular tuft area (enlarged glomeruli) (A), the number of glomerular capillaries (B), the glomerular capillary area (C), and the glomerular ECM area (D) in cases of minor glomerular abnormalities (control), MN cases with FSGS lesion (FSGS +) and without FSGS lesion (FSGS −).
(A) The enlargement of glomerular tuft area (glomerular hypertrophy) was evident in both MN cases with and without FSGS lesion compared to control. However, there was no significantly difference in glomerular tuft area in MN cases with and without FSGS lesion. (B) The decreased number of glomerular capillaries was noted in MN-FSGS(+) compared to control and MN-FSGS(−), suggesting the prominent loss and reduced glomerular capillaries in MN-FSGS(+). (C) The reduced area of glomerular capillaries was noted in MN-FSGS(+) cases compared to control and MN-FSGS(−), indicating the narrowing of glomerular capillaries in MN-FSGS(+). There was no significant difference in glomerular capillary area in control and MN-FSGS(−) cases. (D) The increase of glomerular ECM area was observed in MN with or without FSGS lesion compared to control, suggesting the development of enlarged glomeruli and the narrowing glomerular capillaries with ECM accumulation in MN cases.
Table 2.
Several histological parameters in MN cases with or without FSGS lesion.
Fig 8.
The alteration of glomerular capillaries in cases of idiopathic membranous nephropathy (MN) with/without FSGS lesion.
Representative alterations of glomerular capillary walls were indicated from stage I to Stage IV of MN. The thickening of glomerular capillary walls was seen with ECM accumulation in both MN cases with and without FSGS lesion, with subepithelial deposits in stage I, spike formation in stage II to III, and wash out of deposits in stage IV. However, in MN-FSGS(−) cases, glomerular capillary walls with subepithelial deposits in stage I to IV were characterized by well-preserved fenestra of glomerular endothelial cells, less widening of subendothelial space, mild thickening of glomerular capillary walls and GBM, and relatively preserved foot processes of podocytes. On the other hand, in MN-FSGS(+) cases there were prominent thickening of glomerular capillary walls with ECM accumulation, loss of foot processes of podocytes, and endothelial cell injury, indicated by loss of fenestra, swelling of cytoplasm and dilatation of subendothelial space.
Table 3.
The thickness of glomerular capillary walls (μm) in MN cases with and without FSGS lesion.