Identification of platelet-derived growth factor D in human chronic allograft nephropathy

Abstract

Chronic allograft nephropathy (CAN), a descriptive term denoting chronic scarring injury of the renal parenchyma and vasculature in allograft kidneys arising from various etiologies including chronic rejection, is the most common cause of late allograft failure, but mediators of this progressive injury largely remain unknown. We hypothesized that platelet-derived growth factor D (PDGF-D) and its specific receptor PDGF-Rbeta may be an important mediator in the pathogenesis of CAN and, hence, sought to identify its expression in this setting. Allograft nephrectomies demonstrating CAN, obtained from patients with irreversible transplant kidney failure (n = 15), were compared with renal tissues without prominent histopathological abnormalities (n = 18) and a series of renal allograft biopsies demonstrating acute vascular rejection (AVR) (n = 12). Antibodies to PDGF-D and PDGF-Rbeta were used for immunohistochemistry. Double and triple immunohistochemistry was used to identify cell types expressing PDGF-D. PDGF-D was widely expressed in most neointimas in arteries exhibiting the chronic arteriopathy of CAN and only weakly expressed in a small proportion of sclerotic arteries in the other 2 groups. Double and triple immunolabeling demonstrated that the neointimal cells expressing PDGF-D were alpha-smooth muscle actin-expressing cells, but not infiltrating macrophages or endothelial cells. PDGF-Rbeta expression evaluated in serial sections was localized to the same sites where neointimal PDGF-D was expressed. PDGF-Rbeta was expressed in interstitial cells more abundantly in the CAN group compared with the normal and AVR groups, without demonstrable colocalization of PDGF-D. PDGF-D is present in the neointima of the arteriopathy of CAN, where it can engage PDGF-Rbeta to promote mesenchymal cell migration, proliferation, and neointima formation. PDGF-D may engage the PDGF-Rbeta to promote interstitial injury in chronic allograft injury, but its sources within the interstitium were unidentified.

Fig. 1

PDGF-D and PDGF-Rβ expression in arteries. A: In normal group, triple immunolabeling shows that PDGF-D (brown) is expressed in arterial medial smooth muscle cells that also express alpha-smooth muscle actin (blue-gray); no monocyte/macrophages (purple) are found. There is no expression of PDGF-D seen in the interstitium. B: In serial section of A, PDGF-Rβ (brown) is expressed in the similar distribution of PDGF-D in arterial wall, and is also expressed mildly in interstitium. C: In kidneys with AVR, triple immunolabeling shows that PDGF-D (brown) is expressed in arterial medial smooth muscle cells, some adventitial cells and some neointimal cells that also have alpha-smooth muscle actin (blue-gray) expression; It is not expressed by the subendothelial infiltrating monocyte/macrophages (purple). D: In serial section of C, PDGF-Rβ (brown) is expressed in the similar distribution of PDGF-D in the arterial wall. E: Part of an artery in kidneys with CAN, triple immunolabeling shows that PDGF-D (brown) is expressed in arterial medial smooth muscle cells and the more prominent neointimal layers compared with the other two groups, which also have alpha-smooth muscle actin (blue-gray) expression; It is not expressed by the subendothelial infiltrating monocyte/macrophages and foam cells (purple). The inset shows the framed area with high power. F and its inset: In serial section of D, PDGF-Rβ (brown) is expressed in a similar distribution of PDGF-D in the artery. Original magnification, AD, × 400, E and F, × 100.

Fig 2

PDGF-D, PDGF-Rβ and smooth muscle actin in transplant arteriopathy. A: PDGF-D is expressed by medial smooth muscle cells, neointimal smooth muscle cells and some adventitial cells. B: In a serial section, PDGF-Rβ is expressed in a similar pattern by medial smooth muscle cells and neointimal smooth muscle cells. In addition, extravascular interstitial and adventitial cells strongly express PDGF-Rβ. C: Alpha smooth muscle actin immunolabeling of a serial section demonstrates a pattern of expression similar to PDGF-D, with strong staining of medial smooth muscle cells, neointimal smooth muscle cells and some adventitial cells and indicates co-localization of PDGF-D to these cells. Expression by interstitial myofibroblasts is also seen (*), which lack PDGF-D co-localization. G: glomerulus Original magnification A-C, ×200.

Fig. 3

PDGF-D and PDGF-Rβ expression in tubulointerstitial areas. PDGF-D is expressed uniformly in a few tubuli in A: normal kidneys, B: kidneys with acute vascular rejection (AVR), and C: kidneys with chronic allograft nephropathy (CAN). PDGF-Rβ is expressed in interstitial areas in normal kidneys (D) and in kidneys with AVR (E), and more extensively in kidneys with CAN (F). Original magnification A-E, ×400.

Fig. 4

PDGF-D colocalization with smooth muscle actin and PDGF-Rβ in the interstitium. A and B: Double IHC showing PDGF-D (brown) and α-smooth muscle actin (purple). PDGF-D is expressed by glomerular podocytes and a subset of interstitial cells (A). High power view demonstrates colocalization of PDGF-D and α-smooth muscle actin by interstitial myofibroblasts. C and D. Double IHC showing PDGF-D (purple) and PDGFR-beta (brown). PDGF-D is expressed by glomerular podocytes and a subset of interstitial cells (C). High power view shows PDGF-D colocalized PDGFR-beta in a subset of interstitial myofibroblasts (D). Original magnification A and C ×400, B and D ×1000.

Fig. 5

PDGF-D and PDGF-Rβ expression in glomeruli. PDGF-D is uniformly expressed in visceral epithelial cells and arteriolar wall in A: normal kidneys, B: kidneys with AVR, and C: kidneys with CAN. PDGF-Rβ is expressed weakly in mesangial areas in D: normal kidneys, E: kidneys with AVR, and more prominently in mesangial areas in F: kidneys with CAN. It is also expressed in some parietal epithelial cells and periglomerular areas in all three groups. Original magnification, × 400.