TGF expression and macrophage accumulation in atherosclerotic renal artery stenosis

Abstract

Background and objectives: Atherosclerotic renal artery stenosis (ARAS) reduces renal blood flow and is a potential cause of chronic kidney injury, yet little is known regarding inflammatory pathways in this disorder in human participants. This study aimed to examine the hypothesis that reduced renal blood flow (RBF) in ARAS would be associated with tissue TGF-β activation and inflammatory cell accumulation.

Design, setting, participants, & measurements: This cross-sectional study of ARAS of varying severity compared transjugular biopsy specimens in patients with ARAS (n=12, recruited between 2008 and 2012) with tissue from healthy kidney donors (n=15) and nephrectomy specimens from individuals with total vascular occlusion (n=65). ARAS patients were studied under controlled conditions to measure RBF by multidetector computed tomography and tissue oxygenation by blood oxygen level-dependent magnetic resonance imaging.

Results: Compared with the nonstenotic contralateral kidneys, RBF was reduced in poststenotic kidneys (242±149 versus 365+174 ml/min; P<0.01) as was single-kidney GFR (28±17 versus 41±19 ml/min; P<0.01), whereas cortical and medullary oxygenation were relatively preserved. Tissue TGF-β immunoreactivity was higher in ARAS patients compared with those with both normal kidneys and those with total occlusion (mean score 2.4±0.7 versus 1.5+1.1 in the nephrectomy group and versus 0±0 in donors; P<0.01). By contrast, the number of CD68+ macrophages was higher with greater disease severity (from 2.2±2.7 in normal to 22.4±18 cells/high-power field in nephrectomy samples; P<0.001).

Conclusions: The results of this study indicate robust stimulation of TGF-β associated with macrophage infiltration within the human kidney with vascular occlusive disease.

Figure 1.

Tissue histology in vascular occlusive disease. Tissue sections (H&E stain) from a normal kidney donor at implantation (A), patients with ARAS undergoing transjugular biopsy (B), and a nephrectomy specimen removed for total vascular occlusion of a “pressor” kidney (C). Overall architecture of glomeruli and tubular structures were variable but relatively preserved in ARAS with some degrees of inflammation, as compared with total occlusion where tubular structures are collapsed and largely replaced with fibrosis and inflammatory infiltrates. Original magnification, ×20. H&E, hematoxylin and eosin; ARAS, atherosclerotic renal artery stenosis.

Figure 2.

Scores of fibrosis and tubular atrophy. Semi-quantitative scoring (see text) of tissue specimens for the degree of fibrosis and tubular atrophy indicated more extensive changes with the more severe vascular occlusion. **P<0.01 versus donors. ARAS, atherosclerotic renal artery stenosis; Nx, nephrectomy.

Figure 3.

TGF-β staining. Tissue staining for TGF-β demonstrated widespread expression in ARAS that was not evident in normal kidneys and was much less evident in samples from nephrectomy tissue with total occlusion. TGF-β was identified within parenchymal and glomerular regions independent of the degree of tubular atrophy or evident fibrosis. **P<0.01 versus donors. ARAS, atherosclerotic renal artery stenosis; Nx, nephrectomy.

Figure 4.

CD68+ macrophages in vascular occlusive disease. Counts for CD68+ cells within tissue samples demonstrated more macrophages in ARAS and nephrectomy samples, in addition to CD3+ cells. CD68+ cells were evident in interstitial compartments and interspersed among clusters of inflammatory cells in advanced disease and were positively related to TGF-β expression (see text). **P<0.01 versus donors. ARAS, atherosclerotic renal artery stenosis; Nx, nephrectomy; hpf, high-power field.