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Endothelin and the podocyte - PubMed

Review

Endothelin and the podocyte

Matthias Barton et al. Clin Kidney J. 2012 Feb.

Abstract

In the past decade, research has advanced our understanding how endothelin contributes to proteinuria and glomerulosclerosis. Data from pre-clinical and clinical studies now provide evidence that proteinuric diseases such as focal segmental glomerulosclerosis and diabetic nephropathy as well as hypertension nephropathy are sensitive to treatment with endothelin receptor antagonists (ERAs). Like blockade of the renin-angiotensin system, ERA treatment-under certain conditions-may even cause disease regression, effects that could be achieved on top of renin-angiotensin-aldosterone system blockade, suggesting independent therapeutic mechanisms by which ERAs convey nephroprotection. Beneficial effects of ERAs on podocyte function, which is essential to maintain the glomerular filtration barrier, have been identified as one of the key mechanisms by which inhibition of the endothelin ETA receptor ameliorates renal structure and function. In this article, we will review pre-clinical studies demonstrating a causal role for endothelin in proteinuric chronic kidney disease (with a particular focus on functional and structural integrity of podocytes in vitro and in vivo). We will also review the evidence suggesting a therapeutic benefit of ERA treatment on the functional integrity of podocytes in humans.

Keywords: diabetes; epithelial cell; focal segmental glomerulosclerosis; glomerular; hypertension.

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Figures

Fig. 1.
Fig. 1.

Proposed interactions of endothelin (ET-1) with the glomerular basement membrane (GBM) of the glomerular capillary, its endothelial cells (GEC) and podocytes/slit diaphragm. ET-1 is produced by cells on both sides of the GBM, namely GEC and podocytes. ET-1 is released from GEC and may interact either directly with GBM (1) the slit diaphragm (2) or the podocyte, also in the reverse direction (3). Podocyte-derived ET-1 (4) may also affect the GBM and vice versa. ET-1 activates podocyte endothelin ETA receptors (ETA R) activating mitogen-activated protein kinases (MAPKs) p38 and p44/p42 (5), growth promoters (p21waf/cip1), or inflammation (NF-kappaB) (6). ET-1 also causes disruption of the podocyte F-actin cytoskeleton (7) and slit diaphragm dysfunction via activation of rho kinase and PI3-kinase. Figure reproduced from reference [11] with permission of the publisher.

Fig. 2.
Fig. 2.

Effect of ETA receptor inhibition in laser-dissected glomeruli of rats with FSGS in vivo (a) and in podocytes in vitro (b-f). (a) Darusentan reduced MMP-9 gene expression (a marker of podocyte injury [103]) compared with placebo-treated rats. (b) In vitro treatment with puromycin aminonucleoside (PAN) caused podocyte apoptosis and up-regulation of MMP-9; (c) peptide (BQ) or non-peptide (LU, darusentan) ETA receptor antagonists prevented this effect, as did ETA receptor gene silencing (siRNA) (d). (e) Gene silencing of ETA receptors increased podocyte growth as determined by de novo DNA synthesis. (f) Actin cytoskeleton disruption was largely prevented by ETA antagonists; representative examples of these experiments are shown in Figure 3. ncRNA, non-coding RNA control; O, old; AU, arbitrary units; OLU, old, darusentan. *P < 0.05 versus control (CTL); †P < 0.05 versus PAN alone/old. Figure reproduced from reference [39] with permission of the publisher.

Fig. 3.
Fig. 3.

Endothelin mediates podocyte injury in vitro. (a, b) Actin-phalloidin immunofluorescence (left) and phase-contrast images of actin cytoskeleton fibres and cell morphology (right panels) in a normal podocyte. (c, d) Puromycin aminonucleoside (PAN)-induced foot process effacement, cytoskeleton disruption (disappearance of actin fibres) and cell body shrinkage. (e, f) Prevention of PAN-induced injury by the ETA antagonist BQ-123. (g, h) Prevention of PAN-induced injury by the ETA antagonist darusentan/ LU135252. (i, j) The ETB receptor antagonist BQ-788 had no effect on PAN-induced injury. Figure reproduced from reference [39] and reproduced with permission of the publisher.

Fig. 4.
Fig. 4.

Effect of 4 weeks of treatment with the ERA darusentan on renal structure in established FSGS [39]. (a) Untreated animal, transmission electron microscopy demonstrates GBM hypertrophy and podocyte injury with diffuse foot process effacement and vacuolar degeneration involving autophagy [113]. (b) ERA-treated animal, showing regression of GBM hypertrophy and disappearance of podocyte vacuoles. (c) Untreated animal, light microscopy image (haematoxilin/eosin) demonstrating hypertrophy of podocytes with enlarged nuclei, prominent nucleoles and vacuolar degeneration due to autophagy. (d) Treated animal, showing normal sized podocyte nuclei and virtually complete disappearance of vacuolar degeneration (arrows). Scale bar, 10 μm (c, d). Panels adapted from reference [39] and reproduced with permission of the publisher.

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