Angiotensin II and EGF Receptor Cross-talk in Chronic Kidney Diseases: A New Therapeutic Approach

Abstract and Introduction

Abstract

Mechanisms of progression of chronic renal diseases, a major healthcare burden, are poorly understood. Angiotensin II (AngII), the major renin-angiotensin system effector, is known to be involved in renal deterioration, but the molecular pathways are still unknown. Here, we show that mice overexpressing a dominant negative isoform of epidermal growth factor receptor (EGFR) were protected from renal lesions during chronic AngII infusion. Transforming growth factor-α (TGF-α) and its sheddase, TACE (also known as ADAM17), were induced by AngII treatment, TACE was redistributed to apical membranes and EGFR was phosphorylated. AngII-induced lesions were substantially reduced in mice lacking TGF-α or in mice given a specific TACE inhibitor. Pharmacologic inhibition of AngII prevented TGF-α and TACE accumulation as well as renal lesions after nephron reduction. These findings indicate a crucial role for AngII-dependent EGFR transactivation in renal deterioration and identify in TACE inhibitors a new therapeutic strategy for preventing progression of chronic renal diseases.

Introduction

Regardless of etiology, most human kidney diseases are characterized by an initial injury, followed by progression of renal lesions to complete parenchymal destruction and end-stage renal failure.^[1] Clinical and experimental studies have shown that angiotensin II (AngII), the major renin-angiotensin system effector, has an important role in the biological process leading to renal deterioration. Indeed, pharmacological inhibition of the renin-angiotension system attenuates development of renal lesions in several experimental models of renal injury^[2] and retards progressive loss of renal function in individuals with chronic kidney disease (CKD).^[3] Conversely, individuals with genetic variants associated with higher renin-angiotensin system activity are at increased risk for progression of chronic renal failure.^[4] It has been suggested that AngII causes renal injury through renal hemodynamic effects and stimulation of kidney growth and matrix deposition,^[5] but the molecular pathways underlying these phenomena remain largely unidentified.

AngII acts on at least two structurally and pharmacologically distinct G-protein-coupled receptors (GPCRs), AT₁ and AT₂ (ref. 6). Renal cells predominantly express AT₁ receptors, which mediate the majority of known AngII actions.^[7] AT₁ receptors activate Gq-phospholipase C to generate inositol triphosphate and diacylglycerol, thereby increasing intracellular calcium and stimulating protein kinase C.^[8] Additionally, activation of AT₁ receptors promotes tyrosine phosphorylation and stimulates mitogen-activated protein kinases and proliferation.^[9,10] How AT₁ receptors, which lack intrinsic tyrosine kinase activity, induce these events is unclear, but recent evidence suggests that 'transactivation' of the epidermal growth factor receptor (EGFR) is involved,^[11] and may require several intermediary signaling molecules including Ca²⁺, protein kinase C and cytosolic tyrosine kinases.^[9] Recently, it has been shown that metalloprotease-dependent release of EGFR ligands from cells is also involved in GCPR-induced EGFR transactivation.^[12] Whether and by which molecular mechanisms AngII transactivates EGFR in renal cells during kidney diseases is unknown.

EGFR binds members of a family of growth factors, comprised of EGF, transforming growth factor-α (TGF-α), heparin-binding EGF-like growth factor, amphiregulin, epiregulin, betacellulin and epigen.^[13] All family members are synthesized as membrane-anchored precursors that can be processed by specific metalloproteases to release soluble bioactive factors from the cell surface.^[13] In the kidney, both EGFR and its ligands are abundantly expressed along the nephron, suggesting a paracrine-autocrine system.^[14,15] Addition of EGFR ligands to tubular cells promotes several biological responses in vitro, including cell proliferation,^[16] mesenchymal-epithelial transdifferentiation^[17] and collagen production.^[18] In vivo, activation of EGFR is thought to be involved in the evolution of renal diseases.^[19] Overexpression of the EGFR-related c-erb-B2 receptor induces tubular hyperplasia and the development of renal cysts in transgenic mice.^[20] Conversely, expression of a dominant negative isoform of EGFR in proximal tubules inhibits tubular cell proliferation and interstitial collagen accumulation, leading to reduced renal lesions after nephron reduction.^[21] Other genetic and pharmacological approaches have confirmed the role of EGFR in tubular cyst formation and cell proliferation in polycystic kidney diseases,^[22,23] and in renal fibrosis in an experimental model of hypertension.^[24] Collectively, these results suggest that EGFR could be a major determinant in the development of renal lesions, possibly through enhanced cell proliferation and matrix deposition.

We hypothesized that EGFR transactivation is crucial to the lesion-promoting effects of AngII in the kidney. Using transgenic mice and pharmacological inhibitors, we show that inhibition of the EGFR pathway prevents development of AngII-induced renal lesions. Furthermore, we provide evidence that TACE (tumor necrosis factor-α converting enzyme, also known as ADAM17) and TGF-α are crucial intermediates between AngII signal and EGFR transactivation during kidney diseases, and we identify a new therapeutic target.