Endothelin A receptor activation on mesangial cells initiates Alport glomerular disease

Abstract

Recent work demonstrates that Alport glomerular disease is mediated through a biomechanical strain-sensitive activation of mesangial actin dynamics. This occurs through a Rac1/CDC42 cross-talk mechanism that results in the invasion of the sub-capillary spaces by mesangial filopodia. The filopodia deposit mesangial matrix proteins in the glomerular basement membrane, including laminin 211, which activates focal adhesion kinase in podocytes culminating in the up-regulation of pro-inflammatory cytokines and metalloproteinases. These events drive the progression of glomerulonephritis. Here we test whether endothelial cell-derived endothelin-1 is upregulated in Alport glomeruli, and further elevated by hypertension. Treatment of cultured mesangial cells with endothelin-1 activates the formation of drebrin-positive actin microspikes. These microspikes do not form when cells are treated with the endothelin A receptor antagonist sitaxentan, or under conditions of siRNA knockdown of endothelin A receptor mRNA. Treatment of Alport mice with sitaxentan results in delayed onset of proteinuria, normalized glomerular basement membrane morphology, inhibition of mesangial filopodial invasion of the glomerular capillaries, normalization of glomerular expression of metalloproteinases and pro-inflammatory cytokines, increased lifespan, and prevention of glomerulosclerosis and interstitial fibrosis. Thus endothelin A receptor activation on mesangial cells is a key event in initiation of Alport glomerular disease in this model.

Endothelin-1 mediated induction of extracellular matrix genes in strial marginal cells underlies strial pathology in Alport mice

“…This study demonstrates that progressive SCBM thickening, which results in metabolic and oxidative stress in the stria vascularis of Alport mice, evolves through a mechanism that is remarkably similar to the mechanism of glomerular basement membrane disease (Dufek et al, 2016); Endothelin-1 mediated activation of ET A Rs on strial marginal cells resulting in elevated expression of ECM proteins that accumulate in the SCBMs. We show using both in vivo and in vitro systems, that ET A R blockade results in reduced ECM protein expression, normalization of SCBM thickness and reduced expression of mRNAs encoding ECM proteins that accumulate in the SCBMs.…”

“…More recently we have shown that endothelin-1 (ET-1) activates the accumulation of abnormal GBM laminins (including laminin 211) and initiates epithelial cell dysfunction in the renal glomerulus via activation of the endothelin A receptor subclass (Dufek et al, 2016). Blocking ET A Rs using sitaxentan resulted in the inhibition of ECM accumulation in the GBM and amelioration of glomerular disease initiation and progression.…”

“…Blocking ET A Rs using the small molecule inhibitor, Sitaxentan, ameliorates glomerular and renal disease in Alport mice (Dufek et al, 2016). We examined the cellular distribution of ET A Rs in the stria vascularis in adult mice by immunohistochemistry.…”

“…Al., 2013; Delimont et al, 2014), and more recently that endothelin-1-mediated activation of the endothelin A receptors (ET A Rs) on glomerular mesangial cells activates the invasion of glomerular capillaries by mesangial filopodia (Dufek et al, 2016). Blocking either FAK or ET A Rs ameliorated the dysregulation of pro-pathologic genes, including matrix metalloproteinases (MMPs) in glomerular podocytes and significantly improved GBM architecture and function in these same mice.…”

X-Linked Alport Dogs Demonstrate Mesangial Filopodial Invasion of the Capillary Tuft as an Early Event in Glomerular Damage

“…[5, 6] The α3α4α5 type IV collagen network is more heavily cross-linked and protease-resistant than α1α1α2, and is therefore better suited for maintaining GBM integrity from increasing hydrostatic pressure to which glomeruli are exposed. [2, 7–9] Laminin is the most prevalent non-collagenous protein of the GBM. These cross-shaped heterotrimers consists of an α, β, and γ chain with sixteen different isoforms being identified.…”