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

Abstract

Alport syndrome, a type IV collagen disorder, manifests as glomerular disease associated with hearing loss with thickening of the glomerular and strial capillary basement membranes (SCBMs). We have identified a role for endothelin-1 (ET-1) activation of endothelin A receptors (ETARs) in glomerular pathogenesis. Here we explore whether ET-1 plays a role in strial pathology. Wild type (WT) and Alport mice were treated with the ETAR antagonist, sitaxentan. The stria vascularis was analyzed for SCBM thickness and for extracellular matrix (ECM) proteins. Additional WT and Alport mice were exposed to noise or hypoxia and the stria analyzed for hypoxia-related and ECM genes. A strial marginal cell line cultured under hypoxic conditions, or stimulated with ET-1 was analyzed for expression of hypoxia-related and ECM transcripts. Noise exposure resulted in significantly elevated ABR thresholds in Alport mice relative to wild type littermates. Alport stria showed elevated expression of collagen α1(IV), laminin α2, and laminin α5 proteins relative to WT. SCBM thickening and elevated ECM protein expression was ameliorated by ETAR blockade. Stria from normoxic Alport mice and hypoxic WT mice showed upregulation of hypoxia-related, ECM, and ET-1 transcripts. Both ET-1 stimulation and hypoxia up-regulated ECM transcripts in cultured marginal cells. We conclude that ET-1 mediated activation of ETARs on strial marginal cells results in elevated expression of ECM genes and thickening of the SCBMs in Alport mice. SCBM thickening results in hypoxic stress further elevating ECM and ET-1 gene expression, exacerbating strial pathology.

The Adverse Effects of Environmental Noise Exposure on Oxidative Stress and Cardiovascular Risk

“…All of these vascular alterations support the development of metabolic disorders as envisaged by increased blood glucose levels. ET-1 expression levels were also reported to contribute to the phenotype of Alport (Col4a3 −/− ) mice that display a particular susceptibility to toxic noise and represent a model of glomerular disease associated with hearing loss ( 151 ).…”

Alport syndrome: facts and opinions

“…Normal expression of the collagen IV α345 network in basement membranes of the cochleae is prevented in Alport syndrome, although the mechanism through which this abnormality leads to hearing loss in Alport patients remains uncertain 14– 16 . Findings in Alport mice suggest that the hearing loss may arise from dysfunction of the stria vascularis mediated through endothelin-1 14, 17, 18 , but there are no corresponding human data. On the other hand, studies of human Alport cochleae suggest that the absence of the collagen IV α345 network may disturb cochlear micromechanics 15, 16 , but there are no supportive animal data.…”

Alport Syndrome

“…The generation of radial tension of the spiral ligament on the basilar membrane via the extracellular matrix is necessary for reception of high-frequency sound. The lateral aspect of the spiral ligament is populated by tension fibroblasts expressing nonmuscle myosin and α-smooth muscle actin [40]. On the basis of the foregoing, it was assumed that in AS, the loss of the α3α4α5 network eventually weakens the interaction of fibroblasts with their extracellular matrix, resulting in reduced tension on the basilar membrane and the inability to respond to high-frequency sounds [40].…”

“…The lateral aspect of the spiral ligament is populated by tension fibroblasts expressing nonmuscle myosin and α-smooth muscle actin [40]. On the basis of the foregoing, it was assumed that in AS, the loss of the α3α4α5 network eventually weakens the interaction of fibroblasts with their extracellular matrix, resulting in reduced tension on the basilar membrane and the inability to respond to high-frequency sounds [40]. Findings in Alport mice suggest that the hearing loss may arise from dysfunction of the stria vascularis mediated through endothelin-1 [40,41].…”