Alport syndrome is characterized by renal disease associated with sensorineural hearing loss. While much is known about the molecular nature of Alport glomerular and interstitial kidney disease, the mechanisms underlying the hearing loss phenotype remain relatively underexplored. In a series of recent papers and some unpublished results, we have revealed a mechanism for glomerular disease initiation involving activation of endothelin-1 that activates the formation of mesangial filopodia through the endothelin A receptor (ETAR). The filopodia invade the capillaries progressively leaving punctate deposits of mesangial matrix proteins, including laminin 211, in the glomerular basement membrane (GBM). The laminin 211 activates focal adhesion kinase on podocytes, leading to maladaptive gene expression that drives glomerular pathogenesis. Inhibiting this pathway by blocking ETAR has a profound effect on glomerular disease progression in the mouse model. As in the GBM, the strial capillary basement membranes (SCBMs) gradually thicken in Alport mice. These events result in a hypoxic environment in the scala media and a sensitivity to noise-induced hearing loss with a significant drop in the endocochlear potential (EP), proving that in the mouse, hearing loss is due to strial dysfunction. We show preliminary evidence that endothelin-1, laminin 211, collagen ?1(IV), and laminin ?5 are up-regulated in the stria vascularis of Alport mice relative to wild type mice, and are associated with FAK activation. Endothelin A receptors (ETARs) are present on strial marginal cells, and ETAR blockade prevents SCBM thickening and accumulation of matrix in the SCBM. Our central hypothesis is: Treatment of Alport mice with the ETAR antagonist Sitaxentan will prevent SCBM thickening and normalize strial function, preventing hearing loss and protecting animals from the inner ear metabolic stresses and pathology normally associated with Alport syndrome in the mouse model. We will address this in four specific aims: In the first we will determine whether ETAR blockade in the mouse model normalizes expression of ECM proteins and MMPs, SCBM thickness and permeability. In the second aim we will utilize a strial marginal cell line to probe the mechanism of ET-1 induction and ETAR signaling as it relates to induction of genes encoding ECM and MMPs. In the third we will determine whether normalization of SCBM thickness via ETAR blockade results in normalization of endocochlear potentials (EPs) and protection from noise induced hearing loss. Lastly, we will determine whether we have achieved metabolic rescue and return of normoxia by measuring noise induced mitochondrial ROS, oxidized/reduced glutathione ratios, and ATP levels in the stria of Alport mice compared to Alport mice under ETAR blockade. The discovery of this pathway suggests that a single drug target, in this case small molecule inhibitors that block ETAR, may provide a means of ameliorating both the glomerular and inner ear pathologies associated with Alport syndrome.
Alport syndrome is characterized by renal disease associated with sensorineural hearing loss. Both symptoms are delayed onset and progressive. We have evidence that the mechanism of disease initiation in the renal glomerulus of the kidney and the stria vascularis in the ear are very similar, suggesting a single drug target could ameliorate both symptoms. This proposal aims to evaluate this mechanism in the stria vascularis of Alport mice using in vivo and in vitro approaches.
| Cosgrove, Dominic; Liu, Shiguang (2017) Collagen IV diseases: A focus on the glomerular basement membrane in Alport syndrome. Matrix Biol 57-58:45-54 |
| Meehan, Daniel T; Delimont, Duane; Dufek, Brianna et al. (2016) Endothelin-1 mediated induction of extracellular matrix genes in strial marginal cells underlies strial pathology in Alport mice. Hear Res 341:100-108 |
| Dufek, Brianna; Meehan, Daniel T; Delimont, Duane et al. (2016) Endothelin A receptor activation on mesangial cells initiates Alport glomerular disease. Kidney Int 90:300-310 |
