Abstract
Purpose :
Alterations to cilia are responsible for a wide range of severe disease, with one feature of such ciliopathies being the variable involvement of multiple organs. Prompted by its pleiotropy, we evaluated whether cases of Axenfeld-Rieger Syndrome (ARS) caused by the transcription factor FOXC1, reflected ciliary dysfunction.
Methods :
Patients with FOXC1-attributable ARS were assessed for phenotypes indicative of a ciliopathy. Measurements of cilia length, and biochemical analyses of cilia-dependent Platelet Derived Growth Factor Receptor α and Hedgehog (Hh) signaling were undertaken in murine fibroblasts and renal collecting duct cells, in which Foxc1 dosage was altered. The accumulation of Gli2 at the ciliary tip was measured using cells stably expressing Gli2-mGFP, while RNA-sequencing was performed to detect expression of ciliary genes.
Results :
Patients with FOXC1-attributable ARS (n=41) exhibit a prevalence of ciliopathy-associated phenotypes comparable to syndromic ciliopathies. Alteration to the level of Foxc1 via shRNA mediated inhibition and mRNA overexpression, induced reciprocal effects on cilia length in vitro. These structural changes were associated with substantially perturbed cilia-dependent signaling (PDGFRα and Hh) and altered ciliary compartmentalization of Gli2, a key effector of the Hh pathway. Consistently, RNA-sequencing revealed that Foxc1 regulates the expression of multiple ciliary genes, including a motor Kinesin with an essential role in Hh signal transduction.
Conclusions :
These findings demonstrate that the clinical features of ARS phenocopy recognized ciliopathies, and that increased and decreased Foxc1 gene dosage, impact cilia structure and function in vitro. Taken together with perturbation of essential developmental pathways, and the dynamic localisation of ciliary proteins, these data suggest that ARS represents an unrecognized ciliopathy.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.