Abnormalities of the vitreoretinal interface caused by dysregulated Hedgehog signaling during retinal development

Mutations in Patched (PTCH), encoding the Hedgehog (Hh) receptor, underlie Basal Cell Naevus syndrome (BCNS) and, in addition to tumor predisposition, are associated with a wide range of 'patterning' defects. The basis for the underlying patterning problems in Hh-dependent tissues in BCNS and their long-term consequences on tissue homeostasis are, however, not known. Hh signaling is required for normal growth and organization of the mammalian retina and we show that PtchlacZ+/- mice exhibit vitreoretinal abnormalities resembling those found in BCNS patients. The retinas of PtchlacZ+/- mice exhibit abnormal cell cycle regulation, which culminates in photoreceptor dysplasia and Müller cell-derived gliosis. In BCNS, the intraretinal glial response results in epiretinal membrane (ERM) formation, a proliferative and contractile response on the retinal surface. ERMs are a cause of significant visual loss in the general, especially elderly, population. We hypothesize that alteration of Müller cell Hh signaling may play a role in the pathogenesis of such age-related 'idiopathic' ERMs.