Mechanism dissection and gene therapy of the LCA3 mouse model

Abstract

Purpose: Leber congenital amaurosis (LCA) is a severe hereditary disease that causes visual impairment in infants and children. Our lab previously identified SPATA7 as the LCA3 gene, mutations in which cause LCA and retinitis pigmentosa. As no known protein domain has been identified in SPATA7, its function remains elusive and needs to be investigated in order to offer clues about its disease mechanism, which form the basis for future treatment of human patients.

Methods: To investigate the disease mechanism of LCA cause by mutation in SPATA7, a knock-out mouse model was generated. A combination of histology, immunohistochemistry, physiology, genetics, molecular and cell biology, as well as gene therapy techniques is applied to this newly established model.

Results: Similar with the phenotype observed in human patients, progressive degeneration of photoreceptor cells and rapid decrease of ERG were detected in the Spata7 knock-out mice. Further characterization indicated that the photoreceptor degeneration phenotype was largely due to apoptosis of rod photoreceptor cells. As SPATA7 is located specifically at the connecting cilium of photoreceptor cells, we hypothesized that it might be involved in protein transportation from the inner segment to the outer segment. Indeed, accumulation of Rhodopsin was detected in the inner segments and cell bodies of photoreceptors, which likely to trigger photoreceptor cell death. Consistently, time course studies indicated that Rhodopsin mislocalization preceded photoreceptor cell death in the Spata7 mutant retina. Finally, reduction in the dose of rod opsin suppressed photoreceptor apoptosis and rescued the retina degeneration phenotype in the Spata7 mutant. Gene therapy using rAAV carrying Spata7 cDNA is carried out in the Spata7 mutant retina. Consistent with the idea that Spata7 is important for Rho localization rather than photoreceptor cell development, excellent rescue of the mutant phenotype is obtained.

Conclusions: Together these results suggest that SPATA7 is required for proper protein trafficking and apoptosis of Rod photoreceptor cells trigged by mislocalized Rho is likely the disease mechanism for LCA3 patients. Gene therapy is likely a viable option for treating LCA3 patients.

Keywords: 740 transgenics/knock-outs • 695 retinal degenerations: cell biology • 625 opsins