Paper of the week: Focussing on the importance of APP in the retina

Ho, T., Vessey, K. a., Cappai, R., Dinet, V., Mascarelli, F., Ciccotosto, G., & Fletcher, E. (2012). Amyloid Precursor Protein Is Required for Normal Function of the Rod and Cone Pathways in the Mouse Retina. PLoS ONE, 7(1), e29892.

Amyloid precursor protein (APP) is a naturally occurring transmembrane protein found in the brain that has been intensely studied for its role in pathology, particularly Alzheimer’s disease. However, APP is also produced in the retina for reasons that are not well understood.

To investigate this further, mice genetically engineered to be APP-deficient were tested for their retinal responses and visual function. The authors had previously found that APP was involved in retinal cell development, and hypothesized that APP-deficient mice would show abnormal retinal responses to visual stimulation.

Retinal function was assessed using electroretinography (ERG) using custom made Ag-AgCl electrodes and a PowerLab. Scope was used to coordinate full-field optical flashes and record ERG responses.

APP-deficient mice showed subtle differences in ERG responses to flashes of light. For instance, both rod and cone photoreceptor responses showed a significant reduction in ‘b-wave’ amplitude, with larger oscillatory potentials on the leading edge of the b-wave. However, no change in the kinetics of oscillatory potentials or a-wave amplitudes were found, suggesting a possible circuit level role of APP in retinal processing via interneuron signaling (amacrine cells). 

To investigate whether these differences in ERG responses led to possible visual deficits, tests of the ability of mice to track a moving stimulus were performed. However, no differences in visual acuity were found. These results suggest that, while APP may play a role in modulation of the inner retinal circuitry, it is not required for retinal architecture or basic visual function.

17 February 2012