Abstract
Abstract: :
Purpose: In the study of animal models of retinitis pigmentosa, e.g. the rd mouse, it is necessary to identify which apoptosis related signaling pathways are functioning in the photoreceptors and if they differ from those in normal mice. The phosphatidylinositol 3-kinase (PI3K)/Akt kinase system is a signaling pathway which has been found to promote survival in different types of cells. The purpose of this study was to compare Akt activity in photoreceptors in normal and rd mice. Methods: Retinas were collected from C3H normal and rd mice at various ages (P1-P36), fixed, cryo-sectioned, and immunostained with antibodies directed towards total Akt and activated Akt. In addition, retinal samples from these two mouse strains were separated by SDS-PAGE, transferred onto PVDF membranes and treated according to standard Western blot protocols using antibodies against total and phosphorylated Akt. Results: On Western blots reacted with antibodies against either total or active Akt, retinal samples from both mouse strains gave rise to a single band of about 60 kD. In sections of rd and normal retinas, the cone photoreceptors first reacted with antibodies against active Akt at P5 and remained immunopositive on into adulthood. For a brief period during development (PN7-PN11), the rod photoreceptors were also reactive for active Akt. In the rd mouse, however, Akt remained active in the rods until they died via apoptosis. Conclusions: In both normal and rd mice, Akt is constitutively active in the cones. It is also noteworthy that Akt is only transiently active in normal mouse rod photoreceptors, but remains active in rd rods during the time they undergo apoptosis. It is possible that when these cells are stressed, the PI3K-Akt pathway is activated in an attempt at self-preservation. Since a number of growth factors are known to exert their survival effects through the PI3K-Akt pathway, it would be interesting to see if additional stimulation of Akt by pharmacological means might help to rescue these cells from apoptosis.
Keywords: apoptosis/cell death • photoreceptors • signal transduction: pharmacology/physiology