Abstract
Abstract: :
Purpose: To understand the apoptotic degeneration of photoreceptors in animal models of retinitis pigmentosa, e.g. the rd1 mouse, it is necessary to unravel the signalling pathways that govern the development and life / death decisions of these cells in both normal and affected mice. We have previously reported that the PI3–kinase / Akt–kinase pathway becomes engaged in the developing retina, so that at postnatal day (PN) 11 most, if not all, cell types of the retina are positive for phospho–Akt immunostaining. While the Akt pathway is regarded as having anti–apoptotic effects, the c–jun N–terminal kinase (JNK) pathway seems, at least in some instances, to drive apoptosis. Here we have examined if JNK is activated in the mouse retina and if there is a difference between normal and rd1 mice in this respect. Methods: Retinas were collected from C3H mice at PN11 (when the degenerative processes in the rd1 retina are well under way), fixed, cryo–sectioned and immunofluorescence stained using primary, monoclonal antibodies towards the Thr183 / Tyr185 phosphorylated form of JNK (Cell Signaling Technology). Results: JNK was present and activated, as determined by immunostaining for phospho–JNK, in several retinal cell types at PN11, with the strongest staining in profiles reminiscent of Müller cell processes. There was in this context no readily observable difference between normal and rd1 retinas. Within the photoreceptor layer (ONL), cytoplasmic staining was generally rather weak in both normal and rd1 retina, although cones (judged by their number, position and shape) had a stronger reaction than the rods. In addition to this cytoplasmic labelling, however, the ONL of the rd1 retina displayed foci of clear staining presumably in nuclei. These granular or condensed profiles were more frequent in the central than in the peripheral retina and mostly situated in the inner part of the ONL. Conclusions: JNK is present and active in the developing mouse retina. The different immunostaining in the ONL of normal and rd1 retinas may be related to the fact that at PN11 several rd1 photoreceptors are in the process of apoptosis, as shown previously by TUNEL–stainings. Such a link, if proven, could mean that phosphorylation, and hence activation, of JNK plays a part in the degeneration of photoreceptors of the rd1 mouse.
Keywords: apoptosis/cell death • signal transduction • photoreceptors