Abstract
Purpose::
Our purpose is to determine whether or not gp130 and LIFR activation is essential for these effects, and to determine which signal transduction pathways activated by the receptors are essential for neuroprotection versus reduced function. In addition, we seek to determine whether the cytokines exert these effects through direct action on photoreceptor cells or if signaling through Muller glial cells is required.
Methods::
LIF and LIF05 (antagonist) were expressed in bacteria (JM109) and purified using ion-exchange chromatography. These molecules were then used for in vitro cell stimulations and intravitreal injections into mouse eyes. Western blot experiments were used to measure the signal transduction pathways activated by LIF in presence or absence of the antagonist, LIF05. Electroretinograms (ERGs) were used to study the effects of gp130 activation (or inhibition) on retinal function.
Results::
LIF induced STAT3 and MAPK activation in Müller cells. LIF05 was able to antagonize this action. When injected into the vitreous, both LIF and LIF05 lead to loss of photoreceptor function albeit by different mechanisms. LIF reduced function by reducing the expression of proteins in the phototransduction cascade, while LIF05 reduced function by focal loss of photoreceptors.
Conclusions::
In previous studies we have shown that transgenic expression of LIF blocks the expression of key photoreceptor transcription factors Crx and NRL leading to loss of retinal function. Combining this observation with our new results we propose that activation of gp130 by LIF causes loss of function by altering the expression of phototransduction proteins. Inhibition of gp130 by LIF05 causes the loss of function by inducing photoreceptor cell death. These observations suggest that gp130 activation is essential for the neuroprotective activity of endogenous LIF or other IL-6 family cytokines. Our data also suggest these cytokines are protective in part by their ability to reduce phototransduction sensitivity.
Keywords: neuroprotection • retinal degenerations: cell biology • signal transduction