Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, C138
Retinal Growth Hormone: A Survival Factor During Neurogenesis
S. Harvey1, W. Lin1, M. Baudet1, E. Parker1, E. J. Sanders1
1. Physiology, University of Alberta, Edmonton, Alberta, Canada.
In previous studies we have demonstrated the presence of growth hormone (GH) and its receptor (GHR) in the neural retina, in which it is abundantly expressed in retinal ganglion cells (RGCs) (Baudet et al 2003). Retinal GH acts as an autocrine/paracrine factor within RGCs to promote cell survival during developmental waves of apoptosis in early chick embryos, since the immunoneutralization of retinal GH results in RGC death in vitro (Harvey et al 2009). The physiological significance of retinal GH in retinal neurogenesis was further investigated in the present study, in which its expression was suppressed by siRNA knockdown. A specific siRNA targeting axon 4 of the chicken GH gene was intravitreally injected in 100 nl into the eyes of chick embryos at embryonic day (ED) 3 of the 21 day incubation period. This siRNA effectively reduced retinal GH expression by approximately 40%. Controls received a scrambled siRNA or were un-injected. Apoptotic cells were identified at ED 5 by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) of ocular flat mounts. Following siRNA injection, the number of apoptotic cells in the neural retina was significantly increased (P<0.05, by > 2 fold) in comparison with both control groups. The same siRNA was also transfected into immunopanned ED 7 RCGs, in which it induced a 63% knockdown of endogenous GH and the death of approximately 40% of the treated cells. RCG death after GH knockdown was mediated by a caspase-dependent pathway, since a broad spectrum caspase inhibitor (Q-VD-OPh) reduced the amount of cell death by 70%, to the level in RCG cultures transfected with the control siRNA. These results demonstrate a physiological role of retinal GH in cell survival during early chick embryogenesis, at a time when RGCs undergo developmental waves of apoptosis. Retinal GH therefore has an autocrine/paracrine role as a neurotrophic factor during neurogenesis.
Where applicable, experiments conform with Society ethical requirements