Growth hormone promotes the survival of retinal cells in vivo

Growth hormone (GH) is synthesized and present in the developing chick retina, where it may have local actions in retinal cell differentiation similar to those of conventional growth factors. We have previously shown that retinal GH has neuroprotective effects in retinal ganglion cells. In this paper, we extend our earlier functional studies by examining the in vivo effects of a GH siRNA (NR-cGH-1) after microinjection into the eye cup of the developing chick embryo in ovo. We show that intra-vitreous cGH siRNA lowers both GH mRNA and insulin-like growth factor-1 (IGF-1) mRNA levels in the retina in vivo, and concomitantly elevates the numbers of apoptotic cells in the retina. These effects are apparent 6 h after treatment, and persist for at least 24 h. The apoptotic cells induced by GH withdrawal were primarily located close to the optic fissure of the developing eye, and were distributed in clusters, suggesting that there are sub-populations of retinal cells that are particularly susceptible to apoptotic stimuli. These results support our view that a GH/IGF-1 axis in retinal cells regulates retinal cell survival in vivo.

Research highlights
► That the knock-down of GH in the embryonic chick retina, using a specific GH siRNA, results in a simultaneous knock-down of IGF-1 mRNA.
► The knock-down of GH in the embryonic chick retina results in the death of retinal cells.
► This demonstrates that retinal GH has functional significance.
► This indicates an autocrine or paracrine role for GH in early neurogenesis of the chick embryo.