Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, C60

Oral Communications

Coexistence of autocrine/paracrine and endocrine growth hormone in embryonic retinal ganglion cells

C. G. Martinez-Moreno1, M. Luna2, C. Aramburo2, S. Harvey1

1. Physiology, University of Alberta, Edmonton, Alberta, Canada. 2. Neurobiologia Celular y Molecular, Instituto de Neurbiologia, Universidad Nacional Autonoma de Mexico, Juriquilla, Queretaro, Quer

Growth hormone (GH) exerts its biological effects through the GH receptor (GHR), which is present in the chicken embryo eye from ED (embryonic day) 2 of the 21-day-incubation period. In the embryo, GH gene expression also occurs in the neural retina from ED2 and retinal GH induces the survival and differentiation of retinal ganglion cells, as these local autocrine or paracrine actions are blocked following the immunoneutralization of endogenous GH or when retinal GH production is reduced by siRNA knockdown (1). Retinal GH is therefore of functional importance before the ontogenic appearance of pituitary somatotrophs (at ED12) and the onset of pituitary GH secretion and the appearance of GH in peripheral plasma (at ED15-17). Endocrine actions of pituitary GH in the development and function of the chicken embryo eye are, however, unknown. This possibility has therefore been investigated in ED15 embryos. In ovo systemic injections of Cy3-labelled GH (150 µg, via the chorioallantonic vein) demonstrated that GH in the bloodstream was translocated into the neural retina and internalized into retinal ganglion cells (RGC's). Pituitary GH may therefore also be functionally involved in retinal development during late embryogenesis. Cy3-labelled GH was similarly internalized into QNR/D cells (which provide an experimental model for chick embryo RGCs) (2) after its addition into incubation media. The uptake of exogenous GH was by a receptor-mediated mechanism and maximal after 30-60 min, and was followed by degradation of the internalized hormone. The exogenous (endocrine) was, however, biologically active, since, within the QNR/D cells it promotes IGF-1 expression. Interestingly, the labeled GH accumulated in perinuclear regions of the QNR/D cells, but was not found in the neurite outgrowths, in which endogenous retinal GH is located. This suggests that exogenous (endocrine) and endogenous (autocrine/paracrine) GH are both involved in retinal function in late embryogenesis and they co-exist in separate intracellular compartments within retinal ganglion cells.

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