Endogenous growth hormone in human retinal ganglion cells correlates with cell survival

Purpose: Locally synthesized growth hormone (GH) may act as a survival factor in several tissues. Experimental studies with chick retinal ganglion cells (RGCs) suggest that GH, synthesized within the developing retina, may have autocrine or paracrine roles in the regulation of the waves of cell death characteristic of RGC differentiation. There is also evidence that GH may have a similar neuroprotective function in the rat retina, however, there is no information concerning such a role in the human retina. In this paper we extended our earlier work by determining whether the local expression of retinal GH correlates with RGC apoptosis in human retinas. Methods: In the absence of experimental approaches to survival factor function in the human retina, we have used a correlative immunocytochemical technique to determine how the expression of GH relates to cell death in RGCs. We used sections of human retinas, taken postmortem, that we double-labeled for GH and apoptotic cell death using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). Results: We found that approximately 35% of cells in the ganglion cell layer (GCL) were both GH positive and GH receptor (GHR) positive, and that GH colocalized with GHR in these cells. However, none of the apoptotic cells in the GCL were GH immunoreactive. Labeling of sections with the RGC marker, synuclein, indicated that at least 95% of the cells in the GCL were RGCs, leading us to conclude that the majority of the cells that we have examined in the GCL are RGCs. Conclusions: The results are consistent with the earlier proposal, based on in vivo and in vitro experimental chick embryo studies, that GH promotes survival in adult human RGCs.