Expression of growth hormone and growth hormone receptor genes in human eye tissues

Abstract

ABSTRACT In humans, the polygenic growth hormone (GH) locus is located on chromosome 17 and contributes with three types of proteins: pituitary GH which consists of at least two isoforms one of 22kDa and the other of 20kDa, placental GH, which also exhibits isoforms, and chorionic somatomammotropin hormone (CSH). While pituitary GH results from the expression of the GH‐1 (GH‐N) gene, placental GH is produced by the expression of the GH‐2 (GH‐V) gene and CSH is contributed by expression of the CSH‐1 and CSH‐2 genes. The location where GH‐1 is expressed is the anterior pituitary and the rest of the genes in the locus are expressed in placenta. On the other hand, expression and synthesis of GH in extra‐pituitary tissues, including the eye, has been recently described. However, the physiological role of GH in the eye has not yet been elucidated, although a possible neuroprotective role has been hypothesized. Thus, we analyzed GH‐1, GH‐2, CSH1/2, Pit‐1, GHR, GHRH, GHRHR, SST, SSTR1, SSTR2, SSTR3, SSTR4, and SSTR5 to elucidate the expression and regulation of the GH locus in the human eye. Through qPCR analysis, we only found evidence of GH‐1 expression in retina, choroid and trabecular meshwork; its transcript turned out to be the same as pituitary GH mRNA found in major species, and no splicing variants were detected. PIT1 was absent in all the ocular tissues implying an independent GH‐1 expression mechanism. We found evidence of GHR in the cornea, choroid coat and retina. These results suggest autocrine and/or paracrine regulation, possibly exerted by GHRH and SSTs (since their mRNAs and receptors were found predominantly in retinal, choroidal and corneal tissues) since expression of both molecules was detected in different ocular tissues, as well as in the same tissues where GH‐1 expression was confirmed. Our results add solid evidence about the existence of a regulatory local system for GH expression and release in the human eye. HIGHLIGHTSThe expression of GH‐1 was evidenced in the human eye, while GH‐2, CSH‐1, CSH‐2, and CHS‐L were not detected.GH and GHR proteins were present not only in retinal ganglion cells, but also in the entire human retina.GH and GHR were predominantly expressed in cornea epithelium.The expression of the GH‐1 gene in the eye appears to be independent of the pituitary transcriptional factor Pit‐1.