Endocrine Abstracts

Gene arrays are a powerful tool to search for novel targets of drug action and disease-specific patterns of gene expression. GH has pleiotropic actions and thus a wide range of potential gene targets. Using an accessible tissue, namely peripheral blood mononuclear cells (PBMNCs), we have started to explore the use of gene arrays in the context of the in-vivo response to GH treatment.

PBMNCs were obtained with consent and ethical permission from 2 prepubertal GH deficient children and 1 healthy adult. One of the children had a second sample taken after 3 months on rhGH (Saizen, 0.033mg/kg/d). Total RNA was extracted, reverse transcribed with 33P-dCTP and hybridised to separate filters (InVitrogen) on which 5760 gene sequences were embedded. Only genes expressed at >1.6x background intensity were analysed.

The number of genes expressed above background varied markedly; 1722 in the adult, 283 in child 1 and 718 in child 2. When genes were ranked by level of expression, 97 of the top 100 ranked in child 2 were also expressed in child 1, and all were present in the adult. On rhGH, there were 56 genes that increased by >1.5 fold (max 2.3) and 33 genes that decreased by >1.5 fold (max 1.9). 18 of these genes (12+, 6-) were related to cell signalling, including 2 tyrosine phosphatases and 2 phosphokinases. 17 genes (14+, 3-) were regulators of metabolism.

The fold changes in response to GH in vivo were modest, but comparable to those seen in human fibroblasts exposed in-vitro to rhGH. Genes were both up and down-regulated by rhGH. There is heterogeneity in basal gene expression in PBMNCs, but the highest expressing genes are replicated in the GHD children and a healthy adult. Further evaluation of inter-individual responses to GH in PBMNCs is now required.