ESPE Abstracts

Mutations in the GH1 gene cause isolated growth hormone deficiency (IGHD) by affecting production, secretion, and stability of growth hormone as well as its binding to GHR. A smaller isoform of GH1 is inactive and is linked to IGHD. While studying the impact of small GH isoform, we noticed that cells with the short 17.5 kD version of GH looked different from the control cells. We found that the production of short GH isoform distorts the cell morphology, contributing to detrimental effects seen in the patients. We hypothesized that cellular distortion caused by small GH isoform and overall GH secretion can be a target and a tool for experimental approaches for reversing the damaging effects of small GH protein, thereby providing potential treatments for IGHD. It is known that increasing cAMP enhances 26S proteasome activity and the degradation of cell proteins, including the selective breakdown of misfolded proteins, and recently, an increase in cGMP levels has also been shown to regulate protein degradation. Inhibitors of phosphodiesterase 5 (PDE5; e.g., Viagra (sildenafil)), which raise cGMP by inhibiting its hydrolysis to GMP, are widely used for the treatment of erectile dysfunction and pulmonary hypertension, and stimulators of soluble guanylyl cyclases (riociguat), which stimulate cGMP synthesis, are used as treatments for pulmonary hypertension and heart failure. Using our model of cellular morphology changes, we investigated the impact of chemicals that enhance cGMP levels by inhibiting PDE5 or activating guanyl cyclases. The cells expressing a small isoform of GH consistently show distorted rounded morphology. Treatment with BAY 41-2272, a cGMP inducer slightly improved the cell morphology in small isoform GH expressing cells. BAY 41-2272 did not show any adverse effects of normal and WT GH expressing cells. Treatment of sildenafil to cells expressing 17.5 kD isoform of GH markedly improved the cell morphology compared to untreated cells, especially after 48h when a larger percentage of cells that were distorted (rounder shapes) regained the shape of normal cells expressing WT GH and no damage to cells expressing WT-GH was observed. Another PDE5 inhibitor tadalafil also caused a marked improvement in cell morphology caused by the expression of a small GH isoform. Overall, it seems the strategy to regulate the cGMP levels in cells transfected in small GH isoform works and needs further investigation. A detailed analysis of the impact of PDE5 inhibitors on GH expression and secretion will be presented.