Effect of ghrelin on the expression and activity of tyrosine hydroxylase, an enzyme involved in hypertension

LONGO CARBAJOSA; CORRADI G; CERNIELLO FM; CARRETERO OA; CORNEJO P; PERELLO M; GIRONACCI MM

Congreso; Inter-American Society of Hypertension Meeting 2017; 2017

Cellular protein degradation is a highly complex, temporally controlled, and tightly regulated process that plays a fundamental role in cell life and death as well as in health and disease. The ubiquitin-proteasome system (UPS) is the major pathway for intracellular protein degradation in eukaryotic cells. Aberrations in the UPS are implicated in the pathogenesis of many diseases including cancer, neurodegenerative, immune and cardiovascular diseases. The identification of proteasome modulators is a promising approach in a number of pathologies.Tyrosine hydroxylase (TH), the enzyme that catalyses the first and rate-limiting step in catecholamines biosynthesis, is involved in the development and maintenance of hypertension. TH half-life has been reported to be around 20 h. In a previous work we demonstrated that TH protein expression and activity are short-term modulated by the UPS. We also demonstrated that proteasome activity is diminished in hypothalamus and brainstem of spontaneously hypertensive rats (SHR), which may be a cause of the augmented TH expression and activity seen in hypertension. Ghrelin, a hormone produced mainly in stomach upon specific stimuli, is involved in several metabolic and cardiovascular processes. Emerging evidence indicates the potential involvement of ghrelin in low-grade inflammatory diseases such as atherosclero¬sis and hypertension. Ghrelin exhib¬its protective effects on the development of atherosclerosis via multiple pathways, includ¬ing induction of vasodilation and decrease of AngII-induced inflammatory factors secretion. The high expression of ghrelin receptor in the heart and large vessels provides evidence that indicates ghrelin is a promising new therapeutic agent for cardiovascular diseases. Cells that produce low levels of ghrelin and express its receptor are also found in the kidney, hypothalamus, pituitary gland, and the immune system, among others. In the brain the receptor for ghrelin has been shown to localize in the main cardiovascular control centers in neurons of the nucleus tractus solitarius, and central administration of ghrelin attenuates renal and adipose tissue sympathetic nervous activity. Furthermore, when ghrelin is microinjected into the nucleus of the solitary tract, the region of the brain that is important for controlling the autonomic nervous system, significant decreases in heart rate and mean arterial pressure are observed. Also, subcutaneous administration of ghrelin has been shown to suppress myocardial infarction (MI) - induced increases in plasma norepinephrine concentration. In ghrelin knockout mice, the plasma norepinephrine concentration is higher than in wild-type mice 30 minutes after MI. Some reports indicate that ghrelin plasma level is significantly higher in SHR group compared with the normotense group. The available data suggests there is a disturbance of circulating ghrelin in hypertension and that ghrelin might play a role in the regulation of blood pressure.The aim of this study is to examine the effect of ghrelin on TH degradation by the UPS.PC12 cells were incubated in presence or absence of ghrelin 100nM. The expression of TH and PSer40TH, the active form of the enzyme, were evaluated by Western blot and immunofluorescence analysis.Our results showed that ghrelin induced a decrease in TH expression in PC12 cells in a time-dependent manner. TH activity can be short-term regulated by phosphorylation at Ser residues. We also found that phosphorylation of TH Ser-40 was increased in cells treated with ghrelin during 15 min. PSer40TH was also increased in mouse accumbens brain area after 20 min ghrelin perfusion.Given that TH expression and activity are short-term regulated by the UPS we tested whether proteasome activity could be modulated by ghrelin. A significant increase in proteasome activity was observed after incubating cells in the presence of ghrelin during different times.In conclusion, these results suggest that ghrelin may play a certain role in hypertension by TH regulation via proteasome activation. However, this mechanism needs further study.