Ascorbic acid augments the adenylyl cyclase-cAMP system mediated POMC mRNA expression and β-endorphin secretion from hypothalamic neurons in culture

• Published in: Brain research 1996-01, Vol.706 (2), p.243-248
• Main Authors: Yang, Zhiyu, Copolov, David L., Lim, Alan T.
• Format: Article
• Language: English
• Subjects: 1-Methyl-3-isobutylxanthine - pharmacology; Adenylyl cyclase; Adenylyl Cyclases - metabolism; Animals; Ascorbic acid; Ascorbic Acid - pharmacology; beta-Endorphin - metabolism; Biological and medical sciences; Bucladesine - pharmacology; Cell culture; Cells, Cultured; Colforsin - pharmacology; Cyclic AMP - agonists; Fundamental and applied biological sciences. Psychology; Hormones and neuropeptides. Regulation; Hypothalamus; Hypothalamus - cytology; Hypothalamus - drug effects; Hypothalamus - metabolism; Hypothalamus. Hypophysis. Epiphysis. Urophysis; Neurons - drug effects; Neurons - metabolism; Pro-Opiomelanocortin - genetics; Rats; Rats, Sprague-Dawley; RNA, Messenger - blood; Vertebrates: endocrinology; β-Endorphin
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/0006-8993(95)01135-8

Besides acting as an important cofactor in the biosynthesis of catecholamine, ascorbic acid (AA) also modulates the activity of peptidylglycine-α-amidating monooxygenase for the post-translational modification of neuropeptides such as a-MSH and TRH. We report here a novel action of AA in modulating the secretion of immunoreactive β-endorphin (ir-β EP) and mRNA expression of proopiomelanocortin (POMC) following the activation of cAMP-dependent protein kinase A pathway in rat hypothalamic neurons. Primary cultures of hypothalamic neurons from neonatal rats as previously described were employed in the present studies. Six days after plating, cultures were replenished with serum-free media and incubated with vehicle or various doses of AA in the presence or absence of forskolin, 3-isobutyl-l-methylxanthine (IBMX), N 6,2′- O-dibutyryladenosine 3′5′-(cyclic)monophosphate [(BU) 2cAMP]. Whereas the basal ir-β EP release was 22.0 ± 0.4 pg/well (mean ± S.E.; n = 3), 10 NM of forskolin treatment increased ir-β EP release approximately 4.2-fold. Co-incubation with AA enhanced forskolin induced ir-β EP release and that this enhancing effect of AA was both time related and dose-dependent, with an ED 50 of approximately 10 μM and an E max of 100 μM. At the concentration of 10 μM, AA augmented ir-β EP release approximately 6.1-fold that of cultures treated with forskolin alone. A similar potentiating effect of AA was also seen in cultures co-treated with IBMX or with (BU) 2cAMP. These enhancing effects of AA were similarly found in the abundance of total cAMP and of POMC mRNA of cultures which received identical treatments. However, it is important to point out that AA alone did not modulate ir-β EP release or the abundance of POMC mRNA or total cAMP levels of the hypothalamic cultures when protein kinase A pathway was not activated. We thus conclude that AA augments cAMP-dependent protein kinase A pathway-induced production and release of β EP from rat hypothalamic neurons in culture. Furthermore, this biological effect of AA is, at least in part, mediated through enhancing the responsiveness of the adenylyl cyclase-cAMP system.