The Sustained Phase of Tyrosine Hydroxylase Activation In vivo
Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthetic pathway for catecholamine synthesis. Stress triggers an increase in TH activity, resulting in increased release of catecholamines from both neurons and the adrenal medulla. In response to stress three phases of TH activation have been identified (acute, sustained and chronic) and each phase has a unique mechanism. The acute and chronic phases have been studied in vivo in a number of animal models, but to date the sustained phase has only been characterised in vitro. We aimed to investigate the effects of dual exposure to lipopolysaccharide (LPS) in neonatal rats on TH protein, TH phosphorylation at serine residues 19, 31 and 40 and TH activity in the adrenal gland over the sustained phase. Wistar rats were administered LPS (0.05 mg/kg, intraperitoneal injection) or an equivolume of non-pyrogenic saline on days 3 and 5 postpartum. Adrenal glands were collected at 4, 24 and 48 h after the drug exposure on day 5. Neonatal LPS treatment resulted in increases in TH phosphorylation of Ser40 at 4 and 24 h, TH phosphorylation of Ser31 at 24 h, TH activity at 4 and 24 h and TH protein at 48 h. We therefore have provided evidence for the first time that TH phosphorylation at Ser31 and Ser40 occurs for up to 24 h in vivo and leads to TH activation independent of TH protein synthesis, suggesting that the sustained phase of TH activation occurs in vivo.
KeywordsLPS Tyrosine hydroxylase Adrenal gland Sustained phosphorylation
Tris-buffered saline with Tween
This work was supported by the National Health and Medical Research Council of Australia, Hunter Medical Research Institute and University of Newcastle, Australia.
Conflict of interest
The authors declare no conflicts of interest.
- 8.Bobrovskaya L, Damanhuri HA, Ong LK, Schneider JJ, Dickson PW, Dunkley PR, Goodchild AK (2010) Signal transduction pathways and tyrosine hydroxylase regulation in the adrenal medulla following glucoprivation: an in vivo analysis. Neurochem Int 57(2):162–167. doi: 10.1016/j.neuint.2010.05.009 PubMedCrossRefGoogle Scholar
- 11.Bobrovskaya L, Gilligan C, Bolster EK, Flaherty JJ, Dickson PW, Dunkley PR (2007) Sustained phosphorylation of tyrosine hydroxylase at serine 40: a novel mechanism for maintenance of catecholamine synthesis. J Neurochem 100(2):479–489. doi: 10.1111/j.1471-4159.2006.04213.x PubMedCrossRefGoogle Scholar
- 18.Walker AK, Nakamura T, Byrne RJ, Naicker S, Tynan RJ, Hunter M, Hodgson DM (2009) Neonatal lipopolysaccharide and adult stress exposure predisposes rats to anxiety-like behaviour and blunted corticosterone responses: implications for the double-hit hypothesis. Psychoneuroendocrinology 34(10):1515–1525. doi: 10.1016/j.psyneuen.2009.05.010 PubMedCrossRefGoogle Scholar
- 20.Shanks N, Larocque S, Meaney MJ (1995) Neonatal endotoxin exposure alters the development of the hypothalamic-pituitary-adrenal axis: early illness and later responsivity to stress. J Neurosci Off J Soc Neurosci 15(1 Pt 1):376–384Google Scholar
- 29.Nankova B, Kvetnansky R, McMahon A, Viskupic E, Hiremagalur B, Frankle G, Fukuhara K, Kopin IJ, Sabban EL (1994) Induction of tyrosine hydroxylase gene expression by a nonneuronal nonpituitary-mediated mechanism in immobilization stress. Proc Natl Acad Sci U S A 91(13):5937–5941PubMedCrossRefGoogle Scholar
- 33.Nunez C, Laorden ML, Milanes MV (2007) Regulation of serine (Ser)-31 and Ser40 tyrosine hydroxylase phosphorylation during morphine withdrawal in the hypothalamic paraventricular nucleus and nucleus tractus solitarius-A2 cell group: role of ERK1/2. Endocrinology 148(12):5780–5793. doi: 10.1210/en.2007-0510 PubMedCrossRefGoogle Scholar