ERK phosphorylation in intact, adult brain by alpha(2)-adrenergic transactivation of EGF receptors.
Our previous work demonstrated dexmedetomidine-activated phosphorylation of extracellular regulated kinases 1 and 2 (ERK(1/2)) in primary cultures of mouse astrocytes and showed that it is evoked by alpha(2)-adrenoceptor-mediated transactivation of epidermal growth factor (EGF) receptors, a known response to activation of G(i/o)- or G(q)-coupled receptors [Li, B., Du, T., Li, H., Gu, L., Zhang, H., Huang, J., Hertz, L., Peng, L., 2008a. Signaling pathways for transactivation by dexmedetomidine of epidermal growth factor receptors in astrocytes and its paracrine effect on neurons. Br. J. Pharmacol. 154, 191-203]. Like most studies of transactivation, that study used cultured cells, raising the question whether a similar effect can be demonstrated in intact brain tissue and the brain in vivo. In the present study we have shown that (i) dexmedetomidine-mediated ERK(1/2) phosphorylation occurs in mouse brain slices with a similar concentration dependence as in cultured astrocytes (near-maximum effect at 50nM); (ii) intraperitoneal injection of dexmedetomidine (3microg/kg) in adult mice causes rapid phosphorylation of the EGF receptor (at Y845 and Y992) and of ERK(1/2) in the brain; (iii) both EGF receptor and ERK(1/2) phosphorylation are inhibited by intraventricular administration of (a) AG 1478, a specific inhibitor of the receptor-tyrosine kinase of the EGF receptor; (b) GM 6001, an inhibitor of metalloproteinase(s) required for release of EGF receptor agonists from membrane-bound precursors; or (c) heparin, neutralizing heparin-binding EGF (HB-EGF). Thus, in intact brain HB-EGF, known to be expressed in brain, may be the major EGF agonist released in response to stimulation of alpha(2)-adrenoceptors, the released agonist(s) activate(s) EGF receptors, and ERK(1/2) is phosphorylated as a conventional response to EGF receptor activation. Our previous paper (see above) showed that dexmedetomidine evokes no ERK(1/2) phosphorylation in cultured neurons, but neurons respond to astrocyte-conditioned medium (and to EGF) with ERK(1/2) phosphorylation. The present findings therefore suggest that EGF receptor transactivation in astrocytes in the mature brain in vivo is an important process in response to alpha(2)-adrenoceptor stimulation and may lead to phosphorylation of ERK(1/2) both in astrocytes themselves and in adjacent neurons.
Du
Ting
T
Department of Clinical Pharmacology, China Medical University, Shenyang, PR China.
Li
Baoman
B
Liu
Shufang
S
Zang
Peizhuo
P
Prevot
Vincent
V
Hertz
Leif
L
Peng
Liang
L
D000818:Animals; D000925:Anticoagulants / Q000494:pharmacology; D001253:Astrocytes / Q000187:drug effects / Q000201:enzymology; D015153:Blotting, Western; D001923:Brain Chemistry / Q000187:drug effects*; D020927:Dexmedetomidine / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D047468:Immunoprecipitation; D008297:Male; D051379:Mice; D010766:Phosphorylation; D011480:Protease Inhibitors / Q000494:pharmacology; D011799:Quinazolines; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology; D020032:Tyrphostins / Q000494:pharmacology
D000925:Anticoagulants; D004151:Dipeptides; D004791:Enzyme Inhibitors; D006993:Hypnotics and Sedatives; C078131:N-(2(R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl)-L-tryptophan methylamide; D011480:Protease Inhibitors; D011799:Quinazolines; D018341:Receptors, Adrenergic, alpha-2; D020032:Tyrphostins; C101044:RTKI cpd; D020927:Dexmedetomidine; D006493:Heparin; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases