Pharmacological modulation of nerve growth factor synthesis: a mechanisticcomparison of vitamin D receptor and beta(2)-adrenoceptor agonists

Increasing nerve growth factor (NGF) in the PNS is a rational strategy for treating certain neurodegenerative disorders. The present studies were unde rtaken to compare two compounds, a vitamin D-3 analogue (CB1093) with minim al calcaemic effects, and clenbuterol, a long-acting beta (2)-adrenoceptor agonist, both of which induce NGF synthesis in vivo. Clenbuterol caused sig nificant increases in both NGF mRNA and protein in 3T3 cells; with maxima a t 10 nM and at 8-12 h exposure. Effects of clenbuterol on NGF mRNA were ant agonized by propranolol. Mobility shift assays on whole cell extracts showe d that clenbuterol increased AP1 binding in 3T3 cells prior to increasing N GF synthesis. Clenbuterol was without effect on NGF mRNA levers in L929 cel ls, whereas CB1093 caused significant increases in both NGF mRNA and protei n levels in both 3T3 and L929 cells. Stimulation was almost maximal at 24 h exposure and was sustained for at least 72 h. The magnitude of the increas e was much greater in L929 (700% increase) than in 3T3 cells (80%). Binding to the vitamin D nuclear receptor (VDR), which acts as a transcription fac tor itself, was increased as early as 30 min after exposure to of CB1093 an d maintained up to 24 h. Increased VDR binding preceded increased NGF mRNA. A 150% increase in AP-1 binding was also evident. This study demonstrates that CB1093 and clenbuterol stimulate NGF levels in vitro and that AP-1 bin ding could be a commonality between the mechanism of NGF induction of these two compounds. (C) 2000 Elsevier Science B.V. All rights reserved.