Characteristics of brain injury-derived neurotrophic peptide-binding sites on rat brain synaptosomes and neurons in culture

Abstract

Brain injury-derived neurotrophic peptide is the fragmental 13-mer peptide of the novel neurotrophic factor which was extracted and purified from Sponge Gelform made of gelatin implanted at the mechanically-induced injury site in neonatal rat brains. Brain injury-derived neurotrophic peptide supports survival of septal cholinergic and mesencephalic dopaminergic neurons in culture, and rescues hippocampal neurons in culture from glutamate neurotoxicity. Here we studied the binding characteristics of brain injury-derived neurotrophic peptide to synaptosomes from normal adult rat brains and neurons in culture from neonatal rat brains. [ 125I]Asp-[Tyr 11]-brain injury-derived neurotrophic peptide binding to rat brain synaptosomes was specific and saturable. Equilibrium binding studies revealed that [ 125I]Asp-[Tyr 11]-brain injury-derived neurotrophic peptide bound to 1.1 pmol/mg protein with a K d (dissociation constant) of 0.17 μM in hippocampal synaptosomes and to 2.0 pmol/mg protein with a K d of 0.38 μM in septal synaptosomes. [ 125I]Asp-[Tyr 11]-brain injury-derived neurotrophic peptide could bind to a subpopulation of hippocampal neurons in culture from embryonic rat brains. Affinity cross-linking with the car☐yl-reactive cross-linking reagent I-ethyl-3-(3-dimethylaminopropyl)-carbodiimide-HCl and [ 125I]Asp-[Tyr 11]-brain injury-derived neurotrophic peptide produced radiolabeled bands corresponding to 100,000, 50,000 and 40,000 mol. wt molecules on hippocampal neurons in culture. These results suggest that the 13-mer sequence of brain injury-derived neurotrophic peptide plays a crucial role in expressing the neurotrophic properties of the factor.