Nerve growth factor (NGF) loop 4 dimeric mimetics activate ERK and AKT andpromote NGF-like neurotrophic effects

Previous work indicating that nerve growth factor (NGF) protein loops 2 and 4 interact with TrkA receptors raise the possibility that small molecule m imetics corresponding to TrkA-interacting domains that have NGF agonist act ivity can be developed. We applied our previously developed strategy of dim eric peptidomimetics to address the hypothesis that loop 4 small molecule d imeric mimetics would activate TrkA-related signal transduction and mimic N GF neurotrophic effects in a structure-specific manner. A loop 4 cyclized p eptide dimer demonstrated NGF-like neurotrophic activity, whereas peptides with scrambled sequence, added or substituted residues, or cyclized in mono meric form were inactive. Activity was blocked by the TrkA inhibitors K252a and AG879 but not by NGF p75 receptor blocking antibody. Dimeric, but not monomeric, peptides partially blocked NGF activity. This profile was consis tent with that of a NGF partial agonist. ERK and AKT phosphorylation was st imulated only by biologically active peptides and was blocked by K252a. The ERK inhibitor U0126 blocked the neurite- but not the survival-promoting ac tivity of both NGF and active peptide. These studies support the proof of c oncept that small molecule NGF loop 4 mimetics can activate NGF signaling p athways and can mimic death-preventing and neurite-promoting effects of NGF . This finding will guide the rational design of NGF single-domain mimetics and contribute to elucidating NGF signal transduction mechanisms.