Abstract

Brain-derived neurotrophic factor (BDNF) is a central modulator of neuronal development and synaptic plasticity in the central nervous system (CNS). This renders the BDNF-modulated tropomyosin receptor kinase B (TrkB) a promising drug target to treat synaptic dysfunctions. Using GRowth factor-driven expansion and INhibition of NotCH during maturation, the so-called GRINCH neurons were derived from human induced pluripotent stem (hiPS) cells. These GRINCH neurons were employed as model cells for pharmacological profiling of two TrkB-agonistic antibodies, hereafter referred to as AB2 and AB20. In next generation sequencing (NGS) studies, AB2 and AB20 stimulated transcriptional changes, which extensively overlapped with BDNF-driven transcriptional modulation. In regard to TrkB phosphorylation, both AB2 and AB20 were only about half as efficacious as BDNF. However, with respect to the TrkB downstream signaling, AB2 and AB20 displayed increased efficacy values, providing a stimulation at least comparable to BDNF in respect of VGF transcription as well as of AKT and CREB phosphorylation. In a complex structure of the TrkB-d5 domain with AB20, determined by x-ray crystallography, the AB20 binding site was found to be allosteric in regard to the BDNF binding site while AB2 was known to act orthosterically with BDNF. In agreement with this finding, AB2 and AB20 acted synergistically at higher concentrations to drive TrkB phosphorylation. Whilst TrkB downstream signaling declined faster after pulse stimulation with AB20 than with AB2, AB20 restimulated TrkB phosphorylation more efficiently than AB2. In conclusion, both antibodies displayed some limitations and some benefits in regard to future applications as therapeutic agents.