RNA Aptamer-Based Functional Ligands of the Neurotrophin Receptor, TrkB

Abstract

Many cell surface signaling receptors, such as the neurotrophin receptor, TrkB, have emerged as potential therapeutic targets for diverse diseases. Reduced activation of TrkB in particular is thought to contribute to neurodegenerative diseases. Unfortunately, development of therapeutic reagents that selectively activate particular cell surface receptors such as TrkB has proven challenging. Like many cell surface signaling receptors, TrkB is internalized upon activation; in this proof-of-concept study, we exploited this fact to isolate a pool of nucleasestabilized RNA aptamers enriched for TrkB agonists. One of the selected aptamers, C4-3, was characterized with recombinant protein-binding assays, cell-based signaling and functional assays, and, in vivo in a seizure model in mice. C4-3 binds the extracellular domain of TrkB with high affinity (K D ϳ2 nM) and exhibits potent TrkB partial agonistic activity and neuroprotective effects in cultured cortical neurons. In mice, C4-3 activates TrkB upon infusion into the hippocampus; systemic administration of C4-3 potentiates kainic acid-induced seizure development. We conclude that C4-3 is a potentially useful therapeutic agent for neurodegenerative diseases in which reduced TrkB activation has been implicated. We anticipate that the cell-based aptamer selection approach used here will be broadly applicable to the identification of aptamer-based agonists for a variety of cell-surface signaling receptors.

Aptamers as Promising Molecular Recognition Elements for Diagnostics and Therapeutics in the Central Nervous System

“…Further work in seizure models used an aptamer that binds to the extracellular domain of neurotrophin receptor (TrkB) [156]. TrkB is a receptor involved in cell signaling and plays a role in regulation of neuronal function and plasticity.…”

Development of Cell-SELEX Technology and Its Application in Cancer Diagnosis and Therapy

“…They demonstrated that, when applied to HER2-expressing breast cancer cells, the HER2 aptamer-Bcl-2 siRNA conjugates selectively internalize into HER2(+)-cells and silence Bcl-2 gene expression. Moreover, Bcl-2 silencing sensitizes these cells to chemotherapy (cisplatin), suggesting a potential new therapeutic approach for treating breast cancers with HER2(+)-status [42]. These studies indicated that technology might promote the widespread use of RNA-based reagents for targeted therapeutic applications.…”

Aptamers: Problems, Solutions and Prospects

“…Aptamers inhibit target enzymes by binding to the catalytic center or inducing conformation changes in a protein’s structure [93, 74]. However, when an aptamer is similar to an activating ligand, it can induce enzyme activation [94, 95]. …”