hNGF Peptides Elicit the NGF-TrkA Signalling Pathway in Cholinergic Neurons and Retain Full Neurotrophic Activity in the DRG Assay

In the last decade, Nerve Growth Factor (NGF)-based clinical approaches have lacked specific and efficient Tyrosine Kinase A (TrkA) agonists for brain delivery. Nowadays, the characterization of novel small peptidomimetic is taking centre stage in preclinical studies, in order to overcome the main size-related limitation in brain delivery of NGF holoprotein for Central Nervous System (CNS) pathologies. Here we investigated the NGF mimetic properties of the human NGF 1–14 sequence (hNGF1–14) and its derivatives, by resorting to primary cholinergic and dorsal root ganglia (DRG) neurons. Briefly, we observed that: 1) hNGF1–14 peptides engage the NGF pathway through TrkA phosphorylation at tyrosine 490 (Y490), and activation of ShcC/PI3K and Plc-γ/MAPK signalling, promoting AKT-dependent survival and CREB-driven neuronal activity, as seen by levels of the immediate early gene c-Fos, of the cholinergic marker Choline Acetyltransferase (ChAT), and of Brain Derived Neurotrophic Factor (BDNF); 2) their NGF mimetic activity is lost upon selective TrkA inhibition by means of GW441756; 3) hNGF1–14 peptides are able to sustain DRG survival and differentiation in absence of NGF. Furthermore, the acetylated derivative Ac-hNGF1–14 demonstrated an optimal NGF mimetic activity in both neuronal paradigms and an electrophysiological profile similar to NGF in cholinergic neurons. Cumulatively, the findings here reported pinpoint the hNGF1–14 peptide, and in particular its acetylated derivative, as novel, specific and low molecular weight TrkA specific agonists in both CNS and PNS primary neurons.

Gambogic amide selectively upregulates TrkA expression and triggers its activation

BACKGROUND

Gambogic amide is the first identified small molecular agonist for TrkA receptor. It mimics NGF functions by selectively activating TrkA receptor and preventing neuron death. However, its function different from that of NGF remains unknown.

METHODS

In the current study, we detect the effect of gambogic amide on TrkA expression using TrkA-expressing cell lines in vitro and hippocampi from mice treated with gambogic amide.

RESULTS

We have confirmed that gambogic amide displays robust neurotrophic activities in provoking neurite outgrowth in vitro. However, gambiogic amide displays a different kinetics from NGF in activating TrkA signals. NGF swiftly provokes TrkA activation and quickly induces TrkA degradation, while gambogic amid selectively upregulates TrkA protein and mRNA levels in a time-dependent manner. Administration of this compound in mice also activates TrkA receptor in hippocampus and promotes TrkA transcription and expression.

CONCLUSION

This study provides a novel mechanism of how gambogic amide regulates TrkA receptor, other than mimicking NGF in triggering TrkA activation.