Selective inhibitors of the TrkC.T1 receptor reduce retinal inflammation and delay neuronal death in a model of retinitis pigmentosa.

The heterogeneity of receptor isoforms can cause an apparent paradox where each isoform can promote different or even opposite biological pathways. One example is the neurotrophin receptor TrkC. The trkC mRNA translates a full-length receptor tyrosine kinase (TrkC-FL) whose activation by the growth factor NT3 promotes neuronal survival. In some diseases, the trkC mRNA is spliced to a kinase-truncated isoform (TrkC.T1) whose activation by NT3 up-regulates tumor necrosis factor alpha (TNF-α) causing neurotoxicity. Since TrkC.T1 expression is significantly increased at the onset of neurodegeneration, we hypothesized that in disease TrkC.T1-mediated toxicity prevails over TrkC-FL-mediated survival. To study this, we developed small molecules that selectively antagonize NT3-driven TrkC.T1 neurotoxicity without compromising TrkC-FL survival. In a genetic mouse model of retinitis pigmentosa, therapeutic administration of TrkC.T1 antagonists prevents elevation of TNF-α and reduces photoreceptor neuronal death. This work demonstrates the importance of accounting for functional and structural heterogeneity in receptor-ligand interactions, illustrates chemical biology strategies to develop isoform-selective agents, validates TrkC.T1 as a druggable target, and expands the therapeutic concept of reducing neurotoxicity as a strategy to achieve neuroprotection.