Optical activation of TrkB receptors

Brain-derived neurotrophic factor (BDNF), via activation of tropomyosin receptor kinase B (TrkB), plays a critical role in neuronal proliferation, differentiation, survival, and death. Dysregulation of TrkB signaling is implicated in neurodegenerative disorders and cancers. Precise activation of TrkB receptors with spatial and temporal resolution is greatly desired to study the dynamic nature of TrkB signaling and its role in related diseases. Here we develop different optogenetic approaches that use light to activate TrkB receptors. Utilizing the photosensitive protein Arabidopsis thaliana cryptochrome 2 (CRY2), the light-inducible homo-interaction of the intracellular domain of TrkB (iTrkB) in the cytosol or on the plasma membrane is able to induce the activation of downstream MAPK/ERK and PI3K/Akt signaling as well as the neurite outgrowth of PC12 cells. Moreover, we prove that such strategies are generalizable to other optical homo-dimerizers by demonstrating the optical TrkB activation based on the light-oxygen-voltage domain of aureochrome 1 from Vaucheria frigida. The results open up new possibilities of many other optical platforms to activate TrkB receptors to fulfill customized needs. By comparing all the different strategies, we find that the CRY2-integrated approach to achieve light-induced cell membrane recruitment and homo-interaction of iTrkB is most efficient in activating TrkB receptors. The optogenetic strategies presented are promising tools to investigate BDNF/TrkB signaling with tight spatial and temporal control.