The serotonergic system in the human brain modulates several physiological processes, and altered serotonergic neurotransmission has been implicated in the neuropathology of several psychiatric disorders. The study of serotonergic neurotransmission in psychiatry has long been restricted to animal models, but advances in cell reprogramming technology have enabled the generation of serotonergic neurons from patient-induced pluripotent stem cells (iPSCs). While iPSC-derived human serotonergic neurons offer the possibility to study serotonin (5-HT) release and uptake, particularly by 5-HT-modulating drugs such as selective serotonin reuptake inhibitors (SSRIs), a major limitation is the inability to reliably quantify 5-HT secreted from neurons in vitro. Herein, we address this technical gap via a novel sensing technology that couples 5-HT-specific DNA aptamers into nanopores (glass nanopipettes) with orifices of ~10 nm to detect 5-HT in complex neuronal culture medium with higher selectivity, sensitivity, and stability than existing methods. The 5-HT aptamers undergo conformational rearrangement upon target capture and serve as gatekeepers of ionic flux through the nanopipette opening. We generated human serotonergic neurons in vitro and detected secreted 5-HT using aptamer-coated nanopipettes in a low nanomolar range, with the possibility of detecting significantly lower (picomolar) concentrations. Furthermore, as a proof of concept, we treated human serotonergic neurons in vitro with the SSRI citalopram and detected a significant increase in extracellular 5-HT using the aptamer-modified nanopipettes. We demonstrate the utility of such methods for 5-HT detection, raising the possibility of fast quantification of neurotransmitters secreted from patient-derived live neuronal cells.
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This research was supported by the Takeda-Sanford Consortium Innovation Alliance grant program and the JPB foundation. This project received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement number GrapheneCore3 881603. KCV was supported by the Swiss National Science Foundation (SNSF) outgoing postdoctoral fellowship. Research supported in part by the American Heart Association and the Paul G. Allen Frontiers Group Grant #19PABHI34610000/TEAM LEADER: Fred H. Gage/2019, Annette C. Merle-Smith, Robert and Mary Jane Engman Foundation, and Lynn and Edward Streim. NN was supported by the ETH Zurich Postdoctoral Fellowship (COFUND 18-1 FEL-35). DM was supported by the Swiss National Science Foundation Ambizione Grant (PZ00P2_174217/1). The authors acknowledge Prof. Unwin for sharing the WEC-SPM software package that was used to control the nanopipette instrument and Dr. Alex Colburn for supplying a low-noise current amplifier (University of Warwick). The authors also acknowledge technical assistance from Stephen Wheeler (ETH Zurich).
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Nakatsuka, N., Heard, K.J., Faillétaz, A. et al. Sensing serotonin secreted from human serotonergic neurons using aptamer-modified nanopipettes. Mol Psychiatry (2021). https://doi.org/10.1038/s41380-021-01066-5