CellREADR-mediated BDNF overexpression in serotonergic neurons as therapeutic approach to promote stress resilience

• Applicant: Privatdozentin Dr. Julia Leschik
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cognitive, Systems and Behavioural Neurobiology ; Molecular and Cellular Neurology and Neuropathology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549883853

Major depression (MD) can originate from chronic stress, and coincides with reduced expression of brain-derived neurotrophic factor (BDNF) and with a dysregulated serotonergic activity. We recently showed that inducible overexpression of BDNF specifically in serotonergic neurons of the adult mouse brain protects against the impairing behavioral consequences of chronic social defeat stress. Transgenic mice showed increased stress resilience and acted similarly as antidepressant-treated wild-type mice. Hence, heightened BDNF expression in serotonergic neurons could be a conceivable novel therapeutic approach to increase stress resilience and counteract stress-related pathologies in humans. This is of importance, since common antidepressant treatments, which - without exception – also upregulate BDNF, have the disadvantage of not targeting specific neuronal populations, which is discussed as a cause of treatment-resistant MD. To make our findings translatable to eventual future human therapy we aim at using the novel technique of sequence-guided mRNA editing in order to achieve serotonergic cell type specificity of therapeutic BDNF expression. The so-called CellREADR (Cell access through RNA sensing by endogenous ADAR) approach uses the presence of a cell type-specific endogenous marker mRNA as an address to selectively manipulate this distinct cell population to express a protein of interest, i.e., a therapeutic effector protein. The mechanism works via sensing the cell-type specific mRNA with a complementary so-called readrRNA. Subsequent double stranding of RNA then recruits ADARs (adenosine deaminases acting on RNA), which catalyze A (adenosine) to I (inosine) RNA editing of a previously introduced stop codon in the readrRNA, which also contains the sequences encoding the effector protein. After successful editing and abolishing the stop codon, translation of the downstream effector RNA sequence is induced. Our goal is to design a CellREADR sensing the mRNA of tryptophan hydroxylase 2 (TPH2), which is a marker for serotonergic neurons in the midbrain raphe nuclei, and leading to selective BDNF expression in serotonergic neurons after RNA editing. Functional efficiency will be evaluated at the cellular and behavioral level in adult mice. First, application of TPH2-CellREADRBDNF will be performed by recombinant adeno-associated viral vectors (AAVs), which will be combined with a specific doxycycline-inducible system to temporally control BDNF expression. This will allow adjusting and analyzing the therapeutic window of BDNF expression in temporal relation to the chronic stress negative outcomes. AAVs will be administered either by stereotactic injection into the mouse brain or non-invasively by intravenous injection. As a prove-of-concept experiment, at last, we aim at testing the possibility to use lipid- and polymer-based nanoparticle-mediated transfer of readrRNA, which could open up new routes of cell type-specific therapy in the future.

• DFG Programme: Research Grants