Activity-dependent gene regulation in neurons: energy coupling and a novel biosensor
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Multiple brain disorders are associated with hypoinhibition of neural circuits that are controlled by inhibitory neurons using the neurotransmitter γ-aminobutyric acid (GABA). GABA activates type A receptors (GABARs) to mediate the majority of inhibitory neurotransmission and changes in GABAR subunit composition have profound effects on brain function. In fact, down-regulation of one of the three β isoforms, β1, is associated with alcoholism, autism, epilepsy, schizophrenia, and bipolar disorder. These conditions also present with mitochondrial defects and metabolic dysregulation. In the first Aim of my thesis, I ask whether the core promoter of the human GABAR β1 subunit gene (GABRB1) can be regulated by the same transcription factor, the nuclear respiratory factor 1 (NRF-1) that controls oxidative phosphorylation and mitochondrial biogenesis in neurons. The ENCODE database of NRF-1 binding in human embryonic stem cells was used to identify an interaction of NRF-1 with GABRB1. Using a variety of approaches: electro mobility shift, promoter/reporter luciferase assays, gene silencing and bioinformatics, we demonstrate that GABRB1 contains a canonical NRF-1 element responsible for the majority of GABRB1 promoter- luciferase activity in transfected primary neurons. Moreover, we show that endogenous NRF-1 is responsible for a substantial amount of luciferase activity in our studies. Altogether, our results suggest GABRB1 is a target gene for NRF-1, providing a possible link between mitochondria related energy metabolism and transcriptional regulation of β1-containing GABARs in neurological disease. Synthesis of NRF-1 is regulated by the transcription factor cAMP response element binding protein (CREB), an important memory molecule implicated in multiple brain disorders. The second Aim of my thesis was to develop a molecular sensor that can be used in living neurons to signal the presence of CREB dependent gene regulation. We employ a split complement bioluminescent sensor to monitor interaction of protein surfaces that link CREB with its co-factor CBP and demonstrate that it can detect activation of CREB via its serine 133 phosphorylation site and activation through an undiscovered mechanism. We also show that this sensor can be used to monitor BDNF signaling providing the foundation for its future use in in vivo models of disease where BDNF is implicated.