Using Human iPSC Models to Determine the Mechanism of Inflammation-Induced Disruption of Dopamine Neurotransmission

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PROJECT SUMMARY The current proposal will use innovative stem cell technology to explore the mechanism(s) by which inflammation affects dopamine (DA) neurotransmission, with a special focus on inflammation's effects on presynaptic DA vesicles. Inflammation is believed to play a pivotal pathophysiologic role in ~30% of depressed patients and is associated with effects on reward circuitry, leading to motivational deficits and ultimately anhedonia. Anhedonia is a core and disabling symptom of depression, which is the leading cause of disability worldwide. Studies in laboratory animals and humans indicate that one of the major targets of inflammation in the brain is DA in the ventral striatum, a subcortical brain region that has been shown to be uniquely accessible to peripheral inflammatory mediators including interleukin (IL)-6 through disruption in the blood brain barrier. In vivo microdialysis in non-human primates and rodents demonstrate that administration of inflammatory cytokines including IL-6 reduces extracellular DA availability and release, and neuroimaging studies in humans demonstrate reduced striatal DA turnover following administration of the inflammatory cytokine interferon-alpha. What remains unknown, however, are the specific cellular and molecular mechanisms by which inflammatory cytokines such as IL-6 disrupt DA neurotransmission. Our preliminary findings indicate that in vitro IL-6 treatment of human induced pluripotent stem cell (hiPSC)-derived DA neurons (which express IL-6 receptors) directly decreases DA availability and downregulates gene expression in pathways associated with synaptic vesicular function. These effects occurred in the absence of cellular toxicity, and the gene expression changes were reversed by baricitinib, an FDA-approved drug that was developed at Emory and blocks IL-6 signaling through inhibition of Janus Kinases 1 and 2. In the current project, we aim to further elucidate the mechanisms by which IL-6 affects DA neurotransmission using human iPSC-derived DA neurons. Specifically, we will determine the impact of IL-6 on synaptic vesicular function in the presence or absence of baricitinib in hiPSC-derived DA neurons (Aim 1). We will further determine the impact of IL-6 on alternative splicing of the DRD2 gene, which in turn can regulate synaptic vesicular function in DA neurons (Aim 2). These studies will also include DA neurons expressing the depression-associated DRD2 variant rs1076560, which is associated with alternate DRD2 splicing. Taken together, the proposed experiments will provide an important proof of principle for the use of stem cell technology to reveal the mechanisms of inflammation's effects on DA neurotransmission, shedding new light on pathogenic mechanisms underlying DA system deficits in psychiatric disorders, while providing a platform for drug development aligned with Emory's drug discovery pipeline.