PhD Candidate McGill University Montreal, Quebec, Canada
Abstract: Midbrain dopaminergic (mDA) cells represent a distinct cell type important in motor control. mDA cells are highly metabolically active and very sensitive to redox states compared to other neural cell types, but the nature of this sensitivity is not well understood. We hypothesize that mDA cells are programmed to allow high redox states early in development, prior to differentiation of unique dopaminergic cell features. To test this hypothesis, we compared the metabolic profile of ventral neuroectoderm, an early mDA progenitor cell state, to neuroectodermal cells, which both underwent dual-SMAD inhibition and differed solely in their exposure to sonic hedgehog (SHH), an essential ventralizing morphogen. iPSCs were induced from six control human lines and cells were treated in induction media for 7 days. Metabolic profiling was conducted using two complementary liquid chromatography-mass spectrometry (LC-MS/MS) approaches, ion-pairing reversed-phase LC-MS/MS and hydrophilic interaction liquid chromatography, for a comprehensive coverage of central carbon metabolism. We found that metabolites from the transsulfuration pathway were significantly upregulated in ventralized neuroectodermal cells. The transsulfuration pathway produces sulfur-containing metabolites, such as glutathione and taurine, which can act as antioxidants and regulate cellular redox balance. RNA-seq analysis of these two cell types at this developmental timepoint showed that a subset of genes encoding enzymes of the transsulfuration pathway were upregulated in ventralized neuroectoderm. This suggests that ventralized neuroectoderm is equipped with a distinctly active transsulfuration mechanism early in development, likely to reduce oxygen free radicals from high mitochondrial ATP production. Dopaminergic cell redox states may thus be programmed much earlier than previously thought and may allow for the differentiation of unique dopaminergic cell features such as extensive branching, dopamine production, and calcium flux.
