single cell RNA-seq of oligodendrocyte progenitors FACS sorted from Aclyfl/fl (Control) or Pdgfra-creERT;Aclyfl/fl (Acly CKO) forebrains at postnatal day 5
Myelination is one of the final milestones of post-natal brain development in rodent and man. Oligodendrocytes, the myelinating glia of the CNS, are differentiated from proliferative progenitor cells called OPCs. Local and systemic signals act on OPCs to promote their proliferation and survival in the developing forebrain before growth arrest and differentiation. During this period, altricial mammals, like rodent, experience a dramatic shift in nutrient source (e.g., maternal blood or milk) and composition (e.g., carbohydrate or fatty acid). The influence of metabolism on neural cells is of growing interest, but how metabolic changes in the early postnatal brain impact OPC dynamics remains poorly understood. Here we show that a glucose oscillation in developing forebrain is detectable by MALDI MS imaging and correlates with a temporal and region-specific transition of OPCs from proliferation to differentiation. In dorsal cortex and white matter regions, glucose levels decline in the second postnatal week during a critical window when OPCs slow proliferation and begin differentiation. In ventral regions we observe continually elevated glucose and OPCs persist in a proliferative state, thereby suggesting that glucose availability serves as a local signal promoting progenitor expansion, or cell cycle exit and differentiation, in early brain. When OPCs are cultured in low glucose, we detect glucose-responsive histone acetylation changes and a transcriptional signature of cell cycle exit and differentiation. Mechanistically, we link the activity of the metabolic enzyme ATP citrate lyase, which converts glucose-derived citrate to the central metabolite acetyl-CoA, to acetylation and proliferation dynamics downstream of glucose availability in cultured cells. Pharmacological inhibition or genetic deletion of ACLY in cultured OPCs results in reduced histone acetylation and levels of cell cycle related transcripts, and reduced proliferation, supporting the hypothesis that glucose bioavailability influences OPC dynamics via ACLY. A transgenic animal model of conditional ACLY deletion in OPCs timed to the period of high glucose availability in brain results in decreased histone acetylation and growth-arrest leading to a depletion of the oligodendrocyte pool and hypomyelination. Finally, we link the emergence of ketone bodies in brain to the period of reduced glucose availability and show that alternative sources of acetyl-CoA that bypass glucose rescue Acly-/- OPC viability. Our results support a temporal-metabolic model centered on glucose availability in the timing of OPC growth arrest, and that alternative substrates of acetyl-CoA such as ketone body serve as a metabolic bridge during glucose fluctuations to promote oligodendrocyte survival and differentiation. Overall design: Single cell transcriptomics of OPCs that were FACS isolated from Control or conditional Acly knockout brain. The Pdgfra-creERT tamoxifen inducible line was crossed to Aclyfl/fl line. OPCs were sorted by CD140a labeling (PDGFRa) and collected for single cell transcriptomics on 10x platform.