Metformin enhances human oligodendrocyte function by altering metabolism
Metformin rejuvenates adult rat oligodendrocyte progenitor cells (OPCs) allowing more efficient differentiation into oligodendrocytes and improved remyelination of CNS axons and therefore is of interest as a possible therapeutic in demyelinating diseases such as multiple sclerosis (MS). We set out to test whether metformin had a similar effect in human stem cell derived-OPCs. We assessed the suitability of human monoculture, organoid and transplantation into immunodeficient mice (chimera model) culture systems in simulating in vivo adult human oligodendrocytes, finding most close resemblance in the chimera model. Metformin increased myelin proteins and/or sheaths in all models even when human cells had fetal signatures. In the chimera model, metformin led to a marked increase in mitochondrial area both in the human transplanted cells and in the mouse axons with associated increase in transcripts related to mitochondrial function and metabolism. Human oligodendrocytes from MS brain donors treated pre-mortem with metformin also expressed similar transcripts suggesting that metformin's brain effect is not cell-specific, altering metabolism in both oligodendrocytes and axons leading to more myelin production, in part through mitochondrial changes.  This bodes well for ongoing clinical trials testing metformin for neuroprotection. Overall design: Human embryonic stem cell-derived (hESC) oligodendroglia were generated and processed for single-cell RNA sequencing (scRNAseq) using the 10X Genomics pipeline across three model systems: monolayers, organoids, and chimeric animals. In the monolayer model, oligodendroglia were grown in vitro and then prepared for sequencing. For the organoid model, cortical brain organoids containing oligodendroglial cells were cultures in vitro, with ten organoids pooled together per sample for scRNAseq. In the chimeric model, chimeric human-mouse animals were created by injecting GFP+ hESC-derived oligodendrocyte progenitor cells (OPCs) into the rostral and caudal corpus callosum of myelin-deficient and immunodeficient Shi/Shi x Rag2-/- mice. A total of 500,000 cells were distributed between both hemispheres. Following transplantation, chimeric animals were treated daily with 10mg/ml metformin or vehicle (ddH2O) by oral gavage for 21 days, between days 42-63 post transplantation. At day 70 post transplantation, the corpus callosum region of each animal was processed for scRNAseq, with sorted live cells pooled from two animals per sample.