Pro-Inflammatory Molecules Implicated in Multiple Sclerosis Divert the Development of Human Oligodendrocyte Lineage Cells
Background and Objectives: Oligodendrocytes (OL) and their myelin-forming processes are targeted and lost during the disease course of Multiple Sclerosis (MS), targeted by infiltrating leukocytes and their effector cytokines. Myelin repair is considered to be dependent on recruitment and differentiation of oligodendrocyte precursor cells (OPCs). The basis of failure of re-myelination during the disease course of MS remains to be defined. The aim of this study is to determine the impact of pro-inflammatory molecules tumor necrosis factor (TNF) and interferon gamma (IFN) on the differentiation of human OPCs. Methods: We generated human OPCs from induced pluripotent stem cells with a reporter gene under the OL-specific transcription factor SOX10. We treated the cells in vitro with TNF or IFN and evaluated effects in terms of cell viability, expression of OL-lineage markers, and co-expression of astrocyte markers. To relate our findings to the molecular properties of OPCs as found in the MS brain we re-analyzed publicly available single nuclear RNAseq datasets. Results: Our analysis indicated that both TNF and IFN decreased the proportion of cells differentiating into the OL-lineage; consistent with previous reports. We now observe the TNF effect is linked to aberrant OPC differentiation. A subset of O4+, reporter-positive cells co-expressed the astrocytic marker Aquaporin-4 (AQP4). On the transcriptomic level, the cells acquire an astrocyte-like signature alongside a conserved reactive phenotype. Analysis of single-nuclear RNAseq datasets from human MS brain revealed a subset of OPCs expressing an astrocytic signature. Discussion: In the context of MS, these results imply that OPCs are present but inhibited from differentiating along the OL-lineage, with a subset acquiring a reactive and stem-cell like phenotype, reducing their capacity to contribute towards repair. These findings help define a potential basis for the impaired myelin repair in MS and provide a prospective route for regenerative treatment.