Single-cell Sequencing Reveals Brain/Spinal Cord Oligodendrocyte Precursor Heterogeneity and Requirement for mTOR in Cholesterol Biosynthesis and Myelin Maintenance

Abstract

Brain and spinal cord oligodendroglia have distinct functional characteristics, and cell autonomous loss of individual genes can result in different regional phenotypes. However, sequencing studies to date have not revealed distinctions between brain and spinal cord oligodendroglia. Using single-cell analysis of oligodendroglia during myelination, we demonstrate that brain and spinal cord precursors are transcriptionally distinct, defined predominantly by cholesterol biosynthesis. We further identify mechanistic target of rapamycin (mTOR) as a major regulator promoting cholesterol biosynthesis in oligodendroglia. Oligodendroglial-specific loss of mTOR compromises cholesterol biosynthesis in both the brain and spinal cord. Importantly, mTOR loss has a greater impact on cholesterol biosynthesis in spinal cord oligodendroglia that corresponds with more pronounced developmental deficits. However, loss of mTOR in brain oligodendroglia ultimately results in oligodendrocyte death, spontaneous demyelination, and impaired axonal function, demonstrating that mTOR is required for myelin maintenance in the adult brain.

Marked regional glial heterogeneity in the human white matter of the central nervous system

“…Oligodendrocytes also vary with tissue region, notably with SPARC -expressing Oligo_F cells being significantly more abundant in the spinal cord compared to BA4 and CB (Figure 5a) confirmed by immunofluorescence co-labelling of SPARC and OLIG2 on FFPE samples from different donors (Figure 5f,g, Table S4). The myelin sheaths around spinal cord axons are longer and thicker than those in the brain even on the same diameter axon 5 , and now this can be explained by the abundance of Oligo_F oligodendrocytes in the CSC, as these express more genes important for cholesterol biosynthesis and myelination (similarly to mice 60 ), including PLP1, CNP , and MAG and of HCN2 (known to control mouse myelin sheath length 33 ) (Figure 2c–d, Figure 5h, Extended Data Figure 2c,Table S3). Differential gene expression analysis also showed that CSC OPCs and oligodendrocytes expressed more Src Kinase-Associated Phosphoprotein 2 gene ( SKAP2 ), important for OPC mobility and myelin sheath formation in mouse spinal cord 61 (Figure 5a,h).…”