p70S6 kinase regulates oligodendrocyte differentiation and is active in remyelinating lesions

Abstract

The p70 ribosomal S6 kinases (S6K1 and S6K2) are downstream targets of the mechanistic target of rapamycin (mTOR) signaling pathway. S6K1 specifically has demonstrated functions in regulating cell size in Drosophila and in insulin-sensitive cell populations in mammals. Prior studies demonstrated that the mechanistic target of rapamycin pathway promotes oligodendrocyte differentiation and developmental myelination; however, how the immediate downstream targets of mTOR regulate these processes has not been elucidated. Here, we tested the hypothesis that S6K1 regulates oligodendrocyte differentiation during developmental myelination and remyelination processes in the CNS. We demonstrate that S6K activity peaks in oligodendrocyte lineage cells at the time when they transition to myelinating oligodendrocytes during developmental myelination in mouse spinal cord. We further show S6K activity in differentiating oligodendrocytes in acute demyelinating lesions induced by lysophosphatidyl-choline injection or by experimental autoimmune encephalomyelitis in mice. In demyelinated lesions, the expression of the S6K target, phosphorylated S6 ribosomal protein (pS6RP), was transient and highest in maturing oligodendrocytes. Interestingly, we also identified S6K activity in oligodendrocyte lineage cells in active multiple sclerosis lesions. Consistent with its predicted function in promoting oligodendrocyte differentiation, we demonstrate that specifically inhibiting S6K1 in cultured oligodendrocyte precursor cells significantly impairs cell lineage progression and expression of myelin basic protein. Finally, we used zebrafish to show in vivo that inhibiting S6K1 function in oligodendroglial cells reduces their differentiation and the number of myelin internodes produced. These data reveal an essential function of S6K1 in promoting oligodendrocyte differentiation during development and remyelination across multiple species.

Cholesterol biosynthesis defines oligodendrocyte precursor heterogeneity between brain and spinal cord

“…We measured phosphorylation of S6RP, a downstream target of mTOR, in brain and spinal cord O4 + cells and found higher levels in spinal cord compared with the brain ( Figure S3F ). A recent report demonstrated that S6RP activation in differentiating oligodendrocytes correlates with the peak of myelination in both brain and spinal cord, but no comparison was made on the relative activation in each region ( Benardais et al, 2022 ). We next asked whether brain and spinal cord oligodendroglia respond differently to the loss of mTOR at the transcriptome level.…”

Increasing glutathione levels by a novel posttranslational mechanism inhibits neuronal hyperexcitability

“…β-tubulin was used as a loading control to ensure effective protein transfer and equal sample loading across all wells. For detecting total-S6 ribosomal protein, the same blot was stripped using the Restore™ PLUS Western blot stripping buffer (Thermo Fisher Scientific, Waltham, MA, USA) for ∼8min, washed with 1X tris buffered saline (TBS), blocked for 1 h with 5% BSA, and then probed using the total S6 ribosomal protein [ [66] , [67] , [68] ] rabbit primary antibody (1:1000, 32 kDa). All antibodies were purchased from Cell Signaling Technology (Danvers, MA, USA).…”