Mechanistic Target of Rapamycin Regulates the Oligodendrocyte Cytoskeleton during Myelination

Abstract

During differentiation, oligodendrocyte precursor cells (OPCs) extend a network of processes that make contact with axons and initiate myelination. Recent studies revealed that actin polymerization is required for initiation of myelination whereas actin depolymerization promotes myelin wrapping. Here, we used primary OPCs in culture isolated from neonatal rat cortices of both sexes and young male and female mice with oligodendrocyte-specific deletion of mechanistic target of rapamycin (mTOR) to demonstrate that mTOR regulates expression of specific cytoskeletal targets and actin reorganization in oligodendrocytes during developmental myelination. Loss or inhibition of mTOR reduced expression of profilin2 and ARPC3, actin polymerizing factors, and elevated levels of active cofilin, which mediates actin depolymerization. The deficits in actin polymerization were revealed in reduced phalloidin and deficits in oligodendrocyte cellular branching complexity at the peak of morphologic differentiation and a delay in initiation of myelination. We further show a critical role for mTOR in expression and localization of myelin basic protein (Mbp) mRNA and MBP protein to the cellular processes where it is necessary at the myelin membrane for axon wrapping. Mbp mRNA transport deficits were confirmed by single molecule RNA FISH. Moreover, expression of the kinesin family member 1B, an Mbp mRNA transport protein, was reduced in CC11 cells in the mTOR cKO and in mTOR inhibited oligodendrocytes undergoing differentiation in vitro. These data support the conclusion that mTOR regulates both initiation of myelination and axon wrapping by targeting cytoskeletal reorganization and MBP localization to oligodendrocyte processes.

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

“…In contrast, Gsn, which functions in actin-severing, is normally upregulated as an oligodendrocyte progresses from MFOL to MOL 5,14,19 as seen in cluster 1 (additional supplementary files), but was downregulated in cluster 7. These data are consistent with the impaired initiation of myelination and continued hypomyelination observed in mTOR cKO developing spinal cord 8,21 .…”

“…It was also not surprising that loss of mTOR in differentiating oligodendrocytes impacted genes involved in cytoskeletal reorganization. Our previous studies have defined specific mTOR-regulated cytoskeletal targets in developing oligodendroglia in vitro and in vivo during both early stages of morphological differentiation and in later stages of myelin wrapping 21,22 . Cytoskeletal dynamics are essential as MFOLs mature to MOLs and must shift from promoting process extension requiring microtubule and actin polymerization to initiating axon wrapping requiring depolymerization 19,23–25 .…”

The Infantile Leukoencephalopathy-Associated Mutation of C11ORF73/HIKESHI Proteins Generates De Novo Interactive Activity with Filamin A, Inhibiting Oligodendroglial Cell Morphological Differentiation

“…We further investigated the effects of the C4S mutation on signaling through mammalian target of Rapamycin (mTOR). Phosphorylation of ribosomal S6 and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) proteins as the outputs of signaling through mTOR are known to be associated with oligodendrocyte differentiation and myelination [ 19 , 20 ]. Immunoblotting with an anti-phosphorylated S6 or 4E-BP1 antibody revealed decreased phosphorylation levels in cells harboring the C4S mutant constructs ( Figure 6 D).…”

Tuberous Sclerosis Complex as Disease Model for Investigating mTOR-Related Gliopathy During Epileptogenesis

“…In a recent study, the involvement of mTOR signaling in cytoskeletal reorganization during oligodendrocyte development, as well as in initiation of myelination, was demonstrated. Moreover, the importance of the mTOR pathway on oligodendroglial branching complexity was observed (147). One study demonstrated a decrease in both myelin content and oligodendrocytes in and around cortical lesions of mTORopathy specimens (138).…”