mTOR Signaling Regulates Metabolic Function in Oligodendrocyte Precursor Cells and Promotes Efficient Brain Remyelination in the Cuprizone Model

Abstract

In demyelinating diseases, such as multiple sclerosis, primary loss of myelin and subsequent neuronal degeneration throughout the CNS impair patient functionality. While the importance of mechanistic target of rapamycin (mTOR) signaling during developmental myelination is known, no studies have yet directly examined the function of mTOR signaling specifically in the oligodendrocyte (OL) lineage during remyelination. Here, we conditionally deleted Mtor from adult oligodendrocyte precursor cells (OPCs) using Ng2-Cre ERT in male adult mice to test its function in new OLs responsible for remyelination. During early remyelination after cuprizone-induced demyelination, mice lacking mTOR in adult OPCs had unchanged OL numbers but thinner myelin. Myelin thickness recovered by late-stage repair, suggesting a delay in myelin production when Mtor is deleted from adult OPCs. Surprisingly, loss of mTOR in OPCs had no effect on efficiency of remyelination after lysophosphatidylcholine lesions in either the spinal cord or corpus callosum, suggesting that mTOR signaling functions specifically in a pathway dysregulated by cuprizone to promote remyelination efficiency. We further determined that cuprizone and inhibition of mTOR cooperatively compromise metabolic function in primary rat OLs undergoing differentiation. Together, our results support the conclusion that mTOR signaling in OPCs is required to overcome the metabolic dysfunction in the cuprizone-demyelinated adult brain.

CRISPR/CasRx-Mediated RNA Knockdown Reveals That ACE2 Is Involved in the Regulation of Oligodendroglial Cell Morphological Differentiation

“…In addition, the treatment of cells with Lonafarnib greatly decreased the levels of Akt phosphorylation (Figure 7). These results are consistent with the fact that Ras is a positive regulator of oligodendroglial cell differentiation and myelination [19][20][21][24][25][26].…”

“…The intracellular domain of ACE2 preferentially formed an immune complex with the GTP-bound, endogenous Ras, which can become formed in the presence of excessive GTP (Figure 4B). Similar results were obtained in the case of the interaction with endogenous Ras downstream effectors phosphoinositide 3-kinase α and β (Figure S4; Figure S5), which are known to be direct upstream regulators of Akt kinase [19][20][21][24][25][26][27]. Taken together with the above results, it is suggested that Ras and the Ras signaling complex can be trapped to ACE2.…”

“…In addition, the intracellular region of ACE2 preferentially interacted with the active GTP-bound form of small GTPase Ras. Then, inhibition of Ras with a Ras inhibitor resulted in inhibiting their morphological differentiation, consistent with the fact that Ras signaling is required for differentiation and, in turn, myelination in oligodendrocyte cells [19][20][21][24][25][26]. It is suggested that, in the presence of ACE2, it inhibits morphological differentiation by trapping Ras.…”

“…It is well known that the activities of Akt kinase are critically required for oligodendroglial cell differentiation and, in turn, myelination as well as remyelination [24,25]. Knockdown of ACE2 with the cognate siRNA increased the levels of Akt phosphorylation, whose position at Ser-473 is essential for Akt activation (Figure 3A).…”

“…Collectively, since ACE2 as the transmembrane molecule results in interacting preferentially with the active, GTP-bound form of Ras, it is possible that in the presence of ACE2, ACE2 capture the active Ras, inhibiting downstream cytoplasmic molecules including Akt kinase signaling molecules (see the schematic diagram in the Figure 8). Their sequential activation is essential for triggering oligodendroglial cell differentiation and myelination [19][20][21][24][25][26]. On the other hand, in the absence or low amounts of ACE2, GTP-bound Ras can stimulate downstream cytoplasmic signaling to promote differentiation.…”