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J Clin Invest. 2018 May 1;128(5):2025-2041. doi: 10.1172/JCI94158. Epub 2018 Apr 16.

A TLR/AKT/FoxO3 immune tolerance-like pathway disrupts the repair capacity of oligodendrocyte progenitors.

Author information

1
Department of Pediatrics, Oregon Health & Science University (OHSU), Portland, Oregon, USA.
2
Division of Neuroscience, Oregon National Primate Research Center, Beaverton, Oregon, USA.
3
Department of Neurology, OHSU, Portland, Oregon, USA.
4
Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
5
Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
6
Department of Cell, Developmental and Cancer Biology, OHSU, Portland, Oregon, USA.

Abstract

Cerebral white matter injury (WMI) persistently disrupts myelin regeneration by oligodendrocyte progenitor cells (OPCs). We identified a specific bioactive hyaluronan fragment (bHAf) that downregulates myelin gene expression and chronically blocks OPC maturation and myelination via a tolerance-like mechanism that dysregulates pro-myelination signaling via AKT. Desensitization of AKT occurs via TLR4 but not TLR2 or CD44. OPC differentiation was selectively blocked by bHAf in a maturation-dependent fashion at the late OPC (preOL) stage by a noncanonical TLR4/TRIF pathway that induced persistent activation of the FoxO3 transcription factor downstream of AKT. Activated FoxO3 selectively localized to oligodendrocyte lineage cells in white matter lesions from human preterm neonates and adults with multiple sclerosis. FoxO3 constraint of OPC maturation was bHAf dependent, and involved interactions at the FoxO3 and MBP promoters with the chromatin remodeling factor Brg1 and the transcription factor Olig2, which regulate OPC differentiation. WMI has adapted an immune tolerance-like mechanism whereby persistent engagement of TLR4 by bHAf promotes an OPC niche at the expense of myelination by engaging a FoxO3 signaling pathway that chronically constrains OPC differentiation.

KEYWORDS:

Extracellular matrix; Inflammation; Neurological disorders; Neuroscience

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