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

Abstract

ers by interactions of FoxO3 with the chromatin-remodeling factor Brg1 and the TF Olig2, which are involved in control of OPC differentiation (14-16). Hence, central myelination failure is regulated by a noncanonical TLR4/AKT/FoxO3 signaling pathway utilized by bHAf to induce a tolerance-like state that selectively constrains OPC maturation and myelination. ResultsNeonatal hypoxic-ischemic WMI promotes MDa HA depolymerization. To investigate the status of MDa HA in chronic neonatal WMI, we employed our preterm-equivalent rat hypoxia-ischemia (H-I) model, which generates myelination failure and replicates key features of human WMI ( Figure 1A) (17). MDa HA turnover in the ECM after H-I was visualized with a biotinylated HA-binding protein (HABP) and costained with glial fibrillary acidic protein (GFAP) as a marker of WMI. Unlike in age-matched uninpro-myelination signal (13). This tolerance-like action of bHAf was mediated through TLR4 but not via CD44 or TLR2. As in TLR4-mediated IT, bHAf 's influence on myelination was reversible when MDa HA depolymerization was attenuated or bHAf was removed. AKT desensitization was similarly reversible in vivo in neonatal WMI. Moreover, bHAf actions were mediated via a noncanonical TRIF-dependent pathway, also involved in IT, rather than the canonical MyD88 arm of TLR4 signaling. AKT desensitization resulted in maturation-dependent activation of the FoxO3 transcription factor (TF), which selectively constrained preOL maturation in a bHAf-dependent fashion. A role for activated FoxO3 in human myelination failure was supported by selective localization of nuclear FoxO3 to OPCs in human preterm WMI and multiple sclerosis (MS) plaques. bHAf-mediated OPC maturation arrest appears to be regulated at the FoxO3 and myelin basic protein (MBP) promot- (Contralateral). Only the lesion group had a significant reduction in HA recovery. (E) Incubation of MDa HA with the lesion lysate generated HAf below ~650 kDa. Lesion-lysate activity was sensitive to heat inactivation but insensitive to deferoxamine (50 μM). B and C: control n = 2; H-I n = 4 animals for each age group (P4 and P14). D: n = 6 (H-I), n = 5 (control), and n = 4 (hypoxia) animals (P7). E: n = 4 separate experiments on 4 different animals at P4 after H-I at P3; one representative experiment is shown. *P < 0.05 by ANOVA. Mean ± SD. Scale bars: 300 μm (B and C). The Journal of Clinical Investigation R E S E A R C H A R T I C L E2 0 2 7 jci.orgVolume 128 Number 5 May 2018 with MBP-labeled oligodendrocytes (Supplemental Figure 2A). To confirm de novo progressive myelin generation, we undertook ultrastructural studies that identified axons wrapped with multilamellar myelin sheaths ( Figure 2B). In contrast to vehicle-treated slices, which displayed robust myelination of the corpus callosum, slices incubated with MDa HA until 21 days in vitro (DIV21) displayed a pronounced reduction in myelinated axons ( Figure 2C). Myelination failure was not related to decreased OPC survival, since MDa HA treatment did not enhance OPC degeneratio...

A modified flavonoid accelerates oligodendrocyte maturation and functional remyelination

“…We previously reported that the activities of PH20, Hyal2, and Hyal5 blocked OPC maturation when expressed by OPCs in vitro, with PH20 having the greatest inhibitory activity. We also found that digestion products of HA in a specific size range blocked remyelination in vitro and in vivo (Preston et al, ; Srivastava et al, ). Hyal5 has not been detected in OPCs or in the CNS (Preston et al, ) while PH20 RNA has been reported to only be transiently expressed by OPCs or other cells, especially following CNS insults (Hagen et al, ; Preston et al, ; Sherman & Back, ; Sloane et al, ; Xing et al, ).…”

“…Vcpal (e.g., Sloane et al, 2010;Preston et al, 2013, pp. 266-80;Srivastava et al, 2018). We found that the effects of S3 were reversed if cultures were treated with 25 U of recombinant PH20 (Figure 4d,f)…”

“…To demonstrate that the effects of S3 on OPC maturation were dependent on blocking hyaluronidase activity, we treated cultures with increasing amounts of rPH20. We reasoned that this approach would demonstrate specificity because: (a) We have clearly shown that S3 blocks rPH20 activity; (b) the digestion products generated by PH20 are sufficient to block OPC maturation and remyelination (e.g., Preston et al, ; Srivastava et al, ); (c) No activities other than HA depolymerization have been attributed to PH20, which has been carefully studied both in basic and commercial settings, and has been examined for off target effects in clinical trials (e.g., Infante et al, ); and (d) The effects of HMW HA on OPC maturation can be blocked in OPC cultures and in in vivo models of demyelination by Vcpal (e.g., Sloane et al, ; Preston et al, , pp. 266–80; Srivastava et al, ).…”

“…To investigate whether hyaluronidase activity from OPCs attenuates OL maturation following perinatal CNS injury, we employed an in vitro slice culture model of perinatal white matter injury (Dean et al, ). In this model, extensive reactive astrogliosis is accompanied by high levels of hyaluronidase activity such that adding HMW HA to cultures generates bioactive HA digestion products that inhibit OPC maturation (Srivastava et al, ). As shown in Figure A, a composite image of one such slice, the majority of MBP+, olig2+ cells continue to reside in the white matter (outlined area) in these slices throughout the culture period, with some superficial MBP+ cells scattered throughout the cortex.…”

“…CD44, for example, can regulate Wnt‐induced β ‐catenin signaling (Chang et al, ; Schmitt, Metzger, Gradl, Davidson, & Orian‐Rousseau, ); CD44‐HA interactions can influence AKT activity which may in turn induce further HA synthesis (e.g., Liu & Cheng, ; Zhu et al, ); similar to the effects of LINGO‐1, low molecular weight forms of HA lead to reduced levels of gelsolin (Lee et al, ); and estradiol can influence HA synthesis (Freudenberger et al, ). Thus, signaling by HA through CD44 or other HA receptors (e.g., toll‐like receptors; Black et al, ; Campo et al, ; Foley et al, ; Garantziotis et al, ; Jiang et al, ; Li, Potts‐Kant, Garantziotis, Foster, & Hollingsworth, ; Liang et al, ; Riehl, Santhanam, Foster, Ciorba, & Stenson, ; Scheibner et al, ; Sloane et al, ; Srivastava et al, ; Sunabori, Koike, Asari, Oonuki, & Uchiyama, ; Taylor et al, ; Termeer et al, ) may affect multiple signaling pathways in OPCs that regulate OPC maturation. How different sizes of HA digestion products induce distinct signaling is unclear.…”