Heparanome-Mediated Rescue of Oligodendrocyte Progenitor Quiescence following Inflammatory Demyelination

Abstract

The proinflammatory cytokine IFN-γ, which is chronically elevated in multiple sclerosis, induces pathologic quiescence in human oligodendrocyte progenitor cells (OPCs) via upregulation of the transcription factor PRRX1. In this study using animals of both sexes, we investigated the role of heparan sulfate proteoglycans in the modulation of IFN-γ signaling following demyelination. We found that IFN-γ profoundly impaired OPC proliferation and recruitment following adult spinal cord demyelination. IFN-γ-induced quiescence was mediated by direct signaling in OPCs as conditional genetic ablation ofIFNγR1(Ifngr1) in adult NG2+OPCs completely abrogated these inhibitory effects. Intriguingly, OPC-specific IFN-γ signaling contributed to failed oligodendrocyte differentiation, which was associated with hyperactive Wnt/Bmp target gene expression in OPCs. We found that PI-88, a heparan sulfate mimetic, directly antagonized IFN-γ to rescue human OPC proliferation and differentiationin vitroand blocked the IFN-γ-mediated inhibitory effects on OPC recruitmentin vivo. Importantly, heparanase modulation by PI-88 or OGT2155 in demyelinated lesions rescued IFN-γ-mediated axonal damage and demyelination. In addition to OPC-specific effects, IFN-γ-augmented lesions were characterized by increased size, reactive astrogliosis, and proinflammatory microglial/macrophage activation along with exacerbated axonal injury and cell death. Heparanase inhibitor treatment rescued many of the negative IFN-γ-induced sequelae suggesting a profound modulation of the lesion environment. Together, these results suggest that the modulation of the heparanome represents a rational approach to mitigate the negative effects of proinflammatory signaling and rescuing pathologic quiescence in the inflamed and demyelinated human brain.SIGNIFICANCE STATEMENTThe failure of remyelination in multiple sclerosis contributes to neurologic dysfunction and neurodegeneration. The activation and proliferation of oligodendrocyte progenitor cells (OPCs) is a necessary step in the recruitment phase of remyelination. Here, we show that the proinflammatory cytokine interferon-γ directly acts on OPCs to induce pathologic quiescence and thereby limit recruitment following demyelination. Heparan sulfate is a highly structured sulfated carbohydrate polymer that is present on the cell surface and regulates several aspects of the signaling microenvironment. We find that pathologic interferon-γ can be blocked by modulation of the heparanome following demyelination using either a heparan mimetic or by treatment with heparanase inhibitor. These studies establish the potential for modulation of heparanome as a regenerative approach in demyelinating disease.

Chronic demyelination of rabbit lesions is attributable to failed oligodendrocyte progenitor cell repopulation

“…This corresponded to a substantial relative reduction in the rate proliferation with the peak occurring at 8 weeks after induction of demyelination. Furthermore, unlike mouse lesions (Saraswat et al, 2021b), the transcriptional regulator Prrx1 was specifically upregulated in numerous OPCs at the lesion edge. Prrx1 expression in human OPCs induces a reversible state of quiescence inhibiting proliferation and thereby preventing efficient myelination (Wang et al, 2018).…”

“…Interestingly, IFN-g directly drives OPC quiescence via upregulation of PRRX1 in human OPCs 55 . This can be reversed by modulation of pharmacological modulation of the local heparanome within regions of demyelination rescuing both remyelination and axonal injury 50 . It is interesting to speculate that in large volume lesions, the transition of the microglia/macrophage response from proinflammatory to immunomodulatory phenotype occurs before the lesion achieves a sufficient density of OPC and thereby instead of promoting remyelination acts instead to limit OPC recruitment resulting in an overall failure of myelin regeneration.…”

“…Further supporting the association of axonal injury and myelin regeneration, induction of OL differentiation and remyelination following ablation of the muscarinic receptor in OPCs prevents axonal loss in EAE 49 . In contrast, an increase in pro-inflammatory signaling such as IFN-g administered at the time of demyelination prevents efficient OPC recruitment and exacerbates axonal injury 50 . Likewise, in the rabbit model we observed axonal loss and injury marked by App1 following demyelination at 7 dpl.…”

“…Poor Recruitment in Rabbit Model of Demyelination reversible state of quiescence inhibiting proliferation and thereby preventing efficient myelination (Wang et al, 2018). Prrx1 itself is regulated by both interferon-γ and BMP signaling (Wang et al, 2018, Saraswat et al, 2021b and increased Prrx1 expression in the rabbit suggest that the lesion environment may differ substantially from the mouse brain. Intriguingly, we also observed prominent examples of cells expressing cytoplasmic Olig2 expression in the rabbit lesion that is associated with an astroglial switch in stem/progenitor cells (Setoguchi, 2004) and observed in rare cells in EAE (Cassiani-Ingoni et al, 2006).…”

“…To do this we utilized the rabbit lysolecithin model of demyelination which is characterized by chronic demyelination for at least 6 months post-injection (Blakemore, 1978, Waxman et al, 1979, Foster et al, 1980). We found that OPC recruitment was substantially inferior to corresponding small rodent models and closely resembled the pattern observed in MS. Failed recruitment was associated with a protracted period of OPC activation, an upregulation of quiescence associated marker Prrx1 (Wang et al, 2018, Saraswat et al, 2021b), and an apparent decoupling of OPC recruitment and differentiation with the innate immune response. Fascinatingly, when smaller murine sized lesions were created in the rabbit, OPC recruitment was similarly deficient resulting in delayed OL generation, indicating that delayed recruitment in the rabbit is not entirely volume-dependent.…”