Transcriptional heterogeneity between primary adult grey and white matter astrocytes underlie differences in modulation of in vitro myelination

Abstract

Background Multiple sclerosis (MS) is an inflammation-mediated demyelinating disease of the central nervous system that eventually results in secondary axonal degeneration due to remyelination failure. Successful remyelination is orchestrated by astrocytes (ASTRs) and requires sequential activation, recruitment, and maturation of oligodendrocyte progenitor cells (OPCs). In both MS and experimental models, remyelination is more robust in grey matter (GM) than white matter (WM), which is likely related to local differences between GM and WM lesions. Here, we investigated whether adult gmASTRs and wmASTRs per se and in response to MS relevant Toll-like receptor (TLR) activation differently modulate myelination. Methods Differences in modulation of myelination between adult gmASTRs and wmASTRs were examined using an in vitro myelinating system that relies on a feeding layer of ASTRs. Transcriptional profiling and weighted gene co-expression network analysis were used to analyze differentially expressed genes and gene networks. Potential differential modulation of OPC proliferation and maturation by untreated adult gmASTRs and wmASTRs and in response to TLR3 and TLR4 agonists were assessed. Results Our data reveal that adult wmASTRs are less supportive to in vitro myelination than gmASTRs. WmASTRs more abundantly express reactive ASTR genes and genes of a neurotoxic subtype of ASTRs, while gmASTRs have more neuro-reparative transcripts. We identified a gene network module containing cholesterol biosynthesis enzyme genes that positively correlated with gmASTRs, and a network module containing extracellular matrix-related genes that positively correlated with wmASTRs. Adult wmASTRs and gmASTRs responding to TLR3 agonist Poly(I:C) distinctly modulate OPC behavior, while exposure to TLR4 agonist LPS of both gmASTRs and wmASTRs results in a prominent decrease in myelin membrane formation. Conclusions Primary adult gmASTRs and wmASTRs are heterogeneous at the transcriptional level, differed in their support of in vitro myelination, and their pre-existing phenotype determined TLR3 agonist responses. These findings point to a role of ASTR heterogeneity in regional differences in remyelination efficiency between GM and WM lesions.

Ponesimod inhibits astrocyte‐mediated neuroinflammation and protects against cingulum demyelination via S1P 1 ‐selective modulation

“…The precise mechanism through which this prevention occurs is not known but appears to involve increase in oligodendrocytes and reduction in microglia and astrocytes (Figure 4). The mechanisms might likely include non‐cell autonomous effects that involve astrocyte S1P 1 engagement, which would be consistent with the documented astrocyte influences on myelination 46–50 . Future MS imaging studies on myelin preservation with ponesimod could clarify the effects on the cingulum and other pathways associated with MS.…”

“…28 In addition, high levels of astrocytic metallothionein (MT) genes overlapped with Huntington disease 44 and astrocytomas, 45 suggesting that ponesimod inhibition of MT-gene expressing astrocytes may have therapeutic utility for treating other diseases. The vast diversity of astrocytes throughout the brain with disease relevance, 26,29,46 implicates myriad potential effects that could be accessed by ponesimod for neuro-inflammatory processes and related effects on myelination. 42,[46][47][48][49][50] To assess ponesimod activities on myelination, cuprizone challenge with or without ponesimod was employed in preventative and therapeutic paradigms.…”

“…The vast diversity of astrocytes throughout the brain with disease relevance, 26,29,46 implicates myriad potential effects that could be accessed by ponesimod for neuro-inflammatory processes and related effects on myelination. 42,[46][47][48][49][50] To assess ponesimod activities on myelination, cuprizone challenge with or without ponesimod was employed in preventative and therapeutic paradigms. Beyond generalized demyelination, a characteristic of MS, clinical studies correlated fatigue with demyelination.…”

“…The mechanisms might likely include non-cell autonomous effects that involve astrocyte S1P 1 engagement, which would be consistent with the documented astrocyte influences on myelination. [46][47][48][49][50] Future MS imaging studies on myelin preservation with ponesimod could clarify the effects on the cingulum and other pathways associated with MS.…”

Shaping of Regional Differences in Oligodendrocyte Dynamics by Regional Heterogeneity of the Pericellular Microenvironment

“…By contrast, astrocytes from the white matter of normal young adult rats express extracellular matrix (ECM) genes more abundantly than gray matter astrocytes (Werkman et al, 2020; Figure 2). ECM genes enriched in white matter astrocytes include ECM genes that are upregulated in reactive astrocytes, such as CD44 and collagen genes though they are expressed at a lower level in normal white matter (Zamanian et al, 2012).…”