Medicine & Pharmacology, Pathology & Pathobiology; multiple sclerosis; neuroinflammation; astrocytes; myelin; bioinformatics
We previously reported that in multiple sclerosis (MS) patients with a progressive form of the disease, spinal cord periplaques extend distance away from plaque borders and are characterized by the co-occurrence of partial demyelination, astrocytosis and low-grade inflammation. However, transcriptomic analyses comparing periplaques to adjacent normal-appearing white matter (NAWM) areas did not allow providing a comprehensive view of molecular events in astrocytes vs oligodendrocytes. Here, we re-assessed our transcriptomic data with the aim of identifying functionally-relevant co-expression networks that would reflect astrocyte vs oligodendrocyte molecular signatures in periplaques. We identified an astrocytosis-related gene module comprising GFAP, the hub gene CX43/GJA1 and a set of transcripts forming a TGFB/SMAD1/SMAD2 genomic signature. Partial demyelination was characterized by a co-expression network which, besides myelin genes, comprised a highly significant number of translation/elongation-related genes. Interestingly, the main oligodendrocyte-related hub we identified was NDRG1, a gene previously shown to be specifically silenced in the NAWM of MS patients. This result indicated that NDRG1 down-regulation could be an important event in the process of periplaque partial demyelination. To establish a putative link between NDRG1 down-regulation and a cytokine/chemokine signature, we then sought to identify cytokine/chemokine genes whose mRNA levels inversely correlated with those of NDRG1. Following this approach we found 5 candidate immune-related genes whose up-regulation associated with NDRG1 down-regulation: TGFB1, PDGFC, IL-17D, IL-33, and IL-12A. From these results we propose that in the spinal cord of MS patients with progressive forms of the disease, TGFB1 may limit acute inflammation but concurrently induce astrocytosis and an alteration of oligodendrocytes terminal differentiation.