Distinct patterns of gene transcription in relapsing autoimmune encephalomyelitis: differences between first and second disease episode

Introduction: The pathogenesis of multiple sclerosis is marked by an early inflammatory and secondary neurodegenerative phase with axonal loss causing permanent disability. Immuno-modulatory therapies are partially effective at early stages while neuroprotective treatment is not available. To identify new therapeutic targets we compared transcriptional patterns of in-flammatory vs. neurodegenerative disease phases in a rat model of relapsing experimental autoimmune encephalomyelitis (EAE).

Methods: EAE was induced in female Dark Agouti rats (n=30) by immunization with myelin oligodendrocyte glycoprotein (rMOG 1–125, 100µg in CFA). Natural disease progression was characterized over 30 days using an established clinical score. Subgroups of rats (n=3) were sacrificed during the first inflammatory (day 9 and 11) and the second demyelinating disease episode (day 18 and 22). Total RNA was isolated from the lumbothoracic spinal cord of EAE and naïve control animals. Reverse transcribed cRNA was analyzed using Affymetrix RAE230A gene array chips (15923 genes) and Array Assist 5.1 software. To validate array results and quantify gene regulation real-time RT-PCR was performed on the same mRNA for selected genes.

Results: Distinct transcriptional patterns were identified for the first [days 9 and 11, total of 2802 annotated genes (>1.5-fold regulation, p<0.05)] and second disease episode (days 18 and 22, total of 2270 genes). At the onset of each episode 437 gene regulations were identical, while n=196 were specific for the first and n=477 for the second episode. At maximal disease manifestation 1834 genes were found in both, n=922 only in the first and n=371 only in the second episode. Amongst others, distinct upregulation was observed for iNOS, CXCL2 and MIP-1 alpha in the first and CXCL13, CCL5 and P2Y12 in the second episode and confirmed by RT-PCR. Furthermore, upregulation of genes involved in IgG and complement formation, macrophage regulation and collagen production were predominant in the second episode.

Conclusions: Early inflammatory and chronic degenerative episodes of relapsing EAE exhibit distinct patterns of gene transcription. Gene expression in the second disease episode was charaterized by a shift of the chemokine profile towards B cell chemoattractants. More com-prehensive functional analysis of the gene array data is in progress to identify new therapeutic targets for the chronic neurodegenerative stage of multiple sclerosis.