MicroRNA (miRNA) are a class of post-transcriptional regulators of gene expression targeting mRNA for translational repression and/or degradation. We analyzed the expression of 365 miRNA in lymphocytes in relapsing-remitting MS patients, and show the first evidence for distinct miRNA expression profiles in CD4 1 , CD81 and B cells in MS when compared with those in healthy volunteers. MiR-17-5p, which is involved in autoimmunity, was up-regulated in CD4 1 cells from MS patients. This was correlated with alterations in the expression of potential target genes of miR-17-5p, i.e. phosphatase and tensin homology and phosphatidyl-inositol-3-kinase regulatory subunit 1, which were down-regulated upon stimulation of CD4 1 cells with anti-CD3/CD28 in vitro. Functional experiments with a synthetic inhibitor of miR-17 supported the link between miRNA expression and the altered target gene expression. Moreover, we found distinct responses of deregulated miRNA to stimulation, i.e. miR-17-5p and miR-193a were strongly upregulated, in contrast to the down-regulation of miR-497, miR-1 and miR-126. Other deregulated miRNA did not respond to the stimulation probably due to other, non-T-cell activation related, mechanisms in their mode of action. Our findings support the role of miRNA-dependent regulatory mechanisms in the immunopathogenesis of MS.Key words: Autoimmune disease . Expression . Lymphocytes . MicroRNA . MS Supporting Information available onlineIntroduction MS results from a combination of environmental and genetic factors [1]. Genetic evidence suggests the existence of multiple susceptibility factors underlying MS. In the last couple of years, genomewide association studies have started to provide more information on genes that contribute to the risk of developing MS [2][3][4]. Large-scale transcriptional analysis with microarray technology has provided further insights into the molecular mechanisms of pathogenesis of MS. This approach has yielded several candidate genes responsible for the heterogeneous expression of the disease [5]. However, gene regulation is influenced by post-genomic regulatory mechanisms, e.g. micro-RNA (miRNA). MiRNA are small, endogenous non-coding RNA of approximately 22 nucleotides. They are transcribed in the nucleus, and after processing and export into the cytoplasm, they silence expression of target genes in a sequence-specific manner [6]. Repression of target genes is due to translational repression (imperfect sequence match) or mRNA cleavage (perfect match). MiRNA are key regulators of a wide variety of biological processes, e.g. cell proliferation and differentiation, apoptosis, signal transduction and organ development [7][8][9] It has been shown that miRNA are important in the homeostasis and function of the immune system [14][15][16][17]. Zhou et al. [18] showed that miR-150 is up-regulated during B-and T-cell maturation. Furthermore, Wu [19] reported different expression profiles of miRNA in antigen-specific naive, effector and memory CD8 1 T cells. In two recent reports [20,21...

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Heme is not only a very important prosthetic group that modulates the structure and activity of heme proteins but also a regulatory molecule that controls metabolic pathways and the biosynthesis of various proteins. However, investigation into heme regulatory effects in higher vertebrates has been hampered by the lack of a suitable animal model. A knockout mouse with targeted disruption of porphobilinogen deaminase, the third enzyme of the heme pathway, has been generated in our laboratory and used in the present study as an in vivo model of heme deficiency to explore diverse heme regulatory properties. In this model with a defined heme disturbance, we observed a superinductive response of d-aminolevulinate synthase, the first enzyme in heme synthesis, after phenobarbital treatment. We also found that limited heme is associated with decreased induction of cytochrome P450 by phenobarbital as a consequence of impaired gene transcription. This inhibitory effect is isoenzymespecific, being significant for cyp2a5. The activity and mRNA level of this particular cytochrome P450 are significantly lower in the phenobarbital-induced porphobilinogen deaminase-deficient mice (55% and 43%, respectively), but its expression can be restored to normal values when exogenous heme is administered. Other heme proteins, namely neuronal nitric oxide synthase and soluble guanylate cyclase, function normally in mice with limited heme. Our results demonstrate that the expression of various heme proteins is differentially regulated in conditions of reduced heme availability. Moreover, our findings emphasize the importance of heme protein function in the genesis of pathophysiological manifestations in acute intermittent porphyria.

Our findings provided deeper insight into the mode of action of natalizumab, with possible implications for understanding both the effects of natalizumab on MS activity and its specific adverse event profile.