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Promoting Oligodendrogenesis and Myelin Repair Using the Multiple Sclerosis Medication Glatiramer Acetate

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Promoting Oligodendrogenesis and Myelin Repair Using the Multiple Sclerosis Medication Glatiramer Acetate Promoting oligodendrogenesis and myelin repair using the multiple sclerosis medication glatiramer acetate Viktor Skihara, Claudia Silvaa, Andrew Chojnackia, Axinia Do¨ringa, William B. Stallcupb, Samuel Weissa, and V. Wee Yonga,1 aHotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada and bThe Burnham Institute for Medical Research, La Jolla, CA 92037 Communicated by Michael Sela, Weizmann Institute of Science, Rehovot, Israel, August 30, 2009 (received for review May 31, 2009) The formation of oligodendrocytes (oligodendrogenesis) and my- are immunoreactive for neurotrophic factors such as BDNF (7). elin is regulated by several neurotrophic factors. Strategies to However, any approach to use leukocytes to deliver neurotro- increase the level of these trophic molecules may facilitate repair phic factors for repair must balance their potential detriments in in demyelinating conditions, such as multiple sclerosis (MS). Be- exacerbating the pathology of MS. cause leukocytes are a source of neurotrophic factors, and as Glatiramer acetate (GA), a medication used in relapsing- glatiramer acetate (GA) generates T helper 2 (Th2) lymphocytes remitting MS (8), generates GA-reactive T lymphocytes that are that are not known to be harmful, we tested the hypothesis that of the T helper 2 (Th2) anti-inflammatory bias (9, 10). GA- GA regulates oligodendrogenesis and myelin formation. First, we reactive Th2 cells accumulate in the CNS, where they have been generated GA-reactive Th2 cells and determined that they pro- shown to produce not only anti-inflammatory cytokines but also duced transcripts for neurotrophic factors, including insulin-like neurotrophic factors (11). Importantly, Th2 cells have not been growth factor-1 (IGF-1). The conditioned medium from GA-reactive found to be neurotoxic, unlike the proinflammatory Th1 or Th17 T cells elevated IGF-1 protein and promoted the formation of lymphocytes that destroy neurons in tissue culture (12). More oligodendrocyte precursor cells (OPCs) from embryonic brain- recently, GA has also been found to modulate monocytoid cells derived forebrain cells in culture. We next subjected mice to into those that express anti-inflammatory cytokines (13). NEUROSCIENCE lysolecithin-induced demyelination of the spinal cord. At 7 days Here, we have tested the hypothesis that T cells exposed to GA after the insult, the number of OPCs in the demyelinated dorsal elevate neurotrophic factors that are important for oligoden- column was higher than that in uninjured controls, and was further drogenesis in culture. Furthermore, we have used mice with increased by the daily s.c. injection with GA. Increased OPC gen- lysolecithin-induced demyelination to address whether treat- eration by GA was associated temporally with the elevation of ment with GA would increase OPC numbers and remyelination IGF-1 and brain-derived neurotrophic factor (BDNF) in the spinal within the lesioned spinal cord. These studies have relevance to cord. Finally, the resultant remyelination at 28 days was higher in the biology of harnessing the benefits of inflammation to evoke mice treated with GA during the first 7 days of injury compared repair. with vehicle controls. These results indicate that GA promotes oligodendrogenesis and remyelination through mechanisms that Results involve the elevation of growth factors conducive for repair. T Cells Exposed to GA Elevate Their Production of Growth Factors in Vitro. Cells obtained from the lymph nodes of GA-pretreated beneficial inflammation ͉ neurotrophic factors ͉ oligodendrocyte ͉ mice (Fig. S1) were incubated with APCs and GA, resulting in regeneration ͉ remyelination a proliferative response (Fig. S2) that suggested the presence of T cells reactive to GA. Cell conditioned medium from these ultiple sclerosis (MS) is characterized by inflammation GA-reactive cells was then examined for the accumulation of IFN-␥, a Th1 cytokine, and for IL-5, a Th2 cytokine. Increasing Mand demyelination in the CNS. The demyelinated lesions ␥ can be repaired and, indeed, the extent of remyelination is culture periods with GA resulted in loss of detectable IFN- and substantial in some patients (1). There is increasing interest in steady accumulation of IL-5 (Fig. S2), indicating that the GA- facilitating remyelination as its benefits extend beyond restora- reactive T cells were of the Th2 phenotype, as reported by others tion of nerve impulse conduction to preventing axonal degen- (9–11). With this confirmation, we examined the capacity of eration, since axon and myelin units have dynamic interactions GA-reactive T cells to produce growth factors. From several involving survival signaling. mouse donors previously treated with GA, lymph node cells were Much has been learned about the process of remyelination (2) restimulated with GA and RNA was harvested. Fig. 1 shows that and key steps include the proliferation and maturation of increases in transcripts encoding IGF-1 and PDGFaa were oligodendrocyte precursor cells (OPCs) and the appropriate evident after 3 days of GA treatment. Transcripts for BDNF was interactions of oligodendrocyte processes with axons to form variable, with three cultures elevating this trophic factor in myelin. A large number of molecules are critically involved in the response to GA whereas three did not. proliferation, maturation and survival of OPCs, and among these The cell-conditioned medium collected from T cells over 3 are neurotrophic factors such as platelet-derived growth factor days of culture was analyzed for IGF-1 protein content. IGF-1 (PDGF), insulin-like growth factor-1 (IGF-1) and brain-derived neurotrophic factor (BDNF) (3–6). Accordingly, strategies that Author contributions: V.S. and V.W.Y. designed research; V.S., C.S., A.C., and A.D. performed have been used to induce remyelination in animals have included research; W.B.S. and S.W. contributed new reagents/analytic tools; C.S., A.C., A.D., and V.W.Y. the provision of neurotrophic factors through infusion or gene analyzed data; and V.S., C.S., A.C., A.D., W.B.S., S.W., and V.W.Y. wrote the paper. therapy. The authors declare no conflict of interest. Another means to deliver growth factors to the nervous system Freely available online through the PNAS open access option. takes advantage of the observation that leukocytes are rich 1To whom correspondence should be addressed. E-mail: [email protected]. sources of neurotrophic factors. Indeed, even the disease- This article contains supporting information online at www.pnas.org/cgi/content/full/ promoting inflammatory cells of perivascular cuffs in MS lesions 0909607106/DCSupplemental. www.pnas.org͞cgi͞doi͞10.1073͞pnas.0909607106 PNAS Early Edition ͉ 1of6 Downloaded by guest on September 24, 2021 Fig. 1. GA-reactive T cells in tissue culture produce growth factors. Real-time PCR analyses and GADPH-normalized levels show that compared with non-GA exposed cells (control), treatment of T cells with GA resulted in increase in levels of IGF-1 and PDGFaa. Each circle, square, or triangle within a given growth factor dataset represents a separate culture. *, P Ͻ 0.05; **, P Ͻ 0.01, compared with non-GA exposed controls (t test). protein was significantly elevated in T-cell cultures treated with GA, either collected at first in vitro restimulation with GA (day 3), or after restimulation a week after (day 10) (Fig. S2). Conditioned Medium from GA-Reactive T Cells Increases the Number of OPCs in Culture. We evaluated whether growth factors produced Fig. 3. GA treatment increases injury-induced rise of OPC numbers. (A) The by GA-reactive T cells (Fig. 1) were sufficient to regulate the number of PDGR␣-positive OPCs were counted in the dorsal column of 10 formation of OPCs from neural precursor cells. Single cells from sections, each spaced 100 ␮m apart and centered around the lesion epicenter. the anterior entopenduncular area (AEP) of embryonic day 15 The sum per mouse was then plotted in A, where each value is from a separate mouse. There were 7 uninjured mice, 8 lysolecithin-vehicle mice, and 11 mice were exposed to conditioned medium collected from lysolecithin-GA animals. **, P Ͻ 0.01; ***, P Ͻ 0.001 (one way ANOVA with GA-reactive T cells for 72 h. Fig. 2 and Fig. S3 show that there Bonferroni multiple comparison test). (B) Data of OPC numbers (mean Ϯ SEM) were significantly more OPCs and Ki67-positive cells when the in discrete sections around the lesion epicenter are displayed, to indicate that embryonic brain cells were incubated with medium from GA- the increase in OPCs induced by GA is widespread across several sections reactive T cells, compared with medium from control T cells (not containing demyelination. *, P Ͻ 0.05, one way ANOVA with Bonferroni restimulated with GA). These results show that GA-reactive T multiple comparison test. All analyses were blinded. cells secrete factors conducive for oligodendrogenesis. day 7. In the area of demyelination, a dense accumulation of GA Treatment of Mice with Lysolecithin Injury Increases the Number Iba1ϩ microglia/macrophages was readily observed. Moreover, of OPCs in the Lesioned Spinal Cord. We next investigated whether OPCs identified by PDGFR␣ immuno-labeling and as discrete GA could increase OPC numbers in vivo. To better simulate cells could be discerned (Fig. S4). We blindly enumerated conditions in patients, we injected mice daily with s.c. GA. the number of OPCs in the dorsal column across 10 sections Previous studies have shown that significant demyelination (14, of the spinal cord, each spaced 100 ␮m apart, and centered 15) and newly generated OPCs (16) could be found by day 7 after around the epicenter of injury. Fig. 3 shows that in mice lysolecithin administration, so we chose this time point for subjected to lysolecithin injury and treated s.c. with PBS vehicle, analysis. Fig. S4 of MBP immunoreactivity shows that demyeli- the average total number of OPCs in the dorsal column summed nation of the dorsal column of the spinal cord was extensive at across 10 sections of individual mice averaged 257.
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