Expression of a myelin proteolipid protein (Plp)-lacZ transgene is reduced in both the CNS and PNS of Plp(jp) mice

Myelin repair and functional recovery mediated by neural cell transplantation in a mouse model of multiple sclerosis

Cellular therapies are becoming a major focus for the treatment of demyelinating diseases such as multiple sclerosis (MS), therefore it is important to identify the most effective cell types that promote myelin repair. Several components contribute to the relative benefits of specific cell types including the overall efficacy of the cell therapy, the reproducibility of treatment, the mechanisms of action of distinct cell types and the ease of isolation and generation of therapeutic populations. A range of distinct cell populations promote functional recovery in animal models of MS including neural stem cells and mesenchymal stem cells derived from different tissues. Each of these cell populations has advantages and disadvantages and likely works through distinct mechanisms. The relevance of such mechanisms to myelin repair in the adult central nervous system is unclear since the therapeutic cells are generally derived from developing animals. Here we describe the isolation and characterization of a population of neural cells from the adult spinal cord that are characterized by the expression of the cell surface glycoprotein NG2. In functional studies, injection of adult NG2(+) cells into mice with ongoing MOG35-55-induced experimental autoimmune encephalomyelitis (EAE) enhanced remyelination in the CNS while the number of CD3(+) T cells in areas of spinal cord demyelination was reduced approximately three-fold. In vivo studies indicated that in EAE, NG2(+) cells stimulated endogenous repair while in vitro they responded to signals in areas of induced inflammation by differentiating into oligodendrocytes. These results suggested that adult NG2(+) cells represent a useful cell population for promoting neural repair in a variety of different conditions including demyelinating diseases such as MS.

The expression of TAG-1 in glial cells is sufficient for the formation of the juxtaparanodal complex and the phenotypic rescue of tag-1 homozygous mutants in the CNS

Myelinated fibers are organized into specialized domains that ensure the rapid propagation of action potentials and are characterized by protein complexes underlying axoglial interactions. TAG-1 (Transient Axonal Glycoprotein-1), a cell adhesion molecule of the Ig superfamily, is expressed by neurons as well as by myelinating glia. It is essential for the molecular organization of myelinated fibers as it maintains the integrity of the juxtaparanodal region through its interactions with Caspr2 and the voltage-gated potassium channels (VGKCs) on the axolemma. Since TAG-1 is the only known component of the juxtaparanodal complex expressed by the glial cell, it is important to clarify its role in the molecular organization of juxtaparanodes. For this purpose, we generated transgenic mice that exclusively express TAG-1 in oligodendrocytes and lack endogenous gene expression (Tag-1(-/-);plp(Tg(rTag-1))). Phenotypic analysis clearly demonstrates that glial TAG-1 is sufficient for the proper organization and maintenance of the juxtaparanodal domain in the CNS. Biochemical analysis shows that glial TAG-1 physically interacts with Caspr2 and VGKCs. Ultrastructural and behavioral analysis of Tag-1(-/-);plp(Tg(rTag-1)) mice shows that the expression of glial TAG-1 is sufficient to restore the axonal and myelin deficits as well as the behavioral defects observed in Tag-1(-/-) animals. Together, these data highlight the pivotal role of myelinating glia on axonal domain differentiation and organization.

Human bone marrow-derived mesenchymal stem cells induce Th2-polarized immune response and promote endogenous repair in animal models of multiple sclerosis

Cell-based therapies are attractive approaches to promote myelin repair. Recent studies demonstrated a reduction in disease burden in mice with experimental allergic encephalomyelitis (EAE) treated with mouse mesenchymal stem cells (MSCs). Here, we demonstrated human bone marrow-derived MSCs (BM-hMSCs) promote functional recovery in both chronic and relapsing-remitting models of mouse EAE, traced their migration into the injured CNS and assayed their ability to modulate disease progression and the host immune response. Injected BM-hMSCs accumulated in the CNS, reduced the extent of damage and increased oligodendrocyte lineage cells in lesion areas. The increase in oligodendrocytes in lesions may reflect BM-hMSC-induced changes in neural fate determination, since neurospheres from treated animals gave rise to more oligodendrocytes and less astrocytes than nontreated neurospheres. Host immune responses were also influenced by BM-hMSCs. Inflammatory T-cells including interferon gamma producing Th1 cells and IL-17 producing Th17 inflammatory cells and their associated cytokines were reduced along with concomitant increases in IL-4 producing Th2 cells and anti-inflammatory cytokines. Together, these data suggest that the BM-hMSCs represent a viable option for therapeutic approaches.

Identification of direct regulatory targets of the transcription factor Sox10 based on function and conservation

Background

Sox10, a member of the Sry-related HMG-Box gene family, is a critical transcription factor for several important cell lineages, most notably the neural crest stem cells and the derivative peripheral glial cells and melanocytes. Thus far, only a handful of direct target genes are known for this transcription factor limiting our understanding of the biological network it governs.

Results

We describe identification of multiple direct regulatory target genes of Sox10 through a procedure based on function and conservation. By combining RNA interference technique and DNA microarray technology, we have identified a set of genes that show significant down-regulation upon introduction of Sox10 specific siRNA into Schwannoma cells. Subsequent comparative genomics analyses led to potential binding sites for Sox10 protein conserved across several mammalian species within the genomic region proximal to these genes. Multiple sites belonging to 4 different genes (proteolipid protein, Sox10, extracellular superoxide dismutase, and pleiotrophin) were shown to directly interact with Sox10 by chromatin immunoprecipitation assay. We further confirmed the direct regulation through the identified cis-element for one of the genes, extracellular superoxide dismutase, using electrophoretic mobility shift assay and reporter assay.

Conclusion

In sum, the process of combining differential expression profiling and comparative genomics successfully led to further defining the role of Sox10, a critical transcription factor for the development of peripheral glia. Our strategy utilizing relatively accessible techniques and tools should be applicable to studying the function of other transcription factors.

Constitutively active Akt induces enhanced myelination in the CNS

The serine/threonine kinase Akt regulates multiple cellular functions. The current studies identify a new role for Akt in CNS myelination. In earlier studies on cultured oligodendrocytes, we showed that neuregulin signals through phosphatidylinositol-3'-OH kinase and Akt to enhance survival of oligodendrocytes. However, when transgenic animals were generated that overexpressed constitutively active Akt in oligodendrocytes and their progenitor cells, no enhanced survival of oligodendrocytes or progenitors was found. No alteration in the proliferation or death of progenitors was noted. In contrast, the major impact of Akt overexpression in oligodendrocytes was enhanced myelination. Most interestingly, oligodendrocytes in these mice continued actively myelinating throughout life. Thus, expression of constitutively active Akt in oligodendrocytes and their progenitor cells generated no more oligodendrocytes, but dramatically more myelin. The increased myelination continued as these mice aged, resulting in enlarged optic nerves and white matter areas. In older animals with enlarged white matter areas, the density of oligodendrocytes was reduced, but because of the increased area, the total number of oligodendrocytes remained comparable with wild-type controls. Interestingly, in these animals, overexpression of Akt in Schwann cells did not impact myelination. Thus, in vivo, constitutively active Akt enhances CNS myelination but not PNS myelination and has no impact developmentally on oligodendrocyte number. Understanding the unique aspects of Akt signal transduction in oligodendrocytes that lead to myelination rather than uncontrolled proliferation of oligodendrocyte progenitor cells may have important implications for understanding remyelination in the adult nervous system.

Proteomic analysis of nuclear factors binding to an intronic enhancer in the myelin proteolipid protein gene

The myelin proteolipid protein gene (Plp1) encodes the most abundant protein found in CNS myelin, accounting for nearly one-half of the total protein. Its expression in oligodendrocytes is developmentally regulated - peaking during the active myelination period of CNS development. Previously, we have identified a novel enhancer (designated ASE) in intron 1 DNA that appears to be important in mediating the surge of Plp1 gene activity during the active myelination period. Evidence suggests that the ASE participates in the formation of a specialized multi-protein/DNA complex called an enhanceosome. The current study describes an optimized, five-step, DNA affinity chromatography purification procedure to purify nuclear proteins from mouse brain that bind to the 85-bp ASE sequence, specifically. Electrophoretic mobility shift assay analysis demonstrated that specific DNA-binding activity was retained throughout the purification procedure, resulting in concomitant enrichment of nucleoprotein complexes. Identification of the purported regulatory factors was achieved through mass spectrometry analysis and included over 20 sequence-specific DNA-binding proteins. Supplementary western blot analyses to determine which of these sequence-specific factors are present in oligodendrocytes, and their developmental and regional expression in whole brain, suggest that Puralpha and Purbeta rank highest among the candidate factors as constituents of the multi-protein complex formed on the ASE.