Marija Sajic

Impulse Conduction Increases Mitochondrial Transport in Adult Mammalian Peripheral Nerves In Vivo

Observations of nerve axons in vivo reveal that electrical activity increases the number and speed of transported mitochondria, showing how sudden increases in energy demand may be satisfied.

Spinal changes associated with mechanical hypersensitivity in a model of Guillain-Barre syndrome

Guillain-Barré syndrome (GBS) is an inflammatory disease of the peripheral nervous system which can cause pain via mechanisms that are poorly understood. Here, we show that in rat experimental autoimmune neuritis (EAN) mechanical allodynia developed up to 9 days before the onset of detectable neurological deficits. Allodynia was associated with an increase in the number of microglial cells in the dorsal horn of the spinal cord. The expression of the chemokine CX3CL1 (fractalkine) and its receptor CX3CR1 were also higher in EAN than in control dorsal horns suggesting spinal microglia and CX3CL1/CX3CR1 may play a role in the pain-like behaviour.

Mitochondrial dysfunction is an important cause of neurological deficits in an inflammatory model of multiple sclerosis

Neuroinflammation can cause major neurological dysfunction, without demyelination, in both multiple sclerosis (MS) and a mouse model of the disease (experimental autoimmune encephalomyelitis; EAE), but the mechanisms remain obscure. Confocal in vivo imaging of the mouse EAE spinal cord reveals that impaired neurological function correlates with the depolarisation of both the axonal mitochondria and the axons themselves. Indeed, the depolarisation parallels the expression of neurological deficit at the onset of disease, and during relapse, improving during remission in conjunction with the deficit. Mitochondrial dysfunction, fragmentation and impaired trafficking were most severe in regions of extravasated perivascular inflammatory cells. The dysfunction at disease onset was accompanied by increased expression of the rate-limiting glycolytic enzyme phosphofructokinase-2 in activated astrocytes, and by selective reduction in spinal mitochondrial complex I activity. The metabolic changes preceded any demyelination or axonal degeneration. We conclude that mitochondrial dysfunction is a major cause of reversible neurological deficits in neuroinflammatory disease, such as MS.

Mesenchymal Stem Cells Lack Efficacy in the Treatment of Experimental Autoimmune Neuritis despite In Vitro Inhibition of T-Cell Proliferation

Mesenchymal stem cells have been demonstrated to ameliorate experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, prompting clinical trials in multiple sclerosis which are currently ongoing. An important question is whether this therapeutic effect generalises to other autoimmune neurological diseases. We performed two trials of efficacy of MSCs in experimental autoimmune neuritis (EAN) in Lewis (LEW/Han MHsd) rats, a model of human autoimmune inflammatory neuropathies. No differences between the groups were found in clinical, histological or electrophysiological outcome measures. This was despite the ability of mesenchymal stem cells to inhibit proliferation of CD4+ T-cells in vitro. Therefore the efficacy of MSCs observed in autoimmune CNS demyelination models do not necessarily generalise to the treatment of other forms of neurological autoimmunity.

Origins of Gliogenic Stem Cell Populations Within Adult Skin and Bone Marrow

The generation of Schwann cells from precursors within adult skin and bone marrow is of significant clinical interest because of the opportunities for disease modelling and strategies for remyelination. Recent evidence has suggested that glial cells can be generated from (i) mesenchymal stem cells (MSCs) within adult bone marrow and (ii) skin-derived precursor cells (SKPs) within adult skin. However, there is a need to clarify the developmental mechanism whereby such multipotent adult stem cell populations generate glia. We used Wnt1-Cre/Rosa26R(LacZ) and Wnt1-Cre/Rosa26R(YFP) neural crest reporter mice to test the hypothesis that (i) MSCs and (ii) SKPs represent adult gliogenic precursor cells of neural crest origin. We demonstrate that, although labeled cells can be identified within long bone preparation, such cells are rarely found in marrow plugs. Moreover, we did not find evidence of a neural crest origin of bone marrow-derived MSCs and were not able to provide a developmental rationale for the derivation of glial cells from MSCs using this approach. In contrast, we provide robust evidence for the neural crest origin of SKPs derived from adult skin. These precursor cells reliably generate cells with a Schwann cell phenotype, expressing appropriate transcription factors and Schwann cell markers. We demonstrate multiple anatomical origins of gliogenic SKPs within adult skin. We conclude that SKPs, rather than bone marrow-derived MSCs, represent a more defined and developmentally rational source for the study and generation of Schwann cells from readily accessible adult tissues.

The role of CD8+ T cells in a model of multiple sclerosis induced with recombinant myelin oligodendrocyte glycoprotein

Background and objectives: Since CD8+ T cells may be important in the pathogenesis of multiple sclerosis (MS), we examined their role in the DA rat experimental autoimmune encephalomyelitis (EAE) model induced by immunization with recombinant myelin oligodendrocyte glycoprotein (rMOG). Methods: The inflammatory infiltrate in the spinal cord of affected animals was assessed by histology, electrophysiology and flow cytometry during the course of the disease (the first peak, remission and the second peak). The proportions of activated/memory effector (CD8+CD44+) and putative suppressor (CD8+CD28-, CD8+CD25high) CD8+ T cells in the draining lymph nodes were determined. To explore the role of CD8+ T cells, similar experiments were performed in CD8+ T cell depleted rats, before, during and after the first peak of the disease. Results: Throughout the disease, both CD4+ T cells and macrophages/activated microglia outnumbered CD8+ T cells within the spinal cord. The number of putative suppressor CD8+ T cells increased significantly both during and after the first peak suggesting the induction of a regulatory CD8+ T-cell response. However, antibody-mediated depletion of CD8+ T cells before induction of the disease, or after the first peak, did not significantly alter the incidence, severity or course of rMOG-induced EAE. Conclusions: The findings suggest that CD8+ T cells do not play a significant role in the pathogenesis or regulation of EAE induced by rMOG in DA rats. In this respect, rMOG-induced EAE is not an appropriate model for studying the role of CD8+ T cells in MS.

Mitochondrial Dysfunction and Transport in Demyelinating Disease with Inflammation

Demyelinating diseases with inflammation affect both the central and peripheral nervous systems. The histopathological hallmark of these devastating, and sometimes life-threatening, diseases is segmental demyelination of long axonal tracts and varying degrees of inflammation, with important long-term consequences for the function and survival of axons and neurons. Mitochondria are essential for the function of all cells, but maybe more so for neurons, in both physiological and pathological conditions. Healthy neurons utilise a sensitive, responsive and dynamic mitochondrial population for their varied basal metabolism. It is not surprising, then, that mitochondria also play a fundamental role in adaptive mechanisms which enable neurons to survive pathological events such as loss of myelin sheath and exposure to inflammatory mediators. Indeed, it is believed that the survival of axons in such an environment, and perhaps recovery to full functionality, critically depends on the adaptive capacity of its mitochondrial population. This chapter will present and interpret currently available, published knowledge relating to the role of neuronal mitochondria in neuroprotection and neurodegeneration during demyelinating inflammatory diseases of the central and peripheral nervous systems.

Demyelination Models in the Spinal Cord

Disruption of axonal conduction within the central nervous system has obvious, negative consequences on numerous functions, including the ability to execute movement successfully. One important cause of axonal conduction deficits is primary demyelination, that is, the loss of the myelin sheaths but sparing of the axons which they surround. Such demyelination leads to conduction deficits ranging from action potential slowing and loss of transmission fidelity, to conduction block, and this latter, most severe consequence is almost inevitably the first consequence of the loss of a whole internode(s) of myelin. Several methods have been developed to induce primary demyelination in the spinal cord and some of the more common of these will be discussed in this chapter.