The Initiation of Neuroinflammatory Axon Damage - from Mice to Men

Thomas Misgeld, M.D., and Martin Kerschensteiner, M.D.

Ludwig-Maximilians University Munich

Funded in September, 2007: $200000 for 3 years
LAY SUMMARY . ABSTRACT . BIOGRAPHY .

LAY SUMMARY

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How Nerve Fibers Get Damaged by Inflammation: A Study of Ultrastructural Signatures

The aim of this study is to better understand how the nervous system is damaged in multiple sclerosis. This will be achieved by combining in vivo imaging and electron microscopy to identify early "signatures," i.e., the first subcellular changes that indicate nerve fiber damage.

In multiple sclerosis, immune cells enter the brain and the spinal cord to produce local inflammation. These immune cells damage nerve fibers and their insulating sheath, myelin. Trying to understand the first changes that nerve fibers undergo when they are attacked by immune cells has been difficult, mainly because the imaging technologies available to study nerve fiber damage in humans in vivo have very limited resolution and cannot reveal single nerve fibers. In contrast, high resolution imaging of living nerve fibers has recently become possible in the animal model of multiple sclerosis, known as EAE. This technique is currently used in the laboratories of Drs. Kerschensteiner and Misgeld to follow structural changes that nerve fibers undergo as they are being attacked.

In this project, Kerschensteiner and Misgeld plan to further develop this in vivo approach to now extend beyond the cellular level to events that take place inside cells, at the so called "subcellular" level. The aim is to reveal the first changes that initiate inflammatory damage in nerve fibers by combining in vivo imaging in EAE with an ultrastructural technique called serial-section electron microscopy (serial EM). Until recently, serial EM was limited to the analysis of very small tissue volumes, but new approaches to serial EM are beginning to provide ultrastructural reconstructions of sufficiently large tissue volumes that make investigations of localized nerve fiber damage feasible.  Ultrastructural information obtained by serial EM in EAE will point towards the molecular events that initiate damage to nerve fibers.  As serial EM can also be applied to post mortem tissue derived from humans, it is possible to assess the presence of the same ultrastructural signatures in human MS. In this way, the investigators hope to gain valuable insight into the subcellular events that result in inflammatory nervous system damage.

Significance:  By directly comparing early stages of nerve fiber damage in EAE and MS, this approach can bridge between animal models and the human disease. The results could provide new markers to detect early stages of nerve fiber damage in humans and facilitate studies aimed at preventing it.

ABSTRACT

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The Initiation of Neuroinflammatory Axon Damage - from Mice to Men

Axon damage is an important hallmark of neuroinflammatory lesions and causes persistent neurological deficits in multiple sclerosis (MS). Current pathological techniques only permit the end stages of axon damage to be detected. Consequently, we know little about how inflammatory axon damage is initiated and what subcellular and molecular changes precede it. Moreover, we lack markers to identify emerging axon damage, especially in human MS tissue.

To gain insight into the initiation of axon damage in MS and its animal model, experimental autoimmune encephalomyelitis (EAE), we plan to combine in vivo imaging with serial-section electron microscopy (serial EM). With this approach, we aim to define ultrastructural "signatures," i.e., the characteristic electron microscopic changes that identify early stages of axon damage. After defining such signatures for axon damage in acute EAE lesions, we plan to analyze the underlying subcellular dynamics and molecular changes using in vivo imaging. Finally, we will determine the prevalence of these ultrastructural ‘signatures’ in MS tissue using a novel technique for large-scale analysis by electron microscopy (automated tape-collecting lathe ultramicrotomy, ATLUM).

Our approach will provide dynamic and molecular information that correlates with specific ultrastructural signatures. Based on these data, the ultrastructural changes can be functionally interpreted as indicating the activation of specific axon damage pathways in the human disease. Thus, the proposed combination of techniques will help bridge the gap between the animal model and MS, a human disease for which we currently lack dynamic information at the subcellular and molecular levels.

INVESTIGATOR BIOGRAPHIES

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Thomas Misgeld, M.D., and Martin Kerschensteiner, M.D.

Thomas Misgeld, M.D., is the group leader at the assistant professor level at the Institute of Neuroscience, Technical University Munich, Germany. His training consisted of medical studies at the Technical University Munich (1991-1998), residency training at the Institute of Clinical Neuroimmunology, Ludwig-Maximilians University Munich and Max-Planck-Institute of Neurobiology, Martinsried, Germany (1998-2000), post-doctoral fellow at the Department of Anatomy and Neurobiology, Washington University, St. Louis (2000-2004), and post-doctoral fellow at the Department of Cellular and Molecular Biology, Harvard University, Cambridge (2004-2006).

Dr. Misgeld’s laboratory studies the mechanisms by which axons and synapses are dismantled during development and in neurological diseases. The laboratory employs in vivo microscopy techniques combined with transgenic labeling of neurons and glia, with the aim to reveal the cellular behaviour that underlies axonal and synaptic plasticity.

Martin Kerschensteiner, M.D., is the group leader at the assistant professor level at the Institute of Clinical Neuroimmunology, Ludwig-Maximilians University Munich (LMU Munich), Munich, Germany. His training consisted of medical studies at the RWTH Aachen and the LMU Munich (1992-1999), residency training in the Department of Neurology, LMU Munich (1999-2001), post-doctoral fellow at the Brain Research Institute, ETH Zurich, Zurich Switzerland (2001-2003), and post-doctoral fellow at the Department of Cellular and Molecular Biology, Harvard University, Cambridge (2003-2005).

Dr. Kerschensteiner’s laboratory focuses on the mechanisms of axonal damage and repair in inflammatory and traumatic CNS disease. In ongoing studies he uses a combination of in vivo imaging and molecular biology to investigate the cellular and molecular interactions that lead to axon loss and limit axonal repair in the spinal cord. The long term aim of his laboratory is to develop new therapeutic strategies that improve neuronal protection and repair.