In vivo imaging of astrocytes to investigate their functional and structural interactions with the blood brain barrier, immune cells and the demyelinating axon in the animal model of Multiple Sclerosis.

• Applicant: Privatdozent Dr. Volker Siffrin
• Subject Area: Molecular and Cellular Neurology and Neuropathology ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279791496

Multiple sclerosis (MS) is the most common chronic inflammatory disease of the central nervous system (CNS) that causes prolonged and severe disability in young adults in North America and Europe. Early damage of neuroaxonal structures has been recognized as a major aspect of MS pathology and correlates best with later disability. However, it is not clear why the extent of accumulation of disability over time varies between individual patients. Recent reports suggest that differences in disability accumulation might derive from genetic variations in safeguarding CNS glutamate homeostasis. We have recently demonstrated a direct effect of CD4+ T cells on neuronal damage formation. One important mechanism of immune cell mediated neuronal damage in our study was (glutamate-mediated) excitotoxicity. Glutamate homeostasis is a major task of astrocytes, which have the capacity to remove excitotoxic substances from the extracellular space and are responsible for local confinement of transmitter release. Up to date astrocytes range among the most neglected players in MS pathogenesis with an alleged bystander role as scar forming cells. We aim to better understand the involvement of astrocytes in the pathophysiology in neuroinflammatory conditions. We will investigate the role of astrocytes in established EAE lesions in respect to neuronal and myelin damage. We are primarily interested in the metabolic and detoxification role of astrocytes for the axono-glial unit in the inflamed CNS. We will use different transgenic models to analyze Ca2+ dynamics in neurons/axons and/or astrocytes. Furthermore we will interfere with astrocyte biology using different pharmacological and transgenic approaches to analyze the effect on axonal integrity. We will analyze FACS-sorted astrocytes from different days after EAE induction by conventional molecular biology methods. We will critically evaluate the results from the animal model on the background of the results from genetic MS susceptibility and disease progression studies. In addition, we will confirm this data in an own patient cohort. Furthermore, we plan to characterize in vivo the role of astrocytes in the developing EAE lesion with focus on the blood brain barrier (BBB) and their interaction with immune cells. We will use our two-photon microscopy imaging method to investigate the interaction of astrocytes with immune cells at the blood brain barrier of EAE lesions. Here, the focus will be on the developing lesion, i.e. before onset and in the onset of clinical signs to investigate the early involvement of astrocytes in the pathophysiology of these lesions. These experiments will highlight the overall role of astrocytes for lesion evolution, damage, protection and/or repair in the inflamed CNS. These findings might open up new therapeutic targets to stop neurodegeneration and progressing disability in MS patients.

• DFG Programme: Research Grants