Imaging neuroinflammatory axonal injury at nanoscale resolution

• Applicant: Dr. Ivana Nikic-Spiegel
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Molecular and Cellular Neurology and Neuropathology
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 317530061

Multiple sclerosis (MS) is the leading cause of non-traumatic neurological disability in young adults. Current therapies are effective in modulating inflammatory phases of the disease, but cannot stop progressive phases. As the main pathological correlate of the progressive neurological disability is axonal injury, a deeper understanding of how axons are damaged in MS will enable the development of new therapies. I have previously identified a novel form of axonal injury, focal axonal degeneration (FAD). In vivo imaging showed that FAD is a sequential process, characterized by intermediate stages that are stable and can even spontaneously recover. Reversibility is important, as it suggests the existence of a therapeutic window of opportunity. However, this process is very poorly understood at the molecular level, and we do not know what determines if axons will recover or degenerate. We also do not know what mediates initial axonal changes. The aim of my Emmy Noether project was to study the primary sites of injury, nodes of Ranvier, and analyze how their architecture is changed in neuroinflammatory conditions. Furthermore, I wanted to characterize the dynamic changes in the axonal shape, and the contribution of the cytoskeleton and membrane-shaping proteins to it, and their relevance for FAD reversibility. To this aim, I developed an in vitro system which offers us a better control over the onset of injury. This was complemented with novel genetic code expansion tools for engineering of fluorescent labels with bioorthogonal click chemistry in neurons. Together, this has provided us with a unique perspective to unravel molecular mechanisms of axonal injury. In the 6th year, we would like to focus on one of our more recent findings. While performing studies of cytoskeletal changes at the nanoscale level, we noticed accumulations of neurofilament light chain (NFL) in neuronal nuclei. It has been described in the literature that NFL can accumulate in cell bodies and axonal swellings of diseased neurons, but as nuclear accumulations have not been reported before, we aim to investigate this further. We will address this question by looking at the dynamics of NFL with live-cell imaging and our recently developed click chemistry labelling tags. In addition, we aim to establish proximity-based labelling to look at the interactions of NFL. This will allow us to identify interaction partners of NFL in healthy and injured neurons. Keeping in mind important roles of NFL and their use as a biomarker of numerous neurological diseases, understanding NFL’s response to injury at the cellular and molecular level is highly relevant.

• DFG Programme: Independent Junior Research Groups