Role of human extracellular matrix properties in central nervous system regeneration
Oligodendrocytes constitute one of the four principal central nervous system (CNS) cell types - next to neurons, astrocytes and microglia. Oligodendrocytes form myelin sheaths around neuronal axons, ensuring efficient signal conduction in these axons. In Multiple Sclerosis (MS), a chronic immune-mediated demyelinating disease of unknown etiology, loss of myelin appears during both an initial relapsing-remitting phase and a subsequent secondary-progressive phase. The loss of myelin is associated with clinical disability, including pain, paralysis, vision loss and cognitive incline. Conversely, the generation of new myelinating oligodendrocytes and the repair of myelin, called oligodendrogenesis and remyelination respectively, are prerequisites for functional recovery. The pathological hallmark of MS is the presence of focal demyelinated lesions with partial axonal preservation and reactive astrogliosis. Focal demyelinated lesions can be partly or completely repaired by spontaneous remyelination. However, these regenerative processes are efficient only in a small subset of MS patients. Thus, for the development of highly effective remyelinating therapies it is particularly important to identify the factors that are suppressive or permissive of myelin regeneration.
While the determinants of lesion progression versus lesion repair in MS are still completely unknown, evidence points to the involvement of microenvironmental factors, including biomechanical and compositional extracellular matrix (ECM) properties. While past experimental approaches were often based on animal models, and have lead to the identification of a a few of individual ECM components as regulators of myelin repair. However, a fast growing body of conflicting data on the functional role of such singular components points to the necessity of a more holistic and human approach towards ECM-driven myelin regeneration:
In this project, we aim at identifying the correlative and causal relations between EMC mechanical as well as structural properties, ECM composition and the regenerative potential of human demyelinating and remyelinting MS lesions. Neuropathologically characterized human MS lesion tissue will be divided and subjected to 1) testing of biomechanical properties using microindentation together with structural characterization using label-free two-photon autofluorescence and second harmonic imaging and 2) decellularization of the ECM. The latter will allow us to study the lesion’s ECM as a whole without interference of cellular components. Isolated ECM will be again characterized for its biomechanical and structural properties and used as matrix for human myelinating stem cell cultures for the study of ECMmediated myelination efficiency. Stem cell fate and functional myelination studies will be performed in a microscopy based setting. These experiments will, for the first time, allow us to connect the biomechanical and structural properties of individual MS lesions and lesion-derived ECM with the efficiency of functional myelination in an ex vivo setting.
While we have broad insight into the promyelinating and myelin-supressive signaling effects of singular brain matrix components, nothing is known about the effect of the lesion ECM as a whole. Thus, in a next step, we aim at identifying the lesion type-specific ECM-mediated signaling pattern. Experimentally, we will look at phosphorylation patterns of multiple pro-oligodendrogenic and anti-myelinating signaling pathways on a single cell basis using high-contenct microscopy and advanced image analysis. Immunohistochemical and proteomic analysis of the individual decellularized lesion ECM will further enable us to characterize the different ECM components that underlie the individual biomechanical and regenerative properties. Lastly, through in vitro-mimicry studies, we aim at identifying which mechanical and biochemical properties may be used to functionally overcome brain ECM-associate inhibition of remyelination.
Taken together, through the integration of knowledge and methods from the fields of biomechanical engineering, biochemistry and regenerative cell biology, this project aims at characterizing key regulating brain ECM properties and identifying functional cellular regenerative mechanisms
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