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Title: Modifications of perineuronal nets to regulate plasticity
Author: van't Spijker, Heleen Merel
ISNI:       0000 0004 7653 1262
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Modifications of perineuronal nets to regulate plasticity Heleen Merel van 't Spijker Perineuronal nets (PNNs) are macromolecular structures formed by neurons after closure of critical periods of plasticity. During development, the central nervous system (CNS) goes through critical periods of plasticity; a period when substantial changes occur to adapt to the environment, during which many synapses are formed and also discarded. When a region of the CNS has finished its development and reached an efficient neuronal circuit, the capacity for plasticity needs to be reduced to preserve the formed circuit. PNNs are formed around neurons during this period of reduced plasticity. PNNs consist of a backbone of hyaluronan, bound by chondroitin sulfate proteoglycans (CSPGs). Here, I present my studies on the possible modifications of PNNs to regulate plasticity. Firstly, I have investigated the potential use of 4-methylumbelliferone (4-MU) to reduce PNN formation in vivo. 4-MU reduces the formation of hyaluronan. Since hyaluronan is the backbone of PNNs, I hypothesized 4-MU treatment would reduce PNN formation. For this study, I developed a method to orally administer 4-MU to rats. Subsequently, I investigated whether 4-MU treatment can improve recovery of rats after spinal cord injury, both with behavioural tests and with immunohistochemistry. Secondly, I have investigated a new binding partner of PNNs, neuronal pentraxin 2 (Nptx2). Nptx2 is secreted by neurons and regulates AMPA receptor diffusion. Nptx2 knockout mice show a prolonged critical period of plasticity in the visual cortex. Here, I have identified Nptx2 as a new binding partner of PNNs. Nptx2 is found in isolated PNN protein preparations and is removed from the surface of neurons by digestion of PNNs with chondroitinase ABC. I also determined Nptx2 facilitates PNN formation in vitro. Addition of Nptx2 to the medium of cortical neurons leads to an increase of neurons that start to form PNNs, as well as an increase in size and density of PNNs. These findings indicate Nptx2 may be used as a modulator of PNNs. Thirdly, I investigated the interaction between Nptx2 and PNNs. I developed a sandwich ELISA to determine which glycan chains from PNNs bind to Nptx2. Nptx2 binds to chondroitin sulfate E and hyaluronan. To investigate the binding properties of Nptx2, I performed quartz crystal microbalance with dissipation monitoring for Nptx2 films. Furthermore, I developed crystals of purified Nptx2 and hyaluronan for x-ray crystallography. The here presented results provide new insights in potential approaches to modulate PNN formation. Both lines of research provide a further understanding of the factors which regulate PNNs and may allow for the development of treatments for PNN related disorders.
Supervisor: Fawcett, James ; Kwok, Jessica Sponsor: Pinsent Darwin Studentship
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: perineuronal net ; Nptx2 ; NARP ; proteoglycan ; hyaluronan ; neuronal plasticity