The Role of Fractalkine Signalling in Central Nervous System Precursor Cells
Creators: Watson, Adrianne E.S.
Publisher: name: University of Alberta Library
Year: 2024

<p>Oligodendrocyte and neural precursor cells (OPCs and NPCs, respectively) in the central nervous system (CNS) have important roles in development and homeostasis. During<br>
development, precursors build the CNS. In adulthood, they maintain their ability to proliferate and generate differentiated progeny: astrocytes, oligodendrocytes, and neurons. This indicates their tremendous potential to regenerate and repair the injured or degenerated CNS. However, this process is highly inefficient in neurodegenerative disorders such as multiple sclerosis (MS).</p>

<p>How can we engage existing NPC and OPCs (collectively CNS progenitor cells) for enhanced regeneration? The fate and function of CNS progenitors is highly regulated by extrinsic factors in their environment, including signals from the extracellular matrix, direct cell-to-cell contact, and secreted signalling factors, such as chemokines. Notably, previous reports indicate neuronally derived chemokines can modulate CNS progenitor chemotaxis, survival, proliferation, and differentiation.</p>

<p>Neuronally secreted fractalkine (FKN/CX3CL1) is well known to regulate microglia, resident CNS macrophages, in development, homeostasis, and disease contexts. Recently, fractalkine receptor Cx3cr1 was shown to be expressed by NPCs and OPCs during early development, which regulates oligodendrogenesis (Voronova et al., 2017). Here, we ask whether CX3CR1 activation could similarly engage postnatal and adult CNS progenitors for enhanced oligodendrocyte generation, and if fractalkine signalling could facilitate oligodendrogenesis and regeneration after a demyelinating insult.</p>

<p>First, we investigate the role of fractalkine-CX3CR1 signalling in healthy conditions. We demonstrate that postnatal and adult murine subventricular zone (SVZ) NPCs and OPCs express Cx3cr1 and bind fractalkine, while exogenous fractalkine increases oligodendrocyte genesis from murine postnatal SVZ NPCs and OPCs in vitro and adult SVZ NPCs in vivo. Interestingly, we also show OPCs secrete fractalkine, and inhibition of this endogenous fractalkine signalling<br>
reduces SVZ oligodendrocyte formation. Moreover, we show that fractalkine signalling is an important regulator of oligodendrocyte genesis in other brain areas, such as postnatal cerebellum.</p>

<p>We then ask if fractalkine could increase oligodendrogenesis after demyelinating injury. We first confirm that OPCs and microglia/macrophages express Cx3cr1 in the demyelinated murine CNS. We then show that direct administration of fractalkine into the murine brain after cuprizone<br>
demyelination enhances oligodendrocyte and myelin regeneration by modulating OPC differentiation and microglia/macrophage activation in vivo. Notably, we demonstrate that fractalkine increases in vitro oligodendrogenesis by modulating both OPC and microglia biology. </p>

<p>Finally, we investigate whether small molecule CX3CR1 agonists could enhance oligodendrocyte genesis. We test two previously reported CX3CR1 agonists and one CX3CR1 modulator for oligodendrogenesis in cortical OPC cultures. We show both agonists, E-6130 and Axxam 21, enhance oligodendrocyte genesis in OPC culture, while CX3CR1 modulator AZD8797 has no effect. Moreover, select structural derivatives of E-6130 and Axxam 21 show similar or enhanced potency compared to parent compounds, while one derivative of E-6130 shows increased potency with a more favourable metabolic profile. Together, these data show that fractalkine signalling in NPCs and OPCs modulates oligodendrogenesis in healthy conditions, and increases oligodendrocyte genesis and remyelination after a demyelinating injury. Moreover, CX3CR1 activation via novel small molecules can similarly increase oligodendrogenesis; thus, CX3CR1 represents a promising target for pro-remyelinating therapies.</p>