DOI
https://doi.org/10.25772/A6V2-Z536
Defense Date
2021
Document Type
Thesis
Degree Name
Master of Science
Department
Pharmacology & Toxicology
First Advisor
Dr. Aron Lichtman
Abstract
Novel pharmacological and genetic advancements increased interest in the sphingosine-1-phosphate receptor-1 (S1P1) as a potential therapeutic target. S1P1 plays a critical role in the mechanism of action of Fingolimod/FTY720, a therapy currently FDA-approved for the treatment of relapsing-remitting multiple sclerosis (RRMS) (Camm et al., 2014). To prevent RRMS, FTY720 downregulates S1P1 on lymphocytes to impair their trafficking and sequester cells in the lymphoid organs to prevent further pathogenic attack (Brinkmann et al., 2010). Recent developments in pre-clinical models suggest FTY720 holds therapeutic potential to treat other diseases, such as neuropathic pain, a debilitating chronic pain caused by a lesion or disease to the nervous system (Harold Merskey et al., n.d.). In fact, in the experimental allergic encephalomyelitis (EAE) mouse model of multiple sclerosis (MS), FTY720 reverses MS-associated pain behaviors (Doolen et al., 2018). Although FTY720 produces antinociceptive effects in several neuropathic pain models (Coste et al., 2008; Yamazaki et al., 2020; Zhang et al., 2015), the exact mechanisms remain unknown. However, recent literature implicates S1P1 facilitates the antinociceptive effects of FTY720 in neuropathic pain models (Squillace et al., 2020a; Welch et al., 2012).
S1P1 is found throughout the body (Brinkmann, 2007) and is highly expressed in brain and spinal cord regions associated with pain perception and modulation of nociception (Blondeau et al., 2007; Bryan et al., 2008; Edsall & Spiegel, 1999; Toman & Spiegel, 2002). S1P1 is a primary target of research due to its known role in the anti-MS mechanisms of FTY720 and its proliferation in tissues associated with pain mechanisms (Sim-Selley et al., 2009). In addition, S1P contributes to mechanical hypersensitivity in an S1P1-dependent manner (Khodorova et al., 2017). Likewise, pharmacological and genetic tools reveal reversal of hypersensitivity and neuropathic pain is through a S1P1-mediated mechanism (Chi & Nicol, 2010; Xie et al., 2012). Furthermore, the S1P1 contributes to the antinociceptive effects of FTY720 in a chronic constrictive injury (CCI) model of neuropathic pain despite receptor downregulation in the spinal cord suggesting FTY720 produces acute effects through S1P1 agonism and sustained effects through S1P1 functional antagonism (Sim-Selley et al., 2018). As S1P1 is expressed throughout the body, it is important to understand which cell types modulate the antinociceptive effects of FTY720. Several studies implicate the antinociceptive effects of FTY720 through multiple cell types of the nervous system, such as neural-derived cells of the nervous system (i.e., neurons, oligodendrocytes and astro-glia) or other glia like microglia (Chen et al., 2019; Healy & Antel, 2015). While studies established a role of astro-glial S1P1 in the development of hypersensitivity, Chen and colleagues (2019) utilized astrocyte specific KO mice derived from a human GFAP promoter driven Cre line known to target recombination in the neural progenitor stage in several regions of the CNS (Chen et al., 2019). The lack of specificity of Cre-driven strains limits interpretation; therefore, we propose investigation of the contributions of S1P1 signaling and determine which cell types, such as neurons and supporting glial cells, are involved in the antinociceptive effects of FTY720 in a neuropathic pain model of peripheral nerve injury.
The results of this dissertation re-establish FTY720 produces acute and sustained antinociceptive effects in the CCI model of neuropathic pain in a dose-dependent and sex-independent manner. Our use of the well-established pharmacological S1P1 antagonist, NIBR0213, confirms S1P1 agonism contributes to acute antinociception of FTY720. Using global S1P3 knockout mice, we rule out the involvement of this receptor in acute and sustained antinociception following FTY720. Using cell-specific S1P1 knockout mice, we reveal that S1P1 expressed on specific cells of the nervous system (neurons, oligodendrocytes, macrophages, microglia and astroglia) do not contribute to the establishment of CCI-induced-mechanical hypersensitivity. S1P1 knockout on neuronal-derived cells (neurons, astroglia, and oligodendrocytes) but not GFAP-driven knockout on astroglia specifically, altered acute antinociceptive effects of FTY720. Given their role in pain mechanisms and signaling, we conclude neuronal-S1P1 mediates FTY720-induced antinociception. Likewise, based on results in the GFAP-driven knockout mice following repeated administration of FTY720, we determine the sustained effects of FTY720 are dependent upon active S1P1 signaling on astroglia. Our results indicate that neuronal S1P1 drives acute FTY720-induced antinociception and astroglial S1P1 signaling contributes to the maintenance of these antinociceptive effects. Therefore, neuronal-astroglial S1P1-dependent mechanisms modulate the antinociceptive effects of FTY720 in the CCI model of neuropathic pain.
Rights
© Lauren Moncayo
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
8-12-2021