Activation of the cannabinoid receptor CB<sub>2</sub> has been shown to induce directed leukocyte migration and inhibit leukocyte chemotaxis towards CC chemokines. However, the role that CB<sub>2</sub> plays in regulating macrophage chemotaxis remains understudied. Using a real-time chemotaxis assay and a panel of chemically diverse CB<sub>2</sub> agonists, I set out to examine whether CB<sub>2</sub> modulates primary macrophage chemotaxis. Of 14 agonists tested, only a subset acted as bona fide macrophage chemoattractants. Surprisingly, despite being pertussis toxin-sensitive, neither pharmacological inhibition nor genetic ablation of CB<sub>2</sub> had any effect on CB<sub>2</sub> agonist-induced macrophage chemotaxis. Furthermore, the activation of CB2 had no effect on CCL2 or CCL5- induced macrophage chemotaxis. Therefore, the activation of CB2 does not inhibit CC chemokine-induced macrophage migration and a non-CB<sub>1</sub>/CB<sub>2</sub>, G<sub>i/o</sub>-coupled GPCR must transduce CB2 agonist-induced macrophage chemotaxis. To identify the GPCR responsible, I examined primary murine macrophage GPCR expression and found that they express 124 non-sensory GPCRs. Functional screening of candidate receptors demonstrated that the putative cannabinoid receptors GPR18 and GPR55 and the lipid binding GPCRs LPAR1&5, CYSLTR1&2 and GPER1, were not responsible for CB<sub>2</sub> agonist-induced macrophage chemotaxis. Alongside, a ligand-directed virtual screen, combined with functional testing, uncovered a novel chemotaxis positive chemical scaffold. Importantly, compounds in this series containing a photoaffinity label retained activity and will aid in the identification of the target(s) responsible for CB<sub>2</sub> agonist-induced macrophage chemotaxis in future photocrosslinking experiments. Finally, I assessed whether CB2 controls innate immune cell recruitment in vivo using the zymosan-induced dorsal air pouch inflammation model and animals genetically deleted for CB<sub>2</sub>. I found that CB<sub>2</sub><sup>-/-</sup> mice had increased air pouch neutrophil and monocyte numbers, as well as pro-inflammatory mediators, during the acute inflammatory phase. Interestingly, mixed bone marrow chimera experiments demonstrated that lack of CB<sub>2</sub> specifically in the myeloid population is responsible for increased neutrophil trafficking. Therefore these data demonstrate that CB<sub>2</sub> acts to regulate neutrophil recruitment during the acute inflammatory response.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:730317 |
| Date | January 2016 |
| Creators | Taylor, Lewis |
| Contributors | Greaves, David |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:e7f3c9de-8418-480e-af09-317c91f796fd |
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