Title: Targeting the NaV1.7 Interactome for Pain Relief in Arthritis
Funder: Versus Arthritis

Abstract: Chronic pain arising from arthritic diseases places a considerable burden on both the individuals affected and society as a whole. The pain experienced presents itself with both allodynia and hyperalgesia and the aim of all analgesic therapies is to return pain sensitivity to normal levels, rather than switch off pain completely because of the protective aspects of pain. Current analgesic therapies are often limited, either by an inability to sufficiently reduce pain, or due to deleterious side effects. We believe that targeting arthritic pain at its source, i.e. neurones that innervate the affected joints, will provide a novel route to pain relief. Our preliminary data show expression of the voltage-gated sodium channel NaV1.7 to be increased in sensory neurones back-labelled from ankle joints in the complete Freund’s adjuvant (CFA) induced arthritis. Although direct blockade of NaV1.7 is appealing, full inhibition could produce a congenital insensitivity to pain-like phenotype as exhibited by humans with hypofunction NaV1.7 mutations. Therefore, our objectives are to determine how NaV1.7 modulation changes during arthritis and then to prevent that modulation such that pain is normalised, rather than switched off. NaV subunits do not exist on the plasma membrane as isolate proteins, but rather form complexes made up of multiple protein assemblies (the NaV interactome) that modulate the levels of NaV subunits reaching the plasma membrane, as well as the biophysical properties of the ion channels themselves. We hypothesis that in arthritis the NaV1.7 interactome is altered such that changes in the NaV1.7-binding-partners enhance its function resulting in increased pain. However, the nature and composition of these localised protein clusters, and how they may change in diseases states is poorly resolved. Using the selective proteomic proximity labelling assay using tyramide (SPPLAT) established in our labs and antibodies provided by our industrial collaborators at AstraZeneca, we will first determine which NaV1.7 interactome proteins change during arthritis and thus might be responsible for sensitising its function, which we will then verify using immunohistochemistry in back-labelled articular sensory neurones. We will next use heterologous expression systems to determine how different NaV1.7 interactome proteins modulate NaV1.7 plasma membrane trafficking and biophysical properties. Those candidate proteins of interest will then be overexpressed in sensory neurones of wild-type mice to determine if the same effects are observed in a neuronal environment and these experiments will also be conducted in mice lacking NaV1.7 in sensory neurones to be sure that the effects are NaV1.7 specific. Having identified which NaV1.7 interactome proteins sensitise NaV1.7 function, we will use a behavioural dynamic weight bearing assay as a readout of CFA-induced pain and determine how reducing levels of different NaV1.7 interactome proteins affects mouse behaviour; again, this would be conducted in both wild-type and mice lacking NaV1.7 in sensory neurones. Lastly, we will take human DRG tissue and determine NaV1.7/interactome protein coexpression in human neurones, experiments that will help to determine the potential for translation of our findings into the clinic and thus fully exploit the results from our animal model.


Research activity codes: 2.1 BIOLOGICAL AND ENDOGENOUS FACTORS
Health categories: INFLAMMATORY AND IMMUNE SYSTEM