Intra-articular AAV-PHP.S mediated chemogenetic targeting of knee-innervating dorsal root ganglion neurons alleviates inflammatory pain in mice

Objective Joint pain is the major clinical symptom of arthritis that affects millions of people. Controlling the excitability of knee-innervating dorsal root ganglion (DRG) neurons (knee neurons) could potentially provide pain relief. Therefore, our objective was to evaluate whether the newly engineered adeno-associated virus (AAV) serotype, AAV-PHP.S, can deliver functional artificial receptors to control knee neuron excitability following intra-articular knee injection. Methods AAV-PHP.S virus packaged with dTomato fluorescent protein and either excitatory (G q ) or inhibitory (G i ) designer receptors activated by designer drugs (DREADDs) was injected into the knee joint of adult mice. Labelling of DRG neurons by AAV-PHP.S from the knee was evaluated using immunohistochemistry. Functionality of G q - and G i -DREADDs was evaluated using whole-cell patch clamp electrophysiology on acutely cultured DRG neurons. Pain behavior in mice was assessed using a digging assay, dynamic weight bearing and rotarod, before and after intra-peritoneal administration of the DREADD activator, Compound 21. Results We show that AAV-PHP.S can deliver functional genes into the DRG neurons when injected into the knee joint in a similar manner to the well-established retrograde tracer, fast blue. Short-term activation of AAV-PHP.S delivered Gq-DREADD increases excitability of knee neurons in vitro, without inducing overt pain in mice when activated in vivo. By contrast, in vivo G i -DREADD activation alleviated complete Freund’s adjuvant mediated knee inflammation-induced deficits in digging behavior, with a concomitant decrease in knee neuron excitability observed in vitro. Conclusions We describe an AAV-mediated chemogenetic approach to specifically control joint pain, which may be utilized in translational arthritic pain research.