Abstract
Nerve growth factor (NGF) and its receptors TrkA and p75 play a key role in the development and function of peripheral nociceptive neurons. Here, we describe novel technology to selectively photoablate TrkA-positive nociceptors through delivery of a phototoxic agent coupled to an engineered NGF ligand and subsequent near-infrared illumination. We demonstrate that this approach allows for on demand and localized reversal of pain behaviors in mouse models of acute, inflammatory, neuropathic, and joint pain. To target peripheral nociceptors, we generated a SNAP-tagged NGF derivative NGF that binds to TrkA/p75 receptors but does not provoke signaling in TrkA-positive cells or elicit pain behaviors in mice. NGF was coupled to the photosensitizer IRDye700DX phthalocyanine (IR700) and injected subcutaneously. After near-infrared illumination of the injected area, behavioral responses to nociceptive mechanical and sustained thermal stimuli, but not innocuous stimuli, were substantially reduced. Similarly, in models of inflammatory, osteoarthritic, and neuropathic pain, mechanical hypersensitivity was abolished for 3 weeks after a single treatment regime. We demonstrate that this loss of pain behavior coincides with the retraction of neurons from the skin which then reinnervate the epidermis after 3 weeks corresponding with the return of mechanical hypersensitivity. Thus NGF-mediated photoablation is a minimally invasive approach to reversibly silence nociceptor input from the periphery, and control pain and hypersensitivity to mechanical stimuli.