Direct activation of Airway Sensory C-fibers by SARS-CoV-2 Spike protein

Abstract

Activation of sensory nerves, in particular nociceptive C-fibers, is a feature of most respiratory viruses. Evidence of such activation is found in the classical consequences of C-fiber activation including sneezing, sore throat, coughing, and reflex secretions. As well as causing the troubling symptoms of viral infection, the activation of these nerves allows viruses to escape the body and be transmitted to other hosts, i.e. nociceptor activation amplifies spread in a community. In addition, activation of airway vagal C-fibers can lead to strong reflex bronchoconstriction and excessive secretions that likely contribute to the exacerbation of asthma particularly in children. In theory, viral infection leads to C-fiber activation by two general mechanisms. The first is that viral infection of epithelial cells leads to the production of a mediator(s) that stimulates the C-fiber terminals. The second is that the virus itself directly activates the nerves. We used three orthogonal approaches to address our hypothesis that the coronavirus spike protein directly activates (evokes action potential discharge) vagal C-fibers in mouse airways. We used male C57/BL6 mice to evaluate whether coronavirus spike protein interacts; directly with C-fiber terminals in an isolated vagus-trachea/lung preparation. Action potentials were recorded using extracellular electrodes positioned near the relevant cell bodies in the vagal sensory nodose/jugular ganglion complex. Spike protein S1 (4ug/ml) was perfused through the mouse trachea into the receptive field of an identified C-fiber (c.v. <1 m/s). 40% of C-fibers (12 out of 30) responded acutely to the S1 protein with action potential discharge. In the same type of ex-vivo experimental set-up, two-photon imaging technique was also used to evaluate the % of fibers activated by spike protein. Consistent with our electrophysiological studies we found that 45% of the C-fibers (241 fibers out of 538 fibers in 4 experiments) were stimulated by the S1protein. To determine whether spike protein was indirectly activating C-fibers in the lung, i.e. requiring other cells within the airway tissue, we evaluated its effect on neurons dissociated from the vagal ganglia with Fura-2 calcium imaging. Again, ~ 40% of the isolated neurons (65 out of 163 neurons) responded to spike protein. These data support our hypothesis that the spike protein can directly activate neurons independently of airway tissue. This supports the hypothesis that some of the nerve-related effects of SARS CoV-2 infection may involve the direct activation of sensory C-fibers. R35 HL144887 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.