TLR2/NF-κB signaling in macrophage/microglia mediated COVID-pain induced by SARS-CoV-2 envelope protein

Summary: Pain has become a major symptom of long COVID-19 without effective therapy. Apart from viral infection pathological process, SARS-CoV-2 membranal proteins (envelope [S2E], spike [S2S] and membrane [S2M]) also present pro-inflammatory feature independently. Here, we aim to uncover the neuroinflammatory mechanism of COVID-pain induced by SARS-CoV-2 membranal proteins. We detected the three proteins in both peripheral sensory ganglions and spinal dorsal horn of COVID-19 donors. After intradermal and intrathecal injection, only S2E triggered pain behaviors, accompanied with upregulated-phosphorylation nuclear factor kappa B (NF-κB), which was significantly attenuated by minocycline in mice. We further identified Toll-like receptor 2 (TLR2) among TLRs as the target of S2E to evoke inflammatory responses leading to COVID-pain. This study identified the nociceptive effect of S2E through directly interacting with macrophage/microglia TLR2 and inducing the following NF-κB inflammatory storm. Clearing away S2E and inhibiting macrophage/microglia TLR2 served as perspective therapeutic strategies for COVID-19 pain.