MicroRNA21 Meets Neuronal TLR8: Non-canonical Functions of MicroRNA in Neuropathic Pain

Toll-like receptors (TLRs) are well-known as patternrecognition receptors in the immune system for recognizing pathogen-associated and damage-associated molecular patterns [1]. TLRs play an essential role in the innate and adaptive immune responses. To date, 10 functional TLRs have been identified in humans (TLR1–TLR10) and 12 in mice (TLR1–TLR9 and TLR11–TLR13)[1]. TLRs are evolutionarily conserved type I transmembrane proteins and comprise an ectodomain characterized by leucine-rich repeats mediating the recognition of ligands, a transmembrane region, and cytosolic Toll-interleukin (IL)-1 receptor domains that activate the downstream signaling pathways [1].