Monocyte-derived macrophage recruitment mediated by TRPV1 is required for eardrum wound healing

Abstract

The tympanic membrane (TM), or eardrum, is a thin, sensitive tissue critical for hearing by vibrating and transmitting sound waves to the inner ear. TM perforation and development of otitis media and conductive hearing loss are commonly seen in the clinic. In this study, we demonstrate the role of TRPV1 signaling mediated macrophage recruitment and angiogenesis in TM repair. By creating a wounded TM mouse model with a perforation in the anteroinferior region of the pars tensa -- a region in humans often damaged in traumatic injury, we observed a massive accumulation of macrophages in the vicinity of the acutely wounded TM. Using 5-Ethynyl-2-deoxyuridine pause labeling and a chimeric bone marrow transplant model, we found that most of the recruited macrophages did not originate from local tissue-resident macrophages but rather from blood-circulating monocytes. Parallel to macrophage recruitment, angiogenesis was observed near the wound on day 3 after perforation and further progressed by day 7. The angiogenic process was strongly associated with the recruited macrophages, as macrophage depletion resulted in a notable reduction in angiogenesis. At the transcriptional level, we found that macrophages facilitate angiogenesis through several signaling pathways. Additionally, we identified direct intercellular communication between macrophages and endothelial cells mediated by phosphoprotein 1 signaling. Furthermore, Gene Ontology analysis of bulk RNA sequencing data from TMs revealed that the macrophage recruitment is associated with neuroinflammatory responses. Using a fluorescence reporter mouse driven by TRPV1, we discovered that the TM contains rich sensory nerve fibers expressing TRPV1. A genetic mutation in the Trpv1 gene resulted in a marked decrease in the expression of neuroinflammatory genes, such as Tac1. This decrease subsequently resulted in reduced macrophage recruitment, impaired angiogenesis, and delayed wound healing. Together, these findings highlight the crucial role of TRPV1 signaling in monocyte migration and macrophage-related angiogenesis, both of which are crucial for facilitating healing of the TM. These results also open new opportunities for clinical interventions. Targeting TRPV1 signaling could enhance TM immunity, improve blood circulation, promote the repair of damaged TM, and ultimately prevent middle ear infections.