Single-cell RNA sequencing analysis of mouse cochlea identifies a novel proinflammatory CD74+CD14+ macrophage subset in mice with age-related and noise-induced hearing loss.

Age-related hearing loss (ARHL) and noise-induced hearing loss (NIHL) are both associated with the activation of immune responses. However, the immune microenvironment within the cochlea in ARHL and NIHL remains poorly understood. Therefore, we profiled the immune cells in ARHL and NIHL using single-cell RNA sequencing analyses. We observed an increase in CD74+CD14+ macrophages (Mφ) in ARHL and NIHL, with this subset being associated with inflammatory pathways, immune cell chemotaxis and other processes that involved in inflammatory responses. ARHL and NIHL are linked to the degeneration of spiral ganglion neurons. We demonstrated enhanced cellular communication between CD74+CD14+ Mφ and spiral ganglion neurons in both conditions, with CD74+CD14+ Mφ being the most interactive immune cells with spiral ganglion neurons in ARHL. In this study, we highlight the common and distinct characteristics of Mφ in ARHL and NIHL, providing new potential therapeutic targets for these two types of hearing loss.