IL-17a induces age-related olfactory dysfunction by impairing regeneration and promoting respiratory metaplasia in mice

The olfactory epithelium (OE) undergoes life-long renewal and regeneration. This process is supported by the globose basal cells (GBC) during the homeostatic state, as well as horizontal basal cells (HBC) during severe damage. Inflamm-aging refers to the low-grade, chronic and progressive state of heightened pro-inflammation associated with aging. However, the impact of inflamm-aging on OE homeostasis, regeneration, and the inflammatory microenvironment is not fully understood. In this study using mouse models, we elucidate the role of interleukin-17a (IL-17a) in OE regeneration and olfactory function. Our findings implicate that inflamm-aging in aged OE promotes the recruitment and activation of immune cells, accompanied by crosstalk between HBC and T cells. Elevated expression of IL-17a in aged OE triggers inflammatory signals and impairs olfactory function. Administration of IL-17a inhibitor Y-320 or neutralizing antibody promotes sensory neuronal regeneration and reverses age-related respiratory metaplasia in OE. Co-culturing mouse OE organoids with Th17 cells impairs neuronal generation and enhances the transformation towards respiratory cells, while neutralizing antibody against IL-17a alleviates neuronal loss and respiratory transformation. Additionally, conditional knockout of IL-17a in T cells facilitates OE regeneration by promoting HBC recruitment and differentiation into GBC. Collectively, our study identifies a function of IL-17a in OE regeneration and age-related deficits in olfactory function, providing evidence for further investigation of IL-17a as a possible therapeutic target against presbyosmia. The olfactory epithelium (OE) undergoes changes during aging and this may affect inflammatory responses and immune cell infiltration. Here the authors look at the effect of aging on OE and how this involves cross talk between T cells and horizontal basal cells involving Il17a expression in OE which is increased in aging and inhibition of IL-17a function reduces respiratory metaplasia.