Lgr5⁺ cells are required and dynamically participate in olfactory epithelium regeneration: a revisiting shows Lgr5 expression in multiple cell lineages

Abstract

Olfactory sensory neurons (OSNs) located in the olfactory epithelium (OE) detect thousands of volatile environmental odors to form the sense of smell. OSNs are generated from basal cells, which show the characteristics of progenitor/stem cells. In the mammalian OE, persistent neurogenesis occurs during lifetime, providing a unique model to study the tissue turnover and fate determination of stem cells. Methods: Immunohistochemical analysis and RNAscope in situ hybridization indicated the localization of leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) in the intact and injured OE. Lineage tracing was conducted to analyze the dynamic role of Lgr5 + cells in the OE homeostasis and regeneration. We also used DTR-driven genetic depletion of Lgr5 + cells and lentivirus-mediated Lgr5 downregulation to demonstrate the essential role of Lgr5 + cells in the OE regeneration. Results: We show that Lgr5 marks horizontal basal cells (HBCs) in the OE of adults but not newborns. We revisit the role of Lgr5 + cells in the OE homeostasis and regeneration, and find that Lgr5 + cells participate in the OE homeostasis from neonatal to one-month-old age, as well as in the OE regeneration post injury. During the OE regeneration, Lgr5 is transiently expressed in apical supporting cells, immature neurons, and mature sensory neurons. The Lgr5 + cells become or generate HBCs in the regenerated OE. DTR-driven cell depletion shows that Lgr5 + cells are not necessary in the adult OE homeostasis, but required in the recovery of OE from injury. Lgr5 down-regulation by lentiviral infection also demonstrates the essential role of Lgr5 expression in the OE regeneration. Conclusion: Our study elucidates the role of Lgr5 + cells in the OE homeostasis and regeneration, potentially providing a candidate to cell-based therapy against olfactory dysfunction.

Type 2 and Non-type 2 Inflammation in the Upper Airways: Cellular and Molecular Alterations in Olfactory Neuroepithelium Cell Populations

“…Interestingly, it has been described that supporting/sustentacular cells may affect basal stem cell activation and subsequent OE regeneration [ 67 ]. Thus, the ablation of supporting cells but not neuronal depletion in the OE is sufficient for the HBC activation [ 68 , 69 ].…”

“…GBCs are the main actively proliferating cell population in the OE, being not only responsible for the selfrenewal of ONs, but they also are the main cells for regeneration of ONs after minor and selective injury. HBCs are considered to be a reservoir for stem cells that remain inactive in OE homeostasis, being activated by direct and severe epithelial injury and differentiated, mainly into GBCs, which differentiate into almost all epithelial cell types including ONs, and sustentacular cells [5••, [64][65][66][67]. All these data suggest a transition in basal cells from unipotent specified differentiation to multipotent state when the OE is subjected to injury [67].…”

“…HBCs are considered to be a reservoir for stem cells that remain inactive in OE homeostasis, being activated by direct and severe epithelial injury and differentiated, mainly into GBCs, which differentiate into almost all epithelial cell types including ONs, and sustentacular cells [5••, [64][65][66][67]. All these data suggest a transition in basal cells from unipotent specified differentiation to multipotent state when the OE is subjected to injury [67].…”