Even though epithelial thickness and nuclear density were not in- "uenced by HFD, we examined the tracheal epithelial lining cells for a change in the proportion of the main cellular subtypes; basal, club, ciliated, and the undetermined cells. No signi$cant e!ects of HFD were detected on the cellular subtypes (Fig. 1F, G). Aging caused a propor- tional decrease in basal, club, and ciliated cells (Fig. 1F, G). As basal cells are the stem cells of mouse trachea responsible for self-renewal and di!erentiation into club and ciliated cells (Hegab et al., 2015b), these $ndings suggest that HFD exerts minimal in"uence on the self- renewal and di!erentiation potential of basal stem cells in vivo.